Preparation Of Modified Spinel LiMn₂O₄ Cathode Materials And Investigation For Its Electrochemical Performance

Lithium-ion battery has been recognized as promising alternative power for electric and hybrid vehicles because of its important advantages,such as high energy density,long life,low cost,environmental benign,no memory effect and etc.Cathode material is one of the most important components for the lithium-ion battery(LIB),and it plays a crucial role for the performance of the battery.Spinel LiMn2O4 is a kind of important cathode materials which is expected to become the ideal power source for electric vehicles and hybrid vehicles for its rich resources,low cost,safety and etc.However,its application in LIB has been limited by its poor stability,enhancing the stability of lithium manganate has becoming a hot research topic in the field of materials for lithium ion batteriesIn this work,we synthesized spinel LiMn2O4 cathode materials by a high-temperature solid-state method,and attempted to enhance the performance of the material through doping two types of transition metals(Ni and Mo)simultaneously,and coating with carbon materials film derived from organic material.The effect of Ni,Mo Co-doped and carbon coating on the performance of spinel lithium manganate was intensively investigated.It is shown that the capacity and stability of lithium manganate have been greatly improved through Ni,Mn Co-doped and carbon coated.The sample with optimal composition,LiNi0.03Mo0.01Mn1.96O4,had a discharge capacity at 1C of 114 mAh.g-1,and exhibited significantly improved stability: after 300 charge–discharge cycles at 1C,its capacity retention was 91.2%,whereas the capacity retention of the undoped LiMn2O4 was only 61.9% after 300 cycles.On the basis of Ni,Mo co-doped spinel lithium manganese oxide via solid-phase synthesis,we tried to coat the LiNi0.03Mo0.01Mn1.96O4 composite materials with carbon film derived from cellulose or sucrose.It was shown that,carbon coated with different carbon sources have different effects on the properties of materials.When coated with ethyl cellulose,the cyclic stability and the rate performance of the material had been greatly improved,and the influence of carbon coated amount on the properties of the material was also investigated.When LiNi0.03Mo0.01Mn1.96O4 was modified by 3 wt% carbon with ethyl cellulose,its capacity retention were 93.6% and 88.1% at 5C and 10 C after 400 cycles,and its capacity was up to 110 mAhg-1 and 95 mAhg-1,respectively.The cyclic stability and capacity of the material at high rate have been significantly improved.In this work,XRD,SEM/TEM,XPS,EIS were used to characterize the structure of the materials.The effects of doping and coating on the structure of the materials and the relationship between the structure and properties of the materials were revealed.