Electrochemical and Electronic Devices

Abstract

The present invention provides an electrochemical device comprising a negative electrode, the negative electrode comprising a current collector (1), a first coating (2), and a second coating (3), the second coating (3) being disposed on at least one surface of the current collector (1), the first coating (2) being disposed between the current collector (1) and the second coating (3), the first coating (2) comprising inorganic particles, and the peel force F between the first coating (2) and the second coating (3) satisfying the condition of 15 N≦F≦30 N. In this electrochemical device, by providing the first coating (2) comprising inorganic particles between the current collector (1) and the second coating (3) of the negative electrode, the adhesion between the current collector (1) and the second coating (3) can be effectively improved, the binder content of the second coating (3) can be reduced, and the proportion of negative electrode active material in the negative electrode can be increased, thereby improving the energy density of the lithium-ion battery.

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemical technology, and in particular to electrochemical apparatus and electronic devices. [Background technology]

[0002] During the manufacturing and use of lithium-ion batteries, the negative electrode active material is prone to detachment from the electrode surface, for example, after cold rolling, which is prone to decarbonization and reduces the battery capacity. During the use of the battery, the volume of the negative electrode material changes, which may cause the negative electrode material to detach from the surface of the electrode piece, creating a safety hazard.

[0003] In prior art, the decarbonization of the electrode pieces was often mitigated by coating a single conductive layer on the surface of the current collector. However, the conventional conductive layer was often too thick, resulting in a loss of energy density. At the same time, the conventional conductive layer limited the number of effective adhesion sites between the anode graphite and the conductive layer, resulting in decarbonization even after long battery cycles. Therefore, it is necessary to find a new way to increase the viscosity of the electrode pieces and reduce the shedding of the anode active material. Summary of the Invention

[0004] An object of the present invention is to provide an electrochemical device that enhances the adhesion between the negative electrode active material in the negative electrode piece and the electrode piece by providing a suitable coating between the negative electrode active material layer and the current collector.

[0005] A first aspect of the present invention is an electrochemical device including a negative electrode, the negative electrode including a current collector, a first coating, and a second coating, the second coating being disposed on at least one surface of the current collector, the first coating being disposed between the current collector and the second coating, the first coating including inorganic particles, and a peel force F between the first coating and the second coating being 15 N / m ≦F≦30N / m To provide an electrochemical device that satisfies the above requirements.

[0006] In some embodiments of the first aspect of the present invention, the particle diameter Dv50 of the inorganic particles satisfies 50 nm≦Dv50≦1 μm.

[0007] In some embodiments of the first aspect of the present invention, the inorganic particles have a Mohs hardness of 2.5 to 7.5.

[0008] In certain embodiments of the first aspect of the present invention, the inorganic particles comprise at least one of boehmite, aluminum powder, quartz sand, apatite, nanoceramic, and zircon.

[0009] In some embodiments of the first aspect of the present invention, the first coating further comprises a conductive agent, a binder, and a dispersant, and the mass percentages of the inorganic particles, the binder, the conductive agent, and the dispersant, based on the total mass of the first coating, are (2% to 10%):(30% to 60%):(30% to 60%):(2% to 5%).

[0010] In some embodiments of the first aspect of the present invention, the binder comprises at least one of styrene butadiene rubber, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polyacrylic acid ester, polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride, formaldehyde resin, cyclodextrin, and cyanoacrylate.

[0011] In some embodiments of the first aspect of the present invention, the dispersing agent comprises at least one of sodium methylol cellulose, lithium methylol cellulose, sodium alginate, propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate protein, casein, sodium polyacrylate, polyoxyethylene, and polyvinylpyrrolidone.

[0012] In certain embodiments of the first aspect of the present invention, the conductive agent comprises at least one of a zero-dimensional conductive agent and a one-dimensional conductive agent.

[0013] In some embodiments of the first aspect of the present invention, at least one of the following characteristics is met. The zero-dimensional conductive agent includes at least one of conductive carbon black, acetylene black, and ketjen black, and the Dv50 of the zero-dimensional conductive agent is 50 nm to 1 μm; The one-dimensional conductive agent includes at least one of a conductive carbon tube and a conductive carbon rod, and the average diameter of the one-dimensional conductive agent is 50 nm to 1 μm.

[0014] In some embodiments of the first aspect of the present invention, the thickness L of the first coating satisfies 100 nm≦L≦2 μm.

[0015] In some embodiments of the first aspect of the present invention, the coat weight X of the first coating is 0.02 mg / cm 2 ≦X≦0.15mg / cm 2 Satisfy.

[0016] In some embodiments of the first aspect of the present invention, the coverage of the first coating is between 50% and 100%.

[0017] In some embodiments of the first aspect of the present invention, the peel force between the first coating and the current collector is 10 N / m to 300 N / m.

[0018] In some embodiments of the first aspect of the present invention, the resistance of the negative electrode is 1 mΩ to 100 mΩ.

[0019] A second aspect of the present invention provides an electronic device comprising an electrochemical device provided by the first aspect of the present invention.

[0020] The electrochemical device of the present invention includes a first coating containing inorganic particles between the negative electrode current collector and the second coating, where the inorganic particles are encapsulated in a binder to form a stronger adhesive unit. The formation of the adhesive unit increases the adhesive strength and number of adhesive sites of the first coating, thereby effectively improving the adhesion between the current collector and the second coating. The stronger adhesive unit also increases the internal cohesion of the first coating layer, which can partially offset the tensile stress of the current collector, thereby increasing the strength of the current collector and making it less susceptible to breakage during processing. Furthermore, the first coating increases the adhesion between the second coating and the current collector, thereby reducing the binder content in the second coating and increasing the proportion of negative electrode active material in the negative electrode, thereby increasing the energy density of lithium-ion batteries. [Brief explanation of the drawings]

[0021] In order to more clearly explain the embodiments of the present invention and the technical solutions of the prior art, the following briefly introduces the necessary drawings used in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings from these drawings without any creative efforts. [Figure 1] FIG. 1 is a schematic diagram showing the structure of a negative electrode piece. DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to clarify the objectives, technical solutions and advantages of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and are not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative effort fall within the scope of protection of the present invention.

[0023] A first aspect of the present invention is an electrochemical device including a negative electrode, as shown in FIG. 1 , the negative electrode including a current collector 1, a first coating 2, and a second coating 3, the second coating 3 being disposed on at least one surface of the current collector 1, the first coating 2 being disposed between the current collector 1 and the second coating 3, the first coating 2 including inorganic particles, and a peel force F between the first coating 2 and the second coating 3 being 15 N. / m ≦F≦30N / m To provide an electrochemical device that satisfies the above requirements.

[0024] In the present invention, the second coating layer 3 may be a negative electrode active material layer. The inventors have found that adding inorganic particles to the first coating 2 significantly increases the peel strength between the first coating 2 and the second coating 3. Without being limited by any theory, the inventors believe that this is because the inorganic particles are encapsulated in the binder to form stronger adhesive units, increasing the adhesive strength and adhesive sites between the active material in the second coating 3 and the first coating 2.

[0025] The peeling force between the first coating layer and the negative electrode active material layer of the present invention is 15N. / m ~30N / m In the prior art, the peel force between the negative electrode active material layer and the current collector or adhesive coating can reach 10 N. / m The negative electrode piece of the present invention has a significantly higher peel strength between the negative electrode active material layer and the electrode piece than conventional negative electrode pieces.

[0026] Those skilled in the art should understand that the current collector of the present invention may have the first coating and the second coating on one surface thereof, or may have the first coating and the second coating on both surfaces thereof, and those skilled in the art should select according to actual needs.

[0027] In some embodiments of the first aspect of the present invention, the particle size Dv50 of the inorganic particles satisfies the range 50 nm≦Dv50≦1 μm. The inventors have found through research that an average particle size Dv50 of the inorganic particles greater than 50 nm can prevent aggregation of the inorganic particles, while an average particle size Dv50 of the inorganic particles greater than 1 μm can cause the surface of the first coating to become uneven, affecting the performance of the lithium-ion battery. By controlling the average particle size Dv50 of the inorganic particles within this range, on the one hand, the thickness of the first coating does not increase the thickness of the negative electrode, thereby avoiding a loss of volumetric energy density of the lithium-ion battery, and on the other hand, the surface flatness of the first coating can be ensured, thereby avoiding an impact on the performance of the lithium-ion battery.

[0028] In some embodiments of the first aspect of the present invention, the inorganic particles have a Mohs hardness of 2.5 to 7.5. The inventors have found through research that inorganic particles with too low a hardness are prone to deformation during the cold rolling process, resulting in poor stability of the internal structure of the first coating and affecting the strength of the adhesive bond formed between the inorganic particles and the binder. However, inorganic particles with too high a hardness result in significant wear on the coating device. The type of inorganic particles used in the present invention is not particularly limited, as long as they have a Mohs hardness in the range of 2.5 to 7.5, and the objectives of the present invention can be achieved. For example, the inorganic particles may include at least one of boehmite, aluminum powder, quartz sand, apatite, nanoceramics, and zircon. The Mohs hardness of zircon is approximately 7.5, the Mohs hardness of quartz sand is approximately 7, the Mohs hardness of nanoceramics is approximately 6, the Mohs hardness of boehmite is approximately 3, the Mohs hardness of aluminum powder is 2.75, and the Mohs hardness of apatite is 5. The inventors have found that the inorganic particles of the present invention are suitable as an additive for the first coating 2 because they have high compatibility with organic substances and are easily dispersed.

[0029] In some embodiments of the first aspect of the present invention, the first coating further comprises a conductive agent, a binder, and a dispersant, and the mass percentages of the inorganic particles, the binder, the conductive agent, and the dispersant, based on the total mass of the first coating, are (2% to 10%):(30% to 60%):(30% to 60%):(2% to 5%). Through research, the inventors found that if the mass of inorganic particles in the total mass of the first coating is less than 2%, the high strength effect of the inorganic particles will not be realized; if the mass of inorganic particles in the total mass of the first coating is more than 10%, the inorganic particles will be difficult to disperse, prone to particle aggregation, and the internal resistance of the electrode pieces will increase; by controlling the mass of the dispersant to 2% to 5% of the total mass of the first coating, the internal structure of the first coating can be made uniform and stable, and the aggregation of inorganic particles can be effectively prevented; if the mass of the binder in the total mass of the first coating is less than 30%, the adhesive effect will be insignificant; if the mass of the binder in the total mass of the first coating is more than 60%, the binder content will be too high and prone to inorganic particle aggregation; and by controlling the mass of the conductive agent to 30% to 60% of the total mass of the first coating, the conductivity of the negative electrode can be improved.

[0030] In the present invention, the type of binder is not particularly limited as long as the objectives of the present invention can be achieved. For example, the binder can include at least one of styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride, polyvinyl chloride, formaldehyde resin, cyclodextrin, and cyanoacrylate. The addition of a binder can increase the viscosity of the first coating layer, thereby increasing the adhesive strength between the first coating layer and the negative electrode current collector and between the first coating layer and the second coating layer, and can also reduce the binder content in the second coating layer.

[0031] In the present invention, the type of dispersant is not particularly limited as long as the objectives of the present invention can be achieved. For example, the dispersant can include at least one of methylol cellulose sodium, methylol cellulose lithium, sodium alginate, propylene glycol alginate, methyl cellulose, sodium starch phosphate, carboxymethyl cellulose sodium, sodium alginate protein, casein, sodium polyacrylate, polyoxyethylene, and polyvinylpyrrolidone. The addition of a dispersant can improve the uniformity and stability of the internal structure of the first coating and prevent aggregation of inorganic particles.

[0032] In some embodiments of the first aspect of the present invention, the conductive agent may include at least one of a zero-dimensional conductive agent and a one-dimensional conductive agent.

[0033] In the present invention, the types of zero-dimensional conductive agent and one-dimensional conductive agent are not particularly limited as long as the objectives of the present invention can be achieved. For example, the zero-dimensional conductive agent can include at least one of conductive carbon black, acetylene black, superconducting carbon black, granular graphite, and Ketjen black, with the zero-dimensional conductive agent having an average particle diameter Dv50 of 50 nm to 1 μm, and the one-dimensional conductive agent can include at least one of conductive carbon tubes and conductive carbon rods, with the one-dimensional conductive agent having an average diameter of 50 nm to 1 μm. The addition of a conductive agent can improve the conductivity of the negative electrode. By controlling the average particle diameter or average diameter of the conductive agent within the above range, the thickness of the first coating can be effectively controlled and loss of volumetric energy density of the lithium-ion battery can be avoided.

[0034] In some embodiments of the first aspect of the present invention, the thickness L of the first coating 2 satisfies 100 nm≦L≦2 μm, preferably 200 nm≦L≦1 μm. By controlling the thickness of the first coating 2 within the above range, an increase in the thickness of the negative electrode can be effectively controlled, and the energy density of the lithium-ion battery can be improved.

[0035] In some embodiments of the first aspect of the present invention, the coat weight X of the first coating 2 is 0.02 mg / cm 2 ≦X≦0.15mg / cm 2 By controlling the coating weight of the first coating within the above range, the thickness and coating uniformity of the first coating can be effectively controlled, the performance of the first coating can be effectively exhibited, and the energy density of the lithium-ion battery can be improved.

[0036] In some embodiments of the first aspect of the present invention, the coverage of the first coating on the current collector is 50% to 100%. By controlling the coverage of the first coating to 50% or more, the first coating functions effectively, improving the performance of the lithium-ion battery.

[0037] In some embodiments of the first aspect of the present invention, the peel force between the first coating 2 and the current collector 1 is 10 N / m to 300 N / m.

[0038] In some embodiments of the first aspect of the present invention, the resistance of the negative electrode piece is 1 mΩ to 100 mΩ. The inventors have found through research that when the resistance of the negative electrode piece is within the above range, the polarization of the lithium ion battery can be increased, the release of electrical energy can be reduced, and the safety of the lithium ion battery can be improved.

[0039] In the negative electrode of the present invention, the current collector is not particularly limited, and may be any negative electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, or a composite current collector. The negative electrode active material layer contains a negative electrode active material, and the negative electrode active material is not particularly limited, and may be any negative electrode active material known in the art. For example, it may contain at least one of artificial graphite, natural graphite, mesocarbon microbeads, silicon, silicon-carbon, silicon oxide, soft carbon, hard carbon, lithium titanate, and niobium titanate. In the present invention, the thicknesses of the negative electrode current collector and the negative electrode active material layer are not particularly limited, and may be any thickness that achieves the objectives of the present invention. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

[0040] The positive electrode in the present invention is not particularly limited as long as the objectives of the present invention can be achieved. For example, the positive electrode typically includes a positive electrode current collector and a positive electrode active material layer. Here, the positive electrode current collector is not particularly limited and may be a positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, or a composite current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not particularly limited and may be a positive electrode active material known in the art, such as at least one of nickel cobalt manganese oxide (811, 622, 523, 111), nickel cobalt lithium aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, and lithium titanate. In the present invention, the thicknesses of the positive electrode current collector and the positive electrode active material layer are not particularly limited as long as the objectives of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0041] Optionally, the positive electrode may further include a conductive layer located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0042] The lithium ion battery of the present invention further includes a separator for isolating the positive electrode from the negative electrode, preventing short circuits within the lithium ion battery, and allowing electrolyte ions to pass freely through the separator to complete the electrochemical charge and discharge process. In the present invention, the separator is not particularly limited as long as it can achieve the object of the present invention.

[0043] For example, at least one of polyolefin (PO) separators mainly made of polyethylene (PE) or polypropylene (PP), polyester films (e.g., polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex or aramid films, woven films, nonwoven films (nonwoven fabrics), microporous membranes, composite membranes, separator sheets, laminate films, and spun films may be used.

[0044] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a porous nonwoven fabric, film, or composite membrane. The material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic material.

[0045] For example, the inorganic layer contains inorganic particles and a binder, and the inorganic particles are not particularly limited and can be, for example, at least one selected from alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, etc. The binder is not particularly limited and can be, for example, one or a combination of two or more selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene), and the like.

[0046] The lithium ion battery of the present invention further includes an electrolyte, which may be at least one of a gel electrolyte, a solid electrolyte, and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent.

[0047] In some embodiments of the first aspect of the present invention, the lithium salt is at least one selected from LiPF, LiBF, LiAsF, LiClO, LiB(C6H5), LiCH3SO, LiCF3SO, LiN(SO2CF3), LiC(SO2CF3), LiSiF, LiBOB, and lithium difluoroborate. For example, LiPF can be selected as the lithium salt because it can provide high ionic conductivity and improve cycle characteristics.

[0048] The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, another organic solvent, or a combination thereof.

[0049] The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

[0050] Examples of the linear carbonate compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compounds include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Illustrative examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

[0051] Illustrative examples of the carboxylic acid ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonate lactone, caprolactone, and combinations thereof.

[0052] Illustrative examples of such ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0053] Illustrative examples of such other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, and combinations thereof.

[0054] The process for preparing an electrochemical device is well known to those skilled in the art, and is not particularly limited in the present invention. For example, an electrochemical device can be produced by stacking a positive electrode and a negative electrode with a separator interposed therebetween, winding or folding the stack as necessary, placing the stack in a case, injecting an electrolyte into the case, and sealing the case. Furthermore, an overcurrent protection element, lead plates, etc. may be placed in the case as needed to prevent pressure buildup and overcharge / overdischarge within the electrochemical device.

[0055] A second aspect of the present invention provides an electronic device comprising an electrochemical device provided by the first aspect of the present invention.

[0056] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic organizer, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor.

[0057] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0058] Measurement method and device:

[0059] Measurement method for the average particle size Dv50 of inorganic particles: The average particle size Dv50 of the inorganic particles was measured using a Malvern laser particle sizer MS 3000.

[0060] Dv50 refers to the particle size of inorganic particles at which the cumulative volume reaches 50% from the small diameter side in the volume-based particle size distribution. In other words, the volume of inorganic particles smaller than this particle size accounts for 50% of the total volume of inorganic particles.

[0061] First and second coating thickness measurements: 1) The negative electrode piece to which the first and second coatings were applied was removed from the completed lithium ion battery. 2) Using a plasma cutting technique, the negative electrode piece obtained in 1) was cut along the thickness direction of the negative electrode piece to obtain cross sections of the first coating and the second coating. 3) The cross sections of the first and second coatings obtained in 2) were observed under an SEM (electron microscope) (the observed cross section length had to be 2 cm or more), and the thicknesses of the first and second coatings were measured under the SEM. Each layer had to be measured at 15 or more different positions, and the average thickness value of all measurement positions for each layer was recorded as the thickness value of the corresponding layer.

[0062] How to measure the coverage of the first coating: (1) The actual area of ​​the pole piece is S1. (2) After the above-mentioned pole piece was immersed in deionized water for 2 hours, the graphite layer on the pole piece was wiped off, and the area of ​​the exposed undercoat layer was designated as S2. (3) The coating coverage B was calculated using the following formula: B = S2 / S1 × 100%.

[0063] Measuring the adhesion between the first and second coatings 1) The negative electrode pieces prepared in Examples 1 to 19 and Comparative Examples 1 and 2 were taken and cut into samples with a width of 30 mm and a length of 100 to 160 mm using a cutter blade. 2) Special double-sided tape was attached to the steel plate, and the tape width was 20 mm and the length was 90 to 150 mm. 3) The pole piece sample cut out in step (1) was attached to double-sided tape with the measurement surface facing down. 4) A paper tape with the same width as the pole piece and a length 80 to 200 mm longer than the length of the sample was inserted under the pole piece and fixed with wrinkle tape. 5) Turn on the SANSTest tensile testing machine, and adjust the limit block to the appropriate position until the indicator light comes on. 6) Click Test, the device will enter test mode and read the data after it finishes.

[0064] Measurement of adhesion between the first coating and the current collector 1) In Examples 1 to 19 and Comparative Examples 1 and 2, in the process of preparing the negative electrode pieces, a first coating was formed on the current collector, and a negative electrode piece not coated with a negative electrode active material layer was taken, and a sample having a width of 30 mm and a length of 100 to 160 mm was cut out with a cutter blade. 2) Special double-sided tape was attached to the steel plate, and the tape width was 20 mm and the length was 90 to 150 mm. 3) The pole piece sample cut out in step (1) was attached to double-sided tape with the measurement surface facing down. 4) A paper tape with the same width as the pole piece and a length 80 to 200 mm longer than the length of the sample was inserted under the pole piece and fixed with wrinkle tape. 5) Turn on the SANSTest tensile testing machine, and adjust the limit block to the appropriate position until the indicator light comes on. 6) Click Test, the device will enter test mode and read the data after it finishes.

[0065] Cycle characteristic test: The test temperature was 25°C / 45°C. The battery was charged to 4.4 V at a constant current of 0.7 C, then charged to 0.025 C at a constant voltage, and allowed to stand for 5 minutes before discharging to 3.0 V at 0.5 C. The capacity obtained in this step was designated the initial capacity. A cycle test was conducted with a 0.7 C charge / 0.5 C discharge. The ratio of the capacity at each step to the initial capacity was calculated, and a capacity decay curve was obtained. The number of cycles required to achieve a capacity retention rate of 90% at 25°C was designated the room-temperature cycle characteristic of the lithium-ion battery, and the number of cycles required to achieve a capacity retention rate of 80% at 45°C was designated the high-temperature cycle characteristic of the lithium-ion battery. The cycle characteristics of the material were determined by comparing the number of cycles required for these two tests.

[0066] Discharge Rate Test: At 25°C, the battery was discharged to 3.0V at 0.2C, allowed to stand for 5 minutes, charged to 4.45V at 0.5C, charged to 0.05C at a constant voltage, allowed to stand for 5 minutes, and the discharge rate was adjusted. Discharge tests were performed at 0.2C, 0.5C, 1C, 1.5C, and 2.0C to obtain the discharge capacity. The capacity obtained at each rate was compared with the capacity obtained at 0.2C, and the rate characteristics were compared by comparing the ratio of 2C to 0.2C.

[0067] Example 1 <Preparation of first coating slurry> Carbon nanotubes and Sodium carboxymethylcellulose (CMC) is placed in a stirring tank and dispersed uniformly, and a certain amount of deionized water is added to accelerate the dispersion until no colloids appear. Sodium carboxymethylcellulose After the three components were completely dissolved, a certain amount of quartz sand was added and the three components were mixed and dispersed again. Finally, styrene butadiene rubber, which is a binder, was added and dispersed again to obtain a first coating slurry. Sodium carboxymethylcellulose The mass ratio of the quartz sand and the styrene-butadiene rubber was 37:4:4:55, and the Dv50 of the quartz sand was 200 nm.

[0068] <Preparation of negative electrode piece containing first coating> The obtained first coating slurry was applied to the surface of a copper foil serving as a negative electrode current collector to obtain a first coating having a thickness of 380 nm. The coverage of the first coating was 90%, and the coating weight of the first coating was 0.08 mg / cm. 2 It was.

[0069] The negative electrode active materials, graphite, styrene-butadiene polymer, and sodium carboxymethylcellulose, were mixed in a weight ratio of 97.5:1.3:1.2, and deionized water was added as a solvent to prepare a slurry with a solids content of 70%. The slurry was uniformly applied to a first coating, dried at 110°C, and cold-rolled to obtain a negative electrode piece having a first coating and a negative electrode active material layer coated on one side, with the negative electrode active material layer having a thickness of 150 μm.

[0070] After completing the above steps, the same steps were repeated on the back side of the negative electrode piece, resulting in a negative electrode piece with double-sided coating. After coating was complete, the negative electrode piece was cut into a sheet measuring 76 mm x 851 mm, and a tab was welded onto it for later use.

[0071] <Preparation of positive electrode piece> The positive electrode active materials, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a 75% solids slurry. The mixture was then uniformly stirred. The slurry was then uniformly coated onto one surface of a 10 μm-thick aluminum foil current collector and dried at 90°C to obtain a positive electrode piece with a coating thickness of 110 μm. After completing these steps, the positive electrode piece was coated on one side. The same steps were then repeated on the other surface of the same positive electrode piece, resulting in a positive electrode piece coated on both sides. After coating was complete, the electrode piece was cut into 38 mm x 58 mm pieces for future use.

[0072] <Preparation of electrolyte> In a dry argon atmosphere, organic solvents ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to obtain an organic solution, and then lithium hexafluorophosphate, a lithium salt, was added to the organic solvent and dissolved and mixed uniformly to obtain an electrolyte solution with a lithium salt concentration of 1.15 mol / L.

[0073] <Preparation of separator> Alumina and polyvinylidene fluoride were mixed in a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry with a solid content of 50%.The ceramic slurry was then uniformly coated onto one side of a porous substrate (polyethylene, 7 μm thick, 0.073 μm average pore size, 26% porosity) using a microgravure coating method, and dried to obtain a two-layer structure consisting of a ceramic coating and a porous substrate.The ceramic coating was 50 μm thick.

[0074] Polyvinylidene fluoride (PVDF) and polyacrylate were mixed in a mass ratio of 96:4 and dissolved in deionized water to form a polymer slurry with a solid content of 50%. The polymer slurry was then uniformly applied to both surfaces of the two-layer structure of the ceramic coating and porous substrate using a microgravure coating method, and dried to obtain a separator, of which the thickness of the single layer coating formed by the polymer slurry was 2 μm.

[0075] <Preparation of lithium-ion batteries> The positive electrode, separator, and negative electrode pieces prepared above were stacked in this order, with a separator placed between the positive and negative electrode pieces for isolation, and then wound up to obtain an electrode assembly. The electrode assembly was then placed in an aluminum laminate film packaging bag, dehydrated at 80°C, and the prepared electrolyte was injected. The resulting lithium-ion battery was then vacuum packaged, left to stand, formed, and shaped.

[0076] Example 2 The same as Example 1 except that the quartz sand was replaced with zircon powder.

[0077] Example 3 The same as Example 1 except that the quartz sand was replaced with boehmite.

[0078] Example 4 carbon nanotubes, Sodium carboxymethylcellulose The results were the same as in Example 3, except that the mass ratio of the styrene-butadiene rubber and boehmite was adjusted to 37:4:3:56.

[0079] Example 5 carbon nanotubes, Sodium carboxymethylcellulose The same as in Example 3 except that the mass ratio of the styrene-butadiene rubber and the boehmite was adjusted to 37:4:5:54.

[0080] Example 6 carbon nanotubes, Sodium carboxymethylcelluloseThe results were the same as in Example 3, except that the mass ratio of the styrene-butadiene rubber and boehmite was adjusted to 37:4:10:49.

[0081] Example 7 The binder, styrene butadiene rubber, was replaced with a mixture of formaldehyde resin and cyclodextrin in a mass ratio of 1:1, and carbon nanotubes, Sodium carboxymethylcellulose The same as in Example 3 except that the mass ratio of the cellulose acylate, boehmite, and binder was adjusted to 57:4:4:35.

[0082] Example 8 The binder styrene butadiene rubber was replaced with a mixture of polyvinyl alcohol and polyacrylic acid in a mass ratio of 4:6, the carbon nanotubes were replaced with conductive carbon rods, the dispersant CMC was replaced with polyvinylpyrrolidone (PVP), and the mass ratio of the conductive carbon rods, PVP, boehmite, and binder was adjusted to 43:4:4:49. It was the same as Example 3.

[0083] Example 9 The same as Example 3 was performed except that the binder styrene butadiene rubber was replaced with polyacrylonitrile, the carbon nanotubes were replaced with acetylene black, the dispersant CMC was replaced with casein, and the mass ratio of acetylene black, casein, boehmite, and polyacrylonitrile was adjusted to 39:3:4:54.

[0084] Example 10 The same as in Example 3 except that the binder styrene butadiene rubber was replaced with polyacrylic acid, the dispersant CMC was replaced with sodium alginate (SA), and the mass ratio of carbon nanotubes, sodium alginate, boehmite, and polyacrylic acid was adjusted to 38:2:4:56.

[0085] Example 11 The binder styrene butadiene rubber was replaced with a mixture of polyacrylonitrile, polyacrylic acid and polyacrylic acid ester in a mass ratio of 4:5:1, and carbon nanotubes, Sodium carboxymethylcellulose The same as in Example 3 except that the mass ratio of the cellulose acylate, boehmite, and binder was adjusted to 32:5:4:59.

[0086] Example 12 Carbon nanotubes are replaced with conductive carbon black, and the coating weight is 0.02 mg / cm 2 The results were the same as in Example 3, except that the temperature was adjusted to

[0087] Examples 13 to 17 Coating weight: 0.05 mg / cm 2 , 0.08 mg / cm 2 , 0.1 mg / cm 2 , 0.13 mg / cm 2 , 0.15 mg / cm 2 The procedure was the same as in Example 12, except that the temperature was adjusted to

[0088] Example 18 The same as in Example 3, except that the Dv50 of the boehmite was adjusted to 50 nm and the thickness of the first coating was adjusted to 1000 nm.

[0089] Examples 19 to 26 The same as in Example 18 except that the particle diameter Dv50 of the boehmite was adjusted to 100 nm, 150 nm, 200 nm, 300 nm, 350 nm, 400 nm, 800 nm, and 1000 nm.

[0090] Example 27 The same as in Example 3, except that the Dv50 of the boehmite was adjusted to 100 nm and the thickness of the first coating was adjusted to 100 nm.

[0091] Examples 28 to 34 The same as in Example 27, except that the thickness of the first coating was adjusted to 220 nm, 300 nm, 380 nm, 580 nm, 650 nm, 800 nm, and 1700 nm.

[0092] Examples 35 to 39 The same procedures were carried out as in Example 3, except that the coverage of the first coating was adjusted to 100%, 80%, 70%, 60%, and 50%, respectively.

[0093] Comparative Example 1 carbon nanotubes, Sodium carboxymethylcellulose The same as in Example 1 except that the mass ratio of the quartz sand and the styrene-butadiene rubber was adjusted to 41:4:0:55.

[0094] Comparative Example 2 Same as Example 3 except that boehmite was replaced with alumina.

[0095] Comparative Examples 3 and 4 The coating weight is 0.01 mg / cm 2 , 0.16 mg / cm 2 The procedure was the same as in Example 12, except that the temperature was adjusted to

[0096] Comparative Examples 5 and 6 The same procedure as in Example 18 was carried out except that the particle diameter Dv50 of the boehmite was adjusted to 45 nm and 1050 nm.

[0097] Comparative Examples 7 and 8 The same as in Example 27, except that the thickness of the first coating was adjusted to 2100 nm and 50 nm.

[0098] Comparative Example 9 The same as in Example 3 except that the coverage of the first coating was adjusted to 45%.

[0099] Tables 1 to 5 show the parameters and measurement results for each of the examples and comparative examples.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3]

[0103] [Table 4]

[0104] [Table 5]

[0105] The electrochemical device of the present invention has a significantly improved peel strength between the first coating and the second coating of the negative electrode piece, both of which are 15N. / m or more, and the adhesion of the pole pieces is improved, which leads to corresponding improvements in the rate and cycle performance of the battery.

[0106] As can be seen from Examples 1 to 3 and Comparative Examples 1 and 2, adding inorganic particles to the first coating has a significant effect on increasing the peel strength of the pole pieces, and the type of inorganic particles also affects the viscosity of the pole pieces. Through research, the inventors unexpectedly discovered that when the Mohs hardness of the inorganic particles is 2.5 to 7.5, the effect of improving the adhesive strength of the pole pieces becomes more pronounced. For example, when alumina is added (Mohs hardness is 9), the peel strength between the first coating and the second coating is only 5N. / m From 7N / m When boehmite was used, the / m rose to.

[0107] As can be seen from Examples 4 to 6, when the mass content of inorganic particles is 2% to 10%, the pole pieces have higher adhesive strength, and the peel force between the first coating and the second coating is 20 N. / mIn some preferred embodiments of the present invention, the content of inorganic particles is 2% to 5%.

[0108] As can be seen from Examples 7 to 11, when the mass content of the binder is within the range of 30% to 60%, the mass content of the conductive agent is within the range of 60% to 30%, and the mass content of the dispersant is within the range of 2% to 5%, the peel force between the first coating and the second coating is 15 N. / m The peel strength between the first and second coatings increased with increasing binder content, and the conductive agent content gradually decreased with increasing binder content. As can be seen from Example 11, the adhesive strength of the pole pieces improved with decreasing conductive agent content, but the discharge rate characteristics and cycle performance of the battery decreased. Therefore, in some embodiments of the present invention, the binder mass content is 30% to 60%, and the conductive agent content is 30% to 60%.

[0109] Furthermore, as can be seen from Examples 7 to 11, even when different types of binders, dispersants, and conductive agents of the present invention are used, a high peel strength can be achieved between the first coating and the second coating.

[0110] As can be seen from Examples 12 to 17 and Comparative Examples 3 and 4, the coating weight of the first coating affects the adhesive strength of the pole piece, and when the coating weight is 0.02 to 0.08 mg / cm 2 When the coating weight is 0.08 to 0.15 mg / cm, the peel strength between the first and second coatings increases with increasing coating weight. 2 Therefore, in some preferred embodiments of the present invention, the coating weight X of the first coating is 0.02 mg / cm or less. 2 ≦X≦0.15mg / cm 2 Meet the following.

[0111] As can be seen from Examples 18 to 26 and Comparative Examples 5 and 6, when the particle size Dv50 of the inorganic particles is 200 nm or less, the peel force between the first coating and the second coating gradually increases with increasing particle size, whereas when the particle size exceeds 200 nm, the peel force between the first coating and the second coating gradually decreases with increasing particle size. Therefore, in some preferred embodiments of the present invention, the particle size of the inorganic particles is 50 nm to 1 μm.

[0112] As can be seen from Examples 27 to 34 and Comparative Examples 7 and 8, when the thickness of the first coating is 380 nm or less, the peel force between the first coating and the second coating gradually increases with increasing coating thickness, whereas when the thickness of the first coating is greater than 380 nm, the peel force between the first coating and the second coating gradually decreases with increasing coating thickness, and the energy density of the battery also decreases with increasing coating thickness. Therefore, in some preferred embodiments of the present invention, the thickness of the first coating is 100 nm to 2 μm.

[0113] As can be seen from Example 3, Examples 35 to 39 and Comparative Example 9, the higher the coverage of the first coating, the stronger the adhesion of the pole pieces. In some embodiments of the present invention, the coverage of the first coating on the surface of the current collector is 50% to 100%.

[0114] It should be noted here that the adhesion strength of the pole piece includes the peeling force between the first coating and the current collector and the peeling force between the first coating and the second coating, and since the peeling force between the first coating and the current collector is much greater than the peeling force between the first coating and the second coating, in the present invention, the peeling force between the first coating and the second coating mainly reflects the adhesion strength of the pole piece.

[0115] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. An electrochemical device comprising a negative electrode, the negative electrode comprising a current collector, a first coating, and a second coating; the second coating is disposed on at least one surface of the current collector, and the first coating is disposed between the current collector and the second coating; the electrochemical device is a lithium ion battery; the first coating includes inorganic particles, a conductive agent, and a binder; the inorganic particles include at least one of boehmite, aluminum powder, quartz sand, apatite, nanoceramic, and zircon; The particle diameter Dv50 of the inorganic particles satisfies 50 nm≦Dv50≦1 μm, a thickness L of the first coating satisfies 100 nm≦L≦2 μm; the second coating is a negative electrode active material layer, a peel force F between the first coating and the second coating satisfies 15 N / m≦F≦30 N / m; The electrochemical device, wherein the peel force between the first coating and the current collector is 10 N / m to 300 N / m.

2. 2. The electrochemical device according to claim 1, wherein a peel force F between the first coating and the second coating satisfies 16 N / m≦F≦25 N / m.

3. 2. The electrochemical device according to claim 1, wherein the particle diameter Dv50 of the inorganic particles satisfies 50 nm≦Dv50≦800 nm.

4. 2. The electrochemical device according to claim 1, wherein the particle diameter Dv50 of the inorganic particles satisfies 100 nm≦Dv50≦400 nm.

5. 2. The electrochemical device according to claim 1, wherein the particle diameter Dv50 of the inorganic particles satisfies 150 nm≦Dv50≦350 nm.

6. 2. The electrochemical device according to claim 1, wherein the inorganic particles have a Mohs hardness of 2.5 to 7.

5.

7. 2. The electrochemical device of claim 1, wherein the first coating further comprises a dispersant, and the mass percentages of the inorganic particles, the binder, the conductive agent, and the dispersant, based on the total mass of the first coating, are (2% to 10%):(30% to 60%):(30% to 60%):(2% to 5%).

8. the binder contains at least one of styrene butadiene rubber, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polyacrylic acid ester, polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride, formaldehyde resin, cyclodextrin, and cyanoacrylate; the dispersing agent comprises at least one of sodium methylol cellulose, lithium methylol cellulose, sodium alginate, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate protein, casein, sodium polyacrylate, polyoxyethylene, and polyvinylpyrrolidone; the conductive agent includes at least one of a zero-dimensional conductive agent and a one-dimensional conductive agent; The electrochemical device according to claim 7 , wherein at least one of the following is satisfied:

9. The conductive agent is The zero-dimensional conductive agent includes at least one of conductive carbon black, acetylene black, and ketjen black, and the Dv50 of the zero-dimensional conductive agent is 50 nm to 1 μm; The one-dimensional conductive agent includes at least one of a conductive carbon tube and a conductive carbon rod, and the average diameter of the one-dimensional conductive agent is 50 nm to 1 μm; The electrochemical device according to claim 8 , wherein at least one of the following is satisfied:

10. The coating weight X of the first coating is 0.02 mg / cm ２ ≦X≦0.15mg / cm ２ The electrochemical device according to claim 1 , wherein

11. 2. The electrochemical device of claim 1, wherein the coverage of the first coating is between 50% and 100%.

12. 2. The electrochemical device according to claim 1, wherein the resistance of the negative electrode is 1 mΩ to 100 mΩ.

13. An electronic device comprising an electrochemical device according to any one of claims 1 to 12.

Images