Review—Manganese Dissolution from Spinel Cathode: Few Unanswered Questions

The choice of cathode material critically influences the performance, cost and energy density in a Li ion battery. LiMn2O4 (LMO) cathode is an attractive cathode material because of its high rate capability, low cost, safety and non-toxicity. However, low cycle life or capacity fading with cycling is a big hurdle in the practical application of LMO cathodes. The dominant cause of the capacity fading, Mn dissolution from LMO, is still a challenge to overcome. In this review, we attempt to emphasize the loopholes in the understanding related to the Mn dissolution phenomenon in LMO cathodes in the presence of both aqueous and non-aqueous electrolytes. The underlying mechanism behind the dissolution process is often explained with the help of ionic charge disproportionation argument. Nevertheless, there are experimental and theoretical evidence in the literature to counter the simplistic view of dissolution due to charge disproportionation. Moreover, the correlation between the metal dissolution and the capacity fading is not causally established yet in the literature which hinders the formulation for a systematic strategy to prevent the capacity loss. In the current article we discuss all the relevant investigations related to the understanding of the cause, effect and prevention strategies of Mn-dissolution. We attempt to point out the gaps and contradictions in the literature and motivate further targeted studies in this seminally important material for better Li-ion batteries having higher rate capability and capacity retention.