Synthesis,Interface Engineering And Performance Of Polymer Lithium Metal Batteries

Lithium(Li)metal is generally recognized as the most promising anode material owing to its ultrahigh theoretical specific capacity and the lowest electrochemical potential of-3.04 V versus the standard hydrogen electrode.Matching lithium metal anode with high voltage LiCoO2(LCO)cathode can significantly improve the energy density of the battery.However,the generation of lithium dendrites and low coulombic efficiency lead to low battery cycling life and safety problems.These issues can be addressed by replacing liquid electrolyte with safe solid polymer electrolytes(SPEs).However,the low ionic conductivity and Li+ transfer number of SPEs at ambient temperature are obstructing their wide application.Meanwhile,the severe structure destruction of LiCoO2(LCO)and its serious side reactions with SPE limit the upper operating voltage of LCO.In order to improve the energy density and cycling stability of solid lithium metal batteries,we optimized the properties and interfacial stability of solid polymer electrolyte and the commercial LCO positive cathode materials.The main research contents are as follows:(1)We prepared a new organic-inorganic composite electrolyte(PEO-LAGP-SN).The succinonitrile(SN),which has high dielectric constant,can reduce the crystallinity of poly(ethylene oxide)PEO and improve the electrode/electrolyte interface stability.During the preparation,Li+ enrichment areas could be in-situ formed near the surface of Li1.5Al0.5Ge1.5(PO4)3(LAGP)particles,which could provide fast Li+ pathways.The crystallinity of PEO decreases effectively with the introduction of LAGP and SN.Thus,the optimized composite electrolyte(SPE-14-15)exhibits excellent ionic conductivity.Notably,the Li | SPE | LFP all-solid-state lithium metal battery(LMB)can deliver a specific capacity performance.Moreover,for the first time,various electrochemical techniques combined with scanning electron microscope(SEM)analysis were performed to systematically investigate various chemical and kinetic properties of several composite SPEs on the deposition morphology of Li-ion under different SPEs.(2)A poly(vinylene carbonate-alt-tetraethylene glycol diacrylate)(PVC-EGDA)SPE was synthesized for the first time,which was served as an electrolyte for 4.50 V class LCO solid polymer lithium metal battery.The interface resistance can be reduced by the in-situ curved method.The interfacial stability was confirmed by Ac impedance(EIS)and X-ray photoelectron spectroscopy(XPS),those results elucidates that it played a multirole in enhancing the electro-oxidative resistance and suppressing the lithium dendrities.The Li | PVC-EGDA | LCO batteries can achieve high reversible capacity and capacity retention during all cycles.Moreover,for the first time,we illuminated the morphology of lithium particles is strongly influenced by the polymer dielectric constant and the surface energy of the polymer electrolyte in the initial stage.(3)We achieved stable cycling of a mulifuctional hierarchical core double-shell structure LiCoO2(MS-LCO)cathode material by a scalable sol-gel method,which consists of the fast lithium-ion conductive outermost layer,the intermediated La&Zr co-doping layer.The results of XPS,GITT,XRD and DFT results indicate that La can be doped into Li site,improving the rate performance,and Zr can be doped into Co site,improving the surface stability.The outermost layer hinders direct contact between electrolytes and LiCoO2 particles,which alleviates the decomposition of electrolyte and reduces the loss of active cobalt.At the same time,the La&Zr elements co-doping layer reveals enhanced structural stability at higher voltage.Due to this surface passivating feature,the electrochemical performance of core double-shell cathode has also been evaluated in a solid lithium battery with PVC-EGDA-based and PEO-based inorganic/organic composite electrolyte.This study indicates that the surface passivating layer is effective to suppress the decomposition of polymer electrolyte at high voltage caused by the highly oxygen in LiCoO2.In summary,the lithium dendrites can be suppressed by improving the properties of polymer electrolyte.At the same time,the interfacial stability of cathode materials and electrolyte can be tuned under high voltage by reasonable design of the structure of LCO cathode materials.The results of this paper can also provide some directions for the design of new polymer electrolyte and mutistage high voltage cathode materials to better stabilize the high-energy LMBs.