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From The Economist of 30 Jul 2020:

To provide buyers with some peace of mind, carmakers guarantee their batteries, typically for eight years or around 200,000 km. Producers are now, though, planning to go much further than that, with the launch of “million mile” batteries.

American law says batteries must last 100,000 miles. This is accomplished by not letting batteries discharge too much. By not charging too fast. And by charging and operating most often at temperatures closer to 50 degrees F.

To be able to charge on a 90 degree F day, I can only assume a Tesla has some sort of battery cooling system.

The lithium-ion (Li-ion) batteries which power electric cars age in two ways: with time and with use. Battery-makers call time-dependent ageing “calendar ageing”. It is a consequence of the gradaul degradation of some of the materials employed in battery construction. This degradation reduces a battery’s ability to hold a charge—though even here it is possible to ameliorate the problem to a certain extent. Leaving a car with a fully rather than partly charged battery, for example, can increase the rate of calendar ageing. ...

Each cycle of discharge and recharge takes its toll. Lithium is so highly reactive that stopping it getting tied up in other chemical compounds while a battery is in use is hard. Even a small amount of diversion per cycle adds up, reducing the amount of the element available to store energy. On top of this, changing up faster than ions can be absorbed by the anode may result in a layer of lithium “plating” building up on the anode’s surface, reducing its storage capacity.

Plating becomes yet more of a problem if it leads to the development of structurs called dendrites. These are small, finger-like fibres which project into the electrolyte from points on the anode where plating is especially elevated. If a dendrite reaches the cathode the battery will short-circuit, causing it to heat up rapidly and possibly catch fire. ...

Once a battery’s capacity falls below 80% of its starting value, it is generally thought no longer suitable for use in vehicles. Some reckon that, on average, Li-ion battteries lose 2% of their capacity a yaer. This may not seem much, but by the time a vehicle is six years old it could mean it is halfway through its useful life.

Most of the article recites GM claims. As if GM is well ahead of everyone else with its Ultium batteries. Production starts in Ohio next year.

Elon Musk has hinted that Tesla, a Californian maker of electric vehilces of which he is boss, has a million-mile battery in the works. Rumours suggest this could be unveiled in September.

Plans are afoot to let electric-vehicle ownrs connect their jalopies to the grid in a way that will store surplus electricity generated in times of plenty by wind and sunshine and release it during hours of peak demand, with the owner collecting a fee for doing so. That means these grid-buffering vehicles will be racking up lots of charging cycles even when they are not moving.