Preparation And Electrochemical Properties Of 5v Cathode Materials Of Lithium-ion Battery Research

LiNi_0.5Mn_1.5O₄ cathode material, which has the advantage of a potential plateau at about 4.7V, as well as environmentally friendly, low cost, good safety performance, good cycle performance, high power and high energy density, is expected to be one of the best cathode materials for the power battery.In this paper, how to reduce the 4V plateau of LiNi_0.5Mn_1.5O₄ cathode material was concerned, in order to synthesize high voltage cathode material with high specific capacity and excellent cycle stability. Constant current charge-discharge test, Cycle Voltammagram(CV), AC impedance, X-ray Diffraction(XRD) and Scan electron microscope(SEM) were used to characterize the performance of the cathode material. The main contents include:(1) LiNi_0.5Mn_1.5O₄ cathode material was synthesized by Sol-Gel-SCR (Self-Combustion Reaction), and many influencing factors were considered, such as, the order of addition of raw materials, initial pH, selection of raw materials, the relative amounts of citric acid, sintering temperature, annealing time, the best level of nickel and lithium excess. LiNi_0.5Mn_1.5O₄ cathode material, synthesized with optimum conditions, showed excellent electrochemical performance. The initial discharge capacity was 121.7mAh/g, and the discharge capacity of 20th cycle was 119.5mAh/g, so the discharge capacity retention ratio rate was 98.2%, which showed well cycle performance. In the charge-discharge performance curve, the 4V discharge platform was disappeared.(2) To further improve the electrochemical properties of the cathode material, the Ga-doping and In-doping LiMδNi_0.5-δMn_1.5O₄(M=Ga, In) were prepared.The discharge capacity of the cathode materials was not raised by doping at room temperature, charge and discharge rate of 0.2C, but greatly enhanced the rate property. XRD results showed that, Ga entered into the spinel lattice and occupied the nickel position. SEM results showed that Ga-doping did not change the grain size and morphology. Charge and discharge performance tests showed that LiGa_δNi_0.5-δMn_1.5O₄(δ=0.02) showed the highest discharge capacity and cycle stability. The CV curves indicated thatδ=0.02 sample showed well cycling performance. The AC impedance curves also indicated thatδ=0.02 sample showed more excellent cycle stability, due to the lowest electrochemical impedance.(3) Li₄Ti₅O₁₂-coated LiNi_0.5Mn_1.5O₄ cathode material was prepared. Experimental results showed that the best heat treatment temperature of coating precursor is 600℃. The discharge capacity retention rate of Li₄Ti₅O₁₂-coated LiNi_0.5Mn_1.5O₄ cathode materials was much higher than that of the uncoating material, which of the 2wt.% Li₄Ti₅O₁₂-coated LiNi_0.5Mn_1.5O₄ samples was 99.3%. CV and AC impedance curves showed that the cycle performance of cathode materials was improved after Li₄Ti₅O₁₂-coating. The 2wt.% Li₄Ti₅O₁₂-coatig, due to the lowest electrochemical impedance, would be most beneficial to the Lithium-ion diffusion, and greatly improved the cycle stability.