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Li-ion battery recycling challenges
Xiaotu Ma,1 Luqman Azhari,1 and Yan Wang1,*
SUMMARY
Lithium-ion battery (LIB) recycling is critical given the continued
electrification of vehicles and mass generation of spent LIBs. However, industrial-level recycling is hampered by a variety of factors
that make large-scale recycling difficult while maintaining economic
viability. Here, we address these challenges and provide guidance
toward solutions and future work.
Why is Li-ion battery recycling critical?
As part of an ongoing goal to reduce greenhouse gas emissions and limit the impact
of global warming, electric vehicles (EVs) are being widely adopted globally. To
date, more than 20 countries have announced plans toward electrification goals or
banning of traditional internal combustion engine (ICE) cars by no later than 2050,
and more than 120 countries and the European Union have announced net-zero
pledges in the coming decades.1 Moreover, car companies are beginning to aggressively pursue the electrification of their respective fleets; Mercedes-Benz has
announced that it will electrify its entire future lineup by 2030; Audi has declared
that it will abandon the manufacture of all ICEs entirely by 2033 while launching
only all-electric vehicles by 2026; Ford, General Motors (GM), and Stellantis intend
to ensure that 40%–50% of their sales are for zero-emission vehicles by 2030; and
Volvo is going to replace its entire lineup with all-electric cars by 2030. With such
aggressive growth of EV production, the demand for battery-related raw materials,
like Ni, Co, Mn, Li, and graphite, has naturally led to an increase in mining and production. However, even at the current level, there would be a long lead time to meet
the expected demand of the global supply chain.2 As a result, it is predicted that
there will be a severe shortage of raw materials in the future, especially for Li and Co.
Meanwhile, because the average lifespan of LIBs is 1–3 years for consumer electronics and 8–10 years for EVs or energy storage systems,3 approximately 0.2 million
tons of spent consumer LIBs and 0.88 million tons of spent power LIBs will be generated by 2023.4 If the spent LIBs cannot be adequately handled, the considerable
amount of spent LIBs will create significant environmental concerns, particularly as
toxic heavy metals and gases, such as Co, Ni, Mn, and HF, could be released into
the environment from improperly handled spent LIBs.2 Large accumulations of spent
LIBs combined with improper handling can also pose as a significant fire and explosion hazard.5 However, spent LIBs can also be viewed as a resource. The internal
materials in spent LIBs are all battery-grade, so they can be reintroduced into the
production of new batteries. Therefore, the recycling of spent LIBs could provide
a secondary source of materials generation to feed into the supply chain for new battery manufacturing. Furthermore, employing recovered cathode materials could
save over 20% of the total cost of a LIB, and more potential savings can be realized
by recycling more components beyond cathode materials from spent LIBs.6 In summary, LIB recycling can play a critical role in alleviating the current and future supply
chain concerns, prevent possible pollution and environmental hazards, and
generate sustainable and continuous economic benefits. It is a key piece of the
1Department of Mechanical Engineering,
Worcester Polytechnic Institute, Worcester, MA
01609, USA
*Correspondence: yanwang@wpi.edu
https://doi.org/10.1016/j.chempr.2021.09.013
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Figure 1. The technical challenges and commercialization challenges associated with recycling
lithium-ion batteries
puzzle toward the realization of sustainable LIB development for a greener society.
In this paper, we will discuss both the technical and business challenges of LIB recycling, which is shown in Figure 1.
Technical challenges
Our group has summarized recent advancements in fundamental research and industry practice of LIBs recycling including pyrometallurgical, hydrometallurgical,
and direct recycling methods.3 In the current state, none of the existing LIBs recycling technologies are ideal, as there are still many challenges and limitations to
resolve. Alongside this, the development of commercial LIBs is ever evolving. In
the efforts to achieve higher energy densities, longer driving range, and improve
safety, a significant amount of work has been focused solely on inventing new materials and improving battery design, which has consistently driven the fast evolution of
LIBs.7 Nevertheless, this rapid evolution of battery design and materials in use makes
recycling much more challenging, as described below.
Evolving battery design
LIBs typically exist in three main types of enclosures: cylindrical, prismatic, and
pouch cells. Cylindrical cells exist in many sizes, with the two most common sizes being 18,650 and 26,650. Prismatic cells are rigid and rectangular, also with different
sizes. Lastly, pouch cells come in even more different shapes and sizes and often
do not have a standard size in the industry. These three different types of LIB
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enclosures are furthermore used to form different modules and packs, presenting
particular challenges in attempts toward disassembly and pre-treatment. In particular, some modules consist of epoxy resin-bonded cells that are especially difficult
to remove or recycle.8 Additionally, because different layouts and contents of modules and packs can differ in order to improve space utilization efficiency for specific
EV designs, manufacturers are keen to develop and incorporate new battery configurations. For example, Tesla announced a ‘‘tabless" battery design in its Battery Day
event. BYD’s blade battery pack was introduced to increase the space utilization of
the battery pack by over 50% and bring LiFePO4 (LFP) cathodes back to the market.
CATL’s new cell-to-pack (CTP) technology increased volume utilization rates by up
to 20% and production efficiency by 50%.
Although these improved cell, module, and pack designs have helped popularize
EVs, they bring challenges for those interested in spent LIB recycling. The direct recycling process will incur the most difficulties because these special and varying battery designs make the necessary disassembly and separation of components much
more challenging. Pyrometallurgical processes, on the other hand, would face negligible challenges from evolving battery design because of their low requirements on
pre-treatment. However, it is less cost-effective because this process can only
recycle cathode materials and current collectors at a practical level.3 The hydrometallurgical process offers a compromise in between, which combines the advantages
of both the pyrometallurgical and direct recycling processes. Nevertheless, the
disassembly and pre-treatment technologies need to be further developed to lower
the recycling cost. Meanwhile, future battery designs should consider whether subsequent disassembly and separation is possible as a means to facilitate recycling.
Evolving battery materials
Since LiCoO2 (LCO) was first commercialized in 1991, the materials used in LIB cathodes have developed rapidly. Today, layered oxides, spinel oxides, and polyanion
oxides are the three main types of cathode materials. These cathodes can also be
composed of a variety of elements, such as Ni, Mn, and Co. In particular, LiNixMnyCo1-x-yO2 (NMC) is considered the most promising cathode material,9 and there
is a trend toward increasing Ni content while reducing Co content to increase the
capacity and reduce materials cost. Along with a variety of existing chemistries,
manufacturers could also use a blended mixture of two or more types of cathode materials in their batteries to obtain a desired performance. Therefore, recycling processes must consider how to potentially deal with blended cathode materials with
different chemistries and convert these materials to a formulation useful for current
batteries.
Anode materials are also being developed, from graphite to silicon-based, with a
goal to eventually utilize a lithium metal anode. Graphite is currently the anode material of choice in current LIBs but is often not recycled because of its low-added
value. However, with a large number of LIBs to be recycled, researchers should start
considering recycling technologies specifically for anode materials. Fortunately,
graphite and silicon-based anode materials are relatively inert, which means they
can be extracted easily in most recycling processes. However, it is still a challenge
to recover or regenerate original structures and performance. The layered structure
of graphite has been observed to collapse or become blocked by the intercalation of
Li ions after extended cycling.10 Silicon anodes experience severe expansion and
contraction during lithiation/delithiation processes, resulting in the breakage and
cracking of protective shells and subsequent pulverization of individual silicon
particles.
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All-solid-state batteries and Li metal batteries
There is an expectation in the future that all-solid-state batteries (ASSBs) will be adopted
because of their superior thermal and performance stability, lower cost, and enhanced
energy density compared with current LIBs.11 In fact, Toyota has begun road tests for
their prototype ASSB EV since June 2020. Volkswagen, Ford, and BMW are also
increasing their investment in ASSBs. However, recycling of ASSBs is nearly non-existent, and different types of solid-state electrolyte (SSE) chemistries and Li metal anodes
will pose additional challenges in the recycling processes. We have discussed the recycling of ASSBs in detail in previous work.11 The main challenge is the separation process,
which must include the separation of SSE from other battery components as well as the
separation of different types of SSE with potentially mixed feedstocks. Simultaneously,
although Li metal provides a high energy density as an anode, it will pose a significant
safety hazard because of its high reactivity. Thus, manufacturers need to consider recycling in ASSB design and material selection.
Commercialization challenges
Scaling up
Scaling up has two meanings. One is the path from academic research to initial industrial adoption and commercialization. Although academic researchers always
have innovative ideas, the systems are typically bench scale and simplified. In comparison, the industrial environment is large scale and complicated to economically
facilitate adequate throughput. Therefore, the mismatch of information between
academia and industry can limit the development of recycling technology (this is
also true for other fields).
The other meaning of scaling up is at the industrial scale and concerns the increase of
the throughput beyond pilot-scale plants. For example, the global spent LIBs will
reach around 2 million metric tons per year by 2030. However, less than 5% of spent
LIBs are actually collected and recycled today.12 Any notable level of LIB recycling
must occur at scales far beyond that of pilot plants, with the necessary capital and
economic viability at a level comparable with the amount of spent LIBs produced.
The main challenges that cause low recycling rates are the diversity, complexity,
lack of regulation, and non-standardization of LIBs, resulting in barriers for sorting,
disassembly, and pre-treatment steps, which reduces the profits of recycling processes and render them economically non-viable. Besides, there is a range of nontechnical challenges, such as the logistics concerning collection, transportation,
and storage of spent LIBs at a large scale.8 All these factors can limit the scaling
up of LIB recycling.
Economic benefits
Today, commercial recycling processes rely on the profits from recovering the valuable cathode materials in LIBs. However, Co, the most valuable element in the cathode, is intentionally being decreased in new cathode material chemistries, and thus
makes traditional LIB recycling more challenging economically. Therefore, optimizing or moving on from current recycling technologies to improve profits and
maintain economic viability is necessary and urgent, which brings plenty of research
opportunities to examine cost reduction and enrich business models, such as better
disassembling technologies, sorting and separating methods, universal recycling
process, design for recycling, and standardization of batteries.
Battery materials requirements/testing
It is also quite challenging to convince large battery manufacturers to accept recycled materials into their production lines. It must first be assured that the
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performance of recycled materials can match that or exceed that of virgin materials.
Most lab-scale tests are from coin cells or single-layer pouch cells with low electrode
loading (less than 0.62mAh/cm2) and low active material composition (80 wt %),
both of which are far behind the typical industrial requirements (3mAh/cm2 of electrode loading and 95 wt % of active materials composition in multi-layer pouch
cells). Thus, typical lab testing is far from convincing industrial manufacturers to
adopt recycled materials. Therefore, reliable testing needs to be conducted at
form factors beyond coin cells and single-layer pouch cells. Also, a side-by-side comparison with state-of-the-art virgin materials at industry level formulations and form
factors are necessary to deliver competitive benchmarking and alleviate concerns
around utilizing recycled material. Thus, collaborations with industry are encouraged to help universities or laboratories understand and meet industrial
requirements.
Summary
With the rapidly increased demand and wide adoption of LIBs, large amounts of
spent LIBs are being produced every year, posing critical concerns on supply chains
and the environment. LIB recycling is critical to sustain future supply chains and prevent significant environmental pollution. Furthermore, LIB technology is very dynamic, especially for cathode materials. For instance, the cathode materials in a
spent LIB may be considered obsolete by the time they reach end-of-life, and
even though they can be recovered to their original performance level, they may
no longer be desired or even accepted for further use. Thus, it is essential to understand the trend of LIBs when planning to recycle LIBs, as it can guide research on
optimizing regenerated materials and recycling processes. Besides, collaborations
between academia and industry are necessary and encouraged. Such collaborations
will help academia understand the actual needs of recycling technologies and material testing standards. With a better foundation, industry partners can convert
academic ideas to actual processes and products. We believe that the sustainable
recycling process will be realized for all types of current and future LIBs with the close
research and development between academia and industry.
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