Silicon is regarded as a promising anode material for increasing the energy density of lithium-ion batteries. In practice, it is often mixed with graphite. Here, one of the challenges is the irreversible loss of lithium during the first charge and discharge cycle. To compensate for this effect, additional active cathode material may be required, amongst other things – which increases the amount of material used and the cost of the battery cell.
This is where the pre-lithiation process developed by Asahi Kasei comes into play. The company uses relatively inexpensive lithium carbonate as an additional source of lithium. Its decomposition voltage is normally above the typical operating voltage range of lithium-ion batteries, which has made it difficult to use for pre-lithiation until now. Special electrolyte additives are now designed to enable decomposition even at lower voltages. During the first charge cycle, this provides additional lithium, which is intended to compensate for the initial capacity loss of the silicon-containing anode.
In internal tests, Asahi Kasei evaluated the process using an NMC cell whose anode consists of 90 per cent graphite and 10 per cent silicon monoxide (SiO). The energy density reportedly increased by 10 per cent. The company also cites improved cycle stability and lower costs per watt-hour. The company also does not provide specific details regarding absolute energy density, cycle life, or cost savings.
