Synthesis,Modification And Electrochemical Performance Of LiNi_0.80Co_0.15Al_0.05O₂ Cathode Materials For Lithium-ion Batteries

In the face of energy crisis and environmental pollution,lithium-ion batteries have been widely used in various portable electronic devices,electric vehicles,and energy storage.Improving the energy density and reducing costs are the most challenging in the development of lithium ion battery.The cathode material is an important part of the lithium-ion battery,and its cost accounts for about 30%to 40%of the battery cost.At present,the specific capacity of battery is limited by the cathode material.Therefore,it is urgent to develop a cathode material with high specific energy,low cost,long-life and safety.The Ni-richcathode material is one of the most promising material,which has advantages of low cost,high capacity,and low toxicity.However,Ni-rich materials exhibit a rapid capacity fade,impedance rise,and poor thermal stability during cycling.Doping Al is verified very effectively to improve the caycle stability because it can stabilize the charge-transfer resistance on the cathode.The most widely studied NCA(LiNi0.80Co0.15Al0.05O2)cathode material,which has attracted widesperad attention forits high capacity(-200 mAh·g-1).Concentration gradient materials with a low nickel surface layer can also be prepared to improve the cycle performance of the Ni-rich cathode material.In this article,a systematically studyon preparation and modification of Ni-rich LiNi0.80Co0.15Al0.05O2cathode materials is proposed.Firstly,the precursors with regular spherical morphology and uniform element distribution are successfully synthesized by a hydroxide co-precipitation method.The influences of pH and concentration of ammonia on the size distribution of precursors revealed thatthe concentration of ammonia was too high and the size distribution of precursor was broadened.Furthermore,the pHof reaction system was higher and the higher ammonia concentration could be tolerated.At the same time,the effect of sintering temperature on LiNi0.80Co0.15Al0.05O2 material was also studied.It was found that the primary particles of NCA cathode material were bigger and the cation mixing wasintensified with the calcination temperature increase.If the calcination temperature is too high,fewer Ni3+ exist in the crystal lattice because of the higher stability of Ni2+.In order to investigate the effect of Al-doping on the structure,morphology and electrochemical performance of Ni-rich layered oxides,the NCA cathode materials(LiNi0.8Co0.15Al0.05O2)were prepared by two different methods employing different aluminum sources.The results show that Al-doping can reduce the degree of cation mixing and maintain the stability of the layered structure,thereby reducing the voltage drop and improving its cycle performance.The NCA material prepared by co-precipitation method employing NaAlO2 as the aluminum source which possesses a morphology of dense microspheres with a uniform size distribution and a well-layered structure of low Ni2+/Li+ mixing,shows the best performance.The as-prepared NCA cathode material delivers a high discharge capacity(198 mAh·g-1 at 0.1C)corresponding to 94.6%coulombic efficiency and good cyclic stability(a capacity retention of 70%after 200 cycles at 1C)between 3.0V and 4.3V.Finally,precursor with a core-shell structure was prepared by co-precipitation method,and then the metal element was diffused into a concentration-gradient LiNi0.80Co0.15Al0.05O2 material through a high-temperature calcination process,and it was found that the concentration-gradient materials have a better cycle performance(a capacity retention of 73%after 200 cycles at 1C)between 3.0V and 4.3V.