Ars Technica busts a long-running myth about batteries – that they’re always five years away from any real improvement – with a look at how better batteries are already changing the way our tech works:
A lot can be done—and a lot has been done—to make a better lithium-ion battery. In fact, gains in the amount of energy they can store have been on the order of five percent per year. That means that the capacity of your current batteries is over 1.5 times what they would have held a decade ago.
“There’s energy density, there is power density, there is cost, there is cycle life, there is calendar life, there is safety,” Argonne National Laboratory’s Venkat Srinivasan told Ars. “What typically happens is that, in batteries, it’s a compromise of these different things.” Even just sticking to lithium-ion batteries, there are configurations and designs that can emphasize certain of these characteristics at the expense of something else. Energy density could be boosted a bit, for example, but maybe it comes at a higher cost or with a reduced cycle life.
This may be one of the causes of the frustration or skepticism directed toward news about battery research. A study may identify a way to significantly improve one characteristic, generating an exciting top-line conclusion. But the design may be impractically poor in some other way. While battery researchers learn from what does and doesn’t work, this means that a lot of laboratory batteries you may read about will never hit the market.
However, this also means there are a lot of knobs that can be used to customize a specific battery design. Even seemingly subtle things, like the exact thickness of the anode or cathode layer that gets deposited on its metal foil, can affect behavior. The thicker the cathode relative to its foil backing, for example, the greater the energy density of your battery, since less of the total volume is taken up by the foil. But a thicker material layer also means a longer journey for lithium ions and electrons. That generates more heat during battery operation and leads to shorter cycle life. Keep the cathode thinner, on the other hand, and it can handle higher charge and discharge rates, since the shorter journey is easier.
Some things—like faster charging—might be easy to notice in use or highlighted in a product’s marketing. Since companies tend not to give out detailed technical specs (especially if they’re not the ones making the battery), critical functions like thermal management or cell-level charge-balancing tend to fly under the radar. But improvements at the battery pack level have necessarily occurred alongside improvements inside the cells.
The original commercial lithium-ion battery, produced by Sony in the early 1990s, had an energy density of under 100 watt-hours per kilogram. That number has climbed over time, with the familiar cylindrical 18650 cells on the market hitting 200 watt-hours per kilogram by 2010. According to BloombergNEF, batteries used in electric vehicles have gotten as high as 300 watt-hours per kilogram in the last couple of years.
That has been easy to see if you’ve followed EVs at all, as the early options had nowhere near the range of what we see today. The first Tesla Model S offered about 210 miles of range, while it can now be purchased with up to 390 miles. The first Nissan Leaf could go about 75 miles, while a 2020 model can go 225 miles.
That’s not entirely down to increased energy density in the battery cells, of course. There are other variables, like the efficiency of the vehicle and the number of cells in the pack.
There’s a lot more at the link – the spiderweb diagrams alone are worth checking out.