A method for supplementing sodium in a sodium-ion battery and a sodium-ion battery after sodium supplementation

Abstract

The present invention provides a sodium supplementation method for a sodium-ion battery and a sodium-ion battery after sodium supplementation, belonging to the technical field of sodium-ion batteries. The sodium supplementation method includes the following steps: mixing a stabilizer, a sodium salt, and a solvent to obtain a sodium supplementation solution, and dividing the sodium supplementation solution into two portions; mixing a coal-based hard carbon negative electrode material, a conductive adhesive, the first portion of the sodium supplementation solution, and a binder to obtain a mixed slurry, coating the mixed slurry on a current collector to obtain a negative electrode sheet; performing a first cold roll pressing on the negative electrode sheet, then spraying the second portion of the sodium supplementation solution, and subsequently performing a second hot roll pressing to obtain a sodium-supplemented negative electrode sheet; assembling the sodium-supplemented negative electrode sheet with a positive electrode sheet, an electrolyte, and a separator, and then performing pre-sealing aging and formation treatment to form a package. The present invention solves the defects of performance attenuation and low initial efficiency caused by many impurities in the coal-based hard carbon negative electrode material, optimizes the structure of the electrode sheet and the ion transport channel, improves the capacity in the plateau region and the slope region, and also improves the energy density and service life of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a method for supplementing sodium in a sodium-ion battery and a sodium-ion battery after sodium supplementation. Background Art

[0002] The energy storage mechanism of sodium-ion batteries is similar to that of lithium-ion batteries, and sodium resources are rich in reserves and low in cost. Therefore, it is expected to replace lithium-ion batteries and be widely used in the field of large-scale energy storage.

[0003] Hard carbon materials are considered to be a commercially valuable anode material for sodium-ion batteries. However, the raw coal used in the preparation contains impurities such as ash. Although ash removal can be achieved by methods such as pickling, it is difficult to completely remove the impurities. The remaining impurities may have an adverse effect on the sodium storage performance of the battery, and also cause the materials after pyrolysis to carbonize to vary in terms of graphitization degree, carbon layer spacing, and surface chemical composition, thus bringing difficulties to the optimization of electrochemical performance. Moreover, during the long-term cyclic use of the battery, the performance stability of the coal-based hard carbon anode also needs to be improved.

[0004] For this reason, researchers have proposed a pre-sodiation method to solve the above problems. Currently, the common pre-sodiation methods for sodium-ion batteries mainly include the following several types: in-situ doping pre-sodiation, electrochemical pre-sodiation, chemical pre-sodiation, and contact pre-sodiation. Among them, the contact pre-sodiation method directly contacts the metal sodium sheet with the negative electrode plate of the battery to implement pre-sodiation, wets the interface between the sodium sheet and the negative electrode plate with the electrolyte, and controls the contact pressure between the sodium sheet and the negative electrode plate by applying an external force, thereby controlling the depth and uniformity of pre-sodiation. This method is beneficial to controlling the pre-sodiation degree of the electrode, but its production process conditions are relatively high and it is not easy to scale up.

[0005] Therefore, how to effectively avoid the defects of material performance attenuation and low initial efficiency caused by many impurities in hard carbon materials, optimize the electrode structure and ion transport channels, further improve the capacity in the plateau region and the slope region, and improve the energy density and service life of the battery are technical problems that need to be solved urgently. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a sodium supplementation method for a sodium-ion battery and the sodium-ion battery after sodium supplementation. Starting from the perspective of battery systematic design, the present invention adopts a two-step sodium supplementation method for coordinated cooperation. By means of slurry dispersion, sodium salt and coal-based hard carbon negative electrode material are dispersed evenly to increase the plateau capacity and stabilize the potential in the plateau region. At the same time, by spraying the sodium supplementation solution onto the surface of the electrode sheet, the compactness of the SEI film is increased, thereby reducing the loss of sodium ions in the positive electrode and electrolyte, improving the charge and discharge characteristics in the slope region, optimizing the transmission path and kinetic process of sodium ions in the coal-based hard carbon negative electrode material, increasing the ion diffusion rate in the slope region, and making the charge and discharge of the sodium-ion battery in the slope region faster and more efficient. Moreover, the two-step sodium supplementation method can also avoid the problems of electrode structure damage and performance degradation caused by excessive pre-sodiation.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides a sodium supplementation method for a sodium-ion battery, and the sodium supplementation method includes the following steps:

[0009] (1) Mix a stabilizer, sodium salt and a solvent to obtain a sodium supplementation solution, and divide the sodium supplementation solution into two portions.

[0010] (2) Mix a coal-based hard carbon negative electrode material, a conductive adhesive, the first portion of the sodium supplementation solution and a binder to obtain a mixed slurry, and then coat the mixed slurry on a current collector to obtain a first-time sodium-supplemented negative electrode sheet.

[0011] (3) Perform a first cold rolling on the first-time sodium-supplemented negative electrode sheet, then spray the second portion of the sodium supplementation solution on the surface of the negative electrode sheet, and then perform a second hot rolling to obtain a second-time sodium-supplemented negative electrode sheet.

[0012] (4) Assemble the second-time sodium-supplemented negative electrode sheet with a positive electrode sheet, an electrolyte and a separator, and then perform pre-sealing aging and formation treatment to package and form.

[0013] Starting from the perspective of battery systematic design, the present invention adopts a two-step sodium supplementation method for coordinated cooperation. By means of slurry dispersion, sodium salt and coal-based hard carbon negative electrode material are dispersed evenly to increase the plateau capacity and stabilize the potential in the plateau region. At the same time, by spraying the sodium supplementation solution onto the surface of the electrode sheet, the compactness of the SEI film is increased, thereby reducing the loss of sodium ions in the positive electrode and electrolyte, improving the charge and discharge characteristics in the slope region, optimizing the transmission path and kinetic process of sodium ions in the coal-based hard carbon negative electrode material, increasing the ion diffusion rate in the slope region, and making the charge and discharge of the sodium-ion battery in the slope region faster and more efficient. Moreover, the two-step sodium supplementation method can also avoid the problems of electrode structure damage and performance degradation caused by excessive pre-sodiation.

[0014] In the present invention, through the rolling process, the coal-based hard carbon anode material and the sodium salt are more closely packed, increasing the density of the electrode, improving the conductivity of the electrode, optimizing the structure and porosity of the electrode. At the same time, when the subsequent formation process is carried out, the ionized sodium ions can play a role both inside and on the surface of the electrode plate, making the capacity more stable and forming less "dead sodium".

[0015] The present invention adopts two-step sodium supplementation to avoid the destruction of the electrode structure and the decline in performance caused by excessive pre-sodiation.

[0016] Preferably, the stabilizer in step (1) includes any one or a combination of at least two of vinylene carbonate, ethylene carbonate, propylene carbonate, fluorinated ethylene carbonate, 1,3-propane sultone or ethylene sulfite.

[0017] Preferably, the sodium salt in step (1) includes any one or a combination of at least two of sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium hexafluorophosphate or boron-containing sodium salt.

[0018] Preferably, the solvent in step (1) includes water.

[0019] Preferably, in terms of mass content, the components in the sodium supplementation solution in step (1) include: 0.5-30% of the stabilizer, for example, it can be 0.5%, 1%, 5%, 10%, 15%, 20%, 25% or 30%, etc., 0.5-70% of the sodium salt, for example, it can be 0.5%, 1%, 10%, 20%, 30%, 40%, 50%, 60% or 70%, etc., and the balance is the solvent.

[0020] In the present invention, if the content of the stabilizer is too high, it will lead to slow ion migration and a decrease in conductivity, thus affecting the battery rate performance, and will also cause an increase in battery side reactions and a deterioration in cycle performance; if the content of the stabilizer is too low, it will lead to poor battery thermal stability and storage performance, and is prone to safety problems. If the content of the sodium salt is too high, it will lead to accelerated growth of negative electrode dendrites causing internal short circuits, and will also cause the electrode plate to expand, gas generation inside the battery leading to battery deformation, resulting in an unstable SEI film, an increase in side reactions, and situations such as low energy density and poor cycle performance.

[0021] Preferably, in terms of mass content, the components in the sodium supplementation solution in step (1) include: 0.5-5% of the stabilizer, 0.5-20% of the sodium salt, and the balance is the solvent.

[0022] Preferably, the raw material for preparing the coal-based hard carbon anode material in step (2) is coal-based substances.

[0023] Preferably, the coal-based substances include any one or a combination of at least two of anthracite, lean coal, meager coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long flame coal or lignite, and preferably long flame coal.

[0024] Preferably, the conductive adhesive in step (2) comprises a conductive agent, a thickening agent and a solvent.

[0025] Preferably, the conductive agent comprises any one or a combination of at least two of carbon black, acetylene black, graphene or carbon nanotubes.

[0026] Preferably, the thickening agent comprises sodium carboxymethyl cellulose.

[0027] Preferably, based on the total mass of the conductive adhesive, the mass content of the conductive agent is 1-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., and the mass content of the thickening agent is 0.5-2%, for example, it can be 0.5%, 1%, 1.5% or 2%, etc.

[0028] Preferably, the solid content of the mixed slurry in step (2) is 30-70 wt%, for example, it can be 30 wt%, 40 wt%, 50 wt%, 60 wt% or 70 wt%, etc.

[0029] Preferably, based on the total weight of the mixed slurry in step (2), the content of the coal-based hard carbon anode material is 70-96%, for example, it can be 70%, 75%, 80%, 85%, 90%, 95% or 96%, etc., the content of the conductive agent is 0.5-20%, for example, it can be 0.5%, 1%, 5%, 10%, 15% or 20%, etc., the content of the thickening agent is 0.5-5%, for example, it can be 0.5%, 1%, 2%, 3%, 4% or 5%, etc., and the content of the binder is 0.5-10%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0030] Preferably, in the first sodium supplement solution in step (2), the mass of the stabilizer accounts for 0.5-5% of the mass of the solvent in the first sodium supplement solution, for example, it can be 0.5%, 1%, 2%, 3%, 4% or 5%, etc.

[0031] Preferably, in the first sodium supplement solution in step (2), the mass of the sodium salt accounts for 0.05-5% of the mass of the coal-based hard carbon anode material in the mixed slurry, for example, it can be 0.05%, 0.1%, 1%, 2%, 3%, 4% or 5%, etc.

[0032] Preferably, in step (3), the first cold roll pressing reaches 60-80% of the designed compaction density, for example, it can be 60%, 65%, 70%, 75% or 80%, etc.

[0033] Preferably, the pressure of the first cold roll pressing in step (3) is 1-100 MPa, for example, it can be 1 MPa, 5 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa or 100 MPa, etc., and the temperature is 20-35 °C, for example, it can be 20 °C, 22 °C, 24 °C, 26 °C, 28 °C, 30 °C, 32 °C, 34 °C or 35 °C, etc.

[0034] Preferably, the component contents of the second sodium supplement solution in step (3) are the same as those of the first sodium supplement solution in step (2).

[0035] It should be noted that when spraying the second sodium supplement solution, based on 0.5-500 mg of sodium salt per 1 kg of active material, the spraying amount and spraying rate of the second sodium supplement solution are confirmed according to this ratio, the surface loading of the coated electrode, the rolling and running speed of the belt, and the formula of the sodium supplement solution.

[0036] In the present invention, the spraying speed should match the designed surface loading of the electrode and the rolling and running speed of the belt. If the spraying rate is too low, the sodium content in the electrode will be low; if the spraying rate is too high, the sodium content in the local area of the electrode will be high, and the spraying speed is uneven, resulting in poor uniformity of the sodium supplement density of the electrode, and thus the battery performance varies.

[0037] Preferably, the pressure of the second hot roll pressing in step (3) is 1-50 MPa, for example, it can be 1 MPa, 5 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa or 50 MPa, etc., and the temperature is 50-150 °C, for example, it can be 50 °C, 75 °C, 100 °C, 125 °C or 150 °C, etc.

[0038] Preferably, the second hot roll pressing in step (3) is up to the designed compaction density.

[0039] Preferably, the positive electrode sheet in step (4) includes a current collector and a positive electrode active layer provided on one surface of the current collector.

[0040] It should be noted that the present invention does not limit the type of the positive electrode active layer. Exemplarily, the materials of the positive electrode active layer can be, for example, layered transition metal oxides, polyanion-type compounds or Prussian blue-based and other positive electrode materials. The current collector can be, for example, aluminum foil, etc.

[0041] Preferably, the time of the pre-sealing and aging in step (4) is 5-48 h, for example, it can be 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h, etc.

[0042] Preferably, the steps of the formation treatment in step (4) include primary formation and secondary formation.

[0043] Preferably, the pressure of the first formation is atmospheric pressure, and the temperature is 40 - 85°C, for example, it can be 40°C, 50°C, 60°C, 70°C, or 80°C, etc. It should be noted that atmospheric pressure refers to one atmosphere.

[0044] Preferably, the pressure of the second formation is 10 - 300 KPa, for example, it can be 10 KPa, 50 KPa, 100 KPa, 150 KPa, 200 KPa, 250 KPa, or 300 KPa, etc., and the temperature is 60 - 85°C, for example, it can be 60°C, 70°C, 80°C, or 85°C, etc.

[0045] Preferably, the sodium supplementation method includes the following steps:

[0046] (a) Mix a stabilizer, a sodium salt, and a solvent to prepare a sodium supplementation solution, and divide the sodium supplementation solution into two portions; each component in the sodium supplementation solution is calculated by mass content, including: 0.5 - 30% of the stabilizer, 0.5 - 70% of the sodium salt, and the balance is the solvent.

[0047] Mix a conductive agent, a thickening agent, and a solvent to prepare a conductive adhesive; based on the total mass of the conductive adhesive, the mass content of the conductive agent is 1 - 10%, and the mass content of the thickening agent is 0.5 - 2%.

[0048] (b) Stir and mix the coal-based hard carbon negative electrode material and the conductive adhesive, then add the first portion of the sodium supplementation solution and continue to stir and mix, and then add a binder and stir and mix and degas under vacuum to obtain a mixed slurry with a solid content of 30 - 70 wt%, and then coat the mixed slurry on a current collector aluminum foil, and dry to obtain a first sodium-supplemented negative electrode sheet.

[0049] Among them, based on the weight of the solid components in the mixed slurry, the content of the coal-based hard carbon negative electrode material is 70 - 96%, the content of the conductive agent is 0.5 - 20%, the content of the thickening agent is 0.5 - 5%, and the content of the binder is 0.5 - 10%; the mass of the stabilizer in the first portion of the sodium supplementation solution accounts for 0.5 - 5% of the mass of the solvent in the first portion of the sodium supplementation solution; the mass of the sodium salt in the first portion of the sodium supplementation solution accounts for 0.05 - 5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry.

[0050] (c) Cold roll the primary sodium-supplemented negative electrode sheet to 60-80% of the designed compaction density for the first time. The pressure of the first cold rolling is 1-100 MPa, and the temperature is 20-35 °C. Then, spray the second portion of sodium-supplemented solution on the surface of the negative electrode sheet. The component contents of the second portion of sodium-supplemented solution are the same as those of the first portion of sodium-supplemented solution. Subsequently, perform drying, and then perform secondary hot rolling to the designed compaction density. The pressure of the secondary hot rolling is 1-50 MPa, and the temperature is 50-150 °C to obtain the secondary sodium-supplemented negative electrode sheet.

[0051] (d) Assemble the secondary sodium-supplemented negative electrode sheet, the positive electrode sheet and the separator to obtain a dry battery cell, and then wind, die-cut, weld the tab and inject the electrolyte. Subsequently, perform pre-sealing aging for 5-48 h.

[0052] Then, perform the first formation of the aged battery cell in an atmospheric environment with low humidity (i.e., relative humidity less than 30%) to 50-95% SOC (for example, it can be 50% SOC, 55% SOC, 60% SOC, 65% SOC, 70% SOC, 75% SOC, 80% SOC, 85% SOC, 90% SOC or 95% SOC, etc.). The temperature is 40-85 °C. After vacuum exhaust, perform the second formation to 100% SOC. The pressure of the second formation is 10-300 KPa, and the temperature is 60-85 °C. The currents of the first formation and the second formation are both 0.01-0.5 C (for example, it can be 0.01 C, 0.1 C, 0.2 C, 0.3 C, 0.4 C or 0.5 C).

[0053] After the formation is completed, perform encapsulation and molding, and then discharge at a rate of 0.01-0.5 C (for example, it can be 0.01 C, 0.1 C, 0.2 C, 0.3 C, 0.4 C or 0.5 C) to 0% SOC to obtain the sodium-supplemented sodium-ion battery.

[0054] In the present invention, discharging to 0% SOC at a rate of 0.01-0.5 C can further optimize the sodium insertion / extraction channels and storage sites of the negative electrode, and improve the structural stability of the electrode sheet and the balance of the internal system of the battery.

[0055] In the second aspect, the present invention provides a sodium-supplemented sodium-ion battery, which is obtained by using the sodium-supplementing method as described in the first aspect.

[0056] It should be noted that the sodium-ion battery obtained in the present invention can be a battery assembled by any one of the processes such as button-type, bean-type battery and cylindrical winding, square winding, square stacking, soft-pack winding, soft-pack stacking, etc.

[0057] The numerical ranges described in the present invention include not only the above-listed point values, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the said range.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) Starting from the perspective of battery system design, the present invention adopts a two-step sodium supplementation method for coordinated cooperation. That is, through the slurry dispersion method, sodium salts and the coal-based hard carbon negative electrode material are evenly dispersed to increase the plateau capacity and stabilize the potential in the plateau region. Also, by spraying the sodium supplementation solution onto the surface of the electrode sheet, the compactness of the SEI film is increased, thereby reducing the loss of sodium ions in the positive electrode and the electrolyte, improving the charge-discharge characteristics in the slope region, optimizing the transmission path and kinetic process of sodium ions in the coal-based hard carbon negative electrode material, increasing the ion diffusion rate in the slope region, and making the charge and discharge of the sodium-ion battery in the slope region faster and more efficient. Moreover, the two-step sodium supplementation method can also avoid problems such as electrode structure damage and performance degradation caused by excessive pre-sodiation.

[0060] (2) Through the rolling process, the coal-based hard carbon negative electrode material and sodium salts are more closely packed, increasing the density of the electrode, improving the conductivity of the electrode, optimizing the structure and porosity of the electrode. At the same time, when the subsequent formation process is carried out, the ionized sodium ions can play a role both inside and on the surface of the electrode sheet, making the capacity performance more stable and forming less "dead sodium". BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is the process flow chart of the sodium supplementation method provided in Example 1 of the present invention.

[0062] Figure 2 is the cycle curve of the sodium-ion battery after sodium supplementation provided in Example 1 of the present invention.

[0063] Figure 3 is the SEM image of the negative electrode sheet after sodium supplementation provided in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the said embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0065] Example 1

[0066] This example provides a sodium supplementation method for a sodium-ion battery, and its process flow chart is as Figure 1 shown. The sodium supplementation method includes the following steps:

[0067] (1) Mix the stabilizer, sodium salt, and deionized water to prepare a sodium supplement solution, and divide the sodium supplement solution into two portions; by mass content, each component in the sodium supplement solution includes: 15% stabilizer, 35% sodium salt, and the balance is deionized water.

[0068] Mix the conductive agent, thickening agent, and deionized water to prepare a conductive adhesive; based on the total mass of the conductive adhesive, the mass content of the conductive agent is 5%, and the mass content of the thickening agent is 1%.

[0069] Among them, the stabilizer is vinylene carbonate, the sodium salt is sodium bis(fluorosulfonyl)imide, the conductive agent is carbon black, and the thickening agent is sodium carboxymethyl cellulose.

[0070] (2) Sequentially crush, perform low-temperature carbonization for impurity removal, purification, pulverize, and perform high-temperature carbonization on lump long-flame coal to obtain a coal-based hard carbon negative electrode material, then stir and mix it with the conductive adhesive, then add the first portion of the sodium supplement solution and continue to stir and mix, and then add the binder and stir and mix and perform vacuum degassing to obtain a mixed slurry with a solid content of 50 wt%, and then coat the mixed slurry on the current collector aluminum foil, and after drying, obtain a primary sodium-supplemented negative electrode sheet.

[0071] Among them, based on the weight of the solid components in the mixed slurry, the content of the coal-based hard carbon negative electrode material is 80%, the content of the conductive agent is 10%, the content of the thickening agent is 2%, and the content of the binder is 5%; the mass of the stabilizer in the first portion of the sodium supplement solution accounts for 2.5% of the mass of the solvent in the first portion of the sodium supplement solution; the mass of the sodium salt in the first portion of the sodium supplement solution accounts for 2.5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry.

[0072] (3) Perform a first cold roll pressing on the primary sodium-supplemented negative electrode sheet to 70% of the designed compaction density, the pressure of the first cold roll pressing is 30 MPa, the temperature is 25 °C, then spray the second portion of the sodium supplement solution on the surface of the negative electrode sheet (spraying rate: at a rate of 200 mg of sodium salt per 1 kg of active material), the components of the second portion of the sodium supplement solution are the same as those of the first portion of the sodium supplement solution, then perform drying, and then perform a second hot roll pressing to the designed compaction density, the pressure of the second hot roll pressing is 10 MPa, the temperature is 100 °C, to obtain a secondary sodium-supplemented negative electrode sheet.

[0073] (4) Assemble the secondary sodium-supplemented negative electrode sheet, the positive electrode sheet (including aluminum foil, and a positive electrode active layer provided on one side surface of the aluminum foil, the material of the positive electrode active layer includes polyanion-type compound, Super P, CMC, and SBR), and the separator (i.e., polypropylene PP membrane) to obtain a dry battery cell, then perform winding, die cutting, tab welding, and injection of electrolyte (i.e., sodium hexafluorophosphate solution), and then perform 24 h of pre-sealing and aging.

[0074] Then, the aged battery cells are subjected to a first formation to 70% SOC in an atmospheric environment with low humidity (i.e., 1% RH) at a temperature of 60°C. After vacuum exhaust, a second formation is carried out to 100% SOC at a pressure of 150 KPa and a temperature of 70°C. The currents for both the first and second formations are 0.3C.

[0075] After the formation is completed, packaging and shaping are carried out, and then discharging is performed at a rate of 0.3C to 0% SOC to obtain a sodium-ion battery after sodium supplementation.

[0076] Figure 2 The cycle curve of the sodium-ion battery after sodium supplementation provided in this embodiment is shown. It can be seen from the figure that after 200 cycles of the sodium-ion battery after sodium supplementation, the specific capacity hardly decays, and the capacity retention rate is close to 100%.

[0077] Figure 3 The SEM image of the negative electrode sheet after sodium supplementation provided in this embodiment is shown. It can be seen from the figure that the particle morphology after sodium supplementation has not changed, and it still shows an irregular particle distribution.

[0078] Example 2

[0079] This embodiment provides a method for supplementing sodium in a sodium-ion battery. The method for supplementing sodium includes the following steps:

[0080] (1) Mix a stabilizer, a sodium salt, and deionized water to prepare a sodium supplementation solution, and divide the sodium supplementation solution into two portions; by mass content, each component in the sodium supplementation solution includes: 10% stabilizer, 60% sodium salt, and the balance is deionized water.

[0081] Mix a conductive agent, a thickening agent, and deionized water to prepare a conductive adhesive; based on the total mass of the conductive adhesive, the mass content of the conductive agent is 1%, and the mass content of the thickening agent is 2%.

[0082] Among them, the stabilizer is ethylene carbonate, the sodium salt is sodium perchlorate, the conductive agent is acetylene black, and the thickening agent is sodium carboxymethyl cellulose.

[0083] (2) Sequentially crush, perform low-temperature carbonization for impurity removal, purification, pulverization, and high-temperature carbonization on massive long-flame coal to prepare a coal-based hard carbon negative electrode material. Then, stir and mix it with the conductive adhesive, then add the first portion of the sodium supplementation solution and continue to stir and mix. Subsequently, add a binder, stir and mix, and perform vacuum degassing to obtain a mixed slurry with a solid content of 30 wt%. Then, coat the mixed slurry on a current collector aluminum foil and dry it to obtain a negative electrode sheet for the first sodium supplementation.

[0084] Among them, based on the weight of the solid components in the mixed slurry, the content of the coal-based hard carbon negative electrode material is 70%, the content of the conductive agent is 15%, the content of the thickening agent is 5%, and the content of the binder is 1%; the mass of the stabilizer in the first sodium supplementation solution accounts for 1% of the mass of the solvent in the first sodium supplementation solution; the mass of the sodium salt in the first sodium supplementation solution accounts for 5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry.

[0085] (3)Cold roll the first sodium-supplemented negative electrode sheet to 60% of the designed compaction density for the first time. The pressure of the first cold rolling is 20 MPa and the temperature is 25 °C. Then, spray the second sodium supplementation solution on the surface of the negative electrode sheet (spraying rate meter: the rate of 200 mg sodium salt per 1 kg active material). The component contents of the second sodium supplementation solution are the same as those of the first sodium supplementation solution. Subsequently, perform drying, and then perform secondary hot rolling to the designed compaction density. The pressure of the secondary hot rolling is 10 MPa and the temperature is 50 °C to obtain a second sodium-supplemented negative electrode sheet.

[0086] (4)Assemble the second sodium-supplemented negative electrode sheet, the positive electrode sheet (including aluminum foil and a positive electrode active layer provided on one side surface of the aluminum foil, and the material of the positive electrode active layer includes polyanion-type compound, Super P, CMC, and SBR), and the separator (i.e., PP membrane) to obtain a dry battery cell. Then, perform winding, die-cutting, pole ear welding, and electrolyte injection (i.e., sodium hexafluorophosphate solution), and then perform pre-sealing aging for 12 h.

[0087] Then, perform the first formation of the aged battery cell to 50% SOC in an atmospheric environment with low humidity (i.e., 1% RH) at a temperature of 85 °C. After vacuum exhaust, perform the second formation to 100% SOC. The pressure of the second formation is 300 KPa and the temperature is 85 °C. The currents of both the first formation and the second formation are 0.1C.

[0088] After the formation is completed, perform encapsulation and molding, and then discharge at a rate of 0.1C to 0% SOC to obtain a sodium-supplemented sodium-ion battery.

[0089] Example 3

[0090] This example provides a sodium supplementation method for a sodium-ion battery. The sodium supplementation method includes the following steps:

[0091] (1)Mix the stabilizer, sodium salt, and deionized water to prepare a sodium supplementation solution, and divide the sodium supplementation solution into two portions; by mass content, each component in the sodium supplementation solution includes: 30% stabilizer, 10% sodium salt, and the balance is deionized water.

[0092] Mix a conductive agent, a thickening agent and deionized water to prepare a conductive adhesive; based on the total mass of the conductive adhesive, the mass content of the conductive agent is 10%, and the mass content of the thickening agent is 1%.

[0093] Among them, the stabilizer is fluoroethylene carbonate, the sodium salt is sodium hexafluorophosphate, the conductive agent is carbon nanotubes, and the thickening agent is sodium carboxymethyl cellulose.

[0094] (2) Sequentially crush, perform low-temperature carbonization for impurity removal, purification, pulverization and high-temperature carbonization on massive long-flame coal to obtain a coal-based hard carbon negative electrode material, then stir and mix it with the conductive adhesive, then add the first portion of sodium supplementation solution and continue to stir and mix, and then add a binder and stir and mix and perform vacuum defoaming to obtain a mixed slurry with a solid content of 70 wt%, and then coat the mixed slurry on a current collector aluminum foil, and obtain a primary sodium-supplemented negative electrode sheet after drying.

[0095] Among them, based on the weight of the solid components in the mixed slurry, the content of the coal-based hard carbon negative electrode material is 96%, the content of the conductive agent is 0.5%, the content of the thickening agent is 0.5%, and the content of the binder is 0.5%; the mass of the stabilizer in the first portion of sodium supplementation solution accounts for 5% of the mass of the solvent in the first portion of sodium supplementation solution; the mass of the sodium salt in the first portion of sodium supplementation solution accounts for 5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry.

[0096] (3) Perform primary cold rolling of the primary sodium-supplemented negative electrode sheet to 80% of the designed compaction density, the pressure of the primary cold rolling is 10 MPa, the temperature is 25 °C, and then spray the second portion of sodium supplementation solution on the surface of the negative electrode sheet (spray rate meter: the rate of 200 mg sodium salt per 1 kg active material), the component contents of the second portion of sodium supplementation solution and the first portion of sodium supplementation solution are the same, then perform drying, and then perform secondary hot rolling to the designed compaction density, the pressure of the secondary hot rolling is 5 MPa, the temperature is 150 °C, to obtain a secondary sodium-supplemented negative electrode sheet.

[0097] (4) Assemble the secondary sodium-supplemented negative electrode sheet, the positive electrode sheet (including aluminum foil, and a positive electrode active layer provided on one surface of the aluminum foil, the material of the positive electrode active layer includes a polyanion-type compound, Super P, CMC and SBR) and the separator (i.e., a PP film) to obtain a dry battery cell, then perform winding, die cutting, tab welding and electrolyte injection (i.e., sodium hexafluorophosphate solution), and then perform 48 h of pre-sealing and aging.

[0098] Then perform primary formation of the aged battery cell to 95% SOC in a normal pressure environment with low humidity (i.e., 1% RH), the temperature is 40 °C, perform vacuum exhaust, and then perform secondary formation to 100% SOC, the pressure of the secondary formation is 50 KPa, the temperature is 60 °C, and the currents of the primary formation and the secondary formation are both 0.5 C.

[0099] After formation is completed, encapsulation and molding are carried out, and then it is discharged to 0% SOC at a rate of 0.5C to obtain a sodium-ion battery after sodium supplementation.

[0100] Example 4

[0101] The difference between this example and Example 1 is that the content of the stabilizer in the sodium supplementation solution described in step (1) is 40%.

[0102] The remaining preparation methods and parameters are the same as those in Example 1.

[0103] Example 5

[0104] The difference between this example and Example 1 is that the content of the sodium salt in the sodium supplementation solution described in step (1) is 80%.

[0105] The remaining preparation methods and parameters are the same as those in Example 1.

[0106] Example 6

[0107] The difference between this example and Example 1 is that the spraying rate of the second portion of the sodium supplementation solution described in step (3) is recorded as: the rate of 50 mg of sodium salt per 1 kg of active material. The remaining preparation methods and parameters are the same as those in Example 1.

[0108] Example 7

[0109] The difference between this example and Example 1 is that the spraying rate of the second portion of the sodium supplementation solution described in step (3) is recorded as: the rate of 500 mg of sodium salt per 1 kg of active material.

[0110] The remaining preparation methods and parameters are the same as those in Example 1.

[0111] Comparative Example 1

[0112] The difference between this example and Example 1 is that spraying of the second portion of the sodium supplementation solution is not carried out.

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Performance Test

[0115] The sodium-ion batteries after sodium supplementation obtained from the above examples and comparative examples are subjected to initial efficiency calculation and rate performance testing. The testing conditions for the rate performance include: 1.5 - 3.5 V, discharging at 0.2C, and successively carrying out charging tests at 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 0.2C to test their charging rates.

[0116] The test results are shown in Table 1.

[0117] Table 1

[0118]

[0119] Analysis:

[0120] As can be seen from the above table, the present invention adopts a two-step sodium supplementation method for coordinated cooperation, which increases the platform capacity and stabilizes the platform region potential, and also increases the compactness of the SEI film, optimizing the transmission path and kinetic process of sodium ions in the coal-based hard carbon anode material. Moreover, the two-step sodium supplementation method can also avoid the problems of electrode structure damage and performance degradation caused by excessive pre-sodiation.

[0121] As can be seen from Example 1 and Examples 4-5, if the content of the stabilizer is too high, it is not conducive to ion migration, thus affecting the battery rate performance, and will also lead to an increase in battery side reactions, resulting in poor rate and cycle performance; if the content of the sodium salt is too high, it is not conducive to the formation of the SEI film, with an increase in side reactions and an energy density difference.

[0122] As can be seen from Example 1 and Examples 6-7, if the spraying rate is too low, it is not conducive to the adsorption of sodium salt on the electrode sheet, resulting in too little sodium supplementation; if the spraying rate is too high, it is not conducive to the improvement of the Coulomb efficiency of the battery cell, with an increase in sodium salt, leading to an increase in side reactions, a decrease in the initial efficiency, and an increase in the electrode sheet swelling rate, which will further affect the safety of the battery.

[0123] As can be seen from Example 1 and Comparative Example 1, if only one-step sodium supplementation is carried out, it is not conducive to the improvement of the battery initial efficiency. Compared with two-step sodium supplementation, while forming the SEI film on the negative electrode surface, the one-step sodium supplementation amount is limited and the sodium salt consumption is relatively large, while two-step sodium supplementation can supplement more sodium salts on the electrode sheet surface, reducing the interfacial impedance on the negative electrode surface when forming the SEI film and further improving the battery initial efficiency.

[0124] The applicant declares that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for replenishing sodium in a sodium ion battery, characterized in that: The sodium supplementation method comprises the following steps: (1) mixing a stabilizer, a sodium salt and a solvent to obtain a sodium replenishing solution, and dividing the sodium replenishing solution into two portions; The stabilizer in step (1) is selected from any one of vinylene carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sultone or vinyl sulfite, or a combination of at least two thereof; The components in the sodium supplement solution of step (1) include, by weight, 0.5-30% of a stabilizer, 0.5-70% of a sodium salt, and the remainder being a solvent; (2) Mixing a coal-based hard carbon negative electrode material, a conductive glue, a first portion of a sodium replenishment solution and a binder to obtain a mixed slurry, and then coating the mixed slurry on a current collector to obtain a primary sodium replenishment negative electrode sheet; (3) cold rolling the primary sodium-supplemented negative electrode sheet, spraying a second portion of sodium-supplementing liquid on the surface of the negative electrode sheet, and then hot rolling a second time to obtain a secondary sodium-supplemented negative electrode sheet; (4) Assembling the secondary sodium supplemented negative electrode plate with the positive electrode plate, electrolyte and separator, and then performing pre-sealing aging and formation treatment, and packaging and molding.

2. The sodium supplementation method according to claim 1, characterized in that The sodium salt in step (1) includes any one of sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium hexafluorophosphate or a boron-containing sodium salt or a combination of at least two thereof; And / or, the solvent in step (1) includes water.

3. The sodium supplementation method according to claim 1, characterized in that The components in the sodium supplement solution of step (1) include, by weight, 0.5-5% of a stabilizer, 0.5-20% of a sodium salt, and the remainder being a solvent.

4. The sodium supplementation method according to claim 1, characterized in that The raw material for preparing the coal-based hard carbon negative electrode material in step (2) is coal-based material; The coal-based material includes any one of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, weakly sticky coal, non-sticky coal, long flame coal or lignite, or a combination of at least two thereof; And / or, the conductive adhesive in step (2) comprises a conductive agent, a thickener and a solvent; Based on the total mass of the conductive adhesive, the mass content of the conductive agent is 1-10%, and the mass content of the thickener is 0.5-2%.

5. The sodium supplementation method according to claim 4, characterized in that: The solid content of the mixed slurry in step (2) is 30-70wt%; And / or, based on the total weight of the mixed slurry in step (2), the content of the coal-based hard carbon negative electrode material is 70-96%, the content of the conductive agent is 0.5-20%, the content of the thickener is 0.5-5%, and the content of the binder is 0.5-10%; and / or, in step (2), the mass of the stabilizer in the first sodium-supplementing solution accounts for 0.5-5% of the mass of the solvent in the first sodium-supplementing solution; And / or, in step (2), the mass of the sodium salt in the first sodium replenishing solution accounts for 0.05-5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry.

6. The sodium supplementation method according to claim 1, characterized in that: Step (3) the primary cold rolling is performed to 60-80% of the designed compaction density; And / or, the pressure of the cold rolling in step (3) is 1-100 MPa and the temperature is 20-35°C; and / or, the contents of the components of the second sodium-replenishing solution in step (3) and the first sodium-replenishing solution in step (2) are the same; And / or, the pressure of the secondary hot roller pressing in step (3) is 1-50 MPa and the temperature is 50-150°C; And / or, the second hot rolling in step (3) is performed to a designed compaction density.

7. The sodium supplementation method according to claim 1, characterized in that: The positive electrode sheet in step (4) includes a current collector and a positive electrode active layer disposed on a surface of one side of the current collector; And / or, the pre-sealing aging time in step (4) is 5-48h; And / or, the chemical treatment step in step (4) includes primary chemical treatment and secondary chemical treatment; The pressure of the primary formation is normal pressure and the temperature is 40-85°C; The secondary formation has a pressure of 10-300 KPa and a temperature of 60-85°C.

8. The sodium supplementation method according to claim 1, characterized in that: The sodium supplementation method comprises the following steps: (a) mixing a stabilizer, a sodium salt and a solvent to prepare a sodium replenishing solution, and dividing the sodium replenishing solution into two parts; the components in the sodium replenishing solution include, by weight content: 0.5-30% of a stabilizer, 0.5-70% of a sodium salt, and the remainder being a solvent; The conductive agent, thickener and solvent are mixed to prepare a conductive adhesive; based on the total mass of the conductive adhesive, the mass content of the conductive agent is 1-10%, and the mass content of the thickener is 0.5-2%; (b) stirring and mixing the coal-based hard carbon negative electrode material and the conductive glue, then adding the first portion of the sodium supplement solution and continuing to stir and mix, then adding the binder and stirring and mixing and vacuum degassing to obtain a mixed slurry with a solid content of 30-70wt%, and then coating the mixed slurry on a current collector aluminum foil, and drying to obtain a primary sodium supplement negative electrode sheet; Wherein, based on the weight of the solid components in the mixed slurry, the content of the coal-based hard carbon negative electrode material is 70-96%, the content of the conductive agent is 0.5-20%, the content of the thickener is 0.5-5%, and the content of the binder is 0.5-10%; the mass of the stabilizer in the first sodium replenishment solution accounts for 0.5-5% of the mass of the solvent in the first sodium replenishment solution; the mass of the sodium salt in the first sodium replenishment solution accounts for 0.05-5% of the mass of the coal-based hard carbon negative electrode material in the mixed slurry; (c) subjecting the primary sodium-supplemented negative electrode sheet to a primary cold roller pressing to 60-80% of the designed compaction density, the primary cold roller pressing pressure being 1-100 MPa and the temperature being 20-35° C., and then spraying a second portion of sodium-supplementing solution on the surface of the negative electrode sheet, wherein the second portion of sodium-supplementing solution has the same content of each component as the first portion of sodium-supplementing solution, followed by drying, and then subjecting the secondary hot roller pressing to a designed compaction density, wherein the secondary hot roller pressing pressure is 1-50 MPa and the temperature is 50-150° C., to obtain a secondary sodium-supplemented negative electrode sheet; (d) assembling the secondary sodium-supplemented negative electrode sheet, the positive electrode sheet and the separator to obtain a dry battery cell, which is then rolled, die-cut, tab-welded and injected with electrolyte, followed by 5-48h pre-sealing aging; Then the aged battery cell is subjected to a primary formation to 50-95% SOC at a temperature of 40-85°C in a low humidity and normal pressure environment, and a secondary formation to 100% SOC after vacuum exhaust, wherein the pressure of the secondary formation is 10-300KPa, the temperature is 60-85°C, and the current of the primary formation and the secondary formation is 0.01-0.5C; After the formation is completed, the battery is packaged and then discharged to 0% SOC at a rate of 0.01-0.5C to obtain a sodium-supplemented sodium-ion battery.

9. A sodium-supplemented sodium ion battery, characterized in that: The sodium-supplemented sodium ion battery is obtained by the sodium-supplementing method according to any one of claims 1 to 8.

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