Device found to retain 95% capacity after driving 500,000 kilometres
The quest for safer, durable and inexpensive batteries for electric vehicles crossed a new milestone recently. Tests conducted on a prototype solid-state battery built by United States-based company QuantumScape retained 95 per cent of its capacity after driving after completing 1000 charging cycles.
For an electric car with a range of 500-600 kilometres, this corresponds to a total mileage of more than half a million kilometres. Typically the industry standard target for this development phase of a solid state battery is about 700 charging cycles and a maximum capacity loss of 20 per cent. The results indicate a big breakthrough in the history of lithium ion batteries.
This was announced by PowerCo, global automaker Volkswagen’s battery company that conducted the tests over several months. The device can be a potential solution to multiple challenges electric vehicle (EV) batteries face at the moment regarding cost, safety, capacity, charging time as well as durability.
The battery tested by PowerCo is different from the lithium-ion battery used in EVs today. It uses a solid electrolyte as opposed to a liquid electrolyte used in conventional lithium-ion batteries.
Typically, cells used in EV batteries have four essential components — two electrodes, a liquid electrolyte and a separator. While liquid electrolyte is widely used for its high ionic conductivity and wettability and helps move ions from the cathode to the anode while charging and the anode to cathode with discharging, it poses safety and performance challenges.
In comparison, the solid-state electrolyte, which also serves as a separator, offers improved temperature tolerance, does not leak and is non-flammable. Studies have shown that solid electrolytes can adapt to higher-than-ambient temperatures (60-120°C), which may make them more suitable for Indian conditions.
While in all solid-state batteries, the liquid electrolyte is completely replaced, several solid-state battery concepts have initially used liquid electrolytes as catholyte or anolyte on electrodes to guarantee sufficiently high ionic conductivity, especially at the interface between the electrolyte and the electrode materials.
Seen as a futuristic technology, it took 40 years to solve the research question of solid-state batteries. For decades, researchers have tried to harness the potential of solid-state and lithium-metal batteries, which hold substantially more energy in the same volume and charge in a fraction of the time compared to traditional lithium-ion batteries.
All through these 40 years, researchers struggled to push the technology up the development ladder. It was stuck at the laboratory level because the scientists could not provide satisfactory answers to the questions of high cycle life, good thermal stability and high current density.
Solid-state batteries can use metallic lithium for the anode and oxides or sulphides for the cathode, increasing energy density. Materials that hold promise for use as electrolytes include ceramics ( oxides, sulphides, phosphates) and solid polymers.
QuantumScape’s anode-free solid-state lithium-metal cell is built in 24 layers and can easily be replicated for series cell production. The next step for series production is to scale the manufacturing processes.
Anode-free cells have no active materials on the anode in the beginning. It has neither carbon nor predeposited lithium on the current collector and all the lithium metal is drawn directly from the cathode during the first charge. The potential advantage of these devices is an increase in energy density.
Several automotive companies are invested in solid-state battery technologies. The Volkswagen Group has been involved with QuantumScape since 2012 and is one of the main investors in the company. Others include BMW which has invested $20 million in 2022 in Solid Power to expand production of solid-state batteries and Toyota and Hyundai that have announced the launch of their solid-state battery EV in 2025.
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