阅读说明：本技术 柔性锂离子电池及其制备方法 (Flexible lithium ion battery and preparation method thereof ) 是由 邓永红 柯若弘 韩兵 于 2020-05-14 设计创作，主要内容包括：本发明属于锂离子电池技术领域,尤其涉及一种柔性锂离子电池,其特征在于,包括：正极片、隔膜和负极片；其中,所述正极片包含多层叠层设置的正极薄膜,所述负极片包含多层叠层设置的负极薄膜,所述隔膜、所述正极薄膜中粘结剂和所述负极薄膜中粘结剂组分相同。本发明柔性锂离子电池,多层叠层设置正负极片,能够有效缓解极片在形变过程中的应力,避免了单层结构极片在变形过程中因最外层形变量大于内层导致极片易于断裂的现象,从而提高了柔性电池的稳定性和安全性。采用与正负极粘结剂相同的材料作为隔膜,通过同种物质之间的亲和力不但使得正极片、负极片和隔膜之间结合紧密,更有利于离子在不同功能层之间的传输,提高了电池的电化学性能。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a flexible lithium ion battery which is characterized by comprising the following components in parts by weight: a positive plate, a diaphragm and a negative plate; the positive plate comprises a positive film and the negative plate comprises a negative film, wherein the positive film and the negative film are stacked in a multi-layer mode, and the diaphragm, the binder in the positive film and the binder in the negative film are the same in component. According to the flexible lithium ion battery, the positive and negative pole pieces are arranged in the multi-layer lamination manner, so that the stress of the pole pieces in the deformation process can be effectively relieved, the phenomenon that the pole pieces are easy to break due to the fact that the deformation of the outermost layer is larger than that of the inner layer in the deformation process of the pole pieces with the single-layer structure is avoided, and the stability and the safety of the flexible battery are improved. The material which is the same as the anode and cathode binders is used as the diaphragm, and the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, so that the transmission of ions among different functional layers is facilitated, and the electrochemical performance of the battery is improved.)

1. A flexible lithium ion battery, comprising: a positive plate, a diaphragm and a negative plate; the positive plate comprises a positive film and the negative plate comprises a negative film, wherein the positive film and the negative film are stacked in a multi-layer mode, and the diaphragm, the binder in the positive film and the binder in the negative film are the same in component.

2. The flexible lithium ion battery of claim 1, wherein the separator, the binder in the positive electrode film, and the binder in the negative electrode film are simultaneously selected from the group consisting of: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid; and/or the presence of a gas in the gas,

the thickness of the positive electrode film is 10 micrometers-1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter; and/or the presence of a gas in the gas,

the positive plate comprises 2-50 layers of the positive film; the negative plate comprises 2-50 layers of negative films; and/or the presence of a gas in the gas,

in the positive electrode film and the negative electrode film, the conductive agents are respectively and independently selected from: the mass ratio is (6-8): 1, a particulate conductive agent and a fibrous conductive agent; and/or the presence of a gas in the gas,

in the positive electrode film, the positive electrode active material is selected from: at least one of lithium cobaltate, lithium iron phosphate and ternary materials; and/or the presence of a gas in the gas,

in the negative electrode film, the negative electrode active material is selected from: at least one of lithium titanate, graphite and silicon-based material.

3. A preparation method of a flexible lithium ion battery is characterized by comprising the following steps:

obtaining positive electrode slurry containing a positive electrode active substance, a positive electrode binder, a positive electrode conductive agent and a positive electrode solvent, depositing the positive electrode slurry on a substrate, and drying and separating to obtain a positive electrode film;

obtaining negative electrode slurry containing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent and a negative electrode solvent, depositing the negative electrode slurry on a substrate, and drying and separating to obtain a negative electrode film;

laminating and laminating the multiple layers of positive electrode films to obtain a positive electrode plate;

laminating and pressing the multilayer negative electrode films to obtain a negative electrode sheet;

obtaining a diaphragm, and assembling the diaphragm, the positive plate and the negative plate to obtain a flexible lithium ion battery; wherein the positive electrode binder, the negative electrode binder and the separator adopt the same components.

4. The method of claim 3, wherein the positive electrode binder, the negative electrode binder, and the separator are simultaneously selected from the group consisting of: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid; and/or the presence of a gas in the gas,

the thickness of the diaphragm is 10-50 microns; and/or the presence of a gas in the gas,

the positive electrode conductive agent and the negative electrode conductive agent both comprise the following components in percentage by mass (6-8): 1 and a fibrous conductive agent.

5. The preparation method of the flexible lithium ion battery according to claim 4, wherein the positive electrode conductive agent and the negative electrode conductive agent both comprise (6-8) by mass: 1, Super P and carbon nanotubes; and/or the presence of a gas in the gas,

in the positive electrode slurry, the mass ratio of the positive electrode active substance to the positive electrode binder to the positive electrode conductive agent is (72-80): (8-20): (7-9); and/or the presence of a gas in the gas,

in the negative electrode slurry, the mass ratio of the negative electrode active material to the negative electrode binder to the negative electrode conductive agent is (72-80): (8-20): (7-9).

6. The method for preparing the flexible lithium ion battery according to any one of claims 3 to 5, wherein the thickness of the positive electrode film is 10 micrometers to 1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter; and/or the presence of a gas in the gas,

the positive plate comprises 2-50 layers of the positive film; the negative electrode sheet comprises 2-50 layers of negative electrode films.

7. The method of claim 6, wherein the positive active material is selected from the group consisting of: at least one of lithium cobaltate, lithium iron phosphate and ternary materials; and/or the presence of a gas in the gas,

the negative active material is selected from: at least one of lithium titanate, graphite and silicon-based materials; and/or the presence of a gas in the gas,

the positive electrode solvent and the negative electrode solvent are each independently selected from: at least one of methyl pyrrolidone, dimethyl formamide, dimethyl sulfoxide and water.

8. The method for preparing the flexible lithium ion battery according to any one of claims 3 to 5 or 7, wherein the step of laminating and laminating the plurality of positive electrode thin films comprises the following steps: the adjacent positive electrode films are bonded by depositing the positive electrode solvent, and then the laminated multiple positive electrode films are pressed and dried to obtain a positive electrode sheet; and/or the presence of a gas in the gas,

the step of laminating and laminating the plurality of layers of negative electrode films comprises the following steps: and depositing the negative electrode solvent between the adjacent negative electrode films to enable the adjacent films to be bonded, and then laminating and drying the laminated multilayer negative electrode films to obtain the negative electrode sheet.

9. The method for preparing a flexible lithium ion battery according to any one of claims 4 to 5, wherein the step of obtaining the positive electrode slurry comprises: mixing the positive electrode binder with the positive electrode solvent to obtain a positive electrode binder solution; mixing the positive active substance with the granular conductive agent, grinding for more than 20 minutes, and drying to obtain positive powder; mixing the positive electrode binder solution, the fibrous conductive agent, the positive electrode powder and the positive electrode solvent to obtain positive electrode slurry; and/or the presence of a gas in the gas,

the step of obtaining the negative electrode slurry includes: mixing the negative electrode binder with the negative electrode solvent to obtain a negative electrode binder solution; mixing the negative active material with the granular conductive agent, grinding for more than 20 minutes, and drying to obtain negative powder; and mixing the negative electrode binder solution, the fibrous conductive agent, the negative electrode powder and the negative electrode solvent to obtain negative electrode slurry.

10. The method for preparing a flexible lithium ion battery according to claim 9, wherein the mass percentage concentration of the positive electrode active material in the positive electrode slurry is 20% to 35%; and/or the presence of a gas in the gas,

in the negative electrode slurry, the mass percentage concentration of the negative electrode active substance is 20-35%; and/or the presence of a gas in the gas,

the positive electrode solvent and the negative electrode solvent are the same solvent.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a flexible lithium ion battery and a preparation method thereof.

Background

With the progress of intelligent technology in recent years, various flexible devices become the main force of the electronic market, and the slow development of flexible batteries severely restricts the development and utilization of flexible consumer electronics. The rapid development of wearable electronic equipment and intelligent equipment has increased the demand for energy storage devices with high energy density, low manufacturing cost and good flexibility.

However, current lithium ion battery materials are not flexible and the current collector is easily damaged during bending, and poor contact of particles during bending of the electrode material results in contact resistance. At present, the battery mainly comprises an electrode, an electrolyte, a diaphragm and a shell, wherein the preparation and development of the flexible electrode are the key points of the whole flexible battery. In the preparation process of the traditional positive/negative electrode plate, a positive electrode or negative electrode active material and additives such as a conductive agent, a binder, a thickening agent and the like are mixed and stirred to form slurry, and then the slurry is coated on a flexible aluminum foil or a copper foil to prepare the positive/negative electrode plate. However, most of the positive and negative electrode active materials are rigid particulate materials, and problems such as separation and falling of the active materials occur when the rigid active particles and the metal current collector are bent, which may cause damage to electrode sheets, penetration of separators, and the like, and thus, the battery may fail. Thus failing to meet the demand for flexible devices and limiting the development of flexible batteries.

The existing reports about flexible batteries generally have the defects of low capacity or poor bending performance, and cannot meet the market demands.

Disclosure of Invention

The invention aims to provide a flexible lithium ion battery, and aims to solve the technical problems of low capacity, poor bending performance and the like of the conventional flexible lithium ion battery.

The invention also aims to provide a preparation method of the flexible lithium ion battery.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

a flexible lithium ion battery comprising: a positive plate, a diaphragm and a negative plate; the positive plate comprises a positive film and the negative plate comprises a negative film, wherein the positive film and the negative film are stacked in a multi-layer mode, and the diaphragm, the binder in the positive film and the binder in the negative film are the same in component.

Preferably, the separator, the binder in the positive electrode film and the binder in the negative electrode film are simultaneously selected from: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid.

Preferably, the thickness of the positive electrode thin film is 10 micrometers to 1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter.

Preferably, the positive electrode sheet comprises 2-50 layers of the positive electrode film; the negative electrode sheet comprises 2-50 layers of negative electrode films.

Preferably, in the cathode thin film and the anode thin film, the conductive agent is independently selected from: the mass ratio is (6-8): 1 and a fibrous conductive agent.

Preferably, in the positive electrode thin film, the positive electrode active material is selected from: lithium cobaltate, lithium iron phosphate and/or ternary material.

Preferably, in the negative electrode thin film, the negative electrode active material is selected from: at least one of lithium titanate, graphite and silicon-based material.

Correspondingly, the preparation method of the flexible lithium ion battery comprises the following preparation steps:

obtaining positive electrode slurry containing a positive electrode active substance, a positive electrode binder, a positive electrode conductive agent and a positive electrode solvent, depositing the positive electrode slurry on a substrate, and drying and separating to obtain a positive electrode film;

obtaining negative electrode slurry containing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent and a negative electrode solvent, depositing the negative electrode slurry on a substrate, and drying and separating to obtain a negative electrode film;

laminating and laminating the multiple layers of positive electrode films to obtain a positive electrode plate;

laminating and pressing the multilayer negative electrode films to obtain a negative electrode sheet;

obtaining a diaphragm, and assembling the diaphragm, the positive plate and the negative plate to obtain a flexible lithium ion battery; wherein the positive electrode binder, the negative electrode binder and the separator adopt the same components.

Preferably, the positive electrode binder, the negative electrode binder and the separator are simultaneously selected from: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid.

Preferably, the membrane has a thickness of 10 to 50 microns.

Preferably, the positive electrode conductive agent and the negative electrode conductive agent both comprise the following components in mass ratio of (6-8): 1 and a fibrous conductive agent.

Preferably, the positive electrode conductive agent and the negative electrode conductive agent both comprise the following components in mass ratio of (6-8): 1, and carbon nanotubes.

Preferably, in the positive electrode slurry, the mass ratio of the positive electrode active material, the positive electrode binder and the positive electrode conductive agent is (72-80): (8-20): (7-9).

Preferably, in the negative electrode slurry, the mass ratio of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent is (72-80): (8-20): (7-9).

Preferably, the thickness of the positive electrode thin film is 10 micrometers to 1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter.

Preferably, the positive electrode sheet comprises 2-50 layers of the positive electrode film; the negative electrode sheet comprises 2-50 layers of negative electrode films.

Preferably, the positive electrode active material is selected from: lithium cobaltate, lithium iron phosphate and/or ternary material.

Preferably, the negative active material is selected from: at least one of lithium titanate, graphite and silicon-based material.

Preferably, the cathode solvent and the anode solvent are each independently selected from: at least one of methyl pyrrolidone, dimethyl formamide, dimethyl sulfoxide and water.

Preferably, in the step of laminating and laminating the plurality of positive electrode thin film stacks: and depositing the anode solvent between the adjacent anode films to enable the adjacent films to be bonded, and then laminating and drying the laminated multiple anode films to obtain the anode sheet.

Preferably, in the step of laminating the plurality of negative electrode thin film stacks: and depositing the negative electrode solvent between the adjacent negative electrode films to enable the adjacent films to be bonded, and then laminating and drying the laminated multilayer negative electrode films to obtain the negative electrode sheet.

Preferably, the step of obtaining the positive electrode slurry includes: mixing the positive electrode binder with the positive electrode solvent to obtain a positive electrode binder solution; mixing the positive active substance with the granular conductive agent, grinding for more than 20 minutes, and drying to obtain positive powder; and mixing the anode binder solution, the fibrous conductive agent, the anode powder and the anode solvent to obtain anode slurry.

Preferably, the step of obtaining the anode slurry includes: mixing the negative electrode binder with the negative electrode solvent to obtain a negative electrode binder solution; mixing the negative active material with the granular conductive agent, grinding for more than 20 minutes, and drying to obtain negative powder; and mixing the negative electrode binder solution, the fibrous conductive agent, the negative electrode powder and the negative electrode solvent to obtain negative electrode slurry.

Preferably, in the positive electrode slurry, the mass percentage concentration of the positive electrode active material is 20% to 35%.

Preferably, in the negative electrode slurry, the mass percentage concentration of the negative electrode active material is 20-35%.

Preferably, the same solvent is used for the positive electrode solvent and the negative electrode solvent.

The flexible lithium ion battery provided by the invention comprises: the negative electrode plate comprises a negative electrode film and a diaphragm, wherein the positive electrode plate comprises a positive electrode film and a negative electrode film, the positive electrode film is arranged in a multilayer lamination mode, the negative electrode film comprises a negative electrode film, and the diaphragm and the binder in the positive electrode film and the binder in the negative electrode film adopt the same components. On the one hand, the positive plate and the negative plate are both made by laminating and pressing a plurality of layers of films, the battery pole piece with a multi-layer laminated structure can effectively relieve the stress of the pole piece in the deformation process, and the phenomenon that the pole piece is easy to break due to the fact that the deformation of the outermost layer of the pole piece is larger than that of the inner layer of the pole piece in the deformation process of the pole piece with a single-layer structure is avoided, so that the stability and the safety of the flexible. On the other hand, the binder is used for providing a flexible support body for the positive plate and the negative plate, the material which is the same as the binder is used as the diaphragm, and the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, so that the transmission of ions among different functional layers is facilitated, and the electrochemical performance of the battery is improved.

The preparation method of the flexible lithium ion battery provided by the invention comprises the following steps of firstly, preparing a positive film and a negative film by respectively adopting positive slurry and negative slurry; laminating and laminating the multiple layers of positive electrode films to obtain a positive plate, and laminating the multiple layers of negative electrode films to obtain a negative plate; and assembling the diaphragm, the positive plate and the negative plate to obtain the flexible lithium ion battery, wherein the positive binder, the negative binder and the diaphragm adopt the same components. According to the preparation method of the flexible lithium ion battery, on one hand, the binder is used for providing the flexible support body for the positive plate and the negative plate, the material which is the same as the binder is used as the diaphragm, the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, the transmission of ions among different functional layers is facilitated, and the electrochemical performance of the battery is improved; on the other hand, the positive plate and the negative plate are both made of multilayer thin film lamination, the stress of the pole piece in the deformation process can be effectively relieved by the battery pole piece with the multilayer lamination structure, the phenomenon that the pole piece is easy to break due to the fact that the deformation of the outermost layer of the pole piece is larger than that of the inner layer of the pole piece in the deformation process of the pole piece with the single-layer structure is avoided, and therefore stability and safety of the flexible battery are improved.

Drawings

Fig. 1 is a schematic structural diagram of a flexible battery provided in an embodiment of the present invention.

FIG. 2 is an SEM image of the electrode plate in examples 1 to 4 of the present invention.

FIG. 3 is a graph of the resistance of the comparative example 1 pole piece (left) and example 1 pole piece (right) of the present invention in a tensile test.

FIG. 4 is a graph of the resistance of the comparative example 2 pole piece (left) and example 2 pole piece (right) of the present invention in a tensile test.

FIG. 5 is a graph of the resistance of the comparative example 3 pole piece (left) and example 3 pole piece (right) of the present invention in a tensile test.

FIG. 6 is a graph of the resistance of the comparative example 4 pole piece (left) and example 4 pole piece (right) of the present invention in a tensile test.

Fig. 7 is a rate capability test chart of the graphite-lithium iron phosphate soft package battery in embodiment 6 of the invention.

Fig. 8 is a graph of rate capability test of the graphite-lithium cobaltate soft package battery of example 7 of the invention.

Fig. 9 is a graph of rate capability test of graphite-NCM 622 pouch cells of example 8 of the present invention.

Detailed Description

In order to make the purpose, technical solution and technical effect of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the weight in the description of the embodiment of the present invention may be a unit of mass known in the chemical industry field such as μ g, mg, g, kg, etc.

As shown in fig. 1, an embodiment of the present invention further provides a flexible lithium ion battery, including: a positive plate, a diaphragm and a negative plate; the positive plate comprises a positive film and the negative plate comprises a negative film, wherein the positive film and the negative film are stacked in a multi-layer mode, and the components of the diaphragm and the binder in the positive film are the same as those in the negative film.

The flexible lithium ion battery provided by the embodiment of the invention comprises: the positive plate comprises a positive film and a negative film, wherein the positive film and the negative film are arranged in a multi-layer laminated manner, and the diaphragm adopts the same components as the binder in the positive film and the binder in the negative film. On the one hand, the positive plate and the negative plate are both made by laminating and pressing a plurality of layers of films, the battery pole piece with a multi-layer laminated structure can effectively relieve the stress of the pole piece in the deformation process, and the phenomenon that the pole piece is easy to break due to the fact that the deformation of the outermost layer of the pole piece is larger than that of the inner layer of the pole piece in the deformation process of the pole piece with a single-layer structure is avoided, so that the stability and the safety of the flexible. On the other hand, the binder is used for providing a flexible support body for the positive plate and the negative plate, the material which is the same as the binder is used as the diaphragm, the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, the transmission of ions among different functional layers is facilitated, the capacity density of the battery is improved, and the resistance change is small in the deformation process of the plates.

In some embodiments, the binder in the positive film and the binder in the negative film are selected from the group consisting of: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid.

In some embodiments, the thickness of the positive electrode thin film is 10 micrometers to 1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter. The positive electrode film and the negative electrode film prepared by deposition in the embodiment of the invention are respectively 10 micrometers-1 millimeter, and the positive/negative electrode film with the thickness is not only beneficial to separation from a substrate after deposition film formation, but also ensures that the films have excellent flexibility. If the thickness of the film is too thin, the film is easy to break, is not beneficial to separation from the substrate after the film is formed, and is also not beneficial to the lamination arrangement of subsequent multilayer films; if the thickness of the film is too thick, the flexibility of the film is reduced, thereby reducing the performance of the flexible lithium ion battery.

In some embodiments, the positive plate comprises 2-50 layers of positive film; the negative plate comprises 2-50 layers of negative films. The number of layers of films contained in the positive/negative electrode plate can be flexibly set according to the capacity of the battery prepared actually, the surface capacity of the electrode plate can be flexibly adjusted by changing the number of layers of the films in the electrode plate, and the electrode plate with 2-50 layers of films is set to fully meet the requirement of the conventional flexible battery on the surface capacity. In addition, after the number of layers of one pole piece is determined, the number of layers of the other pole piece can be determined according to the capacity balance constant. The optimal idea is that under the condition that the thickness of the battery is the same, the thickness of wet coating is reduced so as to increase the layer number of the pole pieces, thereby improving the flexibility of the battery under the condition of ensuring the capacity of the battery.

In a specific embodiment, the thickness of the positive electrode film is 10 micrometers to 50 micrometers, the thickness of the negative electrode film is 10 micrometers to 50 micrometers, and the positive electrode sheet comprises 5 to 10 layers of positive electrode films; the negative plate comprises 5-10 layers of negative films.

In some embodiments, the conductive agent in the positive electrode thin film and the negative electrode thin film is independently selected from: the mass ratio is (6-8): 1 and a fibrous conductive agent. The conductive agent in the embodiment of the invention simultaneously comprises the granular conductive agent and the fibrous conductive agent, and the granular conductive agent and the fibrous conductive agent form a conductive network structure wound by point lines in the positive/negative electrode slurry, so that the conductivity of the positive/negative electrode plate can be effectively improved, and the electrical property of the electrode plate can be improved; and the positive/negative active material can be attached to the conductive network structure, so that the influence of the falling of particles such as the positive/negative active material from the pole piece on the capacity exertion and the safety performance of the pole piece is prevented. The mass ratio of the granular conductive agent to the fibrous conductive agent is (6-8): 1, the proportion can form an optimal conductive network structure in the pole piece. If the content of the fibrous conductive agent is too high, the fibrous conductive agent is easy to agglomerate, so that the conductivity of the pole piece is reduced, and a stress concentration point exists in the pole piece, so that the flexibility of the pole piece is poor. If the content of the fibrous conductive agent is too low, the conductive network structure is not good, active substances in the pole piece cannot be well attached to the conductive network, and the pole piece is easy to generate a powder falling phenomenon; meanwhile, the active substance and the conductive agent cannot be in good contact with each other, so that the conductive performance of the pole piece is poor. In some embodiments, the positive electrode conductive agent and the negative electrode conductive agent both comprise (6-8) by mass: 1, and carbon nanotubes.

In some embodiments, the positive electrode active material in the positive electrode thin film is selected from: lithium cobaltate, lithium iron phosphate and/or ternary material. In some embodiments, the negative electrode active material in the negative electrode film is selected from: at least one of lithium titanate, graphite and silicon-based material. In the positive/negative electrode film of the flexible lithium ion battery in the embodiment of the invention, the positive/negative electrode active material is not particularly limited, the positive electrode active material includes but is not limited to at least one of lithium cobaltate, lithium iron phosphate and ternary materials, the negative electrode active material includes but is not limited to at least one of lithium titanate, graphite and silicon-based materials, and the application range is wide.

Correspondingly, the embodiment of the invention provides a preparation method of a flexible lithium ion battery, which comprises the following preparation steps:

s10, obtaining positive electrode slurry containing a positive electrode active substance, a positive electrode binder, a positive electrode conductive agent and a positive electrode solvent, depositing the positive electrode slurry on a substrate, and drying and separating to obtain a positive electrode film;

s20, obtaining negative electrode slurry containing a negative electrode active substance, a negative electrode binder, a negative electrode conductive agent and a negative electrode solvent, depositing the negative electrode slurry on a substrate, and drying and separating to obtain a negative electrode film;

s30, laminating and pressing a plurality of layers of positive electrode films to obtain a positive electrode plate;

s40, laminating and pressing the multiple layers of negative electrode films to obtain a negative electrode sheet;

s50, obtaining a diaphragm, and assembling the diaphragm, a positive plate and a negative plate to obtain a flexible lithium ion battery; wherein, the positive electrode binder, the negative electrode binder and the diaphragm adopt the same components.

The preparation method of the flexible lithium ion battery provided by the embodiment of the invention comprises the following steps of firstly, respectively preparing a positive film and a negative film by adopting positive slurry and negative slurry; laminating and laminating the multiple layers of positive electrode films to obtain a positive plate, and laminating the multiple layers of negative electrode films to obtain a negative plate; and assembling the diaphragm, the positive plate and the negative plate to obtain the flexible lithium ion battery, wherein the positive binder, the negative binder and the diaphragm adopt the same components. According to the preparation method of the flexible lithium ion battery provided by the embodiment of the invention, on one hand, the binder is utilized to provide the flexible support body for the positive plate and the negative plate, and the material which is the same as the binder is adopted as the diaphragm, so that the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, the transmission of ions among different functional layers is facilitated, and the electrochemical performance of the battery is improved; on the other hand, the positive plate and the negative plate are both made of multilayer thin film lamination, the stress of the pole piece in the deformation process can be effectively relieved by the battery pole piece with the multilayer lamination structure, the phenomenon that the pole piece is easy to break due to the fact that the deformation of the outermost layer of the pole piece is larger than that of the inner layer of the pole piece in the deformation process of the pole piece with the single-layer structure is avoided, and therefore stability and safety of the flexible battery are improved.

Specifically, in step S10, a positive electrode slurry including a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and a positive electrode solvent is obtained, deposited on a substrate, dried, and separated to obtain a positive electrode thin film. According to the embodiment of the invention, the positive electrode slurry containing the positive electrode active material, the positive electrode binder, the positive electrode conductive agent and the positive electrode solvent is deposited on the substrate, and the positive electrode film is separated from the substrate after drying, so that the positive electrode film is obtained. In some embodiments, aluminum foil, copper foil, or the like may be used.

Specifically, in step S20, a negative electrode slurry including a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a negative electrode solvent is obtained, deposited on a substrate, dried, and separated to obtain a negative electrode thin film. According to the embodiment of the invention, the negative electrode slurry containing the negative electrode active material, the negative electrode binder, the negative electrode conductive agent and the negative electrode solvent is deposited on the substrate, and the negative electrode film is separated from the substrate after drying at the temperature of about 60-80 ℃ to obtain the negative electrode film. In some embodiments, aluminum foil, copper foil, or the like may be used.

In some embodiments, the positive electrode conductive agent and the negative electrode conductive agent both comprise (6-8) by mass: 1 and a fibrous conductive agent. The conductive agent in the embodiment of the invention simultaneously comprises the granular conductive agent and the fibrous conductive agent, and the granular conductive agent and the fibrous conductive agent form a conductive network structure wound by point lines in the positive/negative electrode slurry, so that the conductivity of the positive/negative electrode plate can be effectively improved, and the electrical property of the electrode plate can be improved; and the positive/negative active material can be attached to the conductive network structure, so that the influence of the falling of particles such as the positive/negative active material from the pole piece on the capacity exertion and the safety performance of the pole piece is prevented. The mass ratio of the granular conductive agent to the fibrous conductive agent is (6-8): 1, the proportion can form an optimal conductive network structure in the pole piece. If the content of the fibrous conductive agent is too high, the fibrous conductive agent is easy to agglomerate, so that the conductivity of the pole piece is reduced, and a stress concentration point exists in the pole piece, so that the flexibility of the pole piece is poor. If the content of the fibrous conductive agent is too low, the conductive network structure is not good, active substances in the pole piece cannot be well attached to the conductive network, and the pole piece is easy to generate a powder falling phenomenon; meanwhile, the active substance and the conductive agent cannot be in good contact with each other, so that the conductive performance of the pole piece is poor.

In some embodiments, the positive electrode conductive agent and the negative electrode conductive agent both comprise (6-8) by mass: 1, wherein the Super P has the characteristics of high specific surface area, close packing and the like, and is favorable for the close contact of particles to form a conductive network in an electrode; the carbon nano tube with the one-dimensional structure can be used as a conductive agent to well cloth a perfect conductive network, is compounded with the Super P in the pole piece to form a conductive network structure wound by point lines, has excellent conductivity, is in point-line contact with a living substance, can improve the compaction density of the pole piece, and has great effects of improving the capacity and rate performance of the battery, prolonging the cycle life of the battery and reducing the interface impedance of the battery. In some embodiments, the positive electrode conductive agent and the negative electrode conductive agent comprise, by mass, 6: 1. 7: 1 or 8:1, and carbon nanotubes.

In some embodiments, in the positive electrode slurry, the mass ratio of the positive electrode active material to the positive electrode binder to the positive electrode conductive agent is (72-80): (8-20): (7-9). In some embodiments, in the negative electrode slurry, the mass ratio of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent is (72-80): (8-20): (7-9). According to the embodiment of the invention, the proportion of the active substance, the binder and the conductive agent in the positive/negative electrode slurry fully ensures the electrochemical performance of the positive/negative electrode plate prepared by deposition, the binder content serving as a support material of the electrode plate enables the slurry to have good film-forming performance, and the electrode plate film taking the binder as a flexible support body is easily obtained by separation from the substrate after deposition and film forming, so that the electrode plate film has good flexibility, and the stability of the electrode plate is improved. If the content of the binder is too low, the positive/negative electrode slurry is too thin, the film forming property of the slurry is poor, the supporting effect of the binder on the pole piece film is poor, and the flexible pole piece film is difficult to obtain; if the content of the binder is too high, the content of active substances and conductive agents in the pole piece is correspondingly reduced, so that the electrochemical properties such as conductivity, capacity and the like of the pole piece are reduced, and the binder with too high content makes the slurry too viscous, which is not beneficial to uniform deposition of the slurry, has poor film forming property, and is difficult to obtain a pole piece film with good film layer uniformity.

In some embodiments, the positive active material is selected from: lithium cobaltate, lithium iron phosphate and/or ternary material. In some embodiments, the negative active material is selected from: at least one of lithium titanate, graphite and silicon-based material. In some embodiments, the positive electrode solvent and the negative electrode solvent are each independently selected from: at least one of methyl pyrrolidone, dimethyl formamide, dimethyl sulfoxide and water. The preparation method of the flexible lithium ion battery provided by the embodiment of the invention is suitable for the preparation of batteries of different material systems at present, the positive electrode active material comprises but is not limited to at least one of lithium cobaltate, lithium iron phosphate and ternary materials, the negative electrode active material comprises but is not limited to at least one of lithium titanate, graphite and silicon-based materials, and the application range is wide.

In some embodiments, the thickness of the positive electrode thin film is 10 micrometers to 1 millimeter; the thickness of the negative electrode film is 10 micrometers-1 millimeter. The positive electrode film and the negative electrode film prepared by deposition in the embodiment of the invention are respectively 10 micrometers-1 millimeter, and the positive/negative electrode film with the thickness is not only beneficial to separation from a substrate after deposition film formation, but also ensures that the films have excellent flexibility. If the thickness of the film is too thin, the film is easy to break, is not beneficial to separation from the substrate after the film is formed, and is also not beneficial to the lamination arrangement of subsequent multilayer films; if the thickness of the film is too thick, the flexibility of the film is reduced, thereby reducing the performance of the flexible lithium ion battery.

In some embodiments, the step of obtaining the positive electrode slurry comprises: mixing a positive electrode binder with a positive electrode solvent to obtain a positive electrode binder solution; mixing the positive active substance with the granular conductive agent, grinding for more than 20 minutes, and drying to obtain positive powder; and mixing the positive electrode binder solution, the fibrous conductive agent, the positive electrode powder and the positive electrode solvent to obtain positive electrode slurry.

In some embodiments, the step of obtaining the anode slurry comprises: mixing a negative electrode binder and a negative electrode solvent to obtain a negative electrode binder solution; mixing a negative electrode active substance with a granular conductive agent, grinding for more than 20 minutes, and drying to obtain negative electrode powder; and mixing the negative binder solution, the fibrous conductive agent, the negative powder and the negative solvent to obtain negative slurry.

In the step of obtaining the cathode/anode slurry, firstly, the binder is dissolved in the solvent to form the binder solution, so that the subsequent mixing uniformity of the binder and other components is facilitated, and in some embodiments, the mass percentage concentrations of the cathode binder solution and the anode binder solution are respectively 8-20%. And then, mixing the active substance and the granular conductive agent, and grinding for more than 20 minutes to further refine the particle sizes of the active substance and the granular conductive agent, so that the large-particle raw material substances are prevented from being difficult to uniformly disperse in subsequent mixed slurry, the dispersion stability of the subsequent positive/negative electrode slurry is improved, and the film forming uniformity is improved. Then, the binder solution, the fibrous conductive agent, the ground powder and the solvent are mixed to form the positive/negative electrode slurry with uniform and stable dispersion.

In some embodiments, the positive electrode active material is present in the positive electrode slurry at a concentration of 20% to 35% by mass. In some embodiments, the negative electrode active material is present in the negative electrode slurry at a concentration of 20% to 35% by mass. The embodiment of the invention comprises the positive/negative electrode slurry of the active substance with the mass percentage concentration of 20-35%, which not only ensures the content of the active substance in the slurry, thereby ensuring the electrochemical performance of the film, but also ensures the dispersion stability of each component in the slurry, is beneficial to the film forming performance of the subsequent film, and ensures that the prepared film has good uniformity; if the mass percentage of the active substance in the slurry is too low, the content of other components in the slurry is correspondingly low, and the viscosity of the slurry is too low, the forming stability of the slurry on the substrate is poor, so that a film with an expected thickness is difficult to prepare, and the formed film is difficult to separate from the substrate, which is not beneficial to the preparation of a subsequent pole piece.

Specifically, in step S30, a plurality of positive electrode films are laminated and bonded to obtain a positive electrode sheet.

Specifically, in step S40, the negative electrode sheet is obtained by laminating and pressing a plurality of negative electrode films.

In the preparation steps of the positive plate and the negative plate, the corresponding positive/negative plate with the multilayer laminated structure can be obtained by laminating and pressing the multilayer films, the preparation process is simple, the battery plate with the multilayer laminated structure can effectively relieve the stress of the plate in the deformation process, and the phenomenon that the plate is easy to break due to the fact that the deformation of the outermost layer of the single-layer structure plate is larger than that of the inner layer in the deformation process is avoided, so that the stability and the safety of the flexible battery are improved.

In some embodiments, the step of laminating the plurality of positive electrode thin film stacks comprises: and depositing a positive electrode solvent between adjacent positive electrode films in a spraying mode or the like to enable the adjacent films to be bonded, and then laminating and drying the laminated multiple positive electrode films to obtain the positive electrode sheet.

In some embodiments, the step of laminating the plurality of negative electrode thin film stacks comprises: and depositing a negative electrode solvent between the adjacent negative electrode films in a spraying mode or the like to enable the adjacent films to be bonded, and then laminating and drying the laminated multilayer negative electrode films to obtain the negative electrode sheet.

In the lamination and lamination step of the multilayer cathode film or the multilayer anode film, a deposition solvent is sprayed between adjacent films, the solvent can be combined with the adjacent film layers after soaking and softening the surfaces of the films, and then the laminated composite film layers are laminated and dried to obtain the cathode/anode sheet with the multilayer lamination structure. Specifically, a deposition solvent can be sprayed on the surface of a first layer of film, the solvent enables a binder in the film to be wetted and softened, a second layer of film is arranged on the softened surface of the first film in a laminated mode, the two layers of films can be well combined together through the softened surfaces, then a 3 rd layer of film is arranged on the surface of the second layer of film in a laminated mode after the deposition solvent is sprayed on the surface of the second layer of film, and the like until a composite film layer with an expected layer number structure is obtained, a certain pressure is applied to the surface of the composite film layer to enable the laminated multiple film layers to be compacted and combined tightly, solvent components are dried out at the temperature of 60-80 ℃, and the positive/negative plate with the multilayer laminated structure is obtained.

In some embodiments, the positive plate comprises 2-50 layers of positive film; the negative plate comprises 2-50 layers of negative films. The number of layers of films contained in the positive/negative electrode plate can be flexibly set according to the capacity of the battery prepared actually, the surface capacity of the electrode plate can be flexibly adjusted by changing the number of layers of the films in the electrode plate, and the electrode plate with 2-50 layers of films is set to fully meet the requirement of the conventional flexible battery on the surface capacity. In addition, after the number of layers of one pole piece is determined, the number of layers of the other pole piece can be determined according to the capacity balance constant. The optimal idea is that under the condition that the thickness of the battery is the same, the thickness of wet coating is reduced so as to increase the layer number of the pole pieces, thereby improving the flexibility of the battery under the condition of ensuring the capacity of the battery. In a specific embodiment, the thickness of the positive electrode film is 10 micrometers to 50 micrometers, the thickness of the negative electrode film is 10 micrometers to 50 micrometers, and the positive electrode sheet comprises 5 to 10 layers of positive electrode films; the negative plate comprises 5-10 layers of negative films.

In some embodiments, the same solvent is used for the positive electrode solvent and the negative electrode solvent. The positive/negative pole pieces in the embodiment of the invention adopt the same solvent, so that the compatibility of each film layer is better, and the stability of the battery is further improved.

Specifically, in step S50, obtaining a diaphragm, and assembling the diaphragm, a positive plate and a negative plate to obtain a flexible lithium ion battery; wherein, the positive electrode binder, the negative electrode binder and the diaphragm adopt the same components. According to the embodiment of the invention, the diaphragm, the positive plate and the negative plate are assembled to obtain the flexible lithium ion battery, and the positive binder, the negative binder and the diaphragm adopt the same components. According to the embodiment of the invention, the material which is the same as the binder is used as the diaphragm, and the positive plate, the negative plate and the diaphragm are tightly combined through the affinity among the same substances, so that the transmission of ions among different functional layers is facilitated, and the electrochemical performance of the battery is improved. In addition, because the diaphragm is made of the same material as the binder, when the battery is assembled, the surface of the pole piece or the diaphragm can be softened by directly spraying a deposition solvent on the surface of the diaphragm or the positive pole piece or the negative pole piece, so that the diaphragm is tightly combined between the positive pole piece and the negative pole piece, the stability and the safety of the battery are improved, and the process is simple and easy to operate.

In some embodiments, the positive electrode binder, the negative electrode binder, and the separator are simultaneously selected from: at least one of polyvinylidene fluoride, polyimide, polystyrene, polyethylene, polypropylene, polytetrafluoroethylene and polyacrylic acid, which not only has better adhesive property and plays a supporting role in the positive plate and the negative plate, but also bonds various functional materials in the pole piece to form an organic whole machine, so that the pole piece has good flexibility and is not easy to fall off; and has excellent ion conduction function, and when the materials are used as a diaphragm, the materials can separate a positive plate and a negative plate of the battery and prevent the positive plate and the negative plate from contacting and being short-circuited.

In some embodiments, the thickness of the separator is 10 to 50 microns, which will affect the safety performance of the battery if the separator is too thin, and which will not only increase the transmission path of ions, affect the performance of the battery, but also reduce the flexibility of the battery if the separator is too thick.

In order to clearly understand the details and operations of the above embodiments of the present invention for those skilled in the art and to obviously show the advanced performance of the flexible lithium ion battery and the manufacturing method thereof according to the embodiments of the present invention, the above technical solutions are illustrated by a plurality of examples.