Design And Process Optimization Of High Specific Energy Lithium Ion Battery

At present,due to the excessive exploitation of fossil energy and seriously highlighted environmental issues,the clean energy has gradually attracted the attention of every country in the world,such as wind energy,solar energy and other renewable energy sources,and as an important measure of energy conservation and emission reduction,electric vehicles?EVs?have also developed rapidly in recent years.Efficient energy storage system is the key to the effective utilization of renewable energy,and also the core component that directly determines the cruising range and service life of new energy vehicles.Compared to other battery,lithium-ion batteries?LIBs?has the advantages of high voltage,high energy density and power density,long cycling life.However,the current energy density of LIBs still falls short of expectations,which cannot meet people's demand for the long range of EVs.Therefore,the energy density of LIBs urgently needs to be improved.High nickel ternary composite positive and silicon-based negative are the most practical and feasible schemes to improve the energy density of batteries.The technology of high nickel positive materials has been basically mature and realized scale application,such as lithium nickel-cobalt aluminate?NCA?.Silicon is considered a promising cathode material for improving the energy density of lithium-ion batteries,with a theoretical capacity of up to 3579 mAh g^-1.However,it is difficult to realize industrial application due to its volume expansion as high as 297%in the cyclic process,which is easy to cause electrode powder and inactivation,and its capacity rapidly decays.After the silicon is oxidized and combined with graphite to form SiO_x/C,on the one hand,the deformation of the electrode can be effectively buffered,and on the other hand,the specific capacity of the negative electrode can be increased,thereby increasing the energy density of the battery.Compared with graphite negative,SiOx/C negative consumes more active lithium in the first cycle,and in the subsequent cycle due to its volume effect,may lead to a solid electrolyte film?SEI?constantly broken,regeneration,active lithium and electrolyte will be continual expend in this process.Therefore,the capacity of the negative and positive ratio?N/P?and electrolyte fluid injection rate will greatly influence the performance of lithium ion battery,and also this paper mainly revolves around the two problems.The main research contents and achievements of this topic are as follows:?1?different N/P ratio of battery is designed and prepared,and the first charge and discharge efficiency,performance and cycle performance,parameters such as energy density was studied.It turns out that when the N/P is between 1.0 and 1.1,NCA||SiO_x/C pouch cells show the best electrochemical performances.Particularly,when the N/P is 1.03,its capacity retention rate is as high as 80.2%after 500 cycles.?2?The pouch battery that is completely discharged after the cycle is disassembled in the glove box and assembled into a pair of lithium button batteries,and the mechanism of the capacity loss of the electrode is studied.Test results prove that both positive and negative lost part of their active lithium host sites,in which negative account for almost 90%in total.Although the positive electrode lost only 5.14%of its capacity,the transition metals dissolve and migrate to the negative,influenced the stability of SEI.And the negative,although just has a very low Si content,shows32.41%dilation in thickness which is almost treble as much that of graphite.?3?the effects of different electrolyte injection amounts on the initial coulombic efficiency and cycling performance of the battery were investigated.The results show that 2.5 g Ah^-1 is an ideal electrolyte injection amounts for 10 Ah pouch battery.The above results indicate that in silicon-based LIBs,N/P ratio,electrode porosity,electrolyte consumption and other parameters have a significant impact on battery performance.Meanwhile,the result also manifests that in the development and manufacturing of LIBs,engineering problems are as important as finding new materials or other methods of optimization and improvement.