Green Preparation Of NCM811 Cathode Material And Thermal Management Of Its Lithium-ion Battery

The wide application of electric vehicles（EVs）and hybrid electric vehicles（HEVs）is subject to battery life and safety issues.Layered LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）cathode material has attracted much attention due to its high reversible capacity as well as low cobalt content,and has become one of the most competitive cathode materials for the next generation of LIBs.The new green and low cost preparation process of NCM811 cathode materials is proposed.The temperature effect of the electrochemical performance for the commercial Al₂O₃-coated NCM811 is investigated.Furthermore,the thermal characteristics and thermal management of the cylindrical lithium-ion batteries（LIBs）with Al₂O₃-coated NCM811as the cathode material are studied.There are the conclusions as follows:（1）The alternatives of eco-friendly chelating agents to NH₃·H₂O as well as sintering in oxygen-free atmosphere are essential for the LiNi_0.8Co_0.1Mn_0.1O₂in terms of lowing NH₃-derived pollution and preparation cost.The Ni_0.8Co_0.1Mn_0.1（OH）₂precursor is successfully synthesized with hydroxide co-precipitated method via using the citric acid and the sodium glutamate as the composite chelating agents.The NCM811 cathode material is obtained via calcining the mixture of H₂O₂pre-oxidized Ni_0.8Co_0.1Mn_0.1（OH）₂precursor and Li OH in the flowing CO₂-free air.The obtained NCM811 cathode material exhibits the first discharge capacities of 182.6 m Ah/g at 0.5C and the discharge capacity after 200 cycles of 141.2 m Ah/g,respectively.Meanwhile,it delivers the best discharge capability at 1C,2C and 5C posing 177.1,160.8 and 131.5 m Ah/g.The analysis results of XRD,XPS,EIS and GITT show the enhanced electrochemical performance of the prepared NCM811could be attributed to the decrease of the Ni O phase content,the oxygen deficiency and the formation of well-ordered structure on the surface of the LiNi_0.8Co_0.1Mn_0.1O₂.（2）The comprehensive experimental studies on the temperature dependence of the Al₂O₃-coated NCM811 cathode material have been conducted in the temperature range of-15℃ to 55℃.The results indicate that the aging rate of cycled cell possesses the minimum value at 25℃,and the rate performance enhances with increasing operation temperature.Three kinds of equivalent circuit models are revealed,and the variation of R_ct^-1values with the absolute temperature is agreement with the Arrhenius law.The poor cycle stability of Al₂O₃-coated NCM811 samples operated at elevated temperature is ascribed to the Li⁺loss owing to the increase in SEI thickness.While the performance loss of samples at the low temperature can contribute to the slow kinetic of the lithiation and delithiation reaction.（3）For a typical air cooling thermal management system,the inlet and outlet of air flow on both sides of the battery module would increase the temperature difference.In here,a novel cooling strategy based on air distribution pipes is proposed for the cylindrical LIBs module.The maximum temperature as well as temperature difference can be maintained below 35℃ and 3.5℃ at 2C and 3C discharge processes with the proposed air distribution pipe,respectively.Moreover,it is an efficient and a practical cooling strategy with no need to modify the arrangement of the battery module.（4）To maintain the maximum temperature within the optimum range and to improve the temperature uniformity of cylindrical lithium-ion battery,a liquid cooling method based on the half-helical duct was proposed.The effects of inlet mass flow rate,pitch and number of helical duct,fluid flow direction and diameter of helical duct on the thermal performance of battery at 5C discharge rate were analyzed numerically.The results show that the maximum temperature of LIBs would retain within 31℃,and temperature difference drops to 5℃ after the flow direction is optimized.In comparison to the thermal management with jacket liquid cooling method,the thermal management with half-helical duct liquid cooling method might be better and more effective owing to the low fluid volume and no stagnant zone.（5）Coupled thermal-hydraulic model integrated with liquid cooling half-helical duct and air cooling distribution pipe is established.The cooling performance of the hybrid thermal management scheme is analyzed when the LIBs discharge at 5C rate.The air cooling cannot control the temperature difference of the LIBs within 5℃.With the increase of the inlet mass flow,liquid cooling can effectively reduce the maximum temperature difference of LIBs following a minor rise in power consumption,revealing the excellent cooling performance of the liquid cooling.