Preparation,Modification And Properties Of Lithium Nickel-Cobalt-Aluminum Oxide Nickel-rich Cathode Materials

Nowadays,energy and environment play important roles in the sustainable development of human society.In the context of low carbon economy,new energy vehicles become one of the significant ways to save energy and reduce emissions.As the main or auxiliary power source of new energy vehicles,batteries have become the limitations of the development of new energy vehicles.Compared with other batteries,lithium ion battery has the advantage of high working voltage,high energy density,excellent cycling performance,low self-discharge,excellent cycle performance and so on.It has been widely utilized on PHEV and EVs.In particular,the application of electric vehicles has strict requirements on safety,long-term performance and service life.In order to promote the development of electric vehicles,researchers are looking for outstanding electrode materials,especially the nickle-rich cathode materials of lithium ion batteries.Nickel rich cathode materials are expected to become the next generation of lithium ion battery anode materials due to their low cost,high capacity.However,with the increase of nickel content,the synthesis of materials become difficult.Ni³⁺is easily reduced to Ni²⁺under high temperature cycling,with occupying the lithium layer vacancy,causing phase structure transformation and forming electrochemically inert NiO-like phase,which generates microcracks and releases oxygen,thus deteriorating cycling and thermal stability and reducing the safety of lithium ion batteries.In this paper,LiNi_0.815Co_0.15Al_0.035O₂?LNCAO?was prepared by high-temperature solid phase method.The difference of on the morphology,structure and electrochemical properties of nickel rich cathode materials with different lithium sources and sintering temperature and atmosphere was investigated.With lithium hydroxide as the source of lithium,precursor and lithium salts of mole ratio of 1:1.05,presintering in temperatures of 550 ^oC for 4 hour,finally sintering 16 hour at 750 ^oC temperature got obvious layered structure,smaller cation disordering,uniform morphology of LiNi_0.815Co_0.15Al_0.035O₂with excellent electrochemical stability,the process under the condition of the preparation of nickel rich materials at 2.7–4.3 voltage range,under the 1 C(180 mA g^-1)current density,the reversible capacity reached 165.4 mAh g^-1,and the highest coulomb efficiency was 91.7%in the first cycle.After 100 cycles of charge and discharge circulation,the capacity retention rate reached 93.2%.On the basis,GO was prepared by the improved Hummers method.After thermal reduction,RGO was obtained.LiNi_0.815Co_0.15Al_0.035O₂/RGO?LNCAO/RGO?was successfully prepared by a simple liquid phase method.The differences in the structure,morphology and electrochemical properties of the composites prepared with different graphene additions were also investigated.Under the appropriate amount of graphene addition?2%?,the composite material has superior cycle stability and rate performance,under the charging and discharging current of 0.1 C,at 2.7–4.3 V,the specific discharge capacity is 215.8 mAh g^-1,and the capacity retention rate is 85.8%after 200 cycles at 1C current,at 5 C current density,The reversible specific capacity of the composite reached 140.2 mAh g^-1.Composite material with good electrochemical performance may be the cause of the special structure of graphene coating can suppress the direct contact between the electrode materials and electrolyte,reduce corrosion effect of electrode material with electrolyte and graphene has ultrahigh electrical conductivity and thermal conductivity,which can improve the cycle stability and the rate performance.The soft packages of lithium ion batteries were prepared by using composite material with 2%graphene as cathode and the commercial graphite as anode,after graphene coated material thermal stability and cycle stability have been improved,in the process of charging and discharging,the structure of graphene coating can reduce the side effects between the electrode materials and electrolyte.The coating of RGO reduces the mixing of lithium and nickel,increase the specific surface area of the LNCAO and broaden the transmission channel of lithium ions.This work revealed the role of graphene in improving material cycling,thermal stability and rate performance,and provided favorable guidance for nickel-rich layered cathode materials in lithium battery and other energy storage device in the future.