A carbon-coated slurry for carbon-coated current collector, a preparation method thereof, a carbon-coated current collector, and a lithium ion battery

Abstract

This invention belongs to the field of battery materials technology, providing a carbon-coated slurry for carbon-coated current collectors, its preparation method, a carbon-coated current collector, and a lithium-ion battery. The carbon-coated slurry includes a temperature-sensitive binder, a carbon-based conductive agent, ceramic materials, and a solvent. The temperature-sensitive binder includes an aqueous matrix and thermally expandable microspheres doped in the aqueous matrix. This invention introduces a temperature-sensitive binder containing thermally expandable microspheres into the carbon-coated slurry. When the battery temperature abnormally rises to the initial expansion temperature of the microspheres, the microspheres expand violently, disrupting the continuous network formed by the conductive agent, achieving a "thermal shutdown" effect. This converts the heat signal into a rapidly increasing resistance signal, actively and quickly cutting off the current path, thus providing safety protection before thermal runaway occurs. This built-in mechanism can intervene in the thermal runaway process at its source, preventing the continuous accumulation of heat from triggering a chain reaction, and fundamentally improving the thermal safety of lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a carbon coating slurry for carbon coating current collectors and its preparation method, carbon coating current collectors, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used due to their high energy density and good cycle performance, but the risk of thermal runaway remains a key bottleneck restricting their safety. Traditional current collectors (mainly aluminum and copper foil) exhibit high surface activity under conditions of internal short circuits, overcharging, or heating, easily undergoing violent exothermic reactions with the electrolyte, accelerating the spread of thermal runaway. Especially under extreme abuse conditions, localized high temperatures can cause the separator to melt, leading to direct contact between the positive and negative electrodes, triggering a chain reaction of exothermic reactions, and even fire and explosion. Against this backdrop, developing carbon-coated current collectors with safety coatings has become an important technological path to improve the intrinsic safety of batteries. This technology constructs a functional coating on the surface of traditional metal current collectors, utilizing the physical barrier effect and chemical stability of the coating to effectively prevent direct contact between the current collector and the electrolyte, suppressing interfacial side reactions. Simultaneously, the coating enhances the current collector's heat resistance, mechanical strength, and adhesion to active materials, mitigating the occurrence and development of internal short circuits from multiple dimensions. This technological approach aims to construct a "passive safety defense line" at the level of key battery components, thereby providing core material support for the development of next-generation lithium batteries with high energy density and high safety.

[0003] However, existing functional coatings for carbon-coated current collectors still have many technical shortcomings in practical applications. First, the interfacial bonding between commonly used carbon coating materials and metal current collectors is weak. Under conditions of repeated charging and discharging of batteries causing volume expansion and contraction, electrode rolling, and even abuse such as needle punching and extrusion, the coating is prone to cracking, peeling, or even partial detachment, resulting in partial exposure of the current collector to the electrolyte, thus weakening its safety protection effect. Second, most coatings are rigid inorganic particle stacking structures, which are brittle and lack flexibility, making it difficult to adapt to the bending and deformation of flexible or high-area-capacity electrodes, limiting their application in new battery structures. Furthermore, although some coatings can reduce interfacial contact resistance, they are prone to thermal decomposition or side reactions with the electrolyte at high temperatures (>150℃), failing to maintain a stable physical barrier in the early stages of thermal runaway.

[0004] Therefore, fundamentally improving the thermal safety of lithium-ion batteries and meeting the urgent need for high-safety current collectors is a technical challenge that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a carbon-coated current collector slurry, its preparation method, the carbon-coated current collector, and a lithium-ion battery. This invention introduces a temperature-sensitive binder with a thermal expansion switching effect into the carbon-coated slurry. When the internal temperature of the battery abnormally rises and reaches or even exceeds the initial expansion temperature of the thermally expanding microspheres, the microspheres undergo violent volume expansion, physically disrupting the continuous conductive network formed by the conductive agent. This achieves a "thermal shutdown" effect on the current, meaning the heat signal is converted into a rapidly increasing resistance signal in real time, actively and quickly cutting off the current path, thus providing safety protection before thermal runaway occurs. This transformation of traditional passive protection materials into a built-in safety mechanism with active early warning and power-off functions can intervene at the source of the battery's thermal runaway process, preventing the continuous accumulation of heat from triggering a chain of exothermic reactions, fundamentally improving the thermal safety of lithium-ion batteries. In summary, this solution provides a forward-looking, built-in safety solution for constructing novel lithium-ion batteries with built-in temperature sensing and overcurrent self-protection functions, and is expected to significantly improve the safety threshold of high-energy-density lithium battery systems, possessing significant scientific value and broad application prospects.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a carbon coating slurry for carbon-coated current collectors, the carbon coating slurry comprising a temperature-sensitive binder, a carbon-based conductive agent, a ceramic material, and a solvent.

[0007] The temperature-sensitive adhesive comprises an aqueous matrix and thermally expandable microspheres doped in the aqueous matrix.

[0008] This invention introduces a temperature-sensitive binder with a thermal expansion switching effect into the carbon coating slurry. When the internal temperature of the battery rises abnormally and reaches or exceeds the initial expansion temperature of the thermally expanding microspheres, the microspheres undergo violent volume expansion, physically disrupting the continuous conductive network formed by the conductive agent. This achieves a "thermal shutdown" effect on the current, meaning the heat signal is converted into a rapidly increasing resistance signal in real time, actively and quickly cutting off the current path, thus providing safety protection before thermal runaway occurs. This transformation of traditional passive protection materials into a built-in safety mechanism with active early warning and power-off functions can intervene at the source of the battery's thermal runaway process, preventing the continuous accumulation of heat from triggering a chain of exothermic reactions, fundamentally improving the thermal safety of lithium-ion batteries. In summary, this solution provides a forward-looking, built-in safety solution for constructing novel lithium-ion batteries with built-in temperature sensing and overcurrent self-protection functions, and is expected to significantly improve the safety threshold of high-energy-density lithium battery systems, possessing significant scientific value and broad application prospects.

[0009] The temperature-sensitive binder introduced in this invention consists of two key processes: a conductivity mechanism under normal conditions and a resistance transition mechanism under triggered conditions. 1) Conductivity mechanism under normal conditions: Ceramic materials (such as boehmite particles) form the main framework, and conductive agents (conductive carbon black particles) are composited with the ceramic materials (such as adhering to the surface of boehmite and filling the pores), forming a three-dimensional permeable network through point-to-point contact; thermally expanded microspheres are dispersed as solid particles in the system and are encapsulated by the aqueous matrix; current is transmitted through tunneling effect and direct contact conduction between conductive agent (conductive carbon black) particles. The overall resistance of the coating depends on the integrity of the conductive network and the contact resistance; at this time, the temperature-sensitive binder firmly bonds the components, and the microspheres are in a "dormant" unexpanded state, which does not significantly interfere with the conductive network. 2) Resistive transition mechanism in the triggered state: When the temperature reaches or exceeds the initial expansion temperature of the thermally expanding microsphere, heat is transferred to the microsphere, and the diameter of the microsphere can expand to several times its original size, and the volume can expand to tens of times. This is a highly nonlinear physical change. Therefore, the rapidly expanding microsphere acts as a powerful "expansion source," generating huge radial compressive forces on the tightly bonded conductive agent-ceramic material-water matrix around it. This compressive force directly causes adjacent conductive particles to be pushed apart and separated, and the originally point-contact conductive nodes are physically broken. The tunneling effect distance is greatly extended to the point of failure, similar to a continuous conductive network being divided into countless isolated conductive particles. "Isolated island"; at the same time, the water-based matrix softens due to the temperature exceeding its glass transition temperature, the modulus decreases, and it is even less able to resist the deformation caused by the expansion of microspheres, which instead promotes the dissociation process of the conductive network; although the insulating skeleton (such as boehmite skeleton) is stable, it cannot prevent this local structural reorganization dominated by internal expansion. At this time, the internal structure of the coating has undergone irreversible (or highly delayed) permanent changes: the conductive network is severely damaged, the microspheres become hollow large-volume foams, and the coating resistance will stabilize at an extremely high level, which is equivalent to connecting a huge resistor in series with the current collector, thereby effectively limiting or blocking abnormal current and realizing the safety protection function.

[0010] It should be noted that the thermal expansion microspheres provided by this invention can be purchased directly, for example, from Nouryon, model Expansion 091DU80.

[0011] Preferably, the aqueous matrix comprises polyurethane.

[0012] Preferably, the doping amount of the thermally expandable microspheres is 5-15 wt% of the solid mass of the aqueous matrix, for example, it can be 5 wt%, 10 wt% or 15 wt%, preferably 10 wt%.

[0013] In this invention, the appropriate doping amount of thermally expandable microspheres can fully realize the "thermal shutdown" effect on the current, that is, the heat signal is converted into a rapidly increasing resistance signal in real time, actively and quickly cutting off the current path, thereby achieving safety protection before thermal runaway occurs. This built-in safety mechanism, which transforms traditional passive protection materials into active early warning and power-off functions, can intervene in the thermal runaway process of the battery at the source, avoid the continuous accumulation of heat and the chain exothermic reaction, and fundamentally improve the thermal safety of lithium-ion batteries.

[0014] Preferably, the thermally expandable microspheres comprise a polymer shell and a low-boiling-point liquid foaming agent encapsulated within the polymer shell.

[0015] When the internal temperature of the battery rises abnormally and reaches or even exceeds the initial expansion temperature of the thermal expansion microspheres, the glass transition temperature of the polymer shell of the thermal expansion microspheres is surpassed. The shell changes from a glassy state to a highly elastic state, softens and loses its rigidity. After the shell softens, the low-boiling-point liquid foaming agent inside rapidly vaporizes, generating huge internal pressure. Driven by the internal high pressure, the softened shell is rapidly expanded like a balloon. The diameter of the microsphere can expand to several times its original size, and the volume can expand to tens of times. This is a highly nonlinear physical change. Therefore, the rapidly expanding microsphere acts as a powerful "expansion source" and exerts huge radial extrusion force on the tightly bonded conductive agent-ceramic material-water matrix around it. This extrusion force directly causes adjacent conductive particles to be pushed away and separated. The originally point-contact conductive nodes are physically broken, and the tunneling effect distance is greatly extended to the point of failure. It is similar to a continuous conductive network being divided into countless isolated conductive "islands".

[0016] It should be noted that the low-boiling-point liquid foaming agent may be selected from at least one of alkanes having 3-6 carbon atoms, such as one or more of n-pentane, isopentane, neopentane, and cyclopentane, or selected from hydrofluorocarbon foaming agents, etc.

[0017] Preferably, the initial expansion temperature of the thermally expandable microspheres is 80-85℃, for example, it can be 80℃, 82℃ or 85℃.

[0018] Preferably, the polymer shell is made of polyurethane.

[0019] Preferably, the carbon-based conductive agent comprises conductive carbon black.

[0020] Preferably, the ceramic material comprises boehmite.

[0021] Preferably, based on the total solid mass of the carbon-coated slurry, the total content of the carbon-based conductive agent and ceramic material is 50-65%, for example, it can be 50%, 55%, 60% or 65%, etc.

[0022] Preferably, the mass ratio of the carbon-based conductive agent to the ceramic material is (1-5):(5-10), wherein the selection range of the carbon-based conductive agent "1-5" can be, for example, 1, 2, 3, 4 or 5, and the selection range of the ceramic material "5-10" can be, for example, 5, 6, 7, 8, 9 or 10.

[0023] This invention selects conductive carbon black and boehmite as carbon-based conductive agent and ceramic material, respectively. The two materials have completely opposite properties: one is a conductor and the other is an insulator. The amount and ratio of the two added are the "golden balance point" that determines the final comprehensive performance of the coating. It directly affects the coating's conductivity, mechanical strength, thermal stability, compatibility with electrolyte, and most importantly, its temperature-sensitive switching performance. The reasons are as follows: 1) Conductive carbon black is the only conductive phase, and its content must reach and exceed the "penetration threshold" to form a continuous conductive path, giving the coating a low initial sheet resistance. If the mass ratio of carbon-based conductive agent to ceramic material is too low, i.e., there is relatively too little conductive carbon black, the conductive network will be imperfect, the initial resistance will be too high, and the normal performance of the battery will be affected. Boehmite, as a hard ceramic particle, is the structural skeleton of the coating, providing mechanical strength, hardness, and puncture resistance, preventing the coating from falling off or pulverizing during battery assembly and use. If the mass ratio of carbon-based conductive agent to ceramic material is too high, i.e., there is relatively too little boehmite, the coating will be too "soft" and "brittle", with insufficient mechanical strength, and the binder may be "diluted" by too much conductive carbon black, resulting in a decrease in adhesion. 2) In order to achieve a sharp jump in resistance at temperature triggering, the initial conductive network must be efficient but "fragile", i.e., the conductive particles are in a "critical contact" state. If there is too much conductive carbon black, a very dense, multi-connected conductive network will be formed, even when heated. Even after the expanded microspheres push away some particles, a large number of redundant conductive pathways remain, resulting in a slow and limited increase in resistance. The "switching effect" is sluggish and cannot achieve an exponential leap. If there is too little conductive carbon black, the conductive network will become sparse, approaching the edge of the penetration threshold. Its initial resistance is already too high, and the expansion of the microspheres may directly cause the network to collapse completely. However, because the initial network is too weak, this change lacks the dramatic contrast from "good conductivity" to "insulation" and may affect the efficiency of normal battery operation. Boehmite, as an insulating rigid particle, occupies a large volume in the coating. The appropriate mass ratio of carbon-based conductive agent to ceramic material means that the conductive particles just fill the pores between the boehmite skeleton to form an optimal conductive network. When the microspheres expand due to heat, what they need to "push away" are mainly these conductive particles filling the pores. At this time, the appropriate boehmite content provides the necessary rigid boundary, so that the expansion force of the microspheres can be more effectively concentrated on the point of breaking the conductive contact, rather than being absorbed by the relaxation of the entire coating structure.

[0024] Preferably, based on the total solid mass of the carbon coating slurry, the content of the temperature-sensitive adhesive is 35-50%, for example, it can be 35%, 40%, 45% or 50%, etc.

[0025] Preferably, the mass ratio of the temperature-sensitive adhesive to the carbon-based conductive agent is (4-9):(1-3), wherein the selection range of the temperature-sensitive adhesive "4-9" can be, for example, 4, 5, 6, 7, 8 or 9, and the selection range of the carbon-based conductive agent "1-3" can be, for example, 1, 2 or 3.

[0026] Preferably, the mass ratio of the temperature-sensitive adhesive to the ceramic material is (4-9):(3-10), wherein the selection range of the temperature-sensitive adhesive "4-9" can be, for example, 4, 5, 6, 7, 8 or 9, and the selection range of the ceramic material "3-10" can be, for example, 3, 4, 5, 6, 7, 8, 9 or 10.

[0027] In this invention, a synergistic effect exists between the temperature-sensitive binder, the carbon-based conductive agent, and the ceramic material at a suitable mass ratio: 1) Relationship between the temperature-sensitive binder and the carbon-based conductive agent: The temperature-sensitive binder acts as a bonding medium, bonding and fixing discrete conductive particles, helping them form and maintain a stable three-dimensional conductive network. The adhesive force and rheological properties of the temperature-sensitive binder affect the dispersion state and network uniformity of the conductive particles; 2) Relationship between the carbon-based conductive agent and the ceramic material: Ceramic material particles, as hard and insulating primary particles, form the basic porous framework structure of the coating, while conductive particles act as secondary fillers, adhering to the surface of the ceramic material particles and filling their particles. 3) The relationship between thermosensitive binder and ceramic material: "Connection" and "anchor point". The thermosensitive binder firmly bonds the ceramic material particles together and makes them adhere tightly to the current collector matrix, forming the overall mechanical basis of the coating. Without the thermosensitive binder, the ceramic material is just loose powder. In addition, as rigid particles, ceramic material particles can provide a reaction force fulcrum for the expansion of thermosensitive binder. When the microspheres expand, the soft water matrix will deform, but the adjacent ceramic material particles are not easy to move. This makes the expansion force more concentrated on the relatively easier-to-move conductive particles, thereby amplifying the efficiency of destroying the conductive network.

[0028] Preferably, the carbon coating slurry further includes a pH adjuster. For example, it could be a sodium hydroxide solution.

[0029] Preferably, the pH of the carbon coating slurry is 5-8, for example, it can be 5, 6, 7 or 8.

[0030] The present invention adjusts the pH of the carbon coating slurry to 5-8, which is beneficial to improving the uniformity and dispersibility of the slurry.

[0031] Preferably, the carbon coating slurry further includes a wetting agent, and the amount of the wetting agent added is 5-15% of the total mass of the carbon coating slurry, for example, it can be 5%, 10% or 15%.

[0032] For example, the wetting agent may be a polyether siloxane, a modified polyether siloxane, or an alcohol reagent, such as isopropanol.

[0033] In this invention, the main function of the wetting agent is to reduce the surface tension of the slurry and improve the film quality of the coating.

[0034] Preferably, the carbon coating slurry further includes a dispersant. For example, it could be ethylenediaminetetraacetic acid (EDTA).

[0035] Preferably, the solid content of the carbon coating slurry is 12-18 wt%, for example, it can be 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, or 18 wt%.

[0036] In a second aspect, the present invention provides a method for preparing a carbon coating slurry for a carbon-coated current collector as described in the first aspect, the preparation method comprising the following steps: Prepare the temperature-sensitive adhesive solution.

[0037] The carbon-based conductive agent, ceramic material, the temperature-sensitive adhesive liquid, and solvent are mixed to obtain the carbon-coated current collector slurry.

[0038] Preferably, the method for preparing the temperature-sensitive adhesive solution includes the following steps: The temperature-sensitive adhesive solution is prepared by blending waterborne polyurethane emulsion, wetting agent and thermally expanded microspheres, followed by curing and defoaming treatment.

[0039] Preferably, the solid content of the temperature-sensitive adhesive solution is 15-25 wt%, for example, it can be 15 wt%, 20 wt%, or 25 wt%.

[0040] Preferably, the viscosity of the temperature-sensitive adhesive solution is 800-3000 mPa·s, for example, it can be 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 2000 mPa·s, 2500 mPa·s, or 3000 mPa·s, etc.

[0041] Preferably, the amount of the wetting agent added is 0.5-1.5% of the mass of the waterborne polyurethane emulsion, for example, it can be 0.5%, 1.0% or 1.5%.

[0042] Preferably, during the maturation process, the stirring rate is 150-200 rpm, for example, 150 rpm, 175 rpm, or 200 rpm.

[0043] Preferably, the aging process takes 25-35 minutes, for example, 25 minutes, 30 minutes, or 35 minutes.

[0044] This invention controls the stirring rate during the curing process to a low rate, which can, to a certain extent, balance the uniform dispersion of microspheres with the integrity of the shell, and preferentially avoid the cracking of the microsphere shell and premature foaming caused by high-speed shearing; at the same time, it compensates for the uneven dispersion problem that may be caused by low-speed stirring by extending the stirring time.

[0045] Preferably, during the mixing process, a dispersant, a pH adjuster, and a wetting agent are also added.

[0046] Preferably, the preparation method includes the following steps: (1) Preparation of temperature-sensitive adhesive solution: In an aqueous polyurethane emulsion with a solid content of 15-25 wt% (e.g., 15 wt%, 20 wt%, or 25 wt%), a wetting agent is slowly added at a stirring rate of 250-350 rpm (e.g., 250 rpm, 300 rpm, or 350 rpm). Then, thermally expanded microspheres are slowly added at a stirring rate of 150-200 rpm (e.g., 150 rpm, 175 rpm, or 200 rpm). After this, a curing treatment is performed at a stirring rate of 150-200 rpm for 25-35 minutes. Then, a defoamer is added and the mixture is stirred at a stirring rate of 150-200 rpm (e.g., 150 rpm, 175 rpm, or 200 rpm) for 5-15 minutes (e.g., 5 minutes, 10 minutes, or 15 minutes). Finally, the mixture is allowed to stand to defoam, resulting in the thermosensitive adhesive solution.

[0047] The thermosensitive adhesive solution has a solid content of 15-25 wt%; a viscosity of 800-3000 mPa·s; an addition amount of wetting agent of 0.5-1.5% of the mass of the waterborne polyurethane emulsion; and a doping amount of thermally expandable microspheres of 5-15 wt% of the solid mass of the waterborne polyurethane emulsion.

[0048] (2) Under stirring conditions, the temperature-sensitive adhesive solution is diluted to obtain a diluted adhesive solution with a solid content of 4-6 wt% (e.g., 4 wt%, 5 wt% or 6 wt%) and a viscosity of 100-300 mPa·s (e.g., 100 mPa·s, 150 mPa·s, 200 mPa·s, 250 mPa·s or 300 mPa·s). Then, a dispersant, a carbon-based conductive agent, a ceramic material, a pH adjuster and a wetting agent are added in sequence. After homogenization, a carbon-coated current collector slurry is obtained.

[0049] The carbon-based conductive agent includes conductive carbon black, and the ceramic material includes boehmite; the carbon-based conductive agent and the ceramic material are added in multiple stages.

[0050] For example, "multiple times" refers to 2 times, 3 times, or 4 times, etc.

[0051] Preferably, the dilution process includes: stirring deionized water and temperature-sensitive adhesive solution at a stirring rate of 1000-1200 rpm (e.g., 1000 rpm, 1050 rpm, 1100 rpm, or 1200 rpm).

[0052] Preferably, during the addition of the dispersant, the stirring rate is 1000-1200 rpm, for example, 1000 rpm, 1050 rpm, 1100 rpm or 1200 rpm.

[0053] Preferably, the step of adding the carbon-based conductive agent and ceramic material in multiple stages includes: The carbon-based conductive agent and ceramic material are added in two separate portions, with a stirring speed of 2000-2600 rpm during the addition process (e.g., 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, or 2600 rpm, etc.).

[0054] Preferably, during the addition of the wetting agent, the stirring rate is 10-15 rpm, for example, 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm.

[0055] Thirdly, the present invention provides a carbon-coated current collector, the carbon-coated current collector comprising a current collector substrate and a coating disposed on at least one side surface of the current collector substrate, the coating being made of a carbon-coating slurry for carbon-coated current collectors as described in the first aspect.

[0056] Preferably, the method for preparing the coating includes: The carbon-coated current collector is coated with carbon slurry on at least one side of the current collector substrate, and then baked to form a coating.

[0057] Fourthly, the present invention provides a lithium-ion battery, wherein the electrode plates of the lithium-ion battery include a carbon-coated current collector as described in the third aspect.

[0058] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0059] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces a temperature-sensitive binder with a thermal expansion switching effect into the carbon coating slurry. When the internal temperature of the battery rises abnormally and reaches or even exceeds the initial expansion temperature of the thermal expansion microspheres, the thermal expansion microspheres will undergo violent volume expansion, physically destroying the continuous conductive network formed by the conductive agent, thereby achieving a "thermal shutdown" effect on the current. That is, the heat signal is converted into a rapidly increasing resistance signal in real time, actively and quickly cutting off the current path, thus achieving safety protection before thermal runaway occurs. This transformation of traditional passive protection materials into a built-in safety mechanism with active early warning and power-off functions can intervene in the thermal runaway process of the battery at its source, avoiding the continuous accumulation of heat that triggers a chain of exothermic reactions, and fundamentally improving the thermal safety of lithium-ion batteries. In summary, this solution provides a forward-looking, built-in safety solution for constructing a new type of lithium-ion battery with built-in temperature sensing and overcurrent self-protection functions. It is expected to significantly improve the safety threshold of high-energy-density lithium battery systems and has important scientific value and broad application prospects.

[0060] (2) The present invention has low production cost and low maintenance cost, which is conducive to its widespread use. Detailed Implementation

[0061] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0062] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0063] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0064] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0065] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0066] It should be noted that the main raw materials used in the preparation of the temperature-sensitive adhesive in the following embodiments include: ① waterborne polyurethane dispersion, solid content ~35%, Tg ~65℃, model A Bayer Dispercoll U53; ② thermally expandable microspheres (T0=80℃, T max =95℃), purchased from Nouryon, model number Expansion 091DU80; ③ Nonionic wetting agent, purchased from BYK Chemical, model number BYK-346; ④ Defoamer, purchased from BYK Chemical, model number BYK-024; ⑤ Ethanol, purchased from Sinopharm Group, model number Fisher-A995-4F, HPLC 4L, Sinopharm code FA9954F4L; ⑥ Deionized water.

[0067] It should be noted that the main raw materials used in the preparation of the carbon coating slurry in the following embodiments include: ① Binder: self-made temperature-sensitive binder; ② Conductive carbon black: Cabot Chemical, model SHYT-150P; ③ Boehmite: purchased from Sinopharm Group, model: 3.4µm (Wokai), 500g, Sinopharm code XW01131823603; ④ Sodium hydroxide: purchased from Sinopharm Group, model: AR (Shanghai Test) (flakes), 500g, Sinopharm code 10019764; ⑤ Isopropanol: purchased from Sinopharm Group, model: HPLC (Shanghai Test), ≥99.7%, 500mL, Sinopharm code 40064360; ⑥ Deionized water, self-made; ⑦ Ethylenediaminetetraacetic acid: purchased from Sinopharm Group, model: AR (Shanghai Test), ≥99.5%, 250g, Sinopharm code 10009617.

[0068] Example 1 This embodiment provides a carbon coating slurry for carbon-coated current collectors, the carbon coating slurry comprising a temperature-sensitive binder, conductive carbon black, boehmite, pH adjuster, wetting agent, dispersant, and pure water.

[0069] The temperature-sensitive adhesive comprises a polyurethane matrix and thermally expandable microspheres doped in the polyurethane matrix; the doping amount of the thermally expandable microspheres is 10 wt% of the solid mass of the polyurethane matrix; the thermally expandable microspheres comprise a polyurethane shell and a low-boiling-point liquid foaming agent encapsulated inside the polyurethane shell.

[0070] Based on the total solid mass of the carbon coating slurry, the total mass of the conductive carbon black and boehmite is 50%, and the mass ratio of the conductive carbon black to boehmite is 2:8; based on the total solid mass of the carbon coating slurry, the mass of the temperature-sensitive binder is 50%; the mass ratio of the temperature-sensitive binder to the conductive carbon black is 5:1, and the mass ratio of the temperature-sensitive binder to the boehmite is 5:4.

[0071] The pH adjuster is a 0.1 mol / L sodium hydroxide solution; the pH of the carbon coating slurry is 6.5; the wetting agent is isopropanol, and the amount added is 10% of the total mass of the carbon coating slurry; the dispersant is ethylenediaminetetraacetic acid, and the amount added is 3% of the total solid mass of the carbon coating slurry; the solid content of the carbon coating slurry is 15 wt%.

[0072] This embodiment also provides a method for preparing the above-mentioned carbon coating slurry for carbon-coated current collectors, the preparation method comprising the following steps: (1) Preparation of temperature-sensitive adhesive solution: (1-1) Provide an aqueous polyurethane dispersion, dilute it with deionized water to a solid content of 20wt% to obtain an aqueous polyurethane emulsion; provide thermally expandable microspheres and vacuum dry them at 40℃ for 2h for later use.

[0073] (1-2) In the waterborne polyurethane emulsion, a nonionic wetting agent (BYK-346) is slowly added at a stirring rate of 300 rpm, and then thermally expanded microspheres are slowly sprinkled in at a stirring rate of 175 rpm. After that, the mixture is cured at a stirring rate of 175 rpm for 30 min. Then, 2-3 drops of defoamer (BYK-024) are added and stirred at a stirring rate of 175 rpm for 10 min. Finally, the mixture is allowed to stand to defoam, and the temperature-sensitive adhesive solution is obtained.

[0074] The thermosensitive adhesive solution has a solid content of 20 wt%; the viscosity of the thermosensitive adhesive solution is 1900 mPa·s; the amount of nonionic wetting agent added is 1% of the mass of the waterborne polyurethane emulsion; and the amount of thermally expanding microspheres doped is 10 wt% of the solid mass of the waterborne polyurethane emulsion.

[0075] (2) In a 200L double-star mixing tank, deionized water and the temperature-sensitive adhesive solution are stirred and dispersed at a stirring rate of 1100rpm for 30min, and then diluted to obtain a diluted adhesive solution with a solid content of 5wt% and a viscosity of 150mPa·S.

[0076] Add the dispersant ethylenediaminetetraacetic acid and stir at 1100 rpm for 30 min to disperse.

[0077] Add half of the conductive carbon black and half of the boehmite, and stir at 2300 rpm for 30 min. Then add the remaining conductive carbon black and boehmite, and stir at 2300 rpm for 30 min.

[0078] Add deionized water to reduce the solid content of the slurry to 20 wt%, and stir and disperse at a stirring rate of 2300 rpm for 30 min.

[0079] Add 0.1 mol / L sodium hydroxide solution as a pH adjuster to make the pH of the slurry 6.5.

[0080] Isopropanol was added as a wetting agent, and the mixture was stirred at 12 rpm for 40 minutes before being discharged.

[0081] The discharged slurry was homogenized twice on a homogenizer at a pressure of 600 bar to obtain a carbon coating slurry for carbon coating current collectors.

[0082] Example 2 This embodiment provides a carbon coating slurry for carbon-coated current collectors, the carbon coating slurry comprising a temperature-sensitive binder, conductive carbon black, boehmite, pH adjuster, wetting agent, dispersant, and pure water.

[0083] The temperature-sensitive adhesive comprises a polyurethane matrix and thermally expandable microspheres doped in the polyurethane matrix; the doping amount of the thermally expandable microspheres is 5 wt% of the solid mass of the polyurethane matrix; the thermally expandable microspheres comprise a polyurethane shell and a low-boiling-point liquid foaming agent encapsulated inside the polyurethane shell.

[0084] Based on the total solid mass of the carbon coating slurry, the total mass of the conductive carbon black and boehmite is 55%, and the mass ratio of the conductive carbon black to boehmite is 1:10; based on the total solid mass of the carbon coating slurry, the mass of the temperature-sensitive binder is 45%; the mass ratio of the temperature-sensitive binder to the conductive carbon black is 9:1, and the mass ratio of the temperature-sensitive binder to the boehmite is 9:10.

[0085] The pH adjuster is a 0.1 mol / L sodium hydroxide solution; the pH of the carbon coating slurry is 7; the wetting agent is isopropanol, and the amount added is 5% of the total mass of the carbon coating slurry; the dispersant is ethylenediaminetetraacetic acid, and the amount added is 3% of the total solid mass of the carbon coating slurry; the solid content of the carbon coating slurry is 15 wt%.

[0086] This embodiment also provides a method for preparing the above-mentioned carbon coating slurry for carbon-coated current collectors, the preparation method comprising the following steps: (1) Preparation of temperature-sensitive adhesive solution: (1-1) Provide an aqueous polyurethane dispersion, dilute it with deionized water to a solid content of 15wt% to obtain an aqueous polyurethane emulsion; provide thermally expandable microspheres and vacuum dry them at 40℃ for 2h for later use.

[0087] (1-2) In the waterborne polyurethane emulsion, a nonionic wetting agent (BYK-346) is slowly added at a stirring rate of 250 rpm, and then thermally expanded microspheres are slowly sprinkled in at a stirring rate of 150 rpm. After that, the mixture is cured at a stirring rate of 150 rpm for 35 min. Then, 2-3 drops of defoamer (BYK-024) are added and stirred at a stirring rate of 150 rpm for 15 min. Finally, the mixture is allowed to stand to defoam, and the temperature-sensitive adhesive solution is obtained.

[0088] The thermosensitive adhesive solution has a solid content of 15 wt%; the viscosity of the thermosensitive adhesive solution is 1000 mPa·s; the amount of nonionic wetting agent added is 1% of the mass of the waterborne polyurethane emulsion; and the amount of thermally expanding microspheres doped is 5 wt% of the solid mass of the waterborne polyurethane emulsion.

[0089] (2) In a 200L double-star mixing tank, deionized water and the temperature-sensitive adhesive solution are stirred and dispersed at a stirring rate of 1000rpm for 30min, and then diluted to obtain a diluted adhesive solution with a solid content of 4wt% and a viscosity of 100mPa·S.

[0090] Add the dispersant ethylenediaminetetraacetic acid and stir at 1000 rpm for 30 min to disperse.

[0091] Add half of the conductive carbon black and half of the boehmite, and stir at 2000 rpm for 30 minutes. Then add the remaining conductive carbon black and boehmite, and stir at 2000 rpm for 30 minutes.

[0092] Add deionized water to reduce the solid content of the slurry to 20 wt%, and stir and disperse at a stirring speed of 2000 rpm for 30 min.

[0093] Add 0.1 mol / L sodium hydroxide solution as a pH adjuster to make the pH of the slurry 5.

[0094] Isopropanol was added as a wetting agent, and the mixture was stirred at 10 rpm for 40 minutes before being discharged.

[0095] The discharged slurry was homogenized twice on a homogenizer at a pressure of 600 bar to obtain a carbon coating slurry for carbon coating current collectors.

[0096] Example 3 This embodiment provides a carbon coating slurry for carbon-coated current collectors, the carbon coating slurry comprising a temperature-sensitive binder, conductive carbon black, boehmite, pH adjuster, wetting agent, dispersant, and pure water.

[0097] The temperature-sensitive adhesive comprises a polyurethane matrix and thermally expandable microspheres doped in the polyurethane matrix; the doping amount of the thermally expandable microspheres is 15 wt% of the solid mass of the polyurethane matrix; the thermally expandable microspheres comprise a polyurethane shell and a low-boiling-point liquid foaming agent encapsulated inside the polyurethane shell.

[0098] Based on the total solid mass of the carbon coating slurry, the total mass of the conductive carbon black and boehmite is 60%, and the mass ratio of the conductive carbon black to the boehmite is 5:5; based on the total solid mass of the carbon coating slurry, the mass of the temperature-sensitive binder is 40%; the mass ratio of the temperature-sensitive binder to the conductive carbon black is 4:3, and the mass ratio of the temperature-sensitive binder to the boehmite is 4:3.

[0099] The pH adjuster is a 0.1 mol / L sodium hydroxide solution; the pH of the carbon coating slurry is 7.5; the wetting agent is isopropanol, and the amount added is 15% of the total mass of the carbon coating slurry; the dispersant is ethylenediaminetetraacetic acid, and the amount added is 3% of the total solid mass of the carbon coating slurry; the solid content of the carbon coating slurry is 15 wt%.

[0100] This embodiment also provides a method for preparing the above-mentioned carbon coating slurry for carbon-coated current collectors, the preparation method comprising the following steps: (1) Preparation of temperature-sensitive adhesive solution: (1-1) Provide an aqueous polyurethane dispersion, dilute it with deionized water to a solid content of 25wt% to obtain an aqueous polyurethane emulsion; provide thermally expandable microspheres and vacuum dry them at 40℃ for 2h for later use.

[0101] (1-2) In the waterborne polyurethane emulsion, a nonionic wetting agent (BYK-346) is slowly added at a stirring rate of 350 rpm, and then thermally expanded microspheres are slowly sprinkled in at a stirring rate of 200 rpm. After that, the mixture is cured for 25 minutes at a stirring rate of 200 rpm. Then, 2-3 drops of defoamer (BYK-024) are added and stirred at a stirring rate of 200 rpm for 5 minutes. Finally, the mixture is allowed to stand to defoam, and the temperature-sensitive adhesive solution is obtained.

[0102] The thermosensitive adhesive solution has a solid content of 25 wt%; a viscosity of 3000 mPa·s; an addition amount of 1% of the mass of the waterborne polyurethane emulsion; and a doping amount of 15 wt% of the solid mass of the waterborne polyurethane emulsion.

[0103] (2) In a 200L double-star mixing tank, deionized water and the temperature-sensitive adhesive solution are stirred and dispersed at a stirring rate of 1200rpm for 30min, and then diluted to obtain a diluted adhesive solution with a solid content of 6wt% and a viscosity of 300mPa·S.

[0104] Add the dispersant ethylenediaminetetraacetic acid and stir at 1000 rpm for 30 min to disperse.

[0105] Add half of the conductive carbon black and half of the boehmite, and stir at 2600 rpm for 30 min. Then add the remaining conductive carbon black and boehmite, and stir at 2600 rpm for 30 min.

[0106] Add deionized water to reduce the solid content of the slurry to 20 wt%, and stir and disperse at a stirring rate of 2600 rpm for 30 min.

[0107] Add 0.1 mol / L sodium hydroxide solution as a pH adjuster to make the pH of the slurry 8.

[0108] Isopropanol was added as a wetting agent, and the mixture was stirred at 15 rpm for 40 minutes before being discharged.

[0109] The discharged slurry was homogenized twice on a homogenizer at a pressure of 600 bar to obtain a carbon coating slurry for carbon coating current collectors.

[0110] Example 4 The difference between this embodiment and Embodiment 1 is that, based on the total solid mass of the carbon coating slurry, the mass of the temperature-sensitive adhesive is 40%.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 5 The difference between this embodiment and Embodiment 1 is that, based on the total solid mass of the carbon coating slurry, the mass of the temperature-sensitive adhesive is 35%.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Example 6 The difference between this embodiment and Embodiment 1 is that, based on the total solid mass of the carbon coating slurry, the total mass of the conductive carbon black and boehmite is 50%, and the mass ratio of the conductive carbon black to boehmite is 5:5.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 7 The difference between this embodiment and Embodiment 1 is that no dispersant is added to the carbon coating slurry.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 8 The difference between this embodiment and embodiment 1 is that the amount of thermal expansion microspheres added in step (1) is adjusted so that the amount of thermal expansion microspheres in the temperature-sensitive adhesive is 1 wt% of the solid mass of the polyurethane matrix.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 9 The difference between this embodiment and embodiment 1 is that the amount of thermal expansion microspheres added in step (1) is adjusted so that the amount of thermal expansion microspheres in the temperature-sensitive adhesive is 20wt% of the solid mass of the polyurethane matrix.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 10 The difference between this embodiment and embodiment 1 is that the amount of conductive carbon black and boehmite added in step (2) is adjusted so that the mass ratio of conductive carbon black to boehmite in the carbon coating slurry is 1:15.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 11 The difference between this embodiment and embodiment 1 is that the amount of conductive carbon black and boehmite added in step (2) is adjusted so that the mass ratio of conductive carbon black to boehmite in the carbon coating slurry is 7:5.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Example 12 The difference between this embodiment and Embodiment 1 is that the amount of temperature-sensitive adhesive liquid added is adjusted so that the mass ratio of temperature-sensitive adhesive to conductive carbon black in the carbon coating slurry is 4:5.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Example 13 The difference between this embodiment and Embodiment 1 is that the amount of temperature-sensitive adhesive liquid added is adjusted so that the mass ratio of temperature-sensitive adhesive to conductive carbon black in the carbon coating slurry is 10:1.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 14 The difference between this embodiment and Embodiment 1 is that the amount of temperature-sensitive adhesive liquid added is adjusted so that the mass ratio of temperature-sensitive adhesive to boehmite in the carbon coating slurry is 3:10.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Example 15 The difference between this embodiment and Embodiment 1 is that the amount of temperature-sensitive adhesive liquid added is adjusted so that the mass ratio of temperature-sensitive adhesive to boehmite in the carbon coating slurry is 10:3.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Comparative Example 1 The difference between this comparative example and Example 1 is that step (1) is omitted, and the temperature-sensitive adhesive is replaced with an equal amount of polyacrylic acid (PAA) adhesive.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Comparative Example 2 The difference between this comparative example and Example 1 is that boehmite is not added in step (2), that is, the carbon coating slurry does not contain boehmite.

[0137] The remaining preparation methods and parameters are consistent with those in Example 1.

[0138] Performance testing The carbon-coated current collector is prepared based on the carbon-coating slurry provided in the above embodiments and comparative examples. The steps include: coating the carbon-coating slurry on one side surface of an aluminum foil, baking it to form a coating with a thickness of 1 μm, and thus obtaining the carbon-coated current collector.

[0139] The penetration resistance of the above-mentioned carbon-coated current collector was tested after treatment at different temperatures. The test steps included: taking a sample strip with a length and width of 20cm×5cm, cutting the sample strip into small samples of 5cm×5cm, and then placing the samples in a vacuum drying oven and baking them at 60℃, 80℃ and 100℃ for 20min respectively. Then, the penetration resistance was tested under a film resistance meter, and the test data were recorded.

[0140] The test results are shown in Table 1.

[0141] Table 1 analyze: As shown in Table 1, this invention introduces a temperature-sensitive binder with a thermal expansion switching effect into the carbon coating slurry. When the internal temperature of the battery rises abnormally and reaches or even exceeds the initial expansion temperature of the thermal expansion microspheres, the microspheres undergo violent volume expansion, physically disrupting the continuous conductive network formed by the conductive agent. This achieves a "thermal shutdown" effect on the current, meaning the heat signal is converted into a rapidly increasing resistance signal in real time, actively and quickly cutting off the current path, thus providing safety protection before thermal runaway occurs. This transformation of traditional passive protection materials into a built-in safety mechanism with active early warning and power-off functions can intervene at the source of the battery's thermal runaway process, preventing the continuous accumulation of heat from triggering a chain of exothermic reactions, fundamentally improving the thermal safety of lithium-ion batteries. In summary, this solution provides a forward-looking, built-in safety solution for constructing novel lithium-ion batteries with built-in temperature sensing and overcurrent self-protection functions. It is expected to significantly improve the safety threshold of high-energy-density lithium battery systems, possessing significant scientific value and broad application prospects.

[0142] A comparison of Examples 1 and 7 shows that if no dispersant is added to the carbon coating slurry, the dispersion uniformity of conductive carbon black and boehmite decreases, resulting in uneven local conductive networks in the coating. This manifests as an increase in penetration resistance under normal conditions (60°C), and the temperature-sensitive switching effect is also negatively affected. This indicates that the absence of dispersant reduces the overall performance consistency of the coating and weakens the reliability of the thermal shutdown effect.

[0143] As can be seen from the comparison between Example 1 and Examples 8-9, if the doping amount of thermally expanding microspheres in the temperature-sensitive binder is too small, the number of thermally expanding microspheres will be insufficient, and the total volume expansion generated when heated will be limited, which will not be able to effectively destroy the carbon black conductive network, resulting in a weak temperature-sensitive switching effect and failure to achieve an effective current cut-off function. If the doping amount of thermally expanding microspheres in the temperature-sensitive binder is too large, the excessive insulating microspheres will dilute the conductive network, resulting in a significant increase in the initial resistance under normal conditions (60°C), affecting the normal rate performance of the battery. At the same time, the coating structure becomes too loose after the microspheres expand, which limits the further increase in resistance and reduces the temperature-sensitive switching contrast.

[0144] As can be seen from the comparison between Example 1 and Examples 10-11, if the mass ratio of conductive carbon black to boehmite in the carbon coating slurry is too small, the conductive carbon black content is insufficient, and a complete conductive penetration network cannot be formed, resulting in a significant increase in the initial resistance under normal conditions (60°C), which seriously affects the normal charge and discharge performance of the battery. If the mass ratio of conductive carbon black to boehmite in the carbon coating slurry is too large, the conductive network is too dense and redundant. Even if the thermally expanded microspheres push away some carbon black particles due to thermal expansion, there are still a large number of bypass conductive paths, resulting in a sluggish temperature-sensitive switching effect and an inability to achieve an exponential increase in resistance.

[0145] A comparison of Examples 1 and 12-13 shows that if the mass ratio of thermosensitive binder to conductive carbon black in the carbon coating slurry is too small, the content of thermosensitive binder is insufficient, the adhesion between the components inside the coating decreases, and the carbon black conductive network is easily destroyed prematurely when the microspheres expand. At the same time, due to the lack of binder, a stable initial conductive structure cannot be maintained, resulting in a high resistance under normal conditions and a limited increase in resistance at high temperatures, leading to poor thermosensitive switching performance. If the mass ratio of thermosensitive binder to conductive carbon black in the carbon coating slurry is too large, the conductive carbon black is relatively insufficient, and the conductive network is already sparse under normal conditions. Although the thermosensitive switching has a certain effect, the initial conductivity has deviated from the optimal range, and the increase in high temperature is far less than the infinite increase in Example 1.

[0146] A comparison of Examples 1 and 14-15 shows that if the mass ratio of the thermosensitive binder to boehmite in the carbon coating slurry is too small, the boehmite, as an insulating rigid skeleton, will be excessive, occupying too much volume and squeezing the formation space of the carbon black conductive network, resulting in discontinuous conductive paths under normal conditions. At the same time, the excessive boehmite absorbs the compressive force of the microsphere expansion, weakening the efficiency of destroying the carbon black network. If the mass ratio of the thermosensitive binder to boehmite in the carbon coating slurry is too large, the coating lacks sufficient rigid skeleton support, and the structure is too soft. When the thermally expanding microspheres expand, the expansion force is absorbed by the overall deformation of the coating rather than concentrated on the carbon black conductive nodes, resulting in a weakened thermosensitive switching effect and the inability to achieve a dramatic increase in resistance.

[0147] As can be seen from the comparison between Example 1 and Comparative Example 1, if the temperature-sensitive adhesive is replaced with an equal amount of PAA adhesive, the coating will not have a temperature-sensitive switching effect at all. Since the PAA adhesive does not contain thermally expanding microspheres, it cannot generate volume expansion to destroy the conductive network when the temperature rises. Therefore, the penetration resistance remains basically unchanged with the temperature rise. The battery cannot automatically cut off the current under thermal runaway conditions, and the safety cannot be improved.

[0148] As can be seen from the comparison between Example 1 and Comparative Example 1, if the carbon coating slurry does not contain boehmite, the coating lacks a rigid ceramic skeleton support. When the thermally expanding microspheres are heated and expanded, the coating undergoes uniform deformation and the expansion force is dispersed and absorbed, failing to effectively concentrate on destroying the carbon black conductive network. At the same time, the absence of boehmite leads to a relative increase in the proportion of carbon black in the coating, making the conductive network more dense and redundant. The temperature-sensitive switching effect is extremely weak, and it is impossible to achieve an effective current interruption function.

[0149] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A carbon coating slurry for carbon-coated current collectors, characterized in that, The carbon coating slurry includes a temperature-sensitive binder, a carbon-based conductive agent, ceramic materials, and a solvent; The temperature-sensitive adhesive comprises an aqueous matrix and thermally expandable microspheres doped in the aqueous matrix.

2. The carbon coating slurry for carbon-coated current collectors according to claim 1, characterized in that, The aqueous matrix includes polyurethane; And / or, the doping amount of the thermally expandable microspheres is 5-15 wt% of the solid mass of the aqueous matrix; And / or, the thermally expanded microspheres include a polymer shell and a low-boiling-point liquid foaming agent encapsulated inside the polymer shell; And / or, the initial expansion temperature of the thermally expanding microspheres is 80-85℃.

3. The carbon coating slurry for carbon-coated current collectors according to claim 2, characterized in that, The polymer shell is made of polyurethane; And / or, the carbon-based conductive agent includes conductive carbon black; And / or, the ceramic material includes boehmite; And / or, based on the total solid mass of the carbon-coated slurry, the total content of the carbon-based conductive agent and ceramic material is 50-65%; And / or, the mass ratio of the carbon-based conductive agent to the ceramic material is (1-5):(5-10); And / or, based on the total solids mass of the carbon coating slurry, the content of the temperature-sensitive adhesive is 35-50%; And / or, the mass ratio of the temperature-sensitive adhesive to the carbon-based conductive agent is (4-9):(1-3); And / or, the mass ratio of the temperature-sensitive adhesive to the ceramic material is (4-9):(3-10).

4. The carbon coating slurry for carbon-coated current collectors according to claim 1, characterized in that, The carbon coating slurry also includes a pH adjuster; And / or, the pH of the carbonized slurry is 5-8; And / or, the carbon coating slurry further includes a wetting agent, wherein the amount of the wetting agent added is 5-15% of the total mass of the carbon coating slurry; And / or, the carbon coating slurry also includes a dispersant; And / or, the solid content of the carbon coating slurry is 12-18 wt%.

5. A method for preparing a carbon coating slurry for a carbon-coated current collector as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: Prepare the temperature-sensitive adhesive solution; A carbon-based conductive agent, ceramic material, the temperature-sensitive adhesive liquid, and a solvent are mixed to obtain the carbon-coated current collector slurry.

6. The preparation method according to claim 5, characterized in that, The preparation method of the temperature-sensitive adhesive solution includes the following steps: The temperature-sensitive adhesive solution is prepared by blending waterborne polyurethane emulsion, wetting agent and thermally expanding microspheres, followed by curing and defoaming treatment.

7. The preparation method according to claim 6, characterized in that, The solid content of the temperature-sensitive adhesive solution is 15-25 wt%. And / or, the viscosity of the temperature-sensitive adhesive solution is 800-3000 mPa·s; And / or, the amount of the wetting agent added is 0.5-1.5% of the mass of the waterborne polyurethane emulsion; And / or, during the ripening process, the stirring rate is 150-200 rpm; And / or, the curing time is 25-35 min; And / or, during the mixing process, dispersants, pH adjusters and wetting agents are also added.

8. The preparation method according to claim 5, characterized in that, The preparation method includes the following steps: (1) Preparation of temperature-sensitive adhesive solution: In an aqueous polyurethane emulsion with a solid content of 15-25 wt%, a wetting agent is added at a stirring rate of 250-350 rpm, followed by the addition of thermally expanded microspheres at a stirring rate of 150-200 rpm. After that, the mixture is allowed to mature at a stirring rate of 150-200 rpm for 25-35 minutes. Then, an antifoaming agent is added and the mixture is stirred at a stirring rate of 150-200 rpm for 5-15 minutes. Finally, the mixture is allowed to stand to defoam, thus obtaining the temperature-sensitive adhesive solution. The thermosensitive adhesive solution has a solid content of 15-25 wt%; a viscosity of 800-3000 mPa·s; an addition amount of wetting agent of 0.5-1.5% of the mass of the waterborne polyurethane emulsion; and a doping amount of thermally expandable microspheres of 5-15 wt% of the solid mass of the waterborne polyurethane emulsion. (2) Under stirring conditions, the temperature-sensitive adhesive solution is diluted to obtain a diluted adhesive solution with a solid content of 4-6 wt% and a viscosity of 100-300 mPa·s. Then, a dispersant, a carbon-based conductive agent, a ceramic material, a pH adjuster and a wetting agent are added in sequence. After homogenization, a carbon coating slurry for carbon current collector is obtained. The carbon-based conductive agent includes conductive carbon black, and the ceramic material includes boehmite; the carbon-based conductive agent and the ceramic material are added in multiple stages.

9. A carbon-coated current collector, characterized in that, The carbon-coated current collector includes a current collector substrate and a coating disposed on at least one surface of the current collector substrate, the coating being made using a carbon-coating slurry for carbon-coated current collectors as described in any one of claims 1-4.

10. A lithium-ion battery, characterized in that, The electrode sheets of the lithium-ion battery include the carbon-coated current collector as described in claim 9.

Images