Synchronized achieving amount reduction and efficiency increase of lithium salt-type additive by alternating current pulse discharge technology

Lithium bis(oxalate)borate (LiBOB) is well known for its protection of graphite anodes in lithium-ion batteries (LIBs) by forming a passivated solid electrolyte interface (SEI) layer. However, the underlying film-formation mechanism of LiBOB remains poorly understood, thereby its utilization efficiency has received little attention. In this work, we resort to in situ techniques to determine the crux of limiting the complete decomposition of LiBOB during the initial SEI formation lies in the BOB-derived soluble products which accumulate on the graphite surface and hinder its subsequent sustained decomposition. Then alternating current pulse (AC) discharge technology is employed to promote the self-decomposition of LiBOB. The complementation results of electrochemical/physical characterizations and theoretical calculations reveal that AC not only facilitates the diffusion of soluble products, but also promotes the synergy reaction of the soluble products with LiPF6, generating a smooth and uniform SEI rich in inorganics (LiF and LixPOyFz) and B-containing cross-linking polymers. More significantly, a thinner SEI is obtained in AC by reducing the LiBOB amount in half. The as-resulted cell exhibits higher rate performance (280 mAh g−1 at 2 C) and better cycling stability (320 mAh g−1 after 200 cycles at 1 C, 98 % capacity retention), synchronously achieving "amount reduction and efficiency increase" of expensive additives. This study provides an entirely novel method for reinforcing the SEI films using external electric fields, and enriches the strategies for improving the performance of LIBs via interfacial engineering.