阅读说明：本技术 阻燃结构及其制备方法、锂电池结构 (Flame-retardant structure, preparation method thereof and lithium battery structure ) 是由 赵宇明 丁庆 于 2020-12-04 设计创作，主要内容包括：本申请涉及储能技术领域,具体公开一种阻燃结构及其制备方法、锂电池结构。阻燃结构包括阻燃隔膜层和聚乙烯微球膜层,阻燃隔膜层包括有机聚合物层,以及设置于所述有机聚合物层内的阻燃剂；聚乙烯微球膜层包括聚乙烯微球和有机溶剂的混合物,设置于所述阻燃隔膜层的外表面。该阻燃结构应用于锂电池中时,在锂电池热失控过程中,锂电池仍然具有一定的放电容量,随着锂电池不断升温,阻燃结构中的聚乙烯微球膜层能够熔化覆盖在电池负极表面,阻断锂离子的传输,抑制热失控。当温度持续升高,阻燃隔膜层中的阻燃剂释放出来,使电解液不可燃,避免起火和爆炸,正负极材料依然能回收再利用,解决了资源浪费的问题。另外还兼容了电池的电化学性能。(The application relates to the technical field of energy storage, and particularly discloses a flame-retardant structure, a preparation method of the flame-retardant structure and a lithium battery structure. The flame-retardant structure comprises a flame-retardant diaphragm layer and a polyethylene microsphere film layer, wherein the flame-retardant diaphragm layer comprises an organic polymer layer and a flame retardant arranged in the organic polymer layer; the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent and is arranged on the outer surface of the flame-retardant diaphragm layer. When this fire-retardant structure was applied to among the lithium cell, at the lithium cell thermal runaway in-process, the lithium cell still had certain discharge capacity, along with the lithium cell constantly heaies up, and polyethylene microsphere rete among the fire-retardant structure can melt and cover on battery negative pole surface, blocks the transmission of lithium ion, restraines the thermal runaway. When the temperature is continuously raised, the flame retardant in the flame-retardant diaphragm layer is released, so that the electrolyte is not combustible, the fire and explosion are avoided, the anode and cathode materials can still be recycled, and the problem of resource waste is solved. In addition, the electrochemical performance of the battery is compatible.)

1. A fire retardant structure, comprising:

a flame retardant separator layer comprising an organic polymer layer, and a flame retardant disposed within the organic polymer layer;

the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent and is arranged on the outer surface of the flame-retardant diaphragm layer.

2. The flame retardant structure of claim 1 wherein the organic polymer layer comprises a mixture of one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethylmethacrylate.

3. The flame retardant structure of claim 1, wherein the flame retardant comprises any one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and methyl diphenyl phosphate.

4. The flame retardant structure of claim 1, wherein the flame retardant is present in the flame retardant separator layer in an amount between 5 wt% and 30 wt%.

5. The flame retardant structure of claim 1 wherein the polyethylene microspheres are present in the polyethylene microsphere film layer in an amount between 5 wt% and 40 wt%.

6. Flame retardant structure according to claim 1, characterized in that the loading of polyethylene microspheres is between 5 and 20mg cm^-2In the meantime.

7. The structure of claim 1, wherein the organic solvent comprises a mixture of any one or more of N-methyl pyrrolidone, an aqueous solution in which a surfactant is dispersed, 1-methyl-2 pyrrolidone, dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, and ethanol.

8. A method for preparing a flame-retardant structure, characterized in that the method for preparing a flame-retardant structure comprises:

forming a mixture of an organic polymer and a flame retardant into a flame retardant membrane layer of a fibrous structure;

and coating the mixture of the polyethylene microspheres and the organic solvent on the outer surface of the flame-retardant membrane layer to form a polyethylene microsphere membrane layer.

9. The method of making a flame retardant structure according to claim 8, wherein the step of forming the mixture of organic polymer and flame retardant into a flame retardant membrane layer of a fiber structure comprises:

dissolving an organic polymer and a flame retardant in an organic solvent according to a preset weight ratio to form a solution;

and stretching and thinning the solution under a preset voltage through an electrostatic spinning process to form fibers, so as to prepare the flame-retardant diaphragm layer with a fiber structure.

10. A lithium battery cell structure, comprising:

a positive electrode and a negative electrode;

the flame-retardant structure is arranged between the anode and the cathode, the flame-retardant structure comprises a flame-retardant diaphragm layer and a polyethylene microsphere film layer arranged on the outer surface of the flame-retardant diaphragm layer, the flame-retardant diaphragm layer comprises an organic polymer layer and a flame retardant arranged in the organic polymer layer, and the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent.

Technical Field

The invention relates to the technical field of energy storage, in particular to a flame-retardant structure, a preparation method thereof and a lithium battery structure.

Background

The lithium ion battery occupies the electric automobile market in China at present, is also applied to the power grid energy storage market in a large scale, and is one of key technologies for solving the current energy problem. However, the frequent occurrence of battery fire and explosion accidents makes thermal runaway and thermal safety problems to be of great concern.

As for the thermal runaway process of the battery cell, decomposition of the solid electrolyte film on the surface of the negative electrode, reaction and heat generation of the negative electrode and the electrolyte, melting of the separator, thermal runaway of the positive electrode material, decomposition of the electrolyte, and short circuit of the battery occur first, and the ejection of the electrolyte finally causes ignition and even explosion of the battery. In the face of this problem, there is no good solution at present, and therefore, solving the thermal runaway and thermal safety problems of the battery is one of the problems to be solved urgently in the art.

Disclosure of Invention

Based on this, it is necessary to provide a flame retardant structure, a preparation method thereof and a lithium battery structure aiming at the problems of thermal runaway and thermal safety of the battery.

A flame retardant structure, comprising:

a flame retardant separator layer comprising an organic polymer layer, and a flame retardant disposed within the organic polymer layer;

the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent and is arranged on the outer surface of the flame-retardant diaphragm layer.

In one embodiment, the organic polymer layer comprises a mixture of one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate.

In one embodiment, the flame retardant comprises any one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and methyl diphenyl phosphate.

In one embodiment, the flame retardant is present in the flame retardant membrane layer in an amount between 5 wt% and 30 wt%.

In one embodiment, the content of the polyethylene microspheres in the polyethylene microsphere film layer is between 5 wt% and 40 wt%.

In one embodiment, the loading of the polyethylene microspheres is between 5 and 20mgcm^-2In the meantime.

In one embodiment, the organic solvent includes a mixture of any one or more of N-methylpyrrolidone, an aqueous solution in which a surfactant is dispersed, 1-methyl-2 pyrrolidone, dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, and ethanol.

A method of making a flame retardant structure, the method of making a flame retardant structure comprising:

forming a mixture of an organic polymer and a flame retardant into a flame retardant membrane layer of a fibrous structure;

and coating the mixture of the polyethylene microspheres and the organic solvent on the outer surface of the flame-retardant membrane layer to form a polyethylene microsphere membrane layer.

In one embodiment, the step of forming the mixture of organic polymer and flame retardant into the flame retardant separator layer of fibrous structure comprises:

dissolving an organic polymer and a flame retardant in an organic solvent according to a preset weight ratio to form a solution;

and stretching and thinning the solution under a preset voltage through an electrostatic spinning process to form fibers, so as to prepare the flame-retardant diaphragm layer with a fiber structure.

A lithium battery structure comprising:

a positive electrode and a negative electrode;

the flame-retardant structure is arranged between the anode and the cathode, the flame-retardant structure comprises a flame-retardant diaphragm layer and a polyethylene microsphere film layer arranged on the outer surface of the flame-retardant diaphragm layer, the flame-retardant diaphragm layer comprises an organic polymer layer and a flame retardant arranged in the organic polymer layer, and the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent.

The flame-retardant structure comprises a flame-retardant diaphragm layer and a polyethylene microsphere film layer, wherein the flame-retardant diaphragm layer comprises an organic polymer layer and a flame retardant arranged in the organic polymer layer, the polyethylene microsphere film layer comprises a mixture of polyethylene microspheres and an organic solvent, and the polyethylene microsphere film layer is arranged on the outer surface of the flame-retardant diaphragm layer. When this fire-retardant structure was applied to among the lithium cell, at the lithium cell thermal runaway in-process, the lithium cell still had certain discharge capacity, along with the lithium cell constantly heaies up, and the polyethylene microballon rete among the fire-retardant structure can melt and cover on battery negative pole surface, blocks the transmission of lithium ion, and then restraines the thermal runaway. When the temperature continuously rises, the flame retardant in the flame-retardant diaphragm layer is released, so that the electrolyte is not combustible, the fire and explosion are avoided, the anode and cathode materials of the battery can still be recycled even though the battery fails, and the problem of resource waste is solved. Meanwhile, as the application does not adopt the flame-retardant electrolyte for flame retardance as the traditional method, but adopts the flame-retardant structure, the problems of thermal runaway and thermal safety are solved, and simultaneously, the electrochemical performance of the battery is compatible.

Drawings

FIG. 1 is a schematic structural diagram of a flame retardant structure provided in one embodiment of the present application;

FIG. 2 is a block flow diagram of a method of making a flame retardant structure provided in example two of the present application;

fig. 3 is a block flow diagram of step S20 in the method for preparing a flame retardant structure provided in example two of the present application;

fig. 4 is a schematic structural diagram of a lithium battery provided in the third embodiment of the present application;

fig. 5 is a comparison graph of long cycle performance of a lithium battery provided in the third embodiment of the present application with a general battery at room temperature.

Description of reference numerals:

100. a flame retardant structure; 101. a flame retardant separator layer; 1011. an organic polymer layer; 1012. a flame retardant; 102. a polyethylene microsphere film layer; 1021. polyethylene microspheres; 1022. an organic solvent; 200. a positive electrode; 300. a negative electrode; 400. and (3) an electrolyte.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The lithium ion battery occupies the electric automobile market in China at present, is also applied to the power grid energy storage market in a large scale, and is one of key technologies for solving the current energy problem. However, the frequent occurrence of battery fire and explosion accidents makes thermal runaway and thermal safety problems to be of great concern. Particularly, the economy and the safety of the energy storage battery system are the restricting factors for the popularization of the energy storage system, the number of the batteries of the energy storage system is large, the thermal runaway of a single battery can easily cause the thermal runaway, the fire and even the explosion of a module and the system, and the consequences can not be estimated. Therefore, the safety of the battery is guaranteed from the aspect of the single battery, and an energy storage system with intrinsic safety is expected to be obtained.

As for the thermal runaway process of the battery cell, decomposition of the solid electrolyte film on the surface of the negative electrode, reaction and heat generation of the negative electrode and the electrolyte, melting of the separator, thermal runaway of the positive electrode material, decomposition of the electrolyte, and short circuit of the battery occur first, and the ejection of the electrolyte finally causes ignition and even explosion of the battery.

In order to solve the above problems, the means for ensuring the safety of the battery is mainly based on the electrolyte under the premise that the battery material system is relatively determined. Mainly, nonflammable electrolytes such as a flame-retardant electrolyte, an ionic liquid electrolyte, and a high-concentration electrolyte are used. However, the current flame-retardant electrolyte has good effect, but sacrifices the electrochemical performance of the battery.

Therefore, in order to solve the problems of thermal runaway and thermal safety of the lithium battery and ensure the electrochemical performance of the lithium battery, the application provides a flame-retardant structure, a preparation method of the flame-retardant structure and the lithium battery structure.

Example one

Referring to fig. 1, the present embodiment provides a flame retardant structure 100, and the flame retardant structure 100 includes a flame retardant membrane layer 101 and a polyethylene microsphere film layer 102.

The flame retardant separator layer 101 includes an organic polymer layer 1011 and a flame retardant 1012 disposed within the organic polymer layer 1011. Specifically, the flame-retardant membrane layer 101 may be a fiber membrane with a shell-core structure, the organic polymer layer 1011 is a shell, and the flame retardant 1012 in the organic polymer layer is a core. The fibrous structure may be formed by an electrospinning preparation process. When a certain high temperature condition is met, the organic polymer layer 1011 is melted, and the flame retardant 1012 in the organic polymer layer is released, so that the environment where the flame retardant structure 100 is located does not catch fire or explode.

The polyethylene microsphere film layer 102 includes a mixture of polyethylene microspheres 1021 and an organic solvent 1022, and the polyethylene microsphere film layer 102 is disposed on the outer surface of the flame retardant membrane layer 101. The polyethylene microsphere film layer 102 may be disposed on only one outer surface of the flame-retardant barrier layer 101, or may be disposed on the entire outer surface of the flame-retardant barrier layer 101. When the polyethylene microsphere film layer 102 is prepared, the polyethylene microspheres 1021 are dissolved in the organic solvent 1022 to form a mixture, when the content of the polyethylene microspheres 1021 is appropriate, a stable suspension can be formed, when the content of the polyethylene microspheres 1021 is kept constant, the mixture has spin-coating property, and the mixture can be coated on the outer surface of the flame-retardant membrane layer 101 to form the polyethylene microsphere film layer 102.

When the external environment reaches a certain temperature condition, the polyethylene microsphere film layer 102 on the outer surface of the flame-retardant diaphragm layer 101 is pre-melted, and when the flame-retardant structure 100 is applied to a lithium battery, the polyethylene microsphere film layer 102 is melted and then covers the surface of the negative electrode 300, so that the continuous transmission of lithium ions under a high-temperature condition can be blocked, and the purpose of inhibiting thermal runaway is further achieved.

The flame-retardant structure 100 comprises a flame-retardant membrane layer 101 and a polyethylene microsphere film layer 102, wherein the flame-retardant membrane layer 101 comprises an organic polymer layer 1011 and a flame retardant 1012 arranged in the organic polymer layer 1011, the polyethylene microsphere film layer 102 comprises a mixture of polyethylene microspheres 1021 and an organic solvent 1022, and the polyethylene microsphere film layer 102 is arranged on the outer surface of the flame-retardant membrane layer 101. When the flame retardant structure 100 is applied to a lithium battery, the lithium battery still has a certain discharge capacity in the thermal runaway process of the lithium battery, and as the temperature of the lithium battery is continuously raised, the polyethylene microsphere film layer 102 in the flame retardant structure 100 can be melted and covered on the surface of the battery cathode 300 to block the transmission of lithium ions, so that the thermal runaway is inhibited. When the temperature continuously rises, the flame retardant 1012 in the flame-retardant diaphragm layer 101 is released, so that the electrolyte 400 is not combustible, fire and explosion are avoided, the anode and cathode materials of the battery can still be recycled even though the battery fails, and the problem of resource waste is solved. Meanwhile, as the application does not adopt the flame-retardant electrolyte for flame retardance as in the traditional method, the flame-retardant structure is adopted, the problems of thermal runaway and thermal safety are solved, and the electrochemical performance of the battery is compatible.

In one embodiment, the organic polymer layer 1011 includes a mixture of one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate. For example, polyvinylpyrrolidone, polyvinyl alcohol, or a mixture of polyvinylpyrrolidone and polyvinyl alcohol, or a mixture of polyacrylonitrile and polymethyl methacrylate, or polyvinylidene fluoride-hexafluoropropylene copolymer is selected. Preferably, polyvinylidene fluoride-hexafluoropropylene copolymer is selected for use in this embodiment.

In one embodiment, the flame retardant 1012 includes any one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and methyl diphenyl phosphate. For example, triphenyl phosphate, triethyl phosphate, or methyl diphenyl phosphate is used. Preferably, triphenyl phosphate or methyl diphenyl phosphate is used in this embodiment.

In one embodiment, the flame retardant 1012 is present in the flame retardant barrier layer 101 in an amount between 5 wt% and 30 wt%. In practical applications, the content of the flame retardant 1012 can be set according to practical requirements, for example, 5 wt% or 7 wt% or 15 wt% or 30 wt%. Preferably, the content of the flame retardant 1012 in this embodiment is set to be 7 wt% to 15 wt%, and may be 7 wt% or 10 wt% or 15 wt%.

It should be noted that the more the flame retardant 1012 is, the better the flame retardant effect is, but the more the flame retardant 1012 is, the inactive substance in the lithium battery, and the energy density of the battery is decreased because the flame retardant 1012 is too much. Therefore, the self-extinguishing time and the energy density after the addition of the flame retardant 1012 need to be considered in practical use. In this example, the content of the flame retardant 1012 is set to 7 wt% to 15 wt%, and a good balance between the energy density of the battery and the self-extinguishing time can be achieved.

In one embodiment, the content of the polyethylene microspheres 1021 in the polyethylene microsphere film layer 102 is between 5 wt% and 40 wt%. In practical applications, the content of the polyethylene microspheres 1021 can be set as required, for example, 5 wt% or 20 wt% or 5 wt%.

Preferably, the content of the polyethylene microspheres 1021 in this embodiment is set between 10 wt% and 15 wt%, and may be 10 wt%, or 12 wt%, or 15 wt%, etc. When the content of the polyethylene microspheres 1021 is within 10 wt% to 15 wt%, a better suspension can be formed, and the liquid is more stable and can be coated more uniformly when used for spin coating.

In one embodiment, the loading of polyethylene microspheres 1021 is between 5 and 50mgcm^-2In the meantime. Preferably, the loading of polyethylene microspheres 1021 is between 5 and 20mgcm^-2In the meantime. Setting the loading capacity of the polyethylene microspheres 1021 to be 5-20mgcm^-2Meanwhile, on one hand, the polyethylene microspheres 1021 can be ensured to completely cover the surface of the negative electrode 300 when the external temperature rises, and on the other hand, the dosage is controlled as little as possible, so that the influence of the addition of the polyethylene microspheres 1021 on the overall energy density of the lithium battery is weakened.

In one embodiment, the organic solvent 1022 includes a mixture of any one or more of N-methylpyrrolidone, an aqueous solution in which a surfactant is dispersed, 1-methyl-2 pyrrolidone, dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, and ethanol. For example, N-methylpyrrolidone, an aqueous solution in which a surfactant is dispersed, or a mixture of 1-methyl-2-pyrrolidone and dimethyl sulfoxide, and the like.

Preferably, in this embodiment, the organic solvent 1022 is N-methylpyrrolidone.

Example two

The embodiment provides a method for manufacturing a flame retardant structure 100, and referring to fig. 2, the method for manufacturing the flame retardant structure 100 includes the following steps:

step S20, the mixture of organic polymer and flame retardant 1012 is made into a fiber-structured flame retardant membrane layer 101.

The formed flame-retardant membrane layer 101 is a fiber membrane with a shell-core structure, the organic polymer is a shell, and the flame retardant 1012 in the organic polymer is a core. The fibrous structure may be formed by an electrospinning preparation process. When a certain high temperature condition is met, the organic polymer layer 1011 is melted, and the flame retardant 1012 in the organic polymer layer is released, so that the environment where the flame retardant structure 100 is located does not catch fire or explode, and the thermal safety problem is avoided.

Step S22, coating a mixture of polyethylene microspheres 1021 and an organic solvent 1022 on the outer surface of the flame-retardant membrane layer 101 to form a polyethylene microsphere film layer 102.

Specifically, a mixture of polyethylene microspheres 1021 and organic solvent 1022 is first formed. In this embodiment, the polyethylene microspheres 1021 are first dissolved in the organic solvent 1022 to form a mixture, and when the content of the polyethylene microspheres 1021 is appropriate, a stable suspension can be formed, and when the content is kept constant, the mixture has spin coatability.

A mixture (i.e., a suspension) of polyethylene microspheres 1021 and organic solvent 1022 is then applied directly to the outer surface of flame retardant membrane layer 101 by spin coating.

Preferably, after coating, drying treatment is carried out, and specifically, the drying time can be set to be between 24 hours and 72 hours, and the drying temperature can be set to be between 20 ℃ and 60 ℃.

Further preferably, the drying time is set to be between 20 ℃ and 40 ℃ and the drying time is set to be between 24 hours and 32 hours. The lowest temperature is selected to reduce energy consumption in the drying process, and the higher drying temperature leads the film obtained by spin coating to crack, so the temperature range of 20-40 ℃ is comprehensively considered and selected. Meanwhile, the drying time is also reduced as much as possible to improve the drying efficiency, so the time range of 24 hours to 32 hours is comprehensively considered and selected.

When the formed flame-retardant structure 100 is applied to a lithium battery, the lithium battery still has a certain discharge capacity in the thermal runaway process of the lithium battery, and as the temperature of the lithium battery is continuously increased, the polyethylene microsphere film layer 102 in the flame-retardant structure 100 can be melted and covered on the surface of the battery cathode 300 to block the transmission of lithium ions, so that the thermal runaway is inhibited. When the temperature is continuously increased, the flame retardant 1012 in the flame-retardant diaphragm layer 101 is released, so that the electrolyte 400 is not combustible, fire and explosion are avoided, the anode and cathode 300 materials of the battery can still be recycled even though the battery fails, and the problem of resource waste is solved. Meanwhile, as the application does not use the flame-retardant electrolyte 400 for flame retardance as in the traditional method, but adopts the flame-retardant structure 100, the problems of thermal runaway and thermal safety are solved, and simultaneously, the electrochemical performance of the battery is compatible.

In one embodiment, referring to fig. 3, step S20, the step of forming the mixture of the organic polymer and the flame retardant 1012 into the flame retardant membrane layer 101 of the fiber structure, includes:

step S201, the organic polymer and the flame retardant 1012 are dissolved in the organic solvent 1022 according to a predetermined weight ratio to form a solution. The preset weight ratio can be set according to actual requirements and can be 1: 1.

Step S202, stretching and thinning the solution to form fibers under a preset voltage through an electrostatic spinning process, and manufacturing the flame-retardant membrane layer 101 with a fiber structure. Specifically, the solution can be loaded into a syringe with a precision needle, and the syringe can be advanced at a preset speed using a high voltage power supply to apply a high voltage to collect the resulting electrospun fiber on a grounded target.

In one embodiment, in step S201, the organic polymer includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate. For example, polyvinylpyrrolidone, polyvinyl alcohol, or a mixture of polyvinylpyrrolidone and polyvinyl alcohol, or a mixture of polyacrylonitrile and polymethyl methacrylate, or polyvinylidene fluoride-hexafluoropropylene copolymer is selected. Preferably, polyvinylidene fluoride-hexafluoropropylene copolymer is selected for use in this embodiment.

In one embodiment, in step S201, the flame retardant 1012 includes any one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and methyl diphenyl phosphate. For example, triphenyl phosphate, triethyl phosphate, or methyl diphenyl phosphate is used. Preferably, triphenyl phosphate or methyl diphenyl phosphate is used in this embodiment.

In one embodiment, in step S201, the organic solvent 1022 may include a solvent mixture of dimethylacetamide and acetone. Wherein the mass ratio of the dimethylacetamide to the acetone is 4: 6.

in a specific example, triphenyl phosphate and polyvinylidene fluoride-hexafluoropropylene copolymer (molecular weight 45.5 ten thousand) were dissolved in a solvent mixture of dimethylacetamide and acetone in a weight ratio of 1:1 (mass ratio 4:6) to give a transparent solution. The solution was then loaded into a syringe with a precision needle and the resulting electrospun fiber was collected on a grounded target pad of about 10 cm X10 cm using a high voltage power supply to apply a voltage of 15kV and propel the syringe at a rate of 0.4 ml per hour. Thereby forming flame retardant barrier layer 101.

In one embodiment, the flame retardant 1012 is present in the flame retardant barrier layer 101 in an amount between 5 wt% and 30 wt%. In practical applications, the content of the flame retardant 1012 can be set according to practical requirements, for example, 5 wt% or 7 wt% or 15 wt% or 30 wt%. Preferably, the content of the flame retardant 1012 in this embodiment is set to be 7 wt% to 15 wt%, and may be 7 wt% or 10 wt% or 15 wt%.

It should be noted that the more the flame retardant 1012 is, the better the flame retardant effect is, but the more the flame retardant 1012 is, the inactive substance in the lithium battery, and the energy density of the battery is decreased because the flame retardant 1012 is too much. Therefore, the self-extinguishing time and the energy density after the addition of the flame retardant 1012 need to be considered in practical use. In this example, the content of the flame retardant 1012 is set to 7 wt% to 15 wt%, and a good balance between the energy density of the battery and the self-extinguishing time can be achieved.

In one embodiment, in step S22, the content of the polyethylene microspheres 1021 in the polyethylene microsphere film layer 102 is between 5 wt% and 40 wt%. In practical applications, the content of the polyethylene microspheres 1021 can be set as required, for example, 5 wt% or 20 wt% or 5 wt%.

Preferably, the content of the polyethylene microspheres 1021 in this embodiment is set between 10 wt% and 15 wt%, and may be 10 wt%, or 12 wt%, or 15 wt%, etc. When the content of the polyethylene microspheres 1021 is within 10 wt% to 15 wt%, a better suspension can be formed, and the liquid is more stable and can be coated more uniformly when used for spin coating.

In one embodiment, the loading of polyethylene microspheres 1021 is between 5 and 50mgcm^-2In the meantime. Preferably, the loading of polyethylene microspheres 1021 is between 5 and 20mgcm^-2In the meantime. Setting the loading capacity of the polyethylene microspheres 1021 to be 5-20mgcm^-2Meanwhile, on one hand, the polyethylene microspheres 1021 can be ensured to completely cover the surface of the negative electrode 300 when the external temperature rises, and on the other hand, the dosage is controlled as little as possible, so that the influence of the addition of the polyethylene microspheres 1021 on the overall energy density of the lithium battery is weakened.

In one embodiment, the organic solvent 1022 includes a mixture of any one or more of N-methylpyrrolidone, an aqueous solution in which a surfactant is dispersed, 1-methyl-2 pyrrolidone, dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, and ethanol. For example, N-methylpyrrolidone, an aqueous solution in which a surfactant is dispersed, or a mixture of 1-methyl-2-pyrrolidone and dimethyl sulfoxide, and the like. Preferably, in this embodiment, the organic solvent 1022 is N-methylpyrrolidone.

EXAMPLE III

The present embodiment provides a lithium battery structure including a positive electrode 200, a negative electrode 300, and a flame retardant structure 100, referring to fig. 4.

The flame-retardant structure 100 is disposed between the positive electrode 200 and the negative electrode 300, the flame-retardant structure 100 includes a flame-retardant separator layer 101 and a polyethylene microsphere film layer 102 disposed on an outer surface of the flame-retardant separator layer 101, the flame-retardant separator layer 101 includes an organic polymer layer 1011 and a flame retardant 1012 disposed in the organic polymer layer 1011, and the polyethylene microsphere film layer 102 includes a mixture of polyethylene microspheres 1021 and an organic solvent 1022. The polyethylene microsphere film layer 102 may be disposed on an outer surface of the flame-retardant separator layer 101 facing the negative electrode 300, or may be disposed on an entire outer surface of the flame-retardant separator layer 101.

In addition, the lithium battery structure also comprises an electrolyte 400, and the lithium salt of the electrolyte 400 can be LiPF₆The solvent can be a mixture of two or three of ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, methyl ethyl carbonate and the like.

In the thermal runaway process of the lithium battery, the lithium battery still has a certain discharge capacity, and as the temperature of the lithium battery is continuously increased, for example, the temperature is increased to 120 ℃, the polyethylene microsphere film layer 102 in the flame retardant structure 100 can be melted and cover the surface of the battery cathode 300 to form an ion blocking film, so that the transmission of lithium ions is blocked, and further the thermal runaway is inhibited. When the temperature is continuously increased, for example, the temperature is increased to over 160 ℃, the flame retardant 1012 in the flame-retardant diaphragm layer 101 is released, so that the electrolyte 400 is incombustible, ignition and explosion are avoided, the anode and cathode 300 materials of the battery can still be recycled even though the battery fails, and the problem of resource waste is solved. Meanwhile, as the application does not use the flame-retardant electrolyte 400 for flame retardance as in the traditional method, but adopts the flame-retardant structure 100, the problems of thermal runaway and thermal safety are solved, and simultaneously, the electrochemical performance of the battery is compatible.

The present embodiment, the first embodiment and the second embodiment belong to the same inventive concept, and specific contents of the flame retardant structure 100 may refer to the specific descriptions in the first embodiment and the second embodiment, which are not repeated herein.

In addition, the present application also includes a process of testing the physicochemical properties of the flame retardant structure 100, and a process of testing the electrochemical performance of a battery assembled using the flame retardant structure 100.

The flame retardant structure 100 described above was tested for physicochemical properties:

(1) the flame retardant structure 100 and a conventional PP-PE-PP separator were tested for flammability and the duration of burning was observed after ignition.

(2) The shrinkability of the flame-retardant structure 100 and the common PP-PE-PP diaphragm at different temperatures was tested, mainly the shrinkage ratio of the diaphragms at 25 ℃, 40 ℃, 60 ℃, 80 ℃, 100 ℃ and 120 ℃.

Electrochemical performance of a battery assembled using the flame retardant structure 100 was tested:

first is a comparison of long cycle performance and rate performance at room temperature. Then the discharge specific capacity of the battery formed by the flame-retardant structure 100 and the common battery at different temperatures of 25 ℃, 40 ℃, 60 ℃, 80 ℃, 100 ℃ and 120 ℃ is obtained.

According to the test, the general PP-PE-PP separator is continuously burned, and the flame retardant structure 100 is extinguished in a short time. Referring to fig. 5, the capacity retention rate of the flame retardant structure 100 and the common separator after 30 cycles is not much poor in terms of the electrochemical performance of the battery, i.e., the flame retardant structure 100 does not adversely affect the battery performance, whereas the addition of a conventional flame retardant to the electrolyte has an effect on the battery performance.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.