Relationships between Structural Changes and Electrochemical Kinetics of Li-Excess Li_1.13Ni_0.3Mn_0.57O₂ during the First Charge

Li-excess cathode material, Li 1.13 Ni 0.3 Mn 0.57 O 2, was synthesized by the sol–gel method. The material has a reversible discharge capacity of 200 mAh g –1 at a current density of 40 mA g –1 . In situ synchrotron X-ray diffraction, electrochemical impedance spectroscopy (EIS), and the galvanostatic intermittent titration technique (GITT) were applied to study the relationships between structural changes and electrochemical kinetics of Li 1.13 Ni 0.3 Mn 0.57 O 2 during the first charge. When the charging potential was below 4.4 V, the c/a structural parameter of the material gradually increased, resulting in a higher layered character. The lithium diffusion coefficients during this process were about 10 –14 cm 2 s –1 . When the charging potential was increased to 4.8 V, the bulk of the material was still maintained in a layered structure with space group symmetry R 3̅ m . The lithium diffusion coefficient and the charge transfer kinetics rapidly decreased because of the high kinetic barriers associated with concurrent Li + extraction, oxygen loss, and structural rearrangement. Both the lithium diffusion coefficient and the charge transfer kinetics show further decrease at the end of the first charge, indicating severely sluggish kinetics of the “Li-poor” Li 1.13– x Ni 0.3 Mn 0.57 O 2 phase.