Understanding Interfacial Properties between Li-Rich Layered Oxide and Electrolyte Containing Triethyl Borate

Boron-containing electrolyte additives have been successfully used to improve the cyclability for Li-rich layered oxide, a hopeful cathode of high energy density lithium ion battery, but available mechanisms on their contribution are diversified. In this paper, we provide evidence to confirm the mechanism that Li-rich layered oxide is protected by a solid electrolyte interface (SEI) layer derived from boron-containing electrolyte additives. Triethyl borate (TEB), a simple boron-containing molecule, is selected as the electrolyte additive, and a representative Li-rich layered oxide, Li­[Li0.2Mn0.54Ni0.13Co0.13]­O2, is synthesized for understanding the interfacial properties between the oxide and the electrolyte through physical and electrochemical characterizations. Cyclability tests display that the as-prepared oxide exhibits a fast capacity decrease in the standard electrolyte, 1.0 M LiPF6, in a mixed carbonate solvent of ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethylene carbonate (EC) (EMC/DMC/EC = 5/2/3, in weight), with only 30% capacity retention after 150 cycles at 0.5 C (1 C = 250 mAh g–1), which can be improved to 79% when 3% TEB is introduced. Physical characterizations demonstrate that the as-prepared oxide suffers a severe structural destruction accompanied by thick deposits from electrolyte decomposition products, but the crystal structure of the oxide is well protected by a uniform solid electrolyte interface (SEI) layer formed from the preferential oxidation of TEB.