| Lithium ion battery is one of the most widely used electrochemical energy storage systems.It has the advantages of high energy density and long cycle life.However,conventional lithium ion batteries use organic electrolyte,which brings flammable and explosive safety problems.Using polymer solid electrolyte instead of organic electrolyte can effectively avoid this problem.However,the ionic conductivity of polymer electrolyte is poor and the ion transport number is low.To improve the electrochemical performance of polymer solid electrolyte in this paper,the modified PEO based composite polymer electrolyte was prepared by introducing inert Zr O2 and inert Y-doped Zr O2(YSZ)into the PEO polymer electrolyte system to study its electrochemical properties,and the modification effect was evaluated by assembly of all solid state batteries.Firstly,PEO/Li TFSI polymer electrolyte was prepared by solution casting method,and the effects of electrolyte composition and temperature on physical properties and ionic conductivity of polymer electrolyte were studied.When EO:Li=16:1,the electrolyte has a good film-forming ability and ionic conductivity at room temperature,which is 5.65×10-5 S/cm.As the temperature rises to 60?,the ionic conductivity of the electrolyte increases to 2.34×10-4 S/cm.For improving the electrochemical performance of electrolyte,inorganic filler Zr O2 was added to PEO polymer electrolyte to prepare composite electrolyte PEO/Zr O2(ZCPE),and the influence of filler concentration on the performance of ZCPE was explored.The results show that Zr O2 can improve the film forming ability and mechanical strength of ZCPE.When the Zr O2 mass ratio was 10%,the conductivity of ZCPE was 9.8×10-5 S/cm at room temperature and increased to 3.51×10-4 S/cm at 60?.In order to further improve the ionic conductivity of PEO based electrolyte,Y-doped Zr O2(YSZ)was used as inorganic filler to prepare composite electrolyte PEO/YSZ(YCPE).YSZ was uniformly dispersed in YCPE without obvious agglomeration and Li TFSI was fully dissociated in the polymer matrix.When YSZ mass ratio was 5%,the electrochemical window of YCPE was improved from 4.8 V to5.2 V.Due to the effect of interaction between oxygen vacancy in YSZ as Lewis acid base and Li TFSI,the ion tramsport number of YCPE increased from 0.24 to 0.34.The electrochemical stability between YCPE and lithium was tested by assembled Li symmetric battery.YCPE could work stably for 100 h at a current density of 0.5m A/cm2 without short circuit.To further evaluate the electrochemical performance of polymer electrolytes,Li Fe PO4 positive electrode and Li negative electrode were used toassemble all-solid batteries.At 60? and the current of 0.5 C,the initial discharge specific capacity of the battery which uses PEO/Li TFSI as electrolyte is 112.6 m Ah/g.After 50 cycles the capacity is reduced to 107.8 m Ah/g and the capacity retention rate is95.7%.Under the same conditions,when YCPE is used as electrolyte,the initial discharge specific capacity of the battery increases to 164.5 m Ah/g,and after 50 cycles,the capacity decreases to 156.3 m Ah/g,with a capacity retention rate of 95.2%.At the current of 1 C,when PEO/Li TFSI is used as electrolyte,the initial discharge specific capacity of the battery is 109.8 m Ah/g.After 50 cycles,it is reduced to 95.1 m Ah/g,with a capacity retention rate of 86.6%.Under the same conditions and YCPE as electrolyte,the initial discharge specific capacity of the battery is 150.5 m Ah/g.After 50 cycles,the specific capacity is reduced to 143.1 m Ah/g and the capacity retention rate is94.7%. |
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