Electrochemical devices and electronic devices

Abstract

This application provides an electrochemical device and an electronic device. The electrochemical device includes: a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector and a positive active material layer on the positive current collector. The negative electrode includes a negative current collector and a negative active material layer on the negative current collector. The positive active material layer includes a positive electrode material, and the negative active material layer includes a negative electrode material, satisfying: m 正 It is 0.08 mg / mm 2 Up to 0.21 mg / mm 2 S 正 175mAh / g to 190mAh / g, m 负 It is 0.05 mg / mm 2 Up to 0.11 mg / mm 2 S 负 355mAh / g to 365mAh / g and 0.3≤D 1 v10 / D 2 v10≤1.7; where m 正 S is the weight of a single-sided positive electrode active material layer per unit area of ​​the positive electrode current collector. 正 The specific capacity of the positive electrode material is expressed in mAh / g. 负 S is the weight of the single-sided negative electrode active material layer per unit area of ​​the negative electrode current collector. 负 D represents the specific capacity of the negative electrode material. 1 v10 is the positive electrode material Dv10, D 2 v10 is Dv10, the negative electrode material. The electrochemical device of this application can improve energy density while enhancing cycle performance.

Description

[0001] This application is a divisional application of the invention patent filed on March 31, 2021, with application number 202110350909X and invention title "Electrochemical Device and Electronic Device". Technical Field

[0002] This application relates to the field of electrochemical energy storage, and more particularly to positive electrochemical devices and electronic devices. Background Technology

[0003] Electrochemical devices, such as lithium-ion batteries, are widely used in electronic products such as laptops, mobile phones, and digital cameras, as well as in electric vehicles. With the increasing application of electrochemical devices, the market demand for their energy density is getting higher and higher. Some technologies increase the energy density of electrochemical devices by increasing their operating voltage. However, charging and discharging at high voltages can easily lead to irreversible phase transitions and structural collapse of materials. Furthermore, they are prone to reacting with the electrolyte, causing damage to the material surface and gas generation problems, which in turn affect the safety performance and service life of the electrochemical device. It is evident that the existing improvement solutions are unsatisfactory, and further improvements are expected. Summary of the Invention

[0004] Embodiments of this application provide an electrochemical device and an electronic device;

[0005] This application discloses an electrochemical device, comprising: a positive electrode, a negative electrode, an electrolyte, and a separating membrane;

[0006] The positive electrode includes a positive current collector and a positive active material layer located on the positive current collector, and the negative electrode includes a negative current collector and a negative active material layer located on the negative current collector. The positive active material layer includes a positive electrode material, and the negative active material layer includes a negative electrode material, and satisfies Formula I.

[0007] Formula I: 37≤227×m 负 ×S 负 / (S 正 ×m 正 )-S 正 ≤75; where m 正 S is the weight of the positive electrode active material layer per unit area of ​​the positive electrode current collector. 正 The specific capacity of the positive electrode material is expressed in mAh / g. 负 S is the weight of the negative electrode active material layer per unit area of ​​the negative electrode current collector. 负 The specific capacity of the negative electrode material.

[0008] In some embodiments, at least one of (a) to (f) is further satisfied: (a) 0.52 ≤ m negative / m positive ≤ 0.62; (b) 1.1 ≤ d negative / d positive ≤ 1.4, where d negative is the thickness of the negative electrode active material layer and d positive is the thickness of the positive electrode active material layer; (c) m positive is from 0.08 mg / mm2 to 0.21 mg / mm2; (d) S positive is from 175 mAh / g to 190 mAh / g; (e) m negative is from 0.05 mg / mm2 to 0.11 mg / mm2; (f) S negative is from 355 mAh / g to 365 mAh / g.

[0009] In some embodiments, the following is further satisfied: 0.3 ≤ D 1 v10 / D 2 v10 ≤ 1.7, and 0.7 ≤ D 1 v50 / D 2 v50 ≤ 2.3; D 1 v10 and D 1 v50 are the Dv10 and Dv50 of the positive electrode material respectively; D 2 v10 and D 2 v50 are the Dv10 and Dv50 of the negative electrode material respectively.

[0010] In some embodiments, the tap density A of the positive electrode active material layer and the tap density B of the negative electrode active material layer satisfy: 1.96 ≤ A / B ≤ 3.07.

[0011] In some embodiments, the positive electrode material includes Li x Co y M z O 2-a F a , where 0.9 < x < 1.05, 0.95 ≤ y < 1, 0 ≤ z < 0.05, 0 ≤ a < 2, and M includes at least one of Al, Mg, Ti, Zr, Ni, Mn, Y, Nb, La, V, Zn, Mo, Ru, Ta, W, Re, Sn, Ge, or Ga.

[0012] In some embodiments, the following is further satisfied: 5.2 ≤ D 1 v90 / D 1 v10 ≤ 10.6 and 2 ≤ D 2 v90 / D 2 v10 ≤ 10; D 1 v90 and D 1 v10 are the Dv90 and Dv10 of the positive electrode material respectively; D 2 v90 and D 2 v10 are the Dv90 and Dv10 of the negative electrode material respectively.

[0013] In some embodiments, when the electrochemical device is in a state of charge of 30% to 60%, the interlayer spacing d of the (002) crystal plane of the negative electrode material is... 002 nm and the cell parameter cm of the cathode material satisfy: 3.50 ≤ c / d 002 ≤4.20.

[0014] In some embodiments, the electrochemical device was tested with a three-electrode electrode at 25°C, and the test results satisfied: 0.05V ≤ V1 - V 正 ≤0.08V; where V1 is the voltage difference between the positive and negative electrodes obtained by three-electrode testing of the electrochemical device when it is 100% charged, in volts (V). 正 The voltage of the positive electrode material obtained through a three-electrode test is expressed in volts.

[0015] In some embodiments, the negative electrode active material layer includes Co, and the mass content of Co is from 500 ppm to 1500 ppm based on the mass of the negative electrode active material layer.

[0016] This application also proposes an electronic device comprising any of the above-mentioned electrochemical devices.

[0017] This application proposes an electrochemical device and an electronic device. The electrochemical device proposed in this application controls the weight per unit area of ​​the negative electrode active material layer, the specific capacity of the negative electrode material, the specific capacity of the positive electrode material, and the weight of the positive electrode active material layer within a certain range, and takes into account their mutual influence, so that they satisfy the above formula I, so that the electrochemical device has comprehensive and balanced excellent performance, and can improve energy density while improving cycle performance. Detailed Implementation

[0018] The following embodiments are intended to enable those skilled in the art to fully understand this application, but do not limit this application in any way.

[0019] Electrochemical devices, such as lithium-ion batteries, are widely used in consumer electronic devices such as laptops and mobile phones, as well as electric devices such as drones and electric vehicles. As users demand higher energy density from electrochemical devices, some technologies increase the operating voltage of the devices to release more energy. However, high operating voltage can easily lead to irreversible phase changes in materials and increase side reactions in the electrolyte, resulting in increased gas production. Therefore, providing an electrochemical device that balances high energy density and low expansion is an urgent problem to be solved.

[0020] This application proposes an electrochemical device, comprising: a positive electrode, a negative electrode, and a separator; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode current collector may be, for example, aluminum foil, and the positive electrode active material layer on the positive electrode current collector may be located on one or both sides of the positive electrode current collector; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, the negative electrode current collector may be, for example, copper foil, and the negative electrode active material layer may be located on one or both sides of the negative electrode current collector; the positive electrode active material layer comprises a positive electrode material, the positive electrode material may include, for example, at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, etc.; the negative electrode active material layer comprises a negative electrode material, the negative electrode material may include, for example, graphite; the electrochemical device in the embodiments of this application satisfies Formula I;

[0021] Formula I: 37≤227×m 负 ×S 负 / (S 正 ×m 正 )-S 正 ≤75;

[0022] Where, m 正 S is the weight of a single-sided positive electrode active material layer per unit area of ​​the positive electrode current collector. 正 The specific capacity of the positive electrode material is expressed in mAh / g, m 负 S is the weight of the single-sided negative electrode active material layer per unit area of ​​the negative electrode current collector. 负 The specific capacity of the negative electrode material.

[0023] During the charging and discharging process of an electrochemical device, a certain amount of ions (e.g., lithium ions) migrate and insert into the negative electrode material. In this embodiment, the weight per unit area of ​​the negative electrode active material layer, the specific capacity of the negative electrode material, the specific capacity of the positive electrode material, and the weight per unit area of ​​the positive electrode active material layer are controlled. Considering their mutual influence, they are controlled to satisfy the above formula I, which helps to ensure that the amount of ion insertion / extraction is controlled within a certain range during the ion insertion / extraction process. This ensures that the maximum amount of ions extracted increases the energy density of the battery, while maintaining the stability of the positive electrode material itself. For the negative electrode material, the improved stability of the positive electrode material can prevent the structural collapse caused by excessive extraction of the positive electrode material, resulting in the partial decomposition of the structure into the electrolyte and accumulation on the surface of the negative electrode material, thus avoiding excessive expansion of the negative electrode material and its impact on cycle life.

[0024] Furthermore, m 正 It is 0.08 mg / mm 2 Up to 0.21 mg / mm 2 S 正 The range is from 175mAh / g to 190mAh / g, m 负 It is 0.05 mg / mm 2Up to 0.11 mg / mm 2 S 负 The capacity is between 355 mAh / g and 365 mAh / g. Controlling this within a certain range improves the overall performance of the electrochemical device.

[0025] In some embodiments of this application, 0.5 ≤ m 负 / m 正 ≤0.6. In some embodiments of this application, the weight of the positive active material layer per unit area of ​​the positive current collector and the weight of the negative active material layer per unit area of ​​the negative current collector are correlated. By limiting the relationship between the positive electrode material, negative electrode material, positive active material layer, and negative active material layer to satisfy Equation I, while considering the specific capacity of the negative electrode material and the positive electrode material, m is controlled. 负 and m 正 The ratio is within a certain range, so as to ensure that the negative electrode material can accommodate enough ions to be inserted and removed from the positive electrode material without causing waste. When the weight of the positive active material layer per unit area on the positive electrode current collector is large, it is beneficial to ensure a better volumetric energy density. When it is small, it is beneficial to ensure a better charging speed. It can be adjusted according to the needs.

[0026] In some embodiments of this application, 1.1≤d 负 / d 正 ≤1.4, where d 负 d represents the thickness of the negative electrode active material layer. 正 The thickness of the positive electrode active material layer is given. In this application, the thicknesses of the negative electrode active material layer and the positive electrode active material layer are related because the rates of ion insertion and extraction need to be balanced. If the rate of ion extraction (e.g., lithium ions) from the positive electrode during charging is greater than the rate of ion insertion from the negative electrode, ions will accumulate on the surface of the negative electrode active material layer. Therefore, some embodiments of this application control d... 负 and d 正 The ratio of ions to the positive and negative electrodes is beneficial for the transfer of ions between them.

[0027] In some embodiments of this application, the electrochemical device also satisfies: 0.3 ≤ D 1 v10 / D 2 v10≤1.7, and 0.7≤D 1 v50 / D 2 v50≤2.3;D 1 v10 and D 1 v50 represents Dv10 and Dv50 of the cathode material, respectively; D 2 v10 and D 2v50 represents Dv10 and Dv50 of the negative electrode material respectively. In some embodiments, the areas of particles with different particle sizes are different. Therefore, the particle size will affect the rates of ion deintercalation and intercalation. If the rates of ion deintercalation in the positive electrode material and the negative electrode material are inconsistent, it will lead to an increase in polarization. In some embodiments of the present application, by controlling the proportional relationship of the particle sizes of the positive electrode material and the negative electrode material within the above range, it is beneficial for the ions to deintercalate from the positive electrode material and also beneficial for the ions to intercalate into the negative electrode material.

[0028] In some embodiments of the present application, the tap density A of the positive electrode active material layer and the tap density B of the negative electrode active material layer satisfy: 1.96 ≤ A / B ≤ 3.07. In some embodiments, the higher the tap density, the lower the porosity and the fewer the ion transport channels. Considering the relationship between the rates of ion deintercalation and intercalation in the positive electrode material and the negative electrode material, in order to balance the reaction rates of the positive electrode and the negative electrode during the charge and discharge process of the electrochemical device, it is necessary to control the relationship between the tap densities of the positive electrode active material layer and the negative electrode active material layer within the above range, so as to ensure both the energy density of the electrochemical device and the normal deintercalation and intercalation of ions in the positive electrode and the negative electrode.

[0029] In some embodiments of the present application, the positive electrode material includes Li x Co y M z O 2-a F a , where 0.9 < x < 1.05, 0.95 ≤ y < 1, 0 ≤ z < 0.05, 0 ≤ a < 2, and M includes at least one of Al, Mg, Ti, Zr, Ni, Mn, Y, Nb, La, V, Zn, Mo, Ru, Ta, W, Re, Sn, Ge or Ga. In some embodiments of the present application, using the above materials can ensure that the positive electrode material can release more lithium at a relatively high voltage while maintaining the structural stability.

[0030] In some embodiments of the present application, the electrochemical device also satisfies: 5.2 ≤ D 1 v90 / D 1 v10 ≤ 10.6, and 2 ≤ D 2 v90 / D 2 v10 ≤ 10; D 1 v90 and D 1 v10 represent Dv90 and Dv10 of the positive electrode material respectively; D 2 v90 and D 2v10 represents Dv90 and Dv10 of the negative electrode material, respectively. In some embodiments, controlling the ratio of Dv90 to Dv10 of the positive electrode material is beneficial for lithium-ion insertion / extraction, reducing polarization, and improving the stability and specific capacity of the positive electrode material, such as stability under high voltage systems. Controlling the ratio of Dv90 to Dv10 of the negative electrode material is beneficial for rapid lithium-ion insertion. Simultaneously, controlling the positive electrode material particles and the negative electrode material can improve their compatibility. By rationally matching the parameter relationships of the positive and negative electrode materials, the improvement effect can be further enhanced.

[0031] In some embodiments of this application, Raman scanning was performed on particles within a 100 μm × 100 μm area of ​​the negative electrode material to obtain the G peak (1350 cm⁻¹) of all particles within this area. -1 ) and D peak (1580cm) -1 The peak intensities of ) are denoted as I. D and I G It should be noted that different devices may have errors; therefore, the G peak and D peak described here can represent the peak at 1350 cm⁻¹. -1 and 1580cm -1 The peak value within the range of ±50 satisfies 0.3≤I D / I G ≤0.5, I D / I G This reflects the defect concentration of the negative electrode material. The presence of certain defects on the surface of the negative electrode material is beneficial for the intercalation and deintercalation of lithium ions on the surface of the negative electrode material particles.

[0032] In some embodiments of this application, during the charging and discharging process of the electrochemical device, the interlayer spacing d of the (002) crystal plane of the negative electrode material... 002 nm and the cell parameter cm of the cathode material satisfy: 3.50 ≤ c / d 002 ≤4.20. The interlayer spacing of the negative electrode material and the unit cell parameters of the positive electrode material can be tested using X-ray diffraction.

[0033] In some embodiments of this application, the electrochemical device was tested at 25°C using a three-electrode method, and the test results satisfied the condition: 0.05V ≤ V1 - V 正 ≤0.08V; where V1 is the voltage difference between the positive and negative electrodes obtained by three-electrode testing of the electrochemical device when it is 100% charged, in volts (V). 正 The voltage of the positive electrode material obtained through a three-electrode test is expressed in volts. This indicates that the electrochemical device in the embodiments of this application has high cycle stability.

[0034] In some embodiments of this application, the negative electrode active material layer includes Co element, and the mass content of Co element is 500ppm to 1500ppm based on the mass of the negative electrode active material layer.

[0035] In some embodiments, the negative electrode active material layer further includes a binder; the binder includes at least one of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene, styrene-butadiene rubber, acrylate or epoxy resin.

[0036] In some embodiments, the negative electrode material may include one or more mixtures of soft carbon, hard carbon, natural graphite, artificial graphite, silicon, silicon oxide, silicon-carbon, lithium titanate, and silicon-oxygen composites capable of receiving and releasing lithium ions.

[0037] In some embodiments, the positive electrode current collector can be an Al foil, or other positive electrode current collectors commonly used in the art can be used. In some embodiments, the thickness of the positive electrode current collector can be from 1 μm to 20 μm. In some embodiments, the positive electrode active material layer can be coated only on a portion of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer can be from 10 μm to 200 μm. The thickness of the positive electrode active material layer refers to the thickness of the positive electrode active material layer on one surface of the positive electrode current collector. It should be understood that these are merely exemplary, and other suitable thicknesses can be used.

[0038] In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene comprises at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, are effective in preventing short circuits and can improve battery stability through a turn-off effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 100 μm.

[0039] In some embodiments, the separator is a porous membrane made of polypropylene or polyethylene, or a porous membrane made of inorganic materials such as ceramic nonwoven fabric, or may be composed of two or more porous membranes stacked in a laminated structure.

[0040] In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the separator. The porous layer comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina (Al₂O₃), silicon oxide (SiO₂), magnesium oxide (MgO), titanium oxide (TiO₂), hafnium dioxide (HfO₂), tin oxide (SnO₂), cerium dioxide (CeO₂), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The binder for the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the separator's heat resistance, oxidation resistance, and electrolyte wetting properties, and enhance the adhesion between the separator and the electrode.

[0041] In some embodiments of this application, the electrochemical device is either wound or stacked.

[0042] In some embodiments, the electrochemical device includes a lithium-ion battery, but this application is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, wherein the electrolyte solution includes a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, LiPF6 is chosen as the lithium salt because it provides high ionic conductivity and improves cycle characteristics.

[0043] The non-aqueous solvent may be a carbonate compound, an ether compound, other organic solvents, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof. Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of the 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, or combinations thereof.

[0044] Examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof. Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, or combinations thereof.

[0045] Embodiments of this application also provide electronic devices including the aforementioned electrochemical apparatus. The electronic devices in these embodiments are not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0046] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example, and the lithium-ion battery preparation methods in each embodiment and comparative example are as follows.

[0047] Cathode material Li x Co y M z Preparation of O2: After mixing cobalt-containing compounds, lithium-containing compounds and compounds containing element M, the mixture is sintered at 800℃ to 1100℃ for 10h to 30h to obtain uncoated lithium cobalt oxide; then, a compound containing certain heteroatoms, a lithium-containing compound and uncoated lithium cobalt oxide are mixed and sintered at 600℃ to 1000℃ for 5h to 10h to obtain lithium cobalt oxide.

[0048] Preparation of the positive electrode: The lithium cobalt oxide (molecular formula Li) prepared above is used... x Co y M z O2, acetylene black, and polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 to form a uniform positive electrode slurry. This positive electrode slurry is then coated onto aluminum foil, dried, cold-pressed, cut into sheets, and welded with tabs to obtain the positive electrode. 正 This represents the mass (mg) of the active material per unit area of ​​the positive electrode material on one side. The weighing area is 1540.25 mm². 2 The mass m of the electrode sheet coated with positive active material 正0 Weigh the mass m of positive current collectors (aluminum foil) of the same area. 正1 m 正 =(m 正0 -m 正1 ) / 2. d 正 The test method involves measuring the thickness d of the positive electrode sheet using a micrometer. 正0 The thickness d of the positive current collector was measured using a micrometer. 正1 d 正 =d 正0 -d 正1 .

[0049] Negative electrode preparation: Graphite, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in a deionized water solvent at a weight ratio of 95:2:3 to form a uniform negative electrode slurry. This negative electrode slurry was then coated onto copper foil pre-coated with a base coating (carbon black) with a thickness of 1.5 μm. After drying, the coated negative electrode was cold-pressed under different roller pressures, cut into sheets, and welded. 负 This represents the mass (mg) of the active material per unit area of ​​the negative electrode material on one side. The weighing area is 1540.25 mm². 2 The mass m of the electrode sheet coated with negative electrode active material 负0 Weigh the mass m of the negative electrode current collector (copper foil) of the same area. 负1 m 负 =(m 负0 -m负1 ) / 2. d 负 The testing method involves measuring the thickness d of the negative electrode sheet using a micrometer. 负0 The thickness d of the negative electrode current collector was measured using a micrometer. 负1 d 负 =d 负0 -d 负1 .

[0050] Preparation of electrolyte: Under a dry argon atmosphere, LiPF6 was added to a solvent containing ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1 and mixed thoroughly. The concentration of LiPF6 was 1.15 mol / L. Then, fluoroethylene carbonate and adiponitrile were added and mixed thoroughly to obtain the electrolyte. Based on the total weight of the electrolyte, the content of fluoroethylene carbonate was 3% and the mass content of adiponitrile was 2%.

[0051] Preparation of the separator: A 7 μm thick porous polyethylene polymer film was used as the separator.

[0052] Preparation of lithium-ion batteries: The positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes. Then they are wound and placed in the outer packaging foil, and the prepared electrolyte is injected. After vacuum sealing, standing, formation and shaping, lithium-ion batteries are obtained.

[0053] The methods for determining the various performance parameters of the examples and comparative examples are as follows.

[0054] 1. X-ray diffraction (XRD) test

[0055] Test method for the diffraction peak of the (002) crystal plane of the negative electrode material (hereinafter referred to as "002 peak") and the c-axis variation of the positive electrode material: The negative electrode active material graphite was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with Cu Kα as the target material; the voltage and current were 40KV / 40mA, the scanning angle range was 5° to 80°, the scanning step size was 0.00836°, and the time of each step was 0.3s.

[0056] X-ray diffraction principle: When X-rays strike an object at an angle θ, some photons change direction due to collisions with atoms, creating scattered rays. When the wavelength λ of the scattered rays is the same as that of the incident rays and has a certain phase relationship, they interfere with each other, forming a diffraction phenomenon, i.e., Bragg's law, 2dsinθ=λ (d is the interplanar spacing). Therefore, d 002 =λ / (2sinθ), where θ is the angle at the position of the maximum peak intensity of peak 002.

[0057] 2. Particle size test

[0058] The particle size distribution was determined according to GB / T 19077-2016. The specific procedure involved weighing 1g of sample and mixing it thoroughly with 20mL of deionized water and a trace dispersant. The mixture was then sonicated for 5 minutes in an ultrasonic device. The solution was then poured into a Hydro 2000SM sample introduction system for testing. The testing equipment used was a Mastersizer 3000 manufactured by Malvern. During the test, the intensity of the scattered light was measured as the laser beam passed through the dispersed particle sample to determine the particle size. The data was then used to analyze and calculate the particle size distribution that formed the scattering spectrum. The refractive index of the particles used in the test was 1.8. Each sample was tested three times, and the final particle size was determined by averaging the three tests, yielding Dv10, Dv50, and Dv90.

[0059] 3. Co elemental content analysis test

[0060] Weigh 0.5g of powder and mix it with the remaining 10mL of HNO3 solution. Use microwave digestion to dissolve the trace elements in the powder into the solution. Introduce the digested solution into an ICP (inductively coupled plasma optical emission spectrometer). The inductively coupled plasma optical emission spectrometer (ICP-OES) detects the content of different substances based on the characteristic radiation energy emitted when the outer electrons of gaseous atoms in the sample return from the excited state to the ground state after being excited.

[0061] 4. Powder compaction

[0062] The powder compaction test standard refers to GB / T 24533-2009 "Graphite Anode Materials for Lithium-ion Batteries". The specific test method involves weighing a sample of 1.0000±0.0500g and placing it in a test mold (CARVER#3619 (13mm)). The sample is then placed in a testing device (Sansi Zongheng UTM7305) with a testing tonnage ranging from 0.3t to 5.0t. The powder compaction densities mentioned in this paper are all measured at 5t. The formula for calculating compaction density is: Compaction density = Mass of anode material / Area of ​​anode material subjected to force / Thickness of sample.

[0063] 5. Test of lithium plating on the negative electrode

[0064] The lithium-ion battery under test was placed at 0℃ and allowed to stand for 5 minutes. It was then charged at a constant current of 0.8C to 4.45V, followed by constant voltage charging at 4.45V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V, and then allowed to stand for 5 minutes. This charging and discharging process was repeated 10 times. The battery was then fully charged, disassembled in a dry room, and the state of the negative electrode was photographed and recorded.

[0065] Lithium plating degree determination: Based on the state of the negative electrode after full charge disassembly, if the negative electrode is golden yellow and the area of ​​gray is less than 2%, it is determined to be no lithium plating; if most of the negative electrode is golden yellow, but some areas are gray, and the gray area is between 2% and 20%, it is determined to be slight lithium plating; if part of the negative electrode is gray, but some golden yellow can still be observed, and the gray area is between 20% and 60%, it is determined to be lithium plating; if most of the negative electrode is gray, and the gray area is greater than 60%, it is determined to be severe lithium plating.

[0066] 6. Three-electrode potential monitoring test

[0067] The fabrication and lithium plating of the three-electrode battery are consistent with the fabrication method of the lithium-ion battery described above. The difference is that a copper wire is connected to the battery as a reference electrode during the lithium-ion battery fabrication process. Lithium is plated on the negative electrode at a current of 20 μA for 6 hours. After lithium plating, the potential change of the battery during charging and discharging is monitored using a multi-channel temperature measuring instrument. The lithium-plated cell is then charged with a constant current of 1.5C to voltage V1, and then charged with a constant voltage of V1 to 0.05C; after resting for 5 minutes, it is discharged with a constant current of 1.0C to 3.0V, and then rested for 5 minutes. Finally, V1 and V2 are obtained. 正 The voltage.

[0068] 7. Test method for lithium-ion liquid phase transport impedance (Rion)

[0069] The lithium-ion battery was tested using a Bio-Logic VMP3B electrochemical workstation manufactured by Biologie AG (France), with a frequency range of 30 mHz to 50 kHz and an amplitude of 5 mV. After data acquisition, impedance complex plane plots were used to analyze the data and obtain the lithium-ion liquid phase transport impedance (Rion).

[0070] 8. Loop Testing Method

[0071] The battery under test was placed at a test temperature of 45℃ and allowed to stand for 5 minutes. Then, it was charged with a constant current of 1.5C to 4.48V, followed by a constant voltage charge of 4.48V to 0.05C. After standing for 5 minutes, it was discharged with a constant current of 1.0C to 3.0V, and then allowed to stand for 5 minutes. The capacity at this point was recorded as D0. This charge-discharge cycle was repeated 500 times, and the final discharge capacity was recorded as D1. After cycling at 45℃, the capacity decay rate was D1 / D0, expressed as a percentage.

[0072] Table 1 lists the relevant performance parameters and test results of the positive and negative electrode materials in the relevant embodiments and comparative examples. The only difference between the embodiments and comparative examples shown in Table 1 is the parameters shown in Table 1; all other preparation parameters are the same.

[0073] Table 1

[0074]

[0075] Note: Equation I is 227 × m 负 ×S 负 / (S 正 ×m 正 )-S 正

[0076] As shown in Table 1, m in Examples 2 to 4 正 and S 正 Similarly, m in Examples 5 to 7 正 and S 正 The same as in Examples 8 to 10. 正 and S 正 The same as in Examples 11 to 13. 正 and S 正 The same as in Examples 14 to 16. 正 and S 正 The same as in Examples 17 to 19 正 and S 正 The same applies, by adjusting m 负 and S 负 The numerical values ​​obtained are the same as those calculated by Equation I.

[0077] As shown in Table 1, the capacity retention rates of Examples 1 to 21 after 500 cycles at 45°C and 1.5C / 1C are all higher than those of Comparative Examples 1 and 2. This is because the values ​​calculated according to Formula I in Examples 1 to 21 are 37 to 75, while the values ​​calculated according to Formula I in Comparative Example 1 are too small, and the values ​​calculated according to Formula I in Comparative Example 2 are too large, both of which are detrimental to the cycle performance of lithium-ion batteries. As shown in Example 21, Formula I, m 正 S 正 and m 负 All are within the range, while S 负 If the value is less than the specified range, under this condition, the negative electrode material will lack sufficient lithium intercalation sites due to its low capacity, and excessive lithium in the positive electrode will easily accumulate on the surface, leading to precipitation and thus reducing cycle life. Therefore, the value calculated by Equation I must be satisfied, and m must also be satisfied. 正 It is 0.08 mg / mm 2 Up to 0.21 mg / mm 2 S 正 The range is from 175mAh / g to 190mAh / g; m 负 It is 0.05 mg / mm 2 Up to 0.11 mg / mm 2 S 负 The cycling capacity was 355 mAh / g to 365 mAh / g, as shown in Examples 1 to 20, with higher cycling performance compared to Example 21. As shown in Comparative Example 3, Formula I, m 正S 正 m 负 and S 负 None of them are within the range, and m 正 and m 负 The values ​​are all higher than the set range values, so even if the positive and negative electrode materials have sufficient lithium intercalation space, due to m 正 and m 负 Excessive polarization leads to a large number of lithium ions remaining on the surface of the active material, ultimately resulting in a decrease in both ionization and cycling performance.

[0078] As shown in Examples 1 and 2, the value calculated according to Formula I in Example 1 is smaller than that in Example 2. The specific capacity of the positive electrode material is the same in both examples, and the specific capacity of the negative electrode material is also the same. However, the m value in Example 1... 正 and m 负 Significantly larger than m in Example 2 正 and m 负 That is, the mass of the positive and negative active material layers loaded per unit area of ​​the positive and negative current collectors is very large. Therefore, the lithium plating in Example 2 is better than that in Example 1. This is because the thicker the positive and negative active material layers per unit area, the longer the lithium ions in the positive electrode material need to travel to enter the negative electrode material at the same lithium insertion / extraction rate. Therefore, the lithium plating in Example 2 is better than that in Example 1, and the cycle performance is also better.

[0079] As shown in Examples 2 to 4, 5 to 7, 8 to 10, 11 to 13, 14 to 16, and 17 to 19, in m 正 S 正 When the specific capacity of the negative electrode material remains constant, the cycle performance of the lithium-ion battery improves and lithium plating is reduced. This is because the lower the specific capacity of the negative electrode material, the lower the content of intercalated lithium ions during the lithium insertion / extraction process, leading to improved stability of the negative electrode material. Therefore, negative electrode materials with higher specific capacity are more stable. As in Examples 2 and 5, the calculated values ​​of Formula I are the same, and the m values ​​in both are... 正 S 负 Same, but m in Example 2 负 Slightly larger than m in Example 5 负 The final embodiment has better cycles and parsing than embodiment 2, while the opposite is true for embodiments 8 and 11, and embodiments 14 and 17, although the m of embodiments 8 and 14 is better. 负 All are greater than m in Examples 11 and 17. 负 However, the cycles in Examples 14 and 17 are actually better because m 负 The lithium ions released from the positive electrode material need to be controlled within a certain range so that they are just received by the negative electrode material. Too many or too few ions will affect the balance, thus affecting the performance.

[0080] As shown in Examples 1, 2, 8, and 14, the cycle retention rate improves with increasing values ​​calculated by Equation I. When the specific capacity of the positive and negative electrode materials remains constant, higher specific capacity results in poor cycle stability and easier lithium deposition. This is because m 正 When the surface potential difference is small, uneven lithium intercalation makes it easier for the cathode material to undergo excessive desorption, ultimately leading to poor structural stability. Therefore, it satisfies the range of Equation I, and m... 正 S 正 m 负 and S 负 Controlling it within a certain range can ensure both good dynamics and good cycle performance.

[0081] Table 2 shows m 负 / m 正 The ratio and d 负 / d 正 The ratio of the compaction density to the battery performance is shown in Table 2. The only difference between the examples and the comparative examples shown in Table 2 is the parameters shown in Table 2; all other preparation parameters are the same.

[0082] Table 2

[0083]

[0084] In Table 2, m in Examples 22 to 26 负 / m 正 Equal, in Examples 27 to 30 m 负 / m 正 equal.

[0085] As shown in Examples 22 to 24, when the positive electrode material and the negative electrode material are combined in a certain mass ratio, d 负 / d 正 As the compaction density B of the negative electrode active material layer increases, the three electrode potentials of the battery and the Co content in the disassembled negative electrode active material layer after 500 cycles at 1.5C under 45°C increase, leading to an increase in liquid phase transport impedance. This is because as the compaction density of the negative electrode active material layer increases, the thickness of the negative electrode active material layer decreases, making it difficult for lithium ions to enter the negative electrode active material layer. Therefore, the liquid phase transport impedance increases, leading to an increase in the overpotential on the surface of the negative electrode material, and also increasing V1-V. 正 The potential is increased.

[0086] The negative electrode material in Comparative Example 4 and Example 22 had the same mass ratio and similar thickness ratio as the positive electrode material. However, the compaction density of the negative electrode active material layer in Comparative Example 4 was greater than that in Example 22, which ultimately led to a significant increase in liquid phase transmission impedance. This is because the increased compaction density reduced the porosity between particles in the negative electrode active material layer, resulting in fewer channels for lithium ions to enter the inner layer from the surface, thus significantly increasing the impedance.

[0087] Table 3 shows the effect of particle size on the electrical performance of the positive and negative electrode materials. The only difference between the examples and comparative examples shown in Table 3 is the parameters listed in Table 3; all other preparation parameters are the same. Table 3:

[0088]

[0089]

[0090] In Table 3, Examples 32 to 44 achieve D by controlling the Dv10 of the positive electrode material within a certain range and changing the Dv50 and Dv90 of the positive and negative electrode materials. 1 v10 / D 2 v10, D 1 v50 / D 2 v50, D 1 v90 / D 1 v10 and D 2 v90 / D 2 Adjustment of the v10 ratio.

[0091] As shown in Examples 32 to 43 in Table 3, the DC resistance (DCR) increases with the increase of particle size, regardless of whether it is a positive or negative electrode material. This is because with the increase of particle size, lithium ions need to take a longer path when they leave the positive electrode material and insert into the negative electrode material, which leads to an increase in resistance.

[0092] Comparing Example 32 and Example 36, when the D of the negative electrode material 2 v10 adds D 1 v10 / D 2 A decrease in the v10 ratio leads to an increase in DCR; this is because increased particle size results in increased polarization due to lithium insertion / extraction, causing more lithium ions to accumulate on the particle surface, thus increasing DCR. 1 v50 / D 2 The ratio of v50 changes in the same way. Therefore, when matching positive and negative electrode materials, the ratio of the particle size of the positive and negative electrode materials should be controlled within a certain range. This is beneficial for the rapid extraction of lithium from the positive electrode material and its rapid insertion into the negative electrode material.

[0093] In Comparative Example 5, the negative electrode material D 2 V90 is too large, while the D of the cathode material is too large. 1 If the V10 value is too small, lithium in the positive electrode material can be quickly extracted during charging. However, due to the large particle size of the negative electrode material, the lithium extracted from the positive electrode material cannot be successfully inserted into the negative electrode material. Instead, lithium accumulates on the surface of the negative electrode active material layer, eventually leading to lithium plating.

[0094] In Comparative Example 6, when the D of the positive electrode material... 1 When v90 is too large, D 1 v90 / D 1 v10 exceeds the limit. The downside of this situation is that the cathode material cannot be delithiated smoothly, which ultimately leads to an increase in DCR.

[0095] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with technical features having similar functions disclosed in this application.

Claims

1. An electrochemical device, characterized by, Comprising: a positive electrode, a negative electrode, an electrolyte, and a separator; the positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the negative electrode includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the positive electrode active material layer includes a positive electrode material, the negative electrode active material layer includes a negative electrode material, and satisfies: m 正 is 0.08 mg / mm 2 to 0.21 mg / mm 2 , S 正 is 175 mAh / g to 190 mAh / g, m 负 is 0.05 mg / mm 2 to 0.11 mg / mm 2 , S 负 is 355 mAh / g to 365 mAh / g and 0.3 ≤ D 1 v10 / D 2 v10 ≤ 1.7; 37 ≤ 227 x m 负 x S 负 / (S 正 x m 正 ) - S 正 ≤ 75; wherein m 正 is the weight of the single-sided positive active material layer per unit area on the positive current collector, S 正 is the gram capacity of the positive electrode material, in mAh / g, m 负 is the weight of the single-sided negative active material layer per unit area on the negative current collector, S 负 is the gram capacity of the negative electrode material, D 1 v10 is the Dv10 of the positive electrode material, D 2 v10 is the Dv10 of the negative electrode material.

2. The electrochemical device of claim 1, wherein at least one of (a) to (b) is also satisfied: (a) 0.52≤m 负 / m 正 ≤0.62; (b) 1.1 < d 负 / d 正 ≤ 1.4, wherein d 负 is the thickness of the negative electrode active material layer, and d 正 is the thickness of the positive electrode active material layer.

3. The electrochemical device of claim 1, wherein Further satisfying: 0.7 < D 1 v50 / D 2 v50 < 2.3; wherein D 1 v50 is the Dv50 of the cathode material; D 2 v50 is the Dv50 of the negative electrode material.

4. The electrochemical device according to claim 1, wherein the compaction density A of the positive electrode active material layer and the compaction density B of the negative electrode active material layer satisfy: 1.96 < A / B < 3.07, A and B are both in g / cm 3 .

5. The electrochemical device according to claim 1, wherein The positive electrode material includes Li x Co y M z O 2-a F a wherein 0.9 < x < 1.05, 0.95 < y < 1, 0 < z < 0.05, 0 < a < 2, 0.95 < y + z < 1.05, and M includes at least one of Al, Mg, Ti, Zr, Ni, Mn, Y, Nb, La, V, Zn, Mo, Ru, Ta, W, Re, Sn, Ge, or Ga.

6. The electrochemical device of claim 1, wherein Further satisfying: 5.2 < D 1 v90 / D 1 v10 < 10.6, and 2 < D 2 v90 / D 2 v10 < 10; wherein D 1 v90 and D 1 v10 are Dv90 and Dv10 of the positive electrode material, respectively; D 2 v90 and D 2 v10 are Dv90 and Dv10 of the negative electrode material, respectively.

7. The electrochemical device of claim 1, wherein The electrochemical device, at 30% to 60% state of charge, the interlayer distance d 002 nm of the (002) crystal plane of the negative electrode material and the unit cell parameter c nm of the positive electrode material satisfy: 3.50 ≤ c / d 002 ≤ 4.

20.

8. The electrochemical device of claim 1, wherein The electrochemical device is subjected to a three-electrode test at 25°C, and the test result satisfies: 0.05 V≤V 1－ V 正 ≤0.08 V. V1 is the voltage difference between the positive electrode and the negative electrode of the electrochemical device obtained by three-electrode test at 100% state of charge, V 正 V is the voltage of the positive electrode material obtained by three-electrode test.

9. The electrochemical device according to claim 1, wherein the negative electrode active material layer includes Co, and the mass content of Co is 500 ppm to 1500 ppm based on the mass of the negative electrode active material layer.

10. An electronic device, comprising: An electrochemical device as described in any one of claims 1 to 9.

Images