Rechargeable batteries keep getting cheaper

When I started working on lithium-ion batteries, in 1993, Sony and Toshiba had introduced the first such commercially available batteries a couple of years earlier. They were mostly used in “the 4 Cs” of small consumer electronics – cassette players, camcorders, cell phones and computers.

If anyone had thought about putting a bunch of lithium-ion batteries together into huge battery packs, for vehicles or utility distribution systems, they would have stopped as soon as they found out the cost: almost $200,000 per kilowatt-hour (kWh) stored. Even if a battery was used 10,000 times, using it to...