Interface Regulation And Performance Study Of Solid-state Lithium Batteries Based On LATP Composite Electrolyte

Solid-state lithium batteries employing solid-state electrolyte and lithium anode have been considered as one of the most promising novel energy-storage battery technology due to their higher safety and energy-density.However,low capacity and short cycle life are often encountered by solid-state lithium batteries,behind which lies in the sluggish ionic conduction caused by low ionic conductivity of solid electrolyte and high interfacial impedance.Organic-inorganic composite electrolyte which combines the joint advantages of polymer and inorganic electrolyte is regarded as the ideal solid electrolyte material,since it possesses high ionic conductivity,high electrochemical stability and favorable interfacial compatibility.Nonetheless,as multicomponent system,the complex internal interfaces in composite electrolyte would cause great effect on ionic transmission and interfacial properties of electrolyte,leading to the bottleneck of further improving high C-rate cycle life of solid-state lithium batteries.Therefore,developing high performance solid electrolyte,clarifying the relationship between ionic transport mechanism and interfacial electrochemical behavior of solid electrolyte and battery performance,would provide convincible knowledge reserve for the future energy-storage technology plan.This paper proposes several technological methods to improve Li⁺conductivity and interfacial properties of solid electrolyte and cycling stability of electrode based on microstructure adjustment and molecular bonding strategy,also pursues closely into the relative mechanism.To realize the practical application of Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）inorganic solid electrolyte in all-solid-state lithium batteries,we prepare LATP electrolyte with uniform distribution of grain size which avoids the grain over-growing through moderating the polyester molecular structure of gel precursor.The room temperature ionic conductivity of the obtained LATP electrolyte improves to 6.70×10^-4 S/cm.Furthermore,we employ LATP filler-modified PEO electrolyte to construct LATP/Li interfacial layer which can provide continuous ionic conduction pathways at interface and also isolate the direct contact between bulk LATP and environment with high lithium chemical potential.This ensures the 400 h cycling of symmetric lithium battery with stable overpotential and interfacial resistance at 60℃and 0.05 m A/cm².Furthermore,composite cathode prepared through the introduction of interfacial electrolyte ensures the favorable cycling stability of all-solid-state lithium battery at 80℃and 0.05 C.To endow the room temperature cycling feasibility of LATP-based solid-state lithium batteries,we construct LATP/PVDF organic-inorganic composite electrolyte based on Polyvinylidene fluoride（PVDF）which possesses great film-forming capability and mechanical property,and acquires room temperature ionic conductivity of 3.27×10^-4S/cm and Li⁺transference number of 0.42.Li Fe PO₄（LFP）||Li battery with LATP/PVDF composite electrolyte remains reversible capacity of 147.4 m Ah/g after cycling at 0.1 C and 100 cycle at room temperature.To solve the electrochemical/mechanical failure of Li Ni_0.5Co_0.2Mn_0.3O₂（NCM）cathode in solid-state batteries,we employ electrospinning technique to design cathode skeleton with well-connected NCM particles,and combine the in-situ polymerization of Polyvinyl carbonate（PVC）ionic conductive addictive to construct composite cathode with higher NCM crystalline stability through the formation of consecutive ionic/electronic conduction network.In comparison with commercial NCM,the discharge capacity of solid-state battery at 0.1 C improves from 135.7 m Ah/g to 150.5 m Ah/g through the introduction of composite cathode,and the capacity retention after cycling for 100 cycles also increases from 75.6%to 88.2%,which settles out the NCM attenuation bottleneck in LATP-based solid-state lithium batteries.On the basis of LATP/PVDF composite electrolyte,we adopt PMMA to build up the organic-inorganic interfacial molecular bridge in order to improve the organic percolation threshold.Room temperature ionic conductivity of the obtained LATP@PMMA/PVDF（LPP）with high LATP content improves to 1.01×10^-3 S/cm,as well as Li⁺transference number to 0.84 and electrochemical stability window broadens to 0～4.91 V.On account of the rapid ionic transport response in bulk electrolyte and interface as well as the more uniform Li⁺flux constructed by the interfacial percolation conduction network,symmetric lithium battery is capable of stably cycling for 300 h at 0.2 m A/cm² and delivers a limit current density of 0.5 m A/cm².In comparison with the organic-inorganic composite electrolyte prepared through the simple mixing of two phases,LPP electrolyte prepared through the interfacial molecular bonding strategy favors the stable cycling of battery at high C-rate,LFP||Li battery obtains a capacity retention of 95.6%after 400cycles at 0.5 C,and NCM||Li battery remains a reversible capacity of 128.8 m Ah/g after100 cycles at 0.5 C,corresponding to a capacity retention of 95.8%.With the purpose of constructing 3D conduction network of composite electrolyte with higher interfacial percolation efficiency,we construct PVDF fiber skeleton embedded with surface-electropositive LATP@Si particles through electrospinning technique based on the steric hindrance effect of electrospun fiber and hydrogen bonding strategy.After the composition of PVC-based gel polymer electrolyte into fiber membrane through in-situ polymerization process,LATP@Si/PVDF/PVC composite electrolyte with alternate directional arrangement of active fillers is obtained.A room temperature ionic conductivity of 1.06×10^-3 S/cm and Li⁺transference number of 0.84are achieved for the composite electrolyte with a low LATP@Si content of 9%.In comparison with the composite electrolyte prepared through solution-casting method,the in-situ polymerization of monomer solution provides effective interfacial ionic transport for solid-state lithium batteries,LFP||Li battery still delivers a reversible capacity of 144.1m Ah/g at 1 C,and the capacity retention reaches 94.1%after 200 cycles at an average coulombic efficiency of 99.7%.