Preparation And Modification Of Li Ni_0.5Mn_1.5O₄ Cathode Material For Lithium-ion Battery

At present,with the shortage of resources and and the increase of environmental protection,the demand for green energy storage devices is increasing.Lithium-ion battery has become a new energy storage device because of its high working voltage and energy density.The LiNi_0.5Mn_1.5O₄ has a 4.7 V discharge platform and a higher discharge capacity,making it a positive cathode material for lithium-ion batteries.This article uses the solid-state method and sol-gel method to prepare high voltage cathode materials LiNi_0.5Mn_1.5O₄,and modified by ion doping,then though the XRD,SEM,cyclic voltammetry,electrochemical impedance spectroscopyand charge-discharge performance test and other methods were applied to study the crystal structure and electrochemical properties.?1?The LiNi_0.5Mn_1.5O₄ prepared by solid-state method has the smaller particle,crystal structure is not complete,and because the calcination process will cause the lack of oxygen,so the impurities existence in the material,which will cause a poor cycle performance of materials.The optimum calcination condition is Calcining 12 h at 900?,the first discharge ratio at 0.2C ratio reaches 123.46 mAh/g,and the capacity can still reach 118.21 mAh/g after50 cycles,and the capacity retention rate is 95.70%.?2?The cycle performance of LiAl_0.1Ni_0.4Mn_1.5O₄ and LiAl_0.1Ni_0.45Mn_1.45O₄ prepared by Al³⁺doping has been significantly improved.Meanwhile,LiAl_0.1Ni_0.45Mn_1.45O₄ has higher specific discharge capacity and cycle performance than LiAl_0.1Ni_0.4Mn_1.5O₄.Doping Cr³⁺will not change the crystalline structure of the material,and wil reduce the formation of impurity phase.When the doping amount is 0.1,the electrochemical performance of the material is better.Because of the electrochemical activity of Cr³⁺,doping Cr³⁺can improve the discharge capacity of the material,and Cr³⁺can also stabilize the crystal structure of the material,thereby improving its cycle performance and large rate performance.The charge discharge curve of the doped F^-material is the same as that of the LiNi_0.5Mn_1.5O₄,which has two voltage platforms,4 V and 4.7 V.Because the electronegativity of F^-ions is larger than that of O^2-,doping F^-can improve the cycling performance of materials,but at the same time,it will increase the content of Mn³⁺.Mn³⁺is beneficial to the rate performance of materials,but too much Mn³⁺will not be conducive to the stability of materials,so the best doping amount is 0.1.?3?The material prepared by sol-gel method,and then study the optimal preparation conditions,lack of oxygen when the calcination temperature is too high,resulting in the formation of impurities from XRD diagram,the materials of calcining 8 h at 850?,which crystal structure is the most complete,the most regular shape and the best electrochemical performance.The discharge specific capacity at 0.2C ratio can reach 130.89 mAh/g,and the capacity retention rate is still up to 97.72%after 50 cycles.?4?We known that doped Fe³⁺will not change the crystal structure of the material,it still belonging to Fd3m space group,but the diffraction summit is slightly skewed towards the lower Angle,at the same time,doping Fe³⁺can improve the cycle performance.because the Fe³⁺has electrochemical activity,so it can improve the discharge capacity of the material.The electrochemical performance of LiNi_0.45Mn_1.45Fe_0.1O₄ is the best,and the discharge specific capacity at 0.2C ratio can reach 133.64 mAh/g.Doping Co³⁺can improve the material performance of reversible,at the same time,doping Co³⁺can improve the cycle performance,From the CV curve,we can see the electrochemical activity of Co³⁺is in the area of more than5 V,and the electrochemical performance of LiCo_0.1Ni_0.45Mn_1.45O₄ is better.