The Research On The Synthesis And Electrochemical Performances Of The Materials For High-energy Lithium Batteries

This paper is focused on the synthesis and the electrochemical performances of the electrode materials and the electrolyte materials for high-energy lithium batteries. The cathode and anode materials here represent high specific capacity, excellent rate capability and good cylability. The solid electrolyte materials are stable with lithium metal electrode and have high lithium ion conductivity under room temperature as well as being able to suppress the growth of lithium dendrite. All of these novel materials can be applied to the next generation of lithium batteries, lithium air batteries and solid-state lithium batteries. The details are summarized as follows:1. A spinel-type LiMn₂O₄/carbon nanotube（CNT） composite cathode material is prepared by hydrothermal reaction followed by heat treatment in air. The composite LiMn₂O₄/CNT contains well-crystallized spinel LiMn₂O₄ and small amount of enwrapped segmented CNT which plays an important role to enhance the electrochemical performance for the cathode material. LiMn₂O₄/CNT shows high discharge specific capacity, excellent high-rate capability and good charge/discharge cyclability;2. Facile synthesis of highly crystalline spinel-type LiMn₂O₄/CNT composite is achieved by a novel two-step approach involving an acetone-assisted hydrothermal reaction. This composite cathode material exhibits high initial specific capacity which is very close to the theoretical value, excellent high-rate capability and great cyclability;3. A composite anode material is developed from a series of preparation processes including a modified Hummers method to achieve graphene oxide（GO）, an in situ reduction reaction and a freeze drying approach to get Mn₃O₄/reduced graphene oxide（RGO）. The introduction of graphene largely increases the electrical conductivity of Mn₃O₄ and the composite material shows high initial capacity and good cyclability;4. A high lithium ion conductivity block copolymer electrolyte with excellent mechanical properties is developed from a polyolefin hard segment and a polyethylene oxide conducting phase, as well as containing lithium bis（fluorosulfonyl）imide（Li FSI） and tetraethylene glycol dimethyl ether（G4）. This new composite polymer electrolyte has competitively high lithium ion conductivities ranging from 10-5⁴′10-4 S·cm-1 under room temperature; the tensile strength at the same temperature varies from 1¹2 MPa.5. A lithium stable, lithium-ion conducting solid electrode, Li1.4Al0.4Ge0.2Ti1.4（PO4）3（LAGTP）-Epoxy（E） with a thin polymer protective layer of polyethelene oxide（PEO）, Li FSI, G4 and Ba Ti O3 is developed by a series of synthetic procedures which mainly includes a tape-casting method and a drop-casting method. The composite solid electrolyte exhibits the steady resistance between two lithium electrodes in a symmetric cell for four months and no lithium dendrite formation is observed at the interface between electrolyte and lithium electrode given by a certain current density.