Functional coating and lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a functional coating and a lithium ion battery comprising the functional coating. The functional coating is used between a diaphragm base material layer and a pole piece active layer in the lithium ion battery, the functional coating comprises organic particles, the components of the organic particles comprise a bicyclic organic matter, the molecular structure of the bicyclic organic matter comprises a 2-mercaptoimidazole five-membered ring and a 2-mercaptoimidazole six-membered ring which share two adjacent carbon atoms, the six-membered ring is a benzene ring or a benzene ring substituted by a characteristic group. The functional coating has good wettability in an electrolyte, can improve the content of the electrolyte at the interface of the diaphragm and a pole piece, improves the rate capability of the battery, also can block a chain reaction causing a thermal safety risk of the battery, and improves the high-temperature safety performance and long-cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a functional coating and a lithium-ion battery including the functional coating. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage media, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. With technological advancements, the market is placing higher demands on batteries' high-rate fast-charging capabilities and safety performance under high-temperature environments.

[0003] Currently, the electrochemical performance and safety of lithium-ion batteries highly depend on the effective wetting of internal materials. Specifically, the pores between the positive and negative electrodes and the separator must be fully filled with electrolyte to ensure efficient and uniform lithium-ion migration. However, existing electrodes (especially thick electrodes and silicon anodes) suffer from insufficient and uneven electrolyte wetting between the electrodes and the separator. Poor wetting leads to a series of serious defects: on the one hand, it significantly increases ion migration resistance, resulting in increased internal resistance and intensified polarization, leading to rapid capacity decay and deterioration of rate performance during high-current charging and discharging; on the other hand, localized areas of electrolyte deficiency can become hotspots with concentrated current density, easily triggering side reactions under harsh conditions such as high temperatures or overcharging, generating large amounts of heat and posing a significant safety hazard of thermal runaway, severely restricting the improvement of battery performance and reliability.

[0004] Therefore, it is very important to invent a battery that can improve the rate performance and high-temperature safety of batteries. Summary of the Invention

[0005] To address the problems of poor wetting and electrolyte deficiency at the interface between the electrode and the separator in existing technologies, this invention provides a functional coating for the substrate layer of the separator and the electrode in a lithium-ion battery (hereinafter referred to as "battery"), as well as a lithium-ion battery including the functional coating. The functional coating exhibits good wettability in the electrolyte, increasing the electrolyte content at the separator-electrode interface, improving the battery's rate performance, and simultaneously preventing chain reactions that could lead to thermal safety risks, thereby improving the battery's high-temperature safety performance and long-cycle stability.

[0006] The first aspect of the present invention provides a functional coating for use between a separator substrate layer and an electrode active layer in a lithium-ion battery. The functional coating comprises organic particles, the composition of which includes a bicyclic organic compound. The molecular structure of the bicyclic organic compound includes a 2-mercaptoimidazole five-membered ring and a six-membered ring sharing two adjacent carbon atoms. The six-membered ring is a benzene ring or a benzene ring substituted with a characteristic group.

[0007] A second aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising an electrode, a separator, and a functional coating as described in the first aspect of the present invention for use between a separator substrate layer and an electrode active layer in a lithium-ion battery, the separator comprising a substrate layer.

[0008] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The bicyclic organic compound includes polar groups (e.g., thiol, secondary amino, imino) in its molecular structure. These polar groups give the bicyclic organic compound high polarity. Bicyclic organic compounds with high polarity have good wettability with electrolyte, thereby increasing the electrolyte content at the interface between the separator and the electrode, reducing battery impedance, and improving the battery's rate performance. At the same time, the thiol group in the bicyclic compound has strong reducing properties, which can effectively capture active free radicals generated in the electrolyte during high temperature and long cycle, block the free radical chain reaction that causes thermal safety risks to the battery, and improve the battery's high temperature safety performance and long cycle stability.

[0009] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 The diagram shown is a schematic diagram of the structure of the separator in the lithium-ion battery of the present invention (the functional coating is located on the surface of the substrate layer of the separator).

[0012] Figure 2 The diagram shown is one of the structural schematic diagrams of the positive electrode sheet in the lithium-ion battery of the present invention (the functional coating is located on both sides of the positive electrode active layer away from the positive electrode current collector).

[0013] Figure 3 The diagram shown is a second schematic diagram of the structure of the positive electrode sheet in the lithium-ion battery of the present invention (the functional coating is located on the side of the positive electrode active layer away from the positive electrode current collector).

[0014] Figure 4 The diagram shown is one of the structural schematic diagrams of the negative electrode sheet in the lithium-ion battery of the present invention (the functional coating is located on both sides of the negative electrode active layer away from the negative electrode current collector).

[0015] Figure 5The diagram shown is a second schematic diagram of the structure of the negative electrode sheet in the lithium-ion battery of the present invention (the functional coating is located on the side of the negative electrode active layer away from the negative electrode current collector).

[0016] Figure 6 The diagram shown illustrates the test of the diaphragm wetting rate. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0018] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0019] In this invention, when the group and molecular structure have isomers, the group and molecular structure include all isomer structures.

[0020] The first aspect of the present invention provides a functional coating for use between a separator substrate layer and an electrode active layer in a lithium-ion battery. The functional coating comprises a bicyclic organic compound. The molecular structure of the bicyclic organic compound comprises a 2-mercaptoimidazole five-membered ring and a six-membered ring sharing two adjacent carbon atoms. The six-membered ring is a benzene ring or a benzene ring substituted with a characteristic group.

[0021] The bicyclic organic compound may be selected from at least one of 2-mercaptobenzimidazole and 2-mercaptobenzimidazole derivatives.

[0022] The molecular structure of the bicyclic organic compound can be as shown in formula (I): (I), wherein R1, R2, R3, and R4 may be the same or different, and each is independently selected from hydrogen atom, C1-C6 alkyl, C1-C6 alkoxy, hydroxyl, amino, cyano, halogen substituent, sulfonic acid group, carboxyl group, and nitro group.

[0023] The molecular structure of the bicyclic organic compound includes polar groups such as thiol (-SH), secondary amino (-NH-), and imine (C=N-). The thiol (-SH), secondary amino (-NH-), and imine (C=N-) groups all originate from the 2-mercaptoimidazole five-membered ring.

[0024] The functional coating of this invention is applied between the separator substrate layer and the electrode active layer in a lithium-ion battery. The functional coating, located between the separator substrate layer and the electrode active layer, comprises a bicyclic compound containing polar groups. This bicyclic organic compound with polar groups has good wettability with the electrolyte, thereby improving the wettability of the functional coating by the electrolyte, increasing the electrolyte content at the separator-electrode interface, reducing the interfacial impedance of the battery, and improving the rate performance of the battery. Under high-temperature conditions or during long-cycle operation, active free radicals generated in the electrolyte undergo chain reactions, leading to a decrease in the long-cycle performance of the battery and even causing safety problems such as fire or explosion. The thiol groups in the bicyclic organic compound of the functional coating of this invention have strong reducing properties, which can capture active free radicals generated by the battery under high temperatures or during long-cycle operation, thereby blocking the chain reaction of free radicals and improving the high-temperature safety performance and long-cycle stability of the battery. In addition, since the main body of the bicyclic organic compound is composed of a five-membered imidazole ring and a six-membered benzene ring, the molecule of the bicyclic organic compound has strong aromaticity and excellent chemical stability. It can maintain the stability of its chemical structure at high temperatures, thereby effectively ensuring the ability of the bicyclic organic compound to capture free radicals in the electrolyte at high temperatures, thus improving the high-temperature safety performance of the battery.

[0025] In this invention, by adding a bicyclic organic compound to the functional coating, the problem of poor wetting at the interface between the electrode and the separator can be improved compared with the prior art, thereby enhancing the battery's rate performance, high-temperature safety performance, and long-cycle performance. To further improve the effect, one or more of the technical features can be further optimized.

[0026] In some instances, the characteristic group is selected from one or more of C1-C6 alkyl, C1-C6 alkoxy, hydroxy, amino, cyano, halogen substituent, sulfonic acid, carboxyl, and nitro groups.

[0027] The C1-C6 alkyl group may be selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, and 3-hexyl.

[0028] The C1-C6 alkoxy group may be selected from one or more of methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, tert-pentoxy, neopentoxy, 2,2-dimethylpropoxy, 1-ethylpropoxy, 1-methylbutoxy, 2-methylbutoxy, n-hexoxy, isohexoxy, 2-hexoxy, and 3-hexoxy.

[0029] In some instances, the molecular structure of the bicyclic organic compound is planar. The bicyclic organic compound molecules exhibit π-π stacking interactions, which help improve the high-temperature adhesion of the functional coating and reduce the interfacial impedance between the separator and the electrode, thereby improving the high-temperature performance of the battery.

[0030] In some instances, the bicyclic organic compound is 2-mercaptobenzimidazole or a 2-mercaptobenzimidazole derivative.

[0031] In some instances, the 2-mercaptobenzimidazole derivative includes one or more of the following: 2-mercapto-5-methylbenzimidazole, 2-mercapto-5-ethylbenzimidazole, 2-mercapto-5-propylbenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-ethoxybenzimidazole, 2-mercapto-5-hydroxybenzimidazole, 2-mercapto-5-aminobenzimidazole, 2-mercapto-5-chlorobenzimidazole, 2-mercapto-5-bromobenzimidazole, 2-mercapto-5-sulfonic acid benzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-fluorobenzimidazole, 2-mercapto-5,6-dichlorobenzimidazole, and 2-mercapto-5-cyanobenzimidazole.

[0032] In some instances, the infrared spectrum of the bicyclic organic compound shows a value at 1600 cm⁻¹. -1 -1650cm -1 The first characteristic peak exists at 2530 cm⁻¹. -1 -2600cm -1 A second characteristic peak is present, wherein the first characteristic peak is the absorption peak of the imine group in the five-membered ring of 2-mercaptoimidazole, and the second characteristic peak is the absorption peak of the thiol group in the five-membered ring of 2-mercaptoimidazole.

[0033] In this invention, the infrared spectrum of the bicyclic organic compound can be obtained by testing with an infrared spectrometer.

[0034] In some instances, the retention time of the bicyclic organic compound in mass spectrometry is 25-40 min (e.g., 25 min, 28 min, 30 min, 33 min, 35 min, 38 min, or 40 min). The mass spectrum of the bicyclic organic compound contains a third, fourth, and fifth characteristic peak. The third characteristic peak is the peak with the highest intensity in the mass spectrum. The fourth characteristic peak is the peak with an intensity only slightly weaker than the third characteristic peak. The third characteristic peak is a characteristic peak of the 2-mercaptobenzimidazole fragment ion, with a mass-to-charge ratio (M / C ratio) of 149-151. The fourth characteristic peak is also a characteristic peak of the benzimidazole fragment ion, with a M / C ratio of 117-119. The fifth characteristic peak is a characteristic peak of the thiol fragment sulfide ion, with a M / C ratio of 31-33.

[0035] In this invention, the mass spectrum of the bicyclic organic compound can be obtained using a mass spectrometer.

[0036] In some instances, the melting point of the bicyclic organic compound is 250°C-320°C (e.g., 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, or 320°C). Controlling the melting point of the bicyclic organic compound within this range can provide thermal insulation, reduce the impact of heat generated by the electrode on the separator substrate layer, further improve the heat resistance of the separator substrate layer, prevent it from shrinking under high temperatures, and further enhance the thermal safety performance of the battery.

[0037] In some instances, the thermal decomposition temperature of the bicyclic organic compound is 250°C-350°C (e.g., 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C).

[0038] In some embodiments, the functional coating comprises organic particles, the organic particles comprising bicyclic organic compounds.

[0039] In some instances, the organic particles have a layered crystal structure. The bicyclic organic compounds can form organic particles with a layered crystal structure through π-π stacking interactions.

[0040] In some instances, the organic particles comprise primary particles and secondary particles, the secondary particles being formed by the agglomeration of the primary particles, wherein the primary particles have a particle size Dv50 of 0.5 μm-1 μm (e.g., 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm), and the secondary particles have a particle size Dv50 of 15 μm-100 μm (e.g., 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, or 100 μm).

[0041] In some instances, the particle size distribution diagram of the organic particles exhibits two peaks, namely a sixth characteristic peak and a seventh characteristic peak. The highest point of the sixth characteristic peak corresponds to a particle size of 0.5 μm-5 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm), and the highest point of the seventh characteristic peak corresponds to a particle size of 15 μm-100 μm (e.g., 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, or 100 μm). The presence of two peaks in the particle size distribution diagram of the organic particles indicates the presence of two different particle sizes, such as primary particles and secondary particles. The highest point of the sixth characteristic peak corresponds to the particle size Dv50 of the mixed particles of primary particles and small-sized secondary particles in the organic particles, and the highest point of the seventh characteristic peak corresponds to the particle size Dv50 of the larger-sized secondary particles in the organic particles.

[0042] In this invention, the particle size distribution map of organic particles can be obtained by measuring and statistically processing the SEM scan image on the surface of the carrier layer using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, etc.). Alternatively, it can be obtained by laser particle size analyzer testing.

[0043] In some instances, at 135°C, the solubility W of the organic particles in the test electrolyte is less than 0.5% (e.g., 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.05%, 0.01%, or within any two of the above values). The test electrolyte consists of lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, with a lithium hexafluorophosphate concentration of 1 mol / L and a volume ratio of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate of 1:1:1. In an environment of 135℃, the solubility W of the organic particles in the test electrolyte was less than 0.5%. The organic particles only underwent slight dissolution at high temperatures, indicating that they possess high heat resistance and can maintain structural stability even at high temperatures. Furthermore, the trace amount of dissolved organic particles allows the bicyclic organic compounds within the particles to be uniformly dispersed in the electrolyte at high temperatures, effectively capturing free radicals generated in the electrolyte, blocking free radical chain reactions, and improving the battery's high-temperature safety and long-term cycle stability. Simultaneously, in lithium-ion batteries, due to the coordination effect of thiol groups... Trace amounts of dissolved bicyclic organic compounds can adsorb onto the transition metals in the positive electrode active particles, allowing the bicyclic organic compounds to adhere to the surface of the positive electrode active particles. This suppresses side reactions between the electrolyte and the positive electrode active particles, improves the stability of the positive electrode active particles, and further enhances the high-temperature safety and long-cycle stability of the battery. 2-Mercaptobenzimidazole and its derivatives have coordination ability with lithium ions and can spontaneously adsorb onto the surface of the negative electrode, acting as a molecular protective layer. This improves the uniformity of lithium ion distribution, thereby improving the uniformity of lithium ion deposition on the surface of the negative electrode and further improving the problem of lithium deposition at the interface of the negative electrode.

[0044] In this invention, the bicyclic organic compounds dissolved from the organic particles can be small molecules.

[0045] In some instances, the primary particle size of the organic particles satisfies the following relationship: 0.2 μm ≤ Dv10 ≤ 0.3 μm (e.g., 0.2 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, or 0.3 μm), 0.5 μm ≤ Dv50 ≤ 1 μm (e.g., 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm). The particle size of the organic particles is 0.85μm, 0.9μm, 0.95μm, or 1μm, with 1μm ≤ Dv90 ≤ 2.5μm (e.g., 1μm, 1.2μm, 1.6μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, or 2.5μm), and Dv90-Dv50 ≤ 1.5μm (e.g., 1.5μm, 1.3μm, 1μm, 0.8μm, 0.5μm, 0.3μm, 0.1μm, 0.05μm, 0.01μm, or within any two of the above values). Controlling the particle size of the organic particles to satisfy the above relationship ensures that the porosity of the functional coating is appropriate, neither too large nor too small. Simultaneously, the presence of certain voids in the functional coating further improves the electrolyte wettability and electrolyte retention capacity of the separator, thereby further improving the rate performance and long-cycle performance of the battery.

[0046] In this invention, Dv10 is the particle size corresponding to 10% of the cumulative particle size distribution in the volumetric particle size distribution of the organic particles; Dv50 is the particle size corresponding to 50% of the cumulative particle size distribution in the volumetric particle size distribution of the organic particles; and Dv90 is the particle size corresponding to 90% of the cumulative particle size distribution in the volumetric particle size distribution of the organic particles. In this invention, the volumetric particle size distribution of the organic particles can be obtained by arbitrarily selecting a 100μm×100μm area in the SEM image of the functional coating surface and performing measurement and statistical processing using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, etc.). The Dv10, Dv50, Dv90, and Dv95 of the organic particles can also be obtained by testing with a laser particle size analyzer. For example, before preparing the diaphragm, the Dv10, Dv50, and Dv90 of the organic particles can be measured using a laser particle size analyzer within 5 minutes after thorough stirring.

[0047] In some instances, in a 5K magnification SEM image of the functional coating surface, the number of organic particles with a diameter greater than 2.5 μm in an area optionally 25 μm × 19 μm is less than or equal to 5 (e.g., 5, 4, 3, 2, 1, or 0). Controlling the number of organic particles with a diameter greater than 2.5 μm in an area optionally 25 μm × 19 μm in the 5K magnification SEM image of the functional coating surface is beneficial for improving the uniformity, density, and smoothness of the functional coating. On the one hand, it can ensure that the chemical function of the functional coating plays a uniform and consistent role inside the battery, which helps to reduce the interfacial resistance between the separator and the electrode. On the other hand, it can prevent large-diameter organic particles from breaking during battery cycling expansion, improve interfacial stability, and reduce the risk of separator puncture, further improving the safety performance of the battery.

[0048] In some instances, the organic particles in the functional coating constitute 90%-99% by weight (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%). Controlling the weight percentage of the organic particles in the functional coating within this range further improves the wettability of the separator in the electrolyte, while also ensuring that the functional coating includes sufficient bicyclic organic compounds. This effectively captures active free radicals generated by the battery at high temperatures or during long cycles, thereby further improving the battery's safety and long-cycle performance.

[0049] In some instances, the functional coating also includes an adhesive.

[0050] In some instances, the adhesive comprises one or more of the following: polyacrylic acid, polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyvinylidene fluoride polyurethane, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers.

[0051] In some instances, the adhesive in the functional coating comprises 1%-10% by weight (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%).

[0052] In some instances, the thickness of the functional coating is 0.2 μm-5 μm (e.g., 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm). Controlling the thickness of the functional coating within the above range can further improve the wettability of the separator in the electrolyte, increase the electrolyte content at the interface between the separator and the electrode, reduce the battery impedance, and thus further improve the rate performance of the battery.

[0053] In this invention, the functional coating can be prepared by the following method: mixing organic particulate raw materials and adhesives in a solvent (e.g., water), stirring thoroughly to form a functional coating slurry, and coating the functional coating slurry onto a carrier to form the functional coating.

[0054] The organic particulate raw material includes primary particles and secondary particles. The particle size Dv50 of the primary particles is 0.5μm-1μm (e.g., 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or 1μm), and the particle size Dv50 of the secondary particles is 15μm-100μm (e.g., 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm). The Dv50 of the organic particulate raw material containing the aforementioned primary and secondary particles is 0.5 μm-5 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm), and the Dv90 is greater than or equal to 15 μm. The particle size distribution diagram of the organic particulate raw material containing the aforementioned primary and secondary particles exhibits two peaks, namely the sixth characteristic peak and the seventh characteristic peak. The highest point of the sixth characteristic peak corresponds to a particle size of 0.5 μm-5 μm, and the highest point of the seventh characteristic peak corresponds to a particle size of 15 μm-100 μm.

[0055] During the formation of the functional coating slurry, thorough stirring is carried out. If the stirring is sufficient, the secondary particles in the organic particulate raw material can be completely broken down into primary particles. In this way, the organic particles in the functional coating are primary particles. If the stirring does not completely break down the secondary particles in the organic particulate raw material, the organic particles in the functional coating are a mixture of primary and secondary particles.

[0056] A second aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising an electrode, a separator, and the functional coating described in the first aspect of the present invention for use between the separator substrate layer and the electrode active layer in the lithium-ion battery.

[0057] In some instances, the electrode includes a positive electrode and a negative electrode, and the location of the functional coating includes one or more of the following: on the surface of the substrate layer of the separator, on the surface of the positive electrode, and on the surface of the negative electrode.

[0058] According to some specific embodiments, the functional coating is located on the surface of the substrate layer of the diaphragm.

[0059] According to some specific embodiments, the functional coating is located on the surface of the positive electrode sheet.

[0060] According to some specific embodiments, the functional coating is located on the surface of the negative electrode sheet.

[0061] According to some specific embodiments, the functional coating is located on the surface of the substrate layer of the separator and on the surface of the positive electrode.

[0062] According to some specific embodiments, the functional coating is located on the surface of the substrate layer of the separator and on the surface of the negative electrode sheet.

[0063] According to some specific embodiments, the functional coating is located on the surface of the positive electrode and on the surface of the negative electrode.

[0064] According to some specific embodiments, the functional coating is located on the surface of the substrate layer of the separator, on the surface of the positive electrode, and on the surface of the negative electrode.

[0065] In some instances, such as Figure 1 As shown, the separator 1 includes a carrier layer 11 and an adhesive layer 12. The adhesive layer 12 is located on at least one side surface of the carrier layer 11. The carrier layer 11 includes a substrate layer 111 and a functional coating 4. The functional coating 4 is located on one or both sides of the substrate layer 111. When the functional coating is located on the surface of the substrate layer of the separator, it can not only increase the electrolyte content at the interface between the separator and the electrode, thus improving the rate performance of the battery, but also block the chain reaction that could cause thermal safety risks to the battery, thereby improving the high-temperature safety performance and long-cycle stability of the battery. Furthermore, compared to the functional coating being located on the surface of the active layer of the electrode, it can also reduce the initial impedance of the battery and improve the heat resistance of the separator, further enhancing the thermal safety performance of the battery.

[0066] In some instances, the thickness of the adhesive layer is 0.5 μm to 5 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm).

[0067] In some instances, the adhesive layer comprises a first polymer, which includes one or more of the following: poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, fluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, acrylate polymers, phenolic resins, polyimides, modified phenolic resins, and modified polyimides.

[0068] In some instances, acrylate polymers include one or more of the following: acrylate-acrylonitrile copolymers, acrylate-ethylene copolymers, acrylate-styrene copolymers, acrylate-acrylonitrile-ethylene copolymers, styrene-acrylate-acrylonitrile copolymers, ethylhexyl acrylate-methyl methacrylate copolymers, butyl acrylate-methyl methacrylate copolymers, methyl acrylate-N,N-dimethylacrylamide copolymers, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymers, ethyl acrylate-N,N-diethylacrylamide copolymers, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0069] In some instances, the acrylates include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, methyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0070] In some instances, the adhesive layer comprises polymer particles, the polymer particles comprising a first polymer.

[0071] In other instances, the adhesive layer comprises a first polymer and optionally first particles, the adhesive layer being a porous structure in which the first polymer is a continuous phase.

[0072] In some instances, the first particle comprises one or more of the following: boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, uracil, cytosine, guanine, 2-mercaptobenzimidazole, N,N'-bis(β-naphthyl)-p-phenylenediamine, and 4-amino-2,6-dihydroxypyrimidine.

[0073] In some instances, the thickness of the substrate layer is 3.5 μm to 16 μm (e.g., 3.5 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm).

[0074] In some instances, the thickness of the substrate layer is 4 μm-10 μm.

[0075] In some instances, the porosity of the substrate layer is 30%-70% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%).

[0076] In some instances, the average pore size of the substrate layer is 30nm-50nm (e.g., 30nm, 33nm, 35nm, 38nm, 40nm, 43nm, 45nm, 48nm or 50nm).

[0077] In some instances, the substrate layer comprises one or more of the following polymer derivatives: polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), or poly(m-phenylene isophthalamide).

[0078] In some instances, the diaphragm satisfies the following relationships: 60 ≤ F1 ≤ 80 (e.g., 60, 63, 65, 68, 70, 73, 75, 78, or 80), 120 ≤ F2 ≤ 140 (e.g., 120, 123, 125, 128, 130, 133, 135, 138, or 140), 50 ≤ ΔF ≤ 70 (e.g., 50, 53, 55, 58, 60, 63, 65, 68, or 70), where ΔF = F2 - F1, F1 is the peel strength between the functional coating and the substrate layer at 25°C, in N / m, and F2 is the peel strength between the functional coating and the substrate layer after baking at 90°C for 2 hours, in N / m. The aforementioned F1 and F2 require testing with diaphragms containing functional coatings of the same thickness, for example, both using diaphragms with a functional coating thickness of 2 μm. F2 needs to be tested while the diaphragm is still hot before it cools. Since the functional coating comprises planar bicyclic organic compounds, there are π-π stacking interactions between the molecules of these compounds. These interactions improve the high-temperature adhesion of the functional coating. Controlling ΔF within the aforementioned range reduces battery impedance and provides a buffer space for the expansion of active particles, improving or even preventing electrode cracking or breakage. When ΔF is below 50, it is not conducive to further reducing battery impedance; when ΔF is above 70, it is not conducive to the functional coating providing a buffer space for the expansion of active particles, thus hindering further improvement in the battery's high-temperature safety performance. The aforementioned peel strengths F1 and F2 can be obtained by the following method. Taking "peel strength F1 of organic coating to substrate layer at 25℃" as an example, a diaphragm strip with a length of 200mm and a width of 20mm is cut. The cut diaphragm strip is fixed to a steel plate with double-sided tape. Then, 3M tape with a width of 15mm is attached to the surface of the diaphragm strip. It is rolled once with a 2kg roller. A universal tensile testing machine is used, with the upper clamp holding the tape and the lower clamp holding the steel plate. 180° peeling is performed at 25℃. The test speed is 100mm / min and the test displacement distance is 100mm. The average peel force (unit N) is obtained during the test. The peel strength is the average peel strength (unit N / m). Average peel strength = average peel force / tape width.

[0079] In some instances, the wetting rate k of the diaphragm is 5 mm / min-7 mm / min (e.g., 5 mm / min, 5.3 mm / min, 5.5 mm / min, 5.7 mm / min, 6 mm / min, 6.3 mm / min, 6.5 mm / min, 6.8 mm / min, or 7 mm / min). The wetting rate k is obtained by testing the following method: the diaphragm is placed vertically, one end of the diaphragm is immersed in the test electrolyte, and timing begins. The wetting height h of the test electrolyte within 5 minutes is recorded. The wetting rate k of the diaphragm is then calculated as h / 5. Specifically, for newly prepared diaphragms, a diaphragm sample with a length of 10 cm and a width of 8 mm is cut from the diaphragm sample. Figure 6 As shown, at 25°C, the diaphragm sample 5 is horizontally stretched and placed on the first sample stage 61 and the second sample stage 62, which are spaced 7 cm apart, along the length of the diaphragm sample 5. The width of the first sample stage 61 is 1 cm, and the first end 51 of the diaphragm extends 2 cm beyond the first sample stage 61. The diaphragm sample is fixed to the second sample stage, and a first reference line is drawn 2 cm away from the first end. A 1 cm wide Teflon tape is used to adhere the surface of the diaphragm sample facing away from the first sample stage and the surface located in the width direction of the diaphragm sample. On the first surface of the first sample stage on both sides, the first edge of the Teflon tape in the width direction is aligned with the first reference line, and the width of the Teflon tape coincides with the width of the first sample stage. A second reference line is drawn 1.5 cm away from the first end. The first end of the diaphragm sample extends from the tail of the first reference line in a direction perpendicular to the horizontal and into the test electrolyte. The test electrolyte is immersed until it is aligned with the second reference line, and timing begins. After 5 minutes, the maximum length of the test electrolyte wetting beyond the second reference line is recorded, which is the wetting height h. The test electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. The concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate is 1:1:1.

[0080] In some examples, the functional coating is disposed on at least one side surface of the separator substrate layer, and the positive and negative electrode surfaces are not provided with functional coatings. The positive electrode includes a positive current collector and a positive active layer located on one or both sides of the positive current collector. The positive active layer includes positive active particles. The lithium-ion battery satisfies the following relationship: 10≤D3 / D1≤85, where D1 is the Dv10 of the primary particles of the organic particles in μm, and D3 is the Dv50 of the positive active particles in μm. Preferably, 0.2μm≤D1≤0.3μm and / or 2μm≤D3≤20μm.

[0081] In some examples, the functional coating is disposed on at least one surface of the separator substrate layer, and the positive and negative electrode surfaces are not coated with functional coatings. The negative electrode includes a negative current collector and a negative active layer located on one or both surfaces of the negative current collector. The negative active layer includes negative active particles. The lithium-ion battery satisfies the following relationship: 20≤D2 / D1≤55, where D1 is the Dv10 of the primary particles of the organic particles in μm, and D2 is the Dv50 of the negative active particles in μm. Preferably, 0.2μm≤D1≤0.3μm and / or 5μm≤D2≤12μm. In some instances, such as Figure 2 and Figure 3 As shown, the positive electrode 2 includes a positive current collector 21 and a positive active layer 22 located on one or both sides of the positive current collector 21. The positive active layer includes positive active particles. The functional coating 4 is located on the surface of the positive active layer 22 away from the positive current collector 21, and the functional coating includes organic particles. Compared to the functional coating being located on the substrate layer surface of the separator or the surface of the negative active layer, the functional coating being located on the surface of the positive active layer away from the positive current collector is more conducive to suppressing side reactions between the electrolyte and the positive active particles, improving the stability of the positive active particles, and further improving the high-temperature safety of the battery.

[0082] In this invention, in the positive electrode sheet, the positive electrode active layer is located on the surface of the positive electrode current collector side, and the functional coating is located on the surface of the positive electrode active layer on the side away from the positive electrode current collector. In the positive electrode sheet, the positive electrode active layer is located on both surfaces of the positive electrode current collector, and the functional coating is located on the surface of the positive electrode active layer on either side (e.g., ...). Figure 3 ), or, the functional coating is located on the surface of the positive electrode active layers on both sides (e.g. Figure 2 ).

[0083] In some examples, the lithium-ion battery satisfies the following relationship: 10 ≤ D3 / D1 ≤ 85 (e.g., 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85), where D1 is the Dv10 of the primary particles of the organic particles in μm, and D3 is the Dv50 of the positive electrode active particles in μm. By controlling the lithium-ion battery to satisfy the above relationship, the thiol groups generated by the trace dissolution in the organic particles adsorb onto the transition metals in the positive electrode active particles through coordination, thereby allowing the thiol groups to be uniformly adsorbed on the surface of the positive electrode active particles. This not only captures active free radicals near the positive electrode but also reduces side reactions occurring in the positive electrode active particles, thereby further improving the high-temperature safety performance of the battery. When D3 / D1 is less than 10, the Dv50 of the positive electrode active particles is too small, and the specific surface area of ​​the positive electrode active particles is large, which is not conducive to the uniform adsorption of thiol groups on the surface of the positive electrode active particles. When D3 / D1 is greater than 85, the Dv50 of the positive electrode active particles is too large, the diffusion path of lithium ions inside the positive electrode active particles is too long, and there are fewer contact points between large particles, which is not conducive to further improving the rate performance of the battery.

[0084] In some instances, the lithium-ion battery satisfies the following relationship: 40≤D3 / D1≤60.

[0085] In some instances, 0.2 μm ≤ D1 ≤ 0.3 μm (e.g., 0.2 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm or 0.3 μm) and / or 2 μm ≤ D3 ≤ 20 μm (e.g., 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm).

[0086] According to some specific implementation methods, D1 is 0.2-0.3, D3 is 2-20, and the lithium-ion battery satisfies the following relationship: 10≤D3 / D1≤85.

[0087] According to some specific implementation methods, D1 is 0.2-0.3, D3 is 2-20, and the lithium-ion battery satisfies the following relationship: 40≤D3 / D1≤60.

[0088] In some examples, the positive electrode active layer further includes a positive electrode conductive agent and a positive electrode binder. The positive electrode active particles may include one or more of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide; the positive electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene; and the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0089] In some instances, such as Figure 4 As shown, the negative electrode 3 includes a negative electrode current collector 31 and a negative electrode active layer 32 located on one or both sides of the negative electrode current collector 31. The negative electrode active layer includes negative electrode active particles. The functional coating 4 is located on the surface of the negative electrode active layer 32 away from the negative electrode current collector 31, and the functional coating includes organic particles. Compared to the functional coating being located on the substrate layer surface of the separator or on the surface of the positive electrode active layer, the functional coating being located on the surface of the negative electrode active layer away from the negative electrode current collector is more conducive to improving the uniformity of lithium ion deposition on the surface of the negative electrode and further improving the interface lithium plating problem of the negative electrode.

[0090] In this invention, in the negative electrode sheet, the negative electrode active layer is located on the surface of the negative electrode current collector side, and the functional coating is located on the surface of the negative electrode active layer on the side away from the negative electrode current collector. In the negative electrode sheet, the negative electrode active layer is located on the surfaces of both sides of the negative electrode current collector, and the functional coating is located on the surface of the negative electrode active layer on either side (e.g., ...). Figure 4 ), or, the functional coating is located on the surface of the negative electrode active layers on both sides (e.g. Figure 5 ).

[0091] In some examples, the lithium-ion battery satisfies the following relationship: 20 ≤ D2 / D1 ≤ 55 (e.g., 20, 25, 30, 35, 40, 45, 50, or 55), where D1 is the Dv10 of the primary organic particles in μm, and D2 is the Dv50 of the negative electrode active particles in μm. Controlling the lithium-ion battery to satisfy the above relationship allows for a better match between the specific surface areas of the organic particles and the negative electrode active particles, improving the lithium-ion transport impedance between the functional coating and the active layer. It also facilitates the uniform dispersion of lithium-ion distribution on the surface of the active layer in the functional coating, further improving the uniformity of lithium-ion deposition on the negative electrode surface and further suppressing interfacial lithium deposition on the negative electrode.

[0092] In some instances, the lithium-ion battery satisfies the following relationship: 35≤D2 / D1≤50.

[0093] In some instances, 0.2 μm ≤ D1 ≤ 0.3 μm (e.g., 0.2 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm or 0.3 μm) and / or 5 μm ≤ D2 ≤ 12 μm (e.g., 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm).

[0094] According to some specific embodiments, D1 is 0.2-0.3, D2 is 5-12, and the lithium-ion battery satisfies the following relationship: 20≤D2 / D1≤55.

[0095] According to some specific embodiments, D1 is 0.2-0.3, D2 is 5-12, and the lithium-ion battery satisfies the following relationship: 35≤D2 / D1≤50.

[0096] In some instances, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder.

[0097] In some instances, the negative electrode active particles comprise silicon-based materials, which include one or more of elemental silicon particles, silicon oxide particles, silicon-carbon composite particles, silicon-nitrogen composite particles, and silicon alloy particles.

[0098] In some instances, the average particle size of the silicon-carbon composite particles is 5 μm-12 μm (e.g., 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm).

[0099] In some instances, the negative electrode conductive agent includes one or more of furnace black, acetylene black, Ketjen black, and carbon nanotubes.

[0100] In some instances, the negative electrode binder includes one or more of polyurethane, acrylic-acrylonitrile copolymer, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0101] According to some specific implementation methods, D1 is 0.2-0.3, D3 is 2-20, and the lithium-ion battery satisfies the following relationship: 10≤D3 / D1≤85; D1 is 0.2-0.3, D2 is 5-12, and the lithium-ion battery satisfies the following relationship: 20≤D2 / D1≤55.

[0102] According to some specific implementation methods, D1 is 0.2-0.3, D3 is 2-20, and the lithium-ion battery satisfies the following relationship: 40≤D3 / D1≤60; D1 is 0.2-0.3, D2 is 5-12, and the lithium-ion battery satisfies the following relationship: 35≤D2 / D1≤50.

[0103] In some instances, the electrolyte comprises a lithium salt, a solvent, and additives. The solvent includes polar solvents.

[0104] In some instances, the electrolyte includes a polar solvent selected from at least one of 2,2-difluoroethyl acetate, ethyl 2,2-difluoroacetate, propyl propionate, ethyl propionate, diethyl carbonate, propylene carbonate, and ethylene carbonate.

[0105] In some instances, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium di(fluorobis(oxalate))phosphate.

[0106] In some instances, the additives can be selected based on battery performance requirements and in conjunction with industry-standard technologies.

[0107] In some instances, the solvent may also include organic solvents other than the aforementioned polar solvents.

[0108] In some instances, the lithium salt accounts for 5%-35% of the total weight of the electrolyte (e.g., 5%, 10%, 15%, 20%, 25%, 30%, or 35%), the solvent accounts for 30%-80% of the total weight of the electrolyte (e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%), and the additives account for 3%-35% of the total weight of the electrolyte (e.g., 3%, 5%, 10%, 15%, 20%, 25%, 30%, or 35%).

[0109] In some instances, the lithium-ion battery is a lithium-ion rechargeable battery.

[0110] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0111] The following examples illustrate the functional coating and lithium-ion battery of the present invention.

[0112] Example 1 The functional coating is located on the surface of the substrate layer in the diaphragm.

[0113] (1) Diaphragm Organic particles (composed of 2-mercaptobenzimidazole) and polyacrylic acid were mixed in water at a weight ratio of 94:6. After thorough stirring, a functional coating slurry with a solid content of 25% was obtained. The functional coating slurry was coated onto one side of a substrate layer (polyethylene) with a thickness of 5 μm and a porosity of 40% using a gravure roller. After drying in a multi-section oven at 60°C, a functional coating with a thickness of 1.98 μm was formed. PVDF was dispersed in DMAC solvent and stirred thoroughly to obtain an adhesive slurry with a solid content of 10%. The adhesive slurry was coated onto the surface of the functional coating and the other side of the substrate layer using a gravure roller. After drying in a multi-section oven at 60°C, a diaphragm oil-based adhesive layer was formed, thus preparing the diaphragm.

[0114] The primary particle size distribution of the organic particles is as follows: Dv10 is 0.246 μm (D1 is 0.246 μm), Dv50 is 0.62 μm, Dv90 is 1.811 μm, and Dv90-Dv50 is 1.191 μm. In the SEM image of the functional coating surface at 5K magnification, the number of organic particles with a diameter greater than 2.5 μm in an area of ​​25 μm × 19 μm is 1. In an environment of 135℃, the solubility W of the organic particles in the test electrolyte is 0.2%. At 25℃, the peel strength F1 between the functional coating and the substrate layer is 69 N / m. After baking at 90℃ for 2 hours, the peel strength F2 between the functional coating and the substrate layer is 128 N / m. ΔF = F2 - F1 = 128 - 69 = 59 N / m. The wetting rate k of the diaphragm is 6.2 mm / min.

[0115] (2) Positive electrode plate Lithium cobalt oxide (Dv50 = 12.7, i.e., D3 = 12.7), polyvinylidene fluoride (PVDF500) binder, and conductive material (Super P: carbon nanotubes = 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 and continuously stirred under the action of a stirrer to form a homogeneous and fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 10 μm and dried in a vacuum oven at 120 °C for 6 hours. Then, it was rolled and slit to obtain the positive electrode sheet.

[0116] (3) Negative electrode plate Graphite, silicon carbide, conductive material (carbon black: carbon nanotubes = 1:1), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber were mixed in an aqueous solvent at a weight ratio of 90:8:1:0.5:0.5 and continuously stirred under the action of a stirrer to form a homogeneous and fluid negative electrode slurry. The slurry was then coated onto both sides of a 10 μm thick negative electrode current collector (copper foil) and dried in a vacuum oven at 120°C for 6 hours. After rolling and slitting, the negative electrode sheet was obtained. The negative electrode active particles consist of graphite and silicon carbide, with a Dv50 of 9.6 μm, i.e., a D2 of 9.6.

[0117] (4) Electrolyte In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate, and ethyl propionate were mixed to form a homogeneous solvent. LiPF6, 1,3,6-hexanetrionitrile, and fluoroethylene carbonate were then slowly added and stirred until homogeneous to obtain the electrolyte. The electrolyte contained 16 wt% LiPF6, 20 wt% fluoroethylene carbonate, and 3 wt% 1,3,6-hexanetrionitrile. The weight ratio of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate, and ethyl propionate was 15:15:50:20.

[0118] (5) Lithium-ion batteries The positive electrode sheet obtained in step (2), the separator obtained in step (1), and the negative electrode sheet obtained in step (3) are wound together to form a bare battery cell. Then, the bare battery cell is placed in an aluminum-plastic film, and the electrolyte obtained in step (4) is injected into the dried bare battery cell. After vacuum sealing, room temperature standing, and high temperature formation, a lithium-ion battery is obtained. Among them, the side of the separator with the functional coating corresponds to the positive electrode sheet, D2 / D1=9.6 / 0.246=39; D3 / D1=12.7 / 0.246=51.6.

[0119] Example 2 group This set of examples illustrates the effects that occur when the position of the functional coating changes.

[0120] Example 2a The procedure is carried out in accordance with Example 1, except that the functional coating is located on the surface of the negative electrode sheet, specifically: Diaphragm: Replace organic particles with alumina particles; Negative electrode sheet: Organic particles (composed of 2-mercaptobenzimidazole) and polyacrylic acid are mixed in water at a weight ratio of 94:6. After thorough stirring, a functional coating slurry with a solid content of 25% is obtained. The functional coating slurry is coated on the surface of the negative electrode active layer on both sides to form a functional coating on the surface of the negative electrode active layer.

[0121] Example 2b The procedure is carried out in accordance with Example 1, except that the functional coating is located on the surface of the positive electrode sheet, specifically: Diaphragm: Replace organic particles with alumina particles; Positive electrode sheet: Organic particles (composed of 2-mercaptobenzimidazole) and polyacrylic acid are mixed in water at a weight ratio of 94:6. After thorough stirring, a functional coating slurry with a solid content of 25% is obtained. The functional coating slurry is coated on the surface of the positive electrode active layer on both sides to form a functional coating on the surface of the positive electrode active layer.

[0122] Example 2c The procedure was carried out in accordance with Example 1, except that the side of the separator with the functional coating corresponds to the negative electrode.

[0123] Example 2d The procedure was carried out in accordance with Example 1, except that organic particles (composed of 2-mercaptobenzimidazole) and polyacrylic acid were mixed in water at a weight ratio of 94:6. After thorough stirring, a functional coating slurry with a solid content of 25% was obtained. The functional coating slurry was coated onto both sides of a substrate layer (polyethylene) with a thickness of 5 μm and a porosity of 40% using a gravure roller. After drying in a multi-section oven at 60°C, a functional coating with a thickness of 1.98 μm was formed. PVDF was dispersed in DMAC solvent and thoroughly stirred to obtain an adhesive slurry with a solid content of 10%. The adhesive slurry was coated onto the surfaces of both sides of the functional coating using a gravure roller. After drying in a multi-section oven at 60°C, a diaphragm oil-based adhesive layer was formed, and a diaphragm was prepared.

[0124] Example 3 Group This set of examples illustrates the effects of changing the specific choice of a bicyclic organic compound.

[0125] This embodiment group is based on Example 1, except that the specific selection of the bicyclic organic compound is changed, as detailed in Table 1-1.

[0126] Table 1-1 Example 4 group This set of examples illustrates the effects that occur when D3 / D1 changes.

[0127] This embodiment group is based on Embodiment 1, except that D3 / D1 is changed, as detailed in Tables 1-2.

[0128] Table 1-2 Example 5 group This set of examples illustrates the effects that occur when D2 / D1 changes.

[0129] This embodiment group is based on Embodiment 1, except that D2 / D1 is changed, as detailed in Tables 1-3.

[0130] Table 1-3 Example 6 group This set of examples illustrates the effects of changes in the weight percentage of organic particles in a functional coating.

[0131] This embodiment group is based on Embodiment 1, except that the weight ratio of organic particles in the functional coating is changed, as detailed in Tables 1-4.

[0132] Example 7 group This set of examples illustrates the effects of changes in the thickness of the functional coating.

[0133] This embodiment group is based on Embodiment 1, except that the thickness of the functional coating is changed, as detailed in Tables 1-4.

[0134] Table 1-4 Example 8 group This set of examples illustrates the effects that occur when the particle size distribution of primary organic particles changes.

[0135] This embodiment group is based on Example 1, except that the particle size distribution of the organic particles is changed, as detailed in Tables 1-5.

[0136] Table 1-5 Comparative Example 1 The procedure was carried out in accordance with Example 1, except that the organic particles were replaced with the same amount of alumina particles by weight.

[0137] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that the organic particles were replaced with 2-mercaptoimidazole and methylbenzene.

[0138] Test case The lithium-ion batteries prepared in the examples and comparative examples were subjected to the following tests.

[0139] 1. Room temperature cycling performance At 25℃±2℃, the battery is charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The initial discharge capacity is recorded as C0. After resting for 10 minutes, the cycle is as follows: 3C constant current and constant voltage charging to 4.25V, cut off at 2C, then 2C constant current and constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current and constant voltage charging to 4.53V, cut off at 0.18C, resting for 5 minutes, and then discharged at 0.7C to 3.0V. After 1000 cycles, the battery is charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The discharge capacity at this point is recorded as C1.

[0140] Capacity retention rate: C = (C1 / C0) × 100%.

[0141] 2. High-temperature cycling performance Under an environment of 45℃±2℃, the battery is charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The initial discharge capacity is recorded as T0. After resting for 10 minutes, the cycle is as follows: 3C constant current and constant voltage charging to 4.25V, cut off at 2C, then 2C constant current and constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current and constant voltage charging to 4.53V, cut off at 0.18C, rest for 5 minutes, and then discharged at 0.7C to 3.0V. After 550 cycles, the battery is charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The discharge capacity at this point is recorded as T1.

[0142] Capacity retention rate: T = (T1 / T0) × 100%.

[0143] 3. Lithium plating test The lithium-ion battery was placed at 25℃±2℃ and charged at a constant current of 3C to the upper limit voltage (4.53V). Then it was charged at a constant voltage of 4.53V to 0.05C and left to stand for 5 minutes. Next, it was discharged at a constant current of 0.5C to 3V, and the discharge capacity at this time was recorded as Q1. After standing for 5 minutes, this was one charge-discharge cycle. This charge / discharge cycle was repeated for 20 cycles. After 20 cycles, the battery was disassembled to check the lithium plating on the negative electrode. When there was no lithium plating, it was represented by "0"; when the lithium plating area accounted for less than 3% of the total area of ​​the negative electrode, it was represented by "1"; when the lithium plating area accounted for 3%-5% of the total area of ​​the negative electrode, it was represented by "2"; when the lithium plating area accounted for more than 5% and less than or equal to 10% of the total area of ​​the negative electrode, it was represented by "3"; and when the lithium plating area accounted for more than 15% of the total area of ​​the negative electrode, it was represented by "4".

[0144] 4. Ratio Performance Under an environment of 25℃±2℃, the battery is charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and then discharged at a constant current of 0.2C to 3.0V. The initial discharge capacity is recorded as D0. After resting for 10 minutes, the cycle is: charged at a constant current and constant voltage of 1C to 4.53V, cut off at 0.18C, rested for 5 minutes, and then discharged at 0.7C to 3.0V. After 200 cycles, the battery is charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and then discharged at a constant current of 0.2C to 3.0V. The discharge capacity at this time is recorded as D1. The cycle capacity retention rate at this time is calculated as (D1 / D0)×100%. If the calculated cycle capacity retention rate is greater than or equal to 80%, the charging rate in the cycle is adjusted to 2C, that is, charged at a constant current and constant voltage of 2C to 4.53V, cut off at 0.18C, rested for 5 minutes, and then discharged at 0.7C to 3.0V. After 200 cycles, the battery is charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The capacity retention rate after 200 cycles at 2C is calculated again. If the calculated capacity retention rate is greater than or equal to 80%, the rate in the cycle is increased until a certain rate is reached, and the battery is charged at constant voltage to 4.53V, cut off at 0.18C, allowed to rest for 5 minutes, and then discharged at 0.7C to 3.0V. If the capacity retention rate after 200 cycles is less than 80%, then the charging rate at this point is the test result of the rate performance, i.e., the maximum charging rate at which the capacity retention rate is greater than or equal to 80% after 200 cycles.

[0145] 5. Hot box test The lithium-ion secondary batteries were heated in a convection air chamber at an initial temperature of (25±3)℃ with a temperature change rate of (5±2)℃ / min, and the temperature was increased to (130±1)℃. The temperature was maintained for 60 minutes before the test was ended. The battery status was recorded. Twenty battery samples were tested for each example and comparative example. If the battery did not explode and / or catch fire, it was considered "passed". If it exploded or caught fire, it was considered "failed". The result was expressed as "number of passes / 20pcs". For example, "20 / 20pcs" means all passed, and "10 / 20pcs" means 10 out of 30 batteries passed.

[0146] The results are recorded in Table 2.

[0147] Table 2 As can be seen from Table 2, by comparing the comparative examples and the embodiments, it can be seen that the rate performance of the battery in the embodiments is significantly improved, the capacity retention rate at room temperature is significantly improved, the capacity retention rate at high temperature is significantly improved, and the high temperature safety performance is significantly improved. This shows that by adding bicyclic organic matter to the functional coating, compared with the prior art, it is possible to improve the problem of poor wetting at the interface between the electrode and the separator, and improve the rate performance, high temperature safety performance and long cycle performance of the battery.

[0148] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A functional coating for use between a separator substrate layer and an electrode active layer in a lithium-ion battery, characterized in that, The functional coating comprises a bicyclic organic compound, and the molecular structure of the bicyclic organic compound comprises a 2-mercapto imidazole five-membered ring and a six-membered ring sharing two adjacent carbon atoms, and the six-membered ring is a benzene ring or a benzene ring substituted by a characteristic group.

2. The functional coating according to claim 1, wherein, The characteristic group is selected from one or more of C1-C6 alkyl, C1-C6 alkoxy, hydroxyl, amino, cyano, halogen substituent, sulfonic acid group, carboxyl and nitro; And / or, the molecular structure of the bicyclic organic compound is a planar structure; And / or, the functional coating comprises organic particles, and the composition of the organic particles comprises a bicyclic organic compound; and / or, in the infrared spectrum of said bicyclic organic compound, there is a first characteristic peak at 1600 cm -1 -1650 cm -1 there is a first characteristic peak at 2530 cm -1 -2600 cm -1 there is a second characteristic peak, wherein said first characteristic peak is an absorption peak of an imine group in a 2-mercaptoimidazole five-membered ring and said second characteristic peak is an absorption peak of a mercapto group in a 2-mercaptoimidazole five-membered ring; And / or, the retention time of the bicyclic organic compound in the mass spectrometry test is 25 min-40 min, and there are third, fourth and fifth characteristic peaks in the mass spectrum of the bicyclic organic compound, wherein the third characteristic peak is the peak with the strongest peak in the mass spectrum, the fourth characteristic peak is the peak with a peak intensity only weaker than the third characteristic peak in the mass spectrum, the third characteristic peak is a characteristic peak of 2-mercapto benzimidazole fragment ion, and the mass-to-charge ratio of the third characteristic peak is 149-151; the fourth characteristic peak is a characteristic peak of benzimidazole fragment ion, and the mass-to-charge ratio of the fourth characteristic peak is 117-119, and the fifth characteristic peak is a characteristic peak of mercapto fragment sulfur ion, and the mass-to-charge ratio of the fifth characteristic peak is 31-33.

3. The functional coating according to claim 2, wherein, The C1-C6 alkyl is selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl and 3-hexyl; And / or, the C1-C6 alkoxy is selected from one or more of methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, tert-pentoxy, neopentoxy, 2,2-dimethylpropoxy, 1-ethylpropoxy, 1-methylbutoxy, 2-methylbutoxy, n-hexoxy, isohexoxy, 2-hexoxy and 3-hexoxy; And / or, the organic particles have a lamellar crystal structure; And / or, the organic particles comprise primary particles and secondary particles, the secondary particles are formed by agglomeration of the primary particles, the Dv50 of the primary particles is 0.5 μm-1 μm, and the Dv50 of the secondary particles is 15 μm-100 μm; And / or, there are two peaks in the particle size distribution graph of the organic particles, which are the sixth characteristic peak and the seventh characteristic peak, respectively, the particle size corresponding to the highest point of the sixth characteristic peak is 0.5 μm-5 μm, and the particle size corresponding to the highest point of the seventh characteristic peak is 15 μm-100 μm.

4. The functional coating of claim 2, wherein, The weight percentage of the organic particles in the functional coating is 90%-99%; And / or, the particle size of the primary particles of the organic particles satisfies the following relationship: 0.2 μm≤Dv10≤0.3 μm, 0.5 μm≤Dv50≤1 μm, 1 μm≤Dv90≤2.5 μm, and Dv90-Dv50≤1.5 μm. and / or, the number of organic particles with a particle size greater than 2.5 μm in the SEM image of the functional coating surface at a magnification of 5K times, in an area of 25 μm x 19 μm, is less than or equal to 5; and / or, the solubility W of the organic particles in the test electrolyte is less than 0.5% at an environment of 135 ℃, the test electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate, the concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate is 1:1:1; and / or, the bicyclic organic compound is 2-mercaptobenzimidazole or a 2-mercaptobenzimidazole derivative, the 2-mercaptobenzimidazole derivative including one or more of 2-mercapto-5-methylbenzimidazole, 2-mercapto-5-ethylbenzimidazole, 2-mercapto-5-propylbenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-ethoxybenzimidazole, 2-mercapto-5-hydroxybenzimidazole, 2-mercapto-5-aminobenzimidazole, 2-mercapto-5-chlorobenzimidazole, 2-mercapto-5-bromobenzimidazole, 2-mercapto-5-sulfonic acid benzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-fluorobenzimidazole, 2-mercapto-5-fluorobenzimidazole, 2-mercapto-5,6-dichlorobenzimidazole, and 2-mercapto-5-cyanobenzimidazole.

5. The functional coating according to any one of claims 1-4, wherein, The melting point of the bicyclic organic compound is 250-320 ℃; and / or, the thermal decomposition temperature of the bicyclic organic compound is 250-350 ℃; and / or, the thickness of the functional coating is 0.2-5 μm.

6. A lithium-ion battery, characterized by The lithium ion battery includes a pole piece, a separator, an electrolyte, and the functional coating for the lithium ion battery between the separator substrate layer and the pole piece active layer according to any one of claims 1-5, and the separator includes a substrate layer.

7. The lithium-ion battery of claim 6, wherein, The pole piece includes a positive pole piece and a negative pole piece, and the position of the functional coating includes one or more of the surface of the substrate layer of the separator, the surface of the positive pole piece, and the surface of the negative pole piece.

8. The lithium-ion battery of claim 7, wherein, The separator includes a carrier layer and a glue layer on at least one side surface of the carrier layer, the carrier layer includes a substrate layer and a functional coating, and the functional coating is on one or both side surfaces of the substrate layer; Preferably, the components of the glue layer include a first polymer, and the first polymer includes one or more of poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), poly(vinylidene fluoride), poly(tetrafluoroethylene), poly(vinyl fluoride), poly(hexafluoropropylene), fluorovinyl-hexafluoropropylene copolymer, vinylidene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, acrylate-based polymer, phenol formaldehyde resin, polyimide, modified phenol formaldehyde resin, and modified polyimide; More preferably, the glue layer includes polymer particles, and the components of the polymer particles include a first polymer. More preferably, the adhesive layer comprises a first polymer and optionally first particles, the adhesive layer is a porous structure consisting of the first polymer as a continuous phase, and the first particles comprise one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine trimer thiocyanate, uracil, cytosine, guanine, 2-mercaptobenzimidazole, N,N'-di(β-naphthyl)-p-phenylenediamine, 4-amino-2,6-dihydroxypyrimidine.

9. The lithium-ion battery of claim 8, wherein, The separator satisfies the following relationship: 60≤F1≤80, 120≤F2≤140, 50≤△F≤70, wherein △F=F2-F1, F1 is the peeling strength between the functional coating and the substrate layer at 25℃, and F2 is the peeling strength between the functional coating and the substrate layer after baking at 90℃ for 2 hours. And / or, the wettability rate k of the separator is 5mm / min-7mm / min, wherein the wettability rate k of the separator is tested by the following method: the separator is placed vertically, one end of the separator is immersed in the test electrolyte and the timing is started, and the wettability height h of the test electrolyte within 5min is recorded, then the wettability rate k of the separator is h / 5; And / or, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one side or both sides of the positive electrode current collector, the positive electrode active layer comprises positive electrode active particles, and the lithium ion battery satisfies the following relationship: 10≤D3 / D1≤85, wherein D1 is the Dv10 of the primary particles of the organic particles, and D3 is the Dv50 of the positive electrode active particles, preferably, 0.2μm≤D1≤0.3μm and / or 2μm≤D3≤20μm. And / or, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on one side or both sides of the negative electrode current collector, the negative electrode active layer comprises negative electrode active particles, and the lithium ion battery satisfies the following relationship: 20≤D2 / D1≤55, wherein D1 is the Dv10 of the primary particles of the organic particles, and D2 is the Dv50 of the negative electrode active particles, preferably, 0.2μm≤D1≤0.3μm and / or 5μm≤D2≤12μm.

10. The lithium-ion battery of claim 7, wherein, The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one side or both sides of the positive electrode current collector, the positive electrode active layer comprises positive electrode active particles, the functional coating is located on the surface of the positive electrode active layer away from the positive electrode current collector, the functional coating comprises organic particles, and the lithium ion battery satisfies the following relationship: 10≤D3 / D1≤85, wherein D1 is the Dv10 of the primary particles of the organic particles, and D3 is the Dv50 of the positive electrode active particles, preferably, 0.2μm≤D1≤0.3μm and / or 2μm≤D3≤20μm. And / or, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on one side or both sides of the negative electrode current collector, the negative electrode active layer comprises negative electrode active particles, the functional coating is located on the surface of the negative electrode active layer away from the negative electrode current collector, the functional coating comprises organic particles, the lithium ion battery satisfies the following relationship: 20≤D2 / D1≤55, wherein D1 is the Dv10 of the primary particles of the organic particles, in units of μm, and D2 is the Dv50 of the negative electrode active particles, in units of μm, preferably 0.2 μm≤D1≤0.3 μm and / or 5 μm≤D2≤12 μm; And / or, the electrolyte comprises a polar solvent selected from at least one of 2,2-difluoroethyl acetate, ethyl 2,2-difluoroacetate, propyl propionate, ethyl propionate, diethyl carbonate, propylene carbonate, ethylene carbonate.

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