Phase-change temperature-control integrated negative electrode for energy storage lithium battery and preparation method of phase-change temperature-control integrated negative electrode

Abstract

The invention provides a phase-change temperature-control integrated negative electrode for an energy storage lithium battery and a preparation method of the phase-change temperature-control integrated negative electrode. The method comprises the following steps: preparing a core-shell structure phase change material microcapsule; constructing a temperature-sensitive three-dimensional interpenetrating conductive network; preparing a multi-layer gradient functional negative electrode slurry system: respectively preparing three types of negative electrode slurry, each type of slurry comprising a negative electrode active material, a conductive agent and a binder, and differentially adding the core-shell structure phase change material microcapsule and the temperature-sensitive three-dimensional interpenetrating conductive network to prepare the multi-layer gradient functional negative electrode slurry system, the mass percent concentration of the core-shell structure phase change material microcapsule in different slurries is in gradient change, and the mass percent concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry is kept consistent; a multi-layer wet method is adopted for sequential coating and integrated forming. According to the invention, the integrated negative electrode with excellent internal temperature control capability and safety performance can be prepared.

Description

Technical Field

[0001] The present invention relates to a lithium battery negative electrode material and a preparation method thereof, and specifically to a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery and a preparation method thereof, belonging to the technical field of lithium-ion batteries. Background Art

[0002] With the global energy transition and the booming electric vehicle industry, demand for energy storage systems and high-energy-density lithium-ion batteries is growing. Lithium-ion batteries are susceptible to generating significant Joule heating under conditions of rapid charge and discharge, high-rate output, or abuse, causing the battery temperature to rise rapidly. Excessive temperatures not only accelerate electrolyte decomposition and destabilize the solid electrolyte interface (SEI) film, reducing the battery's capacity retention and cycle life, but may also induce the growth of lithium dendrites, increasing the risk of internal short circuits.

[0003] Currently, commercial lithium-ion battery thermal management systems mostly utilize external heat dissipation methods, such as forced air cooling and liquid cooling. While these external cooling systems can control the overall temperature of the battery pack or module to a certain extent, they often suffer from bulkiness, complex structures, high energy consumption, and high costs. More importantly, external cooling systems have limited response and control effectiveness for localized hot spots within the battery, particularly within the cell, making it difficult to fundamentally prevent battery performance degradation and safety hazards caused by localized overheating.

[0004] Existing technologies have also explored some aspects of internal thermal management of batteries. For example, by improving the thermal conductivity of the negative electrode material itself, or by coating a thermal insulation layer on the surface of the electrode to slow down heat transfer. However, most of these methods are passive thermal management methods, which make it difficult to actively and intelligently respond to temperature changes inside the battery, and the temperature control effect and range are limited. Introducing phase change materials into batteries is an effective internal thermal management strategy. Phase change materials can undergo phase changes at specific temperatures and absorb or release a large amount of latent heat, but the traditional direct introduction of phase change materials has problems such as leakage, poor compatibility with the electrolyte, and affecting the electrochemical performance of the battery. In addition, relying solely on phase change materials to absorb heat, its temperature control ability still has an upper limit under conditions of continuous high heat generation.

[0005] In summary, developing a technology that can achieve active, efficient and multi-level coordinated temperature control inside the battery, especially a temperature control solution integrated on the negative electrode, which is the key heat-generating component, is of great significance for improving the safety of energy storage lithium batteries and extending their service life. Summary of the Invention

[0006] Based on the above background, the purpose of the present invention is to provide a phase change temperature control integrated negative electrode for energy storage lithium batteries and a preparation method thereof, which can prepare an integrated negative electrode with excellent internal temperature control capability and safety performance.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] A method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery, the method comprising the following steps:

[0009] S1. Preparation of core-shell structured phase change material microcapsules: selecting a core material phase change composition comprising a mixture of at least two organic alkanes with different melting points and doped with a thermal conductivity enhancing nanomaterial, in situ forming a composite polymer shell comprising a polyvinylidene fluoride copolymer and a nano inorganic oxide filler on the surface of a droplet of the core material phase change composition by interfacial polymerization or emulsion solvent evaporation, and chemically grafting molecular chains containing polar functional groups onto the outer surface of the composite polymer shell to form a core-shell structured phase change material microcapsule;

[0010] S2. Constructing a temperature-sensitive three-dimensional interpenetrating conductive network: compounding acid-treated surface-functionalized multi-walled carbon nanotubes with two-dimensional graphene sheets to form a three-dimensional conductive framework, and then in situ free radical polymerization of N-isopropylacrylamide monomers in the presence of the three-dimensional conductive framework and cross-linking to form a temperature-sensitive three-dimensional interpenetrating conductive network;

[0011] S3. Preparing a multilayer gradient functional negative electrode slurry system: preparing three negative electrode slurries respectively, each slurry containing a negative electrode active material, a conductive agent, and a binder, and differentially adding the core-shell structure phase change material microcapsules prepared in step S1 and the temperature-sensitive three-dimensional interpenetrating conductive network prepared in step S2, so that the mass percentage concentration of the core-shell structure phase change material microcapsules in different slurries presents a gradient change, while the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry remains consistent;

[0012] S4. Multi-layer wet sequential coating and integrated molding: The three negative electrode slurries prepared in step S3 are continuously coated on the metal current collector substrate in the order from close to the current collector to far away from the current collector, and the ratio of the wet film thickness and dry film thickness of each functional layer is controlled. After multi-stage programmed temperature-controlled drying and roll-to-roll densification treatment, a phase change temperature-controlled integrated negative electrode is obtained in which the phase change material microcapsules are distributed in a concentration gradient along the thickness direction of the negative electrode and the temperature-sensitive three-dimensional interpenetrating conductive network is dispersed in the entire negative electrode pore structure.

[0013] The purpose of step S1 is to produce phase-change material microcapsules with good encapsulation, adjustable thermal properties, high mechanical strength, and good compatibility with the anode slurry system. A mixture of organic alkanes with different melting points is selected as the core material, allowing the phase transition temperature range to be precisely controlled according to the battery's operating temperature range. The incorporation of thermal conductivity-enhancing nanomaterials significantly improves the core material's thermal conductivity and accelerates the absorption and release of heat during the phase transition. Polyvinylidene fluoride copolymers are introduced into the shell layer to provide good electrochemical stability and a certain degree of flexibility, while nano-inorganic oxide fillers enhance the shell's mechanical strength and thermal stability. The outer shell is chemically grafted to introduce polar functional groups to improve the dispersibility of the hydrophobic microcapsules in common non-aqueous anode slurry solvents (such as NMP) and enhance interfacial bonding with the binder and other components.

[0014] The purpose of step S2 is to construct a conductive network that exhibits excellent conductivity at normal operating temperatures, but exhibits a significant and reversible decrease in conductivity when the temperature exceeds a preset threshold. The three-dimensional conductive framework formed by the composite of multi-walled carbon nanotubes and graphene sheets inherently possesses excellent conductivity and a large specific surface area. This framework is then subjected to acid treatment for surface functionalization, introducing oxygen-containing functional groups to facilitate the subsequent grafting or coating of the thermosensitive polymer N-isopropylacrylamide (PNIPAM). In situ free radical polymerization and crosslinking of PNIPAM monomers in the presence of the conductive framework allows the resulting PNIPAM network to tightly bind to the conductive framework, forming an interpenetrating structure. When the temperature rises above the LCST of PNIPAM, the PNIPAM segments transform from hydrophilic to hydrophobic, shrinking or aggregating, resulting in a volume change. This alters the contact state between the carbon materials or blocks some conductive pathways, significantly reducing the macroscopic conductivity of the entire network. This process is reversible, and conductivity recovers when the temperature is lowered.

[0015] The purpose of step S3 is to design slurries with different component contents to subsequently form a negative electrode structure with a specific functional gradient distribution. The role of the gradient addition of phase change material microcapsules is to add a higher concentration of microcapsules to the slurry close to the current collector to provide stronger heat absorption capacity, and to add a lower concentration of microcapsules to the surface layer slurry close to the diaphragm to reduce the impact on lithium ion transmission and ensure high rate performance. The temperature-sensitive three-dimensional interpenetrating conductive network maintains a consistent concentration in each layer to ensure that the entire negative electrode has current limiting capability at different depths when overheated.

[0016] Step S4 converts the designed slurry system into an integrated negative electrode, and achieves the expected gradient structure and final electrode performance by controlling the ratio of the wet and dry film thicknesses of each layer. Multi-stage programmed temperature-controlled drying is to gently remove the solvent to avoid cracks or component segregation. The roll-to-roll densification treatment is to increase the compaction density of the electrode, improve the contact between particles, reduce the interface resistance, and regulate the final porosity to facilitate electrolyte infiltration and ion transport.

[0017] The temperature-sensitive three-dimensional interpenetrating conductive network can undergo reversible volume expansion when the ambient temperature exceeds a first preset temperature threshold in the range of 35°C to 45°C, resulting in partial obstruction of the conductive path, thereby causing its macroscopic resistivity to reversibly and sharply increase by at least one order of magnitude. During the operation of the lithium battery, when the local temperature reaches a second preset temperature threshold, the phase change temperature-controlled integrated negative electrode can absorb latent heat through the solid-liquid phase change of the phase change material microcapsules, and when the temperature further rises above the first preset temperature threshold, the resistivity of the temperature-sensitive three-dimensional interpenetrating conductive network increases sharply to limit local abnormally large currents, thereby realizing multi-level coordinated internal temperature control and over-temperature protection.

[0018] Preferably, in step S1, the thermal conductivity enhancing nanomaterial is exfoliated graphene or boron nitride nanosheets, the polyvinylidene fluoride copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer, and the nano inorganic oxide filler is silica particles or alumina particles with an average particle size of less than 100 nm, and the added amount of the nano inorganic oxide filler is 3-8 wt% of the shell mass.

[0019] Preferably, in step S1, chemically grafting molecular chains containing polar functional groups onto the outer surface of the composite polymer shell layer specifically includes grafting short-chain polymers or silane coupling agents containing carboxyl groups, hydroxyl groups or sulfonic acid groups.

[0020] The introduction of the above-mentioned polar functional groups can permanently change the chemical properties of the microcapsule surface through covalent bonding, changing it from hydrophobic to a surface that is more easily wetted by polar solvents such as NMP, thereby improving its dispersion uniformity and stability in the slurry, reducing agglomeration, and forming stronger hydrogen bonds with binders such as PVDF, thereby enhancing interfacial bonding.

[0021] Preferably, in step S1, the core-shell phase change material microcapsules formed have an average particle size of 5-25 μm and a phase change latent heat value of not less than 140 J / g. The particle size of the microcapsules is controlled within the range of 5-25 μm to ensure that there is sufficient phase change core material inside to provide sufficient latent heat, while not being too large to significantly affect the compaction density of the negative electrode and the transmission path of lithium ions between the particles.

[0022] Preferably, in step S2, the initiator used for the in-situ free radical polymerization of the N-isopropylacrylamide monomer is azobisisobutyronitrile or potassium persulfate, and the cross-linking agent is N,N'-methylenebisacrylamide.

[0023] Preferably, in step S3, the negative electrode active material is selected from artificial graphite, coated silicon-based negative electrode material, lithiated titanate or a mixture thereof, and the binder is polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose or a mixture thereof.

[0024] Preferably, in step S3, the solid content of the core-shell structure phase change material microcapsules in the three layers of slurry is controlled at 15-25wt%, 8-15wt% and 3-8wt% by weight, respectively.

[0025] The side close to the current collector is one of the main heat-generating areas. Therefore, configuring a higher concentration of phase change microcapsules of 15-25wt% can absorb heat most effectively. The middle layer plays a transitional role. In the surface layer close to the diaphragm, in order to minimize the impact on the rapid transmission of lithium ions and ensure the rate performance of the battery, the concentration of phase change microcapsules is controlled at a lower level of 3-8wt%.

[0026] Preferably, in step S3, the solid content of the temperature-sensitive three-dimensional interpenetrating conductive network in each layer of the negative electrode slurry is uniformly controlled to be 2-5 wt %.

[0027] The addition amount of 2-5wt% is to minimize the negative impact on the overall energy density and ionic conductivity of the electrode while ensuring that the temperature-sensitive three-dimensional interpenetrating conductive network forms an effective conductive network and can achieve significant temperature-sensitive response.

[0028] Preferably, in step S4, the dry film thickness ratio of each functional layer from the current collector layer to the surface layer is controlled to be 2-4:4-6:1-3, the total dry film thickness of the phase change temperature control integrated negative electrode is controlled to be 70-120 μm, and the compaction density of the phase change temperature control integrated negative electrode is controlled to be 1.45-1.75 g / cm³ by roller pressing.

[0029] The control of the dry film thickness ratio corresponds to the gradient concentration distribution of the phase change microcapsules in the slurry.

[0030] A phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery, prepared by any of the above preparation methods.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The present invention discloses a phase-change temperature-controlled integrated negative electrode for energy storage lithium batteries and a preparation method thereof. By integrating gradient-distributed phase-change material microcapsules and a dispersed temperature-sensitive conductive network within the negative electrode, multi-stage coordinated temperature control with active current limiting is achieved. During normal temperature rise, the phase-change material preferentially absorbs heat. When the temperature further rises to a dangerous threshold, the resistivity of the temperature-sensitive conductive network increases dramatically, limiting local current and reducing heat generation at the source, effectively preventing thermal runaway of the energy storage lithium battery.

[0033] The present invention ensures the stability and efficient heat exchange capability of phase change material microcapsules in the battery environment through the core-shell structure design and surface modification. The gradient distribution enables the temperature control function to be concentrated in the area where it is most needed, while minimizing the impact on electrochemical performance. The presence of the temperature-sensitive conductive network provides the battery with an additional internal safety barrier that is independent of the external system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0035] Figure 1 This is a schematic flow chart of a method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to the present invention;

[0036] Figure 2 This is a schematic structural diagram of a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to the present invention;

[0037] Figure 3 This is a comparison chart of temperature change curves of batteries prepared in the embodiments of the present invention and the comparative examples during charge and discharge at different rates;

[0038] Figure 4 It is a comparison chart of the capacity retention rate of the batteries prepared in the embodiment of the present invention and the comparative example after cycle testing. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the scope of protection of the present invention.

[0040] In the present invention, unless otherwise specified, all parts and percentages are by weight. The equipment and raw materials used are commercially available or commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are all universal standard parts or components known to those skilled in the art. Their structures and principles are known to those skilled in the art through technical manuals or routine experimental methods.

[0041] The following detailed description of the embodiments of the present invention is made in conjunction with the accompanying drawings. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, one or more embodiments may be implemented by those skilled in the art without these specific details.

[0042] Raw materials:

[0043] Organic alkanes: n-octadecane, n-eicosane.

[0044] Thermal conductivity enhancing nanomaterials: exfoliated graphene, hexagonal boron nitride nanosheets.

[0045] Shell polymer: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0046] Nano inorganic oxide fillers: fumed silica, nano alumina.

[0047] Surface modifiers: acrylic acid, (3-aminopropyl)triethoxysilane.

[0048] Carbon nanotubes: Multi-walled carbon nanotubes (MWCNTs).

[0049] Graphene sheets: chemically reduced graphene oxide (rGO).

[0050] Thermosensitive monomers / polymers: N-isopropylacrylamide, azobisisobutyronitrile, potassium persulfate, N,N'-methylenebisacrylamide.

[0051] Negative electrode active materials: artificial graphite, silicon-carbon composite materials.

[0052] Conductive agent: conductive carbon black.

[0053] Binder: polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC).

[0054] Solvent: N-methylpyrrolidone (NMP), deionized water.

[0055] Current collector: electrolytic copper foil.

[0056] Example 1

[0057] like Figure 1 A method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery is shown, the method comprising the following steps:

[0058] S1. Preparation of core-shell structured phase change material microcapsules: selecting a core material phase change composition comprising a mixture of at least two organic alkanes with different melting points and doped with a thermal conductivity enhancing nanomaterial, in situ forming a composite polymer shell comprising a polyvinylidene fluoride copolymer and a nano inorganic oxide filler on the surface of a droplet of the core material phase change composition by interfacial polymerization or emulsion solvent evaporation, and chemically grafting molecular chains containing polar functional groups onto the outer surface of the composite polymer shell to form a core-shell structured phase change material microcapsule;

[0059] S2. Constructing a temperature-sensitive three-dimensional interpenetrating conductive network: compounding acid-treated surface-functionalized multi-walled carbon nanotubes with two-dimensional graphene sheets to form a three-dimensional conductive framework, and then in situ free radical polymerization of N-isopropylacrylamide monomers in the presence of the three-dimensional conductive framework and cross-linking to form a temperature-sensitive three-dimensional interpenetrating conductive network;

[0060] S3. Preparing a multilayer gradient functional negative electrode slurry system: preparing three negative electrode slurries respectively, each slurry containing a negative electrode active material, a conductive agent, and a binder, and differentially adding the core-shell structure phase change material microcapsules prepared in step S1 and the temperature-sensitive three-dimensional interpenetrating conductive network prepared in step S2, so that the mass percentage concentration of the core-shell structure phase change material microcapsules in different slurries presents a gradient change, while the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry remains consistent;

[0061] S4, using multi-layer wet sequential coating and integrated molding: the three negative electrode slurries prepared in step S3 are sequentially coated on the metal current collector substrate in the order from close to the current collector to far away from the current collector, and the ratio of the wet film thickness and dry film thickness of each functional layer is controlled. After multi-stage program temperature control drying and roll pressing densification treatment, the following is obtained: Figure 2 The phase change material microcapsules are distributed in a concentration gradient along the thickness direction of the negative electrode, and the temperature-sensitive three-dimensional interpenetrating conductive network is dispersed throughout the phase change temperature control integrated negative electrode pore structure.

[0062] The specific steps are described below.

[0063] S1. Preparation of core-shell phase change material microcapsules (PCM-1)

[0064] Preparation of the core material phase change composition: n-octadecane and n-eicosane were mixed in a mass ratio of 2:1 and heated to 60°C until completely melted. Then, 1.5 wt% of the core material's mass of exfoliated graphene was added. High-speed shear stirring was applied under nitrogen for 30 minutes to obtain a homogeneous oil phase of the core material phase change composition.

[0065] Composite polymer shell formation: 10g PVDF-HFP was dissolved in 90g NMP, and 0.5g (5wt% relative to the mass of PVDF-HFP) of fumed silica with an average particle size of 15nm was added. Ultrasonic dispersion was performed for 1 hour to obtain a shell solution. 50g of the core material phase change composition oil phase prepared in the above step was slowly added dropwise to the shell solution while simultaneously performing high-speed shear emulsification to form an O / W emulsion. Subsequently, deionized water (oil:water volume ratio of 1:5) was slowly added dropwise with stirring to induce PVDF-HFP phase separation and form a shell on the surface of the oil droplet. Stirring was continued until the shell solidified.

[0066] Surface chemical grafting: The microcapsule suspension obtained above was centrifuged, washed with ethanol, and then redispersed in 500 mL of deionized water. 1 g of acrylic acid was added and reacted at 70°C for 3 hours for surface carboxyl grafting. After the reaction, the microcapsules were centrifuged and washed until neutral, then vacuum-dried at 60°C for 24 hours to obtain surface carboxyl-coated core-shell phase change material microcapsules (PCM-1). PCM-1 had an average particle size of approximately 15 μm, a shell thickness of approximately 1.2 μm, a phase transition temperature range of 30-34°C, and a latent heat of 185 J / g.

[0067] S2. Preparation of temperature-sensitive three-dimensional interpenetrating conductive network (T-Net-1)

[0068] Preparation of the 3D conductive framework: 1g of MWCNTs and 0.5g of rGO were added to 100mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1). The mixture was refluxed at 70°C for 4 hours for acid treatment. After the reaction, the mixture was washed with copious amounts of deionized water until neutral and freeze-dried to obtain a surface-functionalized MWCNTs / rGO composite.

[0069] In situ polymerization and crosslinking: 0.5 g of the surface-functionalized MWCNTs / rGO composite was dispersed in 100 mL of deionized water and sonicated for 1 hour. 5 g of NIPAM monomer and 0.05 g of MBA crosslinker were added, and nitrogen was purged for 30 minutes to deoxygenate. Then, 0.02 g of KPS initiator was added, and the reaction was heated to 70°C for 8 hours. After the reaction, the product was washed several times with alternating hot and cold water at approximately 50°C to remove unreacted monomers and oligomers. Finally, the product was freeze-dried to obtain a temperature-sensitive three-dimensional interpenetrating conductive network (T-Net-1).

[0070] S3. Preparation of multilayer gradient functional negative electrode slurry system

[0071] The negative electrode active material is artificial graphite, the conductive agent is conductive carbon black, the binder is PVDF, and the solvent is NMP. The composition ratios of the three negative electrode slurries are shown in Table 1.

[0072] Table 1 Component ratios of three negative electrode slurries

[0073] Components Slurry A (near the current collector layer) wt% Slurry B (intermediate transition layer) wt% Slurry C (near the surface layer of the diaphragm) wt% Artificial graphite 70 77 84 Conductive carbon black 3 3 3 PVDF 7 7 7 PCM-1 20 13 6 T-Net-1 3 3 3

[0074] Add the components into NMP according to the proportions in Table 1, and stir at high speed using a vacuum mixer until the slurry is uniform.

[0075] S4, multi-layer wet sequential coating and integrated molding

[0076] Using a small laboratory coating machine, slurry A, slurry B, and slurry C were sequentially coated on a 9μm thick electrolytic copper foil. The wet film thickness of each layer was controlled so that the dry film thickness ratio of each layer after drying was approximately 3:5:2, and the total wet film thickness was controlled at approximately 250μm.

[0077] After coating, the film was pre-dried at 60°C for 30 minutes and then dried in a vacuum oven at 120°C for 12 hours.

[0078] The dried electrode is rolled using a roller press to control the compaction density at 1.60 g / cm³ and the total dry film thickness at approximately 90 μm.

[0079] Example 2

[0080] The preparation method is the same as that of Example 1, except that:

[0081] In step S1, the thermal conductivity-enhancing nanomaterial in the core phase-change composition was replaced with 1.0 wt% hexagonal boron nitride nanosheets, and the inorganic nanooxide filler was replaced with nanoalumina with an average particle size of 20 nm, added in an amount of 6 wt% based on the shell mass. (3-Aminopropyl)triethoxysilane (APTES) was used for surface chemical grafting, followed by amination. The remaining steps were the same as in Example 1, yielding PCM-2. PCM-2 had an average particle size of approximately 18 μm and a latent heat of phase change of 172 J / g.

[0082] In step S2, the initiator for the in situ free radical polymerization of the NIPAM monomer was changed to AIBN (0.02 g, dissolved in a small amount of acetone and then added). The reaction was carried out in a nitrogen-protected ethanol / water (1:1 volume ratio) mixed solvent. The remaining steps were the same as in Example 1, yielding T-Net-2.

[0083] In step S3, the negative electrode active material was replaced with a mixture of silicon-carbon composite material (SiOx-C) and artificial graphite (AG) (mass ratio 1:4), the binder was replaced with a mixture of SBR and CMC (mass ratio 1:1, solid content 2wt% aqueous solution), and the solvent was deionized water. The PCM-2 addition gradient was: slurry A: 18wt%, slurry B: 10wt%, slurry C: 4wt%. The T-Net-2 addition level was uniformly 2.5wt%. The proportions of the remaining components were adjusted accordingly to maintain the active material content, with a solid content of 50wt%.

[0084] The compaction density in step S4 was controlled at 1.55 g / cm³ and the total dry film thickness was controlled at approximately 95 μm.

[0085] Comparative Example 1 (conventional negative electrode)

[0086] The preparation method is the same as that of Example 1, except that:

[0087] No PCM-1 or T-Net-1 was added. The negative electrode slurry composition was: artificial graphite 90wt%, conductive carbon black 5wt%, and PVDF 5wt%. Single-layer coating was used.

[0088] Comparative Example 2 (Negative Electrode Containing Only Phase Change Material Microcapsules)

[0089] The preparation method is the same as that of Example 1, except that:

[0090] No T-Net-1 was added. The negative electrode slurry composition was: artificial graphite 77wt%, conductive carbon black 3wt%, PVDF 7wt%, and PCM-1 13wt%. Single-layer coating was used.

[0091] Comparative Example 3 (Negative Electrode Containing Only the Thermosensitive Conductive Network)

[0092] No PCM-1 was added. The negative electrode slurry composition was: artificial graphite 87wt%, conductive carbon black 3wt%, PVDF 7wt%, and T-Net-1 3wt%. Single-layer coating was used.

[0093] Comparative Example 4 (Anode with Uniform Mixture of Phase Change Material and Temperature-Sensitive Conductive Network)

[0094] PCM-1 and T-Net-1 were uniformly mixed in a single-layer slurry. The negative electrode slurry composition was: artificial graphite 74wt%, conductive carbon black 3wt%, PVDF 7wt%, PCM-1 13wt%, and T-Net-1 3wt%.

[0095] In a laboratory environment, the negative electrode sheets prepared in the above examples and comparative examples were assembled into batteries with an NCM811 positive electrode, a Celgard 2400 separator, and a 1.0 M LiPF6 in EC / DEC / DMC (1:1:1, v / v / v) electrolyte, and the following performance tests were performed:

[0096] Rate charge and discharge temperature rise test: In an environment of 25°C, the battery is charged and discharged at different rates (1C, 2C, 3C), and the temperature change at the center point of the battery surface is monitored using a thermocouple or infrared thermal imager.

[0097] Cycling performance test: At 25°C, charge and discharge cycles were performed at a rate of 1C, and the capacity retention rate was tested after 500 cycles.

[0098] High-temperature cycle performance test: At 45°C, charge and discharge cycles were performed at a rate of 1C, and the capacity retention rate was tested after 200 cycles.

[0099] Needle puncture safety test: A steel needle is used to puncture a fully charged battery to observe whether thermal runaway occurs and the maximum temperature of the battery surface is recorded.

[0100] Performance test comparison is shown in Table 2. Figure 3 as well as Figure 4 shown.

[0101] Table 2 Performance test comparison

[0102] Test items Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 3C charging maximum temperature rise (ΔT, ℃) 13.5 14.8 28.2 19.5 23.8 17.3 25℃, 1C, 500 cycles capacity retention (%) 91.2 88.5 78.3 85.1 82.4 87.6 45℃, 1C, 200 cycles capacity retention (%) 85.7 82.3 65.1 75.8 72.3 78.5 Highest temperature of needle puncture test (℃) 75 82 >200 (thermal runaway) 135 160 110 Acupuncture fever runaway Not occurred Not occurred occur Slight smoke smoke Not occurred

[0103] As shown in Table 2, the temperature rise of Examples 1 and 2 during 3C charging is significantly lower than that of all the comparative examples, particularly significantly lower than that of Comparative Example 1, which does not contain any temperature-control components. Comparative Examples 2 (containing only PCM) and 3 (containing only T-Net) both exhibited inferior temperature control performance compared to the examples. Comparative Example 4 (a uniform mixture of PCM and T-Net) outperformed Comparative Examples 2 and 3, but still fell short of Examples 1 and 2, which have a gradient structure and optimized design. This demonstrates the synergistic effect of the phase change material microcapsules and temperature-sensitive conductive network in the integrated anode prepared by the present invention, as well as the superiority of the gradient structure design. Under both ambient and high-temperature cycling conditions, the capacity retention of Examples 1 and 2 was significantly higher than that of Comparative Example 1 and also outperformed the other comparative examples. This is due to effective internal temperature control, which mitigates the degradation of battery performance caused by high-temperature side reactions. In the rigorous needle penetration test, neither Example 1 nor Example 2 experienced thermal runaway, effectively controlling the maximum battery surface temperature. However, Comparative Example 1 experienced severe thermal runaway. While some improvement was achieved in Comparative Examples 2, 3, and 4, the performance was not as good as that of the examples. This fully demonstrates the advantages of the multi-level collaborative temperature control mechanism proposed in the present invention in improving battery safety.

[0104] In summary, the preparation method of the phase change temperature control integrated negative electrode for large energy storage lithium batteries and the integrated negative electrode prepared by the present invention achieve excellent internal temperature control effect and can significantly improve the cycle life and safety of lithium batteries.

[0105] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery, characterized in that: The method comprises the following steps: S1. Preparation of core-shell structured phase change material microcapsules: selecting a core material phase change composition comprising a mixture of at least two organic alkanes with different melting points and doped with a thermal conductivity enhancing nanomaterial, in situ forming a composite polymer shell comprising a polyvinylidene fluoride copolymer and a nano inorganic oxide filler on the surface of a droplet of the core material phase change composition by interfacial polymerization or emulsion solvent evaporation, and chemically grafting molecular chains containing polar functional groups onto the outer surface of the composite polymer shell to form a core-shell structured phase change material microcapsule; S2. Constructing a temperature-sensitive three-dimensional interpenetrating conductive network: compounding acid-treated surface-functionalized multi-walled carbon nanotubes with two-dimensional graphene sheets to form a three-dimensional conductive framework, and then in situ free radical polymerization of N-isopropylacrylamide monomers in the presence of the three-dimensional conductive framework and cross-linking to form a temperature-sensitive three-dimensional interpenetrating conductive network; S3. Preparing a multilayer gradient functional negative electrode slurry system: preparing three negative electrode slurries respectively, each slurry containing a negative electrode active material, a conductive agent, and a binder, and differentially adding the core-shell structure phase change material microcapsules prepared in step S1 and the temperature-sensitive three-dimensional interpenetrating conductive network prepared in step S2, so that the mass percentage concentration of the core-shell structure phase change material microcapsules in different slurries presents a gradient change, while the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry remains consistent; S4. Multi-layer wet sequential coating and integrated molding: The three negative electrode slurries prepared in step S3 are continuously coated on the metal current collector substrate in the order from close to the current collector to far away from the current collector, and the ratio of the wet film thickness and dry film thickness of each functional layer is controlled. After multi-stage programmed temperature-controlled drying and roll-to-roll densification treatment, a phase change temperature-controlled integrated negative electrode is obtained in which the phase change material microcapsules are distributed in a concentration gradient along the thickness direction of the negative electrode and the temperature-sensitive three-dimensional interpenetrating conductive network is dispersed in the entire negative electrode pore structure.

2. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In step S1, the thermal conductivity enhancing nanomaterial is exfoliated graphene or boron nitride nanosheets, the polyvinylidene fluoride copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer, and the nano inorganic oxide filler is silicon dioxide particles or aluminum oxide particles with an average particle size of less than 100 nm. The added amount of the nano inorganic oxide filler is 3-8 wt% of the shell mass.

3. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In the step S1, chemically grafting molecular chains containing polar functional groups onto the outer surface of the composite polymer shell layer specifically includes: grafting short-chain polymers or silane coupling agents containing carboxyl groups, hydroxyl groups or sulfonic acid groups.

4. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In the step S1, the core-shell structure phase change material microcapsules formed have an average particle size of 5-25 μm and a phase change latent heat value of not less than 140 J / g.

5. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In the step S2, the initiator used for the in-situ free radical polymerization of the N-isopropylacrylamide monomer is azobisisobutyronitrile or potassium persulfate, and the cross-linking agent is N,N'-methylenebisacrylamide.

6. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In step S3, the negative electrode active material is selected from artificial graphite, coated silicon-based negative electrode material, lithiated titanate or a mixture thereof, and the binder is polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose or a mixture thereof.

7. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In step S3, the solid content of the core-shell structure phase change material microcapsules in the three layers of slurry is controlled to be 15-25 wt%, 8-15 wt% and 3-8 wt% respectively.

8. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In step S3, the solid content of the temperature-sensitive three-dimensional interpenetrating conductive network in each layer of the negative electrode slurry is uniformly controlled to be 2-5 wt %.

9. The method for preparing a phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery according to claim 1, characterized in that: In step S4, the dry film thickness ratio of each functional layer from the current collector layer to the surface layer is controlled to be 2-4:4-6:1-3, the total dry film thickness of the phase change temperature control integrated negative electrode is controlled to be 70-120 μm, and the compaction density of the phase change temperature control integrated negative electrode is controlled to be 1.45-1.75 g / cm³ by roller pressing.

10. A phase-change temperature-controlled integrated negative electrode for an energy storage lithium battery prepared by the preparation method according to any one of claims 1 to 9.

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