Interface And Doping Effect On The Electrochemical Properties Of Li-rich Cathode Material For Li Ion Battery

The lithium-rich layered oxide materials?LLOs?have attracted much attention as candidates for the next generation of LIBs because of their high voltage and high capacity.However,the mechanisms on the high voltage and high capacity are still poorly understood.In this study,based on the first-principles calculation,the interface and doping effect on the electrochemical properties of LLOs is systematically investigated.It is revealed that due to the asymmetric oxidation behavior of Li₂MnO₃/LiMO₂interface,the transition-metal-oxygen?TMO?layer of Li₂MnO₃ phase in LLOs gains more electrons from Li layer than that in pure Li₂MnO₃,which enhances the hybrid between Mn-3d and O-2p states and thus,the activity of Mn in Li₂MnO₃.Moreover,the deintercalated states of LLOs possess smaller layer spacing than pure LiMO₂,which reflects stronger electrostatic interaction between TMO and Li layers.The two factors are both beneficial to the high voltage of the Li-rich materials.On the other band,the asymmetric interface also results in the increase of electronic states of transition metal atoms near the Femi level,which changes the oxidization sequence of Ni²⁺/Ni⁴⁺and Co³⁺/Co⁴⁺and reduces the participation of oxygen in the redox process.As a result,the LLOs possess higher capacity than LiMO₂.Ti dopant increases the average voltage during the half and whole deintercalated process of LLOs,while Sn,Mo,and Ru dopants decrease the average voltage during the half deintercalated process and increase the average voltage during the whole deintercalated process.Ti and Sn doping makes the electronic states of O more localized,increases the effective charge of O in intercalated states,and decreases the generating of O₂ during the deintercalated process,which benefits the capacity.The valence of Mo and Ru dopants both increase during the deintercalated process,and thus,more electrons are provided in the redox process.The Mo doping effectively improves the charge around the O atoms and reduces the O₂ generation.However,the Ru doping gives electrons to Co for charge compensation with no charge increase around the O atoms,which cannot directly restrain the O₂ generation during the charge/discharge process of LLOs.