Secondary battery, and battery module, battery pack, and device containing the same

Abstract

The present application discloses a secondary battery, a battery module, a battery pack, and a device containing the secondary battery. The secondary battery comprises a positive electrode sheet, which comprises a positive electrode current collector, a positive electrode active material layer, and a coating disposed between the positive electrode current collector and the positive electrode active material layer. The coating comprises a conductive agent and a specific copolymer, which enables the secondary battery to simultaneously achieve good overcharge safety and cycle performance.

Description

Technical Field

[0001] The present application relates to a secondary battery, and more particularly to a secondary battery having a coating layer between a positive electrode current collector and a positive electrode active material layer, and a battery module, a battery pack, and a device having the secondary battery. Background Art

[0002] Secondary batteries undergo repeated charging and discharging during use. During charging, a limiting mechanism is required to control the upper charge voltage limit. However, when this limiting mechanism fails and the voltage exceeds the safe voltage, problems such as lithium deposition at the negative electrode, oxygen release at the positive electrode, and heat generation can occur. In severe cases, this can lead to thermal runaway within the battery, resulting in serious safety hazards such as fire and explosion. Therefore, to ensure the safe and widespread use of secondary batteries, improvements in overcharge safety are urgently needed. Summary of the Invention

[0003] The present application is developed in view of the above technical problems, and its purpose is to enable the secondary battery to have both good overcharge safety and cycle performance.

[0004] In order to achieve the above-mentioned object, the present application provides a secondary battery comprising a positive electrode plate, wherein the positive electrode plate comprises: a positive electrode current collector, a positive electrode active material layer, and a coating layer disposed between the positive electrode current collector and the positive electrode active material layer, wherein:

[0005] The coating comprises a conductive agent and a copolymer,

[0006] The copolymer comprises the following structural units (I), (II) and (III),

[0007] (I)

[0008] In the structural unit (I), R1 and R2 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, or an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms.

[0009] The substituent of the alkyl group having 1 to 10 carbon atoms, the alkoxy group having 1 to 10 carbon atoms, and the alkenyl group having 1 to 10 carbon atoms in R1 and R2 is at least one selected from the group consisting of hydroxyl, amino, amide, cyano, and carboxyl groups,

[0010] (II)

[0011] In structural unit (II), R3 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and the substituent in the substituted alkyl group having 1 to 10 carbon atoms, the substituted alkoxy group having 1 to 10 carbon atoms, and the substituted alkenyl group having 1 to 10 carbon atoms in R3 is at least one selected from the group consisting of halogen, hydroxyl, amino, amide, cyano, and carboxyl groups.

[0012] R4 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an inorganic metal ion, or -R 10 NR 11 R 12 The substituent of the alkyl group having 1 to 10 carbon atoms in R4 is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups, and the inorganic metal ion is sodium ion, potassium ion, lithium ion, calcium ion, or magnesium ion.

[0013] Among them, R 10 represents an unsubstituted or substituted alkylene group having 1 to 10 carbon atoms or an unsubstituted or substituted alkenylene group having 2 to 10 carbon atoms, R 10 The substituent of the alkylene group having 1 to 10 carbon atoms and the alkenylene group having 2 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups,

[0014] R 11 and R 12 Each independently represents an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and R 11 and R 12 The substituent of the alkyl group having 1 to 10 carbon atoms and the alkenyl group having 1 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups,

[0015] (III)

[0016] In the structural unit (III), R5 and R6 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, and X - represents an anion selected from the group consisting of halogen ions, sulfate ions, and sulfonate ions, and the substituent of the alkyl group having 1 to 10 carbon atoms in R5 and R6 is at least one selected from the group consisting of halogen, hydroxyl, amino, amide, cyano, and carboxyl.

[0017] By placing the coating comprising the specific copolymer between the positive electrode current collector and the positive electrode active material layer, the safety of the battery during overcharging can be effectively improved, and the probability of overheating, fire or explosion of the battery during overcharging can be greatly reduced.

[0018] In any embodiment, the content of the copolymer in the coating layer may be greater than 50 wt %, optionally 65 wt % to 85 wt %. By setting the content of the copolymer in the coating layer to the above range, electronic conduction between the current collector and the active material layer can be ensured under normal conditions, and a high cycle capacity retention rate can be maintained. In addition, the conductive network of the coating layer is easily destroyed when the battery is overcharged, thereby improving the safety of the battery during overcharge. Furthermore, it can be avoided that the conductive network of the coating layer cannot be destroyed when the battery is overcharged, thereby preventing a significant increase in the resistance of the coating layer.

[0019] In any embodiment, the coating has a thickness of 0.1 to 20 μm, optionally 0.3 to 10 μm, and further optionally 0.5 to 5 μm. By keeping the coating thickness within this range, the miniaturization of the secondary battery, high cycle capacity retention, and excellent overcharge safety can be achieved. Furthermore, on the one hand, this can avoid affecting the conductivity and preventing the battery electrode from becoming too thick, thereby facilitating battery miniaturization; on the other hand, it can prevent the coating's resistance from increasing too little after the temperature rises due to overcharging, thereby preventing it from increasing resistance and polarization.

[0020] In any embodiment, the conductive agent used in the coating layer includes at least one of conductive graphite, conductive carbon black, Ketjen black, acetylene black, carbon fiber, carbon nanotubes, and graphene. By using such a conductive agent in the coating layer, a good conductive network can be formed to ensure good electronic conduction between the current collector and the positive electrode active material layer.

[0021] In any embodiment, the coating layer may further include a binder, thereby making the coating layer relatively stable and increasing the application range of the secondary battery.

[0022] In any embodiment, the average molar number of monomers of structural unit (I) is denoted as a, the average molar number of monomers of structural unit (II) is denoted as b, and the average molar number of monomers of structural unit (III) is denoted as c. The copolymer satisfies the following conditions: 60% ≤ a / (a+b+c) × 100%, and optionally 70% ≤ a / (a+b+c) × 100% ≤ 85%. By setting a / (a+b+c) × 100% within a specific range, the bonding strength between the coating layer and the positive electrode current collector and positive electrode active material layer can be enhanced, thereby maintaining a high cycle capacity retention rate.

[0023] In any embodiment, the average molar number of the monomers of the structural unit (I) is denoted as a, the average molar number of the monomers of the structural unit (II) is denoted as b, and the average molar number of the monomers of the structural unit (III) is denoted as c. The copolymer satisfies the following conditions: b / (a+b+c)×100%≤20%, optionally 5%≤b / (a+b+c)×100%≤15%, optionally 5%≤b / (a+b+c)×100%≤10%. By setting b / (a+b+c)×100% to a specific range, the bonding strength between the coating layer and the positive electrode current collector and positive electrode active material layer can be enhanced, thereby maintaining a high cycle capacity retention rate.

[0024] In any embodiment, the average molar number of the monomers of structural unit (I) is denoted as a, the average molar number of the monomers of structural unit (II) is denoted as b, and the average molar number of the monomers of structural unit (III) is denoted as c. The copolymer satisfies the following conditions: c / (a+b+c)×100%≤20%, optionally 10%≤c / (a+b+c)×100%≤20%. By setting c / (a+b+c)×100% within the above-specified range, the resistance of the coating layer is significantly increased when the battery is overcharged, thereby preventing overcharge.

[0025] In any embodiment, in the structural unit (I), R1 and R2 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, optionally a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear alkyl group having 1 to 3 carbon atoms. This simplifies the manufacturing process and reduces production costs.

[0026] In any embodiment, in the structural unit (II), R3 is a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear alkyl group having 1 to 3 carbon atoms; R4 is a hydrogen atom, an inorganic metal ion, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom, an inorganic metal ion, or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom, a sodium ion, a potassium ion, or a linear or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom, a sodium ion, a potassium ion, or a linear alkyl group having 1 to 3 carbon atoms. This simplifies the manufacturing process and reduces production costs.

[0027] In any embodiment, in the structural unit (III), R5 and R6 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear alkyl group having 1 to 3 carbon atoms; X - The anion selected from the group consisting of halogen ions, optionally chloride ions and bromide ions, further optionally chloride ions.

[0028] In any embodiment, the structural unit (I), the structural unit (II), and the structural unit (III) are copolymerized randomly or in blocks.

[0029] In any embodiment, the number average molecular weight of the copolymer is 10,000 to 100,000, optionally 15,000 to 50,000.

[0030] A second aspect of the present application provides a battery module, which includes the secondary battery according to the first aspect of the present application.

[0031] A third aspect of the present application provides a battery pack, which includes the battery module according to the second aspect of the present application.

[0032] A fourth aspect of the present application provides a device comprising at least one of the secondary battery according to the first aspect of the present application, the battery module according to the second aspect of the present application, or the battery pack according to the third aspect of the present application.

[0033] The battery module, battery pack, and device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of an embodiment of the positive electrode plate in the secondary battery of the present application.

[0035] Figure 2 It is a structural schematic diagram of another embodiment of the positive electrode plate in the secondary battery of the present application.

[0036] Figure 3 Schematic diagram of a secondary battery according to one embodiment of the present application.

[0037] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of the present application is shown.

[0038] Figure 5 is a schematic diagram of a battery module according to one embodiment of the present application.

[0039] Figure 6 is a schematic diagram of a battery pack according to one embodiment of the present application.

[0040] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of the present application is shown.

[0041] Figure 8 FIG2 is a schematic diagram of a device using a secondary battery as a power source according to one embodiment of the present application. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions and advantages of this application more clear, the following will describe the embodiments of the application in detail with reference to the accompanying drawings. However, those skilled in the art should understand that these embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of the present invention.

[0043] For the sake of clarity, this application specifically discloses certain numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. In addition, each individually disclosed point or individual value can itself be combined as a lower limit or upper limit with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0044] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number themselves, and “several” in “one or several” means two or more.

[0045] The above summary of the invention of this application is not intended to describe every disclosed embodiment or every implementation in this application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0046] secondary batteries

[0047] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used. Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded in and released from the positive and negative electrodes. The separator is set between the positive and negative electrodes. It can insulate electrons and prevent internal short circuits, while allowing active ions to pass through and move between the positive and negative electrodes. It plays an isolating role. The electrolyte plays the role of conducting ions between the positive and negative electrodes.

[0048] [Positive electrode]

[0049] Figure 1 This is a schematic structural diagram of an embodiment of the positive electrode sheet in the secondary battery of the present application. Figure 1 As shown, the positive electrode sheet 100 of the present application includes a positive electrode current collector 30, a positive electrode active material layer 10, and a coating 20 disposed between the positive electrode current collector 30 and the positive electrode active material layer 10. Figure 1 Detailed Description of the Invention An embodiment is shown in which the coating layer 20 and the positive electrode active material layer 10 are provided only on one side of the positive electrode current collector 30 , but the present application is not limited thereto. Figure 2 This is a schematic structural diagram of another embodiment of the positive electrode sheet of the present application. Figure 2 As shown, the positive electrode sheet 100' of another embodiment of the present application can be provided with a coating 20, a positive electrode active material layer 10, and a coating 20', a positive electrode active material layer 10' on both sides of the positive electrode current collector 30. Among them, the coating 20 is located between the positive electrode current collector 30 and the positive electrode active material layer 10, and the coating 20' is located between the positive electrode current collector 30 and the positive electrode active material layer 10'. The positive electrode active material layer 10 and the positive electrode active material layer 10' can be the same or different, and optionally they are the same, thereby simplifying the manufacturing process. The coating 20 and the coating 20' can be the same or different, and optionally they are the same, thereby simplifying the manufacturing process.

[0050] The coatings 20 and 20' include a conductive agent and a copolymer. The copolymer includes the following structural units (I), (II), and (III).

[0051] (I)

[0052] (In the structural unit (I), R1 and R2 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, or an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms,

[0053] The substituent of the alkyl group having 1 to 10 carbon atoms, the alkoxy group having 1 to 10 carbon atoms, and the alkenyl group having 1 to 10 carbon atoms in R1 and R2 is at least one selected from the group consisting of hydroxyl, amino, amide, cyano, and carboxyl groups.

[0054] (II)

[0055] (In structural unit (II), R3 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and the substituent in the substituted alkyl group having 1 to 10 carbon atoms, the substituted alkoxy group having 1 to 10 carbon atoms, and the substituted alkenyl group having 1 to 10 carbon atoms in R3 is at least one selected from the group consisting of halogen, hydroxyl, amino, amide, cyano, and carboxyl groups,

[0056] R4 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an inorganic metal ion, or -R 10 NR 11 R 12 The substituent of the alkyl group having 1 to 10 carbon atoms in R4 is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups, and the inorganic metal ion is sodium ion, potassium ion, lithium ion, calcium ion, or magnesium ion.

[0057] Among them, R 10 represents an unsubstituted or substituted alkylene group having 1 to 10 carbon atoms or an unsubstituted or substituted alkenylene group having 2 to 10 carbon atoms, R 10 The substituent of the alkylene group having 1 to 10 carbon atoms and the alkenylene group having 2 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups,

[0058] R 11 and R 12 Each independently represents an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and R 11 and R 12 The substituent of the alkyl group having 1 to 10 carbon atoms and the alkenyl group having 1 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups.

[0059] (III)

[0060] (In the structural unit (III), R5 and R6 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, and X - represents an anion selected from halogen ions, sulfate ions, and sulfonate ions, and the substituent of the alkyl group having 1 to 10 carbon atoms in R5 and R6 is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups.

[0061] By placing a coating comprising the above-mentioned specific copolymer between the positive electrode current collector and the positive electrode active material layer, the resistance of the coating is greatly increased when the battery is overcharged, thereby improving the safety of the battery during overcharge and greatly reducing the probability of overheating, fire or explosion of the battery during overcharge.

[0062] Its mechanism of action is still unclear, but the inventors of this application speculate as follows. That is, under normal conditions, the conductive agent is evenly dispersed in the copolymer, so that the coating has good conductivity, ensuring electronic conduction between the current collector and the active material layer, so that the secondary battery can work well under normal conditions. At this time, the resistance of the coating is recorded as R0. On the other hand, when the battery is overcharged, the temperature inside the battery rises, and the copolymer in the coating undergoes violent molecular chain movement, causing the conductive material dispersed in the copolymer to aggregate, destroying the conductive network of the coating, resulting in a significant increase in the resistance of the coating. The resistance after heating is recorded as R1. After heating, the resistance R1 at above 130°C is more than 5 times the resistance R0 in the normal state. Due to the increase in resistance, the internal polarization of the battery increases rapidly, causing the voltage to rise rapidly, reaching the overcharge cut-off voltage, and it is impossible to continue charging, thereby improving the safety of the battery when overcharged.

[0063] After in-depth research, the inventors found that when the secondary battery of the present application meets the above-mentioned design conditions and optionally meets one or more of the following parameters, the performance of the secondary battery can be further improved.

[0064] In some embodiments, in the above structural unit (I), R1 and R2 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom or a straight-chain, branched or cyclic alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a straight-chain or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a straight-chain alkyl group having 1 to 3 carbon atoms.

[0065] In some embodiments, in the above structural unit (II), R3 is a hydrogen atom, or an unsubstituted or substituted alkyl group with 1 to 10 carbon atoms, optionally a hydrogen atom or a straight-chain, branched or cyclic alkyl group with 1 to 6 carbon atoms, further optionally a hydrogen atom or a straight-chain or branched alkyl group with 1 to 6 carbon atoms, further optionally a hydrogen atom or a straight-chain alkyl group with 1 to 3 carbon atoms; R4 is a hydrogen atom, an inorganic metal ion, or an unsubstituted or substituted alkyl group with 1 to 10 carbon atoms, optionally a hydrogen atom, an inorganic metal ion, or a straight-chain, branched or cyclic alkyl group with 1 to 6 carbon atoms, further optionally a hydrogen atom, a sodium ion, a potassium ion or a straight-chain or branched alkyl group with 1 to 6 carbon atoms, further optionally a hydrogen atom, a sodium ion, a potassium ion or a straight-chain alkyl group with 1 to 3 carbon atoms.

[0066] In some embodiments, in the structural unit (III), R5 and R6 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, optionally a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, further optionally a hydrogen atom or a linear alkyl group having 1 to 3 carbon atoms; X - It is an anion selected from halogen ions, optionally an anion selected from chloride ions and bromide ions, and further optionally a chloride ion.

[0067] In some embodiments, in the copolymer, the average molar number of monomers of structural unit (I) is denoted as a, the average molar number of monomers of structural unit (II) is denoted as b, and the average molar number of monomers of structural unit (III) is denoted as c. The copolymer satisfies the following conditions: a / (a+b+c)×100% is greater than 60%, and optionally is between 70% and 85%. Controlling a / (a+b+c)×100% within a specific range can enhance the bonding strength between the coating and the positive electrode current collector and the positive electrode active material layer, thereby maintaining a high cycle capacity retention rate.

[0068] In some embodiments, in the copolymer, b / (a+b+c)×100% is less than 20%, optionally 5% to 15%, and optionally 5% to 10%. By controlling b / (a+b+c) within a specific range, the bonding strength between the coating and the positive electrode current collector and the positive electrode active material layer can be improved, thereby maintaining a high cycle capacity retention rate.

[0069] In some embodiments, in the copolymer, c / (a+b+c)×100% is less than 20%, and optionally is between 10% and 20%. By controlling c / (a+b+c) within a specific range, the resistance of the coating can be further increased when the battery is overcharged, thereby further improving the overcharge safety of the battery.

[0070] In some embodiments, the number average molecular weight of the copolymer is 10,000 to 100,000, optionally 15,000 to 50,000, and optionally 30,000 to 50,000. By setting the number average molecular weight of the copolymer within the above range, high mechanical strength, high thermal stability, and excellent overcharge safety can be achieved. This can prevent the molecular chains of the copolymer from becoming difficult to move, which would make it difficult to destroy the conductive network of the coating when the battery is overcharged, thereby failing to improve the overcharge safety of the battery. On the other hand, it can prevent the mechanical strength of the coating from being reduced, which would make it easy to break when the battery is subjected to external force. Furthermore, it can prevent the thermal stability of the copolymer from being reduced, which would cause it to melt or degrade when the temperature rises due to overcharging of the battery.

[0071] In some embodiments, the copolymer may further include other structural units, which may include, but are not limited to, structural units derived from olefins, structural units derived from halogenated olefins, structural units derived from cycloalkanes, and the like.

[0072] In some embodiments, the structural unit (I), the structural unit (II), and the structural unit (III) can be copolymerized in a random or block manner.

[0073] The copolymers of the present application can be synthesized by methods commonly used in the art. For example, the methods include, but are not limited to, adding structural unit (I), structural unit (II), structural unit (III), and other structural units as needed, to a reactor, and copolymerizing them under an inert gas (e.g., nitrogen) atmosphere at a certain temperature to produce the copolymers of the present application; polymerizing structural unit (I) and structural unit (II) at a certain temperature, then adding the polymers obtained by polymerizing structural unit (I) and structural unit (II) to a reactor, then adding structural unit (III) and other structural units as needed, and copolymerizing them under an inert gas atmosphere such as nitrogen at a certain temperature to produce the copolymers of the present application, etc.

[0074] In some embodiments, the conductive agent includes at least one of conductive graphite, conductive carbon black, Ketjen black, acetylene black, carbon fiber, carbon nanotubes, and graphene. Including such a conductive agent in the coating can form a good conductive network, ensuring good electronic conduction between the current collector and the positive electrode active material layer.

[0075] In some embodiments, the coating further comprises a binder, which may include, but is not limited to, styrene acrylic emulsion, sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, polyacrylate, and the like.

[0076] In some embodiments, in the coating, the content of the copolymer may be 50% by weight or more, optionally 65% ​​by weight or more. By setting the content of the copolymer in the coating to the above range, it is possible to ensure electronic conduction between the current collector and the active material layer under normal conditions, maintain a high cycle capacity retention rate, and easily destroy the conductive network of the coating when the battery is overcharged, thereby improving the safety of the battery when overcharged, and further, it is possible to avoid the failure to destroy the conductive network of the coating when the battery is overcharged, thereby preventing the resistance of the coating from being significantly increased. Optionally, the content of the copolymer is 85% by weight or less.

[0077] In some embodiments, the conductive agent may be present in an amount of 10 to 25 wt % in the coating. By setting the conductive agent content within the above range, the coating can have good conductivity under normal conditions, ensuring electronic conduction between the current collector and the active material layer, and enabling the secondary battery to operate well under normal conditions.

[0078] In some embodiments, the coating has a thickness of 0.1 to 20 μm, optionally 0.3 to 10 μm, and further optionally 0.5 to 5 μm. By keeping the coating thickness within this range, it is possible to achieve both miniaturization of the secondary battery, a high cycle capacity retention rate, and excellent overcharge safety. Furthermore, on the one hand, this can avoid affecting the conductivity and preventing the battery electrode from becoming too thick, which would be detrimental to battery miniaturization. On the other hand, it can prevent the coating from increasing resistance and polarization due to a temperature rise caused by overcharging.

[0079] In the secondary battery of the present application, the positive electrode active material layers 10 and 10' include a positive electrode active material. The positive electrode active material may include, but is not limited to, lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium titanate, and the like. The positive electrode active material may be one or more of these.

[0080] The positive electrode active material layers 10 and 10' may also optionally include a conductive agent. However, the type of conductive agent is not specifically limited, and those skilled in the art may select one based on actual needs. For example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In the secondary battery of the present application, the positive electrode current collector 30 may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] The positive electrode sheet of the present application can be prepared according to conventional methods in the art. Specifically, a coating can be formed on at least one surface of the current collector by coating methods such as gravure coating, spray coating, or hot pressing. The positive electrode active material, conductive agent, and binder are dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to prepare a positive electrode slurry. The positive electrode slurry is then applied to the coating. After drying and cold pressing, the positive electrode sheet is obtained.

[0083] [Negative electrode]

[0084] In a secondary battery, a negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0085] In the secondary battery of the present application, the negative electrode active material may be any of those commonly used in the art for preparing negative electrodes for secondary batteries, such as graphite or silicon-based materials. The graphite may include artificial graphite, natural graphite, or a mixture thereof. The silicon-based material may be selected from one or more of elemental silicon, silicon oxides (e.g., silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0086] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0087] In the secondary battery of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (e.g., copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0088] In the secondary battery of the present application, the negative electrode active material layer typically comprises a negative electrode active material and, optionally, a binder, a conductive agent, and other optional additives. It is typically formed by coating and drying a negative electrode slurry. The negative electrode slurry is typically formed by dispersing the negative electrode active material, the conductive agent, the binder, and other optional additives in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP) or deionized water.

[0089] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] For example, the binder may be selected from one or more 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).

[0091] Other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0092] [Electrolytes]

[0093] The present invention has no specific restrictions on the type of electrolyte, and the electrolyte can be selected according to the needs. For example, the electrolyte can be solid or liquid.

[0094] In some embodiments, the electrolyte is liquid and generally includes an electrolyte salt and a solvent.

[0095] As an example, 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 difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0096] As an example, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0097] In some embodiments, the electrolyte may optionally include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, additives for improving battery overcharge performance, additives for improving battery high temperature performance, additives for improving battery low temperature performance, etc.

[0098] [Isolation film]

[0099] The present invention does not particularly limit the type of separator. Any known porous separator for secondary batteries may be used. For example, the separator may be selected from one or more of a glass fiber film, a non-woven film, a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, and a multilayer composite film comprising one or more of these.

[0100] In some embodiments, the secondary battery may be a lithium-ion secondary battery.

[0101] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0102] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0103] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0104] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0105] In some embodiments, reference Figure 4 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0106] In some embodiments, secondary batteries can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0107] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0108] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0109] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0110] Figure 6 and Figure 7 The battery pack 1 is used as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0111] Device

[0112] Another aspect of the present application provides a device comprising at least one of the secondary battery, battery module, or battery pack provided herein. The secondary battery can be used as a power source or an energy storage unit for the device. The device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0113] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0114] Figure 8 This is an example device. The device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0115] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0116] Example

[0117] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, they are carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially. The content of each component in the embodiments of the present application, unless otherwise specified, is measured by mass.

[0118] The raw materials used in the preparation of the following copolymers and the structural units generated therefrom are shown in Table 1.

[0119] [Table 1]

[0120]

[0121] 1. Preparation of Copolymer 1

[0122] Raw materials 1-1, 2-1, and 3-1 were dissolved in water at a mass ratio of 80:5:15 and stirred to dissolve. High-pressure nitrogen was then introduced for 10 minutes. Ammonia was added while nitrogen was introduced, and the mixture was heated to 60°C. Iron powder, a 20% aqueous solution of AlCl₃, and K₂S₂O₃ as an initiator were added. The pH of the reaction system was adjusted to approximately 7 using sulfuric acid and sodium hydroxide solution. The reaction temperature was maintained at 65°C and the reaction was allowed to react for 4 hours. Heating was then stopped, stirring was continued, and the mixture was allowed to cool sufficiently before drying and aging for 8 hours to obtain copolymer 1. Copolymer 1 comprises structural unit (I-1), structural unit (II-1), and structural unit (III-1). Copolymer 1 satisfies the following conditions: a / (a+b+c)×100% is 80%, b / (a+b+c)×100% is 5%, c / (a+b+c)×100% is 15%, and the number average molecular weight is 30,000.

[0123] The preparation methods of copolymers 2 to 16 are similar to those of copolymer 1, except that the types of raw materials and the amounts added are adjusted. For details, see Table 2 below.

[0124] The molecular weight and the ratio of each structural unit of each copolymer obtained above can be measured by the following method.

[0125] 1. Molecular Weight Determination

[0126] The obtained copolymer was dissolved in water, and the number average molecular weight of the obtained copolymer was measured using a gel permeation chromatography (GPC) (model: Agilent GPC 50, manufacturer: Agilent).

[0127] 2. Determination of the Ratio of Each Structural Unit

[0128] The prepared copolymer was dissolved in deuterated water to obtain a test sample. The sample was placed in a nuclear magnetic resonance tube and its H spectrum was measured using a 400 MHz nuclear magnetic resonance instrument (model: Bruker Avance III 400 MHz NMR, manufacturer: Bruker). The peak ratios of different monomers were observed to determine the ratios of different monomers.

[0129]

[0130] 2. Preparation of batteries

[0131] (Example 1)

[0132] Preparation of positive electrode

[0133] The prepared copolymer 1, conductive carbon black (Super-P), and binder styrene-acrylic emulsion were added to deionized water at a mass ratio of 70:15:15 and stirred thoroughly to prepare a slurry. The resulting slurry was applied to both sides of the current collector aluminum foil and dried to form a coating with a thickness of 2 μm.

[0134] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are added to the solvent NMP in a mass ratio of 97:2:1, and are fully stirred and mixed to form a uniform positive electrode slurry. The obtained positive electrode slurry is applied to the surface of the coating, and after drying and cold pressing, a positive electrode sheet is obtained.

[0135] Preparation of negative electrode sheet

[0136] The negative electrode active material artificial graphite, the conductive agent conductive carbon black (Super-P), the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 96:1:1.8:1.2, added to deionized water, and fully stirred to form a uniform negative electrode slurry. The obtained negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and then dried, cold pressed, slit, and cut to obtain a negative electrode sheet.

[0137] Preparation of electrolyte

[0138] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a mass ratio of 50:50 to obtain an electrolyte solution.

[0139] Preparation of secondary batteries

[0140] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound into a package, filled with the prepared electrolyte, and sealed to form a secondary battery.

[0141] (Examples 2 to 15)

[0142] The preparation method is similar to that of Example 1, except that different copolymers are used in the coating, as shown in Table 3 below.

[0143] (Comparative Example 1)

[0144] The preparation method is similar to that of Example 1, except that no coating is provided on both surfaces of the positive electrode current collector.

[0145] (Comparative Example 2)

[0146] The preparation method is similar to that of Example 1, except that different copolymers are used in the coating, as shown in Table 3 below.

[0147] The secondary batteries prepared in the above embodiments and comparative examples were tested for battery performance using the following method. The results are shown in Table 3.

[0148] 3. Battery performance test

[0149] 1. Overcharge performance test

[0150] The prepared secondary battery is insulated with insulation cotton, which is placed at both ends of the battery. It is charged at a charging rate of 1C, and the battery surface temperature and battery voltage are monitored during the charging process.

[0151] When the battery surface temperature reaches 120°C or above, and the battery voltage rises sharply to 8.5V within 5 minutes, the situation is judged as "○" and the time required for the battery to rise sharply to 8.5V is recorded;

[0152] When the battery surface temperature reaches 120°C or above and the battery voltage does not rise sharply to 8.5V within 5 minutes, the situation is judged as "×".

[0153] 2. Cycle capacity retention rate

[0154] At 25°C, the secondary batteries prepared in the Examples and Comparative Examples were charged at a constant current rate of 0.5C to a charge cutoff voltage of 4.25V. They were then charged at a constant voltage rate to a current of ≤0.05C, allowed to rest for 30 minutes, and then discharged at a constant current rate of 1C to a discharge cutoff voltage of 2.8V. The battery capacity at this point, C0, was recorded. This method was used to cycle the batteries 1500 times, and the battery capacity after 1500 cycles was recorded as C1. The cycle capacity retention rate of the secondary battery at 25°C was calculated using the following formula.

[0155] The cycle capacity retention rate of the battery at 25°C = C1 / C0×100%.

[0156] [Table 3]

[0157]

[0158] *: Indicates that the battery voltage cannot rise to 8.5V even after long-term overcharging.

[0159] The results in Table 3 above indicate that Examples 1-15, which incorporate the copolymers comprising structural units (I), (II), and (III) of the present application, achieve both good overcharge safety and high cycle capacity retention, thus achieving both good overcharge safety and good cycle performance. On the other hand, Comparative Examples 1 and 2, which do not incorporate the copolymers of the present application, exhibit lower safety during overcharge, with a higher probability of overheating, fire, or explosion. Furthermore, the battery's cycle performance significantly deteriorates.

[0160] In addition, by making the proportions of each structural unit, i.e., a / (a+b+c)×100%, b / (a+b+c)×100%, and c / (a+b+c)×100%, respectively, within appropriate ranges, the time required to reach the overcharge cut-off voltage can be further shortened without significantly affecting the cycle capacity retention rate, thereby further improving the safety of the battery during overcharging.

[0161] (Examples 16 to 18)

[0162] The preparation method is similar to that of Example 4, except that the thickness of the coating is different, as shown in Table 4 below.

[0163] (Examples 19 to 25)

[0164] The preparation method is similar to that of Example 4, except that the mass proportion of the polymer in the coating is different, as shown in Table 4 below.

[0165] Furthermore, the performance of the secondary battery was tested using the above-mentioned battery performance testing method. The results are shown in Table 4.

[0166] [Table 4]

[0167]

[0168] According to the results in Table 4 above, when the thickness of the coating is within an appropriate range, the time required to reach the overcharge cut-off voltage can be further shortened without significantly affecting the cycle capacity retention rate, thereby achieving the miniaturization of the secondary battery, a higher cycle capacity retention rate, and better overcharge safety.

[0169] Furthermore, according to the results in Table 4 above, when the content of the copolymer in the coating is appropriate, the time required to reach the overcharge cut-off voltage can be further shortened while maintaining a high cycle capacity retention rate, further improving the safety of the battery during overcharge. On the other hand, when the content of the copolymer in the coating is too high, the content of the conductive agent is too low, the conductive network is insufficient, and the cycle capacity retention rate is reduced. When the content of the copolymer in the coating is too low, the time required to reach the overcharge cut-off voltage is prolonged.

[0170] Those skilled in the art should understand that the above embodiments are only some specific embodiments for implementing the present application, and in actual applications, various changes and modifications can be made thereto in form and details, all of which fall within the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode plate, wherein the positive electrode plate comprises: A positive electrode current collector, a positive electrode active material layer, and a coating layer disposed between the positive electrode current collector and the positive electrode active material layer, wherein: The coating layer includes a conductive agent and a copolymer, wherein the copolymer includes the following structural unit (I), structural unit (II) and structural unit (III), In the structural unit (I), R1 and R2 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, or an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms. The substituent of the alkyl group having 1 to 10 carbon atoms which may be substituted, the alkoxy group having 1 to 10 carbon atoms which may be substituted, and the alkenyl group having 1 to 10 carbon atoms which may be substituted in R1 and R2 is at least one selected from the group consisting of a hydroxyl group, an amino group, an amide group, a cyano group, and a carboxyl group, In structural unit (II), R3 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkoxy group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and the substituent in the substituted alkyl group having 1 to 10 carbon atoms, the substituted alkoxy group having 1 to 10 carbon atoms, and the substituted alkenyl group having 1 to 10 carbon atoms in R3 is at least one selected from the group consisting of halogen, hydroxyl, amino, amide, cyano, and carboxyl groups. R4 represents a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an inorganic metal ion, or -R 10 NR 11 R 12 The substituent of the alkyl group having 1 to 10 carbon atoms in R4 is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups, and the inorganic metal ion is sodium ion, potassium ion, lithium ion, calcium ion, and magnesium ion. Among them, R 10 represents an unsubstituted or substituted alkylene group having 1 to 10 carbon atoms or an unsubstituted or substituted alkenylene group having 2 to 10 carbon atoms, R 10 The substituent of the alkylene group having 1 to 10 carbon atoms and the alkenylene group having 2 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups, R 11 and R 12 Each independently represents an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted alkenyl group having 1 to 10 carbon atoms, or an aryl group having 5 to 20 carbon atoms, and R 11 and R 12 The substituent of the alkyl group having 1 to 10 carbon atoms and the alkenyl group having 1 to 10 carbon atoms is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups, In the structural unit (III), R5 and R6 each independently represent a hydrogen atom, an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, and X - represents an anion selected from halogen ions, sulfate ions, and sulfonate ions, and the substituent of the alkyl group having 1 to 10 carbon atoms in R5 and R6 is at least one selected from halogen, hydroxyl, amino, amide, cyano, and carboxyl groups.

2. The secondary battery according to claim 1, wherein In the coating layer, the content of the copolymer is 50 wt % or more.

3. The secondary battery according to claim 2, wherein In the coating layer, the content of the copolymer is 65 wt % to 85 wt %.

4. The secondary battery according to claim 1, wherein The thickness of the coating is 0.1 to 20 μm.

5. The secondary battery according to claim 4, wherein The thickness of the coating is 0.3-10 μm.

6. The secondary battery according to claim 1, wherein The conductive agent includes at least one of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, and graphene.

7. The secondary battery according to claim 1, wherein The coating also includes a binder.

8. The secondary battery according to claim 7, wherein The binder includes styrene acrylic emulsion, sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide and polyacrylate.

9. The secondary battery according to claim 1, wherein The average molar number of the monomer of the structural unit (I) is denoted as a, the average molar number of the monomer of the structural unit (II) is denoted as b, and the average molar number of the monomer of the structural unit (III) is denoted as c, then the copolymer satisfies: 60%≤a / (a+b+c)×100%.

10. The secondary battery according to claim 9, wherein The copolymer satisfies: 70%≤a / (a+b+c)×100%≤85%.

11. The secondary battery according to claim 1, wherein The average molar number of the monomer of the structural unit (I) is recorded as a, the average molar number of the monomer of the structural unit (II) is recorded as b, and the average molar number of the monomer of the structural unit (III) is recorded as c, then the copolymer satisfies: b / (a+b+c)×100%≤20%.

12. The secondary battery according to claim 11, wherein The copolymer satisfies: 5%≤b / (a+b+c)×100%≤15%.

13. The secondary battery according to claim 1, wherein The average molar number of the monomer of the structural unit (I) is recorded as a, the average molar number of the monomer of the structural unit (II) is recorded as b, and the average molar number of the monomer of the structural unit (III) is recorded as c, then the copolymer satisfies: c / (a+b+c)×100%≤20%.

14. The secondary battery according to claim 13, wherein The copolymer satisfies: 10%≤c / (a+b+c)×100%≤20%.

15. The secondary battery according to claim 1, wherein In the structural unit (I), R1 and R2 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms.

16. The secondary battery according to claim 15, wherein In the structural unit (I), R1 and R2 are each independently a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms.

17. The secondary battery according to claim 1, wherein In the structural unit (II), R3 is a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms; R4 is a hydrogen atom, an inorganic metal ion, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms.

18. The secondary battery according to claim 17, wherein In the structural unit (II), R3 is a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms; R4 is a hydrogen atom, an inorganic metal ion, or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms.

19. The secondary battery according to claim 1, wherein In the structural unit (III), R5 and R6 are each independently a hydrogen atom, or an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms; X - is an anion selected from halogen ions.

20. The secondary battery according to claim 19, wherein In the structural unit (III), R5 and R6 are each independently a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms; X - It is an anion selected from chloride ion and bromide ion.

21. The secondary battery according to claim 1, wherein The structural unit (I), the structural unit (II) and the structural unit (III) are copolymerized randomly or in blocks.

22. The secondary battery according to any one of claims 1 to 21, wherein The number average molecular weight of the copolymer is 10,000 to 100,000.

23. The secondary battery according to claim 22, wherein The number average molecular weight of the copolymer is 15,000 to 50,000. 24 . A battery module comprising the secondary battery according to claim 1 .

25. A battery pack comprising the battery module according to claim 24.

26. A device comprising the secondary battery according to any one of claims 1 to 23.

27. A device comprising the battery module of claim 24.

28. A device comprising the battery pack of claim 25.

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