The problems with degradation that affects lithium-ion batteries is well understood. Cathode materials are susceptible to cracking over continued charge and discharge cycles, reducing the overall capacity and ability of the battery to operate efficiently. One of the stalling points for solid-state batteries is in the lithium that is also used within them forming 'dentrides' at the anode – tiny but ever-growing build-up of lithium which are a bit like stalactites in miniature.
Lithium is used in solid-state batteries just like it is in lithium-ion batteries which function with liquid electrolytes. The difference is that in a liquid state battery, lithium ions float back and forth between the anode and cathode each time it's cycled to charge or discharge. In a solid-state battery, the same process is carried out through a solid material – as the name suggests.
This transfer in a solid-state battery is more efficient. It produces less heat, and the batteries don't go bang when they're compromised, so there are numerous benefits alongside being smaller and lighter.
Back to the dentride problem, and as these crystalline structures build up over time they can push through the anode and cause tiny short circuits. This is bad for battery life and efficiency. What Samsung's research has done is find a way to mitigate this problem by creating a buffer, in this case by adding a five-micrometer thick layer of silver-carbon composite. If we're delving even further into the chemistry, they also used a solid sulfide electrolyte and a high-nickel layered oxide cathode which further reduced the build-up of lithium deposits.
If all of that didn't make much sense, think about it using this easy-to-understand analogy: if we think of the dentrides as stalactites slowly growing and blocking a path, the silver-carbon composite is like someone with a hammer who comes and chips away at them regularly to keep the path open. It won't stop them growing, but it'll ensure the way is clear for far longer.
Samsung's figures from its prototype battery are impressive when considered in the context of an EV. It can store more than 900 Wh per litre (with Wh/litre being broadly similar to Wh/kg as we've previously used), which is around double that of a regular lithium-ion battery by volume. Effectively, for the same physical size of battery as used in the current 62kWh Nissan LEAF, the car could travel almost 500 miles.
What's more, Samsung's breakthrough technology is astoundingly efficient at dishing out the energy that was put into it during charging. In testing, researchers found that 99.8 per cent of the energy that went in came back out again. And it'll keep achieving high efficiency figures throughout its potential lifespan of around 1000 charge and discharge cycles – which on the aforementioned LEAF could represent somewhere in the region of half a million miles of driving.
As ever with solid-state battery news, with each passing development it feels like we're one step closer to them being a reality, and that holy grail finally being within the industry's grasp. But there are still many steps to go until it's a reality, and then there's the associated cost of an emergent technology. Companies also engaged in the development of solid-state batteries such as TerraWatt reckon that we're still between four and five years until EVs gain solid-state power, and that seems like a reasonable assumption given the amount of development that is still going on.
That being said, the way lithium-ion technology has come on, and still continues to be honed and perfected, Samsung's latest breakthrough could prove to be a major step towards commercial viability.
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