Preparation And Modification Of Al,Mn Co-doped Lithium Lanthanum Zirconium Oxide Solid Electrolyte And Its Composite Solid Electrolyte

All-solid-state batteries have received extensive attention due to their good safety and high energy density,in which the core group becomes the solid electrolyte.The garnet-type solid electrolyte lithium lanthanum zirconium oxide Li7La32r2O12(LLZO)has become one of the strong competitors of electrolytes in all solid-state batteries due to its high ionic conductivity and excellent air stability.However,compared with liquid electrolyte at room temperature,the LLZO ion conductivity is lower,and the solid-solid interface resistance between the electrode and the electrolyte is larger,which seriously limits the practical application of LLZO.In order to improve the ionic conductivity of LLZO at room temperature and reduce the interfacial resistance between electrolyte and electrode,Pechini sol-gel method was used to prepare Al and Mn co-doped lithium lanthanum zirconium oxide(LALZMO)to reduce the particle size of the sample,and increase the ionic conductivity at room temperature.LALZMO is combined with polymer PEO to obtain inorganic/polymer composite electrolyte,which improves the flexibility of LALZMO and increases the contact with the electrode.Composite LLZO@C in LiFePO4 reduces interface resistance and improves electrochemical performance of all solid state batteries.In this paper,Al,Mn co-doped Li6.28Al0.24La3Zr1.7Mn0.3O12(x=0.01-0.05)with cubic phase garnet structure was prepared by Pechini sol-gel method.Different Mn doping affects the structure,density and ionic conductivity of LALZMO.Wherein,when the doping amount of Mn is 0.03,Li6.28Al0.24La3Zr1.7Mn0.3O12 has a particle size of less than 1 ?m,the density of the electrolyte ceramic sheet obtained by calcination is 93%,and the ion conductivity at 30? is 2.16×10-4 S cm-1,the activation energy of the ion diffusion reaction was 0.29 eV.The inorganic/polymer composite solid electrolyte PEO-LiClO4-xLi6.24Al2.4La3Zr1.7Mn0.3O12 was prepared by adding Li6.28Al0.24La3Zr1.7Mn0.3O12 to the polymer PEO to reduce the crystallinity and improve the electrical conductivity.An inorganic polymer composite electrolyte membrane was prepared by solution casting method by adding different doping amounts of LALZMO to the polymer PEO.When the compounding amount is x=0.5,the ionic conductivity can reach 4.44×10-5 S cm-1 at 30?.At the same time,the composite polymer electrolyte exhibits an electrochemical window of 4.6 V and good electrochemical stability.In order to reduce the interfacial resistance between the positive electrode and the electrolyte,a LiFePO4-5%LLZO@C composite positive electrode with cubic phase garnet structure LLZO@C was prepared by Pechini sol-gel method.It is assembled with a PEO-LiClO4-LALZMO inorganic polymer composite electrolyte to have a lower interface impedance,and has a good charge-discharge specific capacity at different discharge rates.The 0.1 C discharge specific capacity is 69.3 mAh g-1.