| Lithium-ion battery is one of the widely used energy storage devices,with the advantages of high energy density and output power.Most of the electrolytes in lithiumion battery use liquid electrolytes,which have the problems of volatility,leakage,and explosion during thermal runaway in battery failure.At present,solid electrolyte is one of the hottest research topics of lithium-ion battery electrolyte.The solid electrolyte has no liquid components and may inhibit the formation of lithium dendrites.It can also directly use lithium metal with high energy density as cathode.Solid electrolyte is promising in the fabrication of all solid-state lithium ion battery of the next generation.In this thesis,the copolymer poly(vinyl pyrrolidone-co-poly(oligo(ethylene oxide)methyl ether methacrylate))(PPO)was successfully synthesized.It is further used to mix with LiTFSI,rare earth oxide Li6.40La3Zr1.40Ta0.60O12(LLZTO)and poly(ethylene oxide)(PEO)to prepare composite solid electrolyte.The ionic conductivity,electrochemical stability,lithium ion transference number(tLi+),cycling stability are studied.The main results are as follows:(1)The random copolymer PPO was synthesized for the first time by free radical polymerization using N-Vinyl-2-pyrrolidone(NVP)and poly(oligo(ethylene oxide)methyl ether methacrylate(OE)as the monomers.The GPC measurement shows that the molecular weight of the PPO copolymer is 52.7 k with PDI=2.04.According to the results of 1H NMR measurement,the actual ratio of the two monomers is OE:NVP=9:1.15 by mole,which is confirmed by the elemental analysis results.FT-IR experiments confirms that PPO has the characteristic groups of NVP and OE,further proving that the polymerization reaction is successful.The solid polymer electrolyte PPO-x%is prepared by adding LiTFSI(5 wt%-20 wt%vs.PPO).With the increase of LiTFSI content,the glass transition temperature(Tg)of PPO-x%rises from-60℃ to39℃,and the room temperature ionic conductivity increases from 1.14×10-6 S/cm to 2.00×10-6 S/cm.At 60℃,the ionic conductivity can reach 2.43×10-5 S/cm(PPO-20%).The electrochemical stability window of PPO-20%can reach 4.3 V,and the lithium ion transference number is 0.33.PPO-20%also shows good cycling performance in lithium plating/stripping experiment.(2)The solid composite electrolyte PPO-20%-yLLZTO is prepared from PPO-20%with the addition of rare earth oxide nano-particle LLZTO(5 wt%～20 wt%vs.PPO).The results show that the Tg of PPO-20%-yLLZTO increases slightly with the increase of LLZTO content,and the room temperature ionic conductivity decreases from 2.24×10-6 S/cm to 1.74×10-6 S/cm.The down performance after addition of LLZTO may be due to the poor interface contact between LLZTO and PPO matrix.As the temperature rises,the ionic conductivity of PPO-20%-10LLZTO reaches 2.68×10-5 S/cm at 60℃.The electrochemical stability window of PPO-20%-10LLZTO increases to 5.0 V,and the lithium ion transference number is 0.20.Although the addition of LLZTO reduces the ionic conductivity of the electrolyte,it increases the electrochemical stability window.(3)In order to improve the film-forming property of the solid electrolyte,the blended polymer solid electrolyte PPOz-20%is prepared based on the PPO-20%with the addition of PEO(10 wt%-50 wt%vs.PPO/PEO).The Tg of PPOz-20%decreases with the increase of PEO,and the appearance of the melting peak indicates that there is a crystalline region in PPOz-20%.The electrochemical measurements show that the room temperature ionic conductivity of PPOz-20%decreases from 2.00×10-6 S/cm to 2.31×10-7 S/cm with the increase of PEO.The ionic conductivity of PP070-20%is measured to be 3.19×10-5 S/cm at 60℃.The electrochemical stability window and lithium ion transference number of PP070-20%is 4.6 V and 0.44,respectively.It also exhibits good cycling performance.The addition of PEO reduces the room temperature ionic conductivity of the electrolyte,but increases the ionic conductivity at high temperature(60℃),and improves the electrolyte film-forming property and electrochemical stability. |
PDF Full Text Request