Tokyo Metropolitan University scientists have developed a new method to make ceramic-based flexible electrolyte sheets for lithium metal batteries.
They have successfully produced a quasi-solid-state sheet electrolyte by combining a garnet-type ceramic, a polymer binder, and an ionic liquid.
The synthesis was carried out at room temperature, requiring significantly less energy than existing high-temperature (> 1000°C) processes.
According to the scientists, the ceramic sheet can function over a wide range of temperatures, making it a promising electrolyte for electric vehicle batteries.
Solid-state inorganic electrolytes are significantly safer that their liquid contemporaries, and a garnet-type 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, 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.
Now a Tokyo Metropolitan team led by Professor Kiyoshi Kanamura has found a way to remedy this by developing a flexible composite LLZO sheet electrolyte which can be made at room temperature.
They cast a LLZO ceramic slurry onto a thin polymer substrate, like spreading butter on toast.
After drying in a vacuum oven, the 75-micron thick sheet electrolyte was soaked in an ionic liquid (IL) to improve its ionic conductivity.
ILs are salts which are liquid at room temperature, known to be highly conductive while being almost non-flammable and non-volatile.
Inside the sheets, the IL successfully filled the microscopic gaps in the structure and bridged the LLZO particles, forming an efficient pathway for Li-ions.
They also effectively reduced interfacial resistance at the cathode.
On further investigation, the scientists found that Li-ions diffused through both the IL and the LLZO particles in the structure, highlighting the role played by both.
According to the scientists, the synthesis is pretty simple and suitable for industrial production.
Image and content: Tokyo Metropolitan University/Eurekalert