Synthesis And Lithium Storage Performances Of Transition Metal Sulfides

All-solid-state lithium batteries have many advantages,such as wide electrochemical window,wide operate temperature range,easy to assemble,and much safer than conventional lithium ion batteries,which are suit for the demands of power batteries and energy storage devices.Currently used conventional cathode materials for all-solid-state lithium batteries,such as LiCoO₂,LiFeO₄ and NCA,are far from meeting the demand for the electric vehicle/hybrid electric vehicle applications due to its theoretical specific capacity limitation.By contrast,the transition metal sulfides materials possess higher theoretical specific capacity and favorable interfacial compatibility with sulfide electrolytes,thus particularly attracted the attention of the researchers.In this thesis,we mainly focus on the synthesis and modification of Co₉S₈ and Ni S electrodes in the solid-state lithium batteries.The main results are listed as follow:?i?Two-dimensional Co₉S₈ nanosheets with the thickness of ¹0nm and lateral size of several hundred nanometers are facilely synthesized through a PVA-assisted precipitation process in an aqueous solution.Compared to the Co₉S₈ nanoparticles with diameter of 40 nm prepared through the same process without PVA,the Co₉S₈ nanosheets exhibit enhanced rate capability and cycling stability due to their unique two-dimensional nanostuctures.When discharging-charging at 1 A·g-1,the Co₉S₈ nanosheets can deliver reversible capacity as high as 746.8 m Ah ·g-1 after 300 cycles,which is much higher than that of Co₉S₈ nanoparticles?63.6 m Ah·g-1?.?ii?Intimate contact at the cathode/solid electrolyte interface is crucial to realize high-performance all-solid-state lithium batteries.A general interfacial architecture,i.e.Li₇P₃S₁₁ electrolyte particles anchored on cobalt sulfide sheets,is developed by an in situ liquid-phase appraoch.The anchored Li₇P₃S₁₁ electrolyte particle size is around 20 nm,leading to an increased contact area and intimate contact interface.All-solid-state lithium batteries employing cobalt sulfide/Li₇P₃S₁₁ nanocomposites in combination with the Li₇P₃S₁₁ catholyte and Super P as the cathode and lithium metal as the anode exhibit excellent cycling stability,showing reversible discharge capacity of 582 m Ah g-1 at 0.38 m A cm-2 after 50 cycles.?iii?Ni S nanorods,with a diameter of 20⁵0 nm and length of 2³ ?m,are controllable prepared by a solvothermal method.One-dimensional nanostructured NiS and lithium metal are firstly employed in a Li/70%Li₂S-29%P₂S₅-1%P₂O₅/Li₁₀ GeP₂S₁₂/NiS all-solid-state lithim battery.Electrochemical performance measurements show that the reversible discharge specific capacities of Ni S nanorods electrodes can achieve as high as 670,401 and 299 m Ah g-1 at the current densities of 100,250 and 500 m A g-1,respectively.Also,it displays excellent cycling stability,showing a discharge specific capacity up to 338 and 243 m Ah g-1 after 100 cycles at current densities of 250 and 500 m A g-1,respectively.The electrochemical reaction mechanism of the Ni S nanorods in all-solid-state lithium batteries is revealed by combination of cyclic voltammetry and ex situ XRD measurements in detail,showing a reversible conversion reaction and basically identical with that in the traditional lithium ion batteries.