Carbonate- Versus Hydroxide-Based Precursor for the Synthesis of Li/Mn Rich Cathodes: Exploring Differences in Discharge Capacities and Cycle Life.

Abstract

Lithium/manganese-rich (LMR)-based cathodes can enhance the specific energy of Li ion batteries and are conventionally synthesized via a carbonate-based precursor (LMR-CO₃). The CO₂ evolution-related voids and enhanced surface area can be avoided by calcination of a hydroxide-based precursor [LMR-(OH)₂]. This way, the LMR releases less oxygen during charge, as seen by a decreased Mn^3+/4+ redox activity and decreased voltage fade. However, the lower specific discharge capacity is attributed to a decreased lithiation amount in the initial cycles for LMR-(OH)₂ and is related to a higher Li⁺ extraction degree, that is, a higher redox oxidation number at the discharged state. Interestingly, this decreases the accompanying amount of detrimental Mn³⁺ and is concluded to improve cycle life, due to, for example, minimized Jahn-Teller distortions and disproportionation reactions. The differences in lithiation (e^- + Li⁺) degrees of the two LMRs emerge at end-of-discharge and can stem from differences in either redox resistance and/or resistance of Li⁺ intercalation, for example, due to slight crystal stacking faults in the course of different synthesis conditions and/or simply from bigger particle sizes.