High Voltage Stability of Interfacial Reaction at the LiMn2O4 Thin-Film Electrodes/Liquid Electrolytes with Boroxine Compounds

Liquid electrolytes with boroxine compounds were prepared, and interfacial reactions at the liquid electrolytes/LiMn 2 O 4 thin-film electrodes were investigated. Boroxine compounds, B 3 O 3 (OR) 3 , with different kinds of substituents [R = CH 3 , CH 2 CH 3 , (CH 2 ) 2 CH 3 , and CH(CH 3 ) 2 ] were dissolved in 1 mol kg ―1 LiCF 3 S03/ethylene carbonate + EMC (1:1 by volume). Both cyclic voltammetry and electrical impedance spectroscopy measurements revealed that interfacial resistance depended on the chain length in the substituent of the boroxine compounds, and the resistance decreased with the increase in the chain length. Moreover, the anodic stability of the elecarolytes was improved up to 5.0 V (vs Li/Li + ) on the film electrodes by the addition of tri-isopropoxy boroxine [R = CH(CH 3 ) 2 ] with a steric structure (branched chain substituent). These results indicate that mixing boroxine compounds with both appropriate chain length and steric structure can be an effective way to develop advanced liquid electrolytes for high voltage rechargeable lithium ion batteries.