Preparations And Eletrochemical Properties Of Graphene-Based Transiton Metal Compounds By Layered Double Hydroxide Precursor For Highly Improved Lithium Storage

In order to meet the growing demand for portable electronic devices, electric vehicles and hybrid electric vehicles (HEVs), the main challenge is to find high capacity and rate capability and long cycle life of the anode materials for lithium-ion batteries (LIBs). Transition metal oxides and sulfides (TMO/TMS) with high theory specific capacity have drawed extensive attention for lithium ion battery anode materials. However, TMO/TMS suffer from the common hurdles of intrinsically low conductivity and huge volume changes upon Li-ion insertion and extraction process, which lead to poor cycling stability and rate performance. To tackle with these problems, one efficient way is to couple metal oxide/sulfides with carbon species to fabricate the hybrids. Graphene is widely used in research of couple with the transition metal compounds upon its high electron mobility, excellent conductivity, large surface area, structural flexibility, and chemical stability. Therefore, to build graphene-based transition metal compounds hybrids has become mainstream materials for electrochemical energy storage and conversion in recent years. In this paper, we successfully prepared graphene/3D graphene aerogel supported transition metal compound (Mn0.25Co0.75O/NiCo2S4/Ni0.96S) composites derived from LDH precursors respectively. The obtained products are capable to show significantly increased capacity, excellent rate capability and good cycling stability.(1) Graphene supported solid solution oxide (Mno.25Coo.750/G) for anode materials:we herein describe a graphene-supported binary active solid solution (Mno.25Co0.75O) calcinated from CoMn-layered double hydroxide/graphene oxide precursor (CoMn-LDH/GO) via separate nucleation and aging step. Ex-situ X-ray diffraction characterization clarifies the topotactic transformation from the CoMn-LDH/GO precursor to the resulting Mn0.25Coo.75O solid solution with increasing temperatures. With the annealing temperature heating to 550℃, crystal phase CoO appears. When calcined at 550-600℃, Mn doping into the CoO phase result in the formation of the Mn-doped CoO solid solution (Mn0.25Co0.75O) during the carbothermal process in Ar atmosphere. Characterizations of high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectra (XPS) revealed that Mn is doped successfully in the crystal lattice of CoO in the form of Mn2+ to form the solid solution by the calcination process. The reversible capacity reaches 980 mA h g-1 after 100 cycles at 100 mA g-1, and especially up to 1087 mA h g-1 after 1300 cycles at a high current density of 2 A g-1.(2) Graphene aerogel supported metal sulfides composite (NiCo2S4/Ni0.96S/3DGA) for anode materials:we reported that bi-active transition metal sulfides NiCo2S4/Ni0.96S supported by three-dimensional graphene aerogel (3DGA) derived from NiCo-LDH/3DGA via a two-step hydrothermal strategy. NiCo2S4/Ni0.96S/3DGA composite electrode exhibits high specific capacity 965mA h g-1 after 200 cycles at 100mA g-1, and at the current density of 1A g-1 displayed good superlong cycling stability 620 mA h g-1 after 800th cycles. Three-dimensional graphene aerogel is light-weight, high specific surface area, porous, which can expose more active sites and offer numerous channels for rapid diffusion of electrolyte ions easier access to surface of the electrode materials, inducing the highly improved electrochemical performances of NiCo2S4/Ni0.96S/3DGA electrode for lithium-ion batteries (LIBs).