Preparation method of an M-Sb alloy encapsulated carbon nanofiber anode material and its application in potassium / lithium ion batteries

Abstract

The present invention discloses a preparation method of an M-Sb alloy encapsulated carbon nanofiber negative electrode material and its application in potassium / lithium ion batteries, wherein M is Bi, Co and / or Ni. In this material, M-Sb metal particles are perfectly encapsulated in carbon fibers, forming a three-dimensional network structure of interconnected nanofibers. The present invention uses antimony salt and M metal salt solutions as metal sources, and polymers such as polyacrylonitrile as carbon sources, and forms fibers by electrospinning, and anneals in an argon atmosphere to obtain an M-Sb / carbon nanofiber composite material sample. The obtained product has high purity, and the metal particles are uniformly distributed, and excellent electrochemical performance is exhibited in potassium / lithium ion batteries. Using this material as the negative electrode material of potassium / lithium ion batteries, the one-dimensional porous structure of carbon fibers and the synergistic effect of active / inactive metals are used to suppress the problem of large volume change during the charge and discharge process of alloying materials, and improve the problems such as poor cycle stability of current alloying negative electrode materials for potassium / lithium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for secondary batteries, and particularly relates to a preparation method of an M-Sb alloy particle encapsulated carbon nanofiber negative electrode material and its application in potassium / lithium ion batteries. Background Art

[0002] Due to advantages such as high energy density and long cycle life, lithium ion batteries have been widely used in portable electronic devices such as mobile phones and laptop computers, as well as in electric vehicles, ships, biomedicine, etc. The abundance of lithium resources in the earth's crust is low (17 ppm) and the distribution is uneven. Therefore, the limited lithium resources have restricted the large-scale application of lithium ion batteries to a certain extent. Metal potassium belongs to the same main group as lithium and sodium, and has similar chemical properties. The reserves of potassium in the earth's crust (17000 ppm) are higher and it is widely distributed. Secondly, in carbonate electrolytes, the + standard electrode potential of K / K + is close to that of Li / Li + In particular, the electrode potential of K / K + (-2.93 V vs. SHE) is lower than that of Na / Na

[0003] (-2.71 V vs. SHE). The low electrode potential can provide higher voltage and energy density for potassium ion batteries. Potassium ions have faster ion transport kinetics at the electrolyte-electrode interface, and potassium ion batteries have more excellent performance in rate performance. Therefore, the research on potassium / lithium ion battery electrode materials is imperative, and both have broad prospects in future energy storage systems. Summary of the Invention

[0004] To solve the above problems, the present invention proposes an M-Sb alloy encapsulated carbon nanofiber anode material, where M is an active / inactive metal. As the anode material for potassium / lithium ion batteries, its unique one-dimensional structure and the introduction of active / inactive metals can improve the performance of the antimony-based material, effectively reducing the volume expansion of the material during cycling. At the same time, the porous structure can increase the contact area between the material and the electrolyte, enhance the conductivity, and significantly improve the electrochemical performance of potassium / lithium ion batteries. In addition, the presence of a catalytically active metal improves the graphitization degree of the carbon material during the heat treatment process. To address the problem that the capacity of this material decreases while the stability is improved, a high-concentration electrolyte is adopted. Within a certain concentration range, the capacity retention rate increases with the increase in concentration. The high-concentration electrolyte can not only passivate the surface of the alloy anode and protect the anode material by enhancing the anti-reduction ability.

[0005] An M-Sb (M = Bi, Co, and / or Ni) alloy encapsulated carbon nanofiber anode material disclosed by the present invention has an interconnected fiber structure with a diameter of 500 nm - 1.2 μm. The fiber surface is smooth, and all M-Sb alloy particles are uniformly embedded in the carbon fiber, with the alloy particle diameter being 20 - 150 nm.

[0006] M-Sb (M = Bi, Co, Ni) metal nanoparticles are perfectly encapsulated inside the one-dimensional porous carbon fiber. The two work together. On the one hand, it improves the conductivity, and on the other hand, it acts as a buffer medium to relieve volume changes. The synergistic effect of the one-dimensional porous characteristic structure of the carbon fiber and the active / inactive metal improves the cycle life of the material and has excellent electrochemical performance when applied in potassium / lithium ion batteries.

[0007] If M is a catalytically active metal (Co, Ni), during the preparation process, metal M has a positive effect on the graphitization degree of the carbon fiber. The composite material has a one-dimensional fiber morphology, and the metal nanoparticles are encapsulated inside the one-dimensional carbon fiber; the carbon fiber can be pure-phase carbon or heteroatom-doped carbon; the surface of the M-Sb alloy particles inside the fiber is coated with a layer of amorphous carbon.

[0008] As the anode material for potassium / lithium ion batteries, this material has excellent electrochemical performance. The preparation method is simple. The M-Sb / carbon nanofiber material prepared by electrospinning has good structural stability and uniform morphology. At the same time, when applied in the anode of potassium / lithium ion batteries, it can exhibit excellent cycle life.

[0009] Another object of the present invention is to apply the prepared M-Sb / carbon nanofiber anode material (such as BiSb@C) to the anode material of potassium ion batteries and test it in a high-concentration electrolyte, providing a solution for a new generation of energy systems.

[0010] The preparation method of M-Sb (M = Bi, Co, Ni) / carbon nanofibers and potassium / lithium ion batteries described in the present invention includes the following steps:

[0011] (1) Dissolve antimony salt and M metal salt in an organic solution, then add a polymer and stir. After electrospinning the obtained solution, collect it; the molar ratio of antimony salt to M metal salt is (1-2):1; the M metal salts include one or more combinations of bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, etc.; the antimony salt is one or more combinations of antimony trichloride, antimony acetate; the polymer is one or more combinations of polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol;

[0012] (2) Vacuum-dry the sample obtained in step (1); place the obtained sample in a tube furnace for sintering. First, in an air atmosphere, heat it at a heating rate of 2-5 °C / min to 200-300 °C and hold for 2-3 h, then heat it at a heating rate of 5-10 °C / min to 600-800 °C and hold for 2-5 h for carbonization treatment to obtain the M-Sb / carbon nanofiber composite.

[0013] The organic solution described in step (1) is preferably N,N-dimethylformamide or N-methylpyrrolidone;

[0014] The suitable range of the average molecular weight of the polymer described in step (1) is 150,000-500,000, and the addition amount fluctuates within 0.5-1.5 g / 10 m solution. When the concentration of the high molecular polymer solution increases to the critical value, the degree of intermolecular interconnection increases and a stable structure and high surface area are maintained. The interconnected structure can more effectively accommodate nanoparticles, making the nanoparticles evenly distributed.

[0015] The preferred method for electrospinning in step (1) is: the needle is 15-20 cm away from the receiver, the pushing speed is 0.1-0.5 mm / min, and the positive high voltage is 10-14 kV.

[0016] Mix the M-Sb / carbon nanofiber composite, conductive agent, and binder evenly according to a mass ratio of 7:2:1, apply it on a copper foil, and after vacuum drying for 12 hours, cut it into electrode sheets with a certain diameter.

[0017] Using the electrode sheet as the working electrode, using metallic potassium / lithium as the reference electrode, adding an electrolyte, and assembling a potassium / lithium ion button battery in a glove box filled with argon.

[0018] The beneficial effects of the present invention:

[0019] 1. The present invention prepares a one-dimensional M-Sb@C carbon nanofiber composite material through electrospinning technology. During the high-temperature annealing process, metal compounds are transformed into metal elements, and the volatilization of the solvent and the release of a part of the gas cause a porous structure to appear on the carbon nanofibers. The unique nanostructure of the composite material can alleviate the volume change during the potassium ion insertion / extraction process and improve the electrical conductivity and structural stability of the composite material.

[0020] 2. The present invention selects the M-Sb / carbon nanofiber material as the negative electrode material for potassium / lithium ion batteries, and uses the one-dimensional porous characteristic structure of carbon fibers and the synergistic effect of active / inactive metals (Bi, Co, and / or Ni) to overcome the problem of large volume change during the charge and discharge process of alloy-type negative electrode materials and improve the problems such as poor cycle stability of the materials.

[0021] 3. For the one-dimensional M-Sb@C carbon nanofiber composite material prepared by electrospinning technology, the size and morphology of the particle size can be controlled.

[0022] 4. Metals with catalytic activity have the effect of improving the structure and properties of the carbon coating layer during the heat treatment process. Due to the high electrical conductivity of graphitized carbon and better ion permeability, alloy particles coated with graphitized carbon have better cycle performance, capacity, and Coulomb efficiency. Description of the Drawings

[0023] Figure 1 are the scanning electron microscope image and transmission electron microscope image of the BiSb@C carbon nanofiber composite material;

[0024] Figure 2 is the X-ray diffraction pattern of the BiSb@C carbon nanofiber composite material;

[0025] Figure 3 is the cycle performance diagram of the BiSb@C carbon nanofiber composite material in electrolytes with different concentrations at a current density of 0.1 A g -1 ;

[0026] Figure 4 are the scanning electron microscope and transmission electron microscope images of the NiSb@C carbon nanofiber composite material;

[0027] Figure 5 is the X-ray diffraction pattern of the NiSb@C carbon nanofiber composite material;

[0028] Figure 6 is the cycle performance diagram of the NiSb@C carbon nanofiber composite material at a current density of 0.5 A g -1 ;

[0029] Figure 7 are the scanning electron microscope and transmission electron microscope images of the Sb / CoSb2@C carbon nanofiber composite material;

[0030] Figure 8 It is the X-ray diffraction pattern of the Sb / CoSb2@C carbon nanofiber composite material;

[0031] Figure 9 It is the cycle life diagram of Sb / CoSb2@C and NiSb@C. Specific implementation mode

[0032] For the convenience of understanding the present invention, the present invention will be described more comprehensively and carefully below in conjunction with the specification drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0033] Example 1

[0034] A two-step method is adopted to prepare the BiSb@C negative electrode material:

[0035] 1) Preparation of the precursor

[0036] Antimony trichloride and bismuth nitrate pentahydrate with a Bi:Sb molar ratio of 1:1 are dissolved in 15 mL of N,N-dimethylformamide, and then 1.8 g of polyacrylonitrile (average molecular weight 150,000) is added and stirred at 60 °C for 5 h.

[0037] 2) Preparation of BiSb@C

[0038] The obtained liquid is subjected to electrospinning and then collected. During electrospinning, the distance between the needle tip and the receiver is 15-20 cm, the pushing speed is 0.1-0.4 mm / min, and the positive high voltage is 10-14 kV; the obtained sample is dried in a vacuum drying oven at 60 °C for 12 h. Under air, it is heated to 250-300 °C at a rate of 5 °C / min and held for 2 h, and heat-treated at 600-800 °C for 3-5 h under an inert atmosphere.

[0039] 3) Research on the electrochemical performance of the potassium ion half-cell

[0040] The obtained active material is mixed with the conductive agent acetylene black and the binder sodium alginate in a ratio of 7:2:1 in water, evenly coated on copper foil, vacuum dried at 60 °C for 12 h, and then cut into electrode sheets with a diameter of 12 mm.

[0041] Using metallic potassium as the reference electrode, and using electrolytes A, B, and C as electrolytes respectively, button cells are assembled in a glove box filled with argon.

[0042] Electrolyte A: 1 mol L -1 Potassium bis(fluorosulfonyl)imide (KFSI) is dissolved in a mixed solution of ethylene carbonate and diethyl carbonate with a mass ratio of 1:1.

[0043] Electrolyte B: 3 mol L -1Potassium bis(fluorosulfonyl)imide (KFSI) is dissolved in a mixed solution of ethylene carbonate and diethyl carbonate with a mass ratio of 1:1.

[0044] C electrolyte: 5 mol L -1 Potassium bis(fluorosulfonyl)imide (KFSI) is dissolved in a mixed solution of ethylene carbonate and diethyl carbonate with a mass ratio of 1:1.

[0045] Figure 1 are the scanning electron microscopy (SEM) image and transmission electron microscopy (TEM) image of BiSb@C. As shown in the images, the BiSb@C material exhibits a fibrous interconnected network structure with a fiber diameter of approximately 500 - 700 nm. The TEM image shows that they are mainly composed of metal particles embedded in carbon nanofibers, and the diameter of the metal particles is approximately 100 - 150 nm.

[0046] Figure 2 is the X-ray diffraction (XRD) pattern of BiSb@C. It can be seen that the sample has a high purity and exhibits characteristic peaks of two metals.

[0047] Figure 3 is for BiSb@C at a current density of 0.1 A g -1 Cycling stability in 1M, 3M, 5M KFSI EC:DEC (1:1 vol%) electrolytes. It can be found that compared with the other two electrolytes, the specific capacity and cycling stability of the composite material are significantly improved in the 5M electrolyte. The BiSb@C negative electrode under 5M electrolyte can provide a high reversible capacity of approximately 204.8 mAh g -1 after 500 cycles, and the capacity retention rate is 82.8%, indicating its good cycling stability.

[0048] Example 2

[0049] A two-step method is adopted to prepare the NiSb@C negative electrode material:

[0050] 1) Preparation of the precursor

[0051] 0.684 g (3 mmol) of antimony trichloride and 0.436 g (1.5 mmol) of nickel nitrate hexahydrate are dissolved in 10 mL of N,N-dimethylformamide, and then 0.9 g of polyacrylonitrile (average molecular weight 150000) is added and stirred at 50 °C for 3 h.

[0052] 2) Preparation of NiSb@C

[0053] The obtained liquid was collected after electrospinning. During electrospinning, the pushing speed was 0.1 - 0.5 mm / min, the distance between the needle and the receiver was 15 - 20 cm, and the positive high voltage was 10 - 14 kV. The obtained sample was dried in a vacuum drying oven at 60 °C for 12 h. Under air atmosphere, it was heated to 280 - 300 °C at a rate of 5 °C / min and held for 2 h, and then heat-treated at 600 - 800 °C for 3 h under an inert atmosphere.

[0054] 3) Electrochemical performance study of lithium-ion half-cells

[0055] The obtained active material was mixed with conductive agent acetylene black and binder sodium alginate in a ratio of 7:2:1 in water, uniformly coated on copper foil, dried in vacuum at 80 °C for 10 h, and then cut into electrode sheets with a diameter of 12 mm.

[0056] Using metallic lithium as the reference electrode, 1M LiPF6 EC / DMC (1:1, vol%) + 5% FEC as the electrolyte, a CR2032 coin cell was assembled in a glove box filled with argon.

[0057] Figure 4 are the scanning electron microscope and transmission electron microscope images of NiSb@C. The SEM image shows that the NiSb@C material has an interconnected fiber structure, the fiber diameter is about 600 - 800 nm, and the surface of the material is smooth. The TEM image shows that NiSb metal particles are uniformly embedded in N-doped carbon fibers, the particle diameter is about 20 - 40 nm, the carbon fibers have a porous structure, and there is a carbon wall with a thickness of about 100 nm, which can relieve the volume change of alloy particles.

[0058] Figure 5 is the X-ray diffraction pattern of NiSb@C. It can be seen that the purity of the sample is relatively high, and metal ions are successfully reduced during the synthesis process.

[0059] Example 3

[0060] A two-step method was adopted to prepare the Sb / CoSb2@C anode material:

[0061] 1) Preparation of the precursor

[0062] 0.684 g of antimony trichloride and 0.435 g of cobalt nitrate hexahydrate were dissolved in 10 mL of N,N-dimethylformamide, and then 0.9 g of polyacrylonitrile (average molecular weight 150000) was added and stirred at 50 °C for 3 h.

[0063] 2) Preparation of NiSb@C

[0064] The obtained liquid was collected after electrospinning. During electrospinning, the pushing speed was 0.2 mm / min and the positive high voltage was 10 - 14 kV. The obtained sample was dried in a vacuum drying oven at 60 °C for 12 h. Under air atmosphere, it was heated to 250 - 300 °C at a rate of 5 °C / min and held for 2 h, and then heat-treated at 600 - 700 °C for 3 h under an inert atmosphere.

[0065] 3) Electrochemical performance study of lithium-ion half-cells

[0066] The obtained active material was mixed with conductive agent acetylene black and binder sodium alginate in a ratio of 7:2:1 in water, evenly coated on copper foil, dried in vacuum at 80 °C for 10 h, and then cut into electrode sheets with a diameter of 12 mm.

[0067] Using metallic lithium as the reference electrode, 1M LiPF6 EC / DMC (1:1, vol%) + 5% FEC as the electrolyte, a CR2032 coin cell was assembled in a glove box filled with argon. As Figure 6 shown, the material has excellent electrochemical performance.

[0068] Figure 7 are the scanning electron microscope and transmission electron microscope images of Sb / CoSb2@C. The SEM image shows that Sb / CoSb2@C is an interconnected fiber structure with a diameter of 900 nm - 1.2 μm, and the fiber surface is smooth. The TEM image shows that all CoSb2 metal particles are uniformly embedded in the N-doped carbon fiber, and the diameter of the metal particles is 30 - 40 nm.

[0069] Figure 8 is the X-ray diffraction pattern of Sb / CoSb2@C. It can be seen that the purity of the sample is relatively high, and during the synthesis process, metal ions were successfully reduced.

[0070] Figure 9 are the cyclic life diagrams of Sb / CoSb2@C and NiSb@C. The first-cycle discharge capacity of the Sb / CoSb2@C electrode is 785.3 mAh g -1 . After 600 cycles, it can maintain a capacity of 620.2 mAh g -1 , and the capacity retention rate is 88.2%.

Claims

1. Use of an electrode sheet containing Sb / CoSb2@C anode material in the preparation of a lithium battery, characterized in that the electrode sheet is prepared by the following steps: 1) Preparation of the precursor Dissolve 0.684 g of antimony trichloride and 0.435 g of cobalt nitrate hexahydrate in 10 mL of N,N-dimethylformamide, then add 0.9 g of polyacrylonitrile with an average molecular weight of 150,000, and stir at 50 °C for 3 h to obtain the precursor; 2) Preparation of Sb / CoSb2@C anode material Electrospinning is carried out on the obtained precursor. During electrospinning, the pushing speed is 0.2 mm / min and the positive high voltage is 10 - 14 kV to obtain a sample; The obtained sample is dried in a vacuum drying oven at 60 °C for 12 h, then heated to 250 - 300 °C at a rate of 5 °C / min in an air atmosphere and held for 2 h; finally, heat treatment is carried out at 600 - 700 °C for 3 h in an inert atmosphere to obtain the anode material. The anode material is an interconnected fiber structure with a diameter of 900 nm - 1.2 μm, in which CoSb2 metal particles are all uniformly embedded in N-doped carbon fibers, and the diameter of the metal particles is 30 - 40 nm; 3) Preparation of the electrode sheet The obtained anode material Sb / CoSb2@C is mixed with conductive agent acetylene black and binder sodium alginate in a mass ratio of 7:2:1 in water, uniformly coated on copper foil, vacuum dried at 80 °C for 10 h, and then cut into electrode sheets with a diameter of 12 mm; The lithium battery is prepared by the following steps: Using the electrode sheet as the working electrode, metallic lithium as the reference electrode, and 1M LiPF6 in a volume ratio of 1:1 of EC / DMC + 5% FEC as the electrolyte, assemble into a CR2032 button battery in a glove box filled with argon.

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