Borate‐Water‐Based 3D‐Slime Interface Quasi‐Solid Electrolytes for Li‐ion Batteries

The development of solid‐state batteries (SSBs) that do not use hazardous materials as electrolytes and are not flammable is progressing rapidly, however the production of sulfide‐based SSBs requires strict low‐dew‐point control due to their high reactivity with atmospheric moisture and the concern of generating hydrogen sulfide, and several issues remain in terms of the cost and recyclability. Thus, low‐cost facile materials and low‐CO2‐emission processes are necessary. With regard to oxide‐type SSBs, which are attracting attention for their safety, there are issues with manufacturing suitability, as high‐temperature sintering of oxide solid electrolyte particles is required. A new quasi‐solid‐state (QSS) electrolyte with 3D‐ionic conduction and adhesive interfaces by combining amorphous Li2B4O7 and water (3D‐Slime Interface Solid Electrolyte: 3D‐SLISE) is synthesized without stringent dew point control and sintering. Electrode and electrolyte slurries containing 3D‐SLISE are applied to current‐collecting foils in air, naturally dried, and used to construct battery laminates. 3D‐SLISE‐QSSBs (LiCoO2 cathode/3D‐SLISE with 7 wt.% bound‐water/Li4Ti5O12 or TiNb2O7 anodes) maintain several hundred cycles of charge/discharge as a 2.35 V lithium‐ion battery. The 3D‐SLISE‐QSSB technology can promote the use of safe and low‐cost batteries, eliminate the need for a dry room during manufacturing, and enable direct recycling of active materials.