Trace Bifunctional Diboron Additive Enables Robust CEI/SEI Interphases for Long-Cycling 4.5 V Li||NCM811 Batteries

Developing efficient, low-cost, multifunctional additives that require small amounts and can simultaneously protect both the cathode and anode remains a major challenge for the practical application of lithium batteries. Herein, bis(2,4-dimethylpentane-2,4-glycolato)diboron (B2hmp2) was introduced to construct a greatly Li+-conductive cathode electrolyte interphases (CEIs) at the LiNi0.8Co0.1Mn0.1O2 (NCM811) surface together with robust solid electrolyte interphases (SEIs). Using a common electrolyte with 0.2 wt % B2hmp2, the Li||Li cells deliver markedly enhanced long-cycling stability, sustaining stable operation for 500 h at 0.5 mA cm-2. Furthermore, following 350 cycles at 0.5 C, the capacity retention of 4.5 V Li||NCM811 cells was elevated from 57.2 to 83.6%. Experimental results reveal that the thin, uniform, boron-rich CEI generated by B2hmp2 effectively mitigates particle microcracking and restrains the dissolution of transition metal ions. Interface analysis reveals that the modified SEI film enriched with B-O species and LiF facilitates uniform Li plating/stripping without dendrite formation and reduces the continuous parasitic decomposition of electrolyte solvents. This article highlights the value of trace diboron for forming desirable electrolyte interphases to obtain the wonderful long-term cycle performance and rate performance of Li||NCM811 cells.