WO2024031448A1

WO2024031448A1 - Polymer, preparation method therefor, positive electrode slurry, positive electrode plate, secondary battery, battery module, battery pack, and electric apparatus

Info

Publication number: WO2024031448A1
Application number: PCT/CN2022/111505
Authority: WO
Inventors: 王正; 陆雷; 胡长远; 王亚龙; 李世松; 张盛武
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-10
Filing date: 2022-08-10
Publication date: 2024-02-15

Abstract

Provided are a polymer, a preparation method therefor, a positive electrode slurry, a positive electrode plate, a secondary battery, a battery module, a battery pack, and an electric apparatus. The polymer comprises a first repeating structure unit represented by structural formula I and a second repeating structure unit represented by structural formula II, wherein R ₁ is selected from formula (III); R ₂ is selected from hydrogen or methyl; R ₃ is selected from hydrogen or C1-C11 alkyl; R ₄ is selected from aminomethyl or C1-C11 alkyl; optionally, R ₃ is selected from C6-C11 alkyl, and R ₄ is selected from C6-C11 alkyl; R ₅ is selected from C1-C8 alkyl; R ₆ and R ₇ are independently selected from C1-C3 alkyl, and R ₈ is selected from hydrogen or methyl; optionally, R ₅ is selected from C4-C8 alkyl. The polymer can improve the interface performance of the electrode assembly in the secondary battery, thereby improving interface dynamics and the cycle performance of the secondary battery.

Description

Polymers and preparation methods thereof, positive electrode slurries, positive electrode sheets, secondary batteries, battery modules, battery packs and electrical devices

Technical field

This application relates to the field of batteries, specifically to a polymer and its preparation method, positive electrode slurry, positive electrode sheet, secondary battery, battery module, battery pack and electrical device.

Background technique

Secondary batteries have the characteristics of high capacity and long life, so they are widely used in electronic equipment, such as mobile phones, laptop computers, battery cars, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools etc. As secondary batteries have made great progress, higher requirements have been placed on the performance of secondary batteries. In order to improve the performance of secondary batteries, materials within the secondary battery, such as negative active materials, are usually optimized and improved. As a carrier of metal ions and electrons in secondary batteries, negative active materials play a role in storing and releasing energy, and have a non-negligible impact on the performance of secondary batteries.

However, when the currently improved anode active materials are used in secondary batteries, the cycle performance and rate performance of the secondary batteries are still poor.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide a polymer and a preparation method thereof, a positive electrode slurry, a positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.

A first aspect of the application provides a polymer including a first repeating structural unit and a second repeating structural unit, the first repeating structural unit having the structural formula shown in Formula I,

Among them, R ₁ is selected from

R ₂ is selected from hydrogen or methyl, R ₃ is selected from hydrogen or C1-C11 alkyl, R ₄ is selected from aminomethyl or C1-C11 alkyl; optionally, R ₃ is selected from C6-C11 alkyl group, R ₄ is selected from C6 to C11 alkyl groups;

The second repeating structural unit has the structural formula shown in Formula II,

Among them, R ₅ is selected from C1 to C8 alkyl; R ₆ and R ₇ are independently selected from C1 to C3 alkyl, and R ₈ is selected from hydrogen or methyl; optionally, R ₅ is selected from C4 to C8. alkyl.

The polymer of the present application is used as a wetting agent in lithium ion batteries. The ester group in the first repeating structural unit is a strong polar group. As an anchoring group, it can be anchored in the activity of the cathode slurry used to prepare secondary batteries. The surface of the group reduces the surface energy of the active particles, and the long polymer chain in the polymer generates sufficient steric hindrance and has dispersion properties, which can avoid agglomeration during the mixing process of the conductive agent in the cathode slurry and the active material, making the slurry The viscosity and solid content are moderate, which improves the dispersion performance, ensures the smooth progress of the homogenization process, and improves the rate performance of secondary batteries. At the same time, the long chain has ester/amino groups, which can improve the affinity of the positive electrode piece to the electrolyte, increase the electrolyte infiltration ability, shorten the infiltration time of the electrode piece, reduce manufacturing costs, and increase production capacity. In addition, the polymer of the present application can improve the interface performance of the electrode assembly in the secondary battery, improve the interface dynamics and the cycle performance of the secondary battery.

In some embodiments, R3 and R4 are independently selected from C3 to C9 alicyclic groups, C3 to C9 alicyclic heterocyclic groups, C6 to C11 aryl groups, or C3 to C11 heteroaryl groups.

As a result, the steric hindrance of the polymer can be further increased, the dispersion performance of the sizing agent can be further improved, and the rate performance of the secondary battery can be improved.

In some embodiments, the polymerization degree ratio of the first repeating structural unit to the second repeating structural unit of the polymer is (1.5-4): 1. As an example, through gel permeation chromatography (GPC), polymer molecules of different molecular weights are separated in order from large to small molecular weight as the eluent flows out, and the relationship between elution volume and molecular weight can be obtained. GPC spectrum can be used to calculate the number average molecular weight. The number average molecular weight/repeating group molecular weight can be used to obtain the degree of polymerization value.

Therefore, the ratio of the degree of polymerization of the first repeating structural unit to the second repeating structural unit is within an appropriate range, ensuring the wetting ability of the positive electrode piece, thereby reducing the battery impedance and improving the electrochemical performance; it can also improve the infiltration ability of the positive electrode piece. Dispersing properties ease storage of gels.

In some embodiments, the polymer has the structure shown in Formula III,

Among them, a, b, c are independently selected from 50 to 120.

As a result, the content of strong polar groups in the polymer is higher, which can further reduce the surface energy of active particles in the cathode slurry, avoid agglomeration during the mixing process of the conductive agent and the active material, and improve the dispersion performance of the cathode slurry.

In some embodiments, the weight average molecular weight of the polymer ranges from 15,000 to 100,000; optionally, the weight average molecular weight of the polymer ranges from 15,000 to 35,000.

Therefore, the weight average molecular weight of the polymer is within the above range, which can fully improve the wetting effect, have better lithium ion migration kinetics, prevent the intercalation and deintercalation of active lithium during the cycle, thereby avoiding secondary battery failure. Impedance increases.

A second aspect of the application also provides a method for preparing a polymer, including the following steps:

Mix the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator, and heat to react to obtain a polymer;

The first repeating structural unit has the structural formula shown in formula I,

Among them, R ₁ is selected from

Therefore, the preparation process of the method of the embodiment of the present application is simple, and the process conditions are easy to adjust; and when the prepared polymer is used in a secondary battery, the cycle performance of the secondary battery is better.

In some embodiments, the mass ratio of the first repeating structural unit, the second repeating structural unit and the initiator is (2-4): (2-4):1.

By controlling the mass ratio of each raw material, the molecular weight of the prepared polymer can be adjusted, and the prepared polymer can effectively exert the effect of the sizing agent.

The third aspect of the application also provides a cathode slurry, including a cathode active material, a conductive agent, a binder, and the polymer of any embodiment of the first aspect of the application or the polymer of any embodiment of the second aspect of the application. Polymer prepared by preparation method.

In some embodiments, the mass fraction of the polymer in the total mass of the cathode slurry is 0.1wt%~0.5wt%, optionally 0.2wt%~0.4wt%, which can improve the electrochemical performance of the secondary battery without loss. Energy Density.

In some embodiments, the solid content of the cathode slurry is 70% to 90%. The polymer of this embodiment is used as a wetting agent. Due to its high dispersion ability and wetting ability, it can be used in cathode slurries with relatively high solid content for coating on the cathode current collector.

The fourth aspect of the present application also provides a positive electrode sheet, including the positive electrode slurry of any embodiment of the third aspect of the present application.

A fifth aspect of the present application also provides a secondary battery, including the positive electrode plate according to any embodiment of the fourth aspect of the present application.

A sixth aspect of the present application also provides a battery module, including the secondary battery according to any embodiment of the fifth aspect of the present application.

A seventh aspect of the present application also provides a battery pack, including the battery module according to any embodiment of the sixth aspect of the present application.

The eighth aspect of the present application also provides an electrical device, including the secondary battery of any embodiment of the fifth aspect of the present application, the battery module of any embodiment of the sixth aspect of the present application, or any of the seventh aspect of the present application. Embodiment battery pack.

Description of drawings

In order to explain the technical solutions of the embodiments of the present application more clearly, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. Those of ordinary skill in the art can also obtain other drawings based on the drawings without exerting creative efforts.

FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

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

FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4 .

FIG. 6 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 7 is a SEM (scanning electron microscope, scanning electron microscope) photograph of the positive electrode plate in Example 3 of the present application.

Figure 8 is an SEM photograph of the positive electrode sheet in Example 14 of the present application.

Figure 9 is an infrared spectrum of the positive electrode plate in Example 1 of the present application.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover.

Detailed ways

Hereinafter, embodiments of the electrolyte solution, secondary battery, battery and electric device of the present application will be specifically disclosed in detail. 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, and are preferably performed sequentially. For example, a 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) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), and may also include step (a). , (c) and (b), and 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, "comprises" and "comprises" may mean that other components not listed may also be included or included, or that only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise specified. 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).

As lithium-ion batteries become more widely used in electric vehicles, portable electronic devices and grid energy storage, higher energy density is urgently needed to meet the current growing market demand. In recent years, in addition to developing new battery chemistries/materials/systems, the design of thick electrode structures does not require changing the electrochemical basis of existing batteries, but improves efficiency by increasing the proportion of electrochemically active substances in the battery. Battery energy density, making it more versatile and easier to implement. Thick electrodes will seriously affect the diffusion rate of lithium ions, causing a decrease in battery rate performance. Higher compaction density will lead to poorer liquid permeability of the electrode piece and uneven distribution of electrode liquid in the electrode, which is not conducive to the transmission of lithium ions. In order not to affect the infiltration of the pole pieces, the infiltration time is usually increased or high temperature is used to stand. However, this process time is increased and the production efficiency is reduced.

The positive electrode sheet is an important component of the lithium-ion battery. It is generally made of active materials, binders, conductive agents, dispersants and solvents evenly mixed to form a slurry, which is then coated on the current collector and prepared after rolling and die-cutting. Become. Among them, the conductive agent generally uses nanoparticles with good conductivity and a large specific surface area. During the mixing process of the conductive agent and the active material, agglomeration is easy to occur, resulting in the slurry being too high or too low, resulting in coating solid content , so a dispersant needs to be added to the positive electrode slurry to reduce the surface energy of the particles, improve the dispersion performance and slurry gel, and ensure the smooth progress of the homogenization process. The dispersion effect will directly affect the consistency of the battery cell performance.

Based on the above problems discovered by the applicant, the applicant added a polymer as a wetting agent in the cathode slurry. The polymer has a strong polar group and acts as an anchoring group to anchor on the surface of the active group and reduce the surface energy of the active particles. , the long polymer chain in the polymer generates sufficient steric hindrance and has dispersion properties; at the same time, the ester and amino groups in the long chain can improve the affinity of the electrode piece for the electrolyte and increase the electrolyte infiltration ability. It can shorten the electrode piece infiltration time, reduce manufacturing costs, and increase production capacity; on the other hand, it can also improve the interface performance of electrode components in secondary batteries, improve interface dynamics and cycle performance of secondary batteries.

polymer

In a first aspect, the application provides a polymer including a first repeating structural unit and a second repeating structural unit, the first repeating structural unit having the structural formula shown in Formula I,

Among them, R ₁ is selected from

According to embodiments of the present application, the polymer can be used as a wetting agent for a positive electrode slurry such as a lithium-ion battery positive electrode sheet to improve the dispersion performance of the positive electrode slurry and the wetting ability of the positive electrode sheet.

According to an embodiment of the present application, the first repeating structural unit has the structural formula shown in Formula I,

Among them, R ₁ is selected from

R ₂ is selected from hydrogen or methyl, R ₃ is selected from hydrogen or C1-C11 alkyl, R ₄ is selected from aminomethyl or C1-C11 alkyl; optionally, R ₃ is selected from C6-C11 alkyl group, R ₄ is selected from C6 to C11 alkyl groups. In some embodiments, if _R1 is selected from

R ₃ is selected from hydrogen, and the branch chain of the first repeating structural unit has a highly polar carboxyl group. In other embodiments, if _R1 is selected from

R ₄ is selected from aminomethyl, and the branch of the first repeating structural unit has a highly polar amide group. In yet other embodiments, if _R1 is selected from

R ₃ is selected from C1 to C11 alkyl, or if R ₁ is selected from

R ₄ is selected from C1 to C11 alkyl groups, then the branch chain of the first repeating structural unit has a highly polar ester group. The strong polar group can be used as an anchoring group to anchor on the surface of the active group of the cathode slurry, reducing the surface energy of the active particles. The long polymer chain of the polymer generates sufficient steric hindrance and has a dispersing effect on the cathode slurry. At the same time, the presence of carboxyl, amide or ester groups in the long chain can improve the affinity of the positive electrode piece to the electrolyte, increase the infiltration ability of the electrolyte, and shorten the infiltration time of the electrode piece.

Optionally, R ₂ is selected from methyl group, which can further increase the steric hindrance of the polymer and improve the dispersion effect of the cathode slurry.

According to an embodiment of the present application, the second repeating structural unit has the structural formula shown in Formula II,

Among them, R ₅ is selected from C1 to C8 alkyl; R ₆ and R ₇ are independently selected from C1 to C3 alkyl, and R ₈ is selected from hydrogen or methyl; optionally, R ₅ is selected from C4 to C8. alkyl. The branch chain of the second repeating structural unit contains an ester group and a tertiary amine group, which is highly polar. It can also be used as an anchoring group to anchor on the surface of the active group, reducing the surface energy of the active particles. The long polymer chain can generate sufficient space. Resistance, with dispersion properties. Moreover, the branch chain of the second repeating structural unit is longer, which further increases the steric hindrance of the polymer and improves the dispersion effect of the cathode slurry. At the same time, the second repeating structural unit has an ester group and an amino group, which can improve the affinity of the positive electrode piece to the electrolyte, increase the infiltration ability of the electrolyte, and shorten the infiltration time of the electrode piece.

Optionally, R ₈ is selected from methyl group, which can further increase the steric hindrance of the polymer and improve the dispersion effect of the cathode slurry.

The polymers in the embodiments of the present application are used as wetting agents in lithium-ion batteries and have the dual functions of dispersing and wetting in the positive electrode slurry, thereby eliminating the need for dispersants in the positive electrode slurry. The first repeating structural unit and the second repeating structural unit have strong polar groups. As anchoring groups, they can be anchored on the surface of the active group of the cathode slurry used to prepare secondary batteries, reduce the surface energy of the active particles, and polymerize The long polymer chain in the material generates sufficient steric hindrance and has dispersion properties, which can avoid agglomeration during the mixing process of the conductive agent and active material in the cathode slurry, making the slurry viscosity and solid content moderate, improving the dispersion performance and ensuring The homogenization process proceeds smoothly, improving the rate performance of the secondary battery. At the same time, the long chain has ester/amino groups, which can improve the affinity of the positive electrode piece to the electrolyte, increase the electrolyte infiltration ability, shorten the infiltration time of the electrode piece, reduce manufacturing costs, and increase production capacity. In addition, the polymer of the present application can improve the interface performance of the electrode assembly in the secondary battery, improve the interface dynamics and the cycle performance of the secondary battery. At the same time, the polymer can also be used in a quasi-dry pole piece system. The preparation of quasi-dry pole pieces breaks the traditional wet coating method and can prepare thick pole pieces to increase the energy density of battery cells. Therefore, the polymers in the embodiments of the present application can improve the wetting ability of the thick electrode plate electrolyte and improve the electrochemical performance.

In some embodiments, R ₃ and R ₄ are independently selected from C3 to C9 alicyclic groups, C3 to C9 alicyclic heterocyclic groups, C6 to C11 aryl groups, or C3 to C11 heteroaryl groups.

The term "aliphatic heterocyclic group" refers to an alicyclic group containing heteroatoms (non-carbon atoms) on the ring, which can be a three-membered heterocyclic ring, a four-membered heterocyclic ring, a five-membered heterocyclic ring, a seven-membered heterocyclic ring, etc. Heteroaryl is a heterocyclic group with aromatic characteristics. The carbon on the aromatic ring can be replaced by nitrogen, oxygen, sulfur and other elements.

In the above solution, the steric hindrance of the polymer can be further increased, the dispersion performance of the sizing agent can be further improved, and the rate performance of the secondary battery can be improved.

In some embodiments, the polymerization degree ratio of the first repeating structural unit to the second repeating structural unit of the polymer is (1.5-4):1. Optionally, the first repeating structural unit and the second repeating structural unit are connected in a random copolymerization manner.

In the above scheme, the polymer is a copolymer including a first repeating structural unit, a second repeating structural unit and a third repeating structural unit, and the ratio of the degree of polymerization of the first repeating structural unit to the second repeating structural unit is within an appropriate range. , making the polymer very suitable for use as a wetting agent in positive electrode slurries such as the positive electrode sheets of lithium-ion batteries, ensuring the wetting ability of the positive electrode sheets, thereby reducing battery impedance and improving electrochemical performance; it can also improve the positive electrode sheets The dispersing properties ease the storage of gels.

Among them, a, b, c are independently selected from 50 to 120. In the formula, a, b, and c represent the degree of polymerization of each repeating structural unit, that is, the statistical average of the number of structural units contained in the polymer molecular chain, and do not necessarily mean that the repeated structure forms a block of a certain length. In the embodiments of the present application, the polymer may be a random copolymer including the structural units shown.

In the above scheme, the polymer with such a structure has a higher content of strong polar groups, which can further reduce the surface energy of the active particles in the cathode slurry, avoid agglomeration during the mixing process of the conductive agent and the active material, and improve the performance of the cathode slurry. The dispersion performance improves the wetting ability of the positive electrode piece.

The weight average molecular weight of a polymer can be measured using conventional means in the art. For example, the weight average molecular weight of a polymer can be measured using laser light scattering techniques, which are well known to those skilled in the art. In the above scheme, the weight average molecular weight of the polymer is within the above range, which can fully improve the wetting effect, have better lithium ion migration kinetics, prevent the insertion and deintercalation of active lithium during the cycle, thereby avoiding the secondary battery The impedance increases.

Polymer preparation method

Among them, R ₁ is selected from

By controlling the mass ratio of each raw material, the molecular weight of the prepared polymer is adjusted, and the prepared polymer can effectively exert the effect of the sizing agent.

In a second aspect, the embodiments of the present application also provide a method for preparing a polymer, including the following steps:

Among them, R ₁ is selected from

In this embodiment, the polymer can be synthesized by adding the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator into a reaction kettle and mixing, under high temperature, high pressure and the action of the initiator. .

The initiator can be benzoyl peroxide. The temperature of the heated polymerization is 80 to 90°C, and the reaction time is 1 to 3 hours. Through heat treatment, the derivatized free radicals react to polymerize to obtain the polymer. Moreover, the heating temperature and heating time will directly affect the molecular weight of the polymer. Such settings can ensure that the polymer has an appropriate molecular weight.

Among the above solutions, the method of the embodiment of the present application has a simple preparation process and easy adjustment of process conditions; and when the prepared polymer is used in a secondary battery, the secondary battery has better cycle performance.

cathode slurry

In a third aspect, embodiments of the present application also provide a positive electrode slurry, including a positive electrode active material, a conductive agent, a binder, and the polymer of any embodiment of the first aspect of the application or any implementation of the second aspect of the application. Polymer prepared by the preparation method of Example.

Only one type of positive electrode active material may be used alone, or two or more types may be used in combination. In some embodiments, the positive active material includes a lithium-containing transition metal oxide, the volume average particle size Dv50 of the positive active material ranges from 3.0 μm to 10 μm, and the specific surface area of the positive active material ranges from 0.4 m ² /g to 2.0 m ² /g. 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 NCM333), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM523), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM211), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM622), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (can also be referred to as NCM811), at least one of lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds.

In other embodiments, the positive active material includes an olivine-structured lithium-containing phosphate, the volume average particle size Dv50 of the positive active material ranges from 1.0 μm to 2.0 μm, and the specific surface area of the positive active material is 10 m ² /g. ~15m ² /g. Examples of lithium-containing phosphates with an olivine structure 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 ), phosphoric acid At least one of a composite material of lithium manganese and carbon, a composite material of lithium manganese iron phosphate, or a composite material of lithium manganese iron phosphate and carbon.

The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene and carbon nanofibers.

The binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer , at least one of tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

The polymer of this embodiment is a wetting agent in the positive electrode slurry. The positive electrode slurry can be obtained by the following preparation method: first mix the positive electrode active material and the conductive agent thoroughly in a certain proportion to obtain solvent-free powder particles; and then The wetting agent, binder and solvent are fully mixed in a certain proportion to form glue. The solvent-free powder particles are kneaded with the above-mentioned glue to form a lump material, and the prepared lump material is further extruded or hot-pressed to obtain a thick film sheet. Then, the thick film sheet is cut and transferred through one or more stages of roller pressing, and then directly compounded with the positive electrode current collector. After drying, the positive electrode sheet can be continuously prepared.

Optionally, the above solvent can be N-methylpyrrolidone, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-propanediol, 1,3-propanediol, One or a combination of two or more 1,3-hexanediol. Drying can be done in a winding three-dimensional oven.

Among them, the material mixing equipment can be mixed with internal mixers, kneaders, and twin-screw equipment. The thick sheet material preparation equipment can be used with screw extruders, hydraulic extruders, plunger extruders, hot presses, and open mills. machine. The threaded elements of the twin-screw element can be combined with one or more of threaded parts, meshing blocks, and toothed discs to fully balance the shear mixing and conveying capabilities. The internal mixing process temperature can be selected from 25 to 100°C, and the extrusion or hot pressing process temperature can be from 25 to 100°C. The transfer and compounding process can be achieved by selecting different roller speeds and different roller roughnesses.

A small amount of solvent is added during the preparation process of the cathode slurry, so the extruded diaphragm can greatly promote particle slippage during the rolling thinning process. The solvent functions like a "lubricant", so the diaphragm is not easy to roll. If the pressure is excessive, the membrane will be softer, the processing performance will be better, the pole pieces will be more easily compacted, and it will be easier to prepare thick pole pieces to achieve high energy density batteries. The amount of solvent added in the positive electrode slurry formula system is much lower than the wet coating process in the industry, which greatly reduces drying energy consumption and reduces environmental pollution. The diaphragm prepared based on this embodiment has a surface non-stick function, so the oven can be a winding oven. Therefore, the length of the oven can be greatly shortened, the floor space of the equipment can be reduced, and technical costs can be reduced.

This embodiment utilizes the affinity of the carboxyl, ester or amide groups in the wetting agent for the electrolyte to increase the electrolyte infiltration ability, which can shorten the pole piece infiltration time, reduce manufacturing costs, and increase production capacity; on the other hand, it can Improve the interface performance of electrode components in secondary batteries, improve interface dynamics and cycle performance of secondary batteries.

In some embodiments, the mass fraction of the polymer in the total mass of the cathode slurry is 0.1 wt% to 0.5 wt%, optionally 0.2 wt% to 0.4 wt%. Without intending to be limited to any theory or explanation, the inventor found that the mass proportion of the wetting agent in the negative electrode film layer is within the above-mentioned appropriate range, which can effectively increase the infiltration of the electrolyte while making the positive electrode plate have a higher energy density, cycle performance and rate performance.

Optionally, the positive active material accounts for 91.5-99.5wt% of the weight of the slurry system. The positive conductive agent accounts for 0.3-4wt% of the weight of the slurry system. The positive electrode binder accounts for 0.5-4wt% of the weight of the slurry system.

In some embodiments, the solid content of the cathode slurry is 70% to 90%. The higher the solid content and viscosity of the slurry, the better the stability of the slurry. The suitable solid content of LiFePO4 is 70% to 85%, and the suitable solid content of the ternary cathode system is 75% to 90%. The polymer of this embodiment is used as a wetting agent. Due to its high dispersion ability and wetting ability, it can be used in cathode slurries with relatively high solid content for coating on the cathode current collector.

Positive electrode piece

In a fourth aspect, the present application also provides a positive electrode sheet, including the positive electrode slurry according to any embodiment of the third aspect of the present application.

The positive electrode sheet includes a positive electrode current collector and a positive electrode slurry disposed on at least one surface of the positive electrode current collector. The positive electrode slurry includes the above-mentioned polymer as a wetting agent. 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.

As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material 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.).

Negative pole piece

The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry disposed on at least one surface of the negative electrode current collector. The negative electrode slurry includes a negative electrode active material.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode slurry 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 layer. 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 slurry optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl At least one of acrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode slurry optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode slurry optionally also includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.

[Isolation film]

In some embodiments, a separator film is further included in the secondary battery. 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.

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.

[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 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 also 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.

In a fifth aspect, the present application also provides a secondary battery, including the positive electrode plate according to any embodiment of the fourth aspect of the present application.

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 battery, active ions are inserted and detached back and forth between the positive and negative electrodes. 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 secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 1 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 2 , 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 secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

A sixth aspect of the present application also provides a battery module, including the secondary battery according to any embodiment of the fifth aspect of the present application. The 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 3 shows a battery module 4 as an example. Referring to FIG. 3 , 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.

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.

A seventh aspect of the present application also provides a battery pack, including the battery module according to any embodiment of the sixth aspect of the present application. 4 and 5 illustrate a battery pack 1 as an example. Referring to FIGS. 4 and 5 , 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.

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.

Figure 6 shows 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. Preparation of negative electrode piece

Dissolve the negative active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC-Na) in the solvent at a mass ratio of 96.6:0.7:1.5:1.2 In deionized water, stir and mix thoroughly to obtain a negative electrode slurry; then apply the negative electrode slurry on the negative electrode current collector, and after drying and other processes, a negative electrode piece is obtained. The compacted density of the negative electrode piece after the pressing process is 1.6g/cm ³ .

2. Preparation of positive electrode pieces

2.1 Preparation of polymer

The monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide were added to the reaction kettle in a mass ratio of 2:2:1 and mixed at a temperature of 80°C. React for 1 hour to obtain polymer. Among them, the monomer corresponding to the first repeating structural unit is acrylic acid, and the monomer corresponding to the second repeating structural unit has the following structural formula:

The polymer has the structural formula shown below

Among them, a is 90 and c is 50.

2.2 Preparation of cathode slurry

The polymer of Example 1 was used as the wetting agent, and the positive active material lithium iron phosphate (LiFePO4), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent were mixed in a mass ratio of 97.3:1.8:0.7:0.2 Dissolve in the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to obtain the positive electrode slurry; apply and cold-press and dry to obtain the positive electrode piece. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 63%.

3. Preparation of electrolyte: In an argon atmosphere glove box (atmosphere: H ₂ O <0.1ppm, O ₂ <0.1ppm), dissolve 1mol/L LiPF6 (lithium hexafluorophosphate) in an organic solvent (EC (ethylene carbonate) /DMC (dimethyl carbonate)/EMC (ethyl methyl carbonate) = 1/1/1 (mass ratio)), stir evenly to obtain the corresponding electrolyte.

4. Preparation of secondary battery: Stack the above-mentioned positive electrode sheet, the 14 μm thick polyethylene film as a separator, and the above-mentioned negative electrode sheet in order, so that the separator film is between the positive electrode sheet and the negative electrode sheet for isolation. function, and winding to obtain the bare battery core. The bare battery core is placed in the aluminum plastic film bag of the battery case, dried and then injected with the above-mentioned electrolyte, and then undergoes processes such as formation and standing to prepare a secondary battery.

Example 2

The difference between Example 2 and Example 1 is that the mass ratio of the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide is 4:4:1, and the polymerization reaction The temperature is 90℃ and the time is 3h. Among them, the monomer corresponding to the first repeating structural unit has the following structural formula:

The monomer corresponding to the second repeating structural unit has the following structural formula:

The polymer has the structural formula shown below

Among them, b is 90 and c is 60.

Example 3

The difference between Example 3 and Example 1 is that the mass ratio of the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide is 4:2:1, and the polymerization reaction The temperature is 85℃ and the time is 2h. Among them, the monomer corresponding to the first repeating structural unit is acrylic acid, and a monomer with the following structural formula:

The polymer has the structural formula shown below

Among them, a is 110, b is 90, and c is 60.

Example 4

The difference between Example 4 and Example 1 is that the mass ratio of the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide is 4:4:1. The monomer corresponding to the first repeating structural unit is nyl methacrylate and a monomer with the following structural formula:

The polymer has the structural formula shown below

Among them, a is 50, b is 50, and c is 50.

Example 5

The difference between Example 5 and Example 1 is that the mass ratio of the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide is 4:2:1. The monomer corresponding to the first repeating structural unit has the following structural formula:

The polymer has the structural formula shown below

Among them, a is 50, b is 50, and c is 50.

Example 6

The difference between Example 6 and Example 1 is that the mass ratio of the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator benzoyl peroxide is 4:2:1. The monomer corresponding to the first repeating structural unit has the following structural formula:

The polymer has the structural formula shown below

Among them, a is 50, b is 50, and c is 50.

Example 7

The difference between Example 7 and Example 3 is: a is 120, b is 80, c is 50, and other preparation methods are the same as in Example 1.

Example 8

The difference between Example 8 and Example 3 is that the positive active material lithium iron phosphate (LiFePO4), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent are mixed in a mass ratio of 97.4:1.8:0.7: 0.1 is dissolved in the solvent N-methylpyrrolidone (NMP), and the positive electrode slurry is obtained after thorough stirring and mixing. The positive electrode piece is obtained after coating and cold pressing and drying. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 63%. Other preparation methods are the same as in Example 1.

Example 9

The difference between Example 9 and Example 3 is that the positive active material lithium iron phosphate (LiFePO4), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent are mixed in a mass ratio of 97.2:1.8:0.7: 0.3 was dissolved in the solvent N-methylpyrrolidone (NMP), stirred thoroughly and mixed evenly to obtain the positive electrode slurry; the positive electrode piece was obtained after coating and cold pressing and drying. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 63%. Other preparation methods are the same as in Example 1.

Example 10

The difference between Example 10 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent are mixed in a mass ratio of 97.1:1.8:0.7 :0.4 is dissolved in the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to obtain the positive electrode slurry; apply and cold-press and dry to obtain the positive electrode piece. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 63%. Other preparation methods are the same as in Example 1.

Example 11

The difference between Example 11 and Example 3 is that the positive electrode active material lithium iron phosphate (LiFePO ₄ ), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent are mixed in a mass ratio of 97:1.8:0.7 :0.5 is dissolved in the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to obtain the positive electrode slurry; apply and cold-press and dry to obtain the positive electrode piece. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 63%. Other preparation methods are the same as in Example 1.

Example 12

The difference between Example 12 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the wetting agent are mixed in a mass ratio of 97.3:1.8:0.7 :0.2 is dissolved in the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to obtain the positive electrode slurry; apply and cold-press and dry to obtain the positive electrode piece. The coating weight is 400mg/1540.25mm ² and the solid content of the slurry is 50%. Other preparation methods are the same as in Example 1.

Example 13

The difference between Example 13 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), conductive carbon, and PTFE are evenly mixed in a dual planetary mixer to obtain solvent-free granular materials, and the wetting agent, PVDF and NMP are mixed into a gel. The liquid and solvent-free granular materials are kneaded into a dough-like material in an internal mixer. After being extruded by a screw into thick sheets, they are thinned by rolling and compounded with a current collector to obtain a positive electrode sheet. Among them, the mass ratio of lithium iron phosphate (LiFePO ₄ ), conductive carbon, PTFE, sizing agent, and PVDF is 97.35:0.7:0.25:0.2:1.5, the solid content of the slurry is 90%, and the pole piece weight is 400mg/1540.25mm ² . Other preparation methods are the same as in Example 1.

Example 14

The difference between Example 14 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), conductive carbon, and PTFE are evenly mixed in a double planetary mixer to obtain solvent-free granular materials, and the wetting agent, PVDF and NMP are mixed into a gel. The liquid and solvent-free granular materials are kneaded into a dough-like material in an internal mixer. After being extruded by a screw into thick sheets, they are thinned by rolling and compounded with a current collector to obtain a positive electrode sheet. Among them, the mass ratio of lithium iron phosphate (LiFePO ₄ ), conductive carbon, PTFE, sizing agent, and PVDF is 97.35:0.7:0.25:0.2:1.5, the solid content of the slurry is 75%, and the pole piece weight is 400mg/1540.25mm ² . Other preparation methods are the same as in Example 1.

Example 15

The difference between Example 15 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), conductive carbon, and PTFE are evenly mixed in a double planetary mixer to obtain solvent-free granular materials, and the wetting agent, PVDF and NMP are mixed into a gel. The liquid and solvent-free granular materials are kneaded into a dough-like material in an internal mixer. After being extruded by a screw into thick sheets, they are thinned by rolling and compounded with a current collector to obtain a positive electrode sheet. Among them, the mass ratio of lithium iron phosphate (LiFePO ₄ ), conductive carbon, PTFE, sizing agent, and PVDF is 97.25:0.7:0.25:0.3:1.5, the solid content of the slurry is 75%, and the pole piece weight is 400mg/1540.25mm ² . Other preparation methods are the same as in Example 1.

Example 16

The difference between Example 16 and Example 3 is that the positive active material lithium iron phosphate (LiFePO ₄ ), conductive carbon, and PTFE are evenly mixed in a double planetary mixer to obtain solvent-free granular materials, and the wetting agent, PVDF and NMP are mixed into a gel. The liquid and solvent-free granular materials are kneaded into a dough-like material in an internal mixer. After being extruded by a screw into thick sheets, they are thinned by rolling and compounded with a current collector to obtain a positive electrode sheet. Among them, the mass ratio of lithium iron phosphate (LiFePO ₄ ), conductive carbon, PTFE, sizing agent, and PVDF is 97.25:0.7:0.25:0.3:1.5, the solid content of the slurry is 75%, and the pole piece weight is 400mg/1540.25mm ² . Other preparation methods are the same as in Example 1.

Comparative example 1

Dissolve the positive active material lithium iron phosphate (LiFePO ₄ ), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 97.5:1.8:0.7. After stirring and mixing evenly, the positive electrode slurry is obtained; after coating, cold pressing and drying, the positive electrode sheet is obtained. The coating weight is 400mg/1540.25mm2, and the solid content of the slurry is 63%. Other preparation methods are the same as in Example 1.

Comparative example 2

The difference between Comparative Example 2 and Example 1 is that the positive active material lithium iron phosphate (LiFePO ₄ ), conductive carbon, and PTFE were mixed evenly in a double planetary mixer to obtain solvent-free granular materials, and PVDF and NMP were mixed into a glue solution. The solvent-free granular material is kneaded into a dough-like material in an internal mixer, extruded by a screw into a thick sheet, and then thinned by rolling and compounded with a current collector to obtain a positive electrode piece. The mass ratio of lithium iron phosphate (LiFePO ₄ ), conductive carbon, PTFE, and PVDF is 97.55:0.7:0.25:1.5, the slurry solid content is 75%, and the pole piece weight is 400mg/1540.25mm ² . Other preparation methods are the same as in Example 1.

Performance Testing

Lithium precipitation test

The secondary batteries prepared in the Examples and Comparative Examples were charged to 3.65V at a constant current of 1C, then charged at a constant voltage of 3.65V to a current of 0.05C, left to stand for 5 minutes, and then discharged to 2.5V at a constant current of 1C. The above is a charge and discharge cycle of the battery. After 10 cycles, it is charged at a constant voltage of 3.65V to a current of 0.05C. Disassemble the battery in a dry environment. The golden color on the surface of the positive electrode indicates that lithium has not been precipitated, and the presence of a silvery-white area indicates that lithium has been precipitated. The test results are shown in Table 1.

Electrolyte Wetting Rate Test

Use a capillary tube (diameter 1 mm) to absorb a certain amount of electrolyte (height 2 cm), so that the suction end of the capillary tube is in contact with the surface of the positive electrode sheet of the secondary battery prepared in the Examples and Comparative Examples. The positive electrode piece has a porous structure. Under capillary force, the electrolyte in the capillary can be sucked out. The time required for the electrolyte to be completely absorbed is recorded, and the electrolyte infiltration rate is calculated.

The electrolyte infiltration rate is calculated by: electrolyte density × electrolyte volume in the capillary/time required for the electrolyte to be completely absorbed. The test results are shown in Table 1.

DCR (DC internal resistance) performance test

At 25°C, the secondary batteries prepared in the Examples and Comparative Examples were charged to a fully charged state at 0.33C, and then discharged at 0.33C with 0.5Cn (Cn represents the battery capacity) to adjust the secondary battery to 50% SOC (charge). electrical state), let it sit for 30 minutes, let it stand for 30 seconds, then let it stand for 30 seconds, then let it stand for 30 seconds, then charge it for 30 seconds.

Calculation method: DCR=(V1-V2)/I, where V1 is the static end voltage, V2 is the discharge cut-off voltage, and I is the discharge current. The test results are shown in Table 1.

Rate performance test

Rate discharge: The secondary batteries prepared in the Examples and Comparative Examples were charged to 3.65V at 0.33C, further charged to a constant voltage of 3.65V until the current was 0.05C, left to stand for 5 minutes, discharged to 2.5V at 0.33C and measured. The discharge capacity during this period is left to stand for 30 minutes; charge to 3.65V at 0.33C, further charge to a current of 0.05C at a constant voltage of 3.65V, let stand for 5 minutes, discharge to 2.5V at 1C and measure the discharge capacity during the period. Leave it for 30 minutes; charge to 3.65V at a constant voltage of 0.33C, charge to a constant voltage of 0.05C, leave it for 5 minutes, discharge it to 2.8V at 3C and measure the discharge capacity, leave it for 30 minutes; charge it to 3.65V at 0.33C , further charge with a constant voltage of 3.65V until the current is 0.05C, let it stand for 5 minutes, discharge it with 5C to 2.5V and measure the discharge capacity during this period, and let it stand for 30 minutes.

Rate charging: The secondary batteries prepared in the Examples and Comparative Examples were charged to 3.65V at 0.33C, further charged to a constant voltage of 3.65V until the current was 0.05C, left to stand for 5 minutes, discharged to 2.5V at 0.33C, and Measure the charging capacity during this period and let it sit for 30 minutes; charge to 3.65V at 1C, further charge to a constant voltage of 3.65V until the current is 0.05C, let it stand for 30 minutes, discharge at 0.33C to 2.5V and measure the charging capacity during this period. Let it stand for 30 minutes; charge to 3.65V at 3C, further charge with a constant voltage of 3.65V until the current is 0.05C, let it stand for 5 minutes, discharge it to 2.5V at 0.33C and measure the charging capacity, let it stand for 30 minutes; Charge at 5C to 4.2V, further charge at a constant voltage of 4.2V until the current is 0.05C, let it sit for 30 minutes, discharge it at 0.33C to 2.5V and measure the charging capacity, and let it stand for 30 minutes. The test results are shown in Table 2.

Test Results

The relevant test results of the secondary batteries of the above embodiments and comparative examples are shown in Table 1 and Table 2 below.

Table 1

Table 2

According to the above results, it can be seen that under the conditions of the same solid content between Examples 1-11 and Comparative Example 1, and under the conditions of the same solid content between Examples 14-16 and Comparative Example 2, the electrolyte infiltration rate can be achieved after adding the sizing agent. Improve, shorten the infiltration time of the electrode piece, reduce the manufacturing cost, while reducing the DCR and improving the rate performance, indicating that adding the sizing agent can improve the lithium ion migration dynamics, reduce the cell impedance, improve the interface between electrode components, and improve the rate performance. Comparing Examples 7-11, it can be seen that the best improvement effect is achieved when the addition amount is in the appropriate range of 0.2-0.4%, and the addition amount is too low to provide sufficient wetting performance. It can be seen from Examples 1-16 that the sizing agent is suitable for systems with different solid contents, and in systems with high solid contents, the electrochemical and kinetic properties are more advantageous due to the different pole piece preparation processes.

Figure 7 is a SEM (scanning electron microscope, scanning electron microscope) photograph of the positive electrode plate in Example 3 of the present application. Figure 8 is an SEM photograph of the positive electrode piece of Example 14. It can be seen from Figures 7 and 8 that the porosity on the outer surface side of the positive electrode piece of Example 14 is significantly greater than the porosity on the outer surface side of the positive electrode piece of Example 3, and it can be seen from the data in Tables 1 and 2 that the solid content In the high pole piece preparation system, the electrolyte infiltration rate is high, which can shorten the time for the electrolyte to infiltrate the battery core, greatly improve the production efficiency of the battery, and improve the dynamic performance.

Figure 9 is an infrared spectrum of the positive electrode plate in Example 1 of the present application. It can be seen that there are ester groups in it, which can improve the affinity of the positive electrode plate for the electrolyte, reduce the surface free energy of the active particles, and increase the electrolyte content. Wetting ability can shorten the soaking time of pole pieces and improve production efficiency.

While the present application has been described with reference to preferred embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any way. The application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

A polymer including a first repeating structural unit and a second repeating structural unit, wherein,

The first repeating structural unit has the structural formula shown in formula I,

Among them, R 1 is selected from
R 2 is selected from hydrogen or methyl, R 3 is selected from hydrogen or C1-C11 alkyl, R 4 is selected from aminomethyl or C1-C11 alkyl; optionally, the R 3 is selected from C6-C11 alkyl group, R 4 is selected from C6～C11 alkyl group;

The second repeating structural unit has the structural formula shown in Formula II,

Among them, R 5 is selected from C1 to C8 alkyl; R 6 and R 7 are independently selected from C1 to C3 alkyl, and R 8 is selected from hydrogen or methyl; optionally, R 5 is selected from C4 to C8. alkyl.
The polymer according to claim 1, wherein R 3 and R 4 are independently selected from C3 to C9 alicyclic groups, C3 to C9 alicyclic heterocyclic groups, C6 to C11 aryl groups or C3 to C11 of heteroaryl.
The polymer according to claim 1, wherein the polymerization degree ratio of the first repeating structural unit and the second repeating structural unit of the polymer (1.5-4): 1.
The polymer according to claim 1, wherein the polymer has a structure represented by formula III,

Wherein, the a, b, c are independently selected from any integer from 50 to 120.
The polymer according to any one of claims 1 to 4, wherein the weight average molecular weight of the polymer is 15,000 to 100,000; optionally, the weight average molecular weight of the polymer is 15,000 to 35,000.
A method for preparing a polymer, which includes the following steps:

Mix the monomer corresponding to the first repeating structural unit, the monomer corresponding to the second repeating structural unit and the initiator, and heat to react to obtain a polymer;

The first repeating structural unit has the structural formula shown in formula I,

Among them, R 1 is selected from
R 2 is selected from hydrogen or methyl, R 3 is selected from hydrogen or C1-C11 alkyl, R 4 is selected from aminomethyl or C1-C11 alkyl; optionally, the R 3 is selected from C6-C11 alkyl group, R 4 is selected from C6～C11 alkyl group;

The second repeating structural unit has the structural formula shown in Formula II,

Among them, R 5 is selected from C1 to C8 alkyl; R 6 and R 7 are independently selected from C1 to C3 alkyl, and R 8 is selected from hydrogen or methyl; optionally, R 5 is selected from C4 to C8. alkyl.
The method for preparing a polymer according to claim 6, wherein the mass ratio of the first repeating structural unit, the second repeating structural unit and the initiator is (2-4): (2-4):1.
A positive electrode slurry, which includes a positive electrode active material, a conductive agent, a binder and a polymer according to any one of claims 1 to 6 or a method for preparing a polymer according to claims 6 or 7 prepared polymer.
The positive electrode slurry according to claim 8, wherein the mass fraction of the polymer in the total mass of the positive electrode slurry is 0.1wt%~0.5wt%, optionally 0.2wt%~0.4wt%.
The positive electrode slurry according to claim 8, wherein the solid content of the positive electrode slurry is 50% to 90%.
A positive electrode sheet prepared from the positive electrode slurry described in any one of claims 8-10.
A secondary battery including the positive electrode plate according to claim 11.
A battery module including the secondary battery according to claim 12.
A battery pack including the battery module according to claim 13.
An electrical device includes the secondary battery according to claim 12, the battery module according to claim 13, or the battery pack according to claim 14.