Preparation And Electrochemical Properties Of Anode Materials For Silicon-based And LiNi_0.5Mn_1.5O₄ Cathode Material For Lithium Ion Batteries

Though silicon dioxide has been considered as a new generation of negative material for its high specific capacity and low lithiation potentials.but its volume expansion is large,resulting in chalking and poor cycle performance.The poor conductivity of ions and electrons leads to poor rate performance and low efficiency of coulomb for the first time.In addition,it is significant to study the electrochemical performance of lithium ion batteries at high temperatures.In this paper,sucrose is used as the carbon source,and silica hydrolyzed by ethyl orthosilicate is used as the silicon source to conduct the process of high temperature pyrolysis carbon coating treatment in order to obtain SiO_x@C materials with different carbon contents.The effect of doping LiF on the electrochemical performance of the material was studied by LiF doping.Method of pre-lithium is adopted to improve the low coulomb efficiency of SiO_x@C material.Furthermore,the sol-gel method is used to synthesize LiNi_0.5-xGa_x Mn_1.5O₄?x=0,0.04,0.06,0.08,0.1?samples with various Ga-doping materials.The cycle performance of the material at high temperature and the effect of different Ga doping amount on the material properties were discussed systematically.After comprehensive analysis of the structural and morphological characterization and electrochemical performance,the conclusions were obtained as following:?1?During the high-temperature pyrolysis,a carbon thermal modification occurs,X is less than 2 in SiO_x,and the optimum carbon content is 41.82%.As this time,the electrochemical performance is optimal,and the first coulombic efficiency is reached69%.When the current density is 0.1 A/g,the specific capacity is 591.3 mAh/g and after100 cycles the specific capacity retention is 94.1%.The specific capacities at current densities of 0.2,0.4,0.8,1.6,0.1 A/g were 550,515.8,451.3,359.1,606.9 mAh/g,respectively.?2?LiF doping can reduce electrochemical impedance and increase the diffusion rate of lithium ion.LiF has a large elastic modulus,low solubility in a carbonate solution,and good chemical stability,so it can help form a stable and reliable SEI film,and can effectively prevent corrosion of the active material by the electrolyte.The SiO_x/LiF@C can still maintain a specific capacity of 504.2 mAh/g and a capacity retention rate of96%after 300 cycles at a current density of 0.3 A/g.The retention rate of SiO_x@C is84.7%at the same test conditions.?3?Pre-lithiation essentially adds lithium to the negative electrode material and forms an SEI film on the surface,thus greatly reducing the irreversible capacity during the first discharge and improving the first effect.The experimental resul ts prove that the coulomb efficiency reached 99.27%after the battery by firstly pre-lithiated for 3 min,and pre-lithiation did not have much influence on the overall electrochemical performance of the material.?4?LiNi_0.5-x.5-x Ga_x Mn_1.5O₄?x=0,0.04,0.06,0.08,0.1?is synthesized by sol-gel method with a disordered Fd3m structure,and Ga doping can inhibit the formation of the Li_xNi_1-x-x O impure phase and improve the crystallinity of the sample.After the optimum doping concentration of LiNi_0.44Ga_0.06Mn_1.5O₄ was cycled 100 times at 3 C discharge rate,the capacity retention rate is 80%,and the capacity retention rate is 98.4%after 50 cycles at 55°C and 1 C and the capacity retention of 98.4%after 50 cycles at 55°C and 1 C.These favorable electrochemical properties are attributed to the fact that Ga doping forms a passivation layer on the surface of the electrode to maintain the structural integrity of the material,improve the conductivity of the material,and reduce polarization.