Effects of Lithium Bis(oxalate)borate Electrolyte Additive on the Formation of a Solid Electrolyte Interphase on Amorphous Carbon Electrodes by Operando Time-Slicing Neutron Reflectometry

Abstract

Comprehensive analyses were performed using neutron reflectivity and hard X-ray photoelectron spectroscopy to understand the structure and composition of the solid electrolyte interphase (SEI) layer during charge-discharge processes and because of the addition of lithium bis(oxalate)borate (LiBOB) to improve the battery performance. The chemical composition of the SEI was assessed using these methods, and the amount of Li⁺ intercalated in the anode during the electrochemical reaction was evaluated. The results demonstrated that Li₂C₂O₄ was produced initially but later decomposed to Li₂CO₃ on the first charge cycle. Presumably, the SEI layer formed by the decomposition of LiBOB was a single dense layer and chemically stable during the further charge-discharge processes owing to the difference in the reaction process. Therefore, the reduced Li⁺ transfer resistance and charging capacity accounted for the substantial improvement contributed by adding LiBOB. Moreover, the charges used for the intercalation of Li⁺ and SEI formation during the two-cycle processes were analyzed. The addition of LiBOB increased the discharge capacity of the anode and provided an additional charge used for SEI formation, presumably for decomposing Li₂C₂O₄, which could reflect the durability of the Li-ion batteries. The electrode, electrolyte, and charge-discharge reactions affect the SEI properties and consequently the electrochemical reactions. Therefore, additional investigations under different charge-discharge conditions would reveal important characteristics such as the charge and discharge efficiency, output performance, and safety.

Keywords: carbon film; hard X-ray photoelectron spectroscopy; intercalation and deintercalation; lithium bis(oxalate)borate; lithium-ion batteries; neutron reflectivity; solid electrolyte interphase.