Nano-structured and High-performance Mn-based Positive Electrode Materials for Lithium-ion Batteries

Abstract

Towards widespread adoption of electric vehicles, Co/Ni-free and high energy density positive electrode materials for lithium-ion batteries are necessary. Among the various positive electrode materials, stoichiometric “zigzag”-type layered LiMnO 2 with orthorhombic space-group symmetry has been extensively studied as potential high-energy and low-cost positive electrode materials. Although orthorhombic LiMnO 2 delivers a large reversible capacity of over 200 mA h g -1 thorough a phase transition from layered to spinel-like phase during charging and discharging, over 30 cycles are required to obtain such a large reversible capacity due to the sluggish phase transition kinetics. In this study, nanostructured LiMnO 2 with both orthorhombic and monoclinic layered domains is synthesized, and its electrochemical performance as positive electrode materials is examined. The nanostructured LiMnO 2 delivers a maximum reversible capacity of >200 mA h g -1 within 5 cycles, indicating that the phase transition kinetics to the spinel-like phase upon electrochemical cycling are faster when compared with orthorhombic LiMnO 2 . Moreover, a significant improvement of cycle performance, i.e., ~90% retention after 100 cycles, is achieved by using a highly concentrated electrolyte solution coupled with lithium phosphate coating through suppression of Mn dissolution into electrolyte. From these results, the feasibility of practical Co/Ni-free high-energy positive electrode materials will be discussed in detail.