Theoretical Calculations And Experimental Studies Of Solid-state Batteries With Lithium Metal Oxide Electrodes And Composite Electrolytes

With the vigorous development of the new energy industry,people are also putting forward higher performance requirements for lithium-ion batteries,such as high energy density,large battery capacity and high safety.The design and preparation of solid-state batteries is a solution that can effectively improve the safety performance of batteries for liquid lithium-ion batteries,which are flammable and explosive when short-circuited and impacted.However,with the introduction of solid state electrolytes,the change in material volume during charging and discharging in solid state batteries has also given rise to a number of challenges.Examples include contact problems at the solid-solid interface,low ionic conductivity at the electrode-electrolyte interface(much less than at the solid-liquid interface in liquid cells)and low electrochemical stability.(1)Theoretical simulations and calculations of solid-state batteries.First Principle approach was used to construct the geometry of the anode Li4Ti5O12(LTO)as well as LiFePO4(LFP).On this basis,the nudged elastic band method is used to simulate the migration behaviour of lithium ions within the cathode bulk phase at the atomic scale.The surface geometry of the corresponding electrodes with low crystalline surface indices was also analysed to predict the best surface model structure with the electrolyte lithium titanium aluminium phosphate(Li1+xAlxTi2-x(PO4)3,LATP).From a structural point of view,the mechanism of lithium ion migration within the electrode bulk phase and the interface of electrode-electrolyte has been elucidated.Analysis of the migration energy barrier shows that the migration energy barrier of lithium ions at the interface is higher than their migration within the bulk phase.Calculations are show that the migration energy barrier for lithium ions in the LTO bulk phase is 0.37-3.488 eV,which is less than its migration energy barrier at the LTO-LATP interface of 5.625-5.928 eV.Lithium ions are show the same mechanism in the LFP bulk phase,with a migration energy barrier of 0.718-8.56 eV in the LFP bulk phase,much smaller than their migration energy barrier of 20.652-35.863 eV at the LFP-LATP interface.The problem of lithium ion transport at the interface has been shown from theoretical calculations to be one of the most critical issues in improving the high performance characteristics of solid state batteries.(2)Preparation of solid-state batteries.The preparation of solid electrolytes was first explored by combining inorganic solid electrolytes with polymeric solid electrolytes to create composite solid electrolytes with good ionic conductivity and viscoelastic interfaces.And for the means of anode preparation process,plasma spraying technology is applied to the preparation of electrodes.The plasma spraying method allows for fast and efficient preparation of the anodes,avoiding the harmful pollution caused by the evaporation of solvents in conventional preparation and achieving an environmentally friendly preparation process.LTO anodes are prepared using the conventional slurry-coating-drying method(wet method)and the plasma spraying method(dry method),respectively.They are each assembled with a composite solid-state electrolyte with a view to producing a solid-state battery with unique and superior performance,as opposed to conventional methods.The experimental data were shown that the first discharge specific capacity of the dry prepared solid state battery LTO-G was 73 mAh·g-1,which was less than that of the wet prepared solid state battery LTO-S(95 mAh·g-1).However,the solid-state battery LTO-G has a higher capacity retention rate after 100 cycles of cycling(49.3%)than the solid-state battery LTO-S(19%)at a 0.1C.Compared to the solid-state battery LTO-S,the solid-state battery LTO-G exhibits a lower interfacial impedance and good long-cycle stability.The LiFePO4 solid-state battery(LFP),prepared by the wet process,has a high specific capacity first discharge specific capacity of 114 mAh·g-1,reaching 67.1%of the theoretical specific capacity.However,the cycling and multiplier performance is poor,with a capacity retention of 23.9%after 100 cycles of testing,and failure at 1C and 2C.(3)Modification of solid-state cell interfaces.In situ self-assembly reactions using composite ionic liquids on wet prepared electrodes as well as composite solid state electrolytes to generate self-passivated interfacial layers.To stabilise interfacial chemistry and electrochemical reactions,reduce lithium ion transport energy barriers and obtain excellent electrochemical performance.The experimental results show that the first discharge specific capacity of the interfacially modified lithium titanate solid-state battery LTO-SGX reaches 153 mAh·g-1,which is higher than that of the unmodified lithium titanate solid-state battery LTO-S(95 mAh·g-1).The solid state battery LTO-SGX also has a capacity retention rate of 55.4%after 100 cycles,and its interfacial impedance has been reduced from 3600 Ω before modification to around 110 Ω.The first discharge specific capacity of the modified lithium iron phosphate solid state battery LFP-SGX is 158 mAh·g-1,a small increase compared to the unmodified solid state battery LFP-S(114 mAh·g-1).The solid-state battery LFP-SGX has a capacity retention rate of 87.3%after 100 cycles,which is 5 times higher than that of the unmodified battery.