An ion-conductive Li1.5Al0.5Ge1.5(PO4)3-based composite protective layer for lithium metal anode in lithium-sulfur batteries

Lithium (Li) metal plays an indispensable role in Li-S batteries, but its fast degradation seriously impedes the practical application of Li-S batteries. Here, an ion-conductive LAGP-based composite protective layer (CPL) consisting of lithium aluminum germanium phosphate (Li1.5Al0.5Ge1.5(PO4)3) and polyvinylidene fluoride (PVDF) is prepared on Li metal anode via a facile casting method. In the presence of LAGP, the negative effect of CPL on the diffusion of Li+ is minimized. Hence, it can not only effectively resist corrosive action of lithium polysulfides (LiPSs) on Li metal anode, but also reduce interfacial polarization and restrain dendritic Li growth. The protected Li anode exhibits exceptional cycling stability and low voltage polarization (∼30 mV at 0.5 mA cm−2) for 300 h. The electrochemical performance of Li-S batteries with protected Li anode is also greatly enhanced. The discharge specific capacity of 832.1 mAh g−1 and an average coulombic efficiency of 92% are obtained for up to 100 cycles at 0.5 C in LiNO3-free electrolyte. Additionally, the rate capability of Li-S batteries is significantly improved, delivering a reversible capacity of 565 mAh g−1 at 4 C. Our results also indicate this protection strategy can be extended to the Li-S pouch cells.