Designation And Electrochemical Investigation Of High-Performance Freestanding Carbon-Based Anode Materials

Lithium-ion batteries?LIBs?have been widely used as daily devices such as smart watch,mobile phone,computer and digital camera due to their large specific capacity,high voltage,long cycle performance and high energy density.With the development of electric vehicles and large capacity energy storage,higher requirements of the energy density of batteries have been put forward.Since the commercialization of LIBs,graphite as commercial anode material only delivers its theoretical specific capacity of 372 mAh g^-1,limiting its further application.Therefore,the anode materials,which deliver high specific capacity,should be developed.At the same time,with the emergence of flexible electronic products?such as werable device,artificial electronic skin and flexible touch screen?,the corresponding energy storage devices should be designed as light,thin and flexible.Therefore,the development of the flexible electrodes with considerable performance is necessary.At present,most works focus on designing flexible electrode instead of using copper and aluminum foil as current collector.The flexible electrodes are often prepared by graphene,CNT,conductive polymers and so on.Based on the relevant literatures,we used two simple methods to prepared a series of high performance flexible electrodes.The structure and electrochemical properties of these materials are studied systematically.The main contents include:?1?Preparation and electrochemical investigation of the phosphorus-SCNT composite as free-standing anode:Phosphorus?P?is considered to be one of the most attractive anodic materials for LIBs owing to its high theoretical specific capacity(2596mAh g^-1).Nevertheless,it suffers intrinsic poor conductivity(10^-14 S m^-1)and large volume expansion?⁴40%?,limiting its further application.It is known that carbon-based materials can be used to modify P anodic materials to improve the electrical conductional and accommodate volume changes of P anode.In this work,to meet the requirements of stable three-dimensional?3D?framework and good electrical conductivity,MWCNT were selected as carbon source.And an oxidation assisted hydrothermal self-assembly process was adopt to prepare inner graphene-CNT hybrid aerogel?SCNT?as the conductive network.And then,red P confined into a 3D SCNT conductive aerogel is prepared.By slicing and rolling,the 3D P-SCNT composite was used as free-standing anode directly.The P-SCNT anode delivers a stable capacity of1600 mAh g^-1 at a current density of 0.1 A g^-1 and a reversible high-rate capacity as high as 807 mAh g^-1 at 2.0 A g^-1 even after 2000 cycles,which owes to the robust bracing SCNT frameworks and stable chemical bonds between red P and SCNT.?2?The designation and electrochemical properties of P-C film as flexible LIBs anode:in order to improve the flexible of the carbon based material,we design a new strategy to embed red P particles into a cross-link-structural carbon film.The P-C film is synthesized via vapor phase polymerization?VPP?following with pyrolysis process,working as flexible binder-free anode for LIBs.The P-C films with various P contents have been investigated systematically.The optimized sample,with 21%P content in the film displays a capacity of 903 mAh g^-1 after 640 cycles at a current density of 100 mA g^-1,and 460 mAh g^-1 after 1000 cycles at 2.0 A g^-1.?3?The electrochemical properties of N/S dual-doped carbon film as flexible LIBs and SIBs anode:heteroatom doping is considered to be one of the most effective approaches to improve the electrochemical activity of carbon-based electrode materials.On the basis of the preparation of the PPy film,we present N and S dual-doped flexible carbon film as a promising free-standing anode for stable high-power and high-energy LIBs or SIBs.The NS-C film delivers high reversible capacities of 965.7 mAh g^-1 in LIBs and 520.1 mAh g^-1 in SIBs at a current density of 100 mA g^-1.Particularly,the film electrodes exhibit excellent high-rate capability and remarkable long-term cyclability.It is believed that the interconnected conducting structure of carbon backbones,heteroatomic defects and increased carbon interlayers distance by stable S-C and N-C bonds are beneficial to ultrafast ion diffusion and electron transport,making the NS-C film become a high-performance free-standing anode for LIBs or SIBs application.In summary,we have successfully designed some simple and practical methods for preparation of the P-SCNT,P-C and NS-C films,which can be used as flexible anodes with excellent electrochemical properties for LIBs or SIBs application.