Battery repurposing is becoming an integral part of the battery industry. In order to make the battery manufacturing industry more sustainable, various stakeholders who use batteries are finding various solutions to reduce the carbon footprint. Battery repurposing is one of the most effective and sustainable methods to reduce a battery’s overall carbon footprint. Usually, new batteries are used for electric vehicles (EVs) to ensure reliable quality, safety, and high performance. The state of health (SoH) of newly manufactured batteries will typically be 100% and will gradually decrease once used. When the battery’s SoH reaches 80% or anywhere below 80%, they are removed from the EV vehicles and utilized for other second-life applications such as energy storage systems etc.
Because of the rapid adoption of EVs, many batteries are expected to enter the second-life market in the upcoming decade. At this rate, the second-life batteries market size is expected to increase from US $430 million in 2019 to $7,392 million by 2030, according to P&S Intelligence. Developing countries like India, Indonesia, the Philippines, Thailand, Sri Lanka, and areas in Africa are also expected to purchase a considerable market share of used batteries for second-life applications. Many of the second-life battery application customers are not properly validating the cells, which leads to various problems which include safety issues, performance decline, etc.
In the battery industry, quality assessment of batteries represents a challenging task, with second-life battery assessments representing an even more complex task. Such batteries require a strict quality assessment to allow for their second life application and any compromise in this area would imply considerable costs for the industry. This article offers suggestions for second-life battery cell consumers, with the top 5 parameters that should be considered before purchasing a used battery for the second-life application.
This article, highlight the most standard and important parameters common to most second-life batteries and does not offer an exhaustive review of all parameters at hand.
Top 5 parameters to look into before purchasing a used battery for second life application
State of Health (SoH)
Battery’s history and prior use
Batteries are composed of different chemistry, with unique features for individual chemistries used for specific applications. The voltage and current of the chemistries will vary with the given form factor. These are some of the chemistries which are used for various applications: Lithium Manganese oxide (LMO), Lithium Iron Phosphate (LFP), Nickel Manganese Cobalt (NMC), Lithium Nickel Cobalt Aluminum Oxide (NCA), Lithium Cobalt Oxide (LCO), Lithium titanate (LTO), etc. The research and development of new materials are evolving to increase the performance (e.g. energy, power, etc.) of batteries
Buyers should know exactly in which application they are going to deploy these second-life batteries. Because these Li-ion cells are classified as Energy cells and Power cells based on their performance and their specific application.
Energy cells - They have a high energy density, Designed for high voltage systems. But it has slow charging and discharging time and it has a longer lifetime.
Power cells - They have a low energy density, Designed for low voltage systems. but it quickly charges and discharges and it has a shorter lifetime.
Buyers should be aware of their dimension constraints beforehand in order to identify which chemistry cell they are going to purchase. Every chemistry has unique voltage and current profiles within the given form factor that will determine the dimensions of the model of the system. Customers should have a tentative budget. The clarity in the budget will also help the customer to choose the most desirable chemistry at the given budget.
State of Health (SOH)
State of health (SoH) is a numeric metric (in percentage points) used as a key parameter to explain the health of the battery at any given point. Typically, the battery’s SoH will be 100% at the time of manufacturing and decreases over time due to usage.
SoH is one of the most important performance parameters. The End of Life (EoL) of the new battery can be set when the battery loses 20% of its initial 100% capacity. The second-life battery starts its working phase at 80% SoH and the EoL of the second-life battery is fixed at 60% and sometimes at 40% SoH, based on its second-life application and battery chemistry.
It is ideal to use batteries with SoH ranging between 80% to 60% for second-life applications. For certain chemistries, you can even use the batteries with 40% SoH but it is completely application-specific.
It is not advisable to use a battery below 40% SoH, although some chemistry cells may perform sufficiently well below 40%, there is a high risk of falling into sudden death of battery is very high below 40% SoH.
There are various parameters to determine the cost of the battery, but SoH is one of the key parameters one should look at while procuring batteries for second-life application. Depending upon the specific application other parameters can be prioritized
Battery form factor
The battery form factor (Dimension details) is another important parameter one should look at before purchasing used batteries. Each form factor has its own performance advantages and unique thermal dissipation model. So it is good to pre-model the system with your preferred form factor and simulate the thermal dissipation and then choose the form factor for bulk purchasing.
Most of the time second-life application industries are not using this process, if you build your system with a perfect form factor it will improve the life of the battery too.
Cylindrical (18650,2170,4680), Prismatic and Pouch are the three traditional form factors of the Li-ion battery. Nowadays, new form factors like blade batteries and 4680 cylindrical cells are coming into the market for specific applications.
A battery’s datasheet is a brief technical document that compiles important technical specifications to explain the technical parameters of the battery cell.
Important parameters you should look for in the battery datasheet:
Number of cycles (Charging and discharging graph)
Cell chemistry and form factor
Note that if one’s battery belongs to a tier 1 manufacturer, then the data in the battery data sheet may be reliable, however, if your battery is from a tier 2 or tier 3 manufacturer, one may need to cross-check the data through third-party validation. Most of the time, second-life application industries do not cross-check datasheet information due to cost and time concerns, yet this is a crucial step.
Battery’s History and prior use
Many second-life sellers do not actually have information pertaining to the battery’s complete history and prior use. The history of batteries will help the assembler to understand the battery better. These are the following information one should know before making a purchase decision:
Who is the battery’s original manufacturer?
When and where was the battery manufactured?
In which application was it deployed?
Was the battery under a cooling system in its first life?
Data acquired by the Battery Management System (BMS).
Are there any safety concerns with this batch of batteries (like fire or overheating)?
Original performance datasheet of the battery provided by the battery manufacturer
Current performance datasheet of the battery provided by the reseller validated by a third party
Such information is crucial to know whether you are buying these batteries from a legal seller because countries have their own import and export policies. With a proper history of the batteries, you will not face any issues during the time of import in your country in which you do the assembly of the second life system. Sometimes you may also get tax benefits, but it depends on the country’s policy. The previous BMS data will help you to understand the battery better and you can decide whether to directly use the modules or if you need to dismantle them into individual cells to deploy in its second life application
This article outlines the top five parameters a buyer should consider before purchasing used batteries for second-life applications. We all know batteries are becoming a major part of the energy industry and the demand for batteries is growing, however adequate, safe, and durable battery use requires careful scrutiny. Its complexity is further increased in the case of a battery’s second-life application.
To make a second-life application safer, industry actors should adopt high-quality standards when analyzing, sorting, and assembling systems using second-life batteries.
About the Author
Intern - Battery Associates
Barath Venkatesan is a Junior consultant at Battery Associates. He has a bachelor’s degree in Nanoscience and Technology and is doing his master's currently in Material Engineering and Nanotechnology at Politecnico di Milano university in Milan, Italy. He is passionate about the circular energy economy and he currently works with various stakeholders in the battery ecosystem to create a sustainable world through the power of batteries.
The views expressed in this article are those of the author alone and not Battery Associates’.