| Traditional lithium-ion batteries(LIBs)have been dominating the market of consumer electronics due to their extremely high energy conversion efficiency,long cycling life and relatively high energy density.However,in order to meet the needs of vigorous development of electric vehicles and large-scale energy storage power stations,it is necessary to develop lithium batteries with higher energy density and safety.As the main anode material for traditional LIBs,graphite has a relatively low theoretical capacity,which limits the energy density of the cells.In addition,traditional LIBs also use organic liquid electrolytes,which have problems such as flammability and liquid leakage,which lead to unavoidable safety hazards.This thesis selects the key materials of high energy density lithium metal batteries(LMBs)and high safety all-solid-state batteries(ASSBs)as the main research direction,attempting to provide some theoretical and experimental bases for the design and application of next-generation lithium batteries.Considering the potential of large-scale applications,the preparation method for some key materials of LMBs and ASSBs in this thesis mainly is phase inversion process,so as to obtain an ideal special microstructure,i.e.bi-modal porous structure with both micron-scale vertically aligned straight channels and simultaneously abundant nanopores.Specifically,for LMBs,we use the phase inversion method to structurally design and modify the cathode,anode,and separator to optimize the electrochemical performance.For ASSBs,we use the phase inversion method to prepare a composite cathode with continuous electronic and ionic pathways,which provides a new idea for the construction of ASSBs.Chapter 1 briefly introduces the working principle and development direction of LIBs,then reviews the research progress of inorganic ceramic electrolytes and polymer electrolytes in ASSBs and summarizes the related current interfacial issues.At the same time,this chapter also reviews the problems and challenges related to lithium metal anodes,as well as commonly used modification strategies reported in literature.Finally,the principle and application of the phase inversion method are briefly introduced,and the background and research content of this thesis are outlined.Chapter 2 summarizes the reagents and instruments required in the experiments of this thesis,and introduces the preparation and characterization methods of the materials,as well as the methods for coin-cell assembly and electrochemical tests.In Chapter 3,high-capacity LiFePO4 thick electrodes with vertically aligned channels are prepared by phase inversion and the electrochemical properties are characterized.Its conductive porous framework provides a high electronic conductivity and facilitates electrolyte penetration,while the unique vertically aligned channels serve as fast ion/electron transport pathways.Therefore,the thick electrode with high areal loading of 20 mg cm-2 exhibits excellent rate capability(110 mAh g-1 at 10 C)and stable cycling performance.Notably,this method can also achieve thick electrodes up to 1.3 m1 in thickness(with an area capacity up to 15.1 mAh m-2).In Chapter 4,three-dimensional porous Cu conductive frameworks with vertical channels are prepared by phase inversion method,and the Cu frameworks are lithiophilically modified by an electroless plating process.This special channel structure in the three-dimensional porous Cu framework can serve as the host for lithium deposition,and its porous structure is beneficial to reduce the local current density.The introduced lithiophilic layer can reduce the nucleation barrier of lithium deposition,which is beneficial to induce uniform deposition of lithium metal and inhibit the formation of lithium dendrites.Therefore,under the condition of high areal capacity up to 12 mAh cm-2 and high current density of 12 mA cm-2,the symmetric battery successfully achieved an ultra-high life span of more than 2000 h.Chapter 5 uses the phase inversion method to modify the commercial polypropylene separators to achieve uniform Li ion flux and high Li ion transference number.The modified layer is a composite membrane composed of PVDF-HFP as skeleton and Y0.08Zr0.92O2-δ(YSZ)as functional filler.Among them,the porous PVDF-HFP framework has a rich and uniform pore structure and can conduct lithium ions after absorbing the electrolyte,which can be used as a redistributor to adjust the distribution of lithium ions.The YSZ nanoparticle additive can absorb the anions in the electrolyte to increase the lithium ion transference number,thereby achieving dendrite-free lithium deposition and fast charging capability.Therefore,the synergistic effect enables lithium metal batteries to achieve high average coulombic efficiency(98.4%over 500 cycles),long lifespan(over 1000 h)and excellent rate performance(155 mAh g-1 at 10C).In Chapter 6,as a spin-off effort to prepare all-solid-state Na-metal battery,we propose a new preparation method to construct composite electrodes with appropriate interface modification.Herein,a solid electrolyte used is NASICON type sodium ion conductor Na3Zr2Si2PO12,which is made as a low-tortuosity skeleton by the phase inversion method.This solid electrolyte skeleton is beneficial to the filling of the electrode slurries.The model electrode slurry here is the precursor of the Na3V2(PO4)3 cathode with the same NASICON type structure.The resulted composite electrolyte/electrode interface can be effectively constructed after high temperature cofiring and used to fabricate ASSBs with Na metal as the anode.Such an ASSB has a reversible specific capacity of 95 mAh g-1 at 0.5C and a stable cycling performance over 50 cycles.The construction of this composite electrode provides a new idea for ceramic-based all-solid-state batteries.In Chapter 7,a positive electrode with a low-tortuosity structure is prepared first by phase inversion method,and then a polymer precursor solution(1 M LiTFSI dissolved in vinylene carbonate)is filled in the positive electrode skeleton and polymerized to form a composite electrode.Consequently,the positive electrode has a porous structure,which is beneficial to the penetration of the polymer precursor,and its unique straightthrough structure can also serve as a fast ion channel,alleviating the problem of usually slow ion transport in thick electrodes.Meanwhile,the polymer electrolyte formed by in-situ polymerization can construct a good interfacial contact with the electrode and reduce the interface impedance.As a result,the solid-state polymer battery(against Li metal)assembled with this composite electrode(15 mg cm-2)can achieve excellent rate performance(82 mAh g-1 at 10C)and stable cycling performance for 250 cycles at 1C(with a capacity retention of 89.0%).Chapter 8 is the exploratory study of a new type of high-performance ceramic anode.We first adopt the B-site doping strategy to change the perovskite Li0.33La0.55TiO3-δ(LLTO)to Li0.33La0.55Ti0.9Ni0.1O3-δ(LLTN).Subsequently we introduce an in-situ exsolution of Ni from the LLTN during the carbon coating process that results in the formation of many Ni nanoparticles on the LLTN matrix.The in-situ exsolution Ni nanoparticles are embedded on the surface of the perovskite matrix,and the conductive network formed with the carbon coating can significantly improve the kinetics of charge transfer.The abundant vacancies introduced by Ni exsolution can largely improve electronic conductivity and provide additional lithium storage sites without substantial volume changes.It turns out that,this anode has a high reversible capacity of 352 mAh g-1 and a low operating voltage(about 1 V).Even at a high current density of 2 A g-1,the capacity can be maintained at 180 mAh g-1 without fading over 10 000 cycles.Therefore,LLTN is a very promising lithium-ion battery anode material with a ultra-long life,low operating potential and fast-charging ability.Chapter 9 gives an overview of this thesis.It expounds the innovations and inadequacies of these works,and also proposes some future work plans. |
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