The Synthesis of Three-Dimensional Hexagonal Boron Nitride as the Reinforcing Phase of Polymer-Based Electrolyte for All-Solid-State Li Metal Batteries.

Powdery hexagonal boron nitride (h-BN), as an important material for electrochemical energy storage, has been typically synthesized in bulk and one/two-dimensional (1/2D) nanostructured morphologies. However, until now, no method has been developed to synthesize powdery three-dimensional (3D) h-BN. This work introduces a novel NaCl-glucose-assisted strategy to synthesize micron-sized 3D h-BN with a honeycomb-like structure and its proposed formation mechanism. We propose that NaCl acts as the template of 3D structure and promotes the nitridation reaction by adsorbing NH 3 . Glucose facilitates the homogeneous coating of boric acid onto the NaCl surface via functionalizing the NaCl surface. During the nitridation reaction, boron oxides (BO 4 and BO 3 ) form from a dehydration reaction of boric acid, which is then reduced to O 2 -B-N and O-B-N 2 intermediates before finally being reduced to BN 3 by NH 3 . When incorporated into polyethylene oxide-based electrolytes for Li metal batteries, 5 wt % of 3D h-BN significantly enhances ionic conductivity and mechanical strength. Consequently, this composite electrolyte demonstrates superior electrochemical stability. It delivers 300 h of stable cycles in the Li//Li cell at 0.1 mA cm -2 and retains 89 % of discharge capacity (138.9 mAh g -1 ) after 100 cycles at 1 C in the LFP//Li full cell.