A battery

Abstract

The application provides a battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating arranged on at least one side surface of the positive electrode current collector; the positive electrode sheet comprises a first region, the positive electrode coating of the first region comprises a positive electrode active layer and a safety coating, the safety coating comprises a plurality of first convex parts and a plurality of first concave parts on the surface far from the positive electrode current collector; the separator comprises a carrier layer and a polymer layer arranged on at least one side surface of the carrier layer, the polymer layer comprises a plurality of second convex parts formed by a first polymer on the surface far from the carrier layer, and the second convex parts are towards the positive electrode sheet; the first convex parts and the second convex parts satisfy the following relationship: 0.4≤A / B≤4.5, wherein A is the average height of the first convex parts, in units of μm, and B is the average height of the second convex parts, in units of μm. The battery provided by the application has excellent safety and cycle stability.

Description

Technical Field

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

[0002] Lithium-ion batteries (LIBs) have become the core power supply component of modern portable electronic devices and are driving the energy revolution of electric transportation and clean energy storage as a key engine. However, their widespread use is also accompanied by safety hazards that cannot be ignored. In particular, under conditions of mechanical abuse (such as crushing and puncture), short-circuit contact between the positive electrode current collector and the negative electrode material layer is a major cause of battery thermal runaway, fire, and even explosion.

[0003] To mitigate the aforementioned short-circuit risks, existing technologies typically employ a safety coating between the positive electrode current collector and the positive electrode active layer to protect the current collector. Currently, these safety coatings often consist of an oil-based binder (such as polyvinylidene fluoride, PVDF) mixed with conductive particles. However, conductive particles are prone to side reactions with the electrolyte at high temperatures, impairing battery performance. Furthermore, these safety coating slurries often use N-methylpyrrolidone (NMP) as a solvent, which is expensive, toxic, and requires significant energy to recycle, failing to meet current requirements for green environmental protection and sustainable development. Therefore, developing a safe and environmentally friendly aqueous safety undercoating has become a hot research topic and a pressing technical challenge in the industry. Summary of the Invention

[0004] This invention provides a battery that can improve the safety performance and high-temperature cycle performance of lithium-ion secondary batteries in high-silicon systems.

[0005] To address the issues of poor environmental performance and severe high-temperature side reactions associated with oil-based safety primers, this invention attempts to develop a water-based safety primer. This primer uses water as a solvent and employs a water-based binder such as polyacrylic acid or polyacrylate. These binders, with their abundant functional groups, exhibit excellent adhesion through strong chemical and hydrogen bonding with the aluminum foil current collector, effectively protecting it. However, in practical applications, interfacial compatibility issues arise between the water-based primer and the positive electrode active material layer. Specifically, the positive electrode active material slurry is typically an oil-based system, using N-methylpyrrolidone (NMP) as a solvent and polyvinylidene fluoride (PVDF) as a binder. When coated onto the surface of the water-based primer, the binder is insoluble in NMP, resulting in weak interfacial forces and insufficient interfacial adhesion between the two layers. This weak interfacial adhesion not only increases the risk of side reactions of the electrolyte at the interface between the positive electrode active layer and the undercoat, but also, with the increasing prevalence of high-silicon systems, the internal stress generated by silicon volume expansion during battery cycling is more likely to cause cracks in the positive electrode active material layer, or even peel off from the safety coating, thus affecting the battery's safety performance and cycle life. Therefore, it is urgent to further optimize and improve the existing aqueous safety undercoat to solve the problem of weak interfacial adhesion between it and the oil-based positive electrode active layer, in order to meet the higher performance requirements of high-silicon systems.

[0006] To achieve the above objectives, the inventors of this invention propose the following technical solution:

[0007] A battery includes a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector. The negative active layer includes a silicon-based material, and the silicon content is 2%-50% based on the total mass of the negative active layer.

[0008] The positive electrode sheet includes a positive current collector and a positive electrode coating disposed on at least one side surface of the positive current collector; the positive electrode coating includes a positive active layer and a safety coating stacked together, the safety coating is disposed between the positive current collector and the positive active layer, the safety coating includes a first material and an adhesive, and the safety coating includes a plurality of first protrusions and a plurality of first recesses on the surface away from the positive current collector;

[0009] The separator includes a carrier layer and a polymer layer located on at least one side surface of the carrier layer, wherein the polymer layer includes a plurality of second protrusions formed of a first polymer on the surface away from the carrier layer, the second protrusions facing the positive electrode sheet;

[0010] The first protrusion and the second protrusion satisfy the following relationship: 0.4 ≤ A / B ≤ 4.5.

[0011] Where A is the average height of the first protrusion in μm, and B is the average height of the second protrusion in μm.

[0012] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0013] By providing a first protrusion and a first recess on the surface of the safety coating away from the positive electrode current collector, the contact area with the positive electrode active layer is increased, improving the interfacial adhesion. Simultaneously, a second protrusion is provided on the separator surface, and the average height A of the first protrusion and the average height B of the second protrusion are further controlled to satisfy: 0.4 ≤ A / B ≤ 4.5. This avoids uneven stress on both sides of the positive electrode active layer due to excessive height differences between the protrusions, preventing detachment and powder shedding. Furthermore, even if unavoidable powder shedding occurs in the positive electrode active layer due to internal stress caused by silicon volume expansion during battery cycling, the detached particles will enter the cavity formed between adjacent second protrusions, preventing puncture of the separator and short circuit. Therefore, the safety and cycle stability of the battery are effectively improved. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the positive electrode sheet according to a specific embodiment of the present invention.

[0015] Among them, 01 is the current collector, 02 is the safety coating, and 03 is the positive electrode active layer.

[0016] Figure 2 This is a schematic diagram of the structure of a safety coating according to a specific embodiment of the present invention;

[0017] Wherein, 04 - first protrusion, 05 - first recess, A ， - Height of the first convex part, d - Depth of the first concave part.

[0018] Figure 3 This is a schematic diagram of the diaphragm structure according to a specific embodiment of the present invention;

[0019] Wherein, 06-carrier layer, 061-substrate layer, 062-heat resistant layer, 07-polymer layer, 08-second protrusion, r-diameter of the second protrusion, B ， - The height of the second convex part.

[0020] Figure 4 This is a schematic diagram of the structure of a positive electrode sheet according to a specific embodiment of the present invention;

[0021] Among them, 01-current collector, 02-safety coating, 03-positive electrode active layer, 09-first region, 10-second region. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In this application, the terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0024] In this application, references to "an embodiment," "an example," or "an example" mean that a specific feature, structure, or characteristic described in connection with that embodiment, example, or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination.

[0025] To mitigate the risk of battery thermal runaway caused by short-circuit contact between the positive electrode current collector and the negative electrode material layer under mechanical abuse conditions (such as extrusion and needle puncture), related technologies typically employ a safety coating (undercoat) between the positive electrode current collector and the positive electrode active layer. These safety coatings are often composed of an oil-based binder (such as polyvinylidene fluoride, PVDF) mixed with conductive particles. However, conductive particles are prone to side reactions with the electrolyte at high temperatures, impairing battery performance. To address the issues of poor environmental friendliness and severe high-temperature side reactions associated with oil-based safety undercoats, the inventors have developed an aqueous safety undercoat. This undercoat effectively inhibits corrosion of the positive electrode current collector at high potentials, alleviates electrolyte erosion of the current collector, and improves the heat dissipation capacity and structural stability of the electrode. However, existing aqueous safety coatings and oil-based positive electrode active layers exhibit poor interfacial compatibility, low interlayer forces, and insufficient interfacial adhesion strength. This problem is further exacerbated during battery charging and discharging: on the one hand, weak interfacial bonding easily leads to electrolyte seepage into the interface between the active layer and the undercoat, inducing more side reactions, accelerating electrolyte decomposition and gas generation; on the other hand, with the widespread application of high silicon content negative electrodes (silicon content 2-50%), the volume expansion effect of batteries during cycling is more significant, and the positive electrode active layer is subjected to repeated mechanical stress, making it more prone to cracks at weak points in the interface. These cracks can extend from the interface to the surface of the positive electrode active layer, and even partially peel off from the safety coating. The accumulation of these problems ultimately leads to accelerated battery capacity decay, internal short circuits and other safety risks, restricting the cycle life and reliability of high energy density batteries.

[0026] To address the shortcomings of existing technologies, this invention provides the following technical solutions:

[0027] The present invention provides a battery comprising a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector. The negative active layer comprises a silicon-based material, and the silicon content is 2%-50% based on the total mass of the negative active layer.

[0028] Reference Figure 1 The positive electrode includes a positive current collector 01 and a positive electrode coating disposed on at least one side surface of the positive current collector; the positive electrode coating includes a positive active layer 03 and a safety coating 02 stacked together, the safety coating 02 being disposed between the positive current collector 01 and the positive active layer 03, as shown in the figure. Figure 2 The safety coating 02 includes a first material and an adhesive, and the safety coating 02 includes a plurality of first protrusions 04 and a plurality of first recesses 05 on the surface away from the positive electrode current collector 01;

[0029] Reference Figure 3The separator includes a carrier layer 06 and a polymer layer 07 located on at least one side surface of the carrier layer 06. The polymer layer 07 includes a plurality of second protrusions 08 formed of a first polymer on the surface away from the carrier layer 06, and the second protrusions 08 face the positive electrode.

[0030] The first convex part 04 and the second convex part 08 satisfy the following relationship: 0.4 ≤ A / B ≤ 4.5.

[0031] Where A is the average height of the first convex part, in μm, and B is the average height of the second convex part, in μm.

[0032] The battery provided by this invention solves the problem of positive electrode active layer detachment and powder shedding caused by poor interfacial compatibility and insufficient adhesion strength between the positive electrode active layer (oil-based system) and the safety coating (water-based system) in the prior art, especially in cases where the interface structure failure is aggravated by the volume expansion of the high-silicon negative electrode system. The main reason is that the surface of the safety coating of the positive electrode sheet of this invention, away from the positive electrode current collector, includes a first convex portion and a first concave portion, which increases the contact area between the safety coating and the positive electrode active layer and improves the adhesion between the two interfaces. At the same time, a second convex portion is provided on the surface of the separator, and the average height A of the first convex portion and the average height B of the second convex portion are further limited to satisfy: 0.4≤A / B≤4.5. On the one hand, this avoids the problem of uneven stress on both sides of the positive electrode active layer caused by excessive height difference between the different convex portions on both sides, which leads to detachment and powder shedding. On the other hand, even if the internal stress generated by the volume expansion of silicon during battery cycling causes unavoidable powder shedding of the positive electrode active layer, the detached powder particles will enter the cavity formed between adjacent second convex portions and will not puncture the separator and cause a short circuit.

[0033] If A / B is less than 0.4, meaning the first protrusion is relatively too short or the second protrusion is relatively too high, on the one hand, the contact area between the safety coating and the positive electrode active layer will increase only slightly, resulting in insufficient interface anchoring force; on the other hand, the tip of the relatively high second protrusion is prone to forming a stress concentration point under compression, causing microscopic damage to the positive electrode active layer and exacerbating the risk of powder shedding. If A / B is greater than 4.5, meaning the first protrusion is relatively too high or the second protrusion is relatively too short, the surface of the safety coating will have excessive undulations. This will lead to uneven thickness of the positive electrode active layer and internal stress concentration. At the same time, the cavity volume formed between the excessively short second protrusions is too small to effectively accommodate the positive electrode powder particles caused by the volume expansion of the high-silicon negative electrode. The positive electrode powder particles are prone to accumulate at the interface, which may lead to the risk of puncturing the separator. Therefore, by controlling A / B within the above range, on the one hand, the first protrusion can fully play its role in increasing the contact area and anchoring the positive electrode active layer; on the other hand, the second protrusion can still maintain a cavity structure of appropriate height after extrusion deformation, effectively capturing positive electrode powder particles caused by the volume expansion of the high silicon negative electrode, while avoiding stress concentration and active layer damage caused by excessive height difference, thereby significantly improving the interface structure stability and long-term cycle safety performance of the battery.

[0034] In this invention, a high-silicon system can be understood as having a silicon content of 2%-50% in the negative electrode active layer. The testing method is as follows: After discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours. Then, it is rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of the ash. The calculation formula is as follows: Si content in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0035] It can be understood that the first convex portion is formed by the safety coating protruding towards the positive electrode active layer; the first concave portion is formed by the safety coating recessing towards the positive electrode current collector.

[0036] In some embodiments, the first protrusion and the first recess can be made by a gravure roller used for gravure coating. Specifically, the size and number of the first protrusion and the first recess can be adjusted by changing the solid content of the coating slurry, the depth and density of the grooves engraved on the gravure roller, etc.

[0037] In some implementations, refer to Figure 3 The carrier layer includes a substrate layer 061 as a supporting framework and a heat-resistant layer 062 disposed on at least one side surface of the substrate layer. The substrate layer 061 includes a polyolefin porous membrane, such as polyethylene (PE), polypropylene (PP) or a composite membrane thereof. The heat-resistant layer 062 is used to improve the high-temperature thermal stability of the separator. Its composition may include first particles, which include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate and melamine trithiocyanate. The composite carrier layer composed of the substrate layer and the heat-resistant layer can significantly improve the thermal safety of the battery while ensuring the basic mechanical properties and ion conduction capacity of the separator.

[0038] In some embodiments, the polymer layer 07 includes fibers formed from a second polymer and first inorganic particles. The polymer layer has a porous structure, and the pores of the porous structure are formed by the intricately interwoven fibers. In some specific embodiments, the average diameter of the fibers is 0.1 μm to 3 μm, for example: 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, or within any two of the above values. In other specific embodiments, the first inorganic particles include porous ceramic particles and / or solid ceramic particles. For example, the first inorganic particles include one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride. The second polymer includes one or more polymers formed by polymerization of ethylene, propylene, acrylonitrile, vinylidene fluoride, vinyl chloride, styrene, methyl methacrylate, polybutadiene-styrene-acrylate, lactic acid, vinyl butyral, carbonate polyurethane, and polyethylene phthalate and their copolymers.

[0039] The average height of the first protrusion 04 is the vertical distance between the highest point of the first protrusion and its substrate (positive electrode current collector surface), see [reference]. Figure 2 A in ，The average height A of the first protrusion can be obtained through the following process: Obtain the positive electrode sample, prepare a flat cross-section by cutting perpendicularly to the electrode surface using focused ion beam or argon ion polishing technology, and observe the cross-sectional morphology at high magnification using scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Due to the differences in material density and particle size between the positive electrode current collector, safety coating, and positive electrode active layer, the interfaces between layers are clearly distinguishable. Select at least 10 different cross-sectional fields of view and measure A of each first protrusion. ， The arithmetic mean is taken as the average height A of the first convex part.

[0040] The protrusion height of the first polymer particle (i.e., the height of the second protrusion) is the dimension by which the first polymer particle protrudes from the first surface. See [reference needed]. Figure 3 B in ， The average height B of the second protrusion can be obtained by the following process: In the SEM image of the membrane cross-section obtained by scanning with a scanning electron microscope, take an area of ​​100μm×100μm on the surface of the polymer layer, and measure the protrusion height of 50 first polymer particles (i.e., the second protrusions) in this area. The average height of the protrusion height of the 50 first polymer particles is the average height. Repeat the above operation 5 times, and take the average value of the 5 test results as the average protrusion height of the first polymer particles. When the number of protrusions is less than 50, change the position and continue to measure until the number is 50. The SEM image of the diaphragm cross-section can be obtained by the following method: a diaphragm sample of a certain size (e.g., 10 mm × 10 mm) is cut from a selected area of ​​the diaphragm. The diaphragm sample is wrapped with copper foil and then cut under freezing conditions (e.g., -80°C) using an ion beam polisher (e.g., Hitachi Arblade 5000) to obtain the cross-section of the diaphragm sample. The diaphragm sample is then sputtered with gold, and then, referring to JY / T010-1996, the SEM image of the diaphragm cross-section is obtained by scanning with a scanning electron microscope (e.g., Sigma 300 scanning electron microscope from ZEISS, Germany) (magnification can be from 1000x to 30000x).

[0041] Exemplary, not restrictive: A / B = 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or any combination thereof.

[0042] Regarding the material of the negative electrode current collector, the present invention does not impose specific limitations. For example, it can be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals. Similarly, the present invention does not impose specific limitations on the material of the positive electrode current collector. For example, it can be selected from any one or more of aluminum foil, aluminum alloy foil, titanium foil, carbon-coated aluminum foil, nickel foil, and composite foils of the above metals.

[0043] In a preferred embodiment, the negative electrode active layer further includes a conductive agent, a binder, and a dispersant, excluding graphite. Exemplarily, the conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; and the dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0044] In some implementations, A satisfies: 1μm≤A≤15μm.

[0045] The first protrusion within the aforementioned height range further ensures a sufficient and uniform mechanical interlocking structure between the safety coating and the positive electrode active layer. This enhances the interfacial adhesion between the two, further mitigating the issues of detachment and powder shedding from the positive electrode active layer, thereby improving the battery's cycle stability and reliability. If A is less than 1 μm, the protrusion height on the safety coating surface is relatively small, failing to effectively increase the contact area with the positive electrode active layer. This results in a limited improvement in interfacial adhesion and limited resistance to the internal stress generated by the volume expansion of the high-silicon anode. If A is greater than 15 μm, the protrusion height is relatively large, reducing the uniformity of the subsequently coated positive electrode active layer thickness and potentially creating stress concentration points at the protrusion tips, which is detrimental to improving the detachment problem of the positive electrode active layer.

[0046] By way of example and not limitation: A is any value or a range of any two of the following: 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm.

[0047] To further ensure the uniformity of interfacial contact between the safety coating and the positive electrode active layer, in some specific embodiments, A satisfies: 2μm≤A≤10μm.

[0048] In some implementations, B satisfies: 0.5μm≤B≤15μm.

[0049] The second protrusion formed by the first polymer particles deforms under pressure during battery cycling expansion. If B is less than 0.5 μm, the height of the second protrusion decreases after compression, resulting in a small cavity volume between adjacent second protrusions. This limits the amount of powder particles that can be accommodated due to the volume expansion of the high-silicon anode, leading to powder accumulation at the interface. If B is greater than 25 μm, the protrusion height is too large, easily forming a local stress concentration point at its tip, causing crack propagation in the active layer and offering limited improvement to the powder shedding problem of the positive electrode active layer. Therefore, controlling B within the above range ensures a sufficient cavity to accommodate the shed powder between adjacent protrusions while avoiding stress concentration caused by excessive protrusion height. This more effectively prevents powder from piercing the separator and causing an internal short circuit, balancing the battery's cycle performance and safety.

[0050] By way of example and not limitation: B is any value or a range of any two of the following: 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm.

[0051] To further improve the cycle performance and safety performance of the battery, in one specific embodiment, 2μm≤B≤10μm.

[0052] The polymer layer is made of materials including but not limited to: polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polysulfonamide (PSA), and aramid (poly(m-phenylene isophthalamide)). These polymer layers have good interfacial adhesion, ensuring that the second protrusion maintains structural integrity during long-term cycling.

[0053] In some implementations, refer to Figure 3 The second protrusion is at least partially embedded in the polymer layer.

[0054] In this configuration, the second protrusion is at least partially embedded in the polymer layer. Partial embedding means that a portion of the individual second protrusion is encased in the polymer layer, while another portion protrudes from the surface of the polymer layer. Alternatively, the second protrusion can be located on the surface of the polymer layer, meaning it is completely and independently laid on the surface of the polymer layer. It is understandable that, regardless of the formation method, during battery cycling, the internal stress generated by the expansion of silicon volume inevitably leads to powder shedding from the positive electrode active layer. The shed powder particles can enter the cavity formed between adjacent second protrusions without puncturing the separator and causing a short circuit.

[0055] In some embodiments, the second protrusion includes a plurality of second sub-protrusions, the diameter of which is greater than or equal to 3 μm. The number of second sub-protrusions within the projected area of ​​the polymer layer surface on which the second protrusion is located is (30-1000) per 10000 μm. 2 .

[0056] Reference Figure 3 The diameter of the second sub-protrusion is the longest diagonal dimension *r* of the particle in the figure. The above embodiment, by limiting the number and distribution of second protrusions with a diameter ≥ 3 μm on the polymer layer, ensures the formation of a uniformly distributed and appropriately sized cavity network on the polymer layer surface. This ensures sufficient cavity volume to accommodate falling powder, preventing powder accumulation and the risk of puncture. On the other hand, if the second protrusions are too concentrated, the spacing between adjacent protrusions becomes too small, causing the cavities to be squeezed and deformed, thus limiting the powder's carrying capacity. Furthermore, overly dense second protrusions may hinder lithium-ion transport, increasing interfacial impedance. Therefore, controlling the number of second protrusions with a diameter ≥ 3 μm on the polymer layer within the aforementioned range can further improve battery safety and cycle stability.

[0057] Exemplary, and not limiting: an orthographically projected area meter of the surface of the polymer layer having a second protrusion, with an orthographically projected area per 10000 μm 2 The number of the second sub-protrusions within are 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, and 480. A range of any value or any combination of two of the following: 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700, 720, 740, 760, 780, 800, 820, 840, 860, 880, 900, 920, 940, 960, 980, and 1000.

[0058] To further ensure the formation of a uniformly distributed and appropriately sized cavity network on the polymer layer surface, the number of second sub-protrusions within the orthographically projected area of ​​the polymer layer surface with the second protrusion is (60-500) per 10000 μm. 2 .

[0059] In this invention, "diameter" refers to the diameter of a single second protrusion. The number of second sub-protrusions with a diameter ≥ 3μm within any 100μm × 100μm area on the surface of the polymer layer can be obtained by testing as follows: In the scanned image, arbitrarily select 5 regions with an area of ​​100μm × 100μm, count the number of protrusions with a diameter ≥ 3μm within each 100μm × 100μm area, and take the average value as the number of protrusions with a diameter ≥ 3μm within any 100μm × 100μm area on the surface of the polymer layer.

[0060] In some embodiments, the number of first protrusions within the orthographically projected area of ​​the surface on which the safety coating has the first protrusion is measured as (10-800) per 10000 μm. 2 .

[0061] By way of example and not limitation: the number of first protrusions within the orthographically projected area of ​​the surface on which the safety coating has the first protrusion is 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, or 32... A range of any one of the following: 0, 340, 360, 380, 400, 420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700, 720, 740, 760, 780, 800, or any combination of both.

[0062] The above embodiments, by limiting the number and distribution of the first protrusions in the safety coating, can further increase the contact area between the safety coating and the positive electrode active layer, thereby improving the interfacial adhesion between the two, while balancing local stress and manufacturing costs. Specifically, if the number of first protrusions per unit area is too small, the distribution of the first protrusions will be sparse, limiting the increase in the contact area between the safety coating and the positive electrode active material layer, resulting in limited improvement in interfacial adhesion; if the number of first protrusions per unit area is too large, it is easy to cause excessive local stress and increase manufacturing difficulty.

[0063] In some embodiments, the average difference between the height of the first protrusion and the depth of the first recess is C, where C satisfies: 0.5μm≤C≤14.5μm.

[0064] When the average difference between the height of the first protrusion and the depth of the first concave part of the safety coating is within the above-mentioned range, the thickness of the safety coating at different points can be guaranteed to be within a relatively suitable range, so as to give full play to the protective effect of the safety coating on the positive electrode. If the height difference between the first protrusion and the first concave part of the safety coating is too large, that is, the coating is too thick in some places and too thin in others, this will reduce the safety of the safety coating and reduce the energy density of the battery.

[0065] Reference Figure 2 The height of the first convex part is A. ， The depth of the first concave portion is d (the vertical distance between the highest point of the first convex portion and the lowest point of the first concave portion), and the difference between the height of the first convex portion and the depth of the first concave portion is A. ， -d, calculate the difference between the height of at least 10 different first protrusions and the depth of the first concave part, and take the average value, which is the average difference C between the height of the first protrusion and the depth of the first concave part.

[0066] Illustrative and not limiting: C is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3 .5μm, 3.8μm, 4.0μm, 4.2μm, 4.5μm, 4.8μm, 5.0μm, 5.2μm, 5.5μm, 5.8μm, 6.0μm, 6.2μm, 6.5μm, 6.8μm, 7.0μm, 7.2μm, 7.5μm, Any value or a range of any two of the following: 7.8μm, 8.0μm, 8.2μm, 8.5μm, 8.8μm, 9.0μm, 9.2μm, 9.5μm, 9.8μm, 10.0μm, 10.2μm, 10.5μm, 10.8μm, 11.0μm, 11.2μm, 11.5μm, 11.8μm, 12.0μm, 12.2μm, 12.5μm, 12.8μm, 13.0μm, 13.2μm, 13.5μm, 13.8μm, 14.0μm, 14.2μm, 14.5μm.

[0067] In some embodiments, the second protrusion includes primary particles and / or secondary agglomerated particles, and the average diameter of the second protrusion is 1-20 μm.

[0068] In this invention, the average diameter of the second protrusion refers to the average of the diameters of all second protrusions within a system. The average diameter of the second protrusion can be obtained by the following method: On the scanned image, draw the smallest square or rectangle that completely surrounds one second protrusion; that is, draw a square or rectangle whose edge line of the second protrusion meets all four sides of the square or rectangle. The length of one side of the square or the length of the long side of the rectangle is the diameter of the second protrusion. Take any 100μm × 100μm area on the polymer coating surface, and average the diameters of any 50 second protrusions to obtain the average diameter. Repeat the above operation 5 times, and take the average of the average diameters. It should be noted that if no 50 protrusions are observed in the image, take multiple images, and average the total number of diameters of the 50 protrusions to obtain the average diameter. An electrolytic scanning electron microscope (Hitachi, Ltd. S-3400N) can be used to observe the surface of the polymer layer at a magnification of 50,000 to obtain the scanned image.

[0069] By controlling the average diameter of the second protrusion within the aforementioned range, it is possible to ensure the formation of a uniformly distributed and appropriately sized cavity network on the surface of the polymer layer, while avoiding damage to the interface structure caused by an excessively large second protrusion, thereby further improving the cycle stability and safety reliability of the battery.

[0070] By way of example and not limitation: the average diameter of the second protrusion is 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8 μm, 8. Any value or a range of any two of the following: 2μm, 8.5μm, 8.8μm, 9μm, 9.2μm, 9.5μm, 9.8μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, and 20μm.

[0071] In some embodiments, the first material comprises inorganic particles, the particle size distribution of which satisfies: 0.01≤(Dv90-Dv10) / Dv50≤4.

[0072] Among them, inorganic particles within the above particle size distribution range can form a denser safety coating on the surface of the positive electrode current collector, which not only increases the contact points with the positive electrode active layer and further strengthens the interfacial adhesion, but also effectively slows down the erosion of corrosive components such as HF in the electrolyte, thereby further ensuring the cycle stability and safety of the battery.

[0073] Exemplary, not restrictive: (Dv90-Dv10) / DV50 = any value or a range of any two of the following: 0.01, 0.20, 0.30, 0.32, 0.35, 0.38, 0.40, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 2.00, 3.00, 3.50, 4.00.

[0074] In order to further form a uniform and stable protective interface and reduce the occurrence of side reactions, in some specific embodiments, the particle size distribution of inorganic particles satisfies: 0.5≤(Dv90-Dv10) / Dv50≤3.

[0075] The aforementioned Dv90, Dv10, and DV50 refer to the particle size values ​​corresponding to 90%, 10%, and 50% (by volume) of the cumulative particle size distribution curve of inorganic particles, respectively, and are generally obtained by laser diffraction particle size distribution instrument.

[0076] In some implementations, 0.03μm≤Dv10≤2μm.

[0077] The above embodiments, by limiting the Dv10 range of the inorganic particles, can further ensure that the safety coating has a certain porosity to guarantee the smooth transport of lithium ions. By way of example and not limitation, the Dv10 of the inorganic particles can be any value or a range of any two of the following: 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.7 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.7 μm, and 2.0 μm.

[0078] In some implementations, 0.05μm≤Dv50≤5.0μm.

[0079] By limiting the Dv50 range of the inorganic particles, the above implementation method can further ensure that the safety coating is mainly constructed with fine particles to form the framework. Small particles can form a denser packing structure, significantly reducing the porosity of the coating, thereby constructing a dense protective barrier on the surface of the positive electrode current collector, effectively slowing down the erosion of the current collector by corrosive components such as HF in the electrolyte. At the same time, small particles provide a larger specific surface area, significantly increasing the number of contact points with the upper positive electrode active layer, further improving the interfacial adhesion between the safety coating and the positive electrode active layer, thereby effectively resisting the interfacial shear stress caused by volume expansion under the high silicon anode system. By way of example and not limitation, the Dv50 of inorganic particles is any value or a range of any two of the following: 0.05 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm.

[0080] In some implementations, 0.1μm≤Dv90≤8μm.

[0081] The above embodiments, by limiting the Dv90 range of inorganic particles, can restrict the content of coarse particles in the safety coating, further ensuring the surface uniformity of the safety coating, and thus providing more comprehensive protection for the positive electrode current collector. By way of example and not limitation, the Dv90 of the inorganic particles can be any value or a range of any combination of 0.1μm, 0.2μm, 0.5μm, 0.8μm, 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, and 8.0μm.

[0082] In some embodiments, the first material includes at least one selected from metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal borides.

[0083] Among them, metal oxides have excellent electrochemical inertness and high dielectric constant, which can form a stable physical barrier on the surface of the positive electrode current collector, effectively slowing down the erosion of the current collector by corrosive components such as HF in the electrolyte. At the same time, their abundant surface hydroxyl groups can form hydrogen bonds with the upper positive electrode active layer, enhancing the interfacial adhesion. In addition to providing heat resistance, metal hydroxides can decompose and absorb heat at high temperatures, synergistically improving the thermal safety of the battery. Metal carbides, metal nitrides and metal borides have high hardness, high thermal conductivity and excellent electrical conductivity, which can form a local conductive network in the safety coating, improving electron transport. At the same time, their high melting point characteristics can also give the safety coating better structural stability.

[0084] In some specific embodiments, examples of metal oxides include aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, and nickel oxide. Examples of metal hydroxides include aluminum hydroxide, boehmite, and magnesium hydroxide. Examples of metal nitrides include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal carbides include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Examples of metal borides include titanium boride, zirconium boride, tungsten boride, and molybdenum boride. Preferably, at least one of Al₂O₃, AlOOH, TiO₂, ZrO₂, SiO₂, MnO₂, MgO, Si₃N₄, and BN is included. More preferably, boehmite is included.

[0085] The above embodiments can achieve diversified optimization of the safety coating function by selecting different specific first materials. For example, alumina, boehmite, and silica can form a hydrogen bond network with the binder through surface hydroxyl groups, while titanium dioxide inhibits interfacial side reactions through photocatalytic activity, and zirconium oxide enhances the stability of the safety coating through high mechanical strength.

[0086] In some embodiments, the binder comprises a polymer and / or a polymer-based metal salt.

[0087] The polymer-based binders described above can form a three-dimensional cross-linked network between inorganic particles and between the particles and the positive electrode current collector through the entanglement of their polymer chains and the adsorption of polar groups. This ensures the structural integrity of the safety coating and its adhesion to the positive electrode current collector, effectively resisting the interfacial shear stress caused by volume expansion in high-silicon anode systems. Meanwhile, polymer-based metal salts, while retaining the film-forming properties of polymers, introduce metal cations (Li... + Na + On the one hand, it further enhances the mechanical strength of the safety coating through ionic crosslinking. On the other hand, it can construct ion-conducting channels in situ in the safety coating, reduce interfacial impedance, and passivate the erosion of the positive electrode current collector by the preferential complexation of metal ions on corrosive components such as HF in the electrolyte, thereby further improving the cycle life and thermal stability of the battery.

[0088] In some specific embodiments, the polymer includes at least one polymer selected from polyacrylic acid, polybutyl acrylate, polyethyl acrylate, polyhydroxyethyl acrylate, and polyacrylamide.

[0089] Among them, all the above polymers contain polar functional groups (such as carboxyl, ester, amide, and hydroxyl groups), which can form strong interactions with the surface of inorganic particles and the positive electrode current collector through hydrogen bonding or coordination, significantly improving the structural integrity and interfacial adhesion of the coating.

[0090] In some specific embodiments, the polymer-based metal salt includes at least one of polyacrylate, polybutyl acrylate, polyethyl acrylate, hydroxyethyl acrylate, and polyacrylamide.

[0091] The above polymer-based metal salts, while retaining the corresponding polymer backbone structure, introduce metal cations (such as Li). + Na + K + (etc.) By enhancing interfacial adhesion through metal cation crosslinking, optimizing electrochemical kinetics through ion conduction, and suppressing side reactions through complexation, multiple synergistic effects of adhesion enhancement, stress buffering, ion transport, and interfacial stability are achieved.

[0092] As for the type of metal element in the polymer-based metal salt, it can be selected according to different battery systems. In some specific embodiments, the polymer-based metal salt includes at least one of polymer-based lithium salt, polymer-based sodium salt, and polymer-based zinc salt.

[0093] In some specific implementations, the mass percentage of the adhesive is W, based on the quality of the safety coating, where W satisfies: 1wt%≤W≤30wt%.

[0094] The binder within the above content range can fully coat the surface of inorganic particles and form a continuous polymer network between inorganic particles and between particles and the positive electrode current collector. During the repeated expansion / contraction cycle of the battery, it can still firmly anchor each component to the positive electrode current collector. At the same time, this content ensures the interfacial bonding strength, keeps the electronic conductive network inside the safety coating unobstructed, maintains low contact resistance between particles, preserves the pore structure between particles, and allows the electrolyte to fully wet and establish a continuous lithium-ion liquid phase transport channel. In addition, if the slurry has the above-mentioned binder content, it also has suitable rheological properties, and the stress release after coating is uniform. After drying, the coating is less prone to cracking and current collector warping.

[0095] By way of example and not limitation, W is any value or a range of any two of the following: 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%.

[0096] To further anchor the safety coating firmly to the positive current collector while balancing its electronic conductivity and ion transport efficiency, in some specific embodiments, 3wt%≤W≤20wt%.

[0097] In some specific embodiments, the weight-average molecular weight of the binder in the safety coating is Mw, and Mw satisfies: 100000 Da ≤ Mw ≤ 1500000 Da.

[0098] The binder molecular chains with the above weight-average molecular weights have a moderate degree of entanglement, which can form a continuous and tough polymer network during the drying process, giving the safety coating sufficient cohesive strength and adhesion to the current collector, effectively resisting the interfacial shear stress caused by volume expansion during battery cycling; at the same time, the above molecular weight range makes the binder have good solubility or dispersibility in solvents, with moderate slurry viscosity and controllable flowability, which is convenient for coating processing.

[0099] By way of example and not limitation, Mw is any value or a range of any two of the following: 100000 Da, 200000 Da, 300000 Da, 500000 Da, 800000 Da, 1000000 Da, 1200000 Da, 1500000 Da.

[0100] To further ensure that the safety coating possesses excellent mechanical stability while also exhibiting good process adaptability and electrochemical performance, in some specific embodiments, 300,000 Da ≤ Mw ≤ 800,000 Da.

[0101] In some specific embodiments, the number average molecular weight of the binder in the safety coating is Mn, where Mn satisfies: 40000 Da ≤ Mn ≤ 600000 Da.

[0102] The binder molecular chains with the above number average molecular weights also have a moderate degree of entanglement, and can form a continuous and tough polymer network during the drying process, giving the safety coating sufficient cohesive strength and adhesion to the current collector to effectively resist the interfacial shear stress caused by volume expansion during battery cycling; at the same time, they have good solubility or dispersibility in solvents, which can make the slurry viscosity moderate and the flowability controllable, making it easy to coat.

[0103] By way of example and not limitation, Mn is any value of 40000 Da, 50000 Da, 80000 Da, 100000 Da, 150000 Da, 200000 Da, 300000 Da, 400000 Da, 500000 Da, 600000 Da, or a range of any combination of both.

[0104] To further ensure that the safety coating possesses excellent mechanical stability while also exhibiting good process adaptability and electrochemical performance, in some specific embodiments, 80000 Da≤Mn≤300000 Da.

[0105] In some embodiments, the first polymer includes fluorinated polymers and / or non-fluorinated polymers. Fluorinated polymers possess excellent electrochemical stability, high purity, and tolerance to electrolytes, enabling the membrane to maintain structural integrity during long-term cycling. Non-fluorinated polymers, on the other hand, have better electrolyte wettability and ion conductivity, which can further improve lithium-ion transport in the membrane and reduce interfacial impedance.

[0106] In some embodiments, the fluoropolymers include one or more of vinylidene fluoride, tetrafluoroethylene, and hexafluoroethylene polymerized to form a fluoropolymer.

[0107] The fluorinated polymers mentioned above, due to the high bond energy and low polarity of the CF bonds in their molecular chains, can further endow the diaphragm with excellent thermodynamic stability, resistance to electrolyte swelling and high pressure resistance, enabling the diaphragm to maintain structural integrity during long-term cycling.

[0108] Non-fluorinated polymers can control the flexibility, hydrophilicity, and ion conductivity of polymer layers by introducing side chain groups with different polarities and flexibility. In some embodiments, non-fluorinated polymers include non-fluorinated polymers formed by polymerizing one or more of styrene, ethylene, propylene, acrylonitrile, methyl methacrylate, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, amides, and imides.

[0109] In some alternative embodiments, the positive electrode active layer includes a positive electrode active material, which includes lithium cobalt oxide with a Dv50 of 8 μm-25 μm.

[0110] Lithium cobalt oxide, as a positive electrode active material, can further improve the cycle stability of batteries under high voltage. Moreover, lithium cobalt oxide in the Dv50 range can give the positive electrode slurry excellent rheological properties, which can be evenly spread and partially embedded in the safety coating during the coating process, forming a stable physical anchoring structure after drying. At the same time, lithium cobalt oxide particles in this particle size range can build a stable skeleton network in the coating, effectively buffering the interfacial shear stress generated during battery cycling (especially the volume expansion of high silicon anode systems), thereby further enhancing the peel strength between the positive electrode active layer and the safety coating, and preventing the positive electrode active layer from falling off and shedding powder.

[0111] By way of example and not limitation, the Dv50 of lithium cobalt oxide is any value or a range of any two of the following: 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm.

[0112] In some embodiments, lithium cobalt oxide includes aluminum, with an aluminum content of 5000ppm-15000ppm based on the total mass of lithium cobalt oxide.

[0113] When lithium cobalt oxide includes aluminum, the high aluminum content doping can form a stable interface passivation layer on the surface of lithium cobalt oxide particles, thereby suppressing the oxidative decomposition side reaction of the electrolyte at the lithium cobalt oxide interface, thus reducing the erosion of the safety coating by byproducts and the interface delamination caused by gas generation.

[0114] By way of example and not limitation, the aluminum content, based on the total mass of lithium cobalt oxide, is any value or a range of any combination of 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 14000 ppm, 15000 ppm.

[0115] In some implementations, the aluminum content can be tested using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS).

[0116] In some embodiments, the positive electrode active layer further includes a conductive agent and a binder. Exemplarily, the conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0117] In some embodiments, the silicon-based material includes a silicon-carbon composite material, which includes a porous carbon matrix and silicon particles distributed in the internal channels of the porous carbon matrix. At least a portion of the surface of the porous carbon matrix includes an amorphous carbon layer, and the interior of the porous carbon matrix has a cavity structure with an aspect ratio of less than or equal to 5.

[0118] It should be noted that the silicon-carbon composite material in this invention is prepared by vapor deposition, in which silicon particles (silane gas is introduced into a fluidized bed reactor) are deposited into a porous carbon matrix (using methods well known to those skilled in the art). The preparation of hollow silicon-carbon differs from that of conventional silicon-carbon in that it is prepared on a porous carbon matrix: SiO2 microspheres, phenolic resin and K2CO3 are dispersed in ethanol at a certain mass ratio, and after thorough mixing at room temperature, the solvent is removed to obtain a solid powder. The obtained powder is then subjected to segmented treatment under a N2 atmosphere, first heated to 200°C and held, then heated to 700°C and held, and after cooling, the SiO2 template is removed by etching with HF solution to obtain a hollow porous carbon matrix.

[0119] The silicon-carbon composite material described in the above embodiments has a hollow cavity structure. When the aspect ratio of the cavity structure meets the above-mentioned range, the shape of the cavity structure is closer to a circle or a uniform ellipse, which can provide a uniform buffer space for the isotropic expansion of silicon. This effectively avoids excessive stress concentration in a specific direction (especially the longest diameter direction), thereby alleviating the compression of the positive electrode active layer by the silicon expansion of the negative electrode sheet, and further reducing the risk of the positive electrode active layer falling off the safety coating. However, when the aspect ratio is greater than 5, the buffer space of the cavity structure for silicon expansion in the shortest diameter direction is limited, which is not conducive to reducing the compression of the positive electrode active layer by the silicon negative electrode sheet.

[0120] By way of example and not limitation, the aspect ratio of the cavity structure is any value of 1, 2, 3, 4, 5, or any combination of both.

[0121] By way of example and not limitation, the longest diameter of the cavity structure is 0.5μm-20μm and the shortest diameter is 0.25μm-20μm.

[0122] In this invention, the longest or shortest diameter of the cavity structure can be obtained by analyzing cross-sectional electron microscope images combined with image analysis software. It should be noted that the longest diameter refers to the diameter in a given direction. For a selected direction, a pair of straight lines parallel to that direction are drawn so that they are exactly tangent to the target contour. The perpendicular distance between these two parallel tangent lines is the diameter in that direction. The maximum value among all measured values ​​in all directions is the longest diameter, which reflects the longest span of the target in the two-dimensional projection. Correspondingly, the minimum value among all measured values ​​in all directions is the shortest diameter, which reflects the shortest span of the target in the two-dimensional projection.

[0123] The method for measuring the longest / shortest diameter of a cavity structure includes: selecting any point on the edge of the cavity cross-section profile of a complete silicon-carbon particle in a cross-sectional SEM, drawing a straight line perpendicular to the tangent at that point to a second point on the other side of the cavity cross-section profile edge, and drawing a line parallel to the tangent at the first point at the second point. The perpendicular distance between these two parallel tangents is the diameter in that direction. The maximum value among all measured values ​​in all directions (at least 4 directions) is the longest diameter of the cavity, and the minimum value among all measured values ​​in all directions is the shortest diameter of the cavity.

[0124] In some implementations, see Figure 4 The positive current collector has at least one side surface including a first region 09 and a second region 10. The first region 09 includes a positive electrode coating, and the second region 10 does not have a positive electrode active layer.

[0125] The positive electrode generally includes a coated area of ​​the positive electrode active layer, namely the first region 09, and an uncoated area of ​​the positive electrode active layer, namely the second region 10. When the second region includes a safety coating, the first protrusion and the first depression in the safety coating can help the positive electrode to accommodate more electrolyte. As the electrolyte in the battery is gradually consumed during battery cycling, the electrolyte concentration in the first region decreases. Driven by the concentration gradient between the first and second regions, the electrolyte in the second region will migrate to the first region to replenish the electrolyte in the battery, thereby further ensuring the cycle life of the battery.

[0126] In some implementations, the positive electrode, separator, and negative electrode are stacked and wound in sequence to form a wound cell, with the second region located on the outermost ring of the wound cell.

[0127] In some embodiments, the wound battery cell further includes an electrolyte comprising a lithium salt and a solvent. The lithium salt serves as an ion source and can be a lithium salt known in the art for use in battery electrolytes. Exemplarily, the lithium salt can be lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium difluorophosphate (LiPF2O2), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium dioxoborate (LiBOB), lithium trifluoromethanesulfonate (LiTFS), lithium bis(malonic acid)borate (LiBMB), lithium difluorooxalate borate (LiDFOB), etc. The lithium borate (LiBDFMB), lithium borate (LiMOB), lithium borate (LiDFMOB), lithium tri(oxalate) phosphate (LiTOP), lithium tri(difluoromalonic acid) phosphate (LiTDFMP), lithium tetrafluorooxalate phosphate (LiTFOP), lithium difluorodioxalate phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (LiN(SO2F)(SO2CF3)), lithium nitrate (LiNO3), and lithium fluoride (LiF). For example, the organic solvent may be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0128] In some specific embodiments, the above-mentioned positive electrode sheet, separator and negative electrode sheet can be stacked in sequence and then wound to obtain a wound battery cell; the wound battery cell is placed in a battery packaging film shell (such as an aluminum-plastic film shell), electrolyte is injected into the outer packaging and sealed to prepare the battery of the present invention.

[0129] The present invention will be further described below with reference to specific embodiments:

[0130] Example 1

[0131] The battery fabrication steps in this example include:

[0132] Step 1: Preparing the positive electrode sheet

[0133] 1.1 Preparation of the positive electrode safety coating: The inorganic particles used were boehmite (Dv10 = 0.02µm, Dv50 = 0.09µm, Dv90 = 0.1µm, (Dv90-Dv10) / Dv50 = 0.9), and the binder was polyacrylic acid (PAA) with a weight-average molecular weight of 600,000 Da and a number-average molecular weight of 150,000 Da. Boehmite:conductive carbon black (SP):PAA = 95:4:1 were weighed by mass and dispersed in deionized water. After stirring, a safety coating slurry was obtained. This slurry was applied to both surfaces of the current collector aluminum foil using a gravure coating process. During the coating process, a first protrusion and a first depression were created. The average height of the first protrusion was 2μm, and the number of first protrusions was 10 per 10,000μm. 2 The average difference between the height of the first protrusion and the depth of the first concave part is 0.5 μm.

[0134] 1.2 Preparation of the positive electrode active layer: Lithium cobalt oxide (LCO): conductive carbon black (SP): polyvinylidene fluoride (PVDF) in a mass ratio of 97.5:1:1.5 was weighed and dispersed in the solvent N-methylpyrrolidone (NMP). After stirring and mixing evenly, the slurry was coated onto the surface of the safety coating away from the aluminum foil. The positive electrode sheet was then obtained through drying, rolling, and die-cutting. The lithium cobalt oxide had a Dv50 of 8 μm and an aluminum content of 5000 ppm.

[0135] Step 2: Preparation of the negative electrode sheet

[0136] Graphite, CVD silicon carbide (sphericity greater than 0.95), conductive carbon black (Super P), and a negative electrode binder mixture were weighed in a weight ratio of 91:7:1:1. The negative electrode binder mixture included sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber in a 1:1 mass ratio. These raw materials were mixed in an aqueous solvent and continuously stirred under the action of a mixer to form a homogeneous, flowing negative electrode slurry. Subsequently, the slurry was coated onto both sides of a 10μm thick current collector copper foil, and then successively dried, rolled, and die-cut to obtain the desired negative electrode sheet.

[0137] Step 3: Preparing the diaphragm

[0138] 3.1 Preparation of heat-resistant layer: 95 parts by weight of alumina and 5 parts by weight of the first binder (polyacrylic acid) are mixed in water and stirred thoroughly to obtain a slurry with a solid content of 25%. The slurry is coated onto one side of a substrate layer (polyethylene) with a thickness of 5 μm and a porosity of 40% by a gravure roller. After drying in a multi-section oven at 60°C, a heat-resistant coating is formed with a thickness of 2 μm.

[0139] 3.2 Preparation of the polymer layer: PVDF and N,N-dimethylacetamide (DMAC) were mixed and thoroughly stirred until dissolved. Alumina (Dv50 of 600 nm) and the first polymer were then added and stirred until uniformly dispersed to obtain a mixed slurry with a solid content of 8%. The mixed slurry was coated onto the surface of the heat-resistant layer using a gravure roller and then dried in a multi-section oven at 60°C to form the polymer layer. The height of the second protrusion was 5 μm, the average particle size of the second protrusion was 1 μm, and the number of second protrusions with an average particle size greater than or equal to 3 μm was 30 per 10000 μm. 2 The first polymer is formed by copolymerization of styrene, acrylonitrile and acrylate monomers.

[0140] PVDF and DMAC are mixed and thoroughly stirred to dissolve. Then, alumina (Dv50 is 600nm) is added and stirred to disperse evenly to obtain a mixed slurry with a solid content of 8%. The mixed slurry is coated on the other side of the substrate layer using a gravure roller. In 100 parts by weight of the mixed slurry, the contents of PVDF and alumina are 0.4 parts by weight and 0.6 parts by weight, respectively.

[0141] Step 4: Preparation of electrolyte

[0142] In an argon-filled glove box (moisture < 1 ppm, oxygen < 1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed thoroughly at a volume ratio of 1:::3:4 to obtain an organic solvent. Then, 14% lithium hexafluorophosphate (based on the total mass of the electrolyte), 15% fluoroethylene carbonate (FEC) (based on the total mass of the electrolyte), and 2.5% succinate (based on the total mass of the electrolyte) were added to the organic solvent. After thorough mixing, and after passing moisture and free acid tests, the desired electrolyte was obtained.

[0143] Step 5: Preparation of Lithium-ion Batteries

[0144] The positive electrode sheet from step one, the negative electrode sheet from step two, and the separator from step three are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step four is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0145] Some parameters of the lithium-ion battery in this example are shown in Table 1.

[0146] Example 2

[0147] The battery preparation method is basically the same as that in Example 1. The dimensions and number of the first protrusions and concave parts are controlled by using a gravure roller with consistent slurry solid content, number of engraved grooves, and depth. Specifically, the difference lies in the use of boehmite (Dv10 = 1µm, Dv50 = 4.8µm, Dv90 = 7.8µm, (Dv90-Dv10) / Dv50 = 1.42) as the inorganic particles used in the safety coating preparation. The mass ratio of boehmite:conductive carbon black (SP):PAA = 85:5:10 is used to prepare the safety coating slurry. The remaining steps are the same as in 1.1 of Example 1. The average height of the first protrusion is 12μm, and the number of first protrusions is 360 per 10000μm. 2 The average difference between the height of the first protrusion and the depth of the first concave part is 5 μm;

[0148] In the process of preparing the positive electrode, lithium cobalt oxide with Dv50=10μm and aluminum content of 10000ppm was used, and the remaining steps were the same as in 1.2 of Example 1.

[0149] In the membrane preparation step, the solid content, agglomeration degree, or coating amount of the first polymer in the mixed slurry in step 3.2 are adjusted. Specifically, the height of the second protrusion is 4 μm, the average particle size of the second protrusion is 10 μm, and the number of second protrusion particles with an average particle size greater than or equal to 3 μm is 350 per 10000 μm. 2 .

[0150] Example 3

[0151] The battery preparation method is basically the same as that in Example 1. The dimensions and number of the first protrusions and concave parts are controlled by using a gravure roller with consistent slurry solid content, number of engraved grooves, and depth. Specifically, the difference lies in the use of boehmite (Dv10 = 2µm, Dv50 = 1.5µm, Dv90 = 8µm, (Dv90-Dv10) / Dv50 = 4) as the inorganic particles used in the preparation of the safety coating. The mass ratio of boehmite:conductive carbon black (SP):PAA = 68:2:30 is used to prepare the safety coating slurry. The remaining steps are the same as in 1.1 of Example 1. The average height of the first protrusion is 13.5μm, and the number of first protrusions is 786 per 10000μm. 2 The average difference between the height of the first protrusion and the depth of the first concave part is 20 μm;

[0152] In the process of preparing the positive electrode, lithium cobalt oxide with Dv50=25μm and aluminum content of 15000ppm was used, and the remaining steps were the same as in 1.2 of Example 1.

[0153] In the membrane preparation step, the solid content, agglomeration degree, or coating amount of the first polymer in the mixed slurry in step 3.2 are adjusted. Specifically, the height of the second protrusion is 3 μm, the average particle size of the second protrusion is 20 μm, and the number of second protrusion particles with an average particle size greater than or equal to 3 μm is 980 per 10000 μm. 2 .

[0154] The preparation methods of Examples 4-13 are the same as those of Example 1, except that the first protrusion is changed by adjusting the solid content of the slurry and the number and depth of the engraved grooves of the gravure roller. The height of the second protrusion is adjusted by changing the solid content, agglomeration degree or coating amount of the first polymer of the mixed slurry in step 2.2, so as to explore the influence of A / B on battery performance. The specific parameter changes are shown in Table 1.

[0155] The preparation method of Example 14 is the same as that of Example 1, except that the negative electrode is prepared by replacing CVD silicon carbon with hollow silicon carbon, wherein the aspect ratio of the cavity structure of the hollow silicon carbon is 5.

[0156] The preparation method of Example 15 is the same as that of Example 1, except that the negative electrode is prepared by replacing CVD silicon carbon with hollow silicon carbon, wherein the aspect ratio of the cavity structure of the hollow silicon carbon is 6.

[0157] Comparative Example 1

[0158] The battery preparation method is basically the same as that in Example 1, except that in step 3.2 of the separator preparation, the first polymer is not added, that is, the prepared separator does not have a second protrusion.

[0159] Comparative Examples 2-3

[0160] The battery preparation method is basically the same as that in Example 1, except that the parameters shown in Table 1 are changed. The size and number of the first protrusion and the first concave are controlled by engraving a gravure roller with the same number and depth of grooves. The size and number of the second protrusion are controlled by changing the solid content, agglomeration degree or coating amount of the first polymer in the mixed slurry in step 3.2. The specific parameter changes are shown in Table 1.

[0161] Test case

[0162] 1. Needle prick test

[0163] The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were discharged to 3.0V at 1C at room temperature, and then charged to 4.5V at a constant current of 1.5C with a cutoff current of 0.02C. This cycle was repeated 5 times. Within 48 hours after the cycle was completed, a steel needle with a diameter of 4mm was used to vertically penetrate the left, middle and right positions of the lithium-ion battery at a speed of 30mm / s. If the battery did not catch fire or explode within 5 minutes, it was considered to have passed the test. 15 batteries were tested in each group, denoted by N. The battery that passed the needle penetration test was recorded as n. "n / N" means that n out of the 15 batteries tested passed the needle penetration test.

[0164] 2. K-value test

[0165] At 25℃±2℃, discharge to the lower limit voltage at 0.2C, charge to 50% SOC at 0.7C, and then place at a high temperature of 45℃±3℃ for 2 days. Then place at room temperature of 25℃±3℃ for 2 days. Measure the voltage with a voltmeter and record it as V1 (mV). Record the test time as T1. Place at room temperature of 25℃±3℃ for 3 days and measure the voltage V2 with a voltmeter. Record the test time as T2. The formula for calculating the K value is K=V1-V2 / (T2-T1), with the unit being mV / H.

[0166] The test results are shown in Table 1.

[0167] Table 1:

[0168]

[0169] As shown in Table 1, compared with Comparative Examples 1-3, Examples 1-15, by setting a first protrusion and a first concave portion on the surface of the safety coating away from the positive electrode current collector, and setting a second protrusion on the surface of the separator, and further adjusting the average height A of the first protrusion and the average height B of the second protrusion to satisfy: 0.4≤A / B≤4.5, can effectively improve the safety and cycle stability of the battery. Specifically, this is reflected in the improved pass rate of the battery's nail penetration test and the lower K value.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The device includes a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector. The negative active layer includes a silicon-based material, and the silicon content is 2%-50% based on the total mass of the negative active layer. The positive electrode sheet includes a positive current collector and a positive electrode coating disposed on at least one side surface of the positive current collector; the positive electrode coating includes a positive active layer and a safety coating stacked together, the safety coating is disposed between the positive current collector and the positive active layer, the safety coating includes a first material and an adhesive, and the safety coating includes a plurality of first protrusions and a plurality of first recesses on the surface away from the positive current collector; The separator includes a carrier layer and a polymer layer located on at least one side surface of the carrier layer, wherein the polymer layer includes a plurality of second protrusions formed of a first polymer on the surface away from the carrier layer, the second protrusions facing the positive electrode sheet; The first protrusion and the second protrusion satisfy the following relationship: 0.4 ≤ A / B ≤ 4.

5. Where A is the average height of the first protrusion in μm, and B is the average height of the second protrusion in μm.

2. The battery according to claim 1, characterized in that, The A satisfies: 1μm≤A≤15μm, preferably 2μm≤A≤10μm; And / or, the B satisfies: 0.5μm≤B≤15μm, preferably 2μm≤B≤10μm.

3. The battery according to claim 1 or 2, characterized in that, The second protrusion is at least partially embedded in the polymer layer, and / or the second protrusion is located on the surface of the polymer layer; And / or, the second protrusion includes a plurality of second sub-protrusions, the diameter of the second sub-protrusions being greater than or equal to 3 μm, and the number of second sub-protrusions within the orthographically projected area of ​​the surface of the polymer layer on which the second protrusion is located is (30-1000) per 10000 μm. 2 Preferably, there are (60-500) per 10000μm 2 ; And / or, based on the orthographic projection area of ​​the surface on which the first protrusion is provided in the safety coating, the number of the first protrusions within the orthographic projection area is (10-800) per 10000 μm. 2 .

4. The battery according to any one of claims 1-3, characterized in that, The average difference between the height of the first protrusion and the depth of the first concave part is C, and C satisfies: 0.5μm≤C≤14.5μm.

5. The battery according to any one of claims 1-4, characterized in that, The second protrusion comprises primary particles and / or secondary agglomerated particles, and the average diameter of the second protrusion is 1-20 μm. And / or, the first material comprises inorganic particles, the particle size distribution of which satisfies: 0.01 ≤ (Dv90 - Dv10) / Dv50 ≤ 4, preferably 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 3. And / or, 0.02μm≤Dv10≤2μm; And / or, 0.05μm≤Dv50≤5μm; And / or, 0.1μm≤Dv90≤8μm.

6. The battery according to any one of claims 1-5, characterized in that, The first material includes at least one of metal oxides, metal hydroxides, metal carbides, metal nitrides and metal borides. Preferably, the first material includes at least one of alumina, boehmite, silicon dioxide, titanium dioxide and zirconium oxide. More preferably, it includes boehmite. And / or, the adhesive comprises a polymer and / or a polymer-based metal salt; preferably, the polymer comprises at least one polymer selected from polyacrylic acid, polybutyl acrylate, polyethyl acrylate, polyhydroxyethyl acrylate, and polyacrylamide, and / or, the polymer-based metal salt comprises at least one selected from polyacrylate, polybutyl acrylate salt, polyethyl acrylate salt, polyhydroxyethyl acrylate salt, and polyacrylamide salt; more preferably, the polymer-based metal salt comprises at least one selected from polymer-based lithium salt, polymer-based sodium salt, and polymer-based zinc salt. And / or, based on the quality of the safety coating, the mass percentage of the adhesive is W, where W satisfies: 1wt%≤W≤30wt%, preferably 3wt%≤W≤20wt%; And / or, the weight-average molecular weight of the adhesive in the safety coating is Mw, and Mw satisfies: 100,000 Da ≤ Mw ≤ 1,500,000 Da, preferably 300,000 Da ≤ Mw ≤ 800,000 Da; And / or, the number average molecular weight of the adhesive in the safety coating is Mn, where Mn satisfies: 40000 Da≤Mn≤600000 Da, preferably 80000 Da≤Mn≤300000 Da.

7. The battery according to any one of claims 1-6, characterized in that, The first polymer includes fluorinated polymers and / or non-fluorinated polymers; Preferably, the fluoropolymer includes one or more fluoropolymers formed by the polymerization of vinylidene fluoride, tetrafluoroethylene, and hexafluoroethylene. Preferably, the non-fluorinated polymer includes one or more of styrene, ethylene, propylene, acrylonitrile, methyl methacrylate, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, amides, and imides to form a non-fluorinated polymer.

8. The battery according to any one of claims 1-7, characterized in that, The positive electrode active layer includes a positive electrode active material, which includes lithium cobalt oxide, and the Dv50 of the lithium cobalt oxide is 8μm-25μm; Preferably, the lithium cobalt oxide includes aluminum, and the aluminum content is 5000ppm-15000ppm based on the total mass of the lithium cobalt oxide.

9. The battery according to any one of claims 1-8, characterized in that, The silicon-based material includes a silicon-carbon composite material, which includes a porous carbon matrix and silicon particles distributed in the internal channels of the porous carbon matrix. At least a portion of the surface of the porous carbon matrix includes an amorphous carbon layer, and the interior of the porous carbon matrix has a cavity structure with an aspect ratio of less than or equal to 5.

10. The battery according to any one of claims 1-9, characterized in that, The positive current collector has at least one side surface including a first region and a second region, the first region including the positive electrode coating, and the second region not having the positive electrode active layer; Preferably, the positive electrode, the separator, and the negative electrode are stacked and wound in sequence to form a wound battery cell, and the second region is located at the outermost ring of the wound battery cell.

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