Preparation And Electrochemical Performance Of Antimon/carbon As Anode Material For Sodium-ion Batteries

Sodium-ion battery is considered one of the most promising electrochemical energy storage technologies to replace Lithium-ion battery due to its advantages of high abundance and low cost.However,the ionic radius（0.102 nm）of sodium is 1.3 times that of lithium（0.076 nm）,and the molar mass（22.99 g/mol）is 3.3 times that of lithium（6.94 g/mol）,making the energy density of sodium-ion batteries slightly lower than that of lithium-ion batteries.Therefore,finding and preparing high-energy-density anode materials for sodium-ion batteries is essential for large-scale energy storage.Among all electrode materials,metallic antimony（Sb）has attracted wide attention due to its high theoretical specific capacity(～660m Ah g^-1),suitable operating voltage（0.5～0.8 V）,and high conductivity(2.56*10⁶ S cm^-1).However,during the alloying process,Sb anode electrode has a severe volume expansion（～390%）,which will lead to electrical contact failure and electrode structure rupture,resulting in serious specific capacity attenuation and sharp reduction of life.To solve this problem,three kinds of Sb/C nanocomposites with different morphologies were constructed in this thesis.The specific research methods are as follows:（1）Synthesis of Sb/P nanospheres connected to carbon fiber filaments by electrostatic spinning,regulation of the size of Sb/P nanospheres and carbon fiber thickness by changing the pushing speed,selection of needle size and temperature,and regulation of the change in specific capacity of Sb/P nanospheres during constant current charging and discharging by changing the ratio of Sb to P.For example,the comparison of electrochemical properties of Sb/P@C samples with different mass ratios of 1:0.1,1:0.5,and 1:1 was explored.The samples are denoted as Sb/P@C-1,Sb@P/C-2,and Sb/P@C-3 respectively.Among the samples prepared at three ratios,the Sb/P@C electrode retains a reversible specific capacity of404.9m Ah g^-1 at 50 m A g^-1 after 100 cycles.The specific capacity can reach 335 m Ah g^-1 at0.5 A g^-1.In the process of high-temperature carbonization,Sb/P nanospheres are formed by connecting Sb and P elements with carbon wires.Thus,loofah-shaped Sb/P@C composite material is constructed and used as the anode electrode of sodium-ion batteries.The synergistic action between Sb/P nanospheres and carbon nanowires makes the composite anode electrode material exhibit good cyclic stability and structural integrity,which can be attributed to the following reasons:1)“Loofah-like”carbon nanofilaments are interlaced to interpenetrate the Sb/P nanospheres and mosaic them within the carbon fibers,reducing the aggregation effect of individual Sb or P nanospheres.This structure not only avoids direct contact between the surface of the Sb/P nanospheres and the electrolyte,which would prevent excessive SEI,but also provides enough space to accommodate the volume changes during the sodization process,enhancing the structural stability of the material and thus improving its electrochemical performance;2)Carbon nanowires provide multiple electron transport channels between Sb/P nanospheres,shortening the diffusion distance of sodium ions,promoting charge transfer,improving the conductivity of composite materials,enhancing the electrochemical reaction kinetics of sodium ions,contributing to increased cycle life and improving the stability of the electrode structure;3)The Sb/P dispersion structure can effectively alleviate the stress strain generated by the anisotropic volume expansion,inhibit the rupture of Sb/P nanospheres during charging and discharging,maintain the integrity of the nanospheres,and help enhance the stability of sodium ion storage.The synthetic strategy can effectively regulate the problems of Sb anode and construct a new nanosphere morphology,and the prepared Sb/P@C anode demonstrates better cycling stability and multiplicative performance.（2）A simple electrostatic spinning combined with in-situ carbonization method was used to synthesize phosphorus-nitrogen co-doped carbon fibers wrapped in hexagonal Sb nanocrystal composite structures（Sb@P-N/C）and to investigate their electrochemical properties.The performance of the undoped sample Sb@C and the sample Sb@N/C with only N doping were compared under the same experimental conditions.With the aid of electrochemical impedance（EIS）,constant current charge/discharge and cyclic voltammetric（CV）curve analyses,the Sb@P-N/C anode electrode demonstrates excellent sodium storage and multiplicative performance,as demonstrated by:1)the specific capacity was maintained at 500.1 m Ah g^-1 over 200 cycles at a current density of 50 m A g^-1;2)the reversible specific capacity was 295.6 m Ah g^-1 after 400 cycles at a high current density of 500 m A g^-1;3)the EIS and CV test results confirmed that P-N co-doping not only increased the charge/discharge specific capacity of the material,but also enhanced the sodium ion diffusion kinetics,resulting in the constructed Sb@P-N/C anode exhibiting a high sodium storage capacity and cycle life.In order to further analyze the electrochemical performance of the Sb@P-N/C anode electrode,a full cell assembly test was carried out in which ternary Na(Fe_1/3Ni_1/3 Mn_1/3)O₂ was selected as the cathode material for the full cell assembly.The specific capacity of 66.8 m Ah g^-1 was maintained for 60 cycles,which implies that the Sb@P-N/C anode has potential for practical applications in sodium-ion batteries.（3）Sb@PCFs composites were prepared and their sodium storage properties were investigated using a controlled and simple electrostatic spinning method in which“Taylor cone”shaped filaments were emitted from the needles under a strong electric field.Sb Cl₃ is added to a precursor solution containing carbon sources（PVP and PMMA）and stirred well,followed by electrostatic spinning,drying and carbonisation to obtain a composite structure of porous carbon fibers（PCFs）encapsulated with Sb particles（Sb@PCFs）.The Sb nanoparticles are embedded in“branch-like”interconnected porous carbon fibers,with the interstitial voids helping to suppress Sb volume expansion and maintain the structural integrity of the composite.In addition,Sb@PCFs composite materials with initial charge-discharge capacity of 434.8/680 m Ah g^-1 and initial coulomb efficiency of 63.9%.The specific capacity after 200 cycles at 50 m A g^-1 was 366.3 m Ah g^-1,with a capacity retention of 84.2%.This can be attributed to the synergistic effect between Sb and PCFs,allowing the Sb@PCFs electrode to exhibit good electrochemical performance.