CN115172694A

CN115172694A - Positive pole piece and electrochemical device and electronic device comprising same

Info

Publication number: CN115172694A
Application number: CN202210816212.1A
Authority: CN
Inventors: 程世杨; 下羽淳平; 郎野
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-01-21
Filing date: 2021-01-21
Publication date: 2022-10-11
Also published as: WO2022156706A1; CN112928249B; CN112928249A

Abstract

The application provides a positive pole piece and contain electrochemical device and electron device of this positive pole piece, wherein positive pole piece contains anodal active material layer, and the element content distribution on anodal active material layer surface satisfies: the molar ratio alpha between the manganese element and the fluorine element is 10 to 80. The positive pole piece can inhibit the generation of hydrogen fluoride in an electrochemical device, and reduces the reaction of the hydrogen fluoride and a manganese-containing positive active material, so that the dissolution of manganese in the positive active material in a high-temperature environment is reduced, the capacity attenuation of the electrochemical device in the high-temperature environment is reduced, and the effects of improving the stability of the electrochemical device in the high-temperature environment and prolonging the service life of the electrochemical device at high temperature are achieved.

Description

Positive pole piece and electrochemical device and electronic device comprising same

The application is a divisional application of Chinese patent application with the invention name of 'a positive pole piece and an electrochemical device and an electronic device comprising the positive pole piece' filed by China patent office on 21/01/2021, and the application number is 202110080043.5.

Technical Field

The present disclosure relates to the field of electrochemical technologies, and particularly to a positive electrode plate, and an electrochemical device and an electronic device including the same.

Background

The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and is widely applied to the fields of electric energy storage, portable electronic equipment, electric automobile power supply and the like. With the continuous expansion of the application range of lithium ion batteries, the market puts higher demands on the lithium ion batteries, for example, the lithium ion batteries are required to be stable in a high-temperature environment.

However, the specific capacity of the conventional lithium ion battery is seriously attenuated at high temperature, which causes the occurrence of side reactions in the lithium ion battery at high temperature, so that the structure of an electrode active material is damaged, and the stability and the service life of the lithium ion battery are influenced. Therefore, a lithium ion battery having a long life span at a high temperature is required.

Disclosure of Invention

The present application is directed to a positive electrode plate, and an electrochemical device and an electronic device including the same, so as to improve stability of the electrochemical device in a high temperature environment.

In the following description of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.

The first aspect of the present application provides a positive electrode sheet, which includes a positive active material layer, the element content distribution on the surface of the positive active material layer satisfies: the molar ratio alpha between the manganese element and the fluorine element is 10 to 80.

The inventors have found that, in a lithium ion battery, a manganese-containing positive electrode active material (e.g., lithium manganate or lithium nickel cobalt manganate) has a relatively high specific capacity decay during charge and discharge, particularly at high temperatures (e.g., above 60 ℃). Because the electrolyte contains trace moisture, water and LiPF in the electrolyte ₆ The reaction forms HF, resulting in a spinel disproportionation reaction. Mn ³⁺ Generation of Mn after disproportionation ⁴⁺ And Mn ²⁺ ，Mn ²⁺ Easy dissolution, accelerated dissolution at high temperature, and the destruction of the structure of the manganese-containing positive electrode active material. In view of this, in another embodiment of the present disclosure, by controlling the molar ratio α between the manganese element and the fluorine element to be 12 to 80, and in another embodiment of the present disclosure, α is 10 to 40, generation of hydrogen fluoride in an electrochemical device can be better suppressed, a reaction between the hydrogen fluoride and a manganese-containing positive electrode active material is reduced, and stability of the manganese-containing positive electrode active material is improved, so that dissolution of manganese in the positive electrode active material in a high temperature environment is reduced, and further capacity fading of the lithium ion battery in the high temperature environment is reduced, so that the lithium ion battery is stored more stably in the high temperature environment, and a service life of the lithium ion battery is prolonged.

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

In other embodiments herein, β/α is from 0.35 to 0.625. It is understood that the positive electrode active material layer may be disposed on one or both surfaces of the current collector, and when the thickness of the positive electrode active material layer on one surface of the current collector is denoted as H, the molar ratio of the manganese element to the fluorine element in the positive electrode active material layer in a depth region from H/3 to 2H/3 from the surface is denoted 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 mn/f ratio inside the positive electrode active material layer is made lower than the mn/f ratio on the surface, which can improve the electron blocking and improve the cycle performance of the lithium ion battery, and can 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.

In some embodiments of the present application, the β ranges from 5 to 50. Without being bound to any theory, when β is too low (e.g., below 5), the manganese to fluorine ratio inside the positive electrode active material layer is too low, which is not favorable for the improvement of the energy density of the lithium ion battery; when β is too high (for example, higher than 50), the manganese-fluorine ratio inside the positive electrode active material layer is too high, and it is 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 the energy density of the lithium ion battery is increased.

In some embodiments of the present application, the positive electrode active material layer includes a positive electrode active material and a metal halide. Wherein, when the average particle diameter of the positive electrode active material is represented as D1 and the average particle diameter of the metal halide is represented as D2, the following relationship is satisfied between D1 and D2: 0.33. Ltoreq. D1/D2. Ltoreq.100, and in further embodiments of the present application 1.5. Ltoreq. D1/D2. Ltoreq.100. Without being limited to any theory, by controlling the relationship between D1 and D2 to satisfy the above-mentioned relational expression, the metal halide is not easy to agglomerate in the positive active material, the stability of the positive active material is further improved, and the generation of hydrogen fluoride in the lithium ion battery is more effectively inhibited.

The average particle diameter in the present application means that a material powder is photographed and observed by an SEM, then 10 material particles are randomly selected from the SEM photograph by using image analysis software, and the area of each of the material particles is obtained, and then, assuming that the material particles are spherical, the particle diameter R (diameter) of each material particle is obtained by the following formula: r = 2X (S/Pi) ^1/2 (ii) a Wherein S is the area of the material particles; the average particle diameter of the material particles was determined by performing processing for determining the particle diameter R of the material particles on 10 SEM images and arithmetically averaging the particle diameters of the obtained 100 (10 × 10) material particles.

In some embodiments of the present application, D1 is from 2 μm to 20 μm and D2 is from 0.2 μm to 6 μm. Without being limited to any theory, when the average particle size of the cathode active material is too small (e.g., less than 2 μm), the specific surface area of the small particles is large, the cathode active material reacts with the electrolyte more easily, and more by-products are generated; when the average particle size of the positive electrode active material is too large (for example, larger than 20 μm), the volume change of large particles is large in the circulation process, and the positive electrode material is more likely to be broken, which is not favorable for improving the stability of the positive electrode active material. By controlling the average particle size of the positive active material within the above range, not only can more byproducts be prevented from being generated, but also the stability of the positive active material can be improved. By controlling the average particle size of the metal halide within the above range, the metal halide is less likely to agglomerate in the positive electrode active material, and the stability of the positive electrode active material is further improved, thereby further suppressing the generation of hydrogen fluoride in the lithium ion battery.

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

In some embodiments of the present application, in the XRD pattern of the positive electrode active material layer, I _A Shows a characteristic peak intensity in the range of 44.7 DEG to 45.1 DEG, I _B Showing a characteristic peak intensity in the range of 45.1 DEG to 45.6 DEG, I _A And I _B Satisfies the following conditions: i is more than 0.5 _A /I _B Is less than 0.8. It is shown that the positive electrode active material layer of the present application contains a metal halide, such as LiF.

In some embodiments herein, the positive active material comprises at least one of compound a) or compound b): the compound a) is Li _x1 Mn _2-y1 Z _y1 O ₄ Wherein Z comprises at least one of Mg, al, B, cr, ni, co, zn, cu, zr, ti or V, x1 is more than or equal to 0.8 and less than or equal to 1.2, and y1 is more than or equal to 0 and less than or equal to 0.1. The compound b) is Li _x2 Ni _y2 Co _z Mn _k M _q O _b-a T _a Wherein M includes B, mg, al, si,At least one of P, S, ti, cr, fe, co, ni, cu, zn, ga, Y, zr, mo, ag, W, in, sn, pb, sb and Ce; t is halogen, at least one of F, cl, br or I; x2, y2, z, k, q, a and b satisfy: x2 is more than or equal to 0.2 and less than or equal to 1.2, y2 is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, 0<k≤1、0≤q≤1、1<b is less than or equal to 2 and a is more than or equal to 0 and less than or equal to 1.

When the positive electrode active material contains the compound a) and the compound b), the charge-discharge cycle performance of the lithium ion battery can be further improved.

The metal halides of the present application include the compound AB _m A can comprise at least one of Li, na, K, mg, ca, sr, ba, zn or Al, B can comprise at least one of F, cl, br or I, wherein m is more than or equal to 1 and less than or equal to 4. The metal halide plays a role in inhibiting the generation of hydrogen fluoride and reducing the reaction of the hydrogen fluoride with the manganese-containing positive electrode active material.

In some embodiments of the present application, after the positive electrode sheet is soaked in the electrolyte at 80 ℃ for 1 day, the mass percentage z of the Mn element to the Li element contained in the electrolyte is: z is more than 0 and less than or equal to 0.5 percent. Wherein the volume ratio of the mass of the positive active material layer contained in the positive pole piece to the electrolyte is 1g/100mL, the volume ratio of the ethylene carbonate to the dimethyl carbonate in the electrolyte is 3: 7, and LiPF ₆ The concentration is 1mol/L. The positive pole piece is only dissolved out by trace Mn element after being soaked in the electrolyte, so that the positive pole piece has higher stability.

In some embodiments of the present application, a conductive agent is included in the positive electrode active material layer. The conductive agent is not particularly limited as long as the conductive property of the positive electrode sheet can be improved, and may include at least one of carbon nanotubes, carbon fibers, acetylene black, graphene, ketjen black, and carbon black, for example.

In some embodiments of the present application, the positive electrode active material layer includes a binder. The binder is not particularly limited as long as the object of the present invention can be achieved, and may include, for example, 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 polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

The method for preparing the positive electrode active material layer is not particularly limited, and a method known to those skilled in the art may be used. For example, when preparing a positive electrode active material layer having different concentrations of metal halide in the thickness direction, the difference in deposition rate and filling property due to the difference in density and particle size between the metal halide and the positive electrode active material can be utilized to achieve different concentrations of metal halide in the thickness direction of the positive electrode active material layer by controlling the drying temperature and rate. For example, the positive electrode active material layers with different concentrations of metal halides in the thickness direction can be prepared by a layered coating mode, wherein the layered coating mode is that positive electrode slurry is coated on the positive electrode current collector layer by layer, the proportion of the positive electrode active material and the metal halides in the positive electrode slurry coated on each layer can be the same or different, and the content difference of the metal halides in the thickness direction can be controlled by setting the proportion of the positive electrode active material and the metal halides in the positive electrode slurry coated on each layer to be different.

As a specific example, the following preparation method can be employed: and uniformly coating the positive electrode slurry on one surface of the current collector, drying at 80-120 ℃, and cold-pressing to obtain the positive electrode piece.

As another specific example, the following preparation method may be employed: uniformly coating the positive electrode slurry with higher metal halide content relative to the positive electrode active material on one surface of a current collector, and drying to form a first coating; and uniformly coating the positive electrode slurry with low metal halide content on the first coating, drying to obtain a second coating, and performing cold pressing to obtain the positive electrode piece.

It will be understood by those skilled in the art 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.

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

In the negative electrode in the present application, the negative electrode current collector is not particularly limited, and any negative electrode current collector known in the art, such as a copper foil, an aluminum alloy foil, a composite current collector, and the like, may be used. The anode active material layer includes an anode active material, and the anode active material is not particularly limited, and any anode active material known in the art may be used. For example, at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon, lithium titanate, and the like may be included.

The lithium ion battery of the present application further includes an electrolyte including a lithium salt and a non-aqueous solvent.

In some embodiments herein, the lithium salt is selected from LiPF ₆ 、LiBF ₄ 、LiAsF ₆ 、LiN(SO ₂ CF ₃ ) ₂ 、LiSiF ₆ And lithium difluoroborate. For example, the lithium salt includes LiPF ₆ Since it can give high ionic conductivity and improve cycle characteristics. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compounds are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, caprolactone, and combinations thereof.

Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of such other organic solvents are dimethylsulfoxide, 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.

The second aspect of the present application further provides an electrochemical device, including the positive electrode sheet described in any one of the embodiments of the first aspect.

In some embodiments of the present application, the electrochemical device is discharged to 25% state of charge (SOC), stored at 80 ℃ for 1 day, disassembled, and the positive electrode piece is washed with dimethyl carbonate solvent, dried at 85 ℃ for 12h, and then raman tested at 258cm ^-1 To 846cm ^-1 Two peaks exist within the wavelength range, with the peak intensity ratio of the most intense peak to the less intense peak being 1.6 to 2.0.

The third aspect of the present application also provides an electronic device comprising the electrochemical device according to any one of the embodiments of the second aspect.

The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

The process of preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, the electrochemical device may be manufactured by the following process: the positive electrode, the isolating membrane and the negative electrode are sequentially stacked, and are placed into the shell after being wound, folded and the like according to needs, electrolyte is injected into the shell and the shell is sealed, wherein the used isolating membrane is the isolating membrane provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as necessary to prevent a pressure rise and overcharge/discharge inside the electrochemical device.

The application provides a positive pole piece and contain this positive pole piece's electrochemical device and electron device, satisfies through the surface element content distribution that makes the positive pole active material layer of positive pole piece: the molar ratio alpha between the manganese element and the fluorine element is 10-80, so that the generation of hydrogen fluoride in the electrochemical device can be better inhibited, and the reaction between the hydrogen fluoride and the manganese-containing positive electrode active material is reduced, so that the dissolution of manganese in the positive electrode active material in a high-temperature environment is reduced, the capacity attenuation of the electrochemical device in the high-temperature environment is further reduced, and the effects of improving the stability of the electrochemical device in the high-temperature environment and prolonging the service life of the electrochemical device at high temperature are achieved.

Drawings

In order to more clearly illustrate the present application and the technical solutions of the prior art, the following briefly introduces embodiments and drawings required in the prior art, and obviously, the drawings in the following description are only some embodiments of the present application, and other technical solutions can be obtained by those skilled in the art according to the drawings.

FIG. 1a is a Raman spectrum obtained by Raman testing of the positive electrode sheet of comparative example 1;

fig. 1b is a raman spectrum obtained after raman testing of the positive electrode sheet of example 1;

FIG. 2a is an EDX-mapping F element map of the positive electrode sheet of comparative example 1;

FIG. 2b is the EDX-mapping F element map of the positive electrode sheet of example 1;

fig. 3 is XRD patterns of the positive electrode sheets of example 1 and comparative example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be apparent that the described embodiments are only a few embodiments of the present application, and not all embodiments. All other technical solutions obtained by a person of ordinary skill in the art based on the embodiments in the present application belong to the protection scope of the present application.

In the embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.

The test method and the test device are as follows:

metal halide distribution test:

and testing the distribution condition of the metal halide in the positive pole piece by adopting SEM-EDX. Firstly, SEM-EDX analysis is carried out on the surface of the positive pole piece, an area with the size of 200 Mum multiplied by 200 Mum is selected from an SEM-EDX picture, and the number N of F atoms in the whole area is tested ₁ Then, the number N of Mn atoms in the range of the area was measured ₂ . The ratio of Mn to F in this area is W ₁ ＝N ₂ /N ₁ . The testing instrument is an OXFORD EDS (X-max-20 mm) ² )。

And (3) Raman spectrum testing:

keeping the surface of the dried positive pole piece flat, placing the positive pole piece flat in a sample stage of a Raman testing instrument (JobinYvon LabRAM HR), correcting the peak position by using a silicon wafer, randomly searching a positive pole piece sample under a 10-fold long focal length, and testing.

XRD test:

and keeping the surface of the dried positive pole piece flat, placing the positive pole piece in a sample table of an XRD testing instrument (model Bruker, D8), and obtaining an XRD diffraction pattern by using a scanning speed of 2 degrees/min and a scanning angle range of 10 degrees to 90 degrees.

And (3) testing the button cell:

button cell preparation：

Cleaning one side of the dried positive pole piece with the positive active material layer coated on the two sides by using N-methylpyrrolidone (NMP), baking for 2h in a vacuum environment at 85 ℃, taking out the positive pole piece, stamping the positive pole piece to obtain a small wafer (positive pole piece) required by a CR2025 button cell, assembling the small wafer (positive pole piece) into the button cell according to foamed nickel, a lithium wafer, a separation film and the positive pole piece in sequence, and injecting 50 microliters of electrolyte (the electrolyte comprises the components of Ethylene Carbonate (EC), propylene Carbonate (PC) and diethyl carbonate (DEC) = 1: 1 and LiPF) ₆ The concentration of (2) is 1.15 mol/L).

Gram capacity test for button cell：

The assembled button cell is charged and discharged for 50 times at a cut-off voltage of 2.7V to 4.3V and under the condition of 25 ℃ and at a current of 0.2C, and the gram capacity is tested and the unit mAh.g is measured ^-1 。

High-temperature storage test in positive pole piece electrolyte：

The button cells were then discharged to 30% soc, the positive electrode plate was taken out of the button cell, immersed in 10mL of electrolyte and sealed, and then stored in an oven at 80 ℃ for 1 day, the electrolyte was filtered through a 450nm filter, and the filtrate was measured for Mn content in g/L by plasma optical direct-reading spectrometer (ICP).

Button cell cycle performance test：

And (3) carrying out first charging and discharging on the button cell in an environment of 45 ℃, carrying out constant current charging at a charging current of 0.5 ℃ until the upper limit voltage is 4.3V, then carrying out constant current discharging at a discharging current of 1C until the final voltage is 2.7V, recording the discharging capacity of the first cycle, then repeating the steps for 50 charging and discharging cycles, and recording the discharging capacity of the 50 th cycle.

Cycle capacity retention ratio = (discharge capacity at 50 th cycle/discharge capacity at first cycle) × 100%.

Full battery test:

high temperature storage test of lithium ion battery：

Discharging the lithium ion battery to 30% SOC, storing in an oven at 60 ℃ for 7 days, and recording as the recovery capacity after 3 times of charge-discharge cycles with 0.2C current, wherein the recovery capacity retention rate is as follows: the recovery capacity of the lithium ion battery after being laid aside/the initial capacity of the lithium ion battery is multiplied by 100 percent.

Lithium ion battery cycle performance test：

The lithium ion battery is charged and discharged for the first time in an environment of 45 ℃, constant current charging is carried out under a charging current of 0.5 ℃ until the upper limit voltage is 4.3V, then constant current discharging is carried out under a discharging current of 1C until the final voltage is 2.7V, the discharging capacity of the first cycle is recorded, and then the steps are repeated for 500 charging and discharging cycles, and the discharging capacity of the 500 th cycle is recorded.

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

Examples

Example 1

< preparation of Positive electrode slurry >

Lithium manganate (LiMn) as positive electrode active material ₂ O ₄ An average particle diameter D1 of 10 μm), a metal halide lithium fluoride (LiF, an average particle diameter D2 of 6 μm), a conductive agent (conductive carbon black Super P),Polyvinylidene fluoride (PVDF) as a binder is mixed according to the mass ratio of 97.5: 0.5: 1, then N-methylpyrrolidone (NMP) is added as a solvent to prepare slurry with the solid content of 75% and the viscosity of 5000mPas, and the slurry is uniformly stirred to obtain the anode slurry.

< full cell preparation >

< preparation of Positive electrode sheet >

And uniformly coating the obtained positive electrode slurry on one surface of a current collector aluminum foil with the thickness of 12 microns, drying at 90 ℃, and cold-pressing to obtain a positive electrode piece with the total thickness of the positive electrode active material layer of 80 microns. Wherein alpha is 80 and beta is 50.

Repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on the two surfaces. Cutting the positive pole piece into the specification of 76mm × 851mm, and welding the pole lugs for later use.

< preparation of negative electrode sheet >

Mixing the negative active material artificial graphite, styrene butadiene rubber and sodium carboxymethylcellulose according to a mass ratio of 96: 2, adding deionized water as a solvent to prepare slurry with the solid content of 60%, adding a proper amount of deionized water, and adjusting the viscosity of the slurry to 5000 Pa.s to prepare the negative slurry. And coating the prepared negative electrode slurry on one surface of a copper foil with the thickness of 12 mu m, drying at 110 ℃, and carrying out cold pressing to obtain a negative electrode plate with the negative electrode active material layer thickness of 40 mu m. And then repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the negative active material layers coated on the two surfaces. Cutting the negative pole piece into the specification of 78mm × 867mm, and welding a lug for later use.

< preparation of separator >

A Polyethylene (PE) porous polymer film having a thickness of 15 μm was used as a separator.

< preparation of electrolyte solution >

Mixing non-aqueous organic solvents of Propylene Carbonate (PC), ethylene Carbonate (EC) and diethyl carbonate (DEC) according to the mass ratio of 1: 1 in an environment with the water content of less than 10ppm, and then adding lithium hexafluorophosphate (LiP) into the non-aqueous organic solventsF ₆ ) Dissolving and mixing uniformly. Wherein, liPF ₆ The molar concentration in the electrolyte was 1.15mol/L.

< preparation of lithium ion Battery >

And (3) stacking the prepared positive pole piece, the prepared isolating film and the prepared negative pole piece in sequence, so that the isolating film is positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into an aluminum-plastic film packaging bag, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

Example 2

Except that at<Preparation of positive electrode slurry>Of the positive electrode active materials, lithium manganate (LiMn) ₂ O ₄ ) The mass ratio of the metal halide (LiF), the conductive agent (conductive carbon black Super P) and the adhesive polyvinylidene fluoride (PVDF) is 97: 1<Preparation of positive pole piece>The procedure of example 1 was repeated except that α was controlled to 40 and β was controlled to 20.

Example 3

The procedure was as in example 2, except that in < preparation of positive electrode sheet >, D1 was 2 μm and β was 50.

Example 4

The same procedure as in example 2 was repeated, except that in < preparation of positive electrode sheet >, D1 was 20 μm and D2 was 0.2. Mu.m.

Example 5

The same procedure as in example 2 was repeated, except that in < preparation of positive electrode sheet >, D2 was 0.2. Mu.m.

Example 6

The same procedure as in example 2 was repeated, except that in < preparation of positive electrode sheet >, the baking temperature was controlled to 80 ℃ so that β became 14.

Example 7

Except that in<Preparation of positive electrode slurry>Lithium manganate (LiMn) as positive electrode active material ₂ O ₄ ) The mass ratio of the metal halide (LiF), the conductive agent (conductive carbon black Super P) and the adhesive polyvinylidene fluoride (PVDF) is 96.5: 1.5: 1<Positive pole piecePreparation of>The procedure of example 2 was repeated except that α was controlled to 25 and β was controlled to 12.

Example 8

Except that at<Preparation of positive electrode slurry>Lithium manganate (LiMn) as positive electrode active material ₂ O ₄ ) The mass ratio of the metal halide (LiF), the conductive agent (conductive carbon black Super P) and the adhesive polyvinylidene fluoride (PVDF) is 95: 3: 1<Preparation of positive pole piece>The procedure of example 2 was repeated except that α was controlled to be 12 and β was controlled to be 5.

Example 9

The procedure of example 2 was repeated, except that sodium fluoride (NaF) was used as the metal halide in < preparation of positive electrode slurry > and α was controlled to 23 and β was controlled to 10 in < preparation of positive electrode sheet >.

Example 10

Except that in<Preparation of positive electrode slurry>In the metal halide, aluminum fluoride (AlF) is selected ₃ ) In a<Preparation of positive pole piece>The procedure of example 2 was repeated except that α was controlled to 22 and β was controlled to 11.

Example 11

Except that at<Preparation of positive electrode slurry>In the metal halide, calcium fluoride (CaF) is selected ₂ ) In a<Preparation of positive pole piece>The procedure of example 2 was repeated except that α was controlled to 20 and β was controlled to 11.5.

Example 12

Except that at<Preparation of positive electrode slurry>In the metal halide, calcium fluoride (MgF) is selected ₂ ) In a<Preparation of positive pole piece>The procedure of example 2 was repeated except that α was controlled to be 18 and β was controlled to be 10.

Example 13

Except that at<Preparation of positive electrode slurry>In the positive electrode active material, lithium manganate (LiMn) is selected ₂ O ₄ ) And NCM material (LiNi) _0.5 Co _0.2 Mn _0.3 O ₂ ) Mixture of (1), liMn ₂ O ₄ And LiNi _0.5 Co _0.2 Mn _0.3 O ₂ In a mass ratio of 88.2: 8.8<Preparation of positive pole piece>Wherein alpha is controlled to be 20 and beta is controlled to be other than 9The rest is the same as in example 2.

Example 14

Except that in<Preparation of positive electrode slurry>In the positive electrode active material, NCM material (LiNi) is selected _0.5 Co _0.2 Mn _0.3 O ₂ ) In a<Preparation of positive pole piece>The procedure of example 2 was repeated except that α was controlled to 20 and β was controlled to 9.

Example 15

The same procedure as in example 2 was repeated, except that in < preparation of positive electrode slurry > the metal halide was a mixture of LiF and LiCl at a molar ratio of 9: 1, and in < preparation of positive electrode sheet > α was controlled to be 42 and β to be 22.

Comparative example 1

Except that in<Preparation of positive electrode slurry>In the positive electrode active material, lithium manganate (LiMn) is not added ₂ O ₄ ) The mass ratio of the conductive agent (conductive carbon black Super P) to the binder polyvinylidene fluoride (PVDF) is 98: 1<Preparation of positive pole piece>The procedure of example 1 was repeated except that α was controlled to 300 or more.

Comparative example 2

Except that in<Preparation of positive electrode slurry>In the method, no metal halide is added, and the positive active material is selected from lithium manganate (LiMn) ₂ O ₄ ) And NCM material (LiNi) _0.5 Co _0.2 Mn _0.3 O ₂ ) Mixture of (2), liMn ₂ O ₄ And LiNi _0.5 Co _0.2 Mn _0.3 O ₂ The mass ratio of (A) to (B) is 88.2:9.8 at<Preparation of positive pole piece>The comparative example 1 was repeated except that α was controlled to 320.

Comparative example 3

The same as example 2 was repeated except that in < preparation of positive electrode sheet >, β was controlled to 0.5 by layer coating.

Comparative example 4

The procedure was as in example 2, except that in < preparation of positive electrode sheet >, β was controlled to 102 by layer coating.

The button cell of each example and comparative example was prepared according to the button cell preparation method of example 1, except that the positive electrode sheet of the button cell was the positive electrode sheet corresponding to each example and comparative example. The average particle diameter of the positive electrode active material of each example and comparative example was D1, and the average particle diameter of the metal halide was D2, as shown in table 1.

See tables 1 and 2 for the preparation parameters and test data for each example and comparative example.

As can be seen from example 1 and comparative example 1, example 13 and comparative example 2, the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery of the present application are significantly improved after the addition of the metal halide in the case of containing the same positive electrode active material. In the positive pole piece without the metal halide, a small amount of fluorine can be detected on the surface of the positive pole piece due to the fluorine contained in the electrolyte.

The surface manganese-fluorine ratio alpha and the internal manganese-fluorine ratio beta of the positive active material layer, and the particle size of the metal halide generally influence the performance of the lithium ion battery. As can be seen from examples 2 to 6 and comparative examples 3 to 4, when β is too small or too large, both the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery are relatively poor, because if β is too small, the internal resistance of the positive electrode active material layer is large; if β is too large, the inside of the positive electrode active material layer lacks effective protection, and thus the structure of the positive electrode material is damaged during high-temperature cycling and storage, resulting in a decrease in high-temperature cycling performance and high-temperature storage performance. Further, as can be seen from comparison of examples 2 to 6, examples 2 and 4 to 6 having β/α in the range of 0.35 to 0.625 have more excellent high-temperature cycle performance and high-temperature storage performance than example 3 having β/α of 1.25, because the relatively low manganese-to-fluorine ratio inside the positive electrode active layer is advantageous in 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.

As can be seen from examples 9 to 12, example 15 and comparative example 1, the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery of the present application are both significantly improved after the addition of different types of metal halides of the present application under the condition of containing the same positive electrode active material.

FIG. 1a shows a Raman spectrum obtained by Raman test after discharging the lithium ion battery using the positive electrode sheet of comparative example 1 to 25% SOC, storing the battery at 80 ℃ for 1 day, washing the disassembled positive electrode sheet with a dimethyl carbonate solvent, drying the positive electrode sheet at 85 ℃ for 12 hours. As can be seen from FIG. 1a, it is in the range of 258 to 846cm ^-1 Two characteristic peaks of lithium manganate are not observed in the wavelength range, which is probably due to the destruction of the surface structure of lithium manganate by HF generated in the lithium ion battery.

FIG. 1b shows the Raman spectrum of a lithium ion battery obtained by discharging the lithium ion battery obtained by using the positive electrode sheet of example 1 of the present application to 25% SOC, storing the battery at 80 ℃ for 1 day, washing the disassembled positive electrode sheet with a dimethyl carbonate solvent, drying the positive electrode sheet at 85 ℃ for 12 hours, and performing Raman test. As can be seen from FIG. 1b, the peak value is in the range of 258 to 846cm ^-1 Two characteristic peaks of lithium manganate still exist in the wavelength range, and meanwhile, the positive pole piece can inhibit the generation of HF.

FIG. 2a is an EDX-mapping F element map of the positive electrode plate after the lithium ion battery using the positive electrode plate of comparative example 1 is formed into capacity. As can be seen from fig. 2a, the F element is distributed as a background component, which may be due to the F element remaining on the positive electrode sheet in the electrolyte.

Fig. 2b is an EDX-mapping F element map of the positive electrode sheet after the lithium ion battery using the positive electrode sheet of example 1 is formed into a capacity. As can be seen from fig. 2b, the F element is in a granular distribution, which indicates that the positive electrode sheet of the present application contains metal halide.

Fig. 3 is XRD patterns of the positive electrode sheets of example 1 and comparative example 1. As can be seen from the figure, in the XRD pattern of example 1, there is one characteristic peak a in the range of 44.7 ° to 45.1 ° and one characteristic peak B in the range of 45.1 ° to 45.6 °; in contrast, in the XRD pattern of comparative example 1, one characteristic peak a was not present in the range of 44.7 ° to 45.1 °. The positive pole piece of the application contains metal halide.

The above description is only a preferred embodiment of the present application and should not be taken as limiting the present application, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A positive pole piece comprises a positive active material layer, wherein in an XRD (X-ray diffraction) spectrum of the positive active material layer, I _A Shows a characteristic peak intensity in the range of 44.7 DEG to 45.1 DEG, I _B Shows a characteristic peak intensity in the range of 45.1 DEG to 45.6 DEG, 0.5 < I _A /I _B ＜0.8。

2. The positive electrode sheet according to claim 1, wherein the element content distribution of the surface of the positive electrode active material layer satisfies: the molar ratio alpha between the manganese element and the fluorine element is 10-80, wherein the element content distribution on the surface of the positive active material layer is obtained by adopting the following test method: performing SEM-EDX analysis on the surface of the positive electrode plate, selecting an area with the size of 200 microns multiplied by 200 microns from an SEM-EDX picture, and testing the number N of fluorine atoms in the area ₁ And the number N of manganese atoms in said area ₂ The molar ratio of manganese element to fluorine element in the area is N ₂ /N ₁ 。

3. The positive electrode sheet according to claim 2, wherein the positive electrode sheet satisfies at least one of the following features (1) to (2):

(1) α is 10 to 40;

(2) The thickness of the positive electrode active material layer is H, the molar ratio of manganese element to fluorine element in the depth region from H/3 to 2H/3 of the surface in the positive electrode active material layer is beta, and beta/alpha is 0.35 to 1.25.

4. The positive electrode sheet according to claim 3, wherein the positive electrode sheet satisfies at least one of the following features (1) to (2):

(1) The beta/alpha is 0.35 to 0.625;

(2) The beta is in the range of 5 to 50.

5. The positive electrode tab of claim 1, wherein the positive electrode active material layer comprises a positive electrode active material and a metal halide.

6. The positive electrode sheet according to claim 5, wherein the positive electrode active material has an average particle diameter of D1 and the metal halide has an average particle diameter of D2, and at least one of the following features (1) to (3) is satisfied:

(1) 0.33≤D1/D2≤100；

(2) The D1 is 2-20 μm, and the D2 is 0.2-6 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 positive electrode active material comprises at least one of compound a) or compound b):

the compound a) Li _x1 Mn _2-y1 Z _y1 O ₄ Wherein Z comprises at least one of Mg, al, B, cr, ni, co, zn, cu, zr, ti or V, x1 is more than or equal to 0.8 and less than or equal to 1.2, and y1 is more than or equal to 0 and less than or equal to 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 halogen, and x2, y2, z, k, q, a and b satisfy: x2 is more than or equal to 0.2 and less than or equal to 1.2, y2 is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, 0<k≤1、0≤q≤1、1<b is less than or equal to 2 and a is more than or equal to 0 and less than or equal to 1;

the metal halide comprises a compound AB _m A comprises at least one of Li, na, K, mg, ca, sr, ba, zn or Al, B comprises at least one of F, cl, br or I, and m is more than or equal to 1 and less than or equal to 4.

8. The positive electrode tab according to claim 6, wherein D1/D2 is 1.5. Ltoreq. D1/D2. Ltoreq.100.

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

10. The electrochemical device of claim 9, wherein the electrochemical device is discharged to 25% SOC, stored at 80 ℃ for 1 day, disassembled, washed with dimethyl carbonate solvent, dried at 85 ℃ for 12 hours, and then subjected to Raman testing at 258cm ^-1 To 846cm ^-1 Two peaks exist in the wavelength range, and the peak intensity ratio of the strongest peak to the second strongest peak is as follows: 1.6 to 2.0.

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