Practical assessment of cobalt-free Li2MnO3-based layered materials for Li battery applications

Abstract

As cost-effective and Co-free positive electrode materials, a solid solution material between Li₂MnO₃ and LiNi_0.5Mn_0.5O₂, Li_1.2Ni_0.2Mn_0.6O₂, delivers a large reversible capacity over 220 mA h g⁻¹ through reversible anionic redox of oxide ions. However, a practical problem of this material is found in the insufficient reversibility as electrode materials associated with partial oxygen loss during charging process. In this study, Li_1.2Al_0.04Ni_0.18Mn_0.58O₂, where Ni and Mn ions in Li_1.2Ni_0.2Mn_0.6O₂ are partially substituted with Al ions, is synthesized via a solid-state reaction. Li_1.2Al_0.04Ni_0.18Mn_0.58O₂ samples with the optimized surface area are further synthesized at different calcination temperatures. Al³⁺-substituted sample with the optimized surface area partially suppresses the capacity fading and voltage decay on continuous electrochemical cycles, ∼ 500 cycles. Moreover, the use of highly concentrated electrolytes with high oxidative stability efficiently improves electrode reversibility of Li_1.2Al_0.04Ni_0.18Mn_0.58O₂. Nevertheless, important practical problems are still found in inevitable voltage decay and inferior charge rate capability, both originating from the character of anionic redox reaction. Further research efforts are necessary to overcome these drawbacks and to adopt Mn-based electrode materials with anionic redox for practical battery applications, especially for electric vehicles.