Synthesis and electrochemical properties of a cubic polymorph of LiNi1/2Mn1/2O2 with a spinel framework

Autor: Kensuke Kajikawa, Yusuke Yamada, Kingo Ariyoshi
Rok vydání: 2021
Předmět:
Zdroj: Journal of Solid State Electrochemistry. 26:257-267
ISSN: 1433-0768
1432-8488
DOI: 10.1007/s10008-021-05087-6
Popis: Employment of high-capacity positive-electrode materials is one of the most effective ways to improve the energy density of Li-ion batteries. The electrochemical properties of Li transition-metal oxides, which make up the Li insertion materials in the positive electrode, depend on their crystal structures. In general, materials composed of LiMO2 (M: a transition metal) with a layered structure (i.e., a two-dimensional framework) exhibit a high capacity, but complete extraction of the Li ions in the framework results in destruction of the structure. LiM2O4 having a spinel structure (i.e., a three-dimensional framework) exhibits excellent toughness, but the number of Li ions in the structure is smaller than that in the layered structure, resulting in a lower reversible capacity. Li2M2O4 with a reduced spinel-framework structure can be expected to have the advantages of both layered and spinel structures: high capacity and robust structure. In this study, a cubic polymorph of LiNi1/2Mn1/2O2, which is thought to be a layered material, was prepared by low-temperature synthesis. The obtained LiNi1/2Mn1/2O2 was electrochemically active and showed a reversible capacity of > 100 mAh g−1 at an upper limit voltage of 4.2 V, which is almost the same as that of a two-dimensional material with a layered structure. To confirm the crystal structure of low-temperature LiNi1/2Mn1/2O2, the change in crystal structure during Li extraction was investigated by ex situ XRD measurements. The isotropic contraction of the cubic lattice during Li extraction causes low-temperature LiNi1/2Mn1/2O2 to have a cubic lattice rather than a layered structure with a pseudo-cubic lattice. The crystal structure of low-temperature LiNi1/2Mn1/2O2 with a cubic lattice and the Li extraction mechanism were elucidated from these results.
Databáze: OpenAIRE
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