Electrochemical device and electric equipment
By setting a thermal induction structure in the cathode sheet of the lithium-ion battery, the lithium anode layer and the cathode current collector are short-circuited and discharged at high temperatures, the problem of thermal runaway in the event of thermal abuse is solved, and the safety performance is improved.
Patent Information
- Application Number
- CN202411928217.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-25
- Publication Date
- 2025-03-18
AI Technical Summary
Lithium-ion batteries are prone to thermal runaway during thermal abuse, which reduces the safety of the battery. It is mainly because the structure collapses at high potentials and high temperatures, causing oxygen release, which triggers a violent reaction with the electrolyte to produce a large amount of heat.
An electrochemical device is designed including a cathode sheet, a thermal induction structure and a lithium anode layer. The thermal induction structure is arranged in the empty foil area of the cathode current collector, including a stacked insulating layer and a lithium anode layer. The insulating layer is melted or decomposed at a temperature of 90°C to 120°C, causing the lithium anode layer to be short-circuit discharged from the cathode current collector, reducing the charge state of the cathode active layer, and improving structural stability.
Through the short-circuit discharge mechanism, the risk of severe reaction with the electrolyte caused by the damage to the cathode material structure is reduced, and the safety performance of the electrochemical device in the case of thermal abuse is improved.
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Figure CN119650815A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device and electrical equipment. Background Art
[0002] With the continuous updating and development of lithium-ion battery technology, the application fields of lithium-ion batteries are also expanding, and the resulting safety issues are increasingly attracting public attention. When the battery is subjected to thermal abuse such as overcharging and hot box testing, thermal runaway may occur, reducing the safety of the battery. Summary of the invention
[0003] The inventors of the present application have found that the cathode material of the battery is mostly lithium cobalt oxide. Lithium cobalt oxide has a high potential when fully charged. Lithium cobalt oxide has a layered structure, which can easily cause the collapse of the layered structure under high potential and high temperature, leading to oxygen release. The lithium cobalt oxide with a destroyed layered structure will react violently with the electrolyte to generate a large amount of heat, causing thermal runaway.
[0004] One object of the present application is to provide an electrochemical device and an electrical equipment, which are helpful to improve safety during thermal abuse.
[0005] The first aspect of the present application provides an electrochemical device, including an electrode assembly, the electrode assembly including a cathode pole piece, the cathode pole piece including a cathode current collector and a cathode active layer, the cathode current collector including an empty foil area not covered by the cathode active layer. The electrode assembly also includes a thermal induction structure, the thermal induction structure is arranged in the empty foil area, the thermal induction structure includes a stacked insulating layer and a lithium anode layer, the insulating layer is arranged between the empty foil area and the lithium anode layer, and the insulating layer can be melted or decomposed at a temperature of 90°C to 120°C.
[0006] In the present application, by setting a thermal sensing structure and limiting the melting or decomposition temperature of the insulating layer to 90°C-120°C, the insulating layer of the electrochemical device melts or decomposes before thermal runaway occurs, so that the lithium anode layer and the cathode current collector are electrically connected to cause short-circuit discharge, thereby reducing the charge state of the cathode active layer and improving the structural stability of the cathode active layer, thereby reducing the risk of generating a large amount of heat due to violent reaction with the electrolyte due to the destruction of the structure of the cathode material, and improving the safety performance of the electrochemical device under thermal abuse.
[0007] According to some embodiments of the present application, the thermal induction structure includes a resistance layer, which is arranged between the empty foil area and the insulating layer. By providing the resistance layer, the short-circuit impedance between the lithium anode layer and the cathode current collector is adjustable, thereby making the short-circuit discharge between the lithium anode layer and the cathode current collector controllable.
[0008] According to some embodiments of the present application, the resistive layer is in contact with the cathode current collector.
[0009] According to some embodiments of the present application, the thermal sensing structure further includes a resistance layer, which is disposed between the insulating layer and the lithium anode layer.
[0010] According to some embodiments of the present application, the resistor layer satisfies at least one of the following conditions: (a) the resistor layer includes an inorganic substance and a conductive agent, the inorganic substance includes one or more of metal oxides, nitrides, and carbides, and the conductive agent includes one or more of carbon black, carbon nanotubes, graphene, or graphite; (b) the mass percentage of the conductive agent in the resistor layer is 5% to 20%; (c) the thickness of the resistor layer is 2μm to 10μm; (d) the film resistance of the resistor layer is 1Ω to 10Ω. By selecting the material of the resistor layer, the content, thickness, and film resistance of the conductive agent, the short-circuit discharge power can be maintained within a controllable range. Low short-circuit power is conducive to reducing short-circuit heat generation, and high short-circuit power is conducive to reducing the charge state of the cathode active layer.
[0011] According to some embodiments of the present application, (a) the insulating layer includes one or more of low-density polyethylene, polyethylene wax, oxidized polyethylene wax, polytetrafluoroethylene-modified polyethylene wax, sulfur, polyethylene oxide, triacetate cellulose, or solid paraffin; (b) the thickness of the insulating layer is 5 μm to 20 μm; (c) the insulating layer can melt or decompose at a temperature of 105° C. to 115° C. By selecting the material, thickness, melting or decomposition temperature of the insulating layer, the insulating layer can have a suitable manufacturing advantage, and the insulating layer can melt or decompose at a suitable temperature to improve thermal runaway.
[0012] According to some embodiments of the present application, the lithium anode layer satisfies at least one of the following conditions: (a) the lithium anode layer includes one or more of lithium titanate, lithium terephthalate or lithium rhodium palmitate; (b) the thickness of the lithium anode layer is 50 μm to 80 μm. By selecting the material and thickness of the lithium anode layer, the degree of reduction of the charge state of the cathode active layer during short-circuit discharge can be controlled, thereby making the short-circuit discharge controllable.
[0013] According to some embodiments of the present application, the electrode assembly has a winding structure, and the thermal sensing structure is arranged at the outermost circle of the cathode electrode, which is conducive to quickly releasing the heat generated by the short circuit to the outside of the electrode assembly and improving the safety performance.
[0014] According to some embodiments of the present application, the electrode assembly has a winding structure including a straight portion and a curved portion, and the thermal sensing structure is provided in the curved portion, which is beneficial to improving the energy density.
[0015] A second aspect of the present application provides an electrical equipment comprising any one of the above-mentioned electrochemical devices. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 Schematic diagram of the structure of an electrochemical device in one embodiment.
[0017] Figure 2 Schematic diagram of the structure of an electrode assembly in one embodiment.
[0018] Figure 3 Schematic diagram of the structure of the cathode electrode in one embodiment.
[0019] Figure 4 Schematic diagram of the structure of the cathode electrode in another embodiment.
[0020] Figure 5 Schematic diagram of the structure of an electrical device in one embodiment. DETAILED DESCRIPTION
[0021] The following specific embodiments are exemplary and non-limiting, and are intended to provide a basic understanding of the present application, and are not intended to identify the key or decisive elements of the present application or to limit the scope of protection. As long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way.
[0022] When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be a component in between. When a component is considered to be "connected to" or "connected to" another component, it can be directly connected to the other component or there may be a component in between.
[0023] Unless otherwise defined, the term "plurality" herein, when used to describe the number of components, specifically refers to the number of components being two or more. In this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone.
[0024] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.
[0025] It should be noted that the electrochemical device includes any device in which an electrochemical reaction occurs, such as all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. Secondary batteries may include nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead storage) batteries, lithium secondary batteries, sodium secondary batteries, zinc secondary batteries, etc. Lithium secondary batteries may include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries. In the content of the embodiments of the present application, lithium ion batteries are used as examples of electrochemical devices to explain the present application.
[0026] See also Figure 1An embodiment of the present application provides an electrochemical device 100, including a housing 10, an electrode assembly 20, an electrolyte (not shown), a first electrode terminal 31 and a second electrode terminal 32. The electrode assembly 20 and the electrolyte are contained in the housing 10. The first electrode terminal 31 and the second electrode terminal 32 are respectively connected to the electrode assembly 20 and extend out of the housing 10 to connect to external components. The first electrode terminal 31 and the second electrode terminal 32 have opposite polarities, for example, the first electrode terminal 31 is a cathode and the second electrode terminal 32 is an anode.
[0027] See also Figure 2 The electrode assembly 20 includes a cathode electrode sheet 21, an anode electrode sheet 22, and a separator 23 disposed between the anode electrode sheet 22 and the cathode electrode sheet 21. In this embodiment, the electrode assembly 20 has a winding structure. Specifically, the electrode assembly 20 is formed by stacking the cathode electrode sheet 21, the separator 23, and the anode electrode sheet 22 in sequence and then winding them. In another embodiment, the electrode assembly 20 has a laminated structure. Specifically, the electrode assembly 20 is formed by stacking a plurality of cathode electrode sheets 21, a plurality of separators 23, and a plurality of anode electrode sheets 22 in sequence.
[0028] The cathode electrode sheet 21 includes a cathode current collector 211 and a cathode active layer 212 disposed on the surface of the cathode current collector 211. The cathode active layer 212 can be disposed on two opposite surfaces of the cathode current collector 211, or only on one surface of the cathode current collector 211, which is not limited in the present application. The first electrode terminal 31 is electrically connected to the cathode current collector 211. The cathode current collector 211 can be any known cathode current collector 211, such as aluminum foil, aluminum alloy foil or composite current collector. The cathode active layer 212 includes a cathode material, which can include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium rich manganese-based material, lithium nickel cobalt aluminum oxide and one or more of the combinations thereof. The cathode active layer 212 can also include a conductive agent and a binder, the conductive agent is used to improve the conductive properties of the cathode material, and the binder is used to bond the particles of each component in the cathode active layer 212 together. The conductive agent may include one or more of conductive carbon black, carbon nanotubes, carbon fibers or graphene, and the binder may include one or more of styrene-butadiene rubber, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride or sodium carboxymethyl cellulose.
[0029] The anode pole piece 22 includes an anode current collector 221 and an anode active layer 222 disposed on the surface of the anode current collector 221. The anode active layer 222 can be disposed on two opposite surfaces of the anode current collector 221, or only on one surface of the anode current collector 221, which is not limited in the present application. The second electrode terminal 32 is electrically connected to the anode current collector 221. The anode current collector 221 can be any known anode current collector 221, for example, copper foil, copper alloy foil or composite current collector. The anode active layer 222 includes an anode material, which can include soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbon composite, lithium titanate, and one or more metals that can form an alloy with lithium. The anode active layer 222 can also include a conductive agent and a binder, the conductive agent is used to improve the conductive properties of the anode material, and the binder is used to bond the particles of each component in the anode active layer 222 together. The conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, carbon fibers or graphene. The binder may be selected from one or more of styrene-butadiene rubber, polyacrylate, polyacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose or polyvinylidene fluoride. Sodium carboxymethyl cellulose and lithium carboxymethyl cellulose may also be used as thickeners in the anode active layer 222 to increase the viscosity or consistency of the slurry, so that the slurry remains in a uniform and stable suspended state or an emulsified state.
[0030] The separator 23 may be any known separator. For example, the separator 23 may be a film made of one or more materials selected from polyethylene, polypropylene, non-woven fabric, and polyfiber.
[0031] The electrolyte can be any known electrolyte. For example, the electrolyte is selected from a solution containing one or more organic carbonates selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or methyl ethyl carbonate as a solvent, and one or more lithium salts selected from LiPF6, LiBF4, LiBOB, LiAsF6, Li(CF3SO2)2N or LiCF3SO3 as a solute.
[0032] The housing 10 may be any known housing suitable for the electrochemical device 100. For example, the housing 10 may be a packaging bag obtained by packaging film, such as aluminum-plastic film, steel-plastic film, etc.; or, the housing 10 may be a metal housing, such as a steel shell, an aluminum shell, etc.
[0033] See also Figure 2 , Figure 3 and Figure 4, the cathode current collector 211 includes an empty foil area 211A that is not covered by the cathode active layer 212. In the present application, at least one surface of the cathode current collector 211 of the empty foil area 211A is not provided with the cathode active layer 212. The electrode assembly 20 also includes a thermal induction structure 24, which is disposed on the cathode current collector 211 of the empty foil area 211A. The thermal induction structure 24 includes an insulating layer 241 and a lithium anode layer 242 that are stacked, and the insulating layer 241 is disposed between the empty foil area 211A and the lithium anode layer 242. The insulating layer 241 can melt or decompose at a preset temperature. When the electrochemical device 100 is thermally abused, the temperature inside the housing 10 will continue to rise. When the preset temperature is reached, at least part of the insulating layer 241 melts or decomposes and then shrinks, so that the lithium anode layer 242 is electrically connected to the cathode current collector 211 to cause short-circuit discharge. On the one hand, the short-circuit discharge between the lithium anode layer 242 and the cathode current collector 211 can reduce the state of charge of the cathode active layer 212 and improve the structural stability of the cathode active layer 212, thereby reducing the risk of generating a large amount of heat due to the destruction of the structure of the cathode material and the violent reaction with the electrolyte, that is, reducing the risk of heat generation by the cathode electrode 21, thereby improving the safety of the electrochemical device 100 during thermal abuse. On the other hand, the short-circuit between the lithium anode layer 242 and the cathode current collector 211 will directly generate heat, and the generated heat will also affect the safety performance.
[0034] In this embodiment, the insulating layer 241 can melt or decompose at a temperature of 90°C to 120°C. When the temperature of the insulating layer 241 reaches 90°C-120°C, the insulating layer 241 melts or decomposes, and the lithium anode layer 242 and the cathode current collector 211 short-circuit discharge. The cathode active layer 212 can be made by coating, curing and other processes, and the curing temperature can be about 100°C. If the melting or decomposition temperature of the insulating layer 241 is less than 90°C, during the process of coating to form the cathode active layer 212, the insulating layer 241 may melt, causing the lithium anode layer 242 to short-circuit with the cathode current collector 211, affecting the manufacturing rate and production safety. If the melting or decomposition temperature of the insulating layer 241 is greater than 120°C, the lithium anode layer 242 will short-circuit discharge with the cathode current collector 211 when the internal temperature of the electrochemical device 100 is high and thermal runaway may have occurred, reducing the state of charge of the cathode active layer 212, which is not conducive to improving safety.
[0035] In some embodiments, the insulating layer 241 can melt or decompose at a temperature of 105° C. to 115° C. When the melting or decomposition temperature of the insulating layer is within the above range, the insulating layer 241 has a lower risk of melting during the coating process to form the cathode active layer 212, thereby improving the manufacturing yield; and the lithium anode layer 242 improves the heat generation of the cathode electrode sheet 21 when the electrochemical device 100 does not experience thermal runaway, i.e., short-circuit discharge with the cathode current collector 211, thereby improving safety performance.
[0036] In some embodiments, the insulating layer 241 is disposed on the surface of the cathode current collector 211 in the empty foil area 211A, and the lithium anode layer 242 is disposed on the surface of the insulating layer 241 away from the cathode current collector 211. When the insulating layer 241 melts or decomposes, the lithium anode layer 242 can contact the cathode current collector 211 to discharge.
[0037] In some embodiments, the insulating layer 241 includes an insulating material, and the insulating material includes one or more of low-density polyethylene, polyethylene wax, oxidized polyethylene wax, polytetrafluoroethylene-modified polyethylene wax, sulfur, polyethylene oxide, triacetate cellulose, or solid paraffin. By selecting the material of the insulating layer 241, the melting or decomposition temperature of the insulating layer 241 can be limited to a suitable temperature range, so that the lithium anode layer 242 and the cathode current collector 211 can contact at the melting or decomposition temperature and short-circuit discharge occurs to reduce the charge state of the cathode active layer, thereby improving safety performance.
[0038] In some embodiments, the insulating layer 241 further includes an adhesive, which is used to improve the bonding strength between the insulating layer 241 and the cathode current collector 211 and the lithium anode layer 242, and reduce the risk of the insulating layer 241 falling off. The adhesive may include one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), or polytetrafluoroethylene (PTFE).
[0039] In some embodiments, the thickness of the insulating layer 241 is 5 μm to 20 μm. For example, the thickness of the insulating layer 241 is 5 μm, 8 μm, 11 μm, 14 μm, 17 μm, 20 μm, or a range consisting of any two values thereof. By limiting the thickness of the insulating layer 241, the insulating layer 241 can have a suitable manufacturing advantage, and the insulating layer 241 can be melted or decomposed at a preset temperature to allow the lithium anode layer 242 and the cathode current collector 211 to short-circuit and discharge.
[0040] In some embodiments, the lithium anode layer 242 includes a lithium-containing anode material, which includes one or more of lithium titanate, terephthalic acid, or dilithium rhodium palmitate.
[0041] In some embodiments, the lithium anode layer 242 further includes a conductive agent. The conductive agent is used to improve the conductivity of the anode material in the lithium anode layer 242. The conductive agent includes one or more of carbon black, carbon nanotubes, graphene, or graphite.
[0042] In some embodiments, the lithium anode layer 242 further includes a binder, which is used to bind together the particles of each component in the lithium anode layer 242. The binder includes one or more of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, or polytetrafluoroethylene.
[0043] In some embodiments, the thickness of the lithium anode layer 242 is 50 μm to 80 μm. For example, the thickness of the lithium anode layer 242 is 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, or a range consisting of any two values therein. By limiting the thickness of the lithium anode layer 242, the degree of reduction in the state of charge of the cathode active layer 212 during short-circuit discharge between the lithium anode layer 242 and the cathode current collector 211 can be controlled, achieving a controllable low-risk short circuit and improving safety performance.
[0044] In some embodiments, the insulating layer 241 covers the entire cathode current collector 211 in the empty foil area 211A and is adjacent to the cathode active layer 212, and the lithium anode layer 242 covers a portion of the insulating layer 241 and is separated from the cathode active layer 212. In other embodiments, the insulating layer 241 covers a portion of the cathode current collector 211 in the empty foil area 211A and is separated from the cathode active layer 212.
[0045] See also Figure 3 In some embodiments, the thermal sensing structure 24 includes a resistor layer 243, which is disposed between the cathode current collector 211 and the insulating layer 241 in the empty foil area 211A. The resistor layer 243 is used to adjust the short-circuit impedance between the lithium anode layer 242 and the cathode current collector 211. The resistor layer 243 is in contact with the cathode current collector 211, and the insulating layer 241 is stacked on the resistor layer 243 and in contact with the lithium anode layer 242. When the insulating layer 241 melts or decomposes, the lithium anode layer 242 is in contact with the resistor layer 243, and the lithium anode layer 242 is electrically connected to the cathode current collector 211 through the resistor layer 243 to discharge.
[0046] See also Figure 4 In other embodiments, the resistance layer 243 is disposed between the insulating layer 241 and the lithium anode layer 242. The insulating layer 241 is in contact with the cathode current collector 211, and the resistance layer 243 is stacked on the insulating layer 241 and in contact with the lithium anode layer 242. When the insulating layer 241 melts or decomposes, the resistance layer 243 is in contact with the cathode current collector 211, and the lithium anode layer 242 is electrically connected to the cathode current collector 211 through the resistance layer 243 to discharge.
[0047] In some embodiments, the size of the resistor layer 243 is the same as the size of the insulating layer 241, and the orthographic projection of the resistor layer 243 in the thickness direction coincides with the orthographic projection of the insulating layer 241 in the thickness direction. In other embodiments, the size of the resistor layer 243 is the same as the size of the lithium anode layer 242, and the orthographic projection of the lithium anode layer 242 in the thickness direction coincides with the orthographic projection of the resistor layer 243 in the thickness direction. In other embodiments, the orthographic projection of the lithium anode layer 242 in the thickness direction falls within the orthographic projection of the resistor layer 243 in the thickness direction, and the orthographic projection of the resistor layer 243 in the thickness direction falls within the orthographic projection of the insulating layer 241 in the thickness direction.
[0048] In some embodiments, the resistor layer 243 includes an inorganic substance, a conductive agent, and an adhesive. The inorganic substance includes one or more of metal oxides, nitrides, and carbides. The inorganic substance includes one or more of metal oxides, nitrides, or carbides. Metal oxides include boehmite, aluminum oxide, or magnesium oxide, etc. Nitrides include boron carbide ceramics or aluminum nitride ceramics, etc. Carbides include silicon carbide ceramics, etc. The conductive agent includes one or more of carbon black, carbon nanotubes, graphene, or graphite. The adhesive includes one or more of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, or polytetrafluoroethylene. By selecting the material of the resistor layer 243, the resistor layer 243 can have a suitable resistance, so that the discharge power of the short-circuit discharge between the lithium anode layer 242 and the cathode current collector 211 can be controlled, and a low short-circuit power is conducive to reducing short-circuit heat generation, and a high short-circuit power is conducive to reducing the charge state of the cathode active layer 212.
[0049] In some embodiments, the mass percentage of the conductive agent in the resistor layer 243 is 5% to 20%. For example, the mass percentage of the conductive agent in the resistor layer 243 is 5%, 8%, 10%, 12%, 15%, 18%, 20%, or a range consisting of any two of these values. By limiting the content of the conductive agent in the resistor layer 243, the resistor layer 243 can have a suitable resistance, thereby making the discharge power of the short-circuit discharge between the lithium anode layer 242 and the cathode current collector 211 controllable.
[0050] In some embodiments, the thickness of the resistor layer 243 is 2 μm to 10 μm. For example, the thickness of the resistor layer 243 is 2 μm, 5 μm, 8 μm, 10 μm, or a range consisting of any two of these values. By limiting the thickness of the resistor layer 243, the resistor layer 243 can have a suitable resistance, thereby making the discharge power of the short-circuit discharge between the lithium anode layer 242 and the cathode current collector 211 controllable.
[0051] In some embodiments, the sheet resistance of the resistor layer 243 is 1Ω to 10Ω. For example, the sheet resistance of the resistor layer 243 is 1Ω, 4Ω, 7Ω, 10Ω, or a range consisting of any two of these values. When the sheet resistance of the resistor layer 243 is within the above range, the short-circuit impedance between the lithium anode layer 242 and the cathode current collector 211 is appropriate, which is conducive to reducing short-circuit heat generation.
[0052] In some embodiments, the sheet resistance of the resistor layer 243 is 1 Ω to 5 Ω. When the sheet resistance of the resistor layer 243 is within the above range, the effect of reducing short-circuit heat generation is better.
[0053] In some embodiments, see Figure 2 The electrode assembly 20 includes a winding structure having a straight portion 201 and a curved portion 202. The curved portion 202 refers to the arc portion of the cathode electrode sheet 21, the arc portion of the anode electrode sheet 22 and the arc portion of the diaphragm 23 after the electrode assembly 20 is wound, and the straight portion 201 refers to the straight portion of the cathode electrode sheet 21, the straight portion of the anode electrode sheet 22 and the straight portion of the diaphragm 23 after the electrode assembly 20 is wound. After the electrode assembly 20 is wound, a flat multi-turn winding structure is formed, and each turn is composed of two staggered straight portions 201 and two curved portions 202. The thermal induction structure 24 is arranged on the cathode electrode sheet 21 of the curved portion 202, which is conducive to reducing the influence of the thermal induction structure 24 on the thickness of the electrode assembly 20 and improving the energy density.
[0054] In some embodiments, see Figure 2 In the case where the electrode assembly 20 has a winding structure, the thermal sensing structure 24 is disposed at the outermost circle of the cathode electrode sheet 21. The outermost circle of the cathode electrode sheet 21 refers to a circle counted from the winding end of the cathode electrode sheet 21. The outermost circle of the cathode electrode sheet 21 is closer to the outside of the electrode assembly 20 than other parts of the cathode electrode sheet 21. The heat generated by the electrode assembly 20 here is easily released to the outside of the electrode assembly 20. The thermal sensing structure 24 is disposed at the outermost circle of the cathode electrode sheet 21, and the electrochemical device 100 is safer when thermally abused.
[0055] See also Figure 5In one embodiment of the present application, an electrical device 200 is provided, including any of the above electrochemical devices 100. The electrochemical device 100 of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.
[0056] The performance of the electrochemical device provided in the present application is described below through specific examples and comparative examples.
[0057] Example 1 Preparation of cathode electrode: Lithium cobalt oxide, acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 96:2:2, and then N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 70%, and stirred evenly. The slurry is evenly coated on one surface of an aluminum foil with a thickness of 9 μm, dried at 100°C, and cold pressed to obtain a cathode electrode with a cathode active layer thickness of 80 μm, and then the above coating steps are repeated on the other surface of the cathode electrode to obtain a cathode electrode with a cathode active layer coated on both sides. The cathode electrode is cut into a specification of 82.4 mm × 1435 mm and welded to the pole ear for standby use.
[0058] according to Figure 2 A resistor layer is coated on the corresponding position of the cathode electrode, and the resistor layer includes boehmite, carbon black and polyacrylic acid. The mass percentage of carbon black in the resistor layer is 15%, the thickness of the resistor layer is 2 μm, and the film resistance of the resistor layer is 4.2Ω.
[0059] An insulating layer is coated on the resistance layer, wherein the insulating layer comprises polyethylene wax and polyacrylic acid, has a thickness of 10 μm, and has a melting point of 90° C.
[0060] A lithium anode layer is coated on the insulating layer, wherein the lithium anode layer comprises lithium titanate and polyvinylidene fluoride and has a thickness of 10 μm.
[0061] Preparation of anode electrode: Artificial graphite, acetylene black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 96:1:1.5:1.5, and then deionized water is added as a solvent to prepare a slurry with a solid content of 70%, and stirred evenly. The slurry is evenly coated on one surface of a copper foil with a thickness of 8 μm, dried at 110°C, and cold pressed to obtain an anode pole piece with a single-sided anode active layer coated with an anode active layer with a thickness of 150 μm, and then the above coating steps are repeated on the other surface of the anode pole piece to obtain an anode pole piece with a double-sided anode active layer coated. The anode pole piece is cut into a specification of 83.7 mm × 1564 mm and welded to the pole ear for standby use.
[0062] Preparation of diaphragm: A polyethylene film having a thickness of 5 μm was used as a separator.
[0063] Preparation of electrolyte: In a glove box filled with a dry argon atmosphere, organic solvents ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:1:1, and then LiPF6 was added to the above mixed organic solution to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.
[0064] Preparation of lithium-ion batteries: The cathode electrode sheet, the separator, and the anode electrode sheet are stacked in order, so that the separator is placed between the cathode electrode sheet and the anode electrode sheet to play a role of isolation, and then they are wound to obtain Figure 2 The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, injected with electrolyte, and vacuum packaged, left to stand, formed, and hot-pressed to obtain a lithium-ion battery.
[0065] Example 2-27 The difference from Example 1 is that at least one of the melting point of the insulating layer, the thickness of the insulating layer, the mass percentage of the conductive agent in the resistor layer, the thickness of the resistor layer, the film resistance of the resistor layer, and the thickness of the lithium anode layer is different.
[0066] Comparative Example 1 The difference from Example 1 is that the resistance layer, the insulating layer and the lithium anode layer are not coated during the preparation of the cathode electrode sheet, that is, the electrode assembly does not have a thermal induction structure.
[0067] Comparative Example 2 The difference from Example 1 is that the melting point of the insulating layer is different.
[0068] The test methods for various parameters of this application are described below.
[0069] Thickness test of each layer of thermal sensing structure: The cross section of the thermal sensing structure in the thickness direction is cut, and the resistance layer, the insulating layer, and the lithium anode layer in the cross section are measured using a CCD detection device (charge coupled device image sensor camera) to obtain the thickness values of the resistance layer, the insulating layer, and the lithium anode layer.
[0070] Diaphragm resistance test: Use Yuanneng Technology's electrode sheet resistor meter (BER2500) to test the resistance of the resistor layer film, and take the average value of the resistance values measured at 12 different positions as the film resistance value.
[0071] Hot box test: Place 10 lithium-ion batteries in a heating box, heat the box to a preset temperature (e.g. 126°C, 130°C or 134°C) at a heating rate of 5°C / min, keep the temperature at the preset temperature for 1 hour, and observe whether the lithium-ion battery burns. If it does not burn, it is considered to have passed. Statistical analysis of the hot box pass rate of lithium-ion batteries at different preset temperatures.
[0072] Table 1 lists the parameters and evaluation results of various embodiments and comparative examples.
[0073] Table 1 As can be seen from Table 1, compared with Comparative Examples 1 and 2, each embodiment is provided with a thermal induction structure, and the melting point of the insulating layer is 90°C-120°C. After the temperature exceeds the melting point of the insulating layer, the insulating layer melts, causing the cathode current collector and the lithium anode layer to short-circuit and discharge, thereby reducing the charge state of the cathode active layer, improving the thermal stability of the cathode active layer, and improving the hot box test performance. Among them, the lithium-ion battery of Comparative Example 1 has a low pass rate in the 130°C hot box test, and cannot pass the 134°C hot box test and the 136°C hot box test. This is because there is no thermal induction structure in Comparative Example 1, and the structure of the cathode material is destroyed at high temperature and reacts violently with the electrolyte to generate a large amount of heat, which reduces the pass rate of the hot box test. The lithium-ion battery of Comparative Example 2 also has a low pass rate in the 130°C hot box test, and cannot pass the 134°C hot box test and the 136°C hot box test. This is because the melting point of the insulating layer in Comparative Example 2 is too high, and the insulating layer melts when the lithium-ion battery has thermal runaway, causing the lithium anode layer and the cathode current collector to short-circuit and discharge. In this case, the effect of improving thermal runaway by reducing the charge state of the cathode active layer is not obvious. In Examples 3-5, the melting point of the insulating layer is 105°C-115°C, the manufacturing rate of the insulating layer is high, and the pass rate of the hot box test is high.
[0074] As can be seen from Table 1, in Examples 1, 7-9, the thickness of the insulating layer is 5μm-20μm, and as the thickness of the insulating layer increases, the pass rate of the hot box test shows a decreasing trend. This is because when the thickness of the insulating layer is too thick, after the temperature exceeds the melting point of the insulating layer, the insulating layer may not be fully melted to cause the cathode current collector and the lithium anode layer to be electrically connected to short-circuit discharge, and the improvement effect on thermal runaway is reduced. When the insulating layer is too thin, the insulating layer is not easy to manufacture, and the manufacturing process becomes more difficult.
[0075] It can be seen from Table 1 that compared with Examples 10 and 23, the diaphragm resistance of the resistance layer in Examples 1 and 11-22 is 1Ω-10Ω, and the pass rate of the hot box test is high. This is because the appropriate resistance balances the effect of improving thermal runaway caused by the short-circuit discharge between the cathode current collector and the lithium anode layer and the effect of the generated heat on thermal runaway. In Example 10, the diaphragm resistance of the resistance layer is less than 1Ω, the diaphragm resistance is small, the short-circuit power between the cathode current collector and the lithium anode layer is large, and the short-circuit heat generation is large, resulting in a high probability of thermal runaway. In Example 23, the diaphragm resistance of the resistance layer is greater than 10Ω, the diaphragm resistance is too large, the short-circuit power between the cathode current collector and the lithium anode layer is small, and the short-circuit discharge between the cathode current collector and the lithium anode layer reduces the charge state of the cathode active layer and thus improves thermal runaway. The effect is limited. Among them, the diaphragm resistance of the resistance layer in Examples 11-19 is 1Ω-5Ω, and the pass rate of the hot box test is higher. It can also be known from Examples 1 and 10-23 that the content of the conductive agent in the resistor layer is negatively correlated with the film resistance of the resistor layer, and the thickness of the resistor layer is positively correlated with the film resistance of the resistor layer.
[0076] It can be seen from Examples 1 and 24-27 that as the thickness of the lithium anode layer increases, the pass rate of the hot box test shows a trend of first increasing and then decreasing. In Example 24, the thickness of the lithium anode layer is less than 50 μm, which is relatively small. The effect of the short-circuit discharge between the lithium anode layer and the cathode current collector on reducing the charge state of the cathode active layer and thus improving thermal runaway is limited, and the pass rate of the conductive hot box test is low. In Example 27, the thickness of the lithium anode layer is greater than 80 μm, which is relatively large. The heat generated by the short-circuit discharge between the lithium anode layer and the cathode current collector has a greater impact on thermal runaway, and the pass rate of the conductive hot box test is low.
[0077] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as limitations on the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.
Claims
1. An electrochemical device, comprising an electrode assembly, wherein the electrode assembly comprises a cathode electrode sheet, wherein the cathode electrode sheet comprises a cathode current collector and a cathode active layer, wherein the cathode current collector comprises an empty foil area not covered by the cathode active layer, wherein: The electrode assembly also includes a thermal induction structure, which is arranged in the empty foil area. The thermal induction structure includes an insulating layer and a lithium anode layer stacked together. The insulating layer is arranged between the empty foil area and the lithium anode layer, and the insulating layer can melt or decompose at a temperature of 90°C to 120°C.
2. The electrochemical device according to claim 1, characterized in that The thermal induction structure further comprises a resistance layer, and the resistance layer is arranged between the empty foil area and the insulating layer.
3. The electrochemical device according to claim 2, characterized in that The resistive layer is in contact with the cathode current collector.
4. The electrochemical device according to claim 1, characterized in that The thermal induction structure further includes a resistance layer, and the resistance layer is arranged between the insulating layer and the lithium anode layer.
5. The electrochemical device according to any one of claims 2 to 4, characterized in that The resistance layer satisfies at least one of the following conditions: (a) the resistance layer comprises an inorganic substance and a conductive agent, the inorganic substance comprises one or more of metal oxides, nitrides, and carbides, and the conductive agent comprises one or more of carbon black, carbon nanotubes, graphene, or graphite; (b) the mass percentage of the conductive agent in the resistance layer is 5% to 20%; (c) the thickness of the resistance layer is 2 μm to 10 μm; (d) The sheet resistance of the resistance layer is 1Ω to 10Ω.
6. The electrochemical device according to claim 1, wherein: The insulating layer satisfies at least one of the following conditions: (a) the insulating layer comprises one or more of low-density polyethylene, polyethylene wax, oxidized polyethylene wax, polytetrafluoroethylene-modified polyethylene wax, sulfur, polyethylene oxide, triacetate cellulose, or solid paraffin; (b) the thickness of the insulating layer is 5 μm to 20 μm; (c) The insulating layer can be melted or decomposed at a temperature of 105°C to 115°C.
7. The electrochemical device according to claim 1, characterized in that The lithium anode layer satisfies at least one of the following conditions: (a) the lithium anode layer comprises one or more of lithium titanate, lithium terephthalate or lithium rhodanoate; (b) The thickness of the lithium anode layer is 50 μm to 80 μm.
8. The electrochemical device according to claim 1, wherein The electrode assembly has a winding structure, and the thermal induction structure is arranged on the outermost circle of the cathode electrode.
9. The electrochemical device according to claim 1, wherein: The electrode assembly is a winding structure having a straight portion and a curved portion, and the thermal sensing structure is arranged at the curved portion.
10. An electrical device, characterized in that: Comprising the electrochemical device according to any one of claims 1 to 9.