Diaphragm, secondary battery, and electric device

Abstract

The invention provides a diaphragm, a secondary battery and an electric device. The separator comprises a base film and a coating layer coated on at least one surface of the base film, the coating layer comprises a composition containing keratin, a thickening agent and an active metal supplement, and the active metal is selected from lithium or sodium.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a separator, a secondary battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power plants, thermal power plants, wind power plants, and solar power plants, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are also put forward for their performance and the like.

[0003] As the number of charge-discharge cycles of secondary batteries increases, the amount of recyclable active metal ions in secondary batteries decreases, and the capacity retention rate of secondary batteries after long-term cycling still needs to be improved. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a separator that can slowly release and supplement active metal ions, thereby improving the capacity retention rate of secondary batteries after long-term cycling. In addition, the purpose of the present application is also to provide a secondary battery and an electrical device including the separator.

[0005] To achieve the above object, the present application provides a separator, a secondary battery, and an electrical device.

[0006] In a first aspect of the present application, there is provided a separator, the separator including a base film and a coating applied on at least one surface of the base film, the coating including a composition containing keratin, a thickener, and an active metal supplement, and the active metal being selected from lithium or sodium.

[0007] Thus, the coating of the separator in the present application includes a composition containing keratin, a thickener, and an active metal supplement, and this composition is used to slowly release and supplement active metal ions. Keratin and the thickener can form a cross-linked network structure that encapsulates the active metal supplement. As the number of charge-discharge cycles of the secondary battery increases, the active metal supplement in the cross-linked network structure slowly releases active metal ions to supplement the consumption of active metal ions in the secondary battery, thereby improving the capacity retention rate of the secondary battery after long-term cycling.

[0008] In some embodiments, the thickener includes at least one of propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium carboxymethylcellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, polyvinylpyrrolidone, arabic gum, pectin, agar, gelatin, seaweed gum, and carrageenan.

[0009] Thus, the above thickener can form a cross-linked network structure with keratin, and the material of the thickener is easily obtained. In addition, some thickeners in the above thickeners, such as sodium carboxymethyl cellulose, can also play a binding role to facilitate the adhesion of the coating to the base film.

[0010] In some embodiments, the active metal is sodium, and the active metal supplement includes at least one of Na2CO3, NaN3, Na2O, Na2TiO3, NaF, Na2SiO3, Na2S, Na3P, Na3N, Na2O2 and Na2N4O2; or,

[0011] The active metal is lithium, and the active metal supplement includes at least one of Li2CO3, LiN3, Li2O, Li2TiO3, LiF, Li2SiO3, Li2S, Li3P, Li3N, Li2O2 and Li2N4O2.

[0012] Thus, the above active metal supplement can supplement the active metal ions consumed in the secondary battery and is easily obtained.

[0013] In some embodiments, based on the total solid content of the composition, the content of keratin is 5 wt% to 35 wt%, the content of the thickener is 2 wt% to 15 wt%, and the content of the active metal supplement is 50 wt% to 90 wt%.

[0014] Thus, by selecting appropriate contents of keratin, thickener and active metal supplement in this application, it helps to improve the function of the coating for slowly releasing active metal ions, and further improves the capacity retention rate after long-term cycling of the secondary battery.

[0015] In some embodiments, the composition further includes a binder; optionally, the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyethylene oxide and sodium polyacrylate. When the binder includes at least one of sodium carboxymethyl cellulose, polyethylene oxide and sodium polyacrylate, the thickener is different from the binder.

[0016] Thus, the coating of this application can also include a binder to further enhance the binding effect, which helps to adhere the coating to the base film, thereby reducing the probability of the coating peeling off from the surface of the base film.

[0017] In some embodiments, based on the total solid content of the composition, the content of keratin is 5 wt% to 35 wt%, the content of the thickener is 2 wt% to 15 wt%, the content of the active metal supplement is 50 wt% to 90 wt%, and the content of the binder is 1 wt% to 5 wt%.

[0018] Thus, by selecting appropriate contents of keratin, thickener, active metal supplement, and binder, the present application further enhances the bonding effect, contributing to improving the adhesion of the coating on the base film.

[0019] In some embodiments, the coating further comprises inorganic particles and a surfactant.

[0020] Optionally, based on the total weight of the coating, the content of the composition is 10 wt% to 45 wt%, the content of the inorganic particles is 45 wt% to 80 wt%, and the content of the surfactant is 5 wt% to 15 wt%.

[0021] Thus, by selecting appropriate contents of inorganic particles, the separator of the present application has good heat resistance and mechanical strength; by selecting appropriate contents of the surfactant, it is beneficial to the uniform mixing of the components in the coating, and the surfactant can also delay the drying process of the coating, enabling the coating to dry at an appropriate speed so as not to crack due to too fast drying.

[0022] In some embodiments, the inorganic particles include at least one of alumina, titanium oxide, silicon oxide, zirconium oxide, boehmite, aluminum nitride, yttrium oxide, and cerium oxide.

[0023] In some embodiments, the surfactant includes an anionic surfactant or an amphoteric surfactant.

[0024] Optionally, the surfactant includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, betaine, sulfobetaine, and amino acid-based surfactants.

[0025] In some embodiments, the base film includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyvinylidene fluoride, polyamide, and polyimide.

[0026] The second aspect of the present application provides a secondary battery, which includes: a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet, and the separator includes the separator of the first aspect of the present application. Thus, the secondary battery has excellent capacity retention rate after long-term cycling.

[0027] The third aspect of the present application provides an electrical device, including the secondary battery of the second aspect of the present application.

[0028] The present application provides a separator, a secondary battery, and an electrical device. The separator includes a composition for slowly releasing and supplementing an active metal, the active metal being selected from lithium or sodium, and the composition includes keratin, a thickening agent, and an active metal supplement. As the number of charge-discharge cycles of the secondary battery increases, the active metal ions are continuously consumed, and the active metal supplement in the separator can slowly release active metal ions for supplementation, thereby improving the capacity retention rate of the secondary battery after long-term cycling. Description of the Drawings

[0029] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0030] Figure 2 is Figure 1 an exploded view of the battery cell shown in an embodiment of the present application.

[0031] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0032] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0033] Figure 5 is Figure 4 an exploded view of the battery pack shown in an embodiment of the present application.

[0034] Figure 6 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0035] Description of the Reference Numerals:

[0036] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. Detailed Embodiments

[0037] Hereinafter, embodiments of the separator, secondary battery, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is just an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] If there is no special instruction, all implementation manners and optional implementation manners of this application can be combined with each other to form a new technical solution.

[0040] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] If there is no special instruction, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0042] If there is no special instruction, the numerical values of the various parameters mentioned in this application can be measured by various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0043] If there is no special instruction, in this application, the term "active metal ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions and sodium ions.

[0044] Secondary batteries may include active metal ion batteries, such as sodium ion batteries and lithium ion batteries, and the working principles of sodium ion batteries and lithium ion batteries are similar. In active metal ion batteries, active metal ions are reversibly embedded and released between the positive electrode and the negative electrode to achieve energy storage and release. However, during the first charge and discharge process of active metal ion batteries, some active metal ions will be consumed due to some irreversible reactions such as the formation of a solid electrolyte membrane at the negative electrode, thereby causing the loss of active metal ions in the positive electrode material, thereby reducing the energy density of the active metal ion battery, that is, reducing the first coulomb efficiency of the active metal ion battery.

[0045] Moreover, as the active metal ion battery is charged and discharged, the active metal ions are continuously consumed, for example, the active metal ions are embedded in the negative electrode, and the amount of active metal ions that can be circulated is reduced. Therefore, as the number of charge and discharge cycles of the active metal ion battery increases, the capacity retention rate of the active metal ion battery decreases.

[0046] Taking sodium-ion batteries as an example, in order to improve the initial coulombic efficiency of sodium-ion batteries, sodium-supplementing additives can be covered on the base film and used as battery separators. During the initial charge and discharge process of the sodium-ion battery, the separator can release sodium ions, which are replenished to the positive electrode through the electrolyte to solve the problem of reduced initial coulombic efficiency of the sodium-ion battery. However, the above-mentioned sodium-supplementing additive releases all sodium ions at once during the initial charge and discharge process. As the number of charge and discharge cycles of the sodium-ion battery increases, sodium ions are continuously consumed, and the sodium-supplementing additive cannot continuously release sodium ions for replenishment.

[0047] Based on this, the present application proposes a separator, a secondary battery and an electrical device.

[0048] A first aspect of the present application provides a separator, comprising a base film and a coating coated on at least one surface of the base film, wherein the coating comprises a composition containing keratin, a thickener and an active metal supplement, wherein the active metal is selected from lithium or sodium.

[0049] Therefore, the diaphragm in the present application includes a base film and a coating coated on the base film, the coating includes a composition for sustained-release supplementation of active metal ions, the active metal is selected from lithium or sodium, and the composition includes keratin, a thickener and an active metal supplement. The keratin and thickener in the coating can form a cross-linked network structure that encapsulates the active metal supplement, for example, through cross-linking. As the number of charge and discharge cycles of the secondary battery increases, the active metal ions are continuously consumed, and the amount of active metal ions that can be circulated in the secondary battery decreases. At this time, the active metal supplement in the cross-linked network structure encapsulated in the coating slowly releases the active metal ions, replenishes the consumption of the active metal ions in the secondary battery, and can thereby improve the capacity retention rate of the secondary battery after long-term cycling.

[0050] The coating on the base film mentioned in the present application includes a composition for sustained release and supplementation of active metals, the composition including keratin, a thickener and an active metal supplement. By disassembling a secondary battery that has undergone a certain number of charge and discharge cycles and measuring the content of active metal ions remaining on the diaphragm, it can be determined whether the solution for sustained release and supplementation of active metal ions of the present application is used. Taking sodium ion batteries as an example, conventional sodium supplement additives release all sodium ions at once during the first charge and discharge process. In this case, for secondary batteries that have undergone a certain number of charge and discharge cycles, the residual sodium ion content on the diaphragm can be ignored. In the technical solution of the present application, sodium ions are slowly released as the secondary battery undergoes a certain number of charge and discharge cycles, that is, for secondary batteries that have undergone a certain number of charge and discharge cycles, sodium ions will still remain on the diaphragm. Therefore, it is possible to determine whether the technical solution of the present application is used by measuring the content of active metal ions remaining on the diaphragm.

[0051] The term "keratin" in this application is the main protein that constitutes the outer layer of hair, horns, claws and human skin. Keratin can protect epithelial tissue cells from damage or pressure. Keratin contains a high level of cysteine, so keratin contains more disulfide bonds, which can play a cross-linking role in the protein peptide chain. Therefore, the chemical properties of keratin are relatively stable and the mechanical strength is relatively high. The spatial structure of keratin has an α-helical structure (α-keratin) and a β-pleated sheet structure (β-keratin). This application has no special restrictions on the spatial structure of keratin, and both α-keratin and β-keratin can be used in coatings.

[0052] In some embodiments, the base film includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyvinylidene fluoride, polyamide, and polyimide.

[0053] In some embodiments, the base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0054] In some embodiments, the thickener includes at least one of propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium carboxymethylcellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, polyvinyl pyrrolidone, gum arabic, pectin, agar, gelatin, alginate and carrageenan.

[0055] In the present application, a cross-linked network structure encapsulating the active metal supplement is formed by a thickening agent and keratin. During the charge and discharge cycles of the secondary battery, the active metal supplement encapsulated in the cross-linked network structure slowly releases active metal ions, thereby improving the capacity retention rate of the secondary battery after long-term cycling. Thus, the above-mentioned thickening agent and keratin can form a cross-linked network structure, and the materials of the thickening agent are easily obtained. In addition, some thickening agents in the above-mentioned thickening agent, such as sodium carboxymethyl cellulose, can also play a binding role to facilitate the adhesion of the coating to the base film.

[0056] In some embodiments, the active metal is sodium, and the active metal supplement includes at least one of Na2CO3, NaN3, Na2O, Na2TiO3, NaF, Na2SiO3, Na2S, Na3P, Na3N, Na2O2, and Na2N4O2; or,

[0057] the active metal is lithium, and the active metal supplement includes at least one of Li2CO3, LiN3, Li2O, Li2TiO3, LiF, Li2SiO3, Li2S, Li3P, Li3N, Li2O2, and Li2N4O2.

[0058] In some embodiments, the particle size range of the active metal supplement is 50 nm to 2 μm; optionally, the particle size range of the active metal supplement is 200 nm to 1 μm.

[0059] Thus, the active metals in the present application include lithium and sodium. For lithium-ion batteries, lithium-ion supplements can be used, and for sodium-ion batteries, sodium-ion supplements can be used.

[0060] In some embodiments, based on the total solid content of the composition, the content of keratin is 5 wt% to 35 wt%, optionally 10 wt% to 30 wt%; the content of the thickening agent is 2 wt% to 15 wt%, optionally 5 wt% to 10 wt%; and the content of the active metal supplement is 50 wt% to 90 wt%, optionally 60 wt% to 85 wt%.

[0061] In a specific embodiment, based on the total solid content of the composition, the content of keratin is 20 wt%, the content of the thickening agent is 10 wt%, and the content of the active metal supplement is 70 wt%.

[0062] Thus, by selecting appropriate contents of keratin, thickening agent, and active metal supplement in the present application, it helps to improve the function of the coating in slowly releasing active metal ions, thereby improving the capacity retention rate of the secondary battery after long-term cycling.

[0063] In some embodiments, the composition further comprises a binder. Optionally, the binder comprises at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyethylene oxide, and sodium polyacrylate. When the binder comprises at least one of sodium carboxymethyl cellulose, polyethylene oxide, and sodium polyacrylate, the thickener is different from the binder.

[0064] Thus, the coating of the present application may further include a binder to further enhance the binding effect, which helps to adhere the coating to the base film, thereby reducing the probability of the coating peeling off from the surface of the base film.

[0065] In some embodiments, based on the total solid content of the composition, the content of the keratin is 5 wt% to 35 wt%, optionally 10 wt% to 30 wt%; the content of the thickener is 2 wt% to 15 wt%, optionally 5 wt% to 10 wt%; the content of the active metal supplement is 50 wt% to 90 wt%, optionally 60 wt% to 85 wt%; and the content of the binder is 1 wt% to 5 wt%, optionally 2 wt% to 5 wt%.

[0066] Thus, by selecting appropriate contents of keratin, thickener, active metal supplement, and binder, the present application further enhances the binding effect, which helps to improve the adhesion of the coating to the base film.

[0067] In some embodiments, the coating further comprises inorganic particles and a surfactant.

[0068] Optionally, based on the total weight of the coating, the content of the composition is 10 wt% to 45 wt%, optionally 15 wt% to 40 wt%; the content of the inorganic particles is 45 wt% to 80 wt%, optionally 50 wt% to 75 wt%; and the content of the surfactant is 5 wt% to 15 wt%, optionally 5 wt% to 10 wt%.

[0069] Here, the content of the composition refers to the weight of the solid substances contained in the composition.

[0070] Thus, the coating of the present application further comprises inorganic particles and a surfactant. Among them, the inorganic particles can improve the heat resistance of the separator and enhance the mechanical strength of the separator, thereby reducing the contact between the positive and negative electrodes caused by the shrinkage of the separator; the surfactant is beneficial to the uniform mixing of the components in the coating, and the surfactant can also delay the drying process of the coating, so that the coating dries at a suitable speed and does not crack due to too fast drying. By selecting appropriate contents of the composition, inorganic particles, and surfactant, the separator has good heat resistance, mechanical strength, and a crack-free coating surface.

[0071] In some embodiments, the inorganic particles include at least one of alumina, titanium oxide, silicon oxide, zirconium oxide, boehmite, aluminum nitride, yttrium oxide, and cerium oxide.

[0072] In some embodiments, the particle size range of the inorganic particles is from 200 nm to 3 μm; optionally, the particle size range of the inorganic particles is from 500 nm to 2 μm.

[0073] Thus, the above-mentioned inorganic particles can improve the heat resistance of the separator and enhance the mechanical strength of the separator, thereby reducing the contact between the positive and negative electrodes caused by the shrinkage of the separator, and further improving the safety of the secondary battery.

[0074] In some embodiments, the surfactant includes an anionic surfactant or an amphoteric surfactant;

[0075] Optionally, the surfactant includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, betaine, sulfobetaine, and amino acid-based surfactants.

[0076] Thus, the above-mentioned surfactant helps to mix the components in the coating evenly, and the surfactant can delay the drying process of the coating, so that the coating dries at a suitable speed and does not crack due to too fast drying.

[0077] This application also provides a method for preparing a separator, the method comprising:

[0078] Providing a base film;

[0079] Providing a composition containing keratin, a thickener, and an active metal supplement, wherein the active metal is selected from lithium or sodium;

[0080] Providing a coating slurry, the coating slurry comprising a composition containing keratin, a thickener, and an active metal supplement; and

[0081] Coating the coating slurry on at least one surface of the base film to form a separator;

[0082] Wherein, providing a composition containing keratin, a thickener, and an active metal supplement includes:

[0083] Dissolving keratin in a solvent to obtain a keratin solution; and

[0084] Adding the thickener and the active metal supplement to the keratin solution and mixing evenly, and filtering to obtain the composition.

[0085] In some embodiments, the solid content range of the composition can be from 40% to 60%, but is not limited thereto.

[0086] In some embodiments, keratin can be dissolved in a weakly alkaline aqueous solution to obtain a keratin solution.

[0087] The weakly alkaline aqueous solution can be an aqueous solution of common alkaline compounds, such as an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, or an aqueous ammonia solution, but not limited thereto. The pH value range of the weakly alkaline aqueous solution can be from 7.5 to 10.

[0088] In some embodiments, a thickening agent and an active metal supplement are added to the keratin solution and mixed evenly. To accelerate the dissolution rate, heating and stirring can be carried out. The heating temperature range can be from 40°C to 80°C; optionally, the heating temperature range can be from 50°C to 70°C, for example, the heating temperature can be 70°C. The stirring rate range can be from 400 r / min to 800 r / min. The mixing duration range can be from 0.5 h to 3 h; optionally, the mixing duration range can be from 0.5 h to 1.5 h, for example, the mixing duration can be 1 h.

[0089] In some embodiments, the coating slurry can be applied by microgravure coating. The present application does not have any special restrictions on the coating method of the coating slurry, as long as it can achieve the method of coating the slurry to form a coating.

[0090] In some embodiments, the thickness range of the coating can be from 0.5 μm to 6 μm; optionally, the thickness range of the coating can be from 2 μm to 4 μm.

[0091] Thus, in the present application, after blending keratin, a thickening agent, and an active metal supplement, a composition for sustained-release supplementation of active metal ions is obtained by filtration. The composition is used to prepare a coating slurry, and the coating slurry is applied to a base film to form a separator. Keratin and the thickening agent in the coating can form a cross-linked network structure that encapsulates the active metal supplement. As the number of charge-discharge cycles of the secondary battery increases, the active metal ions are continuously consumed, and the amount of recyclable active metal ions in the secondary battery decreases. At this time, the active metal supplement in the cross-linked network structure encapsulated in the coating slowly releases active metal ions to supplement the consumption of active metal ions in the secondary battery, thereby improving the capacity retention rate of the secondary battery after long-term cycling.

[0092] In some embodiments, the thickening agent includes at least one of propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, polyvinylpyrrolidone, gum arabic, pectin, agar, gelatin, seaweed gum, and carrageenan.

[0093] Thus, in the present application, the thickener and keratin can form a crosslinked network structure that encapsulates the active metal supplement. During the charge-discharge cycling of the secondary battery, the active metal supplement encapsulated in the crosslinked network structure slowly releases active metal ions to replenish the consumption of active metal ions in the secondary battery, thereby improving the capacity retention rate after long-term cycling of the secondary battery. Thus, the above-mentioned thickener and keratin can form a crosslinked network structure, and these thickeners are easily obtainable. In addition, some of the above-mentioned thickeners, such as sodium carboxymethyl cellulose, can also play a binding role to facilitate the adhesion of the coating to the base film.

[0094] In some embodiments, the active metal is sodium, and the active metal supplement includes at least one of Na2CO3, NaN3, Na2O, Na2TiO3, NaF, Na2SiO3, Na2S, Na3P, Na3N, Na2O2, and Na2N4O2; or,

[0095] the active metal is lithium, and the active metal supplement includes at least one of Li2CO3, LiN3, Li2O, Li2TiO3, LiF, Li2SiO3, Li2S, Li3P, Li3N, Li2O2, and Li2N4O2.

[0096] Thus, the active metals in the present application include lithium and sodium. For lithium-ion batteries, lithium-ion supplements can be used, and for sodium-ion batteries, sodium-ion supplements can be used.

[0097] In some embodiments, based on the total addition amount of the keratin, thickener, and active metal supplement, the addition amount of the keratin is 5 wt% to 35 wt%, optionally 10 wt% to 30 wt%, the addition amount of the thickener is 2 wt% to 15 wt%, optionally 5 wt% to 10 wt%, and the addition amount of the active metal supplement is 50 wt% to 90 wt%, optionally 60 wt% to 85 wt%.

[0098] Thus, by selecting appropriate contents of keratin, thickener, and active metal supplement in the present application, it helps to improve the effect of the coating in slowly releasing active metal ions, thereby improving the capacity retention rate after long-term cycling of the secondary battery.

[0099] In some embodiments, providing a composition containing keratin, thickener, and active metal supplement further includes: adding a binder to the keratin solution.

[0100] Thus, the composition of the present application can also include a binder to further enhance the binding effect, which helps to adhere the coating to the base film, thereby reducing the probability of the coating peeling off from the surface of the base film.

[0101] In some embodiments, based on the total addition amount of the keratin, thickener, binder, and active metal supplement, the addition amount of the keratin is 5 wt% to 35 wt%, optionally 10 wt% to 30 wt%; the addition amount of the thickener is 2 wt% to 15 wt%, optionally 5 wt% to 10 wt%; the addition amount of the binder is 1 wt% to 5 wt%, optionally 2 wt% to 5 wt%; and the addition amount of the active metal supplement is 50 wt% to 90 wt%, optionally 60 wt% to 85 wt%.

[0102] Thus, by selecting appropriate contents of the keratin, thickener, active metal supplement, and binder, the present application further enhances the bonding effect and helps to improve the adhesion of the coating on the base film.

[0103] In some embodiments, the coating slurry further includes inorganic particles and a surfactant.

[0104] Wherein, providing the coating slurry includes: mixing the composition for slow-release supplementation of active metal, inorganic particles, a surfactant, and a solvent to obtain the coating slurry. The solid content range of the coating slurry can be 50% to 65%, but is not limited thereto. Here, the solvent can be deionized water, but is not limited thereto.

[0105] Optionally, based on the total weight of the composition, inorganic particles, and surfactant, the mixing amount of the composition is 10 wt% to 45 wt%, optionally 15 wt% to 40 wt%; the mixing amount of the inorganic particles is 45 wt% to 80 wt%, optionally 50 wt% to 75 wt%; and the mixing amount of the surfactant is 5 wt% to 15 wt%, optionally 5 wt% to 10 wt%.

[0106] Here, the mixing amount of the composition for slow-release supplementation of active metal is based on the weight of the solid matter contained in the composition.

[0107] Thus, by selecting appropriate contents of the composition, inorganic particles, and surfactant, the present application enables the separator to have good heat resistance, mechanical strength, and a coating surface without cracking.

[0108] The present application further provides a secondary battery, which includes: a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate, and the separator includes the separator of the first aspect of the present application.

[0109] Thus, the secondary battery has an excellent capacity retention rate after long-term cycling.

[0110] In addition, the secondary battery and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0111] In one embodiment of the present application, a secondary battery is provided.

[0112] As used herein, the term "secondary battery" refers to a battery cell, a battery module, or a battery pack. These will be described separately below.

[0113] Generally, a secondary battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During battery charging and discharging, active metal ions are inserted into and extracted from between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short - circuit between the positive and negative electrodes and allowing ions to pass through.

[0114] Positive electrode plate

[0115] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0116] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0117] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, when the battery cell is a lithium - ion battery, the positive electrode active material can be a positive electrode active material known in the art for lithium - ion batteries. As an example, the positive electrode active material can include at least one of the following materials: lithium - containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and at least one of its modified compounds, etc. Examples of the olivine-structured lithium-containing phosphate may include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0119] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0120] In the listing of the positive electrode active material in this application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0121] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material can adopt the positive electrode active material known in the art for sodium-ion batteries. As an example, the positive electrode active material may include sodium transition metal oxides, polyanion-type compounds (phosphates, fluorophosphates, pyrophosphates, sulfates), Prussian blue compounds, etc. However, this application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery can also be used.

[0122] As an alternative technical solution of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1. For example, sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2).

[0123] As an alternative technical solution of the present application, the polyanionic compound may be a class of compounds having sodium ions, transition metal ions and tetrahedral (YO4) n- anion units. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be at least one of P, S and Si; n represents the valence state of (YO4) n- .

[0124] The polyanionic compound may also be a class of compounds having sodium ions, transition metal ions, tetrahedral (YO4) n- anion units and halogen anions. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be at least one of P, S and Si, n represents the valence state of (YO4) n- ; the halogen may be at least one of F, Cl and Br.

[0125] The polyanionic compound may also be a class of compounds having sodium ions, tetrahedral (YO4) n- anion units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y may be at least one of P, S and Si, n represents the valence state of (YO4) n-valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO y ) m+ valence state; the halogen can be at least one of F, Cl, and Br.

[0126] The polyanionic compound is, for example, NaFePO4, Na3V2(PO4)3, NaM’PO4F (M’ is one or several of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0 ≤ y ≤ 1), at least one of them.

[0127] The Prussian blue compound can be a kind of compound with sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0128] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode plate can be prepared in the following way: Disperse the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N - methylpyrrolidone) to form a positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0131] Negative electrode plate

[0132] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0133] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0134] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the negative electrode active material can be a negative electrode active material for a battery well-known in the art. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0136] In some embodiments, the negative electrode film layer may optionally further include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0137] In some embodiments, the negative electrode film layer may optionally further include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0139] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0140] Electrolyte

[0141] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0142] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0143] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0144] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0145] In some embodiments, the electrolytic solution may further optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0146] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0147] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte.

[0148] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0149] The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0150] In some embodiments, referring to Figure 2 , the outer packaging can include a housing 51 and a top cover assembly 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0151] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0152] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0153] Optionally, the battery module 4 can further include a housing with a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0154] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0155] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5, a battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0156] A third aspect of the present application provides an electric device, including the secondary battery of the second aspect of the present application. The secondary battery can be used as the power source of the electric device or as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0157] As the electric device, battery cells, battery modules or battery packs can be selected according to its usage requirements.

[0158] Figure 6 is an example electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electric device, a battery pack or a battery module can be used.

[0159] Another example device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery cell can be used as the power source.

[0160] Embodiment

[0161] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0162] The α-keratin used in the examples and comparative examples was purchased from Sigma-Aldrich Co., Ltd.

[0163] The alumina Al2O3 used in the examples and comparative examples, with Dv50 being 500 nm, was purchased from Aladdin Reagent Co., Ltd.

[0164] The positive electrode active material Na3V2(PO4)2F3 used in the examples and comparative examples was purchased from Sigma-Aldrich Co., Ltd.

[0165] The artificial graphite used in the examples and comparative examples was purchased from Aladdin Reagent Co., Ltd.

[0166] Example 1

[0167] 1. Preparation of separator

[0168] 20 parts by weight of α-keratin was added to an aqueous sodium hydroxide solution with a pH of 8 to dissolve and obtain a keratin aqueous solution of 1 mg / L. 70 parts by weight of Na2SiO3 and 10 parts by weight of sodium carboxymethyl cellulose (CMC-Na) were added, and heated and stirred at 70 °C and 600 r / min for 1 h. After cooling, a composition for slow-release supplement of sodium ions was obtained by filtration, and its solid content was 55%.

[0169] The above composition, alumina and sodium dodecyl sulfate (SDS) were added to deionized water according to a weight ratio of 25:65:10, and stirred evenly to obtain a coating slurry with a solid content of 60%. Here, the addition amount of the composition is based on the weight of the solid substance contained in the composition. The coating slurry was coated on a polypropylene base film by a one-time micro-recess coating method, and after drying, a coating was formed on the surface of the base film to obtain a separator. Among them, the thickness of the coating was 5 μm.

[0170] 2. Preparation of secondary battery

[0171] 2.1 Preparation of positive electrode sheet

[0172] The positive electrode active material Na3V2(PO4)2F3, binder polyvinylidene fluoride (PVDF) and conductive agent acetylene black were dispersed and dissolved in an N-methylpyrrolidone (NMP) solvent according to a mass ratio of 90:5:5, and stirred thoroughly and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on a positive electrode current collector aluminum foil, and then dried, cold-pressed and slit to obtain a positive electrode sheet.

[0173] 2.2 Preparation of negative electrode sheet

[0174] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water as a solvent according to a weight ratio of 96.2:0.8:0.8:1.2, and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry was evenly coated on a negative electrode current collector copper foil, and after drying, cold-pressing and slitting, a negative electrode sheet was obtained.

[0175] 2.3 Preparation of electrolyte

[0176] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3:7. 12.5% by mass of NaPF6 relative to the solvent was dissolved in the organic solvent and stirred evenly to obtain an electrolyte solution.

[0177] 2.4 Preparation of secondary battery

[0178] The positive electrode sheet, the separator of Example 1, and the negative electrode sheet were stacked in sequence, with the separator placed between the positive and negative electrode sheets to play an insulating role. Then it was wound to obtain a bare battery core, the tabs were welded to the bare battery core, and the bare battery core was placed in an aluminum shell, baked at 100 °C to remove water, then the electrolyte solution was injected and sealed to obtain a non-charged battery. The non-charged battery was then successively subjected to processes such as standing, thermal and cold pressing, formation, shaping, and capacity testing to obtain a secondary battery.

[0179] Example 1A

[0180] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of the composition for slowly releasing and supplementing active metal, alumina, and sodium dodecyl sulfate was 40:50:10.

[0181] Example 1B

[0182] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of the composition for slowly releasing and supplementing active metal, alumina, and sodium dodecyl sulfate was 15:75:10.

[0183] Example 2

[0184] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of α-keratin, thickener CMC-Na, and active metal supplement Na2SiO3 was 30:10:60.

[0185] Example 3

[0186] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of α-keratin, thickener CMC-Na, and active metal supplement Na2SiO3 was 10:5:85.

[0187] Example 4

[0188] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the thickener was replaced by polyoxyethylene.

[0189] Example 5

[0190] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the thickener was replaced with sodium polyacrylate.

[0191] Example 6

[0192] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the active metal supplement was replaced with Na2CO3.

[0193] Example 7

[0194] 20 parts by weight of α-keratin was added to an aqueous sodium hydroxide solution with a pH of 8 and dissolved to obtain a keratin aqueous solution of 1 mg / L. 70 parts by weight of the active metal supplement Na2SiO3, 8 parts by weight of the thickener gelatin, and 2 parts by weight of the binder styrene-butadiene rubber SBR were added. It was heated and stirred at 70 °C and 600 r / min for 1 h. After cooling, a composition for slow-release supplement of sodium ions was obtained by filtration. Others were prepared in the same manner as in Example 1 to obtain a separator and the corresponding secondary battery.

[0195] Comparative Example 1

[0196] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that the thickener CMC-Na was not added and the addition amount of α-keratin was changed from 20 parts by weight to 30 parts by weight.

[0197] Here, the sum of the weights of the active metal supplement Na2SiO3 and α-keratin in Comparative Example 1 was the same as the sum of the weights of α-keratin, the active metal supplement Na2SiO3, and the thickener CMC-Na in Example 1.

[0198] Comparative Example 2

[0199] A separator and the corresponding secondary battery were prepared in the same manner as in Example 1, except that α-keratin was not added and the addition amount of the thickener CMC-Na was changed from 10 parts by weight to 30 parts by weight.

[0200] Here, the sum of the weights of the active metal supplement Na2SiO3 and the thickener CMC-Na in Comparative Example 2 was the same as the sum of the weights of α-keratin, the active metal supplement Na2SiO3, and the thickener CMC-Na in Example 1.

[0201] The parameters of the above examples and comparative examples are shown in Tables 1 to 3.

[0202] Performance Test of the Separator

[0203] 1. Air Permeability Test

[0204] The air permeability of the separator in the examples and comparative examples was measured using an AirPerm M021A air permeability tester.

[0205] 2. Thermal shrinkage performance test

[0206] Referring to the standard ISO 14616-1997 "Thermally Shrinkable Films of Polyethylene, Ethylene Copolymers and Their Mixtures - Determination of Shrinkage Stress", using an FST-02 film thermal shrinkage rate tester, the test sample was cut into a long strip sample of 15 mm × 130 mm, and the thermal shrinkage rate of the separator heat-treated at 130 °C for 30 min was measured.

[0207] Table 1: Composition of the composition for slow-release supplementation of active metal

[0208]

[0209] Table 2: Composition of the coating

[0210]

[0211] Performance test of secondary battery

[0212] 1. First-cycle charge-discharge specific capacity test

[0213] At 25 °C, the secondary battery was charged at a constant current of 0.33C to the charge termination voltage of 4.3V, and then charged at a constant voltage until 0.05C. The charging capacity Ec0 was measured. Dividing Ec0 by the mass of the positive active material in the secondary battery, the charging specific capacity can be obtained. That is: charging specific capacity (mAh / g) = first-cycle charging capacity / mass of the positive active material.

[0214] Take the above-mentioned charged battery, and discharge it at a constant current of 0.33C to the discharge termination voltage of 2.8V at 25 °C. The discharge capacity was measured as Ed0. Dividing Ed0 by the mass of the positive active material in the battery, the discharge specific capacity can be obtained. That is: discharge specific capacity (mAh / g) = first-cycle discharge capacity / mass of the positive active material.

[0215] The above tests of charging specific capacity and discharge specific capacity were repeated 5 times and the average value was taken.

[0216] 2. Capacity retention rate test

[0217] At 25 °C, the secondary battery was charged at a constant current of 1 / 3C to 4.3V, and then charged at a constant voltage of 4.3V until the current was 0.05C, left standing for 5 min, and then discharged at 1 / 3C to 2.8V. The obtained capacity was recorded as the initial capacity C0. Repeat the above steps for the same secondary battery, and at the same time record the discharge capacity C of the battery after the nth cycle n , then the capacity retention rate P of the battery after each cyclen = C n / C0 * 100%. During this test process, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2,..., and the 800th cycle corresponds to n = 800. The battery capacity retention data corresponding to the examples and comparative examples in Table 3 are the data measured after 800 cycles under the above test conditions, that is, the value of P 800 value.

[0218] Table 3: Performance of the separator and performance of the secondary battery

[0219]

[0220] The smaller the value of the air permeability, the better the air permeability of the separator. As shown in Table 3, the air permeability of the separators of Examples 1, 1A, 1B and Examples 2 to 7 of the present application is either better than that of the separators of Comparative Examples 1 to 2 or comparable to that of the separators of Comparative Examples 1 to 2. This indicates that adding the composition for slowly releasing and supplementing active metal does not have an adverse effect on the air permeability of the separator.

[0221] The smaller the value of the thermal shrinkage rate, the better the dimensional stability of the separator at high temperature. As shown in Table 3, the thermal shrinkage rate of the separators of Examples 1, 1A, 1B and Examples 2 to 7 of the present application is either better than that of the separators of Comparative Examples 1 to 2 or comparable to that of the separators of Comparative Examples 1 to 2. This indicates that adding the composition for slowly releasing and supplementing active metal does not have an adverse effect on the thermal shrinkage rate of the separator.

[0222] Table 3 also shows the test results of the first-cycle charge specific capacity, first-cycle discharge specific capacity and 800-cycle capacity retention rate of the secondary batteries made of the separators of each example and comparative example. By comparing Examples 1, 1A, 1B and Examples 2 to 7 with Comparative Examples 1 to 2, it can be seen that the first-cycle charge specific capacity and first-cycle discharge specific capacity of each example are respectively comparable to those of Comparative Examples 1 to 2. This indicates that during the first-cycle charge and discharge process, the sodium supplementing agent added in each example and comparative example plays a role in supplementing sodium. However, the test results of the 800-cycle capacity retention rate in Examples 1, 1A, 1B and Examples 2 to 7 are far better than those of Comparative Examples 1 and 2. This indicates that although during the first-cycle charge and discharge process, the sodium supplementing agent added in each example and comparative example plays a role in supplementing sodium, as the number of charge and discharge cycles of the secondary battery increases, the sodium supplementing agent in Comparative Examples 1 and 2 no longer plays a role in supplementing sodium, while the slow-release sodium supplementing composition in Examples 1, 1A, 1B and Examples 2 to 7 of the present application still plays a role, achieving the effect of slow-release sodium supplementation.

[0223] It should be noted that this application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having the same composition in terms of technical idea and achieving the same effects within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base film and a coating applied on at least one surface of the base film, and the coating includes a composition containing keratin, a thickening agent, and an active metal supplement, and the active metal is selected from lithium or sodium.

2. The diaphragm according to claim 1, wherein, The thickening agent includes at least one of propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, polyvinylpyrrolidone, gum arabic, pectin, agar, gelatin, seaweed glue, and carrageenan.

3. The diaphragm according to claim 1 or 2, characterized in that, The active metal is sodium, and the active metal supplement includes at least one of Na2CO3, NaN3, Na2O, Na2TiO3, NaF, Na2SiO3, Na2S, Na3P, Na3N, Na2O2, and Na2N4O2; or, The active metal is lithium, and the active metal supplement includes at least one of Li2CO3, LiN3, Li2O, Li2TiO3, LiF, Li2SiO3, Li2S, Li3P, Li3N, Li2O2, and Li2N4O2.

4. The diaphragm according to any one of claims 1 to 3, characterized in that, Based on the total solid content of the composition, the content of keratin is 5wt% to 35wt%, the content of the thickening agent is 2wt% to 15wt%, and the content of the active metal supplement is 50wt% to 90wt%.

5. The diaphragm according to any one of claims 1 to 4, characterized in that, The composition further includes a binder; optionally, the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyoxyethylene, and sodium polyacrylate, and when the binder includes at least one of sodium carboxymethyl cellulose, polyoxyethylene, and sodium polyacrylate, the thickening agent is different from the binder.

6. The diaphragm according to claim 5, characterized in that, Based on the total solid content of the composition, the content of keratin is 5wt% to 35wt%, the content of the thickening agent is 2wt% to 15wt%, the content of the active metal supplement is 50wt% to 90wt%, and the content of the binder is 1wt% to 5wt%.

7. The diaphragm according to any one of claims 1 to 6, characterized in that, The coating further includes inorganic particles and a surfactant; Optionally, based on the total weight of the coating, the content of the composition is 10wt% to 45wt%, the content of the inorganic particles is 45wt% to 80wt%, and the content of the surfactant is 5wt% to 15wt%.

8. The diaphragm according to claim 7, characterized in that, The inorganic particles include at least one of alumina, titanium oxide, silicon oxide, zirconium oxide, boehmite, aluminum nitride, yttrium oxide, and cerium oxide.

9. The diaphragm according to claim 7 or 8, characterized in that, The surfactant includes an anionic surfactant or an amphoteric surfactant; Optionally, the surfactant includes at least one of sodium dodecylsulfonate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, betaine, sulfobetaine, and amino acid-based surfactants.

10. The separator according to any one of claims 1 to 9, characterized in that, The base film includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyvinylidene fluoride, polyamide, and polyimide.

11. A secondary battery, the secondary battery comprising: A positive electrode sheet, a negative electrode sheet, and a diaphragm located between the positive electrode sheet and the negative electrode sheet, characterized in that the diaphragm includes the diaphragm according to any one of claims 1 to 10.

12. An electrical device, characterized in that, The electrical device includes the secondary battery according to claim 11.

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