Phase change temperature control integrated negative electrode for energy storage lithium battery and preparation method thereof

Abstract

The application provides a phase change temperature control integrated negative electrode for energy storage lithium battery and a preparation method thereof. The method comprises the following steps: preparing core-shell structure phase change material microcapsules; constructing a temperature sensitive three-dimensional interpenetrating conductive network; preparing a multi-layer gradient functional negative electrode slurry system: preparing three kinds of negative electrode slurries respectively, each slurry comprising a negative electrode active material, a conductive agent and a binder, and the core-shell structure phase change material microcapsules and the temperature sensitive three-dimensional interpenetrating conductive network being added differently, so that the mass percentage concentration of the core-shell structure phase change material microcapsules in different slurries presents a gradient change, and the mass percentage concentration of the temperature sensitive three-dimensional interpenetrating conductive network in each slurry remains consistent; and adopting multi-layer wet sequential coating and integrated forming. The application can prepare an integrated negative electrode with excellent internal temperature control capability and safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium battery negative electrode material and a preparation method thereof, in particular to a phase change temperature control integrated negative electrode for energy storage lithium battery and a preparation method thereof, and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] With the transformation of global energy structure and the vigorous development of electric vehicle industry, the demand for energy storage systems and high energy density lithium ion batteries is increasing. Under the conditions of rapid charging and discharging, high rate output or abuse, a large amount of Joule heat is easily generated inside the lithium ion battery, which leads to rapid temperature rise of the battery. The excessively high temperature not only accelerates the decomposition of electrolyte, destroys the stability of solid electrolyte interface (SEI) film, reduces the capacity retention rate and cycle life of the battery, but also may induce the growth of lithium dendrites and increase the risk of internal short circuit of the battery.

[0003] At present, the commercial lithium battery thermal management system mostly adopts external heat dissipation methods such as forced air cooling, liquid cooling, etc. Although these external heat dissipation systems can control the overall temperature of the battery pack or module to a certain extent, they often have problems such as large volume, complex structure, high energy consumption, high cost, etc. More importantly, the response and control effect of external heat dissipation systems on the internal part of the battery, especially the local hot spot inside the cell, is limited, and it is difficult to fundamentally prevent the performance degradation and safety hazards caused by local overheating.

[0004] For internal battery thermal management, some explorations have been made in the prior art. For example, by improving the thermal conductivity of the negative electrode material itself, or coating a thermal insulation layer on the surface of the electrode sheet to slow down heat transfer. However, most of these methods belong to passive thermal management, and it is difficult to actively and intelligently respond to the temperature change inside the battery, and the temperature control effect and range are limited. Introducing phase change materials into the battery is an effective internal thermal management strategy, which can change phase at a certain temperature 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 electrolyte, and affecting the electrochemical performance of the battery. In addition, simply relying on the heat absorption of phase change materials has an upper limit on its temperature control capacity under continuous high heat production conditions.

[0005] In summary, it is of great significance to develop a technology that can actively, efficiently and multi-level cooperatively control the temperature inside the battery, especially a temperature control scheme integrated on the negative electrode as the key heat production component, for improving the safety and prolonging the service life of energy storage lithium batteries. SUMMARY

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

[0007] To achieve the above object, the present application provides the following technical solutions:

[0008] A preparation method of a phase change temperature control integrated negative electrode for energy storage lithium batteries, comprising the following steps:

[0009] S1, preparing core-shell structure phase change material microcapsules: selecting a core material phase change composition comprising a mixture of at least two different melting point organic alkanes and doped with thermal conductivity enhanced nanomaterials, using interfacial polymerization or emulsion solvent evaporation method to form a composite polymer shell layer comprising polyvinylidene fluoride copolymer and nano inorganic oxide filler on the surface of the droplets of the core material phase change composition in situ, and chemically grafting a molecular chain containing a polar functional group to the outer surface of the composite polymer shell layer to form core-shell structure phase change material microcapsules;

[0010] S2, constructing a temperature-sensitive three-dimensional interpenetrating conductive network: compounding the surface functionalized multi-walled carbon nanotubes after acid treatment with two-dimensional graphene sheets to form a three-dimensional conductive skeleton, and then performing in-situ radical polymerization and crosslinking of N-isopropyl acrylamide monomers in the presence of the three-dimensional conductive skeleton to form a temperature-sensitive three-dimensional interpenetrating conductive network;

[0011] S3, preparing a multi-layer gradient functional negative electrode slurry system: preparing three kinds of negative electrode slurries respectively, each slurry comprising 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, and the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry remains the same;

[0012] S4, using multi-layer wet sequential coating and integrated forming: sequentially and continuously coating the three kinds of negative electrode slurries prepared in step S3 on a metal current collector substrate in order from close to the current collector to far from the current collector, controlling the wet film thickness and dry film thickness ratio of each functional layer, and after multi-segment program temperature drying and roll compaction densification treatment, obtaining the phase change temperature control integrated negative electrode 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 prepare phase change material microcapsules with good encapsulation, adjustable thermophysical properties, high mechanical strength and good compatibility with negative electrode slurry system. Selecting organic alkane mixture with different melting points as core material can accurately control the phase change temperature range according to the working temperature range of the battery. Incorporating thermal conductivity enhancing nanomaterials can significantly improve the thermal conductivity efficiency of the core material and accelerate the absorption and release of heat during the phase change process. The purpose of introducing polyvinylidene fluoride copolymer in the shell layer is to provide good electrochemical stability and certain flexibility. Nano-inorganic oxide fillers enhance the mechanical strength and thermal stability of the shell layer. Chemical grafting modification is performed on the outer shell layer to introduce polar functional groups, which aims to improve the dispersibility of hydrophobic microcapsules in commonly used non-aqueous negative electrode slurry solvents (such as NMP) and enhance the interfacial bonding force with binders and other components.

[0014] The purpose of step S2 is to construct a conductive network that has good conductivity at normal working temperature and significantly and reversibly reduces conductivity when the temperature exceeds the preset threshold. The three-dimensional conductive framework formed by the composite of multi-walled carbon nanotubes and graphene sheets has excellent conductivity and large specific surface area. Acid treatment is performed on the conductive framework to functionalize the surface and introduce oxygen-containing functional groups, which aims to facilitate the subsequent grafting or coating of temperature-sensitive polymer N-isopropyl acrylamide (PNIPAM). In situ radical polymerization and crosslinking of PNIPAM monomers in the presence of the conductive framework can tightly bind the formed PNIPAM network to the conductive framework, forming an interpenetrating structure. When the temperature rises above the LCST of PNIPAM, the PNIPAM segments change from hydrophilic to hydrophobic, causing shrinkage or aggregation, which changes the volume and thus changes the contact state between carbon materials or blocks part of the conductive path, causing the macroscopic conductivity of the entire network to decrease significantly. This process is reversible, and the conductivity can be restored when the temperature decreases.

[0015] The purpose of step S3 is to design a negative electrode structure with a specific functional gradient distribution by varying the content of different components in the slurry. The gradient addition of phase change material microcapsules provides stronger heat absorption capacity by adding a higher concentration of microcapsules in the slurry near the current collector and reduces the impact on lithium ion transport and ensures high rate performance by adding a lower concentration of microcapsules in the surface layer of the slurry near the separator. 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 when overheating at different depths.

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

[0017] The temperature-sensitive three-dimensional interpenetrating conductive network can reversibly expand in volume when the ambient temperature exceeds the first preset temperature threshold in the range of 35-45°C, causing partial obstruction of the conductive path, thereby causing a reversible sharp increase in its macroscopic resistivity by at least one order of magnitude. During the operation of the lithium battery, when the local temperature reaches the second preset temperature threshold, the phase change temperature control integrated negative electrode can absorb latent heat through the solid-liquid phase change of the microcapsule of the phase change material, 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 the local abnormally large current, thereby achieving multi-level coordinated internal temperature regulation and over-temperature protection.

[0018] As a preferred, in the step S1, the thermal conductivity enhanced nanomaterial is exfoliated graphene or boron nitride nanosheet, the polyvinylidene fluoride-based 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. The addition amount of the nano-inorganic oxide filler is 3-8 wt% of the shell mass.

[0019] As a preferred, in the step S1, the chemical grafting of the molecular chain containing polar functional groups on the outer surface of the composite polymer shell specifically includes grafting short-chain polymers containing carboxyl, hydroxyl or sulfonic acid groups or silane coupling agents.

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

[0021] As a preferred, in the step S1, the average particle size of the core-shell structure phase change material microcapsule formed is 5-25 μm and the phase change latent heat value is not less than 140 J / g. The particle size of the microcapsule is controlled in the range of 5-25 μm, which can ensure that there is enough phase change core material inside to provide sufficient latent heat, and will not be too large to significantly affect the compaction density of the negative electrode and the transport path of lithium ions between particles.

[0022] Preferably, in step S2, the initiator used for the in-situ free radical polymerization of N-isopropylacrylamide monomer is azobisisobutyronitrile or potassium persulfate, and the crosslinking 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, lithium 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 mass percentage of solid content of the core-shell structured phase change material microcapsules in the three layers of slurry is controlled at 15-25 wt%, 8-15 wt%, and 3-8 wt%, respectively.

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

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

[0027] The addition of 2-5 wt% 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 a 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 as 2-4:4-6:1-3, the total dry film thickness of the phase change temperature control integrated negative electrode is controlled at 70-120μm, and the compaction density of the phase change temperature control integrated negative electrode is controlled at 1.45-1.75g / cm³ by roller pressing.

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

[0030] A phase change temperature-controlled integrated negative electrode for energy storage lithium batteries prepared by any of the above 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 its preparation method. By integrating gradient-distributed phase change material microcapsules and a diffusely distributed temperature-sensitive conductive network inside the negative electrode, multi-level coordinated temperature control with active current limiting is achieved. During normal temperature rise, the phase change material preferentially absorbs heat. When the temperature rises further to the dangerous threshold, the resistivity of the temperature-sensitive conductive network increases dramatically, limiting local current and reducing heat generation from the source, effectively preventing thermal runaway of energy storage lithium batteries.

[0033] This invention ensures the stability and efficient heat exchange capability of phase change material microcapsules in the battery environment through core-shell structure design and surface modification. The gradient distribution concentrates the temperature control function in the most needed area, while minimizing the impact on electrochemical performance. The presence of a temperature-sensitive conductive network provides the battery with an additional internal safety barrier that does not rely on external systems. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 This is a schematic flowchart of a method for preparing a phase change temperature-controlled integrated negative electrode for energy storage lithium batteries according to the present invention.

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

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

[0038] Figure 4 This is a comparison chart showing the capacity retention rate of batteries prepared according to embodiments and comparative examples of the present invention after cycle testing. Detailed Implementation

[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 modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0040] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0041] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0042] Raw materials:

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

[0044] Nanomaterials with enhanced thermal conductivity: exfoliated graphene and 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] Temperature-sensitive 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] Adhesives: polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC).

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

[0055] Current collector: electrolytic copper foil.

[0056] Example 1

[0057] like Figure 1 The method shown is a preparation method of phase change temperature control integrated negative electrode for energy storage lithium battery, which includes the following steps:

[0058] S1. Preparation of core-shell structured phase change material microcapsules: Select a core phase change composition containing at least two organic alkanes with different melting points and doped with thermally conductive nanomaterials. Using interfacial polymerization or emulsion solvent evaporation, form a composite polymer shell containing polyvinylidene fluoride copolymers and nano-inorganic oxide fillers in situ on the surface of the droplets of the core phase change composition. Then, chemically graft molecular chains containing polar functional groups onto the outer surface of the composite polymer shell to form core-shell structured phase change material microcapsules.

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

[0060] S3. Preparation of a multilayer gradient functional negative electrode slurry system: Three negative electrode slurries are prepared respectively. Each slurry contains a negative electrode active material, a conductive agent, and a binder. 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 are added in a differentiated manner, so that the mass percentage concentration of the core-shell structure phase change material microcapsules in different slurries shows a gradient change, while the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network in each slurry remains consistent.

[0061] S4. Multi-layer wet sequential coating and integrated molding: The three negative electrode slurries prepared in step S3 are sequentially and continuously coated onto the metal current collector substrate in order from the closest to the current collector to the furthest away from the current collector. The wet film thickness and dry film thickness ratio of each functional layer are controlled. After multi-stage temperature-controlled drying and roller pressing densification treatment, the desired result is obtained as follows: Figure 2 The phase change material microcapsules shown are distributed with a concentration gradient along the thickness direction of the negative electrode, and a temperature-sensitive three-dimensional interpenetrating conductive network is diffused throughout the pore structure of the negative electrode.

[0062] The specific steps are explained below.

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

[0064] Preparation of the core material phase change composition: Octadecylene and eicosane were mixed uniformly at a mass ratio of 2:1 and heated to 60°C until completely melted. Then, 1.5 wt% of exfoliated graphene (core material mass) was added, and the mixture was sheared and stirred at high speed for 30 minutes under nitrogen protection to obtain a homogeneous core material phase change composition oil phase.

[0065] Formation of the composite polymer shell: 10g of PVDF-HFP was dissolved in 90g of NMP, and 0.5g (5wt% relative to the mass of PVDF-HFP) of fumed silica with an average particle size of 15nm was added. The mixture was ultrasonically dispersed for 1 hour to obtain a shell solution. 50g of the core material phase change composition oil phase prepared in the above steps was slowly added dropwise to the shell solution, while high-speed shear emulsification was performed to form an O / W type emulsion. Subsequently, deionized water (oil phase to water volume ratio of 1:5) was slowly added dropwise under stirring to initiate PVDF-HFP phase separation and form a shell on the surface of the oil droplets. Stirring 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 the mixture was reacted at 70 °C for 3 hours to perform surface carboxylation grafting. After the reaction, the microcapsules were centrifuged and washed until neutral, and then vacuum dried at 60 °C for 24 hours to obtain surface carboxylated core-shell phase change material microcapsules (PCM-1). The average particle size of PCM-1 is approximately 15 μm, the shell thickness is approximately 1.2 μm, the phase transition temperature range is 30-34 °C, and the latent heat of phase transition is 185 J / g.

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

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

[0069] In-situ polymerization and crosslinking: 0.5 g of surface-functionalized MWCNTs / rGO composite material was dispersed in 100 mL of deionized water and sonicated for 1 hour. 5 g of NIPAM monomer and 0.05 g of MBA crosslinking agent were added, and nitrogen was purged for 30 minutes to remove oxygen. Then, 0.02 g of KPS initiator was added, and the reaction was carried out at 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, freeze-drying yielded a temperature-sensitive three-dimensional interpenetrating conductive network (T-Net-1).

[0070] S3, Preparation of Multilayer Gradient Functional Anode 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. Composition ratio of three negative electrode slurries

[0073] Component Slurry A (close to current collector layer) wt% Slurry B (intermediate transition layer) wt% Slurry C (close to separator surface layer) 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 each component to NMP according to the proportions in Table 1, and use a vacuum mixer to mix at high speed until the slurry is homogeneous.

[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 onto a 9μm thick electrolytic copper foil. The wet film thickness of each layer was controlled so that the ratio of the dry film thickness of each layer after drying was approximately 3:5:2, and the total wet film thickness was controlled at approximately 250μm.

[0077] After coating, pre-dry at 60℃ for 30 minutes, and then dry in a vacuum oven at 120℃ for 12 hours.

[0078] After drying, the electrode sheets are 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 in 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 nano-inorganic oxide filler was replaced with nano-alumina with an average particle size of 20 nm, added at 6 wt% of the shell mass. Surface chemical grafting was replaced with amination treatment using (3-aminopropyl)triethoxysilane (APTES). The rest was 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 used 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 before being added), and the reaction was carried out in a nitrogen-protected ethanol / water (volume ratio 1:1) mixed solvent. The rest was the same as in Example 1, resulting in T-Net-2.

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

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

[0085] Comparative Example 1 (Conventional Negative Electrode)

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

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

[0088] Comparative Example 2 (Anode containing only phase change material microcapsules)

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

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

[0091] Comparative Example 3 (negative electrode containing only a temperature-sensitive conductive network)

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

[0093] Comparative Example 4 (Anode with uniformly mixed phase change material and temperature-sensitive conductive network)

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

[0095] In a laboratory setting, 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 / discharge temperature rise test: The battery is charged and discharged at different rates (1C, 2C, 3C) at 25℃, and the temperature change at the center point of the battery surface is monitored using a thermocouple or infrared thermal imager.

[0097] Cyclic performance test: At 25℃, charge and discharge cycle at 1C rate, and test the capacity retention rate after 500 cycles.

[0098] High-temperature cycling performance test: The capacity retention rate was tested after 200 charge-discharge cycles at 1C rate under 45℃ conditions.

[0099] Needle penetration safety test: A steel needle penetration test is performed on a fully charged battery to observe whether thermal runaway occurs and record the highest temperature on the battery surface.

[0100] Performance test comparisons are shown in Table 2. Figure 3 as well as Figure 4 As shown.

[0101] Table 2 Performance Test Comparison

[0102] Test item Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Maximum temperature rise (ΔT, °C) during 3C charging 13.5 14.8 28.2 19.5 23.8 17.3 Capacity retention rate at 25 °C, 1C, 500 cycles (%) 91.2 88.5 78.3 85.1 82.4 87.6 Capacity retention rate at 45 °C, 1C, 200 cycles (%) 85.7 82.3 65.1 75.8 72.3 78.5 Maximum temperature during needle test (°C) 75 82 >200 (thermal runaway) 135 160 110 Thermal runaway condition during needle test Did not occur Did not occur Occurred Slight smoking Smoking Did not occur

[0103] As shown in Table 2, the temperature rise of Examples 1 and 2 during 3C charging was significantly lower than that of all comparative examples, especially far lower than that of Comparative Example 1, which contained no temperature-controlling components. The temperature control effects of Comparative Example 2 (containing only PCM) and Comparative Example 3 (containing only T-Net) were not as good as those of the Examples, while Comparative Example 4 (a uniform mixture of PCM and T-Net) was better than Comparative Examples 2 and 3, but still not as good as Examples 1 and 2 with their gradient structure and optimized design. This demonstrates the synergistic effect of the phase change material microcapsules and temperature-sensitive conductive network in the integrated negative electrode prepared by this invention, as well as the superiority of the gradient structure design. Under room temperature and high-temperature cycling conditions, the capacity retention rates of Examples 1 and 2 were significantly higher than those of Comparative Example 1, and also better than other comparative examples. This is due to effective internal temperature control, which mitigated the degradation of battery performance caused by high-temperature side reactions. In the rigorous nail penetration test, Examples 1 and 2 did not experience thermal runaway, and the maximum surface temperature of the battery was effectively controlled. Comparative Example 1, however, experienced severe thermal runaway. Although Comparative Examples 2, 3, and 4 showed some improvement, their effects were not as good as those of the Examples. This fully demonstrates the advantages of the multi-level collaborative temperature control mechanism proposed in this invention in improving battery safety.

[0104] In summary, the preparation method of the phase change temperature-controlled integrated negative electrode for large-scale energy storage lithium batteries and the integrated negative electrode obtained therefrom provide the present invention achieve excellent internal temperature control, which can significantly improve the cycle life and safety of lithium batteries.

[0105] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a phase change temperature-controlled integrated negative electrode for energy storage lithium batteries, characterized in that: The method includes the following steps: S1. Preparation of core-shell structured phase change material microcapsules: Select a core phase change composition containing at least two organic alkanes with different melting points and doped with thermally conductive nanomaterials. Using interfacial polymerization or emulsion solvent evaporation, form a composite polymer shell containing polyvinylidene fluoride copolymers and nano-inorganic oxide fillers in situ on the surface of the droplets of the core phase change composition. Then, chemically graft molecular chains containing polar functional groups onto the outer surface of the composite polymer shell to form core-shell structured phase change material microcapsules. S2. Constructing a temperature-sensitive three-dimensional interpenetrating conductive network: Multi-walled carbon nanotubes with acid-treated and surface-functionalized surfaces are combined with two-dimensional graphene sheets to form a three-dimensional conductive framework. Then, in the presence of the three-dimensional conductive framework, N-isopropylacrylamide monomers are subjected to in-situ free radical polymerization and cross-linking to form a temperature-sensitive three-dimensional interpenetrating conductive network. S3. Preparation of a multilayer gradient functional negative electrode slurry system: Three types of negative electrode slurries are prepared respectively. Each slurry contains a negative electrode active material, a conductive agent, and a binder. The core-shell structured phase change material microcapsules prepared in step S1 and the temperature-sensitive three-dimensional interpenetrating conductive network prepared in step S2 are added. The solid content mass percentage of the core-shell structured phase change material microcapsules in the three layers of slurry is controlled at 15-25wt%, 8-15wt%, and 3-8wt%, respectively. The solid content mass percentage of the temperature-sensitive three-dimensional interpenetrating conductive network in each layer of negative electrode slurry is uniformly controlled at 2-5wt%. This results in a gradient change in the mass percentage concentration of the core-shell structured phase change material microcapsules in different slurries, while the mass percentage concentration of the temperature-sensitive three-dimensional interpenetrating conductive network remains consistent in each slurry. S4. Multi-layer wet sequential coating and integrated molding: The three negative electrode slurries prepared in step S3 are sequentially coated onto the metal current collector substrate in order from the closest to the current collector to the furthest away from the current collector. The wet film thickness and dry film thickness ratio of each functional layer are controlled. After multi-stage temperature-controlled drying and roller pressing densification treatment, the phase change material microcapsules are obtained with a concentration gradient distribution along the thickness direction of the negative electrode, and the temperature-sensitive three-dimensional interpenetrating conductive network is dispersed throughout the pore structure of the negative electrode.

2. The method for preparing a phase change temperature-controlled integrated negative electrode for energy storage lithium batteries 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, the nano-inorganic oxide filler is silica particles or alumina particles with an average particle size of less than 100 nm, and the amount of nano-inorganic oxide filler added is 3-8 wt% of the shell mass.

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

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

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

6. The method for preparing a phase change temperature-controlled integrated negative electrode for energy storage lithium batteries 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, lithium 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 energy storage lithium batteries 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, and the total dry film thickness of the phase change temperature control integrated negative electrode is controlled to be 70-120μm. The compaction density of the phase change temperature control integrated negative electrode is controlled to be 1.45-1.75g / cm³ by roller pressing. 3 .

8. A phase change temperature-controlled integrated negative electrode for energy storage lithium batteries prepared by the preparation method according to any one of claims 1-7.

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