Preparation Of Cellulose Aerogel And Its Composites Based On Battery Thermal Management

In order to deal with the extreme change of global climate,the shortage of fossil fuels and other problems,and strive to achieve the goal of"carbon neutrality",the development of renewable energy is imperative.Lithium-ion battery is the most potential new energy vehicle power battery with high specific energy,long cycle life and stable discharge and other advantages.However,lithium-ion battery is sensitive to temperature,and improper operating temperature can easily lead to performance degradation,life shortening,thermal runaway and even spontaneous combustion and self-detonation.Therefore,the research of battery thermal management system is of great significance for the development of new energy vehicles.Based on the battery thermal insulation material aerogel only heat insulation and battery thermal management phase change materials only heat dissipation and no heat insulation.The battery thermal management system needs to be further optimized.Based on this,the composite aerogel was prepared and combined with phase change material for the battery thermal management system,as follows:Al₂O₃-Si O₂/cellulose composite aerogel is prepared by sol-gel method and directional freeze-drying method.And the effects of the content of Al₂O₃-Si O₂ sol on the microstructure,structure and properties of the material are studied.The results show that the composite aerogel materials are crosslinked by covalent bonds,and the skeleton is composed of filamentous fibers and sheet structures.When the volume ratio of Al₂O₃-Si O₂ sol to microcrystalline cellulose solution is 2:10,the comprehensive performance of the sample（CA3）is the best.CA3 has the advantages of low density（0.12 g/cm³）,low thermal conductivity（0.0362 W/（m·K））,mesoporous structure,high compressive strength(σ_70%is 1.368 MPa)and other structures and properties.In addition,the composite aerogel is mainly condensed phase flame retardant,CA3 shows good flame retardant performance,EHC of 12.58 MJ/kg,p HRR of 154.69 k W/m².On the basis of the above research,the flame retardant and hydrophobic modification of CA3 is carried out by boric acid and dimethyldimethoxy-silane.The effects of boric acid solution with different concentration on the microstructure,structure and properties of composite aerogel are investigated.The results show that the crosslinking of boric acid and cellulose by chemical bond increases the cross linking and surface roughness of composite aerogel sheet structure.When the concentration of boric acid solution is 0.5mol/L,the comprehensive performance of the sample（CAP3）is the best.The density of CAP3 is 0.137 g/cm³,the low thermal conductivity is 0.0401 W/（m·K）,and theσ_70%is4.261 MPa,and the contact Angle is 100.1°.In addition,the modified composite aerogel CAP3 realized the synergistic effect of condensed phase flame retardancy and vapor phase flame retardancy,showing excellent flame retardancy performance,with EHC of5.68 MJ/kg and p HRR of 92.27 k W/m².Combined with CAP3 and PCM,the dual-function composite structure of heat dissipation and heat insulation was constructed for the thermal management system of lithium ion battery.The distribution of temperature field under normal and low temperature conditions are studied.The results show that the dual-function system can effectively reduce the maximum temperature of the battery pack（within 50℃）under normal conditions.At the end of 4 C rate discharge at 25℃,the maximum temperature of the battery pack is 49.6℃.The maximum temperature of the battery is 12℃at the end of 4 C power discharge at-20℃.The results show that the dual-function composite structure has the best temperature control performance and temperature uniformity.It can effectively control temperature in low temperature and normal working conditions,and has good adaptability to changes in environmental temperature.