Research On Composite Polymer Electrolyte For Solid-State Lithium Batteries

Solid-state lithium batteries using solid electrolytes are highly desirable because of their high energy density,long cycle life and high safety.Exploring solid electrolyte with high ionic conductivity,excellent flexibility and high interfacial stability is of prime importance for the development of safe solid-state lithium batteries.However,low room-temperature ionic conductivity,poor physical contact with electrode materials,and high electrolyte/electrode interfacial impedances are great concerns in practical application.In this paper,we have prepared a series of polymer-based electrolytes,including polyethylene oxide(PEO)composite polymer electrolyte enhanced by organic cage-type cucurbit[6]uril(CB[6]),PEO/garnet composite solid electrolyte reinforced with polyvinylidene fluoride(PVDF),polymer-in-salt polysiloxane-based electrolyte with cellulose acetate(CA)skeleton,and high transference number intercalated poly(ethylene carbonate)/lithium montmorillonite(PEC/LiMNT)composite solid electrolyte.The ionic conductivity,lithium ion transference number,mechanical flexibility,thermal,electrochemical and interfacial stability of composite polymer electrolyte were investigated.The synergistic effect of solid electrolyte and three-dimensional lithium anode is more favorable to inhibit the growth of lithium dendrites.The assembled solid-state lithium batteries with composite cathode show excellent electrochemical performances.These main results are as follows:(1)The self-standing flexible PEO/CB[6]composite polymer electrolyte(CPE)was prepared by solvent-free hot-pressing method.PEO-lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)with 35 wt%CB[6]composite electrolyte exhibits wide electrochemical window at 55?(4.7V vs.Li+/Li)and high thermal stability.The interfacial resistance of lithium anode and PEO/CB[6]with 35 wt%CB[6]is stable at about 60 after one week.This is because that the nanosized CB[6]particles with high volume fraction in polymer matrix is favorable to increase the interfacial contact area between electrolyte and lithium anode.The addition of CB[6]can significantly low the interfacial resistance of electrolyte and lithium anode.In addition,the electrolyte with CB[6]can suppress the lithium dendrite growth.At 0.5 C rate and operation temperature of 55?,the LiFePO4|Li battery assembled with PEO/CB[6]CPE demonstrates excellent cycling performance with high capacity retention of 96.8%at 100th cycle and 86.5%at 200th cycle,which indicates that such PEO/CB[6]CPE membranes are able to present stable electrode/electrolyte interface and inhibit lithium dendrite growth for achieving high-safety solid-state batteries.(2)A polymer/garnet composite solid electrolyte was fabricated with PEO,PVDF,lithium salt LiTFSI and Li6.75La32r1.75Ta0.25O12(LLZTO)powders by solution-casting method.The composite electrolyte exhibits high ionic conductivity of 2.0×10-4S cm-1at55?,wide electrochemical window 5 V,high ionic transference number 0.45 and improved interfacial stability with lithium anode.In addition,a composite cathode framework was also prepared using Al2O3@Ni0.5 Co0.2 Mn0.3O2(Al2O3@NCM)material as active material,and the PEO8-LiTFSI electrolyte slurry was perfused into the conventional cathode to obtain an integrated composite cathode framework,which improves interfacial contact between cathode and electrolyte.The assembled solid-state battery with Al2O3@NCM composite cathode framework and PEO-LLZTO-PVDF composite electrolyte exhibits enhanced cycling stability at 55? and 0.2C.(3)The polymer-in-salt polysiloxane polymer electrolyte was fabricated with bi-grafted polysiloxane copolymer,LiTFSI and PVDF,which shows higher ionic conductivity(7.8×10-4S cm-1at25?).To obtain the satisfactory ionic conductivity and high mechanical property of solid electrolyte simultaneously,cellulose acetate matrix was combined as a rigid substrate to prepare polymer-in-salt polysiloxane composite electrolyte that possesses high ionic conductivity(4.0×10-4 S cm-1),enhanced mechanical strength(6.8 MPa),wide electrochemical stability window(4.7V vs.Li+/Li),high ionic transference number(0.52),and excellent interfacial stability with lithium anode at ambient temperature.The assembled lithium sulfur battery with polymer-in-salt polysiloxane composite electrolyte exhibits good room-temperature cycling performance at 1 C,which indicates that such polymer-in-salt polysiloxane based composite electrolyte membrane can effectively inhibit the growth of lithium dendrites and diffusion of polysulfides.(4)A high transference number intercalated composite solid electrolyte was prepared by the combination of solution-casting and hot-pressing method using layered lithium montmorillonite,poly(ethylene carbonate),lithium bis(fluorosulfonyl)imide(LiFSI),high-voltage fluoroethylene carbonate additive,and poly(tetrafluoroethylene)binder.The electrolyte presents high ionic conductivity(3.5×10-4S cm-1),wide electrochemical window(4.6V vs.Li+/Li)and high ionic transference number(0.83)at 25?.In addition,3D lithium anode is also fabricated via a facile thermal infusion strategy.The synergistic effect of high transference number intercalated electrolyte and 3D lithium anode is more favorable to suppress lithium dendrites in a working battery.The solid-state batteries based on LiFePO4(A12O3@NCM),high transference number intercalated composite solid electrolyte,and 3D lithium anode deliver admirable cycling stability with high discharge capacity 145.9mAh g-1(150.7mAh g-1)and capacity retention91.9%after200cycles at 0.5C(92.0%after100cycles at0.2C)at25?.These results illustrates that the synergistic effect of high transference number intercalated electrolyte and 3D lithium anode obviously improves the cycling stability of solid-state lithium battery.