Study On The Preparation Of Doped Llzo Electrolyte And The Modification Of Its Interface With Li Metal

In the 21st century,mobile electronic devices and power vehicles have developed rapidly,and more requirements have been placed on the performance and safety of batteries.Electrolyte is an important part of battery.The liquid electrolyte is organic and has a conductivity of about 10^-2 S/cm,but the properties of the liquid electrolyte prevents it from inhibiting the growth of lithium dendrites and the shuttle effect in the electrolyte,leading to degradation of its performance.Solid electrolytes are mainly classified into organic-inorganic composite electrolytes,sulfide electrolytes,and oxide solid electrolytes.Among them,oxide solid electrolytes have become research hotspot due to their stability in air,stability to lithium metal,and good conductivity.The garnet type solid electrolyte is the most comprising electrolyte in the oxide electrolyte.The LLZO solid electrolyte not only has a conductivity of up to 10^-4 S/cm¹0^-3 S/cm,but also the chemical stability to Li.The shear modulus of 56 Gpa⁶0 GPa（over 8.5 GPa of lithium dendrite growth）makes it more prospective for the next generation of batteries–all solid state batteries.In this study,mainly concerned LLZO material,the ionic conductivity is improved by doping and other processes.At the same time,the interface buffer layer is introduced to reduce the interface resistance and improve the performance of the lithium battery.At present,the ionic conductivity of pure LLZO electrolyte is pretty low,and it is necessary to optimize the phase structure by doping to obtain LLZO electrolyte in cubic phase.In this study,by doping Ca²⁺,the Li⁺diffusion channal has been optimized and the sintering temperature has been lowed from 1200℃ to 1150℃.Also,the introduction of Nb⁵⁺into the Zr site increases the Li⁺ vacancies and the mobility of Li⁺.From further study,when the Nb was 0.2 wt% and the ball milling time was 36 h,the LLZO powder was pressed at 500 MPa,and then the obtained LLZO electrolyte was sintered at 1100℃ for 14 h under an argon atmosphere.The ionic conductivity was eventually increased from 1.52×10^-4 S/cm to 7.46×10^-4 S/cm.A buffer layer is introduced to the interface betwwen LLZO and Li metal to improve the contact between them and reduce the interface resistance.In this study,an interfacial buffer layer was introduced by ALD method and spin coating method respectively.From the research,the LLZO should be deposited for 400 cycles in the ALD machine,and then the obtained sample was annealed at 300℃ for 60 min.The resistance is reduced from about 3500Ωto 58Ω,which significantly improves the battery performance.At the same time,to overcome the harsh requirements of equipment for ALD method,the ZnO buffer layer was introduced by spin-coating method.When the concentration of the sol gel solution was 0.6 mol/L,once spin-coated and then annealed at 260℃,we finally obtain a thin film layer of ZnO with the thickness of about 600 nm and the interface resistance is reduced from about 3500Ω to 450Ω.Although it is less optimized than the ALD method,but the spin coating method requires shorter time and lower requirements to the machine.