Studies On Safety Performance Of LiNi_0.8Co_0.15Al_0.05O₂/LiMn₂O₄ Blend Materials

Lithium-ion batteries（LIBs）have been widely used in electric vehicles for the excellent performance.However,it is also worth noting that LIBs can generate a large amount of heat during the charging-discharging process.And on extreme working conditions,accumulated heat in batteries can cause the failure of power systems and even safety accident.Therefore,it is highly important for the development of electric vehicles to improve the safety of batteries.Affected by this factor,the research of improving the safety of materials has been a hot field to improve the safety of lithium-ion batteries.On the basis of summarizing the research results about safety properties of lithium ion batteries and materials,this thesis presents researches on the layered LiNi_0.8Co_0.15Al_0.05O₂ and spinel LiMn₂O₄ material and their blends.The evolution of structure and safety properties was studied with Rietveld method combined with thermodynamic research.The layered NCA cathode materials were charged to different voltage to study the effect of state of charge on the structure and properties.It has been shown that the layered cathode material undergoes a reversible phase transition,namely a phase transition from H1 phase to M phase,M phase to H2 phase,H2 phase to H3 phase on3.748V,4.017V,4.227V respectively.The crystal structure changed with the phase transition,the cell parameters a and b decreased while c increased during the phase transition.Lithium ion was extracted from cathode and nickel element was oxidized to Ni4+during the charging process.The decomposition temperature of cathode material varied with the final charge voltage,for materials charged to 3.6 V,3.8 V,4.0 V,4.2 V,the temperature was 176.01℃,176.849℃,176.716℃,166.023℃respectively.The safety of layered cathode materials can be improved by blending with spinel cathode material LiMn₂O₄.The evolution of crystal structure and safety properties of layered material was systematically studied after blending with LiMn₂O₄.When the mass ratio of LMO was 20%,the blended cathode material exhibited a better anti-overcharge behavior with less heat was generated during the overcharge experiment.Meanwhile,the rate property of blended materials got enhanced as a result of the decrease of electrical impedance.The amount of Ni⁴⁺in charged cathode material was reduced with the amount of LMO in the blended materials increased,thus the blended materials with a high ratio of LMO showed better safety properties.Simultaneously,the direct contact area between NCA powders and electrolyte was reduced and the side reaction got suppressed.All these factors led to a better cathode material with excellent electrical and safety properties.The study results can provide a reference for the research and design of a safer lithium-ion battery.