CN111682147B - A double-coated separator that simultaneously suppresses lithium dendrites and shuttling effects and its preparation method - Google Patents

Abstract

The invention belongs to the technical field of battery diaphragm materials, and particularly relates to a double-coating diaphragm capable of simultaneously inhibiting lithium dendrite and shuttle effect and a preparation method thereof. The double-coating membrane comprises a membrane and coating materials coated on two sides of the membrane, wherein the coating materials comprise Zn-MOF materials and ZnNC carbon materials; the preparation method comprises the following steps: the preparation method comprises the steps of preparing a Zn-MOF powder material and a ZnNC carbon material, respectively preparing the Zn-MOF powder material and the ZnNC carbon material into slurry, and coating the slurry on two sides of a battery diaphragm to obtain a double-coating diaphragm, wherein the double-coating diaphragm simultaneously has the protection effect on a lithium cathode and the inhibition effect on lithium polysulfide shuttling, is applied to a lithium sulfur battery, and has excellent electrochemical cycling stability through electrochemical detection.

Description

A double-coated separator capable of simultaneously suppressing lithium dendrites and shuttling effects and its preparation method

technical field

The invention belongs to the technical field of battery separator materials, and in particular relates to a double-coated separator capable of simultaneously suppressing lithium dendrites and shuttle effects and a preparation method thereof.

Background technique

A lithium-sulfur battery is a secondary battery that uses elemental sulfur or sulfur-containing materials as the positive electrode, and metallic lithium or lithium storage materials as the negative electrode. The charging and discharging process of lithium-sulfur batteries involves multi-step complex electrochemical reactions, and the active material undergoes a complex phase transition process of solid-liquid-solid phase, which creates some thorny problems that seriously restrict the practical application of lithium-sulfur batteries. Mainly include: positive electrode active material sulfur and product lithium sulfide have poor conductivity, volume expansion, rapid capacity fading caused by polysulfide ion shuttle effect, poor safety caused by lithium dendrites and pulverization. A variety of solutions have been proposed for the key materials of lithium batteries such as positive electrode, negative electrode, separator and electrolyte, but the lithium dendrite and lithium polysulfide shuttle effect still plague the development of high-performance lithium-sulfur batteries.

Lithium-sulfur batteries use metal lithium as the negative electrode. Due to the uneven precipitation of lithium ions on the surface, it is easy to grow dendrites, resulting in the pulverization of metal lithium, dead lithium, and eventually piercing the separator, resulting in safety accidents such as short circuit and fire in the battery. , the use of ordinary commercial separators in batteries cannot achieve effective and uniform deposition of lithium dendrites, which will cause lithium dendrites to quickly puncture the separator and cause short circuits in the battery.

Obviously, the successful solution to the safety problem of lithium anode is the premise and guarantee for the practical application of lithium-sulfur batteries. In order to protect the lithium negative electrode, additives such as inorganic salts or small organic molecules are usually added to the electrolyte to form a stable SEI film on the surface. Functional coatings that induce uniform deposition of Li-ion flux. For example, Cui Yi's research group coated the copper nitride precursor colloidal solution on the lithium surface. With the progress of the lithium intercalation process, an artificial interface rich in Li ₃ N that conducts lithium ions rapidly and can be generated through an in-situ reaction. The artificial SEI film increased the cycle efficiency of the lithium-copper battery to 97.4% in a carbonate electrolyte system with a current density of 1 mA cm ^-2 , and also increased the life of the matching lithium titanate battery by nearly 40%. Guo Yuguo et al. used polyphosphoric acid to treat lithium metal to form a Li ₃ PO ₄ base film on its surface, which acts as a physical barrier between lithium metal and electrolyte, preventing their contact reaction and reducing the corrosion consumption of metal lithium. The high ionic conductivity, low surface energy, and uniform current distribution of Li ₃ PO ₄ effectively induce the uniform deposition of Li ion flow and suppress the formation of dendrite Li. Liu Jie from Nanjing University used the biofilm in the egg shell as a functional layer to coat the separator. Due to the attraction of the biofilm to the positive and negative charges, when facing the lithium negative electrode, the lithium ions can be evenly deposited and distributed on the surface, which can better inhibit Growth of lithium dendrites.

Lithium polysulfides produced in the reaction must pass through the separator to be shuttled to the negative electrode, which means that the modification of the separator is also an effective way to inhibit lithium polysulfide shuttle. Due to the simple preparation process, stable structure, and light weight of the coating, coating a layer of functional coating on the ordinary separator has little effect on the overall energy density of the battery, and is an effective method to inhibit the shuttle of polysulfide ions.

Through the above literature research, it can be learned that the coating of functional coatings on ordinary separators can not only effectively suppress the dendrite problem of lithium anodes in lithium-sulfur batteries, but also better eliminate the shuttle effect of lithium polysulfides. However, so far, only one of the problems reported in the literature or inventions is often considered, and the construction of multifunctional diaphragm coatings that can solve these two bottleneck problems is still rarely reported.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a double-coated diaphragm that simultaneously suppresses lithium dendrites and shuttle effects and a preparation method thereof. The double-coated diaphragm has a protective effect on lithium negative electrodes and inhibits lithium polysulfide shuttling. effect.

Technical content of the present invention is as follows:

The present invention provides a double-coated diaphragm that simultaneously suppresses lithium dendrites and shuttle effects, the double-coated diaphragm includes a diaphragm and a coating material coated on both sides of the diaphragm, and the coating material includes a Zn-MOF material and ZnNC carbon materials;

The present invention also provides a method for preparing a double-coated diaphragm that simultaneously suppresses lithium dendrites and the shuttle effect, comprising the following steps: preparing Zn-MOF powder material and ZnNC carbon material, and preparing Zn-MOF powder material and ZnNC carbon material The materials are adjusted into slurry and coated on both sides of the battery separator to obtain a double-coated separator, also known as Janus separator;

The preparation of the Zn-MOF powder material comprises the following steps: dissolving adenine to obtain solution A, dissolving 4,4-biphenyl dicarboxylic acid to obtain solution B, dissolving zinc acetate and polyvinylpyrrolidone to obtain solution C, and then Mix solution A, solution B and solution C, add a mixed organic solvent for stirring reaction, centrifuge, wash and dry to obtain Zn-MOF powder material;

The mixed organic solvent includes a mixture of N,N-dimethylformamide (DMF), anhydrous methanol and water;

The mixing ratio of the solution A, solution B and solution C is 1:1: (1~4);

The preparation of the ZnNC carbon material comprises the following steps: calcining the Zn-MOF powder material under a high-temperature inert gas atmosphere to obtain the ZnNC carbon material;

The operation of making the Zn-MOF powder material and ZnNC carbon material into slurry respectively includes mixing Zn-MOF powder material with binder and N-methylpyrrolidone to make slurry 1, ZnNC carbon material and adhesive Adhesive and N-methylpyrrolidone were mixed to form slurry 2, and coated on both sides of the diaphragm respectively. The obtained double-coated diaphragm was the Janus diaphragm, and the adhesive included PVDF adhesive.

The beneficial effects of the present invention are as follows:

The double-coated separator of the present invention has the protection effect on the lithium negative electrode and the inhibition effect on the lithium polysulfide shuttle, and the ordinary separator cannot realize the effective and uniform precipitation of lithium dendrites, which will easily cause the lithium dendrites to puncture the separator quickly, resulting in a short circuit of the battery , and the Zn-MOF and ZnNC coating materials synthesized by the present invention can have a stable cycle at a high current density, and can better inhibit lithium dendrites, thereby protecting the lithium negative electrode;

The prepared double-coated separator is applied to lithium-sulfur batteries, and it has excellent electrochemical cycle stability through electrochemical detection.

Description of drawings

Fig. 1 is the scanning electron microscope picture of Zn-MOF powder material;

Fig. 2 is the powder diffraction pattern of Zn-MOF powder material;

Fig. 3 is the scanning electron micrograph of ZnNC carbon material;

Fig. 4 is the powder diffraction pattern of ZnNC carbon material;

Figure 5 is a cross-sectional electron microscope image of the Janus diaphragm;

Fig. 6 is a diagram of the long-term cycle performance of a Zn-MOF-coated diaphragm-modified lithium-lithium symmetric battery at a current density of 1 mA/cm ² and a capacity of 2 mAh/cm ² ;

Figure 7 is a comparison chart of the cycle performance of lithium-sulfur batteries assembled with different separators at a current density of 2C.

Detailed ways

The present invention will be described in further detail below through specific examples of implementation and description of the accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the protection scope of the present invention. After reading the present invention, those skilled in the art Modifications to various equivalent forms of the present invention fall within the scope of the appended claims of this application.

Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents in the conventional market.

Example 1

Preparation of a dual-coated separator that simultaneously suppresses lithium dendrites and shuttling effects:

1) Preparation of Zn-MOF powder material: Dissolve 1mmol of adenine and 1mmol of 4,4-biphenyldicarboxylic acid (with a molar ratio of 1:1) in 20mL of DMF and ultrasonically dissolve to obtain solution A and solution B for later use , 1mmol of zinc acetate and 1g of polyvinylpyrrolidone were dissolved in 20 mL of DMF and ultrasonically dissolved to obtain solution C for later use. Mix solution A, solution B and solution C in a volume ratio of 1:1:1, and add volume The activated ratio is 5:4:1, dispersed in DMF, methanol and deionized water, and stirred at room temperature for 12 hours;

After the reaction stopped, centrifuge at 8000r/min for 5min to obtain a white powder, which was washed with DMF and MeOH in turn, and dried in an oven to obtain a Zn-MOF powder material, as shown in Figure 1. Zn-MOF powder The scanning electron microscope image of the material shows that it forms a uniform honeycomb spherical shape. Figure 2 is the powder diffraction pattern of the Zn-MOF powder material, which shows that it is completely matched;

2) Preparation of ZnNC carbon material: calcining the Zn-MOF powder material prepared in step 1) in a tube furnace under a nitrogen atmosphere, calcining at 800°C for 2h, and the heating rate is 5°C/min, and the product ZnNC carbon is obtained after calcination Material, as shown in Figure 3 is the scanning electron microscope image of ZnNC carbon material, forming a uniform honeycomb spherical shape, Figure 4 is the powder diffraction pattern of ZnNC carbon material, it can be seen that it is an amorphous carbon material, and it can be seen that it is completely matched;

3) Preparation of double-coated separator: disperse the Zn-MOF powder material and PVDF binder in step 1) according to the ratio of 6:1, and use N-methylpyrrolidone solution to disperse it into slurry 1, and prepare step 2 ) ZnNC carbon material and PVDF binder according to the ratio of 6:1, using N-methylpyrrolidone solution to disperse it into slurry 2;

Take a common commercial Celgard diaphragm, apply slurry 1 on one side of the diaphragm, dry in a vacuum oven at 60°C for 24 hours, then coat slurry 2 on the other side of the diaphragm, and dry it in a vacuum oven at 60°C After drying for 24 hours, cut it into discs with a diameter of 19 mm using a microtome to obtain a double-coated separator-Janus separator. Figure 5 shows the cross-sectional electron microscope image of the Janus separator, in which the Zn-MOF coating is 7.27 μm thick, while the ZnNC coating is 6.55 μm, with a 25 μm thick Celgard in between.

Example 2

Preparation of a dual-coated separator that simultaneously suppresses lithium dendrites and shuttling effects:

1) Preparation of Zn-MOF powder material: Dissolve 1mmol of adenine and 1mmol of 4,4-biphenyldicarboxylic acid in 20mL of DMF and ultrasonically dissolve it for later use; dissolve 1mmol of zinc acetate and 1g of polyvinylpyrrolidone in 20mL of Ultrasonic dissolution in DMF for standby, mix the above three DMF solutions with a volume ratio of 1:1:2, add the activated volume ratio of 5:4:1 and disperse them in DMF, methanol and deionized water, at room temperature Stir for 18h;

After the reaction is stopped, centrifuge at 8000r/min for 5min to obtain a white powder, which is washed with DMF and MeOH in turn, and dried in an oven to obtain a Zn-MOF powder material;

2) Preparation of ZnNC carbon material: Calcining the Zn-MOF powder material prepared in step 1) in a tube furnace under a nitrogen atmosphere, calcining at 800°C for 4h, and the heating rate is 5°C/min, and the product ZnNC carbon is obtained after calcination Material;

3) Preparation of double-coated separator: disperse the Zn-MOF powder material and PVDF binder in step 1) according to the ratio of 6:1, and use N-methylpyrrolidone solution to disperse it into slurry 1, and prepare step 2 ) ZnNC carbon material and PVDF binder according to the ratio of 6:1, using N-methylpyrrolidone solution to disperse it into slurry 2;

Take a common commercial Celgard diaphragm, apply slurry 1 on one side of the diaphragm, dry in a vacuum oven at 60°C for 24 hours, then coat slurry 2 on the other side of the diaphragm, and dry it in a vacuum oven at 60°C After drying for 24 hours, cut it into discs with a diameter of 19 mm using a microtome to obtain a double-coated separator—Janus separator.

Example 3

Preparation of a dual-coated separator that simultaneously suppresses lithium dendrites and shuttling effects:

1) Preparation of Zn-MOF powder material: 1 mmol of adenine and 1 mmol of 4,4-biphenyl dicarboxylic acid were dissolved in 20 mL of DMF and ultrasonically dissolved for use, and 1 mmol of zinc acetate and 1 g of polyvinylpyrrolidone Dissolve in 20 mL DMF and ultrasonically dissolve for later use. Mix the above three DMF solutions at a volume ratio of 1:1:4, and add the activated dispersant in DMF, methanol and deionized water at a volume ratio of 5:4:1. water, stirred at room temperature for 24h;

After the reaction stopped, centrifuge at 8000 r/min for 5 min to obtain a white powder, which was washed with DMF and MeOH in turn, and dried in an oven to obtain a Zn-MOF powder material;

2) Preparation of ZnNC carbon material: calcining the Zn-MOF powder material prepared in step 1) in a tube furnace under a nitrogen atmosphere, calcining at 800°C for 6h, and heating up at a rate of 5°C/min, and the product ZnNC carbon is obtained after calcination Material;

3) Preparation of double-coated separator: disperse the Zn-MOF powder material and PVDF binder in step 1) according to the ratio of 6:1, and use N-methylpyrrolidone solution to disperse it into slurry 1, and prepare step 2 ) ZnNC carbon material and PVDF binder according to the ratio of 6:1, using N-methylpyrrolidone solution to disperse it into slurry 2;

Take a common commercial Celgard diaphragm, apply slurry 1 on one side of the diaphragm, dry in a vacuum oven at 60°C for 24 hours, then coat slurry 2 on the other side of the diaphragm, and dry it in a vacuum oven at 60°C After drying for 24 hours, cut it into discs with a diameter of 19 mm using a microtome to obtain a double-coated separator—Janus separator.

Electrochemical performance test of coated separator applied to battery:

1. The electrochemical performance test of Zn-MOF coated separator for lithium lithium symmetric battery:

In the glove box, lithium sheets were used as positive and negative electrodes respectively, Celgard or Celgard coated with the Zn-MOF material prepared in Example 1 was used as separator, and 1.0 M LiTFSI DOL/DME (v:v, 1:1) As the electrolyte, it is assembled into a lithium-lithium symmetrical battery, and the prepared lithium-lithium battery is used for the test data of the electrochemical test system;

As shown in Figure 6, it is a graph of the long-term cycle performance of a lithium-lithium symmetric battery coated with a Zn-MOF membrane at a current density of 1 mA/cm ² , showing that it can operate at 1 mA/cm ² , 2 mAh/cm Under the conditions of ² , it can still cycle stably for 2000h, and the polarization is stable below 89mV, indicating that the Zn-MOF coating can better inhibit lithium dendrites, thereby protecting the lithium negative electrode. The commercial separator of Zn-MOF material cannot achieve effective and uniform deposition of lithium dendrites, and the polarization voltage reaches nearly 300mV when the cycle is less than 400h. It shows that the Zn-MOF coating can effectively realize the uniform deposition of lithium anode, thereby inhibiting the growth of lithium dendrites.

2. The electrochemical performance test of the double-coated diaphragm of the present invention-Janus diaphragm is used for lithium-sulfur battery:

React S and Ketjen Black at a ratio of 1:4 in a 155°C reactor for 24 hours to prepare a C/S composite, and prepare a C/S composite, Super-P, and LA132 binder at a ratio of 8:1:1 The ratio of the slurry was prepared by dispersing with n-propanol solution, coated on aluminum foil, and dried in a vacuum oven at 60°C for 24 hours;

It was cut into electrode disks with a diameter of 12 mm by a slicer, and electrode sheets with a sulfur loading of 5 mg/cm ² were prepared using scrapers of different thicknesses. In the glove box, the prepared electrode was used as the positive electrode, the lithium sheet was used as the negative electrode, Celgard or the Janus separator coated with double-coated materials was used as the separator, 1.0 M LiTFSI DOL/DME (v:v, 1:1) As the electrolyte, it is assembled into a CR-2302 button battery, wherein the Zn-MOF coating layer faces the lithium negative electrode, and the ZnNC coating layer faces the sulfur positive electrode, and the prepared lithium-sulfur battery is used in the electrochemical test system for test data;

Figure 7 is a comparison chart of the cycle performance of lithium-sulfur batteries assembled with different coating separators at a current density of 2C. It can be seen that the performance of the Janus separator with double coatings is much better than that of the uncoated Celgard separator, or only coated One of the coatings, Zn-MOF or ZnNC, is much better. Lithium-sulfur batteries assembled with Janus separators still have good cycle stability even at a current density of 2C, and can be cycled stably up to 1000 cycles. It shows that the Janus separator developed by the present invention can effectively suppress the lithium dendrite and the shuttle effect at the same time.

Claims (3)

1. A preparation method of a double-coating diaphragm for simultaneously inhibiting lithium dendrite and shuttle effect is characterized by comprising the following steps: preparing a Zn-MOF powder material and a ZnNC carbon material, respectively preparing the Zn-MOF powder material and the ZnNC carbon material into slurry, and coating the slurry on two sides of a battery diaphragm to obtain a double-coating diaphragm;

the preparation method of the Zn-MOF powder material comprises the following steps: dissolving adenine to obtain a solution A, dissolving 4,4-biphenyldicarboxylic acid to obtain a solution B, dissolving zinc acetate and polyvinylpyrrolidone to obtain a solution C, mixing the solution A, the solution B and the solution C, adding a mixed organic solvent to carry out stirring reaction, centrifuging, washing and drying to obtain a Zn-MOF powder material;

the mixing volume ratio of the solution A, the solution B and the solution C is 1:1 (1~4);

the preparation method of the ZnNC carbon material comprises the following steps: calcining the Zn-MOF powder material in a high-temperature inert gas atmosphere to obtain a ZnNC carbon material;

the operation of respectively mixing the Zn-MOF powder material and the ZnNC carbon material into slurry comprises the steps of mixing the Zn-MOF powder material with a binder and N-methylpyrrolidone to prepare slurry 1, mixing the ZnNC carbon material with the binder and the N-methylpyrrolidone to prepare slurry 2, and respectively coating the slurry 1 and the slurry 2 on two sides of a diaphragm to obtain the double-coating diaphragm.

2. The method for preparing the double-coated separator according to claim 1, wherein the mixed organic solvent comprises a mixture of N, N-dimethylformamide, anhydrous methanol and water.

3. The method of making a double coated membrane of claim 1 wherein the binder comprises a PVDF binder.

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