CN106384800A - Preparation method of modified diaphragm for lithium-sulfur batteries - Google Patents

Abstract

The invention relates to a preparation method for a modified diaphragm of a lithium-sulfur battery, belonging to the technical field of lithium-sulfur batteries. The preparation method comprises: 1) reacting crown ether and sodium alginate aqueous solution to obtain a mixed solution, extracting the mixed solution with an extractant, and separating and obtaining the lower layer extract; 2) using a basement membrane as a filter membrane to extract the obtained extract Perform vacuum filtration, or coat the obtained extract on the base membrane, and dry to obtain the modified membrane. In the present invention, sodium alginate and crown ether are chelated to obtain a coordination compound, the sodium ion of sodium alginate (SA) is closely embedded in the cavity of crown ether, and the obtained chelate has good hydrophobicity; the coordination compound is adopted The modification of the diaphragm fully exerts the physical and chemical properties of the chelate such as cation selectivity and anion repellency, and the surface morphology of the modified diaphragm is significantly changed; the modified diaphragm improves the cycle stability of the lithium-sulfur battery And high capacity retention rate, suitable for promotional use.

Description

A preparation method for modified separator of lithium-sulfur battery

technical field

The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a preparation method for modified diaphragms of lithium-sulfur batteries.

Background technique

In 1991, Sony released the first commercial lithium-ion battery; lithium-ion batteries subsequently revolutionized consumer electronics. With the widespread use of digital products such as mobile phones and notebook computers, lithium-ion batteries have been widely used in such products due to their excellent performance, and are gradually developing into other product application fields. However, with the popularization of mobile life, people have put forward higher requirements for the battery life and safety of lithium-ion batteries, especially in the field of new energy vehicles, making batteries with high capacity, light weight, high energy density, high Excellent features such as power density, high cycle performance, and fast charging have become new challenges to meet the needs of the times.

In recent years, emerging lithium-sulfur batteries use elemental sulfur as the positive electrode material, because elemental sulfur as the anode material has a high theoretical specific capacity of 1675mAh/g, and when the original battery is formed with metal elemental lithium as the negative electrode material, its capacity can reach 2600Wh/kg, basically meets the current fast-paced mobile life's demand for battery energy storage, and also meets the requirements of new energy vehicles for batteries. In addition, elemental sulfur also has the advantages of wide sources, low price, low pollution and low pollution, which provide many conditions for it to be used as the second generation of emerging energy storage batteries.

However, in the actual battery charge-discharge process, the weak conductivity of elemental sulfur materials and the dissolution of soluble polysulfides, an intermediate product produced during charge-discharge cycles, in the electrolyte solution need to be resolved. Therefore, researchers have proposed a variety of solutions to improve the cycle stability of lithium-sulfur batteries, such as improving the conductivity by preparing sulfur composite cathode materials; limiting the "shuttle" of polysulfides through microporous/mesoporous carbon materials and dissolution; through nanomaterials (carbon nanotubes/graphene, etc.) to explore and improve the framework and size of the sulfur carrier to improve the charge and discharge efficiency of lithium-sulfur batteries; by preparing modified diaphragms with different functions, the small pore size of the modified diaphragms can be utilized And its unique physical and chemical properties to block the loss of polysulfides in solution.

Most of the currently reported lithium-sulfur batteries are based on the preparation of positive electrode composite materials, and different types of porous structure carriers are studied to compound sulfur elements. However, there are few reports on the preparation method of modified separators, and the technology of fully combining the chemical properties of polysulfides for the modification of lithium-sulfur battery separators needs to be further explored and applied.

Contents of the invention

The purpose of the present invention is to provide a preparation method for a modified diaphragm for a lithium-sulfur battery. The modified diaphragm obtained can improve the cycle stability of the lithium-sulfur battery and improve the problem of rapid capacity decay of the lithium-sulfur battery.

In order to achieve the above object, the technical solution adopted in the present invention is:

A method for preparing a modified diaphragm for lithium-sulfur batteries, comprising the following steps:

1) Mix crown ether and sodium alginate aqueous solution to react to obtain a mixed solution, extract the mixed solution with an extractant, and separate to obtain the lower layer extract; wherein, 10-50 μL of sodium alginate is used for every 0.1-0.3 g of sodium alginate crown ether;

2) using the base membrane as a filter membrane to carry out vacuum filtration on the extract obtained in step 1), and drying to obtain the modified diaphragm;

Alternatively, the extract obtained in step 1) is coated on the base membrane, and dried to obtain the modified membrane.

As a polymer material, sodium alginate (SA) is widely used in the field of materials and chemical industry due to its unique chemical properties. Sodium alginate (SA) molecules contain neatly arranged carboxyl (-COOH) and hydroxyl (-OH) groups, which belong It is an anionic polymer material, but its chemical properties are hydrophilic, so it cannot directly infiltrate the separator of polypropylene material.

The preparation method of the modified diaphragm for lithium-sulfur batteries of the present invention is to first fully dissolve sodium alginate (SA) in water, add an appropriate amount of crown ether, and extract the crown ether-sodium alginate (SA) with a suitable extractant. ) chelate; the sodium alginate and the crown ether are chelated to obtain a coordination compound; in the coordination compound, the sodium ion of sodium alginate (SA) is tightly embedded in the cavity of the crown ether (such as As shown in Figure 1), the chelate prepared has good hydrophobicity; the coordination compound is placed on the surface of the base membrane to modify the diaphragm, and the cation selectivity and anion repellency of the chelate are fully exerted. Physical and chemical properties, the surface morphology of the modified separator has been significantly changed, and the pore size has become smaller; the modified separator has improved the cycle stability and high capacity retention of lithium-sulfur batteries, and is suitable for popularization and use.

The extractant is any one or more of carbon tetrachloride (CCl ₄ ), toluene (PhMe), and dimethylsulfoxide (DMSO). The amount of extractant added is determined by the amount of sodium alginate and crown ether to ensure that the extractant is in excess. Generally, the amount of the extractant added is: 20ml of the extractant is used for every 0.1-0.3g of sodium alginate.

The crown ether is any one or more of 15-crown-5, 18-crown-6, and 12-crown-4.

Taking 15-crown-5 as an example, the chemical reaction formula involved in the preparation method of the modified diaphragm for lithium-sulfur batteries in the present invention is as follows:

In the sodium alginate aqueous solution, the mass ratio of sodium alginate to water is 0.1-0.3:10-20. The sodium alginate aqueous solution is obtained by adding a certain quality of sodium alginate (SA) into water and stirring at normal temperature to fully dissolve the sodium alginate. The rotational speed of the stirring is 300-500 r/min, and the stirring time is 12-24 hours. The water used here is deionized water.

The reaction time is 12-24 hours. The reaction temperature conditions were normal temperature.

Stirring is carried out during the reaction process, and the stirring speed is 300-500 r/min.

The base membrane is a polyolefin membrane with a pore diameter of 2-200nm. The base film can be a single-layer film or a multi-layer polyolefin composite film. Preferably, the base film is a polypropylene separator.

In step 2), the amount of the extract solution filtered or coated per unit membrane area is: the unit membrane area corresponds to the mass of raw material sodium alginate is 0.04-0.06 mg/cm ² . That is, a membrane area of 1 cm ² corresponds to the use of the extract prepared in step 1) based on 0.04-0.06 mg of raw material sodium alginate.

The relative vacuum degree of the vacuum suction filtration is -0.06～-0.1MPa.

The drying temperature is 25-50°C.

The preparation method of the modified diaphragm for lithium-sulfur batteries of the present invention is obtained by vacuum-filtering the obtained extract and drying the obtained extract; the purpose of the suction filtration is to use a certain degree of vacuum A gradient distribution of chelates is formed on the surface, which better exerts its repelling and blocking effect on polysulfides; the obtained modified separator is compared under the scanning electron microscope and found that the pore size is significantly smaller, which can effectively block the shuttle of polysulfides and avoid the formation of lithium Sulfur battery capacity decay; compared with the prior art, the lithium-sulfur battery using the modified diaphragm also shows characteristics such as high specific capacity, high cycle performance, and high stability. The whole preparation process has the advantages of wide material sources, simple process flow, mild conditions, and strong operability. The modification method can significantly change the shape of the diaphragm, and the cost is relatively low, which is conducive to commercial promotion.

The modified separator for the lithium-sulfur battery obtained in the present invention has the modified side facing the positive electrode during use, which can improve the discharge specific capacity and cycle stability of the lithium-sulfur battery, and the preparation process of the modified separator is simple and low in cost, and is suitable for large-scale industrial production .

Description of drawings

Fig. 1 is the theoretical model figure of diaphragm modification of the present invention;

Figure 2 is a comparison of surface morphology at different magnifications before and after modification of the modified separator for lithium-sulfur batteries in Example 1, where (a) ×5000 before modification, (b) ×5000 after modification, (c) ×5000 after modification Before modification × 10000, (d) after modification × 10000 (e) before modification × 30000, (f) after modification × 30000;

FIG. 3 is a comparison chart of electrical performance tests of the lithium-sulfur batteries of Examples 1-3 at a rate of 0.1C.

detailed description

The present invention will be further described below in combination with specific embodiments.

Example 1

The preparation method for the modified diaphragm of the lithium-sulfur battery in this embodiment comprises the following steps:

1) Add 0.1 g of sodium alginate (SA) solid powder into 20 ml of deionized water, and stir at a speed of 400 r/min for 12 hours at room temperature to fully dissolve the sodium alginate to obtain an aqueous solution of sodium alginate;

Use a pipette to add 20 μL of 15-crown-5 to the obtained sodium alginate aqueous solution. Under normal temperature conditions, fully oscillate and stir for reaction. The stirring speed is 400r/min, and the stirring reaction time is 12h; Add 20ml of carbon tetrachloride to vibrate and shake well, transfer to the separatory funnel to fully rest and separate to obtain the lower layer extract;

2) Using a common polypropylene membrane (average pore size: 20 nm) as a filter membrane, the obtained extract was subjected to vacuum filtration (relative vacuum degree -0.095 MPa), and then dried at 30° C. to obtain the modified membrane. Wherein, the amount of filtered extract per unit membrane area is: the unit membrane area corresponds to the mass of raw material sodium alginate is 0.05 mg/cm ² .

The comparison of the surface morphology of the diaphragm in this embodiment before and after modification under different magnifications is shown in Fig. 2 . It can be seen from Figure 2 that the microscopic morphology of the separator has changed significantly before and after modification. The surface of the modified separator is denser and the pore size is smaller, which can effectively block the shuttle of polysulfides and avoid the capacity decay of lithium-sulfur batteries. .

The obtained diaphragm is cut into a diaphragm with a diameter of 18mm, which is used between the positive electrode and the negative electrode of the lithium-sulfur battery, with the modified side facing the positive electrode; the mass ratio of sulfur:BP2000 conductive carbon black:PVDF=7:2:1 is used for pulping , the slurry was evenly coated on the aluminum foil, placed in a vacuum drying oven at 65°C and dried for 12 hours to obtain a positive electrode; a lithium sheet was used as a negative electrode to assemble a button battery to obtain a lithium-sulfur battery.

The electrical performance rate test of the lithium-sulfur battery was carried out, and the results are shown in Figure 3. It can be seen from FIG. 3 that the specific capacity of the lithium-sulfur battery obtained in this example is still maintained at 700mAh/g after 150 cycles at a rate of 0.1C.

Example 2

The preparation method for the modified diaphragm of the lithium-sulfur battery in this embodiment comprises the following steps:

1) Add 0.2 g of sodium alginate (SA) solid powder into 20 ml of deionized water, and stir at a speed of 500 r/min for 18 hours at room temperature to fully dissolve the sodium alginate to obtain an aqueous solution of sodium alginate;

Use a pipette to add 20 μL of 18-crown-6 to the obtained sodium alginate aqueous solution. Under normal temperature conditions, fully oscillate and stir for reaction. The stirring speed is 500r/min, and the stirring reaction time is 18h; Add 20ml of carbon tetrachloride to vibrate and shake well, transfer to the separatory funnel to fully rest and separate to obtain the lower layer extract;

2) Using a common polypropylene diaphragm (average pore size 50nm) as a filter membrane to vacuum filter the obtained extract (relative vacuum degree is -0.095MPa), and then dry it at 40°C to obtain the modified diaphragm. Wherein, the amount of filtered extract per unit membrane area is: the unit membrane area corresponds to the mass of raw material sodium alginate is 0.05 mg/cm ² .

The obtained diaphragm is cut into a diaphragm with a diameter of 18mm, which is used between the positive electrode and the negative electrode of the lithium-sulfur battery, with the modified side facing the positive electrode; the mass ratio of sulfur:BP2000 conductive carbon black:PVDF=7:2:1 is used for pulping , the slurry was evenly coated on the aluminum foil, placed in a vacuum drying oven at 65°C and dried for 12 hours to obtain a positive electrode; a lithium sheet was used as a negative electrode to assemble a button battery to obtain a lithium-sulfur battery.

The electrical performance rate test of the lithium-sulfur battery was carried out, and the results are shown in Figure 3. It can be seen from FIG. 3 that the specific capacity of the lithium-sulfur battery obtained in this example is still maintained at 600mAh/g after 150 cycles at a rate of 0.1C.

Example 3

The preparation method for the modified diaphragm of the lithium-sulfur battery in this embodiment comprises the following steps:

1) Add 0.3 g of sodium alginate (SA) solid powder into 20 ml of deionized water, and stir at a speed of 300 r/min for 24 hours at room temperature to fully dissolve the sodium alginate to obtain an aqueous solution of sodium alginate;

Use a pipette to add 20 μL of 15-crown-5 to the obtained sodium alginate aqueous solution. Under normal temperature conditions, fully oscillate and stir for the reaction. The stirring speed is 300r/min, and the stirring reaction time is 24h; Add 20ml of carbon tetrachloride to vibrate and shake well, transfer to the separatory funnel to fully rest and separate to obtain the lower layer extract;

2) Using a common polypropylene membrane (average pore size 100nm) as a filter membrane to vacuum filter the obtained extract (relative vacuum degree is -0.095MPa), and then dry it at 50°C to obtain the modified membrane. Wherein, the amount of filtered extract per unit membrane area is: the unit membrane area corresponds to a mass of raw material sodium alginate of 0.06 mg/cm ² .

The obtained diaphragm is cut into a diaphragm with a diameter of 18mm, which is used between the positive electrode and the negative electrode of the lithium-sulfur battery, with the modified side facing the positive electrode; the mass ratio of sulfur:BP2000 conductive carbon black:PVDF=7:2:1 is used for pulping , the slurry was evenly coated on the aluminum foil, placed in a vacuum drying oven at 65°C and dried for 12 hours to obtain a positive electrode; a lithium sheet was used as a negative electrode to assemble a button battery to obtain a lithium-sulfur battery.

The electrical performance rate test of the lithium-sulfur battery was carried out, and the results are shown in Figure 3. It can be seen from FIG. 3 that the specific capacity of the lithium-sulfur battery obtained in this example is still maintained at 600mAh/g after 150 cycles at a rate of 0.1C.

Example 4

The preparation method for the modified diaphragm of the lithium-sulfur battery in this embodiment comprises the following steps:

1) Add 0.1 g of sodium alginate (SA) solid powder into 10 ml of deionized water, and stir at a speed of 500 r/min for 12 hours at room temperature to fully dissolve the sodium alginate to obtain an aqueous solution of sodium alginate;

Use a pipette to add 40 μL of crown ether (a mixture of 15-crown-5 and 12-crown-4 in a mass ratio of 1:1) to the obtained sodium alginate aqueous solution, and react with sufficient shaking and stirring at room temperature , the rotating speed of stirring is 500r/min, and the time of stirring reaction is 12h; After the completion of the reaction, add 10ml of carbon tetrachloride to vibrate and shake well, transfer to the separatory funnel and separate to obtain the lower layer extract after fully resting;

2) Using a common polypropylene diaphragm (average pore size 150nm) as a filter membrane to vacuum filter the obtained extract (relative vacuum degree is -0.095MPa), and then dry it at 25°C to obtain the modified diaphragm. Wherein, the amount of filtered extract per unit membrane area is: the unit membrane area corresponds to a mass of raw material sodium alginate of 0.04 mg/cm ² .

The obtained diaphragm is cut into a diaphragm with a diameter of 18mm, which is used between the positive electrode and the negative electrode of the lithium-sulfur battery, with the modified side facing the positive electrode; the mass ratio of sulfur:BP2000 conductive carbon black:PVDF=7:2:1 is used for pulping , the slurry was evenly coated on the aluminum foil, placed in a vacuum drying oven at 65°C and dried for 12 hours to obtain a positive electrode; a lithium sheet was used as a negative electrode to assemble a button battery to obtain a lithium-sulfur battery.

The electrical performance rate test of the lithium-sulfur battery showed that the specific capacity of the lithium-sulfur battery obtained in this example remained at 600mAh/g after 150 cycles at a rate of 0.1C.

Through the electrical performance rate test of the lithium-sulfur battery obtained in Examples 1-4, it can be seen that the modified diaphragm obtained in the present invention has a significantly smaller pore size than that before modification, and can effectively block the shuttle of polysulfides, thereby avoiding the loss of lithium-sulfur battery capacity. ; The lithium-sulfur battery using the modified diaphragm of the present invention shows the characteristics of high specific capacity, high cycle performance, high stability, etc., and the preparation process has the advantages of wide material sources, simple process flow, mild conditions, and strong operability , the cost is relatively low, which is conducive to commercial promotion.

Claims (10)

1. a kind of preparation method for lithium-sulfur cell modified diaphragm it is characterised in that：Comprise the following steps：

1) crown ether is mixed with sodium alginate aqueous solution and carry out reacting to obtain mixed liquor, with extractant, mixed liquor is extracted, point From the extract obtaining lower floor；Wherein, the corresponding crown ether using 10～50 μ L of the sodium alginate of every 0.1～0.3g；

2) adopt basement membrane as filter membrane to step 1) gained extract carries out vacuum filtration, is drying to obtain described modified diaphragm；

Or, by step 1) and gained extract is coated on basement membrane, is drying to obtain described modified diaphragm.

2. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Described extractant For any one or more in carbon tetrachloride, toluene, dimethyl sulfoxide.

3. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Described crown ether is Any one or more in 15- crown ether-5, hexaoxacyclooctadecane-6-6,12- crown ether-4.

4. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Described alginic acid In sodium water solution, sodium alginate is 0.1～0.3 with the mass ratio of water:10～20.

5. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Described reaction Time is 12～24h.

6. according to claim 1 or 5 be used for lithium-sulfur cell modified diaphragm preparation method it is characterised in that：Reacted It is stirred in journey, the rotating speed of stirring is 300～500r/min.

7. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Described basement membrane is Polyalkene diaphragm, aperture is 2～200nm.

8. the preparation method for lithium-sulfur cell modified diaphragm according to claim 7 it is characterised in that：Described basement membrane is Polypropylene diaphragm.

9. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Step 2) in, Per membrane area filters or the amount of coating extract is：The quality of the corresponding raw material sodium alginate of per membrane area is 0.04～ 0.06mg/cm².

10. the preparation method for lithium-sulfur cell modified diaphragm according to claim 1 it is characterised in that：Step 2) in, The temperature of described drying is 25～50 DEG C.