Charging Towards Sustainability: Exploring Battery Recycling and Reusability
Advisor: Brian Moshofsky
Onsite Mentor: Juner Zhu
I will conduct my research by reading academic journals and industry publications. I will also attend/watch recordings of battery sustainability workshops Through this literature review, I hope to discover the latest advancements, challenges, and emerging trends in sustainable battery technologies.
Then, I will explore potential design modifications that could enhance the safety and feasibility of reused batteries, such as the integration of advanced sensor technologies and a disassembly-friendly structure. To test my ideas, I will construct prototype batteries and perform tests on safety, efficiency, and durability. I will also explore compatibility with existing infrastructure. By disassembling used batteries, rather than building new ones, I will see how my designs can be incorporated into already existing batteries. At the end, I will present the data that I have collected and discuss future modifications that could be done to improve battery designs for recycling.
Project Blog
Post 1: 01: Welcome!
Hi everyone! Welcome to week 1 of my Senior Project blog post journey!
For my Senior Project, I will be focusing on developing a better battery for recycling.
Why This Project
Recently, there has been rising awareness of the environmental impact of fossil fuels. In response, many countries have invested heavily in sustainable and clean energy solutions, especially in electric vehicles, whose widespread adoption of renewable energy technologies has significantly increased the use of lithium-ion batteries. In addition to EVs, Li-ion batteries are also found in everyday items, such as smartphones and computers, which also gained popularity in the last couple of decades due to the rise of the digital age. This surge, however, has led some experts to claim that a worldwide lithium shortage could come as early as 2025. For instance, a recent report expects an average of 20.4% year-on-year annual growth for China’s lithium demand for EVs alone in the next decade. In contrast, China’s lithium supply will only grow by 6% over the same period, which is less than one-third of the forecasted demand.
There is also increased scrutiny over how the metals are being extracted. For example, cobalt is being unethically mined in the Democratic Republic of Congo. The work is dangerous, the people there barely get enough money to live, and mines are sprouting up everywhere, taking over people’s land and homes. Finally, when batteries will need to be disposed of, at the end of their lives, it can pose an environmental concern. Improper disposal of batteries can lead to the release of hazardous materials, contributing to pollution and environmental degradation.
As I mentioned, we are approaching a time when the old batteries of EVs are nearing the end of their lives, so, instead of mining for new metals and worrying about a metal shortage, we should be recycling our old ones.
What I'm doing
I will start with a literature review, in which I will focus on current battery recycling and reusability, giving me a foundational understanding of current challenges and gaps in the field. I will then explore potential design modifications that could enhance the safety and feasibility of reused batteries. Some examples include the integration of advanced sensor technologies to monitor key parameters and a disassembly-friendly structure.
I will construct prototype batteries, incorporating the selected design modifications. These prototypes will undergo rigorous testing, including safety parameters, efficiency, and durability. I will also focus on measuring performance metrics, safety parameters, and environmental impact through life cycle analysis, so I can determine the feasibility and effectiveness of the design. Some of the things I will explore will be compatibility with existing infrastructure. I will be disassembling used batteries (rather than building new ones), which will allow me to see how my designs can be incorporated into already existing batteries. I will be looking at adaptability to variability, and whether batteries of different designs can use the same technology.
Sources
Shan, L. Y. A worldwide lithium shortage could come as soon as 2025. CNBC. https://www.cnbc.com/2023/08/29/a-worldwide-lithium-shortage-could-come-as-soon-as-2025.html
Post 2: 02: The Lithium-Ion Battery
Hi everyone! In this post, I will explain everything you need to know about the lithium-ion battery for my project.
Battery Basics
Let's first go over some basic background on batteries.
A battery is a device that stores chemical energy and converts it into electrical energy. It typically consists of one or more electrochemical cells, which are composed of two electrodes, an anode and a cathode, separated by an electrolyte and a separator. When a battery is connected to an electrical circuit, chemical reactions occur at the anode (oxidation) and cathode (reduction), causing electrons to flow from the negative terminal (anode) to the positive terminal (cathode), generating an electric current. Ions then move through the electrolyte to complete the circuit. The separator prevents short-circuiting from direct contact between the two electrodes.
There are many different types of batteries, categorized into primary (single-use) and secondary (rechargeable) batteries. Primary batteries are commonly used in applications where recharging is not necessary. They often provide a convenient, portable power source for devices such as remote controls, flashlights, clocks, and various other consumer electronics. Examples of primary batteries include alkaline (the most common household battery) and lithium metal. Secondary batteries, on the other hand, can be recharged and reused multiple times. These batteries are commonly used in applications where frequent battery replacement is inconvenient or costly, such as in portable electronics, electric vehicles, and renewable energy storage systems. Examples of primary batteries include lead-acid (found in non-electric cars) and lithium-ion.
In my project, I will be focusing on lithium-ion batteries, which is the most widely used battery in consumer electronics.
Lithium-ion Batteries (LIBs)
Lithium-ion batteries (LIBs) use lithium ions (hence the name) as the charge carriers. The cathode typically contains lithium transition metal oxides such as lithium cobalt oxide (LiCoO2) (LCO), lithium iron phosphate (LiFePO4) (LFP) and lithium manganese oxide (LiMn2O4) (LMO). LCO is most commonly used as the cathode because of its durability and high energy density. The anode typically contains graphite, which allows the lithium ions to intercalate during charging and de-intercalate during discharging.
LIBs are one of the most advanced secondary batteries, in terms of gravimetric and volumetric energy. Some advantages of lithium-ion batteries include a high energy density, a higher energy efficiency, and a lower self-discharge rate. They are found everywhere, most notably in portable consumer electronics, electric vehicles, and energy storage.
LIB Configurations
Lithium-Ion Batteries (LIBs) comes in a variety of form factors (configurations), which can be categorized into: cylindrical, coin, prismatic, and pouch.
Coin Cells
Starting with the simplest one, coin cells, also called button cells, are compact and have a flat, disc-like shape, similar to a coin or button (hence the name). They consist of electrodes (anode and cathode), electrolytes, separators, housing, insulators, springs, and spacers. I have already explained electrodes, electrolytes, and separators above. Coin cell housing is typically a stainless steel metal can and acts as the negative terminal of the battery. An insulating ring prevents electrical contact between the positive and negative terminals. Finally, springs and spacers help with structural integrity when in inserted into a device. Due to their size, they are used in small electronic devices such as watches, calculators, and key fobs.
Cylindrical Cells
Cylindrical cells are cells enclosed in a rigid cylinder can and are the most common. These cells are easy to manufacture and have good mechanical stability. Its components include electrodes, separators, electrolytes, cylindrical cans, and terminal collectors. The electrode materials and electrolytes are enclosed within a cylindrical metal can and have metal tabs attached to the can, which serve as the positive and negative terminals for external electrical connections. They are widely used due to their reliability, availability, and compatibility with a range of electronic devices and systems. In electric vehicles, cylindrical cells are grouped together into modules and combined into larger battery packs.
Prismatic Cells
Prismatic cells are packaged in a hard, welded aluminum or steel casing and feature a rectangular or square shape. It consists of electrodes, separators, electrolytes, and prismatic enclosures. The electrode materials and electrolytes are enclosed within a rectangular casing, which provides protection and insulation for the cell’s internal components. Similar to cylindrical cells, prismatic cells have metal tabs or leads attached to the casing, serving as the positive and negative terminals for external electrical connections. Prismatic cells offer advantages in terms of space utilization, packing efficiency, and mechanical stability. Their flat shape allows for efficient space utilization, making them suitable for applications that require compact and high-capacity battery packs, such as electric vehicles and energy storage systems.
Pouch Cells
Finally, we have pouch cells. Rather than using a metallic cylinder and glass-to-metal electrical feed-through, conductive foil-tabs were welded to the electrodes and brought to the outside in a fully sealed way. It consists of electrodes, separators, electrolytes, pouch packaging, and current collectors. The electrode materials and electrolyte are contained within a flexible, laminated pouch made of polymer materials, which is designed to be lightweight, thin, and durable. Current collectors, usually made of aluminum or copper, are attached to the electrodes to facilitate the flow of electrical current. Pouch cells have the highest packaging efficiency and great energy density, but tend to swell and therefore are more vulnerable to penetration. Unlike other cell formats, no universal sizes exist and each manufacturer designs its own (which is be a good thing, as they can be resized to fit each application's needs). They are found in thin profile handheld devices like mobile phones and modern tablets.
Sources
Deng, D. Li‐ion batteries: basics, progress, and challenges. Energy Science & Engineering 2015, 3 (5), 385–418. https://doi.org/10.1002/ese3.95.
Kumar, R. Lithium-Ion battery for electric transportation. In CRC Press eBooks; 2024; pp 156–172. https://doi.org/10.1201/9781003464556-8.
Post 3: 03: The Recycling Process of Lithium-Ion Batteries
Hi everyone! In this post, I will discuss the importance of battery recycling and the lithium-ion battery recycling process.
Circular Economy
When talking about recycling (in general), you might see the phrase "circular economy" come up a lot (or at least I did in my research).
A circular economy is an economic system designed to minimize waste and make the most of resources by reusing, repairing, or recycling materials and products, rather than being disposed of after use. This approach aims to create a closed-loop system where resources are continuously circulated within the economy, reducing the need for new resource extraction and minimizing environmental impact.
Some materials that exist in such a circular economy include glass, paper/card, steel, aluminum, plastic bottles, car catalysts and lead acid batteries. These are all well established and mature markets which grow at a manageable rate.
However, when new disruptive products and innovations come to the market with large growth potential, a product can rapidly become an environmental issue if a circular economy has not been designed with the product. Examples include the rapid growth of PET bottles, the rapid growth of waste electrical and electronic equipment (WEEE) or the rapid demise of cathode ray tubes.
Disruptive growth in technologies can occur when a new product becomes easy to mass produce, bringing it within the reach of a larger potential market. In the case of batteries, a key disruption was environmental regulation and focus on renewable energy, which has led to a shift from internal combustion engine to electric vehicles and an increase in the demand for metals such as Co, Ni, Li and Nd.
Recycling a Li-Ion Battery
Note: Battery recycling methods vary depending on the type of battery, so the following steps are specific to LIBs.
Before a battery is sent to a recycling facility, it is first evaluated for reuse—either being put back into a device similar to their original one or being repurposed in a different type of product or application. In the end, reuse simply delays the inevitable recycling of batteries when it finally hits the end of its life.
First, batteries go through pretreatment processes to separate the battery elements and prepare the valuable components for further processing. It consists of 3 main stages: discharge, dismantling, and separation.
A battery first needs to be discharged of any remaining power to prevent short circuits. There are many methods to do this; the most common is to use a salt solution, such as sodium sulfate (Na2SO4) or sodium chloride (NaCl). After discharging, the battery is disassembled and and separated into the categories: cathode, anode, and organic diaphragm. While this step can be done by hand; for mass amounts of batteries, machines do most of the work through shredding, sieving, magnetic classification, and segregation. Finally, the separation stage can consist of physical (such as floatation), mechanical (such as shredding and crushing), thermal (such as organic components evaporation), chemical (such as dissolution of binder or foils), and mechano-chemical processes.
After these steps, there remain:
“Black mass” (a granular material made up of the shredded cathodes and anodes of the batteries)
Copper and aluminum foils (which held the anode and cathode material)
Separators (thin plastic films)
Other plastics
Steel canisters
Electrolyte
Black mass contains the materials that can be further processed and made into new battery cathodes and anodes.
Recovering Black Mass
To recover black mass, there are currently 2 main methods: pyrometallurgy and hydrometallurgy.
Pyrometallurgy uses heat, such as through smelting or roasting, to convert the metal oxides used in battery materials to either metals or metal compounds. It consists of thermal reduction, smelting, and salt roasting. It results in elemental 'building blocks' that can be used to make new cathodic substances. Pyrometallurgy is often used due to its rapidity, simplicity, and flexibility. However, this method also requires large amounts of energy and releases toxic gases (such as CO2). This method also results in low product purity and only recovers copper of the foil and nickel and cobalt from positive electrodes, and not other materials like plastics, graphite, and aluminum.
Hydrometallurgy uses aqueous solutions to dissolve and extract metals from battery resources. It consists of leaching and recovering high-value elements from the leachate. The leachant usually consists of inorganic acids such as nitric acid (HNO3), phosphoric acid (H3PO4), hydrochloric acid (HCl), and sulfuric acid (H2SO4). Elements in the leachate are then extracted through separation and purification methods such as solvent extraction, electrolysis, and precipitation. Compared to pyrometallurgy, hydrometallurgy generates less emissions and needs less energy. It also recovers the metals individually, as opposed to the pyrometallurgical process, where metals are recovered as alloys. However, this method requires first sorting, which increases cost and complexity. It also releases unwanted wastewater.
Finally, there is also a third battery recycling method currently in development: direct recycling, which saves energy by skipping the shredding step and preserves the highly engineered cathode structure. However, one of the main obstacles that this method currently faces is the multiple material inputs, which can result in a lower efficiency and purity of the recycled batteries. Direct recycling is also relatively new, so it is currently only seen at the laboratory level and has yet to be tested and used by the industry.
Thus, there really is no 'perfect' way to recycle batteries, as they each have their drawbacks.
Sources
Dobó, Z.; Dinh, T.; Kulcsár, T. A review on recycling of spent lithium-ion batteries. Energy Reports 2023, 9, 6362–6395. https://doi.org/10.1016/j.egyr.2023.05.264.
Zanoletti, A.; Carena, E.; Ferrara, C.; Bontempi, E. A review of Lithium-Ion battery recycling: Technologies, sustainability, and open Issues. Batteries 2024, 10 (1), 38. https://doi.org/10.3390/batteries10010038.
Post 4: 04: The Issues with Lithium-Ion Battery Recycling
Hi everyone! In this post, I will look at the current issues with lithium-ion battery recycling.
There are many reasons to the low purity results of lithium ion battery recycling. Some of which (high energy and complexity) I have discussed in blog 03. In this blog, I will be looking a bit deeper and finding flaws that I might be interested in finding a solution to.
Successful Recycling of Lead-Acid Batteries
To evaluate the future of lithium ion battery recycling it is helpful to compare it with the successful lead acid battery market. These batteries were used to power the first EVs back in 1859 (they were later replaced by internal combustion engines).
The lead acid cell has, through numerous iterations, become standardized and is designed for recycling. Modern lead acid batteries are able to reuse >98% by mass of the material. This is due in part to the simplicity of their design, where the anode and cathode are Pb and PbO2, respectively. The lead acid battery is self-contained in one unit, not assembled into modules and packs, so it needs no disassembly prior to recycling. Finally, recycling a lead acid battery is also relatively simple: the case is crushed, allowing the sulphuric acid electrolyte to escape, and the lead electrodes are separated from the polypropylene casing and separator by density. The lead is smelted and the polypropylene can be reused in new casings.
Thus, it is economical to recycling lead acid batteries due to the relatively high cost of lead, and the process is an efficient one due to the uniformity of the materials used and battery design. The materials recycled from the lead acid batteries are then used to manufacture new batteries, closing the loop. This is why recycling rates of these batteries are almost 100% in the USA, Japan and most of Europe.
Structure & Design
Unlike the lead acid battery, the structure of lithium ion batteries is much more complex, with a series of small cells being collected together to make a module and a number of modules are assembled to make the overall battery pack. An automotive battery pack is composed of hundreds or thousands of cells, which not only have to be individually opened but also disassembled from the ensemble. The complex structure and risks associated with electric shock and potential fires make safe dismantling slow and labor intensive. For this reason, current approaches start with crushing the battery, in the same approach to lead acid batteries, but, for LIBs, this requires more steps, more energy and more chemicals.
There is also great variation in lithium ion battery cathode chemistries (such as variations of NCA, NMC, LMO, LCO and LFP). As there is no one-size-fits-all battery recycling method, and individually processing each type is costly and time consuming, the battery recycling method is generalized and ends up being economical. This is exasperated by the rapid advances in battery technology: two versions of the same car model may even have different battery chemistries. Thus, a desire for quick treatment and simple recycling, given present modest volumes, has led to processing techniques that are chemistry agnostic, resulting in lower purity products.
Module Issues
In automotive applications, battery packs need to be both power and energy dense, which can only be achieved by aggregating cells into modules, and modules into packs. Increasing the number of cells in a module decreases the ratio of active material to cell case and complicates the issue of opening cells.
One of the main issues is the way in which the cells, modules and packs are assembled. The cells themselves are hermetically sealed and the modules and packs are often glued together with adhesives. This provides rigidity, but means that they can often only be dissolved in molecular organic solvents. This prevents disassembly from becoming a viable recycling method due to the time and solvent requirements. Thus, the structures are clearly established for safety and potentially cell longevity, but at the expense of recycling efficiency.
Cell Issues
As I have discussed previously, there are various form factors of cells, each with their own shapes and sizes. The cells themselves are also constantly being improved to increase safety and performance, which usually comes at the cost of recycling efficiency.
For example in consumer electronics, prismatic cells are often stacked using a Z-fold configuration with parallel terminal tags (this design allows for easy automated manufacturing of the cells). To maximize the energy density, thinner current collectors, tags and separators are utilized where possible, and high loadings of active material are coated upon the current collectors, with low porosities. For safety reasons separators are often either slightly thicker to further separate the anode and cathode, or coated in a thin ceramic layer to help prevent short circuiting. For larger cell formats Z-fold configurations are more difficult, and therefore stacking or winding is more prevalent, for example in electric vehicle cell manufacturing. Stacking with individual separator sheets leads to an excess of separator, which is then incorporated into the pouch sealing, reducing the excess, but adding complexities in the separation of the anode and cathode from the cell during disassembly.
There is also development in the area of safety, as batteries are famously known to catch on fire easily. Some solutions, including shear thickening electrolytes to limit puncture damage, strengthened separators to stop dendrite penetration, redox shuttle additives to stop overcharging, and flame retardants in the electrolyte
and separator, add to the complexity of the cell and will reduce recycling efficiency.
Lack of Standardization
While the hazard labelling of lithium ion batteries is strongly regulated, there is a lack of compositional labelling for easy identification. Most battery packs contain no information about the chemistry of the anode, cathode or electrolyte, meaning that cells from the different packs need to be dealt with by the same process. The presence of different elements and binders can affect the efficiencies of separation and lead to contamination. Improved battery labelling would enable different battery chemistries to be separated before processing and would prevent contamination between different chemistries.
With no standardization of cells and the predominance of cells from small portable devices, this means that initial recycling approaches will be more similar to solid municipal waste, producing streams of lower purity. Additionally, the lack of standardization on pack and cell level coupled with the complexity of storage, transportation and handling of batteries all contribute to the increased cost and decrease the incentive to recycle.
Sources
Thompson, D. L.; Hartley, J.; Lambert, S.; Shiref, M.; Harper, G.; Kendrick, E.; Anderson, P. A.; Ryder, K. S.; Gaines, L.; Abbott, A. P. The importance of design in lithium ion battery recycling – a critical review. Green Chemistry 2020, 22 (22), 7585–7603. https://doi.org/10.1039/d0gc02745f.
Mao, J.; Ye, C.; Zhang, S.; Xie, F.; Zhou, R.; Davey, K.; Guo, Z.; Qiao, S. Toward practical lithium-ion battery recycling: adding value, tackling circularity and recycling-oriented design. Energy and Environmental Science 2022, 15 (7), 2732–2752. https://doi.org/10.1039/d2ee00162d.
Post 5: 05: The Role of Design in Lithium-Ion Battery Recycling
Hi everyone! In this post, I will explore how battery design can be used to improve battery recycling.
Battery Design For Recycling
As the name implies, this takes into account the recycling process when the batteries are designed, which can increase efficiency during recycling compared to conventional methods that involve shredding old batteries in their entirety. I've already touched on some issues of current battery structure design in recycling in blog 04.
There are 3 main pillars to battery design: pack and module design, cell design, and material design.
Pack and Module Design
One example of module (consists of multiple cells) design is standardizing screw connections and junctions between modules or cells to simplify the automated disassembly of cells. Efforts has also been made in providing regulations in battery classification and labeling, which may facilitate automatic sorting processes.
Cell Design
One example of cell design is substituting polymeric organic binders with water-soluble binders, which can potentially be effortlessly eliminated during the recycling process by washing with water. However, water-soluble binders may not provide the same long-lasting adhesion of the batteries’ active substances to metal foils as the current polymeric organic binders.
Material Design
One example of material design is the design of nanostructured hybrid materials based on carbon and metal oxidesm which can improve the kinetics of charge transfer and alleviate structural strain during charge and discharge processes. Additionally, the improvement of the metal oxide-based electrode materials can be obtained by the use of materials with better cycling performance, such as nanosheets, nanorods, and nanospheres.
Ease of Disassembly
Now, let's take a closer look at some specific design changes that can be used to facilitate recycling processes.
The main issue that I will be looking at is how to open the pack, module and cell easily. Clearly the outer pack design needs to be as robust as possible, so it does not fail in service, but this does not preclude mechanisms which are easier to open. Metallic tools need to be avoided to decrease the possibility of shorting the cell and igniting the contents.
Additionally, pack and module designs vary significantly, even within a manufacturer’s own fleets. It is common to assemble groups of cells into modules but the number of cells and configurations vary. Typically, regardless of the arrangement, cells in a module are permanently affixed to one another and are not intended to be broken down. Thus, any attempt to disassemble these joints are likely to be a destructive process.
Connections between modules are typically more serviceable and may employ technologies such as threaded or torqued connections or bespoke, mechanically constrained push-fit connections. The repeatable functionality of these connections makes the modules both more easily replaceable and simpler to disassemble at the end of life.
At the cell level, the polymer separator between the electrodes can be used as a method to separate the active components of the cell. One example used a vacuum conveyor equipped with pinch grips and a series of skimmers to separate the anode from the cathode and the separator. A Z-fold uses a single sheet of separator wound alternately between the anode and cathode in a cell. As the Z-fold is flattened out the anode and cathode will automatically be partitioned onto opposite sides of the separator. However, these separators can be very fragile and often rip during disassembly.
Recently, Chinese battery manufacturer BYD has developed long, thin cells called blades, which fit into a grid and can impart structural strength to the battery pack. This could remove the need for separate modules and glues, enabling simple disassembly and exchange for cells when faults develop. The optimized pack structure could also enable an increase of 50% in space utilization and lead to safer operation of cells.
Binders
The separation of active from inactive materials such as binder in cathode materials is necessary for economical and sustainable recycling. Organic-based binders, including PVDF, are widely used in cathode sheet production because of good electrochemical stability and adhesive property. Removing these binders can be done via heat-treatment, or toxic organic solvents, such as N-methyl-2-pyrrolidone (NMP). New organic binders with good solubility in mild organic solvents and binder distribution and adhesion forces that are well-characterized will have a direct relevance to recycling. Alternatively, a more straightforward mechanical-method can be used to separate PVDF from active components relying on decreased hardness and modulus of elasticity.
Water soluble binders, including carboxy methylcellulose (CMC), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or polyacrylic acid (PAA) are preferred as these are more environmental benign. A recent report discovered that aqueous-processed NCM 811 cathodes at pouch cells exhibited excellent capacity retention through 1000 cycles at C/3 of B70% compared with B76% for NMP processed cells. It also discovered that water-soluble binders boost recovery of NCM523 cathode compounds from spent electrodes using water, and that the regenerated NCM523 exhibited comparable electrochemical performance with that of the original state.
Electrolyte
Replacing flammable carbonates-based electrolytes with recyclable aqueous and solid-state electrolyte could be used to increase recycling safety. Aqueous-based electrolytes provide safe, low cost and scalable energy storage, together with reduced costs in battery recycling. However, compared with more traditional organic electrolytes, large-scale application of aqueous electrolyte is restricted by limited energy density and poor lifespan because of the narrow electrochemical window of water. High concentrate Li salt, especially containing LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), is an important component in these electrolytes. During recycling, these are harmful to the environment because of the high fluorine species. The development of low-concentration, or even fluorine-free aqueous electrolyte with acceptable electrochemical performance would therefore boost sustainability in recycling. Additionally, the use of solid-state electrolytes (SSEs) including, oxides and sulfides, boosts battery safety and separation efficiency, especially sulphide-based SSEs that can be dissolved in low-cost solvents such as alcohols.
Separator
Polyolefin materials are widely used as separator material in LIBs because of excellent mechanical properties, compatibility, chemical stability and low-cost. With traditional recycling of pyrometallurgy and hydrometallurgy, or judicious combination at small and large scale, separators combust to form carbon species. However, it is practical for the separator in spent batteries to be removed and used via direct recycling or re-used following facile treatment.
Currently, we don't know if there is a difference in electrochemical performance between cells using a fresh or recycled separator. There might be a practical design to modify the separator to boost recycling, based for example on fire-retardant, porous MOF-based,or anti-dendrite, separators.
Sources
Thompson, D. L.; Hartley, J.; Lambert, S.; Shiref, M.; Harper, G.; Kendrick, E.; Anderson, P. A.; Ryder, K. S.; Gaines, L.; Abbott, A. P. The importance of design in lithium ion battery recycling – a critical review. Green Chemistry 2020, 22 (22), 7585–7603. https://doi.org/10.1039/d0gc02745f.
Mao, J.; Ye, C.; Zhang, S.; Xie, F.; Zhou, R.; Davey, K.; Guo, Z.; Qiao, S. Toward practical lithium-ion battery recycling: adding value, tackling circularity and recycling-oriented design. Energy and Environmental Science 2022, 15 (7), 2732–2752. https://doi.org/10.1039/d2ee00162d.
Post 6: 06: The Use of Adhesives in Battery Design
Hi everyone! In this post, I will look at the use of adhesives in designing better batteries for recycling.
Battery Connections
Some examples of joining methods can be physical (clips, screws, springs etc.), metallic (welds and solders), inorganic cements or organic adhesives. Unfortunately, the in-service properties are generally at odds with the end-of-life requirements. In service the joint needs to be durable and non-reactive whereas at end-of-life it needs to be soluble or reactive.
Barriers in Recycling
Most recycling processes start with a disassembly of the battery pack down to either module or cell level. From there, most physical and hydrometallurgical recovery start with shredding to break joints and separate the different phases which results in cross-contamination between components and results in low value product streams.
Dismantling the cell down into individual electrode materials as an alternative to shredding, can significantly improve economics and product purity but it is hampered by the complexity of the component joining techniques. However, because pack, module, and cell design vary, it is hard to achieve fully automated disassembly. Current designs make disassembly complex due to the array of connectors used, the scale and packing of the cells and mechanical and chemical damage to the components during service. One of the biggest barriers to disassembly was the number of screws when disassembling from pack to module and the number of welds and structural adhesives as well as the number of modules when going down to cell level.
Cost savings (with respect to using new material) of up to 20% could be achieved using shredding whereas cell dismantling could recover material with up to 80% cost reduction. The advantages of shredding are that it rapidly reduces the active battery into a safer format. It is a process that is easily scaled, although the atmosphere around the shredder does need to be controlled. However, shredding does not separate aluminum from lithium metal oxide efficiently and attrition milling down to sub-mm scale is required to get reasonable separation. Additionally, impurities incorporated into recycled cathode material can significantly affect the performance of cells.
Battery disassembly is also limited by the use of non-reversible adhesives in products. In some cases, with thoughtful design and strategic placement, non-reversible adhesive bonds can potentially facilitate recycling, where they enable a “path of preferential breakage” which aids material recovery. Finally, moves to make the battery pack a structural element of the vehicle have led to an increased use in structural adhesives and permanent welds to increase pack rigidity.
Designs For Disassembly
Some examples of pack, module and cell design which can be adopted for simplified disassembly and recycling are:
Fewer, but larger cells
Minimal use of thermoset adhesives
Fewer fixing types
Cells that are more easily opened
Electrode binders that can be fully dispersed using water
The polymeric components can be split into two types depending on their applications:
Extracellular: These hold the cells, modules, cooling components and the Battery Management System (BMS) together and are chosen primarily for their strength.
Intracellular: These are chosen largely for their inertness and flexibility and maintain the active material in contact with the current collector.
Extracellular Adhesives
In most pack and module designs currently used in the automotive sector, structural adhesives provide rigidity and strength to the assembly. These are inexpensive to apply and irreversibly provide the strength needed to minimize movement of cells during use. Most of the adhesives used are thermosets, based commonly on epoxides or polyurethanes.
An important design for disassembly would be to avoid using structural adhesives as the only form factor imparting strength to a module or pack. One method could be to create a permanent link between pouch or prismatic cells and strategically place a small amount of adhesive at a point where selected directional movement could physically break the bond. One such arrangement could involve hinging the cells at alternate ends to create a zigzag conformation. This decreases the degrees of freedom that each cell can independently move in and generates levers between the cells. This could significantly decrease the amount of adhesive that needs to be applied to impart structural rigidity.
One possible alternative adhesive is pressure sensitive adhesives. Pressure sensitive adhesives (PSAs) are a versatile class of viscoelastic materials which form bonds using initial pressure and flow, unlike conventional adhesives, which bond once they have hardened through a chemical or physical process. PSAs do not require additional agents such as heat, water, or solvents to activate. The three main characteristics to be considered are ultimate adhesion, shear resistance and initial tack. Ultimate adhesion is the measure of the strength of the fully formed bond once the adhesive has set, shear resistance correlates to the adhesive resisting forces parallel to its surface and initial tack corresponds to the property that controls the instantaneous formation between the adhesive and adherend. Contact adhesives are easier to apply than thermoset resins and their application over large surface areas make debonding slow and necessitates large volumes of solvents.
Comparing Various PSAs
In a test to compare the effectiveness of different types of commercially available PSAs including glue dots, double-sided tape, and Velcro, a peel test with tensile testing apparatus was used to simulate how a real module of cells using the zigzag conformation would be pulled apart. Results are shown below:
Pressure Sensitive Adhesive | Average Load (N) | Maximum Load (N)
No Adhesive | 6.02 | 9.76
Glue Dots | 15.83 | 22.65
Velcro Strips | 31.9 | 67.89
Double Sided Tape | 58.67 | 103.77
Double-sided tape is the strongest adhesive of the set closely followed by Velcro. Both provide viable solutions to holding a zig-zag-configuration cell together, however weight and spacing must be considered alongside the ease of removal of adhesive. In contrast to glue dots or double-sided tape, using Velcro increased the thickness of the sample design by nearly 35%, decreasing the power density. Additionally, a weight calculation was carried out to evaluate each adhesive for the test sample, where it was found that Velcro contributes a relatively high amount of additional weight, while the glue dots contribute almost no weight.
Comparing the ease of removal of the adhesives, the double-sided tape was found to be the most difficult to remove, due to the sticky residue left behind. However, even this residue can be removed relatively easily with an acetone wash or by hand. Both Velcro and the glue dots did not leave residual material behind, thus making them a preferential choice in this respect as they would not require the additional removal step and therefore provide the simplest disassembly procedure. This is particularly useful in the area of pack or module repair and may decrease the proportion of cells being scrapped during production.
Sources
Scott, S.; Islam, Z.; Allen, J. K.; Yingnakorn, T.; Alflakian, A.; Hathaway, J.; Rastegarpanah, A.; Harper, G.; Kendrick, E.; Anderson, P. A.; Edge, J.; Lander, L.; Abbott, A. P. Designing lithium-ion batteries for recycle: The role of adhesives. Next Energy 2023, 1 (2), 100023. https://doi.org/10.1016/j.nxener.2023.100023.
Post 7: 07: Battery Designs for Recycling at the Cell Level
Hi everyone! In this post, I will explore some battery designs that can be used to improve battery recycling at the cell level.
Intracellular Polymer Binders
Once the cell is opened and the electrodes are separated, the next challenge is to separate the active material from the current collector and the polymeric binder. Polymeric binders provide adhesion and interconnectivity between electrode components, but they cause significant issues when left as a residue within battery waste streams obtained via shredding, known as the ‘black mass’. Interactions between the binder and the other electrode components occur during slurry mixing via two mechanisms: direct binding, where the binder is physically adsorbed to adjacent particles forming interparticle bridge and indirect binding, where the polymer forms a chemically inert network which constrains the particles.
Sufficient dispersion of particles is also imperative in the formation of homogeneous slurries and is dependent on numerous factors, such as the density, flexibility and polarity of polymers, to promote electrostatic repulsion. Usage of appropriate solvents for a given polymer facilitates dissolution and aid in dispersion of particles within the slurries. For instance, the conventional polyvinylidene fluoride (PVDF) binder possesses a high dipole moment necessitating the use of polar solvents, such as N-methyl-2-pyrrolidone (NMP), to dissolve the polymer and resist flocculation within the electrode manufacturing process.
Binders also play an important role in electrochemical performance as key attributes of the binders such as flexibility and oxidation/reduction resistance, can dictate the degree of structural changes and chemical decomposition, impacting the amount of capacity fade and consequently the lifetime of these batteries.
Alternative Binders
Recently, alternative water miscible binders have been the focus of research to reduce the usage of toxic solvents used in conventional electrode slurries, such as NMP. However, implementation of alternative binders is also essential to facilitate simplified and low energy separation of the electrode materials during battery disassembly. Fluorinated binders, such as PVDF, require high temperature pyrolysis to be removed, which produces toxic gaseous products such as HF during decomposition. In-service breakdown products from PVDF, such as HF, are capable of reacting with transition metal oxides within the cathode active materials, decreasing their capacity.
These conditions could be significantly improved if an alternative binder is used in manufacturing. At present, the use of alternative binders has been largely limited to current and next generation anodes, with the most common example being carboxymethyl cellulose (CMC)/styrene butadiene rubber (SBR), due to CMC being dispersible in water and SBR possessing good thermal stability, flexibility and adhesion. Additionally, other water miscible binders, such as guar gum, gelatin, sodium alginate and chitosan have been investigated, showing similar properties to the CMC/SBR binders, with the possibility to be further enhanced via modification. These water dispersible binder systems eliminate the need for the intensive conditions required for conventional battery separation steps, allowing facile separation of the active material and current collector, promoting the production of higher purity waste streams and simplifying subsequent recycling procedures.
Incorporation of alternative binders into the cathode, as well as the anode, would simplify subsequent recycling procedures, minimize the use of harmful solvents, additives and high-power consuming processes, as well as attaining better recovery of the cathode active materials, which currently make up the majority of the value of end-of-life batteries.
Environmental Impact
To assess the effect alternative electrode binders have on battery disassembly, a ultrasound delamination technique was used. This has already been shown to have a beneficial technoeconomic analysis compared to many hydrometallurgical processes. Only delamination was assessed, so that the environmental impact of replacing the conventional binders can be emphasized. To obtain the input materials for this process from the opened module, the cells acquired in the previous step would have to be opened before the cell components, i.e. electrodes, separators, electrolyte and packaging, are separated into distinct waste streams.
Two scenarios were investigated for electrode delamination, one being a reference scenario, using PVDF and CMC/SBR as the cathode and anode binders respectively. This scenario was compared to a hypothetical pouch cell using water miscible binder systems in both electrodes. Electrode delamination of the cathode and anode will result in the formation of four distinct waste streams; the separated anode/cathode active materials, and their respective current collector foils.
Figure 2 (a) shows a significant reduction in the GWP of ultrasonic delamination when alternative binders are utilized within the electrodes, with the recovery of both types of active material reducing their environmental impact. Figure 2 (b) and (c) show the power requirements and the GWP associated with solvent usage of ultrasonic delamination. This allows determination of whether the changes to the power output of the ultrasound or the solvents and additives used will reduce GWP the most. Since the anode already uses a water miscible polymer, CMC/SBR, the reduction in GWP is not as extensive as that seen for the cathode, where PVDF is utilized. Although the impact that changing the anode material has on GWP is smaller than for the cathode, the elimination of additives and associated manufacturing routes can be significant, when dealing with the considerable amount of battery waste which will be seen in the coming years.
While ultrasonic delamination is effective at removing the active material from the current collectors, the binders are still adhered to the active material particles, requiring high temperature processing in order to remove the binder. Overall, when comparing the reference scenarios to the best alternative scenarios, i.e. using the glue dot and ‘water miscible’ scenarios, the % reduction in GWP in producing the separate anode and cathode material is 150% and 173%, respectively. A similar reduction will also be observed in processing costs of battery recycling, when comparing the reference and alternative scenarios. It is reasonable to assume that novel cell designs, new structural adhesives and water miscible binders will minimize recycling processing costs.
Sources
Scott, S.; Islam, Z.; Allen, J. K.; Yingnakorn, T.; Alflakian, A.; Hathaway, J.; Rastegarpanah, A.; Harper, G.; Kendrick, E.; Anderson, P. A.; Edge, J.; Lander, L.; Abbott, A. P. Designing lithium-ion batteries for recycle: The role of adhesives. Next Energy 2023, 1 (2), 100023. https://doi.org/10.1016/j.nxener.2023.100023.
Post 8: 08: The Use of Debondable Adhesives
Hi everyone! In this post, I will be talking about debondable adhesives and how they might facilitate the battery recycling process.
Debondable Adhesives
Another way to tackle some of the issues is through the use of debondable adhesives. Debondable adhesives are designed to create a strong bond between two surfaces but can also be easily removed or debonded without damaging the materials or leaving residue behind. The primary stimuli for debonding are magnetic, ultrasound, UV light, chemical, thermal, and electrical.
In Battery Recycling
At the cell level, debondable adhesives used for binding the electrode current collectors to the active materials can be debonded, in milliseconds, using focussed, high-powered ultrasound as the stimulus. This process has several significant benefits: ultrasound is not generally experienced during material lifetime, reducing the risk of accidental debonding; recycling metrics are substantially better than for other techniques; and while already efficient, there is potential for future improvement with modification of the adhesive (binder) used. Therefore, on a cellular level, debonding of adhesives could be highly beneficial for recycling.
Unfortunately, there are numerous issues with debondable adhesives at battery pack and module level due mostly to the service conditions and the materials used. UV is an inappropriate stimulus, as the bonded substrates are not transparent at the appropriate wavelengths and the possibility of exposure to UV radiation during product lifetime is high. Within modules, thermally conductive adhesives are generally required to facilitate cooling, rendering thermal debonding highly problematic. In addition, a battery pack that falls apart on exposure to high or low temperatures would be catastrophic during vehicle lifetime, particularly in extreme weather events or during vehicle fires. Use of electrically debonding adhesives would also be highly unsuitable, as the conductive additives would cause short circuits and fires. Magnetic debonding also poses issues, due to the presence of magnetic components within the battery pack. Chemical debonding is also limited as many reagents are incompatible with the battery pack. All chemical redox reagents must be avoided for debonding due to risk of metal corrosion and water is too prevalent in the environment to be a safe debonding stimulus. Thus, while it is possible debondable adhesives could have some use in battery packs, however a more sensible strategy would focus on design that minimize adhesive use.
Sources
Mulcahy, K. R.; Kilpatrick, A. F. R.; Harper, G. D. J.; Walton, A.; Abbott, A. P. Debondable adhesives and their use in recycling. Green Chemistry 2022, 24 (1), 36–61. https://doi.org/10.1039/d1gc03306a.
Post 9: 09: The Role of Binders in Lithium-Ion Batteries
Hi everyone! In this post, I will explain the important tasks of binders in lithium-ion batteries.
Binders
Binders in lithium-ion batteries serve several vital functions that are crucial for both the performance and longevity of these batteries. One of their primary roles is to maintain the structural integrity of the electrode materials. They help hold together the active material particles (like lithium cobalt oxide or graphite) and conductive additives in a cohesive composite. Additionally, they also ensure good electrical contact within the electrode through maintaining a connection between the active material particles and the current collector, which is vital for efficient electron transfer and overall battery performance. While binders themselves are generally electrical insulators, they must not impede the movement of lithium ions. This ensures that the battery maintains good ionic conductivity, crucial for its charging and operational efficiency.
Binders must also accommodate the volume changes that occur in the electrode materials during charging and discharging. A good binder is flexible enough to absorb these changes without cracking or losing contact with the active material or current collector. This flexibility contributes significantly to the battery’s durability and cycle life. Binders also need to be chemically stable and inert in the battery’s electrolyte to prevent chemical degradation, which can lead to the breakdown of the electrode structure and battery failure.
In the manufacturing process, binders aid in creating a uniform slurry of the active material, which can be coated smoothly onto the current collector. This uniformity is essential for consistent battery quality and performance. Moreover, binders contribute to the environmental stability of the battery, protecting the electrodes from humidity, temperature variations, and other environmental factors.
Polyvinylidene fluoride (PVDF) is a common binder used in lithium-ion battery electrodes due to its chemical stability, mechanical strength, and good adhesion properties. It helps in forming a strong bond between the active material particles and the current collector, enhancing the electrode's structural stability during repeated charge-discharge cycles.
How They Work
Most binders realize the cohesion by physical interlocking or chemical bonding. Adhesion is a complicated process that is influenced by the bulk composition, surface chemistry, and the morphology (size, aspect ratio, and surface roughness) of both binders and the materials to be cohered. Moreover, the environmental temperature and humidity also affect the adhesion forces and even the mechanisms, which makes the process more intricate. One most typical example is dopamine and its derivatives, which are the most widely studied binder family. The catechol group is believed to be capable of interacting with almost all surfaces including metals, oxides and polymers via different mechanisms.
A recent study found that dopamine is capable of forming high-strength yet reversible bonds with both organic and inorganic surfaces via the adjustment of its own oxidation states. It developed a facile surface modification approach, in which a self-polymerization of dopamine produced an adherent coating on a wide variety of surfaces, where the wettability, processibility and many other characteristics of the materials could be highly changed. The study also discovered a highly reversible nanostructured adhesive, which could be even applied under water.
Another example commonly used in LIBs is carboxymethyl cellulose (CMC). CMC is believed to act as a surfactant to enhance the dispersity of the hydrophobic graphite. SBR contributes most of the adhesion forces in electrodes by physical interlocking. In Si-based electrodes, it is the carboxyl groups in CMC that form dynamic H-bonds and covalent bonds with the hydroxyl groups on the Si surfaces. That is to say, the same binder may work in different ways when used in different systems. Therefore, it is necessary to understand the properties of AMs in batteries to develop binders with better performance.
Sources
Takamori, N.; Yamazaki, T.; Furukawa, T.; Jayakumar, T. P.; Badam, R.; Matsumi, N. Facile Stabilization of Microsilicon Oxide Based Li-Ion Battery Anode Using Poly(vinylphosphonic acid). ACS Applied Energy Materials 2024, 7 (4), 1403–1410. https://doi.org/10.1021/acsaem.3c02127.
Zhang, L.; Wu, X.; Qian, W.; Pan, K.; Zhang, X.; Li, L.; Jia, M.; Zhang, L. Exploring more functions in binders for lithium batteries. Electrochemical Energy Reviews/Electrochemical Energy Reviews 2023, 6 (1). https://doi.org/10.1007/s41918-023-00198-2.
Post 10: 10: Aqueous Binders in Lithium-Ion Batteries
Hi everyone! In this post, I will look at some new improvements for binders in LIBs, such as water-soluble binders.
Improvements
Lithium-ion batteries are widely used in various applications but need improved binders to enhance their performance to meet evolving demands. This is because silicon oxide (SiO), a promising anode material due to its high capacity and low cost, faces several challenges. These include poor conductivity, which leads to slower charging rates, and significant expansion during charging.
Polyvinylphosphonic Acid
A recent study utilized polyvinylphosphonic acid (PVPA) as a binder for a micro-SiO electrodes, achieving superior performance compared to conventional cells. The study produced electrodes containing PVPA, PAA, and PVDF as binders, and their performance was assessed through electrochemical experiments and density functional theory. PVPA demonstrated notably stronger adhesion (3.44 N/m) to a copper support compared to conventional PAA (2.03 N/m), leading to significantly enhanced durability in lithium-ion batteries.
The PVPA-based cell also delivered almost twice the discharging capacity compared to the PAA-based cell after 200 cycles, with the PVPA-based half-cell achieving 1300 mAhg-1SiO after the same cycle count. Even after 200 cycles of charge-discharge, exfoliation from the current collector was not observed in scanning electron microscopy, unlike with PVDF or PAA binders. Furthermore, the stronger adhesion of PVPA helps stabilize the SiO-based anode, preventing its exfoliation even with significant volume expansion.
The study concluded that PVPA binder should be very useful in extending the life of high-performing lithium-ion secondary batteries. Particularly in the application of electric vehicles, there has been intense interest in enabling long life for lithium-ion secondary batteries. The use of PVPA will offer improved alternatives to commercially available binders, such as polyacrylic acid (PAA) and polyvinylidene fluoride.
Sources
Lingappan, N.; Kong, L.; Pecht, M. The significance of aqueous binders in lithium-ion batteries. Renewable & Sustainable Energy Reviews 2021, 147, 111227. https://doi.org/10.1016/j.rser.2021.111227.
Takamori, N.; Yamazaki, T.; Furukawa, T.; Jayakumar, T. P.; Badam, R.; Matsumi, N. Facile Stabilization of Microsilicon Oxide Based Li-Ion Battery Anode Using Poly(vinylphosphonic acid). ACS Applied Energy Materials 2024, 7 (4), 1403–1410. https://doi.org/10.1021/acsaem.3c02127.
Post 11: 11: Future Experiments
Hi everyone! In this post, I will outline a future experiment that will test various aqueous binders, focusing on strength and solubility in water.
Experiment
A potential experiment that can help support this research is to evaluate the performance and recyclability of battery electrodes using various aqueous binders, focusing on strength and also solubility in water.
Setup
To prepare, use multiple aqueous binders, such as polyvinyl alcohol, guar gum, or Alginate-based binders, to form multiple samples of the slurry. They would be then coated onto current collectors to make the electrode film, which is what the testing would be done on.
Testing
First, we must see their feasibility in use, by conducting tests that stimulate usage over the course of a battery lifetime. Thus, I can conduct tensile strength tests on the electrode films to measure their mechanical properties and performance tests using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and charge-discharge cycling tests to evaluate the electrochemical behavior and capacity retention.
To evaluate their feasibility in recycling, I can immerse the electrodes in deionized water to test the solubility and ease of separation of the binder from the active material. For collected data, I will measure the time required for binder dissolution and the completeness of active material recovery. And finally, I will analyze the recovered materials using a scanning electron microscope to assess their condition and potential for reuse.
To analyze the data, I will compare the mechanical strength and electrochemical performance of electrodes using the various binders with each other and also with traditional solvent-based binders, such as PVDF. Finally, I will identify any trade-offs between mechanical or electrochemical performance and recyclability.
Results
The expected results of this experiment should show that aqueous binders have adequate mechanical strength and electrochemical performance and the solubility tests should reveal that aqueous binders can be easily separated from the active materials, leading to a more straightforward recycling process.
Some future perspectives include assessing the scalability of using aqueous binders in industrial applications, considering factors such as cost, production speed, and compatibility with existing manufacturing processes or investigating hybrid systems that combine the benefits of multiple binders.
Sources
Scott, S.; Terreblanche, J.; Thompson, D. L.; Lei, C.; Hartley, J. M.; Abbott, A. P.; Ryder, K. S. Gelatin and alginate binders for simplified battery recycling. Journal of Physical Chemistry. C./Journal of Physical Chemistry. C 2022, 126 (19), 8489–8498. https://doi.org/10.1021/acs.jpcc.2c01282.
Post 12: 12: Conclusions
Hi everyone! As I wrap up my Senior Project journey, I wanted to share some thoughts and lessons learned from this project.
First off, I would like to say thanks to my advisors (Dr. Juner Zhu from Northeastern University, his post-doc Royal
Ihuaenyi, and Dr. Mo from BISV) for finding time out of their busy schedules and helping me throughout my journey.
If I was to do all over again, I would definitely want to start way earlier; like, during the summer. At the start, I was undecisive as to which project I wanted to do; and battery was actually not one of the ideas that I originally came up with. Since it was a last-minute decision, I had to do a lot of background research before I found battery recycling as a potential project. I was also late to reach out to potential internal advisors, and finally, I actually didn't finalize my experiment until a few weeks before the Senior Project was over, and by that time, it was too late to order supplies and materials. So, yeah, I would have definitely wanted to start over the summer, and by the time school started, I would want to have an idea confirmed as well as an external advisor, so all I really needed to do was to find an internal advisor and then go into the details of how the project was going to work, such as outlining a plan for each week.
A second thing (this one's specific to me) was that I should have reached out to any labs that I could do my work in. I had planned to do my lab work in BISV, but I underestimated the required equipment that was needed, and that hindered my progress in any experiments. I see now why most of the Senior Projects are CS or mostly online research and data collection (such as surveys).
Nonetheless, I was still able to learn a lot about battery recycling and share that with you. And after experiencing going through a research project, I have learned my lessons and next time, in college, when I go through the same steps again for another research project, I will make sure I don't make the same mistakes again.
I hope you enjoyed following me and my Senior Project. And if you're a future student looking at doing a Senior Project, I hope my journey has given you inspiration and I wish you the best.
Until we meet again. Kevin Xuan signing off.