Fabrication Of High Specific Energy Lithium-ion Batteries Based On Pre-lithiation Strategy And Its Performance Study

Lithium-ion battery（LIB）is regarded as one of the most promising electrochemical energy storage systems because of its high energy density,no memory effect and low self-discharge.The demand for LIB energy density is increasing year by year in the rapidly developing society,and the development of high specific energy LIBs is imminent.The development of silicon-based high-capacity anode materials is one of the closest technical routes to industrialization of high specific energy LIBs,however,their lower first-time efficiency seriously affects the full battery capacity performance.Pre-lithiation technology can provide excess lithium source to supplement the first irreversible capacity loss of the full cell,and can effectively address the impact of low coulombic efficiency of silicon-based materials.In this paper,we investigate the preparation and application of pre-lithiation materials and the optimization of full-cell design,and finally realize the batch production of high specific energy LIBs.The main research contents include:（1）Pre-lithiation material preparation:Based on the alloying reaction between metallic lithium and metallic aluminum,a key aluminum-lithium alloy（ALA）pre-lithiation material was designed and prepared,which is easy to process,safe and stable,and can provide more than 1000 m Ah g^-1of active lithium.The effects of different solvents,addition methods,cathode materials and addition amounts on the pre-lithiation performance of ALA were investigated experimentally,and the improvement effect of ALA on the first-time efficiency of graphite,hard carbon and silicon-carbon anodes was verified.The mechanism of ALA as a bifunctional pre-lithiation additive in the full cell was further demonstrated by SEM and XPS analysis test methods.The results show that ALA can not only improve the first charge capacity of lithium cobaltate electrode by 21.26 m Ah g^-1as a cathode additive,but also improve the first efficiency of silicon-carbon cathode from 77.83%to more than 100%by adapting to conventional lithium-ion battery cathode materials.（2）Full battery lightweight design optimization:Using Negative/Positive（N/P）as the entry point,we focus on the impact of different N/P designs on the energy density and cycling stability of full batteries.Reducing the N/P of the battery from 1.2 to 1.08 can increase the energy density by 5%,but the cycle life will be reduced by 60%.Combined with the three-electrode test and failure analysis,it is found that the failure of low N/P battery is caused by lithium precipitation at the negative electrode,and the cycle stability of the battery can be greatly improved by the voltage regulation strategy.The optimized cell design combines high specific energy and long cycle characteristics,which provides more detailed and reliable data to support the preparation and application of high specific energy LIBs.（3）Engineering fabrication and failure analysis of high nickel ternary/silicon carbon lithium-ion batteries:Based on the pre-lithiation strategy and full cell lightweight design,90161227-71 Ah high nickel/silicon carbon system lithium-ion batteries have been developed and realized batch engineering fabrication.The energy density of the prepared battery exceeds 300 Wh kg^-1and has a good cycle life,with a capacity retention rate of over80%after 600 cycles.The failure analysis revealed that the loss of active lithium during cycling led to a serious lithium deficiency in the cathode material,and the continuous destruction and generation of SEI film at the solid/liquid interface caused by the crushing change of the cathode silicon-carbon material was the main reason for the loss of active lithium.