Electrochemical separation method for stable sulfur isotope

Abstract

The invention discloses an electrochemical separation method for stable sulfur isotopes, which comprises the following steps: carrying out charge / discharge treatment through a metal-sulfur battery, enriching sulfur isotopes with relatively large atomic weight on a positive electrode side, and enriching sulfur isotopes with relatively small atomic weight on an electrolyte and a negative electrode side; the positive active material of the sulfur-containing battery contains stable sulfur isotope. According to the method disclosed by the invention, by utilizing the chemical interaction difference between polysulfide anions formed by different stable sulfur isotopes and alkali (alkaline earth) metal cations and organic solvent molecules in the electrolyte of the metal-sulfur-based secondary battery, a positive (negative) electrode electrochemical process of the metal-sulfur-based secondary battery is carried out; and spatial separation and enrichment of stable sulfur isotopes on different components in the battery are realized. The single-stage separation ratio can reach more than 10, the series stage number of the sulfur isotope separation device can be obviously reduced, and the separation energy consumption and cost are reduced.

Description

Technical Field

[0001] The invention belongs to the interdisciplinary field of isotope science and electrochemistry, and specifically relates to an electrochemical separation method for stable sulfur isotopes. Background Art

[0002] Isotopes refer to the same element with the same number of protons and electrons but different numbers of neutrons, and usually have similar physical and chemical properties. The discovery of isotopes has greatly promoted the development of science and broadened the depth and breadth of people's understanding and exploration of the world. Isotope separation technology is the basis of isotope scientific research and application. Due to the needs of the nuclear industry, isotope separation technology has made great progress. At present, uranium-235 ( 235 U), heavy water (D 2 O), lithium-6 ( 6 Li), Boron-10( 10 B) produced in tons, and established the cascade theory of large-scale isotope separation process; carbon-13 ( 13 C), nitrogen-15 ( 15 N), oxygen-18 ( 18 O) are produced in kilogram quantities. These isotopes are used as important tracers in medical testing, geological exploration, atmospheric environment monitoring, archaeology, military fields, etc. However, due to the very similar physical and chemical properties between isotopes, separation is very difficult. The current isotope separation technology is mainly based on mass differences. Therefore, common isotope research is basically concentrated in the first and second periods of the periodic table. After the third period, the mass difference between isotopes is less than 1 / 10, separation is more difficult, and related research is very rare.

[0003] Sulfur, located in the third period, is an important non-metallic element in the earth's crust. It has four natural isotopes: 32 S. 33 S. 34 S. 36 S, and the corresponding atomic abundances are 94.99% ( 32 S), 0.75%( 33 S), 4.25%( 34 S), 0.01%( 36 S). Among them, people mainly focus on the atoms with higher abundance. 32 S and 34 S. Stable sulfur isotopes have been widely studied and applied in the fields of nuclear physics, agricultural science, physiology and medicine, astronomy, ecology and geology. For example, 32 S and 34 S can be used to monitor the atmospheric S cycle in ecosystems, control soil and water acidification, and produce some important radioactive isotopes through neutron-induced nuclear reactions. 34 S and32 The mass difference of S is only 1 / 16, the physical and chemical properties are almost the same, the separation cost is very high, and the purity is ~99% 34 The price of sulfur is about 20,000 yuan per gram, which is also the main factor limiting the widespread application of sulfur isotopes. The separation coefficient is the main parameter used to measure the efficiency of isotope separation, which refers to the ratio of the two isotopes in the product phase to the ratio of the two isotopes in the initial phase. It can be expressed as:

[0004] α=(x A / y A ) / (x B / y B ) (1)

[0005] Among them, α is the separation coefficient (or separation ratio), x A and A represent the molar fractions of the two isotopes in phase A, x B and B Respectively represent the molar fractions of the two isotopes in phase B. Since the separation ratio of isotopes is usually very close to 1, in order to more intuitively describe the isotope effect, people also use thousandths to express the separation efficiency, that is:

[0006] δ(‰)=(α-1)×1000 (2)

[0007] Currently, the commonly used sulfur isotope separation methods are fractionation and chemical exchange, which are convenient for large-scale production. Among them, the single-stage separation coefficient of fractionation is relatively low, usually below 1.01, and it requires the use of highly toxic hydrogen sulfide as a production raw material. However, hydrogen sulfide distillation is still the main method for producing heavy sulfur isotopes, because there is a large amount of research data on this process, such as data on isotope exchange equilibrium and the fluid dynamics results of hydrogen sulfide in a distillation tower. The chemical exchange method usually involves SO 2 and HSO 3 - The exchange reaction of SO 2 Gas was passed into NaHSO 3 When the solution is dissolved, the heavy sulfur isotopes tend to enter the solution and replace HSO 3 - The light sulfur isotopes in the solution phase are enriched. Relatively speaking, the separation coefficient of the chemical exchange method is relatively high, but it is basically below 1.05. It usually takes hundreds of cascades to obtain a product with high purity, and the production cost is extremely high. According to the report in document 1 (TRMills, Sep. Sci. Technol. 1990, 25, 1919-1930), by distilling sulfur-containing compounds, the separation coefficient of the chemical exchange method is relatively high, but it is basically below 1.05. It usually takes hundreds of cascades to obtain a product with high purity, and the production cost is extremely high. 32 S and 34 Separation of S. Among them, H 2 S32 S / 34 The separation ratio of S is 1.0023, SF 4 middle 32 S / 34 The separation ratio of S is 0.9978 (i.e. 34 S is enriched in the product phase, corresponding to 34 S / 32 S separation ratio 1.0022), SF 6 middle 32 S / 34 The separation ratio of S is 0.9985, and COS 32 S / 34 The separation ratio of S is 1.0006, CH 3 SH 32 S / 34 The separation ratio of S is 1.0011. Reference 2 (TEEriksen, Acta Chem. Scand. 1972, 26, 573-580) studied the effect of temperature on the separation effect. The following chemical exchange reaction was achieved 34 Enrichment of S in solution:

[0008]

[0009] 25℃ 34 S / 32 The S separation ratio is 1.0109±0.0006, the separation ratio at 35°C is 1.0110±0.0008, and the separation ratio at 45°C is 1.0113±0.0009. Reference 3 (MA Boris, AS Polevoi, Russ. Chem. Rev. 1983, 52, 213) reviewed a large number of reports on the separation of sulfur isotopes by distillation and chemical exchange, and found that most of the work had a single-stage separation ratio for sulfur isotopes below 1.01, and some were even lower than 1.001. In addition to the above methods that can achieve the separation of sulfur isotopes, the segregation of sulfur elements is also involved in microbial metabolism. According to reference 4 (DE Canfield, B. Thamdrup, Science 1994, 266, 1973-1975), during bacterial metabolism, 34 S is enriched in sulfate at a ratio of 12.6 to 15.3 parts per thousand and depleted in sulfite at a ratio of 7.3 to 8.6 parts per thousand. Reference 5 (LA Chambers, PA Trudinger, Geomicrobiol. J. 1979, 1, 249-293) reviewed the microbial fractionation of stable sulfur isotopes, δ 34S(‰) ​​is basically within ±50, and the isotope effect of sulfur in microorganisms is poorly controllable, making it unsuitable for mass production of sulfur isotopes, but mainly used to study biological mechanisms.

[0010] The small mass difference between sulfur isotopes makes the separation efficiency of existing physical and chemical methods extremely low, which in turn leads to extremely high energy consumption. Hundreds of cascades also bring about a series of problems such as huge land occupation and difficult production management. The development of isotope science, especially heavy isotopes above the third period, urgently needs a cheap, simple and efficient isotope separation method. Summary of the invention

[0011] In order to solve the low efficiency and high cost of separating stable sulfur isotopes in the prior art, the present invention utilizes the differences in chemical interactions between polysulfide anions formed by different stable sulfur isotopes and alkali (alkaline earth) metal cations and organic solvent molecules in the metal-sulfur-based secondary battery electrolyte, and realizes the spatial separation and enrichment of stable sulfur isotopes on different components in the battery through the electrochemical process of the positive (negative) electrode of the metal-sulfur-based secondary battery. The electrochemical separation method of stable sulfur isotopes of the present invention uses commercial raw materials, mature device preparation processes and simple processing methods to achieve efficient separation between different stable sulfur isotopes, and the single-stage separation ratio can reach more than 10, corresponding to δ 34 S(‰) ​​is higher than 10000, which is two orders of magnitude higher than conventional physical or chemical separation methods (separation ratio is usually less than 1.02, δ 34 S(‰) ​​is usually in the single digit to double digits), which is expected to significantly reduce the number of series stages of isotope separation equipment, reduce separation energy consumption and cost, achieve efficient separation of isotopes of elements above the third period, and promote the development of isotope science, which has extremely high theoretical significance and practical value.

[0012] The present invention provides an electrochemical separation method for stable sulfur isotopes, comprising the following steps: a sulfur-containing battery is subjected to charge / discharge treatment, sulfur isotopes with relatively large atomic weight are enriched on the positive electrode side, and sulfur isotopes with relatively small atomic weight are enriched on the negative electrode side in the electrolyte; and the positive electrode active material of the sulfur-containing battery contains stable sulfur isotopes.

[0013] The sulfur-containing battery further comprises a negative electrode, a separator and an electrolyte, which are assembled together into a sulfur-containing battery. Further, the sulfur-containing battery is selected from a lithium-sulfur battery, a sodium-sulfur battery, a potassium-sulfur battery, a calcium-sulfur battery, a magnesium-sulfur battery or an aluminum-sulfur battery.

[0014] Figure 1The present invention is based on the principle of separating sulfur isotopes by electrochemical methods. During the electrochemical reaction, sulfur will generate soluble polysulfide anions and diffuse to the negative electrode. The differences in different sulfur isotopes in this process lead to their enrichment in different components. Heavier sulfur isotopes are enriched on the positive electrode side because polysulfide anions have lower solubility, are more difficult to migrate, and are more difficult to deposit on the negative electrode side; lighter sulfur isotopes are enriched in the electrolyte and negative electrode sides because polysulfide anions have higher solubility, are easier to migrate, and are easier to deposit on the negative electrode side. The inventor unexpectedly discovered that during the charge and discharge cycle of a sulfur-containing battery (sulfur is contained in the positive electrode active material), sulfur isotopes of different atomic weights are spatially separated and enriched in different components of the battery, and the separation efficiency is much higher than the sulfur isotope separation means known in the prior art, achieving efficient separation between different stable sulfur isotopes, and the single-stage separation ratio can reach more than 10, δ 34 S(‰) ​​is higher than 10000, which is two orders of magnitude higher than conventional physical or chemical separation methods (separation ratio is usually less than 1.02, δ 34 S(‰) ​​is usually within 30), which is expected to significantly reduce the number of series stages of isotope separation equipment, reduce separation energy consumption and cost, and has high theoretical significance and practical value.

[0015] Furthermore, the stable sulfur isotope is selected from 32 S. 33 S. 34 S and 36 S, in a preferred embodiment of the present invention, the stable sulfur isotopes include 32 S and 34 S, this is because 33 S and 36 The abundance of S is very low, so the separation is mainly based on 32 S and 34 S separation. Relatively large or small atomic weight refers to the four stable sulfur isotopes that exist in nature, in order from small to large atomic weight: i.e. 32 S. 33 S. 34 S. 36 S, as long as the positive electrode active material of the sulfur-containing battery contains two or more stable sulfur isotopes, spontaneous enrichment will occur during the battery cycle, and then the stable sulfur isotopes will be separated. There is no absolute limit on which sulfur isotope has a relatively large (small) atomic weight in the separation. For example, for 32 S and 34 S, 32 S has a relatively small atomic weight. 34 S has a relatively large atomic weight; 34 S and 36 S, 34 S has a relatively small atomic weight. 36S has a relatively large atomic weight. Considering its natural abundance, economic value, and practical value, the main consideration is 32 S and 34 Separation of S. That is, in the preferred technical solution of the present invention, separation 32 S and 34 S, but it does not exclude the involvement of two other 33 S. 36 Separation of S isotopes.

[0016] Furthermore, the active material containing stable sulfur isotopes includes one or a combination of two or more of a single sulfur cathode material, a polysulfide cathode liquid, and a sulfur-based polymer cathode material formed by stable sulfur isotopes; the single sulfur cathode material is selected from at least one of a monoclinic sulfur cathode material and an orthorhombic sulfur cathode material.

[0017] Furthermore, the monoclinic sulfur positive electrode material / orthorhombic sulfur positive electrode material is a composite of monoclinic sulfur / orthorhombic sulfur formed by stable sulfur isotopes and a conductive substrate, wherein the stable sulfur isotopes account for 10-99wt%, preferably 30-70wt%, such as 40wt%, 50wt%, 60wt%. The conductive substrate is not particularly limited, and can be any conductive material conventionally used in the art for preparing sulfur-containing positive electrodes, including but not limited to graphite, carbon nanotubes, graphene, carbon fiber, conductive carbon black, porous carbon, hollow carbon spheres, Ketjen black, foamed copper, foamed nickel, titanium dioxide (TiO 2 ), vanadium pentoxide (V 2 O 5 ), manganese dioxide (MnO 2 ), titanium nitride (TiN), titanium carbide (TiC), cobalt selenide (CoSe), cobalt diselenide (CoSe 2 ), one or more of nickel selenide (NiSe).

[0018] The composite method of monoclinic sulfur / orthorhombic sulfur and the conductive substrate is not particularly limited and is a conventional method in the art, for example, comprising the following steps:

[0019] (S1) Monoclinic sulfur / orthorhombic sulfur and a conductive substrate are mixed by mechanical mixing. The mixing method is not particularly limited, and uniform mixing is sufficient, such as mechanical stirring, ball milling or dry mixing. The mechanical stirring speed is 200-1000rpm / min, preferably 500-800rpm / min, the ball milling speed is 200-600rpm / min, preferably 350-450rpm / min, and the mixing time is 5-60min, preferably 20-40min. The temperature during mixing is 0 to 60°C, preferably 20 to 40°C.

[0020] (S2) In a sealed container, under an inert atmosphere or vacuum, the mixture is heated to be thoroughly mixed; for S, the heating temperature is 120 to 180° C., preferably 140 to 160° C., and the heating time is 1 to 12 h, preferably 6 to 10 h.

[0021] The polysulfide positive electrode liquid is prepared by dissolving polysulfide in an organic solvent. The polysulfide is formed by polysulfide anions and alkali (alkaline earth) metal cations, and is selected from one or more of lithium polysulfide, sodium polysulfide, potassium polysulfide, calcium polysulfide, magnesium polysulfide, and aluminum polysulfide. The organic solvent is selected from one or more of ether solvent molecules, carbonate solvent molecules, (sub) sulfone solvent molecules, nitrile solvent molecules, amide solvent molecules, and polymer solvent molecules. The molar concentration of polysulfide anions is 0.1 mol / L to 8 mol / L, preferably 1 mol / L to 5 mol / L.

[0022] The sulfur-based polymer positive electrode is selected from one or more of an organic sulfur polymer derived from a nitrile compound, an organic sulfur polymer derived from an olefin / alkyne compound, and an organic sulfur polymer derived from a thiol compound. Further, the organic sulfur polymer derived from a nitrile compound is a short-chain polysulfide-S x -covalently bonded to a cyclic carbon skeleton containing pyridine nitrogen, including but not limited to polyacrylonitrile sulfur (SPAN) and sulfur covalent triazine skeleton (S-CTF-1); the organic sulfur polymer derived from the olefin / alkyne compound is formed by the cleavage of the unsaturated bonds of unsaturated hydrocarbons and sulfur bonding, including poly 1,3-diisopropenylbenzene sulfide (poly Sr-DIB), 3-hexyl substituted polythiophene sulfide (S-P3HT), and poly 1,3-diethynylbenzene sulfide (poly S-DEB); the organic sulfur polymer derived from the thiol compound is formed by the copolymerization of the thiol group of a linear thioether with an open-ring sulfur, including trithiocyanate sulfur (S-TTCA), polycaprolactam sulfur (S-BOP), and polythiol-reduced graphene oxide sulfur (S-GSH).

[0023] The raw materials of the positive electrode containing the active material of the stable sulfur isotope include the active material containing the stable sulfur isotope, the conductive additive, and the binder; the mass ratio thereof is 8:1:1. The preparation method of the positive electrode containing the active material of the stable sulfur isotope is well known in the art, and includes the following steps: grinding and mixing the active material containing the stable sulfur isotope, the conductive additive, the binder and the solvent, coating them on the surface of the current collector, and drying to obtain the base material.

[0024] Preferably, the conductive additive is selected from one or more of Super P, Ketjen black, graphene, and conductive carbon nanotubes; the binder is selected from one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR); the solvent is selected from one or more of N-methylpyrrolidone, ethanol, and water. The drying time is 6-24 hours, preferably 10-16 hours, and the drying temperature is 50-100°C, preferably 60-80°C.

[0025] The negative electrode includes one or more alkali (alkaline earth) metals such as lithium, sodium, potassium, calcium, magnesium, and aluminum. Further, the negative electrode includes any form of the above substances as electrochemically active materials, including but not limited to alloying, surface modification, and structurally modified negative electrodes. The alloyed negative electrode includes but is not limited to lithium-indium alloy, lithium-aluminum alloy, lithium-silver alloy, lithium-silicon alloy, lithium-antimony alloy, lithium-tin alloy, lithium-copper alloy, lithium-sodium alloy, sodium-silicon alloy, sodium-phosphorus alloy, sodium-germanium alloy, sodium-potassium alloy, sodium-lead alloy, sodium-bismuth alloy, sodium-antimony alloy, lead-calcium alloy, and calcium-magnesium alloy; the surface modification includes but is not limited to polymer protection, inorganic coating, and organic / inorganic composite coating; the structural modification includes but is not limited to copper-based, carbon-based, and nickel-based three-dimensional structural designs.

[0026] The electrolyte includes a liquid electrolyte, a solid-liquid mixed electrolyte or a polymer-based solid electrolyte. The electrolyte solvent is selected from one or more of ether solvent molecules, carbonate solvent molecules, (sulfide) solvent molecules, nitrile solvent molecules, amide solvent molecules and polymer solvent molecules; the cation of the electrolyte salt is the above metal cation, and the anion includes but is not limited to phosphate, borate, perchlorate, nitrate, trifluoromethylsulfonate, bis (trifluoromethylsulfonic acid) imide and halogen anion.

[0027] The ether solvent molecule is selected from diethyl ether (Et 2O), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-Me-THF), dimethoxymethane (DMM), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (tri-EGGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), 2-methyl-1,3-dioxolane (2-Me-DOL), 4-methyl-1,3-dioxolane (4-Me-DOL) and 1,4-dioxane (1,4-Dioxane) One or more; the carbonate solvent molecule is selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butyl methyl carbonate (BMC), γ-butyrolactone (γ-BL), γ-valerolactone (γ-VL) and ε-caprolactone (ε-CL); the (sub)sulfone solvent molecules are selected from one or more of dimethyl sulfoxide (DMSO), cyclopentane (SUL) and methyl ethyl sulfone (MES); the nitrile solvent molecules are selected from one or more of acetonitrile (AN), succinonitrile (SN), trimethoxypropionitrile (MPN) and triethoxypropionitrile (EPN); the amide solvent molecules are selected from one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP) and tetramethylurea (TMU); the polymer solvent molecules are selected from one or more of polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polymethyl methacrylate (PMMA).

[0028] The separator includes a single layer or multiple layers of polymer membranes and glass fiber membranes. The polymer membranes include but are not limited to polypropylene (PP), polyethylene (PE) and their stacked combinations. When a solid or solid-liquid mixed electrolyte is used, a separator may not be used.

[0029] The battery is assembled in the order of positive electrode, separator, and negative electrode, and the electrolyte is added between the positive and negative electrodes, including but not limited to button batteries, Swagelok batteries, soft-pack batteries, cylindrical batteries, electrolytic cells, etc. The minimum distance between the positive and negative electrodes is the thickness of the separator, and the maximum distance is unlimited.

[0030] The charge / discharge process is to apply a charge / discharge protocol to the battery device through an external circuit to cause an electrochemical redox reaction of the positive / negative active material. The charge / discharge protocol is a combination of one or more of the following steps, including but not limited to discharge only, charge only, single cycle charge / discharge, multiple cycle charge / discharge, static process, current control process, voltage control process, capacity control process, etc.

[0031] The present invention also proposes a method for optimizing the separation efficiency of sulfur isotopes by adjusting the above conditions, including adjusting the types and concentrations of solvents, salts and additives in the electrolyte, replacing different negative electrodes, adjusting the distance between the positive and negative electrodes, adjusting the battery discharge and charge current, voltage, number of cycles, etc. Optimizing the separation efficiency of sulfur isotopes by regulating the parameters mentioned in the invention also falls within the scope of protection of the present invention.

[0032] During the electrochemical cycle of the sulfur-containing battery of the present invention, the sulfur element of the positive electrode active material forms polysulfide, dissolves into the electrolyte, forms a "metal-sulfur" interaction with the metal cation, combines with the polysulfide anion, and interacts with the polarity of the organic solvent molecules, which jointly promotes the enrichment and separation of stable sulfur isotopes in the charge and discharge cycle of the sulfur-containing battery. The electrochemical reaction kinetics of polysulfide is related to the solubility of the electrolyte. When the electrochemical reaction kinetics of the polysulfide is better, the soluble polysulfide will be quickly converted into an insoluble end product, and the existence time in the system is reduced, so that the dissolution of the polysulfide is reduced; the solubility of the electrolyte is the solubility of the electrolyte for polysulfide, which is an intrinsic thermodynamic property and is related to the sublimation heat and dissociation energy of the solute. The greater the solubility for polysulfide, the more polysulfide can be dissolved. The diffusion and migration process of polysulfide in the electrolyte forms a concentration gradient in the electrolyte, driving the polysulfide to diffuse from the high concentration area on the positive electrode side to the low concentration area on the negative electrode side. The diffusion migration process is related to the diffusion coefficient of polysulfide. The larger the diffusion coefficient, the faster the polysulfide diffuses to the negative electrode side. After the polysulfide undergoes a chemical redox reaction with the negative electrode active material, part of it is reduced to a soluble low-order intermediate product and diffuses back to the positive electrode, and part of it is further reduced to form a solid final product and deposited on the negative electrode side. There are differences in the dissolution process, diffusion migration process, and reduction and deposition process of polysulfides of different isotopes from the positive electrode side to the electrolyte, which ultimately leads to the sulfur isotopes with greater polysulfide solubility, easier migration and easier deposition on the negative electrode side, that is, sulfur isotopes with relatively smaller atomic weights are enriched in the electrolyte and the negative electrode; sulfur isotopes with smaller polysulfide solubility, more difficult migration and more difficult deposition on the negative electrode side, that is, sulfur isotopes with relatively larger atomic weights are enriched on the positive electrode side. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the principle of electrochemical separation of sulfur isotopes;

[0034] Figure 2 The mixed sulfur positive electrode sheet in Example 1 32 S / 34 S content;

[0035] Figure 3 In Example 1, the negative electrode sheet after charge and discharge 32 S / 34S content (a) and ratio (b);

[0036] Figure 4 In Example 1, after charging and discharging, the electrolyte 32 S / 34 S;

[0037] Figure 5 In Example 2, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0038] Figure 6 In Example 3, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0039] Figure 7 In Example 4, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0040] Figure 8 In Example 5, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0041] Fig. 9 In Example 6, the negative electrode sheet after charge and discharge 32 S / 34 S content (a) and ratio (b);

[0042] Fig.10 In Example 7, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0043] Fig.11 In Example 8, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0044] Fig.12 In Example 9, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0045] Fig.13 In Example 10, the negative electrode sheet after charge and discharge 32 S / 34 The ratio of S;

[0046] Fig.14 The initial sulfur electrode (a) and the negative electrode (b) after charge and discharge in Example 11 32 S / 34 The ratio of S;

[0047] Fig.15 In Example 12, the initial sulfur electrode (a) and the negative electrode (b) after charge and discharge 32 S / 34 The ratio of S;

[0048] Fig.16 The initial sulfur electrode (a) and the negative electrode (b) after charge and discharge in Example 11 32 S / 34 The ratio of S. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with specific embodiments.

[0050] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described can be obtained from commercial sources.

[0051] The sulfur isotope ratios in the initial positive electrode materials of the following embodiments and the sulfur isotope ratios in the negative electrode after electrochemical treatment were obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) testing, and the sulfur isotope ratios in the electrolyte were obtained by inductively coupled plasma mass spectrometry (ICP-MS) testing.

[0052] The negative electrodes after cycling listed in Table 1 32 S / 34 S ratio and separation ratio are 32 S / 34 The average value after the S ratio fluctuation stabilizes, that is, the ratio of all points in the stable stage is added and then divided by the number of points. Example 4 takes the average value of the first 0-1200s part, because in the high-concentration salt system, the surface layer of the negative electrode sheet is the part that directly contacts the electrolyte, so the influence of the electrolyte concentration mainly depends on the surface situation.

[0053] Example 1

[0054] (I) Preparation of S / C composite materials containing a certain proportion of stable sulfur isotopes

[0055] 34 S powder (Cambridge Isotope Laboratory, USA), 32 S powder (natural S) and ordered mesoporous carbon CMK-3 were prepared in a mass ratio of 206:194:600 ( 32 S and 34 S) were thoroughly ground and mixed, and the mixture was sealed in a container with an argon atmosphere, heated to 150°C and kept warm for 10 hours. After cooling to room temperature, the obtained 32 S / 34 S / C composite material with S molar ratio of 1:1.

[0056] The mixture was sealed in an argon atmosphere container, heated to 150°C and kept warm for 10 hours. After cooling to room temperature, 32 S / 34 S / C composite material with S molar ratio of 1:1.

[0057] (II) Preparation of mixed sulfur cathode sheets

[0058] The S / C composite conductive additive (Super P) and polyvinylidene fluoride (PVDF) binder prepared in (a) were mixed in a 1-methyl-2-pyrrolidone (NMP) solvent at a mass ratio of 8:1:1 and slurried. The obtained slurry was scraped onto a carbon-coated aluminum foil, dried at 60°C for 24 hours, and then cut into 10 mm discs to obtain a mixed sulfur positive electrode sheet.

[0059] (III) ToF-SIMS test of mixed sulfur cathode 34 S and 32 The content ratio of S

[0060] The mixed sulfur cathode obtained in (ii) was subjected to ToF-SIMS deep etching test, with the primary ion source being 30 keV Bi 3+ The sputtering ion source is 2keV Cs + The test results are as follows: Figure 2 As shown, with the increase of etching depth, 34 S and 32 The S content is always the same, proving that the obtained mixed sulfur cathode sheet 34 S and 32 The molar ratio of S is 1:1, such as Figure 2 shown.

[0061] (IV) Battery Assembly

[0062] In an argon atmosphere glove box, the composite sulfur cathode obtained in (II), lithium sheet, Whatman glass fiber separator, and battery were assembled. The electrolyte used was 1 mol / L lithium perchlorate (LiClO 4 ) was dissolved in DOL / DME (volume ratio 1:1) and the added amount was 180 μL.

[0063] (V) Battery Cycle

[0064] The battery obtained in (IV) was subjected to constant current charge and discharge test on a blue battery tester, with a test voltage range of 1.5 to 2.8 V and a charge and discharge rate of 0.1C (according to 34 S and 32 The theoretical specific capacity of the composite sulfur positive electrode with a S molar ratio of 1:1 was calculated to be 1C = 1624 mA / g), and it was cycled 10 times in the order of discharge first and then charge.

[0065] (VI) After the cycle, the negative electrode34 S and 32 S content ratio test

[0066] Step 1) Disassemble the battery after the cycle in (V) in an argon atmosphere glove box, take out the lithium sheet, drain the residual solvent on the surface and then perform ToF-SIMS test. The test results are as follows Figure 3 As shown in a, the negative electrode 32 The S content is always higher than 34 S, thus we get 32 S / 34 The ratio of S is 1.8 (such as Figure 3 b), compared with the test results of (iii), we get 32 S / 34 The separation ratio of S was 1.8. All test conditions and results are listed in Table 1.

[0067] Step 2) The Whatman diaphragm filled with electrolyte in the cycled battery is immersed in isopropanol solvent to extract sulfur compounds, and then diluted and tested by ICP-MS. The test results are as follows Figure 4 As shown, sample 1, sample 2, and sample 3 are three sets of parallel samples tested under the same conditions. 32 S and 34 The average molar ratio of S is 1.856, and compared with the initial sulfur mixed sulfur cathode sheet, the electrolyte 32 S had an enrichment effect, and the separation ratio was 1.856.

[0068] Example 2

[0069] The other conditions are the same as those in Example 1, except that

[0070] In step (iv), the separator is a Celgard PP / PE / PP film;

[0071] In step (V), the charge and discharge cycle is performed once. Figure 5 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0072] Example 3

[0073] The other conditions are the same as those in Example 1, except that

[0074] In step (iv), the separator is a PP / PE / PP film of Celgard, and the electrolyte salt is lithium bis(trifluoromethanesulfonyl)imide;

[0075] In step (V), the charge and discharge cycle is performed once. Figure 6 Shows the negative electrode side after cycling 32 S / 34All test conditions and results are listed in Table 1.

[0076] Example 4

[0077] The other conditions are the same as those in Example 1, except that

[0078] The concentration of lithium perchlorate in step (iv) is 5 mol / L;

[0079] In step (V), the charge and discharge cycle is performed once. Figure 7 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0080] Example 5

[0081] The other conditions are the same as those in Example 1, except that

[0082] In step (iv), the separator is Celgard PP / PE / PP membrane and the electrolyte is 2 mol / L LiPF 6 Dissolved in a gel electrolyte formed by DOL / DME with a volume ratio of 8:1;

[0083] In step (V), the charge and discharge cycle is performed once. Figure 8 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0084] Example 6

[0085] The other conditions are the same as those in Example 1, except that

[0086] In step (a), only natural S powder is used to mix with carbon. Fig. 9 a shows the initial sulfur cathode sheet 32 S / 34 The ratio of S, Fig. 9 b shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0087] Example 7

[0088] The other conditions are the same as those in Example 1, except that

[0089] In step (a), only natural S powder is used to mix with carbon;

[0090] In step (iv), the separator is Celgard PP / PE / PP membrane and the electrolyte is 2 mol / L LiPF 6Dissolved in a gel electrolyte formed by DOL / DME with a volume ratio of 8:1;

[0091] In step (V), the charge and discharge cycle is performed once. Fig.10 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0092] Example 8

[0093] The other conditions are the same as those in Example 1, except that

[0094] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Dissolved in TEGDME;

[0095] In step (V), the charge and discharge cycle is performed once. Fig.11 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0096] Example 9

[0097] The other conditions are the same as those in Example 1, except that

[0098] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Soluble in TEGDME. Fig.12 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0099] Example 10

[0100] The other conditions are the same as those in Example 1, except that

[0101] In step (a), only natural S powder is used to mix with carbon;

[0102] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Dissolved in TEGDME;

[0103] In step (V), the charge and discharge cycle is performed once. Fig.13 Shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0104] Embodiment 11

[0105] The other conditions are the same as those in Example 1, except that

[0106] In step (a), only commercially available 34 S powder is mixed with carbon;

[0107] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Dissolved in TEGDME;

[0108] In step (V), the charge and discharge cycle is performed once. Fig.14 a shows the initial sulfur cathode sheet 32 S / 34 The ratio of S, Fig.14 b shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0109] Example 12

[0110] The other conditions are the same as those in Example 1, except that

[0111] Step (1) 32 S powder and 34 The molar ratio of S powder is 1:3;

[0112] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Dissolved in TEGDME;

[0113] In step (V), the charge and discharge cycle is performed once. Fig.15 a shows the initial sulfur cathode sheet 32 S / 34 The ratio of S, Fig.15 b shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0114] Embodiment 13

[0115] The other conditions are the same as those in Example 1, except that

[0116] Step (1) 32 S powder and 34 The molar ratio of S powder is 3:2;

[0117] In step (iv), the negative electrode is a sodium sheet and the electrolyte is 1 mol / L NaClO 4 Dissolved in TEGDME;

[0118] In step (V), the charge and discharge cycle is performed once. Fig.16 a shows the initial sulfur cathode sheet 32 S / 34 The ratio of S, Fig.16 b shows the negative electrode side after cycling 32 S / 34 All test conditions and results are listed in Table 1.

[0119] Table 1 Separation effect of S isotopes

[0120]

[0121]

[0122] It can be seen from the above examples that the present invention can achieve efficient separation of sulfur isotopes through a simple electrochemical method, and achieve proportional regulation by adjusting the electrolyte, negative electrode, battery processing procedures and other conditions. From the data in Table 1, the following rules can be obtained:

[0123] 1) Increasing the concentration of electrolyte salt can amplify the separation of sulfur isotopes. The separation efficiency of Example 4 is greater than that of Examples 1-3, and can reach more than 3. The use of gel electrolyte can further amplify the separation ratio of sulfur isotopes. The separation ratio of Example 5 can reach more than 5. However, the use of highly concentrated salt electrolytes and gel electrolytes themselves will inhibit the migration of polysulfide anions, which may reduce the yield. In actual production applications, the separation ratio and yield issues need to be comprehensively considered.

[0124] 2) Changing the negative electrode material can amplify the separation of sulfur isotopes. The separation ratio achieved by using metallic sodium as the negative electrode is greater than that achieved by using metallic lithium as the negative electrode. Example 8 uses Na as the negative electrode, and its separation ratio is about 10, which is greater than that of Examples 1-5 using lithium as the negative electrode. For natural S, the separation ratio of Example 10 using sodium as the negative electrode (separation ratio 1.74) is greater than that of Example 6 (separation ratio 1.25) and Example 7 (separation ratio 1.48) using lithium as the negative electrode.

[0125] 3) When lithium metal is used as the negative electrode, the separation ratio of sulfur isotopes increases with the increase in the number of battery cycles. The separation ratio of Example 1 is greater than that of Examples 2 and 3.

[0126] 4) When sodium metal is used as the negative electrode, the separation ratio decreases with increasing number of cycles, and the separation ratio of Example 9 (separation ratio 1.3) is much lower than that of Example 8 (separation ratio 10). This proves that more cycles are not necessarily better, and achieving a greater separation ratio with fewer cycles can effectively improve the yield.

[0127] It is worth noting that for business 34 S, a product with a purity of up to 96.7%, can still achieve an isotope separation ratio of more than 10, which is of great significance for the preparation of high-purity isotopes.

[0128] The present invention uses an equal amount of32 S / 34 The initial sulfur electrode of S theoretically verified the feasibility of electrochemical separation of sulfur isotopes and applied this method to natural S powder and commercially available 34 We also prepared other ratios of S powder. 32 S / 34 The mixed sulfur pole piece of S simulates the cascade process in isotope separation and proves 32 S content from 3.3% (commercial 34 The electrochemical method can be used in the range of 95% (natural S) to 95% (natural S). 32 S and 34 S was effectively separated, and the separation ratio was much higher than that reported in previous literature. Tables 2 and 3 list the methods and effects of separating sulfur isotopes in existing literature.

[0129] Table 2 Separation of sulfur isotopes by distillation

[0130]

[0131] Table 3 Separation of sulfur isotopes by chemical exchange

[0132]

[0133] Note: The data in Table 2 and Table 3 are from MA Boris, A. S. Polevoi, Russ. Chem. Rev. 1983, 52, 213.

Claims

1. A method for electrochemical separation of stable sulfur isotopes, It is characterized in that The following steps are involved: The metal-sulfur battery is charged / discharged, the positive electrode side is enriched with sulfur isotopes with relatively large atomic weight, and the electrolyte and the negative electrode side are enriched with sulfur isotopes with relatively small atomic weight; the positive electrode active material of the sulfur-containing battery contains stable sulfur isotopes.

2. The electrochemical separation method of stable sulfur isotopes according to claim 1, It is characterized in that The metal-sulfur battery also includes a negative electrode, a separator and an electrolyte, which are assembled together into a sulfur-containing battery; further, the metal-sulfur battery is selected from a lithium-sulfur battery, a sodium-sulfur battery, a potassium-sulfur battery, a calcium-sulfur battery, a magnesium-sulfur battery or an aluminum-sulfur battery.

3. The electrochemical separation method of stable sulfur isotopes according to claim 1, It is characterized in that The stable sulfur isotopes are selected from 32 S. 33 S. 34 S and 36 A combination of two or more of S; preferably 32 S and 34 Separation of S.

4. The electrochemical separation method of stable sulfur isotopes according to claim 1, It is characterized in that The active material containing stable sulfur isotopes includes one or a combination of two or more of a single sulfur cathode material, a polysulfide cathode liquid, and a sulfur-based polymer cathode material formed by stable sulfur isotopes; the single sulfur cathode material is selected from at least one of a monoclinic sulfur cathode material and an orthorhombic sulfur cathode material.

5. The electrochemical separation method of stable sulfur isotopes according to claim 4, It is characterized in that The monoclinic sulfur positive electrode material / orthorhombic sulfur positive electrode material is obtained by compounding monoclinic sulfur / orthorhombic sulfur formed by stable sulfur isotopes and a conductive substrate, wherein the stable sulfur isotopes account for 10-99wt%, preferably 30-70wt%; The conductive substrate includes graphite, carbon nanotubes, graphene, carbon fiber, conductive carbon black, porous carbon, hollow carbon spheres, Ketjen black, foamed copper, foamed nickel, titanium dioxide (TiO 2 ), vanadium pentoxide (V 2 O 5 ), manganese dioxide (MnO 2 ), titanium nitride (TiN), titanium carbide (TiC), cobalt selenide (CoSe), cobalt diselenide (CoSe 2 ), one or more of nickel selenide (NiSe).

6. The electrochemical separation method of stable sulfur isotopes according to claim 5, It is characterized in that The composite method of monoclinic sulfur / orthorhombic sulfur and a conductive substrate comprises the following steps: (S1) mixing monoclinic sulfur / orthorhombic sulfur and a conductive substrate by a mechanical mixing method; (S2) heating the mixture in a sealed container under an inert atmosphere or vacuum to allow the mixture to be thoroughly mixed; Furthermore, the heating temperature is 120 to 180° C., preferably 140-160° C., and the heating time is 1-12 h, preferably 6-10 h.

7. The electrochemical separation method of stable sulfur isotopes according to claim 4, It is characterized in that The polysulfide positive electrode liquid is prepared by dissolving polysulfide in an organic solvent; the polysulfide is formed by polysulfide anions and alkali metal cations or alkaline earth metal cations; specifically selected from one or more of lithium polysulfide, sodium polysulfide, potassium polysulfide, calcium polysulfide, magnesium polysulfide, and aluminum polysulfide; Furthermore, the organic solvent is selected from one or more of ether solvent molecules, carbonate solvent molecules, (sulfone) solvent molecules, nitrile solvent molecules, amide solvent molecules and polymer solvent molecules. The molar concentration of polysulfide anions is 0.1 mol / L to 8 mol / L, preferably 1 mol / L to 5 mol / L.

8. The electrochemical separation method of stable sulfur isotopes according to claim 4, It is characterized in that The sulfur-based polymer positive electrode is selected from one or more of an organic sulfur polymer derived from a nitrile compound, an organic sulfur polymer derived from an olefin / alkyne compound, and an organic sulfur polymer derived from a thiol compound; Furthermore, the organic sulfur polymer derived from the nitrile compound is a short-chain polysulfide-S x -covalently bonded to a cyclic carbon skeleton containing pyridine nitrogen, including but not limited to polyacrylonitrile sulfur (SPAN) and sulfur covalent triazine skeleton (S-CTF-1); the organic sulfur polymer derived from the olefin / alkyne compound is formed by the cleavage of the unsaturated bonds of unsaturated hydrocarbons and sulfur bonding, including poly 1,3-diisopropenylbenzene sulfide (poly Sr-DIB), 3-hexyl substituted polythiophene sulfide (S-P3HT), and poly 1,3-diethynylbenzene sulfide (poly S-DEB); the organic sulfur polymer derived from the thiol compound is formed by the copolymerization of the thiol group of a linear thioether with an open-ring sulfur, including trithiocyanate sulfur (S-TTCA), polycaprolactam sulfur (S-BOP), and polythiol-reduced graphene oxide sulfur (S-GSH).

9. The electrochemical separation method of stable sulfur isotopes according to claim 1, It is characterized in that The raw materials of the positive electrode of the sulfur-containing battery include an active material containing stable sulfur isotopes, a conductive additive, and a binder; Preferably, the mass ratio of active material, conductive additive and binder is 8:1:1; Preferably, the conductive additive is selected from one or more of Super P, Ketjen black, graphene, and conductive carbon nanotubes; the binder is selected from one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR); the solvent is selected from one or more of N-methylpyrrolidone, ethanol, and water; Preferably, the negative electrode includes one or more alkali (alkaline earth) metals such as lithium, sodium, potassium, calcium, magnesium, and aluminum.

10. The electrochemical separation method of stable sulfur isotopes according to claim 2, It is characterized in that The electrolyte includes a liquid electrolyte, a solid-liquid mixed electrolyte or a polymer-based solid electrolyte. The electrolyte solvent is selected from one or more of ether solvent molecules, carbonate solvent molecules, (sulfone) solvent molecules, nitrile solvent molecules, amide solvent molecules and polymer solvent molecules; the cations of the electrolyte salt are the same metal cations in the metal-sulfur battery, and the anions include phosphate, borate, perchlorate, nitrate, trifluoromethylsulfonate, bis (trifluoromethylsulfonate) imide and halogen anions; The ether solvent molecule is selected from diethyl ether (Et 2 O), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-Me-THF), dimethoxymethane (DMM), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (tri-EGGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), 2-methyl-1,3-dioxolane (2-Me-DOL), 4-methyl-1,3-dioxolane (4-Me-DOL) and 1,4-dioxane (1,4-Dioxane) One or more; the carbonate solvent molecule is selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butyl methyl carbonate (BMC), γ-butyrolactone (γ-BL), γ-valerolactone (γ-VL) and ε-caprolactone (ε-CL); the (sub)sulfone solvent molecules are selected from one or more of dimethyl sulfoxide (DMSO), cyclopentane (SUL) and methyl ethyl sulfone (MES); the nitrile solvent molecules are selected from one or more of acetonitrile (AN), succinonitrile (SN), trimethoxypropionitrile (MPN) and triethoxypropionitrile (EPN); the amide solvent molecules are selected from one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP) and tetramethylurea (TMU); the polymer solvent molecules are selected from one or more of polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polymethyl methacrylate (PMMA).

11. The electrochemical separation method of stable sulfur isotopes according to claim 2, It is characterized in that The separator includes a single-layer or multi-layered polymer film or a glass fiber film; the polymer film includes polypropylene (PP), polyethylene (PE) and a stacked combination thereof; when a solid or solid-liquid mixed electrolyte is used, a separator may not be used.

12. The electrochemical separation method of stable sulfur isotopes according to claim 2, It is characterized in that The charge / discharge process is to apply a charge / discharge protocol to the battery device through an external circuit to cause an electrochemical redox reaction in the positive / negative active materials; the charge / discharge protocol is a combination of one or more of the following steps, including discharge only, charge only, single-cycle charge and discharge, multi-cycle charge and discharge, static process, current control process, voltage control process or capacity control process.

Images