Electrochemical device

Abstract

The application relates to the technical field of batteries, and provides an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet and a separator; the separator comprises a base film and a ceramic layer arranged on at least one side surface of the base film, the ceramic layer comprises interval distributed stripes and interval areas located in the middle of adjacent stripes, the width of the stripe is A1 mu m, the width of the interval area is A2 mu m, A is A1 / A2; a negative electrode active material layer of at least one side surface of the negative electrode sheet is provided with a plurality of linear recesses away from the surface of the negative electrode current collector, the width of the linear recess is B1 mu m, the depth of the linear recess is B2 mu m, B is B1 / B2; the electrochemical device satisfies the relationship 3<=B<=11 and 5<=A* B<=50. The electrochemical device can relieve the volume expansion caused by the silicon-containing negative electrode, improve the dischargeable depth under the condition of large-rate discharge, and has good low-temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrochemical device. BACKGROUND

[0002] Lithium ion batteries are widely used in 3C consumer products, electric vehicles, etc. With the increasingly fierce market competition, battery technology is developing towards greater capacity and higher charging power. Silicon (Si) is considered to be one of the most promising anode materials due to its high theoretical specific capacity. The theoretical specific capacity of fully lithiated silicon can reach 4200 mAh / g (about 10 times that of graphite). However, the lithium storage mechanism of silicon-based anodes is an alloying reaction mechanism, and the silicon material will undergo severe volume expansion during the lithiation process. In the battery charging and discharging cycle, repeated volume changes will lead to the collapse of the structure of the electrode material. At the same time, when lithium ion batteries face the demand for large rate discharge, they often encounter the problem of insufficient available discharge depth, which limits their performance in certain application scenarios.

[0003] Therefore, it is urgent to develop a new battery to meet the growing demand for high power and long time discharge of battery systems. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide an electrochemical device which can alleviate the volume expansion caused by the silicon-containing anode and at the same time can improve the dischargeable depth under large rate discharge conditions.

[0005] In order to achieve the above-mentioned purpose, the present application provides an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet and a separator located between the positive and negative electrode sheets.

[0006] The separator comprises a base film and a ceramic layer provided on at least one side surface of the base film, the ceramic layer comprises a plurality of spaced stripes and a plurality of interval regions located in the middle of adjacent stripes, the width of the stripe is A1 μm, the width of the interval region is A2 μm, and A is A1 / A2.

[0007] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, and a plurality of linear recesses are opened on the surface of the negative electrode active material layer of at least one side surface of the negative electrode sheet away from the negative electrode current collector, the width of the linear recess is B1 μm, the depth of the linear recess is B2 μm, and B is B1 / B2.

[0008] The electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50.

[0009] The present application has the following beneficial effects by adopting the above technical scheme:

[0010] The electrochemical device provided by the application can alleviate the volume expansion problem of the silicon-containing negative electrode sheet, optimize the available discharge depth of the electrochemical device under a large rate condition, and further reduce the minimum remaining power (SOC) level required by the electrochemical device in the effective discharge process, thereby significantly enhancing the power supply capacity of the electrochemical device. In addition, the electrochemical device provided by the application also has good discharge capacity under low temperature conditions, and the performance of the battery in a cold environment is good.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges are included in the range unless specifically stated otherwise. For numerical ranges, the endpoints are included in the range unless specifically stated otherwise. The ranges and individual points are also inclusive of values which are approximately the same as those stated. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 A structure diagram of a separator in the application is shown.

[0013] Figure 2 A structure diagram of a separator in the application is shown.

[0014] Figure 3 A structure diagram of a negative electrode sheet in the application is shown.

[0015] REFERENCE NUMERALS

[0016] 11, base film; 12, ceramic layer; 13, glue layer; 2, linear recess; B1, width of linear recess; B2, depth of linear recess. DETAILED DESCRIPTION

[0017] The specific embodiments of the application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the application, and are not intended to limit the application.

[0018] Unless otherwise defined, all scientific and technical terms used in the application have the same meaning as commonly understood by one of ordinary skill in the art to which the application relates.

[0019] To achieve the above-mentioned purpose, the application provides an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet and a separator between the positive and negative electrode sheets.

[0020] The separator comprises a base film and a ceramic layer arranged on at least one side surface of the base film, the ceramic layer comprises a plurality of spaced stripes and a plurality of interval regions located between adjacent stripes, the width of the stripe is A1 μm, the width of the interval region is A2 μm, A is A1 / A2.

[0021] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, the surface of the negative electrode active material layer of at least one side surface of the negative electrode sheet away from the negative electrode current collector is provided with a plurality of linear recesses, the width of the linear recess is B1 μm, the depth of the linear recess is B2 μm, B is B1 / B2.

[0022] The electrochemical device satisfies the relationship 3≤B≤11 (such as 3, 4, 5, 6, 7, 8, 9, 10, 11) and 5≤A×B≤50 (such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50).

[0023] In the present application, the diaphragm is coated with a striped ceramic layer, which can enhance the migration rate of active ions in the electrolyte, and optimize the distribution of electrolyte inside the electrochemical device during the charging and discharging process. At the same time, the negative electrode sheet contains regularly arranged micropores caused by linear recesses, and when the width-depth ratio B of the linear recesses is in the range of 3-11, it can accelerate the diffusion of lithium ions inside the electrode, reduce the polarization of the negative electrode under the condition of large current fast charging, effectively prevent the problem of lithium precipitation on the negative electrode, and increase the contact area between the electrode and the electrolyte, reduce the internal resistance of the electrochemical device. Under the condition that the above relationship is met, the charging and discharging capacity of the electrochemical device under high rate condition is enhanced, the cycle performance of the electrochemical device under fast charging condition is significantly improved, the available discharge depth of the electrochemical device is improved, especially the available discharge depth of the electrochemical device under low temperature condition is improved, and the minimum remaining power (SOC) level required by the electrochemical device during effective discharge is significantly reduced, thereby significantly enhancing the power supply capacity of the electrochemical device under high rate working condition. In the electrochemical device provided by the present application, the ceramic layer of the diaphragm is coated in a striped manner, combined with the negative electrode sheet provided with linear recesses, and controlled to meet the above relationship, which can also alleviate the volume expansion problem caused by the silicon-containing negative electrode sheet. When AxB is too small, on the one hand, it indicates that the stripe width A1 is relatively narrow, the interval is relatively wide, the continuity of the ceramic layer is deviated, which easily affects the contact interface of the diaphragm and the electrode sheet and affects the ion conduction efficiency; on the other hand, it indicates that the line width B1 of the linear recess of the negative electrode sheet is small, which cannot significantly improve the ion transmission efficiency, and further cannot significantly improve the available discharge depth. When AxB is too large, on the one hand, it indicates that the interval width A2 is narrow and the stripe area is wide, which can provide limited liquid storage space and cannot effectively optimize the distribution of electrolyte inside the electrochemical device during the charging and discharging process; on the other hand, it indicates that the width B1 of the linear recess is large, which will cause the surface consistency of the negative electrode sheet to deviate, which will also affect the contact interface of the diaphragm and the electrode sheet and affect the ion conduction efficiency.

[0024] The width of the stripe and the interval width can be selected according to the structure of different electrochemical devices and the base film of different materials by those skilled in the art. In some embodiments, A1 is 25-100, such as 25, 30, 40, 50, 60, 70, 80, 90, 100. In some embodiments, A2 is 6.7-50, such as 6.7, 10, 20, 30, 40, 50. The direction of the stripe has no special requirement, which can be parallel to the length direction of the diaphragm or perpendicular to the length direction of the diaphragm, or can have a certain angle with the length direction of the diaphragm.

[0025] In some embodiments, A is 1-5, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5. When A is in this range and the electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50, the spacing region of the ceramic layer can provide more ion transmission channels and electrolyte storage space, effectively improving the migration rate of active ions. When A is too large, it will affect the storage capacity of the battery cell, and cannot effectively optimize the distribution of electrolyte in 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.

[0026] The linear recesses on the negative electrode sheet can be prepared by laser wire drawing, and regular micron-level holes are formed on the surface of the negative electrode active material of 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.

[0027] In some embodiments, B1 is 80-100, such as 80, 85, 90, 95, 100. In some embodiments, B2 is 10-20, such as 10, 12, 14, 16, 18, 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 recesses are within this range, the available discharge depth of the electrochemical device can be further optimized, thereby reducing the minimum remaining power (SOC) level required by the electrochemical device during effective discharge, thereby significantly enhancing the power supply capability of the electrochemical device, and especially improving the charging and discharging capability and low-temperature cycle performance under low-temperature conditions, and improving the performance of the electrochemical device in cold environments.

[0028] As shown in Figure 3 At least one side surface of the negative electrode sheet has a plurality of linear recesses 2 on the surface away from the negative electrode current collector. The width B1 of the linear recesses and the depth B2 of the linear recesses are as shown in Figure 3 .

[0029] In some embodiments, the thickness H of the stripe in the ceramic layer of the separator is 0.5-5 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm. In the present application, the thickness of the spacing region can be 0.

[0030] In some embodiments, the ceramic layer contains 40-96 wt% of ceramic material, 3-60 wt% of binder, and optionally 0.7-3 wt% of dispersant.

[0031] In some embodiments, the ceramic material comprises at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride. The binder and dispersant can be conventional materials in the art, for example the binder can comprise at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of vinylidene fluoride-trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, an acrylate polymer such as polymethyl methacrylate, polyacrylic acid, a polyacrylate, polyvinylpyrrolidone, a polyvinyl ether, a styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene or polyhexafluoropropylene. The dispersant can comprise at least one of ethylene oxide, polyvinylpyrrolidone.

[0032] In some embodiments, the ceramic material has a particle size Dv50 of 0.1 μm to 2.5 μm, such as 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm. It can be appreciated that the ceramic material particles can have the same or different particle sizes. When the particle size of the ceramic material is within this range, the liquid storage capacity of the separator and the migration rate of lithium ions can be further improved, and the charge-discharge performance of the battery can be improved.

[0033] Dv50 refers to the particle size corresponding to the cumulative particle size distribution percentage of 50% of the sample, which can be determined by a particle size analyzer.

[0034] In some embodiments, the base film has a thickness of 4 μm to 20 μm, such as 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm.

[0035] In some embodiments, the base film separator is a woven film, a non-woven film, a polyolefin film or a separator paper.

[0036] In some embodiments, the polyolefin film comprises at least one of polyethylene, polypropylene.

[0037] In one embodiment, the base film has a transverse direction (TD) elongation at break of 20% to 200%, such as 20%, 40%, 60%, 80%, 100%, 120%, 140%, 160%, 180%, 200%. The test method is that the base film is prepared into a sample with a width of 15 mm along the TD direction, the initial distance between the clamps of the tensile testing machine is set to 50 mm, and the sample is tested at a tensile speed of 100 mm / min until the base film breaks, and the distance between the clamps at the time of break is recorded as L TDmm, then the elongation at break in the TD direction = (L TD -50) / 50×100%.

[0038] In one embodiment, the elongation at break of the base film in the machine direction (MD) is 50% to 300%, such as 50%, 100%, 150%, 200%, 250%, and 300%. The test method is as follows: the base film is prepared into a sample with a width of 15 mm along the MD direction, the initial distance between the clamps of the tensile testing machine is set to 50 mm, and the test is conducted at a tensile speed of 100 mm / min until the diaphragm breaks. The distance between the clamps at the time of break is recorded as L. MD mm, then the elongation at break in the MD direction = (L MD -50) / 50×100%.

[0039] In one embodiment, the puncture strength of the basement membrane is 100 gf to 600 gf, for example, 100 gf, 200 gf, 300 gf, 400 gf, 500 gf, and 600 gf. The test method is to flatten the basement membrane in a fixture and clamp it. A puncture needle with a diameter of 1.0 mm and a spherical tip with an R of 0.5 mm is inserted perpendicularly to the membrane surface at a rate of 100 mm / min until the membrane is punctured. The maximum puncture force is recorded, which is the membrane puncture strength.

[0040] In one embodiment, the peel strength between the ceramic layer and the base film is 30 to 200 N / m, for example, 30 N / m, 50 N / m, 100 N / m, 150 N / m, or 200 N / m. Testing method: Take a stainless steel plate of a certain size, apply double-sided tape to the center, and remove the paper layer. Take a coated diaphragm sample and place one side of the base material against the top surface of the double-sided tape. Apply 15 mm wide 3M release tape, with the adhesive surface facing the coating layer. Use a rubber roller to roll back and forth naturally on the 3M release tape to ensure even distribution of the adhesive. Use a 180° peel method and test the peel strength of the coating using a tensile testing machine. Peel strength = peel force / width of release tape × 100%.

[0041] In some embodiments, the diaphragm further comprises a coating layer located on the surface of the base film and / or the surface of the ceramic layer. That is, the coating layer may be provided on one or both sides of the base film. For example, Figure 1 As shown, when the base film 11 includes a one-side adhesive layer 13, the adhesive layer 13 can be arranged on the surface of the base film 11 away from the ceramic layer 12. Of course, if the diaphragm includes a one-side adhesive layer, the adhesive layer can also be arranged on the surface of the ceramic layer. Figure 2As shown, when the adhesive layer 13 is arranged on both sides of the base film 11, one side of the adhesive layer 13 is arranged on the surface of the base film 11 away from the ceramic layer 12, and the other side is arranged on the surface of the ceramic layer 12. If the ceramic layer is arranged on both surfaces of the base film, the adhesive layer is arranged on both surfaces of the ceramic layer. The surface densities of the adhesive layers on both sides of the base film can be the same or different.

[0042] In some embodiments, the difference between the surface densities of the adhesive layers on both sides of the base film is Δm, and the unit is g / m 2 , Δm≤4, such as 0 g / m 2 , 0.5 g / m 2 , 1 g / m 2 , 1.5 g / m 2 , 2 g / m 2 , 2.5 g / m 2 , 3 g / m 2 , 3.5 g / m 2 , or 4 g / m 2 . When the difference between the surface densities Δm is controlled within the range of not more than 4 g / m 2 , the adhesion and hardness between the separator and the negative electrode are optimal, the thickness change caused by silicon expansion is alleviated, the lithium ion transmission path is shortened, the thickness expansion and cycle lithium precipitation problems of the lithium ion battery during use are effectively improved, and the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device are improved. However, when Δm exceeds this range, the surface density of the adhesive layer of the separator is too large, and the coating amount is too much, which is easy to cause sol blocking hole phenomenon during electrolyte soaking, which will hinder the ion transmission efficiency and affect the charge-discharge capacity of the electrochemical device.

[0043] In some embodiments, the adhesive layer comprises polymer particles.

[0044] In some embodiments, the average particle size of the polymer particles is 0.2 μm to 5 μm, such as 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.

[0045] The average particle diameter of the polymer particles can be tested by observing the surface of the porous layer at a magnification of 50,000 times using an electron beam radiation type scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). The image size at this time is 2.5 μm x 1.8 μm. Note that the number of pixels is 1,280 pixels x 960 pixels, and the size of 1 pixel is 2 nm x 1.9 nm. For the average particle diameter, the smallest square or rectangle that completely surrounds one particle is drawn on the obtained image, that is, a square or rectangle in which the end of the particle is in contact with four sides of the square or rectangle is drawn, and in the case of a square, the length of one side is set as the particle diameter, and in the case of a rectangle, the length of the long side (major axis diameter) is set as the particle diameter. For any 81 particles, the particle diameter of each is measured, and the number average thereof is set as the average particle diameter. Note that in the case where more than 81 particles are observed in the photographed image, the number average of the particle diameters of any 81 particles in the image is set as the average particle diameter, and in the case where 81 particles are not observed in the image, a plurality of images are photographed, and the number average of the particle diameters of 81 particles in total is set as the average particle diameter.

[0046] The polymer can be a polymer conventionally used in the art, such as can include, but is not limited to, polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluoroethylene, polyvinylidene fluoride, acrylate-based copolymers such as polymethyl methacrylate, polyolefins such as polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of fluoroalkenyl monomers such as polyvinylidene fluoride-trifluorochloroethylene copolymer, copolymers of fluoroalkenyl monomer units and olefin monomer units such as polyvinylidene fluoride-ethylene copolymer, copolymers of fluoroalkenyl monomer units and acrylic monomer units such as polyvinylidene fluoride-acrylic acid copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and modified compounds of the above copolymers.

[0047] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material in which silicon is present in the form of silicon particles.

[0048] In some embodiments, the average particle diameter D Si of the silicon particles is nm and satisfies: 5≤D Si / A≤30, such as can be 5, 6, 8, 10, 15, 20, 25, 30, when the electrochemical device satisfies this range, the discharge depth of the electrochemical device can be effectively improved, the minimum remaining power (SOC) level at which the electrochemical device can effectively supply power can be reduced, and the long-term stable operation of the electrochemical device can be facilitated. When D SiWhen A is too small, on the one hand, it represents that the particle size of silicon is too small, and the mechanical stress of the material is increased, which has caused the destruction of the structure and the capacity attenuation; on the other hand, it represents that A is too large, which will affect the liquid storage capacity of the negative plate, and cannot effectively optimize the distribution of the electrolyte in the electrochemical device during the charging and discharging process, thereby affecting the charging and discharging performance of the electrochemical device. When D Si When A is too large, on the one hand, it represents that the particle size of silicon is too large, and the specific surface area is too low, which has no significant effect on the improvement of ion conduction efficiency, and is not conducive to the improvement of the available discharge depth of the electrochemical device; on the other hand, it represents that A is too small, which will adversely affect the heat resistance of the electrochemical device, thereby threatening the thermal safety performance of the electrochemical device.

[0049] In some embodiments, the average particle size of the silicon material is 10 nm to 60 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or 60 nm. When the electrochemical device satisfies 5≤D Si When A≤30 and the appropriate particle size of silicon is matched, smaller silicon particles can provide a larger specific surface area, improve the energy density of the electrochemical device, and also increase the liquid storage space and ion transmission channel, which can significantly improve the ion conduction efficiency, improve the charging and discharging rate and cycle life, ensure that the electrochemical device also has excellent cycle performance under low temperature conditions, and reduce the minimum SOC level that can be effectively discharged under low temperature. However, too small particle size will also increase the mechanical stress between particles in the negative plate, which is easy to cause the destruction of the structure and the capacity attenuation of the electrochemical device.

[0050] D Si The average value of the particle size of 50 silicon particles can be calculated by observing and marking the size of the silicon particles through a transmission electron microscope (TEM).

[0051] In some embodiments, the content of silicon in the negative active material is 3 to 20 wt%, such as 3 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%. The design of linear recesses and the reasonable matching of the content of silicon can further improve the charging and discharging efficiency of the electrochemical device, reduce the minimum SOC level that can be effectively discharged, and improve the available discharge depth of the electrochemical device.

[0052] In some embodiments, the thickness of the negative active material layer accounts for 90% to 95% of the thickness of the negative tab, such as 90%, 91%, 92%, 93%, 94%, or 95%. Such design, in combination with the aforementioned linear recess design, can further optimize the available discharge depth of the electrochemical device, and in turn reduce the minimum remaining power level (SOC) required for the electrochemical device during effective discharge, thereby significantly enhancing the power supply capability of the electrochemical device. The thickness of the negative active material layer is counted based on the total thickness of the negative active material layer, such as the thickness of the negative active material layer on both sides of the negative current collector, in the case of two negative active material layers, the thickness of the negative active material layer is the sum of the thickness of the two negative active material layers.

[0053] In some embodiments, the surface resistance of the negative tab is R, in mΩ, and the electrochemical device satisfies the relationship Am / R≤0.2, such as 0.01, 0.05, 0.1, 0.15, or 0.2. The surface resistance R of the negative tab is a strong related factor that determines the available discharge depth of the electrochemical device, which is mainly affected by the active material composition and particle size, conductive agent, and binder used. When the relationship is satisfied, the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device can be further improved. When Am / R is too large, it means that the surface density of the separator adhesive layer is too large, and the coating amount is too much, which is prone to sol blocking phenomenon during electrolyte soaking, which will hinder the ion transmission efficiency and affect the charge-discharge capability of the electrochemical device.

[0054] In some embodiments, R is 10 to 60, such as 10, 20, 30, 40, 50, or 60. When the surface resistance of the negative tab is in the range of 10 to 60 mΩ, it is beneficial for the discharge of the electrochemical device and improves the low-temperature charge-discharge performance and low-temperature cycle performance of the electrochemical device. When R is too large, it will increase the electrical energy loss of the battery during charge and discharge, reducing the charge-discharge efficiency of the battery; when R is too small, it will cause the current density of the battery during charge and discharge to be too high, accelerating the aging and degradation of the battery materials.

[0055] In some embodiments, the thickness of the negative tab is 70 μm to 120 μm, such as 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, or 120 μm.

[0056] In some embodiments, the spacing between adjacent linear recesses is 0.8 mm to 5 mm, such as 0.8 mm, 1.5 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm.

[0057] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide (SiO x , 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 active material further comprises a carbon-based material, which comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0059] In some embodiments, the negative active material layer further comprises a conductive agent and a binder. In one embodiment, the conductive agent comprises at least one of conductive carbon black (such as Super-P), acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, carbon fiber. In one embodiment, the binder comprises at least one of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polytetrafluoroethylene, polyethylene oxide.

[0060] In some embodiments, the negative active material layer comprises 80-99.8 wt% of the negative active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0061] In some embodiments, the negative active material layer comprises 90-99.6 wt% of the negative active material, 0.2-5 wt% of the conductive agent, and 0.2-5 wt% of the binder.

[0062] The negative current collector can be a negative current collector commonly used in the art, such as a copper foil or a composite current collector, etc.

[0063] In one embodiment, the positive electrode sheet comprises a positive current collector and a positive active layer located on at least one side surface of the positive current collector.

[0064] In some embodiments, the positive current collector can be a positive current collector commonly used in the art, such as an aluminum foil or a composite current collector, etc.

[0065] The positive active layer is not particularly limited, and the positive active layer can be composed of a positive active material, a conductive agent, a binder, etc. according to the convention in the art. Among them, the positive active material, the conductive agent, the binder, etc. can all be selected from conventional materials in the art, for example, the positive active material can be selected from one or more of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganate, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotube, conductive graphite, graphene, and the binder can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, styrene butadiene rubber, and styrene propylene rubber.

[0066] In some embodiments, the mass percentage content of each component in the positive active material layer is: 80-99.8 wt% of the positive active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0067] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt % of positive electrode active material, 0.2-5 wt % of conductive agent, and 0.2-5 wt % of binder.

[0068] The electrochemical device may further include an electrolyte, which may be a conventional electrolyte in the art and will not be described in detail herein.

[0069] In some embodiments, the electrochemical device is a lithium-ion battery, such as a lithium-ion secondary battery.

[0070] Unless otherwise specified, other options for the electrochemical device are conventional options in the art. The electrochemical device can be assembled in a conventional manner in the art.

[0071] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0072] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0073] The present invention will be described in detail below with reference to specific embodiments. These embodiments are intended to help you understand the present invention but are not intended to limit it.

[0074] Example 1

[0075] (1) Diaphragm preparation

[0076] like Figure 1 As shown, the diaphragm includes a base film 11, a ceramic layer 12 located on one surface of the base film 11, and a rubber coating layer 13 located on the side of the base film 11 away from the ceramic layer 12. The ceramic layer 12 includes a plurality of spaced stripes and a plurality of spacers located between adjacent stripes. The diaphragm preparation method is as follows.

[0077] The ceramic material, binder, dispersant and solvent are mixed to obtain ceramic slurry; the ceramic slurry is coated on one side of the base film layer by roller coating, and after high-temperature baking, a base film layer coated with a ceramic layer on one side is obtained; a glue layer is coated on the other side of the ceramic surface to obtain a finished diaphragm.

[0078] The base film is a polyethylene microporous film with a thickness of 7 μm, a needle puncture strength of 300 gf, a TD direction elongation at break of 120%, and a MD direction elongation at break of 150%.

[0079] The ceramic material is boehmite, and the Dv50 is 1 pm. The binder is polymethyl methacrylate, the dispersant is ethylene oxide, and the solvent is water; the mass ratio of the ceramic material, the binder, the dispersant, and the solvent is 35:4:1:60. The stripe width of the ceramic layer is 50 pm, the interval width is 25 pm, the coating thickness is 1.5 pm, and the peeling strength between the ceramic layer and the base film is 120 N / m. That is, A1 is 50, A2 is 25, and A is 2.

[0080] The adhesive layer is prepared using polymethyl methacrylate, and the thickness of the adhesive layer is 1 pm. The average particle size of the polymethyl methacrylate particles is 0.8 pm. The difference in the areal density of the coating on the two sides of the base film is 0 g / m 2 That is, Am is 0.

[0081] (2) Preparation of the positive electrode sheet

[0082] First, lithium cobalt oxide is mixed with Super-P conductive agent and activated carbon as the active material at a mass ratio of 1:1. Then, PVDF is added as the binder, and the active material, the conductive agent, and the binder are dissolved in N-methyl pyrrolidone solvent at a mass ratio of 97.5:1.35:1.15 to ensure uniform mixing. After that, the obtained positive electrode slurry is uniformly coated on both sides of the aluminum foil current collector and subjected to drying treatment to form a positive electrode film. Finally, the lithium ion battery positive electrode sheet is completed through the steps of cold pressing, cutting into a sheet, and welding the electrode lug.

[0083] (3) Preparation of the negative electrode sheet

[0084] Silicon-carbon material is used as the negative electrode active material, and the silicon content in the negative electrode active material is 4%. The silicon in the silicon-carbon material exists in the form of silicon particles, and the average particle size D si of the silicon particles is 30 nm. 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, and then dispersed in deionized water to form a negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of the copper foil current collector and dried to form a negative electrode film. Finally, the negative electrode sheet is prepared through the processes of cold pressing, cutting into a sheet, laser wire marking, and welding the electrode lug. The D Si / A is 15.

[0085] In the negative electrode sheet, the laser wire marking forms a linear recess on the surface of the negative electrode active material layer of the negative electrode sheet, the width of the linear recess is B1 pm, and the depth of the linear recess is B2 pm, where B1 is 90, B2 is 15, B = B1 / B2 = 6; A x B is 12; and the distance between adjacent linear recesses is 2.5 mm.

[0086] The surface resistance of the negative electrode sheet is 35 mΩ, and Δm / R is 0. The total thickness of the two layers of negative electrode active material layers is 70 μm, and the thickness of the negative electrode sheet is 75 μm, i.e., the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode sheet is 93%.

[0087] (4) Preparation of electrolyte

[0088] Lithium hexafluorophosphate (LiPF6) is selected as the lithium salt, and ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and vinylene carbonate are mixed in a mass ratio of 8:85:5:2 to form a mixed solvent. Then, the lithium salt and the solvent are mixed in a mass ratio of 8:92 to obtain the electrolyte.

[0089] (5) Preparation of lithium ion battery

[0090] The prepared positive electrode sheet, negative electrode sheet, and separator are wound and assembled into a roll core, and after drying, liquid injection packaging, and other processes, a lithium ion battery is obtained. The ceramic layer in the separator is adjacent to the positive electrode sheet, and the adhesive layer is adjacent to the negative electrode sheet.

[0091] Example 2 group and Comparative Example 1 group

[0092] The method described in Example 1 is followed, except that at least one of A1, A2, B1, and B2 is different, as shown in Table 1.

[0093] The areal density difference of the coating layers on both sides of the base film in the prepared lithium battery is within 2 g / m 2 , i.e., Δm≤2, and the surface resistance R of the negative electrode sheet is within 15-40 mΩ, and Δm / R≤0.1.

[0094] Example 3 group

[0095] The method described in Example 1 is followed, except that D Si is different, as shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] Example 4

[0100] The method described in Example 1 is followed, except that at least one of 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 is different, as shown in Table 2.

[0101] Table 2

[0102] Number H / μm Dv50 / μm Pitch / mm Silicon content Δm R Δm / R Example 1 1.5 1 2.5 4％ 0 35 0 Example 4-1 0.5 0.3 1 * 1.7 20 0.08 Example 4-2 1 0.7 * * 0.8 20 0.04 Example 4-3 3 1.5 * * 2.5 20 0.13 Example 4-4 6 3 * * 7.5 20 0.38 Example 4-5 3 * 6 8％ 2.5 65 0.04 Example 4-6 3 * 4 15％ 2.5 17 0.15 Example 4-7 3 * 1 20％ 2.5 12 0.21 Example 4-8 3 * 0.5 25％ 2.5 8 0.31

[0103] Example 4

[0104] The procedure described in Example 1 was followed, except that the base film was different, and its property parameters were as shown in Table 3.

[0105] Table 3

[0106]

[0107]

[0108] Test Example

[0109] The lithium ion batteries prepared from the examples and comparative examples were subjected to performance determination, and the specific method was as follows, and the results were shown in Table 4.

[0110] (1) Minimum residual capacity (SOC) test for effective discharge

[0111] The lithium ion battery was wrapped with foam, and the surface temperature of the lithium ion battery was monitored. ① Adjust the oven temperature to 25℃, and stand for 5 min; ② discharge at 0.5C to the lower limit voltage; ③ stand for 15 min; ④ charge at 1.8C to the upper limit voltage, and the cutoff current is 0.05C; stand for 30 min; ⑤ repeat the second step to the fourth step to make CO; ⑥ adjust the oven temperature to 0℃, and stand for 120 min; ⑦ discharge at 7.5C for 15s, and the sampling frequency is 100ms; ⑧ stand for 30 min; ⑨ discharge at 1C to adjust to the target SOC; ⑩ stand for 90 min; Repeat the procedures from the seventh step to the tenth step, and change the SOC to the required SOC at this temperature, until the discharge cutoff voltage at 0℃ and SOC is lower than the lower limit voltage, and record the minimum residual capacity (SOC) for effective discharge.

[0112] (2) Cycle performance test

[0113] Test the initial thickness and initial capacity of the lithium ion battery under the condition of 10℃, and then discharge at 10C to the lower limit cutoff voltage; stand for 30 min; charge at 3C to the upper limit cutoff voltage, and constant voltage to 0.05C; stand for 5 min; and then cycle for 600T, and pause after every 100T, and then test the thickness and capacity of the lithium ion battery under full charge state.

[0114] Thickness expansion rate = (battery thickness after different cycle times-initial thickness) / initial thickness x 100%.

[0115] Capacity retention rate = battery capacity after different cycle times / initial capacity x 100%.

[0116] (3) Rate performance test

[0117] Place the lithium-ion battery at 25°C for 5 minutes; discharge it at 0.5C to 2.5V, charge it at 1C to 4.2V, maintain constant voltage at 0.05C, and discharge it at 0.2C to obtain the initial capacity; place it for 30 minutes; charge it at 1C to 100% SOC at room temperature; place it for 15 minutes, let it stand at 0°C for 2 hours, and discharge it at a rate of 10C to the lower limit voltage. Record the discharge capacity and calculate the 10C discharge capacity retention rate of the battery using the following formula.

[0118] 10C discharge capacity retention rate (%) = discharge capacity / initial capacity × 100%.

[0119] Table 4

[0120]

[0121]

[0122] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0123] 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 in the scope of protection of the present invention.

Claims

1. An electrochemical device, characterized in that The electrochemical device includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrode sheets; The diaphragm comprises a base film and a ceramic layer disposed on at least one surface of the base film, wherein the ceramic layer comprises a plurality of stripes distributed at intervals and a plurality of spacer regions located between adjacent stripes, wherein the width of the stripes is A1 μm, the width of the spacer regions is A2 μm, and A is A1 / A2, and A1 is 25-100; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side 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 of the negative electrode sheet away from the negative electrode current collector. The width of the linear recess is B1 μm, the depth of the linear recess is B2 μm, B is B1 / B2, and B1 is 80-100. The electrochemical device satisfies the relationship 3≤B≤11 and 5≤A×B≤50, where A is 1 to 5; The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material, in which silicon exists in the form of silicon particles; the average particle size D of the silicon particles Si The unit is nm and satisfies: 5≤D Si / A≤30.

2. The electrochemical device according to claim 1, wherein A2 is 6.7~50; and / or, B2 is 10~20.

3. The electrochemical device according to claim 1, wherein The average particle size D of the silicon particles Si 10 to 60; and / or 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 content of silicon in the negative electrode active material is 3-20 wt %.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that The diaphragm further comprises a coating layer located on the surface of the base film and / or the surface of the ceramic layer.

5. The electrochemical device according to claim 4, characterized in that The difference in surface density of the coating on both sides of the base film is Δm, in g / m 2 , Δm≤4.

6. The electrochemical device according to claim 4, characterized in that The rubber coating layer includes polymer particles.

7. The electrochemical device according to claim 4, characterized in that The surface resistance of the negative electrode sheet is R, with a unit of mΩ, and the electrochemical device satisfies Δm / R≤0.

2.

8. The electrochemical device according to claim 7, characterized in that R is 10~60.

9. The electrochemical device according to any one of claims 1 to 3, characterized in that: The thickness of the negative electrode sheet is 70μm~120μm; and / or The distance between adjacent linear recesses is 0.8 mm to 5 mm.

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

12. The electrochemical device according to claim 11, characterized in that The ceramic material includes at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride.

13. The electrochemical device according to claim 11, wherein The particle size Dv50 of the ceramic material is 0.1μm~2.5μm.

14. The electrochemical device according to any one of claims 1 to 3, 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; and / or The elongation at break of the base film in the TD direction is 20% to 200%; and / or The elongation at break of the base film in the MD direction is 50% to 300%; and / or The puncture strength of the basement membrane is 100gf~600gf; and / or The peel strength between the ceramic layer and the base film is 30~200N / m.

Images