Design,Preparation And Energy Storage Performance Of Micro/Nano Structured W-based Composite

As a green energy storage device,lithium ion batteries(LIBs)have been widely applied in every field,due to their outstanding advantages,such as higher working voltage,longer cycle life,no memory effect.Nevertheless,with the rise of radio frequency technology,sensors,smart clothes and smart packages at the age of Internet of Things,the commercial LIBs can’t meet higher requirements.Transition metal oxides(TMOs)have been widely considered as one of the most potential anode materials for LIBs,which have high specific capacity,the abundant source,the cheaper price.Especially,the synergic and interfacial effect of different metals in mixed TMOs can contribute to enhance capacity.However,intrinsic qualities of the oxides are limiting the practical application,for example,low electronic.conductivity,and volume changes during discharge/charge processes.So an ingenious design to prepare stable micro/nano structures can effectively remit above issues.Besides,exploring the growth mechanism of mixed TMOs which have specific structure can guide the synthesis of other related materials.In addition,as another state-of-the-art rechargeable batteries,lithium sulfur batteries(LSBs)gradually climb the stage of new energy storage device,due to high specific capacity(1675 mA h/g),the abundant source of silfur and non-pollution.As far as the research statement at the present,the prime problems which influence the LSBs to commercialize are including insulating nature of sulfur and the corresponding discharge products,the dissolution of long-chain polysulfides and so on.The carbon-host materials can efficiently confine polysulfides to remit shuttling,which were functionalized by heteroatom doping and hybridization with polar inorganic molecular.The necessity to advance LSBs is to reasonably prepare cathode materials which have high conductivity and high sulfur content.In the thesis,the controllable preparation of the tungsten-based micro/nano composites were accomplished by hydrothermal or reflux method,which have been researched as electrode materials.The main contents of the thesis are as follows:(1)The synthesis of ZnWO4 hierarchical hexangular microstars(HHMs)via a two-step hydrothermal method without the addition of any surfactants.TEM,SEM and XRD were used for analyzing the composition,morphology and the change of interphases at different reaction time.Based on the above results and discussion,a mechanism of in-situ formation and crystallographic fusion was put forward to explain the formation process of 3D hexagonal structures.When used for anode material of LIBs,ZnWO4 HHMs displayed better rate performance and cycling stability than some reported works.Depending on the stable and highly crystalline structure as well as synergic effects between different metal ions,ZnWO4 HHMs could well buffer the volume change and provide more active sites.After 90 cycles,the complete structures of HHMs were detectable by SEM,further illustrating the important roles of the stable structure for electrochemical performance.(2)In the work,the composite of W2C and N/P doped reduced graphene oxides(W2C@N/P-rGO)had been synthesized through a simple low-temperature reflux method.Reduced graphene oxides possesses high electronic conductivity after high-temperature reduction,which can enhance the efficiency of electron transport.Heteroatom doping and incorporation with W2C were applied to functionalize the rGO materials.W2C@N/P-rGO was evaluated as the host material of sulfur for LSBs,and showed outstanding electrochemical stability.For W2C@N/P-rGO cathode with about 68%sulfur content,the discharge capacity retained about 400 mA h/g after 500 cycles at 1 C(1 C = 1675 mA/g).High sulfur content and excellent battery performance mainly depend on the masterly assembly and complementary advantages of different materials.