Modified Manganese Oxides As Anode Materials For Li-ion Batteries

Recently,with the rapid depletion of fossil fuels such as oil and natural gas,new energy forms such as solar and wind energy have attracted much research attention.Optimal utilization of alternative energy requires the development of high performance chemical power source.Compared to other chemical power source,lithium ion batteries are safe and associated with relatively higher power density,longer cycle life,better cycling performance.Therefore,they have been widely used in lightweight mobile devices such as laptops,digital cameras and cell phones.However,the electrical performance of current lithium ion batteries can not meet the requirements for high power devices electric vehicles?EVs?or hybrid electric vehicles?HEVs?.As one of three major components?cathode,anode and electrolyte?in lithium ion battery,anode has been one of the focus in lithium ion battery research.Due to relatively high specific capacity,manganese oxides have been considered as potential anode materials for a long time.However,the application of manganese oxides as anode materials for lithium ion battery has been hindered by the low electric conductivity,low lithium ion diffusion rate,as well as the poor cycling performance arising from irreversible volume change during charge and discharge processes and resulting pulverization.Targeting to develop materials with improved electrochemical performance,we used titanium oxide and nitrogen to modify manganese oxide,in order to increase the electric conductivity,lithium diffusion rate and decrease pulverization due to volume changes.1.Micron-sized MnCO₃ was prepared with a hydrothermal method before it was converted to MnO₂ by calcination at 400 ? for 4 hours.After that,hydrolysis of tetrabutyl titanate and post thermal treatment was performed to prepare TiO₂/MnOx complex.Compared to MnO2,the complex shows better cycling performance and the specific capacity remains at 1032 mAh/g after 250 cycles at a current density of 100 mA/g.The improved performance may be ascribed to the decreased volume expansion due to the introduction of TiO₂,higher electric conductivity owing to the presence of Mn³⁺,and synergetic effect between the dispersed TiO₂ nanoparticles and MnOx microspheres.7Li NMR results prove that TiO₂/MnOx cormposite is associated with both insertion?TiO2?and conversion reaction?MnOx?mechanism for lithium ion battery.2.Manganese sesquioxide coated on melamine foams were prepared by hydrothermal method using manganese nitrate and ethanol.After calcinating the resulting material at high temperatures in N₂ atmosphere,manganese monoxide on C-N networks were obtained.Due to the presence of C-N networks,the structure stability and the efficiency of electron transfer for the materials have been increased.The pores and channels generated during the calcination processes facilitate the lithium ions'transportation.Therefore,the specific capacity and cycling stability have been greatly enhanced.MnO-MF-500 can maintain a specific capacity of 590 mAh/g after 160 cycles which accounts for 78%of theoretical capacity?755mAh/g?of manganese monoxide?MnO?.