Secondary battery, preparation method thereof and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a secondary battery, a preparation method thereof and an electric device. The preparation method of the secondary battery comprises the steps that a positive pole piece and electrolyte are provided, the positive pole piece comprises a positive current collector and a positive active layer arranged on at least one side of the positive current collector, and the positive active layer comprises a positive active material; the positive electrode active layer further comprises a first reactive monomer, and at least one of the positive electrode active layer and the electrolyte comprises a second reactive monomer; one of the first reaction monomer and the second reaction monomer comprises at least two epoxy groups, and the other one comprises a functional group capable of being subjected to polymerization reaction with the epoxy groups. According to the scheme, the problems of dissolution and migration of transition metal in the positive electrode active material can be well solved.

Description

Technical Field

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

[0002] The positive electrode materials for secondary batteries include ternary materials, lithium manganese oxide, lithium cobalt oxide, and lithium manganese iron phosphate, all of which generally contain transition metals. During the cycling process of a secondary battery, these transition metals can easily leach from the positive electrode material, dissolve into the electrolyte, and migrate to the negative electrode side via the electrolyte, causing deposition and leading to performance degradation of the secondary battery. Summary of the Invention

[0003] This application is made in view of the above-mentioned technical problems, and its purpose is to address the problem of dissolution and migration of transition metals in positive electrode active materials.

[0004] To achieve the above objectives, this application provides a secondary battery, a method for preparing the same, and an electrical device thereof.

[0005] The first aspect of this application provides a method for preparing a secondary battery, comprising:

[0006] A positive electrode sheet and an electrolyte are provided. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer contains a positive active material.

[0007] The positive electrode active layer also includes a first reactive monomer, and at least one of the positive electrode active layer and the electrolyte includes a second reactive monomer;

[0008] One of the first reactant monomer and the second reactant monomer contains at least two epoxy groups, and the other contains a functional group capable of undergoing polymerization with the epoxy groups.

[0009] In this embodiment of the application, by adding a first reactive monomer to the positive electrode active layer and adding a second reactive monomer to at least one of the positive electrode active layer and the electrolyte, the first reactive monomer can undergo a polymerization reaction with the second reactive monomer to generate epoxy resin after the positive electrode sheet is made or the positive electrode sheet is assembled with the electrolyte and other components into a secondary battery.

[0010] Specifically, when the positive electrode active layer contains both a first reactive monomer and a second reactive monomer, since both are dispersed within the positive electrode active layer, there is a high probability that the first and second reactive monomers can come into contact with each other. These two reactive monomers can then undergo an in-situ polymerization reaction to generate epoxy resin. The generated epoxy resin, like the first and second reactive monomers, will also be dispersed within the positive electrode active layer and can come into contact with the positive electrode active material also dispersed therein.

[0011] When the positive electrode active layer contains a first reactive monomer and the electrolyte contains a second reactive monomer, after assembling the positive electrode sheet, electrolyte, and other components into a secondary battery, the positive electrode active layer is immersed in the electrolyte. The second reactive monomer can then diffuse with the electrolyte to the surface and interior of the positive electrode active layer, thereby contacting the first reactive monomer dispersed in the positive electrode active layer and undergoing an in-situ polymerization reaction within the positive electrode active layer to generate epoxy resin. Similarly, the generated epoxy resin, like the first reactive monomer, will be dispersed in the positive electrode active layer and can contact the positive electrode active material also dispersed therein.

[0012] When the positive electrode active layer contains both a first reactive monomer and a second reactive monomer, and the electrolyte contains the second reactive monomer, the reaction process of the two reactive monomers can be combined with the above two situations.

[0013] Positive electrode active materials typically contain transition metals. The epoxy resin formed by the first and second reactants can contact the positive electrode active material, thus improving the dissolution and migration of these transition metals. The underlying principles may include:

[0014] 1) Some epoxy resin may be distributed on the surface of the positive electrode active material. This epoxy resin can block the contact between the positive electrode active material and the electrolyte, thereby preventing substances such as HF in the electrolyte from attacking the positive electrode active material and mitigating the dissolution of transition metals in the positive electrode active material; 2) If Figure 1 As shown in Figure (b), epoxy resins typically contain abundant hydroxyl groups with strong coordination effects. The hydroxyl groups contained in the epoxy resin distributed on the surface of the positive electrode active material can form chemical bonds with the transition metals of the positive electrode active material, thereby anchoring the transition metals on the surface or in the bulk phase of the positive electrode active material and preventing the transition metals from dissolving out of the positive electrode active material; 3) The hydroxyl groups in the epoxy resin can also coordinate with the dissolved transition metal ions, preventing them from migrating to the negative electrode side, so that the dissolved transition metal ions will not migrate to the negative electrode side for deposition.

[0015] In some embodiments, the molar ratio of epoxy groups to functional groups capable of polymerizing with epoxy groups is (1-2):1, optionally (1.5-2):1. Under suitable ratios, the first and second reactive monomers can be fully polymerized to form an epoxy resin.

[0016] In some embodiments, the first reactive monomer contains at least two epoxy groups, and the second reactive monomer contains at least two functional groups capable of polymerizing with the epoxy groups.

[0017] The first and second reactant monomers can undergo polymerization reactions through these functional groups to form epoxy resin in situ in the positive electrode active layer, thereby improving the dissolution and migration of transition metals in the positive electrode active material.

[0018] In some embodiments, the first reactive monomer includes one or more of glycidyl ether epoxy resin monomers, biphenyl epoxy resin monomers, fluorinated epoxy resin monomers, and silicone epoxy resin monomers. An exemplary glycidyl ether epoxy resin monomer includes bisphenol A diglycidyl ether. resorcinol diglycidyl ether One or more of the following; exemplary biphenyl epoxy resin monomers include Exemplary fluorinated epoxy resin monomers include The epoxy resins formed by the polymerization of these monomers can all improve the dissolution and migration of transition metals in positive electrode active materials.

[0019] In some embodiments, the functional groups capable of polymerizing with epoxy groups include one or more of amino, hydroxyl, and carboxyl groups. These functional groups can polymerize with epoxy groups to form epoxy resin in situ in the positive electrode active layer, and provide hydroxyl, carboxyl, amino, and other functional groups to the epoxy resin. The formed epoxy resin not only blocks the contact between the electrolyte and the positive electrode active material, but these functional groups of the epoxy resin can also be directionally adsorbed on the transition metal sites of the positive electrode active material, anchoring the transition metal in the positive electrode active material and preventing it from detaching and dissolving from the crystal structure. At the same time, it can also coordinate with already dissolved transition metal ions, preventing them from migrating to the negative electrode side.

[0020] In some embodiments, the second reactant includes NH2-R 1 -NH2,R 1 This includes alkylene groups having 2 to 10 carbon atoms. An exemplary second reactant includes hexamethylenediamine. One or more of ethylenediamines. This type of second reactive monomer can cause ring-opening of epoxy groups and polymerization to form an epoxy resin containing a -CHOH-CH2-NH- structure. This epoxy resin contains both hydroxyl and amino groups, which can be directionally adsorbed onto the transition metal sites of the positive electrode active material, anchoring the transition metal in the positive electrode active material and preventing it from detaching and dissolving from the crystal lattice structure. At the same time, it can also coordinate with already dissolved transition metal ions to prevent them from migrating to the negative electrode side.

[0021] In some embodiments, the mass content of the first reactive monomer in the positive electrode active layer is 0.008% to 0.5%, optionally 0.08% to 0.5%.

[0022] Based on this, when the electrolyte contains a second reactive monomer, the mass content of the second reactive monomer in the electrolyte is 0.01% to 3%, optionally 0.1% to 0.7%; or, when the positive electrode active layer contains a second reactive monomer, the mass content of the second reactive monomer in the positive electrode active layer is 0.001% to 0.08%.

[0023] Under appropriate mass content, the first and second reactant monomers can react effectively and polymerize in situ in the positive electrode active layer to form epoxy resin, thereby improving the dissolution and migration of transition metals in the positive electrode active material.

[0024] In other embodiments, the second reactive monomer comprises at least two epoxy groups, and the first reactive monomer comprises at least two functional groups capable of polymerizing with the epoxy groups. In this case, the mass content of the first reactive monomer in the positive electrode active layer is 0.001% to 0.08%. Meanwhile, if the electrolyte contains the second reactive monomer, the mass content of the second reactive monomer in the electrolyte is 0.07% to 4%.

[0025] When the second reactant monomer contains at least two epoxy groups and the first reactant monomer contains at least two functional groups that can polymerize with epoxy groups, the first reactant monomer and the second reactant monomer can still react in situ in the positive electrode active layer to generate epoxy resin, thereby improving the dissolution and migration problems of transition metals in the positive electrode active layer.

[0026] A second aspect of this application provides a secondary battery, comprising:

[0027] The positive electrode sheet and the electrolyte, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer comprising a positive active material and having epoxy resin dispersed therein.

[0028] In the secondary battery of this application embodiment, epoxy resin is dispersed in the positive electrode active layer. The epoxy resin can improve the dissolution and migration of transition metals in the positive electrode active material. This can mitigate the decomposition of the SEI film on the negative electrode caused by transition metal deposition, reduce lithium loss due to SEI film decomposition, and enable the secondary battery to exhibit good cycle performance and storage performance. Simultaneously, it can prevent the formation of dendrites from transition metal deposition on the negative electrode, which could pierce the separator and cause micro-short circuits, thus improving the safety of the secondary battery.

[0029] In some embodiments, the mass content of epoxy resin in the positive electrode active layer is 0.01% to 0.6%, optionally 0.1% to 0.5%. In the secondary battery of this application embodiment, the epoxy resin has a suitable mass content in the positive electrode active layer. On the one hand, the epoxy resin can be effectively used to improve the dissolution and migration of transition metals in the positive electrode active material. On the other hand, the epoxy resin will not occupy too much of the proportion in the positive electrode active layer, so that a sufficiently high proportion of the positive electrode active material can be reserved, thereby not having a significant adverse effect on the capacity of the positive electrode sheet.

[0030] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0031] The aforementioned secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The secondary battery in this embodiment exhibits excellent cycle performance and storage performance; therefore, applying this secondary battery to an electrical device can significantly improve the user experience of the device. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram (a) showing the transition metal of the positive electrode active material dissolved in the electrolyte in one embodiment of this application, and a schematic diagram (b) showing the adsorption and anchoring of the transition metal in the positive electrode active material by the hydroxyl groups in the epoxy resin.

[0034] Figure 2 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0035] Figure 3 for Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown.

[0036] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0037] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0038] Figure 6 for Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0039] Figure 7This 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.

[0040] Figure label:

[0041] 01-Housing, 02-Cover plate, 03-Electrode assembly, 04-Battery cell, 05-Battery module, 06-Upper housing, 07-Lower housing. Detailed Implementation

[0042] The following detailed description of the implementation of the detection system and detection method of this application is provided with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] 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.

[0047] 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.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] Commonly used positive electrode active materials for secondary batteries include ternary materials, lithium manganese oxide, lithium cobalt oxide, and lithium manganese iron phosphate. During cycling, some transition metals in the positive electrode active material dissolve in the electrolyte and migrate towards the negative electrode side, as well as deposit on the negative electrode side, leading to deterioration in cycle performance. For example... Figure 1 As shown in Figure (a), taking a ternary material as the positive electrode active material as an example, the Mn in the ternary material... 3+ Due to the Gantyler effect, a disproportionation reaction occurs to generate soluble Mn. 2+ Meanwhile, trace amounts of H2O in the electrolyte readily react with LiPF6 in the electrolyte to form HF: LiPF6 + H2O → LiF + 2HF + POF3. HF attacks the positive electrode, causing some Mn to be released. 2+ Dissolved in the electrolyte. Dissolved Mn 2+ Migrating and depositing on the negative electrode side, these Mn molecules catalyze the decomposition of the SEI film on the negative electrode surface, causing the SEI film to be continuously decomposed. 2+ Dendrites may form after deposition, which can puncture the separator and cause micro-short circuits. Macroscopically, this manifests as a decrease in the cycle performance and storage performance of the secondary battery.

[0050] To address the aforementioned issues, some studies have attempted to form a coating layer on the surface of the positive electrode to resist the attack of HF on the positive electrode and inhibit the dissolution of transition metals. The selection of the coating material is crucial to this technical solution. The coating material itself must possess excellent stability and not react with substances in the positive electrode or the electrolyte. Selecting a suitable coating material from those already maturely applied in batteries would be a relatively quick approach.

[0051] Epoxy resin is a widely used material in solid electrolytes. It can form a stable network structure in solid electrolytes, which helps to improve the ionic conductivity of the electrolyte. At the same time, epoxy resin itself has good stability and will not react with substances in the positive electrode or the electrolyte. It can be explored to use it in the positive electrode to form a coating layer in order to improve the dissolution and migration of transition metals in the positive electrode.

[0052] However, in practice, due to the insolubility of epoxy resin, it is difficult to uniformly disperse it in the cathode slurry, thus hindering the formation of a uniform coating layer. Furthermore, the bonding force between the epoxy resin-containing active layer and the cathode current collector is weak, making it prone to detachment. Therefore, the technical approach of using epoxy resin to form a coating layer in the cathode to improve the dissolution, migration, and deposition of transition metals in the cathode has remained difficult to achieve.

[0053] Based on this, this application proposes a method for preparing a secondary battery. By adding two reactants used to form epoxy resin to the electrolyte and the positive electrode respectively, or by dispersing the two reactants in the positive electrode, the two reactants can react in situ in the positive electrode to generate epoxy resin. The epoxy resin is uniformly dispersed in the positive electrode, thereby solving the problem of dissolution and migration of transition metals in the positive electrode active material. The secondary battery obtained using this method exhibits good cycle performance and storage performance.

[0054] [Rechargeable Battery]

[0055] The method for preparing the secondary battery in this application embodiment includes:

[0056] A positive electrode sheet and an electrolyte are provided. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer contains a positive active material.

[0057] The positive electrode active layer also includes a first reactive monomer, and at least one of the positive electrode active layer and the electrolyte includes a second reactive monomer;

[0058] One of the first reactant monomer and the second reactant monomer contains at least two epoxy groups, and the other contains a functional group capable of undergoing polymerization with the epoxy groups.

[0059] In the embodiments of this application, the positive electrode active layer further includes a first reactive monomer, and at least one of the positive electrode active layer and the electrolyte includes a second reactive monomer, including any one of the following (1) to (3): (1) the positive electrode active layer includes a first reactive monomer, and the electrolyte includes a second reactive monomer; (2) the positive electrode active layer includes a first reactive monomer and a second reactive monomer, and the electrolyte includes a second reactive monomer; (3) the positive electrode active layer includes a first reactive monomer and a second reactive monomer. The positive electrode active layer includes a positive electrode active material and a first reactive monomer (and may also include a second reactive monomer). Typically, these positive electrode active materials and the first reactive monomer (or the second reactive monomer) are uniformly dispersed in the positive electrode active layer. It is understood that during the preparation of the secondary battery, and in the newly made secondary battery, HF is usually not present. Even if HF is generated during subsequent secondary battery testing and operation, the amount of HF is very small, so that HF ​​will not usually react with the first reactive monomer or the second reactive monomer, or the effect of HF on the first monomer or the second reactive monomer can be ignored.

[0060] If one of the first and second reactant monomers contains at least two epoxy groups, and the other contains a functional group capable of polymerizing with the epoxy groups, then the first reactant monomer can polymerize with the second reactant monomer to form an epoxy resin. During the preparation of the secondary battery, gas chromatography-mass spectrometry (GC-MS) or infrared spectroscopy can be used to test the positive electrode active layer (or the raw material of the positive electrode active layer) and the electrolyte (or the raw material of the electrolyte) to identify the functional groups. Based on the types of functional groups, it can be confirmed whether the positive electrode active layer and the electrolyte contain the first and second reactant monomers. After the secondary battery is prepared and after it is in operation, the first and second reactant monomers have reacted to form an epoxy resin, and the epoxy resin is dispersed in the positive electrode active layer. GC-MS or infrared spectroscopy can be used to identify whether the epoxy resin is dispersed in the positive electrode active layer.

[0061] In this embodiment of the application, by adding a first reactive monomer to the positive electrode active layer and adding a second reactive monomer to at least one of the positive electrode active layer and the electrolyte, the first reactive monomer can undergo a polymerization reaction with the second reactive monomer to generate epoxy resin after the positive electrode sheet is made or the positive electrode sheet is assembled with the electrolyte and other components into a secondary battery.

[0062] Specifically, when the positive electrode active layer contains both a first reactive monomer and a second reactive monomer, since both are dispersed within the positive electrode active layer, there is a high probability that the first and second reactive monomers can come into contact with each other. These two reactive monomers can then undergo an in-situ polymerization reaction to generate epoxy resin. The generated epoxy resin, like the first and second reactive monomers, will also be dispersed within the positive electrode active layer and can come into contact with the positive electrode active material also dispersed therein.

[0063] When the positive electrode active layer contains a first reactive monomer and the electrolyte contains a second reactive monomer, after assembling the positive electrode sheet, electrolyte, and other components into a secondary battery, the positive electrode active layer is immersed in the electrolyte. The second reactive monomer can then diffuse with the electrolyte to the surface and interior of the positive electrode active layer, thereby contacting the first reactive monomer dispersed in the positive electrode active layer and undergoing an in-situ polymerization reaction within the positive electrode active layer to generate epoxy resin. Similarly, the generated epoxy resin, like the first reactive monomer, will be dispersed in the positive electrode active layer and can contact the positive electrode active material also dispersed therein.

[0064] When the positive electrode active layer contains both a first reactive monomer and a second reactive monomer, and the electrolyte contains the second reactive monomer, the reaction process of the two reactive monomers can be combined with the above two situations.

[0065] Positive electrode active materials typically contain transition metals. The epoxy resin formed by the first and second reactants can contact the positive electrode active material, thus improving the dissolution and migration of these transition metals. The underlying principles may include:

[0066] 1) Some epoxy resin may be distributed on the surface of the positive electrode active material particles. This epoxy resin can block the contact between the positive electrode active material and the electrolyte, thereby preventing substances such as HF in the electrolyte from attacking the positive electrode active material and mitigating the dissolution of transition metals in the positive electrode active material; 2) If Figure 1 As shown in Figure (b), epoxy resins typically contain abundant hydroxyl groups with strong coordination effects. The hydroxyl groups contained in the epoxy resin distributed on the surface of the positive electrode active material can form chemical bonds with the transition metals of the positive electrode active material, thereby anchoring the transition metals on the surface or in the bulk phase of the positive electrode active material and preventing the transition metals from dissolving out of the positive electrode active material; 3) The hydroxyl groups in the epoxy resin can also coordinate with the dissolved transition metal ions, preventing them from migrating to the negative electrode side, so that the dissolved transition metal ions will not migrate to the negative electrode side for deposition.

[0067] In some embodiments, the molar ratio of epoxy groups to functional groups capable of polymerizing with the epoxy groups is (1-2):1, optionally (1.5-2):1, for example, any one or a range between any two of 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, and 2:1. At suitable ratios, the first and second reactants can be fully polymerized to form an epoxy resin.

[0068] In some embodiments, the first reactive monomer contains at least two epoxy groups, and the second reactive monomer contains at least two functional groups capable of polymerizing with the epoxy groups.

[0069] The first and second reactant monomers can undergo polymerization reactions through these functional groups to form epoxy resin in situ in the positive electrode active layer, thereby improving the dissolution and migration of transition metals in the positive electrode active material.

[0070] In some embodiments, the first reactive monomer includes one or more of glycidyl ether epoxy resin monomers, biphenyl epoxy resin monomers, fluorinated epoxy resin monomers, and silicone epoxy resin monomers. An exemplary glycidyl ether epoxy resin monomer includes bisphenol A diglycidyl ether. resorcinol diglycidyl ether One or more of the following; exemplary biphenyl epoxy resin monomers include Exemplary fluorinated epoxy resin monomers include The epoxy resins formed by the polymerization of these monomers can all improve the dissolution and migration of transition metals in positive electrode active materials.

[0071] In some embodiments, the functional groups capable of polymerizing with epoxy groups include one or more of amino, hydroxyl, and carboxyl groups, optionally including amino groups. These functional groups can polymerize with epoxy groups to form epoxy resin in situ in the positive electrode active layer, and provide hydroxyl, carboxyl, amino, and other functional groups to the epoxy resin. For example, in the case of including an amino group, the reaction between the amino group and the epoxy group can be referred to the following reaction formulas (1) and (2).

[0072] Reaction formula (1):

[0073] Where R is a structural unit linked to an amino group;

[0074] Reaction (2):

[0075]

[0076] This reaction can generate epoxy resin containing the -CHOH-CH2-NH- structure. The formed epoxy resin can not only block the contact between the electrolyte and the positive electrode active material, but these functional groups of the epoxy resin can also be directionally adsorbed on the transition metal sites of the positive electrode active material, anchoring the transition metal in the positive electrode active material and preventing it from detaching and dissolving from the crystal structure. At the same time, it can also coordinate with the already dissolved transition metal ions, preventing them from migrating to the negative electrode side.

[0077] In some embodiments, the second reactant includes NH2-R 1 -NH2,R 1 Including alkylene groups with 2 to 10 carbon atoms, i.e., R 1 It can include -C n H 2n - where n is 2 to 10, for example, n can be any one of 2, 3, 4, 5, 6, 7, 8, 9, and 10. An exemplary second reactant monomer includes hexamethylenediamine. One or more of ethylenediamines. This type of second reactive monomer can cause ring-opening of epoxy groups and polymerization to form an epoxy resin containing a -CHOH-CH2-NH- structure. This epoxy resin contains both hydroxyl and amino groups, which can be directionally adsorbed onto the transition metal sites of the positive electrode active material, anchoring the transition metal in the positive electrode active material and preventing it from detaching and dissolving from the crystal lattice structure. At the same time, it can also coordinate with already dissolved transition metal ions to prevent them from migrating to the negative electrode side.

[0078] In some embodiments, the mass content of the first reactive monomer in the positive electrode active layer is 0.008% to 0.5%, optionally 0.08% to 0.5%, and even more optionally 0.08% to 0.43%. For example, the mass content can be any one or a range between any two of 0.008%, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.43%, 0.45%, and 0.5%.

[0079] Based on this, when the electrolyte contains a second reactive monomer, the mass content of the second reactive monomer in the electrolyte is 0.01% to 3%, optionally 0.1% to 0.7%, further optionally 0.1% to 0.68%, and even more optionally 0.13% to 0.68%. For example, this mass content can be any one or any two of 0.01%, 0.05%, 0.1%, 0.13%, 0.15%, 0.2%, 0.4%, 0.6%, 0.68%, 0.7%, 1%, 1.5%, 2%, 2.5%, and 3%. When the positive electrode active layer contains a second reactive monomer, the mass content of the second reactive monomer in the positive electrode active layer is 0.001% to 0.08%, optionally 0.01% to 0.08%. For example, this mass content can be any one or any two of 0.001%, 0.005%, 0.01%, 0.05%, 0.07%, and 0.08%.

[0080] Under appropriate mass content, the first and second reactant monomers can react effectively and polymerize in situ in the positive electrode active layer to form epoxy resin, thereby improving the dissolution and migration of transition metals in the positive electrode active material.

[0081] In other embodiments, the second reactive monomer contains at least two epoxy groups, and the first reactive monomer contains at least two functional groups capable of polymerizing with the epoxy groups. Understandably, in this case, the types of functional groups contained in the first and second reactive monomers, the ratio between the functional groups, and the specific types of each functional group correspond to the first reactive monomer containing at least two epoxy groups and the second reactive monomer containing at least two functional groups capable of polymerizing with the epoxy groups described above.

[0082] In this case, the mass content of the first reactive monomer in the positive electrode active layer is 0.001% to 0.08%, optionally 0.01% to 0.08%, for example, the mass content can be any one or a range between any two of 0.001%, 0.005%, 0.01%, 0.05%, 0.07%, and 0.08%. Meanwhile, if the electrolyte contains a second reactive monomer, the mass content of the second reactive monomer in the electrolyte is 0.07% to 4%, for example, the mass content can be any one or a range between any two of 0.07%, 0.1%, 0.5%, 2%, 2.5%, 3%, 3.5%, 3.85%, and 4%.

[0083] When the second reactant monomer contains at least two epoxy groups and the first reactant monomer contains at least two functional groups that can polymerize with epoxy groups, the first reactant monomer and the second reactant monomer can still react in situ in the positive electrode active layer to generate epoxy resin, thereby improving the dissolution and migration problems of transition metals in the positive electrode active layer.

[0084] The secondary batteries prepared according to the above method include:

[0085] The positive electrode sheet and the electrolyte, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer comprising a positive active material and having epoxy resin dispersed therein.

[0086] Whether epoxy resin is dispersed in the positive electrode active layer can be identified by GC-MS or infrared spectroscopy.

[0087] In the secondary battery of this application embodiment, epoxy resin is dispersed in the positive electrode active layer. The epoxy resin can improve the dissolution and migration of transition metals in the positive electrode active material. This can mitigate the decomposition of the SEI film on the negative electrode caused by transition metal deposition, reduce lithium loss due to SEI film decomposition, and enable the secondary battery to exhibit good cycle performance and storage performance. Simultaneously, it can prevent the formation of dendrites from transition metal deposition on the negative electrode, which could pierce the separator and cause micro-short circuits, thus improving the safety of the secondary battery.

[0088] In some embodiments, the epoxy resin content in the positive electrode active layer is 0.01% to 0.6% by mass, optionally 0.1% to 0.5%. For example, the mass content can be any one or a range between any two of 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, and 0.6%.

[0089] Epoxy resin can be quantitatively analyzed using GC-MS or thermogravimetric analysis. In the secondary battery of this application embodiment, the epoxy resin has a suitable mass content in the positive electrode active layer. On the one hand, the epoxy resin can be effectively used to improve the dissolution and migration of transition metals in the positive electrode active material. On the other hand, the epoxy resin will not occupy too much of the positive electrode active layer, allowing for a sufficiently high proportion of the positive electrode active material, thereby not having a significant adverse impact on the capacity of the positive electrode sheet.

[0090] In some embodiments, at least a portion of the epoxy resin is coated on the surface of the positive electrode active layer. This partial epoxy resin coating can form a coating layer on the surface of the positive electrode active layer, better preventing contact between the positive electrode active material and the electrolyte, reducing the attack of substances such as HF in the electrolyte on the positive electrode active material, and improving the dissolution of transition metals. Simultaneously, the epoxy resin coating layer can fix transition metal ions already dissolved in the electrolyte to the surface of the positive electrode active layer, preventing the migration of transition metal ions to the negative electrode side.

[0091] In some embodiments, the positive electrode active material comprises a transition metal, including one or more of Mn, Ni, Co, and Fe. The strong coordinating groups in the epoxy resin can be directionally adsorbed onto the transition metal sites in the positive electrode active material, anchoring the transition metal within the material and preventing it from detaching and dissolving from the crystal structure. Furthermore, even if some of the transition metal dissolves, it will be fixed to the surface of the positive electrode active layer by the strong coordinating groups in the epoxy resin through coordination, and will not migrate to the negative electrode side.

[0092] In some embodiments, the positive electrode active material includes one or more of the following: ternary materials, lithium iron phosphate (such as LiFePO4, or LFP), lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate, lithium manganese iron phosphate, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, and lithium nickel manganese oxide. Exemplary ternary materials include LiNi... 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2. These positive electrode active materials can be used alone or in combination of two or more. The solutions in the embodiments of this application can effectively improve the dissolution and migration problems of transition metals in these positive electrode active materials.

[0093] In some embodiments, the mass content of the positive electrode active material in the positive electrode active layer may include, but is not limited to, 70% to 98%, or 80% to 98%, for example, any one of 70%, 75%, 80%, 85%, 90%, 92%, 94%, 96%, 98%, or any range between two.

[0094] Typically, a secondary battery consists of a negative electrode, a positive electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. 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. For more information on the positive electrode, other components of the electrolyte, and other structural elements of a secondary battery, such as the negative electrode and separator, please refer to the following content.

[0095] [Positive electrode plate]

[0096] The positive electrode sheet of this application embodiment includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. In addition to the positive active material mentioned above, the positive active layer also includes a conductive agent and a binder.

[0097] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0098] In some embodiments, the positive current collector includes one or more of a metal foil and a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate [such as a substrate of PP (polypropylene), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PS (polystyrene), PE (polyethylene), etc.].

[0099] In some embodiments, the binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0100] In some embodiments, the conductive agent in the positive electrode active layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] The mass content of binder and conductive agent in the positive electrode active layer can be independently, including but not limited to 0.5% to 10%, or 1% to 10%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between the two.

[0102] In some embodiments, the positive electrode active layer may optionally include additives, which may include additives that can improve certain properties of the positive electrode, such as additives with lithium replenishment effects, or additives that can improve the regulation of CEI composition.

[0103] In some implementations, the positive electrode sheet can be prepared in the following manner:

[0104] The components used to prepare the positive electrode sheet, such as the positive active material, the first reactive monomer (and in some cases, the second reactive monomer may also be added), the conductive agent, the binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is coated on at least one side of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained.

[0105] The embodiments of this application can use the commonly used process to prepare the positive electrode sheet without requiring additional modifications to the preparation process of the positive electrode sheet. The process is simple and the cost is low.

[0106] [Negative electrode plate]

[0107] The secondary battery of this application embodiment includes a negative electrode sheet, which includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a negative active material.

[0108] In some embodiments, the negative electrode active material includes one or more of graphite (artificial graphite, natural graphite), soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanium-based materials. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. Titanium-based materials may include lithium titanate. It is understood that this application is not limited to these materials, and other materials that can be used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0109] The mass content of the negative electrode active material in the negative electrode active layer can be 70% to 98%, or 90% to 98%, for example, any one of the values ​​of 70%, 75%, 80%, 85%, 90%, 92%, 94%, 96%, 98%, or any range between two.

[0110] In some embodiments, the negative electrode active layer further includes a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The mass content of the conductive agent in the negative electrode active layer includes 0.5% to 10%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range between any two.

[0111] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners, like CMC (carboxymethyl cellulose), CMC-Na (sodium carboxymethyl cellulose), etc.

[0112] The negative electrode sheet in the battery of this application also includes a negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] In some embodiments, the negative current collector includes one or more of a metal foil and a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate [such as a substrate of PP (polypropylene), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PS (polystyrene), PE (polyethylene), etc.].

[0114] In some implementations, the negative electrode sheet can be prepared in the following manner:

[0115] The components used to prepare the negative electrode sheet, such as negative electrode active material, binder, and conductive agent (and may also include any other components), are dispersed in a solvent (e.g., water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0116] In some embodiments, the negative electrode sheet is prepared using LOM (Layered Solid Manufacturing) coating technology. Specifically, multiple negative electrode slurries with different compositions can be prepared and sequentially coated onto at least one side of the negative electrode current collector. For example, multiple negative electrode slurries with different binder mass contents can be prepared and sequentially coated onto at least one side of the negative electrode current collector in order of decreasing binder mass content.

[0117] Electrolyte

[0118] The electrolyte acts as a conductor of ions between the positive and negative electrodes. In addition to potentially containing the second reactive monomer described above, the electrolyte in this embodiment may also include a solvent and an electrolyte salt dissolved in the solvent.

[0119] The solvent can be a non-aqueous organic solvent, such as one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB).

[0120] The electrolyte salt may include one or more of the following: LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0121] The concentration of the electrolyte salt in the electrolyte solution can range from 0.5 to 1.5 mol / L, for example, any one of 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, or 1.5 mol / L, or any range between two values. The mass content of the electrolyte salt in the electrolyte solution can range from 5% to 15%, for example, any one of 5%, 6%, 8%, 10%, 12%, 14%, or 15%, or any range between two values.

[0122] The electrolyte may also 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.

[0123] The electrolyte can be prepared as follows:

[0124] In a protective atmosphere (e.g., argon atmosphere), electrolyte salts and other components (such as second reaction monomers and additives) are added to a solvent and stirred until homogeneous to obtain an electrolyte solution.

[0125] The embodiments of this application can use commonly used processes to prepare electrolytes without requiring additional modifications to the electrolyte preparation process. The process is simple and low-cost.

[0126] [Isolation membrane]

[0127] In a secondary battery, the separator is usually stacked between the positive and negative electrodes to separate them, preventing electrons from passing freely and thus preventing short circuits. At the same time, it allows ions in the electrolyte to pass freely between the positive and negative electrodes.

[0128] In the secondary battery of this application embodiment, the type of separator can be any known porous structure separator with good chemical and mechanical stability.

[0129] The material of the separator membrane may include one or more of the following: glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF). The separator membrane can be a single-layer film or a multi-layer composite film; there are no particular restrictions. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different; there are no particular restrictions.

[0130] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0131] [Outer Packaging]

[0132] The secondary battery may include an outer packaging that can be used to encapsulate an electrode assembly containing a positive electrode, a negative electrode, a separator, and an electrolyte.

[0133] The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell; or it can be a soft package, such as a pouch. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] The outer packaging can be cylindrical, square, or any other shape. For example, Figure 2The battery cell, as an example, has a square outer packaging shape.

[0135] Reference Figure 3 The outer packaging may include a housing 01 and a cover plate 02. The housing 01 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 01 has an opening communicating with the receiving cavity, and the cover plate 02 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 03 via a winding or stacking process. One or more electrode assemblies 03 are encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 03.

[0136] [Battery cells, battery modules, battery packs]

[0137] The secondary battery in this application embodiment can be at least one of a battery cell, a battery module, or a battery pack. Depending on the packaging form, secondary batteries are classified as battery cells, battery modules, and battery packs. A battery cell is the most basic unit, including an electrode assembly and an electrolyte. The electrode assembly typically consists of a positive electrode, a negative electrode, and a separator. The positive and negative electrodes are alternately stacked, with a separator placed between them for isolation, to obtain the electrode assembly (also called a cell). Alternatively, the cell can be obtained by winding. The cell is placed in a casing, injected with electrolyte, and sealed to obtain a battery cell. The battery cell mainly relies on the movement of active metal ions in the electrolyte between the positive and negative electrodes to function.

[0138] In some battery packaging technologies, one or more individual battery cells can be integrated into a battery module, and then one or more battery modules can be assembled into a battery pack. In other battery packaging technologies, one or more individual battery cells can be directly installed in a housing to form a battery pack, eliminating the intermediate state of battery modules, thereby reducing the weight of the battery pack and increasing the energy density of the battery.

[0139] refer to Figure 4 This is an example battery module. In the battery module, multiple battery cells 04 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other arbitrary way. Furthermore, these multiple battery cells 04 can be secured using fasteners.

[0140] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells 04 are received.

[0141] refer to Figure 5 and Figure 6This is an example of a battery pack. The battery pack may include a battery compartment and multiple battery modules 05 disposed within the battery compartment. The battery compartment includes an upper body 06 and a lower body 07, with the upper body 06 covering the lower body 07 to form a closed space for accommodating the battery modules 05. The multiple battery modules 05 can be arranged in any manner within the battery compartment.

[0142] [Electrical appliances]

[0143] This application also provides an electrical device, which includes the aforementioned secondary battery.

[0144] The aforementioned secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The secondary battery in this embodiment exhibits excellent cycle performance and storage performance; therefore, applying this secondary battery to an electrical device can significantly improve the user experience of the device.

[0145] Electrical devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0146] As an electrical device, the battery can be selected as a single battery cell, battery module, or battery pack according to its usage requirements.

[0147] 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 device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0148] The embodiments of this application are described in detail below. 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 in accordance with 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.

[0149] Example 1

[0150] 1. Preparation of positive electrode sheet

[0151] Ternary material (NCM523), bisphenol A diglycidyl ether, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were dispersed in NMP at a mass ratio of 96.80:0.04:2:1.16 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[0152] 2. Preparation of negative electrode sheet

[0153] The negative electrode sheet was prepared using LOM (Layered Solid Manufacturing) coating technology. Specifically, graphite, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener were dispersed in deionized water at a mass ratio of 97.25:0.7:0.95:1.1 and stirred until homogeneous to obtain the upper slurry. Graphite, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener were dispersed in deionized water at a ratio of 96.35:0.4:2.15:1.1 and stirred until homogeneous to obtain the lower slurry. The lower and upper slurries were then uniformly coated sequentially onto the negative electrode current collector. After drying, cold pressing, and slitting, the negative electrode sheet was obtained.

[0154] 3. Separating membrane

[0155] Polypropylene film is used as the separator.

[0156] 4. Electrolyte

[0157] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. Then, 12.5% ​​(mass content) of LiPF6, 4.5% (mass content) of Mn(TFSI)2, and 0.07% (mass content) of hexamethylenediamine were added and stirred evenly to obtain the electrolyte.

[0158] 5. Battery assembly

[0159] The prepared and slit positive electrode sheet, negative electrode sheet, and separator are placed in the order of "separator-negative electrode sheet-separator-positive electrode sheet" and wound up. Then, the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses aluminum tabs and the negative electrode uses copper tabs. The battery cell with the electrode tabs welded is wrapped with an aluminum-plastic film. The battery cell is vacuum dried at 175℃ for 24 hours. Then, liquid injection, standing, formation, secondary liquid injection, and capacity testing are performed to obtain the prepared soft-pack battery cell.

[0160] Example 2

[0161] The difference between this embodiment and Embodiment 1 is that the mass ratio of the ternary material (NCM523), bisphenol A diglycidyl ether, conductive carbon black, and binder polyvinylidene fluoride (PVDF) is 96.75:0.09:2:1.16, and the mass content of hexamethylenediamine in the electrolyte is 0.14%.

[0162] Example 3

[0163] The difference between this embodiment and Embodiment 1 is that the mass ratio of the ternary material (NCM523), bisphenol A diglycidyl ether, conductive carbon black, and binder polyvinylidene fluoride (PVDF) is 96.41:0.43:2:1.16, and the mass content of hexamethylenediamine in the electrolyte is 0.68%.

[0164] Comparative Example 1

[0165] The difference between this comparative example and Example 1 is that bisphenol A diglycidyl ether was not added to the positive electrode slurry, and hexamethylenediamine was not added to the electrolyte.

[0166] Comparative Example 2

[0167] The difference between this comparative example and Example 3 is that the preparation method of the positive electrode sheet includes the following steps:

[0168] NCM523, conductive carbon black, and PVDF were dispersed in NMP at a mass ratio of 96.41:2:1.16 and stirred until homogeneous to obtain a positive electrode slurry. 0.5% (by mass in the positive electrode active layer) of epoxy resin (obtained by reacting bisphenol A diglycidyl ether with hexamethylenediamine) was added to the positive electrode slurry and stirred until homogeneous. The slurry was then uniformly coated onto the surface of aluminum foil and dried in a vacuum oven at 120℃ for 12 hours to obtain the positive electrode sheet.

[0169] Because epoxy resin has low solubility in NMP, it cannot dissolve in high-solids positive electrode slurry and is difficult to disperse evenly. After coating the positive electrode slurry onto aluminum foil, there are obvious particulate matter in the film layer, and the resulting positive electrode sheet is unqualified and cannot be used to make secondary batteries.

[0170] [Characteristics and Testing]

[0171] 1g of epoxy resin powder was added to 265mL of NMP and stirred until homogeneous. The mixture was then filtered through a microporous membrane, and the supernatant was subjected to gas chromatography-mass spectrometry (GC-MS) analysis. The positive electrode active layer from Example 3 was scraped off from the positive electrode sheet, and the resulting powder was added to NMP and stirred until homogeneous. The mixture was then filtered through a microporous membrane, and the supernatant was subjected to GC-MS analysis (injection port temperature was 250℃). The results showed that both supernatants contained the same fragment peaks [fragment peaks appeared at three main positions in the spectra of both supernatants: m / z 15 (methyl), 37–40 (benzene ring), and 97 (the main fragment peak of bisphenol A diglycidyl ether), and the fragment peak at m / z = 37–40 showed the same splitting pattern], indicating that epoxy resin was formed in situ in the positive electrode active layer of Example 3.

[0172] The positive electrode active layers of Examples 1, 2 and Comparative Example 1 were tested using the same method. The test results showed that the positive electrode active layers of Examples 1 and 2 also contained epoxy resin, while the positive electrode active layer of Comparative Example 1 did not contain epoxy resin.

[0173] Meanwhile, the powder scraped from the positive electrode active layer was subjected to thermogravimetric analysis. The powder weight loss data of Comparative Example 1 and Example 3 before 400°C are shown in the table below.

[0174] [Table 1]

[0175] Group Powder weight loss (%) before 400℃ Comparative Example 1 0.376 Example 3 0.833

[0176] The powder weight loss of Example 3 before 400°C increased by 0.457% compared to Comparative Example 1. This increase in weight loss can be attributed to the thermal decomposition of epoxy resin. Therefore, the mass content of epoxy resin in the positive electrode active layer of Example 3 can be considered to be about 0.457%, which is close to the theoretical mass content (0.5%) calculated based on the amount of bisphenol A diglycidyl ether and hexamethylenediamine used.

[0177] Following the same method, the mass content of epoxy resin in the positive electrode active layer in Examples 1 and 2 is shown in Table 2 below.

[0178] In addition, cycle performance and storage performance tests were conducted on the secondary batteries of each embodiment and comparative example, and the test results are shown in Table 2.

[0179] [Table 2]

[0180]

[0181] In Table 2, the mass content of epoxy resin refers to the mass content of epoxy resin in the positive electrode active layer. Furthermore, the mass content of epoxy resin in Table 2 is based on data obtained from thermogravimetric analysis, rounded to one decimal place.

[0182] Test results show that by adding bisphenol A diglycidyl ether to the positive electrode active layer and hexamethylenediamine to the electrolyte, epoxy resin can be successfully formed in situ in the positive electrode active layer. The formation of epoxy resin improves the cycle performance and storage performance of the secondary battery.

[0183] Example 4

[0184] 1. Preparation of positive electrode sheet

[0185] NCM523, bisphenol A diglycidyl ether, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were dispersed in NMP at a mass ratio of 89.57:0.43:5:5 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[0186] 2. Preparation of negative electrode sheet

[0187] Same as Example 1.

[0188] 3. Separating membrane

[0189] Same as Example 1.

[0190] 4. Electrolyte

[0191] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a volume ratio of 3 / 7. Then, 12.5% ​​(mass content) of LiPF6, 4.5% (mass content) of Mn(TFSI)2, and 2.83% (mass content) of hexamethylenediamine are added and stirred evenly to obtain the electrolyte.

[0192] 5. Battery assembly

[0193] The prepared and diced positive electrode, negative electrode, and separator are placed in the order of "separator-negative electrode-separator-positive electrode" and then placed in the casing and injected with electrolyte to form a coin cell with a diameter of about 0.7 cm. Then, it is left to stand and form.

[0194] Example 5

[0195] 1. Preparation of positive electrode sheet

[0196] NCM523, bisphenol A diglycidyl ether, hexamethylenediamine, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were dispersed in NMP at a mass ratio of 89.5:0.43:0.07:5:5 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[0197] 2. Preparation of negative electrode sheet

[0198] Same as Example 1.

[0199] 3. Separating membrane

[0200] Same as Example 1.

[0201] 4. Electrolyte

[0202] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a volume ratio of 3 / 7. Then, 12.5% ​​(mass content) of LiPF6 and 4.5% (mass content) of Mn(TFSI)2 are added and stirred evenly to obtain the electrolyte.

[0203] 5. Battery assembly

[0204] Same as Example 4.

[0205] The mass content, specific capacity, and coulombic efficiency of epoxy resin in the secondary batteries of Examples 4 and 5 were tested, and the results are shown in Table 3 below.

[0206] [Table 3]

[0207]

[0208] Note: Since Examples 4 and 5 use a button cell system, while Comparative Example 1 and Examples 1 to 3 use a pouch cell system, and the positive electrode composition of Examples 4 and 5 is different from that of Comparative Example 1 and Examples 1 to 3, there are significant differences in the cycle retention rates in Tables 3 and 2.

[0209] In Example 4, bisphenol A diglycidyl ether was added to the positive electrode active layer, and hexamethylenediamine was added to the electrolyte. In Example 5, bisphenol A diglycidyl ether and hexamethylenediamine were added together to the positive electrode active layer. The results showed that the cycle retention rate of Example 5 was higher than that of Example 4.

[0210] According to Examples 1 to 3, the scheme of adding bisphenol A diglycidyl ether to the positive electrode active layer and hexamethylenediamine to the electrolyte improves the cycle retention rate of the battery compared to the case without the introduction of bisphenol A diglycidyl ether and hexamethylenediamine. That is, under the same system, Example 4 improves the cycle retention rate of the battery compared to the case without the introduction of bisphenol A diglycidyl ether and hexamethylenediamine. The cycle retention rate of Example 5 is even better than that of Example 4, indicating that the scheme of Example 5 can also improve the cycle retention rate of the battery. Therefore, whether bisphenol A diglycidyl ether is added to the positive electrode active layer and hexamethylenediamine is added to the electrolyte, or both bisphenol A diglycidyl ether and hexamethylenediamine are added to the positive electrode active layer, epoxy resin can be successfully formed in situ in the positive electrode active layer, thereby significantly improving the cycle performance of the secondary battery. Moreover, when bisphenol A diglycidyl ether and hexamethylenediamine are added to the positive electrode active layer together, the capacity utilization and coulombic efficiency are even better.

[0211] In view of the improved cycle performance and storage performance of the secondary batteries observed in Examples 1 to 5 above, this application designed the following experiments to explore its underlying mechanism.

[0212] Experiment 1

[0213] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. Then, 12.5% ​​(mass content) of LiPF6 and 0.9% (mass content) of Mn(TFSI)2 were added and stirred evenly to obtain the electrolyte of Experiment 1.

[0214] Experiment 2

[0215] Add 0.51g of bisphenol A diglycidyl ether and 0.09g of hexamethylenediamine to 40g of the electrolyte from Experiment 1 to obtain the electrolyte from Experiment 2.

[0216] Experiment 3

[0217] Add 0.09g of hexamethylenediamine to 40g of the electrolyte from Experiment 1 to obtain the electrolyte from Experiment 3.

[0218] Experiment 4

[0219] Add 0.36g of ethanol to 40g of the electrolyte from Experiment 1 to obtain the electrolyte from Experiment 4.

[0220] Experiment 5

[0221] Add 0.51g of bisphenol A diglycidyl ether to 40g of the electrolyte from Experiment 1 to obtain the electrolyte from Experiment 5.

[0222] All groups were sealed and allowed to stand for 72 hours. The supernatant was then filtered and sent for ICP analysis to test the Mn content in the solution. 2+ Li + The content and test results are as follows.

[0223] [Table 4]

[0224]

[0225] According to the test results, Li in Experiment 2 + The content showed no significant change compared to Experiment 1, indicating that the epoxy resin did not affect the activity of Li. + It has an adsorption effect, and therefore will not affect Li + Therefore, the formation of epoxy resin in the positive electrode active layer should not have a significant side effect on the normal electrochemical reaction of the secondary battery.

[0226] The test results also showed that in Experiment 2, after bisphenol A diglycidyl ether formed an epoxy resin with hexamethylenediamine, the Mn content in the electrolyte was lower than that in Experiment 1. 2+ The significantly reduced content indicates that epoxy resin can selectively adsorb dissolved transition metals. In secondary batteries, utilizing epoxy resin in the positive electrode to adsorb dissolved transition metals can reduce the migration of transition metals to the negative electrode side, alleviate the SEI film decomposition problem caused by transition metal migration and deposition on the negative electrode side, and improve the cycle performance and storage performance of secondary batteries.

[0227] The epoxy resin formed by the reaction of bisphenol A diglycidyl ether and hexamethylenediamine in Experiment 2 can adsorb transition metals mainly because it contains hydroxyl and amino functional groups with strong coordination effects, which can coordinate and complex with transition metals. Therefore, this application investigated whether compounds containing only hydroxyl and amino functional groups could achieve a similar effect to epoxy resin, i.e., Experiments 3-5. Experiments 3-5 were conducted based on Experiment 1, with the addition of hexamethylenediamine, ethanol, and bisphenol A diglycidyl ether to the electrolyte, respectively. The test results showed that the adsorption effect of these compounds on transition metals was significantly lower than that of the epoxy resin in Experiment 2. It can be concluded that adding any of these compounds to the positive electrode active layer would not effectively prevent the dissolution and migration of transition metals in the positive electrode active material.

[0228] The battery performance testing methods mentioned above are as follows:

[0229] 1) Cycle retention rate

[0230] At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the secondary battery after X cycles is calculated, i.e., the cycle retention rate in Tables 2 and 3, where X is 1000 in Table 2 and 15 in Table 3.

[0231] 2) Storage retention rate

[0232] At 25°C, the secondary battery was charged to 4.2V at a constant current of 1C, then charged to less than 0.05C at a constant voltage of 4.2V, and then discharged to 2.8V at a constant current of 1C. The discharge capacity of this discharge is the discharge capacity C0 of the secondary battery before high-temperature storage.

[0233] Then, the secondary battery was charged to 4.2V with a constant current of 1C. The secondary battery was then stored at 60℃ for 30 days. After storage, the secondary battery was placed in an environment of 25℃ and then discharged to 2.8V with a constant current of 1C. After that, the secondary battery was charged to 4.2V with a constant current of 0.05C. Then, it was charged to 0.05C with a constant voltage of 4.2V. Finally, the secondary battery was discharged to 2.8V with a constant current of 0.5C. The discharge capacity of this discharge is C1 of the secondary battery after high-temperature storage.

[0234] Storage retention rate = (C1-C0) / C0*100%.

[0235] 3) Capacity

[0236] At 25°C, the secondary battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current was less than 0.05C, and then discharged at a constant current of 1C to 2.8V. The discharge capacity C0 was recorded.

[0237] Specific capacity = C0 / mass of positive electrode active material (i.e., mass of NCM523).

[0238] 4) Coulomb efficiency

[0239] At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, and then charged at a constant voltage of 4.2V until the current is less than 0.05C, to obtain the initial charge capacity C2; then it is discharged at a constant current of 1C to 2.8V, to obtain the initial discharge capacity C0.

[0240] Coulomb efficiency = C2 / C0 * 100%.

[0241] 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 method for preparing a secondary battery, characterized in that, include: A positive electrode sheet and an electrolyte are provided, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, and the positive active layer comprises a positive active material; The positive electrode active layer further includes a first reactive monomer, and at least one of the positive electrode active layer and the electrolyte includes a second reactive monomer. One of the first reactive monomer and the second reactive monomer contains at least two epoxy groups, and the other contains a functional group capable of undergoing a polymerization reaction with the epoxy groups.

2. The method for preparing a secondary battery according to claim 1, characterized in that, The molar ratio of the epoxy group to the functional group capable of polymerizing with the epoxy group is (1-2):

1.

3. The method for preparing a secondary battery according to claim 1 or 2, characterized in that, The molar ratio of the epoxy group to the functional group capable of polymerizing with the epoxy group is (1.5-2):

1.

4. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that, The first reactive monomer contains at least two epoxy groups, and the second reactive monomer contains at least two functional groups capable of undergoing polymerization with the epoxy groups.

5. The method for preparing a secondary battery according to claim 4, characterized in that, The first reactive monomer includes one or more of glycidyl ether epoxy resin monomers, biphenyl epoxy resin monomers, fluorinated epoxy resin monomers, and silicone epoxy resin monomers.

6. The method for preparing a secondary battery according to claim 5, characterized in that, The glycidyl ether epoxy resin monomers include one or more of bisphenol A diglycidyl ether and resorcinol diglycidyl ether; and / or The biphenyl-based epoxy resin monomers include And / or, The fluorinated epoxy resin monomer includes 7. The method for preparing a secondary battery according to any one of claims 1 to 6, characterized in that, Functional groups capable of undergoing polymerization with the epoxy group include one or more of amino, hydroxyl, and carboxyl groups.

8. The method for preparing a secondary battery according to any one of claims 4 to 7, characterized in that, The second reactive monomer includes NH2-R 1 -NH2,R 1 Including alkylene groups with 2 to 10 carbon atoms.

9. The method for preparing a secondary battery according to claim 8, characterized in that, The second reaction monomer includes one or more of hexamethylenediamine and ethylenediamine.

10. The method for preparing a secondary battery according to any one of claims 4 to 9, characterized in that, The mass content of the first reactive monomer in the positive electrode active layer is 0.008% to 0.5%.

11. The method for preparing a secondary battery according to claim 10, characterized in that, The mass content of the first reactive monomer in the positive electrode active layer is 0.08% to 0.5%.

12. The method for preparing a secondary battery according to any one of claims 4 to 11, characterized in that, The electrolyte contains the second reactive monomer, and the mass content of the second reactive monomer in the electrolyte is 0.01% to 3%; or, the positive electrode active layer contains the second reactive monomer, and the mass content of the second reactive monomer in the positive electrode active layer is 0.001% to 0.08%.

13. The method for preparing a secondary battery according to claim 12, characterized in that, The electrolyte contains the second reactive monomer, and the mass content of the second reactive monomer in the electrolyte is 0.1% to 0.7%.

14. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that, The second reactive monomer contains at least two epoxy groups, and the first reactive monomer contains at least two functional groups capable of undergoing polymerization with the epoxy groups.

15. The method for preparing a secondary battery according to claim 14, characterized in that, The mass content of the first reactive monomer in the positive electrode active layer is 0.001% to 0.08%.

16. The method for preparing a secondary battery according to claim 14 or 15, characterized in that, The electrolyte contains the second reactive monomer, and the mass content of the second reactive monomer in the electrolyte is 0.07% to 4%.

17. A secondary battery, characterized in that, The secondary battery is obtained by the preparation method according to any one of claims 1 to 16, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive current collector and a positive active layer disposed on at least one side of the positive current collector, and the positive active layer comprises a positive active material and disperses epoxy resin.

18. The secondary battery according to claim 17, characterized in that, The epoxy resin in the positive electrode active layer has a mass content of 0.01% to 0.6%.

19. The secondary battery according to claim 17 or 18, characterized in that, The epoxy resin in the positive electrode active layer has a mass content of 0.1% to 0.5%.

20. An electrical appliance, characterized in that, Includes the secondary battery described in any one of claims 17 to 19.

Images