Diaphragm and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention provides a diaphragm and a preparation method thereof, a battery, a battery pack and electric equipment, the diaphragm comprises a base membrane and a functional coating located on at least one side surface of the base membrane, the functional coating comprises a sodium supplementing agent, and the sodium supplementing agent comprises aromatic diphenol sodium. According to the invention, the first coulombic efficiency, the low-temperature rate capability, the high-temperature cycle life and other performances of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, specifically to a separator and its preparation method, a battery, a battery pack, and an electrical device. Background Technology

[0002] Due to the abundance and low cost of sodium resources, sodium-ion batteries (SIBs) have become a promising candidate battery as the demand for large-scale energy storage systems continues to grow. However, due to the inherent sodium deficiency of sodium-ion cathode materials, the large radius of sodium ions making intercalation and deintercalation between the positive and negative electrodes difficult, and the irreversible sodium loss caused by the formation of solid electrolyte films on the electrode surface (such as the SEI film on the negative electrode surface), sodium-ion batteries generally suffer from problems such as low initial coulombic efficiency (first-time efficiency), poor low-temperature rate performance, and poor high-temperature cycling performance. For example, the inherent sodium deficiency of sodium-ion cathode materials results in a low initial charging capacity; at the same time, the large radius of sodium ions makes diffusion in the separator and electrolyte difficult, increasing the difficulty of intercalation and deintercalation between the positive and negative electrodes, affecting the rate performance and cycle performance of the battery; negative electrode materials used in sodium-ion batteries, such as hard carbon, usually contain many defective carbon sites and surface oxygen-containing functional groups (hydroxyl and carboxyl groups), which irreversibly consume active sodium. + During the charging and discharging process of sodium-ion batteries, an SEI film forms on the surface of the negative electrode, causing irreversible sodium capacity loss, resulting in poor initial coulombic efficiency (first-time efficiency) and poor cycle stability of sodium-ion batteries.

[0003] Current technologies primarily compensate for irreversible sodium loss by pre-replenishing the positive and negative electrodes with sodium. This is typically done directly in the electrode precursors, such as by incorporating sodium powder into the electrode slurry used to form the electrode coating. However, due to sodium's high reactivity and spontaneous combustion upon contact with water, the pre-replenishment process has an extremely low safety factor, requiring strict control of anhydrous and oxygen-free environments, making it difficult to operate and limiting its application. Replenishing sodium through the separator avoids the problems associated with pre-replenishing the positive and negative electrodes and has gradually gained widespread attention and application. However, limited by factors such as the type of sodium replenishing agent used, existing sodium-replenishing separators have limited effectiveness in replenishing sodium for sodium-ion batteries, especially in simultaneously improving the initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle performance of sodium-ion batteries. Summary of the Invention

[0004] This invention provides a separator and its preparation method, a battery, a battery pack, and an electrical device, which can improve the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life, effectively overcoming the defects of the prior art.

[0005] In one aspect, the present invention provides a diaphragm comprising a base membrane and a functional coating located on at least one side surface of the base membrane, the functional coating comprising a sodium supplement agent comprising sodium aromatic diphenolate.

[0006] According to one embodiment of the present invention, the aromatic diphenol sodium includes ortho-aromatic diphenol sodium.

[0007] According to one embodiment of the present invention, the ortho-aromatic diphenol sodium includes one or more of sodium catechol, sodium anthracite, and sodium anthracene.

[0008] According to one embodiment of the present invention, the functional coating further includes a solid electrolyte.

[0009] According to one embodiment of the present invention, the mass ratio of the sodium supplement to the solid electrolyte is (0.25 to 0.75):1.

[0010] According to one embodiment of the present invention, the solid electrolyte includes a NASICON-type solid electrolyte.

[0011] According to one embodiment of the present invention, the chemical formula of the NASICON-type solid electrolyte is Na. x M y (PO4)3, 0 < x ≤ 4, 0 < y ≤ 4, M includes one or more of divalent, trivalent, tetravalent, and pentavalent metal ions.

[0012] According to one embodiment of the present invention, the divalent metal ion includes Mg. 2+ Ca 2+ 、Sr 2+ Ba 2+ Zn 2+ Co 2+ One or more of the following; and / or, the trivalent metal ions include Al 3+ ,Sc 3+ Pr 3+ Eu 3+ Lu 3+ Y 3+ Yb 3+ One or more of the following; and / or, the tetravalent ions include Si 4+ Hf 4+ 、Ge 4+ One or more of the following; and / or, the pentavalent metal ions include Nb 5+ .

[0013] According to one embodiment of the present invention, the functional coating further includes a conductive agent, which includes one or more of acetylene black, graphene, super conductive carbon black, carbon nanotubes, and carbon fibers.

[0014] According to one embodiment of the present invention, the functional coating further includes an adhesive, the adhesive comprising one or more of polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, nitrile rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate.

[0015] According to one embodiment of the present invention, the thickness of the functional coating is 1 to 3 μm.

[0016] In another aspect, the present invention provides a method for preparing the above-mentioned diaphragm, comprising the following steps: coating a slurry containing the sodium supplementer onto at least one side surface of the base membrane to form the functional coating, thereby obtaining the diaphragm.

[0017] In another aspect, the present invention provides a battery comprising the above-described separator or a separator prepared according to the above-described separator preparation method.

[0018] According to one embodiment of the present invention, the device further includes a positive electrode and a negative electrode, with the separator located between the positive electrode and the negative electrode; the negative electrode includes a negative electrode active material, which includes hard carbon.

[0019] In another aspect, the present invention provides a battery pack comprising the aforementioned battery.

[0020] In another aspect, the present invention provides an electrical device comprising a SANSAN battery or the aforementioned battery pack.

[0021] The present invention provides a separator and its preparation method, a battery, a battery pack and an electrical device thereof. The separator includes a base membrane and a functional coating located on at least one side of the surface of the base membrane. The functional coating includes a sodium supplement agent, which includes sodium aromatic diphenolate, and can improve the battery's initial coulombic efficiency, low-temperature rate performance and high-temperature cycle life. Detailed Implementation

[0022] 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.

[0023] This invention provides a diaphragm, including a base membrane and a functional coating located on at least one side surface of the base membrane, wherein the functional coating includes a sodium replenishing agent, which includes sodium aromatic diphenolate.

[0024] According to the inventor's research and analysis: Sodium aromatic diphenolate can release sodium ions (Na+) during battery charging and discharging. + This technology, by providing additional sodium ions, compensates for sodium loss due to irreversible sodium consumption caused by factors such as the formation of the SEI film in the negative electrode, effectively improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life. Specifically, sodium aromatic bisphenol A generates quinone byproducts containing C=O groups after sodium replenishment during charging. These C=O groups can react with negative electrode materials such as hard carbon, reducing sp3 carbon defects in these materials. Simultaneously, during battery charging and discharging, the C=O functional group participates in the sodicization reaction, generating CO-Na groups during discharge and C=O and Na groups during charging. + The redox reaction between the C=O group and the battery is reversible, which can effectively improve the reversible capacity of anode materials such as hard carbon, enhance the high and low temperature performance of the battery, and improve the battery's initial coulombic efficiency, low temperature rate performance and high temperature cycle life.

[0025] Specifically, the aforementioned aromatic diphenol sodium includes an aryl group and two sodium hydroxyl groups (-O-Na) substituted on the aryl group. The aryl group may include one or more of phenyl, naphthyl, and anthracene groups, which is beneficial for improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0026] In some embodiments, the aforementioned aromatic diphenol sodium may include one or more of sodium quinone (i.e., two sodium hydroxy groups substituted on the phenyl group), sodium naphthol (i.e., two sodium hydroxy groups substituted on the naphthyl group), and sodium anthracene (i.e., two sodium hydroxy groups substituted on the anthracene group), which is beneficial for improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0027] According to further research by the inventors, the aforementioned aromatic diphenol sodium may include ortho-aromatic diphenol sodium, in which two sodium hydroxyl groups are substituted at the ortho position of the aryl group. This is beneficial for further improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life. The reason for this is that ortho-aromatic diphenol sodium has a relatively large irreversible capacity (for example, the irreversible capacity of ortho-aromatic diphenol sodium is generally greater than that of para-aromatic diphenol sodium), making it more suitable as a sodium replenishing agent. At the same time, ortho-aromatic diphenol sodium has greater solubility in the electrolyte, which is more conducive to the C=O functional group in ortho-aromatic diphenol sodium participating in the sodiumization reaction. Introducing ortho-aromatic diphenol sodium into the functional coating of the separator is more conducive to improving the sodium replenishment effect of the separator, thus improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0028] In some embodiments, the above-mentioned ortho-aromatic diphenol sodium includes one or more of sodium catechol (1,2-dihydroxybenzene sodium), sodium catechol, and sodium catechol anthracene, which is beneficial to improving the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0029] Specifically, taking sodium 1,2-dihydroxyphenyl as an example, sodium 1,2-dihydroxyphenyl has properties such as high specific capacity (up to 347.9 mAh / g) and low decomposition voltage (generally 2.4-2.8V), which are beneficial to improving the battery's initial coulombic efficiency, low-temperature rate performance and high-temperature cycle life, and increasing the utilization rate of sodium supplement.

[0030] Specifically, the above-mentioned sodium o-naphthol may include compounds having the structure shown in Formula 1 and / or compounds having the structure shown in Formula 2:

[0031]

[0032] Specifically, the above-mentioned sodium anthracene may include compounds having the structure shown in Formula 3 and / or compounds having the structure shown in Formula 4:

[0033]

[0034] The aromatic diphenol sodium in the embodiments of the present invention can be prepared by conventional methods in the art, such as by reacting aromatic phenolic compounds with NaH to generate the corresponding aromatic diphenol sodium. For example, the corresponding ortho-aromatic diphenol sodium can be generated by reacting ortho-aromatic phenolic compounds with NaH. The ortho-aromatic compounds may include one or more of ortho-phenol, ortho-naphthol, and ortho-anthraphenol.

[0035] For example, the above-mentioned ortho-naphthol may include compounds having the structure shown in Formula 5 and / or compounds having the structure shown in Formula 6:

[0036]

[0037] For example, the above-mentioned ortho-anthraphenols have the structure shown in Formula 7 and / or the structure shown in Formula 8:

[0038]

[0039] Taking sodium 1,2-dihydroxyphenyl as an example, 1,2-diphenol and NaH react in tetrahydrofuran (THF) at room temperature (RT) for 12-36 hours (specifically 24 hours), then heated to 100±2℃, followed by the addition of vinyl acetate (VAC). The chemical reaction formula for the formation of sodium 1,2-dihydroxyphenyl is shown below:

[0040] 1,2-Dihydroxyphenyl sodium

[0041] According to the inventors' research, sodium 1,2-dihydroxyphenylene oxide generates a byproduct (1,2-benzoquinone) containing C=O groups after charging and sodium replenishment. This byproduct can reduce sp3 carbon defects in anode materials such as hard carbon based on the reaction between the C=O groups and these materials. Simultaneously, during battery charging and discharging, the C=O functional group participates in the sodium formation reaction, generating CO-Na groups during discharge and C=O and Na groups during charging. + The redox reaction between sodium 1,2-dihydroxyphenyl sodium and C=O groups is reversible, which can effectively improve the reversible capacity of anode materials such as hard carbon and enhance the high and low temperature performance of the battery. The reaction formula for the formation of 1,2-benzoquinone after sodium supplementation during charging is shown below:

[0042]

[0043] In this embodiment of the invention, the structure of the sodium supplement in the diaphragm can be determined by methods such as infrared spectroscopy (for example, the ortho-hydroxybenzene configuration of sodium catechol can be determined by infrared spectroscopy).

[0044] In some embodiments, the functional coating may further include a solid electrolyte (i.e., the functional coating may be a solid electrolyte layer containing a solid electrolyte), which is beneficial to further reduce the membrane conductivity and improve the low-temperature rate performance of the battery while improving the battery's first efficiency and cycle life.

[0045] Furthermore, the mass ratio of the sodium supplement to the solid electrolyte can be (0.25–0.75):1, for example, 0.25:1, 0.35:1, 0.50:1, 0.65:1, 0.75:1, or any combination thereof. This helps to improve the sodium supplementation effect while maintaining the membrane's good permeability, liquid absorption rate, and low sodium ion transport resistance. It also further improves the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0046] In some embodiments, the solid electrolyte includes a NASICON-type solid electrolyte, which has high ionic conductivity, a wide electrochemical window, outstanding mechanical properties and good air stability. Moreover, its conductivity is not sensitive to temperature and can exhibit good ionic conductivity even at low temperatures. Therefore, it helps to improve the ionic conductivity of the battery, reduce low-temperature discharge voltage drop and cycle performance, and further improve the battery's initial coulombic efficiency, low-temperature rate performance and high-temperature cycle life.

[0047] In some embodiments, the chemical formula of the aforementioned NASICON-type solid electrolyte may be Na. x M y (PO4)3, 0 < x ≤ 4, 0 < y ≤ 4, x and y satisfy the above Nax M2(PO4)3 is electrically neutral, and M includes one or more of divalent, trivalent, tetravalent, and pentavalent metal ions.

[0048] For example, Na x M y In (PO4)3, x is, for example, a range consisting of 1, 1.5, 2, 2.5, 2.7, 2.9, 3, 3.2, 3.4, 3.6, 3.8, 4, or any two of them.

[0049] For example, Na x M y In (PO4)3, y is, for example, a range consisting of 1, 1.5, 1.8, 2, 2.2, 2.5, 3, 3.5, 4, or any two of them.

[0050] The aforementioned divalent metal ions may include Mg 2+ Ca 2+ 、Sr 2+ Ba 2+ Zn 2+ Co 2+ One or more of them.

[0051] The aforementioned trivalent metal ions may include Al 3+ ,Sc 3+ Pr 3+ Eu 3+ Lu 3+ Y 3+ Yb 3+ One or more of them.

[0052] The aforementioned tetravalent ions may include tetravalent metal ions or tetravalent nonmetal ions.

[0053] Specifically, the tetravalent metal ion may include Hf 4+ 、Ge 4+ One or more of the following, wherein the tetravalent nonmetallic ion may include Si 4+ .

[0054] The aforementioned pentavalent metal ions may include Nb 5+ .

[0055] In general, M may also include zirconium (Zr). For example, the chemical formula of NASICON-type solid electrolytes may be Na. x Zr a A 2-a Si2(PO4)3, 0<a≤2, where a is, for example, 1.5, 1.6, 1.7, 1.8, 1.9 or 2, and A can include one or more of the above-mentioned divalent, trivalent, tetravalent and pentavalent metal ions.

[0056] The aforementioned functional coating may or may not include a conductive agent. When the functional coating includes a conductive agent, the conductive agent may include one or more of acetylene black, graphene, super conductive carbon black, carbon nanotubes, and carbon fibers, which help improve the conductivity of the separator and enhance the sodium replenishment effect during battery charging and discharging.

[0057] In the above-mentioned functional coating, the mass ratio of conductive agent to solid electrolyte can be (0-5):100, for example, 0:100, 1:100, 2:100, 3:100, 4:100, 5:100 or any combination thereof.

[0058] The aforementioned functional coating also includes an adhesive, which may include one or more of polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, nitrile rubber, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate, to form an adhesive-coated separator, which can improve the stability of the battery after hot pressing, and also improve the battery's initial coulombic efficiency, low-temperature rate performance, and high-temperature cycle life.

[0059] In this embodiment of the invention, a sodium-supplementing layer can be provided on one side of the base film, or functional coatings can be provided on both opposite sides of the base film. When a functional coating is provided on one side of the base film, the functional coating can be located on the side of the base film facing the positive electrode or the side facing the negative electrode when the separator is applied to a battery. When functional coatings are provided on both opposite sides of the base film, the functional coating is located on the side of the base film facing the positive electrode and on the side of the base film facing the negative electrode.

[0060] In some embodiments, the thickness of the functional coating is 1 to 5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any combination thereof, preferably 1 to 3 μm, which helps to ensure that the membrane has good mechanical properties while avoiding excessive thickness of the functional coating and ensuring that the membrane has high permeability.

[0061] It should be noted that the thickness of the aforementioned functional coating refers to the thickness of the functional coating on one side of the separator. For example, when functional coatings are provided on both sides of the base membrane, the thickness of the aforementioned functional coating (1-5 μm) refers to the thickness of the functional coating on any side of the base membrane (e.g., the side of the base membrane facing the positive electrode or the side of the base membrane facing the negative electrode).

[0062] In some embodiments, the thickness of the base film may be 8 to 10 μm, for example, 8 μm, 9 μm, 10 μm or any combination thereof.

[0063] In some embodiments, the base membrane includes one or more of polyolefins, nonwovens, and polyetherimides, such as polyethylene. For example, the base membrane may include a polyethylene porous membrane (or polyethylene film) formed of polyethylene.

[0064] The present invention also provides a method for preparing the above-mentioned diaphragm, comprising: coating a slurry containing a sodium supplement agent onto at least one side surface of a base membrane to form a functional coating, thereby obtaining the above-mentioned diaphragm.

[0065] The aforementioned slurry containing sodium supplementer (composite coating slurry) may further include a solid electrolyte, a conductive agent, a binder, and a solvent. In the aforementioned slurry containing sodium supplementer, the mass ratio of sodium supplementer to solid electrolyte may be (0.25–0.75):1, the mass ratio of conductive agent to solid electrolyte may be (0–5):1, the mass percentage of binder may be 0.25%–0.75%, for example, 0.25%, 0.3%, 0.4%, 0.5%, 0.75%, or any combination thereof, with the balance being solvent.

[0066] The conductive agent may include one or more of acetylene black, graphene, superconducting carbon black, carbon nanotubes, and carbon fibers. The binder may include one or more of polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, nitrile rubber, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate.

[0067] The solvents mentioned above may include organic solvents, specifically N-methylpyrrolidone (NMP).

[0068] In a specific implementation, a solid electrolyte, a sodium supplement, a conductive agent, a binder, and a solvent can be mixed to obtain a slurry containing a sodium supplement; then, the slurry containing the sodium supplement is coated onto at least one side of the base membrane, and after drying, a functional coating is formed on at least one side of the base membrane to obtain the aforementioned diaphragm.

[0069] This invention also provides a battery comprising the above-described separator or a separator prepared according to the above-described separator preparation method. This battery has advantages corresponding to the above-described separator, which will not be elaborated further.

[0070] Specifically, the battery also includes a positive electrode, a negative electrode, and an electrolyte. The separator is located between the positive and negative electrodes and is used to separate the positive and negative electrodes to prevent them from short-circuiting due to contact.

[0071] The positive electrode sheet in this embodiment of the invention may specifically include a positive current collector and a positive active layer formed of a positive active material disposed on the surface of the positive current collector.

[0072] In the specific preparation of the positive electrode sheet, the binder can be mixed with NMP to obtain a binder slurry; the positive electrode active material, conductive agent, the above binder slurry, and solvent are mixed evenly to prepare a positive electrode slurry; the positive electrode slurry is coated onto the positive electrode current collector, and then dried, rolled, and slit to obtain the positive electrode sheet. The drying temperature can be 110–130°C, for example, 110°C, 120°C, 130°C, or any combination thereof.

[0073] In some embodiments, the mass percentage of the binder in the above-mentioned adhesive slurry may be 2% to 3%, for example, 2%, 2.5%, 3% or any combination thereof.

[0074] In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder; more specifically, it comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0075] The positive electrode active material (sodium electrode main material) may include one or more of the following: tunnel-type positive electrode active material, layered positive electrode active material, and polyanionic positive electrode active material, wherein the tunnel-type positive electrode active material may include Na 0.44 MnO2, layered positive electrode active materials may include Na 0.67 Ni 0.33 Mn 0.67 O2, polyanionic positive electrode active materials may include Na4Fe 2.91 (PO4)2P2O7, Na3V2(PO4)3 and Na3V2(PO4)2F3; the positive electrode current collector can be made of at least one of aluminum foil or nickel foil.

[0076] In addition, the conductive agent in the positive electrode active layer can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber.

[0077] In addition, the binder in the positive electrode active layer can be selected from at least one of polyvinylidene fluoride (PVDF), 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.

[0078] The negative electrode sheet of the present invention specifically includes a negative electrode current collector and a negative electrode active layer formed of a negative electrode active material disposed on the surface of the negative electrode current collector.

[0079] In the specific preparation of the negative electrode, a binder (tackifier) ​​can be mixed with water to prepare a binder slurry; the negative electrode active material, conductive agent, the above-mentioned binder slurry, SBR emulsion (a synthetic rubber emulsion obtained by emulsion polymerization of styrene and butadiene), and water are mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is coated onto the negative electrode current collector, and after drying, rolling and slitting, a negative electrode sheet is obtained. The drying temperature can be 110–130℃, for example, 110℃, 120℃, 130℃, or any combination thereof.

[0080] In some embodiments, the mass percentage of the binder in the above-mentioned adhesive slurry may be 1.2% to 1.4%, for example, it may be a range of 1.2%, 1.3%, 1.4% or any two of these.

[0081] In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0082] The negative electrode active material may include hard carbon material; the negative electrode current collector layer material may be at least one of aluminum foil, copper foil, nickel foam, and copper foam; the conductive agent may be at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the binder may be at least one of sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0083] In some embodiments, the negative electrode active material may include hard carbon. The functional coating of the aforementioned separator contains a sodium replenishing agent. After charging and replenishing sodium, the sodium replenishing agent generates a byproduct (1,2-benzoquinone) containing C=O groups. This byproduct can reduce the sp3 carbon defects of the hard carbon based on the reaction between the C=O groups and the hard carbon. Simultaneously, during battery charging and discharging, the C=O functional group participates in the sodium formation reaction, generating CO-Na groups during discharge and C=O and Na groups during charging. + The redox reaction between the carbon and C=O groups is reversible, which can effectively improve the reversible capacity of hard carbon, enhance the high and low temperature performance of the battery, and improve the battery's initial coulombic efficiency, low temperature rate performance, and high temperature cycle life.

[0084] The embodiments of the present invention do not strictly limit the choice of electrolyte. For example, aqueous electrolyte or non-aqueous electrolyte can be used. The non-aqueous electrolyte may include one or more of the solvents commonly used in sodium-ion battery electrolytes, as well as electrolyte salts commonly used in sodium-ion electrolytes. For example, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), butene 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 salt may include one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium chloride, sodium nitrate, and sodium fluoride.

[0085] In practice, the positive electrode, separator, and negative electrode are stacked sequentially to form a stacked cell, or the positive electrode, separator, and negative electrode are stacked sequentially and then wound to form a wound cell core. The resulting core is then placed in a casing for encapsulating the cell, and electrolyte is injected into it. The cell then undergoes high-temperature impregnation, formation, aging, and capacity testing to produce a sodium-ion battery (sodium-ion secondary battery). In this cell, the separator is larger than the positive and negative electrode plates to completely cover them, preventing short circuits caused by contact between the positive and negative electrodes.

[0086] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art. For example, the housing includes a metal housing, and the metal housing includes, for example, a steel housing.

[0087] This invention also provides a battery pack, which includes the battery described above. This battery pack has advantages corresponding to the separator described above, which will not be elaborated further.

[0088] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0089] This invention also provides an electrical device that includes the aforementioned battery or battery pack. This device offers advantages corresponding to the aforementioned negative electrode, which will not be elaborated further.

[0090] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations.

[0091] The present invention will be further described below through specific embodiments.

[0092] Example 1

[0093] 1. Preparation of the diaphragm

[0094] Na3Zr2Si2(PO4)3(NZSPO), sodium 1,2-dihydroxyphenylene, carbon black, PVDF, and NMP were mixed evenly in a mass ratio of 100:25:1:3:71 to obtain a slurry containing a sodium supplement. The slurry containing the sodium supplement was coated on both sides of a 9 μm thick polyethylene porous membrane. After drying, a functional coating was formed with a thickness of 2 μm on each side, thus obtaining a diaphragm.

[0095] 2. Preparation of the positive electrode sheet

[0096] PVDF and NMP are mixed to obtain an adhesive slurry, wherein the mass percentage of PVDF in the adhesive slurry is 2.5%.

[0097] According to Na 0.67 Ni 0.33 Mn 0.67 The mass ratio of O2, carbon black, and PVDF is 95:2.5:2.5. Na... 0.67 Ni 0.33 Mn 0.67 O2, carbon black and the above binder slurry are mixed, and an appropriate amount of NMP is added and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on aluminum foil, dried at 120°C, rolled and slit to obtain a positive electrode sheet;

[0098] 3. Preparation of negative electrode sheet

[0099] CMC-Na was mixed with water to prepare an adhesive slurry; the mass percentage of CMC-Na in the adhesive slurry was 1.3%;

[0100] The hard carbon, carbon black, CMC-Na, and SBR are mixed in a mass ratio of 96:1:1.5:1.5. After adding an appropriate amount of water, the mixture is stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto an aluminum foil, dried at 120°C, rolled and slit to obtain a negative electrode sheet.

[0101] 4. Preparation of sodium-ion batteries

[0102] The above-mentioned positive electrode, separator, and negative electrode are wound into a core, wherein the separator completely covers the positive electrode and the negative electrode. The resulting core is then placed in a steel shell and injected with electrolyte. After high-temperature wetting, formation, aging, and capacity testing, a sodium-ion battery is produced.

[0103] The electrolyte composition is as follows: the mass ratio of EMC, EC and PC is 1:1:1, and the concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L.

[0104] Following the process of Example 1, the separators, positive electrode sheets, negative electrode sheets, and sodium-ion batteries of Examples 2 to 17 and Comparative Examples 1 to 2 were prepared. The conditions such as the solid electrolyte, sodium supplement, mass ratio of sodium supplement to solid electrolyte, and thickness of the single-sided functional coating in the separators of each example and comparative example are summarized in Table 1.

[0105] The difference between Example 6 and Example 1 is that no solid electrolyte was added to the functional coating of the diaphragm in Comparative Example 2. When forming the functional coating, a slurry containing sodium supplement was prepared by mixing sodium 1,2-dihydroxyphenyl sodium, conductive carbon black, PVDF, and NMP in a mass ratio of 100:1:3:71.

[0106] The difference between Comparative Example 1 and Example 1 is that no sodium supplement was added to the functional coating of the diaphragm in Comparative Example 1. When forming the functional coating, a slurry containing sodium supplement was prepared by mixing NZSPO, conductive carbon black, PVDF, and NMP in a mass ratio of 100:1:3:71.

[0107] The difference between Comparative Example 2 and Example 1 is that the functional coating of the diaphragm in Comparative Example 3 did not contain sodium supplementer and solid electrolyte. When forming the functional coating, conductive carbon black, PVDF and NMP were mixed in a mass ratio of 1:3:71 to prepare a slurry containing sodium supplementer.

[0108] Except for the differences mentioned above and those shown in Table 1, the remaining conditions of Examples 2-17 and Comparative Examples 1-2 are the same as those of Example 1.

[0109] Test Example 1

[0110] The conductivity of the diaphragms in each embodiment and comparative example was tested using the four-probe method, and the results are shown in Table 2.

[0111] Test Example 2

[0112] 1. The initial coulombic efficiency (first efficiency) of the sodium-ion batteries in each embodiment and comparative example was tested: the sodium-ion batteries were charged to 4.0V at a constant current of 0.1C; after standing for 30 minutes, they were discharged to 2.0V at 0.1C, and the initial coulombic efficiency of the sodium-ion batteries was tested. The results are shown in Table 1.

[0113] 2. The -10℃ low-temperature discharge performance of the sodium-ion batteries in each embodiment and comparative example was tested: The sodium-ion batteries were charged at 1C constant current and constant voltage to 4.0V, and cut off at 0.05C; the sodium-ion batteries were placed in an environmental chamber at -10℃ for 6 hours, and the initial voltage (the voltage in the last 0.1s during the 6 hours in the environmental chamber at -10℃) V0 of the battery was measured; then, the sodium-ion batteries were discharged at 3C for 10s, and the final voltage (the final voltage after discharging the sodium-ion batteries at 3C for 10s) V1 was measured, and the low-temperature discharge voltage drop ΔV (ΔV is the difference between V0 and V1) was tested. The results are shown in Table 2.

[0114] 3. The cycle life of the sodium-ion batteries in each embodiment and comparative example was tested: After the sodium-ion batteries were placed in an environment of 45°C for 4 hours, they were charged to 4.0V at 1C constant current and constant voltage, the cutoff current was 0.05C, and then rested for 10 minutes; then they were discharged to 2.0V at 1C constant current and rested for 10 minutes; the charge and discharge cycles were repeated until the cycle capacity retention rate was less than 70%, and the capacity retention rate after 800 cycles was recorded. The results are shown in Table 2.

[0115] Test Example 3

[0116] The sodium-ion batteries of each embodiment and comparative example were disassembled, and the positive electrode in the sodium-ion battery was replaced with a sodium sheet. The sodium sheet was then assembled with the remaining parts of the sodium-ion battery to form a coin cell. The specific capacity of the coin cell was tested: the sodium-ion battery was charged at 1C constant current and constant voltage to 4.0V, with a cutoff current of 0.05C, and left to rest for 10 minutes; it was then discharged at 1C constant current to 2.0V, left to rest for 10 minutes, and cycled 3 times. After this cycle, the battery was disassembled, and the positive electrode in the sodium-ion battery was replaced with a sodium sheet. The sodium sheet was then assembled with the remaining parts of the sodium-ion battery (including the separator and the negative electrode) to form a coin half cell (negative electrode coin cell); the coin half cell was discharged at 0.1C constant current to 0.2V at 25°C, left to rest for 10 minutes, and then charged at 0.1C constant current to 2.0V, and cycled 100 times. The specific capacity of the third discharge was recorded. The specific results are shown in Table 2.

[0117] Table 1. Relevant parameters of the functional coating of the diaphragm.

[0118]

[0119] Note: "None" in Table 1 indicates that the functional coating does not contain this component.

[0120] Table 2. Test results of separator and battery performance

[0121]

[0122] As can be seen from Table 1, compared with Comparative Examples 1 and 2, Examples 1 to 17, by setting a functional coating on the surface of the separator and introducing sodium aromatic diphenolate as a sodium supplement in the functional coating, can improve the first efficiency of the battery, increase the specific capacity of the negative electrode coin cell, that is, increase the reversible capacity of the negative electrode material, and improve the high-temperature cycle capacity retention rate of the battery, thus improving the high-temperature cycle life of the battery. At the same time, it can also maintain the high conductivity of the separator and reduce the low-temperature discharge voltage drop of the battery, thus improving the low-temperature rate performance of the battery.

[0123] Further, as can be seen from Examples 1 to 5, Examples 1 to 3, by further controlling the mass ratio of sodium supplement to solid electrolyte within the range of (0.25 to 0.75):1, are beneficial to further improve the first efficiency of the battery, while also reducing the low-temperature discharge voltage drop and improving the high-temperature cycle capacity retention rate of the battery, thus further improving the overall performance of the battery.

[0124] Further, as can be seen from Examples 2, 7 to 10, Examples 2, 8 to 9, by further controlling the thickness of the functional coating within the range of 1 to 3 μm, are beneficial to further reduce the low-temperature discharge voltage drop of the battery, improve the low-temperature rate performance of the battery, and increase the reversible capacity of the negative electrode material, as well as the first-efficiency and high-temperature cycle performance of the battery.

[0125] Further, as can be seen from Examples 2, 13 and 14, Example 2, by further employing sodium ortho-aromatic diphenol, can further reduce the low-temperature discharge voltage drop of the battery, improve the low-temperature rate performance of the battery, and at the same time improve the reversible capacity of the negative electrode material, as well as the battery's first-efficiency and high-temperature cycle performance.

[0126] 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 diaphragm, characterized by The diol sodium salt includes one or more of sodium catechol, sodium naphthalene, and sodium anthracene.

2. The separator according to claim 1, characterized in that The diol sodium salt includes one or more of sodium catechol, sodium naphthalene, and sodium anthracene.

3. The diaphragm of claim 2, wherein The diol sodium salt includes one or more of sodium catechol, sodium naphthalene, and sodium anthracene.

4. The separator according to claim 1 or 2, characterized in that, The functional coating further includes a solid-state electrolyte.

5. The diaphragm of claim 4, wherein The mass ratio of the diol sodium salt to the solid-state electrolyte is (0.25-0.75):

1.

6. The diaphragm of claim 4 or 5, wherein The solid-state electrolyte includes a NASICON-type solid-state electrolyte.

7. The diaphragm of claim 6, wherein The chemical formula of the NASICON-type solid-state electrolyte is Na x M y (PO4)3, 0 < x ≤ 4, 0 < y ≤ 4, M includes one or more of a divalent metal ion, a trivalent metal ion, a tetravalent ion, a pentavalent metal ion.

8. The separator according to claim 7, wherein, The divalent metal ion comprises one or more of Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ , Co 2+ . and / or the trivalent metal ion comprises one or more of Al 3+ , Sc 3+ , Pr 3+ , Eu 3+ , Lu 3+ , Y 3+ , Yb 3+ . and / or the tetravalent ion comprises one or more of Si 4+ , Hf 4+ , Ge 4+ . and / or the pentavalent metal ion comprises Nb 5+ .

9. The separator according to any one of claims 1 to 3, wherein The functional coating further includes a conductive agent, and the conductive agent includes one or more of acetylene black, graphene, super-conductive carbon black, carbon nanotubes, and carbon fibers.

10. The separator according to any one of claims 1 to 3, wherein The functional coating further includes a binder, and the binder includes one or more of polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, butadiene-styrene rubber, butyronitrile rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate.

11. The separator according to any one of claims 1 to 3, characterized in that The thickness of the functional coating is 1-3 μm.

12. A method of producing the separator according to any one of claims 1 to 11, characterized by, The method includes the step of applying a slurry containing the diol sodium salt to at least one side surface of the base film to form the functional coating, thereby producing the separator.

13. A battery, characterized by The battery includes the separator according to any one of claims 1-11 or the separator produced according to the method of claim 12.

14. The battery of claim 13, wherein, The battery further includes a positive electrode sheet and a negative electrode sheet, and the separator is located between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet includes a negative active material, and the negative active material includes hard carbon.

15. A battery pack, characterized by The battery includes the battery according to claim 13 or 14.

16. An electrical device, characterized by The electrical device includes the battery according to claim 13 or 14 or the battery pack according to claim 15.

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