CN110880575A - Composite diaphragm, preparation and application thereof in lithium-sulfur battery - Google Patents

Composite diaphragm, preparation and application thereof in lithium-sulfur battery Download PDF

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CN110880575A
CN110880575A CN201811040154.8A CN201811040154A CN110880575A CN 110880575 A CN110880575 A CN 110880575A CN 201811040154 A CN201811040154 A CN 201811040154A CN 110880575 A CN110880575 A CN 110880575A
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lithium
layer
philic
metal
composite
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赖延清
洪波
范海林
董庆元
张治安
张凯
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Central South University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract

The invention discloses a preparation method and application of a composite diaphragm for a lithium-sulfur battery. The composite diaphragm consists of a lithium affinity layer (facing a lithium cathode), an insulating lithium conduction layer and a liquid absorption layer (facing a sulfur anode). This has the advantage that the lithium-philic layer can react with the tips of the lithium dendrites to consume the lithium dendrites and prevent the lithium dendrites from continuing to grow to pierce the membrane. The insulating lithium-conducting layer serves to conduct lithium ions but effectively block electrons. The liquid absorbing layer is used for absorbing and storing electrolyte and preventing polysulfide dissolved in the positive electrode from being transmitted between the positive electrode and the negative electrode. Thanks to this unique structural advantage, lithium-sulfur batteries composed of such composite separators exhibit long cycle life and excellent cycle performance.

Description

Composite diaphragm, preparation and application thereof in lithium-sulfur battery
Technical Field
The invention belongs to the field of energy storage, and particularly relates to preparation and application of a composite diaphragm for a lithium-sulfur battery.
Background
The lithium-sulfur battery is a lithium metal battery which takes metal lithium as a negative electrode and elemental sulfur or composite sulfur as a positive electrode. Due to the ultrahigh theoretical specific capacity (3860mAh/g) of the metal lithium, the lowest electrode potential (-3.045V) and the high theoretical specific capacity (1675mAh/g) of the sulfur anode, the lithium-sulfur battery has the ultrahigh energy density of 2600Wh/kg, which is more than ten times of the energy density of the current commercial lithium ion battery. Meanwhile, the lithium-sulfur battery is known as the most promising next-generation energy storage device by virtue of the cost advantage of the sulfur anode. Thus, lithium sulfur batteries have been widely noticed and developed by governments and researchers of various countries. Behind these developments, lithium sulfur batteries have been under great development. Such as Haoshen Zhou et al [ Bai, s.; liu, x.; zhu, k.; wu, s.; zhou, H, Metal-organic frame-based separator for lithium-sulfur materials Nature Energy2016, 1(7), 16094-16099.]The MOF modified graphene oxide is used as a sulfur-blocking lithium-conducting diaphragm to realize 500-cycle stable circulation at 0.5C multiplying power. And Qiang Zhang et al [ Cheng, X. -B.; peng, h. -j.; huang, J. -Q.; wei, F.; zhang, q., deborite-free nanostructured anode: enterprise of lithium in a 3D fibrous matrix for ultra-stable lithium-sulfur materials, Small 2014.10(21), 4257-.]The stable circulation of 2000 circles is realized by adopting the 3D porous lithium boron alloy as the cathode under 1C. Despite the promising success of lithium-sulfur batteries, practical applications have not yet been achieved. Because, the current major research is difficult to satisfy the high current density (> 5 mA/cm) of the lithium-sulfur battery at the same time2) And high sulfur loading (10 mg/cm)2) In this way, high practical specific capacities (> 1000mAh/g) and long cycle lives (> 500 cycles) are obtained. It is not possible to achieve the simultaneous growth of dendrites on the surface of the negative electrode and disordered shuttling of polysulfides on the surface of the positive electrode. The uncontrollable growth of dendrites on the surface of the negative electrode leads to low coulombic efficiency and consumption of electrolyte, and even great potential safety hazard. While disordered shuttling of polysulfides on the surface of the positive electrode results in active sulfurEventually making it difficult to improve the performance of the lithium sulfur battery.
Disclosure of Invention
The invention aims to provide a composite separator for solving the common problem of lithium-sulfur batteries, namely the problem that dendritic crystal growth cannot be inhibited and the shuttle of polysulfide cannot be prevented at the same time.
The second purpose of the invention is to provide an application method of the composite diaphragm in a lithium-sulfur battery.
A third object of the present invention is to provide a lithium-sulfur battery loaded with the composite separator of the present invention.
A composite diaphragm comprises a lithium-philic layer, an insulating lithium-conducting layer and a liquid absorbing layer which are sequentially compounded;
the lithium-philic layer comprises a lithium-philic material (lithium-philic particles); the lithium-philic material is at least one of a simple substance of M metal and a compound of M metal; wherein, the M metal is a metal which can perform alloying reaction with Li;
the liquid absorbing layer comprises a material capable of absorbing electrolyte;
the insulating lithium-conducting layer is a polymer capable of conducting lithium ions and blocking electrons.
The composite diaphragm is of a sandwich structure, the middle layer is an insulating lithium-conducting layer (diaphragm substrate), and the upper surface and the lower surface of the insulating lithium-conducting layer are respectively compounded with a lithium-philic layer and a liquid absorbing layer. According to the composite diaphragm disclosed by the invention, the lithium-philic layer can generate an alloying reaction with the tip of the lithium dendrite, so that the lithium dendrite is consumed by adopting a chemical method, and the situation that the diaphragm is pierced by the lithium dendrite due to the continuous growth of the lithium dendrite is avoided. The insulating lithium-conducting layer serves to conduct lithium ions but effectively block electrons. The liquid absorbing layer is used for absorbing and storing electrolyte and preventing polysulfide dissolved in the positive electrode from being transmitted between the positive electrode and the negative electrode. Thanks to the unique structure and the control of the components of the three-layer structure, the three-layer structure can achieve a significant synergistic effect with each other, and can significantly improve the electrical performance of the assembled battery, for example, significantly synergistically improve the charging and discharging coulombic efficiency and the cycle life of the battery, and particularly synergistically improve the high current density (> 5 mA/cm)2) The cycle performance of the following.
In the present invention, the lithium-philic material is preferably a material in the form of particles. The lithium-philic material provided by the invention is a simple metal (simple M metal) or a compound of the metal (compound of the M metal) which can perform an alloying reaction with lithium. When the lithium-philic material is a compound of M metal, it is subjected to a substitution reaction with Li in advance, and then to an alloying reaction with the substituted M metal.
Preferably, the M metal is at least one of zinc, gallium, germanium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, iridium, platinum, gold, mercury, thallium, lead and bismuth; further preferred is at least one of zinc, gallium, tin and bismuth.
Preferably, the compound of the M metal is at least one of an oxide and a sulfide of the M metal. Compared with the simple substance of the M metal, the oxide and the sulfide of the M metal can be formed in the lithium-philic layer, and the lithium oxide and the lithium sulfide coating can prevent the alloy substance from being pulverized and cracked in the charging and discharging processes.
Preferably, the lithium-philic layer may further contain at least one of an alloy of Li — M metal, lithium oxide, and lithium sulfide. The alloy formed by Li-M metal, lithium oxide and lithium sulfide can be obtained in situ by the reaction of the lithium-philic material and lithium.
Research finds that the particle size of the lithium-philic material is controlled, which is helpful for further improving the performance of the battery.
Preferably, the size (D50 granularity) of the lithium-philic particles is 2-9500 nm; preferably 5-8000 nm; further preferably 10 to 6000 nm; more preferably 50 to 700 nm. It has been found that the electrical performance of the battery, particularly the high rate cycling performance, is further improved at the preferred particle size of the lithium-philic particles.
Preferably, the lithium-philic layer further comprises a binder.
More preferably, the adhesive is at least one of polyethylene, polypropylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene chloride, styrene butadiene rubber and polybutylene.
Researches find that the content of the lithium-philic material in the lithium-philic layer can be controlled, the harm of lithium dendrite can be further effectively avoided, and the cycle performance of the battery can be further improved.
The content of the lithium-philic material is 20-97 wt.%; preferably 30 to 95 wt.%; further preferably 50-90 wt.%; even more preferably 60 to 80 wt.%; the balance of adhesive. The cycle performance is more excellent in the preferable content range.
The thickness of the lithium-philic layer is 0.08-120 mu m; preferably 0.1 to 100 μm; more preferably 1.6 to 60 μm. It was found that the electrical properties are better at the preferred thickness range.
The material of the insulating lithium-conducting layer is conductive lithium and non-conductive polymer.
Preferably, the polymer of the lithium-conducting insulation layer is at least one of polyethylene, polypropylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene chloride, styrene-butadiene rubber and polybutylene.
The thickness of the insulating lithium-conducting layer is 1-100 mu m.
Preferably, the thickness of the insulating lithium-conducting layer is 5-60 μm.
Preferably, in the liquid absorbent layer, the material capable of adsorbing the electrolyte is a material capable of adsorbing polysulfides in the electrode liquid.
Preferably, the liquid absorbing layer is made of at least one of carbon paper, carbon cloth, carbon nanotube paper, graphene paper, hollow carbon fibers and glass fibers. Studies have found that graphene paper performs best as a liquid absorbent layer, followed by carbon nanotube paper and carbon cloth as liquid absorbent layers, and then carbon paper, hollow carbon fibers and glass fibers.
The thickness of the liquid absorption layer is 0.5-600 mu m; preferably 1 to 500 μm; more preferably 3 to 300 μm; more preferably 24 to 180 μm. The electrical properties are better at the preferred thickness range.
The invention provides an application of the composite diaphragm, which is used as a diaphragm of a lithium-sulfur battery.
Further preferably, in the application, the lithium-philic layer of the composite separator faces the lithium metal negative electrode; the liquid absorption layer of the composite diaphragm faces to the positive electrode.
The invention also provides a lithium-sulfur battery, which comprises a positive electrode, a negative electrode, a diaphragm for separating the positive electrode from the negative electrode, and electrolyte for soaking the positive electrode, the negative electrode and the diaphragm.
Has the advantages that:
the composite diaphragm for the lithium-sulfur battery comprises a lithium-philic layer, an insulating lithium-conducting layer and a liquid absorbing layer. The lithium-philic layer is beneficial to consuming lithium dendrites growing on the surface of the negative electrode, and the harm caused by the continuous growth of the dendrites is avoided. The insulating lithium-conducting layer serves to conduct lithium ions but effectively block electrons. And the liquid absorbing layer is used for absorbing and storing electrolyte, and preventing polysulfide dissolved in the positive electrode from being transmitted between the positive electrode and the negative electrode.
According to the invention, through the control of the sandwich structure and the material structures of the lithium-philic layer and the liquid absorbing layer, the purposes of synergistically improving the coulombic efficiency and the electrical cycle performance, especially the cycle performance under high multiplying power, can be achieved. Tests show that the coulombic efficiency of 200 cycles is as high as 99.6%, the cycle number of cycles can be as high as 856 cycles when the capacity is lower than 80%, and the cycle performance is 3 times that of a single lithium-philic layer or a liquid absorbing layer.
Drawings
FIG. 1 is an SEM photograph of zinc sulfide from example 1.
FIG. 2 is an ESD image of zinc sulfide in example 1.
Fig. 3 is a schematic view of the composite separator of example 1, in which 1 is a lithium-philic particle, 2 is an adhesive, 3 is an insulating lithium-conducting layer, and 4 is a liquid-absorbing layer.
Detailed Description
The following is a detailed description of the preferred embodiments of the invention and is not intended to limit the invention in any way, i.e., the invention is not intended to be limited to the embodiments described above, and modifications and alternative compounds that are conventional in the art are intended to be included within the scope of the invention as defined in the claims.
Example 1
Clean commercial carbon paper is taken as a liquid absorption layer (5 mu m), and then the surface of the carbon paper is coated with a layer of polyethylene polymerThis was used as a lithium conducting insulating layer (15 μm) in polyethylene dispersed MNP solvent. After drying, a layer of zinc sulfide (particle size 2 μm, shown in fig. 1 and 2) and polyethylene mixture (zinc sulfide and polyethylene in MNP solvent dispersed at 70% by mass) was coated on the surface of the lithium conductive insulating layer as a lithium-philic layer (5 μm). Subsequently, the composite separator was used as a separator (fig. 3), lithium metal was used as a negative electrode, and an S-rich carbon nanotube positive electrode containing 1 wt.% of LiNO in a volume ratio of 1M LiTFSI/DOL: DME (1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 1.
Comparative example 1
A commercial PE diaphragm is used as a diaphragm (25 mu M), metal lithium is used as a negative electrode, a carbon nano tube positive electrode rich in an S simple substance is used, and 1 wt.% LiNO is contained in a volume ratio of 1: 1 of 1M LiTFSI/DOL: DME3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 1.
Comparative example 2
Clean commercial carbon paper was taken as a wicking layer (5 μm) and the carbon paper surface was subsequently coated with a layer of polyethylene polymer (in polyethylene dispersed MNP solvent) to serve as an insulating lithium conducting layer (15 μm). After drying, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1M LiTFSI/DOL/DME (volume ratio is 1: 1) contains 1 wt.% LiNO3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 1.
Comparative example 3
A clean and smooth glass plate was taken as a substrate, and then the surface was coated with a layer of polyethylene polymer (in MNP solvent dispersed with polyethylene) as an insulating lithium conducting layer (15 μm). After drying, it was peeled off from the glass plate, and coated on the surface with a mixture of zinc sulfide (particle size of 2 μm) and polyethylene (zinc sulfide and polyethylene in an MNP solvent dispersed at 70% by mass) as a lithium-philic layer (5 μm). Then, the composite diaphragm is taken as a diaphragm, and gold is taken asLithium is used as a negative electrode, a carbon nano tube positive electrode rich in S simple substance contains 1 wt.% LiNO by 1M LiTFSI/DOL: DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
Comparative example 4
The present case compares copper sulfide, it can not form lithium alloying, specifically as follows:
clean commercial carbon paper was taken as a wicking layer (5 μm) and the carbon paper surface was subsequently coated with a layer of polyethylene polymer (in polyethylene dispersed MNP solvent) to serve as an insulating lithium conducting layer (15 μm). After drying, a layer of copper sulfide (with a particle size of 2 μm) and polyethylene mixture (copper sulfide and polyethylene dispersed in 70% by mass of MNP solvent) is coated on the surface of the insulating lithium-conducting layer to form a composite layer (5 μm). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 wt.% LiNO is contained in a volume ratio of 1M LiTFSI/DOL to DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 1.
Figure BDA0001791332390000061
Example 2
Clean commercial carbon cloth was taken as a liquid absorbent layer (40 μm), and then a layer of polypropylene polymer (in MNP solvent dispersed in polypropylene) was coated on the surface of the carbon cloth to serve as an insulating lithium conducting layer (25 μm). After drying, a layer of silver particles (with a particle size of 0.5 μm) and a polypropylene mixture (silver particles and polypropylene in MNP solvent dispersed at a mass ratio of 70%) was coated on the surface of the lithium-conductive insulating layer as a lithium-philic layer (12 μm). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 wt.% LiNO is contained in a volume ratio of 1M LiTFSI/DOL to DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 2.
Example 3
Clean commercial carbon cloth was taken as a liquid absorbent layer (40 μm), and then a layer of polypropylene polymer (in MNP solvent dispersed in polypropylene) was coated on the surface of the carbon cloth to serve as an insulating lithium conducting layer (25 μm). After drying, a layer of silver oxide particles (with a particle size of 0.5 μm) and polypropylene mixture (silver oxide particles and polypropylene in MNP solvent dispersed at a mass ratio of 70%) is coated on the surface of the lithium-conductive insulating layer to form a lithium-philic layer (12 μm). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 wt.% LiNO is contained in a volume ratio of 1M LiTFSI/DOL to DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 2.
Example 4
Clean commercial carbon cloth was taken as a liquid absorbent layer (40 μm), and then a layer of polypropylene polymer (in MNP solvent dispersed in polypropylene) was coated on the surface of the carbon cloth to serve as an insulating lithium conducting layer (25 μm). After drying, a layer of silver sulfide particles (with a particle size of 0.5 μm) and polypropylene mixture (silver sulfide particles and polypropylene are dispersed in MNP solvent with a mass ratio of 70%) is coated on the surface of the lithium-conductive insulating layer to form a lithium-philic layer (12 μm). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 wt.% LiNO is contained in a volume ratio of 1M LiTFSI/DOL to DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 2.
TABLE 2
Figure BDA0001791332390000071
The results show that the performance of silver sulfide is superior to that of silver oxide, and is better than that of simple substance silver.
Example 5
The lithium-philic material in the embodiment of the scheme is zinc sulfide, tin sulfide, antimony sulfide or germanium sulfide, and specifically comprises the following components:
taking clean commercial graphene paper as imbibitionLayer (30 μm) and then graphene paper surface coated with a layer of polypropylene polymer (in MNP solvent with polypropylene dispersed) to serve as a lithium conducting insulating layer (35 μm). After drying, respectively coating a layer of zinc sulfide, tin sulfide, antimony sulfide and germanium sulfide particles (the particle sizes are all 1 mu m) and a polypropylene mixture (zinc sulfide tin sulfide, antimony sulfide or germanium sulfide particles and polypropylene are respectively dispersed in an MNP solvent according to the mass ratio of 60%) on the surface of the insulating lithium-conducting layer to be used as a lithium-philic layer (16 mu m). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 MLiTFSI/DOL/DME (volume ratio is 1: 1) contains 1 wt.% LiNO3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 3.
TABLE 3
Figure BDA0001791332390000081
The results show that the preferred lithium philic particles (zinc sulfide, tin sulfide) perform better.
Example 6
The granularity of the lithium-philic particles is explored in the example, and specifically as follows:
clean commercial graphene paper was taken as a liquid absorbent layer (30 μm), and then a layer of polytetrafluoroethylene polymer (in a polytetrafluoroethylene-dispersed MNP solvent) was coated on the surface of the graphene paper to serve as an insulating lithium-conducting layer (50 μm). After drying, a layer of zinc sulfide (with particle sizes of 2, 8, 50, 700, 7100 and 9500nm respectively) and a polytetrafluoroethylene mixture (zinc sulfide particles with different particle sizes are respectively dispersed in MNP solvent with polytetrafluoroethylene according to the mass ratio of 65%) are respectively coated on the surface of the insulating lithium-conducting layer to serve as a lithium-philic layer (30 mu m). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and LiNO with the volume ratio of 1M LiTFSI/DOL to DME (1: 1) contains 2 wt.% LiNO3And forming a lithium-sulfur battery for the electrolyte, and carrying out a charge-discharge cycle test at a rate of 2C.
The results of the tests are shown in table 4.
TABLE 4
Figure BDA0001791332390000091
The result shows that the performance is better in the preferable particle size range (10-6000 nm, and more preferably 50-700 nm).
Example 7
In the case of screening the content of the lithium-philic material, the content is specifically as follows:
clean commercial graphene paper was taken as a liquid absorbent layer (20 μm), and then a layer of polytetrafluoroethylene polymer (in a polytetrafluoroethylene-dispersed MNP solvent) was coated on the surface of the graphene paper to serve as an insulating lithium-conducting layer (40 μm). After drying, respectively coating a layer of zinc sulfide (with the particle size of 7.1 μm) and a layer of polytetrafluoroethylene mixture (the mass ratio of zinc sulfide particles to polytetrafluoroethylene is respectively 20%, 40%, 60%, 80%, 92% and 97% in a dispersed MNP solvent) on the surface of the insulating lithium-conducting layer to serve as a lithium-philic layer (25 μm). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 MLiTFSI/DOL/DME (volume ratio is 1: 1) contains 1 wt.% LiNO3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 5.
TABLE 5
Figure BDA0001791332390000092
Figure BDA0001791332390000101
The result shows that the performance is better in the preferable content ratio range (60-80%).
Example 8
The influence of this case example probing lithium-philic layer thickness specifically is as follows:
clean commercial carbon nanotube paper is taken as a liquid absorption layer (40 μm), and then a layer of polytetrafluoroethylene polymer (a polytetrafluoroethylene dispersed MNP solution) is coated on the surface of the carbon nanotube paperIn agent) was used as an insulating lithium-conducting layer (20 μm). After drying, respectively coating a layer of zinc sulfide (with the particle size of 20nm) and a polytetrafluoroethylene mixture (zinc sulfide particles and polytetrafluoroethylene are respectively dispersed in MNP solvent with the mass ratio of 55%) on the surface of the insulating lithium-conducting layer to serve as a lithium-philic layer (the thicknesses of the coated lithium-philic layer are respectively 0.08, 0.18, 1.6, 45, 75 and 120 microns). Then, the composite diaphragm is taken as a diaphragm, metal lithium is taken as a negative electrode, a carbon nano tube positive electrode rich in S simple substance is taken, and 1 wt.% LiNO is contained in a volume ratio of 1M LiTFSI/DOL to DME (volume ratio is 1: 1)3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 6.
TABLE 6
Figure BDA0001791332390000102
The result shows that the performance is better in the preferable thickness range (1.6-60 mu m) of the lithium-philic layer.
Example 9
The present case discusses the liquid-absorbing layer material, as follows:
clean commercial carbon paper, carbon cloth, carbon nanotube paper, graphene paper, hollow carbon fiber and glass fiber are taken as liquid absorbing layers (60 mu m), and a layer of polytetrafluoroethylene polymer (in a polytetrafluoroethylene-dispersed MNP solvent) is coated on the surfaces of the liquid absorbing layers to serve as an insulating lithium conducting layer (20 mu m). After drying, a layer of zinc sulfide (with the particle size of 1 μm) and a polytetrafluoroethylene mixture (zinc sulfide particles and polytetrafluoroethylene are dispersed in MNP solvent in a mass ratio of 70%) are respectively coated on the surface of the insulating lithium-conducting layer to form a lithium-philic layer (the thickness of the coated lithium-philic layer is 30 μm). Then, the composite membranes are taken as membranes, metal lithium is taken as a negative electrode, a carbon nanotube positive electrode rich in S simple substance is taken, and 1M LiTFSI/DOL/DME (volume ratio is 1: 1) contains 1 wt.% LiNO3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in table 7.
TABLE 7
Figure BDA0001791332390000111
The results show that the graphene paper has the best performance as a liquid absorbent layer, and the carbon nanotube paper and the carbon cloth are used as the liquid absorbent layer, and the carbon paper, the hollow carbon fiber and the glass fiber are used as the liquid absorbent layer.
Example 10
The present case discusses the thickness of the imbibing layer as follows:
clean, commercial graphene paper of different thicknesses was taken as liquid absorbent layers (0.5, 1.8, 24, 180, 420, 600 μm), and then a polyvinylidene chloride polymer (in a polyvinylidene chloride-dispersed MNP solvent) was coated on the surfaces of the liquid absorbent layers to serve as an insulating lithium-conducting layer (30 μm). After drying, a layer of zinc sulfide (particle size 1 μm) and a polyvinylidene chloride mixture (zinc sulfide particles and polyvinylidene chloride are dispersed in MNP solvent with the mass ratio of 80%) are respectively coated on the surface of the insulating lithium-conducting layer to form a lithium-philic layer (the thickness of the coated lithium-philic layer is 30 μm). Then, the composite membranes are taken as membranes, metal lithium is taken as a negative electrode, a carbon nanotube positive electrode rich in S simple substance is taken, and 1M LiTFSI/DOL/DME (volume ratio is 1: 1) contains 1 wt.% LiNO3The lithium sulfur battery was formed for the electrolyte and charge-discharge cycle tests were performed at 1C rate.
The results of the tests are shown in Table 8.
TABLE 8
Figure BDA0001791332390000121
The results show that the performance is better in the preferable thickness range (24-180 mu m) of the liquid absorbing layer.

Claims (10)

1. A composite diaphragm is characterized by comprising a lithium-philic layer, an insulating lithium-conducting layer and a liquid absorbing layer which are sequentially compounded;
the lithium-philic layer comprises a lithium-philic material; the lithium-philic material is at least one of a simple substance of M metal and a compound of M metal; wherein, the M metal is a metal which can perform alloying reaction with Li;
the liquid absorbing layer comprises a material capable of absorbing electrolyte;
the insulating lithium-conducting layer is a polymer capable of conducting lithium ions and blocking electrons.
2. The composite separator of claim 1, wherein the M metal is at least one of zinc, gallium, germanium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, iridium, platinum, gold, mercury, thallium, lead, bismuth;
preferably, the compound of the M metal is at least one of an oxide and a sulfide of the M metal.
3. The composite separator according to claim 1 or 2, wherein the lithium-philic particles have a size of 2 to 9500 nm; preferably 5-8000 nm; further preferably 10 to 6000 nm; more preferably 50 to 700 nm.
4. The composite separator according to any one of claims 1 to 3, wherein said lithium-philic layer further comprises a binder;
more preferably, the adhesive is at least one of polyethylene, polypropylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene chloride, styrene butadiene rubber and polybutylene;
in the lithium-philic layer, the content of the lithium-philic material is 20-97 wt.%; preferably 30-95 wt.%; further preferably 50-90 wt.%; even more preferably 60 to 80 wt.%; the balance of adhesive.
5. The composite separator according to claim 4, wherein the lithium-philic layer further allows at least one of an alloy of Li-M metal, lithium oxide, and lithium sulfide.
6. The composite separator according to any one of claims 1 to 5, wherein the thickness of said lithium-philic layer is 0.08 to 120 μm; preferably 0.1 to 100 μm; more preferably 1.6 to 60 μm.
7. The composite separator of claim 1, wherein the polymer of the lithium conducting insulating layer is at least one of polyethylene, polypropylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene chloride, styrene butadiene rubber, and polybutylene;
preferably, the thickness of the insulating lithium-conducting layer is 1-100 μm; more preferably 5 to 60 μm.
8. The composite separator according to claim 1, wherein in the liquid absorbing layer, the material capable of adsorbing the electrolyte is a material capable of adsorbing polysulfides in the electrode liquid; preferably at least one of carbon paper, carbon cloth, carbon nanotube paper, graphene paper, hollow carbon fiber and glass fiber;
preferably, the thickness of the liquid absorption layer is 0.5-600 μm; preferably 1 to 500 μm; more preferably 3 to 300 μm; more preferably 24 to 180 μm.
9. Use of a composite separator according to any one of claims 1 to 8 as a separator for a lithium-sulphur battery;
more preferably, the lithium-philic layer of the composite separator faces the lithium metal negative electrode; the liquid absorption layer of the composite diaphragm faces to the positive electrode.
10. A lithium-sulfur battery comprising a positive electrode, a negative electrode, a separator for separating the positive electrode from the negative electrode, and an electrolyte for immersing the positive electrode, the negative electrode, and the separator, wherein the composite separator according to any one of claims 1 to 8 is used as the separator, and the lithium-philic layer of the composite separator faces the metallic lithium negative electrode, and the liquid absorbing layer faces the positive electrode.
CN201811040154.8A 2018-09-06 2018-09-06 Composite diaphragm, preparation and application thereof in lithium-sulfur battery Pending CN110880575A (en)

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