Ecmweb 8795 Ev Batteries Pr
Ecmweb 8795 Ev Batteries Pr
Ecmweb 8795 Ev Batteries Pr
Ecmweb 8795 Ev Batteries Pr
Ecmweb 8795 Ev Batteries Pr

Recharged for Reuse

Feb. 15, 2017
The benefits and safety challenges of a second life for EV batteries.

Electric vehicle (EV) use is steadily increasing on a global scale, thanks to two main drivers. First, automakers are looking for ways to address global warming concerns and emissions mandates. This — combined with government incentives to reduce greenhouse gas emissions in the auto sector (and rebates/other incentives to purchasers of electric vehicles) — is one sector driving growth. At the same time, the price of lithium batteries has been decreasing steadily while performance is up, making them an attractive option for use in electric propulsion systems.

Batteries used in electric vehicles vary in size from the smaller hybrid type to very large systems used for pure electric vehicles. They can contain anywhere from 30 to more than 7,000 cells, depending upon the type of battery being used.

By the year 2023, industry analysts forecast $26 billion in sales of electric vehicles throughout the world. According to a 2015 Navigant Research Leaderboard Report, “Lithium Ion Batteries for Transportation,” the global market for lithium-ion (Li-ion) batteries for light-duty consumer hybrid electric vehicles (HEVs) and plug-in electric vehicles (PEVs) is expected to grow by a compound annual growth rate (CAGR) of 31.9% to 61.3 GWh between 2015 and 2020. The majority (72%) of demand for Li-ion EV batteries is expected to come from battery electric vehicles (BEVs) due to the larger battery packs typical of such vehicle types.

This combination of factors results in a growing number of EV batteries that will be available for repurpose in the coming years, leading to the question of what can be done with them. The batteries used in electric vehicles vary in size from a smaller hybrid type battery to the very large systems used for pure electric vehicles. These batteries can contain anywhere from 30 to more than 7,000 cells, depending upon the type of battery and cells being used. It’s important to note that once an EV battery’s capacity has dropped to below 80% of its original capacity, its useful life for EV applications has essentially come to an end — meaning the battery needs to be replaced with a new one. Currently, Li-ion batteries are not commercially viable for recycling compared to their lead acid battery counterparts. It is prohibitively expensive to recycle Li-ion batteries because the recovery potential is not great.

With this potential resource of a large volume of Li-ion batteries that still contain most of their energy, it makes sense to try to find a new use for them. Enter the concept of “second life” for these batteries, which is under consideration by the auto industry and others.

Energy storage infrastructure

The question then becomes finding the best new application for these repurposed batteries. It seems that a very viable market is in energy storage systems. Electric utilities and others are looking to energy storage to resolve a variety of issues, including support for renewable energy, support for power generation during peak times to improve power quality, support for the transmission of power on the grid including improvement of power reliability, absorbing power surges due to excess generation, or other events on the grid. In addition, some jurisdictions are mandating increased levels of renewable energy along with energy storage to support these increases in renewables. For example, the California Public Utilities Commission (CPUC) had mandated that there be 1.3GW of energy storage installed in the state by 2020.

In addition to requirements for reliability of the power they supply, public utilities are under pressure to keep the costs of generation and storage as low as possible. Although declining, the price of batteries (including Li-ion units) is still high enough to make them an expensive resource for utilities. Therefore, obtaining safe and reliable Li-ion batteries at lower costs would be beneficial. This potential marketplace is also of great interest for the automakers who are trying to get more value out of these very complex battery systems, which comprise a major portion of the overall production cost of an electric vehicle.

Initially, the major users of repurposed EV batteries would be the electric utilities looking for a lower cost alternative to new battery systems. However, there is a growing possibility that second life EV batteries could end up serving in commercial or even residential applications. As energy storage applications become more widespread outside of electric utility-scale projects, there could be a market for what may be less expensive, but still safe, batteries for energy storage systems (ESSs).

EV battery chemistries, morphologies, battery vulnerabilities, importance of mitigation

What has to be evaluated are the types of batteries that could be considered for repurposing — and how to determine if these batteries are safe to be used in second-life applications after being used in an electric vehicle. Currently, EV batteries feature several Li-ion chemistries:

• Li(NiCoMn)O2 (referred to as “NMC”);

• Li(NiCoAl)O2 (referred to as “NCA”); and

• LiFePO4 (referred to as “iron phosphate” or “lithium iron phosphate”). This option is less-used because while the iron phosphate chemistry is considered to be more stable, it is not always a practical choice due to its lower energy density.

It’s important to note that all of these battery chemistries make use of organic solvent electrolytes and have the ability to enter what is referred to as thermal runaway, if subject to enough abuse or designed or manufactured improperly.

Li-ion batteries have been proven to be a generally safe and practical energy solution, when used as directed. They are virtually everywhere in today’s technology-driven world because they power many of the devices and products used by people on a daily basis — from electronics to EVs and now even energy storage systems. However, there have been incidents that have garnered a lot of attention, the most recent of which relates to batteries in some smartphones. This means that Li-ion technology needs to:

1) be designed with safety in mind;

2) have strong manufacturing quality controls; and

3) be used within its specifications in the end use application.

For most incidents that occur in the field, issues are typically related to a problem in one or more of those three areas.

First of all, the chemistry chosen needs to be suitable for the intended application because there are multiple chemistries within the Li-ion battery family. For example, a lithium cobalt oxide chemistry, which is prevalent in electronics applications, is not suitable for a high power application. Secondly, the design of the component cells used in the battery needs to have sufficient safety factor built in so that the cells can withstand the intended use and abuse conditions over the life of the battery. Thirdly, the cells should be manufactured with very strong manufacturing quality controls in place as the cell quality affects the safety of the overall battery.

The global market for Li-ion batteries for EVs is expected to grow to 61.3 GWh by 2020. As these batteries will not be suitable for EV motive use after a 20% loss of their capacity, this results in a significant number of used batteries containing a large portion of their capacity intact (Maxvis/iStock/Thinkstock).

Manufacturing errors, including contaminants introduced during the electrode manufacturing or cell assembly process, use of incorrect components such as using the wrong separators or electrolyte additives, misplaced insulation and incorrectly formed tabs, have been the cause of field incidents in products employing Li-ion batteries. The battery pack controls may be insufficient to maintain the cells within safe operating parameters, due to lack of sufficient monitoring, lack of redundancy of critical safety components, or because of improper operating specifications programmed into the controls. The batteries may be used in systems where there was not determination that various parts of the system worked together or which were unable to keep the battery within its safe operating parameters. This could be due to insufficient compartments, installation in close proximity to hot components that affect the battery, exposure to conductive fluids such as coolant (if employed) or external sources of water, controls and components that do not work appropriately together and result in stresses to the battery or environments outside of the battery specifications.

The way to mitigate these problems is through suitable designs that meet appropriate safety criteria at all levels — from the component level (such as the cell) through the battery design and end product system design. The manufacturing processes of all elements (from critical parts up to the full system) should include suitable controls so that everything is built according to specifications and tested to help ensure quality and safety.

This is critical for products using new batteries, but the same or similar requirements apply to batteries that are repurposed, although there may some additional or different steps needed in the process of manufacturing when using repurposed batteries. The “manufacturer” of a system using second-life batteries is typically not the original manufacturer of the battery. Therefore, it does not have control over the suppliers of critical components in the battery (such as the cells) in the way a manufacturer using new parts and cells does.

The successful second-life manufac­turer must have procedures in place to be able to take a used battery (built by another manufacturer), and assess the health of its various parts for repurposing. The challenge for this manufacturer is that the business does not typically have a direct link to the original cell supplier, BMS designer, and other supply chain players to obtain key information. Sometimes, the source of the used battery (e.g., the vehicle OEM) may be able to supply information on the used battery, but this cannot be guaranteed.

This requires the repurposing manufacturer to obtain all relevant information on the pack and its contents to make an assessment. What they cannot obtain in documentation and information from their supplier, they will need to make up with analysis and testing of the battery and its components because battery systems comprised of repurposed batteries will need to meet the applicable end product battery requirements, including construction requirements and testing. The unique difference from new battery assessments will be the testing and analysis done on the cell portions of the repurposed battery to determine their suitability for being reconfigured into a battery packs for a new application.

Safety requirements and standards

There are a number of UL standards addressing application-specific battery requirements that could be applied to a battery system using repurposed batteries. In addition, a new standard currently in development, UL 1974 - Evaluation for Repurposing Batteries, will address the unique requirements and process of assessing used batteries (such as EV batteries) and evaluating/grading them for reuse in another application. Unlike most other UL standards, UL 1974 will focus on what are essentially the manufacturing processes for repurposing batteries. These include gathering information on the used battery, assessing its health through a review of the battery information, analysis, and testing.

Once the used battery has passed through the repurposing processes, it is built into the end use application battery. At that point, it will need to comply with the battery criteria for its particular application. For example, UL 1973, Batteries for Use in Light Electric Rail (LER) and Stationary Applications would be applied to a battery pack intended for stationary applications while UL 2580, Batteries for Use in Electric Vehicle Applications and UL 2271, Batteries for Use in Light Electric Rail (LEV) Applications cover battery system requirements for motive applications. If a battery is intended for a stationary application, it will be evaluated to UL 1973, even those batteries containing repurposed batteries. If the stationary battery using repurposed batteries is intended for an energy storage application, it and the other components that make up the energy storage system are evaluated to UL 9540, Energy Storage Systems and Equipment.

All of these standards provide a set of safety criteria and a framework for evaluating a battery for certification for a specific application, which is important to manufacturers trying to site stationary batteries and ESSs.

The 2017 edition of the National Electrical Code (NEC) includes new requirements for storage batteries (Sec. 480.3) and ESSs (Art. 706) to be listed to appropriate standards; UL 9540 and UL 1973 are identified as appropriate standards for this purpose. The requirement to list these types of applications will also be included in the ICC International Fire Code and NFPA 1 National Fire Code. Listing of these systems will allow manufacturers to site these systems, with some limitations, indoors.

Although UL 1974 is not mentioned in the above-cited codes, it will be a means for assessing the health and safety of used batteries that can be incorporated into a stationary battery system, which will be subjected to UL 1973 evaluation criteria in order to be certified and installed in locations where these various codes apply. UL 1974 can be a path to acceptance for second-life batteries in their new applications. Compliance with the appropriate safety standards will not only help with code compliance, but will also help assure regulatory authorities, end users, insurers, and other stakeholders for battery systems that due diligence was done to ensure a safer system.

Battery analytical techniques

To support the necessary due diligence, UL 1974 addresses several different aspects of the process of preparing used EV batteries for repurposing, beginning with a gathering of any information that is available on the used batteries. This will require that the repurposing entity/manufacturer have a good relationship with its supplier. If the supplier is also the auto manufacturer, data should be available through documentation records of the construction, use and repair of the battery, information on why it was taken out of service, along with a wealth of detail about the actual battery through mining the battery management system (BMS) data gathered over the life of the battery.

Next, important data on the viability of the battery for reuse can be obtained through visual inspection and non-destructive testing that can be carried on at the complete battery pack level and continue through the disassembly, observation, and testing of subassemblies and parts of the battery. Non-destructive visual examination using techniques, such as X-ray or similar methods, can provide extensive detail down to the cell level regarding any damage it may have sustained, or evidence that various parts of the battery may need to be repurposed or rejected.

Additional testing can be conducted for individual modules or cells, depending upon the configuration, to determine the health and remaining capacity of the cells so these modules or cells can be “graded” for repurposing. This becomes important during reassembly because it’s critical to both safety and performance that systems have well balanced cells.

Finally, there are provisions for the repurposing entity/manufacturer to conduct testing on cells in order to develop and support a database of information to be used for process improvements, and to identify Li-ion battery technologies and designs that better lend them to repurposing. This information may inform automakers and others interested in the repurposing of EV batteries when making design decisions regarding cell chemistry, form factor, and overall battery designs so that these designs lend themselves to being used in the second-life market.

In conclusion

At the current rate of growth of EV sales, there will come a time in the near future when an abundance of Li-ion batteries still containing a good portion of usable energy will be removed from EVs and will become available either for disposal with some level of recycling or for repurposing. Due to the low recyclability value of Li-ion batteries, it makes sense from both a cost-perspective as well as from an environmental standpoint to get the most out of these batteries by, for example, repurposing them for another application such as stationary energy storage, before disposal. In order to effectively offer EV batteries a second life, however, assurances must be made that these batteries will perform as intended and be every bit as safe as a system built of new Li-ion batteries. The development of standards such as UL 1974 will hopefully move the industry forward, as they are intended to fill the gap that currently exists between the used EV battery market and end-use applications that can benefit from the availability of systems incorporating second-life batteries.     

Florence is a principal engineer with UL in Northbrook, Ill. She can be reached at [email protected].

About the Author

Laurie Florence | Principal Engineer

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