Synthesis And Electrochemical Performances Of Ternary Cathode Materials And Full Cells

In this paper,in term of poor thermal stability and poor safety of LiNi_1-x-yCo_xMn_yO₂cathode materials,investigation on the thermal stability and safety of cathode material such as LiNi_1/3Co_1/3Mn_1/3O₂ and LiNi_0.5Co_0.2Mn_0.3O₂,with surface modification and process design of pouch cells was carried out.The specific work was described as follows:Firstly,LiNi_1/3Co_1/3Mn_1/3O₂ cathode material was synthesized by a sol-gel method and subsequently coated with Al₂O₃ film on the surface of LiNi_1/3Co_1/3Mn_1/3O₂.The structure,morphology and elemental composition of the pristine and Al₂O₃–coated samples were analyzed by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?.Electrochemical performances were investigated via the charge/discharge testing,cyclic voltammograms,electrochemical impedance spectroscopy and galvanostatic intermittent titration technique,it revealed that Al₂O₃–coated exhibited rate capability,cycling performance,and thermal stability performance.Enhancing on the electrochemical performance of Al₂O₃–coated samples due to Al₂O₃ coating layer possible attributed to relieve the side effects between the electrolyte and the pristine,enhance Li⁺diffusion coefficient and reduce growth speed of impedance.Analysis from Kelvin probe atomic force microscopy indicates that Al₂O₃–coated decreased work function of composite materials.It would be attributed to reduce oxidation of electrolyte,inhibit the growth of CEI film and enhance thermal stable performances of cathode materials.Secondly,commercial LiNi_0.5Co_0.2Mn_0.3O₂ material and graphite material were used as active material of cathode and anode,and titanium nitride?TiN?nanoparticle with high conductivity and thermal conductivity were added to the cathode,then ternary Li-ion pouch cells with a model of 5463C6 were made.The dispersed state of TiN in the cathode electrode were analyzed by scanning electron microscopy and energy dispersive spectroscopy.Electrochemical performances were investigated via the charge/discharge testing,cyclic voltammograms and electrochemical impedance spectroscopy,research indicates that enhanced of rate performance,capacity retention rate and thermal stable performances after adding TiN nanoparticle was mainly owing to TiN with high conductivity reduce electrode polarization and charge-transfer resistances.Analysis from infrared thermal imager indiceted that TiN with high thermal conductivity can significantly improved the balance of the internal temperature distribution of the cells under high current charge and discharge,simultaneously strengthen security of over-discharge test and nail penetration test.