Secondary battery and preparation method therefor, and electric apparatus and energy storage apparatus

Abstract

A secondary battery and a preparation method therefor, and an electric apparatus and an energy storage apparatus, which belong to the technical field of batteries. The secondary battery comprises an electrode sheet, which comprises a current collector, a first coating layer and an active material layer, wherein the first coating layer comprises a thermoplastic polymer and a conductive agent, and in the thickness direction of the electrode sheet, the first coating layer is provided on at least one surface of the current collector and / or the active material layer. The technical solution of the present application facilitates the improvement in the reliability of secondary batteries.

Description

Secondary batteries and their preparation methods, electrical devices, and energy storage devices Cross-references to related applications

[0001] This application claims priority to Chinese Patent Application No. 202411545244.8, filed on October 31, 2024, entitled “Secondary Battery and Method for Preparation Thereof, Electrical Device, Energy Storage Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a secondary battery and its preparation method, power supply device, and energy storage device. Background Technology

[0003] The new energy industry is attracting increasing attention. Within this industry, battery technology is a crucial factor in its development.

[0004] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, and reliability. How to provide a highly reliable rechargeable battery is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a secondary battery and its preparation method, power supply device, and energy storage device to improve the reliability of the secondary battery.

[0006] In a first aspect, a secondary battery is provided, comprising: an electrode, the electrode including a current collector, a first coating and an active material layer, the first coating including a thermoplastic polymer and a conductive agent, the first coating being disposed on at least one surface of the current collector and / or the active material layer along the thickness direction of the electrode.

[0007] In the embodiments of this application, since the first coating includes a conductive agent, electrons can be conducted between the current collector, the first coating, and the active material layer, which is conducive to the normal operation of the secondary battery. When the temperature of the secondary battery is high, the thermoplastic polymer melts and can form a structure that blocks electron transmission, increasing the resistance of the secondary battery. This can reduce the risk of thermal runaway of the secondary battery and improve its reliability.

[0008] In some embodiments, the first coating is disposed between the current collector and at least a portion of the active material layer along the thickness direction of the electrode. Thus, the secondary battery exhibits both high reliability and good electrical performance.

[0009] In some embodiments, the first coating is disposed between the current collector and the active material layer along the thickness direction of the electrode. This results in a larger area of ​​the first coating compared to a coating disposed between the current collector and a portion of the active material layer. At higher temperatures in the secondary battery, this is more effective in blocking electron transport between the current collector and the active material layer, further increasing the resistance of the secondary battery. Consequently, the secondary battery can reach the cutoff voltage earlier during charging, reducing the risk of thermal runaway due to overcharging and improving the reliability of the secondary battery.

[0010] In some embodiments, the electrode includes two opposing layers of the first coating along the thickness direction of the electrode, with the first coating disposed between the current collector and at least a portion of the active material layer on the same side along the thickness direction of the electrode. Thus, compared to having only one layer of the first coating, having two layers of the first coating is beneficial for better blocking electron transport at higher temperatures in the secondary battery, thereby further improving the reliability of the secondary battery.

[0011] In some embodiments, the total thickness d1 of the first coating satisfies: 0.1 μm ≤ d1 ≤ 10 μm. This results in a suitable thickness for the first coating, which not only improves the energy density of the secondary battery but also effectively blocks electron transport at higher temperatures, thus enhancing the reliability of the secondary battery.

[0012] In some embodiments, 0.5 μm ≤ d1 ≤ 4 μm. This results in a suitable thickness for the first coating, which is beneficial for balancing the energy density and reliability of the secondary battery.

[0013] In some embodiments, the first coating further includes an adhesive. The adhesive provides a suitable bond strength between the first coating and the current collector, preventing the first coating from easily detaching from the current collector.

[0014] In some embodiments, the first coating satisfies at least one of the following: the mass content A of the thermoplastic polymer, based on the total mass of the first coating, satisfies: 40wt% ≤ A ≤ 80wt%; the mass content B of the conductive agent, based on the total mass of the first coating, satisfies: 10wt% ≤ B ≤ 25wt%; and the mass content C of the adhesive, based on the total mass of the first coating, satisfies: 10wt% ≤ C ≤ 35wt%.

[0015] In the above embodiments, the thermoplastic polymer in the first coating has a suitable mass content, which facilitates the formation of a relatively uniform structure that blocks electron transport between the current collector and the active material layer when the temperature of the secondary battery is high, thus improving the reliability of the secondary battery; the conductive agent in the first coating has a suitable mass content, so that the electrode has good conductivity and the secondary battery has good electrical performance when the secondary battery is working normally; the binder in the first coating has a suitable mass content, so that the first coating and the current collector are firmly bonded and the first coating is not easy to fall off.

[0016] In some embodiments, the first coating satisfies at least one of the following: 50wt% ≤ A ≤ 70wt%; 10wt% ≤ B ≤ 20wt%; 10wt% ≤ C ≤ 30wt%.

[0017] In the above embodiments, the thermoplastic polymer, conductive agent and binder in the first coating have more suitable mass content, the first coating is not easy to fall off, and it is beneficial to maintain good electrical performance when the secondary battery is working normally, and also beneficial to block the transmission of electrons when the secondary battery temperature is high, so the secondary battery has better overall performance.

[0018] In some embodiments, the thermal decomposition temperature of the adhesive is 300°C to 600°C.

[0019] In the above embodiments, the binder has a high thermal decomposition temperature. When the temperature of the secondary battery is high, the binder will not decompose, and the risk of the first coating falling off from the current collector is low, thereby facilitating the first coating to play a role in improving the reliability of the secondary battery.

[0020] In some embodiments, the adhesive comprises at least one selected from polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyether acrylate, polyacrylate, polyacrylonitrile, sodium alginate, polyvinylidene fluoride, and polyimide. The above adhesives exhibit good bonding performance and high thermal decomposition temperature, which is beneficial for the adhesion between the first coating and the current collector.

[0021] In some embodiments, the melting point T of the thermoplastic polymer is 100°C to 250°C.

[0022] When the melting point of the thermoplastic polymer is greater than or equal to 100°C, the risk of increased resistance and compromised electrical performance of the secondary battery due to polymer melting during electrode and secondary battery fabrication can be reduced. When the melting point of the thermoplastic polymer is less than or equal to 250°C, at higher battery temperatures, the melting of the thermoplastic polymer forms a structure that blocks electron transport, which helps improve the reliability of the secondary battery. Through these settings, the melting point of the thermoplastic polymer falls within a suitable range, resulting in a secondary battery with good electrical performance and high reliability.

[0023] In some embodiments, the melting point T of the thermoplastic polymer is 100°C to 150°C. This provides a suitable melting point range for the thermoplastic polymer, resulting in good electrical performance and high reliability for the secondary battery.

[0024] In some embodiments, the thermoplastic polymer includes at least one of polystyrene, polyethylene, polypropylene, polyimide, polyphenylene sulfide, polyamide, copolymers of ethylene and acrylic acid, copolymers of butyl acrylate and ethyl methacrylate, and their respective modified polymers. These substances have suitable melting points, which is beneficial for improving the reliability and electrical performance of secondary batteries.

[0025] In some embodiments, the current collector includes a main body and a tab, the tab extending from a first end of the main body, the first end being one end of the main body along a first direction, the main body including a first coating area and a second coating area, the second coating area being disposed between the first coating area and the tab, the active material layer and the first coating layer being disposed on at least one side surface of the first coating area; the electrode further includes a second coating layer, the second coating layer being disposed on at least one side surface of a portion of the tab and the second coating area, the second coating layer including an adhesive and an insulating material.

[0026] In the above embodiments, the second coating helps to reduce the risk of short circuits caused by burrs on the electrode and electrodes with opposite polarity, resulting in higher reliability of the secondary battery.

[0027] In some embodiments, the electrode is a positive electrode. This reduces the risk of short circuits caused by the connection between the positive and negative electrodes.

[0028] In some embodiments, the resistance R1 of the positive electrode is 100mΩ to 1000mΩ.

[0029] In some embodiments, the resistance R1 of the positive electrode is 300mΩ to 800mΩ.

[0030] In the above embodiments, the electrode has a suitable resistance, and the secondary battery has suitable electrical performance.

[0031] In some embodiments, the insulating material includes inorganic insulating materials. Inorganic insulating materials are more compatible with electrolytes in secondary batteries and have higher stability.

[0032] In some embodiments, the inorganic insulating material includes at least one of boehmite, alumina, zirconium oxide, titanium oxide, zinc oxide, and silicon oxide.

[0033] The aforementioned materials have good insulation properties and are compatible with electrolytes. The second coating provides good protection and has a low risk of peeling off, which helps improve the reliability of secondary batteries.

[0034] In some embodiments, based on the total mass of the second coating, the mass content D of the insulating material satisfies: 40wt% ≤ D ≤ 80wt%.

[0035] In the above embodiments, the insulating material has a suitable mass content, and the second coating not only provides good protection but also is not easily detached from the current collector.

[0036] In some embodiments, the total thickness d2 of the second coating satisfies: 40μm≤d2≤100μm.

[0037] In the above embodiments, the second coating has a suitable range, which can not only provide good protection, but also take into account the energy density of the secondary battery.

[0038] In some embodiments, the insulating material comprises an organic insulating material, which includes the thermoplastic polymer. Thermoplastic polymers have good insulating properties, which helps reduce the risk of short circuits caused by the overlap of the positive and negative electrode plates.

[0039] In some embodiments, the electrode further includes an insulating layer comprising the thermoplastic polymer, the insulating layer being disposed at least on a first end face of the main body, the first end face being the end surface of the current collector at the first end. The presence of an insulating layer at the first end face can reduce the risk of short circuits caused by the overlap of the first end face with an electrode of opposite polarity.

[0040] In some embodiments, the thickness d3 of the insulating layer is 10 nm to 200 nm. This provides a suitable thickness for the insulating layer, which is beneficial for both providing some protection and achieving a secondary battery with a suitable energy density.

[0041] In some embodiments, the active material layer includes a positive electrode active material, which includes at least one of lithium phosphate and lithium transition metal oxide.

[0042] In some embodiments, the positive electrode active material includes a lithium-containing phosphate, which includes at least one of lithium iron phosphate, lithium manganese phosphate, or lithium manganese iron phosphate.

[0043] Lithium phosphate-containing structures are relatively stable, and secondary batteries, including those made of lithium iron phosphate, exhibit high stability. Furthermore, when the positive electrode active material includes lithium phosphate, the electrode design of this application further reduces the risks associated with overcharging and other thermal abuse, resulting in higher reliability for the secondary battery.

[0044] In some embodiments, the electrode is a negative electrode, the current collector includes a main body and a tab, the tab extends from a first end of the main body, the first end being one end of the main body along a first direction, and the active material layer and the first coating are disposed on at least one side surface of the main body.

[0045] In some embodiments, the resistance of the negative electrode is 1mΩ to 500mΩ.

[0046] In some embodiments, the resistance of the negative electrode is 1mΩ to 5mΩ.

[0047] In the above embodiments, the negative electrode has a suitable resistance, and the secondary battery has suitable electrical performance.

[0048] In some embodiments, the active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, and silicon-containing materials.

[0049] In some embodiments, the negative electrode active material comprises graphite. Graphite has a suitable coefficient of thermal expansion and good electrical conductivity, which helps to reduce the expansion and impedance of the secondary battery, thereby improving its lifespan and electrical performance.

[0050] In some embodiments, the adhesion force F between the active material layer and the current collector is 50 N / m to 300 N / m.

[0051] In the above embodiments, the adhesion force F is suitable, the active material layer and the first coating layer are not easy to fall off, and the secondary battery has high reliability.

[0052] In some embodiments, the volume average particle size Dv50 of the thermoplastic polymer satisfies: 0.2 μm ≤ Dv50 ≤ 2 μm. This results in a suitable particle size for the thermoplastic polymer, a suitable thickness for the first coating, and a suitable energy density for the secondary battery.

[0053] Secondly, a method for preparing a secondary battery is provided, comprising: providing an electrode sheet to prepare the secondary battery; wherein providing the electrode sheet includes: coating at least a portion of the surface of a first coating region of a current collector with a first slurry and an active material slurry to obtain a first coating layer and an active material layer, wherein the first slurry comprises a thermoplastic polymer emulsion and a conductive agent; drying the first coating layer and the active material layer to obtain the electrode sheet; wherein, along the thickness direction of the electrode sheet, the first coating layer is disposed on at least one surface of the current collector and / or the active material layer. The secondary battery prepared by this method has high reliability.

[0054] In some embodiments, the first slurry further includes a binder. The binder facilitates the coating of the thermoplastic polymer and conductive agent onto the surface of the current collector, thus facilitating the preparation of the first coating.

[0055] In some embodiments, the first slurry satisfies at least one of the following: based on the total mass of the first slurry, the mass content A of the thermoplastic polymer in the thermoplastic polymer emulsion satisfies: 40wt% ≤ A ≤ 80wt%; based on the total mass of the first slurry, the mass content B of the conductive agent satisfies: 10wt% ≤ B ≤ 25wt%; based on the total mass of the first slurry, the mass content C of the binder satisfies: 10wt% ≤ C ≤ 35wt%. Thus, the thermoplastic polymer, binder, and conductive agent in the first slurry have suitable mass contents, and the prepared secondary battery has superior electrical performance and high reliability.

[0056] In some embodiments, the thermoplastic polymer emulsion comprises a thermoplastic polymer and a solvent, and the mass content of the thermoplastic polymer is 40 wt% to 70 wt% based on the total mass of the thermoplastic polymer emulsion. This provides a suitable mass content of the thermoplastic polymer in the emulsion, facilitating uniform distribution of the thermoplastic polymer in both the emulsion and the first slurry.

[0057] In some embodiments, the drying temperature is lower than the melting point of the thermoplastic polymer in the thermoplastic polymer emulsion. This reduces the impact of thermoplastic polymer melting during the drying process on the electron transport capability of the electrode and the electrical performance of the secondary battery.

[0058] In some embodiments, the melting point T of the thermoplastic polymer in the thermoplastic polymer emulsion is 100°C to 250°C. When the melting point of the thermoplastic polymer is greater than or equal to 100°C, the risk of increased resistance and compromised electrical performance of the secondary battery due to polymer melting during electrode and secondary battery fabrication can be reduced. When the melting point of the thermoplastic polymer is less than or equal to 250°C, at higher battery temperatures, the melting of the thermoplastic polymer forms a structure that blocks electron transport, which is beneficial for improving the reliability of the secondary battery. Through the above configuration, the melting point of the thermoplastic polymer has a suitable range, resulting in a secondary battery with good electrical performance and high reliability.

[0059] In some embodiments, coating at least a portion of the surface of the first coating area of ​​the current collector with the first paste includes: coating the first paste on at least a portion of the surface of the first coating area of ​​the current collector by gravure printing to form the first coating. Gravure printing is relatively simple, which helps to reduce the complexity of the process, and gravure printing also helps to obtain a more uniform first coating.

[0060] In some embodiments, the preparation method further includes: applying a second slurry to the second coating area of ​​the current collector to obtain a second coating layer, the second slurry comprising an adhesive and an insulating material, the current collector comprising a body portion and a tab, the body portion comprising a first coating area and a second coating area, the second coating area being disposed between the first coating area and the tab. In this way, a second coating layer can be prepared.

[0061] Thirdly, an electrical device is provided, comprising a secondary battery as described in the first aspect and any possible implementation thereof, and / or a secondary battery prepared by a preparation method as described in the second aspect and any possible implementation thereof.

[0062] Fourthly, an energy storage device is provided, comprising a secondary battery as described in the first aspect and any possible implementation thereof, and / or a secondary battery prepared by a preparation method as described in the second aspect and any possible implementation thereof. Attached Figure Description

[0063] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0064] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0065] Figure 2 is a schematic diagram of an electrode sheet according to an embodiment of this application;

[0066] Figure 3 is a cross-sectional view of the electrode in Figure 2 along the AA direction;

[0067] Figure 4 is a cross-sectional view of the electrode in Figure 2 along the BB direction;

[0068] Figure 5 is a schematic diagram of an electrode sheet according to an embodiment of this application;

[0069] Figure 6 is a cross-sectional view of the electrode in Figure 5 along the AA direction;

[0070] Figure 7 is a schematic diagram of the electrode sheet before cutting according to an embodiment of this application;

[0071] Figure 8 is a schematic diagram of an electrode sheet according to an embodiment of this application;

[0072] Figure 9 is a cross-sectional view of the electrode in Figure 8 along the AA direction;

[0073] Figure 10 is a cross-sectional view of the electrode in Figure 8 along the BB direction;

[0074] Figure 11 is a schematic diagram of a method for preparing an electrode sheet according to an embodiment of this application;

[0075] Figure 12 is a schematic diagram of a battery pack according to an embodiment of this application;

[0076] Figure 13 is a schematic diagram of an electrical device according to an embodiment of this application;

[0077] Figure 14 is a schematic diagram of an energy storage device according to an embodiment of this application.

[0078] Figure label:

[0079] 1: Electrode; 10: Current collector; 20: Active material layer; 11: First coating layer; 101: Main body; 102: Tab; 1011: First coating area; 1012: Second coating area; 1011a: First end face; 12: Second coating layer; 13: Insulating layer; 3: Battery cell; 31: Housing; 32: End cap assembly; 33: Electrode assembly; 331: Tab; 34: Current collector; 322: Electrode terminal; 5: Battery pack; 6: Vehicle; 7: Energy storage device. Detailed Implementation

[0080] The embodiments of the secondary battery, its preparation method, power supply device, and energy storage device of this application are 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 practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0081] 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.

[0082] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0083] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0084] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0085] The development of battery technology must consider multiple design factors simultaneously, such as energy density, cycle life, discharge capacity, charge / discharge rate, and reliability. The design of the electrodes in a secondary battery is crucial to its reliability. Electrodes consist of a current collector and an active material layer, allowing electrons to transfer between them for charging and discharging. Electrode design is critical to the charging and discharging process and overall reliability of the secondary battery. In some operating conditions, such as overcharging, the secondary battery temperature is high, which can easily lead to thermal runaway, negatively impacting reliability. Furthermore, the risk of thermal runaway is high during hot-chamber testing of secondary batteries.

[0086] In some treatment methods, additives are added to the electrolyte of the secondary battery. These additives decompose and produce gas as the battery voltage increases, increasing the battery's polarization and thus bringing the voltage to the cutoff point, reducing the risk of thermal runaway caused by overcharging. However, the addition of additives has a certain impact on the battery's electrical performance, making it difficult to balance electrical performance and reliability.

[0087] In view of this, this application provides a secondary battery, which includes an electrode, the electrode including a current collector, a first coating, and an active material layer. The first coating includes a thermoplastic polymer and a conductive agent. Along the thickness direction of the electrode, the first coating is disposed on at least one surface of the current collector and / or the active material layer. The first coating includes a conductive agent, allowing electrons to be conducted between the current collector, the first coating, and the active material layer, facilitating the normal operation of the secondary battery. When the temperature of the secondary battery is high, the thermoplastic polymer melts, forming a structure that blocks electron transport, increasing the resistance of the secondary battery, thereby reducing the risk of thermal runaway and improving the reliability of the secondary battery.

[0088] [Rechargeable Battery]

[0089] The secondary battery in this application embodiment can be a single battery cell or a battery pack. A single battery cell can be the smallest structural unit in a secondary battery.

[0090] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 2 is a schematic diagram of an electrode according to an embodiment of the present application; Figure 3 is a cross-sectional view of the electrode in Figure 2 along the AA direction; and Figure 4 is a cross-sectional view of the electrode in Figure 2 along the BB direction.

[0091] This application provides a secondary battery, which includes an electrode 1. For example, referring to FIG1, the secondary battery can be a single battery cell.

[0092] The electrode 1 includes a current collector 10, a first coating 11, and an active material layer 20. The first coating 11 includes a thermoplastic polymer and a conductive agent.

[0093] Along the thickness direction of the electrode 1, the first coating 11 is disposed on at least one surface of the current collector 10 and / or the active material layer 20.

[0094] As one example, along the thickness direction of the electrode 1, a first coating 11 is disposed between the current collector 10 and at least a portion of the active material layer 20. As another example, along the thickness direction of the electrode 1, at least a portion of the active material layer 20 is disposed between the current collector 10 and the first coating 11.

[0095] The thickness direction of electrode 1 can be the z-direction shown in Figures 3 and 4. It should be noted that the thickness direction of electrode 1 and current collector 10 in this embodiment are the same.

[0096] An active material layer 20 and a first coating layer 11 are disposed on at least one side surface of the current collector 10 in the thickness direction. As an example, as shown in Figures 3 and 4, both sides of the current collector 10 in the thickness direction are provided with the first coating layer 11 and the active material layer 20. As another example, one side surface of the current collector 10 in the thickness direction is provided with the first coating layer 11 and the active material layer 20, and the first coating layer 11 is disposed between the current collector 10 and at least a portion of the active material layer 20 along the thickness direction of the current collector 10. As yet another example, both sides of the current collector 10 in the thickness direction are provided with the active material layer 20, and one side surface of the current collector 10 in the thickness direction is provided with the first coating layer 11; and on the side surface of the current collector 10 where the first coating layer 11 is disposed, the first coating layer 11 is disposed between the current collector 10 and at least a portion of the active material layer 20 along the thickness direction of the current collector 10.

[0097] Along the thickness direction of the electrode 1, a first coating 11 is disposed between the current collector 10 and at least a portion of the active material layer 20. This can be understood as the area of ​​the first coating 11 being less than or equal to the area of ​​the active material layer 20. As an example, along the thickness direction of the electrode 1, the first coating 11 is disposed between the current collector 10 and the active material layer 20, and on one side surface of the current collector 10 along the thickness direction, the area of ​​the first coating 11 is equal to the area of ​​the active material layer 20. As yet another example, along the thickness direction of the electrode 1, the first coating 11 is disposed between the current collector 10 and a portion of the active material layer 20, and on one side surface of the current collector 10 along the thickness direction, the area of ​​the first coating 11 is less than the area of ​​the active material layer 20.

[0098] Along the thickness direction of the electrode 1, at least a portion of the active material layer 20 is disposed between the current collector 10 and the first coating layer 11. This can be understood as follows: at least a portion of the active material layer 20 has one surface connected to the current collector 10 along its thickness direction, and the other surface connected to the first coating layer 11. In other words, at least a portion of the active material layer 20 has the first coating layer 11 disposed on the side away from the current collector 10.

[0099] Thermoplastic polymers can refer to polymers that soften upon heating, solidify upon cooling, and can soften again. For example, when heated to a certain temperature, a thermoplastic polymer changes from solid particles to a flowable state, and upon cooling, it can become a layered or film-like thermoplastic polymer. The first coating 11 includes a thermoplastic polymer, which melts when the first coating 11 is subjected to a higher temperature, forming a structure that blocks electron transport (e.g., forming a thermoplastic polymer film), reducing the risk of thermal runaway of the secondary battery under thermal abuse conditions.

[0100] As an example, structures that block electron transport can be observed using a scanning electron microscope.

[0101] For example, when the first coating 11 is subjected to a high temperature, the thermoplastic polymer melts and forms a structure that blocks electron transport. This increases the resistance of the secondary battery, allowing it to reach the cutoff voltage earlier during charging. This reduces the risk of thermal runaway due to overcharging and improves the reliability of the secondary battery.

[0102] For example, when the temperature of the secondary battery is high and the separator shrinks, there is a risk of short circuit due to the overlap between the positive and negative electrode plates. In this case, the thermoplastic polymer melts and can form a structure that blocks electron transport, which helps to reduce the risk of short circuit caused by the overlap between the positive and negative electrode plates and reduces the risk of thermal runaway of the secondary battery.

[0103] A conductive agent can refer to a substance capable of conducting electricity. The first coating 11 includes a conductive agent, which facilitates the transfer of electrons between the current collector 10 and the active material layer 20, thereby improving the conductivity of the electrode 1 and giving the secondary battery a suitable resistance and electrical performance.

[0104] The secondary battery in this embodiment can be a prismatic secondary battery or a cylindrical secondary battery. The secondary battery can be a secondary battery with a wound electrode assembly or a secondary battery with a stacked electrode assembly.

[0105] The tabs in the electrode sheet in this embodiment can be tabs formed after cutting. For example, the electrode sheet includes multiple tabs spaced apart. The tabs in the electrode sheet in this embodiment can also be tabs that are not cut. For example, the electrode sheet includes a single continuously extending tab.

[0106] In this embodiment, since the first coating 11 includes a conductive agent, electrons can be conducted between the current collector 10, the first coating 11, and the active material layer 20, facilitating the normal operation of the secondary battery. Along the thickness direction of the electrode 1, the first coating 11 is disposed between the current collector 10 and at least a portion of the active material layer 20, or at least a portion of the active material layer 20 is disposed between the current collector 10 and the first coating 11. When the temperature of the secondary battery is high, the thermoplastic polymer melts and can form a structure that blocks electron transport, increasing the resistance of the secondary battery. This allows the secondary battery to reach the cutoff voltage earlier during charging, reducing the risk of thermal runaway due to overcharging and improving the reliability of the secondary battery.

[0107] In some embodiments, along the thickness direction of the electrode 1, a first coating 11 is disposed between the current collector 10 and at least a portion of the active material layer 20. This facilitates the insertion and extraction of active ions (e.g., lithium ions) from the active material layer 20 under normal operating conditions, resulting in better electrical performance of the secondary battery. Furthermore, when the thermoplastic polymer melts and solidifies, a structure that blocks electron transport (e.g., a thermoplastic polymer film) can be formed between the current collector 10 and the active material layer 20, reducing the risk of thermal runaway under thermal abuse conditions.

[0108] In some embodiments, along the thickness direction of the electrode 1, a first coating 11 is disposed between the current collector 10 and the active material layer 20.

[0109] In this embodiment, compared to the first coating 11 being disposed between the current collector 10 and part of the active material layer 20, the first coating 11 has a larger area. When the temperature of the secondary battery is high, it is more effective in blocking the transmission of electrons between the current collector 10 and the active material layer 20, which helps to further increase the resistance of the secondary battery. As a result, the secondary battery can reach the cutoff voltage earlier during charging, reducing the risk of thermal runaway due to overcharging and improving the reliability of the secondary battery.

[0110] In some embodiments, the electrode 1 includes two first coating layers 11 opposite each other along the thickness direction of the electrode 1, and the first coating layers 11 are disposed between the current collector 10 and at least a portion of the active material layer 20 on the same side along the thickness direction of the electrode 1.

[0111] In this embodiment, compared to providing the first coating 11 only on one side of the current collector 10, providing the first coating 11 on both sides of the current collector 10 is beneficial to better block the transmission of electrons when the temperature of the secondary battery is high, thereby further improving the reliability of the secondary battery.

[0112] In some embodiments, the total thickness d1 of the first coating 11 satisfies: 0.1 μm ≤ d1 ≤ 10 μm.

[0113] The total thickness d1 of the first coating 11 can be 0.1μm, 0.2μm, 0.4μm, 0.5μm, 0.8μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm or any value within the above range.

[0114] The total thickness d1 of the first coating 11 is the average value along the thickness direction. For example, measurements are taken at multiple locations of the first coating 11, and the average value of the total thickness at these multiple locations is taken as the total thickness d1 of the first coating 11.

[0115] When the first coating 11 is disposed on both sides of the current collector 10 along the thickness direction of the electrode 1, as shown in Figures 3 and 4, the total thickness d1 of the first coating 11 can be the sum of the thicknesses of the two first coatings 11, i.e., d1 = d11 + d12; when the first coating 11 is disposed on one side of the current collector 10, the total thickness d1 of the first coating 11 is the thickness of the first coating 11.

[0116] When the first coating 11 is disposed on both sides of the current collector 10, the thickness of the two first coatings 11 can be the same or different. As an example, the thickness of the two first coatings 11 is the same.

[0117] When d1 is greater than or equal to 0.1 μm, the first coating 11 can effectively block electron transport when the temperature of the secondary battery is high; when d1 is less than or equal to 10 μm, the space occupied by the first coating can be reduced, thereby increasing the energy density of the secondary battery.

[0118] In the above embodiments, the first coating 11 has a suitable thickness, which is beneficial to improving the energy density of the secondary battery and can also play a good role in blocking electron transmission when the temperature of the secondary battery is high, so that the secondary battery has high reliability.

[0119] In some embodiments, 0.5 μm ≤ d1 ≤ 4 μm. This results in a suitable thickness for the first coating 11, which is beneficial for balancing the energy density and reliability of the secondary battery.

[0120] Furthermore, setting the thickness to 0.5μm≤d1≤4μm is beneficial for the preparation of the first coating 11. For example, when the first coating 11 is prepared by gravure coating, setting the thickness to 0.5μm≤d1≤4μm is compatible with the gravure coating process, which helps to reduce the complexity of preparing the first coating 11.

[0121] In some embodiments, the first coating 11 further includes an adhesive. With the adhesive, the first coating 11 and the current collector 10 have a suitable bond strength, and the first coating 11 is less likely to detach from the current collector 10.

[0122] In some embodiments, the first coating 11 satisfies at least one of the following: the mass content A of the thermoplastic polymer, based on the total mass of the first coating 11, satisfies: 40wt% ≤ A ≤ 80wt%; the mass content B of the conductive agent, based on the total mass of the first coating 11, satisfies: 10wt% ≤ B ≤ 25wt%; and the mass content C of the binder, based on the total mass of the first coating 11, satisfies: 10wt% ≤ C ≤ 35wt%.

[0123] A can be 40wt%, 50wt%, 60wt%, 70wt%, 80wt% or any value within the above range, B can be 10wt%, 15wt%, 20wt%, 25wt% or any value within the above range, and C can be 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or any value within the above range.

[0124] In the above embodiments, the thermoplastic polymer in the first coating 11 has a suitable mass content, which facilitates the formation of a relatively uniform structure that blocks electron transport between the current collector 10 and the active material layer 20 when the temperature of the secondary battery is high, thus improving the reliability of the secondary battery; the conductive agent in the first coating 11 has a suitable mass content, so that the electrode 1 has good conductivity and the secondary battery has good electrical performance when the secondary battery is working normally; the binder in the first coating 11 has a suitable mass content, so that the adhesion between the first coating 11 and the current collector 10 is relatively strong and the first coating 11 is not easy to fall off.

[0125] In some embodiments, the first coating 11 satisfies at least one of the following: 50wt% ≤ A ≤ 70wt%; 10wt% ≤ B ≤ 20wt%; 10wt% ≤ C ≤ 30wt%.

[0126] In the above embodiments, the thermoplastic polymer, conductive agent and binder in the first coating 11 have more suitable mass content, the first coating 11 is not easy to fall off, and it is beneficial to maintain good electrical performance when the secondary battery is working normally, and also beneficial to block the transmission of electrons when the secondary battery temperature is high, so the secondary battery has better comprehensive performance.

[0127] In some embodiments, the thermal decomposition temperature of the adhesive is 300°C to 600°C.

[0128] Thermal decomposition can only refer to the temperature at which the adhesive begins to decompose.

[0129] The thermal decomposition temperature of the adhesive can be 300℃, 350℃, 400℃, 500℃, 600℃ or any value within the above range.

[0130] In the above embodiments, the binder has a high thermal decomposition temperature. When the temperature of the secondary battery is high, the binder will not decompose, and the risk of the first coating 11 falling off the current collector 10 is low, thereby facilitating the first coating 11 to play a role in improving the reliability of the secondary battery.

[0131] In addition, the electrode sheet has a high temperature during the laser cutting process. Setting the thermal decomposition temperature of the adhesive to 300℃~600℃ can reduce the risk of the adhesive decomposing during the cutting process and causing the coating on the current collector to fall off.

[0132] In some embodiments, the adhesive includes at least one selected from polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyether acrylate, polyacrylate, polyacrylonitrile, sodium alginate, polyvinylidene fluoride, and polyimide. The above adhesives have good bonding performance and high thermal decomposition temperature, which is beneficial for the bonding between the first coating 11 and the current collector 10.

[0133] In some embodiments, the melting point T of the thermoplastic polymer is 100°C to 250°C.

[0134] The melting point T of a thermoplastic polymer can be 100°C, 150°C, 200°C, or any value within the above range.

[0135] The melting point of a thermoplastic polymer is the temperature at which it changes from a solid or semi-solid state to a liquid state.

[0136] When the melting point of the thermoplastic polymer is greater than or equal to 100°C, the risk of increased resistance and compromised electrical performance of the secondary battery due to polymer melting during the fabrication of electrode 1 and the secondary battery can be reduced. When the melting point of the thermoplastic polymer is less than or equal to 250°C, at higher temperatures in the secondary battery, the melting of the thermoplastic polymer forms a structure that blocks electron transport, which is beneficial for improving the reliability of the secondary battery. Through the above settings, the melting point of the thermoplastic polymer is within a suitable range, resulting in a secondary battery with good electrical performance and high reliability.

[0137] In some embodiments, the melting point T of the thermoplastic polymer is 100°C to 150°C. This provides a suitable melting point range for the thermoplastic polymer, resulting in good electrical performance and high reliability for the secondary battery.

[0138] In some embodiments, the thermoplastic polymer includes at least one of polystyrene, polyethylene, polypropylene, polyimide, polyphenylene sulfide, polyamide, copolymer of ethylene and acrylic acid, copolymer of butyl acrylate and ethyl methacrylate, and their respective modified polymers.

[0139] Thermoplastic polymers may include polyolefins, such as polyethylene and polypropylene; polyamides include polyarylamides.

[0140] Thermoplastic polymers may also include copolymers of olefins and esters, and copolymers of esters.

[0141] Thermoplastic polymers may include at least one of the following: modified polymers of polystyrene, modified polymers of polyolefins, modified polymers of polyimide, modified polymers of polyester, modified polymers of polyphenylene sulfide, modified polymers of polyamide, and modified polymers of copolymers of butyl acrylate and ethyl methacrylate.

[0142] In the above embodiments, the substances have a suitable melting point, which is beneficial to improving the reliability and electrical performance of the secondary battery.

[0143] In some embodiments, the current collector 10 includes a main body 101 and a tab 102. The tab 102 extends from a first end of the main body 101, which is one end of the main body 101 along a first direction. The main body 101 includes a first coating area 1011 and a second coating area 1012. The second coating area 1012 is disposed between the first coating area 1011 and the tab 102. The active material layer 20 and the first coating layer 11 are disposed on at least one side surface of the first coating area 1011. The electrode 1 also includes a second coating layer 12, which is disposed on at least one side surface of a portion of the tab 102 and the second coating area 1012. The second coating layer 12 includes an adhesive and an insulating material.

[0144] A portion of the tab 102 is provided with a second coating 12. The tab 102 includes a portion close to the main body 101 along a first direction and a portion away from the main body 101. As an example, at least one side surface of the portion of the tab 102 close to the main body 101 along the first direction is provided with the second coating 12.

[0145] The first direction is parallel to the plane where the current collector 10 is located, and the first direction is the direction in which the tab 102 protrudes relative to the main body 101. For example, the first direction is the y-direction in FIG2.

[0146] As shown in Figures 3 and 4, the first coating area 1011 and the second coating area 1012 are connected, and the second coating area 1012 extends from the first coating area 1011 along the first direction.

[0147] Along the thickness direction of the electrode 1, the second coating 12 can be disposed on both sides of the second coating area 1012, or on one side of the second coating area 1012. For example, as shown in Figures 3 and 4, the second coating 12 is disposed on both sides of the second coating area 1012.

[0148] The second coating 12 includes an adhesive and an insulating material. The adhesive facilitates the bonding of the insulating material to the surface of the current collector 10, and the insulating material provides the second coating 12 with higher resistance or insulation. The second coating 12 reduces the risk of short circuits caused by burrs piercing the electrode plate 1 and the separator, leading to positive and negative electrode contact.

[0149] In the above embodiments, the second coating 12 helps to reduce the risk of short circuit caused by the burrs of the electrode 1 and the electrode with opposite polarity, and the secondary battery has high reliability.

[0150] In some embodiments, the electrode is a positive electrode. For example, the electrode shown in Figures 2 to 4 is a positive electrode, in which the positive electrode includes a second coating 12.

[0151] As an example, the current collector in the positive electrode includes aluminum foil. The burrs on the aluminum foil pose a risk of short circuits and self-discharge when they come into contact with the negative electrode of a fully charged secondary battery. By providing a second coating 12 to the positive electrode, the reliability of the secondary battery can be improved.

[0152] In some embodiments, the resistance R1 of the positive electrode is 100mΩ to 1000mΩ.

[0153] The resistance R1 of the positive electrode can be 100mΩ, 200mΩ, 300mΩ, 400mΩ, 500mΩ, 600mΩ, 700mΩ, 800mΩ, 850mΩ, 900mΩ, 1000mΩ or any value within the above range.

[0154] When the resistance R1 of the positive electrode meets the above range, the secondary battery has good electrical performance. The resistance of the above positive electrode can be applied to a variety of different positive electrode active materials, such as lithium iron phosphate, single-crystal ternary materials, polycrystalline ternary materials and their mixtures.

[0155] In some embodiments, the resistance R1 of the positive electrode is 300mΩ to 800mΩ. This results in a suitable resistance for the positive electrode and good electrical performance for the secondary battery.

[0156] As an example, positive electrode active materials include lithium iron phosphate, with R1 ranging from 300 mΩ to 800 mΩ.

[0157] As another example, the positive electrode active material includes lithium iron phosphate, with R1 ranging from 300 mΩ to 500 mΩ. This results in a lower resistance in the positive electrode, which is beneficial for further improving the electrical performance of the secondary battery (e.g., impedance, rate performance, and cycle performance).

[0158] The resistance of electrode 1 is related to the mass content of the conductive agent and the mass content of the thermoplastic polymer in the first coating 11. The lower the mass content of the thermoplastic polymer and the higher the mass content of the conductive agent, the lower the resistance of the electrode.

[0159] In some embodiments, the insulating material includes inorganic insulating materials.

[0160] Inorganic insulating materials can be those that are non-conductive at the battery's operating voltage (e.g., non-conductive at 5V). For example, inorganic insulating materials can have a specific dielectric constant.

[0161] Inorganic insulating materials can also have certain ion transport properties, but inorganic insulating materials are at least insulating at the battery's operating voltage.

[0162] In some embodiments, the inorganic insulating material includes at least one of boehmite, alumina, zirconium oxide, titanium oxide, zinc oxide, and silicon oxide.

[0163] The above-mentioned materials have good insulation properties and are compatible with electrolytes. The second coating 12 can provide good protection and has a low risk of peeling off, which is beneficial to improving the reliability of the secondary battery.

[0164] In some embodiments, the inorganic insulating material may also be an inorganic insulating material having a dielectric constant of 3 or higher, and may include boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), and silicon oxide (SiO2). x (0<x≤2), Tin dioxide (SnO2), Titanium oxide (TiO2), Calcium oxide (CaO), Zinc oxide (ZnO), Zirconia (ZrO2), Yttrium oxide (Y2O3), Nickel oxide (NiO), Hafnium dioxide (HfO2), Cerium oxide (CeO2), Zirconium titanate (ZrTiO3), Barium titanate (BaTiO3), Magnesium fluoride (MgF2), Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1) and Pb (Mg3Nb) 2 / 3 At least one of O3-PbTiO3 (abbreviated as PMN-PT).

[0165] In some embodiments, the inorganic insulating material has the ability to transport active ions and may include lithium phosphate (Li3PO4) or lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium titanium aluminum phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y Glass-like materials (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y, 0 < x < 4, 0 < y < 2), SiS2 type glass (Li x Si y S z (0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 type glass (Li x P y S z At least one of the following: 0 < x < 3, 0 < y < 3, 0 < z < 7.

[0166] In some embodiments, based on the total mass of the second coating 12, the mass content D of the insulating material satisfies: 40wt% ≤ D ≤ 80wt%.

[0167] D can be 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, or any value within the above range.

[0168] In the above embodiments, the insulating material has a suitable mass content, and the second coating 12 not only provides good protection but is also not easily detached from the current collector 10.

[0169] In some embodiments, the total thickness d2 of the second coating 12 satisfies: 40μm≤d2≤100μm.

[0170] The total thickness d2 of the second coating 12 can be 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm or any value within the above range.

[0171] The total thickness d2 of the second coating 12 is the average value along the thickness direction. For example, measurements are taken at multiple locations on the second coating 12, and the average value of the total thickness at these multiple locations is taken as the total thickness d2 of the second coating 12.

[0172] When the second coating 12 is disposed on both sides of the current collector 10 along the thickness direction of the electrode 1, as shown in Figures 3 and 4, the total thickness d2 of the second coating 12 can be the sum of the thicknesses of the two second coatings 12, i.e., d2 = d21 + d22; when the second coating 12 is disposed on one side of the current collector 10, the total thickness d2 of the second coating 12 is the thickness of the second coating 12.

[0173] When the second coating 12 is disposed on both sides of the current collector 10, the thickness of the two second coatings 12 can be the same or different. As an example, the thickness of the two second coatings 12 is the same.

[0174] In the above embodiments, the second coating 12 has a suitable range, which can not only provide good protection, but also take into account the energy density of the secondary battery.

[0175] In some embodiments, the insulating material includes organic insulating materials.

[0176] In some embodiments, the organic insulating material includes a thermoplastic polymer.

[0177] Thermoplastic polymers have good insulation properties, which helps reduce the risk of short circuits caused by the overlap of the positive and negative electrode sheets. Furthermore, when the insulating material of the second coating 12 includes a thermoplastic polymer, it is also beneficial to form a thermoplastic polymer coating at the first end face 1011a during the process of cutting the current collector 10 with the second coating 12 to prepare the tab 102, thereby reducing the risk of short circuits caused by the overlap of the first end face 1011a with an electrode of opposite polarity.

[0178] Figure 5 is a schematic diagram of an electrode sheet according to an embodiment of this application, and Figure 6 is a cross-sectional view of the electrode sheet in Figure 5 along the AA direction. In some embodiments, for example, as shown in Figures 5 and 6, the electrode sheet 1 further includes an insulating layer 13, which comprises a thermoplastic polymer. The insulating layer 13 is at least disposed on the first end face 1011a of the main body portion 101, and the first end face 1011a is the end surface of the current collector 10 at the first end.

[0179] The first end face 1011a is a surface parallel to the thickness direction of the current collector 10. For example, as shown in Figure 6, the first end face 1011a is a surface parallel to the x and z directions.

[0180] Figure 7 is a schematic diagram of the electrode sheet before cutting according to an embodiment of this application. As an example, referring to Figure 7, the first end face 1011a of the main body 101 at the first end can be formed by the following process: during the cutting of the current collector 10, it is cut along the cutting line 124, and the first end face 1011a is the cut end face of the first coating area 1011. After cutting, the current collector 10 at the first end face 1011a is exposed, and burrs may be generated. By providing an insulating layer 13 at the first end face 1011a, the insulating layer 13 can cover the first end face 1011a and the burrs generated by cutting, reducing the risk of the first end face 1011a and the burrs overlapping with the electrode of opposite polarity.

[0181] In the above embodiments, the insulating layer 13 can cover the main body 101 at the first end face 1011a and the burrs, thereby reducing the risk of short circuit caused by the first end face 1011a colliding with an electrode of opposite polarity.

[0182] In some embodiments, the thickness d3 of the insulating layer 13 is 10 nm to 200 nm.

[0183] The thickness d2 of the insulating layer 13 can be 10nm, 20nm, 30nm, 60nm, 80nm, 100nm, 150nm, 200nm or any value within the above range.

[0184] In the above embodiments, the insulating layer 13 has a suitable thickness, which is beneficial for providing a certain degree of protection and for obtaining a secondary battery with a suitable energy density.

[0185] In some embodiments, the first coating area 1011 of the electrode 1 is provided with a first coating layer 11, the first coating area 1011 and the second coating area 1012 are provided with an active material layer 20, and the second coating area 1012 is not coated with a second coating layer 12. In this way, both the first coating area 1011 and the second coating area 1012 of the main body 101 are coated with an active material layer 20, which is beneficial to improving the energy density of the secondary battery.

[0186] In some embodiments, the active material layer 20 includes a positive electrode active material, which includes at least one of lithium phosphate and lithium transition metal oxide.

[0187] In some embodiments, the positive electrode active material includes a lithium-containing phosphate, which includes at least one of lithium iron phosphate or lithium manganese iron phosphate.

[0188] Lithium phosphate-containing structures are relatively stable, and secondary batteries, including those containing lithium iron phosphate, exhibit high stability. Furthermore, when the positive electrode active material includes lithium phosphate, the design of the electrode 1 in this application further reduces the risks associated with thermal abuse such as overcharging, resulting in higher reliability for the secondary battery.

[0189] Figure 8 is a schematic diagram of an electrode sheet according to an embodiment of this application, Figure 9 is a cross-sectional view of the electrode sheet in Figure 8 along the AA direction, and Figure 10 is a cross-sectional view of the electrode sheet in Figure 8 along the BB direction.

[0190] In some embodiments, for example, as shown in Figures 8 to 10, the current collector 10 includes a main body 101 and a tab 102, the tab 102 extending from a first end of the main body 101, the first end being one end of the main body 101 along a first direction, and an active material layer 20 and a first coating layer 11 disposed on at least one side surface of the main body 101.

[0191] In some embodiments, the electrode shown in Figures 8 to 10 is a negative electrode.

[0192] In some embodiments, the resistance R2 of the negative electrode is 1mΩ to 500mΩ.

[0193] The resistance R2 of the negative electrode can be 1mΩ, 2mΩ, 3mΩ, 4mΩ, 5mΩ, 10mΩ, 30mΩ, 60mΩ, 80mΩ, 100mΩ, 200mΩ, 300mΩ, 400mΩ, 500mΩ or any value within the above range.

[0194] When the resistance R1 of the positive electrode meets the above-mentioned range, the secondary battery exhibits good electrical performance. The resistance of the negative electrode described above can be applied to various different negative electrode active materials, such as graphite, hard carbon, silicon-containing materials, and mixtures thereof. Silicon-containing materials can include silicon-carbon composites, silicon-oxygen composites, mixtures of graphite and silicon, etc.

[0195] In some embodiments, the resistance R2 of the negative electrode is 1mΩ to 5mΩ. This results in a lower resistance for the positive electrode, which is beneficial for further improving the electrical performance of the secondary battery.

[0196] As an example, the negative electrode active material includes graphite, and the resistance R2 of the negative electrode sheet is 1mΩ to 5mΩ.

[0197] As another example, the negative electrode active material includes hard carbon or silicon-carbon composite, and the resistance R2 of the negative electrode sheet is 50mΩ to 500mΩ.

[0198] In some embodiments, the active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, and silicon-containing materials.

[0199] In some embodiments, the negative electrode active material includes graphite. Graphite has a suitable coefficient of thermal expansion and good conductivity, which helps to reduce the expansion and impedance of the secondary battery, thereby improving its lifespan and electrical performance.

[0200] In some embodiments, the adhesion force F between the active material layer 20 and the current collector 10 is 50 N / m to 300 N / m.

[0201] F can be 50 N / m, 60 N / m, 80 N / m, 100 N / m, 200 N / m, 300 N / m or any value within the above range.

[0202] The adhesive force between the active material layer 20 and the current collector 10 can be understood as the force that peels the active material layer and the first coating layer 11 as a whole from the current collector 10.

[0203] In the above embodiments, the active material layer 20 and the current collector 10 have suitable adhesion, which can reduce the risk of the active material layer 20 and the first coating 11 falling off from the current collector 10.

[0204] In some embodiments, the volume average particle size Dv50 of the thermoplastic polymer satisfies: 0.2 μm ≤ Dv50 ≤ 2 μm.

[0205] The volume average particle size Dv50 of the thermoplastic polymer can be 0.2μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.6μm, 1.8μm, 2μm or any value within the above range.

[0206] When the volume average particle size Dv50 of the thermoplastic polymer is less than or equal to 2 μm, it is easier to prepare a first coating 11 with a smaller thickness; when the volume average particle size Dv50 of the thermoplastic polymer is greater than or equal to 0.2 μm, it is beneficial to reduce the agglomeration of the thermoplastic polymer and reduce the difficulty of preparing the thermoplastic polymer.

[0207] In the above embodiments, by setting 0.2μm≤Dv50≤2μm, the thermoplastic polymer has a suitable particle size, the first coating 11 has a suitable thickness, and the secondary battery has a suitable energy density.

[0208] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. The secondary battery can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc.

[0209] As an example, as shown in Figure 1, the secondary battery is a square battery cell. The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31.

[0210] The electrode assembly 33 can be made from a positive electrode, a negative electrode, and an insulating element through a winding process or a stacking process.

[0211] The end cap assembly 32 includes electrode terminals 322. For example, as shown in FIG1, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0212] The battery cell 3 also includes a current collector 34, which is used to connect the tab 331 and the electrode terminal 322 of the electrode assembly 33.

[0213] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0214] [Preparation methods for secondary batteries]

[0215] Figure 11 is a schematic diagram of a method for preparing a secondary battery according to an embodiment of this application. This application provides a method for preparing a secondary battery. For example, referring to Figure 11, the secondary battery preparation method 200 can be used to prepare the secondary battery in the above embodiment. The secondary battery preparation method 200 includes the following steps.

[0216] Step 210: Provide electrode 1 to prepare a secondary battery.

[0217] Electrode 1 may include at least one of a positive electrode and a negative electrode. As an example, the positive electrode, the negative electrode, and the separator are wound together and then processed through shaping and other processes to obtain an electrode assembly. The electrode assembly is then placed in a housing and processed through liquid injection, formation, and other processes to obtain a secondary battery.

[0218] Step 210 includes: coating at least a portion of the surface of the first coating area 1011 of the current collector 10 with a first slurry and an active material slurry to obtain a first coating layer 11 and an active material layer 20, wherein the first slurry includes a thermoplastic polymer emulsion and a conductive agent; drying the first coating layer 11 and the active material layer 20 to obtain an electrode 1; wherein, along the thickness direction of the electrode 1, the first coating layer 11 is disposed between the current collector 10 and at least a portion of the active material layer 20 or at least a portion of the active material layer 20 is disposed between the current collector 10 and the first coating layer 11.

[0219] Thermoplastic polymer emulsions are solutions made by mixing thermoplastic polymers with water. Compared to adding thermoplastic polymers directly, adding thermoplastic polymer emulsions helps to accelerate the uniform mixing of the first slurry.

[0220] Furthermore, compared to solid thermoplastic polymer particles, thermoplastic polymers in thermoplastic polymer emulsions have smaller particle sizes, making it easier to prepare a first coating 11 with a smaller thickness.

[0221] In the embodiments of this application, the secondary battery prepared by the above method has high reliability.

[0222] In some embodiments, the first slurry further includes a binder. The binder facilitates the coating of the thermoplastic polymer and conductive agent onto the surface of the current collector 10, thereby facilitating the preparation of the first coating 11.

[0223] In some embodiments, the first slurry satisfies at least one of the following: based on the total mass of the first slurry, the mass content A of the thermoplastic polymer in the thermoplastic polymer emulsion satisfies: 40wt% ≤ A ≤ 80wt%; based on the total mass of the first slurry, the mass content B of the conductive agent satisfies: 10wt% ≤ B ≤ 25wt%; based on the total mass of the first slurry, the mass content C of the binder satisfies: 10wt% ≤ C ≤ 35wt%. Thus, the thermoplastic polymer, binder, and conductive agent in the first slurry have suitable mass contents, and the prepared secondary battery has superior electrical performance and high reliability.

[0224] In some embodiments, the thermoplastic polymer emulsion comprises a thermoplastic polymer and a solvent, wherein the mass content of the thermoplastic polymer is 40 wt% to 70 wt% based on the total mass of the thermoplastic polymer emulsion.

[0225] Based on the total mass of the thermoplastic polymer emulsion, the mass content of the thermoplastic polymer can be 40wt%, 50wt%, 55wt%, 60wt%, 70wt%, or any value within the above range.

[0226] When the mass content of thermoplastic polymer in the thermoplastic polymer emulsion is greater than or equal to 40 wt%, the thermoplastic polymer emulsion contains a relatively large amount of thermoplastic polymer, which facilitates the preparation of the first slurry and the first coating. When the mass content of thermoplastic polymer in the thermoplastic polymer emulsion is less than or equal to 70 wt%, it is beneficial for the thermoplastic polymer to be uniformly dispersed in the thermoplastic polymer emulsion, reducing the agglomeration of thermoplastic polymer, and the thermoplastic polymer emulsion has better stability.

[0227] In the above embodiments, the thermoplastic polymer in the thermoplastic polymer emulsion has a suitable mass content, which facilitates the uniform distribution of the thermoplastic polymer in the thermoplastic polymer emulsion and the first slurry.

[0228] In some embodiments, the drying temperature is lower than the melting point of the thermoplastic polymer in the thermoplastic polymer emulsion.

[0229] The drying temperature is lower than the melting point of the thermoplastic polymer. This prevents the thermoplastic polymer from melting during the drying process of the electrode, thereby reducing the risk of forming a polymer film between the current collector 10 and the active material layer 20 during the preparation of the secondary battery. As a result, the electrode 1 has better conductivity, and the secondary battery has better electrical performance.

[0230] In some embodiments, the drying temperature of the secondary battery is lower than the melting point of the thermoplastic polymer. This reduces the risk of a polymer film forming between the current collector 10 and the active material layer 20 during the preparation of the secondary battery, thereby improving the conductivity of the electrode 1 and the electrical performance of the secondary battery.

[0231] In some embodiments, the melting point T of the thermoplastic polymer in the thermoplastic polymer emulsion is 100°C to 250°C. When the melting point of the thermoplastic polymer is greater than or equal to 100°C, the risk of increased resistance and compromised electrical performance of the secondary battery due to melting of the thermoplastic polymer during the preparation of electrode 1 and the secondary battery can be reduced. When the melting point of the thermoplastic polymer is less than or equal to 250°C, at higher temperatures in the secondary battery, the melting of the thermoplastic polymer forms a structure that blocks electron transport, which is beneficial for improving the reliability of the secondary battery. Through the above settings, the melting point of the thermoplastic polymer has a suitable range, and the secondary battery exhibits good electrical performance and high reliability.

[0232] In some embodiments, the viscosity P of the first slurry is 50 mPa·s to 500 mPa·s. This facilitates the coating of the first slurry.

[0233] The viscosity P of the first slurry can be 50 mPa·s, 100 mPa·s, 250 mPa·s, 500 mPa·s, or any value within the above range.

[0234] The viscosity P of the first slurry can be specifically limited according to actual needs, and the embodiments of this application include, but are not limited to, this.

[0235] In some embodiments, coating at least a portion of the surface of the first coating area 1011 of the current collector 10 with a first paste includes: coating at least a portion of the surface of the first coating area 1011 of the current collector 10 with a first paste by gravure printing to form a first coating 11.

[0236] As an example, gravure coating can be performed using a gravure coating machine. For instance, a gravure coating machine includes a gravure roller, a pressure roller, and a doctor blade, through which the first coating 11 is applied.

[0237] Gravure printing is a relatively simple process, which helps to reduce the complexity of the process. In addition, gravure printing is also conducive to obtaining a more uniform first coating 11.

[0238] In some embodiments, the preparation method further includes: applying a second slurry to the second coating region 1012 of the current collector 10 to obtain a second coating 12. The second slurry includes an adhesive and an insulating material. The current collector 10 includes a main body 101 and a tab 102. The main body 101 includes a first coating region 1011 and a second coating region 1012. The second coating region 1012 is disposed between the first coating region 1011 and the tab 102. In this way, the second coating 12 can be prepared.

[0239] In some embodiments, step 210 includes cutting the current collector 10, which is provided with the first coating 11, the second coating 12 and the active material layer 20, along the cutting line to obtain the electrode 1.

[0240] As an example, a current collector 10 having a first coating 11, a second coating 12, and an active material layer 20 is cut using a laser.

[0241] [Positive electrode plate]

[0242] In this embodiment, the electrode 1 can be a positive electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector.

[0243] The positive electrode current collector can be a metal foil or a composite current collector. For example, the positive electrode current collector can be an aluminum foil.

[0244] Composite current collectors may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0245] The positive electrode film layer includes a positive electrode active material. This positive electrode active material can be any known battery-grade positive electrode active material. For example, it can be a lithium phosphate with an olivine structure, a lithium transition metal oxide, or a spinel-structured material. The general formula for a lithium phosphate with an olivine structure is Li... a A x Mn 1-y B y P 1-z C z O 4-n D nWherein, 0 < a ≤ 1.1, 0.001 ≤ x ≤ 0.1, 0.001 ≤ y < 0.5, 0.001 ≤ z ≤ 0.1, 0.001 ≤ n ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W, B includes one or more of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, C includes one or more of B, S, Si, and N, and D includes one or more of S, F, Cl, and Br. Lithium-containing phosphates with an olivine structure can include at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate. Lithium transition metal oxides can include ternary materials, lithium-rich manganese-based materials, etc. Spinel-structured materials can include lithium manganese oxide, etc.

[0246] In some embodiments, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 One or more of O2 and its modified compounds.

[0247] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption. The molar content of Li in the positive electrode active material varies depending on the discharge state. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. Similarly, the molar content of O in the examples of positive electrode active materials in this application is only an ideal value. Oxygen release from the crystal lattice causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0248] The positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0249] The positive electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0250] [Negative electrode plate]

[0251] In this embodiment, the electrode 1 can be a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0252] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. Composite current collectors can be formed by depositing metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0253] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0254] The negative electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0255] [Electrolytes]

[0256] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0257] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0258] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0259] Solvents may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0260] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and performance additives that can improve certain battery performance, such as performance additives that improve battery overcharge performance, battery high temperature or low temperature performance, etc.

[0261] [Isolation Component]

[0262] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular limitation on the type of separator; any known porous membrane with good chemical and mechanical stability can be selected.

[0263] The material of the separator membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0264] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0265] [Battery Pack]

[0266] This application provides a battery pack. As an example, the secondary battery is the battery pack. Figure 12 is a schematic diagram of a battery pack according to an embodiment of this application. As shown in Figure 12, the battery pack 5 may include multiple battery cells (not shown in the figure).

[0267] The individual battery cells can be directly assembled into battery pack 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into battery pack 5.

[0268] [Electrical appliances]

[0269] This application provides an electrical device including the secondary battery described in the above embodiments.

[0270] Figure 13 is a schematic diagram of an electrical device according to an embodiment of this application. For example, as shown in Figure 13, the electrical device is a vehicle 6, which includes the secondary battery in the above embodiment.

[0271] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use secondary batteries, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0272] [Energy Storage Device]

[0273] This application provides an energy storage device, including the battery described in the above embodiments.

[0274] Figure 14 is a schematic diagram of an energy storage device according to an embodiment of this application. As shown in Figure 14, this application provides an energy storage device 7, including the secondary battery in the above embodiment.

[0275] Energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For example, energy storage devices can store electrical energy during off-peak hours and provide power to relevant users or electrical devices during peak hours.

[0276] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0277] [Example]

[0278] Example 1

[0279] In Example 1, the structure of the positive electrode can be seen in Figures 2 to 4, and the structure of the negative electrode can be seen in Figures 8 to 10.

[0280] In Example 1, the first coating 11 comprises a thermoplastic polymer, a conductive agent, and a binder. Based on the total mass of the first coating 11, the mass content A of the thermoplastic polymer is 70 wt%, the mass content B of the conductive agent is 20 wt%, and the mass content C of the binder is 10 wt%. The total thickness d1 of the first coating 11 is 4 μm, and the thickness of one side of the first coating 11 is 2 μm. The thermoplastic polymer is polypropylene with a melting point T of 150 °C, the conductive agent is superconducting carbon SP, and the binder is polyacrylate.

[0281] In Example 1, the current collector of the positive electrode sheet is aluminum foil, the positive electrode active material in the active material layer is lithium iron phosphate, the total thickness of the active material layer is 110 μm, and the active material layer is disposed on both sides of the first coating area; a second coating is disposed on both sides of the second coating area and the area of ​​the tab near the main body, the second coating includes a binder PVDF and an inorganic insulating material boehmite, the mass ratio of the binder and the inorganic insulating material is 30:70, and the thickness of the second coating is 70 μm;

[0282] In Example 1, the current collector of the negative electrode sheet is copper foil, the negative electrode active material in the active material layer is graphite, the total thickness of the active material layer is 80 μm, and the active material layer is disposed on both sides of the main body.

[0283] Example 2-3

[0284] The difference between Examples 2-3 and Example 1 lies in the different mass contents of the thermoplastic polymer (A), the conductive agent (B), and the binder (C) in the first slurry. Specific parameters are shown in Table 1.

[0285] Example 4

[0286] The difference between Example 4 and Example 1 is that the total thickness d1 of the first coating 11 is different.

[0287] Example 5

[0288] The difference between Example 5 and Example 1 is that the positive electrode sheet does not have a first coating, while the negative electrode sheet only has a first coating on one side surface.

[0289] Example 6

[0290] The difference between Example 6 and Example 1 is that the type of thermoplastic polymer is different. In Example 6, the thermoplastic polymer is polyethylene, and the melting point T of polyethylene is 100°C.

[0291] Comparative Example 1

[0292] The difference between Comparative Example 1 and Example 1 is that neither the positive electrode nor the negative electrode has a first coating.

[0293] The performance of the electrodes in the above embodiments and comparative examples was tested, and the lithium-ion battery cells were tested after the electrodes were prepared. The preparation method of the lithium-ion battery cells is shown below, and the test results are shown in Table 1.

[0294] [Preparation of lithium-ion battery cells]

[0295] (1) Prepare the slurry for the first coating layer.

[0296] Thermoplastic polymer emulsion, conductive agent, and binder are mixed in a certain proportion, and a solvent is added and stirred until homogeneous. The solvent is water, the conductive agent is SP, and the binder is polyacrylate.

[0297] (2) Coating and drying

[0298] The first coating slurry was applied to aluminum foil and copper foil using a gravure coating method; after drying in an oven at 90℃, the thickness of the first coating after drying is shown in Table 1.

[0299] An active material slurry is coated onto the first coating layer to prepare an active material layer, and then rolled to form positive and negative electrode sheets. The active material in the positive electrode sheet is lithium iron phosphate, and the active material in the negative electrode sheet is graphite.

[0300] (3) Fabrication of lithium-ion battery cells

[0301] The above-mentioned positive electrode, negative electrode, separator, and electrolyte are assembled together to form a lithium-ion battery cell. The separator is a porous polyethylene polymer film, the electrolyte solvent is dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, and the electrolyte salt is 1 mol / L LiPF6.

[0302] In Table 1, d1 is the total thickness of the first coating, A is the mass content of the thermoplastic polymer, B is the mass content of the conductive agent, C is the mass content of the binder, R1 is the resistance of the positive electrode, R12 is the resistance of the positive electrode after heating at 160℃ for 10 minutes, R2 is the resistance of the negative electrode, and R22 is the resistance of the negative electrode after heating at 160℃ for 10 minutes. It should be noted that the electrode resistances in Table 1 are the resistances of the electrodes after cold pressing and before formation. The resistances of the electrodes before and after formation remain essentially unchanged. max The table shows the highest temperature of a single lithium-ion battery cell during the overcharge test. In the table, passing the overcharge test indicates that the lithium-ion battery cell did not catch fire or explode during the test; failing the overcharge test indicates that the lithium-ion battery cell caught fire or even exploded during the test. Table 1 shows the test results for the examples and comparative examples.

[0303] As shown in Examples 1-6 and Comparative Example 1, when the first coating is provided, an overcharge test was performed on the lithium-ion battery cell, and the lithium-ion battery cell did not catch fire or explode. In addition, the positive and negative electrode plates in Examples 1-6 have low resistance, which is conducive to the normal charging and discharging of the lithium-ion battery cell during normal use (e.g., under non-overcharge conditions), so that the lithium-ion battery cell can maintain good electrical performance.

[0304] As shown in Examples 1-6 and Comparative Example 1, when the electrode is heated to 160°C for 10 minutes with the first coating, the resistance of the electrode increases significantly. This indicates that the thermoplastic polymer in the first coating can form a structure that blocks electron transport after being exposed to a certain amount of heat. During the overcharge test, the highest temperature of the lithium-ion battery cell in Examples 1-6 is lower than that in Comparative Example 1. This indicates that the thermoplastic polymer in the first coating can form a structure that blocks electron transport after being exposed to a certain amount of heat, thereby increasing the resistance of the lithium-ion battery cell and reaching the charging cutoff voltage of the lithium-ion battery cell earlier. This can stop charging and reduce the risk of fire and explosion caused by overcharging.

[0305] As shown in Examples 1-3, increasing the mass content of the conductive agent and decreasing the mass content of the thermoplastic polymer helps to reduce the resistance of the electrode. By setting the mass content A of the thermoplastic polymer to 50wt% to 80wt%, the mass content B of the conductive agent to 10wt% to 20wt%, and the mass content C of the binder to 10wt% to 30wt%, the electrode has a lower resistance during normal use, which helps to give the lithium-ion battery cell better electrical performance. However, when the temperature is too high, the electrode has a higher resistance, and no fire or explosion occurred during overcharge testing.

[0306] As shown in Examples 1 and 4, the thickness of the first coating is set in the range of 0.5μm to 4μm. The lithium-ion battery cell will not catch fire or explode during overcharge testing. The lithium-ion battery cell has high reliability and is also conducive to improving the energy density of the lithium-ion battery cell.

[0307] As shown in Example 5, by providing the first coating only on one side of the negative electrode sheet, the lithium-ion battery cell can also pass the overcharge test.

[0308] As shown in Examples 1 and 6, the technical solutions of this application are applicable to a variety of different thermoplastic polymers.

[0309] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0310] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0311] [Confirmation of the first coating]

[0312] The electrode was cut open, and the cross-section of the electrode was observed and photographed using a scanning electron microscope. The first coating and its thickness were observed based on the photographs.

[0313] In addition, the thickness of the first coating can be determined based on the thickness of the coating applied during the preparation process.

[0314] [Resistance Testing]

[0315] A film resistance meter is used to test the resistance of an electrode. As an example, the electrode (positive or negative) is placed between the two probes of the film resistance meter, with the two probes facing each other along the thickness direction of the electrode. The resistance of the electrode can then be measured using the film resistance meter.

[0316] [Confirmation of the melting point of thermoplastic polymers]

[0317] The melting point of thermoplastic polymers can be determined using a differential scanning calorimeter (DSC) device. Specifically, as an example, an 8 mg sample is placed in a DSC device, heated in an N2 atmosphere at a flow rate of 50 ml / min, at a heating rate of 10 °C / min, and with a cutoff temperature of 400 °C, thereby testing the melting point of the thermoplastic polymer.

[0318] For example, the melting point of a thermoplastic polymer can be determined based on the specific type of thermoplastic polymer. As an example, for crystalline thermoplastic polymers, the melting point refers to the melting point of the crystalline thermoplastic polymer; for amorphous thermoplastic polymers, the melting point refers to the glass transition temperature of the amorphous thermoplastic polymer.

[0319] [Identification of thermoplastic polymers, conductive agents, and binders]

[0320] The thermoplastic polymer, conductive agent, and binder, along with their mass ratios, can be determined based on the mass and specific types of thermoplastic polymer emulsion, conductive agent, and binder added during the preparation process. Furthermore, the secondary battery can be disassembled to obtain the electrode sheets, and the first coating can be scraped off using a knife. Thermogravimetric infrared spectroscopy (TG-FTIR) is used to heat the sample with the first coating from room temperature to 600°C, and the composition of the first coating is determined by its thermal decomposition temperature, weight loss ratio, and product composition. During this process, the thermal decomposition temperature of the binder can also be determined.

[0321] [Particle size testing]

[0322] The volume average particle size (Dv50) can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions. For example, before preparing the slurry, take an appropriate amount of thermoplastic polymer emulsion and test the average volume particle size of the material using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009.

[0323] For example, a scanning electron microscope can be used to test the electrode to obtain an image of the area of ​​the first coating of the electrode. The size of a specific area of ​​the image is statistically analyzed (e.g., in a size of 30 μm × 30 μm), and the quantity and size of the thermoplastic polymer are measured. The average particle size of the thermoplastic polymer is then calculated, and the average particle size is used as the volume average particle size Dv50 of the thermoplastic polymer.

[0324] [Overcharge Test]

[0325] The overcharge performance of the secondary battery was tested according to GB36276. If the secondary battery did not catch fire or explode during the entire test, it was considered to have passed the overcharge test. It should be noted that the overcharge test standard in this application is more stringent than the power battery test standard GB38031, and the secondary battery in this embodiment has higher reliability.

[0326] [Temperature test of secondary batteries]

[0327] The temperature sensing wire is placed inside the secondary battery to monitor and record the battery temperature in real time during overcharge testing.

Claims

1. A secondary battery, characterized in that, include: An electrode, the electrode comprising a current collector, a first coating and an active material layer, the first coating comprising a thermoplastic polymer and a conductive agent; Wherein, along the thickness direction of the electrode sheet, the first coating is disposed on at least one surface of the current collector and / or the active material layer.

2. The secondary battery according to claim 1, characterized in that, Along the thickness direction of the electrode, the first coating is disposed between the current collector and at least a portion of the active material layer.

3. The secondary battery according to claim 2, characterized in that, Along the thickness direction of the electrode sheet, the first coating is disposed between the current collector and the active material layer.

4. The secondary battery according to any one of claims 1-3, characterized in that, The electrode includes two first coating layers opposite each other along the thickness direction of the electrode, on the same side along the thickness direction of the electrode, the first coating layer being disposed between the current collector and at least a portion of the active material layer.

5. The secondary battery according to any one of claims 1-4, characterized in that, The total thickness d1 of the first coating satisfies: 0.1μm≤d1≤10μm.

6. The secondary battery according to claim 5, characterized in that, 0.5μm≤d1≤4μm.

7. The secondary battery according to any one of claims 1-6, characterized in that, The first coating also includes an adhesive.

8. The secondary battery according to claim 7, characterized in that, The first coating satisfies at least one of the following: Based on the total mass of the first coating, the mass content A of the thermoplastic polymer satisfies: 40wt% ≤ A ≤ 80wt%. Based on the total mass of the first coating, the mass content B of the conductive agent satisfies: 10wt% ≤ B ≤ 25wt%. Based on the total mass of the first coating, the mass content C of the adhesive satisfies: 10wt% ≤ C ≤ 35wt%.

9. The secondary battery according to claim 8, characterized in that, The first coating satisfies at least one of the following: 50wt% ≤ A ≤ 70wt%; 10wt% ≤ B ≤ 20wt%; 10wt% ≤ C ≤ 30wt%.

10. The secondary battery according to any one of claims 7-9, characterized in that, The thermal decomposition temperature of the adhesive is 300℃~600℃.

11. The secondary battery according to any one of claims 7-10, characterized in that, The adhesive includes at least one of polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyether acrylate, polyacrylate, polyacrylonitrile, sodium alginate, polyvinylidene fluoride, and polyimide.

12. The secondary battery according to any one of claims 1-11, characterized in that, The melting point T of the thermoplastic polymer is 100℃~250℃.

13. The secondary battery according to claim 12, characterized in that, The melting point T of the thermoplastic polymer is 100℃~150℃.

14. The secondary battery according to any one of claims 1-13, characterized in that, The thermoplastic polymers include at least one of the following: polystyrene, polyethylene, polypropylene, polyimide, polyphenylene sulfide, polyamide, copolymer of ethylene and acrylic acid, copolymer of butyl acrylate and ethyl methacrylate, and their respective modified polymers.

15. The secondary battery according to any one of claims 1-14, characterized in that, The conductive agent includes carbon-based materials, which include at least one of carbon black, Ketjen black, acetylene black, superconducting carbon, carbon nanofibers, carbon nanotubes, and graphene.

16. The secondary battery according to any one of claims 1-15, characterized in that, The current collector includes a main body and an electrode tab. The electrode tab extends from a first end of the main body, which is one end of the main body along a first direction. The main body includes a first coating area and a second coating area. The second coating area is disposed between the first coating area and the electrode tab. The active material layer and the first coating layer are disposed on at least one side surface of the first coating area. The electrode further includes a second coating, which is disposed on at least one side surface of a portion of the tab and the second coated area, and the second coating includes an adhesive and an insulating material.

17. The secondary battery according to claim 16, characterized in that, The electrode is a positive electrode.

18. The secondary battery according to claim 17, characterized in that, The resistance R1 of the positive electrode is 100mΩ to 1000mΩ.

19. The secondary battery according to claim 18, characterized in that, The resistance R1 of the positive electrode is 300mΩ to 800mΩ.

20. The secondary battery according to any one of claims 16-19, characterized in that, The insulating material includes inorganic insulating materials.

21. The secondary battery according to claim 20, characterized in that, The inorganic insulating material includes at least one of boehmite, alumina, zirconium oxide, titanium oxide, zinc oxide, and silicon oxide.

22. The secondary battery according to any one of claims 16-21, characterized in that, Based on the total mass of the second coating, the mass content D of the insulating material satisfies: 40wt% ≤ D ≤ 80wt%.

23. The secondary battery according to any one of claims 16-22, characterized in that, The total thickness d2 of the second coating satisfies: 40μm≤d2≤100μm.

24. The secondary battery according to any one of claims 16-19, characterized in that, The insulating material includes organic insulating materials, and the organic insulating material includes the thermoplastic polymer.

25. The secondary battery according to claim 24, characterized in that, The electrode further includes an insulating layer comprising the thermoplastic polymer, and the insulating layer is disposed at least on a first end face of the main body, the first end face being the end surface of the current collector at the first end.

26. The secondary battery according to claim 25, characterized in that, The thickness d3 of the insulating layer is 10nm to 200nm.

27. The secondary battery according to any one of claims 17-26, characterized in that, The active material layer includes a positive electrode active material, which includes at least one of lithium phosphate and lithium transition metal oxide.

28. The secondary battery according to claim 27, characterized in that, The positive electrode active material includes a lithium-containing phosphate, which includes at least one of lithium iron phosphate, lithium manganese phosphate, or lithium manganese iron phosphate.

29. The secondary battery according to any one of claims 1-16, characterized in that, The electrode is a negative electrode, and the current collector includes a main body and an electrode tab. The electrode tab extends from a first end of the main body, which is one end of the main body along a first direction. The active material layer and the first coating are disposed on at least one side surface of the main body.

30. The secondary battery according to claim 29, characterized in that, The resistance R2 of the negative electrode is 1mΩ to 500mΩ.

31. The secondary battery according to claim 30, characterized in that, The resistance R2 of the negative electrode is 1mΩ to 5mΩ.

32. The secondary battery according to any one of claims 29-31, characterized in that, The active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, and silicon-containing materials.

33. The secondary battery according to claim 32, characterized in that, The negative electrode active material includes graphite.

34. The secondary battery according to any one of claims 1-33, characterized in that, The volume average particle size Dv50 of the thermoplastic polymer satisfies: 0.2μm≤Dv50≤2μm.

35. The secondary battery according to any one of claims 1-34, characterized in that, The adhesion force F between the active material layer and the current collector is 50 N / m to 300 N / m.

36. A method for preparing a secondary battery, characterized in that, include: Electrodes are provided to prepare the secondary battery; wherein, The provided electrode includes: A first slurry and an active material slurry are coated on at least a portion of the surface of the first coating area of ​​the current collector to obtain a first coating layer and an active material layer, wherein the first slurry comprises a thermoplastic polymer emulsion and a conductive agent; The first coating and the active material layer are dried to obtain the electrode sheet; Wherein, along the thickness direction of the electrode sheet, the first coating is disposed on at least one surface of the current collector and / or the active material layer.

37. The preparation method according to claim 36, characterized in that, The first slurry also includes a binder.

38. The preparation method according to claim 37, characterized in that, The first slurry satisfies at least one of the following: Based on the total mass of the first slurry, the mass content A of the thermoplastic polymer in the thermoplastic polymer emulsion satisfies: 40wt% ≤ A ≤ 80wt%. Based on the total mass of the first slurry, the mass content B of the conductive agent satisfies: 10wt% ≤ B ≤ 25wt%. Based on the total mass of the first slurry, the mass content C of the binder satisfies: 10wt% ≤ C ≤ 35wt%.

39. The preparation method according to any one of claims 36-38, characterized in that, The thermoplastic polymer emulsion comprises a thermoplastic polymer and a solvent, and the mass content of the thermoplastic polymer is 40 wt% to 70 wt% based on the total mass of the thermoplastic polymer emulsion.

40. The preparation method according to any one of claims 36-39, characterized in that, The drying temperature is lower than the melting point of the thermoplastic polymer in the thermoplastic polymer emulsion.

41. The preparation method according to any one of claims 36-40, characterized in that, The thermoplastic polymer in the thermoplastic polymer emulsion has a melting point T of 100℃ to 250℃.

42. The preparation method according to any one of claims 36-41, characterized in that, The coating of at least a portion of the surface of the first coating area of ​​the current collector with the first slurry includes: The first slurry is applied to at least a portion of the surface of the first coating area of ​​the current collector by gravure printing to form the first coating.

43. The preparation method according to any one of claims 36-42, characterized in that, The preparation method further includes: A second slurry is applied to the second coating area of ​​the current collector to obtain a second coating. The second slurry includes an adhesive and an insulating material. The current collector includes a main body and a tab. The main body includes a first coating area and a second coating area. The second coating area is disposed between the first coating area and the tab.

44. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1-35, and / or the method for preparing the secondary battery according to any one of claims 36-43.

45. An energy storage device, characterized in that, Includes the secondary battery according to any one of claims 1-35, and / or the method for preparing the secondary battery according to any one of claims 36-43.

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