Preparation And Application Of High-Performance Lithium-Ion Battery Electrode Materials Based On Artificial Interfaces

Due to its high energy density,lithium-ion batteries have realized large-scale application.But,the current cycle life of battery still cannot meet people’s requirements for batteries.One of the main obstacles for limiting the improvement of lithium-ion battery cycle performance is the unstable electrode/electrolyte interface.However,the instability of the naturally grown SEI film will cause a large amount of active lithium consumption,which is the main reason for deteriorating the cycle stability of lithium-ion batteries in the system of traditional electrolyte.Therefore,constructing a multifunctional and stable interface on the electrode surface is the key to the development of next-generation high-performance lithiumion batteries.This paper takes the interface modification of electrode materials as the starting point,studying from the functional electrolyte additives to the interface coating,interface design and functional interface construction,to systematacially explore the impact of of multifunctional SEI film on the performance of lithium-ion batteries.Furthermore,the formation mechanism,chemical composition and mechanical properties of SEI film are analyzed with the help of a variety of electrochemical analysis and characterization methods.The main research contents include the following:(1)1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(TTE)is developed as a bifunctional electrolyte additive,which is able to effectively effect the surface of graphite anode and LiNi0.5Co0.2Mn0.3O2(NCM523)cathode.The overall electrochemical performances of the full cell are significantly enhanced with 3 wt%TTE additives in a conventional organic electrolyte.Combining scanning electronic microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),and Fourier transform infrared(FTIR)spectroscopy studies have shown that a uniform,compact,and stable solid electrolyte interphase(SEI)with improved mechanics on the graphite anode and an effective cathode electrolyte interphase(CEI)on the NCM523 cathode is developed.The electron-withdrawing C-F group helps to the stable and compact surface film,which explains the electrochemical enhancement of the NCM523/graphite full cell.(2)The coating technology of sodium maleate(SM)with ion conductivity function for cathode material is developed.Through the ion-conducting organic secondary coating technology,sodium maleate(SM)is coated on the surface of a commercially available LiFePO4 cathode with a carbon coating.The very distinctive features of the secondary coating are highly uniform and continuous.More importantly,SM contains a large number of carbonyl groups to improve lithium ion battery on the LFP surface.The organic layer with nanostructure can effectively suppress the undesirable side reactions at the electrode/electrolyte interface.With 6.0 wt%of the SM coating layer,rate capability and long-term cycling performances of the LiFePO4 cathode at different temperatures are significantly improved.Furthermore,the rising trend of impedance of LFP cathode during electrochemical cycles is effectively suppressed.(3)Developing in-situ growth technology of elastic SEI film,the multifunctional sodium itaconate material was studied to construct an elastic solid electrolyte interface film on the surface of the graphite negative electrode.The nanotuned uniform SI nanolayer on the graphite surface,as a template for SEI film,contributes to a polymer-reinforced SEI film through self-polymerization between the carbon double bonds.With 20 nm of the SI nanolayer template,the overall electrochemical performances including the first Coulombic efficiency,rate capability,cycling stability,and even,the high temperature performance are remarkably improved.Moreover,the impedance rise of the electrode with electrochemical cycles is effectively suppressed.On the other hand,cycle-life of the full cell based on LiFePO4 cathode and the SI-decorated graphite anode is greatly enhanced.After 400 deep charge-discharge cycles,the full cell with bare graphite retained only 72.4%of its initial capacity.By comparison,the full cell with the 20 nm SI-decorated graphite anode shows a capacity retention of 92.2%.(4)On the basis of the above work,the concept of a high-performance 2,2-dimethylvinyl boric acid(DEBA)material is proposed for the first time to construct an elastic solid electrolyte interface film on the surface of a graphite anode to replace the complex electrolyte additives in the lithium ion battery.Herein,a new strategy of SEI precursor is realized by coating a functional nano DEBA film on the surface of natural graphite.Its advantage is that the functional nano layer contributes to the development of a stable and controllable SEI film through in-situ self-polymerization between the DEBA molecules on the graphite surface during the cell formation.With 20 nm DEBA layer,the electrochemical properties of the natural graphite anode in terms of first coulombic efficiency,rate and cycle performance is significantly improved.Meanwhile,the life-span of the full cell with LiNi0.5Co0.2Mn0.3O2(NCM523)cathode is also prolonged and the result is superior to applying traditional electrolyte additive of LiODFB.Clearly,the capacity retention of the full cell with the pristine NG anode is only 64.3%after 200 cycles.By applying 20 nm SEI precursor of DEBA layer,the capacity retention is increased to ca.92.0%,which is much higher than the pristine electrode 64.3%after 200 cycles.With 5 wt%LiODFB additive in the electrolyte,the capacity retention is obtained to be ca.87.3%after 200 cycles.In contrast,the mechanism of the DEBA layer is effectively to inhibit the growth and thickening of the SEI film during the long-term cycle,which helps to develop a stable and controllable SEI film.(5)Since both DEBA and SI are water-soluble small molecule salts and are used for graphite anodes with PVDF as the binder,we propose a non-water-soluble 4-vinylbenzoic acid(4VBA)material to construct a highly stable trans SEI film on the graphite surface for realizing the application of small molecule modification technology in water-based binders.Through experimental date comparison,it is found that the 40 nm 4VBA layer implanted on the graphite surface exhibits the best electrochemical performance.On the one hand,4VBA contributs to form a flexble and stable SEI film,which not only significantly enhances the overall electrochemical performance of the natural graphite electrode under the water-based binder system,but also greatly prolongs the cycle life of the full cell with the LiNi0.6Co0.2Mn0.2O2 cathode.On the other hand,the effectively suppressed surface evolution and the decomposition of electrolyte originated from the stable organic SEI transformed from the implanted 4-VBA after analysis and characterization...