Preparation Of Single-Crystalline Spinel LiMn₂O₄ For High Performance Lithium-ion Battery Cathode Material

Recently, spinel LiMn2O4 cathode material has been thought to be ideal material of power lithium-ion battery material because of the advantages of its rich resources, low cost and high security. As to its poor cycle performance, especially at high temperature, the large-scale application of spinel LiMn2O4 cathode material has been severely hampered. Here, single crystal LiMn2O4 was synthesized by a gel-combustion method using polyvinylpyrrolidone(PVP) as the polymer chelating agent and fuel. We mainly examined the structure, morphology and electrochemical performance of samples at different calcination temperature; The doping effects of Al, Cr, F, Na to spinel LiMn2O4 cathode material synthesized at optimal condition were studied. The crystal structure, morphology and electrochemical performance of samples were characterized using XRD, SEM, EIS and charge-discharge test. The conclusions were as follows:(1) The appropriate calcination temperature was 1000℃, the initial discharge specific capacity of the obtained material can be 104mAh/g at 0.2C, The discharge specific capacity at IOC can be 91.6mAh/g; when cycled 300 times at ambient temperature at the rate of 1C, the discharge specific capacity decreased from 103.1mAh/g to 99.1mAh/g, the capacity retention was 96.1%; when cycled 200 times at 55℃ at the rate of 1C, the discharge specific capacity decreased from 103.2mAh/g to 92.7mAh/g, the capacity retention was 89.8%.(2) Aluminum doped spinel LiMn2O4 had improved rate capability and better cyclic performance, when x=0.03, the doped material had the best performance:at the rate of 0.2C, the initial discharge specific capacity can be 105.2mAh/g, when discharged at the rate of 10C, the discharge capacity was 100.2mAh/g. After the 300th cycle at ambient temperature at the rate of 1C, the discharge specific capacity decreased from 103.5mAh/g to 101.5mAh/g, the capacity retention was 98.1%; After the 200th cycle at 55℃Cat the rate of 1C, the discharge specific capacity can still be 96.7mAh/g, the capacity retention was 93.3%.(3)The increasing content of chromium decreased the initial discharge specific capacity of the obtained material. The doping of chromium had improved rate capability; a small amount of chromium doping can help little with cyclic performance, when chromium content of doping increased, an adverse impact would been seen.(4)A small amount of fluorine doping may improve the initial discharge specific capacity of the obtained material, but fluorine doping had an adverse impact on rate capability and cycle performance.(5)With a small amount of sodium doping, the initial discharge specific capacity was reduced, rate capability became worse, and the change of cyclic performance was not obvious.