Secondary battery and electric device

Abstract

The application relates to a secondary battery and a power consumption device. The secondary battery comprises a positive electrode sheet and a positive electrode tab connected with the positive electrode sheet, the positive electrode tab comprises a first current collector and an overcharge prevention layer, the overcharge prevention layer is arranged on the surface of the first current collector, and the overcharge prevention layer comprises an overcharge prevention additive, insulating particles and a binder.

Description

[0001] Related applications

[0002] This application is a divisional application of the Chinese patent application filed by the applicant on July 26, 2023, with application number 2023109218896 and entitled "Secondary Battery and Power Consumption Device". Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a secondary battery and an electrical device. Background Technology

[0004] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect. However, overcharging can affect the battery's cycle performance, therefore, the overcharging problem remains to be solved. Summary of the Invention

[0005] Therefore, it is necessary to provide a secondary battery and power device that can improve cycle performance while taking into account overcharge protection.

[0006] In a first aspect, this application provides a secondary battery, including a positive electrode sheet and a positive electrode tab connected to the positive electrode sheet. The positive electrode tab includes a first current collector and an overcharge protection layer. The overcharge protection layer is disposed on the surface of the first current collector and includes an overcharge protection additive.

[0007] Not wanting to be limited to any theory, this application improves the positive electrode tab connected to the positive electrode plate in a secondary battery. Specifically, it adds an overcharge protection layer with an overcharge protection additive to the positive electrode tab. This allows the potential of the positive electrode plate to rise during overcharging, inducing a slow reaction of the overcharge protection additive in the positive electrode tab, thus preventing overcharging. Furthermore, the overcharge protection additive is not added to the positive active layer of the positive electrode plate, so it has virtually no impact on the performance of the positive active layer. Compared to placing the overcharge protection additive in the positive active layer, this significantly improves the cycle performance of the secondary battery during long-term use and also reduces the risk of overcharge runaway.

[0008] In any embodiment of this application, the overcharge prevention additive includes at least one of Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, Li2C6O6, Li2CO3, LiN3, LiODFB, Li2O, Li3N, LiF, LiCl, Li2S, LiBH4, CH3COOLi, LiNO3, and Li2SO4.

[0009] In any embodiment of this application, the mass content of Li2C2O4 in the anti-overcharge additive is 50%~95%.

[0010] In any embodiment of this application, the mass content of the overcharge prevention additive is 0.5% to 50% based on the total mass of the overcharge prevention layer.

[0011] In any embodiment of this application, the adhesive includes at least one of polypropylene, polyacrylic acid, polystyrene, polyterephthalic acid, styrene-butadiene rubber, waterborne acrylic resin, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinylidene fluoride.

[0012] In any embodiment of this application, the positive electrode includes a second current collector and a positive active layer disposed on the second current collector;

[0013] The area ratio of the overcharge protection layer to the area of ​​the positive electrode active layer is (1~10):100.

[0014] In any embodiment of this application, the overcharge prevention additive is capable of decomposing and producing gas at a voltage of ≥4.2V.

[0015] In any embodiment of this application, the overcharge protection layer further includes insulating particles;

[0016] The mass content of the insulating particles is 1% to 30% based on the total mass of the overcharge protection layer.

[0017] In any embodiment of this application, the thickness of the overcharge protection layer is 10~150μm.

[0018] In any embodiment of this application, the positive electrode tab further includes a first electrode tab adhesive layer, which is disposed on the surface of the overcharge protection layer away from the first current collector.

[0019] In any embodiment of this application, the overcharge protection layer further includes a conductive agent with a mass content of 0-5%.

[0020] In any embodiment of this application, the thickness of the first tab adhesive layer is 5μm to 100μm.

[0021] In any embodiment of this application, the positive electrode sheet includes a second current collector and a positive active layer disposed on the second current collector. The second current collector and the first current collector are interconnected to form a whole. The surface of the first current collector also includes a blank area disposed adjacent to the overcharge protection layer. The overcharge protection layer is located between the blank area and the second current collector.

[0022] In any embodiment of this application, the positive electrode tab further includes a second electrode tab adhesive layer that is adjacent to and disposed in the same layer as the overcharge protection layer.

[0023] In any embodiment of this application, the thickness of the second tab adhesive layer is 30~150μm.

[0024] In a second aspect, this application provides an electrical device, which includes the secondary battery provided in the first aspect of this application. Attached Figure Description

[0025] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0026] Figure 1 This is a top view schematic diagram of the positive electrode plate and positive electrode tab of a secondary battery according to an embodiment of this application;

[0027] Figure 2 yes Figure 1 A schematic diagram of the cross-section of the positive electrode tab is shown.

[0028] Figure 3 This is a cross-sectional schematic diagram of the positive electrode tab of a secondary battery according to another embodiment of this application;

[0029] Figure 4 This is a top view schematic diagram of the positive electrode tab of a secondary battery according to another embodiment of this application;

[0030] Figure 5 This is a top view schematic diagram of the positive electrode plate and positive electrode tab of a secondary battery according to another embodiment of this application;

[0031] Figure 6 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0032] Figure 7 yes Figure 6 An exploded view of a battery cell according to one embodiment of this application is shown.

[0033] Figure 8 This is a schematic diagram of a battery module according to one embodiment of this application;

[0034] Figure 9 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0035] Figure 10 for Figure 9 An exploded view of a battery pack according to one embodiment of this application is shown;

[0036] Figure 11 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

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

[0038] 1. Battery cell; 11. Housing; 12. Electrode assembly; 13. Cover plate; 121. Positive electrode tab; 1211. First current collector; 1212. Overcharge protection layer; 1213. First electrode tab adhesive layer; 1214. Second electrode tab adhesive layer; 122. Positive electrode sheet; 2. Battery pack; 21. Upper casing; 22. Lower casing; 3. Battery module; 4. Electrical device. Detailed Implementation

[0039] The embodiments of this application are hereby disclosed in detail 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.

[0040] 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.

[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can 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 method may also include step (c), indicating that step (c) can 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.

[0042] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members."

[0043] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0044] Secondary batteries

[0045] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be reactivated and the battery to continue to be used.

[0046] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions move back and forth between the positive and negative electrodes, inserting and extracting. It can be understood that the active ions originate from the positive electrode active material of the positive electrode.

[0047] To facilitate the connection between the secondary battery and the external circuit, it generally also includes electrode tabs. The electrode tab connected to the positive electrode plate is the positive electrode tab, and the electrode tab connected to the negative electrode plate is the negative electrode tab.

[0048] The positive electrode tab includes a first current collector and an overcharge protection layer. The overcharge protection layer is disposed on the surface of the first current collector and includes an adhesive and an overcharge protection additive.

[0049] Please see Figure 1 and Figure 2 The diagram shows the connection between the positive electrode tab 121 and the positive electrode plate 122. The positive electrode tab 121 includes a first current collector 1211 and an overcharge protection layer 1212. The overcharge protection layer 1212 is disposed on the surface of the first current collector 1211 and includes an overcharge protection additive. Please refer to [link to documentation]. Figure 1 The area with the overcharge protection layer 1212 is the overcharge protection zone A.

[0050] Not wanting to be limited to any theory, this application improves the positive electrode tab connected to the positive electrode plate in a secondary battery. Specifically, it adds an overcharge protection layer with an overcharge protection additive to the positive electrode tab. This allows the potential of the positive electrode plate to rise during overcharging, inducing a slow reaction of the overcharge protection additive in the positive electrode tab, thus preventing overcharging. Furthermore, the overcharge protection additive is not added to the positive active layer of the positive electrode plate, so it has virtually no impact on the performance of the positive active layer. Compared to placing the overcharge protection additive in the positive active layer, this significantly improves the cycle performance of the secondary battery during long-term use and also reduces the risk of overcharge runaway.

[0051] In some embodiments, the overcharge protection additive can decompose and produce gas at a voltage of ≥4.2V. Thus, when the secondary battery is overcharged, the overcharge protection additive decomposes and releases gas at an overcharge voltage of ≥4.2V, thereby mitigating damage to the cathode. Simultaneously, the timely gas production responds to overcharge phenomena; for example, gas production can increase the internal pressure of the secondary battery, allowing for timely overcharge intervention through internal pressure monitoring. This includes stopping charging before battery damage or explosion, thereby improving the safety of the secondary battery.

[0052] Furthermore, the gas generation of the overcharge protection additive can be from 4.25V to 6.0V. The overcharge protection additive has a wider operating voltage range, thus allowing for a wider range of normal operation of secondary voltages. For example, it can be used for batteries with a low voltage of 4.2V, providing timely protection during overcharging and avoiding safety issues caused by low-voltage overcharging.

[0053] Furthermore, the gas generated by the overcharge prevention additive includes, but is not limited to, at least one of nitrogen and carbon dioxide. It is understood that, due to the complexity of the gas generation principle, only examples of gas types are provided here; the actual types of gas generated are not limited to these, as long as gas can be generated at the overcharge voltage.

[0054] In some embodiments, the overcharge prevention additive includes at least one of Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, Li2C6O6, Li2CO3, LiN3, LiODFB, Li2O, Li3N, LiF, LiCl, Li2S, LiBH4, CH3COOLi, LiNO3, and Li2SO4.

[0055] Furthermore, the overcharge prevention additive includes at least one of Li2C2O4, Li2C4O4, Li2C4O6, Li2C3O5 and LiN3.

[0056] In some examples, the overcharge prevention additives include Li2C2O4 and Li2C4O6.

[0057] In some examples, the mass content of Li2C2O4 in the overcharge prevention additive is 50% to 95%, and can be selected as 50% to 80%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%.

[0058] In some embodiments, the overcharge protection layer also includes an adhesive that can effectively bond the overcharge protection additive to the surface of the first current collector. In other examples, the overcharge protection layer may be adhesive-free.

[0059] In some embodiments, the mass content of the overcharge protection additive, based on the total mass of the overcharge protection layer, is 0.5% to 50%, optionally 2% to 20%, optionally 5% to 20%, and more preferably 5% to 15%. As an example, the mass content of the overcharge protection additive in the overcharge protection layer can be 0.5%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. Within this range, a better balance between the cycle performance and safety performance of the secondary battery can be achieved.

[0060] In some embodiments, the binder in the anti-overcharge layer includes at least one of polypropylene, polyacrylic acid, polystyrene, polyterephthalic acid, styrene-butadiene rubber, waterborne acrylic resin, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinylidene fluoride.

[0061] Furthermore, the binder in the overfill protection layer includes polypropylene.

[0062] In some embodiments, the overcharge protection layer also includes insulating particles. These insulating particles can serve as a particle-reinforcing phase in the overcharge protection layer, providing support and reinforcement, thereby improving the structural strength of the overcharge protection layer; furthermore, the insulating particles can also improve the heat resistance of the overcharge protection layer.

[0063] Insulating particles include at least one of inorganic particles, organic particles, and organic-inorganic hybrid particles.

[0064] Furthermore, the inorganic particles include, but are not limited to, at least one of alumina, boehmite, zinc oxide, silicon dioxide, titanium dioxide, zirconium oxide, calcium carbonate, boron nitride, and manganese sulfide.

[0065] Furthermore, to prevent overcharging, the mass content of insulating particles is 1% to 30% of the total mass of the layer; alternatively, it can be 5% to 20%. As an example, the mass content of insulating particles to prevent overcharging can be 1%, 2%, 5%, 10%, 15%, 20%, 25%, or 30% of the total mass of the layer.

[0066] Furthermore, the Dv50 particle size of the insulating particles is 1~30μm, and more preferably 5~15μm. The volume average particle size Dv50 of the insulating particles has a well-known meaning in the art and can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as a Malvern Master Size 3000). Here, Dv50 particle size represents the particle size corresponding to the cumulative volume distribution percentage of particles reaching 50% from the smallest particle size side in the particle size distribution.

[0067] In some embodiments, the thickness of the overcharge protection layer is 10~150μm; optionally, it is 30~100μm. As an example, the thickness of the overcharge protection layer can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 80μm, 90μm, 100μm, 120μm, or 150μm.

[0068] In some embodiments, the overcharge protection layer can be prepared by mixing an overcharge protection additive, a solvent, and an optional binder to obtain an overcharge protection slurry, then applying the overcharge protection slurry onto a first current collector, and drying and curing it. The optional binder refers to the option of adding or not adding a binder.

[0069] It is understandable that coating methods include, but are not limited to, spraying, brushing, and spin coating.

[0070] Furthermore, the solvent used in preparing the overcharge protection layer may include at least one of water and an organic solvent. As an example, the organic solvent may be N-methylformamide (NMF).

[0071] In some embodiments, the positive electrode tab further includes a first tab adhesive layer. The first tab adhesive layer is disposed on the surface of the overcharge protection layer away from the first current collector. Thus, the first tab adhesive layer provides insulation protection to the underlying overcharge protection layer. Figure 3As shown, in the positive electrode tab 121, the first current collector 1211 is provided with an overcharge protection layer 1212 and a first electrode tab adhesive layer 1213 in sequence in the overcharge protection zone A.

[0072] It is understood that the components of the first tab adhesive layer can be conventional tab adhesives. The components of the first tab adhesive layer include an adhesive. Furthermore, the adhesive in the second tab adhesive layer can be selected from the same range as the adhesive in the overcharge protection layer, but the specific types in the specific examples can be the same or different.

[0073] In some embodiments, the overcharge protection layer further includes a conductive agent at a mass content of 0-5%. In other words, the content of the conductive agent in the overcharge protection layer can be 0. When the above-mentioned first tab adhesive layer is also provided on the upper surface of the overcharge protection layer, a conductive agent can be added to the composition of the overcharge protection layer to improve the rapid response of the overcharge protection additive in the overcharge protection layer during overcharging. That is, the mass content of the conductive agent in the composition of the overcharge protection layer can be controlled to be greater than 0 and not greater than 5%.

[0074] As an example, the mass content of the conductive agent in the anti-overcharge layer is 0, 0.5%, 1%, 2%, 3%, 4%, or 5%. Optionally, it can be a range consisting of any two of the above values. Further, based on the total mass of the anti-overcharge layer, the mass content of the conductive agent is greater than 0 and not greater than 3%, or is 0.5% to 3%.

[0075] Furthermore, the thickness of the first tab adhesive layer is 5μm to 100μm; as an example, the thickness of the first tab adhesive layer can be 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, or 100μm. It can be selected as 30μm to 100μm.

[0076] In some embodiments, the positive electrode tab further includes a second tab adhesive layer adjacent to and disposed in the same layer as the overcharge protection layer; the area in the positive electrode tab where the second tab adhesive layer is located can serve as an encapsulation area. The encapsulation area where the second tab adhesive layer is located can serve as the encapsulation connection position of the positive electrode tab, providing a sealing function, and is particularly suitable for pouch batteries. Figure 4 As shown, a top view of another positive electrode tab is presented, in which an overcharge protection layer 1212 and a second tab adhesive layer 1214 are formed in the adjacent areas on the surface of the first current collector 1211 (not shown), thus forming an overcharge protection zone and an encapsulation zone. The overcharge protection layer 1212 and the second tab adhesive layer 1214 are disposed in the same layer on the first current collector 1211.

[0077] Furthermore, in addition to the adhesive, the first tab adhesive layer may optionally contain insulating particles. The further selection of insulating particles may be the same as that in the overcharge protection layer, but the specific types may be the same or different in specific examples. The second tab adhesive layer is similar to the first tab adhesive layer.

[0078] Furthermore, the first tab adhesive layer includes an adhesive and insulating particles, wherein the mass content of the insulating particles in the first tab adhesive layer is 1% to 30%; more preferably 5% to 20%. As an example, the mass content of the insulating particles, based on the total mass of the first tab adhesive layer, can be 1%, 2%, 5%, 10%, 15%, 20%, 25%, or 30%. The second tab adhesive layer is similar to the first tab adhesive layer.

[0079] Furthermore, the second tab adhesive layer does not contain conductive agents or overcharge protection additives, unlike the first tab adhesive layer, to give the positive tab better insulation and protection performance.

[0080] Further, the thickness of the second tab adhesive layer is 30~150μm; optionally, it is 30~100μm. As an example, the thickness of the second tab adhesive layer can be 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, or 150μm.

[0081] Positive electrode sheet

[0082] In a secondary battery, the positive electrode typically includes a second current collector and a positive electrode active layer disposed on the second current collector. The positive electrode active layer comprises a positive electrode active material. It can be understood that the second current collector is the positive electrode current collector.

[0083] In some embodiments, the area ratio of the overcharge protection layer in the positive electrode tab to the area of ​​the positive electrode active layer in the positive electrode sheet is (1~10):100. As examples, this area ratio can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, or 10:100. Further, the area ratio can be (3~7):100. Controlling this area ratio can balance the overcharge protection layer having superior overcharge protection performance with the secondary battery having a good energy density.

[0084] Furthermore, the second current collector and the first current collector of the positive electrode tab are interconnected to form a whole. The surface of the first current collector of the positive electrode tab is provided with an overcharge protection layer, and it also includes an uncoated blank area adjacent to the overcharge protection layer. The overcharge protection zone where the overcharge protection layer is located is situated between the blank area and the second current collector. It is understood that the blank area is uncoated and can serve as the electrical connection terminal of the positive electrode tab. Figure 1 and Figure 5 In the specific example shown, the positive electrode tab 121 includes an overcharge protection zone A and a blank area B adjacent to the overcharge protection zone A.

[0085] Optionally, such as Figure 1 and Figure 5As shown, in some examples, the second current collector and the first current collector are integrally formed structures. That is, the positive electrode tab and the positive electrode plate are formed on the same current collector. Further, on this basis, a first tab adhesive layer is formed on the overcharge protection layer of the first current collector 1211, which is particularly suitable for hard-pack batteries.

[0086] Specifically, as Figure 1 shown, there is one blank area B of the first current collector 1211; further, the blank area B has the same width as the overcharge protection area A.

[0087] Specifically, as Figure 5 shown, among the positive electrode tabs, there are multiple blank areas B of the first current collector 1211, and the multiple blank areas B are located on the same side. That is, the multiple blank areas B of the first current collector 1211 are not continuous and can be used as connection sites alone.

[0088] In some other examples, the positive electrode plate and the positive electrode tab are separate structures, that is, the second current collector and the first current collector are separate. For example, as Figure 4 shown, the positive electrode tab can be connected to the positive electrode plate of the electrode assembly by means of a metal connecting piece or the like.

[0089] The second current collector can be a conventional metal foil or a composite current collector, and the composite current collector can be formed by disposing a metal material on a polymer substrate. As an example, the second current collector can be an aluminum foil.

[0090] The specific type of the positive electrode active material can be an active material known in the art that can be used for the positive electrode of a secondary battery, and those skilled in the art can select according to actual needs.

[0091] As an example, the positive electrode active material can include a sodium ion active material, and the sodium ion active material can be a positive electrode active material known in the art for sodium ion batteries. As an example, the sodium ion active material can include at least one of the following materials: Prussian blue (PBA) type, with the chemical formula (NaxMA[MB(CN)6]·zH2O, where MA and MB are transition metal ions, which is a compound composed of sodium, transition metal and cyanide, such as Na4Fe2(CN)6, Na4Fe(CN)6, Na 1.72 MnFe2(CN)6, NaMnMn(CN)6, NaNiFe(CN)6, etc.; oxide type, with the chemical formula NaxMO2, 0 < x ≤ 1, M is a transition metal element, which is composed of transition metal oxides, and the variable-valence transition metals involved mainly include vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu), among which manganese and iron with relatively rich resources are most commonly used, such as NaCrO2, NaMnO2, NaMnO2, Na 0.61 Ti0.48 Mn 0.52 O2, Na[Fe 0.5 Co 0.5 O2, NaMnO2, Na[Ni 0.25 Fe 0.5 Mn 0.25 O2, etc.; and polyanionic compounds with the chemical formula Na x M y [(XO m ) n- ] z M represents a metal ion with variable valence, and X represents elements such as P, S, and V. It is composed of sodium, transition metals, and anions. The main transition metals include iron, vanadium, and cobalt, while the main anions include phosphate, pyrophosphate, fluorophosphate, and sulfate, such as NaMnFe2(PO4)6, Na2MnP2O7, Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na3V2(PO4)2F3, and Na4Co3(PO4)2(P2O7).

[0092] As an example, the positive electrode active material may include lithium-ion active materials, including but not limited to one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of olivine-structured lithium-containing phosphates include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0093] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0094] Understandably, during the charging and discharging process of a battery, there is intercalation and deintercalation of active ions such as lithium (Li), and the content of active ions such as Li in the positive electrode varies depending on the state of discharge. Taking lithium-ion active materials as an example, unless otherwise specified, the Li content in the examples of positive electrode active materials in this application refers to the initial state of the material. When positive electrode active materials are applied to the positive electrode in a battery system, the Li content in the positive electrode active material usually changes after charge-discharge cycles. The Li content can be measured in molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to the state before it is added to the positive electrode slurry. It is understood that materials obtained by appropriate modification based on the listed positive electrode active materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0095] In the examples of positive electrode active materials listed in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual oxygen atom content will fluctuate. The oxygen atom content can be measured in molar content, but is not limited to this.

[0096] The positive electrode active layer may also optionally include a binder, a conductive agent, and other optional additives.

[0097] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0098] As an example, the adhesive may be one or more of the following: styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0099] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a second current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0100] Negative electrode sheet

[0101] The negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector. Understandably, in some examples, the negative electrode film layer may be omitted.

[0102] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0103] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer 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 on the polymer material substrate. The metal material includes, but is not limited to, at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys; the polymer material substrate includes, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0104] Furthermore, the negative electrode film layer includes a negative electrode active material. It is understood that in some examples, the negative electrode film layer may not contain a negative electrode active material.

[0105] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0106] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0107] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners, for example, sodium carboxymethyl cellulose (CMC-Na).

[0109] In some embodiments, 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 such as water to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0110] electrolytes

[0111] The electrolyte acts as a conductor of ions between the positive and negative electrodes. For example, the electrolyte can be liquid, gel, or completely solid.

[0112] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0113] In some embodiments, the electrolyte salt includes at least one of sodium salt, lithium salt, and potassium salt.

[0114] As an example, the sodium salt in the electrolyte salt may be selected from one or more of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]) or sodium bis(trifluoromethanesulfonyl)imide (Na[(CF3SO2)2N]).

[0115] As an example, the lithium salt in the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0116] In some embodiments, the solvent includes at least one of ether solvents, ester solvents, and sulfone solvents.

[0117] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL);

[0118] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propanesulfonate lactone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0119] As an example, the sulfone solvent includes dimethyl sulfoxide (DMSO).

[0120] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0121] Separating membrane

[0122] In some embodiments, the secondary battery also includes a separator. The separator is disposed between the positive electrode and the negative electrode, serving as a barrier.

[0123] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0124] The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0125] Unless otherwise specified, all of the above-mentioned raw materials can be obtained through commercial purchase.

[0126] The shape of the secondary battery in this application embodiment can be cylindrical, square, or other arbitrary shapes. For example... Figure 6 Here is a square-structured battery cell 1 as an example.

[0127] In some implementations, refer to Figure 7The outer packaging may include a shell 11 and a cover plate 13. The shell 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 shell 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. The electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0128] Secondary batteries can be individual battery cells, battery modules, or battery packs.

[0129] Figure 8 This is battery module 3, shown as an example. (See reference...) Figure 8 In battery module 3, multiple battery cells 1 can be arranged sequentially along the length of battery module 3. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 1 can be fixed in place using fasteners.

[0130] Optionally, the battery module 3 may also include a housing with a receiving space in which multiple battery cells 1 are received.

[0131] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0132] Figure 9 and Figure 10 This is battery pack 2 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 2 may include a battery box and multiple battery modules 3 disposed within the battery box. The battery box includes an upper box 21 and a lower box 22, with the upper box 21 covering the lower box 22 to form a closed space for accommodating the battery modules 3. The multiple battery modules 3 can be arranged in any manner within the battery box.

[0133] In addition, the present invention also provides an electrical device comprising a secondary battery provided by the present invention. The secondary battery 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, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices may include, for example, mobile phones, laptops, etc.; electric vehicles may include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0134] As for the aforementioned electrical device, a secondary battery can be selected according to its usage requirements.

[0135] Figure 11 Here is an example of an electrical device 4. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0136] Another example device could be a mobile phone, tablet, laptop, etc.

[0137] To make the objectives, technical solutions, and advantages of this invention clearer and more concise, the invention is described using the following specific embodiments, but the invention is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of the invention and can be used to describe the invention, but should not be construed as limiting the scope of the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0138] To better illustrate the present invention, the following embodiments are provided for further explanation. The specific embodiments are as follows.

[0139] Example 1

[0140] (1) Preparation of positive electrode sheet and positive electrode tab

[0141] Take nickel-cobalt-manganese (NCM111) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2, add N-methylpyrrolidone, mix and stir for 2 hours to obtain positive electrode slurry;

[0142] Insulating particles (Al2O3 particles, Dv50 particle size of 5μm) in a mass ratio of 15:15:70, overcharge additive Li2C2O4 and binder (polypropylene) are mixed and then mixed with solvent water to obtain anti-overcharge slurry.

[0143] The positive electrode slurry is uniformly coated onto the main body area of ​​a 6μm thick aluminum foil for the positive electrode current collector. An overcharge protection slurry is uniformly coated onto one edge of the main body area (i.e., overcharge protection zone A), leaving the outermost edge uncoated as a blank area. After drying, cold pressing, and slitting, the positive electrode slurry forms the positive electrode active layer, and the overcharge protection slurry forms the overcharge protection layer. Correspondingly, from the main body area to the outermost edge, the positive electrode sheet, the overcharge protection layer for the positive electrode tab, and the blank area for the positive electrode tab are formed, respectively. The structures of the positive electrode sheet and the positive electrode tab are as follows: Figure 1 As shown, the blank area is continuous. The thickness of the positive electrode active layer is 150 μm.

[0144] (2) Preparation of negative electrode sheet

[0145] Graphite, styrene-butadiene rubber (SBR) binder, CMC-Na dispersant, and conductive carbon black (Super-P, SP) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96:2:1:1 to prepare a negative electrode slurry. The negative electrode active slurry was then coated onto a 6 μm thick copper foil, dried, and cold-pressed to form a negative electrode active material layer, which was then cut into negative electrode sheets; the thickness of the negative electrode active layer was 150 μm.

[0146] (3) Separating membrane

[0147] Polypropylene film is used as the separator.

[0148] (4) Electrolyte

[0149] LiPF6 was dissolved in a solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1 to prepare an electrolyte with a concentration of 1 mol / L.

[0150] (5) Manufacturing of lithium-ion batteries

[0151] The above-mentioned positive electrode sheet with positive electrode tab, separator, and negative electrode sheet are stacked and wound in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping processes, a lithium-ion battery is obtained.

[0152] Other embodiments 1-26

[0153] The results are basically the same as in Example 1, except that some parameters (the type and content of the overcharge protection additive, the type and content of the insulating particles, the thickness of the overcharge protection layer, and the area ratio of the overcharge protection layer to the positive electrode active layer) are different, as shown in Table 1.

[0154] Examples 27-29

[0155] The difference between Examples 27 and 29 is that the first tab adhesive layer is formed by further coating the surface of the overcharge protection layer of the positive electrode tab. The first tab adhesive layer is a polypropylene layer.

[0156] Example 30

[0157] The example is basically the same as Example 1, except that the positive electrode tab and the positive electrode plate in Example 30 are separate structures, specifically as follows: Figure 4 As shown.

[0158] The specific steps for preparing the positive electrode sheet and positive electrode tab are as follows:

[0159] Nickel-cobalt-manganese (NCM111) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were taken at a mass ratio of 97:1:2. N-methylpyrrolidone was added and the mixture was stirred for 2 hours to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 6μm thick aluminum foil of the positive electrode current collector, and then dried, cold-pressed, and cut to form a positive electrode sheet.

[0160] Insulating particles (Al2O3 particles, Dv50 particle size of 5μm) in a mass ratio of 15:15:70, overcharge additive Li2C2O4 and binder (polypropylene) are mixed and then mixed with solvent water to obtain anti-overcharge slurry.

[0161] An overcharge protection paste is uniformly coated onto a region of a 6μm thick aluminum foil current collector to form an overcharge protection layer. Polypropylene adhesive is then applied to the encapsulation area adjacent to the overcharge protection layer. After drying, cold pressing, and slitting, a positive electrode tab is formed, as shown in the diagram. Figure 4 As shown, an overcharge protection layer 1212 and a second tab adhesive layer 1214 (polypropylene layer) are formed in the same layer in the regions adjacent to the surface of the first current collector 1211 (not shown).

[0162] Comparative Example 1

[0163] This is basically the same as Example 1, except for the preparation of the positive electrode tab and the positive electrode sheet. Details are as follows:

[0164] The positive electrode slurry was prepared by mixing nickel-cobalt-manganese (NCM111) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2, adding N-methylpyrrolidone, stirring for 2 hours, and then adding overcharge additive Li2C2O4 (whose mass is 15% of the total mass of nickel-cobalt-manganese (NCM111) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride).

[0165] Insulating particles (Al2O3 particles) and binder (polypropylene) in a mass ratio of 15:85 are mixed and then mixed with solvent water to obtain tab adhesive.

[0166] The positive electrode slurry is uniformly coated onto the main body area of ​​the positive electrode current collector, and the tab adhesive is uniformly coated onto one edge of the main body area of ​​the positive electrode current collector (i.e., the overcharge protection zone A), leaving the outermost edge uncoated as a blank area. After drying, cold pressing, and slitting, the positive electrode slurry forms the positive electrode active layer, and the tab adhesive forms the tab adhesive layer. Correspondingly, from the main body area to the outermost edge, the positive electrode sheet, the overcharge protection layer of the positive electrode tab, and the blank area of ​​the positive electrode tab are formed, respectively. For example... Figure 1 As shown, the blank areas are continuous.

[0167] The following is a battery performance test.

[0168] (1) Cyclic performance test

[0169] Cyclic capacity retention

[0170] Taking Example 1 as an example, five sodium batteries from Example 1 were grouped together. Each group of sodium batteries was charged at 25°C with a constant current of 1C to 3.7V, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged at a constant current of 1C to 2.5V, yielding the first discharge capacity (Cd1). This charging and discharging process was repeated until the nth cycle, yielding the discharge capacity of the sodium battery after n cycles, denoted as Cdn. The capacity retention rate of each sodium battery was calculated using the following formula, and then the average value was taken. The results are shown in Table 1.

[0171] Capacity retention rate = discharge capacity after n cycles (Cdn) / discharge capacity in the first cycle (Cd1).

[0172] (2) Overcharge protection test

[0173] Taking Example 1 as an example, 20 sodium batteries from Example 1 were grouped together. Each group of sodium batteries was discharged at 0.5C constant current to 3.0V at 25±5℃, left to stand for 12-24 hours, and then charged at 3C constant current to 10V for 7 hours. The results were observed. The judgment criterion was that the battery did not catch fire or explode; otherwise, the overcharge test was passed. The overcharge pass rate was obtained based on the number of batteries that passed and the total number of samples.

[0174] Table 1 shows some parameters and performance test results of the secondary batteries in each embodiment and comparative example.

[0175] Table 1

[0176]

[0177] The " / " indicates that the parameter is not involved.

[0178] As shown in Table 1 above, Comparative Example 1 involves adding an overcharge protection additive to the positive electrode active layer. Compared to Comparative Example 1, each embodiment can effectively improve the cycle performance of the secondary battery while still achieving good overcharge protection.

[0179] Examples 1-8 are basically the same, the difference being the type of overcharge protection additive. As can be seen from Examples 1-5, the batteries prepared in Examples 1 and 5 have better cycle performance, while the batteries prepared in Examples 2-4 have better overcharge protection performance. Examples 6-8 further employ a combination of two overcharge protection additives, achieving both better cycle performance and overcharge protection performance.

[0180] Examples 1 and 9-14 are basically the same, except that the content of the overcharge protection additive is different. The mass content of the overcharge protection additive in the overcharge protection layer is 0.5% to 50%, which can effectively improve the cycle performance of the secondary battery while providing good overcharge protection performance. Furthermore, the mass content of the overcharge protection additive in the overcharge protection layer is 2% to 20%, which can have both good overcharge protection performance and cycle performance.

[0181] Examples 1 and 15-18 are basically the same, except that at least one of the types and contents of insulating particles is different, and the mass content of insulating particles in the overcharge protection layer is further 5% to 20%, which can have both good overcharge protection performance and cycle performance.

[0182] Examples 1 and 19-22 are basically the same, except that the thickness of the overcharge protection layer is different. When the thickness of the overcharge protection layer is within 30-100μm, it can have both good overcharge protection performance and cycle performance.

[0183] Examples 1 and 23-26 are basically the same, except that the area ratio of the overcharge protection layer to the positive electrode active layer is different. When the area ratio of the overcharge protection layer to the positive electrode active layer is in the range of (3~7):100, it can have both good overcharge protection performance and cycle performance.

[0184] Examples 27-29 are basically the same as Example 1, except that a first tab adhesive layer is further coated on the surface of the overcharge protection layer of the positive electrode tab. The difference between Examples 27-29 is that the thickness of the first tab adhesive layer is different, which can provide better insulation protection performance and further improve its cycle performance.

[0185] Example 30 is basically the same as Example 1, except that the positive electrode tab and the positive electrode sheet in Example 30 are separate structures, and the cycle performance and overcharge protection performance of the battery made therefrom are comparable to those of Example 1.

[0186] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode sheet and a positive electrode tab connected to the positive electrode sheet. The positive electrode tab includes a first current collector and an overcharge protection layer. The overcharge protection layer is disposed on the surface of the first current collector and includes an overcharge protection additive, insulating particles, and a binder.

2. The secondary battery as described in claim 1, characterized in that, The overcharge prevention additive includes at least one of Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, Li2C6O6, Li2CO3, LiN3, LiODFB, Li2O, Li3N, LiF, LiCl, Li2S, LiBH4, CH3COOLi, LiNO3, and Li2SO4.

3. The secondary battery as described in claim 2, characterized in that, In the overcharge prevention additive, the mass content of Li2C2O4 is 50%~95%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, Based on the total mass of the overcharge protection layer, the mass content of the overcharge protection additive is 0.5% to 50%, and can be selected as 5% to 20%.

5. The secondary battery as described in claim 4, characterized in that, The adhesive includes at least one of polypropylene, polyacrylic acid, polystyrene, polyterephthalic acid, styrene-butadiene rubber, waterborne acrylic resin, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinylidene fluoride.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The positive electrode includes a second current collector and a positive active layer disposed on the second current collector; The area ratio of the overcharge protection layer to the positive electrode active layer is (1~10):100, and can be selected as (3~7):

100.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The overcharge prevention additive can decompose and produce gas at a voltage of ≥4.2V.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, One or more of the following conditions must be met: (1) Based on the total mass of the overcharge protection layer, the mass content of the insulating particles is 5% to 30%, and can be selected as 5% to 20%; (2) The insulating particles include at least one of inorganic particles, organic particles and organic-inorganic hybrid particles. Optionally, the inorganic particles include at least one of alumina, boehmite, zinc oxide, silicon dioxide, titanium dioxide, zirconium oxide, calcium carbonate, boron nitride and manganese sulfide.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The thickness of the overcharge protection layer is 10μm~150μm, and can be selected as 30μm~100μm.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The positive electrode tab also includes a first electrode tab adhesive layer, which is disposed on the surface of the overcharge protection layer away from the first current collector.

11. The secondary battery as described in claim 10, characterized in that, The overcharge protection layer also includes a conductive agent with a mass content of 0-5%. Optionally, the mass content of the conductive agent in the overcharge protection layer is greater than 0 and not greater than 5%.

12. The secondary battery as described in claim 10 or 11, characterized in that, One or more of the following conditions must be met: (1) The thickness of the first electrode tab adhesive layer is 5μm~100μm, and can be selected as 30μm~100μm; (2) The first tab adhesive layer includes an adhesive and insulating particles; optionally, the mass content of the insulating particles in the first tab adhesive layer is 1% to 30%, and optionally 5% to 20%.

13. The secondary battery according to any one of claims 1 to 12, characterized in that, The positive electrode includes a second current collector and a positive active layer disposed on the second current collector. The second current collector and the first current collector are connected to each other to form a whole. The surface of the first current collector also includes a blank area disposed adjacent to the overcharge protection layer. The overcharge protection layer is located between the blank area and the second current collector.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The positive electrode tab also includes a second electrode tab adhesive layer that is adjacent to and disposed in the same layer as the overcharge protection layer.

15. The secondary battery as described in claim 14, characterized in that, One or more of the following conditions must be met: (1) The thickness of the second electrode tab adhesive layer is 30μm~150μm, and can be selected as 30μm~100μm; (2) The second tab adhesive layer includes an adhesive and insulating particles; optionally, the mass content of the insulating particles in the second tab adhesive layer is 1% to 30%, and optionally 5% to 20%.

16. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in any one of claims 1 to 15.

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