EV Battery Afterlife

Electric vehicles or EV’s, are quickly becoming more popular. As the EV begins to take market shares from other vehicles, many questions arise. One of the questions that has not seen many answers is; what happens to the batteries when they are replaced, or when a car is totaled? The more popular EV’s become the more batteries there are on the road that will someday not be usable as an EV battery. Tesla and Nissan use to be the only EV’s you could get. Now, we as consumers, have more choices. The pool of EV’s is still small when compared to that of the internal combustion engine (ICE) or hybrid powertrains, but many manufacturers are now offering EV’s. This is helping push the sales of EV’s globally. We can see a trend of adoption occur as the major OEM’s (Original Equipment Manufacturer; Ford, GM, Stellantis, BMW, etc. ) begin to offer EV’s. This is especially true as they begin to offer EV variants of the popular models.

Let’s do a quick dive into what makes up an EV battery pack. Don’t worry, I won’t Make this a technical paper. This will be a high level basic component description.

An EV battery pack is made of a few key components. Firstly we have the cells. These cells come in a variety of shapes, voltages, and amp hours. The two most common are cylindrical cells, like you would buy for a flash light or child’s toy (think AAA batteries). The second most common is a pouch type cell, which is just what it sounds like, all the materials are held in a chemical resistant pouch. The next part of a battery is the modules. This is made of cells packaged together into a module of varying size and voltage. The next part that makes up a battery are the bus bars. These connect the various modules together to provide the voltage needed to vehicle. Before we can get that battery power to the vehicle powertrain, we need the next part of the battery, the contactors. The contactors are relays that are designed to handle the high voltage and current levels of the battery pack. These are needed for safety and allow the battery pack to have an “on and off” type function. Keeping this high level, I won’t Go further into how the contactors work. However, a major part needed to make the battery pack actually work, is a battery management system (BMS) and associated sensor. The BMS combined with the sensors monitor the cell/module voltage, temperature, current and manages the contactors. A couple final parts to mention, the thermal system and the power distribution unit. The power distribution unit contains the fuses for the high voltage components that make up the EV.

Now that we have a good description of what parts makeup a battery pack, let’s talk about the batteries life. The purpose of the battery pack is to provide voltage and current to the EV powertrain and all the auxiliary components. This may sound boring, but in reality the life of a battery is fairly exciting. When the driver wants to show off the acceleration of the EV, the battery has to provide all of its available current through the bus bars and the power distribution unit all while keeping its cool. If that wasn’t hard enough it then has to take as much current as possible back in to charge the battery back up. For this we engineers use a charge and discharge curve, which allows careful management of the battery cell.

Unfortunately, it cannot do this forever. Battery packs do have a life span. There is an end of life, typically measured in usable capacity. This is known as the State of Health of the battery pack. This is measured in kilowatt hours (thousands of Watts per hour). This is measured by taking the resting fully charged voltage of a battery pack, and multiplying it by the total Amps that can be drawn from the battery pack in one hour. [For reference the power of a car is measured in Watts, if we multiply the actual Amps (current), during acceleration for example, by the voltage of the battery pack at that point, then we get actual power at that point]. Recently I was part of an industry subject matter expert working group gathered to decide how we would determine what the end of life was on a battery pack. We determined that 70% of its useable capacity is the end of its useable life for an EV. We can also measure the end of life by cycles. Typically this is measured in charge and discharge cycles. There is also a natural degradation of the chemical process in the battery cells. Not to mention possible failures of individual cells, and modules that can cause a batteries life to be shortened. Most EV batteries have not actually seen the end of its natural life. Most battery packs that are replaced are due to some sort of failure of a module/cell, or car wreck. Most of the components in a battery pack are replaceable on there own. The bus bars are essentially a copper or other conductive metal bar and do not wear out. However, the cells/modules, and contactors do wear out. We have to take that into consideration when deciding what to do with a battery pack at the end of its life.

So what do we do with the battery pack at the end of its life, whether natural or otherwise?

This is a question that has not really been addressed.

Most battery packs that are replaced can be refurbished with replacement parts. Tesla and GM do this today with warranty replacement packs. The process is simple, diagnose the failure and replace the failed parts. This type of battery pack already has a second life use. It is sold as a replacement battery pack for reduced capacity battery packs.

What happens when a reduced capacity battery pack is replaced. This type of replacement cannot be repaired since all the cells have reached the end of life or 70% of there usable capacity.

Simply because a battery pack has reached its end of life for an EV, does not mean the battery pack is no longer useable.

This brings us to the original question of what can we do with these batteries? For this I say let’s look at a different market. The market of back up power supplies. In which we use these battery packs to store energy from the grid, Solar, wind, or other power source. Whether for home, businesses or even the electrical grid itself. Since backup power and power storage do not require large amount of current draw, or capacity, these batteries are perfect for this use. Typical power output requirement of an EV is 200kW. Typical power output and input of a home back up system is 50kW. That’s a big difference. That power draw also effects the batteries capacity.

This makes the back up power and energy storage market perfect for these battery packs that can no longer provide the range (capacity) or power that an EV needs.

By taking the EV battery pack and giving it a new life, we take a battery pack that would otherwise end up in a junk yard, or worse a landfill and give it new purpose.

Giving battery packs an after life not only is a great way to reuse a battery but also opens up a new market for potential sellers. The battery pack would have to be checked for safety and operational functionality but that is minor in comparison to storing a battery pack waiting for it to degrade or be torn apart, destroyed, and trashed.

Giving a battery pack a second life makes perfect sense. It keeps it from being a hazard in storage, and it allows the battery pack to be useful. More battery pack manufacturers or even independent companies should look into this market possibility and think about how to reuse the battery pack when it no longer can serve as an EV battery.

Where do we go from here? Maybe battery material recycling, battery pack rebuilding, reusing and repurposing cells and modules for drones or camping battery packs? Only time will tell.