Preparation And Properties Of Sulfideand Poly(Ethylene Oxide)-Based Solid Electrolytes

With the development of electric vehicle and energy storage market,the demand for battery safety is also gradually increasing.Using solid electrolyte instead of traditional electrolyte for all solid state battery is an effective way to solve the problem of battery safety.With the increasing demand for lithium-ion batteries,lithium resource is getting in short supply,and the sodium resources is very rich and low in price.It is considered to be one of the most potential alternative to Li ion batteries.However,the ionic conductivity of the existing solid electrolyte is small,which seriously hinders the development of all solid state batteries.The optimal component design is one of the most effective ways to improve the ionic conductivity of each material.Addition of a proper amount of dopants can induce the lattice distortion,which will reduce the activation energy of the system.Therefore,we doped Sb in solid electrolyte,and prepared Na₃PSe₄ based Na₃P_1-xSb_xSe solid solution system.By means of electrochemical analysis,we found that its ionic conductivity has been greatly improved,this is because the doped antimony,which has the larger atomic radius,caused lattice distortion,and reduce the activation energy of the system,so that the lattice constant increases,and then the unit cell becomes larger,which means the sodium ion channel is be extended.Polymer electrolyte（SPE）film has the advantages of high mechanical strength,good film forming,solvent free leakage,less dendrite growth and good interface stability.In this paper,the film forming of polymer electrolyte system such as polyethylene oxide（PEO）was investigated by solution casting combined with hot pressing technology,and a serious of solid electrolyte film with smooth surface and uniform thickness were prepared.Some kinds of polymer systems doped with inorganic solid electrolyte Na₃Sb S₄（NSS）were modified.When the mass ratio of PEO:NSS was higher than PEO:NSS=8:2,the SPE film with PVA-Na TFSI（ESPVA）skeleton had better film-forming property and higher room temperature ionic conductivity.However,the PEO-NSS-ESPVA electrolyte membrane with sodium is not stable,which needs to be further improved.Blending PEO with other polymers can also improve the performance.In this paper,the PEG 400 which has a short chain with different amounts were blended with PEO.The characterization of the electrolyte membrane of the system proved that the doping of PEG will reduce the crystallinity of PEO,increase the density of the films,and improve the ionic conductivity.At room temperature,the button cell with PEO-5%wt PEG-Li TFSI electrolyte,Li Mn₂O₄positive electrode and lithium metal negative electrode charge with 0.2C current density.The first discharge capacity is 108m Ah/g,and the coulombic efficiency is 95.98%.The maximum discharge capacity is 119m Ah/g.The retention rate of the 100 th charging and discharging circulation capacity was 67%.