CN107665966A - A kind of lithium-sulfur cell - Google Patents

Abstract

The invention discloses a kind of lithium-sulfur cell using multilayer composite membrane.Multilayer composite membrane is the side surface coated polymer layer A and another side surface coating inorganic layers of solid material and polymeric layer B in basilar partition, and solid inorganic material layer is between basilar partition and polymeric layer B.Solid inorganic material layer can increase the mechanical strength of barrier film, when using the ceramic material acted on lithium ion conduction, can effectively improve the ionic conductivity of barrier film, reduce the polarity effect in charge and discharge process.The electrolyte that lithium-sulfur cell uses contains additive, so improve the interface state of positive pole, negative pole, barrier film, so that charging and discharging currents density is more uniform on cathode of lithium surface, and it can effectively reduce the activity of cathode of lithium in the electrolytic solution, the formation possibility of Li dendrite is greatly reduced, improves the stability of cathode of lithium when in use.

Description

A lithium-sulfur battery

technical field

The invention belongs to the field of lithium-sulfur batteries, in particular to a multilayer composite separator for lithium-sulfur batteries.

Background technique

In today's society, while the rapid economic development enables people to obtain ample material life, the energy crisis and environmental pollution problems are increasingly perplexing the survival of human beings. In this severe situation, the development of new green energy and renewable energy, as well as the corresponding energy conversion and storage technologies are urgent problems to be solved by current scientific and technological workers. Due to the current problems, new energy vehicles and other electronic devices emerged as the times require. However, the lithium-ion batteries currently in circulation in the market have low energy density and cannot meet the high energy density requirements of new electrical equipment. It is imperative to develop a new power supply system to meet the requirements of electrical appliances for high energy density and high safety performance.

The traditional lithium-sulfur battery uses metal lithium as the negative electrode and elemental sulfur as the positive electrode. The theoretical specific capacity of lithium is 3860mAh/g, the theoretical specific capacity of sulfur is 1675mAh/g, and the theoretical energy density of the battery is as high as 2600Wh/Kg. It is the lithium secondary battery system with the highest energy density known except for lithium-air batteries. In addition, the source of sulfur as the cathode material is abundant, cheap, and has low toxicity.

Although lithium-sulfur batteries have the incomparable advantages of high energy density compared to lithium-ion batteries currently on the market, their commercialization still faces many difficulties. At present, the problems that limit the commercialization of lithium-sulfur batteries are mainly manifested in the following aspects: (1) The intermediate product Li ₂ S _n (4≦n≦8) produced during the charging and discharging process is easily soluble in the electrolyte, increasing the electrolytic At the same time, it diffuses through the separator to the metal lithium negative electrode under the action of concentration difference, and reacts with lithium to form short-chain Li ₂ S _n (4≦n≦8) and Li ₂ S ₂ and Li ₂ S, which corrode Lithium metal; and form a "shuttle effect", reducing the Coulombic efficiency of the battery. (2) The products Li ₂ S ₂ and Li ₂ S are insoluble in the electrolyte and deposited on the surface of the electrode, and the two are insulators, resulting in the loss of active materials and the change of the interface state between the electrode and the electrolyte, making the cycle performance of the battery worse. Difference. (3) During the charge and discharge process, due to the uneven current density on the surface of the lithium negative electrode, lithium dendrites are formed, resulting in "death" and reducing the cycle life of the battery.

In order to solve the above problems, the following aspects should be taken into consideration: (1) optimize the structure of the positive electrode to suppress the dissolution of Li ₂ S _n (4≦n≦8) from the sulfur cathode; (2) pretreat the lithium negative electrode to suppress the Li The reaction of ₂ S _n (4≦n≦8) with the lithium anode; (3) optimize the composition of the electrolyte and add electrolyte additives to form a stable SEI film on the surface of the lithium anode; (4) develop a composite separator to enhance the strength of the separator , Block the diffusion of Li ₂ S _n (4≦n≦8), and increase the liquid absorption rate of the separator.

In terms of positive electrode preparation, Cui Yi et al. loaded PVP into hollow carbon nanowires to obtain PVP-C composite materials, and then compounded with elemental sulfur to make lithium-sulfur battery positive electrode materials. At a discharge rate of 0.5C, after 100 cycles, The specific discharge capacity is about 810mAh/g (Zheng G, Zhang Q, Cha J J, et al. Amphiphilic surface modification of hollow carbon nanofibers for improved cycle life of lithium-sulfur batteries[J]. Nano letters, 2013, 13(3): 1265-1270). In Chinese patent CN103151524A, sulfur is assembled into the pores of metal-organic framework (MOF) to prepare sulfur composite material, and then it is combined with carbon, which improves the cycle performance of lithium-sulfur batteries, but the loading capacity of S in MOF is relatively low. Small, the energy density of the battery is low.

In terms of lithium anode protection, the American Polyplus company uses plasma-assisted deposition, evaporation and other technologies to separate the ion-conducting layer (generally a glass-ceramic electrolyte containing Al ₂ O ₃ , P ₂ O ₅ , SiO ₂ , etc.) A transition layer with better compatibility (such as Li-Sn, Li-Cu, Li3N, etc.) is deposited on the surface of lithium metal to form a multilayer composite film structure on the surface of lithium to prevent lithium from directly contacting the electrolyte. In this method, multiple transition layers are added during the preparation process to ensure the compatibility between the various layers, but the internal resistance of the battery is increased, and the preparation process is complicated. K. Chung et al. used RF magnetron sputtering to deposit a 0.95 μm thick amorphous, flat and dense LiPON film. A linear voltammetry scan was performed at 0.0-5.5V, and it was found that the LiPON film can inhibit the oxidation and decomposition of the electrolyte under high voltage, and is a good passivation layer. The film makes the current distribution on the electrode surface uniform and improves the cycle stability of the battery (Chung, K; Kim, WS; Choi, YK. Lithium phosphorous oxynitrides as a passive layer for anodes in lithium secondary batteries[J]. JOURNAL OFELECTROANALYTICAL CHEMISTRY, 2004 , 566(2):263-267). Park et al. used ultraviolet light to initiate the polymerization of PEGDME on the surface of the Li negative electrode to form a protective layer to inhibit the direct reaction of S _n ^2- (4≦n≦8) with metal lithium, and then used LiClO4-PVDF-HFP-based GPE in lithium-sulfur batteries, The plasticizer is TEGDME. Experiments have shown that GPE and lithium anode surface polymer protective layer can effectively improve the cycle performance of lithium-sulfur batteries (Lee YM, Choi NS, Park JH, et al.Electrochemical performance of lithium/sulfur batteries with protected Li anodes[J].Journal of Power Sources, 2003, 119-121:964-972).

In terms of optimizing the composition of the electrolyte, Aurbach et al. used EIS, FT-IR, XPS and other methods to analyze the mechanism of adding LiNO3 to the DME+DOL electrolyte to improve the performance of lithium-sulfur batteries, and believed that the main function of _LiNO3 is to protect the metal. Lithium negative electrode. LiNO ₃ can react with DOL and Li ₂ S _n (4≤n≤8) in the electrolyte to form a layer of SEI passivation protection layer on the surface of lithium anode to reduce the shuttle phenomenon in lithium-sulfur batteries (Aurbach D, Pollak E, Elazari R, et al. On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li-Sulfur Batteries [J]. Journal of the Electrochemical Society, 2009, 156(8):694-702). Liang et al. found that adding P ₂ S ₅ to the electrolyte can significantly improve the cycle performance of lithium-sulfur batteries. The lithium-sulfur battery with 5% P ₂ S ₅ added to 1mol/L LiTFSI/TEGDME has a stable discharge specific capacity of 900mAh/g after 20 cycles at a rate of 0.1C, and the specific capacity is not obvious until 40 cycles Attenuation, while the Coulombic efficiency has remained above 90%, and the cycle performance has been greatly improved compared with the lithium-sulfur battery without P ₂ S ₅ (Lin Z, Liu Z, Fu W, et al.Phosphorous Pentasulfide as a Novel Additive for High- Performance Lithium-Sulfur Batteries[J].Advanced Functional Materials,2013,23(8):1064-1069).

In terms of diaphragm modification, Chinese patent CN104393349A made slurry of modified graphene and coated it on the diaphragm to obtain a modified diaphragm, in order to inhibit the "shuttle effect" of polysulfides during the charging and discharging process of lithium-sulfur batteries. ArumuganManthirn et al. coated microporous carbon-polyethylene glycol on one side of the ordinary PP diaphragm to prepare a modified diaphragm. When the lithium-sulfur battery with the modified diaphragm was discharged at a rate of 0.5C, after 200 cycles, the discharge specific capacity was still 795mAh/g. However, the preparation method is complex, the materials are expensive, and there is still a lot of active material loss during charging and discharging (Chung SH, Manthiram AA PolyethyleneGlycol-Supported Microporous Carbon Coating as a Polysulfide Trap for Utilizing Pure Sulfur Cathodes in Lithium-Sulfur Batteries[J].AdvancedMaterials , 2014, 26(43):7352-7357). Ju Lan et al. used plasma grafting to graft lithium sulfonate (SO ₃ Li) groups and methyl methacrylate (MMA) groups on the surface of PP separators. The formation of dendrites in medium, but the preparation method requires high conditions and is difficult to produce in large quantities (Ju Lan, Li Zhihu. Separator surface modification method to improve the cycle performance of lithium metal electrodes [J]. Functional Materials, 2012,12(43): 1640-1642). Chinese patent 104916802A discloses a composite diaphragm for lithium-ion batteries. The composite diaphragm is coated with a polymer layer on one side of a microporous base membrane and coated with a ceramic layer on the other side. The polymer coating improves the wettability and ionic conductivity of the separator, and the ceramic layer contributes to the thermal stability of the separator. The composite separator with this structure has certain advantages in the application of lithium-ion batteries, but in the application of lithium-sulfur batteries, due to the strong activity of metal lithium, it is easy to react with the ceramic layer, so further optimization is required. Chinese patent CN101326658A discloses an organic/inorganic composite diaphragm with a gradient in morphology. A porous active layer containing inorganic solids and a binder polymer is coated on a porous substrate, and the porous active layer has a concentration gradient to enhance the resistance of the diaphragm. Peel and scratch resistance. However, it is difficult to obtain a porous active layer with a good morphological gradient during the preparation process of the separator, and when it is used in a lithium secondary battery, the porous active layer is likely to cause interface instability when it is directly in contact with metal lithium.

Contents of the invention

In order to solve the problem of short cycle life faced by lithium-sulfur batteries, the present invention modifies the diaphragm of lithium-sulfur batteries, the purpose of which is to effectively inhibit the shuttle between the positive and negative electrodes of polysulfides and improve the gap between the lithium negative electrode and the electrolyte. Excellent contact stability, reducing the corrosion of lithium metal, and at the same time, improving the strength of the diaphragm to ensure that the battery has a high safety performance.

The invention provides a lithium-sulfur battery. The diaphragm used in it is a multilayer composite diaphragm. The multilayer composite diaphragm is coated with a polymer layer A on one side of the base diaphragm and coated with an inorganic solid material layer and a polymer layer on the other side. The material layer B, and the inorganic solid material layer is located between the base membrane and the polymer layer B. And when in use, the positive electrode is placed on the polymer layer A side of the multilayer composite separator, and the negative electrode is placed on the polymer layer B side.

The multi-layer composite diaphragm adopts commercially available polyethylene diaphragm, polypropylene diaphragm, polyethylene/polypropylene composite diaphragm, polypropylene/polyethylene/polypropylene composite diaphragm, polyimide diaphragm, non-woven fabric diaphragm One as its base.

The polymer material used in the polymer layer A can be one of PVDF, PTFE, PVP, PEO, LA132, SBR/CMC, PAA, gelatin, cyclodextrin, and sodium alginate;

The polymer material used in the polymer layer B can be polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, polyvinyl acetate, polybutyl methacrylate, polyethyl acrylate, polyethylene oxide, Chlorosulfonated polyethylene, perfluorosulfonate polymer, polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polyacrylamide, styrene-butadiene rubber, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxyethyl One of cellulose, methyl hydroxyethyl cellulose, carboxyethyl cellulose, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and sodium alginate.

The inorganic solid material layer includes ultrafine inorganic solid material and polymer material; and the mass percentage of the inorganic solid material is 15%-75%.

The ultrafine inorganic solid material may or may not have lithium ion conduction properties. Ultrafine inorganic solid materials with lithium ion conduction properties, which can be Li _3x La _2/3-x TiO ₃ (0.04<x<0.17), Li ₁₄ ZnGe ₄ O ₁₆ , Li _1+x A _2-x B _x ( PO ₄ ) ₃ (A = one of Ti, Ge; B = one of Al, Ga, Sc, In, Y; 0≤x≤0.7), Li _5+x La _3-x A _x M ₂ O ₁₂ (A = one of Ba, Sr; M = one of Zr, Ta, Nb, Sb, Bi; 0≤x≤2), xLi ₂ S-(1-x)P ₂ S ₅ ( 0<x<1), xLi ₂ S-(1-x)SiS ₂ (0<x<1), Li ₁₀ GeP ₂ S ₁₂ , Li ₄ GeS, Li ₃ Zn _0.5 GeS ₄ , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li _3.4 Si _0.4 P _0.6 S ₄ , Li _4.8 Si _0.2 Al _0.8 S ₄ , Li ₆ PS ₅ X (X=Cl, Br, I), lithium nitride, lithium phosphate, lithium silicate, lithium aluminate One or more of lithium borohydride; ultrafine inorganic solid materials that do not have lithium ion conductivity, which can be aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, cerium oxide, magnesium oxide, yttrium oxide, tin oxide , lanthanum oxide, aluminum silicate, magnesium silicate, manganese silicate, barium titanate, lead titanate, zirconium titanate, titanium nitride, boron nitride, and boron carbide.

The particle size range of the ultrafine inorganic solid material is 0.5nm-5μm.

The polymer material in the described inorganic solid material layer has bonding and film-forming effects, and can be polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, polyvinyl acetate, polybutyl methacrylate, poly Ethyl acrylate, polyethylene oxide, chlorosulfonated polyethylene, perfluorosulfonate polymer, polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polyacrylamide, styrene-butadiene rubber, carboxymethyl cellulose, carboxymethyl One of sodium cellulose, hydroxyethyl cellulose, methyl hydroxyethyl cellulose, carboxyethyl cellulose, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and sodium alginate.

The thickness of the polymer layer A is 0.2 μm-10 μm; the thickness of the polymer layer B is 0.2 μm-10 μm; the thickness of the inorganic solid material layer is 0.5 μm-10 μm.

The mass ratio of elemental sulfur: conductive carbon: binder in the sulfur positive electrode is 50-80:10-40:10.

The conductive carbon in the sulfur positive electrode is one or more of AB, AC, BP2000, CMK3 and Super P.

The binder used for the sulfur positive electrode is the same as the polymer material used in the polymer layer A, which can be well bonded to the sulfur positive electrode after hot pressing process, which is conducive to the stability of the battery structure and the inhibition of polysulfide dissolution. Improve cycle stability; the polymer material used in the polymer layer B is the same as the polymer material used for bonding in the inorganic material layer.

The lithium-sulfur battery electrolyte contains additives to promote the formation of a solid electrolyte interface film between the inorganic solid material layer, the electrolyte, and the negative electrode, and improve the cycle stability of the negative electrode;

The electrolyte lithium salt in the lithium-sulfur battery electrolyte is one or more of LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiAlCl ₄ , LiBF ₆ , LiCF ₃ SO ₃ and LiN(CF ₃ SO ₂ ) ₂ ; the solvent It is a mixed solvent of DOL and DME with a volume ratio of 1:1-1:9; the electrolyte additive can be vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide , methyl acrylate, γ-butyrolactone, 1,3-propane sultone, 1,4-butane sultone, ethyl methanesulfonate, butyl methanesulfonate, vinylene carbonate , toluene, benzene, quinone imine, decalin, copolymer of dimethylsilane and propylene oxide, polyoxyethylene, dimethyl ether of polyoxyethylene, lithium perfluorooctane sulfonate, LiBOB, LiNO ₃ , SnI _2. One or more of AlI ₃ , P ₂ S ₅ , and bipyridine compounds.

The content of the additive is 0.01moL/L-0.6moL/L.

The advantages of the present invention are:

When the multi-layer composite separator for lithium-sulfur batteries is used, the polymer coating A is close to the side of the sulfur positive electrode, and the hot pressing process is assisted to make the contact between the positive electrode sheet and the separator more sufficient, which can significantly reduce the internal resistance of the battery , and the polymer coating A greatly improves the liquid absorption capacity of the diaphragm, so that the electrolyte soaks in the coating. During charging and discharging, as the number of cycles increases, the polymer coating of the diaphragm has the effect of slowing down the release of the electrolyte. This can improve the cycle performance of the battery.

The polymer coating of the diaphragm has adsorption capacity, which can effectively absorb and dissolve polysulfides in the electrolyte, inhibit the migration of polysulfides to the lithium negative electrode, avoid the reaction between the two, and weaken the polysulfides in the charging and discharging process. "Shuttle effect".

When the multi-layer composite diaphragm for lithium-sulfur battery is used, the inorganic solid material layer is close to the side of the lithium negative electrode. This coating can increase the mechanical strength of the diaphragm. When using a ceramic material with lithium ion conductivity, it can effectively improve the ion density of the diaphragm. Conductivity, reducing the polarization effect during charge and discharge. In addition, the side of the inorganic solid material coating that is in contact with the negative electrode is coated with a polymer layer B that also has the ability to absorb the electrolyte, which can ensure that a sufficient amount of electrolyte additives and lithium negative electrodes are formed during the electrochemical cycle. solid electrolyte membrane. In addition, the existence of the polymer layer also avoids the direct contact between the inorganic solid material layer and the lithium negative electrode, ensuring the interfacial stability of the two.

When the multi-layer composite separator is used in lithium-sulfur batteries, the coatings on both sides are respectively bonded to the positive and negative electrodes and soaked in the electrolyte, so that the polymer and inorganic solid materials on the separator coating and the additives in the electrolyte The interaction forms a solid electrolyte interface film, which improves the interface state of the positive electrode, negative electrode, and separator, makes the charge and discharge current density more uniform on the surface of the lithium negative electrode, and can effectively reduce the activity of the lithium negative electrode in the electrolyte, greatly reducing the The possibility of forming lithium dendrites improves the stability of the lithium negative electrode during use.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention. These examples are only used to specifically illustrate the present invention, not to limit the scope of the present invention.

Example 1

Weigh 5g of PVDF and 95g of NMP to prepare a PVDF solution with a mass fraction of 5%, then mix titanium oxide ceramic particles with a particle size of 50nm with the PVDF solution to make a slurry, and the mass fraction of the ceramic particles in the slurry is 65%. Coat the uniformly mixed inorganic ceramic slurry on one side of a commercially available polyethylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 5 μm.

The PVDF of 8g is taken by weighing, is dissolved in NMP, and preparation PVDF content is 8% solution, and the slurry that obtains is coated on the both sides of above-mentioned single-layer composite diaphragm by pulling method, then diaphragm is heated in blast oven at 60 ℃ drying for 8 hours, after the solvent evaporates, then drying in a vacuum oven at 60 ℃ for 12 hours, the measured thickness of the polymer coating is 8 μm. In this way, a double-sided modified multilayer composite separator was obtained.

Example 2

Sulfur-carbon composite (sulfur loading is 70%), acetylene black, and PVDF are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode, obtained in Example 1. _{CR2016 button} cell was _assembled , and the cycle performance _of the battery was tested. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1239mAh/g, and the capacity retention rate still reaches 87% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1165mAh/g, and the capacity retention rate still reaches 81% after 80 cycles.

Example 3

Weigh 5g of PVDF and 95g of NMP to prepare a PVDF solution with a mass fraction of 5%, and then mix ultrafine boron nitride ceramic particles with the PVDF solution to make a slurry, and the mass fraction of the ceramic particles in the slurry is 65%. Coat the uniformly mixed inorganic ceramic slurry on one side of a commercially available polyethylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 5 μm.

The PVDF of taking 10g is dissolved in NMP, and preparation PVDF content is 10% solution, the slurry that obtains is coated on the both sides of above-mentioned single-layer composite diaphragm by pulling method, then diaphragm is heated in blast oven at 60 Dry at ℃ for 8 hours, and then dry at 60℃ for 12 hours in a vacuum oven after the solvent evaporates. In this way, a double-sided modified multilayer composite separator was obtained, and the thickness of the polymer coating was measured to be 8 μm.

Example 4

Sulfur-carbon composite (sulfur load is 70%), acetylene black, and PVDF are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode, obtained in Example 3. _{CR2016 button} cell was _assembled , and the cycle performance _of the battery was tested. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1343mAh/g, and the capacity retention rate still reaches 84% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1206mAh/g, and the capacity retention rate still reaches 80% after 80 cycles.

Example 5

Weigh 5g of PEO, dissolve it in a certain mass of water and n-propanol (4:1) mixture, prepare a PEO solution with a mass fraction of 5%, and then mix ultrafine Li ₁₀ GeP ₂ S ₁₂ ceramic particles with the PEO solution to prepare A slurry is formed, and the mass fraction of ceramic particles in the slurry is 75%. Coat the well-mixed inorganic ceramic slurry on one side of a commercially available polypropylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 6 μm.

Weigh the PEO of 10g, be dissolved in water and n-propanol (4:1) mixed solution, preparation PEO content is 20% solution, the slurry that is obtained is coated on the both sides of above-mentioned single-layer composite diaphragm, then diaphragm is placed on Dry it in a blast oven at 60°C for 8 hours, and then dry it in a vacuum oven at 60°C for 12 hours after the solvent evaporates. The thickness of the double-sided polymer coatings is measured to be 10 μm. In this way, a double-sided modified multilayer composite separator was obtained.

Example 6

Sulfur-carbon composite (sulfur load is 70%), acetylene black, and PEO are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode, obtained in Example 5. _{CR2016 button} cell was _assembled , and the cycle performance of the battery was tested. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1310mAh/g, and the capacity retention rate still reaches 87% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the battery's initial discharge specific capacity is 1186mAh/g, and the capacity retention rate still reaches 81% after 80 cycles.

Example 7

Weigh 5g of PVP, prepare a PVP aqueous solution with a mass fraction of 5%, and then mix ultrafine titanium oxide ceramic particles with the PVP solution to form a slurry, and the mass fraction of the ceramic particles in the slurry is 70%. Coat the uniformly mixed inorganic ceramic slurry on one side of a commercially available polyethylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 6 μm.

Weigh 10g of PVP, dissolve it in deionized water, prepare an aqueous solution with a PVP content of 10%, apply the obtained slurry on both sides of the above-mentioned single-layer composite diaphragm, and then dry the diaphragm at 60°C in a blast oven Dry for 8 hours. After the solvent evaporates, dry in a vacuum oven at 60° C. for 12 hours. The thickness of the double-sided polymer coatings is measured to be 10 μm. In this way, a double-sided modified multilayer composite separator was obtained.

Example 8

Sulfur-carbon composite (sulfur loading is 70%), acetylene black, and PVP are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode, obtained in Example 7. Assembled CR2016 button cell with 0.85M LiN(CF ₃ SO ₂ ) ₂ electrolyte, DOL:DME=1:2(V:V), 0.3M γ-butyrolactone, and tested the cycle performance of the battery. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1260mAh/g, and the capacity retention rate still reaches 83.5% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1142mAh/g, and the capacity retention rate still reaches 78% after 80 cycles.

Example 9

Take by weighing 5g PMMA, 95g NMP prepares PMMA solution according to mass fraction 5%, then will use the superfine Li ₁₄ ZnGe ₄ O ₁₆ ceramic particles prepared by high temperature solid phase method to mix with PMMA solution to make slurry, the ceramic particle in the slurry The quality score is 80%. Coat the uniformly mixed inorganic ceramic slurry on one side of a commercially available polyethylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 8 μm.

Weigh 10g of PMMA, dissolve it in NMP, and prepare a PMMA content of 10% solution, and apply the resulting slurry on the inorganic solid layer side of the above-mentioned single-layer composite diaphragm, and then place the diaphragm in a blast oven at 60 ° C. Dry for 8 hours. After the solvent evaporates, dry in a vacuum oven at 60° C. for 12 hours. The measured thicknesses of the polymer coatings are 10 μm.

Weigh 10g of PVDF, dissolve it in NMP, prepare a solution with a PVDF content of 10%, and then apply it on the other side of the above-mentioned single-layer composite diaphragm, then dry the diaphragm at 60°C for 8 hours in a blast oven, and wait until the solvent After the volatilization, they were dried in a vacuum oven at 60° C. for 12 hours, and the thicknesses of the polymer coatings were measured to be 10 μm. In this way, a double-sided modified multilayer composite separator was obtained.

Example 10

Sulfur-carbon composite (sulfur loading is 70%), acetylene black, and PVDF are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode, obtained in Example 9. _CR2016 button _battery was _assembled and the cycle performance _of the battery was tested. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1392mAh/g, and the capacity retention rate still reaches 86.4% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1303mAh/g, and the capacity retention rate still reaches 81.6% after 80 cycles.

Example 11

Weigh 5g of PVDF and 95g of NMP to prepare a PVDF solution with a mass fraction of 5%, then mix ultrafine lithium phosphate ceramic particles with the PVDF solution to make a slurry, and the mass fraction of the ceramic particles in the slurry is 80%. Coat the uniformly mixed inorganic ceramic slurry on one side of a commercially available polyethylene diaphragm, then dry the diaphragm at 60°C in a blast oven for 8 hours, and then dry it in a vacuum oven at 60°C after the solvent evaporates. After 12 hours, the thickness of the inorganic ceramic layer was measured to be 10 μm.

The PVDF of taking 10g is dissolved in NMP, and preparation PVDF content is 10% solution, the slurry that obtains is coated on the both sides of above-mentioned single-layer composite diaphragm by pulling method, then diaphragm is heated in blast oven at 60 ℃ drying for 8 hours, after the solvent evaporates, then drying in a vacuum oven at 60 ℃ for 12 hours, the measured thickness of the polymer coating is 10 μm. In this way, a double-sided modified multilayer composite separator was obtained.

Example 12

Sulfur-carbon composite (sulfur loading is 70%), acetylene black, and PVDF are prepared in a ratio of 7:2:1 and coated on a carbon-coated aluminum foil to prepare a positive electrode, and a metal lithium foil is used as a negative electrode, obtained in Example 11. CR2016 button cell was assembled, and the cycle performance of the battery was tested using 0.85M LiN(CF ₃ SO ₂ ) ₂ electrolyte, DOL:DME=1:2(V:V), 0.3M dimethyl sulfoxide. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1275mAh/g, and the capacity retention rate still reaches 86.4% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1154mAh/g, and the capacity retention rate still reaches 78.5% after 80 cycles.

Example 13

Sulfur-carbon composite (sulfur loading is 70%), acetylene black, and PVDF are prepared in a ratio of 7:2:1 and coated on a carbon-coated aluminum foil to prepare a positive electrode, and a metal lithium foil is used as a negative electrode, obtained in Example 11. _{CR2016 button} cell was _assembled , and the cycle performance _of the battery was tested. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1305mAh/g, and the capacity retention rate still reaches 88.3% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1276mAh/g, and the capacity retention rate still reaches 83.5% after 80 cycles.

Example 14

Sulfur-carbon composite (sulfur load is 70%), acetylene black, and PVDF are prepared by coating the slurry with 7:2:1 on the carbon-coated aluminum foil to prepare the positive electrode, and the metal lithium foil is used as the negative electrode. Commercially available polypropylene Diaphragm, electrolyte using 0.85M LiN(CF ₃ SO ₂ ) ₂ , DOL:DME=1:2(V:V), 0.3M LiNO ₃ , assemble CR2016 button battery, and test the cycle performance of the battery. When the battery test temperature is 25°C and the test rate is 0.05C, the first discharge specific capacity of the battery is 1315mAh/g, and the capacity retention rate still reaches 71.4% after 80 cycles. When the battery test temperature is 25°C and the test rate is 0.08C, the first discharge specific capacity of the battery is 1256mAh/g, and the capacity retention rate still reaches 64.2% after 80 cycles.

Claims (11)

1. A kind of 1. lithium-sulfur cell, it is characterised in that：For its barrier film used for multilayer composite membrane, multilayer composite membrane is in substrate A side surface coated polymer layer A and another side surface coating inorganic layers of solid material and polymeric layer B for barrier film, and it is inorganic solid Body material layer is between basilar partition and polymeric layer B；When the composite diaphragm is used in lithium-sulfur cell, sulphur positive pole is placed on The polymeric layer A sides of multilayer composite membrane, negative pole are placed on polymeric layer B sides.
2. 2. lithium-sulfur cell according to claim 1, it is characterised in that：Multilayer composite membrane using commercially available polyethylene every Film, polypropylene diaphragm, polyethylene/polypropylene composite diaphragm, polypropylene, polyethylene/polypropylene composite materials barrier film, polyimides every One kind in film, nonwoven cloth diaphragm is as its substrate.
3. 3. lithium-sulfur cell according to claim 1, it is characterised in that：Polymeric material used in polymeric layer A can be One or two or more kinds in PVDF, PTFE, PVP, PEO, LA132, SBR/CMC, PAA, gelatin, cyclodextrin, sodium alginate；

   Polymeric material used in polymeric layer B can be polyacrylic acid, polymethylacrylic acid, polymethyl methacrylate, poly- Vinylacetate, polybutyl methacrylate, polyethyl acrylate, polyethylene glycol oxide, chlorosulfonated polyethylene, perfluorinated sulfonate gather Compound, polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polyacrylamide, butadiene-styrene rubber, carboxymethyl cellulose, carboxymethyl Sodium cellulosate, hydroxyethyl cellulose, methyl hydroxyethylcellulose, carboxyethyl cellulose, Kynoar-hexafluoropropene copolymerization One or two or more kinds in thing, sodium alginate.
4. 4. lithium-sulfur cell according to claim 1, it is characterised in that：Described solid inorganic material layer includes ultra-fine inorganic Solid material and polymeric material；And the mass percent of solid inorganic material is 15%-75%.
5. 5. lithium-sulfur cell according to claim 4, it is characterised in that：Described ultra-fine inorganic solid material can have lithium Ionic conduction characteristic, or can also not have the one or two or more kinds in lithium ion conduction elastomeric material；Passed with lithium ion The ultra-fine inorganic solid material of characteristic is led, can be Li_3xLa_2/3-xTiO₃(0.04<x<0.17)、Li₁₄ZnGe₄O₁₆、Li_1+xA_2-xB_x (PO₄)₃(one kind in A=Ti, Ge；One kind in B=Al, Ga, Sc, In, Y；0≤x≤0.7)、Li_5+xLa_3-xA_xM₂O₁₂(A= One kind in Ba, Sr；One kind in M=Zr, Ta, Nb, Sb, Bi；0≤x≤2)、xLi₂S-(1-x)P₂S₅(0<x<1)、xLi₂S- (1-x)SiS₂(0<x<1)、Li₁₀GeP₂S₁₂、Li₄GeS、Li₃Zn_0.5GeS₄、Li_3.25Ge_0.25P_0.75S₄、Li_3.4Si_0.4P_0.6S₄、 Li_4.8Si_0.2Al_0.8S₄、Li₆PS₅One in X (X=Cl, Br, I), lithium nitride, lithium phosphate, lithium metasilicate, lithium aluminate, lithium borohydride Kind or more than two kinds；Ultra-fine inorganic solid material without lithium ion conduction characteristic, can be aluminum oxide, zirconium oxide, oxidation Titanium, silica, cerium oxide, magnesia, yittrium oxide, tin oxide, lanthana, alumina silicate, magnesium silicate, manganous silicate, barium titanate, metatitanic acid One or two or more kinds in lead, zirconia titanate, titanium nitride, boron nitride, boron carbide.
6. 6. the lithium-sulfur cell according to claim 4 or 5, it is characterised in that：Described ultra-fine inorganic solid material particle diameter model Enclose for 0.5nm-5 μm.
7. 7. the lithium-sulfur cell according to claim 4 or 5, it is characterised in that：Polymerization in described solid inorganic material layer Thing material has bonding and filming function, can be polyacrylic acid, polymethylacrylic acid, polymethyl methacrylate, poly-vinegar acid Vinyl acetate, polybutyl methacrylate, polyethyl acrylate, polyethylene glycol oxide, chlorosulfonated polyethylene, perfluorinated sulfonate polymerization Thing, polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polyacrylamide, butadiene-styrene rubber, carboxymethyl cellulose, carboxymethyl are fine Tie up plain sodium, hydroxyethyl cellulose, methyl hydroxyethylcellulose, carboxyethyl cellulose, Kynoar, Kynoar-hexafluoro One or two or more kinds in propylene copolymer, sodium alginate.
8. 8. lithium-sulfur cell according to claim 1, it is characterised in that：Described polymeric layer A thickness is 0.2 μm of -10 μ m；Polymeric layer B thickness is 0.2 μm -10 μm；The thickness of solid inorganic material layer is 0.5 μm -10 μm.
9. 9. lithium-sulfur cell according to claim 1, it is characterised in that：Elemental sulfur in sulphur positive pole：Conductive carbon：The matter of binding agent It is 50-80 to measure ratio:10-40:10；

   Conductive carbon is the one or two or more kinds in AB, AC, BP2000, CMK3, Super P in sulphur positive pole.
10. 10. according to the lithium-sulfur cell described in claim 3,7 or 9, it is characterised in that：Binding agent and polymer used in sulphur positive pole Polymeric material used in layer A is identical, handles and can be bonded well with sulphur positive pole through heat pressing process, it is steady to be advantageous to battery structure Fixed and suppression polysulfide dissolving, improves cyclical stability；Institute in polymeric material and inorganic material layer used in polymeric layer B The polymeric material for playing cementation is identical.
11. 11. lithium-sulfur cell according to claim 1, it is characterised in that：Contain addition in described lithium-sulfur cell electrolyte Agent, promote to form solid electrolyte interface film between solid inorganic material layer, electrolyte, negative pole, improve the stable circulation of negative pole Property；Electrolyte lithium salt is LiPF in lithium-sulfur cell electrolyte₆、LiAsF₆、LiClO₄、LiAlCl₄、LiBF₆、LiCF₃SO₃And LiN (CF₃SO₂)₂In one or more；Solvent is volume ratio 1:1-1:9 DOL, DME mixed solvent；Electrolysis additive can be with It is ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, acrylic acid first Ester, gamma-butyrolacton, 1,3- propane sultones, 1,4- butane sultones, ethylmethane sulfonate, butyl methyl sulfonate, carbonic acid It is vinylene, toluene, benzene, quinone imines, naphthalane, the copolymer of dimethylsilane and expoxy propane, polyoxyethylene, polyoxyethylated Dimethyl ether, PFOS lithium, LiBOB, LiNO₃、SnI₂、AlI₃、P₂S₅, one kind in bipyridyliumses compound or two kinds with On；The content of additive is 0.01moL/L-0.6moL/L.