Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device, and belongs to the technical field of electrochemical energy storage. According to the secondary battery, the phase change microcapsules are added into the lower plastic and the phase change layer, the mass percentage content of the phase change microcapsules in the lower plastic is smaller than that of the phase change microcapsules in the phase change layer, and in the charging and discharging process of the secondary battery, the phase change microcapsules are dispersed in the phase change layer through the heat absorption and cooling effects of the phase change microcapsules; the temperature difference of different areas in the secondary battery is reduced, and the temperature distribution uniformity of the different areas in the secondary battery is improved, so that the thermal stability of the secondary battery is improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries are currently the mainstream in new energy vehicles. As one of the most critical components of new energy vehicles, the safety performance of secondary batteries has received widespread attention from relevant professionals and consumers. The key to the thermal runaway problem in new energy vehicles lies in the thermal management of secondary batteries.

[0003] Rechargeable batteries offer advantages such as high energy density, long cycle life, low self-discharge, and no memory effect. However, they are highly sensitive to operating temperatures; excessively high temperatures significantly shorten battery life. Furthermore, due to the low flash point of their electrolytes, they are prone to thermal runaway under conditions such as overcharging or puncture, leading to battery combustion or even explosion. Currently, thermal management systems for rechargeable batteries mainly include air cooling systems, liquid cooling systems, and heat pipe cooling systems. While these systems can address overheating issues to some extent, they also have drawbacks. Air cooling systems have low thermal conductivity, resulting in poor temperature uniformity control within the battery pack, and they consume additional energy. Liquid cooling systems are structurally complex, and leaks can cause short circuits, thus requiring high sealing performance. Additionally, liquid cooling systems are relatively heavy, increasing the overall weight of the lithium battery system and hindering the trend towards lightweight rechargeable batteries. Heat pipe cooling systems suffer from high cost and structural complexity. The internal temperature of a secondary battery is relatively high. The aforementioned thermal management system dissipates heat or heats the battery from the outside, which to some extent exacerbates the temperature difference between the inside and outside of the battery. This temperature difference leads to uneven aging rates of the battery's active materials, which is detrimental to the battery's capacity maintenance during long-term charge and discharge processes. Furthermore, the aforementioned thermal management system is not conducive to efficient energy utilization, as it absorbs and dissipates heat when the secondary battery needs cooling, and requires additional energy input when heating is needed. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect, a secondary battery is provided, including an electrode assembly, a housing, an end cap, and an insulating assembly. The housing forms a receiving cavity for accommodating the electrode assembly. The housing has an opening. The end cap includes a cover plate, a lower plastic part, and an electrode post. The cover plate covers the opening. The lower plastic part is located on the side of the cover plate facing the electrode assembly. The electrode post is disposed on the cover plate. The electrode assembly includes an electrode body and a tab, with the two ends of the tab electrically connected to the electrode body and the electrode post, respectively. The insulating component covers the outer periphery of the electrode body. The insulating component includes an insulating layer and a phase change layer. The insulating layer is located on the surface of the electrode body, and the phase change layer is located on the side of the insulating layer opposite to the electrode body. Both the lower plastic and the phase change layer contain phase change microcapsules; The mass percentage of the phase change microcapsules in the lower plastic is less than the mass percentage of the phase change microcapsules in the phase change layer.

[0006] In some embodiments, the phase change microcapsules have a mass percentage of 20-40% based on the mass of the lower plastic.

[0007] In some embodiments, the phase change microcapsules have a mass percentage of 50-70% based on the mass of the phase change layer.

[0008] In some embodiments, the electrode body includes a tab end and a non-tab end, the tab end being connected to the tab, the non-tab end not being connected to the tab, the mass percentage of the phase change microcapsules in the phase change layer located at the tab end being greater than the mass percentage of the phase change microcapsules in the non-tab end; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the tab end being greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the non-tab end.

[0009] In some embodiments, the housing has a bottom wall, the end cap and the bottom wall are located at both ends of the housing, and the electrode tab is located at the end of the electrode body facing the end cap; The mass percentage of the phase change microcapsules in the phase change layer near the end cap is greater than the mass percentage of the phase change microcapsules in the phase change layer near the bottom wall; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the end cap is greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the bottom wall.

[0010] In some embodiments, the phase change layer includes a first region, a second region, and a third region in the direction from the end cap to the bottom wall, wherein the mass percentage of the phase change microcapsules in the first region is greater than the mass percentage of the phase change microcapsules in the second region, and the mass percentage of the phase change microcapsules in the third region.

[0011] In some embodiments, the phase change microcapsules in the first region have a mass percentage of 65-70%, the phase change microcapsules in the second region have a mass percentage of 50-70%, and the phase change microcapsules in the third region have a mass percentage of 37-65%.

[0012] In some embodiments, the particle size D50 of the phase change microcapsules is 5-30 μm; In some embodiments, the phase change microcapsule includes a core material and a wall material, the wall material being wrapped around the outer surface of the core material, the core material comprising a phase change material; the wall material has a thickness of 0.5-3 μm, and the core material has a diameter of 4-24 μm.

[0013] In some embodiments, the wall material comprises an organic resin and a thermally conductive filler; the core material comprises at least one of n-tetradecyl alcohol, caprylic acid, lauric acid, myristic acid, stearic acid, polyethylene glycol, and paraffin wax.

[0014] In some embodiments, the phase change layer further includes a porous adsorbent material, which includes at least one of hydrophobically modified diatomaceous earth or hydrophobically modified zeolite, and the porous adsorbent material has a mass percentage of 5-20% in the phase change layer.

[0015] Secondly, an electrical device is provided, including the aforementioned secondary battery.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: In the secondary battery of this application, phase change microcapsules are added to the lower plastic and the phase change layer, and the mass percentage of the phase change microcapsules in the lower plastic is less than the mass percentage of the phase change microcapsules in the phase change layer. During the charging and discharging process of the secondary battery, when a certain area of ​​the secondary battery reaches the phase change temperature of the phase change material in the phase change microcapsules, the phase change microcapsules can absorb the heat of that area, making it difficult for the temperature of that area to continue to rise. However, other areas have not reached the phase change temperature of the phase change material in the phase change microcapsules, and the temperature of other areas will continue to rise. This reduces the temperature difference between different areas inside the secondary battery, improves the temperature distribution uniformity of different areas inside the secondary battery, and thus improves the thermal stability of the secondary battery. Attached Figure Description

[0017] Figure 1 A schematic diagram of each component in the battery cell; Figure 2 This is a schematic diagram showing the locations of the three regions in the phase change layer.

[0018] As shown in the diagram: 1. Housing, 2. Insulating component, 3. Lower plastic, 4. Electrode body, 5. First region, 6. Second region, 7. Third region. Detailed Implementation

[0019] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0020] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0021] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0022] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0023] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0024] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0025] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0026] Firstly, such as Figure 1 As shown, a secondary battery is provided, including an electrode assembly, a housing 1, an end cap, and an insulating assembly 2. The housing 1 forms a receiving cavity for accommodating the electrode assembly. The housing 1 has an opening. The end cap includes a cover plate, a lower plastic 3, and an electrode post. The cover plate closes to the opening. The lower plastic 3 is located on the side of the cover plate facing the electrode assembly. The electrode post is disposed on the cover plate. The electrode assembly includes an electrode body 4 and a tab, with the two ends of the tab electrically connected to the electrode body and the electrode post, respectively. The insulating component 2 covers the outer periphery of the electrode body 4. The insulating component includes an insulating layer and a phase change layer. The insulating layer is located on the surface of the electrode body 4, and the phase change layer is located on the side of the insulating layer away from the electrode body 4. Both the lower plastic 3 and the phase change layer contain phase change microcapsules; The mass percentage of the phase change microcapsules in the lower plastic 3 is less than the mass percentage of the phase change microcapsules in the phase change layer.

[0027] In the secondary battery of this application, phase change microcapsules are added to the lower plastic and the phase change layer, and the mass percentage of the phase change microcapsules in the lower plastic is less than the mass percentage of the phase change microcapsules in the phase change layer. During the charging and discharging process of the secondary battery, when a certain region of the secondary battery reaches the phase change temperature of the phase change material in the phase change microcapsules, the phase change microcapsules undergo a phase change. This region is called the phase change region. The phase change microcapsules can absorb the heat of the phase change region and reduce the temperature rise rate of the phase change region. Other regions have not reached the phase change temperature of the phase change material in the phase change microcapsules, and the phase change microcapsules are difficult to undergo a phase change. This region is called the non-phase change region. The temperature of the non-phase change region will continue to rise, reducing the temperature difference between the phase change region and the non-phase change region inside the secondary battery, improving the temperature distribution uniformity of different regions inside the secondary battery, and thus improving the thermal stability of the secondary battery.

[0028] It is understandable that the addition of phase change microcapsules will affect the structural strength of the substrate. Since the phase change microcapsules are distributed in the lower plastic, the structural strength of the lower plastic will be affected. However, the phase change layer is located on the surface of the insulating layer, and the structural strength of the insulating layer will not be affected. In order to maintain a certain structural strength of the lower plastic, the mass percentage of phase change microcapsules in the lower plastic is less than the mass percentage of phase change microcapsules in the phase change layer.

[0029] Test method for the mass percentage content of phase change microcapsules: Thermogravimetric analysis (TGA) is used to measure the content of phase change microcapsules in the sample. The sample is heated in an inert atmosphere, and the mass change curve of the sample with temperature is recorded. The mass loss of the phase change microcapsules in the decomposition stage at high temperature is analyzed. After subtracting the influence of the matrix from the TGA curve of the pure matrix material, the content of phase change microcapsules is calculated according to the mass loss ratio.

[0030] In some embodiments, the mass percentage of the phase change microcapsules is 20-40% based on the mass of the lower plastic; for example, it can be a range of one or any combination of 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%.

[0031] In some embodiments, the mass percentage of the phase change microcapsules is 50-70% based on the mass of the phase change layer; for example, it can be a range of one or any two of 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%.

[0032] In this application, the mass percentage of phase change microcapsules in the lower plastic and phase change layer is within the above range, which can effectively absorb the heat near the tab in the secondary battery, reduce the temperature near the tab in the secondary battery, improve the temperature distribution uniformity in different areas inside the secondary battery, and thus improve the thermal stability of the secondary battery.

[0033] Specifically, the mass percentage of phase change microcapsules in the phase change layer is within the above range, which can ensure the adhesion and toughness of the phase change layer, reduce the risk of phase change layer displacement or detachment caused by electrode component expansion, and thus enable the phase change layer to provide good thermal management performance during the long-term use of the secondary battery.

[0034] In some embodiments, the electrode body includes a tab end and a non-tab end, the tab end being connected to the tab, the non-tab end not being connected to the tab, the mass percentage of the phase change microcapsules in the phase change layer located at the tab end being greater than the mass percentage of the phase change microcapsules in the non-tab end; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the tab end being greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the non-tab end.

[0035] In some embodiments, the housing has a bottom wall, the end caps and the bottom wall are located at opposite ends of the housing, and the tabs are located at the end of the electrode body facing the end cap; the mass percentage of the phase change microcapsules in the phase change layer near the end cap is greater than the mass percentage of the phase change microcapsules in the phase change layer near the bottom wall; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the end cap is greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the bottom wall. This phase change layer structure allows the phase change layer near the end cap to absorb more heat than the phase change layer near the bottom wall; thereby reducing the temperature difference between the regions near the end cap and the regions near the bottom wall inside the secondary battery, improving the uniformity of temperature distribution in different regions inside the secondary battery, and thus improving the thermal stability of the secondary battery.

[0036] In some implementations, such as Figure 2 As shown, from the end cap to the bottom wall, the phase change layer includes a first region 5, a second region 6, and a third region 7, wherein the mass percentage of the phase change microcapsules in the first region 5 is greater than the mass percentage of the phase change microcapsules in the second region 6, which is greater than the mass percentage of the phase change microcapsules in the third region 7.

[0037] Specifically, the direction from the end cap to the bottom wall is denoted as the length direction of the phase change layer, and the length of the phase change layer is denoted as L. The lengths of the first region, the second region, and the third region are all 1 / 3L.

[0038] In this application, the mass percentage of phase change microcapsules in different regions of the phase change layer satisfies the above relationship, such that the heat absorbed by the first region > the heat absorbed by the second region > the heat absorbed by the third region, further reducing the temperature difference between different regions inside the secondary battery, thereby improving the thermal stability of the secondary battery.

[0039] In some embodiments, the mass percentage content of the phase change microcapsules in the first region is 65-70%, for example, it can be a range of one or any two of 65%, 66.5%, 67%, 67.5%, 68%, 68.5%, 69%, 69.5%, 70%; the mass percentage content of the phase change microcapsules in the second region is 50-70%, for example, it can be a range of one or any two of 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%; the mass percentage content of the phase change microcapsules in the third region is 37-65%, for example, it can be a range of one or any two of 37%, 40%, 42%, 45%, 47%, 50%, 53%, 55%, 58%, 60%, 62%, 65%.

[0040] In this application, the mass percentage of phase change microcapsules in different regions of the phase change layer is within the above-mentioned range, such that the heat absorbed by the first region is greater than the heat absorbed by the second region, which in turn is greater than the heat absorbed by the third region. This further reduces the temperature difference between different regions inside the secondary battery, thereby improving the thermal stability of the secondary battery.

[0041] In some embodiments, the particle size D50 of the phase change microcapsules is 5-30 μm; for example, it can be a range of one or any combination of 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm.

[0042] In this application, the particle size D50 of the phase change microcapsules is within the above-mentioned range, which is beneficial to increase the heat transfer efficiency of the phase change microcapsules and ensure the strength of the phase change microcapsules. The particle size D50 is within the above-mentioned range, which helps to improve the dispersibility of the phase change microcapsules, reduce the heat transfer path, increase the specific surface area, increase the thermal conductivity response rate, and improve the mechanical strength of the phase change microcapsules, thereby reducing the risk of phase change material leakage due to shell rupture.

[0043] In this application, the particle size D50 of the phase change microcapsules can be detected by the following method: the particle size of the phase change microcapsules is measured using a scanning electron microscope (SEM). The sample is first brittlely fractured under liquid nitrogen conditions to form a natural fracture surface. The conductivity is enhanced by gold plating or low vacuum mode. Then, high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple regions are randomly sampled, and the average particle size and distribution are statistically analyzed to obtain the particle size distribution of the phase change microcapsules.

[0044] In some embodiments, the phase change microcapsule includes a core material and a wall material, the wall material wrapping the outer surface of the core material, the core material comprising a phase change material; the thickness of the wall material is 0.5-3 μm, for example, it can be a range of one or any combination of 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, and 3 μm; the diameter of the core material is 4-24 μm, for example, it can be a range of one or any combination of 4 μm, 7 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, 22 μm, and 24 μm.

[0045] In this application, the diameter of the core material and the thickness of the wall material are within the above-mentioned range, which can improve the pressure resistance and heat insulation of the wall material, thereby improving the structural stability of the phase change microcapsules and enabling the phase change microcapsules to have a longer service life in complex usage environments.

[0046] In this application, the diameter of the core material and the thickness of the wall material can be detected by the following method: the wall material thickness and core material diameter of the phase change microcapsule are measured using a scanning electron microscope (SEM), the sample is cut using an ultrathin slicer to form a cut surface to expose the cross-section of the phase change microcapsule, the conductivity is enhanced by gold plating or low vacuum mode, and then high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple areas are randomly sampled, and the average wall material thickness and core material diameter and distribution are statistically analyzed to obtain the wall material thickness and core material diameter of the phase change microcapsule.

[0047] In some embodiments, the wall material includes an organic resin and a thermally conductive filler.

[0048] In this application, the thermal conductivity of the thermally conductive filler in the wall material can trigger a larger phase change in the phase change material and absorb heat to cool down. At the same time, it can also diffuse heat to the surroundings, further improving the uniformity of temperature distribution in different areas inside the secondary battery, thereby improving the thermal stability of the secondary battery.

[0049] In some embodiments, the organic resin includes at least one of melamine resin, urea-formaldehyde resin, and phenolic resin.

[0050] In this application, the aforementioned organic resin has excellent mechanical and densification properties. As a wall material, it encapsulates the phase change material, which not only protects the phase change material and prevents leakage during use, but also improves the structural stability of the phase change microcapsules, enabling them to have a longer service life in complex usage environments.

[0051] In some embodiments, the thermally conductive filler includes at least one selected from alumina, zinc oxide, aluminum nitride, and boron nitride.

[0052] In this application, the aforementioned thermally conductive filler can improve the thermal conductivity of the secondary battery and enhance its thermal safety.

[0053] In some embodiments, the core material includes at least one of tetradecyl alcohol, caprylic acid, lauric acid, myristic acid, stearic acid, polyethylene glycol, and paraffin.

[0054] In this application, the aforementioned core material enables the secondary battery to fully utilize its heat storage and heat equalization effects during charging and discharging, which is beneficial to improving the thermal safety of the secondary battery.

[0055] In this application, those skilled in the art can prepare phase change microcapsules using known methods, such as solvent evaporation or in-situ polymerization.

[0056] Specifically, taking urea-formaldehyde resin as the wall material and polyethylene glycol as the core material as an example, the steps for preparing phase change microcapsules by in-situ polymerization are as follows: Polyethylene glycol and an optional emulsifier are added to deionized water and stirred until homogeneous to obtain a core material dispersion. Based on the mass of the core material dispersion, the mass percentage of polyethylene glycol is 20-30%, and the mass percentage of emulsifier is 0-2%. Urea and formaldehyde in a mass ratio of (1:1.5) to (1:2) are added to a reaction vessel to obtain a first mixture. A pH adjuster is added to adjust the pH of the first mixture to 8-9. The mixture is stirred at 60-70℃ for 1-1.5 hours to obtain a wall material prepolymer. The core material dispersion was added to the wall material prepolymer at a mass ratio of (1:1) to (1:2). After stirring evenly at 50-70℃, a second mixture was obtained. Ammonium chloride was added to adjust the pH of the second mixture to 4-5, and the reaction was continued for 2-3 hours to allow the wall material prepolymer to polymerize in situ on the surface of polyethylene glycol to form urea-formaldehyde resin. The product obtained from the reaction was washed and dried to obtain phase change microcapsules.

[0057] In this application, the particle size D50 of phase change microcapsules can be altered by controlling parameters such as emulsification conditions (e.g., stirring speed, emulsification time), material concentration (ratio of phase change material to wall material), type and amount of surfactant, reaction temperature, and pH value. For example, high-speed stirring can refine the particle size, while low-speed stirring tends to form larger particles; increasing the emulsifier concentration can stabilize small particle sizes, but excessive concentration may cause aggregation. Furthermore, the particle size distribution can also be adjusted by controlling the dropping rate of the core material dispersion, the coating reaction time, and post-treatment (e.g., centrifugation, filtration).

[0058] In this application, the diameters of the core material and wall material in the phase change microcapsules can be altered by adjusting the relative contents of the core material dispersion and the first mixture. For example, the particle size of the phase change microcapsules can be controlled by adjusting the ratio of core material to wall material, requiring the calculation of the volume ratio and mass ratio based on the target particle size. For instance, if the core material diameter is 25 μm and the wall material thickness is 5 μm, the core material volume accounts for approximately 36.4%, and the wall material accounts for 63.6% (volume ratio 1:1.74). The mass ratio depends on the densities of both materials (if the densities are the same, it is consistent with the volume ratio). In practice, the ratio needs to be optimized by considering the emulsification process and the amount of emulsifier, and the particle size distribution and coating effect need to be verified experimentally.

[0059] Specifically, the encapsulation rate of the phase change microcapsules prepared by in-situ polymerization is 33-50%, for example, it can be one or any combination of 33%, 35%, 38%, 40%, 42%, 45%, 47%, 50%.

[0060] Specifically, the encapsulation rate of phase change microcapsules can be obtained by testing using the following methods, typically based on the ratio of the enthalpy of melting (or phase change enthalpy) of the microcapsule to the enthalpy of melting (or phase change enthalpy) of the unencapsulated phase change material. For example, if the enthalpy of melting of the microcapsule is ΔH1 and the enthalpy of melting of the unencapsulated phase change material is ΔH2, then the encapsulation rate is calculated as ΔH1 / ΔH2*100%. The specific enthalpy of phase change can be measured using a differential scanning calorimeter.

[0061] In some embodiments, the phase change layer further includes a porous adsorbent material, which includes at least one of hydrophobically modified diatomaceous earth or hydrophobically modified zeolite, and the mass percentage of the porous adsorbent material in the phase change layer is 5-20%; for example, it can be a range of one or any combination of 5%, 7%, 10%, 12%, 14%, 16%, 18%, 20%.

[0062] During long-term charging and discharging, the electrode assembly of a secondary battery expands and compresses the casing. The insulating component containing the phase change layer is located between the electrode assembly and the casing. When the expansion force is too large, the wall material of the phase change microcapsules in the phase change layer ruptures, causing leakage of the phase change material, which contaminates the electrolyte and reduces the effect of the phase change layer on the internal temperature uniformity of the secondary battery. In this application, a porous adsorbent material is added to the phase change layer. The porous adsorbent material can absorb the leaked phase change material and has poor adsorption effect on the electrolyte, thereby maintaining the effect of the phase change layer on the internal temperature uniformity of the secondary battery.

[0063] The hydrophobically modified diatomaceous earth or hydrophobically modified zeolite can be modified with a silane coupling agent that has a hydrophobic effect, such as a long-chain alkyl or fluorocarbon silane. After hydrophobic modification, the adsorption of electrolyte by the hydrophobically modified diatomaceous earth or hydrophobically modified zeolite can be reduced.

[0064] Specifically, examples of long-chain alkyl groups include at least one of octadecyltrimethoxysilane, hexadecyltrimethoxysilane, and dodecyltrimethoxysilane.

[0065] Specifically, as specific examples of fluorocarbon-based silanes, at least one of perfluorodecyltrimethoxysilane, perfluorooctyltrimethoxysilane, and perfluorohexyltrimethoxysilane can be listed.

[0066] In some embodiments, the insulating layer is a Mylar film.

[0067] In some embodiments, the phase change layer can be prepared by the following steps: Phase change microcapsules, binders, and optional additives are added to a solvent to form a phase change slurry; The phase change slurry is coated onto one side of the insulating layer, and after drying and curing, a phase change layer is obtained.

[0068] Specifically, the adhesive includes at least one of butyl acrylate-methyl methacrylate copolymer, butyl acrylate-acrylonitrile copolymer, and polyvinylidene fluoride.

[0069] Specifically, the optional additives include at least one of silane coupling agents, leveling agents, defoamers, and crosslinking agents.

[0070] Specifically, the solvent includes at least one of ethyl acetate and isopropanol.

[0071] This application can adjust the mass percentage of phase change microcapsules in the phase change layer by adjusting the mass percentage of phase change microcapsules in the phase change slurry.

[0072] Specifically, the coating method includes, but is not limited to, at least one of the following: spraying, spin coating, scraping, gravure coating, roller coating, slot coating, dagger-roll coating, dipping, and air knife coating.

[0073] In some embodiments, the electrode assembly includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0074] In some embodiments, the positive electrode may include a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0075] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0076] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0077] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0078] In some embodiments, the positive electrode active material may be, but is not limited to, a chemical formula such as Li a Ni x Co y M z O 2-b N b(where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The cathode active material can be one or more of the following: O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The cathode active material can also be modified. Methods for modifying the cathode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the cathode active material. The materials used for modification can be one or more of the following: Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0079] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0080] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0081] In some embodiments, the negative electrode sheet may include a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0082] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0083] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0084] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0085] In some embodiments, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0086] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0087] In some embodiments, the diaphragm comprises woven or nonwoven polymer fibers. In some embodiments, the porous substrate is a nonwoven material comprising polymer fibers.

[0088] In some embodiments, the diaphragm is, but is not limited to, at least one of polyolefin, polyester, polyacetal, polyamide, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate.

[0089] Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0090] In some embodiments, the thickness of the separator is from 4 μm to 10 μm, for example, but not limited to 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or within any two of the above values. A separator thickness within this range not only allows the separator to possess higher puncture strength to better suppress lithium dendrites, but also maintains lower internal resistance and higher energy density.

[0091] In some embodiments, the porosity of the separator is 30% to 70%, for example, but not limited to 30%, 32%, 35%, 37%, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, or within any two of the above values. A porosity within this range not only facilitates the separator having more ion channels, thereby reducing internal resistance and improving charge / discharge efficiency and high-rate discharge capability, but also gives the separator higher mechanical strength, thus reducing the risk of lithium dendrite penetration.

[0092] In some embodiments, the electrolyte may also include a non-aqueous solvent and a lithium salt.

[0093] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0094] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0095] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0096] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0097] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0098] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0099] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0100] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0101] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0102] Secondly, an electrical device is provided, including the aforementioned secondary battery.

[0103] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art.

[0104] In some implementations, the electrical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0105] Example 1 <Preparation of Phase Change Microcapsules> Polyethylene glycol with a weight average molecular weight of 400 and Span-80 were added to deionized water and stirred at 500 r / min for 30 min at 60°C to obtain a core material dispersion. Based on the mass of the core material dispersion, the mass percentage of polyethylene glycol was 25% and the mass percentage of Span-80 was 1%. Urea and formaldehyde in a mass ratio of 1:2 were added to a reaction vessel to obtain a first mixture. Sodium hydroxide was added to adjust the pH of the first mixture to 8.5. The mixture was stirred at 500 r / min for 1.5 h at 65 °C to obtain a wall material prepolymer. The core material dispersion was added to the wall material prepolymer at a mass ratio of 1:1.5. The mixture was stirred at 500 r / min for 30 min at 60 °C to obtain a second mixture. Ammonium chloride was added to adjust the pH of the second mixture to 4.5, and the reaction was continued for 3 h to allow the wall material prepolymer to polymerize in situ on the polyethylene glycol surface to form urea-formaldehyde resin. The product obtained from the reaction was washed and dried to obtain phase change microcapsules with a particle size D50 of 20 μm. The core material in the phase change microcapsules had a diameter of 18 μm, and the wall material had a thickness of 2 μm.

[0106] The latent heat of phase change and phase change temperature of the phase change microcapsules were tested using a differential scanning calorimeter (DSC). In this embodiment, the latent heat of phase change of the phase change microcapsules was 190 J / g and the phase change temperature was 35℃.

[0107] <Preparation of the lower plastic> The following mixture is prepared by injection molding: 30% phase change microcapsules, 68% polycarbonate, 0.5% antioxidant (butylated hydroxytoluene) and 1.5% flame retardant (decabromodiphenyl ether) are mixed evenly.

[0108] <Preparation of end caps> Assemble the cover plate, lower plastic and pole into an end cap.

[0109] <Preparation of Insulating Components> Ethyl acetate (33% by mass) and isopropanol (10% by mass) were stirred at 600 rpm for 15 min to obtain a mixed solvent. A 32% (w / w) butyl acrylate-methyl methacrylate copolymer solution (35% solids content) was added to a mixed solvent. The solution was stirred at 70°C and 500 rpm until it became clear and free of particles. Then, 1% (w / w) KH550, 1% (w / w) leveling agent BYK-346, 0.5% (w / w) defoamer BYK-024, and 2.5% (w / w) crosslinking agent (hydroxy acrylate) were added sequentially. After stirring evenly, 20% (w / w) phase change microcapsules were added and stirred for 15 min to obtain a phase change slurry. Phase change slurry was coated on one side of a Mylar film with a thickness of 150 μm. After drying and curing, an insulating component was obtained, wherein the thickness of the phase change layer was 100 μm, and the mass percentage of the phase change microcapsules was 65% based on the mass of the phase change layer.

[0110] <Preparation of the positive electrode> Lithium iron phosphate, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode slurry with a solid content of 58% and a viscosity of 4000 mPa·s. The slurry was then coated onto aluminum foil, dried, rolled, and cut into sheets. Positive electrode tabs were obtained by cutting from the corresponding positions of the empty foil area of ​​the aluminum foil. <Preparation of Negative Electrode Sheets> Artificial graphite, super P, CMC, and SBR were added to a deionized water solvent in a mass ratio of 96.5:0.5:1.2:1.8 and stirred thoroughly to form a negative electrode slurry with a solid content of 53% and a viscosity of 3000 mPa·s. The slurry was then coated onto copper foil, dried, rolled, and cut into sheets. The negative electrode tabs were then cut from the corresponding positions of the empty foil areas of the copper foil. <Preparation of Electrolyte> Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1.5:1 to obtain an electrolyte, wherein the molar concentration of lithium hexafluorophosphate was 1 mol / L.

[0111] <Preparation of Secondary Batteries> like Figure 1As shown, the positive electrode, separator and negative electrode are stacked in sequence, and then the four corners of the entire stacked structure are fixed with tape to obtain the electrode assembly of the stacked structure. An insulating component is wrapped around the outer periphery of the electrode body of the electrode assembly, so that the Mylar film in the insulating component is located on the surface of the electrode body, and the phase change layer is located on the side of the insulating layer away from the electrode body. The electrode assembly is placed inside an aluminum shell. Electrolyte is injected into the aluminum shell and then vacuum-sealed. The end cap is fixed to the top seal of the aluminum shell, so that the cover plate in the end cap covers the opening of the aluminum shell. The lower plastic is located on the side of the cover plate facing the electrode assembly, and the electrode post is located on the cover plate. The negative electrode tab and the positive electrode tab are connected to the electrode post respectively. Then, formation and capacity testing are performed to complete the preparation of the secondary battery.

[0112] Example 2 Except for the difference in the mass percentage of phase change microcapsules in the lower plastic compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the lower plastic in this example is 20%.

[0113] Example 3 Except for the difference in the mass percentage of phase change microcapsules in the lower plastic compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the lower plastic in this example is 40%.

[0114] Example 4 Except for the difference in the mass percentage of phase change microcapsules in the lower plastic compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the lower plastic in this example is 15%.

[0115] Example 5 Except for the difference in the mass percentage of phase change microcapsules in the lower plastic compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the lower plastic in this example is 45%.

[0116] Example 6 Except for the difference in the mass percentage of phase change microcapsules in the phase change layer compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the phase change layer of this example is 50%.

[0117] Example 7 Except for the difference in the mass percentage of phase change microcapsules in the phase change layer compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the phase change layer of this example is 70%.

[0118] Example 8 Except for the difference in the mass percentage of phase change microcapsules in the phase change layer compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the phase change layer of this example is 40%.

[0119] Example 9 Except for the difference in the mass percentage of phase change microcapsules in the phase change layer compared to Example 1, the rest is the same as in Example 1; the mass percentage of phase change microcapsules in the phase change layer of this example is 80%.

[0120] Example 10 Except for the structure of the phase change layer, which is different from that of Example 1, the rest is the same as that of Example 1. The structure of the phase change layer in this example is as follows: from the end cap to the bottom wall, the phase change layer is divided into a first region and a second region. The mass percentage of phase change microcapsules in the first region is 70%, and the mass percentage of phase change microcapsules in the second region is 50%.

[0121] Example 11 Except for the structure of the phase change layer, which is different from that of Example 1, the rest is the same as that of Example 1. The structure of the phase change layer in this example is as follows: from the end cap to the bottom wall, the phase change layer is divided into a first region, a second region and a third region. The mass percentage of phase change microcapsules in the first region is 70%, the mass percentage of phase change microcapsules in the second region is 65%, and the mass percentage of phase change microcapsules in the third region is 50%.

[0122] Example 12 Except for the structure of the phase change layer, which is different from that of Example 1, the rest is the same as that of Example 1. The structure of the phase change layer in this example is as follows: from the end cap to the bottom wall, the phase change layer is divided into a first region, a second region and a third region. The mass percentage of phase change microcapsules in the first region is 65%, the mass percentage of phase change microcapsules in the second region is 50%, and the mass percentage of phase change microcapsules in the third region is 37%.

[0123] Example 13 Except for the particle size D50 of the phase change microcapsules, the diameter of the core material, and the thickness of the wall material, which are different from those in Example 1, the rest are the same as in Example 1; in this example, the particle size D50 of the phase change microcapsules is 10 μm, the diameter of the core material is 9 μm, and the thickness of the wall material is 1 μm.

[0124] Example 14 Except for the phase change microcapsule particle size D50, core material diameter, and wall material thickness, which are different from those in Example 1, the rest are the same as in Example 1; in this example, the phase change microcapsule particle size D50 is 5μm, the core material diameter is 4.5μm, and the wall material thickness is 0.5μm.

[0125] Example 15 Except for the particle size D50 of the phase change microcapsules, the diameter of the core material, and the thickness of the wall material, which are different from those in Example 1, the rest are the same as in Example 1; the particle size D50 of the phase change microcapsules in this example is 27 μm, the diameter of the core material is 24 μm, and the thickness of the wall material is 3 μm.

[0126] Example 16 Except for the composition of the wall material in the phase change microcapsule, which is different from that in Example 1, the rest is the same as in Example 1; the wall material of the phase change microcapsule in this example includes urea-formaldehyde resin and alumina, and the mass percentage of alumina is 8.5% based on the mass of the wall material.

[0127] Example 17 Except for the composition of the phase change layer, which differs from that of Example 1, the rest is the same as in Example 1; the phase change layer in this example also includes hydrophobically modified diatomaceous earth, and the mass percentage of hydrophobically modified diatomaceous earth in the phase change layer is 5%; the preparation method of hydrophobically modified diatomaceous earth includes the following steps: Hexadecyltrimethoxysilane was added to anhydrous ethanol and stirred until homogeneous to obtain a hexadecyltrimethoxysilane solution. Diatomaceous earth powder was added to a hexadecyltrimethoxysilane solution and stirred for 3 hours at 70°C and 300 rpm. The resulting product was washed three times with anhydrous ethanol and then dried to obtain hydrophobic modified diatomaceous earth.

[0128] Example 18 Except for the composition of the phase change layer, which is different from that of Example 17, the rest is the same as that of Example 17; in this example, the mass percentage of hydrophobic modified diatomite in the phase change layer is 10%.

[0129] Example 19 Except for the composition of the phase change layer, which is different from that of Example 17, the rest is the same as that of Example 17; in this example, the mass percentage of hydrophobic modified diatomite in the phase change layer is 20%.

[0130] Example 20 Except for the composition of the phase change layer, which is different from that of Example 17, the rest is the same as that of Example 17; in this example, the mass percentage of hydrophobic modified diatomite in the phase change layer is 25%.

[0131] Comparative Example 1 Except for the composition of the lower plastic and phase change layer, which differ from that of Example 1, the rest is the same as that of Example 1; neither the lower plastic nor the phase change layer in this comparative example contains phase change microcapsules.

[0132] Comparative Example 2 Except for the composition of the lower plastic, which differs from that of Example 1, the rest is the same as that of Example 1; the lower plastic in this comparative example does not contain phase change microcapsules.

[0133] Comparative Example 3 Except for the composition of the phase change layer, which is different from that of Example 1, the rest is the same as that of Example 1; there are no phase change microcapsules in the phase change layer of this example.

[0134] Comparative Example 4 Except for the mass percentage of phase change microcapsules in the lower plastic and phase change layer, which differs from Example 1, the rest is the same as in Example 1; in this comparative example, the mass percentage of phase change microcapsules in the lower plastic is 65%, and the mass percentage of phase change microcapsules in the phase change layer is 30%.

[0135] The partial parameters of the secondary batteries in Examples 1-20 and Comparative Examples 1-4 are shown in Table 1.

[0136] Performance testing The secondary batteries of Examples 1-20 and Comparative Examples 1-4 were subjected to performance tests, and the test methods are as follows: (1) Temperature of each area of ​​the secondary battery: The battery cell with temperature sensing wires was used for testing. The temperature sensing wires were led out from the inside of the battery cell through the opening in the top cover. Temperature sensing wire 1 was located at the center of the plastic under the top cover, denoted as T1. Temperature sensing wires 2, 3 and 4 were all located on the large surface of the core near the aluminum shell. Temperature sensing wire 2 was located at the center of the first area, denoted as T2. Temperature sensing wire 3 was located at the center of the second area, denoted as T3. Temperature sensing wire 4 was located at the center of the third area, denoted as T4. The temperature sensing wires were arranged to detect the temperature change during the charging and discharging process. The test was conducted with an ambient temperature of 25°C, 1C charging and 1C discharging, and an ambient temperature of 25°C, 2C charging and 2C discharging, with a 60-minute interval between charging and discharging. The highest temperature during the charging and discharging process in the two processes was obtained and denoted as 1CT1. max 1CT2 max 1CT3 max 1CT4 max 2CT1 max 2CT2 max 2CT3 max 2CT4 max .

[0137] (2) Capacity retention rate: The secondary battery was placed in a charge-discharge test cabinet at a constant temperature of 25°C, with a voltage range of 2.5~4.25V, a charge rate of 1C, and a discharge rate of 1C to obtain the discharge specific capacity of the first cycle, which is recorded as 1C1; the charge-discharge cycle was repeated according to the above steps and parameters until the 500th cycle, and the discharge specific capacity after 500 cycles was obtained, which is recorded as 1C1. 500 ; Capacity retention rate at 1C = 1C 500 / 1C1*100%.

[0138] The secondary battery was placed in a charge-discharge test chamber at a constant temperature of 25°C, with a voltage range of 2.5~4.25V, a charge rate of 2C, and a discharge rate of 2C. The discharge specific capacity of the first cycle was obtained and denoted as 2C1. The above steps and parameters were repeated to charge and discharge the battery until the 500th cycle, and the discharge specific capacity after 500 cycles was obtained and denoted as 2C1. 500 ; 2C capacity retention rate = 2C500 / 2C1*100%.

[0139] The test results are shown in Table 2.

[0140] Table 1 Table 2 As can be seen from the experimental data in Table 1, the temperature distribution uniformity in different regions inside the secondary battery of this application is high, which makes the 1C capacity retention rate and 2C capacity retention rate greater than or equal to 91.5% after 500 cycles.

[0141] The experimental data from Examples 1-5 show that, based on the mass of the lower plastic, the mass percentage of phase change microcapsules in the lower plastic is 20-40%, and the resulting secondary battery retains a 1C capacity of ≥94.3% and a 2C capacity of ≥92% after 500 cycles. This indicates that a mass percentage of phase change microcapsules in the lower plastic of 20-40% can improve the cycle performance of the secondary battery.

[0142] The experimental data from Examples 1 and 6-9 show that, based on the mass of the phase change layer, when the mass percentage of the phase change microcapsules is 50-70%, the resulting secondary battery retains a 1C capacity of ≥94.2% and a 2C capacity of ≥91.9% after 500 cycles. This indicates that a mass percentage of 20-40% of the phase change microcapsules in the phase change layer can improve the cycle performance of the secondary battery.

[0143] Experimental data from Examples 1 and 10-12 show that, from the end cap to the bottom wall, the phase change layer includes a first region, a second region, and a third region. The mass percentage of the phase change microcapsules in the first region is greater than the mass percentage of the phase change microcapsules in the second region, which is greater than the mass percentage of the phase change microcapsules in the third region. The resulting secondary battery retains a 1C capacity of ≥94.9% and a 2C capacity of ≥92.8% after 500 cycles. The phase change layer with the above structure can improve the cycle performance of the secondary battery.

[0144] Experimental data from Examples 1 and 13-15 show that the particle size D50 of the phase change microcapsules is 5-30 μm, and / or the wall material thickness of the phase change microcapsules is 0.5-3 μm, and the core material diameter is 4-24 μm; the resulting secondary battery retains a 1C capacity of ≥94.5% and a 2C capacity of ≥92.2% after 500 cycles; phase change microcapsules within the above parameter range can improve the cycle performance of secondary batteries.

[0145] The experimental data from Examples 1 and 16 show that including thermally conductive fillers in the lower plastic can improve the cycle performance of the secondary battery.

[0146] Experimental data from Examples 1 and 17-20 show that adding porous adsorbent material to the phase change layer results in a secondary battery with a 1C capacity retention rate greater than or equal to 94.5% and a 2C capacity retention rate greater than or equal to 92.4% after 500 cycles. Adding porous adsorbent material to the phase change layer can improve the cycle performance of the secondary battery. When the mass percentage of porous adsorbent material in the phase change layer is 5-20%, the 1C capacity retention rate of the secondary battery after 500 cycles is greater than or equal to 94.9% and the 2C capacity retention rate is greater than or equal to 92.7%. A mass percentage of porous adsorbent material in the phase change layer of 5-20% can further improve the cycle performance of the secondary battery. The experimental data from Examples 1 and Comparative Examples 1-3 show that when the lower plastic and the phase change layer lack phase change microcapsules, or when the mass percentage of phase change microcapsules in the lower plastic is greater than that in the phase change layer, the resulting secondary battery exhibits a 1C capacity retention rate of less than or equal to 93.1% and a 2C capacity retention rate of less than or equal to 91.1% after 500 cycles. This indicates that when the lower plastic and the phase change layer lack phase change microcapsules, or when the mass percentage of phase change microcapsules in the lower plastic is greater than that in the phase change layer, the cycle performance of the secondary battery is inferior to that of the examples.

[0147] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application 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 this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, characterized in that, The device includes an electrode assembly, a housing, an end cap, and an insulating assembly. The housing forms a receiving cavity for accommodating the electrode assembly. The housing has an opening. The end cap includes a cover plate, a lower plastic part, and an electrode post. The cover plate closes to the opening. The lower plastic part is located on the side of the cover plate facing the electrode assembly. The electrode post is disposed on the cover plate. The electrode assembly includes an electrode body and a tab, with the two ends of the tab electrically connected to the electrode body and the electrode post, respectively. The insulating component covers the outer periphery of the electrode body. The insulating component includes an insulating layer and a phase change layer. The insulating layer is located on the surface of the electrode body, and the phase change layer is located on the side of the insulating layer opposite to the electrode body. Both the lower plastic and the phase change layer contain phase change microcapsules; The mass percentage of the phase change microcapsules in the lower plastic is less than the mass percentage of the phase change microcapsules in the phase change layer.

2. The secondary battery as described in claim 1, characterized in that, Based on the mass of the lower plastic, the mass percentage of the phase change microcapsules is 20-40%; and / or, based on the mass of the phase change layer, the mass percentage of the phase change microcapsules is 50-70%.

3. The secondary battery as described in claim 1, characterized in that, The electrode body includes a tab end and a non-tab end. The tab end is connected to the tab, and the non-tab end is not connected to the tab. The mass percentage of the phase change microcapsules in the phase change layer located at the tab end is greater than the mass percentage of the phase change microcapsules in the non-tab end; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the tab end is greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the non-tab end.

4. The secondary battery as described in claim 1, characterized in that, The housing has a bottom wall, the end cap and the bottom wall are located at both ends of the housing, and the electrode tab is located at the end of the electrode body facing the end cap; The mass percentage of the phase change microcapsules in the phase change layer near the end cap is greater than the mass percentage of the phase change microcapsules in the phase change layer near the bottom wall; and / or, the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the end cap is greater than the phase change enthalpy of the phase change material in the phase change microcapsules in the phase change layer near the bottom wall.

5. The secondary battery as described in claim 4, characterized in that, From the end cap to the bottom wall, the phase change layer includes a first region, a second region, and a third region, wherein the mass percentage of the phase change microcapsules in the first region is greater than the mass percentage of the phase change microcapsules in the second region, which is greater than the mass percentage of the phase change microcapsules in the third region.

6. The secondary battery as described in claim 5, characterized in that, The phase change microcapsules in the first region have a mass percentage content of 65-70%, the phase change microcapsules in the second region have a mass percentage content of 50-70%, and the phase change microcapsules in the third region have a mass percentage content of 37-65%.

7. The secondary battery as described in claim 1, characterized in that, The particle size D50 of the phase change microcapsules is 5-30 μm; And / or, the phase change microcapsule includes a core material and a wall material, the wall material being wrapped around the outer surface of the core material, the core material including a phase change material; the thickness of the wall material is 0.5-3 μm, and the diameter of the core material is 4-24 μm.

8. The secondary battery as described in claim 7, characterized in that, The wall material includes organic resin and thermally conductive filler; the core material includes at least one of n-tetradecyl alcohol, caprylic acid, lauric acid, myristic acid, stearic acid, polyethylene glycol, and paraffin wax.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The phase change layer also includes a porous adsorbent material, which includes at least one of hydrophobically modified diatomaceous earth or hydrophobically modified zeolite, and the porous adsorbent material has a mass percentage of 5-20% in the phase change layer.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-9.

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