Electrochemical device

Abstract

An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator includes a base film and a ceramic layer arranged on the surface of at least one side of the base film, the ceramic layer includes stripes distributed at intervals and spacing regions each located between two adjacent stripes, the width of each stripe is A1 μm, the width of each spacing region is A2 μm, and A is A1 / A2; a plurality of linear recesses are provided on the surface, away from a negative electrode current collector, of a negative electrode active material layer on the surface of at least one side of the negative electrode sheet, the width of each linear recess is B1 μm, the depth of each linear recess is B2 μm, and B is B1 / B2; and the electrochemical device satisfies the relational expressions 3≤B≤11 and 5≤A×B≤50. The electrochemical device can alleviate volume expansion caused by a silicon-containing negative electrode and improve the discharge depth under high-rate discharge conditions, and has good low-temperature performance.

Description

Electrochemical device Technical Field

[0001] This disclosure relates to the technical field of batteries, and more specifically to an electrochemical device.

[0002] Background of the Invention

[0003] Lithium-ion batteries are widely used in 3C consumer electronics, electric vehicles, and other fields. As market competition intensifies, battery technology is continuously evolving towards higher capacity and higher charging power. Silicon (Si), with its ultra-high theoretical specific capacity, is considered one of the most promising anode materials, with a theoretical specific capacity of 4200 mAh / g in its fully lithiated state, approximately 10 times that of traditional graphite.

[0004] However, the lithium storage mechanism of silicon-based anodes relies on an alloying reaction, during which the silicon material undergoes significant volume expansion. During battery charge-discharge cycles, this repeated volume change leads to structural collapse of the electrode material. Simultaneously, lithium-ion batteries often encounter insufficient depth of discharge when facing high-rate discharge demands, which limits their performance in certain applications.

[0005] Therefore, developing new types of batteries that can meet the market's demand for high-power, long-duration discharge systems has become an important issue that the industry urgently needs to address. Summary of the Invention

[0006] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide an electrochemical device that can alleviate the volume expansion caused by silicon-containing anodes and improve the depth of discharge under high-rate discharge conditions.

[0007] To achieve the above objectives, this disclosure provides an electrochemical device, which includes a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode.

[0008] The diaphragm includes a base membrane and a ceramic layer disposed on at least one surface of the base membrane. 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, where A is A1 / A2.

[0009] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. A plurality of linear recesses are formed on the surface of the negative electrode active material layer on at least one side surface of the negative electrode sheet away from the negative electrode current collector. The width of the linear recesses is B1μm and the depth of the linear recesses is B2μm, where B is B1 / B2.

[0010] The electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50.

[0011] The adoption of the above-described technical solution in this disclosure has the following beneficial effects:

[0012] In the electrochemical device disclosed herein, the ceramic layer of the separator adopts a striped coating design, paired with a negative electrode sheet with linear recesses on its surface, and controlled to satisfy the aforementioned relationship. This alleviates the volume expansion problem caused by the silicon-containing negative electrode sheet, and also improves the usable depth of discharge under high-rate discharge conditions, thereby reducing the minimum remaining charge (SOC) required for effective discharge and ultimately significantly improving the power supply capacity of the electrochemical device. Furthermore, this electrochemical device exhibits excellent low-temperature discharge performance, maintaining stable performance output even in cold environments.

[0013] 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

[0014] Figure 1 shows a schematic diagram of the structure of a diaphragm in this disclosure.

[0015] Figure 2 shows a schematic diagram of the structure of a diaphragm in this disclosure.

[0016] Figure 3 shows a schematic diagram of the structure of a negative electrode sheet in this disclosure.

[0017] Explanation of reference numerals in the attached figures: 11, base film; 12, ceramic layer; 13, adhesive layer; 2, linear recess; B1, width of the linear recess; B2, depth of the linear recess. Detailed Implementation

[0018] The following provides a detailed description of specific embodiments of this disclosure. 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 this disclosure.

[0019] Unless otherwise defined, all scientific and technical terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure relates.

[0020] To achieve the above objectives, this disclosure provides an electrochemical device comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes;

[0021] The diaphragm includes a base membrane and a ceramic layer disposed on at least one surface of the base membrane. 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, where A is A1 / A2.

[0022] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The surface of the negative electrode active material layer on at least one side surface of the negative electrode sheet away from the negative electrode current collector has a plurality of linear recesses. The width of the linear recesses is B1μm and the depth of the linear recesses is B2μm, where B is B1 / B2.

[0023] The electrochemical device satisfies the relationship 3≤B≤11 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11) and 5≤A×B≤50 (e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50).

[0024] In this disclosure, the ceramic layer of the separator, through a striped coating design, enhances the migration rate of active ions in the electrolyte and optimizes the distribution of the electrolyte within the electrochemical device during charging and discharging. Simultaneously, the negative electrode contains regularly arranged micropores caused by linear recesses. When the width-to-depth ratio B of the linear recesses is in the range of 3 to 11, it accelerates the diffusion of lithium ions within the electrode, reduces the polarization of the negative electrode under high-current fast charging conditions, effectively suppresses lithium plating at the negative electrode, and increases the contact area between the electrode and the electrolyte, reducing the internal resistance of the electrochemical device. When both factors work synergistically and satisfy the above-mentioned relationship, the charge-discharge capability of the electrochemical device under high-rate conditions is significantly enhanced, the cycle performance of the electrochemical device under fast charging conditions is significantly improved, and the usable depth of discharge of the electrochemical device is improved. In particular, it can improve the usable depth of discharge of the electrochemical device under low-temperature conditions, significantly reduce the minimum remaining charge (SOC) level required for effective discharge, and thus significantly improve the power supply capability of the electrochemical device under high-rate operating conditions.

[0025] In the electrochemical device provided in this disclosure, the ceramic layer of the separator is coated with a striped pattern, and paired with a negative electrode sheet with linear recesses, and controlled to satisfy the above-mentioned relationship, which can also alleviate the volume expansion problem caused by silicon-containing negative electrodes. When A×B is too small, on the one hand, it means that the stripe width A1 of the ceramic layer is narrow and the spacing area width A2 is wide, resulting in a deviation in the continuity of the ceramic layer, which can easily affect the contact interface between the separator and the electrode sheet and reduce the ion conduction efficiency; on the other hand, since B=B1 / B2, a small A×B may be due to a small line width B1 or a large depth of the linear recesses of the negative electrode sheet, which makes it difficult to significantly improve the ion transport efficiency, and thus cannot significantly improve the usable discharge depth. When A×B is too large, on the one hand, it means that the spacing area width A2 of the ceramic layer is narrow and the stripe area is wide, which limits the liquid storage space and makes it impossible to effectively optimize the distribution of electrolyte inside the electrochemical device during charging and discharging; on the other hand, the width B1 of the linear recesses may be too large or the depth too small, resulting in a deviation in the surface consistency of the negative electrode sheet, which will also damage the contact interface between the separator and the electrode sheet and affect the ion conduction efficiency.

[0026] Those skilled in the art can select the width of the stripes and the width of the spacing regions according to the structure of different electrochemical devices and the base membrane of different materials. In some embodiments, A1 is 25 to 100, such as 25, 30, 40, 50, 60, 70, 80, 90, or 100. In some embodiments, A2 is 6.7 to 50, such as 6.7, 10, 20, 30, 40, or 50. 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.

[0027] As shown in Figure 1, A1 is the width of the stripe and A2 is the width of the interval. When measuring the width of the stripe A1 and the width of the interval A2, the width of 3-10 stripes and the width of the interval at different positions on the surface of the ceramic layer are measured respectively, and the average value is recorded as A1 and A2.

[0028] In some embodiments, A is 1 to 5, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5. When A is within this range and the electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50, the spacer region of the ceramic layer can provide more ion transport channels and electrolyte storage space, effectively improving the migration rate of active ions. When A is too large, it will affect the electrolyte storage capacity of the cell, making it impossible to effectively optimize the distribution of electrolyte inside the electrochemical device during charging and discharging, thereby affecting the charging and discharging performance of the electrochemical device. If 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.

[0029] The linear recesses on the negative electrode sheet can be prepared by laser wire bonding, forming regular micron-sized linear recesses on the surface of the negative electrode active material in the negative electrode active material layer of the negative electrode sheet. The length of the linear recesses is not particularly limited and can be selected according to the arrangement of the linear recesses and the size of the negative electrode sheet.

[0030] In some embodiments, B1 is 80–100, such as 80, 85, 90, 95, or 100. In some embodiments, B2 is 10–20, such as 10, 12, 14, 16, 18, or 20. When the electrochemical device satisfies the relationship 3 ≤ B ≤ 11 and 5 ≤ A × B ≤ 50, further satisfying that the width and depth of the linear concave portion are within this range can further optimize the usable discharge depth of the electrochemical device, thereby reducing the minimum remaining charge (SOC) level required for effective discharge, thus significantly enhancing the power supply capability of the electrochemical device, especially improving the charge-discharge capability and low-temperature cycle performance under low-temperature conditions, and improving the performance of the electrochemical device in cold environments.

[0031] As shown in Figure 3, a plurality of linear recesses 2 are formed on the surface of the negative electrode active material layer on at least one side of the negative electrode sheet, away from the negative electrode current collector. The width B1 and depth B2 of the linear recesses are shown in Figure 3. When measuring the width B1 and depth B2 of the linear recesses, the width and depth of 3-10 linear recesses located at different positions on the surface of the negative electrode active material layer are measured respectively, and the average values ​​are recorded as B1 and B2.

[0032] In some embodiments, the thickness H of the stripes in the ceramic layer of the diaphragm is 0.5 μm to 5 μm, as shown in Figure 1, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm. In this disclosure, the thickness of the spacer region can be 0. When measuring the thickness H of the stripes in the ceramic layer, the thicknesses of 3-10 stripes located at different positions on the surface of the ceramic layer are measured, and the average value is recorded as H.

[0033] In some embodiments, the ceramic layer comprises 40wt% to 96wt% (e.g., 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 96wt%) of ceramic material and 3wt% to 60wt% (e.g., 3wt%, 6wt%, 9wt%, 10wt%, 15wt%, 20wt%) of ceramic material. The binder comprises 100% to 60% (t%), 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, and 60 wt%), and optionally 0.7 wt% to 3 wt% (e.g., 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, and 3 wt%).

[0034] In some embodiments, 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, at least one selected from 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 (e.g., 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.

[0035] In some embodiments, 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 particles 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.

[0036] 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.

[0037] In some embodiments, the thickness of the base film is 4μm to 20μm, for example, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, or 20μm.

[0038] In some embodiments, the base film is a woven film, a nonwoven film, a polyolefin film, or a separator paper.

[0039] In some embodiments, the polyolefin film is made of at least one of polyethylene and polypropylene.

[0040] 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%.

[0041] 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 MD -50) / 50×100%.

[0042] 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.

[0043] 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 / release adhesive width × 100%.

[0044] In some embodiments, 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, as shown in FIG1, when the base film 11 has an adhesive layer 13 on one side, the adhesive layer 13 may be provided on the surface of the base film 11 away from the ceramic layer 12. Of course, if the diaphragm has an adhesive layer on one side, the adhesive layer may also be provided on the surface of the ceramic layer. As shown in FIG2, when adhesive layers 13 are provided on both sides of the base film 11, one 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 surfaces of the base film, the adhesive layer is provided on both surfaces of the ceramic layer. The areal density of the adhesive layer on both sides of the base film may be the same or different.

[0045] In some embodiments, the areal density difference between the coating layers on both sides of the base film is Δm, in g / m³. 2 Δm≤4, the surface density difference is, for example, 0 g / m³. 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 The surface density difference Δm is controlled to be no more than 4 g / m³. 2 Within this range, the adhesion and hardness between the separator and the negative electrode are optimal, mitigating thickness changes caused by silicon expansion, shortening the lithium-ion transport path, and effectively improving the thickness expansion and lithium plating issues during use. This enhances the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device. However, when Δm exceeds this range, the areal density of the separator coating layer becomes too high, and the coating amount is excessive. This can easily lead to sol-gel blockage during electrolyte immersion, hindering ion transport efficiency and affecting the charge-discharge capability of the electrochemical device.

[0046] In some embodiments, the adhesive layer comprises polymer particles.

[0047] In some embodiments, the average particle size of the polymer particles is 0.2 μm to 5 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm.

[0048] 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.

[0049] 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 at least one of the modified compounds of the above copolymers.

[0050] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material in which silicon exists in the form of silicon particles.

[0051] In some embodiments, the average particle size D of the silicon particles SiThe unit is nm, and it satisfies the following relationship with A: 5 ≤ D Si / A≤30, for example, can be 5, 6, 8, 10, 15, 20, 25, 30. When the electrochemical device meets this range, it can effectively improve the discharge depth of the electrochemical device, reduce the minimum remaining charge (SOC) level at which the electrochemical device can effectively supply power, and contribute to the long-term stable operation of the electrochemical device. When D Si If the A value is too small, it means that the silicon particles are too small. An excessively small particle size increases the mechanical stress on the material, easily causing structural damage and capacity decay. On the other hand, it indicates that the A value is too large, which reduces the electrolyte storage capacity of the negative electrode, making it impossible to effectively optimize the distribution of the electrolyte within the electrochemical device during charging and discharging, thus affecting the charging and discharging performance of the electrochemical device. However, when D... Si When the A value is too large, on the one hand, the particle size of silicon particles is too large and the specific surface area is too low, which has no significant effect on improving ion conduction efficiency and is not conducive to improving the usable discharge depth of electrochemical devices; on the other hand, if the A value is too small, it will have an adverse effect on the heat resistance of electrochemical devices, thereby threatening the thermal safety performance of electrochemical devices.

[0052] In some embodiments, the average particle size of the silicon material is 10 nm to 60 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or 60 nm. When the electrochemical device satisfies: 5 ≤ D Si With an A ≤ 30 and appropriate silicon particle size, smaller silicon particles can provide a larger specific surface area, increasing the energy density of the electrochemical device. They also increase the liquid storage space and ion transport channels, significantly improving ion conduction efficiency, charge / discharge rate, and cycle life. This ensures excellent cycle performance of the electrochemical device even at low temperatures and reduces the minimum state of charge (SOC) required for effective discharge at low temperatures. However, excessively small particle size can increase the mechanical stress between particles within the negative electrode, potentially leading to structural damage and capacity decay in the electrochemical device.

[0053] D Si The size of the silicon particles can be observed using a transmission electron microscope (TEM), and the average particle size of 50 silicon particles can be calculated.

[0054] In some embodiments, the silicon content in the negative electrode active material is 3-20 wt%, such as 3 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%. The design of the linear concave portion and the reasonable combination of 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.

[0055] In some embodiments, the thickness of the negative electrode active material layer accounts for 90% to 95% of the thickness of the negative electrode sheet, for example, 90%, 91%, 92%, 93%, 94%, or 95%. This design, combined with the aforementioned linear recess design, can further optimize the usable discharge depth of the electrochemical device, thereby reducing the minimum remaining charge (SOC) level required for effective discharge and significantly enhancing the power supply capability of the electrochemical device. The thickness of the negative electrode active material layer is calculated as the total thickness of the negative electrode active material layers. For example, if there are negative electrode active material layers on both sides of the negative electrode current collector, the thickness of the negative electrode active material layer is the sum of the thicknesses of the two negative electrode active material layers.

[0056] In some embodiments, the sheet resistance of the negative electrode is R, measured in mΩ, and the electrochemical device satisfies Δm / R ≤ 0.2, for example, 0.01, 0.05, 0.1, 0.15, or 0.2. The sheet resistance R of the negative electrode is a strongly correlated factor determining the usable depth of discharge of the electrochemical device, primarily influenced by the composition and particle size of the active material used, as well as the conductive agent and binder. Satisfying this relationship further improves the low-temperature charge-discharge performance and low-temperature cycling performance of the electrochemical device. When Δm / R is too large, it indicates excessive areal density and coating amount of the membrane coating layer, which can easily lead to sol-gel blockage during electrolyte immersion, hindering ion transport efficiency and affecting the charge-discharge capability of the electrochemical device.

[0057] In some embodiments, R is 10–60, such as 10, 20, 30, 40, 50, or 60. When the sheet resistance of the negative electrode is in the range of 10–60 mΩ, it is beneficial for the electrochemical device to discharge, improving the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device. When R is too large, it leads to increased energy loss during the charge-discharge process, reducing the charge-discharge efficiency of the battery; when R is too small, it leads to excessively high current density during the charge-discharge process, accelerating the aging and degradation of the battery materials.

[0058] In some embodiments, the thickness of the negative electrode sheet is 70μm to 120μm, for example, it can be 70μm, 80μm, 90μm, 100μm, 110μm, or 120μm.

[0059] In some embodiments, the spacing between adjacent linear recesses is 0.8 mm to 5 mm, for example, it can be 0.8 mm, 1.5 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm. When measuring the spacing between adjacent linear recesses, it is necessary to measure the spacing between 3-10 groups of adjacent linear recesses located at different positions on the surface of the negative electrode active material layer, and then calculate the average value.

[0060] In some embodiments, the silicon-based material includes elemental silicon and silicon oxide (SiO2).x , at least one of silicon carbide material, silicon nitride material, silicon alloy (such as silicon-magnesium alloy, silicon-lithium alloy, etc.) when 0 < x < 2).

[0061] In some embodiments, the negative electrode active material further includes 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.

[0062] In some embodiments, the negative electrode active material layer further includes 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 sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polytetrafluoroethylene, and polyethylene oxide.

[0063] In some embodiments, the negative electrode active material layer includes 80-99.8 wt% (such as 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 89 wt%, 90 wt%, 92 wt%, 93 wt%, 95 wt%, 96 wt%, 98 wt%, 99.8 wt%) of negative electrode active material, 0.1-10 wt% (such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%) of conductive agent, and 0.1-10 wt% (such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%) of binder.

[0064] In some embodiments, the negative electrode active material layer includes 90-99.6 wt% of negative electrode active material, 0.2-5 wt% of conductive agent, and 0.2-5 wt% of binder.

[0065] 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.

[0066] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector.

[0067] In some embodiments, the positive electrode current collector can be a positive electrode current collector commonly used in the art, such as aluminum foil or composite current collector, etc.

[0068] 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 be selected from at least one 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 at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene; and the binder may be selected from at least one of polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0069] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% (e.g., 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%, 99.8 wt%) of positive electrode active material, and 0.1-10 wt% (e.g., 0 wt%) of positive electrode active material. Conductive agents in the range of 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, and binders in the range of 0.1-10 wt%, (e.g., 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%).

[0070] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt% positive electrode active material, 0.2-5 wt% conductive agent, and 0.2-5 wt% binder.

[0071] The electrochemical device may further include an electrolyte, which may be a conventional electrolyte in the art and will not be described in detail here.

[0072] In some embodiments, the electrochemical device is a lithium-ion battery, such as a lithium-ion rechargeable battery.

[0073] Unless otherwise specified, other options for the electrochemical device are conventional choices in the art. The assembly of the electrochemical device can all be carried out in accordance with conventional methods in the art.

[0074] The technical solutions of this disclosure will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0075] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0076] The present disclosure is described in detail below with reference to specific embodiments, which are intended to understand rather than limit the present disclosure.

[0077] Example 1

[0078] (1) Preparation of diaphragm

[0079] As shown in Figure 1, 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.

[0080] 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.

[0081] 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.

[0082] 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 25 μm, a coating thickness of 1.5 μm, and a peel strength between the ceramic layer and the base film of 120 N / m. That is, A1 is 50, A2 is 25, and A is 2.

[0083] The coating layer was prepared using polymethyl methacrylate (PMMA) with a thickness of 1 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.

[0084] (2) Preparation of positive electrode

[0085] 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.

[0086] (3) Preparation of negative electrode

[0087] Silicon-carbon material is used as the negative electrode active material, with a silicon content of 4%. The silicon in the silicon-carbon material exists in the form of silicon particles, and the average particle size D of the silicon particles is... si The anode material is 30nm. The negative electrode active material is mixed with Super-P conductive agent, CMC thickener, and 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 is 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 is prepared through cold pressing, cutting into sheets, laser wire bonding, and welding of electrode tabs. Wherein, D... Si / A is 15.

[0088] In the negative electrode sheet, laser wire bonding forms linear recesses on the surface of the negative electrode active material layer. The width of the linear recess is B1μm and the depth is B2μm, where B1 is 90, B2 is 15, B = B1 / B2 = 6, A × B is 12, and the spacing between adjacent linear recesses is 2.5mm.

[0089] The sheet resistivity of the negative electrode is 35 mΩ, and Δm / R is 0. The total thickness of the two negative electrode active material layers is 70 μm, and the thickness of the negative electrode is 75 μm. That is, the thickness of the negative electrode active material layer accounts for 93% of the thickness of the negative electrode.

[0090] (4) Preparation of electrolyte

[0091] Lithium hexafluorophosphate (LiPF6) was selected 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.

[0092] (5) Preparation of lithium-ion batteries

[0093] The prepared positive electrode sheet, negative electrode sheet, 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 sheet, and the adhesive layer is adjacent to the negative electrode sheet.

[0094] Example 2 and Comparative Example 1

[0095] The operation is performed according to the method described in Example 1, except that at least one of A1, A2, B1 and B2 is different, as shown in Table 1.

[0096] In the prepared lithium battery, the difference in coating surface density on both sides of the base film is within 2 g / m². 2 Within a certain range, that is, Δm≤2, the surface resistance R of the negative electrode is in the range of 15~40mΩ, and Δm / R≤0.1.

[0097] Example 3 Group

[0098] The operation is carried out according to the method described in Example 1, except that D Si The differences are shown in Table 1.

[0099] Table 1

[0100] Example 4

[0101] The operation is carried out according to the method described in Example 1, except that at least one of the following is different: H, the particle size Dv50 of the ceramic material, the spacing between adjacent linear recesses, and the mass content of silicon in the negative electrode active material, as shown in Table 2.

[0102] Table 2

[0103] Example 5

[0104] The operation was carried out according to the method described in Example 1, except that the type of base film was different, and its property parameters are shown in Table 3.

[0105] Table 3

[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) Cyclic performance test

[0111] 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.

[0112] Thickness expansion rate = (Battery thickness after different cycle counts - Initial thickness) / Initial thickness × 100%.

[0113] Capacity retention rate = Battery capacity after different cycle cycles / Initial capacity × 100%.

[0114] (3) Ratio Performance Test

[0115] The lithium-ion battery was placed at 25°C for 5 minutes; discharged at 0.5C to 2.5V, charged at 1C to 4.2V, kept constant at 0.05C, and discharged at 0.2C to obtain the initial capacity; placed at 25°C for 30 minutes; charged at 1C to 100% SOC at room temperature; placed at 25 minutes; placed at 0°C for 2 hours; discharged at 10C rate to the lower limit voltage and the discharge capacity was recorded. The 10C discharge capacity retention rate of the battery was calculated using the following formula.

[0116] 10C discharge capacity retention rate (%) = discharge capacity / initial capacity × 100%.

[0117] Table 4

[0118] 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.

[0119] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Any modifications or equivalent substitutions made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode; The diaphragm includes a base membrane and a ceramic layer disposed on at least one surface of the base membrane. 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, where A is A1 / A2. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. A plurality of linear recesses are formed on the surface of the negative electrode active material layer on at least one side surface of the negative electrode sheet away from the negative electrode current collector. The width of the linear recesses is B1μm and the depth of the linear recesses is B2μm, where B is B1 / B2. The electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50.

2. The electrochemical device according to claim 1, characterized in that, A1 is 25 to 100; and / or, A2 is 6.7 to 50; preferably, A is 1 to 5.

3. The electrochemical device according to any one of claims 1-2, characterized in that, B1 is 80–100; and / or, B2 is 10–20.

4. The electrochemical device according to any one of claims 1-3, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material, wherein silicon exists in the form of silicon particles; the average particle size D of the silicon particles is... Si The unit is nm, and it satisfies the following relationship with A: 5 ≤ D Si / A≤30.

5. The electrochemical device according to claim 4, characterized in that, The average particle size D of the silicon particles Si The range is 10nm to 60nm.

6. The electrochemical device according to claim 4, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; and / or, the silicon content in the negative electrode active material is 3wt% to 20wt%.

7. The electrochemical device according to any one of claims 1-6, 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 areal density difference between the coating layers on both sides of the base film is Δm, in g / m³. 2 Δm≤4; Preferably, the adhesive layer comprises polymer particles.

8. The electrochemical device according to claim 7, characterized in that, The sheet resistance of the negative electrode is R, in mΩ, and the electrochemical device satisfies: Δm / R≤0.2; Preferably, R is 10 to 60.

9. The electrochemical device according to any one of claims 1-8, characterized in that, The thickness of the negative electrode sheet is 70μm to 120μm; and / or the spacing between adjacent linear recesses is 0.8mm to 5mm.

10. The electrochemical device according to any one of claims 1-9, characterized in that, The thickness H of the stripes in the ceramic layer of the diaphragm is 0.5 μm to 5 μm.

11. The electrochemical device according to any one of claims 1-10, characterized in that, The ceramic layer comprises 40wt% to 96wt% ceramic material, 3wt% to 60wt% binder, and optionally 0.7wt% to 3wt% dispersant.

12. The electrochemical device according to claim 11, characterized in that, The ceramic material includes at least one 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; and / or the particle size Dv50 of the ceramic material is 0.1 μm to 2.5 μm.

13. The electrochemical device according to any one of claims 1-12, characterized in that, The thickness of the base film is 4μm to 20μm; 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.

14. The electrochemical device according to any one of claims 1-13, characterized in that, The base film has a breaking elongation of 20% to 200% in the TD direction; and / or, the base film has a breaking elongation of 50% to 300% in the MD direction.

15. The electrochemical device according to any one of claims 1-14, characterized in that, The puncture strength of the base film is 100gf to 600gf; and / or the peel strength between the ceramic layer and the base film is 30N / m to 200N / m.

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