Current collector, positive pole piece, electrochemical device and electronic equipment

Abstract

The invention provides a current collector, a positive pole piece, an electrochemical device and electronic equipment, the current collector comprises a polymer layer and a conductive metal layer covering at least one side surface of the polymer layer, and the ratio of the mass percentage content of a carbon element to the mass percentage content of a conductive metal element in the current collector is 0.1-5. The current collector is formed by stacking a polymer layer and a conductive metal layer, the conductive metal layer enables the current collector to have a current collecting effect, and the polymer layer has good strength, ductility and insulativity, plays a buffering role in extrusion and collision, and reduces deformation, so that the internal resistance change rate of an electrochemical device made of the current collector is reduced; and when short circuit occurs, the resistance of the current collector is increased to be almost insulated, so that the safety and the stability of the electrochemical device are improved. The ratio of the mass percentage content of the carbon element to the mass percentage content of the conductive metal element in the current collector per unit area is set to be 0.1-5, so that the current collector can give consideration to good conductivity, strength, safety and stability.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a current collector, a positive electrode, an electrochemical device, and an electronic device. Background Technology

[0002] With the development of technology, electronic products are widely used in daily life. Batteries are used to power these electronic products so that they can operate normally. Batteries are prone to thermal runaway when subjected to abnormal conditions such as impact, compression, or puncture. The large amount of heat and harmful gases released during thermal runaway can cause the battery to catch fire and explode.

[0003] Currently, to improve battery thermal runaway, some technologies reduce the probability of thermal runaway by lowering the battery charging voltage or battery capacity, thereby mitigating the problem. However, this significantly reduces the battery's energy density. Other technologies add PTC (Positive Temperature Coefficient) to the battery's active material layer. As the battery temperature rises, the resistance of the PTC increases, disrupting the conductive pathways of the entire active material layer and preventing further electrochemical reactions. However, the PTC in the active material layer can negatively impact the battery's electrochemical performance. Summary of the Invention

[0004] To overcome the problems existing in related technologies, this disclosure provides a current collector, a positive electrode, and an electrochemical device.

[0005] According to a first aspect of this disclosure, a current collector is provided, the current collector comprising a polymer layer and a conductive metal layer covering at least one surface of the polymer layer;

[0006] In the current collector per unit area, the ratio of the mass percentage of carbon to the mass percentage of conductive metal elements is 0.1-5.

[0007] In some embodiments of this disclosure, the mass percentage of carbon in the current collector per unit area is 5%-80%, and the mass percentage of conductive metal elements is 2%-50%.

[0008] In some embodiments of this disclosure, the elongation of the current collector is ≥10%.

[0009] In some embodiments of this disclosure, the sheet resistance of the current collector is 1mΩ-30mΩ.

[0010] In some embodiments of this disclosure, the material of the polymer layer includes at least one selected from epoxy resin, polytetrafluoroethylene, polyaryletherketone, polyetheretherketone, acrylic resin, polyurethane, polyvinyl alcohol, polybutyl acrylate, polyacrylonitrile, and polyvinylpyrrolidone.

[0011] In some embodiments of this disclosure, the material of the conductive metal layer includes at least one selected from aluminum, copper, titanium, nickel, aluminum alloy, copper alloy, titanium alloy, and nickel alloy.

[0012] In some embodiments of this disclosure, the thickness of the current collector is 2 μm-10 μm.

[0013] According to a second aspect of this disclosure, a positive electrode sheet is provided, the positive electrode sheet comprising a positive electrode material layer stacked thereon and a current collector provided in the first aspect of this disclosure, the positive electrode material layer being disposed on one side surface of the current collector and covering a conductive metal layer of the current collector.

[0014] In some embodiments of this disclosure, the materials forming the positive electrode material layer include a positive electrode active material, a conductive agent, and a binder, and the mass percentage of carbon in the positive electrode material layer per unit area is 0.1%-5%.

[0015] In some embodiments of this disclosure, the adhesion force between the positive electrode material layer and the current collector is ≥50 N / m.

[0016] In some embodiments of this disclosure, the ratio of the mass percentage of carbon in the current collector to the mass percentage of carbon in the positive electrode material layer per unit area is 2-30.

[0017] In some embodiments of this disclosure, the resistance of the positive electrode is ≤30Ω / m.

[0018] In some embodiments of this disclosure, the positive electrode sheet further includes a protective layer disposed between the current collector and the positive electrode material layer;

[0019] The protective layer is formed by a polymer matrix, inorganic fillers, conductive materials, and leveling agents.

[0020] In some embodiments of this disclosure, the adhesion force between the protective layer and the current collector is ≥200 N / m; and / or,

[0021] The adhesion force between the protective layer and the positive electrode material layer is 10N / m-40N / m.

[0022] According to a third aspect of this disclosure, an electrochemical device is provided, the electrochemical device comprising a positive electrode provided in a second aspect of this disclosure.

[0023] According to a fourth aspect of this disclosure, an electronic device is provided, the electronic device comprising the electrochemical device provided in the third aspect of this disclosure.

[0024] The technical solutions provided by the embodiments of this disclosure can include the following beneficial effects: the current collector is formed by stacking a polymer layer and a conductive metal layer. The conductive metal layer makes the current collector conductive, realizing the effect of current collection. The polymer layer, as the carrier of the conductive metal layer, has good strength, ductility, and insulation, and plays a buffering role in compression and collision, reducing deformation and thus reducing the rate of change of internal resistance of the electrochemical device made of the current collector. In the event of a short circuit, the resistance of the current collector increases to almost insulation. By configuring the current collector, this disclosure can improve the high-temperature safety and stability of the electrochemical device without reducing the energy density of the electrochemical device or affecting its electrochemical performance. The mass percentage ratio of carbon to conductive metal in the current collector per unit area is set between 0.1 and 5, so that the current collector can balance good strength, conductivity, and safety and stability.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0027] Figure 1 This is a schematic diagram of a current collector according to an exemplary embodiment.

[0028] Figure 2 This is a schematic diagram of a current collector according to another exemplary embodiment.

[0029] Figure 3 This is a schematic diagram of a positive electrode sheet according to an exemplary embodiment.

[0030] Figure 4 This is a schematic diagram of a positive electrode sheet according to another exemplary embodiment. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0032] With the development of technology, electronic products are widely used in daily life. Batteries are used to power these electronic products so that they can operate normally. Batteries are prone to thermal runaway when subjected to abnormal conditions such as impact, compression, or puncture. The large amount of heat and harmful gases released during thermal runaway can cause the battery to catch fire and explode.

[0033] Currently, to improve battery thermal runaway, some technologies reduce the probability of thermal runaway by lowering the battery charging voltage or battery capacity, thereby mitigating the problem. However, this significantly reduces the battery's energy density. Other technologies add PTC material to the battery's active material layer. As the battery temperature rises, the resistance of the PTC material increases, disrupting the conductive pathways of the entire active material layer and preventing further electrochemical reactions. However, the PTC material in the active material layer can negatively impact the battery's electrochemical performance.

[0034] In view of this, the present disclosure provides a current collector, which is formed by stacking a polymer layer and a conductive metal layer. The conductive metal layer enables the current collector to conduct electricity, achieving the effect of current collection. The polymer layer has good strength, ductility, and insulation, acting as a buffer during compression and impact, reducing deformation and thus lowering the rate of change of internal resistance of the electrochemical device made of the current collector. In the event of a short circuit, the resistance of the current collector increases to almost insulating properties. By configuring the current collector, the present disclosure can improve the high-temperature safety and stability of the electrochemical device without reducing its energy density or affecting its electrochemical performance. The mass percentage ratio of carbon to conductive metal in the current collector per unit area is set between 0.1 and 5, so that the current collector can balance good strength, conductivity, and safety and stability.

[0035] An exemplary embodiment of this disclosure provides a current collector, with reference to... Figure 1 and Figure 2 As shown, the current collector 100 includes a polymer layer 10 and a conductive metal layer 20 covering one or both surfaces of the polymer layer 10. Figure 1 The example shows a current collector 100 with a conductive metal layer 20 disposed on one side surface of the polymer layer 10. Figure 2 The example illustrates a current collector 100 in which conductive metal layers 20 are disposed on both sides of a polymer layer 10. In the current collector 100 per unit area, the ratio of the mass percentage of carbon to the mass percentage of conductive metal is 0.1-5.

[0036] Current collector 100 is a component or structure used to collect current. It is commonly used in electrochemical devices such as primary batteries and secondary batteries. The main function of current collector 100 is to carry positive electrode material to form a positive electrode plate, or to carry negative electrode material to form a negative electrode plate, while collecting current and / or conducting electrons on the positive and / or negative electrodes.

[0037] The polymer layer 10 is formed of a polymer material, giving the current collector 100 good ductility and resistance to breakage. As a supporting carrier for the conductive metal layer 20, the polymer layer 10 provides the current collector 100 with good mechanical strength. Simultaneously, the polymer layer 10 acts as a buffer during compression and impact, reducing deformation and thus lowering the rate of change in internal resistance of the electrochemical device made from the current collector 100, thereby improving stability. Furthermore, due to the low density of the material forming the polymer layer 10, the current collector 100 provided in this disclosure has a lower weight than a metal current collector without increasing the overall thickness. This allows for the placement of more active materials in the electrochemical device formed from the current collector 100, thereby increasing the energy density of the electrochemical device.

[0038] It is understood that the polymer layer 10 can be formed from materials possessing good strength, ductility, thermal stability, chemical stability, and flame retardancy. Exemplarily, the forming material of the polymer layer 10 may include, but is not limited to, polyimide, epoxy resin, polystyrene, polypropylene, polyethylene, chlorinated polyethylene, polyvinylidene fluoride, nitrile rubber, polyurethane, polyvinyl alcohol, nylon-6, polytetrafluoroethylene, ethylene propylene rubber, ethylene-vinyl acetate copolymer, polyetheretherketone, polyaryletherketone, acrylic resin, polybutylene acrylate, polyacrylonitrile, polyvinylpyrrolidone, etc. In some examples, the forming material of the polymer layer 10 may include at least one of epoxy resin, polytetrafluoroethylene, polyaryletherketone, polyetheretherketone, acrylic resin, polyurethane, polyvinyl alcohol, polybutylene acrylate, polyacrylonitrile, and polyvinylpyrrolidone. In some examples, the polymer layer 10 may also be a thin film formed of alumina ceramic, which possesses good high-temperature resistance, thermal stability, chemical stability, and good strength.

[0039] The conductive metal layer 20 is formed of a conductive metal, such as a conductive metal or an alloy of conductive metals. The conductive metal layer 20 enables the current collector 100 to conduct electricity, thus allowing it to collect current. Since the polymer layer 10 serves as the support carrier for the current collector 100, the thickness of the conductive metal layer 20 only needs to ensure the conductivity of the current collector 100 meets requirements; an excessively thick conductive metal layer 20 is unnecessary. In some examples, the thickness of the conductive metal layer 20 can be set to only 500 nm-600 nm, which is sufficient to make the conductivity of the current collector 100 similar to that of conventional metal current collectors. The thinner conductive metal layer 20 significantly reduces the weight of the current collector 100 while maintaining its conductivity, thereby increasing the energy density of the electrochemical device. In some examples, the material forming the conductive metal layer 20 may include at least one of aluminum, copper, titanium, nickel, aluminum alloys, copper alloys, titanium alloys, and nickel alloys.

[0040] In some examples, reference Figure 1 Since the active material is loaded on only one side of the current collector 100 when it is loaded on the surface of the current collector 100, the conductive metal layer 20 can cover only one side of the polymer layer 10 to form the current collector 100. When the active material is loaded on the current collector 100 in the future, the active material is disposed on the side of the current collector 100 on which the conductive metal layer 10 is disposed.

[0041] In other examples, refer to Figure 2 The conductive metal layer 20 covers both sides of the polymer layer 10, forming a sandwich structure for the current collector 100. The polymer layer 10 serves as the middle layer of the current collector 100, giving it good structural stability and excellent conductivity. Subsequently, when loading active materials, the active materials can be placed on either side of the sandwich-structured current collector 100.

[0042] Because the polymer layer 10 has good ductility, it is not easily broken when the electrochemical device is punctured or impacted. Even if it breaks, the conductive metal layer 20 on the surface is relatively thin, and the burrs generated after the conductive metal layer 20 breaks are weak and cannot pierce the diaphragm in the electrochemical device, reducing the risk of the burrs piercing the diaphragm and contacting another electrode, causing a short circuit. In addition, because the polymer layer 10 has good insulation properties and the conductive metal layer 20 is relatively thin, when the electrochemical device short-circuits, the conductive metal layer 20 will melt rapidly before thermal runaway, that is, the conductive metal layer 20 melts like a fuse, causing the resistance of the current collector 100 to increase to almost insulation. The short-circuit current breaks the circuit after contacting the polymer layer 10, so that when the electrochemical device is damaged, it is limited to the puncture site, forming only a "point short circuit" and the short-circuit current does not increase, thereby effectively preventing internal short circuits in the electrochemical device and effectively controlling thermal runaway or even explosion and fire of the electrochemical device.

[0043] In the current collector 100, if the mass percentage of the polymer layer 10 is too large, the thickness of the conductive metal layer 20 may be too small, resulting in poor conductivity of the current collector 100. Conversely, if the mass percentage of the conductive metal layer 20 is too large, the polymer layer 10 may not provide adequate buffering performance or circuit breaking effect. Since the carbon element in the current collector 100 is provided solely by the polymer organic material in the polymer layer 10, and the conductive metal element is provided solely by the conductive metal layer 20, and the current collector 100 is a sheet material with a uniformly layered structure, the mass of the current collector 100 per unit area is fixed. Therefore, given a fixed thickness of the current collector 100, by setting the ratio of the mass percentage of carbon element to the mass percentage of conductive metal element per unit area of ​​the current collector 100 within a certain range, the possible thicknesses of the polymer layer 10 and the conductive metal layer 20 in the current collector 100 can be determined, thereby ensuring that the current collector 100 possesses good conductivity, strength, and safety stability. In some examples, the mass percentage of carbon to the mass percentage of conductive metal elements per unit area of ​​the current collector 100 is 0.1-5. In other examples, the mass percentage of carbon to the mass percentage of conductive metal elements per unit area of ​​the current collector 100 is 0.5-4.8. In still other examples, the mass percentage of carbon to the mass percentage of conductive metal elements per unit area of ​​the current collector 100 is 0.8-4.5.

[0044] In some examples, the mass percentage of carbon in the polymer layer 10 per unit area of ​​the current collector 100 is between 5% and 80%, and the mass percentage of conductive metal in the conductive metal layer 20 is between 2% and 50%. That is, considering the mass of the current collector 100 per unit area as a base X, the ratio of the mass of carbon to base X is 5%-80%, and the ratio of the mass of conductive metal to base X is 2%-50%. With the thickness of the current collector 100 determined, by setting the mass percentage of carbon and the mass percentage of conductive metal in the current collector 100 per unit area, the required thicknesses of the polymer layer 10 and the conductive metal layer 20 in the current collector 100 are determined respectively, thereby ensuring that the current collector 100 possesses good conductivity, strength, and safety stability.

[0045] In some examples, the thickness of the current collector 100 needs to be controlled within a suitable range. If the thickness of the current collector 100 is too small, although a thinner conductive metal layer 20 can ensure that the current collector 100 can effectively collect current, the thinner polymer layer 10 in the current collector 100 can easily lead to a decrease in the strength of the current collector 100, making it unable to provide good support for the active material of the electrochemical device. Furthermore, the electrochemical device is prone to deformation and breakage during cycling, leading to safety issues. Conversely, if the thickness of the current collector 100 is too large, it can easily reduce the thickness of the active material per unit volume of the electrochemical device, resulting in a decrease in the energy density of the electrochemical device. In some examples, the thickness of the current collector 100 can be set between 2 μm and 10 μm. In some examples, the thickness of the current collector 100 can be set between 3 μm and 6 μm.

[0046] In some examples, the conductive metal layer 20 can be formed on the surface of the polymer layer 10 using methods such as evaporation deposition, magnetron sputtering deposition, and electroplating. Evaporation deposition is a process where, under vacuum conditions, a specific heating and evaporation method is used to vaporize the conductive metal material, and the metal atoms are deposited and condensed on the substrate surface to form a film. It should be noted that metals have high melting and boiling points; therefore, when using evaporation deposition to form the conductive metal layer 20, the polymer layer 10 needs to have a certain degree of thermal stability. For example, a polyimide polymer layer 10 can be used to avoid the formation of pores in the polymer layer 10 at high temperatures. Magnetron sputtering deposition is a process where electrons collide with argon gas under the influence of an electric field, and the high-energy argon atoms ionize and then strike the target surface, causing sputtering. The sputtered particles are deposited on the substrate to form a thin film. The conductive metal layer 20 formed by magnetron sputtering has good stability, dense film, good uniformity, and good adhesion to the polymer layer 10.

[0047] The current collector 100 provided in this disclosure has good ductility, which reduces the probability of the current collector 100 breaking when subjected to compression or impact, thereby reducing the probability of short circuits in the electrochemical device and effectively controlling thermal runaway. Ductility is characterized by elongation, which represents the percentage of the material's length elongated before fracture under external force. In some examples, the elongation of the current collector 100 is ≥10%. In some examples, the elongation of the current collector 100 is ≥12%.

[0048] Since the current collector 100 acts as both a carrier for the positive and negative electrode active materials and a collector and conductor for positive and negative electrodes, its function is to conduct electricity. By collecting the current generated by the active materials of the electrochemical device to form a larger current output, the electrochemical device can realize the process of converting chemical energy into electrical energy. Therefore, the current collector 100 needs to have good electrical conductivity. Because the current collector 100 is actually a thin film with a small thickness, sheet resistance is commonly used to evaluate the conductivity and resistivity of thin film structures. Sheet resistance represents the impedance of current per unit area of ​​the material. In some examples, the sheet resistance of the current collector 100 provided in this disclosure is between 1 mΩ and 30 mΩ, which indicates that the current collector 100 has good electrical conductivity.

[0049] In one exemplary embodiment, this disclosure provides a positive electrode sheet, with reference to Figure 3 As shown, the positive electrode 200 includes a positive electrode material layer 210 stacked together and a current collector 100 provided in the above embodiments of the present disclosure. The positive electrode material layer 210 is disposed on one side surface of the current collector 100 and covers the conductive metal layer 20 of the current collector 100.

[0050] The positive electrode 200 is used to fabricate an electrochemical device. In this device, the positive electrode 200 provides a higher electrode potential (relative to the negative electrode) and undergoes an oxidation reaction to release electrons. The positive electrode material layer 210 is formed by coating and compacting a material capable of undergoing an oxidation reaction to release electrons. The positive electrode material layer 210 covers the conductive metal layer 20 of the current collector 100, so that during the discharge process of the electrochemical device, the electrons released by the positive electrode material layer 210 flow to the negative electrode, creating a potential difference between the positive electrode 200 and the negative electrode. The current collector 100 then transmits the generated current to an external circuit.

[0051] In an electrochemical device, the battery cell is formed by a winding or stacking process using a stacked positive electrode 200, a separator, and a negative electrode. Positive ions provided by the positive electrode 200 are transported between the positive and negative electrodes through the pores in the separator, thus completing the charging and discharging process. Therefore, regardless of whether the conductive metal layer 20 is provided on one or both surfaces of the current collector 100, the positive electrode material layer 210 is only provided on one surface of the current collector 100. When the positive electrode 200 is used to manufacture an electrochemical device, simply attaching the surface with the positive electrode material layer 210 to the separator is sufficient to provide positive ions. The side of the positive electrode 200 facing away from the separator does not need a positive electrode material layer 210; even if it were, the positive electrode material layer 210 would not participate in the electrochemical reaction of the electrochemical device, instead increasing the thickness of the positive electrode 200 and reducing the energy density of the electrochemical device.

[0052] Depending on the active material in the positive electrode material layer 210, the type of electrochemical device made from the positive electrode sheet 200 also varies. In some examples, the materials forming the positive electrode material layer 210 include a positive electrode active material, a conductive agent, and a binder. The positive electrode active material, conductive agent, and binder are physically mixed and uniformly loaded onto the surface of the current collector 100, and then cold-pressed to form the positive electrode material layer 210. In some examples, the mass percentage of the positive electrode active material in the positive electrode material layer 210 is between 94% and 99%, the mass percentage of the conductive agent is between 1% and 5%, and the mass percentage of the binder is between 2% and 8%.

[0053] The positive electrode active material is used for oxidation reaction, and may include, but is not limited to, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, etc. The conductive agent may include at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and is used to improve the conductivity of the positive electrode material layer 210. The binder may include at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, polyurethane, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyethylene oxide, and polyamide-imide, and is used to bond the positive electrode active material and the conductive agent, and adhere the positive electrode active material and the conductive agent to the current collector 100 to form the positive electrode material layer 210.

[0054] In some examples, the thickness of the cold-pressed positive electrode material layer 210 can be between 20 μm and 50 μm to ensure that the electrochemical device formed by the positive electrode 200 has good energy density. Since the positive electrode material layer 210 is uniformly loaded on the surface of the current collector 100, the total mass of the positive electrode material layer 210 per unit area can be determined given a fixed thickness. Because the carbon element in the positive electrode material layer 210 is provided by the conductive agent and binder, the mass percentage of carbon element in the positive electrode material layer 210 per unit area is controlled between 0.1% and 5% to ensure that the positive electrode active material per unit mass of the positive electrode material layer 210 results in a high energy density in the electrochemical device, while also ensuring good adhesion between the positive electrode material layer 210 and the current collector 100. In some examples, the mass percentage of carbon element in the positive electrode material layer 210 per unit area can be between 1.0% and 3.5%.

[0055] In some examples, the adhesion force between the positive electrode material layer 210 and the current collector 100 is ≥50 N / m, and there is good adhesion between the positive electrode material layer 210 and the current collector 100, so that the positive electrode active material in the positive electrode material layer 210 and the current collector 100 can achieve good contact and conductivity, reduce the probability of delamination and peeling of the positive electrode material layer 210 and the current collector 100, and ensure that the positive electrode 200 can maintain long-term structural stability and good electrochemical performance, thereby improving the cycle performance and rate performance of the electrochemical device.

[0056] In some examples, since the carbon element in the positive electrode material layer 210 is provided by the conductive agent and binder, the mass percentage of carbon element in the positive electrode material layer 210 per unit area of ​​the positive electrode sheet 200 can reflect the content of the positive electrode active material in the positive electrode material layer 210. Furthermore, the carbon element in the current collector 100 is provided by the polymer layer 10, and the mass percentage of carbon element in the current collector 100 per unit area of ​​the positive electrode sheet 200 can reflect parameters such as the content and thickness of the polymer layer 10. Controlling the ratio of the mass percentage of carbon element in the current collector 100 to the mass percentage of carbon element in the positive electrode material layer 210 per unit area of ​​the positive electrode sheet 200 ensures that the electrochemical device has good energy density and good safety and stability after the positive electrode sheet 200 is formed. In some examples, the ratio of the mass percentage of carbon element in the current collector 100 to the mass percentage of carbon element in the positive electrode material layer 210 per unit area of ​​the positive electrode sheet 200 is 2-30. In some other examples, the ratio of the mass percentage of carbon in the current collector 100 to the mass percentage of carbon in the positive electrode material layer 210 per unit area of ​​the positive electrode 200 is 5-25. In some other examples, the ratio of the mass percentage of carbon in the current collector 100 to the mass percentage of carbon in the positive electrode material layer 210 per unit area of ​​the positive electrode 200 is 8-20.

[0057] During the charging and discharging process of an electrochemical device, positive ions and electrons are transported within the electrode. Positive ions are transported through the electrolyte filling the electrode pores, while electrons are primarily conducted through a three-dimensional network of solid particles, especially conductive agents, to the interface between the active material and the electrolyte to participate in the electrode reaction. The electron conduction characteristics significantly influence the rate performance of the electrochemical device. The main factors affecting the conductivity of the electrode include the interface between the current collector 100 and the positive electrode material layer 210, the distribution of the conductive agent, and the contact state between the positive electrode active materials. Therefore, by measuring the resistance of the positive electrode 200, the uniformity of its microstructure, the formulation characteristics of the positive electrode material layer 210, and the material properties can be determined, thereby predicting the performance of the electrochemical device. In some examples, the resistance of the positive electrode 200 is measured to be ≤30Ω / m, indicating that the positive electrode 200, including the current collector 100, has good conductivity, and the electrochemical device formed by the positive electrode 200 exhibits good electrochemical performance. In some examples, the resistance of the positive electrode 200 was measured to be ≤25Ω / m.

[0058] In one exemplary embodiment, reference Figure 4 As shown, the positive electrode 200, in addition to the stacked current collector 100 and positive electrode material layer 210, also includes a protective layer 220 sandwiched between the current collector 100 and the positive electrode material layer 210. The protective layer 220 is formed from a polymer matrix, inorganic filler, conductive material, and leveling agent. The polymer matrix, inorganic filler, conductive material, and leveling agent are mixed and applied to the surface of the current collector 100 where the conductive metal layer 20 is located by coating, and then cold-pressed to obtain the protective layer 220. The protective layer 220 exhibits a PTC effect, meaning it does not affect electron transport in the electrochemical device at room temperature. The resistance of the protective layer 220 increases with increasing ambient temperature. When the temperature of the electrochemical device reaches a certain value, the resistance of the protective layer 220 can almost completely cut off the conductive path between the positive electrode material layer 210 and the current collector 100, thereby preventing the electrochemical reaction in the electrochemical device and achieving high-temperature safety of the electrochemical device. In some examples, the thickness of the protective layer 220 can be between 0.5 μm and 5 μm.

[0059] In the protective layer 220, the polymer matrix serves as both the PTC matrix and the binder. At room temperature, the polymer matrix acts as a binder, causing the inorganic fillers, conductive materials, leveling agents, and other materials to mix and adhere firmly to the current collector 100, thus giving the protective layer 220 conductivity and preventing interference with electron transport. When the temperature rises, the polymer matrix, as the PTC matrix, expands in volume, increasing the spacing between the conductive materials in the protective layer 220 and consequently increasing the resistance of the protective layer 220.

[0060] Exemplarily, the polymer matrix may include at least one of the following: copolymers of propylene derivatives, polyacrylic acid, polyacrylate, polyacrylic acid ester, polyacrylonitrile, carboxymethyl cellulose salt, polytetrafluoroethylene, polypropylene, nitrile rubber, polyvinylidene fluoride, polyvinylidene chloride, modified polyvinylidene fluoride, modified polyvinylidene chloride, polyvinylidene fluoride copolymer, polyvinylidene chloride copolymer, polyhexafluoropropylene, polyvinylpyrrolidone, polyamide, polyurethane, polyvinyl ether, and polymethyl methacrylate. In some examples, the polymer matrix may include at least one of polyvinylidene fluoride, polyvinylidene chloride, modified polyvinylidene fluoride, modified polyvinylidene chloride, polyvinylidene fluoride copolymer, and polyvinylidene chloride copolymer. In some examples, the mass-average molecular weight of the polymer matrix is ​​between 50W and 100W. In some examples, the elongation of the polymer matrix is ​​not less than 40%.

[0061] The conductive material in the protective layer 220 is used to ensure good conductivity of the protective layer 220 at room temperature. The conductive material can be selected from at least one of conductive carbon-based materials, conductive metal materials, and conductive polymer materials. The conductive carbon-based materials can include at least one of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, flake graphite, and vapor-grown carbon fiber (VGCF). The conductive metal materials can include at least one of aluminum powder, nickel powder, and gold powder. The conductive polymer materials can include at least one of conductive polythiophene, conductive polypyrrole, and conductive polyaniline.

[0062] Inorganic fillers can include, but are not limited to, alumina, titanium dioxide, magnesium oxide, zinc oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, boehmite, gibbsite, barium sulfate, calcium sulfate, calcium silicate, magnesium hydroxide, zirconium oxide, silicon oxide, calcium silicate, calcium carbonate, lithium cobalt oxide, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, lithium titanate, etc. Inorganic fillers can stabilize the protective layer 220, preventing the electrolyte in the electrochemical device from dissolving or swelling the polymer matrix in the protective layer 220, thereby ensuring the PTC effect of the protective layer 220. Furthermore, inorganic fillers can also ensure that the protective layer 220 is not easily deformed during the compaction process of the positive electrode 200.

[0063] The leveling agent allows various materials to adhere uniformly to the surface of the current collector 100 during the formation of the protective layer 220. The leveling agent material may include, but is not limited to, at least one of the following: olefin derivative polymers, acrylate polymers, siloxane polymers, acrylate polymers, alcohol compounds, ether compounds, or fluorocarbon compounds.

[0064] In some examples, in the protective layer 220, the polymer matrix comprises 45%-75% by mass, the conductive material comprises 5%-25% by mass, the inorganic filler comprises 20%-40% by mass, and the leveling agent comprises 2%-5% by mass. In some examples, in the protective layer 220, the polymer matrix comprises 50%-75% by mass, the conductive material comprises 5%-15% by mass, the inorganic filler comprises 15%-45% by mass, and the leveling agent comprises 2%-4% by mass.

[0065] In some examples, after the protective layer 220 and the positive electrode material layer 210 are disposed on the surface of the current collector 100, the protective layer 220 and the positive electrode material layer 210 are cold-pressed to allow the current collector 100 to load as much positive electrode active material as possible. After cold pressing, the adhesion force between the layers of the positive electrode 200 is measured to determine whether the positive electrode 200 can maintain long-term structural stability and good electrochemical performance. In some examples, the adhesion force between the protective layer 220 and the current collector 100 is ≥200 N / m. In some examples, the adhesion force between the protective layer 220 and the positive electrode material layer 210 is 10 N / m-40 N / m. In some examples, the adhesion force between the protective layer 220 and the current collector 100 is ≥200 N / m, and the adhesion force between the protective layer 220 and the positive electrode material layer 210 is 10 N / m-40 N / m.

[0066] In one exemplary embodiment, this disclosure also provides an electrochemical device, which is a device capable of undergoing redox electrochemical reactions. The electrochemical device can be a battery cell, a primary battery, or a secondary battery. Depending on the different positive electrode active materials in the positive electrode material layer of the positive electrode sheet, the electrochemical device can be a lithium-ion battery, a potassium-ion battery, a sodium-ion battery, etc.

[0067] The electrochemical device includes the positive electrode provided in the above embodiments of this disclosure. The electrochemical device is formed by stacking positive electrode sheets, a separator, and negative electrode sheets, and then placing them in a battery pack formed by a battery casing through a winding or stacking process. An electrolyte is injected into the battery pack, followed by encapsulation, formation treatment, and molding. The separator, negative electrode sheet, and electrolyte are all conventional materials in the art and will not be described in detail here. Because the electrochemical device includes the positive electrode provided in the above embodiments of this disclosure, it exhibits good energy density and high-temperature stability. Testing shows that the fully charged voltage of the electrochemical device is not less than 4.5V.

[0068] The safety performance of the electrochemical device was evaluated by conducting an impact test according to GB31241 standard. After fully charging the device according to the prescribed test method, it was placed on a platform. A metal rod with a diameter of 15.8 mm ± 0.2 mm was placed horizontally on the upper surface of the battery's geometric center. A weight of 9.1 kg ± 0.1 kg was dropped freely from a height of 610 mm ± 25 mm onto the surface of the battery containing the metal rod. The device automatically reset after the impact, and the results were observed for 6 hours. The experimental results of the electrochemical device provided in this disclosure show that it did not ignite or explode, indicating that the electrochemical device can effectively prevent thermal runaway and has good safety performance.

[0069] The electrochemical device, after undergoing the impact test, was disassembled, and the adhesion between layers in the stacked structure of the positive electrode was tested again. The results showed that after the impact test, the adhesion between the current collector and the protective layer was no less than 170 N / m, and the adhesion between the protective layer and the positive electrode material layer was 8 N / m-36 N / m. This indicates that after an impact, the positive electrode material layer is not easily detached, and the positive and negative electrodes are unlikely to short-circuit. Therefore, the electrochemical device has good safety performance. Furthermore, it can be seen that after the impact test, the change rate of adhesion between each pair of the current collector, protective layer, and positive electrode material layer is no more than 20%. This indicates that the change rate of adhesion between the electrodes is small after an impact, and the electrochemical device still has good charge and discharge capabilities after an impact, demonstrating a good service life.

[0070] In one exemplary embodiment, this disclosure also provides an electronic device, which may include, but is not limited to, at least one of a mobile phone, tablet computer, laptop computer, wearable device, camera, vehicle-mounted system, electric train, and ship. The specific type of electronic device is not limited in the embodiments of this application. The electronic device may include the electrochemical device provided in the above embodiments of this disclosure. Because electrochemical devices have good high-temperature safety and cycle life, and also have high energy density, the electronic device has a good service life, providing users with a good user experience and safety.

[0071] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0072] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A current collector, characterized in that, The current collector includes a polymer layer and a conductive metal layer covering at least one surface of the polymer layer; In the current collector per unit area, the ratio of the mass percentage of carbon to the mass percentage of conductive metal elements is 0.1-5.

2. The current collector according to claim 1, characterized in that, In the current collector per unit area, the mass percentage of carbon element is 5%-80%, and the mass percentage of conductive metal element is 2%-50%.

3. The current collector according to claim 1, characterized in that, The elongation of the current collector is ≥10%.

4. The current collector according to claim 1, characterized in that, The sheet resistance of the current collector is 1mΩ-30mΩ.

5. The current collector according to claim 1, characterized in that, The polymer layer is made of at least one of epoxy resin, polytetrafluoroethylene, polyaryletherketone, polyetheretherketone, acrylic resin, polyurethane, polyvinyl alcohol, polybutyl acrylate, polyacrylonitrile, and polyvinylpyrrolidone.

6. The current collector according to claim 1, characterized in that, The material of the conductive metal layer includes at least one of aluminum, copper, titanium, nickel, aluminum alloy, copper alloy, titanium alloy, and nickel alloy.

7. The current collector according to claim 1, characterized in that, The thickness of the current collector is 2μm-10μm.

8. A positive electrode sheet, characterized in that, The positive electrode includes a stacked positive electrode material layer and a current collector as described in any one of claims 1-7, wherein the positive electrode material layer is disposed on one side surface of the current collector and covers the conductive metal layer of the current collector.

9. The positive electrode sheet according to claim 8, characterized in that, The positive electrode material layer comprises a positive electrode active material, a conductive agent, and a binder, and the mass percentage of carbon in the positive electrode material layer per unit area is 0.1%-5%.

10. The positive electrode sheet according to claim 9, characterized in that, The adhesion force between the positive electrode material layer and the current collector is ≥50 N / m.

11. The positive electrode sheet according to claim 9, characterized in that, In the positive electrode sheet per unit area, the ratio of the mass percentage of carbon in the current collector to the mass percentage of carbon in the positive electrode material layer is 2-30.

12. The positive electrode sheet according to claim 8, characterized in that, The resistance of the positive electrode is ≤30Ω / m.

13. The positive electrode sheet according to any one of claims 8-12, characterized in that, The positive electrode sheet further includes a protective layer, which is disposed between the current collector and the positive electrode material layer; The protective layer is formed by a polymer matrix, inorganic fillers, conductive materials, and leveling agents.

14. The positive electrode sheet according to claim 13, characterized in that, The adhesion strength between the protective layer and the current collector is ≥200 N / m; and / or, The adhesion force between the protective layer and the positive electrode material layer is 10N / m-40N / m.

15. An electrochemical device, characterized in that, The electrochemical device includes the positive electrode as described in any one of claims 8-14.

16. An electronic device, characterized in that, The electronic device includes the electrochemical device of claim 15.

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