Niobium Doping Modification Of Lithium Nickelate As A Cathode Material For Lithium-ion Batteries

Lithium-ion batteries（LIBs）have become a promising candidate for electric vehicles（EVs）because of their high energy,longevity,and reliability.Cathode materials play a crucial role in determining the electrochemical performance and cost of LIBs.Compared with Ni-rich Li Ni_0.8Co_0.1Mn_0.1O₂ and Li Ni_0.8Co_0.15Al_0.5O₂,LiNiO₂-based Co-free cathode materials are promising cathode materials for automotive LIBs due to their low cost and high energy density.However,the inferior performance and the poor thermal stability limit the practical application of LiNiO₂.To improve the properties of LiNiO₂,this paper proposes a strategy to improve the performance of LiNiO₂ based on the strong Nb-O bond(753 k J·mol^-1),high valence(Nb⁵⁺)and large ionic radius（0.64（?））.The joint experimental method and First-principles calculations investigated the synergistic effect on the phase structure,electronic conductivity,and Li⁺diffusion of LiNiO₂.This synergistic effect can effectively improve lattice stability,lower Li⁺/Ni²⁺cation mixing,expand Li O₆-slab spaces,enhance the conductivity and inhibit the H2–H3 phase transition,thus enhancing the stability of the layered structure,accelerating Li⁺diffusion and alleviating the mechanical damage.Therefore,Li N_0.99Nb_0.01O₂ exhibits higher capacity retention（91.4%after 100 cycles at 0.5C）and superior rate capability(143 m Ah g^-1 at 5 C).As a comparison,the data of bare LiNiO₂ is 69.2%and 127 m Ah g^-1 under the same conditions.These results further demonstrate that the proposed doping strategy can effectively overcome the shortcomings and improve the performance of LiNiO₂.The Nb-doped Li Ni_0.99Nb_0.01O₂ has a delayed activation phenomenon at the beginning of the cycle,in which the specific capacity increases with the number of cycles.In the delayed activation process,the dopant limits the embedding/detachment of Li⁺in the initial cycle,which decreases as the cycle proceeds,widens the diffusion channel for Li⁺and improves the reversibility of phase transition during the following processes.The delayed activation phenomenon delays the decay of the layered structure and improves the cycling stability of the material.