Lithium-silicon batteries – or Li-Si in its chemistry short form – use silicon-based anodes and lithium-ions as their charge carriers. This combination has a relatively large specific capacity, or amount of charge per unit of volume by battery standards. However, the silicon-based anodes soon fracture and crumble after a few cycles. But recent research shows that voltage pulses restore some Li-Si capacity under laboratory conditions.
What Happens When Anode Electrodes Crumble
Some of the electrode material separates from the battery’s charge handling system after it fragments, according to Ars Technica website. This lost material remains inside the battery, depriving the charge system of some of its lithium power. But the research we touched on earlier suggests that some of this loss is reversible.
The root cause of this problem lies in the fact that silicon expands to a relatively large volume to accept lithium-ions. This may cause some of the anode materials to flake off and break away. Reducing the amount of silicon in the anode may moderate the expansion, but this is at the cost of the specific capacity.
How Voltage Pulses Restore Some Li-Si Capacity
Silicon’s ability to store lithium particles at a higher density level than other materials, is an opportunity not to miss. That’s because it could boost electric car driving range to a remarkable extent, and this would be a valuable achievement.
However the problem, as we outlined above, is that the lithium particles tend to fragment in the process. A group of Stanford University researchers reasoned that there must be a way to recover the lost electrode material, given the following assumptions according to Ars Technica:
- The lithium is unlikely to distribute evenly in the silicon fragments.
- This means the material has areas of higher and lower electron densities.
- Pulsing a current through the material would create an uneven electrical field.
- This procedure would cause the lost fragments to ‘bump into’ the electrode.
- Where this happened, they could reconnect with the current handling system.
Applying four volts for five minutes, to a lithium-silicon battery that was 50% degraded, reincorporated a third of the lost fragments into the main system. But the fact that the voltage pulses restored Li-Si capacity in a laboratory, does not mean that this would necessarily work with less-degraded batteries.
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