Investigation On The Interfacial Modification Of Li/LAGP Solid-State Electrolyte In Solid-State Lithium Metal Batteries

With the rapid development of smart electronics,portable electronic devices and electrical vehicles,the demands for energy storage and conversion are increasing.Solid-state lithium metal batteries(SSLMBs)with solid-state electrolytes(SSEs),which can intrinsically avoid the safety hazards of electrolyte leakage and explosion,can match with not only the cathode with high-voltage and high-capacity but also the Li metal anode with low potential and high theoretical capacity.Therefore,the SSLMBs are considered as one of the most promising energy storage devices.However,the inherently poor solid-solid contact between SSE and Li metal anode and the induced nonuniform plating of Li+hinder the electrochemical performance of SSEs and thus the development of SSLMBs.Here,in order to investigate the improvement of the interfacical contact between SSE and Li,the surface modification of the Li1.5Al0.5Ge0.5(PO4)3(LAGP),one of the typical NASICON-type SSE,was investigated.Firstly,the construction of a flexible,stable buffer layer to improve the Li/SSE interface stability was proposed.Furthermore,the highly conductive polymer doping was introduced into the interlayer to improve the electrochemical performance of SSLMBs at large current densities.And the working mechanisms of the buffer layers have been investigated.The main research contents are as follows:(1)A flexible zinc oxide/reduced graphene oxide(ZnO/rGO,GZO)film has been in situ constructed at the interface between LAGP and Li metal anode.The flexible interlayer was beneficial to improve the contact performance at the interface.During cycling,the flexible interlayer can effectively mitigate the huge volume change of the Li anode and suppress the violent side reactions.As a result,the interfacial resistance of Li/GZO@LAGP/Li symmetric cells dramatically decreased to 32 Ω and the critical current density(CCD)can reach 3.0 mA cm-2.The symmetric cells also exibited such highly-stable lithium metal plati1g/stripping performance that can be stably cycled for 800 h with a lower overpotential of merely 60 mV at 0.15 mA cm-2.The full cells with the structure of LFP/GZO@LAGP/Li showed high discharge capacity of 131.6 mAh g-1 in the first cycle at 0.5 C,and can be stably cycled more than 100 times.(2)Based on the aformentioned work,a highly conductive polyaniline has been doped to the reduced graphene oxide layer in the GZO interlayer.The polyaniline/zinc oxide/reduced graphene oxide(PANI/ZnO/rGO,P-GZO)film was thus formed to further improve the diffusion efficiency of Li+and improve the stability of the SSLMBs at high current desities.The polyaniline inserted into the layer gaps of rGO,can expand the interlayer spacing and thereby improve the interlayer flexibility,meanwhile facilitating the intercalation of Li+.During cycling,a fast ion conductor of LixN was formed by the reaction of PANI and Li metal,which provided efficient ion-conducting pathways for Li+,and made contribution to the electrochemical performance stability of SSLMBs at high current densities.The interfacial resistance of the Li/P-GZO@LAGP/Li symmetric cells decreased to 20 Ω,and the CCD reached 6.3 mA cm-2.Meanwhile,the Li/P-GZO@LAGP/Li symmetric cells can be stably cycled for 2000 h at 2.0 mA cm’2.The assembled full cells with three different cathodes of LFP,NCM622 and NCM811 exhibited stable rate capability and high reversible capacity.What’s more attractive was that the NCM811/P-GZO@LAGP/Li full cells with a high-voltage cathode can stably cycle for 80 times.In summary,combining the in situ synthesis method and doping strategy,a flexible,stable and highly-Li+-conductive composite buffer layer was constructed to solve the interface problem between the LAGP and Li anode.The SSLMBs with the buffer layer exhibited improved electrochemical performances,especially the long cycle stability.This work is of great significance for the successful application of Li-ion batteries in future.