Preparation And Modification Of LiNi_0.5Mn_1.5O₄ For The Cathode Of High-voltage Lithium-ion Battery

The LiNi0.5Mn1.5O4 has become a high-profile material for the cathdoe of lithium-ion batteries due to its low price,non-toxicity and high voltage.The main factors affecting the performance of LiNio.5Mn1.5O4 are dissolution and disproportionation of Mn as well as decomposition of electrolyte.In this work,the preparation and surface modification of LiNi0.5Mn1.5O4 have been explored.The structure-performance of the resultant materials have been systematicallystudied.The sol-gel method has been employed to synthesize the spinel LiNi0.5Mn1.5O4.The effect of calcination temperature on the electrochemical performance of LiNi0.5Mn1.5O4 has been investigated.The LiNi0.5Mn1.5O4 obtained at 850? calcination temperature shows best electrochemical performance,the specific capacity of which reaches 121 mAh g-1 at 0.1C.The specific capacity is 89.7 mAh g-1 at 5 C,which is higher than that of LiNi0.5Mn1.5O4 calcinated at 750? and 800?,respectively.To address the issue of dissolution and disproportionation of Mn in LiNi0.5Mn1.5O4,surface coating of LiNi0.5Mn1.5O4 has been carried out on the basis of optimizing the preparation process.Firstly,the surface coating of LiNio.5Mn1.5O4 with boron and phosphorus co-doped carbon has been performed.The boron and phosphorus co-doped carbon efficiently protect LiNi0.5Mn1.5O4 from the electrolyte,avoiding the dissolution and disproportionation of Mn.Moreover,this conductive dense layer of carbonon the surface provides good electronic conductivity.Compared to pure LiNi0.5Mn1.5O4,boron and phosphorus co-doped carbon-coated LiNio.5Mn1.5O4 electrode demonstrates better rate performance and cycling stability.The optimized boron and phosphorus co-doped carbon-coated LiNio.5Mn1.5O4 has a capacity retention of 96%after 200 cycles at 1 C discharge rate.Its capacity is 122.7 mAh g-1 at 1 C discharge rate;it can still reaches 111 mAh g-1 at 5 C discharge rate.Secondly,chromium oxides coating of LiNi0.5Mn1.5O4 was further performed.The chromium oxides coating improves the cycling stability of LiNi0.5Mn1.5O4 at a large current.At a charge/discharge rate of 1 C,the capacity decay is only 7%after 100 cycles.At the same time,the coating layer reduces the side reaction between LiNi0.5Mn1.5O4 and the electrolyte,decreasing the interface impedance.This significantly enhances the electrochemical performance of LiNi0.5Mn1.5O4.The results in this work show that the surface coating with heteroatom-doped carbon and chromium oxides are effective in modifying the electrochemical performance of LiNi0.5Mn1.5O4.