New Cathode Materials with Spinel and Layered Structures

Abstract

From previous researches on a cathode material of the Mg rechargeable battery, spinel-type oxides can be regarded as promising candidates for the cathode material. MgCo₂O₄ with a disordered spinel structure has drawn much attention as a typical cathode recently, but the cathode property is not sufficiently high for practical use. To overcome this problem, we have tried to improve its cathode property by two kinds of approaches. One is a partial substitution of another transition metal for Co in MgCo₂O₄, and a part of results on Mn-substituted materials, MgCo_2−xMn_xO₄, is described in Sect. 1. In addition, we have focused on vanadium-based materials and recently succeeded in finding a new family of the cathode material, i.e., Mg_1+xV_2−xO₄ with a spinel structure. As an example of the vanadium-based materials, a cathode property and a crystal structure of Mg_1.5V_1.5O₄ are introduced briefly in Sect. 2. To gain a deeper understanding of the atomic structures of the spinel-type materials, we have performed neutron and synchrotron X-ray total scattering measurements. In Sect. 3, we present an analytical result of an atomic structure of MgCo₂O₄ nanoparticle. A layered material can be considered to be promising as a cathode material of the Mg rechargeable battery, as in the case of a lithium ion battery. Recently, we have applied delithiated layered material, i.e., Li_0.13Mn_0.54Ni_0.13Co_0.13O_2−δ to the Mg rechargeable battery and then demonstrated that the samples showed 273 mA h g⁻¹ at a first discharge process. The result of cathode property is described in detail in Sect. 4.