Synthesis and Electrochemical Properties of Li2MnO3 Li4Mn5O12 Binary System As Positive Electrode Materials for Lithium Ion Battery

Abstract

Synthesis and Electrochemical Properties of Li2MnO3―Li4Mn5O12 Binary System as Positive Electrode Materials for Lithium Ion Battery Masaki Okada and Yuya Sakaguchi Inorganic Materials Research Laboratory, TOSOH CORPORATION Lithium ion batteries are their high energy density compared with other batteries, progressed recently applied to applications requiring large capacity like for electric power storage system and electric vehicle. The positive electrode materials for a lithium ion battery, lithium metal oxide containing a large amount of rare metallic element such as cobalt or nickel are mainly investigated. Positive electrode material containing a large amount of these rare elements is very difficult to achieve both high energy density and low cost. As a positive electrode material that does not contain a rare metallic element, it is being studied of Li2MnO3 with a layered rock-salt structure. Li2MnO3 shows a large discharge capacity of more than 250mAh/g in the first cycle, but the capacity decreases with charge and discharge cycles. [1-3] In this work, we studied the Li2MnO3―Li4Mn5O12 binary system (Li4/3-4X/5Mn2/3O2-2X/5, 0<X<1) of the positive electrode materials based on Li2MnO3. Li4/3-4X/5Mn2/3O2-2X/5 can be suppressed capacity fading as compared with the conventional Li2MnO3. It may be able to achieve both low cost and high energy density. Li4/3-4X/5Mn2/3O2-2X/5 was prepared by reacting of mixture of MnCO3･0.5H2O and LiOH･H2O as raw material. The mixture was fired at 400～600ºC for 32h in air stream. Crystal structure and multilayered particle structure were investigated through TEM and N2adsorption-desorption isotherm analysis, respectively. The electrochemical characterization of positive electrode material was performed on CR2032 coin type cells. From the TEM images of the prepared samples, the presence of two crystal phases was observed. In addition, the electron diffraction pattern is attributed to the rock salt and the spinel phase, the possibility of a two-phase coexistence structure of Li2MnO3 and Li4Mn5O12 having a twin structure has been suggested. The initial charge and discharge capacity of Li4/3-4X/5Mn2/3O2-2X/5 was reduced as compared with Li2MnO3, but cycle stability was improved (X=0.36, 170mAh/g@50th, 50mA/g, RT). In additionally, capacity fading is suppressed by magnesium substitution of a part of manganese, the substituted sample showed stable cycling at about 200mAh/g (X=0.36, Mg 8mol %). In the viewpoint of the crystal structure and multilayered particle structure, the effect of the characters on capacity and cycle ability will be discussed. [1] Denis Y.W. Yu et.al., J. Electrochem. Soc. 2009 156(6) A417-A424 [2] Denis Y.W. Yu et.al. J. Electrochem. Soc. 2010 157(11) A1177-A1182 [3] Denis Y.W. Yu et.al., J. Electrochem. Soc. 2011 158(9) A1015-A1022