CN109346713B - Silicon negative electrode material of sodium ion battery - Google Patents

Silicon negative electrode material of sodium ion battery Download PDF

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CN109346713B
CN109346713B CN201811165622.4A CN201811165622A CN109346713B CN 109346713 B CN109346713 B CN 109346713B CN 201811165622 A CN201811165622 A CN 201811165622A CN 109346713 B CN109346713 B CN 109346713B
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silicon
amorphous
sodium
battery
crystalline
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CN109346713A (en
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吴川
李莹
白莹
吴锋
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Beijing Institute of Technology BIT
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The modification method of the sodium ion battery silicon negative electrode material comprises the following steps: forming a slurry with crystalline nano-silicon; coating the slurry on a metal substrate, drying and cutting to form a silicon-coated electrode plate; under inert atmosphere, taking metal sodium as a battery cathode and taking the silicon-coated electrode plate as an anode, thereby assembling a sodium-ion battery; the battery is used for carrying out constant-current electrochemical activation treatment on the silicon-coated electrode plate, so that the crystalline silicon material on the silicon-coated electrode plate is subjected to partial non-crystallization transformation after being activated. The electrochemical treatment method for partially amorphizing the crystalline silicon provided by the invention has the advantages of simple process and low cost, and avoids the severe preparation conditions and high cost which are usually used for preparing the amorphous silicon by a vapor deposition method. The part of the amorphous silicon negative electrode material prepared by the method shows high capacity and good cycle performance when applied to the sodium ion battery.

Description

Silicon negative electrode material of sodium ion battery
Technical Field
The invention relates to a sodium ion battery, in particular to a modified silicon negative electrode material for the sodium ion battery.
Background
Currently, human beings face the double dilemma of exhaustion of fossil energy and environmental pollution, and therefore, it is necessary to develop clean renewable energy to reduce the dependence on fossil energy. The secondary battery has high energy density, high conversion efficiency and high flexibility, and is one of the current research hotspots. The secondary batteries that are currently most promising in development are mainly lithium ion batteries and sodium ion batteries. Silicon, as the material with the highest theoretical lithium storage capacity, has been successfully used in commercial lithium ion batteries. Sodium has the characteristics of wide crustal distribution and low cost, and a sodium ion battery is one of the current research hotspots as a powerful candidate in the technical field of large-scale energy storage. However, silicon has been considered to be inactive for sodium storage. Relevant theoretical calculations show that sodium ions are hardly embedded in crystalline silicon materials by consuming a large amount of energy, while the embedding in amorphous silicon consumes much less energy than crystalline silicon, so that the storage of sodium in amorphous silicon is promising. It was calculated that a single amorphous Si could store 0.76 Na, corresponding to a theoretical capacity of 725 mAh/g.
In recent years, there has been experimental study on sodium storage of silicon materials, in which silicon as an active material is substantially partially amorphous or entirely amorphous, confirming the sodium storage activity of amorphous silicon. The prior methods for preparing amorphous silicon materials for storing sodium reported in the literature comprise a thermal plasma chemical vapor deposition method for preparing partial amorphous nano particles, an electron beam evaporation method for preparing amorphous silicon films, a template method for preparing crystalline silicon core/amorphous silicon shell structure nanowires, a vapor deposition method for preparing coiled amorphous films by combining a strain release winding technology and the like, and most of the methods are complex in process and harsh in conditions. Therefore, the method for preparing the partial amorphous silicon negative electrode material and realizing reversible sodium storage, which is simple in process, easy to operate and low in cost, is significant.
Disclosure of Invention
The invention aims to provide a novel electrochemical preparation method for obtaining a silicon negative electrode material of a sodium-ion battery.
According to a first aspect of the present invention, there is provided a process for the activation treatment or modification of a silicon electrode (anode) material for a sodium ion battery, comprising:
mixing crystalline nano-silicon, conductive carbon black and polyvinylidene fluoride to form slurry, wherein the mass ratio of the silicon to the carbon black to the polyvinylidene fluoride is (6-8): (1-3): 1;
coating the slurry on a metal substrate, drying and cutting to form a silicon-coated electrode plate;
assembling a sodium ion battery using metallic sodium as a battery negative electrode and the above silicon-coated electrode sheet as a positive electrode under an inert atmosphere, wherein the electrolyte comprises a sodium salt and an organic solvent, the organic solvent is selected from at least one of Ethylene Carbonate (EC), diethyl carbonate (DEC) and diethylene glycol dimethyl ether (DEGDME), and the sodium salt is selected from sodium hexafluorophosphate (NaPF)6) Sodium perchlorate (NaClO)4) NaTFSI, NaFSI and Na2SO3At least one of (1), the concentration of sodium salt is 0.1-2 mol/L;
and performing electrochemical activation treatment on the silicon coated electrode plate by using the battery, wherein the constant-current charge-discharge current density of the electrochemical activation treatment is 1A/g-40A/g, and the activation cycle frequency is 20-10000 weeks, so that the crystalline silicon material on the silicon coated electrode plate is subjected to partial non-crystallization transformation after being activated.
According to preferred embodiments of the invention: the grain diameter of the nano silicon can be 50-200 nm; the organic solvent can be diethylene glycol dimethyl ether, and the sodium salt can be sodium hexafluorophosphate; the constant current density of the electrochemical activation treatment can be 6A/g-35A/g, more preferably 25A/g-35A/g, and the frequency of the activation cycle is 500-1000 weeks, more preferably 200-800 weeks.
According to a second aspect of the present invention, there is provided a silicon negative electrode for sodium ion batteries, using a silicon-coated electrode sheet modified according to the above method, wherein the degree of amorphousness of silicon is 10% to 80%.
The inventors have unexpectedly discovered that crystalline silicon undergoes a partial amorphization transition during constant current charge-discharge cycling. The invention obtains the partially amorphous silicon material by using a novel electrochemical treatment process of constant current charging and discharging with high current density for a certain cycle for the crystalline silicon particles. The prepared silicon material realizes reversible deintercalation of sodium ions in the material, further realizes high-capacity and high-rate charge and discharge of the battery, and improves the cycle stability of the battery.
The invention adopts a simple and effective electrochemical treatment method of the electrode material to change the crystalline state characteristics of the silicon cathode material of the sodium-ion battery, the prepared silicon cathode material is nano-scale partial amorphous particles, the specific surface area of the material is large, the contact area of the electrode material and electrolyte is large, the sodium ion diffusion path is shortened, and the transmission of sodium ions and the generation of electrode reaction are facilitated. In addition, in the cathode material prepared by the invention, the crystalline silicon part improves the electronic conductivity of the material, the amorphous silicon part provides reversible sodium storage capacity, and the cathode material can realize reversible sodium storage when being applied to a sodium ion battery, and has high capacity and good cycle performance.
The electrochemical treatment method for partially amorphizing the crystalline silicon provided by the invention has the advantages of simple process and low cost, and avoids the severe preparation conditions and high cost which are usually used for preparing the amorphous silicon by a vapor deposition method. The part of the amorphous silicon negative electrode material prepared by the method shows high capacity and good cycle performance when applied to the sodium ion battery.
Drawings
Fig. 1 is a XRD comparison graph of the silicon negative electrode material S1 obtained in example 1 of the present invention and the crystalline silicon material D1 in comparative example 1;
fig. 2 is a TEM image of a silicon anode material S1 obtained in example 1 of the present invention;
FIG. 3 is a TEM image of crystalline silicon material D1 in comparative example 1 according to the present invention;
FIG. 4 is a graph showing the cycle performance of the cell prepared in example 1 of the present invention after 500 cycles of 30A/g current density for 500 cycles of electrochemical amorphization at a voltage range of 0.01 to 3V and 50 cycles of electrochemical amorphization at a current density of 300mA/g at a voltage range of 0.01 to 3V (the first cycle of this low current cycle is taken as the first cycle of the cell cycle).
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
In the present invention, the crystalline silicon material is an unprocessed commercial silicon material conventionally used in the art, and is a crystalline structure, and the particle size of the silicon material commonly used comprises a nanometer scale and a micron scale. In the invention, the adopted crystalline silicon material has the particle size of nano grade preferably, the particle size of nano grade preferably is 50-200nm, the specific surface area of nano grade particles is large, the contact wettability with electrolyte is better, the reactive active sites are increased, and the reversible deintercalation of sodium ions is facilitated.
In the present invention, the raw silicon material is first made into an electrode coating material, which is assembled into a sodium ion battery. The composition of the electrode coating material may be in a manner conventional in the art, for example, the electrode coating material may include: raw silicon material, conductive carbon black and polyvinylidene fluoride binder. In the invention, the mass ratio of the original silicon material, the conductive carbon black and the polyvinylidene fluoride binder is preferably 8: 1: 1.
in the present invention, the sodium salt concentration is preferably 0.5 to 1mol/L, more preferably 0.5 mol/L.
In the present invention, the separator of the sodium ion battery is not particularly limited, and may be a separator of a sodium ion battery that is conventional in the art, such as a glass fiber separator with the brand name CAT 1822-047.
In the present invention, the battery type of the sodium ion battery is not particularly limited, and may be a battery case of a sodium ion battery that is conventional in the art, such as a CR2025 button battery.
In the invention, the current density of the adopted electrochemical activation treatment is 1A/g-40A/g, preferably 6A/g-35A/g, and more preferably 25A/g-35A/g, and the activation current density obviously influences the amorphous proportion, thereby influencing the electrochemical performance of the electrode material.
In the invention, the activation cycle of the electrochemical activation treatment is 20-10000 weeks, preferably 500-1000 weeks, and more preferably 200-800 weeks, and the activation cycle is too short to achieve the ideal activation effect, and too long activation cycle is likely to cause more side reactions, possibly causing the active material to fall off.
According to the invention, the amorphous degree of the prepared partially amorphous silicon material is 10-80%, preferably the amorphous degree of the prepared partially amorphous silicon material is 10-40%, and further preferably the amorphous proportion of the prepared partially amorphous silicon material is 20-30%.
In the invention, the amorphous proportion represents the ratio of the volume of amorphous silicon in the prepared silicon material to the volume of the whole silicon material. The amorphous proportion can be measured by combining Raman test and an amorphous proportion calculation formula. The amorphous proportion calculation formula is as follows:
the crystal proportion is Ic/(Ic + y Ia). times.100%
Amorphous ratio of 100% -crystal ratio
Wherein Ic is the crystalline silicon peak intensity value in the Raman test, Ia is the amorphous silicon peak intensity value in the Raman test, and y is a parameter related to the grain size.
According to the invention, the amorphization of the silicon material takes place both at the surface of the crystal and within the crystal.
The present invention will be described in detail below by way of examples.
The following examples are described by way of sodium ion batteries.
In the following examples, a Rigaku DMAX2400 type X-ray diffractometer was used for X-ray diffraction testing to characterize the structural morphology of the silicon material; observing the microscopic crystal structure of the material by adopting a Tecnai G2F 30S-TWIN type transmission electron microscope; and testing the electrochemical performance of the material by using a LAND CT2001A tester.
Example 1
(1) Mixing 0.12g of original crystalline silicon (nanoscale, ball diameter of 50-200nm, commercially available), 0.015g of conductive carbon black and 300 mu L of polyvinylidene fluoride (N-methyl pyrrolidone solution, 5% of mass fraction), grinding into slurry, coating the slurry on a copper foil, drying in vacuum at 120 ℃ for 12h, cutting to obtain a circular electrode plate with the diameter of 11mm, obtaining a coated electrode material as a battery anode, taking metal sodium as a battery cathode, and using 0.5mol/L of sodium hexafluorophosphate (NaPF)6) The diethylene glycol dimethyl ether (DEGDME) is used as electrolyte, the battery diaphragm is a CAT No.1822-047 glass fiber diaphragm, and the battery diaphragm is assembled into a CR2025 button battery under the argon atmosphere.
(2) And (2) standing the battery obtained in the step (1) for 12 hours, and then performing high-current-density constant-current charging and discharging on a LAND CT2001A tester (blue electronics, Inc., Wuhan city), wherein the current density is 30A/g, and the cycle frequency is 500 weeks, so that the partially amorphous Si electrode material S1 and the battery after electrochemical activation treatment are obtained.
XRD and TEM test analyses were performed on the prepared partially amorphous Si anode material S1, and the results are shown in fig. 1 and fig. 2, respectively. From the XRD spectrum, after undergoing a large current density charge-discharge cycle, the diffraction peak intensity of crystalline Si is significantly weakened, and partial amorphization transformation may occur. According to TEM results, after high-current circulation, the original crystalline silicon spherical morphology is damaged, an obvious amorphous region can be seen under high resolution, but dispersed lattice fringes also exist inside, and the inside and the surface of particles are both amorphized to a certain degree and only partially amorphous.
Performing Raman analysis on the prepared partial amorphous Si electrode, wherein the Raman analysis result is 520cm-1Where crystalline Si appears, at 470-490cm-1The characteristic peak of amorphous Si appears, and the display electrode material contains both amorphous Si and crystalline Si, which proves that the large-current charge-discharge energy enables part of crystalline silicon particles to be converted into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 2
(1) Mixing 0.12g of original crystalline silicon (nanoscale, ball diameter of 50-200nm, commercially available), 0.015g of conductive carbon black and 300 mu L of polyvinylidene fluoride (N-methyl pyrrolidone solution, 5 wt.%), grinding into slurry, coating the slurry on a copper foil, drying in vacuum at 120 ℃ for 12h, cutting to obtain a circular electrode plate with the diameter of 11mm, obtaining a coated electrode material as a battery anode, taking metal sodium as a battery cathode, and using 0.5mol/L of sodium hexafluorophosphate (NaPF)6) The diethylene glycol dimethyl ether (DEGDME) is used as electrolyte, the battery diaphragm is a CAT No.1822-047 glass fiber diaphragm, and the battery diaphragm is assembled into a CR2025 button battery under the argon atmosphere.
(2) And (2) standing the battery obtained in the step (1) for 12 hours, and then performing high-current-density constant-current charging and discharging on a LAND CT2001A tester (blue electronics, Inc., Wuhan city), wherein the current density is 6A/g, and the cycle frequency is 500 weeks, so that the part of amorphous Si electrode material S2 and the battery after electrochemical activation treatment are obtained.
XRD and TEM test analysis is carried out on the prepared partially amorphous Si anode material S2. From the XRD pattern, after the charge-discharge cycle with the current density of 6A/g, the diffraction peak intensity of crystalline Si is weakened, and partial amorphous transformation is possibly generated. According to TEM results, the original crystalline silicon spherical morphology is basically maintained after high-current circulation, an unobvious amorphous region is seen at high resolution, massive lattice stripes also exist in the amorphous region, the surface of particles is amorphized to a certain degree, only a small part of particles are amorphous, and the result proves that charging and discharging energy at the current density of 6A/g enables part of crystalline silicon particles to be converted into amorphous silicon, but the amorphous content is low.
Raman analysis is carried out on the prepared partial amorphous Si electrode, the Raman analysis result shows that crystalline Si and characteristic peaks of the amorphous Si exist, the amorphous Si and the crystalline Si exist in the electrode material, and the fact that the large-current charge-discharge energy enables the partial crystalline silicon particles to be converted into the amorphous silicon is proved.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 3
(1) Mixing 0.12g of original crystalline silicon (nanoscale, ball diameter of 50-200nm, commercially available), 0.015g of conductive carbon black and 300 mu L of polyvinylidene fluoride (N-methyl pyrrolidone solution, 5 wt.%), grinding into slurry, coating the slurry on a copper foil, drying in vacuum at 120 ℃ for 12h, cutting to obtain a circular electrode plate with the diameter of 11mm, obtaining a coated electrode material as a battery anode, taking metal sodium as a battery cathode, and using 0.5mol/L of sodium hexafluorophosphate (NaPF)6) The diethylene glycol dimethyl ether (DEGDME) is used as electrolyte, the battery diaphragm is a CAT No.1822-047 glass fiber diaphragm, and the battery diaphragm is assembled into a CR2025 button battery under the argon atmosphere.
(2) And (2) standing the battery obtained in the step (1) for 12 hours, and then performing high-current-density constant-current charging and discharging on a LAND CT2001A tester (blue electronics, Inc., Wuhan city), wherein the current density is 9A/g, and the cycle frequency is 500 weeks, so that the part of amorphous Si electrode material S3 and the battery after electrochemical activation treatment are obtained.
XRD and TEM test analysis is carried out on the prepared partially amorphous Si anode material S3. From the XRD pattern, after the charge-discharge cycle with the current density of 9A/g, the diffraction peak intensity of crystalline Si is weakened, and partial amorphous transformation is possibly generated. According to TEM results, the original crystalline silicon spherical morphology is basically maintained after high-current circulation, a small number of obvious amorphous regions are seen at high resolution, large crystal lattice stripes exist in the interior, the surface of particles is amorphized to a certain degree, and the particles are only partially amorphous, so that the charging and discharging energy at the current density of 9A/g enables part of crystalline silicon particles to be converted into amorphous silicon, but the amorphous part is less.
Raman analysis is carried out on the prepared partial amorphous Si electrode, the Raman analysis result shows that crystalline Si and characteristic peaks of the amorphous Si exist, the amorphous Si and the crystalline Si exist in the electrode material, and the fact that the large-current charge-discharge energy enables the partial crystalline silicon particles to be converted into the amorphous silicon is proved.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 4
(1) Mixing 0.12g of original crystalline silicon (nanoscale, ball diameter of 50-200nm, commercially available), 0.015g of conductive carbon black and 300 mu L of polyvinylidene fluoride (N-methyl pyrrolidone solution, 5 wt.%), grinding into slurry, coating the slurry on a copper foil, drying in vacuum at 120 ℃ for 12h, cutting to obtain a circular electrode plate with the diameter of 11mm, obtaining a coated electrode material as a battery anode, taking metal sodium as a battery cathode, and using 0.5mol/L of sodium hexafluorophosphate (NaPF)6) The diethylene glycol dimethyl ether (DEGDME) is used as electrolyte, the battery diaphragm is a CAT No.1822-047 glass fiber diaphragm, and the battery diaphragm is assembled into a CR2025 button battery under the argon atmosphere.
(2) And (2) standing the battery obtained in the step (1) for 12 hours, and then performing high-current-density constant-current charging and discharging on a LAND CT2001A tester (blue electronics, Inc., Wuhan city), wherein the current density is 15A/g, and the cycle frequency is 500 weeks, so that the part of amorphous Si electrode material S4 and the battery after electrochemical activation treatment are obtained.
XRD and TEM test analysis is carried out on the prepared partially amorphous Si anode material S4. From the XRD pattern, after the charge-discharge cycle of 15A/g current density for 500 weeks, the diffraction peak of crystalline Si is weakened, and partial amorphous transformation may occur. According to TEM results, after large-current circulation, the spherical shape of the original crystalline silicon is slightly damaged, more obvious amorphous regions are seen at high resolution, dispersed fine lattice stripes exist in the crystalline silicon, the surface and the inside of particles are amorphized to a certain degree, and only part of the particles are amorphous, so that the charging and discharging energy at the current density of 15A/g enables part of crystalline silicon particles to be converted into amorphous silicon.
Raman analysis is carried out on the prepared partial amorphous Si electrode, the Raman analysis result shows that crystalline Si and characteristic peaks of the amorphous Si exist, the amorphous Si and the crystalline Si exist in the electrode material, and the fact that the large-current charge-discharge energy enables the partial crystalline silicon particles to be converted into the amorphous silicon is proved.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 5
The battery assembly method of example 2 was followed, except that in step (2), the current density was 10A/g, and the cycle frequency was 50 weeks, to obtain a partially amorphous Si electrode material S5 after electrochemical activation treatment, and a battery.
XRD, TEM and Raman test analysis are carried out on the prepared partially amorphous Si anode material S5. From the XRD pattern, after the charge-discharge cycle of 10A/g current density for 50 weeks, the diffraction peak intensity of crystalline Si is slightly weakened, and a small part of amorphous transformation may occur. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 6
The battery assembly method of example 2 was followed, except that in step (2), the current density was 10A/g, and the cycle frequency was 100 weeks, to obtain a partially amorphous Si electrode material S6 after electrochemical activation treatment, and a battery.
XRD, TEM and Raman test analysis are carried out on the prepared partially amorphous Si anode material S5. From the XRD pattern, after the charge-discharge cycle of 10A/g current density is carried out for 100 weeks, the diffraction peak intensity of crystalline Si is weakened, and a small part of amorphous transformation is possibly generated. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 7
The battery assembly method of example 2 was followed, except that in step (2), the current density was 10A/g, and the cycle frequency was 200 weeks, to obtain a partially amorphous Si electrode material S7 after electrochemical activation treatment, and a battery.
XRD, TEM and Raman test analysis are carried out on the prepared partially amorphous Si anode material S7. From the XRD pattern, after the charge-discharge cycle of 10A/g current density for 200 weeks, the diffraction peak of crystalline Si is weakened, and a small part of amorphous transformation may occur. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 8
The battery assembly method of example 2 was followed, except that in step (2), the current density was 10A/g, and the cycle frequency was 800 weeks, to obtain a partially amorphous Si electrode material S8 after electrochemical activation treatment, and a battery.
XRD, TEM and Raman test analysis are carried out on the prepared partially amorphous Si anode material S8. From the XRD pattern, after the charge-discharge cycle of 10A/g current density is carried out for 800 weeks, the diffraction peak of crystalline Si is weakened, and a small part of amorphous transformation may occur. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 9
The battery assembly method of example 2 was followed except that in step (2), the current density was 10A/g and the cycle frequency was 1000 weeks, to obtain a partially amorphous Si electrode material S9 after electrochemical activation treatment and a battery.
XRD, TEM and Raman test analysis are carried out on the prepared partially amorphous Si anode material S5. From the XRD pattern, after the crystal Si undergoes a charge-discharge cycle of 10A/g current density for 1000 weeks, the diffraction peak of the crystal Si is weakened, and a small part of amorphous transformation may occur. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Example 10
The battery assembly method of example 1 was followed except that in step (2), the current density was 10A/g and the cycle frequency was 10000 weeks, to obtain a partially amorphous Si electrode material S10 after electrochemical activation treatment and a battery.
XRD, TEM and Raman test analyses were performed on the Si anode material D4. From the XRD spectrum, after undergoing a large current density charge-discharge cycle, the diffraction peak intensity of crystalline Si is significantly weakened, and partial amorphization transformation may occur. According to TEM results, after high-current circulation, the original crystalline silicon spherical morphology is damaged, an obvious amorphous region can be seen under high resolution, but dispersed lattice fringes also exist inside, and the inside and the surface of particles are both amorphized to a certain degree and only partially amorphous.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Comparative example 1
A battery was assembled in the same manner as in example 1, except that the electrochemical treatment for constant current charging and discharging at a large current density was not performed, and Si electrode material D1 and a battery were obtained without the electrochemical activation treatment.
XRD, TEM and Raman test analyses were performed on the Si anode material D1. From the XRD pattern, the electrode material without electrochemical treatment showed good crystalline properties. From the TEM results (as shown in FIG. 3), the original crystalline silicon spherical morphology is kept intact, no amorphous region is seen inside at high resolution, only a silicon oxide layer of 1-2nm is observed on the surface, and the material shows a good crystalline structure. Only the characteristic peak of the crystalline Si appears in the Raman analysis result, which shows that only the crystalline Si exists in the electrode material.
Comparative example 2
The cells were assembled and treated by electrochemical treatment according to the procedure of example 2, except that 1mol/L sodium hexafluorophosphate (NaPF) was used in the step (1)6) The mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) (EC: DEC in a volume ratio of 1:1) was used as an electrolytic solution to obtain an Si electrode material D2 and a battery.
XRD, TEM and Raman test analyses were performed on the Si anode material D2. From the XRD pattern, the electrode material without electrochemical treatment showed good crystalline properties. The XRD pattern shows that after the charge-discharge cycle of 30A/g current density is carried out for 500 weeks, the diffraction peak of crystalline Si is weakened, and a small part of amorphous transformation is possible to occur. The TEM high resolution image can observe a distinct amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Comparative example 3
The cell was assembled and treated electrochemically as in example 2, except that in step (1), micron-sized crystalline silicon particles having a particle size of 50-100 μm were used as the primary coated electrode material to give Si electrode material D3 and a cell.
TEM and Raman test analysis was performed on the Si anode material D3. The TEM high resolution image can observe a small amount of amorphous region, demonstrating the formation of amorphous Si. The Raman analysis result shows characteristic peaks of crystalline Si and amorphous Si, and the display electrode material shows that both the amorphous Si and the crystalline Si exist, so that the high-current charge-discharge energy is proved to convert part of crystalline silicon particles into amorphous silicon.
The results of calculating the amorphous ratio in the partially amorphous Si electrode material are shown in table 1.
Test example 1
(1) The batteries obtained in examples 1 to 10 and comparative examples 1 to 3 were subjected to constant current charge and discharge test with a charge and discharge current density of 300mA/g on a LAND CT2001A tester, and the first week of this small current cycle was taken as the first week of battery cycle. The first charge specific capacity (mAh/g) and the charge specific capacity (mAh/g) after 50 cycles of charge and discharge of the battery were measured, respectively, and the capacity retention rate after 50 cycles of charge and discharge (i.e., the discharge specific capacity after 50 cycles of charge and discharge divided by the first discharge specific capacity × 100%) was calculated, and the results are listed in table 1.
(2) Taking example 1 as an example, the electrochemical activation process of the prepared sodium-ion battery for five hundred weeks and the cycle performance of the battery after activation under the voltage of 0.01-3V and the current density of 300mA/g for 50 weeks are recorded in fig. 4, and as can be seen from fig. 4, the battery has good cycle stability under the voltage of 0.01-3V and the current density of 300 mA/g.
TABLE 1
Figure BDA0001821003470000171
As can be seen from the comparison of examples 1 to 4, as the initial current density of the electrochemical treatment increases, the proportion of amorphous Si in the material gradually increases, the specific charge capacity of the electrode material gradually increases, and the capacity retention rate is high. The electrochemical pretreatment method adopted by the invention can realize the amorphization of the crystalline silicon and can ensure that the prepared electrode can successfully store sodium reversibly.
It can be seen from the comparison of examples 5 to 10 that the increase of the cycle frequency of the electrochemical pretreatment within the range of 50 to 1000 cycles has little influence on the sodium storage performance of the electrode material, and the charging specific capacity and the capacity retention rate of the material are relatively stable, but if the cycle process is too long, the capacity decays violently, and the active material may fall off.
By comparing example 1 with comparative example 1, it can be seen that the electrochemical pretreatment method produces a significant activation of crystalline Si. The sodium storage capacity of crystalline Si is basically negligible, and the Si material after electrochemical treatment has higher reversible specific capacity of sodium storage after partial amorphous transformation.
By comparing example 2 with comparative example 2, it can be seen that the ether electrolyte can be better matched with the partially amorphous Si negative electrode material than the ester electrolyte.
Comparing example 2 with comparative example 3, it can be seen that the size of the original crystalline silicon particles significantly affects the electrochemical sodium storage performance, and the nano-scale crystalline silicon particles can achieve a higher sodium storage capacity after electrochemical treatment.
The method for electrochemically pretreating and activating the crystal Si can successfully prepare a part of amorphous Si electrode materials, and can greatly improve the sodium storage performance of the materials compared with the original crystalline silicon, and realize higher sodium storage capacity, stable cycle performance and coulombic efficiency when being applied to the sodium ion battery. In addition, the electrochemical treatment method provided by the invention has the advantages of simple process, easy operation and low cost, and avoids the harsh preparation conditions of the conventional method and the generated high cost.

Claims (3)

1. An activation treatment method for a silicon electrode material of a sodium-ion battery comprises the following steps:
mixing crystalline nano-silicon with the particle size of 50-200nm with conductive carbon black and polyvinylidene fluoride to form slurry, wherein the mass ratio of the silicon to the carbon black to the polyvinylidene fluoride is 8: 1: 1;
coating the slurry on a metal substrate, drying and cutting to form a silicon-coated electrode plate;
assembling a sodium ion battery using metallic sodium as a battery negative electrode and the above silicon-coated electrode sheet as a positive electrode under an inert atmosphere, wherein the electrolyte comprises a sodium salt and an organic solvent, the organic solvent is selected from at least one of Ethylene Carbonate (EC), diethyl carbonate (DEC) and diethylene glycol dimethyl ether (DEGDME), and the sodium salt is selected from sodium hexafluorophosphate (NaPF)6) Sodium perchlorate (NaClO)4) NaTFSI, NaFSI and Na2SO3At least one of (1), the concentration of sodium salt is 0.1-2 mol/L;
and performing electrochemical activation treatment on the silicon coated electrode plate by using the battery, wherein the constant-current charge-discharge current density of the electrochemical activation treatment is 25-35A/g, and the activation cycle frequency is 200-800 weeks, so that the crystalline silicon material on the silicon coated electrode plate is subjected to partial non-crystallization transformation after being activated.
2. The activation processing method according to claim 1, wherein the organic solvent is diethylene glycol dimethyl ether, and the sodium salt is sodium hexafluorophosphate.
3. A silicon negative electrode for sodium ion batteries, using a silicon-coated electrode sheet activated according to the method of claim 1 or 2, wherein the degree of amorphousness of the silicon is between 10% and 80%.
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