Polymeric Electronic Shielding Layer Enabling Superior Dendrite Suppression for All-Solid-State Lithium Batteries

LiBH₄ is one of the most promising candidates for use in all-solid-state lithium batteries. However, the main challenges of LiBH₄ are the poor Li-ion conductivity at room temperature, excessive dendrite formation, and the narrow voltage window, which hamper practical application. Herein, we fabricate a flexible polymeric electronic shielding layer on the particle surfaces of LiBH₄. The electronic conductivity of the primary LiBH₄ is reduced by 2 orders of magnitude, to 1.15 × 10^-9 S cm^-1 at 25 °C, due to the high electron affinity of the electronic shielding layer; this localizes the electrons around the BH₄^- anions, which eliminates electronic leakage from the anionic framework and leads to a 68-fold higher critical electrical bias for dendrite growth on the particle surfaces. Contrary to the previously reported work, the shielding layer also ensures fast Li-ion conduction due to the fast-rotational dynamics of the BH₄^- species and the high Li-ion (carrier) concentration on the particle surfaces. In addition, the flexibility of the layer guarantees its structural integrity during Li plating and stripping. Therefore, our LiBH₄-based solid-state electrolyte exhibits a high critical current density (11.43 mA cm^-2) and long cycling stability of 5000 h (5.70 mA cm^-2) at 25 °C. More importantly, the electrolyte had a wide operational temperature window (-30-150 °C). We believe that our findings provide a perspective with which to avoid dendrite formation in hydride solid-state electrolytes and provide high-performance all-solid-state lithium batteries.