Study On The Effect Of Functional Additives On The Electrochemical Performance Of Li Mn₂O₄-Based Cells

Since Sony has commercialized lithium-ion batteries in 1990,lithium-ion battery products have brought great convenience to people's lives after 20 years of development in the fields of mobile phones,mobile power supplies,energy storage street lights,electric motorcycles,etc.Lithium-ion batteries are composed of cathode materials,anode materials,separators,electrolytes,shells,etc.Among them,cathode materials are critical in determining the energy density.In commercial lithium-ion battery cathode materials,lithium manganate?LiMn₂O₄?material is widely used due to its low pollution,good rate performance and high safety.This thesis explored many functional additives such as vinylidene carbonate?VC?,fluoroethylene carbonate?FEC?,1,3-propane sultone?PS?,methane methane disulfonate?MMDS?,succinonitrile?SN?,1,2,3-tris?2-cyanoethoxy?propane?TCP?,lithium oxalate borate?LiBOB?,lithium difluorooxalate borate?LiDFOB?on the electrochemical performance of LiMn₂O₄-based cell,focusing on the impact on the TCP on electrochemical performance for the full cell.The physical property test results showed that the viscosity of TCP was 0.79 mm²/s,which was smaller than that of cyclic carbonate?PC?,slightly larger than that of chain carbonate?DEC,DMC,EMC,etc.?and carboxylate?EA,EP,PP,etc.?;as the addition amount of TCP increased,the viscosity of electrolyte gradually increased,and the optimal addition amount of TCP was in the range of 0.5%to 2.0%.The results of the three-electrode tests showed that VC began to decompose at 4.3 V,and PS,MMDS,SN and TCP began to decompose at 5.3 V,while LiBOB and LiDFOB began to decompose violently at around 5.3 V.When the voltage reached 6.0 V,a gentle current platform appeared,and the current hardly increased,indicating that LiDFOB can form a protective film on the surface of the platinum wire to inhibit further oxidative decomposition of the electrolyte on the surface of the platinum wire.The AC impedance test results showed that LiDFOB and FEC reduced the AC impedance among graphite,and other functional additives such as VC,PS,MMDS,LiBOB,SN and TCP increased the AC impedance among graphite.The VC increased the AC impedance of the graphite surface,and PS,FEC,MMDS,LiBOB,SN,TCP,LiBOB and LiDFOB reduced the AC impedance of lithium manganate surface.The electrochemical performance of these functional additives?VC,PS,FEC,MMDS,LiBOB,LiDFOB,SN and TCP?was further explored in lithium manganite-based cells.The results showed that TCP could improve cycle performance at both room temperature and high temperature 45°C.The reason was that the TCP with nitrile group can coordinate with the Mn²⁺dissolved in electrolyte from the lithium manganate cathode material,and thus can reduce the deposition of Mn²⁺at the interface of the anode and inhibit the catalytic decomposition of the electrolyte by Mn²⁺.In summary,from the experimental results of physical properties and electrochemical properties,the conclusion was as follows:the optimal addition amount of TCP is 0.5%².0%.With this addition amount,the functional additive TCP did not affect the viscosity of the electrolyte.It could also significantly improve cycle performance of the battery at the room temperature?25??and high temperature?45??,while it had no significant effect on the low temperature discharge performance.