Morphological and Chemical Control of Oxide Cathode Materials Based on Mn

Abstract

Oxides based on Mn redox couples continue to attract wide attention in lithium battery due to consideration of cost and safety. To bypass issues of capacity and durability associated with John-Teller distortions, substituents such as Ni and Co are introduced in the Mn or Li sites. Ni-Co-Mn ternary materials, e.g. LiNixMnyCozO2, are usually synthesized through methods that involve steps at high temperature, whether to react binary oxides or precursors such as hydroxides made by co-precipitation and other low temperature methods. High temperature calcination results in complex morphologies that hard to control, especially if refined nanoscale features are desired. Further, they inherently under thermodynamic driving forces and, thus, may miss possible intermediate or metastable phases. Here, we report a one-step hydrothermal process to synthesize well-defined nanocrystals of binary Ni-Mn and ternary Ni-Mn-Co cathode materials. TEM showed their morphology varies between rod and octahedron depending on conditions. XRD and EDX revealed that nanorods are composed of layered Li[NixLi(1/3-2x/3)Mn(2/3-3/x)]O2, whereas the octahedra correspond to spinel-type LiMnxNixCo(2-2x)O4. Their electrochemical property showed high voltage range 2-4.9v and large capacity at 150~200mAh/g. The uniform morphology provide the further potential for their surface functionalization with alumina and the quest for faster Li diffusion channels in the near future.