The Other Storage Race

Tesla’s push to extend the life of lithium ion batteries used in cars by repurposing them for less-intensive applications could have a major impact on the business model for a whole slew of other markets.

As anyone with a smartphone knows, batteries degrade over time. A new phone holds a charge longer than one that has been in use for several years, but in the case of a smartphone that’s generally enough. Inside a car, it’s a whole different story. Those batteries need to function optimally for far longer periods of time, which is why Tesla recommends charging batteries only 80% to 90%. Following those guidelines, the batteries should be able to run up to 200,000 miles or more with only minimal degradation, and with the addition of different metals and additives, Tesla is claiming 5X longer life.

Lithium-ion batteries face challenges similar to electromigration in chips. As lithium atoms migrate from the cathode to the anode during charging, they begin to build up up over time. The longer the battery is charged, the greater the buildup and the less time the battery lasts between charges. This can be slowed down somewhat by changing the chemistry of the electrolyte solution, which is what Tesla is planning, but it doesn’t completely solve the problem. Batteries still age, and they age faster when they are charged to 100% and charged more often.

Nevertheless, what isn’t good enough for a car anymore may be good enough for the grid, and this is an interesting strategy for a couple of reasons. First, it provides a way for Tesla to get rid of all those batteries it no longer wants in its cars. So a battery made for a million miles probably won’t last a million miles because most cars don’t last that long. But it will function for years more without the cost of having to recycle and reclaim all of the lithium in those batteries, a dirty process that makes most environmental agencies cringe.

Second, that helps reduce the strain on the world’s lithium supply. No one is quite sure how much lithium will be needed over the next decade or two, but Arm researchers have said that even with coin-sized Li-ion batteries, a trillion connected devices will likely deplete the supply. This is an interesting way to extend the lifetime of what’s already out there, while conserving what may become an increasingly scarce resource.

The big unanswered question, though, is how safe these batteries will be if they are stripped out of vehicles and plugged into the grid. Batteries in a Tesla car are connected to a very sophisticated cooling system to prevent them from overheating and overcharging. Without that, it’s unclear just how safe these batteries will be, or how long they will last.

There is work underway at multiple battery startups and research sites to develop solid-state batteries, which are more stable and less prone to fires. Much of this is based on lithium polymers, although there is some work underway to use other materials such as sodium, as well. If this research proves successful, it could significantly lower the cost of developing new batteries, which would change the economics for re-using old batteries.

For a market that has operated largely out of sight for the past couple decades, battery technology is becoming very public and very interesting to a lot of people.