Asahi Kasei’s pre-doping technology cuts first-cycle capacity loss in silicon-rich cells

Asahi Kasei has developed a lithium pre-doping technology for high-voltage lithium-ion batteries with silicon-based anodes. Lithium carbonate, added to the cathode as an extra lithium source, makes up part of the capacity that silicon-rich cells lose permanently during their first charge and discharge cycle.

EVs are among the applications calling for higher cell energy density, according to Asahi Kasei. Development work has focused on two changes: partially replacing the anode’s graphite with silicon-based materials; and raising the operating voltage of the cathode. The pre-doping technology addresses the penalty that comes with the first.

Silicon holds more lithium per gram than graphite, which is why cell makers blend it into predominantly graphite anodes. The trade-off is a large irreversible capacity loss on the first charge, which limits both cycle life and energy density. Compensating for this means loading in extra cathode active material, which drives up material use and cost.

Lithium carbonate is relatively inexpensive and has an established track record as a battery material, Asahi Kasei says, but its decomposition voltage sits far above the nominal operating range of a lithium-ion cell, which has made it difficult to use for pre-doping. The company’s technology uses special additives in the electrolyte to promote the decomposition of lithium carbonate at the cell voltages at which standard batteries already run. Pre-added to the cathode, the carbonate decomposes on the initial charge and releases its lithium into the cell.

In internal tests on an NMC cell with an anode composed of 90% graphite and 10% silicon monoxide (SiO), Asahi Kasei measured a 10% increase in energy density.

The company also says the technology improves cycle life at low cost per Wh. The company says the technology can be applied without significant modifications to existing battery manufacturing lines and expects it to work across a range of cathode and anode material systems.

The company will now conduct proof-of-concept evaluations with global customers, alongside licensing arrangements that will be phased to each customer’s stage of development.

Source: Asahi Kasei