Construction Of Dual-ion Batteries With High Specific Energy And Its Electrode Interface Tuning And Structure Evolution

To alleviate the increasingly serious energy crisis and environmental pollution problems,the development of rechargeable energy storage technologies is extreme important.Currently,to satisfy the rigid demands for EVs and large grid-scale energy storage equipment,commercial rechargeable Li-ion batteries(LIBs)have been making enormous efforts to improve the energy density and reduce the production cost.In recent years,Dual-ion battery,novel energy storage equipment has received wide researchers' attention gradually because of its high energy density,long cycle life and low cost.However,the development of dual-ion battery is in the preliminary stage,and the energy density still remains to be improved.Besides,few research works are involved the in-situ characterization during the process of charging and discharging.Therefore,this work will start with the design and assemble of novel high energy density dual-ion battery.Combined with in-situ characterization techniques and the corresponding theoretical calculation,hope to explore the reaction mechanism and effect of electrolyte additive during the charging/discharging process.The related research contents are summarized as follows:(1)The MnO-graphite dual-ion battery,Sn-graphite dual-ion battery and Ligraphite dual-ion battery(DIB)have been successfully assembled by matching the graphite as positive electrode and microporous MnO,commercial Sn foil and Li foil as negative electrode,respectively.Microporous MnO was prepared through coprecipitation method.The electrode materials were characterized by SEM,TEM,XRD and XPS tests.According to the electrochemical performances,the MnO-graphite DIB could achieve an energy density of 326Whkg^-1 at a power density of 326Wkg^-1,Sn-graphite DIB could achieve an energy density of 348.7Whkg^-1 at a power density of 348.7Wkg^-1 and Li-graphite DIB could achieve an energy density of 374Whkg^-1 at a power density of 748Wkg^-1.Compared with commercial lithium-ion battery and reported DIB,the DIBs in this paper showed excellent electrochemical performance.(2)The low initial coulombic efficiency of MnO-graphite DIB and corresponding mechanism was investigated.The structural transformation of electrode materials and electrochemical impedance change during the charging/discharging process are obtained by the operando XRD,ex-situ XRD and in-situ EIS.The results indicated that irreversible capacity during the first cycles come from three sources:(1)The kinetic barrier of the PF₆^-intercalation process and irreversible de-intercalation of the PF₆^-on the positive electrode reaction.(2)The decompose reaction of electrolyte and formation of interfacial film.(3)The irreversible conversion reactions on the MnO negative electrode.The coulombic efficiency will increased during the constantly charging/discharging process,due to the decreased source of irreversible capacity and kinetic barrier.(3)The effect mechanism of VC in the Sn-graphite was investigated.The influences on the reaction of battery during the charging/discharging process are obtained by the operando XRD,ex-situ XRD,OEMS and in-situ EIS,The results indicated that the VC could be polymerized into poly(VC)with lithium salts on the surface of the electrode at 4.4V charged state during the first charge process,resulting in the main components of interfacial layers and improved the stability of the interfacial layers and electrolyte.And in the subsequent charging/discharging process,the battery shows better reversibility and stability due to the decreased side reaction of lithium salts and formation of interfacial layer.(4)The effect mechanism of AgPF₆-LiNO₃ hybrid electrolyte additive on the Ligraphite was analyzed and investigated by the LSV,SEM,EIS,adsorption energy and electrochemical performance tests.According to the results of galvanostatic chargedischarge and Li?Li symmetric cells tests,the AgPF₆-LiNO₃ hybrid electrolyte additive has a positive impact on the cycle ability of the battery because of the improved stability on the Li anode.The results of SEM and XPS can be obviously observed that the spontaneous formation a lithiophilic Ag-Li alloy layer by introduce AgPF₆-LiNO₃ hybrid electrolyte additive.Meanwhile,the results of LSV and adsorption energy demonstrate that the Ag-Li alloy layer can decrease the energy barrier,increase the nucleation over-potential,induce homogeneous Li deposition and prolong the time of Li dendrite growth.Accordingly,the Li anode exhibits a superior stability,which ensures the electrochemical performance of Li-graphite DIB.In summary,this work successfully designed and assembled high energy density dual-ion battery by matching different negative electrodes with graphite positive electrode,respectively.The operando XRD,ex-situ XRD,OEMS and in-situ EIS were employed to discuss the reason of low initial coulombic efficiency and the effect mechanism of VC and AgPF₆-LiNO₃ hybrid electrolyte additive.The result can also provide important experimental basis and theoretical support for development of high energy density dual-ion battery.