Investigation On Crystal Structure And Electrochemical Performances Of Cr³⁺?Co³⁺?Al³⁺ Doped LiNi_0.5Mn_1.5O₄

The cathode material is the bottleneck limiting the performance of lithium-ion battery,which has a decisive influence on the energy density and power density of the battery.Spinel LiNi0.5Mn1.5O4 cathode material is one of the most promising cathode material for high-energy and high-power lithium-ion batteries,owing to its high working potential around 4.7 V and relatively large capacity of 147 mAh·g-1.However,the specific capacity of the LiNi0.5Mn1.5O4 cathode material under high current density is unsatisfactory,which deteriorates fast during high rate cycling.In this work,M doped LiNi0.5Mn1.5O4(M=Cr,Co,Al)have been synthesized by polymer assisted method,and the structure of the materials were characterized by X-ray diffraction(XRD)and Fourier Transform Infrared Spectroscopy(FTIR).The electrochemical performance was studied by galvanastatic charge-discharge testing,cyclic voltam-metry(CV)and electrochemical impedance spectroscopy(EIS).The relationship between phase transi-tion and its conductivity was revealed.Subject to the intricate phase transitions upon lithiation/delithiation reaction,the migration of lith-ium ions is hindered by the formation of phase boundaries and new phases during the charge-discharge cycle,the LiNi0.5Mn1.5O4 exhibits unsatisfactory high rate performances.The intricate phase transitions upon electrochemical cycling constrain the high-rate performances of the LiNi0.5Mn3.5O4 cathode.The formation of the rocksalt-like phase causes the diffusion of Li ions asymmetric in the lithiation and de-lithiation reactions.The evolution of multiple cubic phases during electrochemical cycling results in poor diffusivity of Li ions in the LiNi0.5Mn1.5O4.High-resolution XRD scan on the chemically de-lithiated samples reveal that the intricate phase transitions are effectively suppressed in cation doped LiNi0.5Mn1.5O4.The suppression of phase transitions not only enhances the Li ions' diffusivity inside the lattice,but also stabilize the charge transfer interfaces by reducing lattice mismatch and alleviating structural stress during the lithiation and delithiation.As a consquence,cation doped LiNi0.5Mn1.5O4 exhibits excellent electrochemical performances at high rates.The results show that Cr doping signifi-cantly inhibits the phase transition during charge and discharge.LiNi0.4Cr0.1Mn1.5O4 exhibits excellect capacity retention of 97.4%after 100 cycles at the 5 C,Coulomb efficiency of 97.1%in the first cycle.