Electrochemistry

Biography

Biography: Mitsuharu Tabuchi

Abstract

Li-excess positive electrode material (LiMO₂-Li₂MnO₃ solid solution, M=Ni_1/2Mn_1/2 or Ni_1/3Mn_1/3Co_1/3) is a good candidate as its high-capacity (250 mAh/g) and acceptable discharge voltage above 3.5 V for high energy-density lithium-ion battery to EV and PHEV application. Especially LiNi_1/2Mn_1/2O₂-Li₂MnO₃ solid solution (Li_1+x(Ni_yMn_1-y)_1-xO₂, 02-Li₂MnO₃ solid solution [1]. In this work, the synthetic method applies to LiNi_1/2Mn_1/2O₂-Li₂MnO₃ system [2]. As shown in Fig. 1, the homogeneous precursor can be prepared by low-temperature co-precipitation Ni-Mn hydroxide and hydrothermal treatment with an oxidizer, KClO₃ and Li-source, LiOH.H₂O at 220 °C. The precursor calcined with LiOH.H₂O at 850 °C under N₂ atmosphere to obtain better initial electrochemical performance. To improve cycle performance under full-cell configuration, Ti ion substituted for Mn ion by using 30% Ti(SO₄)₂ aq. solution. Although further effort to establish more facile synthetic method must be needed, the Ni- and Ti- substituted Li₂MnO₃ is an attractive candidate as high-capacity “Co-free” positive electrode material. We develop Li-excess LiNiO₂ as high-capacity and better cyclability using thermal decomposition of Li₂NiO₃ [3]. AIST found a new 3.5 V-class Fe- and Ni substituted Li₂MnO₃ positive electrode material with NEC and Tanaka Chemical Co. [4, 5]. These materials are also “Co-free” ones.