Preparation And Properties Of Alumina Nanorods /PPC/Graphite Coating Composite Solid-state Electrolyte Film

Nowadays,the utilization of solid electrolyte instead of liquid electrolyte has become the most effective way to combine high energy density and high security for lithium-ion batteries.Nevertheless,the low ionic conductivity at room temperature,high interfacial impedance,poor electrochemical stability and high cost of raw materials of solid-state electrolytes have been the main limitations for their applications.In this dissertation,due to the wide source of raw materials and good chemical stability of Al₂O₃ nanorods,Al₂O₃ nanorods were compounded with polypropylene carbonate(PPC)to form organic/inorganic composite solid electrolyte films with high ionic conductivity and high electrochemical stability at room temperature.In addition,graphite coating modification further improves the electrode/electrolyte interface bonding and enhances the electrochemical performance of solid-state lithium batteries.The main contents and results are as follows:(1)The preparation process of Al₂O₃ nanorods was optimized by hydrothermal method.The effects of process conditions such as hydrothermal reaction temperature,reaction time,filling volume and surface induction on the morphology and aspect ratio of Al₂O₃ nanorods were investigated.It was found that an Al₂O₃ precursor(AACH)of 5-10?m in length and 300-500 nm in diameter could be obtained by reacting PEG2000 as surfactant at a hydrothermal temperature of 120°C for 24 h and with a filling volume of 70%.Furthermore,Al₂O₃ nanorods with lithium surface(LAO)was prepared by secondary hydrothermal method.LAO precursor was prepared at secondary hydrothermal temperature of 180?and reaction time of 12 h.Al₂O₃ nanorods with a length of 4-7?m and a diameter of 200-300 nm and Al₂O₃ nanorods with lithium surface(LAO)with a length of 4-5?m and a diameter of 100-200 nm were obtained with AACH and LAO precursors sintered at 800?for 2 h.(2)Al₂O₃/PPC composite electrolyte membrane was prepared by scraping coating method.The effects of Al₂O₃ prepared at different sintering temperature,different content and graphite coating interface modified on the composite electrolyte film performance and battery electrochemical performance was investigated.The results show that ionic conductivity under room temperature of the composite electrolyte membrane reached 3.48×10^-4 S/cm,the electrochemical window was above 4.6 V,and the ion migration number reached 0.51.When 10%?-Al₂O₃(sintered at 800?)filled in Al-SE which modified by graphite,the NCM622/Al-SE/Li solid-state battery was composed(the cathode mass of active material is 2.0-3.5 mg/cm²).When a rate at 0.1 C and 0.5 C,the initial discharge capacity was 198.2 m Ah/g and 177.5 m Ah/g,and the residual capacity was 165.8 m Ah/g and 161.3 m Ah/g respectively after 100 cycles.(3)The effects of the filler content and the thickness of the framework on the performance of the electrolyte and the battery were investigated.It is found that the electrochemical stability window of the composite solid electrolyte is 4.8 V and the ionic conductivity at room temperature is 5×10^-4 S/cm.The max discharge capacity of NCM622/PE-SE/Li solid state battery was 163.5m Ah/g when a rate of 0.5 C(the cathode mass of active material is 4.5-5.0 mg/cm²).Besides,the retention capacity was 110.3 m Ah/g after 450 cycles and capacity retention reached up to 67%.(4)The enhancement mechanism of Al₂O₃ nanorods,surface lithiation,interface modification and electrolyte thickness on the electrochemical performance of solid electrolyte and cycling performance of solid battery was analyzed:the rod structure and fast ion conductor structure of inorganic filler provide a fast transport channel for Li⁺,and its Lewis acid promotes the dissociation of lithium salt.The results show that the graphite coating improves the interface bonding and reduces the interface impedance.The efficient ionic conductive Li-Al-O layer and Li C₆ layer are formed on the interface,which effectively inhibits the formation of lithium dendrite during long-term cycling.The synergistic effects of the above factors promote the cycle stability of solid-state battery.