An ultrathin, strong, flexible composite solid electrolyte for high-voltage lithium metal batteries

The urgent need for safe, energy-dense electrochemical storage devices calls for high-voltage solid-state lithium metal batteries. However, state-of-the-art solid-state electrolytes are hindered by two critical issues: the narrow electrochemical window, which prevents the pairing of a lithium metal anode with a high-voltage cathode, and the large thickness which leads to a huge internal resistance and a significant sacrifice in energy density. To simultaneously address both the issues, in this work we develop a poly(acrylonitrile) (PAN)-LiClO4-boron nitrite nanoflake (BNNF) composite electrolyte modified with a BNNF layer (PBCEB). The PAN-LiClO4-BNNF composite can sustain an oxidation voltage of up to 4.5 Vvs.Li/Li(+)while the BNNF modifying layer prevents the PAN-LiClO4-BNNF from the reduction reaction with the lithium metal anode. In the meantime, thanks to the BNNFs, the PAN-LiClO4-BNNF possesses a strong tensile strength (16.0 MPa) and Young's modulus (563.7 MPa), which enables the PBCEB to be as thin as 13.5 mu m (12.0 mu m for the PAN-LiClO4-BNNF and 1.5 mu m for the BNNF modifying layer). As a result, a Li/PBCEB/LiNi(0.8)Co(0.1)Mn(0.1)O(2)full battery delivers a high specific capacity of 173.6 mA h g(-1)at 0.2C and achieves a remarkable capacity retention of 68.1% after 350 cycles at 1C. This work provides an effective approach to develop high-performance composite solid electrolytes for high-voltage lithium metal batteries.