Deep-discharged LiCoMnO₄ Lithium-Ion cathodes with high rate capability and long cycle life

LiCoMnO₄ (LCM) is a promising member of the 5 V spinel cathode materials family, which is capable of providing high specific energy given its high working voltage vs. Li/Li⁺. Most of the prior studies reported in literature on LCM-based battery cells have focused on the operational regime above 3 V. It is widely believed that for this class of Mn-bearing lithiated spinel cathode materials, the Jahn-Teller distortion that occurs when Mn^{4 +} is reduced to Mn^{3 +} upon deep discharge to the regime lower than 3 V would introduce rapid capacity fade. In this work, we show that in solid-state thin film batteries using LCM cathodes, there is considerable available capacity under 3 V associated with the cubic-tetragonal phase transitions without appreciable capacity fade with cycling. This finding is similar to our recent report for a material in the same class of lithiated spinel oxides, LiNi_0.45Mn_1.485Cr_0.05O₄ (LNM), which also showed stable cycling at deep discharge. However, we demonstrate here the LCM cathodes retain a greater fraction of the total capacity at high discharge rates in the lower voltage regime relative to LNM. At elevated temperature, the capacity in 3 V region was increased without compromising cycle life. This work suggests that by using solid-state thin film techniques, we could utilize the capacity of LCM below 3 V despite the Jahn-Teller distortion.