How to Build a Safer, More Energy-Dense Lithium-ion Battery

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Wednesday, May 10, 2017

Chipmaking techniques contribute to a three-dimensional battery design that outperforms today’s best cells.

Hardly a month passes without shocking news of lithium-ion batteries catching fire: Laptops are torched, airlines are grounded, hoverboards go up in flames. The recent fires inside Samsung’s smartphone, the Galaxy Note 7, led to a $US 5 billion recall and then to a discontinuation of the model, moves that together cut Samsung’s market capitalization by many billions.

In January, after months of speculation, Samsung announced that two separate design problems created the battery malfunctions that caused some of the devices to overheat. That different design flaws can produce the same catastrophic outcome underlines the inherently unstable nature of today’s Li-ion batteries. Any mobile product incorporating them is thus potentially unsafe.

That danger is a result of design and production decisions made a quarter century ago when this type of battery was initially commercialized. Those decisions made sense at the time, but today we can do much better, above all by taking advantage of fabrication techniques honed by the chipmaking industry. Our company, Enovix Corp., in Fremont, Calif., has done just that, and we have demonstrated that we can produce Li-ion batteries that are smaller, less expensive, and fundamentally safer than anything now on the market.

Two key challenges faced Sony Corp. when it decided to commercialize the Li-ion battery back in 1991. Its handheld camcorder—a harbinger of many power-hungry portable devices to come—needed a very high capacity battery in a compact package. And audio cassettes were quickly giving way to compact discs.

Thermal Runaway in a Lithium-Ion Battery
How to Build a Safer, More Energy-Dense Lithium-ion Battery 1

The latter is relevant because magnetic recording tape for audio cassettes was made on manufacturing lines that coated a plastic film with a magnetic slurry, dried it, cut it into long strips, and rolled them up. Because the compact disc used a very different production process, Sony suddenly found itself with a surplus of equipment for manufacturing magnetic recording tape and of technicians to run these machines. Managers in Sony’s battery division realized they could solve the problem at a stroke by employing the same manufacturing equipment and personnel to coat chemical slurries onto metal foil, dry it, and cut it into electrode sheets. Then, to form the core of the battery, two sheets were interlayered with a polymer separator, which allows ions, but not electrons, to flow between the electrodes, and the whole stack is wound together like a jelly roll. This same production model—built around coated metal-foil current collectors—has been used by Li-ion battery manufacturers ever since.

This design was clever, but it made it harder to improve these batteries over the long term. For one thing, it wastes space.