Investigation On Synthesis And Modification Of High Voltage LiNi_0.5Mn_1.5O₄as Cathode Material For Lithium Ion Batteries

Spinel LiNi0.5Mn1.5O4has many advantages, sunch as high voltage (4.7V), simple synthesis craft, low cost and environmental friendly. As a result, the study of it has attracted many researchers. This material’s electrochemical performance at high temperature is bad and it exists a4V low voltage plateau. These disadvantages limited its adhibition. This thesis mainly investigated micro-structure and electrochemical performance systematic of spinel LiNi0.5Mn1.5O4synthesized by solid state method which improved by roasting craft, surface modification and annealing treatment.Two-step roasting method reduced roasting temperature and holding time by adding oxalic acid as assisted diffusion agent. At the same time, this method increased specific capability and ratio performance of the material.The new non-isothermal roasting method was presented. The new method has characteristic of low speed of increasing temperature and short time at high temperature. This method controlled particles growing and aggregating effectively and increased the ratio performance. At the same time, it reduced the energy costing.LiNi0.5Mn1.5O4powder was coated with AlPO4which was stability to electrolty and it was investigated that the effect of mass ratio, roasting temperature and holding time on micro-structure and electrochemical performance. The results showed that the coated layer prevented HF in electrolyte to corrode electrode. The sample which coated with1%AlPO4and roasted at600℃for4h had the best electrochemical performance at high temperature (55℃).The material was handled by annealing hot treatment. Roasting at low temperature could help O2at atmosphere diffused into the crystal’s lattice, so the Mn3+decreased and the4V Mn4+/Mn3+discharging voltage plateau was eliminated. As a result the energy density was increased by5%.