阅读说明：本技术 一种三层共挤锂电池隔膜及其制备方法 (Three-layer co-extrusion lithium battery diaphragm and preparation method thereof ) 是由 巢雷 李正林 翁星星 陈朝晖 于 2020-12-28 设计创作，主要内容包括：本发明公开了一种三层共挤锂电池隔膜及其制备方法,所述隔膜为A/B/A三层结构,所述A层包括如下重量百分比的组分：尼龙25～55wt％、乙烯-乙烯醇共聚物5～15wt％、A层造孔剂30～70wt％,所述B层包括如下重量百分比的组分：超高分子量聚乙烯30～70wt％、B层造孔剂30～70wt％。本发明通过耐高温的尼龙层与具有低闭孔温度的超高分子量聚乙烯层相结合,利用共挤技术形成A/B/A三层结构,其中A层、B层具有极大的熔点落差；当锂电池发生热失控时,具有低闭孔温度的B层发生闭孔,阻断电池反应的发生,耐高温的A层提供热保护,防止隔膜坍塌引起短路,两者充分发挥协同作用,降低锂电池发生起火、爆炸的概率,建立锂电池内部安全保护,提升安全性。(The invention discloses a three-layer co-extrusion lithium battery diaphragm and a preparation method thereof, wherein the diaphragm is of an A/B/A three-layer structure, and the A layer comprises the following components in percentage by weight: 25-55 wt% of nylon, 5-15 wt% of ethylene-vinyl alcohol copolymer and 30-70 wt% of a layer A pore-forming agent, wherein the layer B comprises the following components in percentage by weight: 30-70 wt% of ultra-high molecular weight polyethylene and 30-70 wt% of B-layer pore-forming agent. The invention combines a high-temperature resistant nylon layer with an ultra-high molecular weight polyethylene layer with low closed pore temperature, and utilizes a co-extrusion technology to form an A/B/A three-layer structure, wherein the A layer and the B layer have extremely large melting point drop; when the lithium cell takes place the thermal runaway, the B layer that has low obturator temperature takes place the obturator, blocks the emergence of battery reaction, and high temperature resistance A layer provides thermal protection, prevents that the diaphragm from collapsing and arousing the short circuit, and both full play synergistic effect reduce the lithium cell and take place the probability of catching a fire, explosion, establish the inside safety protection of lithium cell, promote the security.)

1. A three-layer co-extrusion lithium battery diaphragm is characterized in that: the diaphragm is of an A/B/A three-layer structure, and the A layer comprises the following components in percentage by weight: 25-55 wt% of nylon, 5-15 wt% of ethylene-vinyl alcohol copolymer and 30-70 wt% of a layer A pore-forming agent, wherein the layer B comprises the following components in percentage by weight: 30-70 wt% of ultra-high molecular weight polyethylene and 30-70 wt% of B-layer pore-forming agent.

2. The three-layer co-extruded lithium battery separator as claimed in claim 1, wherein: the nylon is one of PA66 or a mixture of PA6 and PA 66.

3. The three-layer co-extruded lithium battery separator as claimed in claim 1, wherein: the ethylene-vinyl alcohol copolymer has an ethylene content of 24-48 mol%.

4. The three-layer co-extruded lithium battery separator as claimed in claim 1, wherein: the layer A pore-forming agent is polycaprolactone, and the layer B pore-forming agent is white oil.

5. The three-layer co-extruded lithium battery separator as claimed in claim 1, wherein: the thickness of the diaphragm is 6-30 mu m, the thickness of the layer A is 2-10 mu m, and the thickness of the layer B is 2-10 mu m.

6. A preparation method of a three-layer co-extrusion lithium battery diaphragm is characterized by comprising the following steps:

(1) extrusion and melting: putting the raw materials into two extruders according to the weight percentage ratio, extruding the raw materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping to form a three-layer diaphragm;

(2) longitudinal stretching: longitudinally stretching the three layers of membranes to obtain a membrane C;

(3) and (3) transverse stretching: transversely stretching the membrane D to obtain a membrane D;

(4) washing to form a hole: soaking the membrane D into dichloromethane liquid, taking out and washing to obtain a membrane E;

(5) heat setting and rolling: and (5) taking the membrane E for high-temperature shaping, and finally rolling to obtain the finished battery diaphragm.

7. The preparation method of the three-layer co-extrusion lithium battery diaphragm as claimed in claim 6, wherein the preparation method comprises the following steps: the extrusion process in the step (1) comprises the following steps: the extrusion temperature is 100-280 ℃, the rotating speed of the extruder is 100-200 rpm, the extrusion amount is 200-500 kg/h, and the temperature of the cooling roller is 10-40 ℃.

8. The preparation method of the three-layer co-extrusion lithium battery diaphragm as claimed in claim 6, wherein the preparation method comprises the following steps: the longitudinal stretching temperature in the step (2) is 80-180 ℃, the stretching ratio is 2-8 times, the transverse stretching temperature in the step (3) is 100-180 ℃, and the stretching ratio is 2-8 times.

9. The preparation method of the three-layer co-extrusion lithium battery diaphragm as claimed in claim 6, wherein the preparation method comprises the following steps: the temperature of dichloromethane in the step (4) is 5-30 ℃, and the circulating flow is 3-8 m³。

10. The preparation method of the three-layer co-extrusion lithium battery diaphragm as claimed in claim 6, wherein the preparation method comprises the following steps: and (3) the heat setting temperature in the step (5) is 120-180 ℃.

Technical Field

The invention relates to the technical field of new energy, in particular to a three-layer co-extrusion lithium battery diaphragm and a preparation method thereof.

Background

Under the guidance of national policies, the demand of the electric vehicle market mainly comprising electric automobiles on lithium ion batteries is continuously increased, the safety problem of the batteries is widely regarded in the process of developing high-power lithium ion battery systems, and the existing problems are urgently needed to be further solved.

When extreme environments such as collision, deformation, or internal short circuit occur, a large amount of heat is generated inside the lithium battery, causing the temperature of the battery to rise, resulting in thermal runaway of the battery. The most widely used electrolyte system in commercial lithium ion batteries is mixed carbonate solution of LiPF6, and such solvents have high volatility, low flash point and are very easy to burn. When a certain temperature is reached, a series of decomposition reactions are caused, so that the thermal balance of the battery is destroyed, and the battery burns, and even explodes in severe cases. The thermal runaway of the lithium battery has the characteristics of burstiness and high heating rate, and an internal safety protection mechanism is very necessary to establish. Therefore, a three-layer co-extrusion lithium battery diaphragm and a preparation method thereof are provided.

Disclosure of Invention

The invention aims to provide a three-layer co-extrusion lithium battery diaphragm and a preparation method thereof, and aims to solve the problems in the background technology.

In order to solve the technical problems, the invention provides the following technical scheme: a three-layer co-extrusion lithium battery diaphragm is of an A/B/A three-layer structure, and the A layer comprises the following components in percentage by weight: 25-55 wt% of nylon, 5-15 wt% of ethylene-vinyl alcohol copolymer and 30-70 wt% of a layer A pore-forming agent, wherein the layer B comprises the following components in percentage by weight: 30-70 wt% of ultra-high molecular weight polyethylene and 30-70 wt% of B-layer pore-forming agent.

Further, the nylon is one of PA66 or a mixture of PA6 and PA 66.

Further, the ethylene content in the ethylene-vinyl alcohol copolymer is 24-48 mol%.

Further, the A-layer pore-forming agent is polycaprolactone, and the B-layer pore-forming agent is white oil.

Further, the thickness of the diaphragm is 6-30 microns, the thickness of the layer A is 2-10 microns, and the thickness of the layer B is 2-10 microns.

A preparation method of a three-layer co-extrusion lithium battery diaphragm comprises the following steps:

(1) extrusion and melting: putting the raw materials into two extruders according to the weight percentage ratio, extruding the raw materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping to form a three-layer diaphragm;

(2) longitudinal stretching: longitudinally stretching the three layers of membranes to obtain a membrane C; the longitudinal strength of the membrane is improved;

(3) and (3) transverse stretching: transversely stretching the membrane D to obtain a membrane D; the transverse strength of the membrane is improved;

(4) washing to form a hole: soaking the membrane D into dichloromethane liquid, taking out and washing to obtain a membrane E; dissolving the layer A of pore-forming agent and the layer B of pore-forming agent into dichloromethane liquid to form a microporous structure;

(5) heat setting and rolling: and (4) taking the membrane E for high-temperature shaping, further improving the thermal stability of the membrane, and finally rolling to obtain the finished battery diaphragm.

Further, the extrusion process in the step (1) is as follows: the extrusion temperature is 100-280 ℃, the rotating speed of the extruder is 100-200 rpm, the extrusion amount is 200-500 kg/h, and the temperature of the cooling roller is 10-40 ℃.

Further, the longitudinal stretching temperature in the step (2) is 80-180 ℃, the stretching ratio is 2-8 times, the transverse stretching temperature in the step (3) is 100-180 ℃, and the stretching ratio is 2-8 times.

Further, the temperature of dichloromethane in the step (4) is 5-30 ℃, and the circulating flow is 3-8 m³。

Further, the heat setting temperature in the step (5) is 120-180 ℃.

In the technical scheme, as a preferable scheme, the melting point of nylon is more than 220 ℃, PA66 is selected as the nylon, and the melt flow rate (275 ℃ and 5kg) is 1-20 g/10 min; the molecular weight of the ultra-high molecular weight polyethylene is more than 150 ten thousand; the ethylene-vinyl alcohol copolymer has a melting point of 158 to 195 ℃ and a melt flow rate of (2)2.16kg at 10 ℃) of 2-15 g/10 min; the pore-forming agent of the layer A is Polycaprolactone (PCL), the melt flow rate (160 ℃, 2.16kg) is 0.1-15 g/10min, and the melting point is more than 40 ℃; the B-layer pore-forming agent is white oil, and the kinematic viscosity (40 ℃) of the B-layer pore-forming agent is 43-49 mm²A flash point of greater than 180 ℃.

Compared with the prior art, the invention has the following beneficial effects:

the three-layer co-extrusion lithium battery diaphragm and the preparation method thereof form an A/B/A three-layer structure by combining a high-temperature-resistant nylon layer and an ultra-high molecular weight polyethylene layer with low closed pore temperature and utilizing a co-extrusion technology, wherein the A layer is mainly a high-temperature-resistant nylon layer, the B layer is an ultra-high molecular weight polyethylene layer with low closed pore temperature, the ultra-high molecular weight melting points of the nylon and the polyethylene have a difference of about 100 ℃, and the melting point drop is very large; when the lithium battery is out of control thermally, the layer B with low pore closing temperature is closed, the lithium ion access channel is closed, the battery reaction is blocked, the high-temperature-resistant layer A provides thermal protection, the diaphragm is prevented from collapsing, and the lithium battery is prevented from being short-circuited due to contact of two electrodes, the two layers fully play a synergistic effect, the probability of fire and explosion of the lithium battery is reduced, the internal safety protection of the lithium battery is established, and the safety is improved.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

(1) Preparing raw materials: weighing 55gPA66, 10g of ethylene-vinyl alcohol copolymer, 35g of polycaprolactone, 65g of ultrahigh molecular weight polyethylene and 35g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 2

(1) Preparing raw materials: weighing 50gPA66, 10g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 60g of ultrahigh molecular weight polyethylene and 40g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 3

(1) Preparing raw materials: weighing 50gPA66, 10g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 50g of ultrahigh molecular weight polyethylene and 50g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 4

(1) Preparing raw materials: weighing 50gPA66, 10g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 40g of ultrahigh molecular weight polyethylene and 60g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 5

(1) Preparing raw materials: weighing 50gPA66, 10g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 30g of ultrahigh molecular weight polyethylene and 70g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 6

(1) Preparing raw materials: weighing 55gPA66, 5g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 30g of ultrahigh molecular weight polyethylene and 70g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 120 ℃ and the stretching ratio of 6 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Example 7

(1) Preparing raw materials: weighing 50gPA66, 10g of ethylene-vinyl alcohol copolymer, 40g of polycaprolactone, 30g of ultrahigh molecular weight polyethylene and 70g of white oil for later use;

(2) extrusion and melting: putting the raw materials into two extruders, setting the extrusion temperature to be 280 ℃, the rotating speed of the extruders to be 150rpm, the extrusion amount to be 350kg/h, extruding the materials to a cooling roller through a co-extrusion die head after melting and plasticizing, and cooling and shaping the materials to form a three-layer diaphragm, wherein the temperature of the cooling roller is 25 ℃;

(3) longitudinal stretching: longitudinally stretching the three layers of membranes at the stretching temperature of 120 ℃ and the stretching ratio of 2 times to obtain membranes C;

(4) and (3) transverse stretching: transversely stretching the membrane D at the stretching temperature of 130 ℃ and the stretching ratio of 2 times to obtain a membrane D;

(5) washing to form a hole: soaking the membrane D in dichloromethane liquid at dichloromethane temperature of 5 deg.C and circulation flow of 8m³To prepare a membrane E;

(6) heat setting and rolling: and (3) taking the membrane E for high-temperature setting, wherein the heat setting temperature is 135 ℃, and finally, rolling to obtain the finished battery diaphragm.

Comparative example

Comparative example 1 is an ultra high molecular weight polyethylene alumina ceramic coated membrane produced by a company using a wet and coating process.

Experiment of

The battery separators obtained in examples 1 to 7 and comparative example were used to prepare samples, the properties of which were measured, and the measurement results were recorded:

wherein, the air permeability of the sample is tested by adopting a royal jelly type air permeability instrument;

testing the tensile strength and the puncture strength of the sample by adopting a universal mechanical tester;

testing the liquid absorption rate of the sample by adopting a weighing method;

and testing the heat shrinkage rate of the sample by using a vacuum oven dryer, wherein the testing temperature is 120 ℃, the testing time is 30min, and the size change of the tested sample is detected.

From the data in the table above, it is clear that the following conclusions can be drawn:

the battery separators obtained in examples 1 to 7 were compared with the battery separator obtained in the comparative example, and the results of the measurements were found to be,

1. the battery separators obtained in examples 1 to 7 have significantly increased air permeability, significantly increased tensile strength, puncture strength, and liquid absorption data, and significantly decreased thermal shrinkage data in examples 1 to 4, compared to the battery separators obtained in comparative examples, which fully indicates that the present invention can significantly improve the overall performance of the battery separators manufactured, and that, due to the inverse relationship between air permeability and porosity, it can be seen that the battery separators manufactured in examples 1 to 4 have smaller porosity, can promote rapid closing of the battery separators manufactured at high temperatures, restrict the passage of ions, and, due to the significantly decreased thermal shrinkage, can prevent short-circuiting of the batteries, and improve the safety of the batteries manufactured;

2. the battery diaphragms obtained in the examples 1 to 5 are compared with each other, the air permeability data is gradually reduced along with the increase of the amount of the pore-forming agent, the air permeability of the diaphragm is improved, the pores of the manufactured battery diaphragms are gradually increased, and the increase of the amount of the pore-forming agent is known to be unfavorable for the safety of the batteries therewith;

3. the battery separators obtained in examples 5 to 7 were compared with each other:

in example 5, compared with example 6, the tensile strength and puncture strength of the prepared battery separator were reduced by reducing the amount of the ethylene-vinyl alcohol copolymer without changing the amount of the pore-forming agent, which indicates that the ethylene-vinyl alcohol copolymer can enhance the adhesion between layers;

in example 5, the tensile ratios in the longitudinal stretching and the transverse stretching were decreased to lower the tensile strength, puncture strength, and liquid absorption rate data, as compared with example 7, in the same amount of the components, and it was found that the change in the tensile ratio in the longitudinal stretching and the transverse stretching affects the performance of the battery separator produced.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.