Electrochemical device
By setting a striped ceramic layer and optimizing the proportion of silicon-based materials in lithium-ion batteries, the structural collapse and insufficient depth of discharge caused by the volume expansion of silicon-based anodes are solved, thereby improving the charge and discharge efficiency and low-temperature cycle performance of the batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHUHAI COSMX BATTERY CO LTD
- Filing Date
- 2024-12-20
- Publication Date
- 2026-06-23
AI Technical Summary
Existing lithium-ion batteries suffer from structural collapse and insufficient depth of discharge due to the volume expansion of the silicon-based anode during charging and discharging, making it difficult to meet the requirements for high power and long-term discharge.
By setting a striped ceramic layer on the separator and controlling the silicon content of the negative electrode, the proportion of silicon-based materials used is optimized, which improves the migration rate of lithium ions and the flexibility of the separator, provides a fast lithium ion migration channel and alleviates volume expansion.
It improves the charge and discharge efficiency of lithium-ion batteries, reduces the minimum remaining capacity level, enhances the usable depth of discharge and low-temperature cycle performance, and solves the structural problems caused by volume expansion.
Smart Images
Figure CN122267435A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of electrochemical devices, and more specifically to an electrochemical device. Background Technology
[0002] Lithium-ion batteries are widely used in 3C consumer products, electric vehicles, and other applications. As market competition intensifies, battery technology continues to evolve towards larger capacities and higher charging power. Silicon (Si) is considered one of the most promising anode materials due to its high theoretical specific capacity; the theoretical specific capacity of fully lithiated Si can reach 4200 mAh / g (approximately 10 times that of graphite). However, because the lithium storage mechanism of silicon-based anodes is an alloying reaction, silicon materials undergo significant volume expansion during lithiation. During battery charge-discharge cycles, repeated volume changes can lead to structural collapse of the electrode material. Furthermore, lithium-ion rechargeable batteries often encounter insufficient depth of discharge when facing high-rate discharge demands, limiting their performance in certain applications.
[0003] Therefore, how to alleviate volume expansion and insufficient depth of discharge in order to meet people's growing demand for high-power and long-term discharge of battery systems is an urgent problem to be solved. Summary of the Invention
[0004] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide an electrochemical device that effectively alleviates the volume expansion caused by the silicon anode by controlling the stripe ratio in the ceramic layer on the separator and the silicon content of the anode, thereby improving the charge and discharge efficiency, reducing the minimum remaining charge (SOC) level that can be effectively discharged, and improving the usable depth of discharge.
[0005] To achieve the above objectives, the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The negative electrode comprises a negative current collector and a negative active layer located on at least one side surface of the negative current collector. The negative active layer comprises a negative active material, which is a silicon-based material. The separator comprises a base film and a ceramic layer disposed on at least one side surface of the base film. The ceramic layer comprises a plurality of spaced stripes and a plurality of spacer regions located between adjacent stripes. The width of the stripes is A1 μm, and the width of the spacer regions is A2 μm.
[0006] The electrochemical device satisfies the relationship 0.06≤A×C≤0.9.
[0007] Where A is A1 / A2 and C is the mass content of silicon in the negative electrode active material.
[0008] The present invention, by adopting the above technical solution, has the following beneficial effects:
[0009] In the electrochemical device of the present invention, the striped ceramic coating increases the specific surface area of the ceramic layer, enhances the wettability and electrolyte retention of the separator, and helps to improve the migration rate of lithium ions. The addition of high-energy-density silicon-based material to the negative electrode provides a fast channel for lithium ion migration during charging, thereby improving the charge and discharge speed and performance of the electrochemical device. In this case, by doping the separator with the striped ceramic coating and the negative electrode with silicon and making them satisfy the above-mentioned relationship, the migration rate of active ions can be further improved, the charge and discharge capability of the electrochemical device can be improved, the minimum SOC level for effective discharge can be reduced, the usable depth of discharge of the electrochemical device can be improved, and its low-temperature charge and discharge performance and low-temperature cycle performance can be enhanced.
[0010] In addition, the striped ceramic coating increases the flexibility of the separator, providing space for the extension of the positive electrode and the expansion of the negative electrode. This alleviates the uneven lithium insertion and delithiation of the active material caused by the stretching of the positive electrode due to silicon expansion, and provides an effective solution to improve the usable discharge depth of the battery.
[0011] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values close to those ranges or values. For numerical ranges, endpoint values of various ranges, endpoint values of 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. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description
[0012] Figure 1 The diagram shown is a structural schematic of a diaphragm according to the present invention.
[0013] Figure 2 The diagram shown is a structural schematic of a diaphragm according to the present invention.
[0014] Explanation of reference numerals in the attached figures
[0015] 11. Base film; 12. Ceramic layer; 13. Adhesive coating layer. Detailed Implementation
[0016] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0017] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.
[0018] The first aspect of the present invention provides an electrochemical device, the electrochemical device comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes, the negative electrode comprising a negative current collector and a negative active layer located on at least one side surface of the negative current collector, the negative active layer comprising a negative active material, the negative active material comprising a silicon-based material; the separator comprising a base film and a ceramic layer disposed on at least one side surface of the base film, the ceramic layer comprising a plurality of spaced stripes and a plurality of spacer regions located between adjacent stripes, the width of the stripes being A1 μm, and the width of the spacer regions being A2 μm;
[0019] The electrochemical device satisfies the relationship 0.06 ≤ A × C ≤ 0.9 (e.g., 0.06, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9).
[0020] Where A is A1 / A2 and C is the mass content of silicon in the negative electrode active material.
[0021] In the electrochemical device of this invention, the striped ceramic coating increases the specific surface area of the ceramic layer, enhancing the wettability, electrolyte retention, and heat resistance of the separator, thus contributing to improved lithium-ion migration rate. The striped ceramic coating also increases the material's flexibility, providing space for the extension of the positive electrode and the expansion of the negative electrode, mitigating the problem of reduced battery depth of discharge due to uneven lithium insertion and extraction caused by the tensile stress on the positive electrode caused by silicon expansion. Adding high-energy-density silicon-based materials to the negative electrode provides a rapid pathway for lithium-ion migration during charging, thereby improving the charge / discharge speed and performance of the electrochemical device. In this case, by coating the ceramic layer separator with stripes and doping the negative electrode with silicon to satisfy the above relationship, the reasonable combination of stripe ratio and silicon-doped negative electrode sheet can improve the problem of uneven lithium insertion / extraction rates of positive and negative electrode active materials caused by expansion. This can further improve the migration rate of active ions, effectively improve the charge / discharge efficiency of the electrochemical device, improve the charge / discharge capability of the electrochemical device, reduce the minimum SOC level for effective discharge, improve the usable depth of discharge of the electrochemical device, increase the performance and reliability of the electrochemical device under high-rate operating conditions, and also improve its low-temperature charge / discharge performance and low-temperature cycle performance. If A×C<0.06, then the stripe spacing width of the ceramic layer is too large or the silicon doping content of the negative electrode sheet is too low. The former leads to poor heat resistance and easily results in poor thermal safety performance of the electrochemical device, while the latter is not conducive to improving the charge / discharge speed of lithium-ion batteries and has no significant improvement on charge / discharge performance. When A×C>0.9, the silicon doping content of the negative electrode is too high, or the stripe spacing width of the ceramic layer is too small. The former will affect the thickness expansion during the lithium-ion battery cycle test, causing the active layer of the positive and negative electrodes to be stretched by force, resulting in uneven stress in the active layer and uneven lithium insertion and delithiation rates of the active particles, leading to a worse usable depth of discharge. The latter will result in fewer ion transport channels and electrolyte storage space, which is not conducive to improving cycle performance.
[0022] In one embodiment, A is 1.2 to 10, for example, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10. When A is within this range, the spacer region of the ceramic layer provides more ion transport channels and electrolyte storage space, effectively improving the migration rate of active ions. When A is too small, it will adversely affect the heat resistance of the electrochemical device, thereby threatening the thermal safety performance of the electrochemical device; if A is too large, there will be fewer ion transport channels and electrolyte storage space available, thereby affecting the charge and discharge performance of the electrochemical device.
[0023] In one embodiment, C is 3% to 20%, for example, 3%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, and 20%. When C is in the range of 3% to 20% and 0.06 ≤ A × C ≤ 0.9, a reasonable combination of stripe ratio and silicon content can further improve the charge and discharge efficiency of the electrochemical device, reduce the minimum SOC level for effective discharge, and improve the usable depth of discharge of the electrochemical device.
[0024] Those skilled in the art can select the width of the stripes and the width of the spacing regions based on the structure of different electrochemical devices and the base membrane of different materials. In one embodiment, A1 is 25–100, for example, 25, 30, 40, 50, 60, 70, 80, 90, or 100. In one embodiment, A2 is 5–25, for example, 5, 10, 15, 20, or 25. There are no particular requirements for the direction of the stripes; they can be parallel to the length direction of the membrane, perpendicular to the length direction of the membrane, or at a certain angle to the length direction of the membrane.
[0025] In one embodiment, the ratio B of the thickness H of the stripes in the ceramic layer of the separator to the width A2 of the spacer region is 0.025 to 1.5, for example, 0.025, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, or 1.5. When B is within this range, the lithium-ion conductivity can be improved, and the flexibility of the separator can also be improved, providing space for the extension of the positive electrode and the expansion of the negative electrode. On the one hand, this alleviates the uneven lithium insertion and delithiation of the active material caused by the tensile stress on the positive electrode due to silicon expansion, thus improving the usable discharge depth of the electrochemical device. On the other hand, it alleviates the fracture caused by the pressure on the positive electrode due to silicon expansion, providing an effective solution to the problem of aluminum foil breakage in the positive electrode.
[0026] In one embodiment, the thickness H of the stripes in the ceramic layer of the diaphragm is 0.5 μm to 5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. In this invention, the thickness of the spacer region can be 0.
[0027] In one embodiment, the areal density m of the ceramic layer t 2-4 g / m 2 For example, 2g / m 2 2.5g / m 2 3g / m 2 3.5g / m 2 4g / m 2 .
[0028] In one embodiment, the ceramic layer comprises 40 wt% to 96 wt% (e.g., 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 96 wt%) of ceramic material, 3 wt% to 60 wt% (e.g., 3 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%) of binder, and optionally 0.7 wt% to 3 wt% (e.g., 0.7 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%) of dispersant.
[0029] In one embodiment, the ceramic material includes at least one selected from 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 binder and dispersant can be materials conventional in the art. For example, the binder may include, but is not limited to, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymers (such as polymethyl methacrylate), polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene, or polyhexafluoropropylene. The dispersant may include, but is not limited to, at least one selected from ethylene oxide and polyvinylpyrrolidone.
[0030] In one embodiment, the particle size Dv50 of the ceramic material is 0.1 μm to 2.5 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or 2.5 μm. It is understood that the particle sizes of the ceramic material can be the same or different. When the particle size of the ceramic material is within this range, the electrolyte storage capacity of the separator and the lithium-ion migration rate can be further improved, thereby enhancing the charge and discharge performance of the battery.
[0031] Dv50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% in a sample, which can be determined by a particle size analyzer.
[0032] In one embodiment, the thickness of the base film is 4μm to 20μm, for example, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, or 20μm.
[0033] In one embodiment, the base film is a woven film, a nonwoven film, a polyolefin film, or a separator paper.
[0034] In one embodiment, the polyolefin film is made of at least one of polyethylene and polypropylene.
[0035] In one embodiment, the elongation at break in the transverse direction (TD) of the base membrane is 20% to 200%, for example, 20%, 40%, 60%, 80%, 100%, 120%, 140%, 160%, 180%, and 200%. The testing method involves preparing a 15mm wide sample of the base membrane along the TD direction. The initial distance between the clamps of the tensile testing machine is set to 50mm, and the test is conducted at a tensile speed of 100mm / min until the diaphragm breaks. The distance between the clamps at the point of breakage is recorded as L. TD mm, then the elongation at break in the TD direction = (L TD -50) / 50×100%.
[0036] In one embodiment, the elongation at break in the machine direction (MD) of the base membrane is 50%–300%, for example, 50%, 100%, 150%, 200%, 250%, and 300%. The testing method involves preparing a 15mm wide sample of the base membrane along the MD direction. The initial distance between the clamps of the tensile testing machine is set to 50mm, and the test is conducted at a tensile speed of 100mm / min until the diaphragm breaks. The distance between the clamps at the point of breakage is recorded as L. MD mm, then the elongation at break in the MD direction = (L TD -50) / 50×100%.
[0037] In one embodiment, the puncture strength of the base membrane is 100gf to 600gf, for example, 100gf, 200gf, 300gf, 400gf, 500gf, and 600gf. The test method is to lay the base membrane flat in a fixture and clamp it, and take a puncture needle with Φ = 1.0mm and a spherical tip R = 0.5mm to puncture the membrane surface perpendicularly at a speed of 100mm / min until the membrane is punctured. The maximum value of the puncture force is recorded, which is the puncture strength of the membrane.
[0038] In one embodiment, the peel strength between the ceramic layer and the base film is 30–200 N / m, for example, 30 N / m, 50 N / m, 100 N / m, 150 N / m, or 200 N / m. Test method: Take a stainless steel plate of a certain size, attach double-sided tape to the center, and peel off the paper layer; take a sample coated with a separator, and attach the substrate side to the upper surface of the double-sided tape; take a 15 mm wide 3M release adhesive, with the adhesive layer tightly against the coating layer; use a roller to roll naturally back and forth on the 3M release adhesive to ensure uniform adhesive distribution; use a 180° peel method and a tensile testing machine to test the peel force of the coating. The peel strength is then calculated as peel force / width of the release adhesive.
[0039] In one embodiment, the diaphragm further includes an adhesive layer located on the surface of the base film and / or the surface of the ceramic layer. That is, an adhesive layer may be provided on one or both surfaces of the base film. For example, Figure 1 As shown, when the base film 11 includes a one-sided adhesive coating layer 13, this adhesive coating layer 13 can be disposed on the surface of the base film 11 away from the ceramic layer 12. Of course, if the separator includes a one-sided adhesive coating layer, the adhesive coating layer can also be disposed on the surface of the ceramic layer. Figure 2 As shown, when adhesive layers 13 are simultaneously provided on both sides of the base film 11, one side of the adhesive layer 13 is located on the surface of the base film 11 away from the ceramic layer 12, and the other side is located on the surface of the ceramic layer 12. If the ceramic layer in the diaphragm is distributed on both sides of the base film, the adhesive layer is provided on both sides of the ceramic layer. The areal density of the coating on both sides of the base film can be the same or different.
[0040] In one embodiment, the electrochemical device satisfies: Δm / D Si ≤0.2, for example, 0.01, 0.05, 0.1, 0.15, 0.2, where Δm is the difference in surface density of the coating on both sides of the base film, in g / m³. 2 Silicon in silicon-based materials exists in the form of silicon particles, D Si Δm / D represents the average particle size of silicon particles, in nm. Si Within this range, the membrane and the negative electrode can have suitable adhesion and hardness, which can suppress the volume expansion caused by silicon expansion, shorten the lithium-ion transport path, effectively improve the low-temperature cycle performance of the electrochemical device and the minimum SOC level that can effectively discharge at low temperatures.
[0041] The average particle size of silicon particles can be observed using a transmission electron microscope (TEM), and the size of the silicon particles can be labeled. The average particle size of 50 silicon particles can be calculated.
[0042] In one embodiment, the difference in surface density of the coating on both sides of the base film is less than or equal to 4 g / m². 2 For example, 0g / m 2 0.5g / m 2 1g / m 2 1.5g / m 2 2g / m 2 2.5g / m 2 3g / m 2 3.5g / m 2 4g / m 2 When the electrochemical device satisfies: Δm / D Si ≤0.2, and the difference in surface density is controlled to not exceed 4g / m³. 2Within this range, the adhesion and hardness between the separator and the negative electrode are optimal, suppressing the thickness change of the electrochemical device caused by silicon expansion, shortening the lithium-ion transport path, effectively improving the thickness expansion and lithium plating problems of lithium-ion batteries during use, and enhancing the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device. However, when Δm exceeds this range, it will hinder ion transport efficiency and affect the charge-discharge capability of the electrochemical device.
[0043] In one embodiment, silicon in the silicon-based material exists in the form of silicon particles, and the average particle size of the silicon particles is 10 nm to 50 nm. When the electrochemical device satisfies: Δm / D Si With a silicon particle size ≤0.2 mm and an appropriate particle size, smaller silicon particles can provide a larger specific surface area, increasing the electrolyte storage space and ion transport channels. This can significantly improve ion conduction efficiency, charge / discharge rate, and cycle life, ensuring excellent cycle performance of the electrochemical device even at low temperatures and reducing the minimum state of charge (SOC) required for effective discharge at low temperatures. However, excessively small particle sizes can increase the mechanical stress between particles within the negative electrode, potentially leading to structural damage and capacity decay in the electrochemical device. Excessively large silicon particles reduce the electrolyte storage capacity, negatively impacting charge / discharge rate and cycle life.
[0044] In one embodiment, the adhesive layer comprises polymer particles.
[0045] In one embodiment, the average particle size of the polymer particles is 0.2 μm to 5 μm. Excessively large polymer particles can lead to uneven adhesion between the separator and the electrode, easily worsening the thickness expansion during cell cycling. Conversely, excessively small polymer particles, after immersion in the electrolyte, swell due to the infiltration of small-molecule solvents, causing some molecular chains to break down, thus reducing their adhesiveness. This results in reduced adhesion between the separator and both the positive and negative electrodes, affecting the cell's expansion control and cycling performance during cycling.
[0046] The average particle size of the polymer particles was determined as follows: The surface of the porous layer was observed at 50,000x magnification using an electrolytic radiometric scanning electron microscope (Hitachi, Ltd. S-3400N). The image size was 2.5 μm × 1.8 μm. It should be noted that the pixel count was 1,280 pixels × 960 pixels, and the size of one pixel was 2 nm × 1.9 nm. For the average particle size, the smallest square or rectangle completely surrounding each particle was drawn on the obtained image; that is, the square or rectangle whose ends meet the four sides of the square or rectangle. In the case of a square, the length of one side was taken as the particle size; in the case of a rectangle, the length of the longest side (major axis diameter) was taken as the particle size. For any 81 particles, their individual particle sizes were measured, and the average of these measurements was taken as the average particle size. It should be noted that when more than 81 particles are observed in the captured image, the average number of any 81 particle sizes in the image is taken as the average particle size. When no 81 particles are observed in the image, multiple images are captured, and the average number of a total of 81 particle sizes is taken as the average particle size.
[0047] The polymer may be a polymer conventionally used in the art, such as including but not limited to polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, acrylate copolymers (e.g., polymethyl methacrylate), polyolefins (e.g., polyethylene, polypropylene), polyacrylonitrile, polyethylene oxide, copolymers of fluoroolefin monomers (e.g., vinylidene fluoride-chlorotrifluoroethylene copolymer), copolymers of fluoroolefin monomer units and olefin monomer units (e.g., vinylidene fluoride-ethylene copolymer), copolymers of fluoroolefin monomer units and acrylic monomer units (e.g., vinylidene fluoride-acrylic acid copolymer), styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.
[0048] In one embodiment, the positive electrode includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector; Y is defined as min < the TD-direction elongation of the positive current collector and the MD-direction elongation of the positive current collector>, where Y satisfies: 0.3 ≤ B / Y ≤ 10, for example, 0.3, 0.5, 1, 2, 4, 6, 8, 10. When B / Y < 0.3, it will lead to deviations in the thermal safety performance of the electrochemical device; while when B / Y > 10, it is prone to causing the positive electrode to break off.
[0049] Wherein, min<lateral (TD) elongation of positive electrode current collector and longitudinal (MD) elongation of positive electrode current collector> refers to the smaller value between the TD elongation of positive electrode current collector and the MD elongation of positive electrode current collector.
[0050] When B is in the range of 0.025 to 1.5 and B / Y is between 0.3 and 10, it can effectively provide space for the extension of the electrode. On the one hand, it can alleviate the uneven lithium insertion and delithiation of the active material caused by the stretching of the positive electrode due to silicon expansion, thus improving the usable discharge depth of the electrochemical device. On the other hand, it can effectively improve the problem of positive electrode band breakage, which is conducive to the long-term stable operation of the electrochemical device.
[0051] In this invention, elongation = (length of the current collector at tensile fracture - original length) / original length × 100%. The TD direction elongation or MD direction elongation refers to the elongation along the TD or MD direction, respectively. The elongation test method is as follows: The current collector is cut into rectangular strips with a width of 15mm and a length greater than 50mm. The extension direction of the long side of the strip is consistent with the length direction of the current collector, ensuring smooth edges without gaps (to prevent defects from affecting the test results). The strip is clamped between the upper and lower clamps of a universal tensile testing machine, with the long axis of the strip coinciding with the center line of the clamps. The distance between the upper and lower clamps of the tensile testing machine is a specified distance for the current collector, and the specified distance along the length direction of the current collector is 50mm. At a tensile test speed of 10mm / min, the strip is stretched along its length direction until the current collector breaks, obtaining the dimension along the length direction of the current collector, and calculating the elongation along the length direction of the current collector.
[0052] In one embodiment, Y is 2% to 8%, for example, 2%, 3%, 4%, 5%, 6%, 7%, or 8%. When Y is within this range, it is beneficial to improve the problem of positive electrode band breakage.
[0053] In some embodiments, the positive current collector can be a positive current collector conventionally used in the art, such as an aluminum foil or a composite current collector.
[0054] The positive electrode active layer is not particularly limited, and may include components such as positive electrode active material, conductive agent, and binder according to conventional compositions in the art. The positive electrode active material, conductive agent, and binder can all be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide; the conductive agent may be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene; and the binder may be selected from one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.
[0055] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% positive electrode active material, 0.1-10 wt% conductive agent, and 0.1-10 wt% binder.
[0056] In some embodiments, the mass percentage of each component in the positive electrode active material layer is as follows: 90 - 99.6 wt% of positive electrode active material, 0.2 - 5 wt% of conductive agent, and 0.2 - 5 wt% of binder.
[0057] In one embodiment, the silicon-based material includes at least one of elemental silicon, silicon oxide compound (SiO x , where 0 < x < 2), silicon-carbon material, silicon-nitrogen material, silicon alloy (such as silicon-magnesium alloy, silicon-lithium alloy, etc.).
[0058] In some embodiments, the negative electrode active material further contains a carbon-based material, and the carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.
[0059] In some embodiments, the negative electrode active layer further contains a conductive agent and a binder. In one embodiment, the conductive agent includes at least one of conductive carbon black (such as Super-P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber. In one embodiment, the binder includes at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), polytetrafluoroethylene, and polyethylene oxide.
[0060] In some embodiments, the negative electrode active layer contains 80 - 99.8 wt% of negative electrode active material, 0.1 - 10 wt% of conductive agent, and 0.1 - 10 wt% of binder.
[0061] In some embodiments, the negative electrode active layer contains 90 - 99.6 wt% of negative electrode active material, 0.2 - 5 wt% of conductive agent, and 0.2 - 5 wt% of binder.
[0062] The negative electrode current collector can be a negative electrode current collector commonly used in the art, such as copper foil or composite current collector, etc.
[0063] The electrochemical device may further include an electrolyte, and the electrolyte can be a conventional electrolyte in the art, which will not be elaborated here.
[0064] In some embodiments, the electrochemical device is a lithium-ion battery, such as a lithium-ion secondary battery.
[0065] If there is no special indication, other selections of the electrochemical device are conventional selections in the art. The assembly method of the electrochemical device can be carried out in a conventional manner in the art.
[0066] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0067] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.
[0068] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.
[0069] Example 1
[0070] (1) Preparation of diaphragm
[0071] like Figure 1 As shown, the diaphragm includes a base membrane 11 and a ceramic layer 12 located on one side of the base membrane 11, and an adhesive layer 13 disposed on the side of the base membrane 11 away from the ceramic layer 12. The ceramic layer 12 includes a plurality of spaced stripes and a plurality of spacer regions located between adjacent stripes. The method for preparing the diaphragm is shown below.
[0072] Ceramic materials, binders, dispersants, and solvents are mixed to obtain a ceramic slurry. The ceramic slurry is then coated on one side of the base film layer using a roller coating method. After high-temperature baking, a base film layer with a ceramic layer on one side is obtained. An adhesive layer is then coated on the other side of the ceramic surface to obtain the finished diaphragm.
[0073] The base film is a polyethylene microporous membrane with a thickness of 7 μm, a needle punch strength of 300 gf, a breaking elongation of 120% in the TD direction, and a breaking elongation of 150% in the MD direction.
[0074] The ceramic material is boehmite with a Dv50 of 1 μm. The binder is polymethyl methacrylate, the dispersant is ethylene oxide, and the solvent is water; the mass ratio of ceramic material, binder, dispersant, and solvent is 35:4:1:60. The ceramic layer has a stripe width of 50 μm, a spacing zone width of 15 μm, a stripe thickness of 1.5 μm, a peel strength between the ceramic layer and the base film of 120 N / m, and a areal density of 2.5 g / m³. 2 That is, A1 is 50, A2 is 15, A is 3.3, H is 1.5, and B is H / A2 = 0.1.
[0075] The coating layer was prepared using polymethyl methacrylate (PMMA) with a thickness of 2 μm and an average particle size of 0.8 μm. The areal density difference between the coating layers on both sides of the base film was 0 g / m². 2 That is, Δm is 0.
[0076] (2) Preparation of positive electrode
[0077] First, lithium cobalt oxide is used as the active material and mixed with Super-P conductive agent and activated carbon at a 1:1 mass ratio. Next, PVDF is added as a binder, and the active material, conductive agent, and binder are dissolved in N-methylpyrrolidone solvent at a mass ratio of 97.5:1.35:1.15, ensuring uniform mixing. Then, the resulting positive electrode slurry is uniformly coated on both sides of an aluminum foil current collector and dried to form a positive electrode film. Finally, the lithium-ion battery positive electrode sheet is fabricated through cold pressing, cutting into sheets, and welding electrode tabs.
[0078] The aluminum foil has an elongation of 6.5% in the TD direction and 6% in the MD direction. The minimum elongation of the positive current collector in the TD direction and the elongation of the positive current collector in the MD direction are Y, which is 6%, and the ratio of B to Y is 1.67.
[0079] (3) Preparation of negative electrode
[0080] Silicon-carbon material was used as the negative electrode active material, with a silicon content of 4% (i.e., 4% carbon). The silicon in the silicon-carbon material existed in the form of silicon particles with an average particle size of 30 nm. The negative electrode active material was mixed with conductive carbon black (Super-P) conductive agent, sodium carboxymethyl cellulose (CMC) thickener, and styrene-butadiene rubber (SBR) binder at a mass ratio of 97.1:0.6:1:1.2, then dispersed in deionized water and thoroughly stirred to form a negative electrode slurry. The negative electrode slurry was then uniformly coated onto both sides of a copper foil current collector and dried to form a negative electrode film. Finally, the negative electrode sheet was prepared by cold pressing, cutting into sheets, and welding electrode tabs.
[0081] (4) Preparation of electrolyte
[0082] Lithium hexafluorophosphate (LiPF6) was used as the lithium salt, and a mixed solvent was prepared by mixing ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and vinylene carbonate in a mass ratio of 8:85:5:2. Subsequently, the lithium salt and solvent were mixed at a mass ratio of 8:92 to obtain the electrolyte.
[0083] (5) Preparation of lithium-ion batteries
[0084] The prepared positive electrode, negative electrode, and separator are wound and assembled into a core, and after drying, liquid injection, and encapsulation processes, a lithium-ion battery is obtained. In this battery, the ceramic layer in the separator is adjacent to the positive electrode, and the adhesive layer is adjacent to the negative electrode.
[0085] Example 2 and Comparative Example 1
[0086] The operation is performed according to the method described in Example 1, except that at least one of A1, A2 and C is different, as shown in Table 1.
[0087] Table 1
[0088]
[0089]
[0090] Example 3 Group
[0091] The operation is performed according to the method described in Example 1, except that at least one of A2, H and Y is different, as shown in Table 2.
[0092] Table 2
[0093] serial number A2 A×C H B Y B / Y <![CDATA[Ceramic surface density (g / m 2 )]]> Δm <![CDATA[Δm / D Si ]]> Example 1 15 0.13 1.5 0.1 6％ 1.67 2.5 0 0 Example 3-1 * * 0.3 0.02 * 0.33 0.5 2 0.07 Example 3-2 * * 0.8 0.05 * 0.89 1.3 1.2 0.04 Example 3-3 * * 3 0.2 * 3.33 5 2.5 0.08 Examples 3-4 * * 6 0.4 * 6.67 10 7.5 0.25 Examples 3-5 5 0.40 4 0.8 4％ 20 7.9 5.4 0.18 Examples 3-6 25 0.08 0.5 0.02 8％ 0.25 0.7 1.8 0.06
[0094] Example 4 group
[0095] Examples 4-1 to 4-3: The method described in Example 3-2 is followed, except that D... Si 15, 50 and 100 respectively, Δm / D Si The values are 0.08, 0.02, and 0.01, respectively.
[0096] Example 4-4: Operate according to the method described in Example 3-3, except that D Si =10, Δm / D Si It is 0.25.
[0097] Example 5 group
[0098] The operation was carried out according to the method described in Example 1, except that the particle sizes of the polymer particles and the ceramic material were different, while Δm remained basically unchanged.
[0099] Example 5-1: The average particle size of the polymer particles is 0.25 μm, and the particle size Dv50 of the ceramic material is 0.3 μm.
[0100] Example 5-2: The average particle size of the polymer particles is 1.5 μm, and the particle size Dv50 of the ceramic material is 1.5 μm.
[0101] Example 5-3: The average particle size of the polymer particles is 4 μm, and the particle size Dv50 of the ceramic material is 3 μm.
[0102] Example 6
[0103] The procedure is performed according to the method described in Example 1, except that the base film is different, as shown in Table 3.
[0104] Table 3
[0105]
[0106] Test case
[0107] The performance of the lithium-ion batteries prepared in the examples and comparative examples was measured using the following methods, and the results are shown in Table 4.
[0108] (1) Minimum Remaining Charge (SOC) Test for Effective Discharge
[0109] The lithium-ion battery is wrapped in foam, and its surface temperature is monitored. ① Adjust the furnace temperature to 25℃ and let it rest for 5 minutes; ② Discharge at 0.5C to the lower limit voltage; ③ Let it rest for 15 minutes; ④ Charge at 1.8C constant current to the upper limit voltage, with a cutoff current of 0.05C; let it rest for 30 minutes; ⑤ Repeat steps 2 to 4 to produce C0; ⑥ Adjust the furnace temperature to 0℃ and let it rest for 120 minutes; ⑦ Discharge at 7.5C constant current for 15 seconds, with a sampling frequency of 100ms; ⑧ Let it rest for 30 minutes; ⑨ Discharge at 1C to adjust to the target SOC; ⑩ Let it rest for 90 minutes; Repeat steps 7 through 10, changing the SOC to the required SOC at that temperature, until the discharge cutoff voltage at 0°C and SOC is lower than the lower limit voltage, and record the minimum remaining charge (SOC) for effective discharge.
[0110] (2) Furnace temperature test
[0111] The lithium-ion battery was discharged at 0.5C and fully charged at 1C. The lithium-ion battery was placed in a hot box and heated to 130°C at a rate of (5°C±2°C) / min and maintained for 60min. The experiment was then terminated. The state of the lithium-ion battery before and after the test was recorded. If the lithium-ion battery caught fire, it was considered that the furnace temperature test was failed. The furnace temperature pass rate was expressed as "number of lithium-ion batteries that passed the furnace temperature test / total number of lithium-ion batteries".
[0112] (3) Cyclic performance test
[0113] The initial thickness and initial capacity of the lithium-ion battery were tested at 10℃, then discharged at 10C to the lower cutoff voltage; left to stand for 30 minutes; charged at 3C to the upper cutoff voltage, and kept constant at 0.05C; left to stand for 5 minutes; then cycled 600T, pausing after every 100T, and then the thickness and capacity of the lithium-ion battery under full charge were tested.
[0114] Thickness expansion rate = (Battery thickness after different cycle counts - Initial thickness) / Initial thickness × 100%.
[0115] Capacity retention rate = Battery capacity after different cycle cycles / Initial capacity × 100%.
[0116] (4) Positive electrode breakage test
[0117] After a lithium-ion battery has been cycled to 600T, it is disassembled to confirm whether the positive electrode has broken. The positive electrode breakage rate is expressed as "number of positive electrode plates without breakage / total number of positive electrode plates".
[0118] Table 4
[0119]
[0120]
[0121] A comparison of Examples 1, 2, and Comparative Example 1 shows that when the ceramic layer has a spacer region and the battery satisfies the range of 0.06 ≤ A × C ≤ 0.9, a reasonable combination of the ceramic layer stripe ratio and the negative electrode silicon content can improve ion conductivity and the flexibility of the separator, effectively improving the battery's charge and discharge efficiency, reducing the minimum remaining charge (SOC) level at which the battery can effectively discharge, improving the battery's usable depth of discharge and low-temperature cycle performance, and also helping to alleviate the positive electrode fragmentation problem. When A × C < 0.06, the heat resistance will be poor due to the small ceramic stripe ratio, which may threaten the thermal safety performance of the lithium-ion battery. When A × C > 0.9, the stripe ratio is slightly higher and the negative electrode silicon doping is higher, which will affect the thickness expansion during the lithium-ion battery cycle test and easily cause positive electrode fragmentation.
[0122] A comparison of Examples 1, 3, and 4 shows that when the B / Y ratio is between 0.3 and 10, it effectively provides space for electrode extension, effectively improves the positive electrode band breakage problem, and also helps to improve battery safety and cycle performance; the average particle size of the synergistic silicon particles is in the range of 10–60 nm, Δm / D Si When B / Y is ≤0.2, the low-temperature cycle performance of the battery is effectively improved. When B / Y <0.3, the ceramic layer thickness and stripe ratio are too small, which leads to poor thermal safety performance of the system. When B / Y >10, the ceramic layer thickness and stripe ratio are too large, and the elongation of the positive electrode current collector is deviated. When paired with a silicon-carbon negative electrode system, the stripe breakage phenomenon is prone to occur. At the same time, the difference in surface density between the two coatings is too large, which is not conducive to improving the low-temperature cycle performance and usable depth of discharge of the battery. In addition, even if B / Y is between 0.3 and 10, if the surface density and Δm of the separator ceramic layer are too large or the silicon particle size is too small, it will lead to Δm / D Si A value greater than 0.2 can also hinder ion transport efficiency, affecting the charge-discharge capability and low-temperature cycle performance of lithium-ion batteries.
[0123] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.
[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. An electrochemical device, characterized by, The electrochemical device includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The negative electrode includes a negative current collector and a negative active layer located on at least one side surface of the negative current collector. The negative active layer includes a negative active material, which is a silicon-based material. The separator includes a base film and a ceramic layer disposed on at least one side surface of the base film. The ceramic layer includes a plurality of spaced stripes and a plurality of spacer regions located between adjacent stripes. The width of the stripes is A1 μm, and the width of the spacer regions is A2 μm. The electrochemical device satisfies the relationship 0.06≤A×C≤0.
9. Where A is A1 / A2 and C is the mass content of silicon in the negative electrode active material.
2. The electrochemical device of claim 1, wherein A is 1.2 to 10; and / or C is 3% to 20%; and / or A1 is 25–100; and / or A2 ranges from 5 to 25.
3. The electrochemical device of claim 1, wherein The ratio B of the stripe thickness H to the spacer width A2 in the ceramic layer of the diaphragm is 0.025–1.5; and / or The thickness H of the stripes in the ceramic layer of the diaphragm is 0.5 μm to 5 μm.
4. The electrochemical device of claim 3, wherein The positive electrode sheet includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector; take min < the elongation in the lateral direction of the positive current collector and the elongation in the longitudinal direction of the positive current collector> as Y, where Y satisfies: 0.3≤B / Y≤10; Preferably, Y is 2% to 8%.
5. The electrochemical device according to any one of claims 1, characterized in that, The diaphragm also includes an adhesive layer located on the surface of the base film and / or the surface of the ceramic layer; Preferably, the electrochemical device fulfils: Am / D Si ≤ 0.2, wherein Δm is the difference in coating area density between the two sides of the base film, in g / m 2 ; The silicon in the silicon-based material is present in the form of silicon particles, D Si is the average particle diameter of the silicon particles, in nm.
6. The electrochemical device according to claim 5, characterized in that, The difference in coating area density between the two sides of the base film is less than or equal to 4 g / m 2 ; and / or The average particle size of the silicon particles is 10 nm to 60 nm; and / or The coating layer comprises polymer particles, preferably having an average particle size of 0.2 μm to 5 μm.
7. The electrochemical device according to any one of claims 1-6, characterized in that, The areal density m of the ceramic layer t is 2 to 4 g / m 2 .
8. The electrochemical device according to any one of claims 1-6, characterized in that, The ceramic layer comprises 40wt% to 96wt% ceramic material, 3wt% to 60wt% binder, and optionally 0.7wt% to 3wt% dispersant; Preferably, the ceramic material includes at least one selected from 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. Preferably, the particle size Dv50 of the ceramic material is 0.1 μm to 2.5 μm.
9. The electrochemical device according to any one of claims 1-6, characterized in that, The thickness of the base film is 4 μm to 20 μm; and / or The base film is a woven film, a nonwoven film, a polyolefin film, or a separator paper; preferably, the polyolefin film is made of at least one of polyethylene and polypropylene; and / or The transverse elongation at break of the base film is 20%–200%; and / or The longitudinal elongation at break of the base film is 50%–300%; and / or The puncture strength of the basement membrane is 100gf to 600gf.
10. The electrochemical device according to any one of claims 1-6, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon oxides, silicon-carbon materials, silicon-nitrogen materials, and silicon alloys.