Temperature-sensitive gel and Mylar insulating sheet

Abstract

The invention provides temperature-sensitive gel and a Mylar insulating sheet, and belongs to the technical field of battery cell insulating sheets. According to the temperature-sensitive gel formula, the alkyl modified silicone oil is introduced and matched with the vinyl MQ resin to improve the electrolyte infiltration and storage capacity of the gel, the composite insulation auxiliaries, namely the fumed silica and the aluminum oxide, are added to improve the insulativity, and the prepared Mylar insulation sheet is applied to a battery cell, has the insulativity, prolongs the cycle life of the cell and improves the safety performance of the cell.

Description

Technical Field

[0001] This application belongs to the field of battery cell insulation sheet technology, and in particular relates to a temperature-sensitive gel and Mylar insulation sheet. Background Technology

[0002] Square aluminum-cased batteries are widely used in energy storage systems and electric vehicles due to their advantages such as high structural strength, high energy density, and high assembly efficiency. During the manufacturing process of square aluminum-cased batteries, to ensure safety and reliability, an insulating sheet is typically wrapped around the bare cell. This insulating sheet, known as Mylar insulating sheet, primarily serves to: prevent short circuits caused by contact between the bare cell's electrodes and the aluminum casing; and provide lubrication during cell insertion due to low friction, preventing damage to the outer separator of the bare cell caused by friction with the casing, which could lead to internal short circuits.

[0003] Currently, the most common Mylar insulating sheet materials for square batteries on the market are polymer films such as polyethylene terephthalate (PET), polypropylene (PP), or polyamide (PI). These materials are thermally bonded to the surface of the bare battery cell after being softened by heating, thus tightly wrapping the bare battery cell surface. However, with the increasing demands for long cycle life and high safety performance in fields such as energy storage, this traditional polymer film Mylar sheet has gradually revealed the following defects and limitations.

[0004] Traditional Mylar insulating sheets, such as PET, are dense and electrochemically inert. They tightly wrap around the bare battery cell, forming a physical protective layer, but also hindering the full wetting and diffusion of the electrolyte within the separator plane. During long-term cycling, the electrolyte inevitably depletes and decomposes, leading to electrolyte shortages within the battery. Traditional Mylar insulating sheets lack the ability to replenish electrolyte and may even hinder the uniform distribution of electrolyte after secondary electrolyte injection, thus accelerating battery performance degradation and becoming a factor limiting long cycle life. PET film itself lacks compressibility or elasticity. To ensure insulation distance, it must occupy the inherent gap between the bare cell and the casing. This unutilized space reduces the effective volume available for accommodating active materials and electrolyte within the casing, limiting further increases in battery energy density. It cannot address electrolyte loss during cycle aging or mitigate the risks posed by cell displacement within the casing when subjected to external physical impacts.

[0005] Existing technology discloses a low thermal resistance phase change composite thermally conductive insulating sheet, including a substrate, a thermally conductive silicone layer and a thermally conductive phase change, which has excellent electrical insulation and chemical stability, ultra-low thermal resistance, and improves timely heat conduction. However, the material design can only provide thermal conductivity, adhesion or simple insulation. Its material design cannot meet the dynamic storage and on-demand release of electrolyte inside the battery, and is difficult to apply to the insulation protection of battery cells. Therefore, developing a temperature-sensitive gel that combines insulation, improves the cycle life of the battery cell, and enhances safety performance to replace the traditional Mylar insulating sheet material and produce Mylar insulating sheets has significant research and application value. Summary of the Invention

[0006] To address the technical problem of existing Mylar insulating sheets failing to improve the cycle life and safety performance of battery cells, the primary objective of this invention is to provide a temperature-sensitive gel that can replace traditional Mylar insulating sheet materials, while also possessing insulation properties and improving the cycle life and safety performance of battery cells.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned thermosensitive gel.

[0008] Another object of the present invention is to provide a Mylar insulating sheet made from the above-mentioned thermosensitive gel.

[0009] Another object of the present invention is to provide the application of the above-mentioned Mylar insulating sheet in the preparation of battery cells.

[0010] Another object of the present invention is to provide a battery cell comprising the aforementioned Mylar insulating sheet.

[0011] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A thermosensitive gel comprising the following components in parts by weight: 70-75 parts of vinyl-terminated silicone oil, 4-5 parts of hydrogen-containing silicone oil, 5-8 parts of vinyl MQ resin, 8-12 parts of alkyl-modified silicone oil, 2-6 parts of composite insulating additives, and 0.02-0.12 parts of inhibitors; The vinyl content of the end-vinyl silicone oil is 0.4-0.8%, and the viscosity is 2000-4000 mPa·s. The composite insulating additive includes modified fumed silica and modified aluminum oxide; The fumed silica undergoes surface hydroxyl removal treatment, and the alumina undergoes vinyl grafting treatment. The alkyl-modified silicone oil has 8 to 18 carbon atoms in its alkyl substituents.

[0012] This invention provides a formulation for a temperature-sensitive gel, which introduces alkyl-modified silicone oil and combines it with vinyl MQ resin to enhance the gel's ability to wet and store electrolytes. It also adds composite insulating additives, fumed silica and alumina, to improve insulation, thus providing both insulation and improved cell cycle life and safety performance.

[0013] Traditional silicone gels have limited absorption capacity for organic solvents and the absorption rate is slow. In this solution, the absorption capacity of silicone gels for organic solvents such as electrolytes is improved by reducing the vinyl content and Pt catalyst ratio in the crosslinking aid vinyl MQ resin, increasing the inhibitor content, reducing the degree of crosslinking.

[0014] Meanwhile, at lower crosslinking densities, the free volume and mobility of molecular chains increase, and the migration of charge carriers is stronger, leading to the accumulation of space charge, increased conductivity, and decreased insulation performance. To address this issue, inorganic fillers fumed silica and spherical alumina are introduced into the system to improve the insulation of the gel by blocking ion migration channels, dispersing electric field stress, and extending the breakdown path.

[0015] The long-chain flexible segments introduced by vinyl MQ resin and alkyl-modified silicone oil can increase the effective pore space inside the gel and improve its wettability and liquid retention capacity. When the cell temperature rises to ≥50℃, the flexible segments inside the gel unwind at high temperature, forming temporary pore channels to achieve a slow-release effect. By controlling the structure and proportion of flexible molecular chains (changing the introduced long-chain monomers of flexible molecular chains), the formation conditions of pore channels can be adjusted to further match the cell operating temperature. The above-mentioned gel has high insulation (dielectric strength ≥20kV / mm) and high liquid retention characteristics, while taking into account the chemical stability of silicone gel, making it suitable for long-term storage under cell operating conditions requiring long cycles.

[0016] Preferably, the alkyl substituents in the alkyl-modified silicone oil have 11 to 18 carbon atoms.

[0017] Preferably, the alkyl-modified silicone oil is at least one of dodecylmethyl silicone oil, octylmethyldimethoxysilane, or octadecylmethyl silicone oil.

[0018] Preferably, the vinyl content of the end vinyl silicone oil is 0.43~0.53%.

[0019] Preferably, the molecular weight of the terminal vinyl silicone oil is 20~25 kDa.

[0020] Preferably, the viscosity of the vinyl-terminated silicone oil is 2500~3500 mPa·s.

[0021] Specifically, the viscosity of the vinyl-terminated silicone oil is tested according to T / FSI 018-2019 "Vinyl-terminated dimethyl silicone oils" at a test temperature of 25°C.

[0022] Preferably, the hydrogen content of the hydrogen-containing silicone oil is 0.1~1.0 wt%.

[0023] Preferably, the hydrogen content of the hydrogen-containing silicone oil is 0.3~0.6 wt%.

[0024] Preferably, the molecular weight of the hydrogen-containing silicone oil is 5-6 kDa.

[0025] Preferably, the viscosity of the hydrogen-containing silicone oil is 50~300 mPa·s.

[0026] Preferably, the viscosity of the hydrogen-containing silicone oil is 100~300 mPa·s.

[0027] Specifically, the viscosity of the hydrogen-containing silicone oil is tested according to HGT 2363-1992 "Test Method for Kinematic Viscosity of Silicone Oil", and the test temperature is 25°C.

[0028] Preferably, the vinyl content of the vinyl MQ resin is 0.5~1.5wt%.

[0029] Preferably, the viscosity of the vinyl MQ resin is 500~5000 mPa·s.

[0030] Specifically, the viscosity of the vinyl MQ resin was tested according to GB / T22235-2008, the method for determining the viscosity of liquids, at a test temperature of 25°C.

[0031] Preferably, the specific surface area of ​​the fumed silica is 150~200 m². 2 / g.

[0032] More preferably, the specific surface area of ​​the fumed silica is 150 m². 2 / g.

[0033] Preferably, the alumina has a particle size of 1~5μm.

[0034] More preferably, the alumina has a particle size of 1 μm.

[0035] Preferably, the alumina is spherical alumina.

[0036] Preferably, the mass ratio of fumed silica to alumina is 1:1 to 3:1.

[0037] Preferably, the fumed silica is modified by surface removal of hydroxyl groups.

[0038] Specifically, the surface hydroxyl removal treatment includes the following steps: after drying fumed silica, it is heated and reacted with hexamethyldisilazane.

[0039] After surface hydroxyl removal treatment, fumed silica is added to the gel to fill the free volume of the molecular chains and block the ion migration channels.

[0040] Preferably, the alumina is treated with grafted vinyl groups.

[0041] Specifically, the grafted vinyl treatment includes the following steps: reacting alumina with vinyltriethoxysilane, followed by reflux drying with ethanol by centrifugation.

[0042] Alumina grafted with vinyl groups improves interfacial bonding, and the addition of gel can disperse electric field stress and extend the breakdown path.

[0043] Preferably, the inhibitor comprises acetylcyclohexanol and / or diethyl maleate.

[0044] More preferably, the inhibitor comprises 0.08-0.1 parts of acetylcyclohexanol and 0.02 parts of diethyl maleate.

[0045] This invention also protects a method for preparing the above-mentioned thermosensitive gel, comprising the following steps: S1. Prepolymer synthesis: The vinyl-terminated silicone oil is divided into part A and part B. Part A is mixed with fumed silica and alkyl-modified silicone oil, and part B is mixed with alumina. Then, part A and part B are mixed with vinyl MQ resin to generate a prepolymer. S2. Hydrosilylation reaction: Hydrogen-containing silicone oil, Pt catalyst, and inhibitor are added to the prepolymer, and the reaction is followed by drying to form the prepolymer.

[0046] Preferably, the Pt catalyst has a mass fraction of 30-50 ppm.

[0047] This invention protects a Mylar insulating sheet made of the aforementioned thermosensitive gel.

[0048] This invention replaces the traditional raw material of Mylar insulation sheets with a temperature-sensitive gel. The resulting Mylar insulation sheet combines insulation performance with bare cell protection. The internal network structure of the gel increases the electrolyte storage space inside the cell. During cell cycle heating, the gel structure relaxes due to heat, allowing for the slow release of electrolyte and enhancing cell cycle performance. After absorbing electrolyte, the gel expands and fills the gap between the bare cell and the casing, preventing displacement of the cell within the casing during impacts that could lead to tearing of the tab foil. This effectively improves the cell's resistance to physical impacts and enhances its safety performance.

[0049] The application of the aforementioned Mylar insulating sheet in the preparation of battery cells is also within the scope of protection of this invention.

[0050] Preferably, the battery is a square aluminum-cased battery.

[0051] The present invention also protects a battery cell comprising the aforementioned Mylar insulating sheet.

[0052] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a formulation for a temperature-sensitive gel, which introduces alkyl-modified silicone oil and combines it with vinyl MQ resin to enhance the gel's ability to wet electrolytes. Composite insulating agents fumed silica and alumina are added to improve insulation. The resulting Mylar insulating sheet is used in battery cells, providing both insulation and improved cycle life and safety performance of the cells. Attached Figure Description

[0053] Figure 1 The cycling performance graphs for Example 1 and Comparative Example 1 are shown. Figure 2 This document outlines the preparation and assembly process for temperature-sensitive gels and Mylar insulating sheets. Detailed Implementation

[0054] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0055] I. Description of Reagents Used in Examples / Comparative Examples Vinyl-terminated silicone oil #1: Shanghai Yandi VI401, CAS68083-19-2, vinyl content 0.53%, viscosity 2500 mPa·s; Vinyl-terminated silicone oil #2: Shanghai Yandi VI401, vinyl content 0.43%, viscosity 3500 mPa·s; Vinyl-terminated silicone oil #3: Shanghai Yandi VI401, vinyl content 0.23%, viscosity 10000 mPa·s; Vinyl-terminated silicone oil #4: Shanghai Yandi VI401, vinyl content 1.33%, viscosity 400 mPa·s; Hydrogen-containing silicone oil #1: Shandong Yonglida YLD-202-GG, CAS70900-21-9, hydrogen content 0.3wt%, viscosity (25℃, mm) 2 The value of ( / s) is 300 mPa·s, and the molecular weight is 5~6 kDa; Hydrogen-containing silicone oil #2: Shandong Yonglida YLD-202-GG, CAS70900-21-9, hydrogen content 0.6wt%, viscosity (25℃, mm)2 The value of ( / s) is 100 mPa·s, and the molecular weight is 5~6 kDa; Alkyl-modified silicone oil 1#: n-Dodecylmethyldiethoxysilane, Widmanstätten reagent HBWS-W201, CAS60317-40-0; Alkyl modified silicone oil #2: Polymethyl octylsiloxane, Beijing Bailingwei S13916, CAS68440-90-4; Alkyl modified silicone oil 3#: Octadecyl dimethyl methoxysilane, Rhohn reagent R013375, CAS71808-65-6; Alkyl modified silicone oil 4#: Dimethyl silicone oil, McLean D756799, CAS 63148-62-9; Alkyl modified silicone oil 5#: Isoeicosylmethyl silicone oil, Wuhan Fuxin Chemical CAS200074-76-6; Aryl-modified silicone oil 6#: Methylphenyl silicone oil, Maclean P824385, CAS63148-58-3; Pt catalyst: McLean K799485, CAS68478-92-2; Vinyl MQ Resin 1#: 5202N Vinyl MQ Silicone Resin, Shenzhen Jipeng Silicon Fluorine Materials Co., Ltd., CAS67763-03-5, Vinyl content 0.5wt%, viscosity 5000 mPa·s; Vinyl MQ Resin 2#: 5202N Vinyl MQ Silicone Resin, Shenzhen Jipeng Silicon Fluorine Materials Co., Ltd., CAS67763-03-5, Vinyl content 1.5wt%, viscosity 500 mPa·s; Fumed silica: Aladdin Biochemical N493103, CAS112945-52-5, specific surface area 150 m² 2 / g; Modified fumed silica: After being vacuum dried at 110℃ for 2 hours, fumed silica was mixed with hexamethyldisilazane at a mass ratio of SiO2=1:0.3 and heated at 80℃ for 1 hour to remove surface hydroxyl groups. Alumina: Spherical alumina, Bohuas Nano, CAS1344-28-1, particle size 1μm; Modified alumina: Spherical alumina was dried at 120°C for 3 hours, and then refluxed and centrifuged with a vinyltriethoxysilane (3wt%) ethanol solution.

[0056] II. Preparation Method (1) Preparation method of Mylar insulating sheet S1. Pretreatment with insulating additives: Fumed silica was vacuum dried at 110°C for 2 hours, then mixed with hexamethyldisilazane at a mass ratio of SiO2 = 1:0.3 and heated at 80°C for 1 hour to remove surface hydroxyl groups. After adding gel, it filled the free volume of molecular chains and blocked ion migration channels. Spherical alumina was dried at 120°C for 3 hours, then refluxed and centrifuged with a vinyltriethoxysilane (3wt%) ethanol solution. Grafting vinyl groups improved the interfacial bonding force, and the addition of gel could disperse electric field stress and extend the breakdown path. S2. Prepolymer Synthesis: The main chain monomer end vinyl silicone oil was divided into two parts: Part A (70%) was mixed with pretreated fumed silica and dodecylmethyl silicone oil in a planetary mixer with the following stirring parameters: vacuum degree -0.095MPa, speed 500rpm, time 30 minutes, to form a homogeneous silicone paste; Part B (30%) was ultrasonically dispersed with modified spherical alumina (40kHz, 300W) for 15 minutes to form an alumina-based adhesive; Part A silicone paste and Part B containing alumina-based adhesive were combined, and the crosslinking aid vinyl MQ resin was added. Vacuum planetary stirring was used with the following stirring parameters: vacuum degree -0.09MPa, speed 800rpm, time 40 minutes, temperature ≤40℃, to form a prepolymer and complete vacuum degassing; S3. Hydrosilylation reaction: Add crosslinking agent (hydrogen-containing silicone oil) and Pt catalyst to the above prepolymer, stir at low speed (200 rpm) for 10 minutes to avoid localized violent reactions, add inhibitor (acetylenecyclohexanol / diethyl maleate), and stop stirring when the viscosity is controlled at 5000±200 mPa·s. Heating initiates a hydrosilylation reaction to form a three-dimensional network. Finally, a stepped curing process is used: pre-curing at 40℃ / 1h followed by deep crosslinking at 80℃ / 2h, achieving a Si-H conversion rate of ≥95% during hydrosilylation. After baking at 120℃ for 2~4h to remove internal organic solvents, the product is cut and shaped.

[0057] (2) Assembly method of battery cell containing Mylar insulation sheet This temperature-sensitive gel, Mylar, can be directly applied to the existing assembly process. During the process of primary electrolyte injection, high-temperature settling, formation, and secondary electrolyte injection of the square-shell battery cell, after the primary electrolyte injection, under high-temperature settling conditions, the dried gel structure relaxes and absorbs the excess electrolyte in the shell into the internal three-dimensional network. The electrolyte is then replenished during the secondary electrolyte injection.

[0058] III. Examples / Comparative Examples Table 1. Component formulations for Examples 1-10

[0059] Comparative Example 1 Standard formula gel Vinyl-terminated silicone oil: 100 parts, vinyl content 0.8 wt%, viscosity 500 mPa·s; Hydrogen-containing silicone oil: 6 parts, hydrogen content 1.2wt%, molecular weight 4kDa; Pt catalyst: 50 ppm; Inhibitor: 0.06 parts of acetylcyclohexanol; Vinyl MQ resin: 15 parts, vinyl content 4 wt%, viscosity 2000 mPa·s.

[0060] Table 2. Component formulations of Comparative Examples 2-11

[0061] IV. Test Indicators (1) Insulation performance: Dielectric strength (kV / mm): Refer to GB / T 13542.2-2009, test conditions: electrode spacing 2mm, voltage gradient 5kV / s, record breakdown voltage value; Volume resistivity (Ω·cm): Refer to GB / T 1410-2006. Test conditions: Parallel plate electrodes are used. A DC voltage of 500V is applied. Measure the volume resistivity (unit: Ω·m). Crosslinking density (MPa·SI): measured by nuclear magnetic resonance (NMIR); (2) Safety performance: Filling stability: After the electrolyte filling is completed and the cell has been allowed to stand, the cell is visually inspected and measured with a steel ruler after removing one side of the cover. Tensile strength: Refer to GB / T 1040.2-2025, test conditions: specimen width 10mm, tensile rate 50mm / min, ambient temperature 23℃±2℃; Puncture resistance: 5mm diameter needle, 45° needle tip cone angle, puncture speed: 25±5mm / s; (3) Electrolyte absorption capacity: Test conditions: Sample size 5cm×5cm×0.5mm, immersed in the following three electrolyte base solutions (ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC), immersion temperature 45℃±5℃, immersion time 2h. Weigh the electrolyte base solution before and after immersion, and calculate the percentage of electrolyte absorbed by weight; (4) Cyclic performance: Capacity retention rate ≥ 75% of cycle count.

[0062] V. Test Results of Examples / Comparative Examples Table 3. Test Results of Examples / Comparative Examples

[0063] According to Table 3, Comparative Example 1 uses a conventional gel formulation, resulting in decreased gel filling stability and a poor cycle performance (7500 cycles). Comparative Example 2, without alkyl-modified silicone oil, exhibits low safety and cycle performance of its temperature-sensitive gel. Comparative Example 3 uses alkyl-modified silicone oil with a carbon number lower than the usable range, leading to decreased cycle performance. Comparative Example 4 uses alkyl-modified silicone oil with a carbon number of 20, resulting in reduced tensile strength and puncture resistance due to poor processing performance. Comparative Example 5 uses aryl-modified silicone oil instead of alkyl-modified silicone oil, significantly reducing its electrolyte absorption capacity and rendering it unsuitable as a Mylar insulating sheet. Comparative Examples 6 and 7 had excessive amounts of alkyl-modified silicone oil, resulting in a decrease in tensile strength and puncture resistance, which are considered safety performance indicators. Comparative Example 8 used unmodified fumed silica as its composite insulating agent. Comparative Example 9 used unmodified alumina as its composite insulating agent, which resulted in a decrease in dielectric strength compared to Comparative Examples 8 and 9. Comparative Example 10 used end-vinyl silicone oil #3 with low vinyl content and high viscosity, which negatively impacted processing performance and reduced safety performance. Comparative Example 11 used end-vinyl silicone oil #4 with high vinyl content and high viscosity, which increased crosslinking density, reduced gel storage capacity, and decreased cycle performance due to the excessively high vinyl content.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A temperature-sensitive gel, characterized in that, The components include the following parts by weight: 70-75 parts of vinyl-terminated silicone oil, 4-5 parts of hydrogen-containing silicone oil, 5-8 parts of vinyl MQ resin, 8-12 parts of alkyl-modified silicone oil, 2-6 parts of composite insulating additives, and 0.02-0.12 parts of inhibitors; The vinyl content of the end-vinyl silicone oil is 0.4-0.8%, and the viscosity is 2000-4000 mPa·s. The composite insulating additive includes modified fumed silica and modified aluminum oxide; The fumed silica undergoes surface hydroxyl removal treatment, and the alumina undergoes vinyl grafting treatment. The alkyl-modified silicone oil has 8 to 18 carbon atoms in its alkyl substituents.

2. The thermosensitive gel according to claim 1, characterized in that, The alkyl-modified silicone oil has 11 to 18 carbon atoms in its alkyl substituents.

3. The thermosensitive gel according to claim 1, characterized in that, The alkyl-modified silicone oil is at least one of dodecylmethyl silicone oil, octylmethyldimethoxysilane, or octadecylmethyl silicone oil.

4. The thermosensitive gel according to claim 1, characterized in that, The mass ratio of fumed silica to alumina is 1 to 3:

1.

5. The thermosensitive gel according to claim 1, characterized in that, The vinyl content of the vinyl MQ resin is 0.5~1.5wt%.

6. The thermosensitive gel according to claim 1, characterized in that, The hydrogen content of the hydrogen-containing silicone oil is 0.1~1.0wt%.

7. The method for preparing the thermosensitive gel according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Prepolymer synthesis: The vinyl-terminated silicone oil is divided into part A and part B. Part A is mixed with fumed silica and alkyl-modified silicone oil, and part B is mixed with alumina. Then, part A and part B are mixed with vinyl MQ resin to generate a prepolymer. S2. Hydrosilylation reaction: Hydrogen-containing silicone oil, Pt catalyst, and inhibitor are added to the prepolymer, and the reaction is followed by drying to form the prepolymer.

8. A Mylar insulating sheet, characterized in that, The Mylar insulating sheet is made of the thermosensitive gel described in any one of claims 1 to 7.

9. The application of the Mylar insulating sheet according to claim 8 in the preparation of battery cells.

10. A battery cell, characterized in that, Includes the Mylar insulating sheet as described in claim 8.

Images