Pole piece, preparation method thereof, positive electrode slurry, lithium ion battery and electric device

Abstract

The application relates to a pole piece, a preparation method thereof, a positive pole paste, a lithium ion battery and an electric device. The pole piece comprises a current collector and an active layer arranged on at least one side of the current collector, and the active layer comprises a lithium iron phosphate material. The D50 of the lithium iron phosphate material is beta mu m, the tap density of the lithium iron phosphate material is gamma g / m 3 , a=beta / gamma, 0.7<=a<=1.2, the ratio of the D90 of the lithium iron phosphate material to the D10 of the lithium iron phosphate material is b, 4<=b<=8. By controlling the specific relationship between the D50 of the lithium iron phosphate material and the tap density, and controlling the specific relationship between the D90 of the lithium iron phosphate material and the D10, the low-temperature charging performance and the low-temperature cycle performance of the lithium ion battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a pole piece, a preparation method thereof, a positive electrode slurry, a lithium ion battery and an electric device. BACKGROUND

[0002] Lithium ion batteries are widely used in mobile phones, tablets, notebooks, electric vehicles and energy storage fields. At present, the best working temperature range of lithium ion batteries is under normal temperature (25℃) conditions, and the charging performance thereof is poor under low temperature conditions. The current solution is to add a heating system and a temperature control system in the lithium ion battery system, and the battery system is self-heated under low temperature conditions, so that the battery core works in a suitable temperature range. However, the addition of the heating system and the temperature control system in the lithium ion battery system increases the complexity of the battery system, reduces the system reliability, increases the cost of the battery system, and the self-heating of the system also consumes the energy of the battery system itself. Therefore, the low temperature performance of the battery needs to be improved. SUMMARY

[0003] Therefore, the present application provides a pole piece with good low temperature performance, a preparation method thereof, a positive electrode slurry, a lithium ion battery and an electric device.

[0004] The technical solutions of the present application for solving the above technical problems are as follows.

[0005] In one aspect, the present application provides a pole piece, comprising a current collector and an active layer arranged on at least one side of the current collector, wherein the active layer comprises a lithium iron phosphate material, the D50 of the lithium iron phosphate material is β μm, the tap density of the lithium iron phosphate material is γ g / m 3 , a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of the D90 of the lithium iron phosphate material to the D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0006] In some embodiments, the specific surface area of the lithium iron phosphate material in the pole piece is δ m 2 / g, c = β / δ, 0.03 ≤ c ≤ 0.09.

[0007] In some embodiments, the pole piece has 0.25 μm ≤ D10 ≤ 0.55 μm.

[0008] In some embodiments, the pole piece has 0.5 μm ≤ D50 ≤ 1.1 μm.

[0009] In some embodiments, the pole piece has 1.6 μm ≤ D90 ≤ 4 μm.

[0010] In some embodiments, the pole piece has 4.5 μm ≤ D99 ≤ 8.5 μm.

[0011] In some embodiments, the tap density of the lithium iron phosphate material in the electrode is 0.5 g / m³. 3 ~1.5 g / m 3 .

[0012] In some embodiments, the specific surface area of ​​the lithium iron phosphate material in the electrode is 6 m². 2 / g ~30 m 2 / g.

[0013] This application provides a method for preparing an electrode sheet, comprising the following steps:

[0014] An active layer is disposed on at least one side of the current collector, the active layer comprising lithium iron phosphate material, wherein the D50 of the lithium iron phosphate material is β μm and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0015] This application provides a slurry comprising a lithium iron phosphate material, a first binder, and a first conductive agent, wherein the lithium iron phosphate material has a D50 of β μm and a tap density of γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0016] In some embodiments, the slurry satisfies at least one of the following characteristics:

[0017] (1) The first adhesive comprises at least one of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid and sodium polyacrylate;

[0018] (2) The first conductive agent includes at least one of carbon black, acetylene black, Ketjen carbon, carbon nanotubes and carbon nanofibers;

[0019] (3) The mass ratio of the lithium iron phosphate material, the first binder and the first conductive agent is 95~98:1~3:1~3.

[0020] This application provides a lithium-ion battery, including the above-mentioned electrode sheet or an electrode sheet prepared by the above-mentioned electrode sheet preparation method.

[0021] In some embodiments, the lithium-ion battery includes a positive electrode and a negative electrode, with the electrode sheet serving as the positive electrode. The negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector. The negative electrode active layer includes graphite with a D50 of σ μm and a specific surface area of ​​ω m. 2 / g, d=σ / ω, 2.5≤d≤7.5.

[0022] In some embodiments, in the lithium-ion battery, the tap density of the graphite is θ g / m³. 3 , e = σ / θ, 3 ≤ e ≤ 9.

[0023] In some embodiments, in the lithium-ion battery, the ratio of the D90 of the graphite to the D10 of the graphite is f, where 2 ≤ f ≤ 6.

[0024] In some embodiments, the graphite in the lithium-ion battery satisfies at least one of the following characteristics:

[0025] (1) 2 μm ≤ D10 ≤ 6 μm;

[0026] (2) 4 μm≤D50≤12 μm;

[0027] (3)9 μm≤D90≤16 μm;

[0028] (4)14 μm≤D99≤26 μm;

[0029] (5) The tap density of the graphite is 0.8 g / m³. 3 ~2 g / m 3 ;

[0030] (6) The specific surface area of ​​the graphite is 0.8 m². 2 / g ~3 m 2 / g.

[0031] This application provides an electrical device, including the aforementioned lithium-ion battery.

[0032] Compared with the prior art, the positive electrode slurry of this application has the following beneficial effects:

[0033] The electrode of this application includes lithium iron phosphate material. By controlling the specific relationship between the D50 and tap density of the lithium iron phosphate material, and controlling the specific relationship between the D90 and D10 of the lithium iron phosphate material, its application to lithium-ion batteries can effectively improve the low-temperature charging performance and low-temperature cycling performance of lithium-ion batteries. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 A comparison of the low-temperature cycling performance of the cells prepared in Example 1 and Comparative Example 1 at 5°C with 0.5P / 0.5P 100% DOD.

[0036] Figure 2 The image shows the surface condition of the negative electrode of the battery cell prepared in Example 1 after being charged at -10°C with 0.2P.

[0037] Figure 3 The image shows the surface condition of the negative electrode of the battery cell prepared for Comparative Example 1 after being charged at -10℃ with 0.2P. Detailed Implementation

[0038] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0039] Therefore, this invention is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the invention are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0041] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element preceded by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The indefinite articles “a” and “an” preceding an element or component of the invention are not restrictive in terms of the number of elements or components (i.e., the number of times they appear). Therefore, “an” or “an” should be interpreted as including one or at least one, and singular elements or components also include plural forms, unless the quantity clearly refers only to the singular. “A plurality” means at least two, such as two, three, etc., unless otherwise expressly specified.

[0042] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this invention is within the scope disclosed in the embodiments of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0043] Unless otherwise shown or indicated in the operational embodiments, all figures used to represent the amounts, physicochemical properties, etc., of ingredients in the specification and claims are to be understood to be adjusted by the term "about" in all cases. For example, therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired characteristics by utilizing the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range; for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

[0044] D50: Median particle size, the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%, i.e., the diameter of the particle when the mass of the particles in the particle swarm is evenly divided in half. Its physical meaning is that particles larger than its diameter account for 50% of the total mass, and particles smaller than its diameter also account for 50% of the total mass.

[0045] D10: The particle size at which the cumulative particle size distribution percentage of a sample reaches 10%. Physically, it represents the mass of particles smaller than D10 that account for 10% of the total mass.

[0046] D90: The particle size at which the cumulative particle size distribution percentage of a sample reaches 90%. Physically, it means that 90% of the particles are smaller than D90 by mass.

[0047] D99: The particle size at which the cumulative particle size distribution percentage of a sample reaches 99%. Physically, it means that particles smaller than D99% account for 99% of the total mass.

[0048] One embodiment of this application provides an electrode, including a current collector and an active layer disposed on at least one side of the current collector. The active layer comprises lithium iron phosphate material, wherein the D50 of the lithium iron phosphate material is β μm and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0049] The electrode of this application includes lithium iron phosphate material. By controlling the specific relationship between the D50 and tap density of the lithium iron phosphate material, and controlling the specific relationship between the D90 and D10 of the lithium iron phosphate material, its application to lithium-ion batteries can effectively improve the low-temperature charging performance and low-temperature cycling performance of lithium-ion batteries.

[0050] It is understandable that the active layer can be located on one or both sides of the current collector.

[0051] Furthermore, it can be understood that a includes, but is not limited to, 0.7, 0.8, 0.9, 1, 1.1, 1.2; b includes, but is not limited to, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8; in some examples, it can be any two of these point values ​​as the end value within a range, the same below.

[0052] Optionally, 0.7 ≤ a ≤ 1.1.

[0053] Alternatively, 5 ≤ b ≤ 7.

[0054] In some of these examples, the specific surface area of ​​the lithium iron phosphate material in the electrode is δ m 2 / g, c=β / δ, 0.03≤c≤0.09.

[0055] It is understood that c includes, but is not limited to, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, and 0.09.

[0056] Optionally, 0.05 ≤ c ≤ 0.07.

[0057] Based on controlling the relationship between D50 and tap density, and D90 and D10 of lithium iron phosphate materials, further controlling the relationship between particle size D50 and specific surface area of ​​lithium iron phosphate materials can further improve the low-temperature charging performance and low-temperature cycling performance of lithium-ion batteries.

[0058] In some of these examples, the electrode has a diameter of 0.25 μm ≤ D10 ≤ 0.55 μm.

[0059] It is understood that the D10 of lithium iron phosphate materials includes, but is not limited to, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, and 0.55 μm.

[0060] Optionally, 0.3 μm ≤ D10 ≤ 0.45 μm.

[0061] In some of these examples, the electrode has a diameter of 0.5 μm ≤ D50 ≤ 1.1 μm.

[0062] It is understood that the D50 of lithium iron phosphate materials includes, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, and 1.1 μm.

[0063] Optionally, 0.7 μm ≤ D50 ≤ 0.9 μm.

[0064] In some of these examples, the electrode has a diameter of 1.6 μm ≤ D90 ≤ 4 μm.

[0065] It is understood that the D90 of lithium iron phosphate materials includes, but is not limited to, 1.6 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, and 4 μm.

[0066] Optionally, 1.8 μm ≤ D90 ≤ 3.5 μm.

[0067] In some of these examples, the electrode has a diameter of 4.5 μm ≤ D99 ≤ 8.5 μm.

[0068] It is understood that the D99 of lithium iron phosphate materials includes, but is not limited to, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, and 8.5 μm.

[0069] Optionally, 5.5 μm ≤ D99 ≤ 7.5 μm.

[0070] In some of these examples, the tap density of the lithium iron phosphate material in the electrode is 0.5 g / m³. 3 ~1.5 g / m 3 .

[0071] It is understood that the tap density of lithium iron phosphate materials includes, but is not limited to, 0.5 g / m³. 3 0.6 g / m 3 0.75 g / m 30.8 g / m 3 1 g / m 3 1.1 g / m 3 1.2 g / m 3 1.3 g / m 3 1.4 g / m 3 1.5 g / m 3 .

[0072] In some of these examples, the specific surface area of ​​the lithium iron phosphate material in the electrode is 6 m². 2 / g ~36 m 2 / g.

[0073] It is understood that the specific surface area of ​​lithium iron phosphate materials includes, but is not limited to, 6 m². 2 / g、8 m 2 / g、10 m 2 / g、12m 2 / g, 14.5 m 2 / g、16 m 2 / g、20 m 2 / g、25 m 2 / g、30 m 2 / g、32 m 2 / g、36 m 2 / g.

[0074] Based on controlling the relationship between D50 and tap density, D90 and D10, and particle size D50 and specific surface area of ​​lithium iron phosphate materials, further controlling the particle size ranges of lithium iron phosphate materials such as D10, D50, D90, and D99 can further improve the low-temperature charging performance and low-temperature cycling performance of lithium-ion batteries.

[0075] One embodiment of this application provides a slurry comprising lithium iron phosphate material, a first binder, and a first conductive agent. The D50 of the lithium iron phosphate material is β μm, and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0076] In some of these examples, the first binder in the slurry includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, and sodium polyacrylate.

[0077] In some of these examples, the first conductive agent in the slurry includes at least one of carbon black, acetylene black, Ketjen carbon, carbon nanotubes, and carbon nanofibers.

[0078] It is understood that carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0079] In some of these examples, the mass ratio of lithium iron phosphate material, first binder and first conductive agent in the slurry is 95~98:1~3:1~3.

[0080] It is understood that in the slurry, the mass ratio of lithium iron phosphate material to the first binder is 95~98:1~3; the mass ratio of lithium iron phosphate material to the first conductive agent is 95~98:1~3; and the mass ratio of the first binder to the first conductive agent is 1~3:1~3. Furthermore, the mass ratio of lithium iron phosphate material to the first binder includes, but is not limited to, 95:1, 96:1, 97:1, 98:1, 95:2, 96:2, 97:2, 98:2, 95:3, 96:3, 97:3, and 98:3; the mass ratio of lithium iron phosphate material to the first conductive agent includes, but is not limited to, 95:1, 96:1, 97:1, 98:1, 95:2, 96:2, 97:2, 98:2, 95:3, 96:3, 97:3, and 98:3; and the mass ratio of the first binder to the first conductive agent includes, but is not limited to, 1:1, 1:2, 1:3, 2:1, 2:3, 3:1, and 3:2.

[0081] The slurry provided in this application combines the aforementioned specific lithium iron phosphate material, the first binder, and the first conductive agent in a specific ratio to form the active layer of the electrode, which can greatly improve the low-temperature charging performance and low-temperature cycling performance of lithium-ion batteries.

[0082] One embodiment of this application provides a method for preparing a slurry, comprising the following steps:

[0083] A slurry is prepared by mixing lithium iron phosphate material, a first binder, and a first conductive agent; the D50 of the lithium iron phosphate material is β μm, and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0084] It is understood that the slurry preparation method provided in this application can prepare the above-mentioned slurry, and the above-mentioned slurry can be obtained by the slurry preparation method provided in this application; that is, the slurry preparation method provided in this application and the characteristics of the slurry provided above are mutually applicable.

[0085] One embodiment of this application provides a method for preparing an electrode sheet, comprising the following steps:

[0086] An active layer is disposed on at least one side of the current collector. The active layer comprises lithium iron phosphate material, wherein the D50 of the lithium iron phosphate material is β μm and the tap density of the lithium iron phosphate material is γ g / m³.3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of lithium iron phosphate material is b, 4 ≤ b ≤ 8.

[0087] It is understood that the electrode preparation method provided in this application can produce the aforementioned electrode, and the aforementioned electrode can be produced by the electrode preparation method provided in this application. The features of the aforementioned electrode and the electrode preparation method provided in this application are mutually applicable.

[0088] In some of these examples, the preparation method of the electrode includes the following steps:

[0089] The above-mentioned slurry or the slurry prepared by the above-mentioned slurry preparation method is disposed on at least one side of the current collector, and an active layer is formed on at least one side of the current collector by curing.

[0090] It is understood that this application does not limit the type of current collector; conventional materials in the art are acceptable. For example, when the electrode is a positive electrode, a positive electrode current collector is used; furthermore, the positive electrode current collector includes, but is not limited to, aluminum foil.

[0091] One embodiment of this application provides a lithium-ion battery, including an electrode sheet or an electrode sheet prepared by the above-described electrode sheet preparation method.

[0092] The lithium-ion battery provided in this application, including the electrode sheet described above or the electrode sheet prepared by the above method, can endow the lithium-ion battery with better low-temperature charging performance and low-temperature cycling performance.

[0093] In some examples, the lithium-ion battery includes a positive electrode and a negative electrode, with an electrode sheet serving as the positive electrode and the negative electrode including a negative current collector and a negative active layer disposed on the negative current collector.

[0094] It is understandable that when the above-mentioned electrode is used as the positive electrode, the current collector in the electrode is the positive electrode current collector, and the active layer in the electrode is the positive electrode active layer.

[0095] In some of these examples, in lithium-ion batteries, the D50 of graphite is σ μm, and the specific surface area of ​​graphite is ω m. 2 / g, d=σ / ω, 2.5≤d≤7.5.

[0096] It is understood that d includes, but is not limited to, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5.

[0097] Optionally, 3 ≤ d ≤ 5.

[0098] In some of these examples, the tap density of graphite in lithium-ion batteries is θ g / m³. 3 , e = σ / θ, 3 ≤ e ≤ 9.

[0099] It is understood that e includes, but is not limited to, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, and 9.

[0100] Alternatively, 3 ≤ e ≤ 7.

[0101] In some of these examples, in lithium-ion batteries, the ratio of D90 to D10 of graphite is f, where 2 ≤ f ≤ 6.

[0102] It is understood that f includes, but is not limited to, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, and 6.

[0103] Alternatively, 3 ≤ f ≤ 4.

[0104] In some of these examples, in lithium-ion batteries, 2 μm ≤ D10 ≤ 6 μm.

[0105] It is understandable that the D10 of graphite includes, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm.

[0106] In some of these examples, in lithium-ion batteries, 4 μm ≤ D50 ≤ 12 μm.

[0107] It is understood that the D50 of graphite includes, but is not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, and 12 μm.

[0108] In some of these examples, in lithium-ion batteries, 9 μm ≤ D90 ≤ 16 μm.

[0109] It is understood that the D90 of graphite includes, but is not limited to, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, and 16 μm.

[0110] In some of these examples, in lithium-ion batteries, 14 μm ≤ D99 ≤ 26 μm.

[0111] It is understood that the D99 of graphite includes, but is not limited to, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, and 26 μm.

[0112] In some of these examples, the tap density of graphite in lithium-ion batteries is 0.5 g / m³. 3 ~4 g / m 3 .

[0113] It is understood that the tap density of graphite includes, but is not limited to, 0.5 g / m³.3 0.6 g / m 3 0.8 g / m 3 1 g / m 3 1.2 g / m 3 1.32 g / m 3 1.5 g / m 3 2 g / m 3 2.5 g / m 3 3 g / m 3 3.5 g / m 3 4 g / m 3 .

[0114] In some of these examples, the specific surface area of ​​graphite in lithium-ion batteries is 0.8 m². 2 / g ~3 m 2 / g.

[0115] It is understood that the specific surface area of ​​graphite includes, but is not limited to, 0.8 m². 2 / g、1 m 2 / g, 1.28 m 2 / g, 1.5 m 2 / g、2 m 2 / g, 2.5 m 2 / g、3 m 2 / g.

[0116] In some of these examples, the preparation of the negative electrode in a lithium-ion battery includes the following steps:

[0117] The negative electrode slurry is placed on at least one side of the negative electrode current collector, and then cured to form a negative electrode active layer on at least one side of the negative electrode current collector.

[0118] Furthermore, the negative electrode slurry includes graphite, a second binder, and a second conductive agent.

[0119] In some of these examples, the second binder in the lithium-ion battery includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, and sodium polyacrylate.

[0120] In some of these examples, the second conductive agent in the lithium-ion battery includes at least one of carbon black, acetylene black, Ketjen carbon, carbon nanotubes, and carbon nanofibers.

[0121] It is understood that carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0122] In some of these examples, the mass ratio of graphite, second binder, and second conductive agent in the lithium-ion battery is 94-98:1-3:1-3.

[0123] It is understandable that in lithium-ion batteries, the mass ratio of graphite to the second binder is 94~98:1~3; the mass ratio of graphite to the second conductive agent is 94~98:1~3; and the mass ratio of the second binder to the second conductive agent is 1~3:1~3. Furthermore, the mass ratio of graphite to the second binder includes, but is not limited to, 94:1, 95:1, 96:1, 97:1, 98:1, 94:2, 95:2, 96:2, 97:2, 98:2, 94:3, 95:3, 96:3, 97:3, and 98:3; the mass ratio of graphite to the second conductive agent includes, but is not limited to, 94:1, 95:1, 96:1, 97:1, 98:1, 94:2, 95:2, 96:2, 97:2, 98:2, 94:3, 95:3, 96:3, 97:3, and 98:3; and the mass ratio of the second binder to the second conductive agent includes, but is not limited to, 1:1, 1:2, 1:3, 2:1, 2:3, 3:1, and 3:2.

[0124] It is understood that in some examples, the active layer of the aforementioned electrode (positive and / or negative electrode) can be directly disposed on one side of at least one surface of the current collector; in other examples, other coatings can be disposed on one side of at least one surface before the active layer is disposed; some coatings can also be disposed on the active layer, such as at least one of functional coatings and protective film coatings; further, the functional coating can include carbon material coatings (including at least one of single-walled conductive carbon nanotubes, multi-walled conductive carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, soft carbon and hard carbon) and lithium-philic / sodium-philic metal composite coatings; the protective film coating includes, but is not limited to, at least one of organic polymer coatings, inorganic compound coatings and polymer / inorganic composite material coatings; further, the organic polymer coating includes, but is not limited to, at least one of polyethylene terephthalate (PET) coatings, polypropylene (PP) coatings, polyethylene (PE) coatings, polyvinylidene fluoride (PVDF) coatings, ethylene-vinyl acetate polymer (EVA) coatings.

[0125] The lithium-ion battery provided in this application can be used, but is not limited to, in electrical devices such as vehicles, ships, or aircraft.

[0126] One embodiment of this application provides an electrical device including the aforementioned lithium-ion battery.

[0127] Furthermore, the electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0128] The present application will be described in further detail below with reference to specific embodiments, but the embodiments of the present application are not limited thereto.

[0129] Example 1

[0130] Lithium iron phosphate cathode material: particle size D10 is 0.39 μm, D50 is 0.82 μm, D90 is 2.01 μm, D99 is 6.31 μm, and specific surface area S is 14.50 m². 2 / g, tap density Pz is 0.75 g / m 3 The ratio of D50 to tap density of lithium iron phosphate (LFP) is 1.1 (a), the ratio of D90 to D10 of LFP is 5.15 (b), and the specific surface area of ​​LFP is 0.06 (c).

[0131] Graphite anode material: particle size D10 is 3.40 μm, D50 is 6.40 μm, D90 is 11.90 μm, D99 is 16.58 μm, and specific surface area S is 1.90 m². 2 / g, tap density Pz is 0.99 g / m 3 The ratio of graphite's D50 to specific surface area (d) is 3.37, the ratio of graphite's D50 to tap density (e) is 6.46, and the ratio of graphite's D90 to graphite's D10 (f) is 3.50.

[0132] (1) Preparation of positive electrode slurry: The lithium iron phosphate positive electrode material, the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon black Super P are uniformly mixed in a mass ratio of 96.5%:2%:1.5% to prepare the positive electrode slurry;

[0133] (2) The positive electrode slurry prepared in step (1) is uniformly coated on the positive electrode current collector aluminum foil to obtain the positive electrode sheet;

[0134] (3) Negative electrode slurry: The graphite negative electrode material, the binder styrene-butadiene rubber SBR, the binder carboxymethyl cellulose CMC, and the conductive agent conductive carbon black Super P are uniformly mixed in a mass ratio of 96.8%:1.2%:0.8%:1.2% to prepare the negative electrode slurry;

[0135] (4) The negative electrode slurry prepared in step (3) is uniformly coated on the negative electrode current collector copper foil to obtain the negative electrode sheet;

[0136] (5) The positive electrode sheet prepared in step (2) and the negative electrode sheet prepared in step (4) are wound together with the separator to obtain the electrode core, and the finished battery cell is obtained by baking, liquid injection, static soaking, formation, aging and capacity testing.

[0137] Example 2

[0138] The results are essentially the same as in Example 1, except that the tap density Pz of the lithium iron phosphate cathode material is 1.17 g / m³. 3 The ratio a of the D50 of lithium iron phosphate to the tap density of lithium iron phosphate is 0.7.

[0139] Example 3

[0140] The results are essentially the same as in Example 1, except that the tap density Pz of the lithium iron phosphate cathode material is 0.9 g / m³. 3 The ratio a of the D50 of lithium iron phosphate to the tap density of lithium iron phosphate is 0.91.

[0141] Example 4

[0142] The results are basically the same as in Example 1, except that the particle size D10 of the lithium iron phosphate cathode material is 0.50 μm and the ratio b of D90 to D10 of lithium iron phosphate is 4.

[0143] Example 5

[0144] The results are basically the same as in Example 1, except that the particle size D10 of the lithium iron phosphate cathode material is 0.25 μm and the ratio b of D90 to D10 of lithium iron phosphate is 8.

[0145] Example 6

[0146] The results are essentially the same as in Example 1, except that the specific surface area S of the graphite anode material is 0.91 m². 2 / g; The ratio of D50 to specific surface area of ​​graphite, d, is 7.

[0147] Example 7

[0148] The results are essentially the same as in Example 1, except that the tap density Pz of the graphite anode material is 2.1 g / m³. 3 The ratio e of D50 to tap density of graphite is 3.

[0149] Example 8

[0150] The results are basically the same as in Example 1, except that the D90 of the graphite anode material is 20.4 μm and the ratio f of the D90 of graphite to the D10 of graphite is 6.

[0151] Comparative Example 1

[0152] It is basically the same as Example 1, with the following differences:

[0153] Lithium iron phosphate cathode material: particle size D10 is 0.40 μm, D50 is 1.35 μm, D90 is 4.30 μm, D99 is 7.56 μm, and specific surface area is 12.30 m².2 / g, tap density is 0.82 g / m 3 The ratio of D50 to tap density of lithium iron phosphate (LFP) is 1.64 (a), the ratio of D90 to D10 of LFP is 10.75 (b), and the specific surface area of ​​LFP is 0.11 (c).

[0154] Graphite anode material: particle size D10 is 3.57 μm, D50 is 15.49 μm, D90 is 28.47 μm, D99 is 45.99 μm, and specific surface area is 0.7 m². 2 / g, tap density is 1.32 g / m 3 The ratio of graphite's D50 to specific surface area (d) is 22.12, the ratio of graphite's D50 to tap density (e) is 11.76, and the ratio of graphite's D90 to graphite's D10 (f) is 8.55.

[0155] Comparative Example 2

[0156] The results are essentially the same as in Example 1, except that the tap density Pz of the lithium iron phosphate cathode material is 1.5 g / m³. 3 The ratio a of the D50 of lithium iron phosphate to the tap density of lithium iron phosphate is 0.55.

[0157] Comparative Example 3

[0158] The results are essentially the same as in Example 1, except that the tap density Pz of the lithium iron phosphate cathode material is 0.63 g / m³. 3 The ratio of D50 to tap density of lithium iron phosphate, α, is 1.3.

[0159] Comparative Example 4

[0160] The results are basically the same as in Example 1, except that the particle size D10 of the lithium iron phosphate cathode material is 0.67 μm and the ratio b of D90 to D10 of lithium iron phosphate is 3.

[0161] Comparative Example 5

[0162] The results are basically the same as in Example 1, except that the particle size D10 of the lithium iron phosphate cathode material is 0.2 μm and the ratio b of D90 to D10 of lithium iron phosphate is 10.

[0163] The parameters of the cathode materials used in each embodiment and comparative example are shown in Table 1.

[0164] Table 1

[0165]

[0166] The parameters of the negative electrode materials used in each embodiment and comparative example are shown in Table 2.

[0167] Table 2

[0168]

[0169] The battery cells prepared in each embodiment and comparative example were subjected to performance tests. The test steps are as follows:

[0170] 1. Low-temperature cycling performance test:

[0171] ① Place the battery cells in a 5℃ high and low temperature oven for 6 hours;

[0172] ② Charge 0.5P to 3.65V;

[0173] ③ Let it sit for 10 minutes;

[0174] ④ Discharge 0.5P to 2.5V;

[0175] ⑤ Let it sit for 10 minutes;

[0176] Repeat steps ② to ⑤ to perform a loop test.

[0177] 2. Low-temperature charging capability test:

[0178] ① Place the battery cells in a -10℃ high and low temperature oven for 6 hours;

[0179] ② Discharge 0.5P to 2.5V;

[0180] ③ Let it sit for 10 minutes;

[0181] ④ Verify charging to 3.65V at different rates (0.05P, 0.1P, 0.15P, 0.2P, 0.25P increasing sequentially);

[0182] ⑤ After being left at 25℃ for 120 minutes, the battery is disassembled and the surface condition of the negative electrode is observed.

[0183] The low-temperature cycling performance of the cells prepared in Example 1 and Comparative Example 1 at 5°C with 0.5P / 0.5P 100% DOD is compared as follows: Figure 1 As shown.

[0184] from Figure 1 It can be seen that the battery cell prepared in Example 1 has an energy retention rate of 102% after 500 cycles at 5℃, with no energy decay; while the battery cell prepared in Comparative Example 1 has an energy retention rate of 96% after 30 cycles at 5℃, with faster energy decay.

[0185] The surface condition of the negative electrode of the battery cell prepared in Example 1 after 0.2P charging at -10℃ is as follows. Figure 2 As shown, the surface of the negative electrode of the battery cell prepared in Comparative Example 1 after being charged at -10℃ with 0.2P is as follows. Figure 3 As shown.

[0186] from Figure 2 It can be seen that the battery cell prepared in Example 1 has a golden yellow surface on the negative electrode surface under the low temperature condition of -10℃ and no lithium deposition, and has a 0.2P charging capability under the low temperature condition of -10℃.

[0187] from Figure 3 It can be seen that the battery cell prepared in Comparative Example 1 has a large amount of gray lithium plating products on the negative electrode surface after being charged at 0.2P at a low temperature of -10℃, indicating severe lithium plating. The test showed that it only has a charging capability of 0.05P at a low temperature of -10℃.

[0188] The test results for each embodiment and comparative example are shown in Table 3.

[0189] Table 3

[0190]

[0191] As shown in Table 3, compared with the comparative examples, the cells prepared in each embodiment have better low-temperature charging performance and low-temperature cycling performance. Among them, the low-temperature charging capability at -10℃ of the cells in Examples 1 to 5 is above 0.2P, and the capacity retention rate after 300cls cycling at 5℃ is above 100%, indicating that the low-temperature charging capability and low-temperature cycling performance of the cells in Examples 1 to 5 are superior. In contrast, the cell in Comparative Example 1 only has a low-temperature charging capability of 0.05P at -10℃, and severe lithium plating occurs on the negative electrode surface when charging at 0.2P at -10℃, exhibiting the worst low-temperature cycling performance. The cells in Comparative Examples 2 to 5 have a low-temperature charging capability of 0.1P at -10℃, but their low-temperature cycling performance is significantly lower than that of the examples.

[0192] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0193] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. An electrode sheet, characterized in that, The system includes a current collector and an active layer disposed on at least one side of the current collector. The active layer comprises lithium iron phosphate material, wherein the D50 of the lithium iron phosphate material is β μm and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

2. The electrode sheet as described in claim 1, characterized in that, The specific surface area of ​​the lithium iron phosphate material is δ m 2 / g, c=β / δ, 0.03≤c≤0.

09.

3. The electrode sheet according to any one of claims 1 to 2, characterized in that, The lithium iron phosphate material satisfies at least one of the following characteristics: (1)0.25 μm≤D10≤0.55 μm; (2)0.5 μm≤D50≤1.1 μm; (3)1.6 μm≤D90≤4 μm; (4) 4.5 μm≤D99≤8.5 μm; (5) The tap density of the lithium iron phosphate material is 0.5 g / m³. 3 ~1.5 g / m 3 ; (6) The specific surface area of ​​the lithium iron phosphate material is 6 m². 2 / g ~30 m 2 / g.

4. A method for preparing an electrode sheet, characterized in that, Includes the following steps: An active layer is disposed on at least one side of the current collector, the active layer comprising lithium iron phosphate material, wherein the D50 of the lithium iron phosphate material is β μm and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

5. A slurry, characterized in that, The product comprises lithium iron phosphate material, a first binder, and a first conductive agent. The D50 of the lithium iron phosphate material is β μm, and the tap density of the lithium iron phosphate material is γ g / m³. 3 a = β / γ, 0.7 ≤ a ≤ 1.2, the ratio of D90 to D10 of the lithium iron phosphate material is b, 4 ≤ b ≤ 8.

6. A lithium-ion battery, characterized in that, The electrode includes the electrode prepared by the method described in any one of claims 1 to 3 or the electrode prepared by the method described in claim 4.

7. The lithium-ion battery as described in claim 6, characterized in that, The lithium-ion battery includes a positive electrode and a negative electrode. The electrode sheet serves as the positive electrode. The negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector. The negative electrode active layer includes graphite with a D50 of σ μm and a specific surface area of ​​ω m. 2 / g, d=σ / ω, 2.5≤d≤7.

5.

8. The lithium-ion battery as described in claim 7, characterized in that, The graphite satisfies at least one of the following characteristics: (1) The tap density of the graphite is θ g / m 3 e = σ / θ, 3 ≤ e ≤ 9; (2) The ratio of D90 to D10 of the graphite is f, where 2≤f≤6.

9. The lithium-ion battery according to any one of claims 7 to 8, characterized in that, The graphite satisfies at least one of the following characteristics: (1) 2 μm ≤ D10 ≤ 6 μm; (2) 4 μm≤D50≤12 μm; (3)9 μm≤D90≤16 μm; (4)14 μm≤D99≤26 μm; (5) The tap density of the graphite is 0.8 g / m³. 3 ~2 g / m 3 ; (6) The specific surface area of ​​the graphite is 0.8 m². 2 / g ~3 m 2 / g.

10. An electrical device, characterized in that, Including the lithium-ion battery as described in any one of claims 6 to 9.

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