Structural Design Of Carbon-based Composites And Their Performances For Na/Li-ion Batteries

Lithium-ion batteries(LIB s)have been widely used in new electric vehicles and portable electronic devices due to their advantages of high energy density and long cycle life.Currently,the commercial graphite anode shows low energy density due to its low theoretical capacity(372 mAh g-1).To address this issue,on the one hand,replacing graphite anode with higher capacity materials can effectively improve the energy density.Besides,the price of LIBs tends to increase gradually with the increasing demand for energy and exhaustion of lithium resources.On the other hand,developing other low-cost rechargeable batteries has been one of the most appealing strategies.Due to the extremely abundant in the earth’s crust,sodium-ion batteries(SIBs)have become the most attractive alternative in terms of the low cost of sodium and the similar electrochemical reaction mechanism to LIBs.However,commercial graphite anodes are not suitable for SIBs because of the large radius of Na+.To conquer the challenges in LIBs/SIBs,developing low-cost and high-performance anode materials is of great importance.Due to the advantages of low preparation cost,non-toxic and steady chemical property,carbon-based electrodes are promising anodes for LIB s/SIB s.The construction of three-dimensional(3D)carbon-based nanocomposites can effectively increase the active sites for Li+/Na+storage and alleviate the volume expansion of electrode materials,thus improving capacity and cycle stability.Therefore,developing high-capacity,long-life 3D carbon-based nanocomposites is of great research significance.Based on this,the main research results of this paper are listed as follows:(1)Oxygen-rich graphene vertically grown on 3D N-doped carbon foam(VGOG/3DNCF)was prepared via a hydrothermal combined with calcination method.When VGOG/3DNCF is evaluated as anode for SIB s,the ultra-high oxygen content of C=O groups renders VGOG/3DNCF much more active sites for Na+storage,and the vertical growth structure of graphene on 3D carbon foam can effectively reduce the restacking of graphene and promote the rapid migration of Na+.Meanwhile,the synergistic effect between the fast electron transport framework of 3DNCF and VGOG can effectively alleviate the volume variation during cycling.As a result,VGOG/3DNCF anode delivers extraordinary Na+ storage ability with outstanding reversible capability(508.6 mAh g-1 at 0.1 A g-1),superior rate performance(113.3 mAh g-1 at 5.0 A g-1)as well as remarkable cycle stability(329.3 mAh g-1 over 1000 cycles at 1.0 A g-1).Furthermore,Na3V2(PO4)3@C‖VGOG/3DNCF full SIB can deliever a reversible capacity of 251.8 mAh g-1 after 400 cycles with superior capacity retention of 89.8%.The facile method together with the impressive electrochemical performances provides a new way to facilitate the application of graphene in carbon-based composites.(2)Metal sulfides(TMS)are considered as the potential anode materials due to their high theoretical specific capacity and low cost.However,the poor electrical conductivity,electron/ion transport rate,and structural stability limit their further applications.Herein,a simple yet general and scalable adsorption-annealing strategy is first devised to finely construct core-shell carbon-coated TMS nanoparticles anchored on 3D N-doped carbon foam(TMS@C/3DNCF).The adsorption-annealing strategy enables the preparation of 3D hierarchical structures in which TMS nanoparticles are coated by carbon layer and firmly anchored in 3DNCF.The 3D architectures can not only effectively improve the electrical conductivity and electron/ion transport,but also greatly alleviate the volume expansion of TMS during cycling and guarantee the structural stability of electrode materials.Taking Co9S8@C/3DNCF as an example,the anode can exhibit excellent electrochemical performance in both half-cells and full-cells.Co9S8@C/3DNCF can achieve a high specific capacity of 400.4 mAh g-1 at 1.0 A g-1 after 1400 cycles with excellent capacity retention of 90.5%and excellent rate performances(231.1 mAh g-1 at 5.0 A g-1).Furthermore,Na3V2(PO4)3@C‖VGOG/3DNCF full SIB can demonstrate a high capacity of 377.4 mAh g-1 at 0.5 A g-1 and outstanding capacity retention of 92.1%after 500 cycles,indicating good practical prospects.This unique fabrication process and the advanced architectures may pave a potential way to develop metal sulfide/carbon composites with both good electrochemical activity and structural stability.(3)Metal nitrides(TMN)are ideal anode materials for SIBs because of their higher electronic conductivity and lower sodium intercalation/deintercalation potential compared with TMSs.However,the preparation of metal nitrides often suffers from tedious fabrication processes and/or overused toxic nitrogen sources.Moreover,TMNs anodes often undergo serious cycling performances due to the transition from crystalline phase to amorphous phase as well as the agglomeration and pulverization during cycling process,which greatly limited their practical applications.Herein,a simple adsorption-annealing strategy is proposed to fabricate a composite of core-shell Fe3N@C archored on three-dimensional N-doped carbon foam(Fe3N@C/3DNCF).Due to the unique coordination and adsorption ability of melamine sponge,Fe3N@C nanoparticles can in-situ grow on 3DNCF during annealing.When evaluated as an anode for SIBs,Fe3N@C/3DNCF can exhibit a high reversible capacity of 374.8 mAh g-1 with a super capacity retention of 95.1%after 2000 cycles.Moreover,Na3V2(PO4)3@C‖Fe3N@C/3DNCF full SIB can deliver good cycling performance with a capacity retention of 95.2%at 0.5 A g-1 after 400 cycles.The unique structure can not only accelerate the transport rate of electron/Na+,but also effectively inhibit the pulverization of Fe3N and maintain highly reversible crystallinephase transformation during long-term sodiation/desodiation cycling.The design philosophy as well as the simple preparation method of 3D hierarchical structures open a new way for the application of metal nitrides in carbon-based composites.(4)Metal phosphides(TMP)is a promising anode material for LIBs due to their higher theoretical specific capacity and lower polarization potential compared with TMSs and TMNs.However,the preparation of metal phosphides is more challenging owing to the extensive usage of highly toxic phosphorus sources(such as PH3,NaH2PO2).In addition,since the discharge product(Li3P)shows lower reversibility in the charge process,TMP experience severe capacity decay in LIBs.Based on this,a covalent heterostructure of metal phosphide quantum dots anchored in N,P co-doped carbon nanocapsules(TMP NDs/NPC)were prepared by solvothermal-annealing method.Since TMP NDs/NPC are prepared by annealing P-containing MOF,TMP are covalently coupling with NPC.The covalent coupling can greatly improve electron/ion migration and enhance the reversibility of Li3P via reducing the conversion reaction barrier,which lead to outstanding Li+storage performance.Taking Co2P NDs/NPC as an example,the anode can remain a high capacity of 431.2 mAh g-1 and experience no capacity decay even after 1600 cycles.This facile fabrication method and the design of covalent heterostructures offer potential opportunities to address the challenges of TMP/carbon composites for energy storage.(5)Red phosphorus(RP)is a promising anode material for SIBs due to its abundant resources,high theoretical specific capacity(～2600 mAh g-1)and low working potential(～0.4 V vs.Na+/Na).However,the low electronic conductivity(10-14 S cm-1)and huge volume change during the sodiation/desodiation process,which leads to huge electrochemical polarizations and capacity degradation.In addition,since the lone pair electrons on 3d orbital of phosphorus atoms easily lose electrons in the air and results in the formation of phosphorus oxide species on surface and consequently deteriorates the initial Coulombic efficiency(ICE)and reversible capacity.Therefore,a new RP@BP core-shell hetero structure anchored on three-dimensional N-doped graphene(RP@BP/3DNG)with good air stability were prepared by solvothermal method.The composite of black phosphorus and 3D graphene greatly improves the electronic conductivity of red phosphorus,relieves the volume expansion of phosphorus nanoparticles.Furthermore,the build-in filed at the RP@BP heterointerface induces the shift of electron cloud from BP to RP and lowers down the reaction activity of long-pair electrons of BP atoms,and thus RP@BP/3DNG shows greatly enhanced air stability.As a result,the RP@BP/3DNG exhibits a high reversible capacity of 1440.2 mAh g-1 at 0.05 A g-1,excellent rate performance(521.3 mAh g-1 at 10.0 A g-1)as well as an unprecedented capacity retention rate of 89.3%after 1200 cycles at 10.0 A g-1.The impressive electrochemical performances as well as antioxidative ability make our P-based heterostructure become a new candidate in the applications of energy storage and conversion.