In-situ Preparation And Interfacial Design Of Polyethylene Oxide Based Solid-state Electrolytes

Although the green and sustainable lithium-ion batteries（LIBs）have been used in energy-storing applications to save non-renewable energy,the conventional LIBs don`t meet the fast-growing demand of devices with higher energy density and safety due to the inherent limitations of battery materials.Solid-state lithium metal battery is now recognized as a promising candidate for future energy-storage devices,while the interface issues of electrodes/solid-state electrolytes（SSEs）limite its application.It was reported that in-situ polymerization technology achieved the establishment of solid-solid ultra-conformal interface to improve interface contact.However,few considerations have been directed to the precursor stability to electrodes and the simultaneous chemical/electrochemical performances,which might directly cause high interface impedance,severe lithium dendrites,and eventually lead to the failure of the assembled cells.In this work,a high-performance PEO based SSEs was prepared by in-situ polymerization of ether precursors followed by in-situ formation of the electrode-electrolyte interface layer.A solid-state lithium metal battery was then developed,which was capable of running stably for a long cycle at room temperature and high voltage.The following work was carried out:（1）A high-performance PEO based SSEs was prepared via in-situ copolymerization of the precursor polyethylene glycol dimethacrylate（PEGDMA）and the forming-film additive vinylene carbonate（VC）.Furthermore,the copolymerization was verified by FTIR,NMR and SEM characterization,which improved overall electrochemical performances of novel SSEs including room-temperature ionic conductivity(0.4 m S cm^-1),lithium ion transference number（0.46）and electrochemical stability window（5.1 V）.Meanwhile,VC tended to participate in the formation of stable solid electrolyte interface layers to stabilize Li metal,which extended the life of assembled Li-Li symmetrical batteries by 100 times.The resultant Li Fe PO₄/Li metal batteries showed a super-long cycling performance（>300 cycles）at 1 C at room temperature.In addition,the assembled coin cells with high-loading cathodes(5.5-10.5mg cm^-2)delivered good performances and the assembled pouch cells could successfully power a red LED device,which proved practive application of the novel SSEs.（2）Based on the（1）work,the inorganic buffer layer was constructed in situ on electrode-electrolyte interface via the introduction of LLZTO into the precursor,which improved the stability between SSEs and cathode.Furthermore,The simple interception effect ensured that LLZTO was merely dispersed on surface of SSEs facing the cathode,which eliminate the negative influence of LLZTO on the film formation of lithium anode interface.And the asymmetric SSEs structure was verified by SEM and EDS analysis.The side reaction between SSEs and cathode was effectively alleviated under such protection of inorganic buffer layer and a thin and stable cathode-electrolyte interface layer was resulted as such,enabling the assembled Li-NCM811 battery to stably run for over 200 cycles at 0.5 C at room temperature,and the coulomb efficiency was close to 100%.In addition,the introduction of LLZTO increased the transport path of Li⁺and accelerated the transport of Li⁺at interface,which afforded SSEs a high ion conductivity(up to 0.1 m S cm^-1)at low temperature（-15℃）.The cycling performance of the assembled batteries was preliminarily verified at low temperature.The solid-state lithium metal battery is expected to be applied at low temperature and high voltage.