High performance solid state lithium batteries with a continuous homogeneous Li+ transmission channels

Abstract

Solid state lithium batteries have been encountering a bottle neck of high solid-solid interface resistance of the membrane/electrode assembly, which is one industrial pain point. Herein, the composite solid electrolyte materials were designed and prepared to act as the double functions of solid state electrolyte membrane and the electrode binder for constructing a continuous homogeneous Li+ transmission channels with high compatibility and ionic conductivity. Firstly, dopamine was oxidized and self-polymerized on the surface of polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) to form a polydopamine (PDA) active layer, and the zwitterionic betaine sulfonate (SB) was chemically grafted onto the PDA active layer by Michael addition reaction. Secondly, the composite solid electrolyte materials were prepared by mixing the resultant SB-modified PVDF-HFP was mixed with different contents (0 %, 10 %, 20 %, 30 %) of Li6.75La3Zr1.75Ta0.25O12 (LLZTO) and 20 % bis(trifluoromethane) sulphonyl lithium (LiTFSI). Finally, a series of composite solid electrolyte membranes were prepared by scraping method and labeled as 0%LLZTO/SB-PVDF-HFP/LiTFSI, 10%LLZTO/SB-PVDF-HFP/LiTFSI, 20 %LLZTO/SB-PVDF-HFP/LiTFSI, 30%LLZTO/SB-PVDF-HFP/LiTFSI, respectively. As expected, the cell with optimal 20 %LLZTO/SB-PVDF-HFP/LiTFSI as the solid electrolyte membrane and the electrode binder delivered the reversible capacity of 135.2 mAh/g at 1.0C and maintained high capacity retention of 94.8 % for 200 cycles. The construction of the continuous and homogeneous ion transmission channels should be responsible for high Li-storage performances by improving the interface compatibility of the membrane/electrode assembly and promoting the Li+ transmission.