Secondary batteries

Abstract

This invention discloses a secondary battery in which at least two of the positive electrode, negative electrode, and separator are improved as follows: a groove is formed along the length direction on the surface of the positive electrode; multiple grooves are formed on the surface of the negative electrode; organic polymer particles are embedded in the separator coating, and a certain gap is formed between the protruding organic polymer particles and the coating surface. This invention can effectively improve the liquid retention performance of the battery and increase its cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a rechargeable battery. Background Technology

[0002] High electrolyte retention is crucial for lithium-ion rechargeable batteries, especially as a cornerstone of next-generation high-energy-density batteries (such as silicon-based anodes and high-nickel ternary batteries). High electrolyte retention is not an isolated parameter but directly determines the battery's internal resistance, heat generation, interface stability, and side reaction rate, ultimately affecting its lifespan, power, and safety performance. However, the expansion of silicon-based anodes generates significant internal pressure, compressing the space between the separator and electrodes and discharging some electrolyte from the active area. Furthermore, the limitations of cylindrical battery structures make uniform electrolyte distribution and full wetting within the electrode gaps and pores more challenging, easily leading to "lean electrolyte zones." Therefore, improving electrolyte retention is a key prerequisite for achieving high-performance battery indicators (such as long fast-charge cycle life) in battery design and manufacturing. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the object of this invention is to provide a secondary battery with high liquid retention performance and long cycle life, such as long fast-charge cycle life and long room-temperature cycle life.

[0004] Specifically, the present invention provides a secondary battery, comprising a positive electrode, a negative electrode, and a separator; the secondary battery satisfies at least two of the following conditions: (1) The surface of the positive electrode sheet is provided with at least one groove, and the groove extends along the length direction of the positive electrode sheet; (2) The surface of the negative electrode sheet is provided with a plurality of grooves, the grooves extending along the width direction of the negative electrode sheet, and the plurality of grooves are arranged in parallel; (3) The diaphragm includes a base membrane and a coating disposed on at least one side of the base membrane, the coating including organic polymer particles, at least a portion of the organic polymer particles protruding from the surface of the coating.

[0005] This invention features grooves along the length of the positive electrode surface, allowing the electrolyte to easily enter the grooves after the electrode is wound into a battery cell. This increases the electrolyte storage space in the middle region of the electrode, improving the cell's electrolyte retention. Even under high internal pressure, it ensures that the electrolyte is evenly distributed and fully wets the electrode in the gaps and pores. Similarly, multiple grooves on the negative electrode surface allow the electrolyte to enter and remain inside the cell, improving electrolyte wetting and increasing the cell's electrolyte retention, thus preventing the formation of "depleted electrolyte zones." Embedding organic polymer particles in the separator coating, and creating gaps between the protruding particles and the coating surface, increases the electrolyte storage space of the separator, improving its electrolyte retention performance. Furthermore, adding large-diameter organic polymer particles to the coating creates a porous structure, further improving the separator's electrolyte retention performance. Studies have found that simultaneously improving at least two of the positive electrode, negative electrode, and separator can significantly improve the cell's liquid retention performance, effectively utilize its capacity, and extend its cycle life, such as fast-charging cycle life and room-temperature cycle life. However, improving only one of them cannot improve the battery's fast-charging cycle life. This is because during cycling, the volume change of the electrode material compresses the electrolyte, causing it to "flow" within the core. When no improvement is made or only one aspect is improved, the electrolyte stored inside the core is insufficient, preventing this flow from occurring. This results in a large concentration gradient of the core lithium salt (such as LiPF6) within the core, directly causing capacity loss and increased internal resistance, thus worsening the battery's cycle life.

[0006] According to some embodiments of the present invention, the secondary battery satisfies three of the above conditions.

[0007] According to some embodiments of the present invention, the width d1 of the groove is 2mm-10mm; and / or the depth of the groove is 5μm-20μm; preferably, the width d1 of the groove is 7mm-9mm; and / or the depth of the groove is 5μm-7μm.

[0008] According to some embodiments of the present invention, the at least one groove is disposed in the central region of the positive electrode sheet.

[0009] According to some embodiments of the present invention, the length of the groove is the same as the length of the positive electrode sheet.

[0010] According to some embodiments of the present invention, the cross-sectional shape of the groove includes any one of arc, inverted trapezoid, square, rectangle, and V-shape; and / or, the surface of the positive electrode sheet is provided with a plurality of grooves, and the plurality of grooves are arranged in parallel; and / or, the number of grooves is 1-2.

[0011] According to some embodiments of the present invention, the width d2 of the groove is 10mm-100mm; and / or, the depth of the groove is 1μm-8μm; and / or, the spacing d3 between adjacent grooves is 2cm-6cm; preferably, the width d2 of the groove is 50mm-70mm; and / or, the depth of the groove is 4μm-6μm; and / or, the spacing d3 between adjacent grooves is 4cm-6cm.

[0012] According to some embodiments of the present invention, the length of the groove is less than the width of the negative electrode sheet; and / or, the two ends of the groove are respectively spaced from the corresponding edges of the negative electrode sheet.

[0013] According to some embodiments of the present invention, the protrusion height H of the organic polymer particles is 2μm-25μm; the crosslinking monomers of the organic polymer particles include one or more of ethylene glycol diacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, divinylbenzene, and triethylene glycol dimethacrylate.

[0014] According to some embodiments of the present invention, the negative electrode sheet comprises a silicon-based negative electrode active material; and / or, the secondary battery is a cylindrical battery.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a top view schematic diagram of the positive electrode sheet of the present invention.

[0017] Figure 2 This is a schematic cross-sectional view of the positive electrode sheet of the present invention.

[0018] Figure 3 This is a top view schematic diagram of the negative electrode sheet of the present invention.

[0019] Figure 4 This is a cross-sectional schematic diagram of the diaphragm of the present invention.

[0020] Figure label: 100, Positive electrode; 110, Groove; 200, Negative electrode; 210, Score; 300, Separator; 310, Base film; 320, Coating; 330, Organic polymer particles. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. "Multiple" means two or more. Throughout this document, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0023] 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.

[0024] High electrolyte retention is crucial for lithium-ion rechargeable batteries, especially as a cornerstone of next-generation high-energy-density batteries (such as silicon-based anodes and high-nickel ternary batteries). High electrolyte retention is not an isolated parameter but directly determines the battery's internal resistance, heat generation, interface stability, and side reaction rate, ultimately affecting its lifespan, power, and safety performance. However, the expansion of silicon-based anodes generates significant internal pressure, compressing the space between the separator and electrodes and discharging some electrolyte from the active area. Furthermore, the limitations of cylindrical battery structures make uniform electrolyte distribution and full wetting within the electrode gaps and pores more challenging, easily leading to "lean electrolyte zones." Therefore, improving electrolyte retention is a key prerequisite for achieving high-performance battery indicators (such as long fast-charge cycle life) in battery design and manufacturing.

[0025] Therefore, the present invention provides a secondary battery with high liquid retention performance and long cycle life, such as long fast-charge cycle life and long room-temperature cycle life. Specifically, the secondary battery of the present invention includes a positive electrode, a negative electrode, and a separator; the secondary battery satisfies at least two of the following conditions: (1) The surface of the positive electrode sheet is provided with at least one groove, and the groove extends along the length direction of the positive electrode sheet; (2) The surface of the negative electrode sheet is provided with a plurality of grooves, the grooves extending along the width direction of the negative electrode sheet, and the plurality of grooves are arranged in parallel; (3) The diaphragm includes a base membrane and a coating disposed on at least one side of the base membrane, the coating including organic polymer particles, at least a portion of the organic polymer particles protruding from the surface of the coating.

[0026] This invention features grooves along the length of the positive electrode surface, allowing the electrolyte to easily enter the grooves after the electrode is wound into a battery cell. This increases the electrolyte storage space in the middle region of the electrode, improving the cell's electrolyte retention. Even under high internal pressure, it ensures that the electrolyte is evenly distributed and fully wets the electrode in the gaps and pores. Similarly, multiple grooves on the negative electrode surface allow the electrolyte to enter and remain inside the cell, improving electrolyte wetting and increasing the cell's electrolyte retention, thus preventing the formation of "depleted electrolyte zones." Embedding organic polymer particles in the separator coating, and creating gaps between the protruding particles and the coating surface, increases the electrolyte storage space of the separator, improving its electrolyte retention performance. Furthermore, adding large-diameter organic polymer particles to the coating creates a porous structure, further improving the separator's electrolyte retention performance. Studies have found that simultaneously improving at least two of the positive electrode, negative electrode, and separator can significantly improve the electrolyte retention performance of the battery cell, thereby extending the battery's cycle life, such as fast-charging cycle life and room-temperature cycle life. However, improving only one of them cannot improve the battery's fast-charging cycle life. This is because during cycling, the volume change of the electrode material compresses the electrolyte, causing it to "flow" within the core. When no improvement is made or only one aspect is improved, the electrolyte stored inside the core is insufficient, preventing this flow from occurring. This results in a large concentration gradient of the core lithium salt (such as LiPF6) within the core, directly causing capacity loss and increased internal resistance, thus worsening the battery's cycle life.

[0027] Setting grooves along the length of the positive electrode is easier to implement in terms of manufacturing process; only the coating pad needs to be modified accordingly, making it compatible with existing electrode manufacturing processes. However, setting grooves along the width of the positive electrode is more difficult to implement, significantly increasing the manufacturing complexity. Furthermore, since the coating on the negative electrode is typically thin, and the grooves formed by the coating pad are usually large, setting grooves on the negative electrode is not suitable, increasing the risk of foil leakage. This invention reduces the risk of foil leakage by forming grooves on the negative electrode using laser etching. In addition, setting grooves along the width of the negative electrode increases the number of grooves, improves the wettability of the negative electrode, and thus improves fast-charging performance.

[0028] The organic polymer particles used in the separator coating of this invention have better flexibility than inorganic particles. During battery expansion, they can reduce damage to the electrode, maintain the integrity of the electrode, and reduce the risk of short circuit. In addition, the organic polymer particles have better adhesion and are firmly bonded to the base film. They also have excellent electrolyte wettability, which can quickly and fully absorb and retain the electrolyte, improve ionic conductivity, reduce battery internal resistance, and improve rate performance.

[0029] In some embodiments, the secondary battery satisfies three of the above conditions. This improves the battery's liquid retention performance, thereby increasing its cycle life.

[0030] In some embodiments, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer can be formed by coating the positive current collector with a positive active slurry using a coating die. It is known in the art that a spacer is installed in the coating die, and the shape of the spacer determines the shape of the positive active layer. A spacer matching a preset positive electrode shape can be selected to prepare a corresponding positive electrode with grooves.

[0031] In some embodiments, the at least one groove is disposed in the central region of the positive electrode sheet. The axis of the central region along its length coincides with the axis of the positive electrode sheet along its length. The width of the central region is less than 50% of the width of the positive electrode sheet, for example, less than 40%, less than 30%, less than 20%, or less than 15%. For example, the width of the central region is 0.1%-15% of the width of the positive electrode sheet, for example, 0.1%, 1%, 5%, 10%, or 15%.

[0032] In some embodiments, reference Figure 1 The positive electrode sheet has a groove 110 on its surface. The groove 110 is located in the central region of the positive electrode sheet 100. Typically, due to battery expansion, the electrolyte in the central part of the electrode sheet is drained, easily forming a localized electrolyte-deficient area, leading to a decrease in battery performance. This invention, by providing a groove in the central part of the positive electrode sheet, effectively avoids the formation of an electrolyte-deficient area in the central part of the electrode sheet, thereby improving battery performance.

[0033] In some embodiments, the length of the groove 110 is the same as the length of the positive electrode 100. Here, the length of the positive electrode refers to the length of the positive electrode coating area on the positive electrode, excluding the length of the empty foil area (i.e., the current collector area on the positive electrode that is not coated with active material). The groove extends through the entire length of the positive electrode, ensuring that all areas of the positive electrode have a high liquid retention capacity and avoiding the formation of localized liquid-deficient areas.

[0034] In some embodiments, reference Figure 2The width d1 of the groove 110 is 2mm-10mm, for example, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm. The depth of the groove is 5μm-20μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm. Preferably, the width d1 of the groove is 7mm-9mm, and the depth of the groove is 5μm-7μm. Optimizing the width and depth of the groove is beneficial to further improve the liquid retention capacity of the positive electrode sheet and avoid the formation of a liquid-deficient region inside the cell. If the width and depth of the groove are too small, the liquid retention performance cannot be effectively improved. If the width and depth of the groove are too large, the proportion of positive electrode active material in the cell decreases, and the battery energy density decreases. Therefore, the width and depth of the groove are preferably within the range of the present invention.

[0035] In some embodiments, the cross-sectional shape of the groove 110 includes, but is not limited to, any one of the following: arc-shaped, inverted trapezoidal, square, rectangular, and V-shaped. This improves the liquid retention capacity of the positive electrode sheet.

[0036] In some embodiments, the surface of the positive electrode sheet is provided with a plurality of grooves, which are arranged in parallel. This improves the liquid retention capacity of the positive electrode sheet.

[0037] In some embodiments, the number of grooves is 1-2. This improves the liquid retention capacity of the positive electrode.

[0038] In some embodiments, reference Figure 3 The negative electrode 200 has multiple grooves 210 on its surface. The width d2 of the grooves 210 is 10mm-100mm, for example, 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, or 100mm. The depth of the grooves is 1μm-8μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, or 8μm. The spacing d3 between adjacent grooves is 2cm-6cm, for example, 2cm, 3cm, 4cm, 5cm, or 6cm. Preferably, the width d2 of the grooves is 50mm-70mm. The depth of the grooves is 4μm-6μm. The spacing d3 between adjacent grooves is 4cm-6cm. "Spacing d3 between adjacent grooves" refers to the distance between the edges of adjacent grooves, such as... Figure 3As shown. Optimizing the width, depth, and spacing of the grooves helps to further improve the liquid retention capacity of the negative electrode sheet and avoid the formation of a liquid-deficient region inside the cell. If the width, depth, and spacing of the grooves are too small, the liquid retention performance cannot be effectively improved. If the width, depth, and spacing of the grooves are too large, the proportion of the negative electrode active material in the cell decreases, and the battery energy density decreases. Therefore, the width, depth, and spacing of the grooves are preferably within the range of this invention.

[0039] In some embodiments, the plurality of grooves 210 are arranged in parallel. Optionally, the plurality of grooves 210 are arranged in parallel at equal intervals. This improves the liquid retention capacity of the negative electrode.

[0040] In some embodiments, the length of the notch 210 is less than the width of the negative electrode 200. Here, the width of the negative electrode refers to the width of the negative electrode coating area on the negative electrode, excluding the width of the empty foil area (i.e., the current collector area on the negative electrode that is not coated with active material). The two ends of the notch 210 are spaced apart from the corresponding edges of the negative electrode 200. Typically, due to battery expansion, the electrolyte inside the electrode is easily squeezed out, while the electrolyte at the edge of the electrode is relatively abundant. Therefore, the present invention provides notches inside the negative electrode to improve the electrolyte retention performance inside the electrode.

[0041] In some embodiments, laser etching is used to form grooves 210 on the surface of the rolled negative electrode sheet.

[0042] In some embodiments, reference Figure 4 The diaphragm 300 includes a base membrane 310 and a coating 320. Organic polymer particles 330 are embedded in the base membrane 310 and the coating 320. At least a portion of the organic polymer particles 330 protrudes from the surface of the coating 320. The protrusion height H of the organic polymer particles 330 is 2μm-25μm, for example, 2μm, 5μm, 10μm, 15μm, 20μm, or 25μm. The organic polymer particles protruding from the coating surface form a certain gap with the coating surface, which can increase the electrolyte storage space of the diaphragm. The protrusion height H of the organic polymer particles 330 should not be too small; if it is too small, the electrolyte storage space is limited, and the improvement in electrolyte retention performance is not significant. The protrusion height H should not be too large. If it is too large, the expansion of the electrode will cause the stress at the contact point between the electrode and the organic polymer particles to be more uneven, which will easily lead to stress concentration and cause the electrode to crack. In addition, if the protrusion height H is too large, the length of the electrode needs to be shortened in order to ensure that the core can be inserted into the shell, resulting in capacity loss.

[0043] In some embodiments, the particle size of the organic polymer particles 330 is 6 μm-30 μm, for example, 6 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm. The particle size of the organic polymer particles 330 should generally be larger than the thickness of the coating 320, so that at least a portion of the organic polymer particles 330 can protrude from the coating surface, forming a liquid storage space. Optionally, the particle size of the organic polymer particles 330 may be larger than the total thickness of the base film 310 and the coating 320. This improves the liquid retention performance of the diaphragm.

[0044] In some embodiments, the crosslinking monomers of the organic polymer particles include one or more of ethylene glycol diacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, divinylbenzene, and triethylene glycol dimethacrylate. These monomers can form a stable three-dimensional polymer network through rapid photo-initiated polymerization (such as UV curing), thereby precisely controlling the mechanical strength, thermal stability, pore structure, and compatibility with the electrolyte of the membrane. The organic polymer particles used in this invention are commercially available.

[0045] In some embodiments, the base membrane has a porous structure. The porous base membrane includes one of polyethylene (PE) membrane, polypropylene (PP) membrane, polyimide (PI) membrane, polyethylene terephthalate (PET) membrane, PP / PE / PP composite membrane, or nonwoven membrane.

[0046] In some embodiments, the thickness of the base film is 5 μm-20 μm, for example, 5 μm, 10 μm, 15 μm or 20 μm. The porosity of the base film is 10%-70%, for example, 10%, 20%, 30%, 40%, 50%, 60% or 70%.

[0047] In some embodiments, the coating 320 comprises inorganic ceramic particles, a binder, and organic polymer particles. The mass ratio of the inorganic ceramic particles, the binder, and the organic polymer particles may be (75-85):(3-7):(12-18), for example, 75:7:18, 80:5:15, or 85:3:12.

[0048] In some embodiments, the inorganic ceramic particles include one or more of boehmite, alumina, magnesium hydroxide, magnesium oxide, silicon dioxide, titanium nitride, aluminum nitride, and boron nitride.

[0049] In some embodiments, the adhesive comprises one or more of the following polymers: homopolymers of acrylic monomers, hydrocarbon acrylic monomers, acrylate monomers, or hydrocarbon acrylate monomers; copolymers of at least two of the monomers; and modified compounds of the homopolymers or copolymers.

[0050] In some embodiments, the thickness of the coating is 0.2μm-5μm, for example, 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0051] In some embodiments, the negative electrode comprises a silicon-based negative electrode active material. Compared to graphite negative electrodes, silicon-based negative electrode active materials have a higher specific capacity. However, during charge and discharge, the volume expansion of the silicon-based negative electrode is greater, which generates greater pressure inside the battery, squeezing the space between the separator and the electrode, and causing some electrolyte to be discharged from the active area, easily forming a electrolyte-deficient region. The present invention, through synergistic improvement of at least two of the positive electrode, negative electrode, and separator, can effectively solve the problem of electrolyte-deficient regions caused by the volume expansion of the silicon-based negative electrode.

[0052] In some embodiments, the secondary battery is a cylindrical battery. A positive electrode, a negative electrode, and a separator are wound to form a cell, which is then housed in a cylindrical casing to form a cylindrical battery. The cylindrical casing is typically made of a material with high mechanical strength and is not easily deformed. When using a silicon-based negative electrode, the cylindrical casing restricts cell expansion, leading to greater internal pressure and potentially causing some electrolyte to drain from the active area, resulting in a electrolyte-deficient region. This invention, through synergistic improvements to at least two of the positive electrode, negative electrode, and separator, effectively solves the electrolyte-deficient region problem caused by the limitations of the cylindrical casing structure.

[0053] In some embodiments, the thickness of the negative electrode sheet is 100μm-140μm, for example, 100μm, 120μm, 130μm or 140μm.

[0054] In some embodiments, the thickness of the positive electrode sheet is 120μm-160μm, for example, 120μm, 130μm, 140μm, 150μm or 160μm.

[0055] In some embodiments, the secondary battery further includes an electrolyte. The electrolyte includes an electrolyte and a solvent. The solvent may include at least one of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). The volume ratio of EC to EMC may be 0:100 to 100:0.

[0056] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0057] The large-particle-size organic polymer particles used in the following examples and comparative examples are cross-linked particles of divinylbenzene and triethylene glycol dimethacrylate, which are prepared by suspension polymerization. The specific process is as follows: Phase 1: Preliminary Preparations 1. Preparation of the aqueous phase: Dissolve 2g of polyvinyl alcohol (PVA) in 200mL of hot deionized water (above 80℃) in a beaker, stirring until completely dissolved and transparent. After cooling to room temperature, add 4g of sodium chloride, stir to dissolve, and pour into a three-necked flask. PVA is used as the initiator.

[0058] 2. Preparation of the oil phase (monomer mixture): In a fume hood, accurately weigh 20g of divinylbenzene (DVB) and 6g of triethylene glycol dimethacrylate (TEGDMA) into a small beaker. Add 0.3g of azobisisobutyronitrile (AIBN) and stir slowly until completely dissolved, avoiding vigorous stirring that could introduce air. AIBN is used as a dispersant.

[0059] Phase Two: Suspension and Coagulation Process 1. Initial Dispersion: Start stirring and adjust the aqueous phase speed to 300 rpm to form a stable vortex. Slowly add the oil phase (monomer mixture) to the center of the aqueous phase using a dropper. After addition, increase the speed to 400 rpm and disperse for 15 minutes to form uniformly sized milky white droplets.

[0060] 2. Nitrogen purging and heating: Slowly purge nitrogen or argon gas above the liquid surface for 10 minutes to remove oxygen. Then turn on the water bath and slowly heat the liquid to 70°C.

[0061] 3. Isothermal polymerization: The reaction is carried out at a constant temperature of 65℃ for 8 hours. Initially (approximately 0.5-1 hour), the droplets will become viscous due to the exothermic polymerization, and then gradually harden into particles. Stirring should be maintained steadily throughout the process; fluctuations in the stirring speed will cause the particles to stick together.

[0062] 4. Maturation: Raise the reaction temperature to 80℃ and continue the reaction for 1.5 hours to ensure complete monomer conversion.

[0063] Phase 3: Post-processing and Characterization 1. Cooling and Separation: After the reaction is complete, stop heating and keep stirring until the water temperature drops below 40°C. Pour the reaction mixture into a beaker, let it stand to allow the particles to settle, and discard the supernatant. Wash the product several times with plenty of hot water (about 60°C) and cold water alternately to remove PVA and salts.

[0064] 2. Drying: Place the wet granules in a petri dish and dry them in a vacuum drying oven at 60℃ for 24 hours until constant weight is achieved.

[0065] 3. Sieving and Characterization: Polymer particles with a diameter range of 6μm-30μm were obtained by sieving through a standard sieve. The morphology and size distribution of the particles were observed using an optical microscope or a scanning electron microscope.

[0066] Example 1 (1) Preparation of positive electrode sheet: NCM811, conductive carbon black SP, and polyvinylidene fluoride (PVDF) are added to a mixing tank at a mass ratio of 98:1.5:0.5. N-methylpyrrolidone (NMP) is added to form a positive electrode slurry, which is then uniformly coated onto aluminum foil. During the coating process, a gasket matching the electrode structure is used to prepare a positive electrode sheet with one groove. After drying, rolling, die-cutting, and other processes, the positive electrode sheet is obtained, such as... Figure 1-2 As shown in the figure. The groove is located at the center of the width direction of the positive electrode sheet, and the length of the groove is the same as the length of the electrode sheet. The relevant parameters of the groove are shown in Table 1.

[0067] (2) Preparation of negative electrode sheet: Silicon carbon (silicon content 3wt%), polyacrylic acid (PAA), and conductive carbon black SP are added to a mixing tank at a mass ratio of 97.0:2.5:0.5, and deionized water is added and stirred to disperse evenly to obtain a negative electrode slurry. The negative electrode slurry is then evenly coated on copper foil, and then dried, rolled, laser etched, and die-cut to obtain the negative electrode sheet, such as... Figure 3 As shown, grooves are formed on the negative electrode sheet after roll forming by laser etching. The relevant parameters of the grooves are shown in Table 1.

[0068] (3) Preparation of diaphragm: (a) Preparation of coating slurry: Boehmite, PVDF, and large-particle-size organic polymer particles (crosslinked body of divinylbenzene and triethylene glycol dimethacrylate) were added to a mixing tank at a mass ratio of 80:5:15. NMP was added and stirred to disperse evenly. The mixture was then continuously dispersed at a stirring speed of 1200 rpm for 180 min to prepare a coating slurry with a solid content of 40 wt%.

[0069] (b) Preparation of lithium-ion battery separator: A microgravure plate was used to coat the stirred coating slurry onto the surface of a 9 μm thick polypropylene nonwoven fabric base membrane, followed by oven drying. After drying, a composite separator was obtained, as shown below. Figure 4 As shown in Table 1, the coating thickness is 3 μm and the protrusion height H of the organic polymer particles is shown in Table 1.

[0070] (4) Electrolyte preparation: EC: EMC are mixed at a volume ratio of 30:70 to obtain an organic solvent, and then LiPF6 is added to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0071] (5) Cell preparation: The positive electrode, negative electrode and separator are wound into a core and then assembled into a shell. After liquid injection, sealing, formation and capacity testing, the cylindrical lithium-ion battery is prepared.

[0072] Example 2-41 Lithium-ion batteries were prepared according to the method described in Example 1, with differences shown in Table 1.

[0073] Comparative Example 1 (1) Preparation of positive electrode sheet: NCM811, conductive carbon black SP and PVDF are added to a mixing tank at a mass ratio of 98:1.5:0.5. NMP is added to form a positive electrode slurry, which is then uniformly coated on aluminum foil. After drying, rolling and die cutting, the positive electrode sheet is obtained. The obtained positive electrode sheet does not have a groove structure.

[0074] (2) Preparation of negative electrode sheet: Silicon carbon (silicon content of 3wt%), PAA, and conductive carbon black SP are added to a mixing tank at a mass ratio of 97.0:2.5:0.5, and deionized water is added and stirred to disperse evenly to obtain a negative electrode slurry. The negative electrode slurry is then evenly coated on copper foil, and then dried, rolled, and die-cut to obtain the negative electrode sheet. The obtained negative electrode sheet has no scratches.

[0075] (3) Preparation of diaphragm: (a) Preparation of coating slurry: Inorganic ceramic particles (boehmite) and PVDF are added to a mixing tank at a mass ratio of 95:5, and NMP is added and stirred to disperse evenly. Then, the mixture is continuously dispersed at a stirring speed of 1200 rpm for 180 min to prepare a coating slurry with a solid content of 40wt%.

[0076] (b) Preparation of lithium-ion battery separator: The stirred coating slurry was coated onto the surface of a 9 μm thick polypropylene nonwoven fabric base film using a micro-gravure plate, and then dried in an oven. After drying, a composite separator was obtained, wherein the coating thickness was 3 μm.

[0077] (4) Same as Example 1.

[0078] (5) Same as Example 1.

[0079] Comparative Examples 2-9 Lithium-ion batteries were prepared according to the method described in Example 1, with differences shown in Table 1.

[0080] Test methods (1) Testing the width and depth of the groove in the positive electrode plate Use a width measuring instrument to measure the width of the groove.

[0081] Scanning electron microscope (SEM) images of the cross-section of the positive electrode were acquired, and the groove depth was measured using image tools.

[0082] (2) Testing of the width, depth and spacing of the grooves on the negative electrode sheet Use a width measuring instrument to measure the width of the notch and the spacing between adjacent notches.

[0083] SEM images of the cross-section of the negative electrode sheet were acquired, and the depth of the notch was measured using image processing tools.

[0084] (3) Test of the protrusion height H of the organic polymer particles of the diaphragm SEM images of the diaphragm cross-section were acquired, and the protrusion height H of the organic polymer particles was measured using image processing tools.

[0085] (4) Fast charging cycle life test of lithium-ion batteries First, the lithium-ion battery was activated by three charge-discharge cycles at 25°C and a 0.5C rate. Then, the initial capacity C was tested. Next, it was charged at 25°C at a constant current of 2.5C to reach 80% SOC within 15 minutes. Then, it was discharged at a constant current of 1C to 2.5V. After 500 cycles, the capacity retention rate was measured.

[0086] (5) Room temperature cycle life test of lithium-ion batteries First, the lithium-ion battery was activated by three charge-discharge cycles at 25°C and a 0.5C rate. Then, the initial capacity C was tested. Next, the battery was charged at 25°C and discharged at 0.5C for 800 cycles, and the capacity retention rate was measured.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089] Discussion of Results: By comparing the above embodiments with Comparative Example 1, it can be seen that the present invention effectively improves the liquid retention capacity by improving at least two of the positive electrode, negative electrode and separator, thereby improving the fast charge cycle life and room temperature cycle life of the battery.

[0090] By comparing the above embodiments with Comparative Examples 2-9, it can be seen that Comparative Examples 2-9 only improve one of the positive electrode, negative electrode and separator, and cannot improve the fast charging cycle life of the battery.

[0091] By comparing Comparative Example 1 and Comparative Examples 2-9, it can be seen that improving any one of the positive electrode, negative electrode, and separator can improve the cycle life at room temperature.

[0092] By comparing the above embodiments, it can be seen that improving the positive electrode, negative electrode, and separator simultaneously significantly improves the battery's liquid retention performance and cycle life. Specifically, the optimal fast-charge and conventional cycle performance is achieved when the positive electrode groove width d1 is 8 mm and depth is 5 μm, the negative electrode groove width d2 is 60 mm, depth is 5 μm, spacing d3 is 5 cm, and the protrusion height H of the organic polymer particles on the separator is 4 μm. Improving any two of the positive electrode, negative electrode, and separator simultaneously improves both fast-charge and conventional cycle performance. The best improvement in fast-charge cycle performance is achieved when the negative electrode groove width d2 is 60 mm, depth is 5 μm, spacing d3 is 5 cm, and the protrusion height H of the organic polymer particles on the separator is 4 μm. The best improvement effect on conventional cycle is achieved when the width d1 of the positive electrode groove is 8 mm, the depth is 5 μm, and the protrusion height H of the organic polymer particles on the separator is 4 μm.

[0093] In summary, this invention explores the impact of three technical means—positive electrode groove structure design, negative electrode laser etching, and separator optimization—on the fast charging and conventional cycle life of lithium-ion batteries. These methods enable lithium-ion batteries to effectively utilize their capacity and exhibit good cycle performance. Furthermore, this invention provides important reference for the design and development of high-liquidity, long-life lithium-ion batteries under different systems.

[0094] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0095] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and a separator; the secondary battery satisfies at least two of the following conditions: (1) The surface of the positive electrode sheet is provided with at least one groove, and the groove extends along the length direction of the positive electrode sheet; (2) The surface of the negative electrode sheet is provided with a plurality of grooves, the grooves extending along the width direction of the negative electrode sheet, and the plurality of grooves are arranged in parallel; (3) The diaphragm includes a base membrane and a coating disposed on at least one side of the base membrane, the coating including organic polymer particles, at least a portion of the organic polymer particles protruding from the surface of the coating.

2. The secondary battery according to claim 1, characterized in that, The secondary battery meets three of the above conditions.

3. The secondary battery according to claim 1, characterized in that, The width d1 of the groove is 2mm-10mm; and / or the depth of the groove is 5μm-20μm; Preferably, the width d1 of the groove is 7mm-9mm; and / or, the depth of the groove is 5μm-7μm.

4. The secondary battery according to claim 1, characterized in that, The at least one groove is disposed in the middle region of the positive electrode sheet.

5. The secondary battery according to claim 1, characterized in that, The length of the groove is the same as the length of the positive electrode sheet.

6. The secondary battery according to claim 1, characterized in that, The cross-sectional shape of the groove includes any one of the following: arc, inverted trapezoid, square, rectangle, and V-shape; And / or, the surface of the positive electrode sheet is provided with a plurality of grooves, and the plurality of grooves are arranged in parallel; And / or, the number of the grooves is 1-2.

7. The secondary battery according to claim 1, characterized in that, The width d2 of the groove is 10mm-100mm; and / or the depth of the groove is 1μm-8μm; and / or the spacing d3 between adjacent grooves is 2cm-6cm. Preferably, the width d2 of the groove is 50mm-70mm; and / or, the depth of the groove is 4μm-6μm; and / or, the spacing d3 between adjacent grooves is 4cm-6cm.

8. The secondary battery according to claim 1, characterized in that, The length of the groove is less than the width of the negative electrode sheet; And / or, the two ends of the groove maintain a distance from the corresponding edge of the negative electrode sheet.

9. The secondary battery according to claim 1, characterized in that, The protrusion height H of the organic polymer particles is 2μm-25μm, preferably 3μm-5μm; The crosslinking monomers of the organic polymer particles include one or more of ethylene glycol diacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, divinylbenzene, and triethylene glycol dimethacrylate.

10. The secondary battery according to claim 1, characterized in that, The negative electrode sheet includes a silicon-based negative electrode active material; And / or, the secondary battery is a cylindrical battery.

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