| Improving the performance of anode materials is of great importance for lithium/sodium ion batteries.To address the drawback of volume expansion during the cycling of Mn Se as anode material leading to pulverization and agglomeration,this paper prepared Ge,Sn-modified Mn Se electrospun carbon nanofibers using a combination of electrostatic spinning and heat treatment process and characterized their electrochemical properties.The main research results are as follows.（1）The germanium-doped carbon nanofibers with composite manganese selenide（Ge/α-Mn Se@CNFs）were prepared by electrostatic spinning method and thermal reduction process,in which the coupling of germanium and manganese selenide makes the in situ growth of manganese selenide occur only inside the fiber,avoiding the direct contact between manganese selenide particles and electrolyte while providing a crispy buffer carbon layer for the swelling during the cycling process.In addition,the conductivity of carbon nanofibers is enhanced by Ge,which facilitates the diffusion and transport of ions;the synergistic effect of each phase during cycling facilitates the electrochemical reaction process with buffered volume expansion;the interface composed of multiple phases improves the pseudo-capacitance effect and contributes to a higher increase in specific capacity.When the composite was applied to the anode of lithium-ion batteries,it showed good rate performance and cycling stability:after 200 cycles at 0.1 A g-1 current,it had a high specific capacity of 1514.7m A h g-1,and after 1000 cycles at a current density of 1 A g-1,it had a high specific capacity of 1030 m A h g-1;when applied to the anode of sodium-ion batteries,the electrochemical performance showed that:the specific capacity decreased to 213.6 m A h g-1 after 300 cycles at 0.1 A g-1 current,and the capacity decayed seriously after 1000 cycles at 1 A g-1 current density,mainly because the material collapsed and lost its activity due to the huge volume expansion generated during the cycle.（2）Manganese selenide composite materials（Sn/α-MnSe@CNFs）with tin-doped carbon nanofibers were prepared by electrostatic spinning and heat treatment process.On the one hand,the presence of Sn enhances the overall electrical conductivity of the composite material and facilitates the rapid transport and diffusion of sodium ions;on the other hand,the“alloying”protection mechanism between Sn and Na+during charging and discharging enhances the structural stability and electrical conductivity of the fibers and improves the reaction kinetics;the multi-interface between amorphous carbon,Sn and Mn Se improves the pseudocapacitance effect（the contribution of pseudocapacitance becomes larger as the scanning speed increases）.When Sn/α-Mn Se@CNFs were applied to the anode of Li-ion batteries,a capacity of 1259.0 m A h g-1 remained after 300 cycles at a current density of 0.2 A g-1,and a high capacity of 759.7 m A h g-1 was maintained after 1000 cycles at a current density of 5 A g-1;when applied to the anode of sodium ion batteries,the electrochemical performance results showed that the capacity of 466.1 m A h g-1 was maintained after300 cycles at a current density of 0.1 A g-1 and a stable capacity of 288.7m A h g-1 after 3000 cycles at a current density of 5A g-1,demonstrating its excellent rate performance and long cycle life.Sn/α-Mn Se@CNFs shows great potential for simultaneous application in lithium/sodium ion battery anodes.The modification of Ge/Sn effectively solves the problem of Mn Se growth on the surface of carbon fibers and improves the electrical conductivity and help to buffer volume expansion during the cycling,and secondly,Ge/Sn also promotes charge transfer and improves the reaction kinetics of Mn Se to obtain good electrochemical properties,which provides a new strategy for the design of anode materials for high performance lithium-ion and sodium-ion batteries.This paper includes 42 figures,6 tables and 130 references. |
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