| In order to further improve the safety and energy density of lithium ion batteries,the use of solid electrolytes to replace organic liquid electrolytes is one of the current research hotspots.The garnet-type electrolyte Li7La3Zr2O12(LLZO)has attracted much attention because of its high room temperature Li+conductivity and wide electrochemical window.However,compared to the ionic conductivity of liquid electrolytes,the Li+conductivity of LLZO needs to be further improved.In the thesis,the preparation of Mg and Al co-doped Li7-3y+2xLa3Zr2-xAlyMgxO12(LLZAMO)ceramic electrolyte was investigated,and the performance of solid-state lithium-ion battery based on the sample prepared by optimized process was carried out.In addition,application of LLZAMO as a coating material in the surface modification of high nickel ternary cathode materials for lithium ion batteries was also conducted.The structure and properties of as-prepared samples were studied by using XRD,SEM-EDX,TEM,charge and discharge test,et al.,and the following results were obtained:1)The study on the preparation of Mg-Al co-doped garnet solid electrolyte shows that the addition of Al2O3 and MgO as sintering aids can reduce the calcination temperature of LLZAMO.The amount of Mg and A1 co-doping and the sintering temperature are the main factors affecting the phase structure,density and ionic conductivity of LLZAMO ceramics.The Li6.35Al0.25La3Zr1.95Mg0.05O12 ceramic sheet prepared at a calcination temperature of 1135℃ has a stable cubic phase structure,high density(90.1%)and good ionic conductivity(room temperature Li+conductivity is 3.19×10-4 S·cm-1),and the activation energy is only 0.247 eV.At the same time,the ceramic sheet has a lower electronic conductivity,which is three orders of magnitude lower than the ion conductivity,indicating that it is a fast ion conductor.2)Solid-state lithium-ion battery research based on Li6.35Al0.25La3Zr1.95Mg0.05O12 ceramic sheet reveals that the composition of LLZAMO electrolyte is stable to Li metal,and the electrochemical stability window is 1 V to 5 V,After activation at 50℃ for 1 h,the interfacial resistance of Li/LLZAMO/Li symmetric battery decreases,and Li+can be conducted stably.The assembled solid-state battery Li/LLZAMO/NCM333 can circulate stably in the voltage range of 2.5 V to 4.3 V.Properly increasing the temperature can effectively reduce the interface resistance,which is conducive to Li+transportation.When charging and discharging at a rate of 0.1 C at 50℃,the discharge capacity of Li/LLZAMO/NCM333 battery is 154.6 mAh·g-1,and the polarization is small(the average voltage difference between charge and discharge is 85 mV),and the specific discharge capacity at the first discharge of 0.1 C charge-discharge cycle can reach 134 mAh·g-1.and the coulomb efficiency is more than 98%,the capacity retention after 30 cycles is 84.7%,which shows good rate performance and cycle performance.The results mean that LLZAMO has the potential for application in all-solid-state lithium ion batteries.3)The surface modification of Li[N i0.6Co0.2Mn0.2]O2 with Li6.35Al0.25La3Zr1.95Mg0.05O12 as the coating material shows that a uniform LLZAMO coating can be formed on the surface of Li[Ni0.6Co0.2Mn0.2]O2 material by sol-gel method.The coating amount and the heat treatment temperature after coating are two important factors that affect the properties of the coated material.The optimal process conditions are coating amount 1.0%,and heat treatment temperature 600℃ after coating.Under this optimized process condition,the LLZAMO coated Li[Ni0.6Co0.2Mn0.2]O2 material has a discharge capacity of 181.4 mAh·g-1 at 0.2 C rate,and the capacity retention after 50 cycles can be reached 95.7%.This is attributed to the fact that the LLZAMO coating layer effectively suppresses the corrosion of the electrolyte and the oxidative decomposition of the electrolyte on the surface of the material,thereby effectively slowing the increase of the interface impedance,and thus increasing the capacity and improving the cycle performance. |
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