A short note on Update in Battery Technology - 2022

QuantumScape’s solid-state battery — lithium metal with a solid electrolyte separating the two electrodes — is seen as an exceptionally bright prospect in an increasingly crowded space. Earlier efforts to build a solid-state separator (electrolyte) capable of working with lithium metal had to compromise on aspects such as the cycle life and operating temperature of the battery, and the issue of excess lithium deposits on the anode. QuantumScape claims to have circumvented this: its use of a solid-state separator technology eliminates the side reaction between the liquid electrolyte and the carbon/graphite in the anode of conventional lithium-ion cells. Volkswagen plans to have production running for solid-state batteries by 2025 via the partnership with QuantumScape.

Solid-state batteries: The energy density of lithium-ion cells used in today’s mobile phones and electric vehicles is nearly four times higher than that of older-generation nickel-cadmium batteries. Lithium-ion batteries use aqueous electrolyte solutions, where ions transfer to and fro between the anode (negative electrode generally made of graphite) and cathode (positive electrode made of lithium), triggering the recharge and discharge of electrons. Despite improvements in technology over the last decade, issues such as long charging times and weak energy density persist. While lithium-ion batteries are seen as sufficiently efficient for phones and laptops, they still lack the range that would make EVs a viable alternative to internal combustion engines.

One major problem is that lithium metal is extremely reactive. The main form of lithium corrosion are dendrites, which are branched lithium structures that grow out from the electrode and can potentially pierce through the separator and on to the other end, short-circuiting the cell. In current lithium-ion batteries, in which the electrolyte is a flammable liquid, dendrite formation can trigger a fire. QuantumScape says its solid-state lithium-metal battery replaces the polymer separator used in conventional lithium-ion batteries with a solid-state separator. The replacement of the separator enables the use of a lithium-metal anode in place of the traditionalcarbon/graphite anode. The lithium metal anode is more energy-dense than conventional anodes, which allows the battery to store more energy in the same volume, according to the company. The QuantumScape design is supposed to be ‘anode-free’ in that the battery is manufactured in a discharged state, and the negative electrode forms in situ on the first charge.

The advantages of the solid-state battery technology include higher cell energy density (by eliminating the carbon anode), lower charge time (by eliminating the need to have lithium diffuse into the carbon particles in conventional lithium-ion cells), ability to undertake more charging cycles and thereby a longer life, improved safety Lower cost could be a game-changer, given that at 30 per cent of the total cost, battery expenses are a key driver of the vehicle costs.