| Lithium secondary batteries,as important energy storage devices,are widely used in various fields of industry and life.However,higher requirements have been put on the energy density and security of lithium-ion batteries with the development of social demand and industry.The Li1+xAlxTi2-x?PO4?3?LATP?is an inorganic oxide material with high lithium ion conductivity,which has excellent thermal and electrochemical stability,so it has good application prospects in the field of high energy density and high safety lithium batteries.In this thesis,the LATP is chosen as the research materials to apply it in cathode of high energy density and solid-state electrolyte of high security,which can improve the energy density and security of lithium batteries.The details are as follows:1.The Li Co O2,coated by LATP with Ti-Al doping?C-Li Co O2?,is prepared by sol-gel method.Cyclic voltammetry tests show the LATP coating with high lithium ion conductivity significantly enhance the interface ion transport between Li Co O2 and electrolyte,and the lithium ion diffusion coefficient of C-Li Co O2 increases from 4.02×10-12 cm2 s-1 to 6.96×10-12cm2 s-1.The characteristic results of galvanostatic intermittent titration technique and in-situ X-ray diffraction explain the optimization mechanism of C-Li Co O2 in terms of kinetics and reversibility of phase structure.LATP and Ti-Al co-doping can suppress the side reaction between Li Co O2 and electrolyte.It can also ensure the Li+transport rate and structure stability of Li Co O2 during charging and discharging process at high voltage.Based on the above design,C-Li Co O2 exhibits outstanding rate performance and good cycle stability at ambient or elevated temperature with a high cut-off voltage of 4.5 V.The C-Li Co O2 has the capacity retention of87.5%after 50 cycles with 0.2 C at 30oC,and its charge and discharge rate capability can still reach 150 m A h g-1 at 5 C.It has the capacity retention of 88.8%after 40 cycles with 0.2 C at50oC.2.The LATP pellet with ion conductivity of 1.07×10-4 S cm-1 was prepared by solid state reaction and cold-press with sintering.Then the polyethylene oxide?PEO?is used to modify the LATP solid electrolyte pellet for assembling all solid-state batteries.The flexibility and contact stability with lithium metal anode of PEO improve the interface impedance and compatibility between electrolyte and anode.The all-solid-state batteries based on Li Fe PO4 has a low impedance of 537?at 65oC,and its initial capacity is 143.1 m A h g-1 and remains 116.3m A h g-1 after 100 cycles.In the study of the all-solid-state batteries based Li Co O2 cathode with high energy density,it was found that the LATP coating introduced on the surface of Li Co O2 suppress the side reaction between Li Co O2 cathode and PEO partly,and which can improve the electrochemical performance of the all-solid-state batteries.Further,we study the influence of polymers and lithium salts of interface modified layer on high-voltage solid-state batteries.In the lithium salt aspect,it is found that replacing Li Cl O4 instead of the conventional Li TFSI can improve the stability between Li Co O2 cathode and the electrolyte. |
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