Positive electrode sheet and electrochemical device and electronic device containing the same

Abstract

The present application provides a positive electrode plate, and an electrochemical device and an electronic device comprising the positive electrode plate. The positive electrode plate comprises a positive electrode active material layer, and the element content distribution on the surface of the positive electrode active material layer satisfies the following conditions: the molar ratio α between the manganese element and the fluorine element is 10 to 80. The positive electrode plate of the present application can inhibit the generation of hydrogen fluoride in the electrochemical device, reduce the reaction between hydrogen fluoride and the manganese-containing positive electrode active material, thereby reducing the dissolution of manganese in the positive electrode active material in a high-temperature environment, and further reducing the capacity decay of the electrochemical device in a high-temperature environment, thereby achieving the effect of improving the stability of the electrochemical device in a high-temperature environment and extending the service life of the electrochemical device in a high-temperature environment.

Description

[0001] This application is a divisional application of the Chinese patent application submitted to the China Patent Office on January 21, 2021, with application number 202110080043.5 and invention name "A positive electrode sheet and an electrochemical device and an electronic device containing the positive electrode sheet". Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a positive electrode sheet and an electrochemical device and an electronic device comprising the positive electrode sheet. Background Art

[0003] Lithium-ion batteries, with their high specific energy, high operating voltage, low self-discharge rate, compact size, and light weight, are widely used in various fields, including energy storage, portable electronic devices, and electric vehicle power supply. As the use of lithium-ion batteries continues to expand, the market is placing higher demands on them, such as the requirement for them to be stable even in high-temperature environments.

[0004] However, current lithium-ion batteries experience significant capacity degradation at high temperatures. This is because high temperatures trigger side reactions within the battery, which damage the structure of the electrode active materials and affect the battery's stability and lifespan. Therefore, there is an urgent need for a lithium-ion battery that can maintain a long service life even at high temperatures. Summary of the Invention

[0005] The purpose of the present application is to provide a positive electrode sheet and an electrochemical device and an electronic device comprising the positive electrode sheet, so as to improve the stability of the electrochemical device in a high temperature environment.

[0006] It should be noted that in the following content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0007] A first aspect of the present application provides a positive electrode plate, which includes a positive electrode active material layer, wherein the element content distribution on the surface of the positive electrode active material layer satisfies: the molar ratio α between the manganese element and the fluorine element is 10 to 80.

[0008] The inventors have found that in lithium-ion batteries, manganese-containing positive electrode active materials (such as lithium manganate, lithium nickel cobalt manganate) have a serious capacity decay during the charge and discharge process, especially under high temperature conditions (such as above 60°C). Because the electrolyte contains trace amounts of water, water reacts with LiPF6 in the electrolyte to form HF, resulting in a spinel disproportionation reaction. Mn 3+ After the disproportionation reaction, Mn 4+ and Mn 2+ , Mn 2+It is easy to dissolve, and the dissolution is accelerated under high temperature conditions, causing the structure of the manganese-containing positive electrode active material to be destroyed. In view of this, the present application controls the molar ratio α between the manganese element and the fluorine element to be 12 to 80. In other embodiments of the present application, α is 10 to 40, which can better inhibit the generation of hydrogen fluoride in the electrochemical device, reduce the reaction between hydrogen fluoride and the manganese-containing positive electrode active material, and improve the stability of the manganese-containing positive electrode active material, thereby reducing the dissolution of manganese in the positive electrode active material under high temperature environment, thereby reducing the capacity decay of the lithium-ion battery under high temperature environment, making the lithium-ion battery more stable when stored under high temperature conditions, and extending the life of the lithium-ion battery.

[0009] In some embodiments of the present application, the thickness of the positive electrode active material layer is H, and the molar ratio of manganese element to fluorine element in the positive electrode active material layer at a depth of H / 3 to 2H / 3 from the surface is β, and β / α is 0.35 to 1.25.

[0010] In other embodiments of the present application, β / α is 0.35 to 0.625. It is understandable that the positive electrode active material layer can be provided on one side or both sides of the current collector, then the thickness of the positive electrode active material layer on one side of the current collector is recorded as H, and the molar ratio of manganese to fluorine in the positive electrode active material layer in the depth region of H / 3 to 2H / 3 from the surface is recorded as β. The inventors have found that, without being limited to any theory, by controlling the ratio between β and α within the above range, the manganese-fluorine ratio inside the positive electrode active material layer is lower than the manganese-fluorine ratio on the surface. On the one hand, it is possible to improve electron blocking and improve the cycle performance of the lithium-ion battery. On the other hand, it is possible to further suppress the generation of hydrogen fluoride inside the high-voltage positive electrode active material layer, thereby further improving the stability of the manganese-containing positive electrode active material.

[0011] In some embodiments of the present application, the β range is 5 to 50. Without being limited to any theory, when β is too low (e.g., less than 5), the manganese-fluorine ratio inside the positive electrode active material layer is too low, which is not conducive to improving the energy density of the lithium-ion battery; when β is too high (e.g., greater than 50), the manganese-fluorine ratio inside the positive electrode active material layer is too high, making it difficult to effectively suppress the generation of hydrogen fluoride in the lithium-ion battery. By controlling β within the above range, the generation of hydrogen fluoride in the lithium-ion battery can be further suppressed while improving the energy density of the lithium-ion battery.

[0012] In some embodiments of the present application, the positive electrode active material layer includes a positive electrode active material and a metal halide. The average particle size of the positive electrode active material is denoted as D1, and the average particle size of the metal halide is denoted as D2. The relationship between D1 and D2 satisfies: 0.33 ≤ D1 / D2 ≤ 100. In other embodiments of the present application, 1.5 ≤ D1 / D2 ≤ 100. Without being limited to any theory, by controlling the relationship between D1 and D2 to satisfy the above equation, the metal halide can be prevented from agglomerating in the positive electrode active material, further improving the stability of the positive electrode active material, thereby more effectively suppressing the generation of hydrogen fluoride in lithium-ion batteries.

[0013] The average particle size in this application refers to the observation of the material powder using a scanning electron microscope (SEM). Then, using image analysis software, 10 material particles are randomly selected from the SEM photograph and the area of ​​each of these material particles is calculated. Then, assuming that the material particles are spherical, the particle size R (diameter) of each particle is calculated using the following formula: R = 2 × (S / π) 1 / 2 ; Wherein, S is the area of ​​the material particles; 10 SEM images are processed to determine the particle size R of the material particles, and the particle sizes of the obtained 100 (10×10) material particles are arithmetic averaged to obtain the average particle size of the material particles.

[0014] In some embodiments of the present application, D1 is 2 μm to 20 μm, and D2 is 0.2 μm to 6 μm. Without being limited to any theory, when the average particle size of the positive electrode active material is too small (for example, less than 2 μm), the specific surface area of ​​the small particles is large, and the positive electrode active material is more likely to react with the electrolyte to generate more by-products; when the average particle size of the positive electrode active material is too large (for example, greater than 20 μm), the large particles have a large volume change during the cycle, and the positive electrode material is more likely to break, which is not conducive to improving the stability of the positive electrode active material. By controlling the average particle size of the positive electrode active material within the above range, it is possible to avoid generating more by-products and improve the stability of the positive electrode active material. By controlling the average particle size of the metal halide within the above range, the metal halide can be prevented from agglomerating in the positive electrode active material, further improving the stability of the positive electrode active material, thereby further inhibiting the generation of hydrogen fluoride in lithium-ion batteries.

[0015] In some embodiments of the present application, the surface of the positive electrode active material has a metal halide. The positive electrode active material can be at least partially covered with the metal halide, or can be completely covered with the metal halide, thereby further suppressing the generation of hydrogen fluoride in the lithium-ion battery.

[0016] In some embodiments of the present application, in the XRD pattern of the positive electrode active material layer, I A Indicates the peak intensity of the characteristic peak in the range of 44.7° to 45.1°, I BRepresents the peak intensity of the characteristic peak in the range of 45.1° to 45.6°, I A and I B satisfy: 0.5 < I A / I B < 0.8. It indicates that the positive electrode active material layer of this application contains metal halides, such as LiF.

[0017] In some embodiments of this application, the positive electrode active material includes at least one of compound a) or compound b): Compound a) is Li x1 Mn 2-y1 Z y1 O4, where Z includes at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, 0.8 ≤ x1 ≤ 1.2, 0 ≤ y1 ≤ 0.1. Compound b) is Li x2 Ni y2 Co z Mn k M q O b-a T a , where M includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb and Ce; T is a halogen, at least one of F, Cl, Br or I; x2, y2, z, k, q, a and b respectively satisfy: 0.2 ≤ x2 ≤ 1.2, 0 ≤ y2 ≤ 1, 0 ≤ z ≤ 1, 0 < k ≤ 1, 0 ≤ q ≤ 1, 1 < b ≤ 2 and 0 ≤ a ≤ 1.

[0018] When the positive electrode active material contains the above compound a) and compound b), the charge-discharge cycle performance of the lithium-ion battery can be further improved. <00000八2>

[0019] The metal halide of this application includes compound AB m , A can include at least one of Li, Na, K, Mg, Ca, Sr, Ba, Zn or Al, B can include at least one of F, Cl, Br or I, where 1 ≤ m ≤ 四. The metal halide plays a role in inhibiting the generation of hydrogen fluoride and reducing the reaction between hydrogen fluoride and the manganese-containing positive electrode active material.

[0020] In some embodiments of the present application, after the positive electrode sheet is immersed in an electrolyte at 80°C for one day, the mass percentage z of the Mn element and the Li element contained in the electrolyte is: 0<z≤0.5%. The volume ratio of the positive electrode active material layer contained in the positive electrode sheet to the electrolyte is 1g / 100mL, the volume ratio of ethylene carbonate to dimethyl carbonate in the electrolyte is 3:7, and the LiPF6 concentration is 1mol / L. This indicates that after the positive electrode sheet of the present application is immersed in the electrolyte, only a trace amount of Mn element is dissolved, and therefore the positive electrode sheet has high stability.

[0021] In some embodiments of the present application, the positive electrode active material layer includes a conductive agent. The present application does not particularly limit the conductive agent, as long as it can improve the conductivity of the positive electrode sheet. For example, it can include at least one of carbon nanotubes, carbon fibers, acetylene black, graphene, Ketjen black, or carbon black.

[0022] In some embodiments of the present application, the positive electrode active material layer includes a binder. The present application does not particularly limit the binder, as long as it can achieve the purpose of the present application, for example, it can include at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0023] The present application does not particularly limit the preparation method of the positive electrode active material layer, and a preparation method known to those skilled in the art can be used. For example, when preparing a positive electrode active material layer with different concentrations of metal halide in the thickness direction, the difference in deposition rate and filling property caused by the difference in density and particle size between the metal halide and the positive electrode active material can be utilized, and by controlling the drying temperature and rate, the metal halide can be achieved to have different concentrations in the thickness direction of the positive electrode active material layer. For example, a positive electrode active material layer with different concentrations of metal halide in the thickness direction can also be prepared by layered coating. Layered coating refers to coating the positive electrode slurry on the positive electrode current collector layer by layer. The ratio of positive electrode active material to metal halide in the positive electrode slurry coated in each layer can be the same or different. By setting the ratio of positive electrode active material to metal halide in the positive electrode slurry coated in each layer to be different, the difference in the content of metal halide in the thickness direction can be controlled.

[0024] As a specific example, the following preparation method may be used: the positive electrode slurry is evenly coated on one surface of the current collector, dried at 80° C. to 120° C., and cold pressed to obtain a positive electrode sheet.

[0025] As another specific example, the following preparation method can be used: a positive electrode slurry with a higher metal halide content relative to the positive electrode active material is first evenly coated on one surface of the current collector and dried to form a first coating; then a positive electrode slurry with a lower metal halide content is evenly coated on the first coating, dried to obtain a second coating, and cold pressed to obtain a positive electrode sheet.

[0026] Those skilled in the art should understand that the positive electrode sheet of the present application may have an active material layer on one surface thereof, or may have an active material layer on both surfaces thereof.

[0027] In the positive electrode of the present application, the positive electrode current collector is not particularly limited and can be any positive electrode current collector known in the art, such as aluminum foil, aluminum alloy foil or composite current collector. The positive electrode active material layer includes a positive electrode active material, which is not particularly limited and can be any positive electrode active material known in the art, for example, it can include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium manganese oxide or lithium iron manganese phosphate.

[0028] In the negative electrode of the present application, the negative electrode current collector is not particularly limited and any negative electrode current collector known in the art can be used, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collectors. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited and any negative electrode active material known in the art can be used. For example, it can include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, silicon carbon, lithium titanate, etc.

[0029] The lithium-ion battery of the present application further includes an electrolyte, which includes a lithium salt and a non-aqueous solvent.

[0030] In some embodiments of the present application, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiN(SO2CF3)2, LiSiF6 and lithium difluoroborate. For example, the lithium salt includes LiPF6 because it can provide high ionic conductivity and improve cycle characteristics. The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents or a combination thereof. The above-mentioned carbonate compound can be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof.

[0031] Examples of the above-mentioned linear carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2-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.

[0032] Examples of the carboxylic acid ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, caprolactone, and combinations thereof.

[0033] Examples of the above-mentioned ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0034] Examples of the above-mentioned 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 combinations thereof.

[0035] The second aspect of the present application further provides an electrochemical device, comprising the positive electrode sheet described in any embodiment of the first aspect.

[0036] In some embodiments of the present application, after the electrochemical device is discharged to 25% state of charge (SOC), it is stored at 80°C for 1 day. After disassembly, the positive electrode sheet is washed with dimethyl carbonate solvent and dried at 85°C for 12 hours. Raman testing is performed. -1 Up to 846cm -1 There are two peaks in the wavelength range, and the peak intensity ratio of the strongest peak to the second strongest peak is 1.6 to 2.0.

[0037] The third aspect of the present application further provides an electronic device, comprising the electrochemical device described in any embodiment of the second aspect.

[0038] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted 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.

[0039] The preparation process of an electrochemical device is well known to those skilled in the art and is not particularly limited in this application. For example, an electrochemical device can be manufactured by stacking the positive electrode, separator, and negative electrode in sequence, winding and folding them as needed, and then placing them into a housing. The electrolyte is then injected into the housing and sealed. The separator used is the separator described above. Furthermore, overcurrent protection elements, guide plates, and the like can be placed in the housing as needed to prevent pressure buildup and overcharge and discharge within the electrochemical device.

[0040] The present application provides a positive electrode plate and an electrochemical device and an electronic device comprising the positive electrode plate. By ensuring that the surface element content distribution of the positive electrode active material layer of the positive electrode plate satisfies the following conditions: the molar ratio α between the manganese element and the fluorine element is 10 to 80, the generation of hydrogen fluoride in the electrochemical device can be better suppressed, and the reaction between hydrogen fluoride and the manganese-containing positive electrode active material can be reduced, thereby reducing the dissolution of manganese in the positive electrode active material in a high-temperature environment, and further reducing the capacity decay of the electrochemical device in a high-temperature environment, thereby achieving the effect of improving the stability of the electrochemical device in a high-temperature environment and extending the service life of the electrochemical device in a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the present application and the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other technical solutions can also be obtained based on these drawings.

[0042] Figure 1a This is the Raman spectrum obtained after Raman testing of the positive electrode of Comparative Example 1;

[0043] Figure 1b This is the Raman spectrum obtained after Raman testing of the positive electrode sheet of Example 1;

[0044] Figure 2aThis is the F element spectrum of the EDX-mapping of the positive electrode sheet of Comparative Example 1;

[0045] Figure 2b This is the F element spectrum of the EDX-mapping of the positive electrode sheet of Example 1;

[0046] Figure 3 The XRD patterns of the positive electrodes of Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0047] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described embodiments are only a portion of the embodiments of this application, rather than all of them. All other technical solutions derived by those of ordinary skill in the art based on the embodiments in this application fall within the scope of protection of this application.

[0048] It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0049] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0050] Test methods and equipment:

[0051] Metal halide distribution test:

[0052] SEM-EDX was used to test the distribution of metal halides in the positive electrode. First, SEM-EDX analysis was performed on the surface of the positive electrode. An area of ​​200 μm × 200 μm was selected from the SEM-EDX image. The number of F atoms in the entire area, N1, was measured. Then, the number of Mn atoms within the area, N2, was measured. The Mn / F ratio within the area is W1 = N2 / N1. The test instrument was OXFORD EDS (X-max-20mm 2 ).

[0053] Raman spectroscopy test:

[0054] The dried positive electrode sheet was kept flat on the sample stage of the Raman test instrument (JobinYvonLabRAM HR), and the peak position was corrected using a silicon wafer. Then, the positive electrode sheet sample was randomly searched for at a 10x long focal length for testing.

[0055] XRD test:

[0056] The dried positive electrode sheet was kept flat on the sample stage of an XRD test instrument (model Bruker, D8) and an XRD diffraction pattern was obtained using a scanning rate of 2° / min and a scanning angle range of 10° to 90°.

[0057] Button battery test:

[0058] Button cell preparation :

[0059] One side of the dried positive electrode sheet coated with a positive electrode active material layer on both sides was cleaned with N-methylpyrrolidone (NMP), and then baked in a vacuum environment at 85°C for 2 hours. The positive electrode sheet was taken out and punched out to obtain a small disc (positive electrode sheet) required for a CR2025 button battery. The button battery was then assembled in sequence according to the nickel foam, lithium sheet, isolation membrane, and positive electrode sheet, and 50 microliters of electrolyte was injected (the composition of the electrolyte was: ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 1:1:1, and the concentration of LiPF6 was 1.15 mol / L).

[0060] Button battery capacity test :

[0061] The assembled button cell was charged and discharged 50 times at a current of 0.2C at a cut-off voltage of 2.7V to 4.3V at 25°C to test its gram capacity in mAh.g. -1 .

[0062] Positive electrode electrolyte medium and high temperature storage test :

[0063] The button cell was then discharged to 30% SOC, the positive electrode was removed from the button cell, immersed in 10 mL of electrolyte and sealed, and then stored in an oven at 80°C for 1 day. The electrolyte was filtered through a 450 nm filter head, and the filtrate was measured for Mn content in g / L using a plasma photoelectric direct reading spectrometer (ICP).

[0064] Button battery cycle performance test :

[0065] In an environment of 45°C, the button battery was charged and discharged for the first time. Constant current charging was performed at a charging current of 0.5C until the upper limit voltage reached 4.3V. Then constant current discharge was performed at a discharge current of 1C until the final voltage reached 2.7V. The discharge capacity of the first cycle was recorded. After that, the above steps were repeated for 50 charge and discharge cycles, and the discharge capacity of the 50th cycle was recorded.

[0066] Cycle capacity retention rate=(discharge capacity at the 50th cycle / discharge capacity at the first cycle)×100%.

[0067] Full battery test:

[0068] Lithium-ion battery high temperature storage test :

[0069] The lithium-ion battery is discharged to 30% SOC, then stored in a 60°C oven for 7 days, and then charged and discharged three times with a current of 0.2C, and the recovered capacity is recorded. The recovered capacity retention rate is: the recovered capacity of the lithium-ion battery after storage / the initial capacity of the lithium-ion battery × 100%.

[0070] Lithium-ion battery cycle performance test :

[0071] In an environment of 45°C, the lithium-ion battery was charged and discharged for the first time. Constant current charging was performed at a charging current of 0.5C until the upper limit voltage reached 4.3V. Then constant current discharge was performed at a discharge current of 1C until the final voltage reached 2.7V. The discharge capacity of the first cycle was recorded. After that, the above steps were repeated for 500 charge and discharge cycles, and the discharge capacity of the 500th cycle was recorded.

[0072] Cycle capacity retention rate=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0073] Example

[0074] Example 1

[0075] <Preparation of positive electrode slurry>

[0076] The positive electrode active material lithium manganate (LiMn2O4, average particle size D1 is 10μm), the metal halide lithium fluoride (LiF, average particle size D2 is 6μm), the conductive agent (conductive carbon black Super P), and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.5:0.5:1:1, and then N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75% and a viscosity of 5000mPas, and stirred evenly to obtain a positive electrode slurry.

[0077] <Full Cell Preparation>

[0078] <Preparation of positive electrode sheet>

[0079] The obtained positive electrode slurry was evenly coated on one surface of a 12 μm thick current collector aluminum foil, dried at 90°C, and cold pressed to obtain a positive electrode sheet with a total thickness of 80 μm for the positive electrode active material layer. Here, α is 80 and β is 50.

[0080] Repeat the above steps on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. Cut the positive electrode sheet into a size of 76mm×851mm and weld the tabs before use.

[0081] <Preparation of negative electrode sheet>

[0082] The negative electrode active materials, artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose, were mixed in a mass ratio of 96:2:2. Deionized water was then added as a solvent to form a slurry with a solids content of 60%. An appropriate amount of deionized water was then added to adjust the slurry viscosity to 5000 Pa·s to prepare the negative electrode slurry. The resulting negative electrode slurry was coated on one surface of a 12μm-thick copper foil, dried at 110°C, and cold-pressed to produce a negative electrode sheet with a 40μm-thick negative electrode active material layer. The coating process was repeated on the other surface of the negative electrode sheet to produce a negative electrode sheet coated on both sides with the negative electrode active material layer. The negative electrode sheet was cut into 78mm x 867mm dimensions and welded to the tabs before use.

[0083] <Preparation of Separator>

[0084] A polyethylene (PE) porous polymer film with a thickness of 15 μm was used as the separator.

[0085] <Preparation of Electrolyte>

[0086] In an environment with a water content of less than 10 ppm, a non-aqueous organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) was mixed at a mass ratio of 1:1:1. Lithium hexafluorophosphate (LiPF6) was then added to the non-aqueous organic solvent, dissolved, and mixed thoroughly. The molar concentration of LiPF6 in the electrolyte was 1.15 mol / L.

[0087] <Preparation of lithium-ion batteries>

[0088] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation, and then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and filled with the prepared electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, and shaping.

[0089] Example 2

[0090] Except that in <Preparation of Positive Electrode Slurry>, the mass ratio of the positive electrode active material lithium manganese oxide (LiMn2O4), metal halide (LiF), conductive agent (conductive carbon black Super P), and binder polyvinylidene fluoride (PVDF) is 97:1:1:1, and in <Preparation of Positive Electrode Sheet>, α is controlled to be 40 and β is controlled to be 20, the rest is the same as Example 1.

[0091] Example 3

[0092] Except that D1 is set to 2 μm and β is set to 50 in the "Preparation of Positive Electrode Sheet", the rest is the same as in Example 2.

[0093] Example 4

[0094] Except that D1 is 20 μm and D2 is 0.2 μm in the "Preparation of Positive Electrode Sheet", the rest is the same as Example 2.

[0095] Example 5

[0096] Except that D2 is 0.2 μm in the "Preparation of Positive Electrode Sheet", the rest is the same as Example 2.

[0097] Example 6

[0098] Except that the drying temperature is controlled to 80° C. and β is set to 14 in the preparation of the positive electrode sheet, the rest is the same as in Example 2.

[0099] Example 7

[0100] Except that in <Preparation of Positive Electrode Slurry>, the mass ratio of the positive electrode active material lithium manganese oxide (LiMn2O4), metal halide (LiF), conductive agent (conductive carbon black Super P), and binder polyvinylidene fluoride (PVDF) is 96.5:1.5:1:1, and in <Preparation of Positive Electrode Sheet>, α is controlled to be 25 and β is controlled to be 12, the rest is the same as Example 2.

[0101] Example 8

[0102] Except that in <Preparation of Positive Electrode Slurry>, the mass ratio of the positive electrode active material lithium manganese oxide (LiMn2O4), metal halide (LiF), conductive agent (conductive carbon black Super P), and binder polyvinylidene fluoride (PVDF) is 95:3:1:1, and in <Preparation of Positive Electrode Sheet>, α is controlled to be 12 and β is controlled to be 5, the rest is the same as Example 2.

[0103] Example 9

[0104] Except that in the <Preparation of Positive Electrode Slurry>, sodium fluoride (NaF) is selected as the metal halide, and in the <Preparation of Positive Electrode Sheet>, α is controlled to be 23 and β is controlled to be 10, the rest is the same as Example 2.

[0105] Example 10

[0106] Except that in the <Preparation of Positive Electrode Slurry>, aluminum fluoride (AlF3) is selected as the metal halide, and in the <Preparation of Positive Electrode Sheet>, α is controlled to be 22 and β is controlled to be 11, the rest is the same as Example 2.

[0107] Example 11

[0108] Except that in the <Preparation of Positive Electrode Slurry>, calcium fluoride (CaF2) is selected as the metal halide, and in the <Preparation of Positive Electrode Sheet>, α is controlled to be 20 and β is controlled to be 11.5, the rest is the same as Example 2.

[0109] Example 12

[0110] Except that in the <Preparation of Positive Electrode Slurry>, calcium fluoride (MgF2) is selected as the metal halide, and in the <Preparation of Positive Electrode Sheet>, α is controlled to be 18 and β is controlled to be 10, the rest is the same as Example 2.

[0111] Example 13

[0112] In addition to the preparation of positive electrode slurry, the positive electrode active material is selected from lithium manganese oxide (LiMn2O4) and NCM material (LiNi 0.5 Co 0.2 Mn 0.3 O2), a mixture of LiMn2O4 and LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2 is 88.2:8.8. In the "Preparation of Positive Electrode Sheet", except that α is controlled to be 20 and β is controlled to be 9, the rest is the same as Example 2.

[0113] Example 14

[0114] In addition to the preparation of positive electrode slurry, the positive electrode active material is selected from NCM materials (LiNi 0.5 Co 0.2 Mn 0.3 O2), in <Preparation of Positive Electrode>, except that α is controlled to be 20 and β is controlled to be 9, the rest is the same as Example 2.

[0115] Example 15

[0116] The process is the same as in Example 2 except that in the process of preparing the positive electrode slurry, the metal halide is a mixture of LiF and LiCl with a molar ratio of LiF to LiCl of 9:1, and in the process of preparing the positive electrode sheet, α is controlled to be 42 and β is controlled to be 22.

[0117] Comparative Example 1

[0118] Except that in the <Preparation of Positive Electrode Slurry>, no metal halide is added, the mass ratio of the positive electrode active material lithium manganese oxide (LiMn2O4), the conductive agent (conductive carbon black Super P), and the binder polyvinylidene fluoride (PVDF) is 98:1:1, and in the <Preparation of Positive Electrode Sheet>, α is controlled to be 300, the rest is the same as Example 1.

[0119] Comparative Example 2

[0120] In addition to the addition of metal halide in the preparation of positive electrode slurry, the positive electrode active material is lithium manganese oxide (LiMn2O4) and NCM material (LiNi 0.5 Co 0.2 Mn 0.3 O2), a mixture of LiMn2O4 and LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2 is 88.2:9.8. In <Preparation of Positive Electrode Sheet>, except that α is controlled to be 320, the rest is the same as Comparative Example 1.

[0121] Comparative Example 3

[0122] Except that in the process of <Preparation of Positive Electrode Sheet>, β is controlled to be 0.5 by layered coating, the rest is the same as in Example 2.

[0123] Comparative Example 4

[0124] Except that in the preparation of the positive electrode sheet, β is controlled to be 102 by layered coating, the rest is the same as in Example 2.

[0125] The button cells in each example and comparative example were prepared according to the button cell preparation method of Example 1, except that the positive electrode sheets of the button cells were the corresponding positive electrode sheets of each example and comparative example. The average particle size of the positive electrode active material in each example and comparative example is D1, and the average particle size of the metal halide is D2, as shown in Table 1.

[0126] The preparation parameters and test data of each embodiment and comparative example are shown in Table 1 and Table 2.

[0127]

[0128]

[0129]

[0130] As can be seen from Example 1 and Comparative Example 1, and Example 13 and Comparative Example 2, when containing the same positive electrode active material, the addition of a metal halide significantly improves the high-temperature cycling performance and high-temperature storage performance of the lithium-ion battery of the present application. In the positive electrode without the addition of a metal halide, a small amount of fluorine can still be detected on the surface of the positive electrode due to the fluorine content in the electrolyte.

[0131] The manganese-fluorine ratio α on the surface of the positive electrode active material layer, the internal manganese-fluorine ratio β, and the particle size of the metal halide usually also affect the performance of the lithium-ion battery. It can be seen from Examples 2-6 and Comparative Examples 3-4 that if β is too small or too large, the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are relatively poor. This is because, if β is too small, the internal impedance of the positive electrode active material layer is large; if β is too large, the interior of the positive electrode active material layer lacks effective protection, and thus during high-temperature cycling and storage, the structure of the positive electrode material is destroyed, resulting in a decrease in high-temperature cycling performance and high-temperature storage performance. Further, from the comparison of Examples 2-6, it can be seen that Examples 2 and 4-6 with β / α in the range of 0.35 to 0.625 have better high-temperature cycle performance and high-temperature storage performance than Example 3 with β / α of 1.25. This is because the relatively low manganese-fluorine ratio inside the positive electrode active layer is conducive to suppressing the generation of hydrogen fluoride inside the high-voltage positive electrode active material layer, thereby further improving the stability of the manganese-containing positive electrode active material.

[0132] It can be seen from Examples 9-12, Example 15 and Comparative Example 1 that, when containing the same positive electrode active material, the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery of the present application can be significantly improved after adding different types of metal halides of the present application.

[0133] Figure 1a The Raman spectrum of the lithium-ion battery using the positive electrode sheet of Comparative Example 1 was obtained after being discharged to 25% SOC and stored at 80°C for 1 day. The disassembled positive electrode sheet was washed with dimethyl carbonate solvent and dried at 85°C for 12 hours. Figure 1a It can be seen that in the range of 258 to 846 cm -1 The two characteristic peaks of lithium manganese oxide cannot be observed within the wavelength range, which may be due to the destruction of the surface structure of lithium manganese oxide by HF generated in the lithium-ion battery.

[0134] Figure 1b The lithium-ion battery made with the positive electrode sheet of Example 1 of the present application was discharged to 25% SOC, stored at 80°C for 1 day, and the disassembled positive electrode sheet was washed with dimethyl carbonate solvent and dried at 85°C for 12 hours, and then the Raman spectrum was obtained after Raman testing. Figure 1b It can be seen that in the range of 258 to 846 cm -1 There are still two characteristic peaks of lithium manganese oxide in the wavelength range, which also shows that the positive electrode plate of the present application can inhibit the generation of HF.

[0135] Figure 2a This is the F element spectrum of the EDX-mapping of the positive electrode sheet of the lithium-ion battery using the positive electrode sheet of Comparative Example 1 after the battery is converted into capacity. Figure 2aIt can be seen that the F element is distributed as a background component, which may be due to the F element in the electrolyte remaining on the positive electrode sheet.

[0136] Figure 2b This is the F element spectrum of the EDX-mapping of the positive electrode sheet of the lithium ion battery using the positive electrode sheet of Example 1 after the battery is converted into capacity. Figure 2b It can be seen that the F element is distributed in a granular form, indicating that the positive electrode sheet of the present application contains metal halide.

[0137] Figure 3 The XRD patterns of the positive electrode sheets of Example 1 and Comparative Example 1 are shown. As can be seen from the figure, in the XRD pattern of Example 1, a characteristic peak A exists in the range of 44.7° to 45.1°, and a characteristic peak B exists in the range of 45.1° to 45.6°; whereas in the XRD pattern of Comparative Example 1, a characteristic peak A does not exist in the range of 44.7° to 45.1°. This indicates that the positive electrode sheets of the present application contain metal halides.

[0138] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A positive electrode sheet comprising a positive electrode active material layer, wherein the XRD pattern of the positive electrode active material layer is: A Indicates the peak intensity of the characteristic peak in the range of 44.7° to 45.1°, I B Indicates the peak intensity of the characteristic peak in the range of 45.1° to 45.6°, 0.5<I A / I B <0.8; the element content distribution on the surface of the positive electrode active material layer satisfies: the molar ratio α between the manganese element and the fluorine element is 10 to 80; the thickness of the positive electrode active material layer is H, the molar ratio of the manganese element to the fluorine element in the positive electrode active material layer at a depth of H / 3 to 2H / 3 from the surface is β, and β / α is 0.35 to 0.625; The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of compound a) or compound b): The compound a) Li x1 Mn 2-y1 Z y1 O4, wherein Z comprises at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, 0.8≤x1≤1.2, 0≤y1≤0.1; The compound b) Li x2 Ni y2 Co z Mn k M q O b-a T a , wherein M comprises at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb and Ce; T is a halogen, and x2, y2, z, k, q, a and b respectively satisfy: 0.2 ≤ x2 ≤ 1.2, 0 ≤ y2 ≤ 1, 0 ≤ z ≤ 1, 0 < k ≤ 1, 0 ≤ q ≤ 1, 1 < b ≤ 2 and 0 ≤ a ≤ 1.

2. The positive electrode sheet according to claim 1, wherein: The element content distribution on the surface of the positive electrode active material layer is obtained by the following test method: SEM-EDX analysis is performed on the surface of the positive electrode plate, an area of ​​200μm×200μm is selected in the SEM-EDX image, and the number N1 of fluorine atoms in the area and the number N2 of manganese atoms in the area are tested. The molar ratio between the manganese element and the fluorine element in the area is N2 / N1.

3. The positive electrode sheet according to claim 1, wherein: The positive electrode plate satisfies: α is 10 to 40.

4. The positive electrode sheet according to claim 1, wherein: The positive electrode sheet satisfies: the β range is 5 to 50.

5. The positive electrode sheet according to claim 1, wherein: The positive electrode active material layer includes a metal halide.

6. The positive electrode sheet according to claim 5, wherein: The average particle size of the positive electrode active material is D1, the average particle size of the metal halide is D2, and at least one of the following characteristics (1) to (3) is satisfied: (1) 0.33≤D1 / D2≤100; (2) D1 is 2 μm to 20 μm, and D2 is 0.2 μm to 6 μm; (3) The surface of the positive electrode active material has the metal halide.

7. The positive electrode sheet according to claim 5, wherein: The metal halide includes compound AB m , A includes at least one of Li, Na, K, Mg, Ca, Sr, Ba, Zn or Al, B includes at least one of F, Cl, Br or I, and 1≤m≤4.

8. The positive electrode sheet according to claim 6, wherein: 1.5≤D1 / D2≤100.

9. An electrochemical device comprising the positive electrode sheet according to any one of claims 1 to 8.

10. The electrochemical device according to claim 9, wherein the electrochemical device is discharged to 25% SOC and stored at 80°C for 1 day. After disassembly, the positive electrode sheet is washed with dimethyl carbonate solvent and dried at 85°C for 12 hours. Raman analysis shows that the positive electrode sheet has a peak at 258 cm -1 Up to 846cm -1 There are two peaks in the wavelength range, and the peak intensity ratio of the strongest peak to the second strongest peak is: 1.6 to 2.

0.

11. An electronic device comprising the electrochemical device according to any one of claims 9 to 10.

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