Study On The Preparation And Properties Of LiNi_xCo_yMn_zAl_1-x-y-zO₂ As Cathode Moterial Of Lithium-ion Batteries

In this study,LiNi_?1-x-y-z?Co_xMn_yAl_zO₂ cathode materials for lithium ion batteries were synthesized and the effects of composite ratio,synthesized method,synthesized conditions on electrochemical properties of materials were discussed.Then the materials were modified by doping metal elements.The crystal structure,surface morphology of materials were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,and electrochemical properties were investigated using electrochemical performance tests,EIS and CV.xLiNi_0.5Co_0.2Mn_0.3O₂·?1-x?LiNi_0.80Co_0.15Al_0.05O₂ cathode materials were prepared by high-heating solid-state reaction,and the effects of x value?0.2,0.4,0.6,0.8?,calcination temperature?750,800,850,900oC?and calcination time?12,15,18,21h?on the materials'properties were investigated.The optimum conditions were that the x value was 0.8,the calcination temperature was at 800oC and the calcination time was 21h.Under the optimum conditions,it delivered the initial discharge capacity of the sample was 149.5 mAh/g,the first coulomb efficiency was 80.5%and the capacity retention was 43.9%after cycled at0.1C,0.2 C,0.5 C,1.0 C and then back to 0.1C,respectively.xLiNi_0.5Co_0.2Mn_0.3O₂·?1-x?LiNi_0.80Co_0.15Al_0.05O₂?x=0.2,0.4,0.6,0.8?and Li[Ni_1/3Co_1/3Mn_1/3]_0.99?1-y?[Ni_0.56Co_0.19Mn_0.24]_y Al_0.01O₂?y=0.2,0.4,0.6,0.8?cathode materials were prepared by carbonate co-precipitation process.The synthesis conditions were optimized.Under the same optimum conditions,LiNi_0.5Co_0.2Mn_0.3O₂ and LiNi_0.80Co_0.15Al_0.05O₂ cathode materials were also synthesized.Their electrochemical properties were compared.The x=0.8 sample calcined at 800oC for 18h exhibited the good layer structure and the initial charge-discharge capacities at 0.1C were 185.8,149.5 mAh/g,with a coulomb efficiency of 80.5%.The discharge capacity at 1C was 90.9mAh/g and the capacity retention was 92.5%after 10 cycles.The y=0.2 sample calcined at 850oC for 18h exhibited the initial charge-discharge capacities at 0.1C were 187.1,152.2 mAh/g,with a coulomb efficiency of 87.4%.The discharge capacity at 1C was 84.5 mAh/g and the capacity retention was 100.0%after 10 cycles.Comparison of electrochemical properties of synthesized LiNi_0.5Co_0.2Mn_0.3O₂ and LiNi_0.80Co_0.15Al_0.05O₂ at the same optimal conditions,composite cathode material showed better.Increasing the relative content of aluminum in the compound appropriately decreased thedegreeofcationmixingandimprovedstructurestability.Li(Ni_0.56Co_0.19Mn_0.24Al_0.01)_1-xAl_xO₂andLi(Ni_0.376Co_0.302Mn_0.312Al_0.01)_1-yAl_yO₂cathode materials were prepared.The initial charge-discharge capacities of the x=0.04 sample were199.4,174.9 mAh/g at 0.1C,with a coulomb efficiency of 87.7%.The capacity retention was 90.3%after 30 cycles.The initial charge-discharge capacities of the y=0 sample were152.7,134.2 mAh/g at 0.1C,with a coulomb efficiency of 87.9%.A proper amount of Mg doping decreased the degree of cation mixing and improved cyclestabilityathighrate.Li[Ni0.56Co0.19Mn0.24]?1-x?MgxAl0.01O2and Li[Ni_0.376Co_0.302Mn_0.312]_?1-y?Mg_yAl_0.01O₂ cathode materials were prepared.The initial charge-discharge capacities of the x=0.025 sample were 216.3,181.0 mAh/g at 0.1C,with a coulomb efficiency of 83.7%.The capacity retention was 83.7%after 30 cycles at 1C.The initial charge-discharge capacities of the y=0.05 sample were 181.9,156.4 mAh/g at 0.1C,with a coulomb efficiency of 86.0%.