Diaphragm and preparation method thereof, sodium ion battery and preparation method thereof, and electric equipment

Abstract

The invention provides a diaphragm and a preparation method thereof, a sodium ion battery and a preparation method thereof, and electrical equipment, and relates to the technical field of new energy. The diaphragm provided by the invention comprises the base film and the negative electrode bonding layer and the positive electrode bonding layer which are arranged on two sides of the base film, the sodium supplementing additive is added in the positive electrode bonding layer, and the sodium supplementing additive releases a large amount of gas when a battery cell is activated for the first time, so that a pore-forming effect is achieved on the bonding layers, pore channels of a gluing layer between a pole piece and the diaphragm are increased, and the battery cell is prevented from being damaged. Normal transmission of sodium ions is guaranteed, and sufficient flowing space can be provided for electrolyte. The sodium supplement additive generates a certain amount of sodium ions after being activated for the first time, the sodium supplement effect is achieved, no by-product is left after activation, it is guaranteed that no by-product blocks a channel, and the provided sodium ions have irreversibility relative to sodium supplement substances of the sodium supplement additive.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to a diaphragm and a preparation method thereof, a sodium ion battery and a preparation method thereof, and electrical equipment. Background Art

[0002] With the increase in the penetration rate of new energy power generation, the randomness and volatility of the power generation side are becoming increasingly severe. As a new source of regulation capacity, energy storage has accelerated the demand for installed capacity. Compared with lithium-ion batteries, industrialized sodium-ion batteries have obvious cost advantages and low-temperature performance. Sodium-ion batteries are divided into wound sodium-ion batteries and stacked sodium-ion batteries. Both assembly modes require the diaphragm, positive electrode and negative electrode to be fixed during the production process to prevent the relative movement of the three, resulting in the negative electrode being unable to wrap the positive electrode or the positive and negative electrodes contacting, causing short circuits or sodium precipitation and other safety issues.

[0003] The existing process usually uses a glue-coated diaphragm to heat and activate the adhesive layer to make it adhere to the positive electrode, diaphragm and negative electrode, and then use pressure to bond the three together. However, after hot pressing, the diaphragm, the adhesive layer and the pole piece are completely adhered, resulting in no pores and fewer channels between the diaphragm and the pole piece, which seriously affects the migration of sodium ions and the flow of electrolyte, resulting in increased polarization of the battery cell and reduced rate performance, which seriously affects the electrochemical performance of the sodium ion battery. Summary of the invention

[0004] The purpose of the present application is to provide a diaphragm and a method for preparing the same, a sodium ion battery and a method for preparing the same, and electrical equipment, aiming to solve the problem that the existing diaphragm affects the migration of sodium ions and the flow of electrolyte, resulting in increased polarization of the battery cell and reduced rate performance.

[0005] To achieve the above objectives, the present application provides a separator, comprising: a base film and a negative electrode bonding layer and a positive electrode bonding layer respectively disposed on both sides of the base film;

[0006] Wherein, the positive electrode bonding layer includes a sodium supplement additive.

[0007] In some embodiments, the raw materials of the positive electrode bonding layer include, by weight, 10-20 parts of a positive electrode bonding agent, 5-15 parts of a sodium supplementing additive, 0.2-0.5 parts of a dispersant, and 65-85 parts of a positive electrode solvent;

[0008] The raw materials of the negative electrode bonding layer include, by weight, 5 to 15 parts of a negative electrode bonding agent and 85 to 95 parts of a negative electrode solvent.

[0009] The positive electrode bonding layer and the negative electrode bonding layer are relatively thin and are tightly attached to the positive electrode sheet after hot pressing, so no conductive agent needs to be added to the positive electrode bonding layer and the negative electrode bonding layer.

[0010] Optionally, the thickness of the base film is 9 to 16 μm, for example, it can be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or any value between 9 and 16 μm, and the thickness of the negative electrode bonding layer and the positive electrode bonding layer are each independently 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value between 1 and 5 μm.

[0011] In some embodiments, at least one of the following conditions is met:

[0012] A. The negative electrode binder includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion, polytetrafluoroethylene and styrene-butadiene rubber;

[0013] B. the negative electrode solvent is selected from water or N-methylpyrrolidone;

[0014] C. The positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, (vinylidene fluoride-hexafluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), polymethyl acrylate, and acrylamide-acrylic acid polymer;

[0015] D. the sodium supplement additive is sodium oxalate;

[0016] E. the dispersant comprises at least one of polyacrylamide, sodium polyacrylate, polyacrylate, polyacrylic alcohol and polyvinyl pyrrolidone;

[0017] F. The cathode solvent is selected from water or N-methylpyrrolidone;

[0018] G. The base film is selected from polypropylene or polyethylene.

[0019] In some embodiments, at least one of the following conditions is met:

[0020] A. The negative electrode binder comprises styrene-butadiene rubber;

[0021] B. The negative electrode solvent is water;

[0022] C. the positive electrode binder comprises polyvinylidene fluoride;

[0023] D. the dispersant comprises polyvinyl pyrrolidone;

[0024] E. The cathode solvent is selected from N-methylpyrrolidone.

[0025] The present application also provides a method for preparing the above-mentioned diaphragm, comprising:

[0026] The raw materials of the negative electrode bonding layer are prepared into a negative electrode bonding layer glue solution, coated on one side of the base film, and baked to form a negative electrode bonding layer;

[0027] The raw materials of the positive electrode bonding layer are prepared into a positive electrode bonding layer glue solution and coated on the other side of the base film, and baked to form a positive electrode bonding layer to obtain the separator.

[0028] In some embodiments, at least one of the following conditions is met:

[0029] A. The coating method includes spraying or electrospinning;

[0030] B. The baking temperature is not higher than 55°C.

[0031] The present application also provides a sodium ion battery, the raw materials of which include the above-mentioned diaphragm.

[0032] The present application also provides a method for preparing a sodium ion battery, comprising:

[0033] Assembling the separator with the positive electrode sheet and the negative electrode sheet, and fixing the positive electrode sheet and the negative electrode sheet respectively by hot pressing the positive electrode bonding layer and the negative electrode bonding layer, to obtain a battery cell;

[0034] The battery cell is first activated, gas is evacuated, liquid is replenished, and packaged to obtain the sodium ion battery.

[0035] Among them, the positive electrode sheet is composed of a current collector, an active material, a conductive agent, and a binder, wherein the current collector is preferably aluminum foil; the active material can be any one or more combinations of sodium nickel iron manganese oxide, Prussian blue, Prussian white, sodium iron phosphate, sodium iron pyrophosphate, sodium iron sulfate, sodium vanadium pyrophosphate, and sodium vanadium fluorophosphate, preferably sodium nickel iron manganese oxide; the conductive agent can be any one or more combinations of carbon black, CNT, graphene, and conductive graphite, preferably CNT; the binder can be any one or more combinations of PVDF, PAA, and PTFE, preferably PVDF.

[0036] In some embodiments, at least one of the following conditions is met:

[0037] A. The hot pressing temperature is 60-90°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or any value between 60-90°C;

[0038] B. The hot pressing time is 3-5min;

[0039] C. The hot pressing pressure is 0.1-1.2 mPa;

[0040] D. The current range of the first activation is 0.05C to 0.1C, or the power range is 0.05P to 0.1P;

[0041] E. The time for the first activation is 8-10 hours.

[0042] The present application also provides an electrical device, comprising the above-mentioned sodium ion battery.

[0043] Compared with the prior art, the beneficial effects of this application include:

[0044] The diaphragm provided in the present application includes a base film and a negative electrode bonding layer and a positive electrode bonding layer arranged on both sides of the base film, and a sodium supplement additive is added to the positive electrode bonding layer. The sodium supplement additive releases a large amount of gas when the battery cell is activated for the first time, which has a pore-forming effect on the bonding layer, and increases the pore channels of the glue layer between the electrode and the diaphragm, which not only ensures that sodium ions can be transmitted normally, but also provides sufficient flow space for the electrolyte; the sodium supplement additive produces a certain amount of sodium ions during the first activation, which has a sodium supplement effect, and no by-products remain after activation, which not only ensures that there are no by-products blocking the channel, but also the sodium ions it provides are irreversible relative to its sodium supplement substance.

[0045] The sodium ion battery and electrical equipment provided by the present application use the diaphragm of the present application, so the migration of sodium ions and the flow of electrolyte are not affected by the diaphragm, the polarization of the battery cell is reduced, the rate performance is improved, and the battery has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0047] Figure 1 This is a schematic diagram of the structure of the diaphragm of the present application. DETAILED DESCRIPTION

[0048] As used herein:

[0049] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0050] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0051] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0052] In these examples, parts and percentages are by mass unless otherwise indicated.

[0053] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0054] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0055] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0056] Example 1

[0057] This embodiment provides a diaphragm, and the preparation method thereof comprises the following steps:

[0058] A negative electrode glue is prepared. The negative electrode glue includes a binder and a solvent. The binder is SBR, which is the same series of binder as the negative electrode plate of the battery, and the solvent is water; the binder accounts for 12 parts and water accounts for 88 parts.

[0059] The prepared negative electrode glue is applied on one side of the PE base film by spraying, and the baking temperature is controlled at 55°C to form a negative electrode bonding layer. The thickness of the base film is 9 μm, and the thickness of the negative electrode bonding layer is 2 μm.

[0060] A positive electrode glue is prepared, which includes a binder, a sodium supplement additive, a dispersant and a solvent; the binder is polyvinylidene fluoride, which is the same series of binders as the positive electrode plates of the battery; the sodium supplement additive is sodium oxalate; the dispersant is polyvinyl pyrrolidone; the solvent is N-methylpyrrolidone (NMP); 12 parts of the binder, 8 parts of the sodium supplement additive, 0.2 parts of the dispersant, and 79.8 parts of NMP are added.

[0061] The prepared positive electrode glue solution was coated on the other side of the base film, and the baking temperature was controlled at 55° C. to form a positive electrode bonding layer. The thickness of the positive electrode bonding layer was 5 μm, and the separator of Example 1 was obtained.

[0062] This embodiment also provides a sodium ion battery, the preparation method of which comprises the following steps:

[0063] The positive electrode sheet is prepared by conventional methods from a current collector, an active material, a conductive agent, and a binder, wherein the current collector is aluminum foil; the active material is sodium nickel iron manganese oxide; the conductive agent is carbon nanotubes; the binder is PVDF, of which the amount of active material accounts for 92 parts, carbon nanotubes account for 1 part, and the binder accounts for 7 parts; hard carbon is used as the negative electrode sheet.

[0064] The separator of Example 1 is wound or stacked with the positive electrode sheet and the negative electrode sheet to form a bare battery cell; the bare battery cell is hot pressed at 85°C and the pressure is set to 0.4 MPa for 180S to activate the positive and negative electrode bonding layers to generate viscosity to fix the positive and negative electrode sheets and the separator.

[0065] The hot-pressed coil core is made into a battery cell through processes such as liquid injection and packaging. The battery cell is activated for the first time with a current of 0.1C and a time of 8 hours.

[0066] The battery cell activated for the first time is subjected to processes such as air extraction, liquid replenishment, and packaging to produce the sodium ion battery of Example 1.

[0067] Example 2

[0068] This embodiment provides a diaphragm, and the preparation method thereof is different from that of Embodiment 1 only in that: the positive electrode glue solution formula is: 12 parts of binder, 13 parts of sodium supplement additive, 0.3 parts of dispersant, and 74.7 parts of NMP.

[0069] The other steps and parameters are the same as those in Example 1 and will not be described in detail here.

[0070] Example 3

[0071] This embodiment provides a diaphragm, and the preparation method thereof is different from that of Embodiment 1 only in that: the positive electrode glue solution formula is: 12 parts of binder, 5 parts of sodium supplement additive, 0.2 parts of dispersant, and 82.8 parts of NMP.

[0072] The other steps and parameters are the same as those in Example 1 and will not be described in detail here.

[0073] Comparative Example 1

[0074] This comparative example provides a diaphragm, and the preparation method thereof is different from that of Example 1 only in that: the positive electrode glue solution formula is: 12 parts of binder, 0 parts of sodium supplement additive, 0.2 parts of dispersant, and 87.8 parts of NMP.

[0075] The other steps and parameters are the same as those in Example 1 and will not be described in detail here.

[0076] Comparative Example 2

[0077] Comparative Example 2 provides a diaphragm, which is the base membrane of Example 1, without any coating.

[0078] Comparative Example 3

[0079] This comparative example provides a diaphragm, and its preparation method comprises the following steps:

[0080] A positive electrode glue is prepared, which includes a binder, a sodium supplement additive, a dispersant and a solvent; the binder is polyvinylidene fluoride, which is the same series of binders as the positive electrode plates of the battery; the sodium supplement additive is sodium oxalate; the dispersant is polyvinyl pyrrolidone; the solvent is N-methylpyrrolidone (NMP); 12 parts of the binder, 8 parts of the sodium supplement additive, 0.2 parts of the dispersant, and 79.8 parts of NMP are added.

[0081] The prepared positive electrode glue solution was coated on one side of the base film, and the baking temperature was controlled at 55° C. to form a positive electrode bonding layer, thereby obtaining the separator of Comparative Example 3.

[0082] The preparation steps and process parameters of the sodium ion battery of Comparative Example 3 are the same as those of Example 1 and are not described again here.

[0083] Comparative Example 4

[0084] This comparative example provides a diaphragm, and its preparation method is different from that of Example 1 only in that: when the battery cell is activated for the first time, a current of 0.5C is used for 2 hours. The initial activation current is increased, the battery cell generates severe heat and violent gas production, posing a safety risk.

[0085] The cells after the first activation of the above-mentioned embodiments and comparative examples were disassembled, the diaphragms were taken out and the electrolyte was removed, and the ion conductivity and air permeability of the diaphragms were tested. The testing method is as follows:

[0086] Diaphragm ion conductivity: Soak the cut diaphragm samples in the test electrolyte in advance, and use the conductivity test system to test. The diaphragm ion conductivity value can be calculated based on the diaphragm thickness, resistance and diaphragm test area. The formula is as follows: α=d / (R*S), where α is the diaphragm ion conductivity, d is the diaphragm thickness, R is the diaphragm ion impedance, and S is the diaphragm test effective area.

[0087] Diaphragm air permeability: According to GB / T36363-2018 "Polyolefin Diaphragms for Lithium-ion Batteries", a permeability tester was used to apply a pressure of 1.21 kPa in a temperature, humidity and normal pressure environment, and the area through which 100 mL of air passes was recorded to be 6.45 cm 2 The time required for the diaphragm to be cooled. The longer the time, the worse the diaphragm air permeability. The diaphragm air permeability affects the migration rate of ions. The worse the diaphragm air permeability, the lower the ion migration rate.

[0088] The electrochemical performance tests were performed on the sodium ion batteries of the above embodiments and comparative examples respectively, and the test methods were as follows:

[0089] The percentage of battery cell fluid loss: fluid loss percentage = 1-liquid retention volume / liquid injection volume;

[0090] First effect of battery cell: First effect = first discharge capacity / first charge capacity*100%.

[0091] The test results of the separators and sodium ion batteries of various embodiments and comparative examples are shown in Table 1.

[0092] Table 1. Test results of the separators and sodium ion batteries of various embodiments and comparative examples

[0093]

[0094] According to Table 1, the positive electrode bonding layer and the negative electrode bonding layer in the diaphragm of the embodiment of the present application play the role of fixing the positive electrode sheet and the negative electrode sheet, and the sodium supplement additive plays the role of creating pores for the bonding layer. The pore-forming effect is different by adjusting the dosage ratio of different sodium supplement additives. The gas generated during the first activation creates pores for the bonding layer, increases the ion transmission pore channel, enhances the electrolyte wettability, reduces the static infiltration time of the battery cell, and can reduce the liquid loss of the battery cell; improves the first effect and reduces the internal resistance.

[0095] According to Comparative Examples 1 and 2, the diaphragm of Comparative Example 2 has no coating and only takes 144 seconds to pass 100cc of gas, which is the shortest time. The diaphragm has the best air permeability and high ion conductivity, but the cell liquid loss accounts for a high proportion and the cell initial efficiency is low. The positive electrode bonding layer of the diaphragm of Comparative Example 1 does not contain sodium-supplementing additives and no gas is used for pore formation. Therefore, the diaphragm has the worst air permeability, low ion conductivity, poor electrolyte wettability, high cell liquid loss and low cell initial efficiency.

[0096] According to Comparative Example 4, the embodiment of the present application adopts the first small current charging to make the gas release slowly, the pore formation is more uniform, the sodium ions are released slowly, the SEI film formed is more uniform, the internal resistance of the battery cell is reduced, and it is more conducive to long cycle.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0098] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present application and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A diaphragm, characterized in that: include: A base film and a negative electrode bonding layer and a positive electrode bonding layer respectively disposed on both sides of the base film; Wherein, the positive electrode bonding layer includes a sodium supplement additive.

2. The diaphragm according to claim 1, characterized in that The raw materials of the positive electrode bonding layer include, by weight, 10-20 parts of a positive electrode bonding agent, 5-15 parts of a sodium supplementing additive, 0.2-0.5 parts of a dispersant, and 65-85 parts of a positive electrode solvent. The raw materials of the negative electrode bonding layer include, by weight, 5 to 15 parts of a negative electrode bonding agent and 85 to 95 parts of a negative electrode solvent; Optionally, the base film has a thickness of 9 to 16 μm, and the thicknesses of the negative electrode bonding layer and the positive electrode bonding layer are independently 1 to 5 μm.

3. The diaphragm according to claim 2, characterized in that At least one of the following conditions is met: A. The negative electrode binder includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion, polytetrafluoroethylene and styrene-butadiene rubber; B. the negative electrode solvent is selected from water or N-methylpyrrolidone; C. The positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, (vinylidene fluoride-hexafluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), polymethyl acrylate, and acrylamide-acrylic acid polymer; D. the sodium supplement additive is sodium oxalate; E. the dispersant comprises at least one of polyacrylamide, sodium polyacrylate, polyacrylate, polyacrylic alcohol and polyvinyl pyrrolidone; F. The cathode solvent is selected from water or N-methylpyrrolidone; G. The base film is selected from polypropylene or polyethylene.

4. The diaphragm according to claim 3, characterized in that At least one of the following conditions is met: A. The negative electrode binder comprises styrene-butadiene rubber; B. The negative electrode solvent is water; C. the positive electrode binder comprises polyvinylidene fluoride; D. the dispersant comprises polyvinyl pyrrolidone; E. The cathode solvent is selected from N-methylpyrrolidone.

5. A method for preparing a diaphragm according to any one of claims 1 to 4, characterized in that: include: The raw materials of the negative electrode bonding layer are prepared into a negative electrode bonding layer glue solution, coated on one side of the base film, and baked to form a negative electrode bonding layer; The raw materials of the positive electrode bonding layer are prepared into a positive electrode bonding layer glue and coated on the other side of the base film, and baked to form a positive electrode bonding layer to obtain the separator.

6. The method for preparing a diaphragm according to claim 5, characterized in that: At least one of the following conditions is met: A. The coating method includes spraying or electrospinning; B. The baking temperature is not higher than 55°C.

7. A sodium ion battery, characterized in that: The raw material thereof includes the diaphragm according to any one of claims 1 to 4.

8. A method for preparing a sodium ion battery as claimed in claim 7, characterized in that: include: Assembling the separator with the positive electrode sheet and the negative electrode sheet, and fixing the positive electrode sheet and the negative electrode sheet respectively by hot pressing the positive electrode bonding layer and the negative electrode bonding layer, to obtain a battery cell; The battery cell is first activated, gas is evacuated, liquid is replenished, and packaged to obtain the sodium ion battery.

9. The method for preparing a sodium ion battery according to claim 8, characterized in that: At least one of the following conditions is met: A. The hot pressing temperature is 60-90°C; B. The hot pressing time is 3-5min; C. The hot pressing pressure is 0.1-1.2 mPa; D. The current range of the first activation is 0.05C to 0.1C, or the power range is 0.05P to 0.1P; E. The time for the first activation is 8-10 hours.

10. An electrical equipment, characterized in that: Including the sodium ion battery as described in claim 7.

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