阅读说明：本技术 一种用于锂离子电池的pet基重离子径迹复合隔膜及其制备方法 (PET (polyethylene terephthalate) basic weight ion track composite diaphragm for lithium ion battery and preparation method of PET basic weight ion track composite diaphragm ) 是由 陈林景 姚会军 张琦忠 段敬来 刘杰 胡正国 于 2021-08-05 设计创作，主要内容包括：本发明公开了一种用于锂离子电池的PET基重离子径迹复合隔膜及其制备方法。所述PET基重离子径迹微孔隔膜上孔道为均匀的直通孔道,孔道的直径为30～500nm,孔密度为3×10～(8)～2×10～(10)个/cm～(2),厚度为2～50μm；本发明还提供了一种PET基重离子径迹微孔复合隔膜,包括PET基重离子径迹微孔隔膜和表面涂覆层,表面涂覆层为均匀涂布的纳米陶瓷层。本发明采用的PET基重离子径迹隔膜由于其具有直通孔道特性,缩短了锂离子迁移距离,有利于提高锂离子电池倍率性能。本发明PET基重离子径迹微孔复合隔膜中的均匀涂覆层提高隔膜的孔隙率和抗穿刺性能,保证了锂离子电池的循环稳定性和安全性。(The invention discloses a PET (polyethylene terephthalate) basis weight ion track composite diaphragm for a lithium ion battery and a preparation method thereof. The pore channels on the PET basis weight ion track microporous membrane are uniform straight-through pore channels, the diameter of each pore channel is 30-500 nm, and the pore density is 3 multiplied by 10 8 ～2×10 10 Per cm 2 The thickness is 2-50 μm; the invention also relates toThe PET basis weight ion track microporous composite membrane comprises the PET basis weight ion track microporous membrane and a surface coating layer, wherein the surface coating layer is a uniformly coated nano ceramic layer. The PET basis weight ion track diaphragm adopted by the invention has the characteristic of a through hole channel, so that the lithium ion migration distance is shortened, and the rate performance of the lithium ion battery is favorably improved. The uniform coating layer in the PET basis weight ion track microporous composite diaphragm improves the porosity and the puncture resistance of the diaphragm, and ensures the cycle stability and the safety of a lithium ion battery.)

1. A PET basis weight ion track microporous diaphragm, the pore channel on it is the even straight-through pore channel;

the diameter of the pore channel is 30-500 nm;

the pore density of the PET basic weight ion track microporous diaphragm is 3 multiplied by 10⁸～2×10¹⁰Per cm²；

The thickness of the PET basis weight ion track microporous membrane is 2-50 mu m.

2. A method of making a PET based weight ion track microporous membrane as defined in claim 1, comprising the steps of:

s1, irradiating the PET film by heavy ions to obtain an irradiated PET basis weight ion track film;

s2, chemically etching the PET basis weight ion track film;

and S3, after the chemical etching is finished, drying and then carrying out oxygen plasma treatment to obtain the PET basis weight ion track microporous diaphragm.

3. The method of claim 2, wherein: in step S1, the heavy ions are xenon ions, bismuth ions, or tantalum ions;

the ion energy of the heavy ions is 0.1-100 MeV/u;

the irradiation density is 3 × 10⁸～2×10¹⁰ions/cm²。

4. The production method according to claim 2 or 3, characterized in that: in the step S2, the etching solution adopted by the chemical etching is a sodium hydroxide solution, and the molar concentration is 1-6 mol/L;

the chemical etching temperature is 30-70 ℃, and the time is 1-50 min;

in step S3, the conditions of the oxygen plasma treatment are: and treating for 3-8 min under a vacuum condition.

5. A PET basis weight ion track microporous composite membrane comprising the PET basis weight ion track microporous membrane and a surface coating layer;

the surface coating layer is a nano ceramic layer which is uniformly coated.

6. The PET basis weight ion track microporous composite membrane of claim 5, characterized in that: the nano ceramic layer is made of TiO₂、Al₂O₃、ZrO₂、SiO₂Or MOFs;

the thickness of the surface coating layer is 2-5 mu m.

7. A method of making the PET basis weight ion track microporous composite membrane of claim 5 or 6 comprising the steps of:

the PET-based heavy ion-tracking microporous membrane of claim 1, wherein the surface coating layer is coated on the surface of the PET-based heavy ion-tracking microporous membrane.

8. The method according to claim 7, wherein: PVDF or PTFE is adopted as a binder for coating the surface coating layer;

the mass ratio of the material of the surface coating layer to the binder is 3-9: 1.

9. use of the PET basis weight ion-traced microporous separator of claim 1 or the PET basis weight ion-traced microporous composite separator of claim 5 or 6 as a separator for a lithium ion battery.

10. Use according to claim 9, characterized in that: the electrolyte adopted by the lithium ion battery is any one of the following 1) to 4):

1)LiPF₆ethylene carbonate, diethyl carbonate;

2)LiPF₆ethylene carbonate, diethyl carbonate, ethyl methyl carbonate;

3)LiPF₆ethylene carbonate, diethyl carbonate, dimethyl carbonate;

4)LiPF₆ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate.

Technical Field

The invention relates to a PET (polyethylene terephthalate) basic weight ion track composite diaphragm for a lithium ion battery and a preparation method thereof, belonging to the field of lithium ion battery diaphragms.

Background

The lithium ion battery is used as a simple and efficient energy storage device, plays a key role in the development and application of new energy, and greatly promotes the popularization and application of portable electronic equipment. Currently, the electric automobile industry is developing vigorously, triggering the huge market demand of lithium ion batteries. Among the four basic components of a lithium ion battery (positive electrode, electrolyte, separator and negative electrode), the separator not only accounts for one third of the cost of the battery, but also greatly affects the safety performance of the battery.

The main characteristics of the lithium ion battery diaphragm are structural characteristics, mechanical characteristics and physical and chemical characteristics. The structural characteristics mainly comprise thickness, porosity, pore size and distribution thereof, and air permeability; the mechanical properties of the diaphragm are researched, and the mechanical strength such as tensile strength, puncture strength and the like of the diaphragm are mainly considered; the physical and chemical properties comprise chemical stability, electrochemical stability, wettability, lithium ion conductivity, thermal stability, self-closing property and the like.

The films currently used as lithium ion battery separators mainly include polyolefin films, non-woven fabric separators and composite separators. Among them, polyolefin separators have been implemented for large-scale commercial applications, but problems still remain: electrolyte leakage due to poor affinity with the electrolyte and limited thermal stability threaten the safety of the lithium ion battery. Accordingly, there is a need for improvements to existing diaphragms.

Disclosure of Invention

The invention aims to provide a PET (polyethylene terephthalate) basis weight ion track diaphragm for a lithium ion battery and a composite diaphragm thereof, which have the characteristics of adjustable and controllable pore density and small pore size distribution.

The invention firstly provides a PET basis weight ion track microporous membrane, wherein the pore passages on the membrane are uniform straight-through pore passages;

the diameter of the pore channel is 30-500 nm;

the pore density of the PET basic weight ion track microporous diaphragm is 3 multiplied by 10⁸～2×10¹⁰Per cm²；

The thickness of the PET basis weight ion track microporous membrane is 2-50 mu m.

The invention also provides a preparation method of the PET basis weight ion track microporous membrane, which comprises the following steps:

s1, irradiating the PET film by heavy ions to obtain an irradiated PET basis weight ion track film;

s2, chemically etching the PET basis weight ion track film;

and S3, after the chemical etching is finished, drying and then carrying out oxygen plasma treatment to obtain the PET basis weight ion track microporous diaphragm.

In the above preparation method, in step S1, the heavy ions are xenon ions, bismuth ions, or tantalum ions;

the ion energy of the heavy ions is 0.1-100 MeV/u, for example, the ion energy of xenon is 19.5MeV/u, the ion energy of tantalum is 12.5MeV/u, and the ion energy of bismuth is 9.8 MeV/u;

the irradiation density is 3 × 10⁸～2×10¹⁰ions/cm²。

In the preparation method, in step S2, the etching solution adopted by the chemical etching is a sodium hydroxide solution, and the molar concentration is 1-6 mol/L;

the chemical etching temperature is 30-70 ℃, and the time is 1-50 min.

In the above preparation method, in step S3, the oxygen plasma treatment conditions are as follows: and treating for 3-8 min under a vacuum condition.

On the basis of the PET basis weight ion track microporous membrane, the invention further provides a PET basis weight ion track microporous composite membrane which comprises the PET basis weight ion track microporous membrane and a surface coating layer;

the surface coating layer is a nano ceramic layer which is uniformly coated.

In the composite diaphragm, the nano ceramic layer can be made of TiO₂、Al₂O₃、ZrO₂、SiO₂Or MOFs;

the thickness of the surface coating layer is 2-5 mu m.

The composite membrane can be prepared according to the following method:

coating the surface coating layer on the surface of the IET basic weight ion track microporous membrane;

PVDF or PTFE is adopted as a binder for coating the surface coating layer;

the mass ratio of the material of the surface coating layer to the binder is 4-9: 1;

the solvent can be removed by a constant-temperature drying method, and the temperature can be 30-100 ℃.

The electrolyte applicable to the microporous diaphragm or the composite diaphragm provided by the invention is LiPF₆Ethylene Carbonate (EC) + diethyl carbonate (DEC), LiPF₆Ethylene Carbonate (EC) + diethyl carbonate (DEC) + Ethyl Methyl Carbonate (EMC), LiPF₆Ethylene Carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC), LiPF₆Ethylene Carbonate (EC) + dimethyl carbonate (DMC) + Ethyl Methyl Carbonate (EMC);

it should be noted that the PET-based heavy ion track microporous membrane and the composite membrane thereof provided by the invention can be applied to a lithium ion battery with liquid electrolyte, and LiPF₆The concentration may be 1mol L^-1、2mol L^-1、3mol L^-1。

The PET basic weight ion track microporous composite diaphragm provided by the invention adopts the heavy ion track membrane with adjustable and controllable pore density and uniform pore diameter as the base membrane, and the PET has excellent physical and mechanical properties, good electrical insulation, long-term use at 120 ℃, better fatigue resistance and size stability, and ensures the stability of the heavy ion track microporous diaphragm under the high temperature condition.

The PET basis weight ion track diaphragm adopted by the invention has the characteristic of a through hole channel, so that the lithium ion migration distance is shortened, and the rate performance of the lithium ion battery is favorably improved. The uniform coating layer in the PET basis weight ion track microporous composite diaphragm improves the porosity and the puncture resistance of the diaphragm, and ensures the cycle stability and the safety of a lithium ion battery.

Drawings

Figure 1 is a schematic representation of a PET basis weight ion-track composite membrane of the present invention.

Figure 2 is a scanning electron microscope image of a PET-based heavy ion track membrane made according to example 1 of the present invention.

Figure 3 is a scanning electron microscope image of a PET-based heavy ion track composite membrane made according to example 2 of the present invention.

Fig. 4 is a 0.1C charge-discharge curve diagram of a PET-based heavy ion tracking separator lithium ion battery prepared in example 1 of the present invention.

Fig. 5 is a charge-discharge cycle chart of a PET-based heavy ion-tracking separator lithium ion battery 1C prepared in example 1 of the present invention.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The invention provides a composite diaphragm based on a PET basis weight ion track microporous membrane, wherein the pore passages on the PET basis weight ion track microporous membrane are directionally and uniformly arranged, so that the transmission uniformity of lithium ions in the diaphragm is ensured, and the damage of local unevenness to a positive and negative electrode material is avoided. The functional layer is coated on the surface of the PET basis weight ion track microporous membrane, so that the puncture resistance of the diaphragm is further enhanced, and the safety performance of the lithium ion battery is improved; in addition, the coating layer also improves the porosity of the diaphragm, so that the diaphragm has higher retention rate of electrolyte. The battery diaphragm provided by the invention can realize long-term stable circulation of the lithium ion battery under the high-temperature condition.

A schematic of the composite separator of the present invention based on PET basis weight ion-traced microporous membrane is shown in figure 1.

Examples 1,

1) Irradiating a PET film with the thickness of 12 μm by using heavy ion beams provided by a heavy ion accelerator, wherein the heavy ions provided by the accelerator are xenon ions, the irradiation energy is 19.5MeV/u, and the irradiation density is 7 multiplied by 10⁸ions/cm²。

2) Carrying out chemical etching on the PET film subjected to heavy ion irradiation at the water bath temperature of 40 ℃, wherein the etching solution is 5mol L^-1The etching time of the NaOH solution is 16min, after air blast drying, the direct PET basic weight ion track microporous membrane with the aperture of about 230nm is obtained by oxygen plasma treatment (alternating voltage of 220V, frequency of 50Hz and vacuum condition) for 5min, and the thickness of the direct PET basic weight ion track microporous membrane is about 12 μm.

The scanning electron microscope image of the PET-based heavy ion track microporous membrane prepared in this example is shown in fig. 2, and it can be seen from fig. 2 that the microporous membrane prepared by the method of the present invention has uniform pore distribution, uniform pore diameter, and good consistency.

Preparing a positive pole piece by taking lithium iron phosphate as a positive pole material and LiPF₆Ethylene carbonate and diethyl carbonate (1:1) are used as electrolyte, a commercial lithium sheet is used as a negative electrode, and the PET basis weight ion track microporous membrane prepared in the embodiment is used as a diaphragm to assemble the button cell.

Testing the performance of the battery in a blue battery testing system under the following test conditions: the voltage is 2.4V-4.2V, the multiplying power is 0.2C, and the result is as follows:

the charging and discharging curve of the PET basis weight ion track microporous diaphragm lithium ion battery at 0.1C is shown in figure 4, and the specific capacity can reach 152.9mAh/g in a dark place. As shown in FIG. 5, the 1C charge-discharge cycle chart shows that under the condition, the first discharge specific capacity is 139.6mAh/g, the stable cycle is 220 times, and the retention rate is more than 95%.

Examples 2,

1) Irradiating a PET film with the thickness of 12 μm by using heavy ion beams provided by a heavy ion accelerator, wherein the heavy ions provided by the accelerator are xenon ions, the irradiation energy is 19.5MeV/u, and the irradiation density is 7 multiplied by 10⁸ions/cm²。

2) Carrying out chemical etching on the PET film subjected to heavy ion irradiation at the water bath temperature of 40 ℃, wherein the etching solution is 5mol L^-1Etching with NaOH solution for 16min, drying by blowing, and treating with oxygen plasma (alternating voltage 220V, frequency 50Hz, vacuum condition) for 5min to obtain the straight-through PET basic weight ion track microporous membrane with the aperture of 230 nm.

3) Coating TiO on the surface of a PET base film₂Coating TiO with the thickness of 5 mu m on the surface of the base film by adopting a blade coating process₂Slurry (in which TiO is present)₂Mass ratio to binder PVDF 4:1), the thickness of the coating layer after drying was about 3 μm. The PET basis weight ion track microporous composite membrane for the lithium ion battery is obtained, and the thickness is about 15 mu m.

The scanning electron microscope image of the PET-based heavy ion-track composite membrane prepared in this example is shown in fig. 3, and it can be seen that a layer of granular material is coated on the surface of the PET-based membrane.

Due to Al₂O₃The protective layer has high mechanical strength, and can be coated on the surface of the PI base film to form a protective layer, so that the puncture resistance of the diaphragm can be improved.

A porous structure can be formed in the coating layer due to evaporation of the solvent (NMP) during the drying process, as shown in fig. 3, and the porosity of the separator can be increased.