Bonding coating slurry, negative pole piece, electrochemical device comprising negative pole piece and electronic device

Abstract

The invention provides adhesive coating slurry, a negative pole piece, an electrochemical device comprising the negative pole piece, and an electronic device comprising the negative pole piece. The adhesive coating slurry comprises an adhesive and an interface modifier, and based on the solid mass of the adhesive coating slurry, the mass percentage of the adhesive is 15%-40%, and the mass percentage of the interface modifier is 1%-5%. The interface modifier is introduced into the adhesive coating slurry, so that when the adhesive coating slurry is in contact with the negative active slurry, non-polar groups in the interface modifier and the polar surface of the negative active slurry form mutual exclusion; furthermore, the width of an interpenetrating interface between a bonding coating formed by curing the bonding coating slurry and a negative electrode active material layer is controlled, the capacity loss of the negative electrode active material is reduced, and the energy density and the cycle capacity retention rate of an electrochemical device are improved; meanwhile, a good bonding effect is achieved between the bonding coating and the diaphragm, the shaping quality of the battery cell can be guaranteed, and the production cost is reduced.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and particularly to an adhesive coating slurry, a negative electrode sheet, an electrochemical device including the same, and an electronic device. Background Art

[0002] Currently, lithium-ion batteries are widely used in new energy vehicles, consumer electronic products, energy storage power stations and other fields. The above application fields have put forward requirements for high energy density, high charge and discharge rate, and long cycle life of lithium-ion batteries. The forms of lithium-ion batteries mainly include square, soft-pack, cylindrical, etc., and the preparation processes mainly include Z-shaped stacking and winding. Different battery forms have different requirements for the battery preparation process.

[0003] During the preparation process of the battery cell, sometimes it is necessary to shape the battery cell, including improving the hardness of the battery cell, interface contact, or preventing the misalignment of the electrode sheet, etc. Currently, the commonly used shaping method for the battery cell is to use a polyvinylidene fluoride (PVDF) coated separator and the electrode sheet for hot pressing, so that the electrode sheet and the separator are bonded together.

[0004] In order to enhance the market competitiveness of power batteries, it is becoming increasingly important to control the cost of power batteries. Therefore, it is required to continuously reduce the cost of power batteries from various aspects such as raw materials and manufacturing processes. The method of hot pressing the PVDF coated separator and the electrode sheet has a simple manufacturing process and good shaping effect, but the cost of the PVDF coated separator is relatively high, which increases the manufacturing cost of power batteries to a certain extent. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present application provides an adhesive coating slurry, a negative electrode sheet, an electrochemical device including the same, and an electronic device. The present application introduces an interface modifier into the adhesive coating slurry. By controlling the addition amount of the interface modifier, the depth of the interface that penetrates each other between the adhesive coating formed by curing the adhesive coating slurry and the negative electrode active material layer is further controlled, the loss of the active material capacity is reduced, and the energy density of the electrochemical device is improved; at the same time, the adhesive coating formed by curing the adhesive coating slurry has a good bonding effect with the separator, which can ensure the shaping quality of the battery cell.

[0006] The first aspect of the present application provides an adhesive coating slurry, which includes an adhesive and an interface modifier. Among them, based on the solid mass of the adhesive coating slurry, the mass percentage content of the adhesive is 15% to 40%, and the mass percentage content of the interface modifier is 1% to 5%.

[0007] The second aspect of the present application provides a preparation method, which is used to prepare the aforementioned adhesive coating slurry.

[0008] The third aspect of the present application provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the negative electrode sheet includes a negative electrode current collector, a negative electrode active material layer, and a bonding coating formed by curing the foregoing bonding coating slurry or the bonding coating slurry prepared by the foregoing preparation method.

[0009] The fourth aspect of the present application provides an electronic device, comprising the foregoing electrochemical device.

[0010] The technical solution of the present application can achieve the following beneficial effects:

[0011] By introducing an interfacial modifier into the bonding coating slurry in the present application, the interfacial modifier contains polar groups and non-polar groups. The polar groups combine with small molecule polar substances in the bonding coating slurry, and the non-polar groups at the other end do not combine with small molecule polar substances in the bonding coating slurry and are dispersed inside and on the surface of the slurry. When the bonding coating slurry contacts the negative electrode active slurry, the non-polar groups in the interfacial modifier are mutually exclusive with the polar surface of the negative electrode active slurry, thereby controlling the width of the interfacial layer that mutually penetrates between the bonding coating formed by curing the bonding coating slurry and the negative electrode active material layer, reducing the capacity loss of the negative electrode active material, and improving the energy density and cycle capacity retention rate of the electrochemical device; at the same time, the bonding coating formed by curing the bonding coating slurry has a good bonding effect with the separator, can ensure the shaping quality of the battery cell, and reduce the production cost. Description of the Drawings

[0012] Figure 1 It is a front view schematic diagram of a traditional negative electrode sheet.

[0013] Figure 2 It is a front view schematic diagram of a negative electrode sheet provided by an embodiment of the present application.

[0014] Figure 3 It is another front view schematic diagram of a negative electrode sheet provided by an embodiment of the present application. Detailed Embodiments

[0015] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0016] For the sake of simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0017] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0018] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0019] The list of items connected by the terms "at least one of", "at least one of", "at least one kind of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0020] Bonding coating slurry and its preparation method

[0021] One or more embodiments of the present application provide a bonding coating slurry. The bonding coating slurry includes a binder and an interface modifier. Among them, based on the solid mass of the bonding coating slurry, the mass percentage content of the binder is 15% to 40%, and the mass percentage content of the interface modifier is 1% to 5%.

[0022] In this application, an interface modifier is introduced into the bonding coating slurry. The interface modifier contains polar groups and non-polar groups. The polar groups combine with small-molecule polar substances in the bonding coating slurry, and the non-polar groups at the other end do not combine with small-molecule polar substances in the bonding coating slurry and are dispersed inside and on the surface of the slurry. When the bonding coating slurry contacts the negative electrode active slurry, the non-polar groups in the interface modifier form repulsion with the polar surface of the negative electrode active slurry, thereby controlling the width of the interface that mutually penetrates between the bonding coating formed by curing the bonding coating slurry and the negative electrode active material layer, reducing the capacity loss of the negative electrode active material, and improving the energy density and cycle capacity retention rate of the electrochemical device; at the same time, the bonding coating formed by curing the bonding coating slurry has a good bonding effect with the separator, can ensure the shaping quality of the battery cell, and reduce the production cost.

[0023] In some embodiments, based on the solid mass of the bonding coating slurry, the mass percentage content of the interface modifier is 1% to 5%. It can be understood that the higher the mass percentage content of the interface modifier, the stronger the non-polarity in the slurry. Since one end of the interface modifier is a polar structure and the other end is a non-polar structure, when the interface modifier is too high, the polar groups in the interface modifier will affect the repulsion effect, and at the same time, the cost will increase significantly; the lower the mass percentage content of the interface modifier, the weaker the non-polarity in the slurry, and the poorer the repulsion effect with the polar negative electrode active slurry; limiting the mass percentage content of the interface modifier within the above range can maximize the inhibition of the mutual penetration effect between the bonding coating slurry and the graphite slurry. In some embodiments, the mass percentage content of the interface modifier can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of the above values. In some embodiments, the mass percentage content of the interface modifier is 1.5% to 3%.

[0024] In some embodiments, the interface modifier includes at least one of polyether-modified silicone, fluoroalkyl ethoxy alcohol ether, sodium dodecylbenzenesulfonate or sodium dodecylbenzene sulfate. In some embodiments, the interface modifier is preferably polyether-modified silicone, and its structural schematic diagram is as follows:

[0025]

[0026] The polyether groups in the polyether-modified silicone are polar, while the silicone groups are non-polar. In the bonding coating slurry, both water and ceramics are polar substances. They combine with the polar polyether groups, and the non-polar silicone groups at the other end do not combine with the bonding coating slurry and will disperse inside and on the surface of the slurry. For example, the negative electrode active slurry mainly consists of graphite and water, and the surface of the negative electrode active slurry is polar. Therefore, when the negative electrode active slurry meets the bonding coating slurry, the non-polar silicone groups in the bonding coating slurry will repel the polar solution of the negative electrode active slurry, thereby controlling the depth of the interface where the bonding coating formed by curing the bonding coating slurry penetrates the negative electrode active material layer, reducing the capacity loss of the negative electrode active material, and improving the energy density and cycle capacity retention rate of the electrochemical device.

[0027] In some embodiments, based on the mass of the solids in the bonding coating slurry, the mass percentage of the binder is 15% to 40%. By limiting the binder within the above range, the bonding performance of the bonding coating can be improved, ensuring a good bonding effect between the bonding coating and the separator, thereby ensuring the shaping quality of the battery cell and reducing the production cost. In some embodiments, the mass percentage of the binder can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40% or any range composed of any two of the above values.

[0028] In some embodiments, the binder includes at least one of polyolefin, styrene-butadiene rubber (SBR), and polyacrylate (PAA). In some embodiments, the binder is preferably polyolefin.

[0029] In some embodiments, based on the mass of the solids in the bonding coating slurry, the mass percentage of the ceramic material is 53% to 84%. The introduction of the ceramic material can reduce the cost and the conductivity of the slurry. In some embodiments, the mass percentage of the ceramic can be 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84% or any range composed of any two of the above values.

[0030] In some embodiments, the ceramic material includes at least one of boehmite, alumina, aluminum hydroxide, magnesium hydroxide, garnet, and silica. In some embodiments, the ceramic material is preferably boehmite.

[0031] In some embodiments, the binder coating slurry further includes carboxymethyl cellulose (CMC). Based on the mass of the binder coating slurry solids, the mass percentage of carboxymethyl cellulose is 0.5% to 2%. In some embodiments, the mass percentage of carboxymethyl cellulose can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or a range composed of any two of the above values.

[0032] In some embodiments, the surface tension of the binder coating slurry is 5 mN / m to 50 mN / m. If the surface tension is too large, it indicates that the binder coating slurry has a relatively large polarity and cannot form a mutually exclusive effect with the negative electrode active slurry; if the surface tension is too small, the mutual exclusion between the binder coating slurry and the negative electrode active slurry is too severe, which may affect the stability of the coating. In some embodiments, the surface tension of the binder coating slurry can be 5 mN / m, 10 mN / m, 15 mN / m, 20 mN / m, 25 mN / m, 30 mN / m, 35 mN / m, 40 mN / m, 45 mN / m, 50 mN / m, or a range composed of any two of the above values.

[0033] One or more embodiments of the present application provide a method for preparing the aforementioned binder coating slurry. The preparation method includes:

[0034] S1. Obtain a first slurry, where the first slurry includes a binder;

[0035] S2. Mix the interfacial modifier with the first slurry to form a binder coating slurry.

[0036] In the present application, first, the binder is stirred and mixed with the solvent, and then mixed with the interfacial modifier, which can prevent the molecular damage of the interfacial modifier caused by excessive shearing during the processing and being wrapped by the binder, and can better disperse the interfacial modifier in the slurry.

[0037] Electrochemical device

[0038] One or more embodiments of the present application provide an electrochemical device, which includes a positive electrode plate, the aforementioned negative electrode plate, an electrolyte, and the aforementioned separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate to prevent short circuit between the positive and negative electrodes and allow ions to pass through.

[0039] Negative electrode plate

[0040] One or more embodiments of the present application provide a negative electrode tab, which includes a negative electrode current collector, a negative electrode active material layer, and a bonding coating; the bonding coating is cured from the aforementioned bonding coating slurry or the bonding coating slurry prepared by the aforementioned preparation method.

[0041] In some embodiments, the negative electrode active material layer and the bonding coating are disposed on the surface of the negative electrode current collector, and the bonding coating is located on at least one side (such as Figure 3 shown) of the two sides along the length direction of the negative electrode tab. In some embodiments, the thickness of the bonding coating is 40 μm to 60 μm. In some embodiments, the thickness of the bonding coating is 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, or a range composed of any two of the above values. In some embodiments, the thickness of the bonding coating is 50 μm to 55 μm. In some embodiments, the width of the bonding coating is 2 mm to 8 mm. By limiting the width of the bonding coating within the above range, on the premise of ensuring the bonding effect of the bonding coating, the contact area between the bonding coating and the separator can be greatly reduced, and at the same time, the contact area between the bonding coating and the negative electrode current collector (foil) is also reduced. Compared with the traditional coating method (such as Figure 1 shown), the gluing area is significantly reduced, thereby ensuring the capacity of the negative electrode active material and improving the energy density of the electrochemical device. In some embodiments, the width of the bonding coating is 2 mm, 4 mm, 6 mm, 8 mm, or a range composed of any two of the above values. In some embodiments, the width of the bonding coating is 4 mm to 6 mm. In some embodiments, the ratio of the cross-sectional area of the bonding coating to the cross-sectional area of the negative electrode current collector (foil) is 1.98% to 3.98%.

[0042] In some embodiments, the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the bonding coating is located on at least one side of the two sides along the length direction of the upper surface of the negative electrode active material layer, wherein the upper surface is the surface of the negative electrode active material layer away from the negative electrode current collector (such as Figure 2 shown). In some embodiments, the thickness of the bonding coating is 5 μm to 25 μm. In some embodiments, the width of the bonding coating is 5 mm to 25 mm. By limiting the thickness and width of the bonding coating within the above range, on the premise of ensuring the bonding effect of the bonding coating, the contact area between the bonding coating and the separator can be greatly reduced, and at the same time, the contact area between the bonding coating and the negative electrode current collector (foil) is also reduced. Compared with the traditional coating method (such as Figure 1As shown, the coating area is significantly reduced, which can ensure the capacity of the negative electrode active material and improve the energy density of the electrochemical device. In some embodiments, the thickness of the adhesive coating is 5μm, 10μm, 15μm, 20μm, 25μm, or a range composed of any two of the above values. In some embodiments, the width of the adhesive coating is 5mm, 10mm, 15mm, 20mm, 25mm, or a range composed of any two of the above values. In some embodiments, the thickness of the adhesive coating is from 8μm to 10μm. In some embodiments, the width of the adhesive coating is from 8mm to 10mm. In some embodiments, the ratio of the cross-sectional area of the adhesive coating to the cross-sectional area of the negative electrode current collector (foil) is from 1.98% to 3.98%.

[0043] In some embodiments, the adhesive coating is located on at least one of the two sides of the negative electrode active material layer along the length direction of the negative electrode plate, and the peel strength between the adhesive coating and the negative electrode current collector is from 30N / m to 120N / m. In some embodiments, the peel strength between the adhesive coating and the separator is from 10N / m to 50N / m. The greater the peel strength between the adhesive coating and the negative electrode current collector, the better the adhesion between the adhesive coating and the negative electrode current collector, which can ensure that the adhesive coating does not fall off; the greater the peel strength between the adhesive coating and the separator, the better the adhesion performance between the adhesive coating and the separator, which can ensure that the negative electrode plate and the separator do not shift. In some embodiments, the peel strength between the adhesive coating and the negative electrode current collector is 30N / m, 40N / m, 50N / m, 60N / m, 70N / m, 80N / m, 90N / m, 100N / m, 110N / m, 120N / m, or a range composed of any two of the above values. In some embodiments, the peel strength between the adhesive coating and the separator is 10N / m, 15N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, 45N / m, 50N / m, or a range composed of any two of the above values.

[0044] In some embodiments, the adhesive coating is located on at least one of the two sides of the upper surface of the negative electrode active material layer along the length direction of the negative electrode plate, and the peel strength between the adhesive coating and the separator is from 10N / m to 50N / m. The greater the peel strength between the adhesive coating and the separator, the better the adhesion performance between the adhesive coating and the separator, which can ensure that the negative electrode plate and the separator do not shift. In some embodiments, the peel strength between the adhesive coating and the separator is 10N / m, 15N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, 45N / m, 50N / m, or a range composed of any two of the above values.

[0045] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, graphene, silicon-oxygen composite materials, and silicon-carbon composite materials. In some embodiments, the negative electrode active material is preferably artificial graphite.

[0046] In some embodiments, the negative electrode active material layer further includes a conductive agent, and the conductive agent includes but is not limited to: at least one of carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials include metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer includes polyphenylene derivatives. In some embodiments, the conductive agent is preferably conductive carbon black (SP).

[0047] In some embodiments, the negative electrode active material layer further includes a binder, and the binder includes but is not limited to: at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc. In some embodiments, the binder is preferably styrene-butadiene rubber (SBR).

[0048] In some embodiments, the negative electrode active material layer further includes carboxymethyl cellulose.

[0049] In some embodiments, the negative electrode current collector includes: at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0050] Positive electrode plate

[0051] In some embodiments, the positive electrode plate includes a positive electrode active material layer and a positive electrode current collector.

[0052] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate-based materials, lithium cobalt oxide-based materials, and nickel cobalt-based materials. The lithium iron phosphate-based materials include at least one of Li x Fe y R (1-y) PO4 materials, where R includes at least one of the elements Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B, and Nb, 0.05 ≤ x ≤ 1.2, 0 < y ≤ 1. The lithium cobalt oxide-based materials include Li 1+z Co1-j-k Ma j Mb k At least one of the O2 materials, wherein Ma is at least one of Al, Ga, Hf, Mg, Sn, Zn, and Zr; Mb is at least one of Ni, Mn, V, Mo, Nb, Cu, Fe, In, W, and Cr, 0 ≤ j ≤ 0.01, 0 ≤ k ≤ 0.01, -0.05 ≤ z ≤ 0.08. The nickel-cobalt-based material includes Li a Ni m Co n A (1-m-n) At least one of the O2 materials, wherein A includes at least one of Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag, or Nb, 0.9 ≤ a ≤ 1.2, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, m + n ≤ 1.

[0053] In some embodiments, the positive electrode active material is preferably LiFePO4.

[0054] In some embodiments, the positive electrode active material layer further includes a binder. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber, etc.

[0055] In some embodiments, the positive electrode active material layer further includes a conductive agent. In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, graphene, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0056] In some embodiments, the positive electrode plate further includes a positive electrode current collector, and the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0057] Electrolyte

[0058] In some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent.

[0059] In some embodiments, the lithium salt includes one or more of, but is not limited to, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. In some embodiments, the lithium salt may be LiPF6.

[0060] The non-aqueous solvent includes one or more of, but is not limited to, carbonate compounds, carboxylate compounds, or ether compounds.

[0061] Exemplarily, the carbonate compounds include one or more of, but are not limited to, linear carbonate compounds or cyclic carbonate compounds. Specifically, the linear carbonate compounds include one or more of, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC); the cyclic carbonate compounds include one or more of, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene carbonate (VEC).

[0062] Exemplarily, the carboxylate compounds include one or more of, but are not limited to, methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone.

[0063] Exemplarily, the ether compounds include one or more of, but are not limited to, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.

[0064] Separator

[0065] In some embodiments, the separator includes a polymer, an inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application.

[0066] In some embodiments, the separator includes a base material layer. The base material layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base material layer includes at least one of polyethylene and polypropylene. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0067] The electrochemical devices of the present application include, but are not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: lithium metal secondary battery, lithium ion secondary battery, lithium polymer secondary battery or lithium ion polymer secondary battery.

[0068] In a specific example of the present invention, the electrochemical device is a lithium ion battery. The present application does not specifically limit the type of the lithium ion battery, and it can be any type of lithium ion battery, such as button type, cylindrical type, soft package type lithium ion battery, etc.

[0069] Electronic device

[0070] One or more embodiments of the present application further provide an electronic device, which includes the aforementioned electrochemical device.

[0071] In some embodiments, the electronic devices of the present application include, but are not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries or lithium ion capacitors, etc.

[0072] Hereinafter, the electrochemical devices of the present application will be further described in combination with specific examples and comparative examples.

[0073] Examples and comparative examples

[0074] Hereinafter, examples and comparative examples are given to further specifically illustrate the present application, but the present application is not limited to these examples as long as it does not deviate from its gist.

[0075] The materials, chemical reagents, etc. used in the following examples are all commercially available.

[0076] Example 1

[0077] Preparation of the negative electrode active paste: Graphite, binder SBR, CMC, and conductive agent conductive carbon black (Super P) were mixed according to a mass ratio of graphite:SBR:CMC:Super P = 96.3:1.5:0.8:1.4, deionized water was added, and the mixture was uniformly mixed by a high-speed mixer to obtain the negative electrode active paste.

[0078] Preparation of the bonding coating slurry: Boehmite, CMC, binder polyolefin, and interfacial modifier polyether-modified silicone were mixed at a mass ratio of boehmite: CMC: polyolefin: polyether-modified silicone = 79.5: 0.8: 19.2: 0.5. Deionized water was added and mixed evenly by a high-speed mixer to obtain the bonding coating slurry.

[0079] Preparation of the negative electrode sheet: The negative electrode active slurry and the bonding coating slurry were respectively and evenly coated on one side surface of a negative electrode current collector copper foil with a thickness of 6 μm. Among them, the bonding coating slurry was located on both sides of the negative electrode active slurry. The single-sided coating thicknesses of the negative electrode active slurry and the bonding coating slurry were 60 μm and 50 μm respectively, and the width of the bonding coating was 5 mm. After drying, the above steps were repeated on the other side surface of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing, cutting, and welding the tab, the negative electrode sheet was obtained.

[0080] Preparation of the positive electrode sheet: The positive electrode active material lithium iron phosphate (LiFePO4), conductive agent conductive carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 96: 2: 2. After being stirred evenly under the action of a vacuum mixer, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one side surface of a positive electrode current collector aluminum foil with a thickness of 12 μm. After drying, the above steps were repeated on the other side surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and welding the tab, the positive electrode sheet was obtained.

[0081] Preparation of the electrolyte: Dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of DMC: EC: EMC = 1: 1: 1 as the solvent. Based on the volume of the solvent, 1 mol / L LiPF6 (mass percentage content of 12.5%) was added as the lithium salt to obtain the electrolyte.

[0082] Separator: A 12-μm-thick polypropylene (PP) porous polymer separator was used.

[0083] Preparation of the lithium-ion battery: The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and a bare battery cell was obtained by Z-stacking. The bare battery cell was placed in an outer packaging aluminum-plastic film, the electrolyte was injected, and it was encapsulated. After processes such as formation and grading, a lithium-ion soft-pack battery was obtained.

[0084] Examples 2 to 8

[0085] Examples 2 to 8 were obtained by adjusting the type and mass percentage content of the interfacial modifier, the type of binder, and the mass percentage content of the ceramic on the basis of Example 1. The specific data are shown in Table 1. The other preparation methods of Examples 2 to 8 are the same as those of Example 1.

[0086] Comparative Example 1

[0087] Comparative Example 1 was obtained by not adding an interfacial modifier on the basis of Example 1 and adjusting the mass percentage of the ceramic. The specific data are shown in Table 1. Other preparation methods of Comparative Example 1 are the same as those of Example 1.

[0088] Comparative Example 2

[0089] Comparative Example 2 was obtained by adjusting the mass percentage of the interfacial modifier and the mass percentage of the ceramic on the basis of Example 1. The specific data are shown in Table 1. Other preparation methods of Comparative Example 2 are the same as those of Example 1.

[0090] In Examples 1-8 and Comparative Examples 1-2, polyolefin: polyacrylic acid = 4:1, which means the mass ratio of polyolefin to polyacrylic acid is 4:1; polyolefin: SBR = 4:1, which means the mass ratio of polyolefin to styrene-butadiene rubber (SBR) is 4:1.

[0091] Testing Method

[0092] 1. Testing of the width d of the interpenetrating interface:

[0093] Drop the negative electrode active paste and the binder coating paste on the copper foil respectively. The edges of the negative electrode active paste and the binder coating paste need to be in contact. Dry in an oven at 80 °C. Use an automatic film scraping machine to scrape the negative electrode active material layer and the binder coating to a thickness of 50 μm, and measure the width d of the interpenetrating interface between the active material layer and the binder coating with a film ruler.

[0094] 2. Testing of the peel strength between the binder coating and the copper foil:

[0095] Coat the binder coating paste on the copper foil to a thickness of 50 μm and dry in an oven at 80 °C. Stick the binder coating of the negative electrode sheet on the steel plate with tape attached, and conduct a 180° peel force test on the peel strength between the binder coating and the copper foil through a tensile machine.

[0096] 3. Testing of the peel strength between the binder coating and the separator:

[0097] Hot press the binder coating of the negative electrode sheet and the polypropylene separator. Hot press process: temperature 100 °C, pressure 1500 tons force, time 90 s. Conduct a 180° peel test on the peel strength between the binder coating and the polypropylene separator through a tensile machine.

[0098] 4. Surface tension test:

[0099] The surface tension is tested using a contact angle measuring instrument. The specific steps are as follows: Suspend the slurry to be tested at the end of the needle of the contact angle measuring instrument, where the volume of each drop of the slurry is controlled to be 5 - 30 μL, and input the outer diameter value of the needle of the contact angle measuring instrument and the density value of the slurry to obtain the surface tension of the slurry to be tested.

[0100] 5. Cell capacity test:

[0101] The steps of the cell capacity test are shown in Table 1 below.

[0102] Table 1

[0103]

[0104] 。

[0105] 6. Cycle performance test:

[0106] At 25 °C, the lithium-ion secondary battery is charged at a constant current of 1C to 3.5V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at a constant current of 1C to 2.3V. This is one charge-discharge cycle, and the discharge capacity this time is the discharge capacity of the 1st cycle. The lithium-ion secondary battery is subjected to 500 charge-discharge cycles according to the above method, and the discharge capacity of the 500th cycle is recorded.

[0107] The test data can be seen in Table 2 below.

[0108] Table 2

[0109]

[0110] It can be seen from the data of Examples 1-8 in Table 2 that in this application, an interface modifier is introduced into the bonding coating slurry, and the mass percentage content of the interface modifier is controlled to be 1% to 5%. The surface tension of the bonding coating slurry is 5 mN / m to 50 mN / m. The width d of the interface where the bonding coating cured from the bonding coating slurry and the negative electrode active material layer penetrate each other is controlled within 0.2 mm, effectively avoiding the problem of mutual penetration when the bonding coating and the negative electrode active material layer are in contact. Moreover, the initial value of the cell capacity reaches more than 2.25 Ah, the discharge capacity after 500 cycles reaches more than 2.09 Ah, and the cycle capacity retention rate is higher than 92%. The reason is that the interface modifier introduced into the bonding coating slurry in this application contains polar groups and non-polar groups. The polar groups combine with the small-molecule polar substances in the bonding coating slurry, and the non-polar groups at the other end do not combine with the small-molecule polar substances in the bonding coating slurry and are dispersed inside and on the surface of the slurry. When the bonding coating slurry contacts the negative electrode active slurry, the non-polar groups in the interface modifier form repulsion with the polar surface of the negative electrode active slurry, thereby controlling the width of the interface where the bonding coating cured from the bonding coating slurry and the negative electrode active material layer penetrate each other, reducing the capacity loss of the negative electrode active material, and improving the energy density and cycle capacity retention rate of the electrochemical device; at the same time, the bonding coating cured from the bonding coating slurry has a good bonding effect with the separator, which can ensure the shaping quality of the cell and reduce the production cost.

[0111] It can be seen from the data of Comparative Examples 1-2 in Table 2 that when no or little interface modifier is added, the surface tension of the bonding coating slurry is too high, indicating that the bonding coating slurry has a large polarity and cannot form a repulsive effect with the negative electrode active slurry. The width d of the interface where the bonding coating and the negative electrode active material layer penetrate each other is too large, seriously resulting in the loss of the active material capacity and severely reducing the initial energy density of the electrochemical device; secondly, when the width d of the interface where the bonding coating and the negative electrode active material layer penetrate each other is too large, active lithium cannot be embedded in the negative electrode, causing lithium to deposit on the surface of the negative electrode, further aggravating the side reaction between lithium and the electrolyte, resulting in a decline in the cycle performance, that is, the discharge capacity after 500 cycles decreases and the cycle capacity retention rate decreases. And when the addition amount of the interface modifier is too high, the cost of the bonding coating further increases. Therefore, in this application, the addition amount of the interface modifier is further controlled within the range of 1.5% to 3%, which can not only control the width d of the interface where the bonding coating and the negative electrode active material layer penetrate each other to be less than 0.1 mm, further improve the energy density and cycle performance of the electrochemical device, but also further effectively control the production cost of the battery.

[0112] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some modifications and changes can be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A bonding coating slurry, characterized in that, The bonding coating slurry includes a binder and an interfacial modifier. Among them, based on the solid mass of the bonding coating slurry, the mass percentage content of the binder is 15% to 40%, and the mass percentage content of the interfacial modifier is 1% to 5%.

2. The bonding coating slurry according to claim 1, characterized in that, The bonding coating slurry also satisfies at least one of the following conditions: (1) The bonding coating slurry further includes a ceramic material. Based on the solid mass of the bonding coating slurry, the mass percentage content of the ceramic material is 53% to 84%; (2) The bonding coating slurry further includes a ceramic material. The ceramic material includes at least one of boehmite, alumina, aluminum hydroxide, magnesium hydroxide, garnet, and silica; (3) The binder includes at least one of polyolefin, styrene-butadiene rubber, and polyacrylate; (4) The interfacial modifier includes at least one of polyether-modified siloxane, fluoroalkyl ethoxy alcohol ether, sodium dodecylbenzenesulfonate, and sodium dodecylbenzene sulfate; (5) The bonding coating slurry further includes carboxymethyl cellulose. Based on the solid mass of the bonding coating slurry, the mass percentage content of the carboxymethyl cellulose is 0.5% to 2%.

3. The bonding coating slurry according to any one of claims 1 or 2, characterized in that, The surface tension of the bonding coating slurry is 5 mN / m to 50 mN / m.

4. A preparation method of the bonding coating slurry according to any one of claims 1 to 3, characterized in that, The preparation method includes: S1. Obtain a first slurry, and the first slurry includes the binder; S2. Mix the interfacial modifier with the first slurry to form the bonding coating slurry.

5. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; The negative electrode sheet includes a negative electrode current collector, a negative electrode active material layer, and a bonding coating; the bonding coating is cured from the bonding coating slurry prepared according to the bonding coating slurry of any one of claims 1 to 3 or according to the preparation method of claim 4; The negative electrode active material layer and the bonding coating are disposed on the surface of the negative electrode current collector, and the bonding coating is located on at least one side of the two sides of the negative electrode active material layer along the length direction of the negative electrode sheet; or, The negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the bonding coating is located on at least one side of the two sides of the upper surface of the negative electrode active material layer along the length direction of the negative electrode sheet, wherein the upper surface is the surface of the negative electrode active material layer away from the negative electrode current collector.

6. The electrochemical device according to claim 5, characterized in that, The bonding coating is located on at least one side of the two sides of the negative electrode active material layer along the length direction of the negative electrode sheet, the thickness of the bonding coating is 40 μm to 60 μm, and the width of the bonding coating is 2 mm to 8 mm; Or, The bonding coating is located on at least one side of the two sides of the upper surface of the negative electrode active material layer along the length direction of the negative electrode sheet, the thickness of the bonding coating is 5 μm to 25 μm, and the width of the bonding coating is 5 mm to 25 mm.

7. The electrochemical device according to any one of claims 5 or 6, wherein the bonding coating is located on at least one side of both sides of the negative electrode active material layer along the length direction of the negative electrode tab, the peel strength between the bonding coating and the negative electrode current collector is 30 N / m to 120 N / m, and the peel strength between the bonding coating and the separator is 10 N / m to 50 N / m; or, the bonding coating is located on at least one side of both sides of the upper surface of the negative electrode active material layer along the length direction of the negative electrode tab, and the peel strength between the bonding coating and the separator is 10 N / m to 50 N / m.

8. The electrochemical device according to any one of claims 5 or 6, characterized in that, The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon oxide composite material, or silicon-carbon composite material; and / or, The positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate materials, lithium cobalt oxide materials, and nickel cobalt materials; the lithium iron phosphate materials include Li x Fe y R (1-y) PO4 materials, where R includes at least one of the elements Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B, and Nb, 0.05 ≤ x ≤ 1.2, 0 < y ≤ 1; and / or, the lithium cobalt oxide materials include Li 1+z Co 1-j-k Ma j Mb k O2 materials, where Ma is at least one of Al, Ga, Hf, Mg, Sn, Zn, and Zr; Mb is at least one of Ni, Mn, V, Mo, Nb, Cu, Fe, In, W, and Cr, 0 ≤ j ≤ 0.01, 0 ≤ k ≤ 0.01, -0.05 ≤ z ≤ 0.08; and / or, the nickel cobalt materials include Li a Ni m Co n A (1-m-n) O2 materials, where A includes at least one of the elements Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag, and Nb, 0.9 ≤ a ≤ 1.2, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, m + n ≤ 1.

9. The electrochemical device according to any one of claims 5 or 6, characterized in that, The separator includes a base material layer, and the base material layer includes at least one material of polyethylene and polypropylene.

10. An electronic device, which comprises the electrochemical device according to claim 9.

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