A modified separator, its preparation method and application

Abstract

This invention provides a modified separator, its preparation method, and its application, comprising a base membrane and an alkali metal supplement. The alkali metal supplement includes a sodium supplement or a lithium supplement, the particle size of which is 0.05~1μm, and the alkali metal supplement is embedded in the base membrane. In the modified separator, the base membrane accounts for 50%~95% by mass, and the alkali metal supplement accounts for 5%~50% by mass. This invention helps to suppress lithium dendrites or sodium dendrites, while simultaneously improving the energy density and safety performance of the battery.

Description

Technical Field

[0001] This invention relates to diaphragms, and more specifically to a modified diaphragm, its preparation method, and its applications. Background Technology

[0002] Among secondary batteries, sodium-ion batteries have become a hot topic in the current research field of new secondary batteries due to their similar chemical properties to lithium-ion batteries and their advantages such as abundant resources and low price.

[0003] However, existing sodium-ion batteries suffer from significant irreversible capacity loss in the first week. For example, when hard carbon is used as the negative electrode material, the formation of the SEI film on the negative electrode consumes active sodium from the positive electrode, leading to a very significant irreversible capacity loss. This results in a marked reduction in the capacity and energy density of sodium-ion batteries in practical applications. Furthermore, sodium dendrite formation is also a prominent issue affecting the safety performance of sodium-ion batteries. Summary of the Invention

[0004] This invention provides a modified membrane, its preparation method, and its application, which helps to compensate for irreversible capacity loss and suppress dendrite problems.

[0005] The present invention provides a modified separator, comprising a base membrane and an alkali metal supplement, wherein the alkali metal supplement is embedded in the base membrane, and the alkali metal supplement includes a sodium supplement or a lithium supplement. The particle size of the alkali metal supplement is 0.05~1μm, and in the modified separator, the mass percentage of the base membrane is 50%~95%, and the mass percentage of the alkali metal supplement is 5%~50%.

[0006] Optionally, in the modified diaphragm, the base membrane has a mass percentage content of 82% to 90%, and the alkali-supplementing metal agent has a mass percentage content of 10% to 18%.

[0007] Optionally, the particle size of the alkali-supplementing metal agent is 0.2~0.5μm.

[0008] Optionally, the base membrane comprises one or more composite membranes selected from polyethylene membrane, polypropylene membrane, glass fiber membrane, and cellulose membrane; and / or, the sodium supplement includes Na. x C y O z Where x≥1, y≥1, z≥3; and / or, the lithium supplement includes Li x C y O z , where x≥1, y≥1, z≥3.

[0009] Optionally, the thickness of the modified diaphragm is 4~40 μm.

[0010] The present invention provides a method for preparing the modified membrane as described above, comprising: dispersing the raw materials of the base membrane in a solvent to obtain a slurry; mixing the slurry with the alkali-supplementing metal agent to obtain a mixture; forming a membrane layer from the mixture; and then removing the solvent therein to obtain the modified membrane.

[0011] Optionally, the method further includes: grinding the raw materials of the alkali-supplementing metal agent to obtain the alkali-supplementing metal agent.

[0012] Optionally, the solvent includes one or more of N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide; and / or, the process of mixing the slurry with the alkali-adding metal agent to obtain a mixture includes: mixing the slurry with the alkali-adding metal agent, and then subjecting it to ultrasonic treatment to obtain the mixture.

[0013] Optionally, the process of forming a membrane layer from the mixture and then removing the solvent to obtain the modified membrane includes: subjecting the mixture to vacuum filtration to form a membrane layer, and then drying to obtain the modified membrane.

[0014] The present invention provides a battery comprising the modified separator as described above or the modified separator obtained by the preparation method of the modified separator as described above.

[0015] This invention provides a modified separator, its preparation method, and its application. During the battery formation stage, the alkali metal supplement (sodium or lithium supplement) in the modified separator can decompose. After decomposition, the alkali metal supplement generates sodium or lithium ions to replenish the ions lost in the battery, which helps to compensate for irreversible capacity loss and improve specific capacity. As the alkali metal supplement decomposes, a uniformly distributed pore structure appears on the modified separator, which is conducive to the passage of sodium or lithium ions. This helps to prevent the formation of dendrites (sodium or lithium dendrites) and also helps to improve the energy density of the battery. In addition, it effectively solves the problems of damage to the positive electrode caused by the decomposition of the alkali metal supplement (sodium or lithium supplement) after adding it to the positive electrode, and poor contact between the separator and the electrode caused by the decomposition of the alkali metal supplement after coating the separator surface. It also helps to suppress the problem of gas generation in the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of the modified diaphragm provided in an embodiment of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Sodium replenishment can be used in existing technologies to improve battery capacity and cycle stability. The main sodium replenishment methods reported so far are: (1) electrochemical pre-sodium method; (2) direct pre-sodium method; (3) sodium-rich compound; (4) sodium replenishing agent added to the positive electrode; and (5) sodium replenishing membrane. Among them, electrochemical pre-sodium method, direct pre-sodium method, sodium-rich compound and sodium replenishing agent added to the positive electrode all have problems such as low safety, complicated operation, special selectivity and damage to the positive electrode structure, which make it difficult to apply on a large scale. Sodium replenishing membrane is a more ideal method. However, at present, sodium replenishing membrane usually involves coating the sodium replenishing material of the positive electrode onto the surface of a polymer membrane (such as polypropylene PP or polyethylene PE). As the sodium replenishing agent decomposes, gas is generated, which has an adverse effect on the contact between the membrane and the electrode, resulting in a decrease in the cycle performance of the battery.

[0020] To overcome the shortcomings of the prior art, embodiments of the present invention provide a modified diaphragm, such as... Figure 1 As shown, the modified membrane includes a base membrane and an alkali metal supplement. The alkali metal supplement is embedded in the base membrane. The alkali metal supplement includes a sodium supplement or a lithium supplement. The particle size of the alkali metal supplement is 0.05~1μm. In the modified membrane, the mass percentage of the base membrane is 50%~95%, and the mass percentage of the alkali metal supplement is 5%~50%.

[0021] According to research and analysis, during the battery formation stage, the alkali metal supplement (sodium or lithium supplement) in the modified separator can decompose. After decomposition, the alkali metal supplement produces sodium or lithium ions to replenish the ions lost in the battery. For example, it replenishes lithium ions lost due to SEI formation on the negative electrode surface in lithium-ion batteries, and sodium ions lost due to SEI formation in sodium-ion batteries, thus helping to improve specific capacity. Furthermore, with the decomposition of the alkali metal supplement, a uniformly distributed pore structure appears on the modified separator. The size of these pores is related to the particle size of the alkali metal supplement. By limiting the particle size of the alkali metal supplement to 0.05~1μm, the pore size on the modified separator after formation can be appropriately determined. It facilitates the passage of sodium or lithium ions, and the porosity of the modified separator after formation is related to the amount of alkali metal agent used. By controlling the mass percentage of the alkali metal agent within the above range, it helps to control the porosity of the modified separator after formation to 30%~55%, which is conducive to the passage of sodium or lithium ions. Therefore, it helps to prevent the formation of dendrites (sodium dendrites or lithium dendrites) and also helps to improve the energy density of the battery. In addition, it effectively solves the problems of damage to the positive electrode caused by the decomposition of the alkali metal agent after adding alkali metal agent (sodium agent or lithium agent) to the positive electrode, and poor contact between the separator and the electrode caused by the decomposition of the alkali metal agent after coating the separator surface. It also helps to suppress the problem of battery gas generation.

[0022] It is understandable that the aforementioned alkali-replenishing metal agent is embedded in the base film, that is, the aforementioned alkali-replenishing metal agent exists in the base film in an embedded form.

[0023] The modified diaphragm described above can be a single-layer structure.

[0024] After the modified separator is assembled into a battery, during the battery formation stage, the alkali metal agent, which exists in the base membrane in an embedded form, decomposes and forms pores on the modified separator. Furthermore, by controlling the particle size and mass percentage of the alkali metal agent, the pore size and porosity of the modified separator after formation can be controlled. Specifically, the particle size of the alkali metal agent is related to the pore size of the modified separator after formation, and the mass percentage of the alkali metal agent is related to the porosity of the modified separator after formation. By controlling the particle size of the alkali metal agent to 0.05~1μm, it helps the modified separator form pores with a diameter of 0.05~1μm after formation. By controlling the mass percentage of the alkali metal agent to 5%~50%, it helps control the porosity of the modified separator after formation to 30%~55%, for example, 35%~50%.

[0025] For example, the particle size of the above-mentioned alkali metal supplement can be a range of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 μm or any combination thereof.

[0026] Furthermore, the particle size of the alkali metal supplement can be 0.2~0.5μm.

[0027] For example, in the modified separator, the mass percentage of the base membrane can be 50%, 60%, 70%, 80%, 82%, 90%, 95%, or any combination thereof. By controlling the mass percentage of the base membrane to meet the above range, it can be ensured that the modified separator effectively isolates the positive and negative electrodes, while ensuring the effects of sodium or lithium supplementation and suppression of sodium or lithium dendrites.

[0028] Furthermore, in the modified diaphragm, the mass percentage of the base membrane can be 82% to 90%.

[0029] For example, in the modified separator, the mass percentage of the alkali metal supplement can be 5%, 10%, 20%, 30%, 40%, 50%, or any combination thereof. This helps ensure that the modified separator can effectively suppress sodium or lithium dendrites while also effectively supplementing sodium or lithium ions.

[0030] Furthermore, in the modified diaphragm, the mass percentage of the alkali metal supplement can be 10% to 18%.

[0031] The aforementioned alkali metal supplements may include sodium supplements or lithium supplements.

[0032] Understandably, when the aforementioned alkali metal supplement includes sodium supplement, the modified separator is a sodium-supplemented separator, which can be used in sodium-ion batteries.

[0033] Similarly, when the aforementioned alkali metal supplement includes lithium supplement, the modified separator is a lithium supplement separator, which can be used in lithium-ion batteries.

[0034] The above-mentioned sodium supplements may include Na x C y O z Where x, y, and z are all ≥ 0, and further, x ≥ 1, y ≥ 1, and z ≥ 3. For example, sodium supplements may include one or more of Na2CO3, Na2C2O4, and Na2C4O4.

[0035] The aforementioned lithium supplement may include Li x C y O z Where x≥1, y≥1, z≥3, for example, lithium supplementation agents may include one or more of Li2CO3, Li2C2O4, and Li2C4O4.

[0036] The aforementioned base membrane may include one or more composite membranes selected from biomass-based membranes (e.g., cellulose membranes or their derivatives), petrochemical membranes (e.g., polyethylene membranes (PE), polypropylene membranes (PP)), and glass fiber membranes. Specifically, the aforementioned base membrane may include one or more composite membranes selected from polyethylene membranes, polypropylene membranes, glass fiber membranes, and cellulose membranes. Using a biomass-based membrane (e.g., cellulose membranes or their derivatives) avoids the difficulties in disposing of petrochemical membranes (e.g., polyethylene membranes (PE) and polypropylene membranes (PP)) after disposal.

[0037] The thickness of the modified diaphragm is 4~40μm, for example, 4, 10, 20, 30, 35, 40μm or any combination thereof, preferably 10~35μm.

[0038] The present invention also provides a method for preparing the above-mentioned modified diaphragm, comprising: dispersing the raw materials of the base membrane in a solvent to obtain a slurry; mixing the slurry with an alkali metal supplement to obtain a mixture; forming a membrane layer from the mixture; and then removing the solvent therein to obtain the modified diaphragm.

[0039] The above preparation method is simple and efficient, and will not introduce ineffective components such as adhesives into the battery. It solves the problems of uneven pore distribution and pore size of the separator, and can produce a modified separator with the aforementioned properties.

[0040] The solvents mentioned above may include one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0041] In some embodiments, the process of mixing a slurry with an alkali metal supplement to obtain a mixture includes: mixing the slurry with the alkali metal supplement, and then subjecting it to ultrasonic treatment to obtain the mixture.

[0042] In specific implementation, the above preparation method also includes: grinding the raw materials of the alkali metal supplement (e.g., sand milling) to grind the alkali metal supplement into particles with uniform particle size, thereby obtaining an alkali metal supplement with a particle size of 0.05~1μm.

[0043] In some embodiments, the process of forming a membrane layer from a mixture and then removing the solvent to obtain a modified membrane includes: filtration of the mixture to form a membrane layer, followed by drying (e.g., baking) to remove the solvent, thereby obtaining the modified membrane of the present invention.

[0044] This invention also provides a battery comprising the modified separator described above or a modified separator prepared by the method described above.

[0045] Specifically, the aforementioned batteries may include sodium-ion batteries or lithium-ion batteries.

[0046] Taking sodium-ion batteries as an example, one can imagine that, in addition to the modified separator mentioned above, sodium-ion batteries also include positive electrode plates, negative electrode plates, and electrolytes.

[0047] The aforementioned positive electrode sheet specifically includes a positive current collector and a positive active layer containing positive active material disposed on the surface of the positive current collector.

[0048] The aforementioned positive electrode active material may include one or more of layered oxides, Prussian blue compounds, and polyanionic compounds, such as sodium iron phosphate (NFPP).

[0049] In the specific preparation of the positive electrode sheet, for example, the above-mentioned positive electrode active material, conductive agent, and binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling, and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder, and further comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0050] The areal density of the aforementioned positive electrode can be 110~130 g / m³. 2 .

[0051] The positive electrode current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, carbon fiber, carbon nanotubes, and conductive graphite; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0052] The embodiments of the present invention are not strictly limited to the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in sodium-ion batteries, such as hard carbon, soft carbon, titanium-based materials, metal oxides and sulfides.

[0053] In practice, N-methylpyrrolidone (NMP) can be used as a solvent to prepare the negative electrode slurry together with the above-mentioned negative electrode active material.

[0054] The embodiments of this invention do not strictly limit the selection of the electrolyte, which may include one or more solvents commonly used in sodium-ion battery electrolytes, as well as electrolyte sodium salts commonly used in sodium-ion electrolytes. For example, the solvent may be ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the electrolyte may be one or more of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium fluorotrifluoromethanesulfonylimide. The embodiments of this invention do not particularly limit the concentration of the electrolyte and the ratio of the solvent in the above-mentioned electrolyte. For example, the electrolyte may include EC, PC, and sodium hexafluorophosphate, wherein the volume ratio of EC to PC is 1:1, and the concentration of sodium hexafluorophosphate in the above-mentioned electrolyte is 1 mol / L.

[0055] The embodiments of the present invention do not strictly limit the choice of membrane material. It can be one of the membrane materials commonly used in sodium-ion batteries, such as polypropylene membrane (PP), polyethylene membrane (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun membrane (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven membrane, and membrane with ceramic coating.

[0056] In the preparation of sodium-ion batteries, the positive electrode sheet, the modified separator mentioned above, and the negative electrode sheet are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. After the battery is placed, formed, and resealed, the preparation of the sodium-ion battery (finished battery) is completed.

[0057] The above-mentioned formation is performed under negative voltage, using a current of 0.02C-0.2C.

[0058] It should be noted that after the above formation process is completed, the gas generated in the battery should be extracted.

[0059] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0060] Nanocellulose is a type of cellulose nanofiber with a diameter of 50-500 nm and a length of 0.2-20 μm.

[0061] Example 1

[0062] The modified diaphragm in this embodiment was obtained by the following preparation method:

[0063] Nanocellulose was dispersed in NMP to obtain nanocellulose slurry;

[0064] The above-mentioned nanocellulose slurry was mixed with Na2C2O4 with a particle size of 200nm, and then subjected to ultrasonic treatment to obtain a mixture, wherein the mass ratio of Na2C2O4 with a particle size of 200nm to the mass of nanocellulose was 1:1 (50%:50%).

[0065] The above mixture was subjected to vacuum filtration to form a membrane layer, and then dried to obtain a modified membrane with a thickness of 10 μm.

[0066] Example 2

[0067] This embodiment is basically the same as Embodiment 1, except that:

[0068] The mass ratio of Na2C2O4 with a particle size of 200 nm to that of nanocellulose was 1:19 (5%:95%), and the thickness of the modified membrane was 40 μm; other conditions remained unchanged.

[0069] Example 3

[0070] This embodiment is basically the same as Embodiment 1, except that:

[0071] The mass ratio of Na2C2O4 with a particle size of 200 nm to that of nanocellulose was 1:9 (10%:90%), and the thickness of the modified membrane was 35 μm; other conditions remained unchanged.

[0072] Example 4

[0073] This embodiment is basically the same as Embodiment 1, except that:

[0074] The mass ratio of Na2C2O4 with a particle size of 200 nm to that of nanocellulose was 18:82 (18%:82%), and the thickness of the modified membrane was 20 μm; other conditions remained unchanged.

[0075] Example 5

[0076] This embodiment is basically the same as embodiment 4, except that:

[0077] The thickness of the modified membrane was 20 μm, with Na2C2O4 particles of 100 nm replacing Na2C2O4 particles of 200 nm; other conditions remained unchanged.

[0078] Example 6

[0079] This embodiment is basically the same as embodiment 4, except that:

[0080] The thickness of the modified membrane was 20 μm, with Na2C4O4 having a particle size of 200 nm replacing Na2C2O4 with Na2C4O4 having a particle size of 200 nm; other conditions remained unchanged.

[0081] Example 7

[0082] This embodiment is basically the same as embodiment 4, except that:

[0083] Replace Na2C2O4 with Na2C4O4 with a particle size of 200 nm; keep other conditions unchanged.

[0084] Example 8

[0085] This embodiment is basically the same as embodiment 4, except that:

[0086] Replace the 200 nm Na2C2O4 with Na2C4O4 with a particle size of 500 nm (0.5 μm); keep other conditions unchanged.

[0087] Example 9

[0088] This embodiment is basically the same as embodiment 4, except that:

[0089] Replace Na2C2O4 with Li2C4O4 with a particle size of 200 nm; keep other conditions unchanged.

[0090] Comparative Example 1

[0091] The diaphragm in this comparative example was prepared by the following method:

[0092] Nanocellulose was dispersed in NMP to obtain nanocellulose slurry;

[0093] The above-mentioned nanocellulose slurry was subjected to ultrasonic treatment to obtain a mixture.

[0094] The above mixture was subjected to vacuum filtration to form a membrane layer, and then dried to obtain a membrane with a thickness of 20 μm.

[0095] Comparative Example 2

[0096] A polyolefin membrane (PP) with a thickness of 20 μm.

[0097] Experimental Example 1

[0098] The following parameters of the modified membranes in each embodiment and comparative example were tested:

[0099] The mass percentage of sodium supplement in the modified diaphragm: Since the sodium supplement is soluble in water, the modified diaphragm can be dissolved in water. After its mass becomes constant, the mass of the modified diaphragm after dissolving in water is measured. Then, the mass percentage of sodium supplement is calculated according to the following formula: (mass of the modified diaphragm before dissolving in water - mass of the modified diaphragm after dissolving in water) / mass of the modified diaphragm before dissolving in water. It should be noted that the above masses are the masses measured after the modified diaphragm is dried at 60-80℃.

[0100] Particle size of sodium supplement in modified diaphragm: characterized by scanning electron microscopy (SEM);

[0101] Thickness of the modified diaphragm: tested using a contact thin film thickness gauge;

[0102] Table 1

[0103]

[0104] Experimental Example 2

[0105] The modified separators of each embodiment and comparative example were assembled with positive and negative electrode sheets, and then an electrolyte was injected. After negative pressure formation (using a current of 0.02C-0.2C), a sodium-ion battery was obtained.

[0106] The positive electrode sheet is prepared according to the following process: Sodium iron phosphate (NFPP), carbon black and polytetrafluoroethylene are dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on aluminum foil, and after drying, rolling and cutting, the positive electrode sheet is obtained.

[0107] The negative electrode sheet is prepared by the following process: hard carbon, carbon black and polytetrafluoroethylene are dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform negative electrode slurry; the negative electrode slurry is uniformly coated on aluminum foil, and after drying, rolling and cutting, the negative electrode sheet is obtained.

[0108] The electrolyte consists of EC, PC and sodium hexafluorophosphate, wherein the volume ratio of EC to PC is 1:1, and the concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L.

[0109] The following parameters of the sodium-ion batteries in each embodiment and comparative example were tested:

[0110] 1) Porosity of the modified separator: The formed battery was disassembled to obtain the separator, which was then dried and tested using a separator porosity analyzer.

[0111] 2) Charge / discharge specific capacity: Using a charge / discharge tester, the sodium-ion battery is set to the charging state, i.e., the working electrode is desodiumed, the charging current density is 0.1C, and the operation stops when the cutoff voltage is 4.5V. The first charge specific capacity is calculated; the discharge current density is 0.1C, and the discharge ends when the cutoff voltage is 2.0V. The first discharge specific capacity is calculated. Wherein, the first charge specific capacity (mAh / g) = first charge capacity / mass of positive electrode active material, and the first discharge specific capacity (mAh / g) = first discharge capacity / mass of active material.

[0112] Table 2

[0113]

[0114] Test results show that Examples 2-5 and Example 7 have significantly better sodium replenishment effects than Comparative Example 2, but Comparative Example 1 performs poorly. This indicates that the novel sodium-replenishing membrane can fulfill the basic function of isolating the positive and negative electrodes, and its actual effect is no less than that of the polyolefin membrane, while also exhibiting a significant sodium replenishment effect. Therefore, the preferred mass fraction of the sodium replenishing agent is 10-18 wt.%; the preferred mass fraction of the base membrane (such as cellulose and its derivatives) is 82-90 wt.%. The preferred particle size range of the sodium replenishing agent is 0.2-0.5 μm.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 invention.

Claims

1. A modified diaphragm, characterized in that, The modified membrane includes a base membrane and an alkali metal supplement, wherein the alkali metal supplement is embedded in the base membrane, and the alkali metal supplement includes a sodium supplement or a lithium supplement. The particle size of the alkali metal supplement is 0.05~1μm, and in the modified membrane, the mass percentage of the base membrane is 50%~95%, and the mass percentage of the alkali metal supplement is 5%~50%.

2. The modified diaphragm according to claim 1, characterized in that, In the modified diaphragm, the base membrane has a mass percentage content of 82% to 90%, and the alkali-supplementing metal agent has a mass percentage content of 10% to 18%.

3. The modified diaphragm according to claim 1, characterized in that, The particle size of the alkali-supplementing metal agent is 0.2~0.5μm.

4. The modified diaphragm according to any one of claims 1-3, characterized in that, The base membrane includes one or more composite membranes selected from polyethylene membrane, polypropylene membrane, glass fiber membrane, and cellulose membrane; And / or, the sodium supplement includes Na x C y O z Where x≥1, y≥1, z≥3; And / or, the lithium supplement includes Li x C y O z , where x≥1, y≥1, z≥3.

5. The modified diaphragm according to any one of claims 1-3, characterized in that, The thickness of the modified diaphragm is 4~40μm.

6. A method for preparing the modified diaphragm according to any one of claims 1-5, characterized in that, include: The raw materials for the base film are dispersed in a solvent to obtain a slurry; The slurry is mixed with the alkali-adding metal agent to obtain a mixture. The mixture is made into a film layer, and then the solvent is removed to obtain the modified membrane.

7. The method for preparing the modified diaphragm according to claim 6, characterized in that, Also includes: The raw materials of the alkali-supplementing metal agent are ground to obtain the alkali-supplementing metal agent.

8. The method for preparing the modified diaphragm according to claim 6, characterized in that, The solvent includes one or more of N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide; And / or, the process of mixing the slurry with the alkali-adding metal agent to obtain a mixture includes: mixing the slurry with the alkali-adding metal agent, and then subjecting it to ultrasonic treatment to obtain the mixture.

9. The method for preparing the modified diaphragm according to any one of claims 6-8, characterized in that, The process of forming a film layer from the mixture and then removing the solvent to obtain the modified membrane includes: The mixture is subjected to vacuum filtration to form a membrane layer, and then dried to obtain the modified diaphragm.

10. A battery, characterized in that, The battery includes the modified separator according to any one of claims 1-5 or the modified separator obtained by the preparation method of the modified separator according to any one of claims 6-9.

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