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Abstract: This study provides experimental evidence for proton and hydrogen formation caused by the anodic electropolymerization of cyclohexyl benzene (CHB), which is a popular electrolyte additive for overcharge protection of lithium-ion batteries (LIBs). It is found that considerable H2 evolution is observed in overcharged LiCoO2/graphite cells, especially when CHB is included as an electrolyte additive. In order to confirm the proton generation during the CHB oxidation, Pt/Pt-rotating ring disc electrode (RRDE) measurements are performed in 1M Li(C2F5SO2)2N ethylene carbonate/ethyl methyl carbonate (1/2, v/v) solutions with and without CHB. The cathodic ring current is intimately correlated to the anodic disc current, and the cathodic reaction at the ring is determined to be the reduction of the proton. The proton generation efficiency during the CHB oxidation is as high as 90%. Proton liberation is also observed during the anodic decomposition of the electrolyte solvents, although it occurs in a much less stoichiometric way compared with that during the CHB oxidation. [Copyright &y& Elsevier]

Abstract: Three types of spinel-based cathode powders, namely, LiMn2O4, Li1.07Mn1.93O4, and Li1.06Al0.2Mn1.74O4, are examined with rotating ring-disc collection experiments to measure manganese dissolution and capacity losses in lithium-ion cells. The cyclic voltammograms are similar at high scan rates for all three electrodes. Initially, all electrodes rapidly lose capacity during cycling. After about 25 cycles, the electrodes start to exhibit capacity retention, and the performance matches that of the best spinels. The cation-substituted spinel electrodes experience a moderate capacity loss of 0.2% per cycle over 200 cycles, which is half that suffered by a typical spinel electrode (LiMnO4). Manganese (Mn) dissolution from all the spinel-based samples is monitored in situ under various conditions. The ring cathodic currents for the cation-substituted spinel electrodes are similar to those for LiMn2O4, which shows that the Mn dissolution behaviour is the same for all spinel-based cathode powders. The ring currents reach maximum values at the end-of charge (EOC) and end-of discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from all spinel-based samples occurs during charge–discharge cycling, especially in a charged state at >4.0V and in a discharged state at <3.1V. In addition, lower ring cathodic currents are observed in the cation-substituted spinel cathodes and this indicates that the rate of dissolution of Mn has decreased in these materials. [Copyright &y& Elsevier]