Modification And Electrochemical Performance Of Layered Cobalt-free High-nickel LiNi_0.9Al_0.1O₂ Cathode Material

As the standard power source for electric vehicles（EVs）,the energy density and cost of lithium-ion batteries（LIBs）still constrain the further development of EVs.Layered Co-free Ni-rich materials are considered as the most promising candidate cathode materials for the next generation of LIBs due to their superior energy density and lower raw material costs.However,Co-free Ni-rich cathode materials suffer from rapid capacity degradation due to severe microcracks and structural phase transitions,limiting their large-scale application.Therefore,in this paper,strategies such as dual-site co-doping,multi-element high entropy modification,and single-crystal material preparation were used to enhance the stability of the crystal structure and microstructure of layered Co-free Ni-rich cathode materials,so as to significantly improve their electrochemical performance.The research content of this paper is as follows:（1）LiNi_0.9Al_0.1O₂ cathode material（LNAMW）with excellent structural and cycling properties was prepared through Mg/W dual-site（Li/Ni site）co-doping strategy.XRD,cross-sectional SEM,HRTEM and other characterizations indicate that compared to the undoped LNA90 cathode,the LNAMW cathode has a better layered structure and forms a microstructure with a central radial arrangement.The LNAMW cathode achieved a high capacity retention rate of 100%after 200 cycles at 2.8-4.3 V and 1 C,which is46.3%higher than the LNA90.EIS,CV,TOF-SIMS,as well as post cycle XRD and FESEM analysis indicate that the LNAMW cathode material effectively suppresses structural phase transition and microcrack formation and propagation during cycling,while forming a more stable CEI film on the surface.（2）A Mg/Ti/Sb co-doped and Ce O₂ coated LiNi_0.9Al_0.1O₂ cathode material（HE-LNA90）was prepared through a multi-element high entropy modification strategy.XRD and HRTEM tests have proved that the surface of the modified HE-LNA90 material forms a uniform Ce O₂ coating layer,while other elements improve its lattice structure and layered structure.The electrochemical performance study shows that the modified cathode material has significantly improved cycle stability,magnification performance,and discharge capacity.The HE-LNA90 achieves a capacity retention rate of 90.2%（from 200.3 m Ah/g to 180.6 m Ah/g）for 100 cycles at high voltages of 2.8-4.5 V and 1C,which is significantly higher than 60.1%（from 192.0 m Ah/g to 115.4 m Ah/g）of the Pristine LNA90.After cycling,the HE-LNA90 cathode particles did not crack and the layered structure remained well,effectively inhibiting interfacial side reactions and the formation of CEI films.（3）Single-crystal LiNi_0.9Al_0.1O₂ cathode materials were prepared by three stage temperature sintering using molten salt method.The effects of high temperature sintering on the morphology,structure,and cyclic performance of single-crystal Co-free Ni-rich cathode materials were emphatically studied.XRD refinement results and FESEM tests show that with the increase of sintering temperature,the Li/Ni intermixing and particle size of single-crystal LiNi_0.9Al_0.1O₂ cathode materials increase.The electrochemical performance test shows that the single-crystal LiNi_0.9Al_0.1O₂ cathode material prepared at a high temperature of 840℃（H840-NA90）has the best cycle stability,with a capacity retention rate of 80.2%after 100 cycles at 2.8-4.5 V,but its capacity decreased due to high Li/Ni intermixing.