Fast‐Charging Long‐Life Solid‐State Sodium Metal Batteries Enabled by 2D Boron Nitride Nanosheets Based Quasi‐Solid‐State Electrolytes

Abstract Solid‐state sodium metal batteries (SSMBs) are considered as one highly competitive, high‐energy‐density yet safe energy storage device, however, the conventional quasi‐solid‐state electrolytes (QSSEs) still suffer from low ion conductivity and limited mechanical properties. Herein, a safe, fast‐charging, and long‐life SSMB is reported, utilizing photopolymerized ethoxylated trimethylpropane triacrylate based QSSEs (BN‐QSSE) reinforced by 2D functional fillers of boron nitride nanosheets (BNNSs). The BNNSs with high Young's modulus in BN‐QSSE can simultaneously accelerate and homogenize ion transport for uniform Na deposition and form a robust electrolyte‐Na interface. Only a low proportion of 1% BNNSs in BN‐QSSE can effectively realize high ionic conductivity of 1 × 10 −2 mS cm −1 , achieve a wide electrochemical stability window of 4.85 V (vs. Na/Na + ), and substantively suppress Na dendrites. The resulting Na||BN‐QSSE||Na symmetric batteries exhibit a long life of 600 h at 0.1 mA cm −2 and 0.1 mAh cm −2 . The as‐assembled Na 3 V 2 (PO 4 ) 3 ||BN‐QSSE||Na full batteries display high capacities of 102 mAh g −1 at 1 C and 75 mAh g −1 at a high rate of 15 C, and maintain 93% of the initial discharge capacity after 1000 cycles at 10 C, outperforming most reported SSMBs. The developed 2D filler‐reinforced QSSE provides new opportunities for high‐performance SSMBs.