Secondary battery, preparation method thereof and electric equipment

Abstract

The invention discloses a secondary battery, a preparation method thereof and electric equipment, and belongs to the field of secondary batteries, the secondary battery comprises a pole piece and an isolating membrane, at least part of the surface of the isolating membrane in contact with the pole piece is provided with a polymer layer, and the polymer layer can swell in electrolyte. The secondary battery provided by the invention has excellent cycle performance.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, specifically relating to a secondary battery and its preparation method, as well as electrical equipment. Background Technology

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Improving electrolyte wetting in secondary batteries has become a research hotspot in the field. Existing secondary batteries suffer from poor electrolyte wetting, resulting in poor cycle performance. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a secondary battery, which aims to improve the wetting performance of the electrolyte and thus improve the cycle performance of the secondary battery.

[0005] To achieve the above objectives, the first aspect of this application proposes a secondary battery, the secondary battery comprising an electrode and a separator, wherein at least a portion of the surface of the separator in contact with the electrode is provided with a polymer layer, the polymer layer being swellable in an electrolyte.

[0006] This application includes at least the following beneficial effects: In the secondary battery of this application, a polymer layer is provided between the separator and the battery electrode. The polymer layer can swell into a foam structure in the electrolyte, which can absorb the electrolyte, thereby improving the wetting performance of the electrolyte and enhancing the cycle performance of the secondary battery containing it.

[0007] In some embodiments, the polymer layer is disposed on the separator. This can improve the cycle life of the secondary battery containing it.

[0008] In some embodiments, the polymer layer comprises a polymer, including at least one selected from polyethylene oxide, polyacrylic acid, or styrene-butadiene rubber. This can improve the cycle life of secondary batteries containing it.

[0009] In some embodiments, the weight-average molecular weight of the polymer is 2000-20000. This can improve the cycle life of secondary batteries containing it.

[0010] In some embodiments, the polymeric material comprises 90%-100% of the total mass of the polymeric layer. This can improve the cycle life of secondary batteries containing it.

[0011] In some embodiments, the polymeric material comprises 95%-99% of the total mass of the polymeric layer. This can improve the cycle life of secondary batteries containing it.

[0012] In some embodiments, the polymer layer further includes a lithium salt. This can improve the cycle life of the secondary battery containing it.

[0013] In some embodiments, at least one of the following conditions is met: the mass percentage of the lithium salt is less than or equal to 10% based on the total mass of the polymer layer; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. This can improve the cycle life of secondary batteries containing the lithium salt.

[0014] In some embodiments, at least one of the following conditions is met: the lithium salt accounts for 1%-5% of the total mass of the polymer layer; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium difluorooxalateborate, or lithium hexafluorophosphate. This can improve the cycle life of secondary batteries containing it.

[0015] In some embodiments, the thickness of the polymer layer is 2 μm-10.5 μm. This can improve the cycle life of secondary batteries containing it.

[0016] In some embodiments, the secondary battery further includes an electrolyte, with an electrolyte injection volume of 1.5 g / Ah to 2.25 g / Ah. This can improve the cycle life of the secondary battery containing the electrolyte.

[0017] In some embodiments, the secondary battery further includes an electrolyte comprising a solvent, the solvent being at least one selected from 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, or diethyl sulfone. This can improve the cycle life of the secondary battery containing it.

[0018] In some embodiments, the electrode includes a negative electrode, which includes a negative electrode active material layer, comprising at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, titanates, or lithium metal. This can improve the cycle life of secondary batteries containing such materials.

[0019] In some embodiments, at least one of the following conditions is met: the negative electrode active material layer comprises lithium metal; and at least a portion of the surface of the separator in contact with the negative electrode sheet is provided with a polymer layer. This can improve the cycle life of the secondary battery containing it.

[0020] In some embodiments, the electrode includes a negative electrode, and the polymer layer is disposed on the negative electrode. This can improve the cycle life of the secondary battery containing it.

[0021] In a second aspect, this application proposes a method for preparing a secondary battery, comprising: assembling an electrode and a separator to obtain a secondary battery, wherein at least a portion of the surface of the separator in contact with the electrode is provided with a polymer layer, the polymer layer being swellable in an electrolyte. Thus, the secondary battery prepared in this application has a polymer layer disposed between the separator and the negative electrode, the polymer layer being swellable in the electrolyte to form a foam structure, absorbing the electrolyte, thereby improving the wettability of the electrolyte and enhancing the cycle performance of the secondary battery containing it.

[0022] In some embodiments, the polymer layer is disposed on the separator membrane, and the polymer layer is prepared by dissolving a polymer and a lithium salt in a solvent to obtain a mixed solution, and coating the mixed solution onto at least one side of the separator membrane to obtain the polymer layer. This can improve the cycle life of the secondary battery containing it.

[0023] In some embodiments, at least one of the following conditions is met: the solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, acetone, or toluene; the sum of the masses of the polymer and the lithium salt accounts for 30%-60% of the total mass of the mixed solution; and the coating includes spraying. This can improve the cycle life of secondary batteries containing the polymer.

[0024] In some embodiments, the polymer layer is disposed on the negative electrode sheet, and the polymer layer is prepared by rolling a slurry containing a polymer onto the negative electrode sheet to form the polymer layer. This can improve the cycle life of the secondary battery containing it.

[0025] In a third aspect of this application, this application proposes an electrical device comprising the secondary battery described in the first aspect of this application, or a secondary battery prepared using the method described in the second aspect.

[0026] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0028] Figure 1 This is a schematic diagram of the polymer layer before and after swelling in this application.

[0029] Figure 2 This is a schematic diagram of a battery according to one embodiment of this application.

[0030] Figure 3 yes Figure 2 An exploded view of a battery according to one embodiment of this application is shown.

[0031] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0032] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0033] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0034] Figure 7 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0035] Figure 8 This is a scanning electron microscope image of the negative electrode sheet of the battery prepared in Example 3 of this application after it is fully charged.

[0036] Figure 9 This is a scanning electron microscope image of the negative electrode sheet of the battery prepared in Comparative Example 1 of this application after it is fully charged.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Battery cell; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Battery module; 3. Battery pack; 31. Upper casing; 32. Lower casing. Detailed Implementation

[0039] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] 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.

[0045] Currently, judging from market trends, the application of rechargeable batteries is becoming increasingly widespread. Rechargeable 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, among other fields.

[0046] In secondary batteries, the wetting properties of the electrolyte refer to its ability to contact and form a uniform, continuous liquid film with the battery's internal materials (such as the positive electrode, negative electrode, and separator). This property is crucial to the battery's electrochemical performance because it affects the distribution of the electrolyte within the battery and the efficiency of ion transport, thus influencing the battery's cycle performance.

[0047] Researchers typically improve the wetting properties of electrolytes by improving the electrolyte injection process or adding surfactants, but these methods are often ineffective.

[0048] In the secondary battery of this application embodiment, a polymer layer is provided on the side of one of the negative electrode and the positive electrode opposite to the separator. The polymer layer can swell in the electrolyte. The polymer layer is provided between the separator and the battery electrode. The polymer layer can swell into a foam structure in the electrolyte, which can absorb the electrolyte, thereby improving the wetting performance of the electrolyte and enhancing the cycle performance of the secondary battery containing it.

[0049] The secondary battery disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0050] The first aspect of this application proposes a secondary battery, the secondary battery including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein a polymer layer is provided on the side of the negative electrode and the positive electrode opposite to the separator, and the polymer layer can swell in an electrolyte.

[0051] The secondary battery of this application embodiment includes electrodes and a separator. At least a portion of the surface of the separator in contact with the electrodes is provided with a polymer layer, which can swell in an electrolyte. By providing a polymer layer between the separator and the battery electrodes, the polymer layer can swell into a foam structure in the electrolyte, absorbing some of the electrolyte and improving the wetting properties of the electrolyte. This enhances the effective contact between the electrolyte and the electrodes (positive and negative electrodes) and the separator, thereby improving the cycle performance of the secondary battery containing it.

[0052] It is understood that in the embodiments of this application, the electrode may include a positive electrode and a negative electrode. Regarding the position of the polymer layer, the polymer layer is disposed between the separator and the positive electrode and / or the negative electrode. Taking the negative electrode as an example, the polymer layer may be disposed on the negative electrode and formed on the side of the negative electrode close to the separator, or it may be disposed on the separator and formed on the side of the separator close to the negative electrode, or it may be a separate layer disposed between the negative electrode and the separator. The positive electrode is similar and will not be described in detail here.

[0053] As can be understood, the polymer layer refers to a layer of high-molecular-weight polymers that is deposited on at least a portion of the surface where the separator contacts the electrode. This layer can swell in the electrolyte. Swelling is the phenomenon where the volume of the polymer expands in the electrolyte. When the polymer layer is immersed in the electrolyte, its volume increases; this phenomenon is called swelling. To observe the swelling of the polymer layer in the electrolyte, the secondary battery can be disassembled, and scanning electron microscopy (SEM) images of components containing the polymer layer, such as the separator or the negative electrode, can be taken to observe whether the polymer layer is foam-like.

[0054] In some embodiments of this application, the secondary battery includes a lithium metal battery, and the polymer layer is provided on the side of the negative electrode sheet opposite to the separator. Therefore, during cycling, the expansion of lithium metal and the accumulation of black substances (byproducts of lithium metal production and dead lithium coated with SEI) or SEI can easily lead to abnormal negative electrode wetting. The polymer layer on the side of the negative electrode sheet opposite to the separator can further improve the cycle life of the secondary battery containing it, especially for lithium metal batteries where the negative electrode is prone to poor wetting.

[0055] Furthermore, in practical use, lithium metal batteries suffer from the problem of dead lithium drift due to the formation of pulverized dead lithium. This drifting lithium powder is uncontrolled within the battery, easily leading to short circuits at the positive and negative electrodes, overcharging, and consequently, a significant risk of thermal runaway. In this embodiment, the polymer layer on the side of the negative electrode opposite the separator absorbs the electrolyte, forming a foam-like structure on the separator and lithium metal surface. This structure adsorbs and restricts the drift of pulverized dead lithium to a certain extent, effectively binding the drifting lithium powder and reducing micro-short circuits in the battery, while also mitigating overcharging. On the other hand, the polymer layer, after swelling, possesses a certain degree of elasticity. As the secondary battery expands during cycling, the compression of the foam structure exerts reverse stress on the lithium surface, which can improve the density of lithium deposition to some extent. This provides a certain elastic modulus for lithium metal cycling, improving the deposition morphology of the negative electrode lithium, promoting dense lithium deposition and growth, reducing electrolyte consumption during cycling, and enhancing battery cycle performance.

[0056] In some embodiments of this application, the polymer layer is disposed on the separator. Taking a lithium metal battery as an example, the lithium metal layer of a lithium metal battery is continuously consumed and deposited during cycling. Therefore, placing the polymer layer on the separator relative to the lithium metal anode does not affect the deposition and consumption of lithium metal, and can further improve the cycle life of the secondary battery containing it.

[0057] In some embodiments of this application, the polymer layer is disposed on the negative electrode sheet. The polymer layer can swell into a foam structure in the electrolyte, which can absorb part of the electrolyte, thereby improving the wettability of the electrolyte and enhancing the effective contact between the electrolyte and the electrodes (positive and negative electrodes) and the separator, thus improving the cycle performance of the secondary battery containing it.

[0058] In some embodiments of this application, the polymer layer comprises a polymer, which includes at least one selected from polyethylene oxide (PEO), polyacrylic acid, or styrene-butadiene rubber. The aforementioned polymer can swell in the electrolyte to form a foam structure and is not easily dissolved in the electrolyte, thus absorbing some of the electrolyte and improving the wetting properties of the electrolyte, thereby enhancing the cycle performance of the battery. In other embodiments of this application, the polymer comprises polyethylene oxide (PEO).

[0059] In some embodiments of this application, the polymer further includes at least one of polypropylene (PP), polyethylene (PE), or polyimide (PI). The above-mentioned polymers have good stability and generally do not swell in the electrolyte. They can serve as the backbone of the polymer layer, improve the stability of the polymer layer, and enhance the cycle performance of the secondary battery.

[0060] In some embodiments of this application, the weight-average molecular weight of the polymer is 2000-20000, for example, 2000-19000, 3000-18000, 5000-15000, 8000-10000, etc. By controlling the weight-average molecular weight of the polymer within this range, the polymer can swell in the electrolyte and absorb some of the electrolyte, thereby improving the wetting performance of the electrolyte and enhancing the effective contact between the electrolyte and the electrodes (positive and negative electrodes) and the separator, thus improving the cycle performance of the secondary battery containing it. Furthermore, when the above-mentioned polymer is formed into a polymer layer, it is easily and uniformly dispersed on the separator or electrode. This improves the dispersion effect, allows for uniform swelling in the electrolyte, further enhances the wetting performance, and improves the cycle performance of the secondary battery.

[0061] The weight-average molecular weight of polymers can be measured using methods commonly used in the field, such as light scattering, ultracentrifugation sedimentation rate, and gel chromatography.

[0062] In some embodiments of this application, the polymer content is 90%-100% based on the total mass of the polymer layer. For example, it can be 90%-99%, 91%-98%, 92%-97%, 93%-96%, 94%-95%, etc. Controlling the polymer content in the polymer layer within these ranges ensures good film-forming properties and allows the polymer layer to swell in the electrolyte without easily dissolving, further improving the wetting performance of the electrolyte and enhancing the cycle performance of the secondary battery containing it. In other embodiments of this application, the polymer content is 95%-99% based on the total mass of the polymer layer.

[0063] In some embodiments of this application, the polymer layer further includes a lithium salt. The addition of lithium salt to the polymer layer can improve the lithium-ion conduction capability between the separator and the polymer layer, and between the electrode and the polymer layer, thereby improving the cycle performance of the battery.

[0064] In some embodiments of this application, the mass percentage of the lithium salt is less than or equal to 10% based on the total mass of the polymer layer. For example, the mass percentage of the lithium salt can be 0.1%-9.9%, 0.5%-9%, 1%-8%, 2%-7%, 3%-6%, 4%-5%, etc. Controlling the lithium salt content in the polymer layer within these ranges is sufficient to improve its lithium-ion conductivity and reduce the poor film-forming performance of the polymer layer caused by excessive lithium salt content, thereby further improving the cycle performance of the battery. In other embodiments of this application, the mass percentage of the lithium salt is 1%-5% based on the total mass of the polymer layer.

[0065] In some embodiments of this application, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. Specifically, the above-mentioned lithium salt can improve the lithium-ion conduction capacity of the separator and polymer layer, and the electrode and polymer layer, thereby improving the cycle performance of the battery. In other embodiments of this application, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisfluorosulfonylimide (LiFSI), lithium difluorooxalate borate (LiDFOB), or lithium hexafluorophosphate, for example, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0066] In some embodiments of this application, the thickness of the polymer layer is 2μm-10.5μm. For example, the thickness of the polymer layer can be 2μm-10μm, 2.1μm-8.7μm, 3.5μm-8.5μm, 4μm-5μm, etc. It can be understood that in the embodiments of this application, the thickness of the polymer layer includes the thickness before and after swelling in the electrolyte. For example, if the thickness of the polymer layer prepared is 5μm, the thickness of the polymer layer will increase after swelling. As long as the thickness of the polymer layer before or after swelling is within the range of this application, it is within the protection range of this application. Specifically, controlling the thickness of the polymer layer within the above range can reduce the tendency of the polymer layer to collapse after swelling in the electrolyte due to excessively low polymer layer thickness, and can also reduce the inability of the polymer layer to fully swell and insufficient liquid absorption capacity due to excessively high polymer layer thickness, so that the polymer layer can exist stably in the electrolyte, thereby further improving the cycle performance of the battery.

[0067] It is understood that "the thickness of the polymer layer" is a well-known definition in the art and can be measured using methods known in the art, such as the following methods:

[0068] The secondary battery is disassembled, and the part containing the polymer layer is removed. Taking the polymer layer on the separator as an example, the ion polished cross-sectional morphology (CP) of the separator is obtained by scanning electron microscopy in a liquid nitrogen atmosphere. The thickness of the polymer layer is measured from more than 5 parts selected from the image, and the average value is taken to obtain the thickness of the polymer layer.

[0069] In some embodiments of this application, the secondary battery further includes an electrolyte, and the electrolyte injection volume of the secondary battery is 1.5 g / Ah-2.25 g / Ah. For example, the electrolyte injection volume of the secondary battery can be 1.5 g / Ah-2 g / Ah, 1.51 g / Ah-1.74 g / Ah, 1.55 g / Ah-1.7 g / Ah, 1.6 g / Ah-1.65 g / Ah, etc. It can be understood that the unit of electrolyte injection volume (g / Ah) represents the mass of electrolyte required per ampere-hour of battery. Controlling the electrolyte injection volume of the battery within the above range ensures that the polymer layer maintains the integrity of the coating after swelling; and that the polymer layer is basically fully swollen, achieving good liquid absorption while ensuring good battery wetting, further improving the cycle performance of the battery.

[0070] It is understood that the "filled electrolyte volume of the secondary battery" can be determined using methods known in the art, such as the following methods:

[0071] Weigh the secondary battery to obtain m1. Disassemble the battery, remove the electrolyte, and weigh it again to obtain m2. Then the electrolyte injection volume = (m1-m2) / secondary battery capacity.

[0072] If the capacity of the secondary battery is marked on the label, it can be directly used in the above formula. If it is not marked, the capacity of the secondary battery can be determined by the following method: using a charge / discharge machine to charge the secondary battery and then discharging it with a constant current and a constant voltage, the discharge capacity is taken as the capacity. Specifically, according to the embodiments of this application, the steps to determine the capacity include: first charging at 1 / 3C to 4.25V, then charging at a constant voltage of 4.25V until the current decreases to 0.05C; then discharging at 1 / 3C to 2.5V, and the discharged capacity at this time is the capacity of the secondary battery.

[0073] In some embodiments of this application, the secondary battery further includes an electrolyte comprising a solvent, which includes 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, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone. The polymers such as PEO in the embodiments of this application can swell in the above-mentioned solvents, absorbing part of the electrolyte, thereby improving the wetting properties of the electrolyte, increasing the effective contact between the electrolyte and the electrodes (positive and negative electrodes) and the separator, and improving the cycle performance of the secondary battery containing it.

[0074] In some embodiments of this application, the electrode includes a negative electrode, which includes a negative electrode active material layer. The negative electrode active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, titanate, or lithium metal. In other embodiments of this application, the negative electrode active material layer includes lithium metal, i.e., the secondary battery is a lithium metal battery. This reduces the expansion of the negative electrode active material layer caused by lithium intercalation / deintercalation, thereby improving the cycle performance of the secondary battery.

[0075] In some embodiments of this application, at least a portion of the surface of the separator in contact with the negative electrode sheet is provided with a polymer layer. Taking a lithium metal battery as an example, during cycling, the expansion of lithium metal and the accumulation of black substances (byproducts of lithium metal production and dead lithium coated by SEI) or SEI can easily lead to abnormal negative electrode wetting. The polymer layer is provided on the side of the negative electrode sheet opposite to the separator, which can further improve the cycle life of secondary batteries containing it, especially for lithium metal batteries where the negative electrode is prone to poor wetting.

[0076] In a second aspect, this application proposes a method for preparing a secondary battery, comprising:

[0077] S1. Assemble the electrode and the separator to obtain a secondary battery, wherein at least a portion of the surface of the separator in contact with the electrode is provided with a polymer layer, and the polymer layer can swell in the electrolyte.

[0078] Therefore, in the secondary battery prepared in this application, a polymer layer is provided between the separator and the battery electrode. The polymer layer can swell into a foam structure in the electrolyte, which can absorb part of the electrolyte, thereby improving the wetting performance of the electrolyte and enhancing the effective contact between the electrolyte and the electrode (positive electrode and negative electrode) and the separator, thus improving the cycle performance of the secondary battery containing it.

[0079] In some embodiments of this application, the polymer layer is disposed on the isolation membrane, and the polymer layer is prepared by the following method:

[0080] S11. Dissolve the polymer and lithium salt in a solvent to obtain a mixed solution, and coat the mixed solution onto at least one side of the separator to obtain a polymer layer.

[0081] In some embodiments of this application, a solution containing a polymer and a lithium salt is sprayed onto one side of the separator to form a polymer layer. In this case, see [link to relevant documentation]. Figure 1The left image shows a schematic diagram of the separator before immersion in the electrolyte. The dots in the image are polymers. The polymers form a mesh structure on the separator, which has little impact on the transport of active metal ions (such as sodium ions and lithium ions), and the polymers have better uniformity on the separator. Figure 1 The left image and the right image are schematic diagrams of the separator after immersion in the electrolyte. It can be seen that the polymer can form a foam structure after being immersed in the electrolyte. Figure 1 (See right figure) This improves the wetting properties of the electrolyte, thereby enhancing the cycle performance of secondary batteries containing it.

[0082] In some embodiments of this application, the solvent includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), acetone, or toluene. These solvents can dissolve the polymer and, after spray drying, can form uniformly distributed polymer particles (e.g., ...) on the separating membrane. Figure 1 It has minimal impact on the transport of active metal ions (such as sodium ions and lithium ions), and the polymer layer exhibits better uniformity on the separator. After immersion in the electrolyte, it can form a foam structure, improving the electrolyte's wetting properties and enhancing the cycle performance of secondary batteries containing it. In other embodiments of this application, the solvent includes N-methylpyrrolidone.

[0083] In some embodiments of this application, the total mass of the polymer and the lithium salt accounts for 30%-60% of the total mass of the mixed solution. For example, it can be 30%-59%, 35%-55%, 40%-50%, 45%-48%, etc. By controlling the total mass of the polymer and lithium salt within the above range, the content of polymer and lithium salt is moderate, resulting in a polymer layer with good stability, a low probability of collapsing when dissolved in the electrolyte, and uniform distribution of the polymer on the separator. After being immersed in the electrolyte, it can form a foam structure, which improves the wetting performance of the electrolyte and can further enhance the cycle performance of the secondary battery containing it.

[0084] In some embodiments of this application, the polymer layer is disposed on the negative electrode sheet, and the polymer layer is prepared by the following method:

[0085] S21. A slurry containing a polymer is rolled onto the negative electrode sheet to form a polymer layer.

[0086] In practice, taking PEO as an example, a PEO slurry containing lithium salt is roller-coated onto a carrier such as aluminum foil to form a self-supporting film. Then, the lithium metal anode roll and the PEO coating are bonded together through a roll-pressing composite process to form an anode sheet containing a polymer layer.

[0087] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active metal ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0088] In some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the aforementioned irreversible positive electrode additive.

[0089] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0090] In some embodiments of this application, 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0091] In some embodiments of this application, when the battery is a lithium secondary battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries.

[0092] 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 positive electrode active materials for batteries 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 may 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 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3O2 (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) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure may 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. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0093] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0094] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0095] In some embodiments of this application, when the battery is a sodium secondary battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries.

[0096] As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue sodium compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0097] In some embodiments of this application, the transition metal in the sodium transition metal oxide can be at least one selected from Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu. The chemical formula of the sodium transition metal oxide can satisfy Na y MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < y ≤ 1.

[0098] In some embodiments of this application, the polyanionic compound may be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si; n represents (YO4). n- The price state.

[0099] In some embodiments of this application, the polyanionic compound may also be a sodium ion, transition metal ion, or tetrahedral (YO4) compound. n- A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n- The valence state of halogens can include at least one of F, Cl, and Br.

[0100] In some embodiments of this application, the polyanionic compound may also be a tetrahedral compound containing sodium ions (YO4). n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. M may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may include at least one of P, S and Si, and n represents (YO4). n- The valence state, Z represents transition metal, m represents (ZO) y ) m+ The valence state of halogens can include at least one of F, Cl, and Br.

[0101] As an example, polyanionic compounds can satisfy the chemical formulas NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F3-2y At least one of (0≤y≤1).

[0102] In some embodiments of this application, Prussian blue compounds may be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0103] As an example, Prussian blue compounds can satisfy the chemical formula Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0104] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Na content changes when the positive electrode active material is applied to the battery system.

[0105] In the examples of positive electrode active materials for sodium-ion batteries in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0106] In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0107] In some embodiments of this application, the positive electrode active material 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.

[0108] In some embodiments of this application, the positive electrode active material layer 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.

[0109] In some embodiments of this application, 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, positive irreversible additive 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 after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0110] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0111] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0112] In some embodiments of this application, 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In some embodiments of this application, the negative electrode active material may be any 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 titanates. 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. When the battery is a lithium-ion battery, the titanate includes lithium titanate; when the battery is a sodium-ion battery, the titanate includes sodium titanate. 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.

[0114] In some embodiments of this application, the negative electrode active material 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).

[0115] In some embodiments of this application, the negative electrode active material layer 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.

[0116] In some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0117] In some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0118] In some embodiments of this application, the battery includes a lithium metal negative electrode sheet, which includes a negative electrode current collector and an active material layer disposed on at least a portion of the surface of the negative electrode current collector. The active material layer includes at least one of elemental lithium metal or a lithium metal alloy. By utilizing the low operating voltage and high specific capacity of lithium, the energy density of the battery is significantly improved.

[0119] In some embodiments of this application, the lithium metal alloy has the chemical formula LiR, where R includes at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, or silicon. The active material layer uses the aforementioned lithium metal alloy. The lithium alloy has a higher potential than lithium, exhibits excellent electrolyte stability, and has low side reactions, thus improving the stability of the lithium metal anode, reducing the probability of lithium dendrite formation on the lithium metal anode electrode, and improving the cycle life of the secondary battery.

[0120] In some embodiments of this application, when a lithium metal negative electrode sheet is used, the preparation method is as follows: lithium foil or lithium metal alloy is coated onto the current collector by single-sided rolling, and then cut into negative electrode sheets.

[0121] This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0122] In some embodiments of this application, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0123] In some embodiments of this application, when the battery is a lithium-ion battery, the electrolyte salt may include 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, or lithium tetrafluorooxalate phosphate.

[0124] In some embodiments of this application, when the battery is a sodium-ion battery, the electrolyte salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0125] In some embodiments of this application, the solvent may include at least one selected from 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, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone. Alternatively, an ether solvent may also be used.

[0126] In some embodiments of this application, 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.

[0127] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0128] In some embodiments of this application, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0129] The secondary batteries of this application include single-cell battery forms, battery module forms, and battery pack forms. The following description, with appropriate reference to the accompanying drawings, will illustrate the single-cell battery, battery module, and battery pack of this application.

[0130] In some embodiments of this application, the positive electrode, the negative electrode, and the separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0131] In some embodiments of this application, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0132] In some embodiments of this application, the outer packaging of the battery cell 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-type soft pack. The material of the soft pack can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] It is understood that the secondary battery mentioned above in this application is a single battery cell.

[0134] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 Here is a square-structured battery cell 1 as an example.

[0135] In some embodiments of this application, reference is made to Figure 3 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in a single battery cell 1 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0136] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0137] Figure 4 This is battery module 2 as an example. (See reference...) Figure 4 In battery module 2, multiple battery cells 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 1 can be fixed in place using fasteners.

[0138] Optionally, the battery module 2 may also include a housing with a receiving space in which multiple battery cells 1 are received.

[0139] In some embodiments of this application, the battery modules described above can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0140] Figure 5 and Figure 6 This is battery pack 3 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper box 31 and a lower box 32, with the upper box 31 covering the lower box 32 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0141] In addition, this application also provides an electrical device, which includes the secondary battery provided in the first aspect of this application. The battery cell, 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.

[0142] As the electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0143] Figure 7 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.

[0144] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0145] 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.

[0146] Example 1

[0147] 1. Preparation of positive electrode sheet

[0148] The positive electrode active material (NCM) 811 The conductive agent acetylene black and the binder PVDF (polyvinylidene fluoride) were mixed at a mass ratio of 98:1:1. NMP solvent was added and stirred until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. It was then cut into 40mm × 50mm rectangles to serve as the positive electrode sheet, with a positive electrode surface capacity of 3.5 mAh / cm². 2 .

[0149] 2. Preparation of negative electrode sheet

[0150] A 50μm thick lithium foil is rolled onto a 12μm thick copper foil and then cut into 41mm×51mm rectangles to serve as negative electrode sheets.

[0151] 3. Preparation of electrolyte

[0152] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), take 1.51 g of lithium hexafluorophosphate and add it to a mixed solvent of 3 g EC (ethylene carbonate) and 7 g EMC (ethyl methyl carbonate). Stir thoroughly to form a colorless and transparent electrolyte with a lithium salt concentration of 1 mol / L.

[0153] 4. Separating membrane

[0154] A polymer layer containing PEO is sprayed onto one side of a base membrane (PE membrane, PE membrane thickness 12 μm, PVDF coating near the negative electrode side, PVDF coating thickness 1.5 μm, ceramic alumina coating near the positive electrode side, ceramic alumina coating thickness 1.5 μm). The polymer layer faces the negative electrode, resulting in a separator with a polymer layer coated on one side, and the polymer layer thickness is 1 μm.

[0155] 5. Preparation of secondary batteries

[0156] The positive electrode, separator, and negative electrode are stacked layer by layer, with 11 layers of negative electrode and 10 layers of positive electrode. An extra layer of separator is wrapped around the outermost layer of the stack. This process creates a dry cell, which is then encased in an aluminum-plastic film bag to form a stacked dry cell. (The side coated with PEO faces the lithium metal negative electrode.) 0.3g of the previously prepared electrolyte is injected, at a rate of 1.5g / Ah. The aluminum-plastic film bag is then vacuum-sealed using heat pressing and left to stand at room temperature for at least 6 hours to obtain the battery. The prepared stacked battery has a rated capacity of 1.40Ah.

[0157] The preparation methods of the batteries in Examples 2-13 and Comparative Examples 1-3 are the same as those in Example 1, except that the battery preparation process is different, as shown in Table 1.

[0158] Table 1

[0159]

[0160] The negative electrode sheet was obtained from the batteries of Example 3 and Comparative Example 1 after the first week of full charging. The negative electrode sheet was cut open, and the ion-polished cross-sectional morphology (CP) was determined by scanning electron microscopy. Figure 8 and Figure 9 Both figures show the lower current collector and the lithium layer above it. Figure 8 As can be seen, after the polymer layer is set on the separator in Example 3, the lithium layer deposited on the current collector is relatively dense and thin (average thickness is 38 μm). This is because the polymer layer has a certain elasticity after swelling, which provides a certain elastic modulus for lithium metal cycling and can also play a role in binding lithium, making the deposition of negative electrode lithium more dense. In contrast, the separator in Comparative Example 1 does not have a polymer layer, and the lithium layer deposited on the current collector is relatively loose and thick (average thickness is 55 μm). It can be seen that the setting of the polymer layer can improve the deposition morphology of lithium metal, making the deposition of negative electrode lithium more dense.

[0161] The performance of the batteries in Examples 1-13 and Comparative Examples 1-3 was characterized, and the characterization results are shown in Table 3.

[0162] 1. Whether the polymer layer swelling is complete:

[0163] The dry cell cells of the above embodiments and comparative examples were immersed in electrolyte for 48 hours, and then disassembled to observe whether the polymer layer remained intact after swelling.

[0164] 2. Battery capacity retention rate:

[0165] The lithium metal battery with the above structure was subjected to a cyclic test under a clamping force of 0.5 MPa. The specific steps are as follows:

[0166] The lithium-ion battery is charged at a constant current of 0.5C to voltage U1, and then charged at a constant voltage of U1 to 0.05C, and left to stand for 10 minutes.

[0167] Discharge at a constant current of 0.5C to voltage U2, and let stand for 10 minutes;

[0168] After repeating the above steps 200 times, the volume retention rate was measured. The results are shown in Table 2.

[0169] Table 2

[0170]

[0171] As shown in Table 2, in Examples 1-13 of this application, a polymer layer is disposed between the separator and the battery electrode. This polymer layer can swell into a foam structure in the electrolyte, absorbing the electrolyte and improving its wetting properties, thereby enhancing the cycle performance of the secondary battery containing it. Comparative Examples 1-3 are not within the scope of this application's embodiments, and their battery cycle performance is significantly reduced. Therefore, using the polymer layer of this application can improve the electrolyte wetting properties and enhance the battery cycle performance.

[0172] 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 secondary battery includes an electrode and a separator. At least a portion of the surface of the separator that contacts the electrode is provided with a polymer layer, which can swell in the electrolyte.

2. The secondary battery according to claim 1, characterized in that, The polymer layer is disposed on the isolation membrane.

3. The secondary battery according to claim 1 or 2, characterized in that, The polymer layer comprises a polymer, which includes at least one of polyethylene oxide, polyacrylic acid, or styrene-butadiene rubber.

4. The secondary battery according to claim 3, characterized in that, The weight-average molecular weight of the polymer is 2000-20000.

5. The secondary battery according to claim 3 or 4, characterized in that, Based on the total mass of the polymer layer, the mass percentage of the polymer is 90%-100%.

6. The secondary battery according to any one of claims 3-5, characterized in that, Based on the total mass of the polymer layer, the mass percentage of the polymer is 95%-99%.

7. The secondary battery according to any one of claims 1-6, characterized in that, The polymer layer also includes lithium salt.

8. The secondary battery according to claim 7, characterized in that, At least one of the following conditions must be met: Based on the total mass of the polymer layer, the mass percentage of the lithium salt is less than or equal to 10%; The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate.

9. The secondary battery according to claim 7 or 8, characterized in that, At least one of the following conditions must be met: Based on the total mass of the polymer layer, the mass percentage of the lithium salt is 1%-5%; The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium difluorooxalateborate, or lithium hexafluorophosphate.

10. The secondary battery according to any one of claims 1-9, characterized in that, The thickness of the polymer layer is 2μm-10.5μm.

11. The secondary battery according to any one of claims 1-10, characterized in that, The secondary battery also includes an electrolyte, and the electrolyte injection volume of the secondary battery is 1.5g / Ah-2.25g / Ah.

12. The secondary battery according to any one of claims 1-11, characterized in that, The secondary battery further includes an electrolyte, which comprises a solvent, including 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, or diethyl sulfone.

13. The secondary battery according to any one of claims 1-12, characterized in that, The electrode includes a negative electrode, which includes a negative active material layer, and the negative active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, titanate, or lithium metal.

14. The secondary battery according to claim 13, characterized in that, At least one of the following conditions must be met: The negative electrode active material layer includes lithium metal; At least a portion of the surface of the separator that is in contact with the negative electrode sheet is provided with a polymer layer.

15. The secondary battery according to any one of claims 1-14, characterized in that, The electrode includes a negative electrode, and the polymer layer is disposed on the negative electrode.

16. A method for preparing a secondary battery, characterized in that, include: The electrode and the separator are assembled to obtain a secondary battery, wherein at least a portion of the surface of the separator that contacts the electrode is provided with a polymer layer, and the polymer layer can swell in the electrolyte.

17. The method according to claim 16, characterized in that, The polymer layer is disposed on the isolation membrane, and the polymer layer is prepared by the following method: A polymer and a lithium salt are dissolved in a solvent to obtain a mixed solution, and the mixed solution is coated onto at least one side of the separator to obtain a polymer layer.

18. The method according to claim 17, characterized in that, At least one of the following conditions must be met: The solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, acetone or toluene; Based on the total mass of the mixed solution, the sum of the masses of the polymer and the lithium salt accounts for 30%-60%; The coating includes spraying.

19. The secondary battery according to any one of claims 16-18, characterized in that, The electrode includes a negative electrode, and the polymer layer is disposed on the negative electrode. The polymer layer is prepared by the following method: A slurry containing a high molecular weight polymer is rolled onto the negative electrode sheet to form a polymer layer.

20. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1-15, or the secondary battery prepared by the method according to any one of claims 16-19.

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