Flexible Electrolyte Sheet Breakthrough for Advanced Lithium Metal Batteries

In the near future, lithium metal batteries with a flexible LLZO electrolyte sheet may be used in state-of-the-art electric vehicles (EVs).
Credit: Tokyo Metropolitan University

Mass-producing ceramic-based flexible sheet electrolytes at room temperature.

Researchers at Tokyo Metropolitan University have developed a new method to make ceramic-based flexible electrolyte sheets for lithium metal batteries. They combined a garnet-type ceramic, a polymer binder, and an ionic liquid, producing a quasi-solid-state sheet electrolyte. The synthesis is carried out at room temperature, requiring significantly less energy than existing high-temperature (> 1000°C) processes. It functions over a wide range of temperatures, making it a promising electrolyte for batteries in e.g. electric vehicles.

Fossil fuels account for most of the world’s energy needs, including the electricity we use. But fossil fuels are running out, and burning them also leads to the direct emission of carbon dioxide and other pollutants like toxic nitrogen oxides into the atmosphere. There is a global demand to shift to cleaner renewable energy sources. But major sources of renewable energy like wind and solar power are often intermittent — the wind does not blow all the time and the sun does not shine at night. Advanced energy storage systems are thus required to use renewable, intermittent sources more effectively. Lithium ion batteries have had a profound impact on modern society, powering a wide range of portable electronics and appliances like cordless vacuum cleaners since their commercialization by Sony in 1991. But using these batteries in electric vehicles (EVs) still requires a substantial improvement in the capacity and safety of state-of-the-art Li-ion technology.

This has led to a renaissance of research interest in lithium metal batteries: lithium metal anodes have a much higher theoretical capacity than the graphite anodes in commercial use now. There are still technological hurdles associated with lithium metal anodes. In liquid-based batteries, for example, lithium dendrites (or arms) can grow which might short-circuit the battery and even lead to fires and explosions. That’s where solid-state inorganic electrolytes have come in: they are significantly safer, and a garnet-type (type of structure) ceramic Li7La3Zr2O12, better known as LLZO, is now widely regarded as a promising solid-state electrolyte material for its high ionic conductivity and compatibility with Li metal. However, producing high-density LLZO electrolytes requires very high sintering temperatures, as high as 1200 °C. This is both energy inefficient and time-consuming, making large-scale production of LLZO electrolytes difficult. In addition, the poor physical contact between brittle LLZO electrolytes and the electrode materials usually results in high interfacial resistance, greatly limiting their application in all-solid-state Li-metal batteries.

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