Secondary battery and electric device

Abstract

The application discloses a secondary battery and an electric device, and relates to the technical field of new energy sources.The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive pole current collector and a positive pole active material layer arranged on at least one side of the positive pole current collector, the positive pole active material layer comprises tungsten-containing particles, and the distribution density P of the tungsten-containing particles in the positive pole piece satisfies: 31<=P<=300 particles / cm 2 The positive pole piece contains tungsten-containing particles, on one hand, the tungsten-containing particles can preferentially react with hydrofluoric acid, and the corrosion of the hydrofluoric acid on the positive pole active material body can be alleviated; on the other hand, after the tungsten-containing particles are corroded and dissolved by the hydrofluoric acid, the tungsten-containing particles exist in the form of tungstic acid, the tungstic acid is difficult to dissolve, and a tungstic acid coating layer can be formed on the surface of the positive pole active material body, so that the positive pole active material body can be effectively protected from being corroded by the hydrofluoric acid. Therefore, the effect of long-term protection of the positive pole active material is achieved, and the secondary battery has excellent cycle performance and storage performance.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] The battery is a key component of electric vehicles, and lithium-ion batteries currently dominate the electric vehicle battery market. A lithium-ion battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The performance of the positive electrode material directly determines the energy density, safety performance, and lifespan of the lithium-ion battery. Ternary cathode materials have become the mainstream cathode material in the market due to their higher energy density. However, the layered structure of ternary cathode materials has poor stability and is prone to structural collapse during repeated charge-discharge cycles. The exposed fresh electrode is easily corroded by hydrofluoric acid, a byproduct of the electrolyte. Therefore, it is necessary to find ways to improve this by reducing the corrosion of the cathode material by hydrofluoric acid, thereby ensuring its electrochemical performance.

[0003] The current conventional method is to coat the ternary cathode material with metal oxides to reduce the direct contact between the cathode material and the electrolyte, thereby improving long-term performance. However, conventional metal oxides are easily corroded by hydrofluoric acid, meaning that the protection time of the coating layer that protects the ternary cathode material is limited and cannot guarantee corrosion protection throughout its entire life cycle. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the coating layer of the ternary cathode material, which plays a protective role in the prior art, is easily damaged by hydrofluoric acid corrosion, and the protection time is short, resulting in poor cycle performance and storage performance of lithium-ion batteries.

[0005] To address the aforementioned problems, in a first aspect, the present invention proposes a secondary battery, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising tungsten-containing particles, the distribution density P of the tungsten-containing particles in the positive electrode sheet satisfying: 31 ≤ P ≤ 300 particles / cm³ 2 .

[0006] A further technical solution is that the tungsten-containing particles include elemental tungsten and WO3. p One or more of M2WO4, wherein 2≤p≤3, and M includes at least one of Li and Na.

[0007] A further technical solution is that the compaction density of the positive electrode active material layer is 2.4-3.6 g / cm³. 3 .

[0008] A further technical solution is that the resistance of the positive electrode is 10-300mΩ.

[0009] A further technical solution is that the peeling force of the positive electrode sheet is 5-20 N / m.

[0010] A further technical solution is that the particle size of the tungsten-containing particles is 10-40 μm, and the mass content of the tungsten-containing particles in the positive electrode active material layer is 0.01%-2.0%.

[0011] A further technical solution is that the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes Li x Ni y Co z Mn k O2, where 0.8≤x≤1.1, 0.3<y<1, 0<z<1 and 0<k<1.

[0012] A further technical solution is that the secondary battery also includes a negative electrode sheet. When the secondary battery is charged and discharged to a capacity retention rate of 80%, the negative electrode sheet contains transition metal elements Ni, Co, and Mn. Based on the weight of the negative electrode sheet, the content range of Ni, Co, and Mn elements is as follows: Ni≤600ppm, Co≤120ppm, Mn≤450ppm.

[0013] A further technical solution is that when the secondary battery is stored at 60°C until the capacity retention rate is equal to 80%, the negative electrode sheet contains transition metal elements Ni, Co and Mn. Based on the weight of the negative electrode sheet, the content range of Ni, Co and Mn elements is as follows: Ni≤500ppm, Co≤100ppm, Mn≤380ppm.

[0014] Secondly, this application discloses an electrical device that includes the aforementioned secondary battery, which serves as the power supply for the electrical device.

[0015] Compared with the prior art, the technical effects achieved by the present invention include:

[0016] The positive electrode contains tungsten particles (elemental tungsten or tungsten compounds). On one hand, these tungsten particles preferentially react with hydrofluoric acid, mitigating the corrosion of the positive electrode active material by hydrofluoric acid. On the other hand, after being dissolved by hydrofluoric acid, the tungsten particles exist as tungstic acid, which is difficult to dissolve. This tungstic acid forms a tungstic acid coating on the surface of the positive electrode active material, effectively protecting it from hydrofluoric acid corrosion. This achieves long-term protection of the positive electrode active material, resulting in excellent cycle and storage performance in the secondary battery. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The image shown is an electron microscope image obtained from the test in Example 1. The circled area represents tungsten-containing particles. Detailed Implementation

[0019] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. Similar component reference numerals in the drawings represent similar components. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] This invention provides a secondary battery comprising a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on the current collector. The positive active material layer comprises a positive active material and tungsten-containing particles, wherein the distribution density P of the tungsten-containing particles in the positive electrode sheet satisfies: 31 ≤ P ≤ 300 particles / cm³. 2 .

[0023] The particle density of tungsten-containing particles in the positive electrode is less than 31 particles / cm³. 2 At that time, due to the insufficient amount of tungsten particles, the protective effect on the positive electrode active material was limited, resulting in less improvement in the cycle performance and storage performance of lithium-ion batteries.

[0024] The distribution density of tungsten-containing particles in the positive electrode sheet is higher than 300 particles / cm³. 2When tungsten particles cannot participate in the lithium-ion desorption process, the proportion of positive electrode active material decreases accordingly when the total mass of the electrode sheet is constant, resulting in a decrease in charge and discharge capacity and a decrease in battery energy density.

[0025] In this embodiment of the invention, the positive electrode sheet contains tungsten-containing particles (elemental tungsten or tungsten compounds). On one hand, the tungsten-containing particles preferentially react with hydrofluoric acid, mitigating the corrosion of the positive electrode active material by hydrofluoric acid. On the other hand, after the tungsten-containing particles are dissolved by hydrofluoric acid, they exist in the form of tungstic acid. Tungstic acid is difficult to dissolve, thus forming a tungstic acid coating layer on the surface of the positive electrode active material, effectively protecting the positive electrode active material from hydrofluoric acid corrosion. This achieves long-term protection of the positive electrode active material, resulting in excellent cycle performance and storage performance of the lithium-ion battery.

[0026] Furthermore, the tungsten-containing particles include elemental tungsten with the chemical formula WO3. p The tungsten-containing particles contain one or more of the chemical formula M₂WO₄, where 2 ≤ p ≤ 3, and M includes at least one of Li and Na. In other words, the tungsten-containing particles include at least one of elemental tungsten, WO₂, WO₃, Li₂WO₄, and Na₂WO₄. These tungsten-containing particles can be mixed with the positive electrode material as an additive to prepare a positive electrode sheet containing tungsten particles.

[0027] Furthermore, the compaction density of the positive electrode active material layer is 2.4-3.6 g / cm³. 3 Preferably, the compaction density is 2.8-3.5 g / cm³. 3 A positive electrode sheet with a superior compaction density is beneficial for improving volumetric energy density. A compaction density within the aforementioned range avoids side effects such as electrode breakage and impaired electrolyte wetting during positive electrode sheet processing, while also increasing the battery's volumetric capacity.

[0028] Furthermore, the resistance of the positive electrode is 10-300 mΩ. Preferably, the resistance of the positive electrode is 10-150 mΩ. A lower resistance in the positive electrode is beneficial for electron transport, improving rate performance and cycle performance.

[0029] Further, the peel force of the positive electrode sheet is 5-20 N / m. Preferably, the peel force of the positive electrode sheet is 10-18 N / m. A large peel force in the positive electrode sheet helps prevent film detachment during long-term charge-discharge processes, helps stabilize and maintain the electronic and ionic conductivity of the electrode sheet, thereby improving long-term electrical performance. The peel force of the positive electrode sheet refers to the peel force between the positive active material layer and the positive current collector.

[0030] Furthermore, the particle size of the tungsten-containing particles is 10–40 μm.

[0031] When the particle size of tungsten-containing particles is within the above range, the mass fraction of tungsten-containing particles can be relatively high under the condition that the number of tungsten-containing particles is constant. This can improve the buffering effect of hydrofluoric acid and effectively enhance the cycle and storage performance of lithium-ion batteries.

[0032] In addition, when the particle size of tungsten-containing particles is within the above range, the production yield of the positive electrode rolling process can be improved, and large particle additives can be avoided from directly damaging the rolling equipment.

[0033] The tungsten-containing particles in the positive electrode active material layer have a mass content of 0.01% to 2.0%. When the tungsten-containing particles are within the above range, the battery can be ensured to have excellent cycle performance and high energy density.

[0034] When the mass content of tungsten particles in the positive electrode active material layer is too low (less than 0.01%), the protective effect on the positive electrode active material is limited due to the insufficient tungsten particles, resulting in less improvement in the cycle performance and storage performance of the lithium-ion battery.

[0035] When the mass content of tungsten particles in the positive electrode active material layer is too high (greater than 2%), the tungsten particles cannot participate in the lithium ion intercalation / deintercalation process. As a result, the proportion of positive electrode active material is reduced, the charge / discharge capacity is reduced, and the energy density of the battery is reduced, given a fixed total mass of the electrode sheet.

[0036] Furthermore, the positive electrode active material includes Li x Ni y Co z Mn k O2, where 0.8≤x≤1.1, 0.3<y<1, 0<z<1, and 0<k<1. The positive electrode active material used is a nickel-cobalt-manganese ternary positive electrode material, which has a high energy density.

[0037] Furthermore, the secondary battery also includes a negative electrode sheet. When the secondary battery is charged and discharged to a capacity retention rate of 80%, the negative electrode sheet contains transition metal elements Ni, Co, and Mn. Based on the weight of the negative electrode sheet, the content ranges of Ni, Co, and Mn are as follows: Ni ≤ 600 ppm, Co ≤ 120 ppm, Mn ≤ 450 ppm. The charge-discharge cycle temperature is 25°C, and the rate is 1C. The content of transition metal elements Ni, Co, and Mn can be obtained by ICP testing.

[0038] Due to the protective effect of tungsten-containing particles, less transition metal dissolution occurs in the positive electrode active material after long-term cycling, which is beneficial to improving cycle performance. It should be noted that if the negative electrode contains too high a content of transition metal elements (i.e., Ni > 600 ppm, Co > 120 ppm, Mn > 450 ppm), it indicates that a large amount of transition metal dissolution occurs in the positive electrode active material during lithium-ion battery cycling, resulting in loss of the positive electrode active material and deposition of transition metals on the negative electrode side. This can lead to membrane puncture and cause safety accidents such as battery short circuits.

[0039] Furthermore, when the secondary battery is stored at 60°C until its capacity retention is 80%, the negative electrode contains transition metal elements Ni, Co, and Mn. Based on the weight of the negative electrode, the content ranges of Ni, Co, and Mn are as follows: Ni ≤ 500 ppm, Co ≤ 100 ppm, and Mn ≤ 380 ppm. The content of the transition metal elements Ni, Co, and Mn can be obtained through ICP testing.

[0040] Due to the protective effect of tungsten-containing particles, less transition metal dissolution occurs in the positive electrode active material after long-term storage, which is beneficial to improving storage performance. It should be noted that if the negative electrode contains too high a content of transition metal elements (i.e., Ni > 600 ppm, Co > 120 ppm, Mn > 450 ppm), it indicates that a large amount of transition metal dissolution occurs in the positive electrode active material during lithium-ion battery storage, resulting in loss of the positive electrode active material and deposition of transition metals on the negative electrode side. This can lead to puncture of the separator, causing battery short circuits and other safety accidents.

[0041] This invention provides a method for preparing a positive electrode sheet and a lithium-ion battery. The details are as follows:

[0042] A positive electrode slurry is prepared by mixing ternary cathode material, binder, conductive agent, tungsten-containing particles and solvent in a certain mass ratio. The positive electrode slurry is then uniformly coated onto a positive electrode current collector, and after drying, rolling and forming, a positive electrode sheet is obtained.

[0043] Specifically, the ternary cathode material Li x Ni y Co z Mn kO2 (0.8≤x≤1.1, 0.3<y<1, 0<z<1 and 0<k<1), PVDF (polyvinylidene difluoride) binder, conductive carbon black, tungsten-containing particles, and NMP (N-methyl-2-pyrrolidone) solvent are mixed and slurried to prepare a positive electrode slurry. The positive electrode slurry is uniformly coated onto a positive electrode current collector aluminum foil, and after drying, rolling, and sheet forming, a positive electrode sheet is obtained. The weight ratio of the tungsten-containing particles to the sum of the weights of the ternary positive electrode material, conductive carbon black, and PVDF binder is 0.01%–2.0%, and the content of the NMP solvent is not specifically limited, as long as the slurry can be prepared.

[0044] In some embodiments, the above-described positive electrode sheet is assembled with a negative electrode sheet, a separator, and an electrolyte to form a secondary battery. Specifically, the current collector used in the negative electrode sheet is copper foil, and the negative electrode material is one or more of graphite, mesophase carbon microspheres, amorphous carbon, lithium titanate, or silicon-carbon alloy. The compaction density of the negative electrode material is 1.1-1.7 g / cm³. 3 The separator is a polypropylene membrane with a thickness of 9-18 μm. The electrolyte includes an organic solvent, which may contain linear esters and cyclic esters, with the linear esters having a higher mass percentage than the cyclic esters. The cyclic esters may contain ethylene carbonate (EC) and / or propylene carbonate (PP), and the linear esters may contain at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC).

[0045] Based on the above technical solutions, the present invention provides the following embodiments 1-20, and comparative examples 1-4 are provided to illustrate the technical effects of the present invention. Embodiments 1-20 and comparative examples 1-4 are detailed below:

[0046] Example 1

[0047] Step 1, using ternary cathode material LiNi 0.6 Co 0.1 Mn 0.3 O2, PVDF (polyvinylidene fluoride) binder, SP (conductive carbon black), WO3 containing tungsten particles, and NMP (N-methylpyrrolidone) are mixed and pulped to prepare a positive electrode slurry. This slurry is then uniformly coated onto both sides of the positive electrode current collector aluminum foil. After drying, rolling, and sheet forming, a positive electrode sheet containing a positive electrode active material layer is obtained. The compaction density (PD) of the positive electrode active material layer is 3.45 g / cm³. 3 The weight ratio of ternary cathode material, SP, PVDF, and tungsten-containing particles is 92:5:3:0.16. The tungsten-containing particles have a particle size of 20 μm and a distribution density P of 50 particles / cm³. 2 .

[0048] Step 2: Assemble the positive electrode, negative electrode, separator, and electrolyte into a lithium-ion battery.

[0049] The current collector used in the negative electrode is copper foil, and the negative electrode material is graphite with a compaction density of 1.5 g / cm³. 3 The separator is a polypropylene membrane with a thickness of 10 μm. The electrolyte includes an organic solvent consisting of a mixture of dimethyl carbonate and propylene carbonate in a mass ratio of 6:4, and 1 mol / L lithium hexafluorophosphate.

[0050] Example 2

[0051] The preparation method of Example 2 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.5 Co 0.2 Mn 0.3 O2, adjust the roller pressure to make the compaction density PD of the positive electrode active material layer 3.47 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.1.

[0052] Example 3

[0053] The preparation method of Example 3 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.6 Co 0.2 Mn 0.2 O2 was used to adjust the content of each component in the positive electrode slurry, resulting in a weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles of 92:5:3:0.12 in the positive electrode active material layer.

[0054] Example 4

[0055] The preparation method of Example 4 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.7 Co 0.1 Mn 0.2 O2, adjust the roller pressure to make the compaction density PD of the positive electrode active material layer 3.46 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.18.

[0056] Example 5

[0057] The preparation method of Example 5 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi.0.8 Co 0.1 Mn 0.1 O2, adjust the roller pressure to make the compaction density PD of the positive electrode active material layer 3.46 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.26.

[0058] Example 6

[0059] The preparation method of Example 6 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.33 Co 0.33 Mn 0.33 O2 was used to adjust the content of each component in the positive electrode slurry, resulting in a weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer of 92:5:3:0.14.

[0060] Example 7

[0061] The preparation method of Example 7 is the same as that of Example 1, except that in step 1, the tungsten particles are replaced with Li2WO4, and the content of each component in the positive electrode slurry is adjusted to obtain a weight ratio of ternary positive electrode material, SP, PVDF and tungsten particles in the positive electrode active material layer of 92:5:3:0.05.

[0062] Example 8

[0063] The preparation method of Example 8 is the same as that of Example 1, except that in step 1, the tungsten-containing particles are replaced with W, and the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.47 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.63.

[0064] Example 9

[0065] The preparation method of Example 9 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.51 g / cm³. 3 The content of each component in the positive electrode slurry was adjusted to obtain a weight ratio of ternary positive electrode material, SP, PVDF, and tungsten-containing particles of 92:5:3:1.95 in the positive electrode active material layer. The particle size of the tungsten-containing particles was adjusted to 39 μm.

[0066] Example 10

[0067] The preparation method of Example 10 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 2.40 g / cm³. 3 .

[0068] Example 11

[0069] The preparation method of Example 11 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 2.81 g / cm³. 3 .

[0070] Example 12

[0071] The preparation method of Example 12 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.52 g / cm³. 3 .

[0072] Example 13

[0073] The preparation method of Example 13 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.58 g / cm³. 3 .

[0074] Example 14

[0075] The preparation method of Example 14 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 2.93 g / cm³. 3 .

[0076] Example 15

[0077] The preparation method of Example 15 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.41 g / cm³. 3 . 、

[0078] Example 16

[0079] The preparation method of Example 16 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.55 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.56.

[0080] Example 17

[0081] The preparation method of Example 17 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.58 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.92.

[0082] Example 18

[0083] The preparation method of Example 18 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.60 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:4:4:0.92.

[0084] Example 19

[0085] The preparation method of Example 19 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.43 g / cm³. 3 The content of each component in the positive electrode slurry was adjusted to obtain a weight ratio of ternary positive electrode material, SP, PVDF, and tungsten-containing particles of 92:5:3:0.02 in the positive electrode active material layer. The particle size of the tungsten-containing particles was adjusted to 10 μm.

[0086] Example 20

[0087] The preparation method of Example 20 is the same as that of Example 1, except that in step 1, the pressure of the roller is adjusted so that the compaction density PD of the positive electrode active material layer is 3.54 g / cm³. 3 The content of each component in the positive electrode slurry was adjusted to obtain a weight ratio of ternary positive electrode material, SP, PVDF, and tungsten-containing particles of 92:5:3:0.54 in the positive electrode active material layer. The particle size of the tungsten-containing particles was adjusted to 30 μm.

[0088] Example 21

[0089] The preparation method of Example 20 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.5 Co 0.2 Mn 0.3 O2, adjust the roller pressure to make the compaction density PD of the positive electrode active material layer 3.60 g / cm³. 3 By adjusting the content of each component in the positive electrode slurry, the weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer was obtained as 92:5:3:0.1.

[0090] Comparative Example 1

[0091] The preparation method of Comparative Example 1 is the same as that of Example 1, except that in step 1, the content of each component in the positive electrode slurry is adjusted to obtain a weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles in the positive electrode active material layer of 92:5:3:0.008. The particle size of the tungsten-containing particles is adjusted to 9.5 μm.

[0092] Comparative Example 2

[0093] The preparation method of Comparative Example 2 is the same as that of Example 1, except that in step 1, tungsten particles were not added and the content of each component in the positive electrode slurry was adjusted to obtain a weight ratio of ternary positive electrode material, SP and PVDF in the positive electrode active material layer of 92:5:3.

[0094] Comparative Example 3

[0095] The preparation method of Comparative Example 3 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.5 Co 0.2 Mn 0.3 O2 was used to adjust the content of each component in the positive electrode slurry, resulting in a weight ratio of ternary positive electrode material, SP, PVDF, and tungsten-containing particles of 92:5:3:0.006 in the positive electrode active material layer. The particle size of the tungsten-containing particles was adjusted to 9.5 μm.

[0096] Comparative Example 4

[0097] The preparation method of Comparative Example 4 is the same as that of Example 1, except that in step 1, the ternary cathode material is replaced with LiNi. 0.5 Co 0.2 Mn 0.3 O2 was used to adjust the content of each component in the positive electrode slurry, resulting in a weight ratio of ternary positive electrode material, SP, PVDF and tungsten-containing particles of 92:5:3:1.2 in the positive electrode active material layer.

[0098] The detection method is as follows:

[0099] 1. Detection of the number and composition of tungsten-containing particles: After disassembling the battery, the positive electrode is dried, and tungsten-containing particles are identified using a CT instrument. Then, the particles are characterized by SEM / EDS to determine the metal elements in the tungsten-containing particles.

[0100] 2. Electrode resistance test: Cut the positive electrode into 30x30mm size and test it with a two-probe resistance meter.

[0101] 3. Peel force test: Cut the positive electrode sheet into 40x250mm size and test it with a universal tensile tester.

[0102] 4. The test method for the transition metal element content on the negative electrode side of cycle-fed (EOL) and storage-fed (EOL) batteries is as follows: After cycling or storage, the battery is discharged at a constant current of 1C to 2.8V. Then, the battery is disassembled in a glove box, and the middle portion of the negative electrode is taken for ICP testing. It should be noted that cycle-fed (EOL) refers to the lithium-ion battery being cycled through charge and discharge cycles until its capacity retention is equal to 80%. Storage-fed (EOL) refers to the lithium-ion battery being stored at 60℃ until its capacity retention is equal to 80%.

[0103] 5. The cycle test procedure is as follows: After the battery is clamped, it is placed in a constant temperature room at 25℃ for 30 minutes, discharged at 1C constant current to 2.8V, placed for 10 minutes, charged at 1C constant current to 4.35V, constant voltage to 0.05C, placed for 10 minutes, and the test is stopped when the capacity retention rate is ≤80%.

[0104] 6. The high-temperature storage test procedure is as follows: Charge the battery cell to 4.35V at 25℃, then store it in a 60℃ constant temperature chamber. Test the residual capacity every 30 days and recharge it to 4.35V with a constant current of 1C before storing. The calculation method is as follows: Test the initial furnace capacity Q0 before furnace storage. After every 30 days, take it out of the chamber, cool it down, and test the residual capacity Q. "Q / Q0×100%" is the battery's storage capacity retention rate.

[0105] 7. Battery specific capacity test: At room temperature (25℃), charge the battery at a 1C rate to the cutoff voltage of 4.2V. After resting for 1 hour, discharge the battery at a 1C rate to the cutoff voltage (2.5V) and record the released capacity (mAh). Repeat the above test 3 times and take the average value. Battery specific capacity = capacity / battery mass.

[0106] The electrode parameters of each embodiment and comparative example obtained through the above tests are shown in Table 1 below. The content of transition metal elements on the negative electrode side of the cycle EOL and storage EOL lithium-ion batteries is shown in Table 2. The electrical performance data is shown in Table 3.

[0107]

[0108] Table 1. Comparison of electrode parameters between the examples and comparative examples.

[0109]

[0110]

[0111] Table 2. Comparison of transition metal element content on the negative electrode side of the cyclic EOL and storage EOL lithium-ion batteries of the examples and comparative examples.

[0112]

[0113]

[0114] Table 3 Comparison of electrochemical performance of the examples and comparative examples

[0115] By comparing Example 1 and the comparative example, it can be seen that when tungsten-containing WO3 particles are added and the number of tungsten-containing particles per square centimeter of electrode area is 31 to 300, the cycle performance and storage performance of the lithium-ion battery are better than when no tungsten particles are added, or when the number of tungsten-containing particles per square centimeter of electrode area is less than 31 or greater than 300.

[0116] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0117] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0118] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Since these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations.

[0119] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A secondary battery, characterized in that, The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes tungsten-containing particles, and the distribution density P of the tungsten-containing particles in the positive electrode satisfies: 31 ≤ P ≤ 300 particles / cm³. 2 ; The tungsten-containing particles include elemental tungsten and WO3. p One or more of M2WO4, wherein 2≤p≤3, and M includes at least one of Li and Na; The particle size of the tungsten-containing particles is 10–40 μm.

2. The secondary battery according to claim 1, characterized in that, The compaction density of the positive electrode active material layer is 2.4-3.6 g / cm³. 3 .

3. The secondary battery according to claim 1, characterized in that, The resistance of the positive electrode is 10-300mΩ.

4. The secondary battery according to claim 1, characterized in that, The peeling force of the positive electrode sheet is 5-20 N / m.

5. The secondary battery according to claim 1, characterized in that, The tungsten-containing particles have a mass content of 0.01% to 2.0% in the positive electrode active material layer.

6. The secondary battery according to claim 1, characterized in that, The positive electrode active material layer includes a positive electrode active material, which includes Li. x Ni y Co z Mn k O2, where 0.8≤x≤1.1, 0.3<y<1, 0<z<1 and 0<k<1.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The secondary battery also includes a negative electrode sheet. When the secondary battery is charged and discharged to a capacity retention rate of 80%, the negative electrode sheet contains transition metal elements Ni, Co, and Mn. Based on the weight of the negative electrode sheet, the content range of Ni, Co, and Mn elements is as follows: Ni≤600ppm, Co≤120ppm, Mn≤450ppm.

8. The secondary battery according to claim 7, characterized in that, When the secondary battery is stored at 60°C until the capacity retention rate is equal to 80%, the negative electrode sheet contains transition metal elements Ni, Co and Mn. Based on the weight of the negative electrode sheet, the content range of Ni, Co and Mn elements is as follows: Ni≤500ppm, Co≤100ppm, Mn≤380ppm.

9. An electrical appliance, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 8, wherein the secondary battery serves as the power supply for the electrical equipment.

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