Preparation And Electrochemical Performance Of High Capacity Anode Materials For Lithium/Sodium Ion Batteries

With the ever-growing demands for energy and the intense appeal for reducing carbon emissions,fossil energy exhaustion and environmental pollution have been the growing concern to human beings.It is of urgent need to search for and develop new alternative solutions for easing the imminent energy crisis and environmental pollution.Among numerous available candidates,lithium ion batteries?LIBs?as a predominant power source have been successfully employed in portable electronic devices?PEDs?and electric vehicles?EVs?due to their high working voltage,high energy density,small self-discharge and good cycle performance.However,the large-scale application of LIBs for storing sustainable energy is overwhelmed by the high cost and the scarcity of lithium resources.In this case,sodium-ion batteries?SIBs?are attracting more and more attention as one of the potential and promising alternatives to LIBs due to the similar work mechanism and the overwhelming advantages with regard to the low cost and abundance of sodium resources.Nevertheless,how to achieve high-rate capability and long cycle life in SIBs still remains a great challenge due to the sluggish reaction kinetics and large volume expansion rooted in larger Na ionic radius.As such,it is challenging but crucial to develop suitable electrode materials to realize the application of SIBs.In order to overcome the above-mentioned issues,a serious of nanostructured electrode materials were fabricated and applied in the LIB/SIBs anode to further improve the rate capability and cycling performance,the specific work mainly includes the following aspects:1.A N,P doped porous carbon?NP-C?was fabricated using GO as backbone,which constructed with 2D ultrathin heteroatom-doped carbon layers via an in situ polymerization reaction,followed by calcinations.This method is facile,low cost and environmentally friendly,which is extremely promising for industrial applications.Benefiting from the merits of 3D structure and heteroatom doping,the optimized NP-C demonstrated improved reaction kinetics for charge transfer and transport,evidenced by the superior rate capability of 595 mAh g^-1 at a high current density of 10 A g^-1.Meanwhile,it provided more active Li⁺storage sites with a high reversible capability of980 mAh g^-1 as well as a relative high initial Coulombic efficiency?74%?at a current of 0.5 A g^-1 when used as anode in LIBs.The Li⁺diffusivity of the NP-C electrode was estimated by galvanostatic intermittent titration technique?GITT?,which is larger than that of the graphite electrode.In addition,the charge storage mechanism of the NP-C electrode was investigated using cyclic voltammetry with varying scan rates.2.A simple and green one-pot route was presented to synthesis a hierarchical nanostructure composed of carbon coated SnO₂ nanocrystals on the surface of the CNT using glucose as a mediated agent.During the hydrothermal process,glucose serves as a carbon source and also assists the precipitating Sn⁴⁺on the sidewall of CNT which leads to in-situ formation of SnO₂.The highly conductive CNT construct a three-dimensional?3D?backbone to facilitate the charge transfer,and the 3D CNT with the outermost carbon layer could provide protection to cushion the strain of the SnO₂ interlayer,which prevents the electrical isolation of SnO₂ during cycling.Due to the high electronic conductivity of CNT and the outer carbon layer,the large surface area and shortened ion diffusion length,CNT@SnO₂@C displayed high lithium storage properties and excellent high rate capability in LIBs.3.We demonstrate an easy and scalable approach to fabricate urchin-like MoP nanocrystal embedded into a N-doped carbon framework?MoP@C?through a self-polymerization of diamine hydrochloride followed by an in-situ phosphidation process.In the synthesis process,dopamine molecules are used to control the morphology and serving as carbon source,leading to the successful formation of hierarchical MoP@C.As expected,when used as anode materials for the LIBs,the MoP@C demonstrate the high reversible capacities,long-time cycling and superior rate performance.4.Iron phosphide?FeP?has gained growing attention in recent years because of their high theoretical capacities and relatively low intercalation potentials vs Na/Na⁺.However,the inevitable volume changes during charge and discharge and the low electronic conductivity are still hindering its future development.To cope with these problems,a well-structured carbon-coated FeP nanoparticles anchored on carbon nanotube network?CNT@FeP-C?was synthesized,which could keep the FeP nanoparticles within flexible carbon hosts and maintain monodispersity within the hosts concurrently.The CNT network has the benefit of not only confining the active nanoparticle within flexible conductive hosts but also enhancing the conductivity to facilitate both electron and ion transport.Accordingly,the as-synthesized CNT@FeP-C electrode demonstrates excellent electrochemical performance in terms of long-term cycling?without obvious capacity decay after 1200 cycles?and superior rate capability(272 mAh g^-1 at a current density of 8 A g^-1).5.The sluggish kinetics reaction is considered to be the crucial challenge in achieving the high-power sodium ion batteries.In this study,a reasonable structure design with engineering the intensified pseudocapacitance behavior is highly desired to tackle above problem,which is achieved by constructing a coaxial core-shell nanostructure composed of carbon nanotube as the core and TiO₂@MoO₂nanoparticles embedded in to the carbon matrix.The designed 1D tubular nanostructure can effectively reduce ion diffusion path,increase electric conductivity of the electrode,address the volume stress upon cycling and provide more active sites for electrochemical reactions.Benefiting from the ideal utilization of synergistic effects between TiO₂ and MoO₂,the as-prepared composites show an enhanced reaction kinetics for charge transfer and transport,which evidenced by an excellent rate capability of 150 mAh g^-1 at 20 A g^-1.Moreover,an outstanding cycling stability at 10 A g^-1 for over8000 cycles with a reversibly capacity of 175 mAh g^-1 can be delivered.