A composite current collector and its application

Abstract

The present invention provides a composite current collector and its application, which includes a current collector base layer, a first functional layer and a second functional layer respectively located on both sides of the current collector base layer, and N shrinkable thermosensitive conductive structures, where N≥1; wherein, the first functional layer and the second functional layer at least include a gel layer and a metal layer arranged in layers, and the gel layer includes a polymer matrix and a flame retardant; when the application temperature is lower than the shrinkage temperature of the shrinkable thermosensitive conductive structure, the shrinkable thermosensitive conductive structure electrically connects the metal layer of the first functional layer and the metal layer of the second functional layer; when the application temperature is higher than the shrinkage temperature, the shrinkable thermosensitive conductive structure shrinks, and the metal layer of the first functional layer and the metal layer of the second functional layer are electrically open-circuited, releasing the flame retardant. The composite current collector provided by the present invention can have excellent safety performance and conductive performance at the same time.

Description

[0001] This application claims the priority of a Chinese patent application with the application number 202411099248.8 and the application title "A Composite Current Collector and Its Application" submitted to the Chinese Patent Office on August 12, 2024. The entire content of which is incorporated herein by reference. Technical Field

[0002] The present invention relates to a composite current collector and its application, belonging to the field of electrochemistry. Background Art

[0003] Secondary batteries represented by lithium-ion secondary batteries are widely used in electric vehicles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. With the continuous development and large-scale application of the battery industry, people's requirements for the mass density and safety of batteries are getting higher and higher.

[0004] As one of the core components of the battery, the performance of the current collector directly affects the mass density and safety of the battery. Among them, traditional current collectors for batteries are mostly metal current collectors. However, when metal current collector batteries are damaged by mechanical stress (especially extrusion, puncture, impact), thermal stress, or electrical stress, it is very easy to cause internal short circuits, resulting in thermal runaway of the battery and leading to safety accidents. Therefore, endowing the battery current collector with flame retardant properties is one of the effective means to reduce the internal short circuit problem of the current collector, prevent thermal runaway, and improve safety.

[0005] Currently, the safety performance is usually achieved by introducing flame retardants into the current collector. However, introducing flame retardants will reduce the conductivity of the current collector, severely restricting the development of the battery. How to improve the conductivity of the current collector while ensuring the safety performance of the battery has become an urgent problem in this field. Summary of the Invention

[0006] Aiming at the problems of the above-mentioned prior art, the present invention provides a composite current collector. By improving the structure and composition of the composite current collector, when the lithium-ion battery experiences abnormal situations such as puncture, extrusion, and collision, resulting in internal short circuit, it can prevent the thermal runaway of the lithium-ion battery, thereby improving the safety performance of the lithium-ion battery. At the same time, the current collector also has good conductivity and can reduce the internal resistance of the lithium-ion battery.

[0007] The present invention also provides a pole piece including the above-mentioned current collector.

[0008] On the one hand, the present invention provides a composite current collector, including a current collector substrate, a first functional layer and a second functional layer respectively located on both sides of the current collector substrate, and N shrinkable thermosensitive conductive structures, N≥1;

[0009] Wherein, in a direction gradually away from the current collector base layer, the first functional layer at least includes a gel layer and a metal layer arranged in a stacked manner, and the second functional layer at least includes a gel layer and a metal layer arranged in a stacked manner;

[0010] The gel layer includes a polymer matrix and a flame retardant;

[0011] When the application temperature is lower than the shrinkage temperature of the shrinkable thermosensitive conductive structure, the shrinkable thermosensitive conductive structure penetrates through the first functional layer, the second functional layer, and the current collector base layer, and electrically connects the metal layer of the first functional layer and the metal layer of the second functional layer;

[0012] When the application temperature is higher than the shrinkage temperature, the shrinkable thermosensitive conductive structure shrinks, the metal layer of the first functional layer and the metal layer of the second functional layer are electrically open, and the flame retardant is released.

[0013] For the composite current collector as described above, the shrinkage temperature of the shrinkable thermosensitive conductive structure is 90 - 150 °C.

[0014] For the composite current collector as described above, the area ratio of the shrinkable thermosensitive conductive structure on the surface of the composite current collector is 20% - 60%.

[0015] For the composite current collector as described above, the mass ratio of the polymer matrix to the flame retardant is 1:(0.1% - 5%).

[0016] For the composite current collector as described above, the first functional layer and the second functional layer also independently include an adhesive layer, and the adhesive layer is located between the gel layer and the metal layer;

[0017] And / or, the adhesive layer includes at least one of aramid, polyethylene, hydroxyl-modified silica particles, and a mixture of silica and polyacrylic resin;

[0018] And / or, the thickness of the adhesive layer is 0.01 - 1 μm.

[0019] For the composite current collector as described above, the shrinkable thermosensitive conductive structure penetrates through the current collector base layer and protrudes from the surface of the first functional layer;

[0020] And / or, the shrinkable thermosensitive conductive structure penetrates through the current collector base layer and protrudes from the surface of the second functional layer.

[0021] For the composite current collector as described above, the length of the shrinkable thermosensitive conductive structure protruding from the surface of the first functional layer is L1, and the thickness of the composite current collector is L, satisfying: L1 / L = 1% - 10%;

[0022] And / or, the length of the shrinkable thermosensitive conductive structure protruding from the surface of the second functional layer is L2, and the thickness of the composite current collector is L, satisfying: L2 / L = 1% - 10%.

[0023] For the composite current collector as described above, the material of the shrinkable thermosensitive conductive structure is selected from bismuth-tin alloy or tin-indium alloy; and / or, the polymer matrix includes a cross-linked polymer containing an EO main chain and an amide group block;

[0024] And / or, the flame retardant is a phosphorus-based flame retardant;

[0025] And / or, the current collector base layer is selected from a PET layer or a PVDF layer;

[0026] And / or, the metal layer is selected from copper or aluminum.

[0027] For the composite current collector as described above, the thickness of the current collector base layer is 1 - 10 μm;

[0028] And / or, the thickness of the gel layer is 1 - 5 μm;

[0029] And / or, the thickness of the metal layer is 0.01 - 1 μm;

[0030] And / or, the length of the shrinkable thermosensitive conductive structure is 2.5 - 17 μm.

[0031] On the other hand, the present invention provides an electrode sheet including the composite current collector as described above.

[0032] For the composite current collector provided by the present invention, by arranging functional layers on both sides of the current collector base layer and a shrinkable thermosensitive conductive structure penetrating through the functional layers and the current collector base layer, the lithium-ion battery including this composite current collector can effectively avoid thermal runaway in case of abnormalities and improve the safety performance of lithium ions; at the same time, the composite current collector with a shrinkable thermosensitive conductive structure also has good electrical conductivity and can reduce the resistance of the lithium-ion battery.

[0033] The electrode sheet provided by the present invention includes the above composite current collector, so this electrode sheet has good safety performance and electrical conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural diagram of a composite current collector provided for a specific embodiment of the present invention;

[0035] Figure 2 It is a structural diagram of the composite current collector provided in Example 6 of the present invention;

[0036] Figure 3 It is a structural diagram of the composite current collector provided in Examples 3, 4, and 5 of the present invention;

[0037] Figure 4 Structural diagram of the composite current collector provided in Embodiments 1 and 2 of the present invention;

[0038] Figure 5 Structural diagram of the composite current collector provided in Comparative Example 4 of the present invention.

[0039] Reference numerals: 1 - current collector base layer; 21 - first functional layer, 22 - second functional layer; 201 - gel layer; 202 - metal layer; 203 - adhesive layer; 3 - shrinkable thermosensitive conductive structure. Detailed implementation manners

[0040] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] On the one hand, the present invention provides a composite current collector, as Figure 1 shown, including a current collector base layer 1, a first functional layer 21 and a second functional layer 22 respectively located on both sides of the current collector base layer, and N shrinkable thermosensitive conductive structures 3, N≥1; wherein, in the direction gradually away from the current collector base layer 1, the first functional layer 21 at least includes a gel layer 201 and a metal layer 202 stacked, and the second functional layer 22 at least includes a gel layer 201 and a metal layer 202 stacked; the gel layer 201 includes a polymer matrix and a flame retardant; when the application temperature is less than the shrinkage temperature of the shrinkable thermosensitive conductive structure 3, the shrinkable thermosensitive conductive structure 3 penetrates through the first functional layer 21, the second functional layer 22, and the current collector base layer 1, and electrically connects the metal layer 202 of the first functional layer 21 and the metal layer 202 of the second functional layer 22; when the application temperature is greater than the shrinkage temperature, the shrinkable thermosensitive conductive structure 3 shrinks, and the metal layer 201 of the first functional layer 21 is electrically disconnected from the metal layer 202 of the second functional layer 22, and the flame retardant is released.

[0042] The application temperature in the present invention refers to the ambient temperature of the composite current collector.

[0043] Among them, the shrinkable thermosensitive conductive structure 3 in the present invention includes a shrinkable thermosensitive conductive material, which has the characteristic of volume shrinkage when the application temperature is higher than the shrinkage temperature. Therefore, when the application temperature is lower than the shrinkage temperature of the shrinkable thermosensitive conductive structure 3, the shrinkable thermosensitive conductive structure 3 penetrates through the current collector base layer 1, the first functional layer 21 and the second functional layer 22, and electrically connects the metal layer of the first functional layer 21 and the metal layer of the second functional layer 22; when the application temperature is higher than the shrinkage temperature, the shrinkable thermosensitive conductive structure 3 shrinks, and the metal layer of the first functional layer 21 and the metal layer of the second functional layer 22 are electrically disconnected. After the metal layer of the first functional layer 21 and the metal layer of the second functional layer 22 are electrically disconnected, the current collector is electrically disconnected, increasing the impedance of the battery, preventing the spread of battery thermal runaway, and improving the safety of the battery.

[0044] The structure of the shrinkable thermosensitive conductive structure 3 can be rod-shaped, spherical, reticular, frustum-shaped, etc.

[0045] The present invention does not limit the specific preparation process of the composite current collector, and common preparation processes in the art can be selected according to actual situations.

[0046] In a specific embodiment, the gel layer 201 and the current collector base layer 1 can be combined together by hot melt adhesion or chemical adhesion.

[0047] When the battery undergoes short circuit or local short circuit, causing the temperature inside the battery cell to rise and the application temperature to be higher than the shrinkage temperature, the shrinkable thermosensitive conductive structure 3 shrinks, exposing the gel layer 201. Subsequently, the flame retardant in the gel layer is released, increasing the flame retardancy of the composite current collector and raising the thermal failure temperature of the electrode. When there is a spark at the electrode, it can capture hydrogen radicals and hydroxyl radicals, and at the same time release inert gases to achieve a flame retardant effect, further improving the safety of the battery. At the same time, this setting can effectively prevent the contact between the flame retardant and the electrolyte when the battery does not undergo thermal failure, without affecting the electrochemical performance of the battery.

[0048] According to the technical solution provided by the present invention, after the composite current collector is applied to a lithium-ion battery, it can improve the conductivity of the composite current collector and reduce the internal resistance of the current collector under the use state. When a thermal runaway is triggered by an internal short circuit in the battery, it can increase the safety of the battery through electrical disconnection. The inventor analyzed this phenomenon and believes that it may be: under the use state, the shrinkable thermosensitive conductive structure 3 connects the metal layer 202 and the current collector matrix 1, improving the conductivity. In the thermal runaway state, the shrinkable thermosensitive conductive structure 3 undergoes volume shrinkage, causing electrical disconnection between the metal layer and the current collector matrix, resulting in electrical disconnection of the current collector, increasing the impedance of the battery, preventing the spread of battery thermal runaway, and improving the safety of the battery.

[0049] Further, in a specific embodiment of the present invention, the shrinkage temperature of the shrinkable thermosensitive conductive structure is 90 - 150 °C.

[0050] Specifically, the shrinkage temperature of the shrinkable thermosensitive conductive structure includes, but is not limited to, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, or the range composed of any two of them.

[0051] It can be understood that the type of the shrinkable thermosensitive conductive structure can select the material type that meets the above shrinkage temperature. In a specific embodiment, the type of the shrinkable thermosensitive conductive structure is selected from bismuth - tin alloy or tin - indium alloy.

[0052] When the shrinkage temperature of the shrinkable thermosensitive conductive structure is greater than or equal to 90 °C, the shrinkable thermosensitive conductive structure has more excellent temperature responsiveness, can more accurately control the electrical connection situation at different application temperatures, and improve the safety and conductivity of the battery.

[0053] It can be understood that an appropriate number of shrinkable thermosensitive conductive structures 3 can be set according to the area of the surface of the composite current collector. Further, in a specific embodiment of the present invention, the area ratio of the shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 20% - 60%.

[0054] Wherein, the area ratio of the shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector refers to the ratio of the cross - sectional area of the shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector to the overall surface area of the composite current collector.

[0055] Specifically, the area ratio of the shrinkable thermosensitive conductive structure on the surface of the composite current collector includes, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or the range composed of any two of them.

[0056] When the area ratio of the shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector meets the above range, it can not only give full play to the electrical connection function of the shrinkable thermosensitive conductive structure, improve the conductive performance, but also ensure the mechanical properties of the composite current collector.

[0057] The flame retardant in the present invention can select a flame retardant with high - temperature volatilization performance, such as a phosphorus - based flame retardant, and the polymer matrix can select a cross - linked polymer containing an EO main chain and an amide - group block. Further, in a specific embodiment of the present invention, the mass ratio of the polymer matrix to the flame retardant is 1:(0.1% - 5%).

[0058] Specifically, the mass ratio of the polymer matrix to the flame retardant includes, but is not limited to, 1:0.1%, 1:0.5%, 1:1%, 1:2%, 1:3%, 1:4%, 1:5%, or the range composed of any two of them.

[0059] When the mass ratio of the polymer matrix to the flame retardant is within the above range, not only can the flame retardant effect of the flame retardant be fully exerted, but also the role of the polymer matrix can be exerted to improve the mechanical properties of the gel layer.

[0060] Furthermore, in a specific embodiment of the present invention, the structural diagram of the composite current collector is as Figure 2 shown. The first functional layer 21 and the second functional layer 22 also independently include a bonding layer 203, and the bonding layer 203 is located between the gel layer 201 and the metal layer 202.

[0061] The bonding layer 203 can be selected from inorganic or organic substances containing polar groups. The inorganic substances containing polar groups include, but are not limited to, any one or more of silica, zinc oxide, copper oxide, graphite, graphene, graphene oxide, and carbon nanotubes grafted with hydroxyl or carboxyl groups. The organic substances include, but are not limited to, any one or more of aramid, polyacrylic acid resin, epoxy resin, and cyanoacrylate.

[0062] The present invention does not limit the specific process of connecting the bonding layer 203 to the gel layer 201 and the metal layer 202, and common processes in the art, such as coating, can be selected.

[0063] In the present invention, the bonding layer 203 can improve the bonding force between the gel layer 201 and the metal layer 202, prevent the metal layer 202 from falling off, and further improve the mechanical strength of the composite current collector.

[0064] Furthermore, in a specific embodiment of the present invention, the bonding layer 203 includes at least one of aramid, polyethylene, hydroxyl-modified silica particles, and a mixture of silica and polyacrylic acid resin; and / or, the thickness of the bonding layer 203 is 0.01 - 1 μm.

[0065] The present invention does not limit the specific particle size of the hydroxyl-modified silica particles in the bonding layer 203, and a suitable particle size can be selected according to the actual situation, such as 50 - 1000 nm.

[0066] When the material of the bonding layer 203 meets the above range, it has a more excellent bonding effect and can further improve the mechanical properties of the composite current collector.

[0067] Furthermore, in a specific embodiment of the present invention, as Figure 3As shown, the shrinkable thermally conductive structure 3 penetrates through the current collector base layer 1 and protrudes from the surface of the first functional layer 21; and / or, the shrinkable thermally conductive structure 3 penetrates through the current collector base layer 1 and protrudes from the surface of the second functional layer 22.

[0068] Wherein, when the shrinkable thermally conductive structure 3 penetrates through the current collector base layer 1 and protrudes from the surface of the first functional layer 21, the projection length of the shrinkable thermally conductive structure in the thickness direction of the composite current collector is higher than the thickness of the composite current collector.

[0069] Similarly, when the shrinkable thermally conductive structure 3 penetrates through the current collector base layer 1 and protrudes from the surface of the first functional layer 21, the projection length of the shrinkable thermally conductive structure in the thickness direction of the composite current collector is higher than the thickness of the composite current collector.

[0070] It can be understood that, for the convenience of subsequent processes, it is necessary to control the size of the protruding part according to the actual situation.

[0071] Further, in a specific embodiment of the present invention, the structure of the composite current collector is as Figure 3 shown. The length of the shrinkable thermally conductive structure protruding from the surface of the first functional layer is L1, and the thickness of the composite current collector is L, satisfying: L1 / L = 1% - 10%; and / or, the length of the shrinkable thermally conductive structure protruding from the surface of the second functional layer is L2, and the thickness of the composite current collector is L, satisfying: L2 / L = 1% - 10%.

[0072] Specifically, L1 / L includes but is not limited to 1%, 2%, 4%, 6%, 8%, 10% or the range composed of any two of them; L2 / L includes but is not limited to 1%, 2%, 4%, 6%, 8%, 10% or the range composed of any two of them. When the relationship between the length of the protruding part and the thickness of the current collector meets the above range, it can not only improve the bonding stability of the composite current collector and ensure the mechanical strength of the composite current collector, but also meet the process requirements.

[0073] Further, in a specific embodiment of the present invention, the material of the shrinkable thermally conductive structure 3 is selected from bismuth tin alloy or tin indium alloy; and / or, the polymer matrix includes a cross-linked polymer containing an EO main chain and an amide group block;

[0074] and / or, the flame retardant is a phosphorus-based flame retardant;

[0075] and / or, the current collector base layer 1 is selected from a PET layer or a PVDF layer;

[0076] and / or, the metal layer 202 is selected from copper or aluminum.

[0077] Specifically, bismuth-tin alloy and tin-indium alloy have good electrical conductivity and excellent thermal sensitivity. When the battery undergoes thermal runaway, they can respond immediately to improve the safety of the battery.

[0078] The polymer matrix in the present invention includes a cross-linked polymer containing an EO main chain and an amide group block, where the EO main chain is derived from diglycidyl ether, cyclic ester, and ethylene glycol dimethacrylate; the amide group is derived from cyclic lactam and unsaturated hydrocarbon amide.

[0079] The polymer matrix in the present invention can not only enhance the mechanical strength of the gel layer 201, but also has good chemical compatibility with the flame retardant, the current collector substrate 1, and the adhesive layer 203, preventing slippage and peeling during the application of the composite current collector.

[0080] The phosphorus-based flame retardant in the present invention refers to phosphate flame retardants, such as triethyl phosphate, dimethyl phosphate, etc.

[0081] The phosphorus-based flame retardant can not only effectively reduce the combustion performance of the material, release phosphoric acid compounds at high temperatures to form a protective layer, but also has good compatibility and can fully play its role in the composite current collector.

[0082] Further, in a specific embodiment of the present invention, the thickness of the current collector substrate 1 is 1 - 10 μm; and / or, the thickness of the gel layer 201 is 1 - 5 μm; and / or, the thickness of the metal layer 202 is 0.01 - 1 μm; and / or, the length of the shrinkable thermosensitive conductive structure 3 in the extending direction is 2.5 - 17 μm.

[0083] When the thickness or length of each structure of the composite current collector meets the above range, the battery including the composite current collector has more excellent electrical conductivity and flame retardant performance, and at the same time has higher mechanical properties. The reason is that: the shrinkable thermosensitive conductive structure connects the conductive layers on both sides of the polymer substrate to form an electronic path, greatly reducing the resistance of the composite current collector; the flame retardant is encapsulated in the gel layer, isolating its contact with the electrolyte without affecting the electrochemical performance of the battery. When the battery undergoes thermal runaway or short circuit and causes the electrode to heat up, the shrinkable thermosensitive conductive structure undergoes volume contraction to form a flame retardant release channel, and the flame retardant is released in the electrode to improve the flame retardant performance of the battery; by setting the gel layer, the adhesion between the current collector substrate and the metal layer is improved, and at the same time, a polymer substrate is provided inside the gel layer, which contains a cross-linked polymer that greatly enhances the mechanical strength of the first functional layer and the second functional layer, endowing high adhesion performance while enhancing the mechanical strength of the composite current collector.

[0084] The present invention also provides a pole piece including the composite current collector as described above.

[0085] The electrode provided by the present invention includes either a positive electrode or a negative electrode. It can be understood that the electrode further includes an active layer formed of an active material.

[0086] The present invention does not limit the specific preparation method of the electrode. Taking the composite current collector used for the positive electrode as an example, when specifically preparing the positive electrode, for example, the positive electrode active material, a conductive agent, and a binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the composite current collector, and after drying, rolling, and slitting, the positive electrode is obtained.

[0087] In a specific embodiment, the positive electrode active layer includes, by mass percentage, 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the conductive agent, and 0.5-15 wt% of the binder.

[0088] Among them, the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane.

[0089] It can be understood that a battery including the above-mentioned composite current collector or the above-mentioned electrode can be developed.

[0090] It can be conceived that in addition to the above-mentioned electrode, the battery of the present invention further includes an electrolyte solution and a separator.

[0091] The present invention does not strictly limit the selection of the electrolyte solution, which can include one or more of the solvents commonly used in current battery electrolyte solutions, and the electrolyte lithium salts commonly used in current lithium ion electrolyte solutions. For example: the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, propyl acetate, acetic acid propyl ester, propionic acid propyl ester, sulfolane, γ-butyrolactone, etc.; the lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0092] The present invention does not strictly limit the material selection of the separator, which can be the separator materials commonly used in current batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene bilayer composite film (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene trilayer composite film (PP / PE / PP), cellulose non-woven fabric separator, or a separator with a ceramic coating.

[0093] The battery of the present invention can be manufactured by conventional methods known to those skilled in the art of the present invention.

[0094] In a specific embodiment, when preparing the battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain a bare battery cell, and the bare battery cell is encapsulated into a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85 °C to remove moisture, the electrolyte is injected into the dried battery, and the battery is completed after standing, formation, and secondary sealing.

[0095] Hereinafter, the composite current collector provided by the present invention will be introduced in detail through specific examples.

[0096] Example 1

[0097] The structural diagram of the composite current collector provided in this example is as Figure 4 shown, and the preparation method of the composite current collector includes the following steps:

[0098] 1. PET and indium tin alloy, a heat-shrinkable thermosensitive conductive agent, are mechanically roll-compounded to obtain a composite layer in which the shrinkable thermosensitive conductive structure 3 penetrates the current collector base layer 1. The thickness of the PET layer serving as the current collector base layer 1 is 1 μm, and the indium tin alloy is spherical with a diameter of 17 μm.

[0099] 2. A gel precursor is coated on both sides of the composite layer, including a polymer matrix (ether-based monomer ethylene glycol methacrylate, amide-based monomer hydroxyethyl acrylamide), initiator AIBN, and flame retardant triethyl phosphate. Among them, the mass ratio of the polymer matrix to the flame retardant is 1:3%, and the gel layer 201 is obtained by photo / thermal curing. The thickness of the gel layer 201 is 1 μm.

[0100] 3. An aramid film is mechanically roll-pressed on the surface of the gel layer 201 away from the current collector base layer 1 to modify the hydroxyl group-modified silica of the bonding layer 203, and the thickness of the bonding layer 203 is 0.05 μm.

[0101] 4. A copper metal layer 202 is modified on the surface of the hydroxyl group-modified silica of the bonding layer 203 by chemical vapor deposition. The thickness of the copper metal layer 202 is 0.05 μm, and finally a composite current collector is obtained. The area ratio of the shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 45%.

[0102] Example 2

[0103] The structural diagram of the composite current collector provided in this example is as shown in Figure 4 and the preparation method of the composite current collector includes the following steps:

[0104] 1. Dissolve PVDF in NMP and blend it with the heat-shrinkable thermosensitive conductive agent bismuth-tin alloy to make a suspension, and obtain a composite layer in which the heat-shrinkable thermosensitive conductive structure 3 penetrates the current collector substrate 1 through the solution casting method. The thickness of the PVDF layer as the current collector substrate 1 is 2 μm, and the heat-shrinkable thermosensitive conductive structure 3 is spherical with a diameter of 15 μm.

[0105] 2. Coat the gel precursor on both sides of the composite layer, including a polymer matrix (polyether polymer matrix ethylene glycol methacrylate) and a flame retardant dimethyl phosphate. Among them, the mass ratio of the polymer matrix to the flame retardant is 1:5%, and after standing for 30 min, a gel layer 201 is obtained. The thickness of the gel layer 201 is 1.5 μm.

[0106] 3. Roll the aramid film mechanically on the surface of the gel layer 201 to modify the bonding layer 203 with hydroxyl-modified silica, and the thickness of the bonding layer 203 is 0.08 μm.

[0107] 4. Modify the aluminum metal layer 202 on the surface of the bonding layer 203 by physical vapor deposition. The thickness of the aluminum metal layer 202 is 0.07 μm, and finally a composite current collector is obtained. The area ratio of the heat-shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 20%.

[0108] Example 3

[0109] The structural diagram of the composite current collector provided in this example is as shown in Figure 3 and the preparation method of the composite current collector includes the following steps:

[0110] 1. Dissolve PVDF in NMP and blend it with the heat-shrinkable thermosensitive conductive agent bismuth-tin alloy to make a suspension, and obtain a composite layer in which the heat-shrinkable thermosensitive conductive structure 3 penetrates the current collector substrate 1 through the solution casting method. The thickness of the PVDF layer as the current collector substrate 1 is 2 μm, and the heat-shrinkable thermosensitive conductive structure 3 is rod-shaped with a side length of 100 nm and a length of 5 μm.

[0111] 2. Coat the gel precursor on both sides of the composite layer, including a polymer matrix (polyether polymer matrix ethylene glycol methacrylate) and a flame retardant dimethyl phosphate. Among them, the mass ratio of the polymer matrix to the flame retardant is 1:0.1%, and after standing for 30 min, a gel layer 201 is obtained. The thickness of the gel layer 201 is 1 μm.

[0112] 3. Modify the adhesive layer 203 on the surface of the gel layer 201 by mechanically rolling the aramid film. The thickness of the adhesive layer 203 is 0.02 μm.

[0113] 4. Modify the aluminum metal layer 202 on the surface of the adhesive layer 203 by physical vapor deposition. The thickness of the aluminum metal layer 202 is 0.02 μm. Finally, a composite current collector is obtained. The area ratio of the heat-shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 60%.

[0114] Example 4

[0115] The structural diagram of the composite current collector provided in this example is as Figure 3 shown. The preparation method of the composite current collector includes the following steps:

[0116] 1. Dissolve PVDF in NMP and blend it with the heat-shrinkable thermosensitive conductive agent bismuth-tin alloy to prepare a suspension. A composite layer in which the heat-shrinkable thermosensitive conductive structure 3 penetrates the current collector substrate 1 is prepared by the solution casting method. The thickness of the PVDF layer as the current collector substrate 1 is 0.5 μm. The heat-shrinkable thermosensitive conductive structure 3 is rod-shaped, with a side length of 100 nm and a length of 5 μm.

[0117] 2. Coat the gel precursor on both sides of the composite layer, including a polymer matrix (polyether polymer matrix ethylene glycol methacrylate) and a flame retardant dimethyl phosphate. Among them, the mass ratio of the polymer matrix to the flame retardant is 1:3%. After standing for 30 min, the gel layer 201 is prepared. The thickness of the gel layer 201 is 0.5 μm.

[0118] 3. Modify the adhesive layer 203 on the surface of the gel layer 201 by mechanically rolling the aramid film. The thickness of the adhesive layer 203 is 0.01 μm.

[0119] 4. Modify the aluminum metal layer 202 on the surface of the adhesive layer 203 by physical vapor deposition. The thickness of the aluminum metal layer 202 is 0.05 μm. Finally, a composite current collector is obtained. The area ratio of the heat-shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 45%.

[0120] Example 5

[0121] The structural diagram of the composite current collector provided in this example is as Figure 3 shown. The preparation method of the composite current collector includes the following steps:

[0122] 1. Dissolve PVDF in NMP and blend it with the heat-shrinkable thermosensitive conductive agent bismuth-tin alloy to prepare a suspension. A composite layer in which the heat-shrinkable thermosensitive conductive structure 3 penetrates the current collector substrate 1 is prepared by the solution casting method. The thickness of the PVDF layer as the current collector substrate 1 is 2 μm. The heat-shrinkable thermosensitive conductive structure 3 is rod-shaped, with a side length of 100 nm and a length of 5 μm.

[0123] 2. Apply the gel precursor on both sides of the composite layer, which contains a polymer matrix (polyether polymer matrix ethylene glycol methacrylate) and the flame retardant magnesium hydroxide. Among them, the mass ratio between the polymer matrix and the flame retardant is 1:3.5%, and after standing for 30 minutes, the gel layer 201 is obtained. The thickness of the gel layer 201 is 1 μm.

[0124] 3. Press the aramid film onto the surface of the gel layer 201 through mechanical rolling to modify the adhesive layer 203 PVDF. The thickness of the adhesive layer 203 is 0.02 m.

[0125] 4. Modify the aluminum metal layer 202 on the surface of the adhesive layer 203 by physical vapor deposition. The thickness of the aluminum metal layer 202 is 0.02 μm. Finally, a composite current collector is obtained, and the area ratio of the heat-shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 30%.

[0126] Example 6

[0127] The structural diagram of the composite current collector provided in this example is as Figure 2 shown. The preparation method of the composite current collector includes the following steps:

[0128] 1. Dissolve PVDF in NMP and blend it with the heat-shrinkable thermosensitive conductive agent bismuth-tin alloy to make a suspension. Through the solution casting method, a composite layer in which the heat-shrinkable thermosensitive conductive structure 3 penetrates the current collector substrate 1 is obtained. The thickness of the PVDF layer as the current collector substrate 1 is 2 μm. The heat-shrinkable thermosensitive conductive structure 3 is rod-shaped, with a side length of 100 nm and a length of 5 μm.

[0129] 2. Apply the gel precursor on both sides of the composite layer, including a polymer matrix (polyether polymer matrix ethylene glycol methacrylate) and the flame retardant dimethyl phosphate. Among them, the mass ratio between the polymer matrix and the flame retardant is 1:3%, and after standing for 30 minutes, the gel layer 201 is obtained. The thickness of the gel layer 201 is 1 μm.

[0130] 3. Press the aramid film onto the surface of the gel layer 201 through mechanical rolling to modify the adhesive layer 203. The thickness of the adhesive layer 203 is 0.02 μm.

[0131] 4. Modify the aluminum metal layer 202 on the surface of the adhesive layer 203 by physical vapor deposition so that the metal layer 202 just covers the protruding points of the heat-shrinkable thermosensitive conductive structure. The thickness of the aluminum metal layer 202 is 0.98 μm. Finally, a composite current collector is obtained, and the area ratio of the heat-shrinkable thermosensitive conductive structure 3 on the surface of the composite current collector is 60%.

[0132] Comparative Example 1

[0133] The preparation method of the current collector provided in this comparative example includes the following steps:

[0134] 1. Prepare a through-hole PET film by laser drilling a 2-μm PET film.

[0135] 2. Prepare copper metal layers 202 on both sides of the PET film by physical vapor deposition to obtain a composite current collector with PET as the base layer and copper metal layers 202 on both sides.

[0136] Comparative Example 2

[0137] The preparation method of the current collector provided in this comparative example includes the following steps:

[0138] 1. Preparation of the base film: Prepare a slurry by mixing PET (polyethylene terephthalate) and PI (polyimide) emulsions in a mass ratio of 80:20; electrospin the slurry (voltage is 4.0 KV, melt viscosity is 1000 pcs, nozzle diameter is 0.1 μm) to obtain a base film (through-hole diameter is 0.2 μm, porosity is 50%, thickness is 5 μm);

[0139] 2. Preparation of the polymer thin film: Coat triethyl phosphate, a phosphorus-based flame retardant, on the base film by spray coating (coating temperature is 80 °C, coating unwind tension is 10 N, winding tension is 10 N, stretching speed is 5 m / min, contact pressure is 5 N), and dry (temperature is 60 °C) to obtain a polymer thin film.

[0140] (3) Preparation of the composite current collector: Deposit 2-μm copper foils on both sides in the thickness direction of the polymer thin film by vacuum plating to obtain a high-performance flame-retardant composite current collector.

[0141] This high-performance flame-retardant composite current collector consists of a polymer thin film 2 and two metal layers 2021 arranged in the thickness direction of the polymer thin film 2; among them, the polymer thin film 2 consists of a base film 202 and a flame-retardant layer 201 covering the base film 202; through-holes 211 for ion transmission are provided on the base film 202; the flame-retardant layer 201 contains flame-retardant particles 3, and the flame-retardant particles 3 are prepared from a closed-cell insulating polymer 311 and a flame retardant 312, and a polymer shell 313 formed by the closed-cell insulating polymer 311 coats the outside of the flame retardant 312 to form a core-shell structure particle.

[0142] Comparative Example 3

[0143] The preparation method of the current collector provided in this comparative example includes the following steps:

[0144] 1. Melt-blend a phosphate ester flame retardant and PET, and cast the blended material into a film to form a flame-retardant base layer.

[0145] 2. Select an aramid film for the adhesive layer 203, and bond the aramid film to both sides of the flame-retardant base layer by mechanical rolling.

[0146] 3. A copper metal layer 202 is formed on both sides of the bonding layer 203 away from the flame-retardant base material layer by vacuum evaporation.

[0147] 4. A through-hole is formed in the layered structure formed in step 3) by laser etching, and then an electrically conductive coating formed of graphite is formed on the surface of the layered structure and the through-hole by electrochemical deposition.

[0148] Comparative Example 4

[0149] The structural diagram of the composite current collector provided in this comparative example is as Figure 5 shown, and the preparation method of the composite current collector includes the following steps:

[0150] 1. PVDF is dissolved in NMP, and a current collector support layer is prepared by solution casting. Then PVDF is dissolved in NMP and blended with a heat-shrinkable thermosensitive conductive agent bismuth tin alloy to form a suspension, and a composite layer of a heat-shrinkable thermosensitive conductive structure 3 and a current collector base layer 1 is prepared on both sides of the current collector support layer by solution casting. The heat-shrinkable thermosensitive conductive structure 3 does not penetrate the base layer. The thickness of the PVDF layer as the current collector base layer 1 is 2 μm, and the heat-shrinkable thermosensitive conductive structure 3 is rod-shaped, with a side length of 100 nm and a length of 3 μm.

[0151] 2. A gel precursor is coated on both sides of the composite layer, including a polyether polymer matrix ethylene glycol methacrylate and a flame retardant dimethyl phosphate. After standing for 30 min, a gel layer 201 is prepared, and the thickness of the gel layer 201 is 1 μm.

[0152] 3. An aramid film is mechanically roll-pressed on the surface of the gel layer 201 to modify the bonding layer 203, and the thickness of the bonding layer 203 is 0.02 μm.

[0153] Test Example

[0154] After making the composite current collectors in all the examples and comparative examples into electrode sheets, batteries are assembled with an electrolyte and a separator according to the following method. The method includes:

[0155] 1) Lithium iron phosphate cathode powder (specific type of cathode material) is mixed with a conductive agent Super P and a binder PVDF in a weight ratio of 96.5:1:2.5 respectively, and a cathode slurry is obtained by dispersion. The slurry is coated on the composite current collector, and roll-pressed according to a cathode surface density of 120 g / m 2 to prepare a cathode sheet;

[0156] 2) The graphite anode was mixed with conductive agent Super P and binder CMC / SBR (1:1 wt%) at a weight ratio of 97:1:2. The mixture was dispersed in water and obtained an anode slurry through double-planet mixing. The slurry was coated on the composite current collector, followed by rolling and drying to obtain the anode sheet;

[0157] 3) The cathode sheet, anode sheet and separator were assembled into a lithium-ion battery, and a non-aqueous electrolyte was injected. Among them, the electrolyte components were lithium salt LiPF6, the solvent was EC and DEC, and the additive was FEC. The electrolyte formula was 1M LiPF6 + EC:DEC (1:1 wt%) + 5 wt% FEC.

[0158] 1. Penetration test

[0159] The battery prepared by the above method was tested according to GB / T 31485-2015. The battery that did not catch fire was recorded as passing. 10 batteries were tested in each group, and the passing rate was counted. The specific results are shown in Table 1.

[0160] 2. Resistance test

[0161] The current collectors of all examples and comparative examples were tested for resistance according to GB / T 24343-2009. The test results are shown in Table 1.

[0162] 3. The mechanical properties of the current collectors of all examples and comparative examples were tested. The specific steps were as follows:

[0163] The current collector was cut into dimensions of: length * width * depth = 8 cm * 1.5 cm * 0.5 cm; the sample was loaded into a universal testing machine. The test conditions were: test speed: 200 mm / min, gauge length: 25.00 mm, test temperature: 20 - 30 °C, test humidity: 30 - 60 RH%. The test results are shown in Table 1.

[0164] Table 1

[0165]

[0166] According to Table 1, it can be seen that the penetration passing rate of the composite current collectors provided in Examples 1-6 of the present invention is not less than 50%, the resistance is not higher than 76 mΩ, the tensile strength is not less than 54 MPa, and the fracture strength is not less than 37 MPa. Although the composite current collector provided in Comparative Example 4 also has a relatively high penetration passing rate and mechanical strength, it is obvious that the resistance of the composite current collector provided in Comparative Example 4 is much higher than that of the composite current collectors provided in Examples 1-6, and it cannot meet the requirement of improving the conductivity of the composite current collector. Therefore, the technical solution provided by the present invention can improve the conductivity while meeting the safety performance, and has a certain mechanical strength to meet the use requirements.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite current collector, characterized in that: It includes a current collector substrate, a first functional layer and a second functional layer respectively located on both sides of the current collector substrate, and N shrinkable thermosensitive conductive structures, where N is greater than or equal to 1; Wherein, in a direction gradually away from the current collector substrate, the first functional layer at least includes a gel layer and a metal layer stacked, and the second functional layer at least includes a gel layer and a metal layer stacked; The gel layer includes a polymer matrix and a flame retardant; When the application temperature is lower than the shrinkage temperature of the shrinkable thermosensitive conductive structure, the shrinkable thermosensitive conductive structure penetrates the first functional layer, the second functional layer, and the current collector base layer, and electrically connects the metal layer of the first functional layer and the metal layer of the second functional layer; When the application temperature is greater than the shrinking temperature, the shrinkable thermosensitive conductive structure shrinks, the metal layer of the first functional layer and the metal layer of the second functional layer are electrically disconnected, and the flame retardant is released.

2. The composite current collector according to claim 1, characterized in that: The shrinkage temperature of the shrinkable thermosensitive conductive structure is 90-150°C.

3. The composite current collector according to claim 1, characterized in that: The shrinkable thermosensitive conductive structure accounts for 20%-60% of the surface area of ​​the composite current collector.

4. The composite current collector according to any one of claims 1 to 3, characterized in that: The mass ratio of the polymer matrix to the flame retardant is 1:(0.1%-5%).

5. The composite current collector according to claim 1, characterized in that: The first functional layer and the second functional layer further independently include an adhesive layer, and the adhesive layer is located between the gel layer and the metal layer; And / or, the bonding layer comprises at least one of aramid, polyethylene, hydroxyl-modified silicon oxide particles, and a mixture of silicon oxide and polyacrylic acid resin; And / or, the bonding layer has a thickness of 0.01-1 μm.

6. The composite current collector according to claim 1, characterized in that: The shrinkable thermosensitive conductive structure penetrates the current collector substrate and protrudes from the surface of the first functional layer; And / or, the shrinkable thermosensitive conductive structure penetrates the current collector substrate and protrudes from the surface of the second functional layer.

7. The composite current collector according to claim 6, characterized in that: The length of the shrinkable thermosensitive conductive structure protruding from the surface of the first functional layer is L1, and the thickness of the composite current collector is L, which satisfies: L1 / L=1% to 10%; And / or, the length of the shrinkable thermosensitive conductive structure protruding from the surface of the second functional layer is L2, and the thickness of the composite current collector is L, which satisfies: L2 / L=1% to 10%.

8. The composite current collector according to any one of claims 1 to 3, characterized in that: The material of the shrinkable thermosensitive conductive structure is selected from bismuth-tin alloy or tin-indium alloy; and / or, the polymer matrix comprises a cross-linked polymer containing an EO main chain and an amide group block; And / or, the flame retardant is a phosphorus-based flame retardant; And / or, the current collector substrate is selected from a PET layer or a PVDF layer; And / or, the metal layer is selected from copper or aluminum.

9. The composite current collector according to claim 1, characterized in that: The thickness of the current collector substrate is 1-10 μm; And / or, the gel layer has a thickness of 1-5 μm; And / or, the thickness of the metal layer is 0.01-1 μm; And / or, the shrinkable thermosensitive conductive structure has a length of 2.5-17 μm.

10. A pole piece, characterized in that: Comprising the composite current collector according to claim 1.

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