Secondary battery, preparation method and electric device

Abstract

The invention discloses a secondary battery, a preparation method and a power utilization device, and relates to the technical field of batteries. The secondary battery comprises a diaphragm, the diaphragm comprises a base membrane and a coating at least covering one side of the base membrane, the coating comprises a polymer, and the polymer comprises a first structural unit containing an amidoxime group. The dissolved-out metal ions are adsorbed through the diaphragm coating, the dissolved-out metal ions can be prevented from shuttling back and forth to the negative electrode, and then the problems that the reversible cycle capacity of the battery is attenuated, and the cycle performance is reduced are solved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery, its preparation method, and an electrical device. Background Technology

[0002] Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles and electric cars, as well as in military equipment and aerospace and other fields.

[0003] Improving the cycle performance of rechargeable batteries has always been an industry goal. However, after rechargeable batteries are cycled, metal ions in the positive electrode will dissolve out. The dissolved metal ions will enter the electrolyte and diffuse through the separator to the negative electrode, where they will be reduced and deposited on the surface of the negative electrode. This will cause the reversible cycle capacity of the battery to decrease and the cycle performance to degrade. Summary of the Invention

[0004] This application addresses the aforementioned issues and aims to provide a secondary battery, a method for its fabrication, and an electrical device. It seeks to resolve the problem of reduced battery cycle performance caused by the dissolution of metal ions from the positive electrode after battery cycling.

[0005] To achieve the above objectives, in a first aspect, this application provides a secondary battery including a separator, the separator including a base membrane and a coating covering at least one side of the base membrane, the coating including a polymer, the polymer including a first structural unit containing a amine oxime group.

[0006] This application employs a coating on at least one side of the separator. The polymer in the coating includes a first structural unit containing a metallo-oxime group. Since the metallo-oxime group contains amino (-NH2) and oxime (-C=N-OH), and the N and O atoms in the amino and oxime groups contain lone pairs of electrons, they can combine with metal ions dissolved from the positive electrode in the electrolyte through coordination, thereby achieving the adsorption of dissolved metal ions and preventing the dissolved metal ions from shuttling to the negative electrode. This improves the problem of reversible cycle capacity decay and reduced cycle performance of the battery.

[0007] In any embodiment, the first structural unit includes the structural unit shown in Equation I.

[0008]

[0009] Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

[0010] By changing R1, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial to giving the polymer better chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Formula I allows the polymer to have an appropriate number of adsorption groups (amino, oxime groups).

[0011] In any embodiment, R1 comprises any one of an alkyl group having 1-5 carbon atoms or a phenyl group having 6-10 carbon atoms. R1 contains an alkyl or phenyl group of appropriate length to give the polymer suitable viscosity.

[0012] In any embodiment, the first structural unit includes at least one of the structural units shown in Formulas I-1 to I-6:

[0013]

[0014] In the technical solution of this application, in the structural units shown in I-1 to I-6, the side chain is a metallo-oxime group. The electronegative atoms containing lone pair monomons such as O and N in the metallo-oxime group can chelate with metal ions (such as transition metals such as nickel, manganese, and cobalt) dissolved in the electrolyte, that is, adsorb the metal ions dissolved from the positive electrode of the battery, thereby preventing the dissolved metal ions from shuttling to the negative electrode, and thus improving the problem of reduced cycle performance.

[0015] In any embodiment, the infrared spectrum of the polymer has a wavenumber of 3500-3650 cm⁻¹. -1 3200-3500cm -1 1590-1690cm -1 1320-1400cm -1 and 910-960cm -1 The presence of characteristic infrared peaks at the specified location indicates the presence of OH, C=N, -NH2, CN, and NO groups in the polymer.

[0016] In any embodiment, the coating thickness is 5-12 μm. At this suitable thickness, transition metal ions can be chelated without affecting the passage of lithium ions through the separator.

[0017] In any embodiment, the polymer further includes a second structural unit containing a cyano group. The cyano group contains an electronegative N atom with a lone pair of monotons, which, along with the amino (-NH2) and oxime (-C=N-OH) groups in the first structural unit, possesses the ability to coordinate with metal ions. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode and hindering their migration to the negative electrode, thereby mitigating the problem of reduced cycle performance. Furthermore, the presence of the cyano group contributes to improved chemical stability of the polymer.

[0018] In any embodiment, the second structural unit includes the structural unit shown in Formula II.

[0019]

[0020] Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

[0021] By changing R2, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial for improving the polymer's chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Equation I allows the polymer to possess an appropriate number of cyano groups.

[0022] In any embodiment, the second structural unit includes at least one of the structural units shown in Formulas II-1 to II-6:

[0023]

[0024] In the structural units shown in formulas II-1 to II-6, cyano groups serve as side chains. On one hand, the presence of cyano groups is beneficial for improving the chemical stability of the polymer. On the other hand, the electronegative N atom containing lone-pair monotons in the cyano group has the ability to combine with metal ions through coordination with both the amino and oxime groups in the first structural unit. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode of the battery, hindering the shuttle of dissolved metal ions to the negative electrode, and thus improving the problem of reduced cycle performance.

[0025] In any embodiment, the polymer's infrared spectrum also contains wavenumbers in the range of 2220-2270 cm⁻¹. -1 The presence of characteristic infrared peaks at this location indicates the presence of cyano groups in the polymer.

[0026] In any embodiment, the ratio of the number of structural units n shown in Formula I to the number of structural units m shown in Formula II, n:m, is (1-50):1. Within this suitable range, the ratio of n to m facilitates the formation of multidentate coordination between the polymer and the metal ions dissolved in the electrolyte, further suppressing the degradation of cycle performance.

[0027] In any embodiment, the polymer has a weight-average molecular weight of 5,000 to 500,000. This suitable range of weight-average molecular weight allows the polymer to have an appropriate number of repeating structural units, which is beneficial for adsorbing metal ions dissolved in the electrolyte.

[0028] In any embodiment, the polymer comprises at least one of the compounds shown in Formula III-1 to Formula III-6:

[0029]

[0030] Where 100≤n≤3000, 0≤m<1000 。

[0031] In the polymers shown in Formulas III-1 to III-6, on the one hand, the content of structural units containing a metallo-oxime groups is relatively higher, which is beneficial to increasing the probability of capturing metal ions (such as transition metals nickel, manganese, cobalt, etc.) dissolved in the electrolyte. On the other hand, the cyano group and the metallo-oxime group can work together to form multidentate coordination with the metal ions dissolved in the electrolyte, thereby hindering the shuttle of dissolved metal ions to the negative electrode and thus improving the problem of reduced cycle performance. Furthermore, the presence of the cyano group is beneficial to improving the chemical stability of the polymer.

[0032] In any embodiment, the coating further includes inorganic oxides and a thickener; the mass ratio of the polymer, inorganic oxide, and thickener in the coating is 100:(10-20):(20-40). Alternatively, the coating further includes inorganic oxides, a thickener, and a dispersant. The mass ratio of the polymer, inorganic oxide, thickener, and dispersant in the coating is 100:(10-20):(20-40):(2-10). Under the above suitable ratio, it is beneficial to utilize the polymer in the coating to adsorb metal ions dissolved in the electrolyte, thereby helping to suppress the decline in cycle performance.

[0033] In any embodiment, the coating also satisfies at least one of the following characteristics: (1) the inorganic oxide includes at least one of aluminum oxide, calcium oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite; (2) the thickener includes at least one of sodium carboxymethyl cellulose, polyacryl alcohol, polyvinylidene fluoride, polyacrylonitrile, and polyacrylate; (3) the dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone, and polyacrylamide.

[0034] In any embodiment, the secondary battery includes a positive electrode and a negative electrode, with the coating located at least on the side facing the negative electrode. Positioning the coating facing the negative electrode helps prevent degradation of the polymer within the coating.

[0035] In any embodiment, the positive electrode sheet includes a positive active material, and the positive active material includes Li. a (Ni b Co c Mn d A eO2, wherein A includes at least one of Al, Zr, Mg, Zn, Y, Fe, Nb, W, Zn, Mo, Ba, Ca, Ta and Ti; wherein 0.2 < a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, and b + c + d + e = 1.

[0036] In any embodiment, the base membrane includes at least one of a polyolefin membrane, a nonwoven membrane, a fiber membrane, and a polyaramid membrane.

[0037] In any embodiment, the thickness of the base film is 7-15 μm.

[0038] Secondly, this application provides a method for preparing a secondary battery, including a separator preparation step, wherein the separator preparation step includes:

[0039] Provide a base film;

[0040] A coating is formed on at least one side surface of the base membrane to obtain the diaphragm, wherein the coating comprises a polymer, the polymer comprising a first structural unit containing a amine oxime group.

[0041] The preparation process provided in this application is simple and conducive to industrial application. The polymer in the coating includes a first structural unit containing a metallo-oxime group. Since the metallo-oxime group contains an amino group (-NH2) and an oxime group (-C=N-OH), and the N and O atoms in the amino and oxime groups contain lone pairs of electrons, they can combine with metal ions dissolved from the positive electrode in the electrolyte through coordination, thereby achieving the adsorption of dissolved metal ions and preventing them from shuttling to the negative electrode. This improves the problem of reversible cycle capacity decay and reduced cycle performance of the battery.

[0042] In any embodiment, the first structural unit includes the structural unit shown in Equation I.

[0043]

[0044] Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

[0045] By changing R1, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial to giving the polymer better chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Formula I allows the polymer to have an appropriate number of adsorption groups (amino, oxime groups).

[0046] In any embodiment, the polymer further includes a second structural unit containing a cyano group. The cyano group contains an electronegative N atom with a lone pair of monotons, which, along with the amino (-NH2) and oxime (-C=N-OH) groups in the first structural unit, possesses the ability to coordinate with metal ions. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode and hindering their migration to the negative electrode, thereby mitigating the problem of reduced cycle performance. Furthermore, the presence of the cyano group contributes to improved chemical stability of the polymer.

[0047] In any embodiment, the second structural unit includes the structural unit shown in Formula II.

[0048]

[0049] Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

[0050] By changing R2, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial for improving the polymer's chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Equation I allows the polymer to possess an appropriate number of cyano groups.

[0051] In any implementation, the ratio n:m of the number of structural units n shown in Equation I to the number of structural units m shown in Equation II is (1-50):1.

[0052] In any embodiment, the step of forming a coating on at least one surface of the base membrane to obtain the separator includes:

[0053] The polymer, inorganic oxide, thickener, and solvent are mixed to obtain a slurry;

[0054] The slurry is coated onto at least one side of the base membrane, and the membrane is obtained after drying.

[0055] The solid content of the slurry is 30%-50%.

[0056] In any embodiment, in the step of coating the slurry at least on one side of the base film and drying it to obtain the diaphragm, the coating amount of the slurry is per 50×100mm. 2 Apply 2-4 mg to the affected area.

[0057] Thirdly, this application provides an electrical device including the secondary battery provided in the first aspect. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0059] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0060] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0061] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0062] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0063] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0064] Figure 7 This is an SEM image of the coated separator surface in the secondary battery of Embodiment 1 of this application.

[0065] Figure 8 This is a SEM image of the uncoated separator surface in the secondary battery of Comparative Example 1 of this application.

[0066] Figure 9 This is the infrared spectrum of the polymer prepared in Example 1 of this application.

[0067] Figure 10 This is a SEM image of the base film of the diaphragm in Embodiment 12 of this application, in which the coating is applied to both sides.

[0068] Explanation of reference numerals in the attached figures:

[0069] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0070] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and its power supply device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0071] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0073] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0074] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0075] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0076] After a secondary battery cycle, metal ions will dissolve from the positive electrode. The dissolved metal ions (such as transition metals Co, Mn, Ni, Fe, etc.) will enter the electrolyte and diffuse through the separator to the negative electrode, where they will be reduced and deposited on the surface of the negative electrode. This causes SEI breakage and reconstruction, resulting in continuous lithium consumption, which leads to a decrease in the reversible cycle capacity of the battery and a reduction in cycle performance.

[0077] Currently, the aforementioned problems can be addressed by adding additives to the electrolyte or by coating and doping the surface of the cathode material. However, adding additives to the electrolyte has two drawbacks: firstly, it places stringent requirements on the purity of the additives and the electrolyte environment; secondly, the additives have poor chemical stability and are prone to inducing side reactions on the cathode and anode surfaces due to unstable oxidation or reduction properties, leading to an increase in DC resistance (DCR). Coating and doping the cathode material involves changes to the main cathode material preparation methods, resulting in significant additional processing energy consumption and increased costs.

[0078] Based on this, in a first aspect, embodiments of this application provide a secondary battery including a separator, the separator including a base film and a coating covering at least one side of the base film, the coating including a polymer, the polymer including a first structural unit containing a amine oxime group.

[0079] This application employs a coating on at least one side of the separator. The polymer in the coating includes a first structural unit containing a metallo-oxime group. Since the metallo-oxime group contains amino (-NH2) and oxime (-C=N-OH), and the N and O atoms in the amino and oxime groups contain lone pairs of electrons, they can combine with metal ions dissolved from the positive electrode in the electrolyte through coordination, thereby achieving the adsorption of dissolved metal ions and preventing the dissolved metal ions from shuttling to the negative electrode. This improves the problem of reversible cycle capacity decay and reduced cycle performance of the battery.

[0080] In some embodiments, the first structural unit includes the structural unit shown in Formula I.

[0081]

[0082] Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

[0083] In this document, "alkyl group with 1-10 carbon atoms" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without any unsaturation, having 1 to 10 carbon atoms, and attached to the rest of the molecule by single bonds. Suitable examples include, but are not limited to: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, pentyl, isopentyl, neopentyl, tert-pentyl, cyclopentyl, hexyl, cyclohexyl, heptyl, cycloheptyl, octyl, cyclooctyl, nonyl, and decyl, etc.

[0084] In this article, "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing one hydrogen atom. "Aryl with 6-15 carbon atoms" refers to an aryl group containing 6-15 carbon atoms, and suitable examples include, but are not limited to, phenyl, tolyl, and xylyl.

[0085] By changing R1, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial to giving the polymer better chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Formula I allows the polymer to have an appropriate number of adsorption groups (amino, oxime groups).

[0086] It should be noted that in this application, the membrane coating uses a polymer with adsorption groups (amino, oxime groups). Compared with small molecule compounds that have a chelating effect on metal ions (such as ethylenediaminetetraacetic acid), polymers have stronger chemical stability and are less prone to decomposition.

[0087] In some embodiments, R1 comprises any one of an alkyl group having 1-5 carbon atoms or a phenyl group having 6-10 carbon atoms. The inclusion of an alkyl or phenyl group of appropriate length in R1 gives the polymer suitable viscosity.

[0088] Specifically, the first structural unit includes at least one of the structural units shown in Equations I-1 to I-6:

[0089]

[0090] In the structural units shown in I-1 to I-6, the side chain is a metallo-oxime group. The electronegative atoms containing lone pair monomons such as O and N in the metallo-oxime group can chelate with metal ions (such as transition metals such as nickel, manganese, and cobalt) dissolved in the electrolyte. That is, it adsorbs the metal ions dissolved from the positive electrode of the battery, thereby preventing the dissolved metal ions from shuttling to the negative electrode, and thus improving the problem of reduced cycle performance.

[0091] In some embodiments, the infrared spectrum of the polymer has a wavenumber of 3500-3650 cm⁻¹. -1 3200-3500cm -1 1590-1690cm-1 1320-1400cm -1 and 910-960cm -1 The presence of characteristic infrared peaks at the specified location indicates the presence of OH, C=N, -NH2, CN, and NO groups in the polymer.

[0092] Infrared spectroscopy can be used to identify and analyze functional groups in organic compounds. For example, the presence of chemical bonds or functional groups can be qualitatively or quantitatively analyzed through characteristic infrared absorption peaks. Characteristic infrared absorption peaks correspond to the vibrational modes of a particular chemical bond or functional group in a molecule. The vibrational frequencies of the same functional group will appear within a certain region. Infrared spectra can be obtained using conventional equipment and methods in the art. For example, the infrared spectrum of a polymer can be measured using a Thermo Nicolet IS5 Fourier transform infrared spectrometer, with a 1x1 cm⁻¹ sample size. 2 The diaphragm sample was directly fixed to the infrared reflection acquisition window for measurement, with a measurement range of 4000-4000 cm⁻¹. -1 Acquisition rate 20cm -1 / s.

[0093] In some embodiments, the coating thickness is 5-12 μm. At this suitable thickness, transition metal ions can be chelated without affecting the passage of lithium ions through the separator.

[0094] In some embodiments, the polymer further includes a second structural unit containing a cyano group. The cyano group (-C≡N) contains an electronegative N atom with a lone pair of monomers. It, along with the amino (-NH₂) and oxime (-C=N-OH) groups in the first structural unit, possesses the ability to coordinate with metal ions. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode and hindering their migration to the negative electrode, thereby mitigating the problem of reduced cycle performance. Furthermore, the presence of the cyano group contributes to improved chemical stability of the polymer.

[0095] In some embodiments, the second structural unit includes the structural unit shown in Formula II.

[0096]

[0097] Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

[0098] By changing R2, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial for improving the polymer's chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Equation I allows the polymer to possess an appropriate number of cyano groups.

[0099] Specifically, the second structural unit includes at least one of the structural units shown in Formulas II-1 to II-6:

[0100]

[0101] In the structural units shown in formulas II-1 to II-6, cyano groups serve as side chains. On one hand, the presence of cyano groups is beneficial for improving the chemical stability of the polymer. On the other hand, the electronegative N atom containing lone-pair monotons in the cyano group has the ability to combine with metal ions through coordination with both the amino and oxime groups in the first structural unit. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode of the battery, hindering the shuttle of dissolved metal ions to the negative electrode, and thus improving the problem of reduced cycle performance.

[0102] In some embodiments, the polymer's infrared spectrum also includes wavenumbers in the range of 2220-2270 cm⁻¹. -1 The presence of characteristic infrared peaks at this location indicates the presence of cyano groups in the polymer.

[0103] In some embodiments, the ratio n:m of the number of structural units n shown in Formula I to the number m shown in Formula II is (1-50):1. Within this suitable range, a ratio of n to m facilitates the formation of multidentate coordination between the polymer and metal ions dissolved in the electrolyte, further suppressing the degradation of cycle performance. The ratio of n to m can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27... The range is 1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1, 41:1, 42:1, 43:1, 44:1, 45:1, 46:1, 47:1, 48:1, 49:1, 50:1, or any range consisting of two of the above values.

[0104] The number of structural units n shown in Equation I and the number of structural units m shown in Equation II can be measured using conventional instruments and methods in the art. For example, a 5x5 mm value can be used.2 For the diaphragm sample, the N1s X-ray photoelectron spectrum of the diaphragm surface was collected under vacuum using a K-AlphaXPS X-ray photoelectron spectrometer (XPS). By comparing the intensity ratio of the peak at 399.57 eV (cyano C≡N) and the peak at 400.35 eV (CN) in the N1s spectrum, the ratio of the number of structural units n (containing cyano C≡N) to m (containing CN) shown in Equation I can be obtained.

[0105] In some embodiments, the polymer has a weight-average molecular weight of 5,000 to 500,000. This suitable range of weight-average molecular weight allows the polymer to have an appropriate number of repeating structural units, which is beneficial for adsorbing metal ions dissolved in the electrolyte.

[0106] The weight-average molecular weight of a polymer is a common way of describing the molecular weight distribution of a polymer. The weight-average molecular weight can be measured using conventional instruments and methods in the art. For example, it can be measured using a gel permeation chromatography (GPC) instrument of model PL-GPC50.

[0107] In some embodiments, the polymer comprises at least one of the compounds shown in Formula III-1 to Formula III-6:

[0108]

[0109] Where 100≤n≤3000, 0≤m<1000 。

[0110] In the polymers shown in Formulas III-1 to III-6, on the one hand, the content of structural units containing a metallo-oxime groups is relatively higher, which is beneficial to increasing the probability of capturing metal ions (such as transition metals nickel, manganese, cobalt, etc.) dissolved in the electrolyte. On the other hand, the cyano group and the metallo-oxime group can work together to form multidentate coordination with the metal ions dissolved in the electrolyte, thereby hindering the shuttle of dissolved metal ions to the negative electrode and thus improving the problem of reduced cycle performance. Furthermore, the presence of the cyano group is beneficial to improving the chemical stability of the polymer.

[0111] In some embodiments, the coating further includes inorganic oxides and thickeners; or, the coating further includes inorganic oxides, thickeners, and dispersants. The inorganic oxides provide thermal stability to prevent membrane shrinkage or melting, and offer better mechanical strength and puncture resistance. The thickeners ensure uniform and stable adhesion of the coating to the membrane. The dispersants ensure uniform dispersion of the inorganic oxide particles, preventing particle aggregation. Uniformly dispersed particles can form a more regular microstructure within the coating, which is beneficial for lithium-ion transport.

[0112] In some embodiments, the mass ratio of polymer, inorganic oxide, and thickener in the coating is 100:(10-20):(20-40); or, the mass ratio of polymer, inorganic oxide, thickener, and dispersant in the coating is 100:(10-20):(20-40):(2-10). Under these suitable ratios, the polymer in the coating can effectively adsorb metal ions dissolved in the electrolyte, thereby helping to suppress the degradation of cycle performance. The mass ratio of polymer, inorganic oxide, and thickener in the coating can be 100:10:20, 100:10:25, 100:10:30, 100:10:35, 100:10:40, 100:15:20, 100:15:25, 100:15:30, 100:15:35, 100:15:40, 100:20:20, 100:20:25, 100:20:30, 100:20:35, 100:20:40, or a range of any two of the above values. The mass ratio of polymer, inorganic oxide, thickener, and dispersant in the coating can be 100:10:20:2, 100:10:20:4, 100:10:20:6, 100:10:20:8, 100:10:20:10, 100:10:30:2, 100:10:30:4, 100:10:30:6, 100:10:30:8, 100:10:30:10, 100:10:40:2, 100:10:40:4, 100:10:40:6, 100:10:40:8, 100:10 :40:10, 100:20:20:2, 100:20:20:4, 100:20:20:6, 100:20:20:8, 100:20:20:10, 100:20:30:2, 100:20:30:4, 100:20:30:6, 100:20:30:8, 100:20:30:10, 100:20:40:2, 100:20:40:4, 100:20:40:6, 100:20:40:8, 100:20:40:10 or a range consisting of any two of the above values.

[0113] In some embodiments, the coating also satisfies at least one of the following characteristics: (1) the inorganic oxide includes at least one of aluminum oxide, calcium oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite; (2) the thickener includes at least one of sodium carboxymethyl cellulose, polyacryl alcohol, polyvinylidene fluoride, polyacrylonitrile, and polyacrylate; and (3) the dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone, and polyacrylamide.

[0114] In some embodiments, the secondary battery includes a positive electrode and a negative electrode, with the coating located at least on the side of the separator facing the negative electrode. Positioning the coating facing the negative electrode helps prevent degradation of the polymer within the coating.

[0115] It should be noted that during battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. The separator, placed between the positive and negative electrode plates, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0116] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0117] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0118] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0120] Specifically, in the embodiments of this application, the positive electrode active material includes Li a (Ni b Co c Mn d A e O2, wherein A includes at least one of Al, Zr, Mg, Zn, Y, Fe, Nb, W, Zn, Mo, Ba, Ca, Ta and Ti; wherein 0.2 < a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, and b + c + d + e = 1.

[0121] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0124] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0125] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0126] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0127] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may 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 may 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 may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0128] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may 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).

[0129] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from 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 negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0131] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0132] In some embodiments, the secondary battery also includes an electrolyte, which may be an electrolyte solution comprising an electrolyte salt and a solvent.

[0133] In some embodiments, the electrolyte salt may 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0134] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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.

[0135] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0136] This application does not impose any particular restrictions on the type of base membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the base membrane in the separator can be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. Specifically, in one embodiment of this application, the base membrane includes a polyethylene film.

[0138] Specifically, in the embodiments of this application, the base membrane includes at least one of a polyolefin membrane, a nonwoven membrane, a fiber membrane, and a polyaramid membrane. The thickness of the base membrane can be 7-15 μm.

[0139] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0140] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0141] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0142] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0143] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0144] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0145] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0146] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0147] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0148] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0149] Secondly, embodiments of this application provide a method for preparing a secondary battery, including a separator preparation step, wherein the separator preparation step includes:

[0150] Provide a base film;

[0151] A coating is formed on at least one side surface of the base membrane to obtain the diaphragm, wherein the coating comprises a polymer, the polymer comprising a first structural unit containing a amine oxime group.

[0152] The preparation process provided in this application is simple and conducive to industrial application. The polymer in the coating includes a first structural unit containing a metallo-oxime group. Since the metallo-oxime group contains an amino group (-NH2) and an oxime group (-C=N-OH), and the N and O atoms in the amino and oxime groups contain lone pairs of electrons, they can combine with metal ions dissolved from the positive electrode in the electrolyte through coordination, thereby achieving the adsorption of dissolved metal ions and preventing them from shuttling to the negative electrode. This improves the problem of reversible cycle capacity decay and reduced cycle performance of the battery.

[0153] In any embodiment, the first structural unit includes the structural unit shown in Equation I.

[0154]

[0155] Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

[0156] By changing R1, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial to giving the polymer better chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Formula I allows the polymer to have an appropriate number of adsorption groups (amino, oxime groups).

[0157] In some embodiments, the polymer further includes a second structural unit containing a cyano group. The cyano group contains an electronegative N atom with a lone pair of monomers, which, along with the amino (-NH2) and oxime (-C=N-OH) groups in the first structural unit, possesses the ability to coordinate with metal ions. This allows it to form polydentate coordination with metal ions dissolved in the electrolyte, further adsorbing metal ions dissolved from the positive electrode and hindering their migration to the negative electrode, thereby mitigating the problem of reduced cycle performance. Furthermore, the presence of the cyano group contributes to improved chemical stability of the polymer.

[0158] In some embodiments, the second structural unit includes the structural unit shown in Formula II.

[0159]

[0160] Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

[0161] By changing R2, the steric hindrance or main chain length of the polymer can be adjusted, which is beneficial for improving the polymer's chemical and thermal stability. Within a suitable range, the number n of the structural units shown in Equation I allows the polymer to possess an appropriate number of cyano groups.

[0162] In some implementations, the ratio n:m of the number of structural units n shown in Equation I to the number of structural units m shown in Equation II is (1-50):1.

[0163] In some embodiments, the step of forming a coating on at least one surface of the base membrane to obtain the separator includes:

[0164] The polymer, inorganic oxide, thickener, and solvent are mixed to obtain a slurry;

[0165] The slurry is coated onto at least one side of the base membrane, and the membrane is obtained after drying.

[0166] The solid content of the slurry is 30%-50%.

[0167] The solvent includes water, or the solvent includes water and a dispersant, wherein the dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone, and polyacrylamide.

[0168] In some embodiments, in the step of coating the slurry at least on one side of the base membrane and drying it to obtain the diaphragm, the coating amount of the slurry is per 50 × 100 mm. 2 Apply 2-4 mg to the affected area.

[0169] The polymers in the embodiments of this application can be prepared by conventional preparation methods in the art. As an example, the polymers can be prepared by the following steps:

[0170] Obtain raw material polymers containing structural units with cyano groups;

[0171] The raw material polymer is mixed with a modifier containing hydroxylamine groups, such that at least some of the cyano groups in the raw material polymer are replaced with a hydroxylamine oxime groups, to obtain the polymer.

[0172] It should be noted that the raw material polymer is mixed with a modifier containing hydroxylamine groups, such that at least some of the cyano groups in the raw material polymer are replaced with amine oxime groups. This includes two cases. In one case, all cyano groups in the raw material polymer are completely replaced with amine oxime groups. In this case, the resulting polymer contains only the first structural unit containing amine oxime groups. In the other case, all cyano groups in the raw material polymer are partially replaced with amine oxime groups. In this case, the resulting polymer contains both the first structural unit containing amine oxime groups and the second structural unit containing cyano groups. The ratio between the first and second structural units in the prepared polymer can be adjusted by changing the molar ratio of the raw material polymer to the modifier.

[0173] By replacing the cyano groups in the raw material polymer, a methylamine oxime group can be easily obtained. By changing the ratio of the raw material polymer to the modifier, a polymer containing only methylamine oxime groups or a polymer containing both cyano groups and methylamine oxime groups can be obtained.

[0174] Thirdly, embodiments of this application provide an electrical device including the secondary battery provided in the first aspect.

[0175] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0176] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0177] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0178] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0179] Example

[0180] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0181] Example 1

[0182] This embodiment provides a secondary battery, which is prepared through the following steps:

[0183] (1) Preparation of the diaphragm:

[0184] Preparation of polymer: Weigh 53g (10 -3Polyacrylonitrile (PAN) containing 1 mol (1 mol of cyano groups) (degree of polymerization 1000±50, weight average molecular weight 53000) was added to a flask containing 500 mL of N,N-dimethylacetamide (DMAc) and dissolved at 50 °C. Then, an aqueous solution containing 45 g (0.5 mol) of hydroxylamine hydrochloride and 28 g (0.5 mol) of KOH were added to the flask. In this example, the molar ratio of cyano groups to hydroxylamine hydrochloride in the polyacrylonitrile was 1:0.5. In-situ one-step amylopyridine modification was performed by stirring. After stirring for 2 h, the mixture was cooled to room temperature and centrifuged at 5000 r / min for 30 min. The centrifuged solution was the amylopyridine-modified polyacrylonitrile solution, which was dried at 200 °C. Polymer powder was obtained. XPS analysis showed that the ratio of amylopyridine-containing structural units to cyano-containing structural units in the polymer was n:m = 1:1.

[0185] Preparation of diaphragm coating slurry: Take 5.3 g of the above polymer powder, mix the polymer powder, aluminum oxide, sodium carboxymethyl cellulose and water in a mass ratio of 100:10:20:200, stir and disperse at 500 rpm / min to obtain coating slurry with a solid content of 37.5%.

[0186] Membrane preparation: A coating slurry was applied to one side of a 15µm thick polyethylene membrane, with a coating amount of slurry per 50×100mm. 2 A 2mg coating was applied to the surface area and dried at 60°C using forced air to obtain a diaphragm. After drying, the coating thickness on the diaphragm in this embodiment was 7µm.

[0187] (2) Preparation of the positive electrode sheet: The positive electrode active material (LiNi) is prepared by... 0.9 Co 0.05 Mn 0.05 93g of O2, 5g of conductive agent (super carbon black), and 1g of binder (PVDF) were mixed, and 35g of NMP (N-methylpyrrolidone) was added. The mixture was stirred at 500 r / s, and then wetted, kneaded, and dispersed to obtain a positive electrode slurry, with the viscosity adjusted to 8000 mPa·s. The prepared slurry was coated onto a current collector aluminum foil and then dried in an oven at 80℃, controlling the water content to be less than 150 ppm, to obtain the positive electrode sheet.

[0188] (3) Preparation of negative electrode sheet: The negative electrode material (hard carbon), binder (polyvinyl alcohol) and conductive agent (SP-Li) are mixed and ball-milled in a mass ratio of 90:5:5 to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of copper foil, rolled, and vacuum dried overnight at 110°C to obtain a negative electrode sheet.

[0189] (4) Preparation of electrolyte:

[0190] The electrolyte solvent was prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. Then, LiPF6 was mixed with the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0191] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. In this embodiment, the coated side of the separator faces the negative electrode. The electrode assembly is then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0192] It should be noted that in the embodiments of this application, polymer powder, aluminum oxide, sodium carboxymethyl cellulose and water are mixed to prepare a coating, and then a secondary battery is prepared. The mass ratio of each substance is the initial addition ratio.

[0193] Examples 2-12 and Comparative Examples 1-2 were prepared using similar steps to Example 1, with differences shown in Table 1.

[0194] In Example 5, the cyano group was completely converted to a methylamine oxime group.

[0195] In Example 8, polymer powder, aluminum oxide, sodium carboxymethyl cellulose, water, and polyacrylonitrile were mixed in a mass ratio of 100:10:20:200:5.

[0196] In Example 12, a coating was applied to both sides of the base membrane of the diaphragm, with each coating having a thickness of 7 μm and the total thickness of the two coatings being 14 μm.

[0197]

[0198] Performance testing:

[0199] The secondary batteries using the cathode materials of Examples 1 to 12 and Comparative Examples 1 to 2 were tested as follows:

[0200] (1) Measurement of the microstructure of the coating on the diaphragm:

[0201] The surfaces of the diaphragm in Example 1 and the uncoated diaphragm in Comparative Example 1 were characterized using scanning electron microscopy (CP-SEM). Figure 7 It is evident that the surface roughness of the diaphragm increased in Example 1. And... Figure 8 The surface of the uncoated diaphragm in Comparative Example 1 is smooth.

[0202] (2) Measurement of characteristic peaks of polymers in the coating on the diaphragm:

[0203] The polymer prepared in step 1 of Example 1 was tested using a Thermo Nicolet IS5 Fourier transform infrared spectrometer.

[0204] See Figure 9 The lines of PAN represent the infrared spectrum of the polyacrylonitrile raw material, and PAN-W represents the infrared spectrum of the polymer prepared in Example 1. In the infrared spectrum of the polymer prepared in Example 1, PAN-W, at a wavenumber of 3600 cm⁻¹ cm⁻¹,... -1 3400cm -1 1665cm -1 1350cm -1 945cm -1 2240cm -1 The presence of characteristic infrared peaks at the specified location indicates the presence of OH, C=N, -NH2, CN, NO, and C≡N groups, respectively, in the polymer.

[0205] (3) Coating thickness measurement:

[0206] The thickness of the coating on the diaphragm can be determined by ion polishing cross-sectional morphology analysis (CP) combined with scanning electron microscopy (SEM). See also Figure 10 It shows a SEM image of the base film of the diaphragm in Example 12, which is coated with a coating on both sides.

[0207] (4) Testing of the content of structural units in the polymer and measurement of weight-average molecular weight:

[0208] Gel permeation chromatography (GPC).

[0209] Instrument: PL-GPC50

[0210] Test Method: A 0.2% (w / w) polyacrylonitrile solution was used as a reference, and a matching chromatographic column (oil-based: Waters Styragel HT4, molecular weight 5000-600000) was selected. A 0.2% polymer solution was prepared using purified N,N dimethylformamide (DMF) solvent and allowed to stand for one day. During testing, tetrahydrofuran was first drawn into a syringe and used to rinse the sample, repeating several times. Then, 5 mL of the test solution was drawn, air was expelled from the syringe, and the needle tip was dried. A 2 mL syringe with a filter head (5 μm pore size) was used to filter the sample. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the weight-average molecular weight data was obtained.

[0211] The following example is Example 1.

[0212] The ratio of the first structural unit n containing a amine oxime group to the second structural unit m containing a cyano group was measured.

[0213] Take a 5x5 mm diaphragm 2 The sample was placed on the sample stage, and the N1s X-ray photoelectron spectrum of the membrane surface was collected under vacuum conditions using a K-Alpha XPS X-ray photoelectron spectroscopy (XPS) device. By comparing the intensity ratio k of the peak at 399.57 eV (cyano C≡N) and the peak at 400.35 eV (CN) in the N1s spectrum, the ratio k of the number of structural units n (containing cyano C≡N) to m (containing CN) shown in Equation I can be obtained, which is k = n:m = 1:1.

[0214] (5) Test of transition metal ion content in the electrolyte of disassembled batteries:

[0215] The secondary battery was left to stand at 45℃ for 2 days. The battery was then disassembled, and the electrolyte was removed. The contents of transition metals (TM) nickel (Ni), cobalt (Co), and manganese (Mn) were determined using inductively coupled plasma atomic emission spectrometry (ICP) with an AGILENT 725-ES instrument. The test results are shown in Table 2.

[0216] (6) Secondary battery 0.5C capacity retention test:

[0217] The assembled secondary battery cells were charged to 4.25V at a constant current of 0.5C, then discharged to 2.8V at a constant current of 0.05C and 0.5C. The cells were then cycled 1000 times at room temperature (60℃). The capacity value C1000 was recorded and compared with the initial first-cycle capacity C0. The capacity retention rate was calculated using the formula: Capacity Retention Rate = C1000 / C0 * 100%. The test results are shown in Table 2.

[0218] (7) Secondary battery storage capacity retention rate test:

[0219] The assembled secondary battery cells were charged to 4.25V at a constant current of 0.5C at room temperature (60℃), then fully discharged, and the capacity C0 was recorded. After 120 days, the capacity at 0.5C full discharge was recorded as C1. The discharge capacity from C0 to C120 was then recorded. The 120-day storage capacity retention rate can be obtained using the formula: Capacity Retention Rate = C120 / C0 * 100%. The test results are shown in Table 2.

[0220] Table 2 shows the performance data of the secondary batteries in Examples 1 to 12 and Comparative Examples 1 to 2.

[0221]

[0222]

[0223] As can be seen from Tables 1-2, Examples 1-12, and Comparative Example 1, compared to the battery in Comparative Example 1 without a coating on the separator, the coating provided in the embodiments of this application can effectively reduce the content of transition metals nickel, cobalt, and manganese in the electrolyte of the disassembled battery, and the 0.5C capacity retention rate and 120-day storage capacity retention rate are both higher. This indicates that the separator coating provided in this application can adsorb dissolved transition metal ions, thereby preventing the dissolved metal ions from shuttling to the negative electrode, and thus improving the problem of reversible cycle capacity decay and reduced cycle performance of the battery.

[0224] As can be seen from Examples 1-12 and Comparative Example 2, in Comparative Example 2, an equal amount of small molecule p-benzoquinone dioxime was used to replace the polymer in the coating. Although the coating of small molecule p-benzoquinone dioxime had a small amount of adsorption effect on transition metal ions in the electrolyte, the battery of Comparative Example 2 had a relatively poor 120-day storage capacity retention rate. This is because small molecule p-benzoquinone dioxime is easy to decompose, while the polymer used in this application is not easy to decompose and has better storage performance.

[0225] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The membrane includes a base membrane and a coating covering at least one side of the base membrane, the coating comprising a polymer comprising a first structural unit containing a amine oxime group.

2. The secondary battery according to claim 1, characterized in that, The first structural unit includes the structural unit shown in Equation I. Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

3. The secondary battery according to claim 2, characterized in that, R1 includes any one of alkyl groups having 1-5 carbon atoms or phenyl groups having 6-10 carbon atoms.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The first structural unit includes at least one of the structural units shown in Equations I-1 to I-6:

5. The secondary battery according to any one of claims 1 to 4, characterized in that, In the infrared spectrum of the polymer, at wavenumbers of 3500-3650 cm⁻¹ -1 3200-3500cm -1 1590-1690cm -1 1320-1400cm -1 and 910-960cm -1 It has infrared characteristic peaks at the location.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The coating thickness is 5-12 μm.

7. The secondary battery according to any one of claims 2 to 6, characterized in that, The polymer also includes a second structural unit containing a cyano group.

8. The secondary battery according to claim 7, characterized in that, The second structural unit includes the structural unit shown in Equation II. Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

9. The secondary battery according to claim 8, characterized in that, The second structural unit includes at least one of the structural units shown in Formulas II-1 to II-6:

10. The secondary battery according to any one of claims 7 to 9, characterized in that, The infrared spectrum of the polymer also shows a wavenumber of 2220-2270 cm⁻¹. -1 It has infrared characteristic peaks at the location.

11. The secondary battery according to claim 8 or 9, characterized in that, The ratio of the number of structural units n shown in Equation I to the number of structural units m shown in Equation II, n:m, is (1-50):

1.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The polymer has a weight-average molecular weight of 5,000 to 500,000.

13. The secondary battery according to any one of claims 1 to 12, characterized in that, The polymer comprises at least one of the compounds shown in Formula III-1 to Formula III-6: Where 100≤n≤3000, 0≤m<1000 。 14. The secondary battery according to any one of claims 1 to 13, characterized in that, The coating further includes inorganic oxides and a thickener. Optionally, the mass ratio of the polymer, the inorganic oxide, and the thickener in the coating is 100:(10-20):(20-40); or... The coating further includes inorganic oxides, thickeners and dispersants. Optionally, the mass ratio of the polymer, the inorganic oxides, the thickeners and the dispersants in the coating is 100:(10-20):(20-40):(2-10).

15. The secondary battery according to claim 14, characterized in that, The coating also satisfies at least one of the following characteristics: (1) The inorganic oxide includes at least one of aluminum oxide, calcium oxide, silicon dioxide, magnesium hydroxide, zirconium dioxide, magnesium oxide, and boehmite; (2) The thickener includes at least one of sodium carboxymethyl cellulose, polyacryl alcohol, polyvinylidene fluoride, polyacrylonitrile, and polyacrylate; (3) The dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone and polyacrylamide.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The secondary battery includes a positive electrode and a negative electrode. The coating is located at least on the side of the separator facing the negative electrode.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The secondary battery includes a positive electrode active material, which includes Li. a (Ni b Co c Mn d A e O2, wherein A includes at least one of Al, Zr, Mg, Zn, Y, Fe, Nb, W, Zn, Mo, Ba, Ca, Ta and Ti; wherein 0.2 < a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, and b + c + d + e = 1.

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The base membrane includes at least one of polyolefin membrane, nonwoven membrane, fiber membrane, and polyaramid membrane.

19. The secondary battery according to claim 18, characterized in that, The thickness of the base film is 7-15 μm.

20. A method for preparing a secondary battery according to any one of claims 1 to 19, characterized in that, The process includes a membrane preparation step, which includes: Provide a base film; A coating is formed on at least one side surface of the base membrane to obtain the diaphragm, wherein the coating comprises a polymer, the polymer comprising a first structural unit containing a amine oxime group.

21. The preparation method according to claim 20, characterized in that, The first structural unit includes the structural unit shown in Equation I. Wherein, R1 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-15 carbon atoms, and the number of structural units shown in Formula I is n, where 100≤n≤3000.

22. The preparation method according to claim 20 or 21, characterized in that, The polymer also includes a second structural unit containing a cyano group.

23. The preparation method according to claim 22, characterized in that, The second structural unit includes the structural unit shown in Equation II. Wherein, R2 includes any one of alkyl with 1-10 carbon atoms or aryl with 6-12 carbon atoms, and the number of structural units shown in Formula II is m, 0≤m<1000.

24. The preparation method according to claim 22 or 23, characterized in that, The ratio of the number of structural units n shown in Equation I to the number of structural units m shown in Equation II, n:m, is (1-50):

1.

25. The preparation method according to claim 20, characterized in that, The step of forming a coating on at least one surface of the base membrane to obtain the separator includes: The polymer, inorganic oxide, thickener, and solvent are mixed to obtain a slurry. The slurry is coated onto at least one side of the base membrane, and the membrane is obtained after drying. The solid content of the slurry is 30%-50%.

26. The preparation method according to claim 25, characterized in that, In the step of coating the slurry onto at least one side of the base membrane and drying it to obtain the diaphragm... The coating amount of the slurry is per 50×100mm. 2 Apply 2-4 mg to the affected area.

27. An electrical appliance, characterized in that, This includes a secondary battery as described in any one of claims 1 to 19 or a secondary battery manufactured by the preparation method described in any one of claims 20 to 26.

Images