WO2024000182A1

WO2024000182A1 - Negative electrode slurry and preparation method therefor, secondary battery, battery module, battery pack, and electric apparatus

Info

Publication number: WO2024000182A1
Application number: PCT/CN2022/101995
Authority: WO
Inventors: 魏志婷; 王宁; 王星会; 木赛男
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2024-01-04

Abstract

The present application provides a negative electrode slurry and a preparation method therefor, a secondary battery, a battery module, a battery pack, and an electric apparatus. The negative electrode slurry comprises a negative electrode active material, a conductive agent, and a binder, the binder comprising first sodium carboxymethyl cellulose and second sodium carboxymethyl cellulose, and a difference value of the weight average molecular weight of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose being greater than 2×105. By adding in the negative electrode slurry the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose of which the difference value of the weight average molecular weight is greater than 2×105, the negative electrode slurry having excellent dispersibility and stability is prepared, and formation of a conductive network in a negative electrode sheet is facilitated, thereby improving the power performance and the cycle performance of the battery.

Description

Negative electrode slurry, preparation method thereof, secondary battery, battery module, battery pack and electrical device

Technical field

The present application relates to the technical field of secondary batteries, and in particular to a negative electrode slurry, its preparation method, secondary batteries, battery modules, battery packs and electrical devices.

Background technique

In recent years, secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

The negative electrode sheet is an important part of the secondary battery, which is often prepared from negative electrode slurry. However, the existing negative electrode slurry has high viscosity, poor dispersion, and is prone to gelation and sedimentation, making it difficult to form high-quality negative electrode sheets, thereby affecting the performance and service life of the battery. Therefore, existing negative electrode slurries still need to be improved.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide a negative electrode slurry to improve the dispersibility and stability of the negative electrode slurry, thereby improving battery performance.

A first aspect of the application provides a negative electrode slurry, which includes a negative active material, a conductive agent and a binder. The binder includes a first carboxymethyl cellulose sodium and a second carboxymethyl cellulose sodium. The difference in weight average molecular weight between sodium dicarboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2×10 ⁵ .

Therefore, this application prepares the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose with a weight average molecular weight difference greater than 2×10 ⁵ in the negative electrode slurry to prepare a liquid with excellent dispersion and stability. The negative electrode slurry helps to form a conductive network in the negative electrode sheet, thereby improving the power performance and cycle performance of the battery.

In any embodiment, the weight average molecular weight of the first carboxymethyl cellulose sodium is 500-1.5×10 ⁵ ; the weight average molecular weight of the second carboxymethyl cellulose sodium is 3×10 ⁵ -8×10 ⁵ .

The first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose with a weight average molecular weight within this range can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

In any embodiment, the total mass content of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose is 1% to 2%, based on the total mass of all components in the negative electrode slurry except the solvent. The total amount of the first carboxymethyl cellulose sodium and the second carboxymethyl cellulose sodium added within a suitable range can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

In any embodiment, the mass content of the first sodium carboxymethylcellulose is 0.2% to 1.8%, and the mass content of the second sodium carboxymethylcellulose is 0.2% to 1.8%, based on the negative electrode slurry except for the solvent. Total mass of all components. Appropriate contents of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

In any embodiment, the conductive agent is selected from one or more of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers. The above-mentioned conductive agent has a large specific surface area and can easily form a conductive network in the negative electrode sheet, which can reduce the internal resistance of the battery and improve the power performance and cycle performance of the battery.

A second aspect of the application also provides a method for preparing negative electrode slurry, which method includes:

Mixing the negative active material, the conductive agent and the first sodium carboxymethyl cellulose to prepare a first product; and

The first product and the second sodium carboxymethylcellulose are mixed and stirred to obtain the negative electrode slurry. The weight average molecular weights of the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose are The difference is greater than 2×10 ⁵ .

Therefore, this preparation method can prepare a negative electrode slurry with excellent dispersion and stability, which helps to improve the quality of the negative electrode sheet and the formation of a conductive network therein, thereby improving the power performance and cycle performance of the battery; Moreover, the preparation method has a simple process and can be effectively combined with the existing homogenization process to improve production efficiency and reduce production costs.

In any embodiment, the weight average molecular weight of the first carboxymethyl cellulose sodium is 500-1.5×10 ⁵ ; the weight average molecular weight of the second carboxymethyl cellulose sodium is 3×10 ⁵ -8×10 ⁵ . The first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose with a weight average molecular weight within this range can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

A third aspect of the present application provides a secondary battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The negative electrode sheet is prepared from the negative electrode slurry of the first aspect of the present application.

A fourth aspect of the present application provides a battery module including the secondary battery of the third aspect of the present application.

A fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.

A sixth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application. kind.

Description of drawings

1A-1B are schematic diagrams of a preparation method of negative electrode slurry according to an embodiment of the present application.

FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .

FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Figure 8 is a scanning electron microscope image of a cross-section of a pole piece prepared with the negative electrode slurry in Example 1.

Figure 9 is a scanning electron microscope image of a cross-section of a pole piece prepared with the negative electrode slurry in Comparative Example 2.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cover assembly; 6 negative electrode slurry; 61 conductive agent; 62 negative active material; 63 first sodium carboxymethyl cellulose; 64 first product; 65 second sodium carboxymethyl cellulose.

Detailed ways

Hereinafter, embodiments that specifically disclose the negative electrode slurry, preparation method, negative electrode, battery, and electrical device of the present application will be described in detail with reference to the accompanying drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

In order to improve the power performance of the battery, a large amount of conductive agent is often added to the negative electrode slurry. Conductive carbon materials with high specific surface area, such as graphite, superconducting carbon, acetylene black, carbon nanotubes, etc., are usually selected as conductive agents. However, conductive carbon materials with high specific surface areas are prone to agglomeration, which will reduce the dispersion of the negative electrode slurry, making the slurry prone to sedimentation, clogging the feed pipeline and affecting the coating of the electrode pieces, making it difficult to achieve mass production of the electrode pieces. Carbon nanotubes are a type of conductive carbon material with excellent performance. They can improve the conductivity of the electrode and at the same time suppress the expansion of the negative electrode during battery cycling through a high aspect ratio. However, carbon nanotubes are prone to agglomeration, which affects the formation of the conductive network in the electrode piece and causes gelation in the negative electrode slurry, reducing the stability of the negative electrode slurry.

[Negative electrode slurry]

Based on this, this application proposes a negative electrode slurry, which includes a negative active material, a conductive agent and a binder. The binder includes a first carboxymethyl cellulose sodium and a second carboxymethyl cellulose sodium. The difference in weight average molecular weight between sodium carboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2×10 ⁵ .

As used herein, the term "binder" refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in the polymer multiplied by their corresponding molecular weights.

In this article, the term "negative electrode" also refers to the "anode" in the battery.

As used herein, the term "conductive agent" refers to a material with good electrical conductivity. Therefore, the conductive agent is usually mixed with the negative electrode active material to improve the conductivity of the negative electrode.

In some embodiments, a binder is used to bind the negative active materials together to form a slurry and can hold them in place and adhere them to conductive metal components to form the negative electrode.

In some embodiments, a dispersion medium is included in the negative electrode slurry. In some embodiments, the dispersion medium of the negative electrode slurry is an aqueous solvent, such as water.

The structural formula of sodium carboxymethylcellulose is shown in formula I,

Where, n is an integer, indicating the degree of polymerization of sodium carboxymethylcellulose. The main chain of sodium carboxymethylcellulose is rich in carbon elements and can be easily coated with negative active materials and conductive agents; the sodium carboxylate groups and hydroxyl groups connected to the main chain are hydrophilic and can be easily dissolved in aqueous solvents.

The n values of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose are different, that is, the degree of polymerization and the weight average molecular weight are different.

In some embodiments, the first sodium carboxymethylcellulose has a lower weight average molecular weight. Since the first sodium carboxymethylcellulose has a small degree of polymerization, a short molecular chain, and strong permeability, it is easy to be inserted into and coated on the negative active material and conductive agent. Under the action of the hydrophilic group, the sodium carboxymethylcellulose coating the negative electrode material and the conductive agent can disperse the negative electrode material and the conductive agent in the aqueous solvent; and then through a large amount of the first sodium carboxymethylcellulose molecules The hydrogen bonding effect thickens and stabilizes the dispersed negative active material and conductive agent, thereby improving the dispersion of the negative active material and conductive agent in the negative slurry.

In some embodiments, the second sodium carboxymethyl cellulose has a high degree of polymerization, a long molecular chain, and a large weight average molecular weight. Its structural characteristics allow it to have greater steric hindrance and intermolecular forces to avoid negative electrode activity. Substances and conductive agents settle in the aqueous solvent, which plays a role in improving the stability of the negative electrode slurry.

In some embodiments, the difference in weight average molecular weight between the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2.5×10 ⁵ , optionally greater than 2.6×10 ⁵ , or 2.7×10 ⁵ , or 2.8×10 ⁵ , or 2.9×10 ⁵ , or 3×10 ⁵ .

This application prepares a negative electrode slurry with excellent dispersion and stability by adding the first carboxymethyl cellulose sodium and the second carboxymethyl cellulose sodium with a weight average molecular weight difference greater than 2×10 ⁵ into the negative electrode slurry. The material helps to form a conductive network in the negative electrode piece, thereby improving the power performance and cycle performance of the battery.

In some embodiments, the weight average molecular weight of the first carboxymethyl cellulose sodium is 500-1.5×10 ⁵ ; the weight average molecular weight of the second carboxymethyl cellulose sodium is 3×10 ⁵ -8×10 ⁵ . In some embodiments, the weight average molecular weight of the first carboxymethylcellulose sodium can be selected from 0.1×10 ⁵ to 1.5×10 ⁵ , or 0.12×10 ⁵ to 1.5×10 ⁵ , or 0.1×10 ⁵ to 1.5× 10 ⁵ , or 0.1×10 ⁵ to 1×10 ⁵ ; the weight average molecular weight of the second carboxymethyl cellulose sodium can be selected from 4×10 ⁵ to 7×10 ⁵ .

The weight average molecular weight of the first sodium carboxymethyl cellulose is too high, causing slight gelation in the negative electrode slurry, increasing the internal resistance of the battery, and reducing the power performance and cycle performance of the battery. The weight average molecular weight of sodium carboxymethyl cellulose is too high, which increases the internal resistance of the battery and reduces the power performance and cycle performance of the battery. If the weight average molecular weight of the second sodium carboxymethylcellulose is too low, the stabilizing effect of the second sodium carboxymethylcellulose on the slurry will be reduced, and the slurry will easily settle.

In some embodiments, the total mass content of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose is 1% to 2%, based on the total mass of all components in the negative electrode slurry except the solvent. In some embodiments, the total mass content of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose can be selected from 1.2% to 2%, 1.3% to 2%, 1.4% to 2%, 1.5% ~2%, based on the total mass of all components in the negative electrode slurry except the solvent.

It can be understood that the total mass of all components in the negative electrode slurry except the solvent refers to the remaining mass of the negative electrode slurry after drying under specified conditions. The solvent includes both the solvent added during the slurry preparation process and the various components added. The solvent into which the component is introduced.

The total amount of the first carboxymethyl cellulose sodium and the second carboxymethyl cellulose sodium added is too small, which is not conducive to the dispersion and stability of the negative electrode active material and conductive agent. The negative electrode slurry is prone to gelation, agglomeration and sedimentation. If the total amount of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose is too high, the internal resistance of the battery will increase, the cycle retention rate will decrease, and the power performance and cycle performance of the battery will be damaged.

The total amount of the first carboxymethyl cellulose sodium and the second carboxymethyl cellulose sodium added within a suitable range can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

In some embodiments, the mass content of the first sodium carboxymethylcellulose is 0.2% to 1.8%, and the mass content of the second sodium carboxymethylcellulose is 0.2% to 1.8%, based on the negative electrode slurry except for the solvent. Total mass of all components. In some embodiments, the mass content of the first sodium carboxymethylcellulose can be selected from 0.5% to 1.8%, 0.7% to 1.8%, 1% to 1.8%, 1.2% to 1.8%, 1.5% to 1.8%, 0.2%～1.5%, 0.2%～1.2%, 0.2%～1%.

If the mass content of the first carboxymethylcellulose sodium is too low, the dispersion and stability of the negative electrode slurry cannot be effectively improved, and the negative electrode slurry is prone to gelation and agglomeration, resulting in increased internal resistance of the battery and reduced cycle retention rate. If the mass content of the second carboxymethylcellulose sodium is too low, it cannot effectively stabilize the negative electrode slurry, making the negative electrode slurry prone to sedimentation, thereby increasing the filtration time, which is not conducive to improving production efficiency and causing battery power loss. Performance and cycling performance are degraded.

Appropriate contents of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose can further improve the dispersion and stability of the negative electrode slurry and the power performance and cycle performance of the battery.

In some embodiments, the negative electrode slurry includes a conductive agent selected from one or more of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers. kind.

In some embodiments, the conductive agent is selected from carbon nanotubes and mixtures thereof with one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers.

The above-mentioned conductive agent has a large specific surface area and can easily form a conductive network in the negative electrode sheet, which can reduce the internal resistance of the battery and improve the power performance and cycle performance of the battery.

In some embodiments, the negative active material is selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

In one embodiment of the present application, a method for preparing negative electrode slurry is provided, which method includes:

Prepare a first product by mixing the negative active material, the conductive agent and the first sodium carboxymethylcellulose;

The first product and the second sodium carboxymethylcellulose are mixed and stirred to obtain a negative electrode slurry, and the difference in weight average molecular weight between the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2×10 ⁵ .

In some embodiments, a first product is prepared by mixing a negative active material, a conductive agent, a first sodium carboxymethyl cellulose, and an aqueous solvent. In some embodiments, the negative active material, the conductive agent, and the first sodium carboxymethyl cellulose are mixed and then kneaded with an aqueous solvent to prepare the first product.

1A-1B are schematic diagrams of a preparation method of negative electrode slurry according to an embodiment of the present application. In some embodiments, the process of mixing the negative active material, the conductive agent and the first sodium carboxymethylcellulose to prepare the first product is as shown in Figure 1A. The first sodium carboxymethyl cellulose 63 is added to the negative active material 62 and the conductive agent 61 and mixed to obtain the first product 64 . In the first product 64, the first sodium carboxymethylcellulose 63 coats the surfaces of the negative active material 62 and the conductive agent 61, so that the negative active material 62 and the conductive agent 61 are effectively dispersed in the solvent. The process of mixing and stirring the first product and the second sodium carboxymethyl cellulose to obtain the negative electrode slurry is shown in Figure 1B. The second sodium carboxymethylcellulose 65 is added to the first product 64 formed in the previous step. After stirring, the second sodium carboxymethylcellulose 65 is dispersed in the negative electrode slurry 6, through longer molecular chains and more The strong intermolecular force improves the stability of the slurry 6 and reduces the agglomeration and sedimentation of the negative active material 62 and the conductive agent 61 .

In some embodiments, before kneading, the negative active material 62 , the conductive agent 61 and the first sodium carboxymethyl cellulose 63 are effectively mixed by dry mixing, stirring, etc.

In some embodiments, during the kneading process, an aqueous solvent, such as water, is added to the mixture of the negative active material 62, the conductive agent 61 and the first sodium carboxymethylcellulose 63.

In some embodiments, the first sodium carboxymethyl cellulose can be added to the negative active material and the conductive agent respectively, and then the three can be blended after effectively coating the negative active material and the conductive agent respectively.

In some embodiments, an aqueous solvent, such as water, may be added as the second sodium carboxymethylcellulose 65 is added to the first product 64.

The preparation method can prepare a negative electrode slurry with excellent dispersion and stability, which helps to improve the quality of the negative electrode sheet, form a stable conductive network in the negative electrode sheet, and thereby improve the power performance and cycle performance of the battery; and The preparation method has a simple process and can be effectively combined with the existing homogenization process to improve production efficiency and reduce production costs.

In some embodiments, the weight average molecular weight of the first carboxymethyl cellulose sodium is 500 to 1.5×10 ⁵ , optionally 0.1×10 ⁵ to 1×10 ⁵ ; the second carboxymethyl cellulose sodium has The weight average molecular weight is 3×10 ⁵ to 8×10 ⁵ , and optionally 4×10 ⁵ to 7×10 ⁵ .

In some embodiments, the conductive agent is selected from carbon nanotubes and mixtures thereof with one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers. .

[Negative pole piece]

In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer is composed of the negative electrode slurry in any embodiment of the present application or the negative electrode slurry in any embodiment. The slurry prepared by the preparation method is prepared.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode sheet can be prepared in the following manner: the above-mentioned negative slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

[electrolyte]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[Isolation film]

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

[Secondary battery]

In one embodiment of the present application, a secondary battery is provided, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The negative electrode sheet is prepared from the negative electrode slurry of any embodiment. The battery has better power performance and cycle performance.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the secondary battery, active ions are inserted and detached back and forth between the positive electrode piece and the negative electrode piece. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

This application has no particular limitation on the shape of the battery, which can be cylindrical, square or any other shape. For example, FIG. 2 shows a square-structured battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[Battery module]

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

[battery pack]

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3. The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4. Multiple battery modules 4 can be arranged in the battery box in any manner.

[Electrical device]

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

Fig. 7 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1

1) Negative electrode slurry preparation:

The first step: Add 1.741kg graphite (negative active material), 0.553kg silicon (negative active material), 0.024kg sodium carboxymethylcellulose, and 0.96kg conductive carbon nanotube dispersion into a 5L mixing tank for dry mixing , the stirring speed is 800rpm, the stirring time is 15min, and then 1.168kg of deionized water is added for kneading, the stirring speed is 15rpm, and the first product is obtained by kneading for 90min.

The second step: add 0.024kg of the second carboxymethyl cellulose sodium and 0.43kg of deionized water for dispersion. The stirring speed is 1800rpm and the stirring time is 60min. Finally, add 0.1kg styrene-acrylic emulsion, stirring speed 1200rpm, stirring time 30min, to obtain negative electrode slurry.

The solid content of the conductive carbon nanotube dispersion is 1%, and the solid content of the styrene-acrylic emulsion is 48%. Therefore, the mass ratio of artificial graphite, artificial silicon, conductive carbon nanotubes, polymers in styrene-acrylic emulsion, first sodium carboxymethylcellulose and second sodium carboxymethylcellulose is 73.6:22:0.4:2: 1:1.

The first carboxymethyl cellulose sodium was purchased from Daiichi Industrial Pharmaceutical Co., Ltd., the model is CELLOGEN 5A, the weight average molecular weight is 12,000, and the viscosity is 4 mPa.s; the second carboxymethyl cellulose sodium was purchased from Daiichi Industrial Pharmaceutical Co., Ltd. Company, the model is 5A, the weight average molecular weight is 460,000, and the viscosity is 2000mPa.s.

2) Preparation of negative electrode piece

The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried, cold pressed, and then trimmed, cut into strips, and divided into pieces to obtain the negative electrode piece.

3) Preparation of positive electrode pieces

The positive electrode active material LiCoO ₂ , conductive agent acetylene black, and binder polyvinylidene fluoride are fully stirred and mixed in the N-methylpyrrolidone solvent system at a weight ratio of 97.2:1.3:1.5 to obtain a positive electrode slurry, and then The positive electrode slurry is evenly coated on a current collector aluminum foil with a thickness of 13 μm, dried, cold pressed, and then trimmed, cut into pieces, and divided into strips to obtain a positive electrode piece.

4) Isolation film

Polyethylene (PE) porous polymer film is used as the isolation membrane.

5) Preparation of electrolyte

Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain a non-aqueous organic solvent. Then add LiPF ₆ and stir evenly to complete the electrolyte solution. Preparation, wherein the content of LiPF ₆ is 12.5% of the total mass of the electrolyte.

6) Preparation of battery

Stack the positive electrode sheet, isolation film, and negative electrode sheet in order, so that the isolation film is between the positive and negative electrode sheets for isolation, and wind it to obtain a bare battery core. Place the bare battery core in the outer packaging shell and inject electrolyte into it. liquid and packaged to obtain a lithium-ion battery.

In Comparative Example 1, only the first carboxymethylcellulose sodium in Example 1 was used as the binder, and its mass fraction was 2% of the total mass of all components in the negative electrode slurry except the solvent; in Comparative Example 2, only the first sodium carboxymethyl cellulose was used as the binder. The second sodium carboxymethyl cellulose in Example 1 is used as a separate binder, and its mass fraction is 2% of the total mass of all components in the negative electrode slurry except the solvent; other preparation methods are the same as Example 1.

The batteries of Examples 1 to 22 and the batteries of Comparative Examples 1 to 2 are similar to the battery preparation methods of Example 1, but the raw materials and raw material ratios for negative electrode preparation are adjusted. The specific parameters are shown in Table 1.

In addition, the slurries and batteries obtained in the above-mentioned Examples 1 to 22 and Comparative Examples 1 to 2 were subjected to performance tests, and the test results are shown in Table 1. The test method is as follows:

Carboxymethyl cellulose sodium performance test:

Weight average molecular weight test

Refer to GB/T21863-2008 to test the weight average molecular weight of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose.

Viscosity test method:

The first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose were respectively dissolved in deionized water solvent to prepare a glue solution with a solid content of 1%. Refer to the rotation method in GB/T 10247-2008 to test the viscosity of the respective glue.

Slurry performance test:

Slurry filterability test

First determine the 200 mesh size of the filter, and cut the filter into 25cm*25cm with scissors. Find a clean 500ml beaker and make sure the beaker is clean. Fold the 200-mesh filter into a triangle, pour 500 mL of slurry from the top of the filter, pour it all at once, and start recording the time when the slurry starts to flow into the beaker from the tip of the filter. Record the time it takes to filter 300mL.

Morphology test

Use scissors to cut the cold-pressed pole pieces into 6cm*6cm samples, and then polish them with the IB-19500CP ion cross-section polisher to obtain polished samples with cut surfaces. Afterwards, the samples were tested with a scanning electron microscope using ZEISS sigma 300 equipment in accordance with the standard JY/T010-1996. Randomly select positions in the test samples to observe whether there is agglomeration of the conductive carbon tubes.

Observe the gel and settling state of the slurry

Take 500ml of slurry and place it for different times to observe whether the slurry appears in a jelly gel state, and test its slurry viscosity. If the viscosity of the upper slurry in the test beaker decreases and the lower slurry thickens, it means that the slurry has settled.

Battery related performance tests:

Battery DC impedance

The battery DC impedance test process is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3*C to 4.3V, then charge with a constant voltage of 4.3V until the current is 0.05C, and leave it aside for 5 minutes. Record the voltage V ₁ . Then discharge at 1/3C for 30 seconds and record the voltage V ₂ , then 3*(V ₂ -V ₁ )/C to obtain the internal resistance DCR of the battery.

Cycle capacity retention test

The test process is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3*C to 4.3V, then charge with a constant voltage of 4.3V until the current is 0.05C, leave it for 5 minutes, and then charge it with 1 /3C is discharged to 2.8V, and the resulting capacity is recorded as the initial capacity C ₀ . Repeat the above steps for the same battery above, but change the charge and discharge rates to 4C, and cycle 10 times; then cycle the same battery above for 1000 cycles again at 0.33C, record the capacity C ₁₀₀₀ after 1000 cycles, and the cycle capacity retention rate C ₁₀₀₀ /C ₀ , the larger this value, the better the cycle performance.

The cross-sectional scanning electron microscope picture of the pole piece of Example 1 is shown in Figure 8, and the cross-sectional scanning electron microscope picture of the pole piece of Comparative Example 2 is shown in Figure 9. It can be seen from the comparison that the carbon nanotubes in Example 1 are evenly dispersed in the pole piece, while the carbon nanotubes in Comparative Example 2 appear to be agglomerated and entangled, as shown by the frame line in Figure 9 . It can be seen that containing both the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose in the slurry helps to improve the dispersion of the slurry.

Embodiments 1 to 22 provide a negative electrode slurry. The negative electrode slurry includes negative active materials graphite and silicon, conductive agent carbon nanotubes and a binder. The binder includes a first sodium carboxymethylcellulose and a third The difference in weight average molecular weight of sodium dicarboxymethylcellulose, the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2×10 ⁵ . It can be seen from the comparison between Examples 1, 6 to 22 and Comparative Example 1 in which there is only the first sodium carboxymethylcellulose in the negative electrode slurry that the difference in weight average molecular weight between the two is greater than 2×10 ⁵ in the negative electrode slurry. The sodium carboxymethylcellulose improves the stability of the negative electrode slurry and makes the negative electrode slurry less likely to settle, thereby reducing the internal resistance of the battery and improving the cycle capacity retention rate of the battery. It can be seen from the comparison between Examples 1, 6 to 22 and Comparative Example 2 in which there is only the second sodium carboxymethylcellulose in the negative electrode slurry that the difference in weight average molecular weight between the two sodium carboxymethyl cellulose is greater than 2×10 ⁵ in the negative electrode slurry. The sodium carboxymethylcellulose improves the dispersion of the negative electrode slurry, thereby reducing the internal resistance of the battery and improving the cycle capacity retention rate of the battery. In summary, the negative electrode slurries in Examples 1 to 22 have excellent dispersion and stability, thereby reducing the internal resistance of the battery and improving the cycle capacity retention rate of the battery.

From the comparison between Examples 12 to 15 and Example 16, and the comparison between Examples 18 to 21 and Examples 17 and 22, it can be seen that the weight average molecular weight of the first sodium carboxymethyl cellulose is 500 to 1.5×10 5 , and the weight average molecular weight of the second sodium carboxymethyl cellulose is 500 to 1.5 × 10 ⁵ . When the weight average molecular weight of sodium carboxymethyl cellulose is 3×10 ⁵ to 8×10 ⁵ , the negative electrode slurry has excellent dispersibility and stability, and the battery has reduced internal resistance and improved cycle capacity retention.

It can be seen from Examples 12 to 15 that when the weight average molecular weight of the first sodium carboxymethylcellulose is 0.1×10 ⁵ to 1×10 ⁵ , the dispersibility and stability of the slurry and the capacity retention rate of the battery are further improved, and the battery The internal resistance is further reduced.

It can be seen from Examples 18 to 21 that when the weight average molecular weight of the second carboxymethyl cellulose sodium is 4×10 ⁵ to 8×10 ⁵ , the dispersibility and stability of the slurry and the capacity retention rate of the battery are further improved, and the battery The internal resistance is further reduced.

From the comparison between Examples 1 to 3 and Examples 4 to 5, it can be seen that when the total mass content of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose relative to the negative electrode slurry is 1% to 2%, The dispersion and stability of the slurry and the capacity retention rate of the battery are further improved, and the internal resistance of the battery is further reduced.

From the comparison between Examples 6 to 9 and Examples 10 to 11, it can be seen that the mass content of the first sodium carboxymethyl cellulose is 0.2% to 1.8%, and the mass content of the second sodium carboxymethyl cellulose is 0.2% to 1.8 %, based on the total mass of all components in the negative electrode slurry except the solvent, the dispersion and stability of the slurry and the capacity retention rate of the battery are further improved, and the internal resistance of the battery is further reduced.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications that can be thought of by those skilled in the art are made to the embodiments, and other forms constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present application. .

Claims

A negative electrode slurry, the negative electrode slurry includes a negative electrode active material, a conductive agent and a binder, the binder includes a first carboxymethyl cellulose sodium and a second carboxymethyl cellulose sodium, The difference in weight average molecular weight between the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose is greater than 2×10 5 .
The negative electrode slurry according to claim 1, characterized in that the weight average molecular weight of the first carboxymethyl cellulose sodium is 500-1.5×10 5 ; the weight average molecular weight of the second carboxymethyl cellulose sodium The molecular weight is 3×10 5 to 8×10 5 .
The negative electrode slurry according to claim 1 or 2, characterized in that the total mass content of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose is 1% to 2%, based on The total mass of all components in the negative electrode slurry except the solvent.
The negative electrode slurry according to any one of claims 1 to 3, characterized in that the mass content of the first carboxymethyl cellulose sodium is 0.2% to 1.8%, and the second carboxymethyl cellulose The mass content of sodium is 0.2% to 1.8%, based on the total mass of all components in the negative electrode slurry except the solvent.
The negative electrode slurry according to any one of claims 1 to 4, characterized in that the conductive agent is selected from the group consisting of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and one or more types of carbon nanofibers.
A preparation method of negative electrode slurry, which includes:

Mixing the negative active material, the conductive agent and the first sodium carboxymethyl cellulose to prepare a first product; and

The first product and the second sodium carboxymethylcellulose are mixed and stirred to obtain the negative electrode slurry. The weight average molecular weights of the second sodium carboxymethylcellulose and the first sodium carboxymethylcellulose are The difference is greater than 2×10 5 .
The preparation method according to claim 6, characterized in that the weight average molecular weight of the first carboxymethyl cellulose sodium is 500-1.5×10 5 ; the weight average molecular weight of the second carboxymethyl cellulose sodium It is 3×10 5 ~ 8×10 5 .
A secondary battery, characterized in that it includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, and the negative electrode sheet is prepared from the negative electrode slurry according to any one of claims 1 to 5.
A battery module comprising the secondary battery according to claim 8.
A battery pack, characterized by comprising the battery module according to claim 9.
An electric device, characterized in that it includes at least one selected from the group consisting of the secondary battery of claim 8, the battery module of claim 9, or the battery pack of claim 10.