Study On Modification And Electrochemical Properties Of Li₂MnO₃Cathode Materials For Lithium Ion Batteries

As power energy of electric vehicle or energy storage device, higher specificdischarge capacity and higher rate capacity are required for cathode electrodematerials of Li ion batteries.0.8Li2MnO3·0.2LiCoO2(also named as LMCO) is one ofmost promising cathode materials of Li ion batteries with higher practical specificdischarge capacity (300mAh/g), abundant resource and environmental compatibility.However, the low rate capacity and poor structure stability at high potential (＞4.5V)are the main obstacles for application of LMCO. In this work, electrochemicalperformance of LMCO is improved by carbon coating and metal doping. The studyfound that carbon-coating has a higher electronic conductivity, which can improve therate capacity of LMCO. In this work, LMCO/C cathode materials for Li ion batterieswere synthesized by several carbon source, whose rate capacity were studied. Besides,the structure of LMCO was firmed by Nb doping to improve its cycle performance.Carbon source included PVA, sucrose, glucose. The LMCO/C coated by PVAcould enhance particles aggregation which is harmful to the electrochemicalperformance, while the sample coated by glucose could reduce particles aggregation.The sample coated by glucose at400℃for1h showed the best electrochemicalperformance at current density of20、50、100mA/g, respectively; which increased by10.3,36.7,24.5%compared with the sample without carbon coating. LMCO coatedby mixture glucose and carbon black had an initial capacity of256.8,181.5,132.4mAh/g at current density of50,100,200mA/g, respectively.Carbon coating can improve the rate capacity, nor for the cycle performance. Inthis work, the samples of Nb-doped LMCO were prepared by sol-gel-combustion toimprove rate capacity and cycle performance. When doping content increase from1to4%, size of sample particle decrease and aggregation reduce; while the size of5%Nb doped sample increase. The initial capacities of Nb doped samples were very low,but capacity could increase to a stable value with cycle increasing.3%Nb-LMCOcalcined at800℃for10h had the best electrochemical property, showed200、195mAh/g at current density of20,50mA/g, respectively; which increased by19.4,78.6%compared with LMCO, reflecting that Nb doped LMCO had better ratecapacity and cycle performance. In addition,3%Nb-LMCO/C was studied in this paper. The result showed betterrate capacity and cycle performance. The capacity reached to160mAh/g and couldkeep stable after30th cycle at200mA/g.