Mn 2+ 2+ or Mn 3+ 3+ ? Investigating transition metal dissolution of manganese species in lithium ion battery electrolytes by capillary electrophoresis

摘要

Abstract A new CE method with ultraviolet–visible detection was developed in this study to investigate manganese dissolution in lithium ion battery electrolytes. The aqueous running buffer based on diphosphate showed excellent stabilization of labile Mn 3+ , even under electrophoretic conditions. The method was optimized regarding the concentration of diphosphate and modifier to obtain suitable signals for quantification. Additionally, the finally obtained method was applied on carbonate‐based electrolytes samples. Dissolution experiments of the cathode material LiNi 0.5 Mn 1.5 O 4 (lithium nickel manganese oxide [LNMO]) in aqueous diphosphate buffer at defined pH were performed to investigate the effect of a transition metal‐ion‐scavenger on the oxidation state of dissolved manganese. Quantification of both Mn species revealed the formation of mainly Mn 3+ , which can be attributed to a comproportionation reaction of dissolved and complexed Mn 2+ with Mn 4+ at the surface of the LNMO structure. It was also shown that the formation of Mn 3+ increased with lower pH. In contrast, dissolution experiments of LNMO in carbonate‐based electrolytes containing LIPF 6 showed only dissolution of Mn 2+ .