Study On Structural Regulation And Sodium Storage Performance Of Nanoporous Antimony-based Anodes

At present,metallic Sb becomes one of the ideal SIB anode materials with low cost,abundance and high theoretical specific capacity.However,commercial Sb has always been suffered from pulverization during cycling due to huge volume expansion,resulting in serious capacity fading.In the meanwhile,Sb,as an alloy-type anode for SIB,encounters the problem of poor rate capacity.To solve the issues above,an Sb-based anode with nanoporous structure was synthesized in the current research.The rate capacity of the electrode was significantly improved by the introduction of nanoporous structure.Furthermore,electrochemically inactive compounds were mixed with nanoporous Sb,which effectively enhanced the cycling stability of the electrode.Herein,the sodium storage behavior was disclosed by theoretical and experimental investigation.The enhancement mechanism of hierarchical nanoporous architecture and the electrochemically inactive components on the electrochemical properties of Sb-based anodes has been clarified.Moreover,the fast kinetics mechanism of Sb-based anode materials has been explained.The effect of porous structure of Sb-based anodes on the sodium storage performance was investigated.Through the finite element simulation,it has been discovered that the sodium storage capability of nanoporous Sb(NP-Sb)is much better than the one of bulk Sb(B-Sb),which benefits from the huge specific area and three-dimensional ions/electrons transport pathway.NP-Sb with the pore size of 2?50nm(NP-Sb_(Mg))and with the pore size of 2?10 nm(NP-Sb_(Mn))were obtained by dealloying Sb₂₀Mg₈₀ and Sb₃₄Mn₆₆,respectively.Electrochemical test results show that after 50 cycles and 200 cycles at a C rate of C/2,the corresponding capacity retention maintained 75%and 100%,respectively.By contrast,after 20 cycles at a C rate of C/2,the capacity of B-Sb merely remained less than 30%.Besides,the sodium-ion diffusion coefficient in both two different NP-Sbs are one order of magnitude higher than that in B-Sb,indicating the porous structure effectively improved the rate capability of Sb.Moreover,the pore size influences the sodium storage performance of NP-Sb.Specifically,NP-Sb_(Mg),with larger pore size,has higher electrochemical activity and rate capability,while NP-Sb_(Mn),with smaller pore size,shows more excellent cycling stability.The sodium storage performance and mechanism of hierarchical nanoporous Sb(HNP-Sb)were studied.Through finite element simulation,it was found that the HNP-Sb exhibits higher capacity and reaction rate than NP-Sb.HNP-Sb with large(100?300 nm)and small(2?10 nm)pore sizes was synthesized by dealloying Sb₂₀Mn₈₀.Electrochemical test results show that the capacity retention of HNP-Sb remained 94%after 200 cycles at a C rate of C/2.The amount of sodium reversibly stored in HNP-Sb is?27%higher than in NP-Sb,which can be attributed to the large pores in HNP-Sb.The large pores promote the diffusion of sodium ions in the electrode and improve the activity of the electrode,Besides,the sodium-ion diffusion coefficient in HNP-Sb is?2.3 times higher than that in NP-Sb.Employing kinetic Monte Carlo(KMC)simulation,it is found that only if large pores and small pores exist at the same time,the maximum sodiation rate can be achieved while maintaining the stability of the porous structure.In the meanwhile,an analytic model of the relationship between the material's active specific surface area and the pore geometrical parameters was proposed.The fabrication and sodium storage performance of electrochemically inactive compounds confined Sb-based composite electrodes was investigated.The flexible polyaniline(PANI)in-situ coated NP-Sb_(Mg)composite electrode(NP-Sb/PANI)was fabricated by the chemical solution method coupled with the chemical dealloying method.By regulating the polymerization time,the thickness of PANI on the surface of Sb ligaments was optimized,which restrained the volume expansion of NP-Sb during cycling and consequently improves its cycling stability.Electrochemical test results display that the capacity retention remained 92.8%and 82.8%after 200 and250 cycles at the C rate of C/2,respectively.An Mg F₂ confined NP-Sb_(Mg)composite electrode(NP-Sb/Mg F₂)was prepared by ball milling coupled with the chemical dealloying.The Mg F₂ particles with high bulk modulus effectively restricted the volume expansion of NP-Sb particles,which significantly improves its electrochemical performance.Electrochemical test results show that the capacity of NP-Sb/Mg F₂ remained 551 m Ah·g^-1 after 300 cycles at a C rate of C/2,and the capacity retention remained as high as 93%.Furthermore,the sodium-ion diffusion coefficients in NP-Sb/PANI and NP-Sb/Mg F₂ are much higher than that of NP-Sb.The full cell made from NP-Sb/Mg F₂ exhibits capacity retention of 91.7%and an energy density of?152 Wh·kg^-1 after 1300 cycles at 1C,displaying the comparative performance to commercial Li Fe PO₄,which shows excellent application prospect.Finally,by combining ab initio Monte Carlo simulation and in situ WAXS technique,it was discovered that the amorphous phase formed during(de)sodiation is the main reason for the fast reaction kinetics of Sb.