The Lithium-ion Battery Cathode Materials For Lithium Nickel Oxide Doped Compounds Preparation And Research

The ever-growing demand for portable batteries with high energy density is exerting pressure for the development of advanced lithium-ion batteries with the fast development of wireless electronic equipments. It is well known that LiCoOa was commercially used as cathode material for lithium-ion batteries. Nonetheless, Cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials. Among the candidates, LiNiO2 and the Me-doped lithium nickel oxides were considered the most promising materials based on its lower price and higher specific capacity compared to LiCoO2.Single-phase lithium nickel oxides with the formulas LiNi].xCoxO LiNio.gCoo.2-xAlx02 have been synthesized by using chemical co-precipitation - high temperature solid synthesis method and characterized in this paper. The effect on the physical characteristics and electrochemical performances of the cathode materials in the different experimental conditions were investigated systematically via SEJvK XRD.charge/discharge test and so on.The mid-products of Ni(OH)2N Ni].xCox(OH)2 and Ni0.8Coo.2-xAlx(OH)2+x with narrow particle size distribution and close to stoichiometric ratio prepared by chemical co-precipitation method were used as raw materials with LiOHH2O together. In order to increase their reactivity, the reactants were firstly finely ground before heating. Then they were heat-treated in the tube-furnace at 600~850 for 6~24h in the oxygen. The heating and cooling down speed were both 200/h.The preparation of the stoichiometric LiNiO material appeared to be difficult. The reaction speed was slow and it is very hard to get the perfect crystal structural when calcined under 700 . While the synthesized LiNiO2 was tend to transfer from 2-D layered structure to cubic structure without electrochemical activity over 720 . The sample calcined at 700 for 16h in the oxygen flow showed good physical and electrochemistry characteristics.The effects of partial substitution of cobalt on the crystal structure and electrochemical of LiNiO2 have been investigated. The lattice constantdecrease and the c/a value increase with the addition of cobalt, Which revealed the improvement of 2-D layered structural and electrochemical stability. The SEM showed that the LiNio.gCoo.iCh crystal particle grow up with the reaction temperature and time. The electrochemical characters were improved with longer reacting time for LiNio.gCooOa- The cathode material LiNio.gCoo.2O2 calcined at 750 for 24h in the oxygen flow displayed excellent electrochemical ability. It showed a charge/discharge specific capacity of 183 and 169.8mAh/g respectively at the 0.05C rate and 3.1-4.2V voltage window with only 2.6%/cycle in the first 5 cycles.As a result of aluminum doping, the particle size decreased and the particle distribution range became narrower. The crystal structural and cycling stability was improved with minor adding of aluminum based on its stronger Al-O bond. Excessive aluminum doping would destroy the layered structure because it has smaller ion-radius than nickel and cobalt. The optimum number of Al doping is 5%.