CN116799432A - Lithium-sulfur battery diaphragm and preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of batteries, in particular to a lithium-sulfur battery diaphragm and a preparation method and application thereof. The lithium-sulfur battery diaphragm comprises an electrostatic spinning base film and multi-wall carbon nanotubes loaded on the electrostatic spinning base film; the electrostatic spinning base film takes polyacrylonitrile as a matrix, and the matrix contains nano silicon dioxide. According to the invention, through the synergistic combination of the components, the diffusion of polysulfide in the Li-S battery can be effectively inhibited, the diaphragm has excellent porosity and electrolyte wettability, and the prepared battery has excellent cycle stability and rate capability.

Description

Lithium-sulfur battery separator and preparation method and application thereof

Technical field

The present invention relates to the field of battery technology, and specifically to a lithium-sulfur battery separator and its preparation method and application.

Background technique

Lithium-ion batteries (LIB) are widely used as power supplies for portable electronic devices due to their long cycle life, high power density, and high energy density. However, lithium-ion batteries have always been limited in large-scale applications, such as electric vehicles and stationary energy storage. This has also been motivating many scientific researchers to further develop new batteries to solve the limitations in the above fields. Lithium-sulfur (Li-S) batteries are a promising candidate because the raw material sulfur (S) is abundant, relatively low cost, non-toxic, high theoretical capacity (1675mAh g-1), and high energy density ( 2600Wh kg-1) and many other advantages.

Despite the above-mentioned advantages, lithium-sulfur batteries currently have shortcomings such as short cycle life, large self-discharge, and low Coulombic efficiency, which seriously limit their practical application. These shortcomings are mainly attributed to the entry of lithium polysulfide (Li ₂ S) into the organic electrolyte, resulting in the loss of cathode active materials and the shuttling of polysulfides. In order to obtain high-performance Li-S batteries, it is extremely important to suppress the shuttle diffusion of polysulfides.

In order to solve the challenges faced by Li-S batteries, many efforts have been made, which mainly focus on the combination of S element and conductive materials (such as porous carbon, graphene, carbon nanotubes, conductive polymers and polysulfide absorption capabilities). oxides, such as TiO ₂ , Al ₂ O _3, etc.) are combined to form composite materials. However, these means will lead to complex cathode structure design, which undoubtedly hinders the practicality of Li-S batteries.

As we all know, the separator is an integral and critical component of all liquid electrolyte batteries. The ideal Li-S battery separator not only has good ionic conductivity after absorbing the liquid electrolyte, but also slows down the diffusion of polysulfides during cycling. At present, the commonly used separator material for lithium batteries is microporous polypropylene (PP), but its shortcomings of low porosity and poor electrolyte wettability seriously hinder the electrochemical performance of Li-S batteries, especially rate performance and long-term cycle stability. performance.

In view of this, the present invention is proposed.

Contents of the invention

One object of the present invention is to provide a lithium-sulfur battery separator to solve the technical problem that the separator in the prior art cannot well inhibit the shuttle diffusion of polysulfides, resulting in poor electrochemical performance of the lithium-sulfur battery.

Another object of the present invention is to provide a method for preparing the lithium-sulfur battery separator, which is simple and easy to implement.

Another object of the present invention is to provide the lithium-sulfur battery, which has excellent electrochemical performance.

In order to achieve the above objects of the present invention, the following technical solutions are adopted:

A lithium-sulfur battery separator includes an electrospinning base film and multi-walled carbon nanotubes loaded on the electrospinning base film; the electrospinning base film uses polyacrylonitrile as a base, and the base includes nanometer dicarbons. Silicon oxide.

In one embodiment, the mass ratio of the nano-silica, polyacrylonitrile and multi-walled carbon nanotubes is (200-1000): (2500-3500): (1.5-2.5).

In one embodiment, the particle size of the nano-silica is 10 to 20 nm.

In one embodiment, the multi-walled carbon nanotube has an outer diameter of 8 to 15 nm and a length of 40 to 60 μm.

In one embodiment, the weight average molecular weight of the polyacrylonitrile is 120,000 to 160,000 g/mol.

In one embodiment, the effective area density of the lithium-sulfur battery separator is 0.19-0.26 mg/cm ² .

In one embodiment, the thickness of the lithium-sulfur battery separator is 2.8-3.2 μm.

In one embodiment, the lithium-sulfur battery separator has a porosity of 72% to 77%.

In one embodiment, some or all of the silica is replaced with alumina and/or graphene.

In one embodiment, some or all of the multi-walled carbon nanotubes are replaced with graphene and/or activated carbon.

The preparation method of the lithium-sulfur battery separator as described above includes the following steps:

(a) Electrospinning a mixed system of nanosilica, polyacrylonitrile and organic solvent to obtain an electrospinning base membrane;

(b) Dispersing the multi-walled carbon nanotubes in an alcohol solvent, using vacuum filtration to load the multi-walled carbon nanotubes onto the electrospinning base film to obtain a lithium-sulfur battery separator.

In one embodiment, the preparation method of the mixed system specifically includes: dispersing nano-silica in an organic solvent, and then mixing it evenly with the polyacrylonitrile.

In one embodiment, the usage ratio of the nanosilica and the organic solvent is (0.2-1) g: (40-60) mL.

In one embodiment, the voltage of the electrospinning process is 13-16 kV, and the feed rate of the electrospinning process is 0.7-0.8 mL/min.

In one embodiment, the usage ratio of the multi-walled carbon nanotubes to the alcohol solvent is (1.5-2.5) mg: (350-450) mL.

Lithium-sulfur battery, including a lithium-sulfur battery separator as described above.

Compared with the prior art, the beneficial effects of the present invention are:

(1) In the lithium-sulfur battery separator of the present invention, the electrospun base membrane has a porous structure and good electrolyte wettability. The combination of –C≡N in polyacrylonitrile and nano-SiO ₂ can alleviate the diffusion of polysulfides. ; In addition, the presence of multi-walled carbon nanotubes can further improve the electrochemical performance of Li-S batteries. It can not only increase the contact area with the cathode surface, provide high active material utilization, but also inhibit the migration of polysulfides, thus Their shuttle reaction can be avoided; through the synergistic cooperation of each component, the electrochemical performance of lithium-sulfur batteries can be promoted.

(2) The method of the present invention is simple and efficient. The electrospinning base membrane was prepared through electrospinning technology, and multi-walled carbon nanotubes were loaded on the electrospinning base membrane using simple suction filtration.

(3) The lithium-sulfur battery of the present invention has excellent cycle performance and rate performance.

Description of the drawings

In order to more clearly explain the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings that need to be used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description The drawings illustrate some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting any creative effort.

Figure 1 is a scanning electron microscope image of PAN/SiO ₂ -10 nanofibers;

Figure 2 is a scanning electron microscope image of PAN/SiO ₂ -30 nanofibers;

Figure 3 is the scanning electron microscope image of MWCNT;

Figure 4 is the transmission electron microscope image of MWCNT;

Figure 5 is a high-resolution transmission electron microscope image of MWCNT;

Figure 6 shows the FT-IR spectra of PAN, PAN/SiO ₂ -10 and PAN/SiO ₂ -30 nanofiber membranes;

Figure 7 is the cyclic voltammetry curve of the Li-S battery when the scan rate of PAN/SiO ₂ -10 is 0.1mV s ^-1 ;

Figure 8 is the cyclic voltammetry curve of the Li-S battery when the scan rate of PAN/SiO ₂ -30 is 0.1mV s ^-1 ;

Figure 9 is the cyclic voltammetry curve of the Li-S battery when the scan rate of PAN/SiO ₂ -30-MWCNT is 0.1mV s ^-1 ;

Figure 10 shows the charge and discharge curve of the battery prepared by PAN/SiO ₂ -10 when the current density is 0.2C;

Figure 11 shows the charge and discharge curve of the battery prepared by PAN/SiO ₂ -30 when the current density is 0.2C;

Figure 12 shows the charge and discharge curve of the battery prepared by PAN/SiO ₂ -30-MWCNT when the current density is 0.2C;

Figure 13 shows the cycle performance diagram of the battery prepared by PAN/SiO ₂ -10, PAN/SiO ₂ -30, PAN/SiO ₂ -30-MWCN, the current density is 0.2C;

Figure 14 shows the cycle performance diagram of the battery prepared by PAN/SiO ₂ -30-MWCNT at a high current density of 2C;

Figure 15 is a rate performance diagram of batteries prepared by PAN/SiO ₂ -10, PAN/SiO ₂ -30, PAN/SiO ₂ -30-MWCN;

Figure 16 shows the discharge/charge curve of PAN/SiO ₂ -10 Li-S battery at different rates;

Figure 17 shows the discharge/charge curve of PAN/SiO ₂ -30 Li-S battery at different rates;

Figure 18 shows the discharge/charge curve of PAN/SiO ₂ -30-MWCNT Li-S battery at different rates;

Figure 19 shows the CV curves of different voltage scan rates of PAN/SiO ₂ -10 batteries;

Figure 20 shows the CV curves of different voltage scan rates of PAN/SiO ₂ -30 batteries;

Figure 21 is the CV curve of different voltage scan rates of Li-S battery of PAN/SiO ₂ -30-MWCNT;

Figure 22 is a linear fitting diagram of the peak current of Li-S battery of PAN/SiO ₂ -10;

Figure 23 is a linear fitting diagram of the peak current of Li-S battery of PAN/SiO ₂ -30;

Figure 24 is a linear fitting diagram of the peak current of the Li-S battery of PAN/SiO ₂ -30-MWCNT.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

According to one aspect of the present invention, the present invention relates to a lithium-sulfur battery separator, including an electrospinning base film and multi-walled carbon nanotubes loaded on the electrospinning base film; the electrospinning base film is made of polyacrylonitrile It is a matrix, and the matrix contains nano-silica.

The battery separator of the present invention adopts electrospun polyacrylonitrile (PAN) nanofiber membrane. Compared with -CH ₃ in the polypropylene separator, the cyano (-C≡N) group has the same relationship with Li ₂ S or polysulfide. The binding energy is higher, and it has higher porosity and better electrolyte wettability, which results in better electrolyte wetting and high ionic conductivity, promoting rapid ion transport. In the present invention, nano-silica (SiO ₂ ) is incorporated into polyacrylonitrile, which can be used as an adsorbent for polysulfide. It is combined with polyacrylonitrile to prepare an electrospinning base membrane, which can effectively inhibit the formation of polysulfide in Li-S. Diffusion in the battery; further loading multi-walled carbon nanotubes (MWCNT) on the electrospinning base membrane can provide significantly improved cycle stability and rate performance for Li-S batteries without introducing a complex cathode structure, further Enhanced practicality of Li-S batteries.

In one embodiment, the mass ratio of the nano-silica, polyacrylonitrile and multi-walled carbon nanotubes is (200-1000): (2500-3500): (1.5-2.5). In one embodiment, the mass ratio of the nanosilica, polyacrylonitrile and multi-walled carbon nanotubes includes but is not limited to 200:2500:1.5, 300:3000:1.8, 500:3100:2, 800 :3200:2.2 or 1000:3500:2.5. The present invention uses nano-silica, polyacrylonitrile and multi-walled carbon nanotubes with appropriate mass ratios, and the prepared lithium-sulfur battery separator can better inhibit the diffusion of polysulfide in the Li-S battery and improve cycle stability. performance and rate performance.

In one embodiment, the particle size of the nano-silica is 10 to 20 nm. In one embodiment, the particle size of the nanosilica is 10nm, 12nm, 15nm, 17nm, 19nm or 20nm. The silica of the present invention adopts a suitable particle size, has a large specific surface area, high surface energy, and high chemical reaction activity, and is more conducive to inhibiting the diffusion of polysulfides in Li-S batteries.

In one embodiment, the outer diameter of the multi-walled carbon nanotubes is 8 to 15 nm, such as 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm or 15 nm, and the length is 40 to 60 μm, such as 40 μm, 42 μm, 45μm, 48μm, 50μm, 52μm, 55μm, 60μm, etc. In one embodiment, the multi-walled carbon nanotubes developed in the present invention originate from Shanghai Aladdin Biochemical Technology Co., Ltd.

In one embodiment, the weight average molecular weight of the polyacrylonitrile is 120,000 to 160,000 g/mol. In one embodiment, the weight average molecular weight of the polyacrylonitrile is 120000g/mol, 125000g/mol, 130000g/mol, 140000g/mol, 150000g/mol, 160000g/mol, etc.

In one embodiment, the effective area density of the lithium-sulfur battery separator is 0.19-0.26 mg/cm ² . In one embodiment, the thickness of the lithium-sulfur battery separator is 2.8-3.2 μm. In one embodiment, the lithium-sulfur battery separator has a porosity of 72% to 77%.

In one embodiment, some or all of the silica is replaced with alumina and/or graphene.

In one embodiment, some or all of the multi-walled carbon nanotubes are replaced with graphene and/or activated carbon.

According to another aspect of the invention, the invention also relates to a method for preparing the lithium-sulfur battery separator, which includes the following steps:

(a) Electrospinning a mixed system of nanosilica, polyacrylonitrile and organic solvent to obtain an electrospinning base membrane;

(b) Dispersing the multi-walled carbon nanotubes in an alcohol solvent, using vacuum filtration to load the multi-walled carbon nanotubes onto the electrospinning base film to obtain a lithium-sulfur battery separator.

The preparation method of the lithium-sulfur battery separator of the present invention is simple and efficient. The electrospinning base membrane is obtained by electrospinning technology using a mixed system of nano-silica, polyacrylonitrile and organic solvents. Then, the multi-walled carbon nanotubes are loaded onto the electrospun base membrane through vacuum filtration.

In one embodiment, the preparation method of the mixed system specifically includes: dispersing nano-silica in an organic solvent, and then mixing it evenly with the polyacrylonitrile.

In one embodiment, the organic solvent includes dimethylformamide (DMF, >99.5%, Sigma-Aldrich). In one embodiment, ultrasonic treatment is used to uniformly disperse nanosilica in the above-mentioned organic solvent.

In one embodiment, the usage ratio of the nanosilica and the organic solvent is (0.2-1) g: (40-60) mL. In one embodiment, the usage ratios of the nanosilica and the organic solvent are 0.2g:40mL, 0.3g:45mL, 0.5g:50mL, and 1g:60mL.

In one embodiment, the voltage of the electrospinning process is 13-16kV, such as 13V, 14V, 15V, 16V, etc. The feed rate of the electrospinning treatment is 0.7-0.8mL/min, such as 0.7mL/min, 0.71mL/min, 0.72mL/min, 0.73mL/min, 0.74mL/min, 0.75mL/min, 0.76 mL/min, 0.77mL/min, 0.78mL/min, 0.79mL/min or 0.8mL/min.

In one embodiment, the dosage ratio of the multi-walled carbon nanotubes to the alcohol solvent is (1.5-2.5) mg: (350-450) mL, such as 1.5 mg: 350 mL, 1.8 mg: 370 mL, 2 mg: 400mL, 2.5mg:450mL, etc. In one embodiment, the alcohol solvent includes ethanol solvent.

According to another aspect of the invention, the invention also relates to a lithium-sulfur battery, including a lithium-sulfur battery separator as described above.

The battery of the present invention has excellent cycle stability and rate performance.

Further explanation will be given below with reference to specific embodiments.

Example 1

The preparation method of lithium-sulfur battery separator includes the following steps:

(a) Disperse 0.3g silica (nanoscale powder, 10~20nm, Sigma-Aldrich) in 50mL dimethylformamide (DMF, >99.5%, Sigma-Aldrich), and make it fine with the assistance of ultrasound Disperse, then add 3g of polyacrylonitrile PAN (Mw=150000, Sigma-Aldrich) to prepare a PAN/SiO ₂ solution; pass the evenly mixed PAN/SiO ₂ solution through electrospinning technology (under a high pressure of 15kV, the feed rate is 0.75mL/min) to form a PAN/SiO ₂ electrospinning base membrane, which was named PAN/SiO ₂ -10 according to the ratio of SiO ₂ to PAN;

(b) 2 mg of commercially purchased multi-walled carbon nanotubes (outer diameter: 8 to 15 nm, length: 50 μm, Shanghai Aladdin Biochemical Technology Co., Ltd.) were first dispersed in 400 mL of absolute ethanol (5 mg/L), and then ultrasonically It is fully dispersed with assistance, and then loaded onto the above-mentioned electrospinning base membrane through vacuum filtration.

Example 2

The preparation method of lithium-sulfur battery separator includes the following steps:

(a) Disperse 0.9g silica (nanoscale powder, 10~20nm, Sigma-Aldrich) in 50mL dimethylformamide (DMF, >99.5%, Sigma-Aldrich), and make it fine with the assistance of ultrasound Disperse, then add 3g of polyacrylonitrile PAN (Mw=150000, Sigma-Aldrich) to prepare a PAN/SiO ₂ solution; pass the evenly mixed PAN/SiO ₂ solution through electrospinning technology (under a high pressure of 15kV, the feed rate is 0.75mL/min) to form a PAN/SiO ₂ electrospinning base membrane, which is named PAN/SiO ₂ -30 according to the ratio of SiO ₂ to PAN;

(b) 2 mg of commercially purchased multi-walled carbon nanotubes (outer diameter: 8 to 15 nm, length: 50 μm, Shanghai Aladdin Biochemical Technology Co., Ltd.) were first dispersed in 400 mL of absolute ethanol (5 mg/L), and then ultrasonically It is fully dispersed with assistance, and then loaded onto the above-mentioned electrospinning base membrane through vacuum filtration.

Example 3

The preparation method of lithium-sulfur battery separator includes the following steps:

(a) Disperse 0.2g silica (nanoscale powder, 10~20nm, Sigma-Aldrich) in 50mL dimethylformamide (DMF, >99.5%, Sigma-Aldrich), and make it fine with the assistance of ultrasound Disperse, then add 3g of polyacrylonitrile PAN (Mw=150000, Sigma-Aldrich) to prepare a PAN/SiO ₂ solution; pass the evenly mixed PAN/SiO ₂ solution through electrospinning technology (under a high pressure of 13kV, the feed rate is 0.7mL/min) to form a PAN/SiO ₂ electrospinning base membrane;

(b) 1.5mg of commercially purchased multi-walled carbon nanotubes (outer diameter: 8~15nm, length: 50μm, Shanghai Aladdin Biochemical Technology Co., Ltd.) were first dispersed in 350mL of absolute ethanol (5mg/L), and then It is fully dispersed with the assistance of ultrasound, and then loaded onto the above-mentioned electrospinning base membrane through vacuum filtration.

Example 4

The preparation method of lithium-sulfur battery separator includes the following steps:

(a) Disperse 0.5g silica (nanoscale powder, 10~20nm, Sigma-Aldrich) in 50mL dimethylformamide (DMF, >99.5%, Sigma-Aldrich), and make it fine with the assistance of ultrasound Disperse, then add 3g of polyacrylonitrile PAN (Mw=150000, Sigma-Aldrich) to prepare a PAN/SiO ₂ solution; pass the evenly mixed PAN/SiO ₂ solution through electrospinning technology (under a high pressure of 13kV, the feed rate is 0.7mL/min) to form a PAN/SiO ₂ electrospinning base membrane;

(b) 2.5mg of commercially purchased multi-walled carbon nanotubes (outer diameter: 8~15nm, length: 50μm, Shanghai Aladdin Biochemical Technology Co., Ltd.) were first dispersed in 450mL of absolute ethanol (5mg/L), and then It is fully dispersed with the assistance of ultrasound, and then loaded onto the above-mentioned electrospinning base membrane through vacuum filtration.

Experimental example

1. Map analysis

Figure 1 is the scanning electron microscope image of PAN/SiO ₂ -10 nanofibers; Figure 2 is the scanning electron microscope image of PAN/SiO ₂ -30 nanofibers; Figure 3 is the scanning electron microscope image of MWCNT; Figure 4 is the transmission electron microscope image of MWCNT; Figure 5 is a high-resolution transmission electron microscope image of MWCNT.

Referring to Figures 1 and 2, scanning electron microscopy (SEM) images show the highly porous structure of PAN/SiO ₂ -10 and PAN/SiO ₂ -30, which is different from the crack-like porous structure of the microporous PP separator. Both separators are composed of randomly arranged fibers with average diameters of 625 nm and 600 nm respectively. The porosity of PAN/SiO ₂ -10 and PAN/SiO ₂ -30 is 72% and 75% respectively, which are significantly higher than the 41% porosity of the PP separator. The porosity of PAN/SiO ₂ -30-MWCNT is 76%, the diameter of each multi-walled carbon nanotube is about 50nm, and has a good crystal structure. As shown in Figure 4, the multi-walled carbon nanotubes are in direct contact with S, Provides good electrical conductivity and therefore benefits the electrochemical performance of the battery.

Figure 6 shows the infrared spectra of PAN film, PAN/SiO ₂ -10 film and PAN/SiO ₂ -30 film. The peaks at 1452cm ^-1 , 2243cm ^-1 and 2937cm ^-1 are -CH ₂ and -C of PAN respectively. ≡Characteristic peaks of N and -CH. The peaks of PAN/SiO ₂ -10 and PAN/SiO ₂ -30 at 1084 cm ^-1 are obviously the Si-O-Si stretching vibration peaks of SiO ₂ .

2. Electrochemical performance test

Sulfur (S, 99.5-100.5%, Sigma-Aldrich), conductive carbon black (C-65, TIMCAL Graphite&Carbon Ltd.), and polyvinylidene fluoride (PVDF) in N-methyl- Mix 2-pyrolidone (NMP, 99%, Sigma-Aldrich) into a uniform slurry, then paste the slurry on the carbon-coated aluminum foil, dry it under vacuum at 60°C for 12 hours; lithium metal foil is used as the anode , a mixture of 1MLiTFSI and 0.1M LiNO ₃ mixed in 1,3-dioxopentane and 1,2-dimethoxyethane (volume ratio is 1:1) is used as an electrolyte; After the separators are assembled into batteries, they are tested in a voltage window of 1.7V to 2.8V. The lithium ion diffusion coefficient D _Li ⁺ (cm ² S ^-1 ) was measured by CV at different scan rates and calculated according to the Randles-Sevick equation:

I _p =2.69×10 ⁵ n ^1.5 AD _Li ^+0.5 C _Li ⁺ ν ^0.5

In the formula, I _p is the peak current, n is the number of electrons in the reaction (Li-S battery is 2), A is the electrode area in cm ² , C _Li ⁺ and v represent the lithium ion concentration in the electrolyte, in units mol mL ^-1 , CV scan rate unit is V s ^-1 .

Figure 7 is the cyclic voltammetry curve of Li-S battery when PAN/SiO ₂ -10 scan rate is 0.1mV s ^-1 ; Figure 8 is the Li-S battery when PAN/SiO ₂ -30 scan rate is 0.1mV s ^-1 S battery cyclic voltammogram; Figure 9 is the Li-S battery cyclic voltammogram when the scan rate of PAN/SiO ₂ -30-MWCNT is 0.1mV s ^-1 ; Figure 10 is the battery prepared by PAN/SiO ₂ -10 The charge and discharge curve when the current density is 0.2C; Figure 11 shows the charge and discharge curve of the battery prepared by PAN/SiO ₂ -30 when the current density is 0.2C; Figure 12 shows the charge and discharge curve of the battery prepared by PAN/SiO ₂ -30-MWCNT. Charge and discharge curve when density is 0.2C.

Referring to Figures 7, 8 and 9, Figure 7 shows that the cathode peaks of the battery with PAN/SiO ₂ -10 as separator are about 2.25V and 2.00V, corresponding to the conversion of S into long-chain polysulfide (Li ₂ S _x , 4≤x≤8) (region 1) and long-chain polysulfides are converted into low-order Li ₂ S ₂ or even Li ₂ S (region 2). PAN/SiO ₂ -30 and PAN/SiO ₂ -30-MWCNT also show similar redox reactions. Figure 10, Figure 11 and Figure 12 show the initial charge and discharge current of Li-S batteries at a constant current density of 0.2C for PAN/SiO ₂ -10, PAN/SiO ₂ -30 and PAN/SiO ₂ -30-MWCNT respectively. All three cells exhibit two discharge plateaus and two closely spaced charge plateaus, consistent with their CV plots. As can be seen from Figure 12, among the three samples of the battery, PAN/SiO ₂ -30-MWCNT has the highest capacity. This is because the conductive MWCNT provides sufficient contact with the cathode surface, providing high active material utilization. Rate. In addition, this MWCNT sheet inhibits the migration of polysulfide intermediates and avoids the shuttle effect.

Figure 13 is the cycle performance diagram of the battery prepared by PAN/SiO ₂ -10, PAN/SiO ₂ -30, PAN/SiO ₂ -30-MWCN. The current density is 0.2C; Figure 14 is PAN/SiO ₂ -30-MWCNT. The cycle performance diagram of the prepared battery at a high current density of 2C; Figure 15 is the rate performance diagram of the battery prepared by PAN/SiO ₂ -10, PAN/SiO ₂ -30, PAN/SiO ₂ -30-MWCN. As can be seen from Figure 13, the initial discharge capacity of PAN/SiO ₂ -30 is slightly increased (from 930mAh g ^-1 to 946mAh g ^-1 ) compared with PAN/SiO ₂ -10. In comparison, PAN/SiO ₂ -30-MWCN can be improved to 1182mAh g ^-1 . The battery with PAN/SiO ₂ -30-MWCNT as separator can still provide a high capacity of 741mAh g ^-1 after 100 cycles at a current density of 0.2C. In order to further study the electrochemical performance of the PAN/SiO ₂ -30-MWCNT battery, a long-term cycle test was conducted at a current density of 2C, as shown in Figure 14. At such a high current density, the battery containing PAN/SiO ₂ -30 -MWCNT’s battery can still provide an initial capacity of up to 816mAh g ^-1 , and more importantly, it can still maintain a capacity of 426mAh g ^-1 even after 300 cycles, with a Coulombic efficiency of 96.3%, which further demonstrates its excellent Electrochemical properties. As we all know, rate performance is one of the important indicators of batteries, especially for high-power applications and fast charging capabilities. Therefore, the performance of lithium-sulfur batteries assembled with three different separators was studied. As shown in Figure 15, the current density gradually increased from 0.1C to 1C for every ten consecutive cycles, and then returned to 0.1C. The stable reversible capacities of PAN/SiO ₂ -10 and PAN/SiO ₂ -30 system Li-S batteries dropped from 613mAh g ^-1 and 671mAh g ^-1 to 317mAh g ^-1 and 357mAh g ^-1 respectively. The battery capacity of PAN/SiO ₂ -30-MWCNT slowly dropped from the reversible capacity from 960mAh g ^-1 at 0.1C to 845 (0.2C), 726 (0.5C), and 627 (1C) mAh g ^-1 . Importantly, a high reversible capacity of 842mAh g ^-1 is achieved when the current density is reduced to 0.1C, indicating that highly reversible and efficient Li-S batteries can be achieved using PAN/ _SiO2-30 -MWCNT.

Figure 16 is the discharge/charge curve of PAN/SiO ₂ -10 Li-S battery at different rates; Figure 17 is the discharge/charge curve of PAN/SiO ₂ -30 Li-S battery at different rates; Figure 18 This is the discharge/charge curve of PAN/SiO ₂ -30-MWCNT Li-S battery at different rates. At low current rates, all discharge curves have the double plateau characteristics of typical S cathodes, while the charge curves show two plateaus respectively, which is consistent with their CV plots. The PAN/SiO ₂ -30-MWCNT battery showed two longer discharge plateaus, indicating its high reversible capacity and low polarization characteristics.

Figure 19 is the CV curve of PAN/SiO ₂ -10 battery at different voltage scan rates; Figure 20 is the CV curve of PAN/SiO ₂ -30 battery at different voltage scan rates; Figure 21 is the CV curve of PAN/SiO ₂ -30-MWCNT CV curves of different voltage scan rates for Li-S batteries. Figure 22 is a linear fitting diagram of the peak current of the Li-S battery with PAN/SiO ₂ -10 as the separator; Figure 23 is a linear fitting diagram of the peak current of the Li-S battery with PAN/SiO ₂ -30 as the separator; Figure 24 This is a linear fitting diagram of the peak current of the Li-S battery with PAN/SiO ₂ -30-MWCNT as the separator.

It is important to study the effects of _SiO2 and MWCNTs on lithium ion diffusion because the rate performance is closely related to the diffusion of lithium ions in the battery. The lithium ion diffusion coefficient was evaluated from a series of CV measurements at different scan rates and calculated via the Randles-Sevcik equation. Here, the cathode peaks at 2.2V and 1.95V and the anode peak at 2.45V are defined as A, B and C peaks respectively. According to the Randles-Sevcik equation, the reduction peak current I _p and the square root of the scan rate should result in a straight line, as shown in Figures 22 to 24. According to the slope of the linear fitting, the lithium ion diffusion coefficient of the Li-S battery of PAN/SiO ₂ -10 is calculated to be D _Li ⁺ (A) = 6.17×10 ^-9 cm ² s ^-1 , D _Li ⁺ (B) = 9.56×10 ^-9 cm ² s ^-1 , D _Li ⁺ (C)=2.33×10 ^-8 cm ² s ^-1 . The lithium ion diffusion coefficient of the Li-S battery with PAN/SiO ₂ -30 as separator increases to D _Li ⁺ (A) = 1.05×10 ^-8 cm ² s ^-1 , D _Li ⁺ =2.05×10 ^-8 cm ² s ^-1 , D _Li ⁺ (C)=3.66×10 ^-8 cm ² s ^-1 . The diffusion coefficient of the Li-S battery with PAN/SiO ₂ -30-MWCNT as separator further increases to D _Li ⁺ (A) = 1.12×10 ^-8 cm ² s ^-1 , D _Li ⁺ (B) = 2.09×10 ^{- 8} cm ² s ^-1 , D _Li ⁺ (C) = 4.55×10 ^-8 cm ² s ^-1 .

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions recorded in the foregoing embodiments, or to equivalently replace some or all of the technical features; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention. range.

Claims (10)

1. The lithium-sulfur battery diaphragm is characterized by comprising an electrostatic spinning base film and multi-wall carbon nanotubes loaded on the electrostatic spinning base film; the electrostatic spinning base film takes polyacrylonitrile as a matrix, and the matrix contains nano silicon dioxide.

2. The lithium sulfur battery separator according to claim 1, wherein the mass ratio of the nano silicon dioxide, the polyacrylonitrile and the multi-wall carbon nano tube is (200-1000): (2500-3500): (1.5-2.5).

3. The lithium sulfur battery separator according to claim 1, comprising at least one of the following features (1) to (3):

(1) The particle size of the nano silicon dioxide is 10-20 nm;

(2) The outer diameter of the multi-wall carbon nano tube is 8-15 nm, and the length is 40-60 mu m;

(3) The weight average molecular weight of the polyacrylonitrile was 120000 ～ 160000g/mol.

4. The lithium sulfur battery separator according to claim 1, comprising at least one of the following features (1) to (3):

(1) The effective area density of the lithium sulfur battery diaphragm is 0.19-0.26 mg/cm ² ；

(2) The thickness of the lithium sulfur battery diaphragm is 2.8-3.2 mu m;

(3) The porosity of the lithium sulfur battery diaphragm is 72% -77%.

5. The lithium sulfur battery separator according to claim 1, comprising at least one of the following features (1) to (2):

(1) Replacing part or all of the silicon dioxide with aluminum oxide and/or graphene;

(2) And replacing part or all of the multi-wall carbon nanotubes with graphene and/or activated carbon.

6. The method for preparing a lithium sulfur battery separator according to any one of claims 1 to 5, comprising the steps of:

(a) Carrying out electrostatic spinning treatment on a mixed system formed by nano silicon dioxide, polyacrylonitrile and an organic solvent to obtain an electrostatic spinning base film;

(b) Dispersing the multi-wall carbon nano tube in an alcohol solvent, and loading the multi-wall carbon nano tube onto the electrostatic spinning base film by adopting a vacuum suction filtration mode to obtain the lithium-sulfur battery diaphragm.

7. The method of producing a lithium sulfur battery separator according to claim 6, characterized by comprising at least one of the following features (1) to (2):

(1) The preparation method of the mixed system specifically comprises the following steps: dispersing nano silicon dioxide in an organic solvent, and uniformly mixing with the polyacrylonitrile;

(2) The dosage ratio of the nano silicon dioxide to the organic solvent is (0.2-1) g (40-60) mL.

8. The method for preparing a lithium sulfur battery separator according to claim 6, wherein the voltage of the electrospinning treatment is 13-16 kV, and the feeding rate of the electrospinning treatment is 0.7-0.8 mL/min.

9. The method according to claim 6, wherein the ratio of the multi-walled carbon nanotubes to the alcohol solvent is (1.5-2.5) mg (350-450) mL.

10. A lithium-sulfur battery comprising the lithium-sulfur battery separator according to any one of claims 1 to 5.