A thermal switch regulation type polymer modified positive electrode material, a preparation method and application thereof

Abstract

The application discloses a thermal switch regulation type polymer modified positive electrode material, characterized by comprising positive electrode active particles, silicone rubber and a polymer layer; the polymer layer comprises polymethyl methacrylate-polyacrylonitrile copolymer and 2-methylpropane. The positive electrode material has a thermal switch regulation function, can ensure that a battery has excellent electrical properties under normal working conditions, can switch the heat conduction state of the battery to the heat insulation state under high-temperature conditions, and effectively prevents the battery from being subjected to heat spread. The application further discloses a preparation method of the positive electrode material and application of the positive electrode material in a battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a thermally switchable polymer-modified cathode material, its preparation method, and its application. Background Technology

[0002] Driven by energy transition and dual-carbon goals, the application of lithium-ion batteries in electric vehicles, large-scale power grids and storage, and the low-altitude economy is experiencing massive growth. With continuously rising market demand, the research and development of low-cost, high-energy-density, and high-safety lithium-ion batteries is urgently needed. Currently, achieving high energy density in lithium-ion batteries is mainly achieved by increasing the capacity of the cathode material; however, increasing the capacity of the cathode material usually leads to a decrease in the battery's thermal stability, making it prone to thermal runaway, resulting in thermal propagation, and even fire or explosion.

[0003] The current common technical approach is to use a high-nickel, high-voltage cathode paired with a silicon-carbon anode to improve battery energy density and meet range requirements. However, the high-nickel ternary materials used in the cathode have relatively poor thermal stability. When the internal temperature of the battery rises, the cathode material is prone to lattice distortion or collapse, exacerbating the temperature rise and leading to thermal runaway, inevitably resulting in a catastrophic battery explosion. When a high-energy-density battery is at 100–200°C, the silicon-carbon anode first experiences thermal runaway, and the heat diffuses to the cathode, causing the cathode material to decompose. This releases oxygen, which reacts with the electrolyte, further increasing the battery temperature and creating a positive thermal feedback loop, ultimately leading to fire and explosion. These types of battery fires and explosions seriously endanger the personal and property safety of consumers. Therefore, it is necessary to propose effective solutions to suppress thermal runaway or thermal propagation of cathode materials in terms of lithium-ion battery safety.

[0004] In addition, polymer coating of cathode materials is one of the common existing cathode material modification methods. Most of the modification aims to improve the conductivity of composite materials, thereby improving the overall electrical performance of the battery.

[0005] For example, prior art 1: Chinese patent CN114335467 A discloses a coated modified layered LiMO2 cathode material and its preparation method. The LiMO2 cathode material is coated with a cyclized PAN layer, and the surface layered phase is induced to transform into a rock salt phase, resulting in a layered phase-rock salt phase-PAN surface coupling structure, which improves the electrochemical activity of the cathode material.

[0006] For example, prior art 2: Chinese patent CN107507961 B discloses a method for preparing a conductive polymer-modified positive electrode sheet for lithium-ion batteries. This method involves coating the surface of a lithium-ion battery positive electrode active material with polyvinylcarbazole, and then coating the polyvinylcarbazole-coated positive electrode active material onto a current collector to obtain the lithium-ion battery positive electrode sheet. This patent can effectively reduce interfacial side reactions between the positive electrode active material and the electrolyte, ensure good lithium-ion transfer efficiency, enhance the conductivity of the positive electrode material, and extend the service life of the positive electrode active material.

[0007] The aforementioned existing technologies use polymer coatings to improve the conductivity of the cathode material, but lack research on the thermal stability of the cathode material. While modifying the battery cathode material to improve battery capacity and cycle life, existing technologies neglect critical safety issues, especially their limited ability to suppress battery thermal runaway, hindering further technological development. Summary of the Invention

[0008] One of the objectives of this invention is to provide a thermally switchable polymer-modified cathode material. This cathode material has a thermally switchable function, which can ensure that the battery has excellent electrical performance under normal operating conditions, can switch the battery from a thermally conductive state to an adiabatic state under high temperature conditions, and effectively prevent the battery from experiencing thermal propagation.

[0009] The second objective of this invention is to provide a method for preparing the above-mentioned thermally switchable polymer-modified cathode material.

[0010] The third objective of this invention is to provide applications of the aforementioned thermally controlled polymer-modified cathode material.

[0011] The first objective of this invention is achieved through the following technical solution.

[0012] A thermally switchable polymer-modified cathode material, characterized in that it comprises cathode active particles, silicone rubber, and a polymer layer;

[0013] The polymer layer comprises polymethyl methacrylate-polyacrylonitrile copolymer (hereinafter referred to as PMMA-PAN) and 2-methylpropane.

[0014] The polymer layer is coated on the surface of the positive electrode active particles. The silicone rubber is used to permeate the PMMA-PAN and 2-methylpropane-coated positive electrode active particles.

[0015] This invention pioneered the use of PMMA-PAN and 2-methylpropane to coat positive electrode active particles, combined with silicone rubber impregnation to improve the mechanical stability of the positive electrode material, thus enabling the modified positive electrode material to possess thermally controlled switching functionality. The application of this modified positive electrode material in batteries can, on the one hand, improve the battery's thermal conductivity to ensure excellent electrical performance under normal operating conditions; on the other hand, it allows the battery to rapidly transition from a thermally conductive state at room temperature to a thermally adiabatic state at high temperatures, thereby suppressing thermal propagation. Specifically, when the battery is at room temperature, the thermally controlled polymer-modified positive electrode material provides a good heat transfer loop, ensuring uniform temperature distribution under normal operating conditions and facilitating accelerated lithium-ion migration, thereby increasing battery capacity. When the battery is at high temperatures, the lattice structure of the positive electrode active particles distorts or collapses, and the polymer layer expands in volume, disrupting the heat transfer loop and causing a rapid decrease in the thermal conductivity of the thermally controlled polymer-modified positive electrode material, thus preventing thermal propagation.

[0016] The polymer layer coating amount is 0.08–2 wt% of the mass of the positive electrode active particles. When the polymer layer coating amount is 0.08–2 wt%, it can uniformly coat the positive electrode active particles and avoid excessive polymer layer thickness, thereby providing better thermal conductivity for the polymer-modified positive electrode material. When the polymer layer coating amount is less than 0.8 wt%, the polymer layer thickness is thin and the coating uniformity is poor. The coating layer appears as dotted or discontinuous coating, and the heat transfer channels of the positive electrode material are uneven. When the temperature rises, due to the poor coating effect of the polymer layer, the thermal conductivity remains at a high level, and it is impossible to quickly achieve insulation; in fact, heat may even spread outward. When the polymer coating amount is greater than 2 wt%, the polymer layer is significantly thickened, and the heat transfer channels are too long, hindering the conduction of solid-phase lithium ions and affecting the capacity of the positive electrode material under normal operating conditions. Preferably, the polymer layer coating amount is 1 wt% of the mass of the positive electrode active particles.

[0017] The thickness of the polymer layer is 3 to 10 nm, preferably 5 nm.

[0018] In the polymer-modified cathode material, the mass of the silicone rubber is 1 to 2 wt% of the mass of the cathode active particles.

[0019] The silicone rubber is polydimethylsiloxane rubber.

[0020] The positive electrode active particles can be selected from Li-based layered Li structures. x M y O2 (M = Co, Ni, Mn), spinel-structured LiMn2O4, olivine-structured LiFePO4, and also Na-based transition metal oxides. x MeO2 (Me = Mn, Fe, Ni, Co, V, Cu, Cr, etc.), polyanionic compounds Nax M y (X a O b ) z Z w (M = Fe, V, Ni, Co, etc., X = P, Si, S, etc., and Z = F-, OH-, etc.), Bruce Blue compounds Na x MA[MB(CN)6]·nH2O (MA and MB are transition metal ions), etc.

[0021] The polymer-modified cathode material further includes an organic binder, which is one or more of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone, and sucrose; the amount of the organic binder is 1 to 100 wt% of the mass of the cathode active particles.

[0022] The second objective of this invention is achieved through the following technical solution.

[0023] The preparation method of the above-mentioned thermally switchable polymer-modified cathode material is characterized by comprising the following steps:

[0024] (1) Mix the organic binder and solvent evenly to prepare an organic solvent slurry; add the polymer to the organic solvent slurry, stir thoroughly and evenly, then add the positive electrode active particles and stir evenly again to obtain a positive electrode material slurry, and place it in a drying oven for heating and degassing; the polymer includes PMMA-PAN and 2-methylpropane;

[0025] (2) Pour the positive electrode material slurry obtained in step (1) into a mold and cool it in liquid nitrogen; take the frozen sample out of the mold and dry it with a freeze dryer to obtain polymer-coated positive electrode active particles;

[0026] (3) The silicone rubber base material and the curing agent are mixed evenly to obtain the silicone rubber precursor; then the silicone rubber precursor is impregnated into the positive electrode active particles coated with polymer and cured in a drying oven to obtain the thermally controlled polymer modified positive electrode material.

[0027] The organic binder is one or more of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone, and sucrose; the amount of the organic binder is 1 to 100 wt% of the mass of the positive electrode active particles.

[0028] The solvent is one or more of N-methylpyrrolidone (NMP) and propylene oxide (ECH), and its volume ratio to the mass of the positive electrode active particles is 1-2 mL: 1 g.

[0029] The amount of PMMA-PAN and 2-methylpropane added is 0.8 to 2 wt% of the mass of the positive electrode active particles to ensure uniform coating of the polymer layer with appropriate thickness.

[0030] In step (1), the polymer further includes one or more of polyacrylonitrile and poly(3,4-ethylenedioxythiophene / polystyrene sulfonate) (PEDOT:PSS), and the amount of the polymer added is 0.8 to 100 wt% of the mass of the positive electrode active particles.

[0031] In step (1), the temperature inside the drying oven is 60–90°C.

[0032] In step (2), the positive electrode material slurry is poured into the mold and cooled for 1 to 10 minutes, and then dried in a freeze dryer for 24 to 60 hours.

[0033] In step (3), the siloxane material is polydimethylsiloxane, the curing agent is a silane coupling agent, and the mass ratio of the siloxane material to the curing agent is 5:1 to 20:1.

[0034] In step (3), the amount of silicone rubber precursor impregnated is 1 to 2 wt% of the mass of the positive electrode active particles, and the impregnation time is 6 to 8 h.

[0035] In step (3), the curing temperature inside the drying oven is 60-90℃.

[0036] The third objective of this invention is achieved through the following technical solution.

[0037] The application of the aforementioned thermally controlled polymer-modified cathode material in batteries improves the thermal safety performance of the batteries.

[0038] The battery includes a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence. The positive electrode sheet includes a current collector and a positive electrode active slurry coated on the current collector. The positive electrode active slurry includes the thermally regulated polymer-modified positive electrode material.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] This invention coats the surface of positive electrode active particles with a polymer layer and impregnates it with silicone rubber to obtain the thermally switchable polymer-modified positive electrode material. This invention utilizes this polymer layer coating and silicone rubber impregnation structure to enable the positive electrode material to have thermally switchable function. This positive electrode material not only improves the electrical performance of the battery, but also enhances the battery's thermal safety, switching the battery from a thermally conductive state to an adiabatic state under high temperature conditions, thus suppressing the thermal propagation of the battery.

[0041] When the battery is at room temperature, the thermally controlled polymer-modified cathode material has a good heat transfer circuit and increased thermal conductivity, ensuring uniform battery temperature distribution under normal operating conditions. It can also accelerate lithium-ion migration, increase migration rate, thereby improving battery capacity and energy density.

[0042] When the battery is at a high temperature, the lattice structure of the positive electrode active particles becomes distorted or collapses, and the polymer layer expands in volume, which disrupts the heat transfer circuit. This causes the thermal conductivity of the thermally controlled polymer-modified positive electrode material to drop rapidly, keeping the battery in an adiabatic state, preventing heat spread, and avoiding a catastrophic battery explosion. Attached Figure Description

[0043] Figure 1 This is a graph showing how the thermal conductivity of the battery in Example 4 changes as the temperature applied by the variable temperature testing system increases.

[0044] Figure 2 The graph shows the change of battery temperature over time for Examples 4, 5, and 6, and Comparative Examples 7 and 8, during the application of temperature in the variable temperature test system. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] This invention uses LiNi 0.8 Co 0.1 Mn 0.1 O2 (with an average particle size of 2-10 μm and an average specific surface area of ​​0.45 m²) 2 The following is a specific implementation using the positive electrode active particle ( / g) as an example to illustrate the technical solution of the present invention. The raw materials used in the following examples are all commercially available products; PMMA-PAN and 2-methylpropane are Matsumoto Microsphere HF-48D products purchased from Matsumoto Yushi-Seiyaku Co., Ltd., which consists of PMMA-PAN as the outer shell and 2-methylpropane as the core.

[0047] Example 1

[0048] The thermally switchable polymer-modified cathode material of this embodiment includes cathode active particles, silicone rubber, and a polymer layer coated on the cathode active particles. The polymer layer coating amount is 0.8 wt%, and the polymer layer thickness is 3 nm.

[0049] The specific implementation method is as follows:

[0050] Step 1: Weigh 5g of PVDF and 150mL of NMP into a beaker and stir until homogeneous to obtain an organic solvent slurry; add 0.8g of PMMA-PAN and 2-methylpropane to the organic solvent slurry and stir until homogeneous, then add 100g of positive electrode active particles and stir until homogeneous to obtain a positive electrode material slurry, and place it in an 85℃ drying oven for heating and degassing.

[0051] Step 2: Place the PTFE (polytetrafluoroethylene) mold on a copper plate wrapped with aluminum foil, pour the positive electrode material slurry obtained in Step 1 into the mold, and cool it in liquid nitrogen for 5 minutes. Remove the frozen sample from the mold and dry it in a freeze dryer for 48 hours to obtain polymer-coated positive electrode active particles.

[0052] Step 3: Mix polydimethylsiloxane and silane coupling agent at a mass ratio of 15:1 to obtain a polydimethylsiloxane rubber precursor; then add the precursor to the polymer-coated positive electrode active particles and impregnate for 8 hours, with the impregnation amount accounting for 1 wt% of the mass of the positive electrode active particles, and cure in an 85℃ drying oven to form a thermally switchable polymer-modified positive electrode material.

[0053] In this embodiment, the polymer layer thickness of the thermally switchable polymer-modified cathode material is 3 nm, and it is uniformly coated.

[0054] Example 2

[0055] The thermally controlled polymer-modified cathode material of this embodiment includes cathode active particles, silicone rubber, and a polymer layer coated on the cathode active particles. The polymer layer has a coating amount of 1 wt% and a thickness of 5 nm.

[0056] The specific implementation method is as follows:

[0057] Step 1: Weigh 5g of PVDF and 150mL of NMP into a beaker and stir until homogeneous to obtain an organic solvent slurry; add 1g of PMMA-PAN and 2-methylpropane to the organic solvent slurry and stir until homogeneous, then add 100g of positive electrode active particles and stir until homogeneous to obtain a positive electrode material slurry, and place it in an 85℃ drying oven for heating and degassing.

[0058] Step 2: Place the PTFE (polytetrafluoroethylene) mold on a copper plate wrapped with aluminum foil, pour the positive electrode material slurry obtained in Step 1 into the mold, and cool it in liquid nitrogen for 5 minutes. Remove the frozen sample from the mold and dry it in a freeze dryer for 48 hours to obtain polymer-coated positive electrode active particles.

[0059] Step 3: Mix polydimethylsiloxane and silane coupling agent at a mass ratio of 15:1 to obtain a polydimethylsiloxane rubber precursor; then add the precursor to the polymer-coated positive electrode active particles and impregnate for 6 hours, with the impregnation amount accounting for 1 wt% of the mass of the positive electrode active particles, and cure in an 85°C drying oven to form a thermally switchable polymer-modified positive electrode material.

[0060] In this embodiment, the polymer layer thickness of the thermally switchable polymer-modified cathode material is 5 nm, and it is uniformly coated.

[0061] Example 3

[0062] The thermally switchable polymer-modified cathode material of this embodiment includes cathode active particles, silicone rubber, and a polymer layer coated on the cathode active particles. The polymer layer coating amount is 1.5 wt%, and the polymer layer thickness is 8 nm.

[0063] The specific implementation method is as follows:

[0064] Step 1: Weigh 5g of PVDF and 150mL of NMP into a beaker and stir until homogeneous to obtain an organic solvent slurry; add 1.5g of PMMA-PAN and 2-methylpropane to the organic solvent slurry and stir until homogeneous, then add 100g of positive electrode active particles and stir until homogeneous to obtain a positive electrode material slurry, and place it in an 85℃ drying oven for heating and degassing.

[0065] Step 2: Place the PTFE (polytetrafluoroethylene) mold on a copper plate wrapped with aluminum foil, pour the positive electrode material slurry obtained in Step 1 into the mold, and cool it in liquid nitrogen for 5 minutes. Remove the frozen sample from the mold and dry it in a freeze dryer for 48 hours to obtain polymer-coated positive electrode active particles.

[0066] Step 3: Mix polydimethylsiloxane and silane coupling agent at a mass ratio of 15:1 to obtain a polydimethylsiloxane rubber precursor; then add the precursor to the polymer-coated positive electrode active particles and impregnate for 6 hours, with the impregnation amount accounting for 1 wt% of the mass of the positive electrode active particles, and cure in an 85°C drying oven to form a thermally switchable polymer-modified positive electrode material.

[0067] In this embodiment, the polymer layer thickness of the thermally switchable polymer-modified cathode material is 8 nm, and it is uniformly coated.

[0068] Comparative Example 1

[0069] The comparative example of a thermally switchable polymer-modified cathode material includes cathode active particles, silicone rubber, and a polymer layer coated on the cathode active particles. The polymer layer has a coating amount of 0.04 wt% and a thickness of 1 nm.

[0070] The specific implementation method is as follows:

[0071] Step 1: Weigh 5g of PVDF and 150mL of NMP into a beaker and stir until well mixed to form an organic solvent slurry; add 0.04g of PMMA-PAN and 2-methylpropane to the organic solvent slurry and stir until well mixed, then add 100g of positive electrode active particles and stir further until well mixed to obtain a positive electrode material slurry, and place it in an 85℃ drying oven for heating and degassing.

[0072] Step 2: Place the PTFE (polytetrafluoroethylene) mold on a copper plate wrapped with aluminum foil, pour the positive electrode material slurry obtained in Step 1 into the mold, and cool it in liquid nitrogen for 5 minutes. Remove the frozen sample from the mold and dry it in a freeze dryer for 48 hours to obtain polymer-coated positive electrode active particles.

[0073] Step 3: Mix polydimethylsiloxane and silane coupling agent at a mass ratio of 15:1 to obtain a polydimethylsiloxane rubber precursor; then add the precursor to the polymer-coated positive electrode active particles and impregnate for 6 hours, with the impregnation amount accounting for 1 wt% of the mass of the positive electrode active particles, and cure in an 85℃ drying oven to obtain a polymer-modified positive electrode material.

[0074] The polymer layer thickness in the cathode material obtained in this comparative example is 1 nm, and it is intermittently coated, which indicates that the polymer layer coating amount used in this comparative example is too low.

[0075] Comparative Example 2

[0076] The comparative example of a thermally switchable polymer-modified cathode material includes cathode active particles, silicone rubber, and a polymer layer coated on the cathode active particles. The polymer layer has a coating amount of 4 wt% and a thickness of 15 nm.

[0077] The specific implementation method is as follows:

[0078] Step 1: Weigh 5g of PVDF and 150mL of NMP into a beaker and stir until homogeneous to obtain an organic solvent slurry; add 4g of PMMA-PAN and 2-methylpropane to the organic solvent slurry and stir until homogeneous, then add 100g of positive electrode active particles and stir until homogeneous to obtain a positive electrode material slurry, and place it in an 85℃ drying oven for heating and degassing.

[0079] Step 2: Place the PTFE (polytetrafluoroethylene) mold on a copper plate wrapped with aluminum foil, pour the positive electrode material slurry obtained in Step 1 into the mold, and cool it in liquid nitrogen for 5 minutes. Remove the frozen sample from the mold and dry it in a freeze dryer for 48 hours to obtain polymer-coated positive electrode active particles.

[0080] Step 3: Mix polydimethylsiloxane and silane coupling agent at a mass ratio of 15:1 to obtain a polydimethylsiloxane rubber precursor; then add the precursor to the polymer-coated positive electrode active particles and impregnate for 6 hours, with the impregnation amount accounting for 1 wt% of the mass of the positive electrode active particles, and cure in an 85℃ drying oven to form a polymer-modified positive electrode material.

[0081] The cathode material obtained in this comparative example has a polymer layer thickness of 10 nm and is a thick coating.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 2 is that PMMA-PAN and 2-methylpropane are not added in step 1 of this comparative example. The remaining steps are the same as in Example 2.

[0084] Comparative Example 4

[0085] This comparative example is the positive electrode active material without any coating, i.e., the positive electrode active particle.

[0086] The thermal conductivity of the cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Tables 1-3.

[0087] Table 1

[0088] Example <![CDATA[Thermal conductivity (Wm -1 K -1 )]]> Temperature (°C) Example 1 1.03 25 Example 2 1.33 25 Example 3 1.15 25

[0089] In Examples 1-3, the polymer layer uniformly coats the positive electrode active particles. As shown in Table 1, at 25°C, the thermally regulated polymer-modified positive electrode material of this invention exhibits good thermal conductivity, and the optimal thermal conductivity of 1.33 W / m² is observed when the polymer layer coating amount is 1 wt%. -1 K -1 .

[0090] Table 2

[0091] Example <![CDATA[Thermal conductivity (Wm -1 K -1 )]]> Temperature (°C) Example 2 1.33 25 Comparative Example 1 0.61 25 Comparative Example 2 0.56 25

[0092] As shown in Table 2, at 25°C, both excessive and insufficient polymer layer coating will affect the thermal conductivity of this cathode material.

[0093] Table 3

[0094]

[0095]

[0096] As shown in Table 3, the thermal conductivity of the positive electrode active particles in Comparative Example 4 is 0.45 W / m² at 25℃. -1 K -1 In contrast, the cathode material in Comparative Example 3, which was not coated with PMMA-PAN and 2-methylpropane, had a thermal conductivity of only 0.52 W / m². -1 K -1 However, all of them are far lower than the thermal conductivity (1.33 W / m²) obtained in Example 2. -1 K -1 This indicates that in the thermally switchable polymer-modified cathode material of the present invention, the polymer layer can provide a good heat transfer channel at room temperature, thereby improving lithium-ion migration and enhancing cathode performance.

[0097] Example 4

[0098] (1) Battery preparation: The positive electrode active slurry with the thermally controlled polymer modified positive electrode material of Example 2 as the main component is coated on the current collector to obtain a positive electrode sheet; then the positive electrode sheet, separator and negative electrode sheet are stacked in sequence to obtain a battery;

[0099] (2) Place the battery obtained in step (1) in the charge-discharge test system and charge and discharge it at a 1C rate. The charging cutoff voltage is 4.3V and the discharging cutoff voltage is 2.7V. Test the initial capacity of the battery. After 100 cycles, test the battery capacity again. The results are shown in Table 4.

[0100] (3) Place the battery obtained in step (1) into a variable temperature test system, set the temperature to rise from 25℃ to 300℃ at a heating rate of 5℃ / min, and test the battery's thermal conductivity and its temperature change. The results are as follows: Figure 1 and 2 As shown.

[0101] Example 5

[0102] (1) Battery preparation: The positive electrode active slurry with the thermally controlled polymer modified positive electrode material of Example 1 as the main component is coated on the current collector to obtain a positive electrode sheet; then the positive electrode sheet, separator and negative electrode sheet are stacked in sequence to obtain a battery;

[0103] (2) Place the battery obtained in step (1) in the charge-discharge test system and charge and discharge it at a 1C rate. The charging cutoff voltage is 4.3V and the discharging cutoff voltage is 2.7V. Test the initial capacity of the battery. After 100 cycles, test the battery capacity again. The results are shown in Table 4.

[0104] (3) Place the battery obtained in step (1) into a variable temperature test system, set the temperature to rise from 25℃ to 300℃ at a heating rate of 5℃ / min, and test the temperature change of the battery. The results are as follows: Figure 2 As shown.

[0105] Example 6

[0106] (1) Battery preparation: The positive electrode active slurry with the thermally controlled polymer modified positive electrode material of Example 3 as the main component is coated on the current collector to obtain a positive electrode sheet; then the positive electrode sheet, separator and negative electrode sheet are stacked in sequence to obtain a battery;

[0107] (2) Place the battery obtained in step (1) in the charge-discharge test system and charge and discharge it at a 1C rate. The charging cutoff voltage is 4.3V and the discharging cutoff voltage is 2.7V. Test the initial capacity of the battery. After 100 cycles, test the battery capacity again. The results are shown in Table 4.

[0108] (3) Place the battery obtained in step (1) into a variable temperature test system, set the temperature to rise from 25℃ to 300℃ at a heating rate of 5℃ / min, and test the temperature change of the battery. The results are as follows: Figure 2 As shown.

[0109] Comparative Example 5

[0110] The difference between this comparative example and Example 4 is that the positive electrode active slurry, with the positive electrode material of Comparative Example 1 as the main component, is coated onto the current collector. The remaining experimental steps are the same as in Example 4.

[0111] Comparative Example 6

[0112] The difference between this embodiment and Embodiment 4 is that the positive electrode active slurry, with the positive electrode material of Comparative Example 2 as the main component, is coated onto the current collector. The remaining experimental steps are the same as in Embodiment 4.

[0113] Comparative Example 7

[0114] The difference between this embodiment and Embodiment 4 is that the positive electrode active slurry, with the positive electrode material of Comparative Example 3 as the main component, is coated onto the current collector. The remaining experimental steps are the same as in Embodiment 4.

[0115] Comparative Example 8

[0116] The difference between this embodiment and Embodiment 4 is that the positive electrode active slurry, with the positive electrode material of Comparative Example 4 as the main component, is coated onto the current collector. The remaining experimental steps are the same as in Embodiment 4.

[0117] Table 4

[0118]

[0119] As shown in Table 4, the battery in Comparative Example 7, made using cathode active materials without PMMA-PAN and 2-methylpropane coating, exhibits low thermal conductivity, low specific capacity, and poor cycle stability. The battery in Comparative Example 8, made using cathode active particles without any coating modification, exhibits even worse thermal conductivity, lower specific capacity, and even worse cycle stability. Examples 4, 5, and 6 of this invention all demonstrate high thermal conductivity and specific capacity, especially Example 4, which shows excellent thermal conductivity and capacity. This indicates that applying the thermally regulated polymer-modified cathode material of this invention to batteries can improve battery electrical performance at room temperature. However, the batteries in Comparative Examples 5 and 6, due to uneven coating or excessive thickness of the polymer layer on the cathode material, exhibit lower thermal conductivity and specific capacity than Examples 4-6.

[0120] Depend on Figure 1 Data shows that the battery in Example 4 uses the thermally switched polymer-modified cathode material of the present invention. Its thermal conductivity gradually decreases with increasing applied temperature, especially above 100°C, where the thermal conductivity drops to 0.4 W / m². -1 K -1 This indicates that the polymer-modified cathode material of the present invention has a thermal switching regulation function, which can ensure the thermal conductivity of the material under normal working conditions, while switching to an adiabatic state when the temperature is higher than 100°C. This is mainly due to the unique structural design of the present invention. When the battery is at a high temperature, the lattice structure of the cathode active particles is distorted or collapsed, the polymer layer expands in volume, the heat transfer circuit is destroyed, and the thermal conductivity drops rapidly.

[0121] Figure 2 This is a graph showing the change in battery temperature over time for Examples 4, 5, and 6, and Comparative Examples 7 and 8, during the application of temperature in the variable temperature testing system. Figure 2 Data shows that batteries using polymer-modified cathode materials controlled the temperature rise within less than 350 seconds when thermal runaway occurred. However, for batteries using cathode active materials without PMMA-PAN and 2-methylpropane coating, and batteries using unmodified cathode active particles, the temperature increased continuously over time, potentially leading to battery fire. This indicates that the thermally controlled polymer-modified cathode material of this invention, when applied to batteries, can effectively prevent the spread of thermal runaway and improve battery thermal safety.

Claims

1. A method for preparing a thermally switchable polymer-modified cathode material, characterized in that, Includes the following steps: (1) Mix the organic binder and solvent evenly to obtain an organic solvent slurry; add the polymer to the organic solvent slurry, stir thoroughly and evenly, then add the positive electrode active particles and stir evenly again to obtain a positive electrode material slurry, and put it into a drying oven for heating and degassing; The positive electrode active particles are selected from Li-based layered Li... x M y O2, spinel-structured LiMn2O4, and olivine-structured LiFePO4; the polymer is a microsphere material composed of polymethyl methacrylate-polyacrylonitrile copolymer and 2-methylpropane, with polymethyl methacrylate-polyacrylonitrile copolymer as the shell and 2-methylpropane as the core; the amount of polymethyl methacrylate-polyacrylonitrile copolymer and 2-methylpropane added is 0.8~2wt% of the mass of the positive electrode active particles; (2) Pour the positive electrode material slurry obtained in step (1) into a mold and cool it in liquid nitrogen; take the frozen sample out of the mold and dry it with a freeze dryer to obtain polymer-coated positive electrode active particles; (3) The silicone rubber base material and the curing agent are mixed evenly to obtain a silicone rubber precursor; then the silicone rubber precursor is impregnated into the positive electrode active particles coated with polymer, and the impregnation amount of the silicone rubber precursor is 1~2wt% of the mass of the positive electrode active particles; and then it is placed in a drying oven for curing to obtain the thermally controlled polymer modified positive electrode material.

2. The method for preparing the thermally switched polymer-modified cathode material according to claim 1, characterized in that, The organic binder is one or more of polyvinylidene fluoride, polyvinylpyrrolidone, and sucrose; the amount of the organic binder is 1-100 wt% of the mass of the positive electrode active particles. The solvent is one or more of N-methylpyrrolidone and propylene oxide, and its volume ratio to the mass ratio of the positive electrode active particles is 1~2mL:1g.

3. The method for preparing the thermally switched polymer-modified cathode material according to claim 2, characterized in that, in In step (3), the silicone rubber base material is polydimethylsiloxane, the curing agent is silane coupling agent, the mass ratio of silicone rubber base material to curing agent is 5:1~20:1, and the impregnation time of silicone rubber precursor is 6~8h.

4. The method for preparing the thermally switched polymer-modified cathode material according to claim 3, characterized in that, in In step (1), the polymer further includes one or more of polyacrylonitrile, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonate.

5. The method for preparing the thermally switched polymer-modified cathode material according to claim 4, characterized in that, in In steps (1) and (3), the temperature inside the drying oven is 60~90 ℃; in step (2), after the positive electrode material slurry is poured into the mold, it is cooled for 1~10 min and then dried in a freeze dryer for 24~60 h.

6. A thermally switchable polymer-modified cathode material prepared by the preparation method of claim 1.

7. Application of the thermally switchable polymer-modified cathode material according to claim 6 in a battery.

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