CN114188667A

CN114188667A - Composite diaphragm of rechargeable lithium ion battery and preparation method and application thereof

Info

Publication number: CN114188667A
Application number: CN202111368237.1A
Authority: CN
Inventors: 何伟东; 杨梦邱; 刘远鹏; 袁博韬; 韩杰才; 杨春晖
Original assignee: Harbin Institute of Technology; Chongqing Research Institute of Harbin Institute of Technology
Current assignee: Harbin Institute of Technology; Chongqing Research Institute of Harbin Institute of Technology
Priority date: 2021-11-18
Filing date: 2021-11-18
Publication date: 2022-03-15

Abstract

The invention discloses a composite diaphragm of a rechargeable lithium ion battery and a preparation method and application thereof, belonging to the technical field of lithium ion batteries. The invention adopts a liquid phase method to dope talcum powder in a PVDF matrix to prepare a composite diaphragm and uses LiFePO₄A lithium ion battery with high multiplying power, safety and low cost is designed for the anode. The invention adopts the talcum powder as the diaphragm additive, so that the wettability and the heat resistance of the composite diaphragm are greatly improved. The rate capability and the cycle performance of the lithium iron phosphate anode prepared by the lithium iron phosphate anode at normal temperature are obviously improved.

Description

Composite diaphragm of rechargeable lithium ion battery and preparation method and application thereof

Technical Field

The invention relates to a composite diaphragm of a rechargeable lithium ion battery, a preparation method and application thereof, belonging to the technical field of lithium ion batteries.

Background

Rechargeable Lithium Ion Batteries (LiBs) have the advantages of high working voltage, no memory effect, long service life and the like, and have become hot spots of domestic and foreign research in order to meet the increasing demands of novel portable electronic equipment, remote electric vehicles, solar energy/wind energy storage and the like. With the increasing demand for higher energy, there is a constant need to optimize the key components (cathodes, anodes, electrolytes, separators) in LIBs. Wherein the separator is a non-active component, located between the cathode and the anode, and plays a crucial role in the capacity, cost-effectiveness, lifetime and safety of lithium ion batteries.

Existing polyolefin-based materials, such as Polyethylene (PE) and polypropylene (PP), are widely used as commercial separators of LIBs due to high mechanical strength and low cost, however, their undesirable thermal stability and wettability limit their further applications. Since polyvinylidene fluoride (PVDF) has a strong electron withdrawing group functional group and a low crystallinity, has good thermal stability and good wettability, a great deal of research is currently being conducted around PVDF-based separators to solve the above problems. However, their further development is limited in two ways: firstly, the PVDF base film has low mechanical strength and firm electrodes, and lithium dendrites grown in the charging and discharging process can pierce through a diaphragm to cause short circuit of a battery; secondly, the Li anode has high activity, which causes the discharge capacity to decay rapidly. To break through these bottlenecks, a number of strategies are used to improve the overall performance of PVDF-based membranes. The existing studies show that inorganic particles (ZrO)₂，SiO₂，Al₂O₃，TiO₂) The electrolyte absorption rate, the mechanical strength and the thermal stability of the composite polymer diaphragm are improved to a certain extent by adding or modifying the composite polymer diaphragm through a wet method. However,the compatibility between the electrolyte and the doped inorganic particles is poor, so that the battery assembled by the composite diaphragms has poor rate performance, serious safety problem and low specific discharge capacity.

Therefore, it is necessary to provide a high-rate, safe, low-cost composite separator for lithium ion batteries.

Disclosure of Invention

The invention provides a composite diaphragm of a rechargeable lithium ion battery, a preparation method and application thereof, aiming at solving the technical problems.

The technical scheme of the invention is as follows:

the composite diaphragm of the rechargeable lithium ion battery is prepared from composite slurry, wherein the composite slurry comprises the following raw materials in parts by weight: 83-90% of organic solvent, 9-14% of diaphragm base material and 1-3% of diaphragm additive.

Further limit, the organic solvent is one or more than two of acetone, N-methyl pyrrolidone, N-dimethyl formamide and absolute ethyl alcohol which are mixed according to any proportion.

Further limiting, the diaphragm base material is one or more than two of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate and polysulfone which are mixed in any proportion.

Further limited, the membrane additive is talcum powder and/or montmorillonite.

The preparation method of the composite diaphragm of the rechargeable lithium ion battery comprises the following steps:

uniformly mixing a diaphragm base material and an organic solvent, stirring for 6-8 hours under the condition of an oil bath at 50-80 ℃ until the diaphragm base material is completely dissolved, and cooling to room temperature to obtain a diaphragm base material solution;

adding a diaphragm additive into the diaphragm base material solution obtained in the step one, and stirring at room temperature for 12-24 hours to obtain a composite slurry;

and step three, uniformly coating the composite slurry obtained in the step two on a glass plate, and drying for 8-12 hours at the temperature of 60 ℃ in vacuum to obtain the composite diaphragm.

Further defined, the composite separator had a thickness of 25 μm.

The lithium ion battery prepared by adopting the composite diaphragm comprises a positive plate, a negative plate, the composite diaphragm and electrolyte, wherein the composite diaphragm is arranged between the positive plate and the negative plate; the lithium iron phosphate of the positive plate, the lithium of the negative plate and the electrolyte are 1.0M LiPF₆ in EC:DEC:EMC＝1:1:1Vol％。

Further, the lithium ion battery is a primary battery or a secondary battery.

The invention has the beneficial effects that:

the invention adopts a liquid phase method to dope talcum powder in a PVDF matrix to prepare a composite diaphragm and uses LiFePO₄A lithium ion battery with high multiplying power, safety and low cost is designed for the anode. Has the following advantages:

(1) magnesium silicate mineral talcum powder and the like are used as diaphragm additives, and strong interaction between the additives and electrolyte molecules enables the wettability of the composite diaphragm to be greatly improved;

(2) the magnesium silicate mineral talcum powder is used as a diaphragm additive, and the ultra-strong heat resistance of the talcum powder obviously improves the thermal stability of the prepared composite diaphragm;

(3) magnesium silicate mineral talcum powder is used as a diaphragm additive, and the rate performance and the cycle performance of the lithium iron phosphate anode to the lithium cathode half-cell at normal temperature are obviously improved;

(4) and the preparation method of the composite diaphragm is simple, the production efficiency is high, and the manufacturing cost is low.

Drawings

FIG. 1 is a stress-strain curve of the composite membrane obtained in examples 1 to 7;

FIG. 2 is a graph comparing liquid absorption rates of different composite membranes;

FIG. 3 is a thermogravimetric plot of different composite membranes;

FIG. 4 is a contact angle for different composite membranes;

FIG. 5 is a graph of LFP/Li half-cell rate performance obtained from different composite diaphragm assemblies;

FIG. 6 is a CV diagram of LFP/Li half cells obtained from different composite separator assemblies;

FIG. 7 is an EIS diagram of an LFP/Li half-cell obtained by assembling different composite membranes;

FIG. 8 shows LFP/Li half-cells at 1M LiPF fabricated from different composite membranes₆Circulation diagram under electrolyte.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The experimental procedures used in the following examples are conventional unless otherwise specified. The materials, reagents, methods and apparatus used, unless otherwise specified, are conventional in the art and are commercially available to those skilled in the art.

Example 1:

(1) selecting 90% by mass of acetone and 10% by mass of polyvinylidene fluoride, and uniformly mixing;

(2) fully stirring the mixture in an oil bath kettle at the temperature of 50 ℃ for 6 hours until the polyvinylidene fluoride is completely dissolved;

(3) and uniformly coating the slurry on a clean glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain a PVDF diaphragm of a control group, which is referred to as PVDF for short.

And measuring the thickness of the diaphragm by using a micrometer screw to obtain a thickness of 25 mu m, and punching the polyvinylidene fluoride diaphragm into a round sheet by using a sheet punching machine so as to be used by battery equipment.

Example 2:

(1) selecting 90% by mass of acetone and 9.5% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 5% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with 0.5% of additive by mass;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain a composite diaphragm, which is referred to as T-5 for short.

And measuring the thickness of the diaphragm by using a micrometer screw to obtain a thickness of 25 mu m, and punching the composite diaphragm into a round sheet by using a punching machine so as to be used for battery equipment.

Example 3:

(1) selecting 90% by mass of acetone and 9% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 1% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with 1% of additive by mass;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain the composite diaphragm, which is referred to as T-10 for short.

Example 4:

(1) selecting 90% by mass of acetone and 8.5% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 1.5% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with the additive accounting for 1.5% of the mass fraction;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain a composite diaphragm, which is referred to as T-15 for short.

Example 5:

(1) selecting 90% by mass of acetone and 8% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 2% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with the additive accounting for 2% of the mass fraction;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain the composite diaphragm, which is referred to as T-20 for short.

Example 6:

(1) selecting 90% by mass of acetone and 7.5% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 2.5% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with the additive accounting for 2.5% of the mass fraction;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain a composite diaphragm, which is referred to as T-25 for short.

Example 7:

(1) selecting 90% by mass of acetone and 7% by mass of polyvinylidene fluoride, and uniformly mixing;

(3) taking the high-temperature slurry prepared in the step (2) out of the oil bath pan, and cooling to room temperature; adding 3% of magnesium silicate mineral talcum powder, and fully stirring at room temperature for 12-24h to obtain composite slurry with the additive accounting for 3% of the mass fraction;

(4) and uniformly coating the composite slurry on a glass plate by using a scraper, and drying for 12 hours at the temperature of 60 ℃ in vacuum to obtain a composite diaphragm, which is referred to as T-30 for short.

The separator obtained in the above embodiment is used as a lithium battery separator to be assembled to obtain an LFP/Li half battery, and the capacity retention rate and the specific discharge capacity at the rate of 10C are tested, and the results are shown in the following table:

examples	Capacity retention (%)	High rate (10C) specific discharge capacity (mAhg)^-1)
			1	60	52.1
2	64	68.3
			3	70	90.7
4	60	70.4
			5	53	75.9
6	50	69.4
			7	23	64.5

As can be seen from the table, the assembled LFP/Li half-battery has excellent cycle performance, rate capability and higher specific discharge capacity, and can reach 90.7mAh g under the rate of 10C^-1The discharge specific capacity of the lithium ion battery can last for 300 circles under the circulation at 80 ℃.

Example of effects:

and (3) performance testing and characterization of the composite diaphragm:

(1) tensile property tests were performed on the composite membranes obtained in examples 1 to 7, and the stress-strain curves are shown in fig. 1, and the mechanical strength of the composite membranes was slightly improved with the increase of the proportion of talc, and was higher than that of PVDF films. In terms of toughness, the elongation of T-5 is close to 400%, which is 4 times that of PVDF, but with the continued addition of talc, the elongation drops sharply. The mechanical strength and toughness of the composite films are comprehensively compared, the composite diaphragm with 10% of talcum powder additive is comprehensively and prominently displayed in a drawing, and a T-10 composite film is selected as an ideal film to be further researched and compared with PVDF and PP films.

(2) The liquid absorption rate tests of the PVDF separator, the T-10 separator and the PP separator obtained in examples 1 and 3 were performed, specifically, the three separators were respectively soaked in the commercial electrolyte for 1h, and then the results are shown in fig. 2, where the electrolyte absorption rate of the PVDF separator is much higher than that of the PP, and the maximum electrolyte absorption rate of the T-10 composite membrane is 200%, the maximum electrolyte absorption rate of the PVDF is 150%, and the maximum electrolyte absorption rate of the PP is 120%.

(3) TG tests are carried out on the PVDF diaphragm, the T-10 diaphragm and the PP diaphragm obtained in the embodiment 1 and the embodiment 3, the heating range is 25-800 ℃, the heating rate is 10 ℃/min, the results are shown in figure 3, the T-10 composite membrane starts to lose weight at 458 ℃, the PVDF loses weight at 427 ℃, and the PP loses weight at 289 ℃, which shows that the composite diaphragm material prepared by the method provided by the invention can keep good stability and uniformity and greatly improve the thermal stability of the diaphragm.

(4) The results of hydrophobicity tests on the PVDF separators, T-10 and PP separators obtained in examples 1 and 3 are shown in fig. 4, in which the contact angle of the commercial film PP is 48 ° ± 1.05 °, PVDF is 20 ° ± 1.02 °, and the contact angle of the T-10 composite film is the smallest, 8 ° ± 1.01 °, due to the inherent hydrophilicity of PVDF and the strong compatibility of talc powder with electrolyte.

The composite separator obtained in examples 1 and 3 and the T-10 and PP separator were used as lithium ion battery separators, LFP/Li half batteries were assembled, and the obtained batteries were subjected to a performance test:

(1) the rate performance test of LFP/Li half-cells assembled by PVDF separators, T-10 and PP separators obtained in example 1 and example 3, respectively, resulted in the discharge capacities of cells assembled by T-10 composite separators of 154.4, 152.3, 149.5, 141.7, 117.7 and 90.7mAh g at 0.2C, 0.5C, 1C, 2C, 5C and 10C rates, respectively, as shown in FIG. 5^-1. In addition, when the multiplying power is recovered to 0.2C from 10C, the specific discharge capacity of the LFP/Li half-battery assembled by the T-10 composite diaphragm is recovered to 153.7mAh g^-1It is shown that LFP/Li runs particularly stably on T-10 composite membranes. In contrast, PVDF and PP batteries have lower specific discharge capacities at any rate. And the discharge capacity of the lithium ion channel is improved by adding the talcum powder.

(2) LFP/Li half-cell test CV graphs were assembled using the PVDF separators obtained in example 1 and example 3, T-10, and PP separators, respectively, as shown in fig. 6, with a peak at 3.3V corresponding to reduction and 3.6V corresponding to oxidation. A Solid Electrolyte Interphase (SEI) is formed in the first cycle of the 3.3V reduction, and the remaining two peaks of 3.3V correspond to the reduction reaction of the cell. In contrast, the three peaks at 3.6V are associated with oxidation reactions, respectively.

(3) An LFP/Li half-cell test EIS diagram is assembled by adopting the PVDF membranes, the T-10 membranes and the PP membranes obtained in the example 1 and the example 3 respectively, and as shown in figure 7, in three Nyquist curves, the semi-circle radius of the cell assembled by the T-10 composite membrane is minimum, and the transfer impedance is lowest.

(4) LFP/Li half-cells were assembled using the PVDF membranes, T-10 and PP membranes obtained in examples 1 and 3, respectively, and tested on 1M LiPF₆The cycle performance under the electrolyte is shown in figure 8, and the discharge capacity of the battery assembled by the T-10 composite diaphragm is 127.1mAh g^-1The discharge capacity after 300 cycles was maintained at 87%, and the capacity retention rates of the PVDF and PP separator assembled batteries were 74% and 76%, respectively.

The above embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the above embodiments, and modifications and changes thereof may be made by those skilled in the art within the scope of the claims of the present invention.

Claims

1. The composite diaphragm of the rechargeable lithium ion battery is characterized in that the composite film is prepared from composite slurry, wherein the composite slurry comprises the following raw materials in parts by weight: 83-90% of organic solvent, 9-14% of diaphragm base material and 1-3% of diaphragm additive.

2. The composite separator of claim 1, wherein the organic solvent is one or more of acetone, N-methylpyrrolidone, N-dimethylformamide, and absolute ethyl alcohol, and is mixed in any ratio.

3. The composite separator of claim 1, wherein the separator substrate is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polysulfone mixed at any ratio.

4. The composite separator of a rechargeable lithium ion battery according to claim 1, wherein the separator additive is talc and/or montmorillonite.

5. A method of making a composite separator for a rechargeable lithium-ion battery according to claim 1, comprising the steps of:

6. The method of claim 5, wherein the composite separator has a thickness of 25 μm.

7. A lithium ion battery prepared by using the composite separator of claim 1, wherein the lithium ion battery comprises a positive plate, a negative plate, the composite separator arranged between the positive plate and the negative plate, and an electrolyte;

the lithium iron phosphate of the positive plate, the lithium of the negative plate and the electrolyte are 1.0M LiPF₆，EC:DEC:EMC＝1:1:1Vol％。

8. The lithium ion battery of claim 7, wherein the lithium ion battery is a primary battery or a secondary battery.