Polymer Electrolyte Based Solid-state Lithium Battery

Polymer electrolyte has good flexibility and good interface contact with lithium metal（Li）anode,which is one of the typical electrolyte for all-solid-state Li batteries（ASSLMB）.Polyethylene oxide（PEO）is widely studied as a hosting polymer in ASSLMB due to its advantages of low price and easy processing.However,the high crystallinity of PEO electrolyte and low ion conductivity make it impossible for practical application at room temperature.Adding organic plasticizer of succinonitrile（SCN）can efficiently improve electrochemical performance of the modified polymer electrolyte,where ionic conductivity of PEO-SCN-Li TFSI reaches 1.74×10^-4 S/cm at 25℃,and electrochemical window is greater than 5.0 V.The symmetrical cell can cycle for 500 h at 0.1 m A/cm~2and 0.1 m Ah/cm~2,and Li Fe PO₄（LFP）full battery can delivers 130 m Ah/g in the discharge process.Apparently,PEO-SCN-Li TFSI polymer electrolyte membrane prepared by solution casting can meet the requirements for room temperature operation.Unfortunately,PEO electrolyte releases Li₂O,C₂H₄,and H₂ species while contacting with highly reactive Li metal anode,leading to poor interface contact and triggering Li dendrites growth and high interfical impedance.Herein,a Li tin alloy（Li-Sn）protective layer with mixed ionic and electronic conductivity is constructed at Li metal anode/polymer electrolyte interface via sputtering of metallic Sn film onto Li metal foil,achieving a uniform Li deposition and effective suppression of Li dendrites growth.In addition,Li deposition occurs beneath the alloy layer rather than on the top surface,and the thickness of the alloy layer does not change during the cycling,which realizes spatial isolation of reduction process of Li⁺from the nucleation/growth of Li metal.Therefore,the symmetric cell with the coated Li electrodes can stably cycle for 1300 h at 0.1 m A/cm~2and 0.1 m Ah/cm~2,and the capacity retention rate of LFP battery reaches 92.5%after 300cycles at 0.5 C.Moreover,the protection mechanism and the failure mechanism are studied in detail.The influence of ultra-thin Li-Cu alloy anode in ASSLMB with embedded three-dimensional inert skeleton structure prepared by high-temperature melting method is preliminarily investigated.The cooled Cu Li30 liquid alloy can form Li Cu_x solid solution phase and Li metal phase,and the solid solution nanowires/particles can self-assemble into uniform three dimensional network skeleton structure,which not only effectively reduces real current density on the electrode surface but also improve mechanical strength of the Li alloy anode,maintaining the integrity of the anode structure and the stability of the morphology during the cycling.The symmetric battery based on PEO-SCN-Li TFSI polymer electrolyte is stabilized for 900 h at 0.1 mA/cm~2 and 0.1 mAh/cm~2.