Preparation And Electrochemical Properties Of LiMn₂O₄Cathode Material With Long-life And High Power Density At High Temperature

Rechargeable lithium ion batteries (LIBs) are one of the most promising energy storage devices for electric vehicles (EV) and hybrid electric vehicles (HEV) because of their high energy density, high power density, low cost, superior safety, and stable cycling lifespan. The advanced battery materials and their preparation process are the key to the high performance batteries. The spinel LiMn2O4is generally considered as an excellent alternative to apply in the field of power LIBs because it is suitable voltage plateau, inexpensive, safe and environmentally friendly. Unfortunately, its wide application in lithium ion batteries has been hampered by the problem of capacity decay during cycling, especially at high temperature. The reasons are mainly attributed to the Mn dissolution via a disproportionation reaction (2Mn3+/Mn2++Mn4+) and structural transformation from cubic to tetragonal phase, which is induced by Jahn-Teller distortion of Mn(III) with high spin. Over the years, most of spinel LiMn2O4with good electrochemical performance was manufactured by the corporations Korean and Japan, however, few breakthroughs in the preparation of LiMn2O4cathode material with good electrochemical performance in China have been achieved. In consideration of meeting the social needs of the power lithium ion batteries using spinel LiMn2O4cathode material, in this paper, the designing and preparation of spinel LiMn2O4cathode material with long life and high power density at high temperature have been developed.Porous LiMn2O4microspheres, which are constructed with nanometer-sized primary particles, have been synthesized by a facile method that involves the use of porous MnCO3microspheres as the self-supporting template. The influence of structure and morphology on the electrochemical properties of the obtained LiMn2O4spheres was investigated in detail. In addition, the porous LiMn2O4-based cathode material with long-life and high power density at high temperature was fabricated successfully by Co-doping by lithium ion and transition metal ion.During the exploration, it was found that porous MnCO3microspheres can be synthesized via solvothermal method at200℃for12h and the porous MnCO3microspheres can act as effective templates and precursors to synthesis the porous LiMn2O4-based cathde materials. The porous LiMn2O4-based materials have good crystallinity, high purity and excellent electrochemical performance. By deep research, results have shown that the obtained LiMn2O4material deliver the specific discharge capacity of119,107and98mAh g-1at2,10and20C, respectively, with the corresponding capacity retention of82%,91%and80%for up to500cycles. The high rate performance and good cyclability are believed to be resulted from the porous structure, reasonable primary particle size and high crystallinity of the obtained material, which favor fast Li intercalation/deintercalation kinetics by allowing electrolyte insertion through the nanoparticles and high structural stability during the reversible electrochemical process. The high level of Mn4-conceration on the surface of the sample can alleviate the Jahn-Teller transition, which was triggered normally by the equal amounts of Mn4+/Mn3-concertration on the surface of the LiMn2O4cathode material.The porous Co-doping LiMn2O4by lithium and transition metal ions shows superior cyclability than those other LiMn2O4-based materials such as pure LiMn2O4, lithium-doping LiMn2O4and transition metal-doping LiMn2O4, especially at high temperature. It was found that the Co-doping sample delivered115,112and108mAh g-1at0.5,1and5C, respectively, with the corresponding capacity retention of85.6%,88.9%and89.4%for up to1000cycles. Meanwhile, it can deliver an initial capacity of113mAh g-1at5C with capacity retention was80%after1000cycles at55℃. The good cyclability of the Co-doping LiMn2O4cathode material was attritubted to its structure stability, which was demonstrated by the absence of a tetragonal phase LiMn2O4in the overlithiated state after1000charge-discharge cycles at high temperature.