Interface Modification Of PVCA/PVDF-HFP Polymer Electrolytes And Application Performance Of Solid-state Lithium Metal Battery

The current boom in electric vehicles and other fields is putting new demands on power batteries in terms of energy density and safety performance.The use of organic-inorganic composite solid-state electrolytes to replace liquid electrolytes in solid-state lithium-metal batteries（SSLMB）is a promising next-generation power cell that offers high energy density while avoiding electrolyte leakage and spontaneous combustion.However,solid-state electrolytes face interface problems such as poor electrode-electrolyte interface contact and interface incompatibility,which hinder the performance of SSLMB.To address these interfacial problems,this paper is based on polyvinylidene carbonate（PVCA）and polyvinylidene fluoride-hexafluoropropylene（PVDF-HFP）polymer electrolytes for investigation.Firstly,tetraethylene glycol dimethyl ether（TEGDME）plasticizer was added to enhance the electrochemical performance of PVCA and PVDF-HFP polymer electrolytes.Then,the cathode and anode sides of Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）ceramic pellets were modified respectively to obtain LATP with asymmetric polymer protection layer（i.e.,Janus LATP）,which enhanced the electrode/electrolyte interface contact and LATP/lithium（Li）interfacial compatibility.Afterward,two modified layers of the Janus interface were used as substrates and silicon dioxide（Si O₂）nanoparticles were added to build a bilayer heterogeneous composite electrolyte,solving the interface problems of the cathode and anode sides respectively.The specific studies are as follows.（1）The PVCA+TEGDME polymer layer on the cathode side of the LATP ceramic pellet was formed by in-situ polymerization,while the anode side was coated with PVDF-HFP+TEGDME to obtain Janus LATP.The effect of the addition of the plasticizer TEGDME on the electrochemical performance of the two interfacial modification layers was investigated.According to the investigation,with the increase of TEGDME addition,the ionic conductivity of the modified layer gradually increased,while the electrochemical window showed a trend of first increasing and then decreasing.The optimum addition amounts for the cathode side PVCA layer and the anode side PVDF-HFP layer were 20%and 15%respectively.On the one hand,the PVDF-HFP+TEGDME layer on the anode side effectively improves the interfacial contact of LATP/Li,reducing the interface impedance of Li/Li symmetric cell from 19069（?）to 281（?）.On the other hand,it blocks the contact between LATP and Li,avoiding the occurrence of interface side reactions.Finally,the Li/Li symmetric cell can stably cycle for 3000 h with a polarization voltage of only 44 m V;the Li Fe PO₄/Janus LATP/Li battery exhibits an interfacial impedance of only 188（?）and achieves over 300 stable cycles at 0.5 C with a capacity retention rate of89.9%.（2）The double-layer heterogeneous composite electrolyte PVCA-TEGDME/PVDF-HFP-TEGDME-Si O₂（PPHTSi）was constructed by coating the PVCA precursor solution on the cathode sheet and then overlaying a layer of PVDF-HFP-TEGDME-Si O₂（PHTSi）composite electrolyte using an in-situ composite strategy with in-situ thermal polymerization.Experimental results indicate that when the addition amount of inorganic filler Si O₂ is 10%,the ionic conductivity of PPHTSi-10 bilayer heterostructure composite electrolyte is the highest,reaching 1.39×10^-3 S cm^-1.The battery performance tests demonstrate that the Li/Li symmetric cell can operate stably for 750 h at a current density of0.2 m A cm^-2;the Li Fe PO₄/PPHTSi-10/Li solid-state battery can cycle stably for more than 500 cycles at 0.5 C and the capacity retention rate is 91.7%after 300cycles at 1 C.