Weak solvation electrolyte, sulfur-based battery and electric equipment

Abstract

The invention relates to the technical field of sulfur-based batteries, in particular to a weak solvation electrolyte, a sulfur-based battery and electric equipment. The weak solvation electrolyte comprises a main solvent, electrolyte salt and an additive, the main solvent comprises an organic solvent containing heteroatoms, and the dielectric constant of the main solvent is 0-5; the additive comprises an organic reagent which can be complexed with polysulfide; and the solubility of the polysulfide in the weak solvated electrolyte is less than or equal to 0.5 mol / L in terms of sulfur atoms. The weak solvation electrolyte provided by the invention can inhibit the dissolution of polysulfide, and solves the shuttling problem of the polysulfide from the source; the side reaction of the main solvent and the negative electrode can be reduced, and electrolyte consumption, and corrosion and pulverization of dry battery liquid and the negative electrode are avoided; in addition, by introducing the additive, the reaction kinetics of the solid-phase sulfur species can be improved, so that the rate of the sulfur-based battery is improved. Therefore, by adopting the weak solvation electrolyte, the rate capability and the cycling stability of the sulfur-based battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfur-based batteries, and in particular to a weakly solvated electrolyte, a sulfur-based battery and an electrical device. Background Art

[0002] The energy density of the most successful commercial lithium-ion battery is about 250Wh / kg. However, due to the limitations of the intercalated lithium-containing metal oxide positive electrode and graphite negative electrode, the energy density of lithium-ion batteries is difficult to reach 300Wh / kg. In order to break through the positive and negative electrode limitations of lithium-ion batteries, seeking a new electrochemical reaction system is an effective way to improve battery energy density.

[0003] Sulfur has a very high theoretical specific capacity (such as elemental sulfur: 1672mAh / g), and metal anodes or silicon anodes have lower electrode potentials and higher theoretical specific capacities (such as metal lithium: -3.04V vs. NHE, 3860mAh / g; metal sodium: -2.73V, 1166mAh / g; silicon: 0-0.5V vs. NHE, 4200mAh / g). Therefore, sulfur-based batteries have extremely high theoretical energy density. For example, the theoretical energy density of lithium-sulfur batteries can reach 2600Wh / kg. The energy density of actual soft-pack lithium-sulfur batteries reported so far has reached 500Wh / kg, which is twice that of current commercial lithium-ion batteries. Therefore, metal-sulfur-based batteries are the main development direction of the next generation of high-performance batteries.

[0004] Although sulfur-based batteries have great advantages in terms of energy density, their current cycle life is relatively low, which greatly limits their further development and potential applications. Taking lithium-sulfur batteries as an example, the most widely used electrolyte for lithium-sulfur batteries is a low-concentration ether electrolyte. Its ether solvents (such as 1,3-dioxolane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, etc.) have a strong solvating ability for lithium polysulfide. Therefore, lithium polysulfide has a high solubility in this type of electrolyte, and this type of electrolyte is called a strong solvating electrolyte. At the same time, under the condition of low electrolyte dosage, the dissolution of lithium polysulfide in the electrolyte will reach saturation, resulting in slow reaction kinetics of the sulfur electrode, so that the rate performance of lithium-sulfur batteries under actual working conditions is poor. In conventional ether electrolyte systems, lithium-sulfur batteries face serious challenges: (1) The shuttle effect of lithium polysulfide. Under the action of electric field and concentration gradient, dissolved lithium polysulfide forms a shuttle effect between the positive and negative electrodes, resulting in the loss of active sulfur and corrosion of the lithium negative electrode. (2) Dendrites and pulverization of the metallic lithium negative electrode. In this type of electrolyte, lithium dendrites and "dead lithium" are easily formed during battery charging, and the lithium negative electrode will experience electrode pulverization during long cycles. (3) The reaction kinetics of lithium-sulfur batteries under actual working conditions are slow, and the rate performance is poor (generally within 0.5C). High current density can lead to severe battery polarization and battery failure.

[0005] Therefore, it is necessary to develop a new electrolyte system from the perspective of electrolyte design to reduce the dissolution of lithium polysulfide and the reaction activity of the electrolyte with the metal anode, and at the same time promote the kinetics of polysulfide redox reaction through electrolyte additives.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The first object of the present invention is to provide a weakly solvated electrolyte, which can inhibit the dissolution of polysulfides and solve the shuttling problem of polysulfides from the source; it can also reduce the side reaction between the main solvent and the negative electrode, avoid electrolyte consumption, corrosion and pulverization of battery dry liquid and negative electrode; in addition, the introduction of additives can improve the reaction kinetics of solid-phase sulfur species, thereby improving the rate of sulfur-based batteries. Therefore, the use of the weakly solvated electrolyte can improve the rate performance and cycle stability of sulfur-based batteries.

[0008] The second object of the present invention is to provide a sulfur-based battery having the advantages of high energy density, high rate, long cycle and the like.

[0009] The third object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] The present invention first provides a weak solvation electrolyte, comprising a main solvent, an electrolyte salt and an additive; the main solvent comprises an organic solvent containing heteroatoms, and the dielectric constant of the main solvent is 0 to 5; the additive comprises an organic reagent capable of complexing with polysulfides; and the solubility of the polysulfide in the weak solvation electrolyte is ≤0.5 mol / L in terms of sulfur atoms.

[0012] Furthermore, the heteroatoms in the main solvent include at least one of O, S, N, Si, P, and F.

[0013] Further, the main solvent includes at least one of cyclopentyl methyl ether, 1,1-dimethoxycyclopentane, tetraethyl silicate and dicyclopentyldimethoxysilane.

[0014] Furthermore, the organic reagent capable of complexing with polysulfide includes at least one of thiuram additives, sulfide additives and mercaptan additives.

[0015] Furthermore, the thiuram additive has the following molecular structure:

[0016] Wherein, x≥1, R1, R2, R3, R4 are each independently an alkyl group CH3-(CH2) n -, n≥0.

[0017] Furthermore, the molar concentration of the additive in the weakly solvated electrolyte is ≤1 mol / L, more preferably ≤0.2 mol / L.

[0018] Furthermore, the weakly solvating electrolyte also includes a co-solvent.

[0019] Furthermore, the dielectric constant of the co-solvent is 0-10.

[0020] Furthermore, the volume of the co-solvent accounts for 5 to 95% of the total volume of the weakly solvated electrolyte.

[0021] Furthermore, the co-solvent includes at least one of hydrofluoroether, aromatic hydrocarbons, tetrahydrothiophene and alkanes.

[0022] Further, the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, calcium salt, aluminum salt and iron salt.

[0023] Furthermore, the molar concentration of the electrolyte salt in the weakly solvated electrolyte is 0.1 to 4 mol / L.

[0024] Further, the anions in the electrolyte salt include at least one of perchlorate, dioxalatoborate, difluorooxalatoborate, trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, bisfluoromethanesulfonyl imide, hexafluorophosphate, borate, tetrafluoroborate and hexafluoroarsenate.

[0025] The present invention further provides a sulfur-based battery, comprising the weakly solvated electrolyte.

[0026] Furthermore, the positive electrode in the sulfur-based battery is a sulfur positive electrode, and the sulfur active material in the sulfur positive electrode includes at least one of elemental sulfur, lithium sulfide, sulfur-containing polymers and sulfur-containing small molecules.

[0027] Furthermore, the negative electrode of the sulfur-based battery includes at least one of lithium metal, graphite, hard carbon, silicon, silicon-carbon composite material, sodium metal, potassium metal, magnesium metal, calcium metal, aluminum metal and iron metal.

[0028] Furthermore, the addition amount of the weakly solvated electrolyte in the sulfur-based battery is 0.5 to 20 ul / mg.

[0029] Furthermore, the positive electrode is made of the sulfur active material, sulfur carrier, conductive agent and binder.

[0030] Furthermore, the sulfur carrier includes at least one of Ketjen black, activated carbon, carbon nanotubes, graphene, carbon fiber, mesoporous carbon and microporous carbon.

[0031] Furthermore, the conductive agent includes at least one of carbon nanotubes, graphene, acetylene black, activated carbon and carbon fiber.

[0032] Furthermore, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, LA133, LA132 and styrene-butadiene rubber.

[0033] The present invention also provides an electrical device, comprising the sulfur-based battery.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention is based on the innovation of the composition and properties of the electrolyte. By selecting one or more main solvents with low dielectric constants (or low DN values), a weak solvation electrolyte is constructed. The solubility of polysulfide in the weak solvation electrolyte is ≤0.5 mol / L, which is significantly different from the conventional ether electrolyte (the concentration range of polysulfide is 100-10 mol / L). First, the weak solvation electrolyte in the present invention only has a good dissolution effect on the electrolyte salt, ensuring that the electrolyte has a high ionic conductivity, but the solvation ability of the weak solvation electrolyte for polysulfide is extremely weak, so the solubility of polysulfide is extremely low, which can effectively inhibit the shuttle effect of polysulfide. Secondly, the reaction activity of the weak solvation electrolyte is low, and the side reaction with the metal negative electrode is reduced, so the corrosion effect on the metal negative electrode is inhibited; at the same time, because the shuttling of polysulfide is eradicated, the side reaction of polysulfide with the metal negative electrode is also effectively inhibited, so the weak solvation electrolyte effectively inhibits the corrosion of the metal negative electrode.

[0036] (2) The weakly solvated electrolyte provided by the present invention can improve the rate performance and cycle stability of the sulfur-based battery prepared therefrom.

[0037] (3) The sulfur-based battery based on weakly solvated electrolyte provided by the present invention has the advantages of high energy density, high rate, long cycle, high safety and no self-discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A charge and discharge curve diagram of a button-type lithium-sulfur battery based on a weakly solvated electrolyte provided in Example 1 of the present invention;

[0040] Figure 2 This is a test diagram of the cycle performance of a button-type lithium-sulfur battery based on a weakly solvated electrolyte provided in Example 1 of the present invention;

[0041] Figure 3 A charge and discharge curve diagram of a button-type lithium-sulfur battery based on a weakly solvated electrolyte provided in Example 2 of the present invention;

[0042] Figure 4 This is a test diagram of the cycle performance of a button-type lithium-sulfur battery based on a weakly solvated electrolyte provided in Example 2 of the present invention;

[0043] Figure 5This is a rate performance test diagram of a button-type lithium-sulfur battery based on a weakly solvated electrolyte provided in Example 3 of the present invention;

[0044] Figure 6 This is a rate performance test diagram of a button-type lithium-sulfur battery based on a weakly solvated electrolyte (without additives) provided in Comparative Example 1 of the present invention;

[0045] Figure 7 A charge and discharge curve diagram of a button-type lithium-sulfur battery based on an ether electrolyte provided in Comparative Example 2 of the present invention;

[0046] Figure 8 This is a test diagram of the cycle performance of a button-type lithium-sulfur battery based on an ether electrolyte provided in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0047] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0048] If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0049] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0050] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0051] On the first aspect, in response to the problems of polysulfide shuttling and metal negative electrode dendrites in sulfur-based batteries, the present invention creatively provides a weakly solvated electrolyte for high-rate and long-cycle sulfur-based batteries, which includes a main solvent, an electrolyte salt and additives.

[0052] Specifically, a weakly solvating electrolyte refers to an electrolyte system in which the solvating ability of the electrolyte is weak and polysulfides are insoluble in the electrolyte.

[0053] Wherein, the main solvent comprises an organic solvent containing heteroatoms, wherein the heteroatoms comprise at least one of O, S, N, Si, P, and F, or two, three, four or more of the heteroatoms.

[0054] It is understood that the main solvent includes both chain molecules and cyclic molecules. In terms of molecular polarity, the main solvent molecules have weaker polarity, which is more physically described as the main solvent molecules having a lower dielectric constant, or Lewis basicity, or donor number (DN value), in order to ensure that the solvent molecules have a weaker solvating ability.

[0055] The dielectric constant of the main solvent is 0 to 5, including but not limited to any point value of 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range value between any two of them.

[0056] The additive includes an organic agent capable of complexing with the polysulfide.

[0057] It is understood that polysulfides include but are not limited to lithium polysulfide, sodium polysulfide, magnesium polysulfide, iron polysulfide, etc., and the anion of the polysulfide is a polysulfide anion S x 2- , wherein 2≤x≤8, and the cation is all metal cations covered by the present invention.

[0058] Under the temperature condition of 0-60°C, the solubility of the polysulfide in the weakly solvated electrolyte is ≤0.5 mol / L, calculated as sulfur atom, including but not limited to any point value of 0.4 mol / L, 0.3 mol / L, 0.2 mol / L, 0.1 mol / L, 0.01 mol / L, 0.001 mol / L or the range value between any two thereof; preferably ≤10 mmol / L.

[0059] The composition and solvation structure of the electrolyte are key factors determining the electrochemical performance of sulfur-based batteries.

[0060] The present invention develops a weakly solvated electrolyte, which has the advantages of good chemical stability, good thermal stability, and stability to the negative electrode. In the weakly solvated electrolyte of the present invention, the reaction mechanism of the sulfur electrode in the sulfur-based battery is a solid-solid reaction mechanism, and the reaction mechanism of the metal negative electrode is a dissolution-deposition mechanism. The sulfur-based battery containing the weakly solvated electrolyte has the advantages of high energy density, long cycle life, high safety, and no self-discharge.

[0061] Conventional sulfur-based batteries use a dissolution-deposition reaction mechanism and face problems such as low energy density, lithium polysulfide dissolution shuttling, low coulombic efficiency, poor cycle stability, and severe self-discharge.

[0062] The weakly solvated electrolyte developed by the present invention can effectively solve the above problems. Specifically, the weakly solvated electrolyte has the following advantages:

[0063] (1) It broadens the system range of sulfur-based battery electrolytes, has excellent chemical, electrochemical and thermal stability, and has a broader use space in practical application scenarios. The specific principle is: the main solvent in the present invention can dissociate the electrolyte salt well, giving the electrolyte a higher ionic conductivity and cation migration number, while the viscosity of the electrolyte is low. On the negative electrode side, the weak solvation of the electrolyte means that the reaction activity of the solvent is low, thereby reducing the side reaction between the main solvent and the negative electrode; on the positive electrode side, the antioxidant capacity of the main solvent is significantly improved; the vaporization temperature of the main solvent itself is significantly increased, and the thermal decomposition phenomenon is significantly reduced.

[0064] (2) Eradicate the dissolution and shuttling of polysulfides from the source, realize the solid-solid reaction of the sulfur electrode, and improve the cycle stability of the sulfur-based battery. The specific principle is: the positive electrode reaction of the sulfur-based battery will produce intermediate products such as polysulfides. In conventional high-soluble electrolytes, polysulfides have a high solubility (about 1 to 10 mol / L). The sulfur-based positive electrode is a dissolution-deposition reaction mechanism, which will produce the shuttling phenomenon of polysulfides. In the present invention, a weak solvation electrolyte is constructed by regulating the electrolyte composition, and the solubility of polysulfides is reduced to an extremely low level, reaching below 0.5 mol / L. Therefore, the dissolution and shuttling of polysulfides are completely suppressed. At the same time, the sulfur positive electrode is transformed into a solid-solid reaction mechanism, so the cycle stability of the battery is greatly improved.

[0065] (3) Improve the stability of the negative electrode, reduce dendrites and negative electrode pulverization, and reduce battery safety hazards. The specific principles are: first, the weak solvation of the electrolyte means that the reaction activity of the solvent is low, which can reduce the side reaction between the main solvent and the negative electrode; second, in the weakly solvated electrolyte, the first solvation shell of the cation contains a large number of anions, that is, the coordination between the cation and the anion is strong. This type of electrolyte structure effectively reduces the lowest unoccupied molecular orbital (LUMO) energy level of the coordinated anion, so the anion will be easier to reduce on the negative electrode surface. As a result, the SEI film on the negative electrode surface contains more inorganic elements, such as fluorine, sulfur, nitrogen and oxygen. The SEI film can induce uniform deposition of the negative electrode and reduce the generation of dendrites; third, the SEI film rich in inorganic components is relatively stable, which reduces the repeated growth of the SEI film during the cycle, and thus can slow down the pulverization of the negative electrode.

[0066] (4) Accelerate the kinetics of the solid-solid reaction of the sulfur electrode, improve the rate performance of sulfur-based batteries, and expand the application scenarios of sulfur-based batteries. The additive has a strong complexation with the polysulfide, the intermediate product of the discharge of the sulfur electrode, which promotes the diffusion, migration and electron gain and loss of polysulfide on the surface of the sulfur electrode, significantly improving the reaction kinetics of the sulfur electrode, thereby giving the sulfur-based battery excellent rate characteristics. The improvement of rate characteristics is conducive to the application prospects of sulfur-based batteries in fields such as power batteries and drones.

[0067] Furthermore, the weak solvation electrolyte developed by the present invention has wide universality and can be applied to various types of battery systems. The weak solvation electrolyte of the present invention can be applied to a variety of battery systems (MS), wherein M is a metal negative electrode or a non-metal negative electrode, including lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, aluminum, iron, graphite, silicon, lithiated graphite, lithiated silicon, silicon / carbon, etc., and S is elemental sulfur, sulfur-containing polymers and sulfur-containing organic molecules, etc. According to the specific characteristics of the positive and negative electrodes of the battery, different weak solvation electrolytes can be prepared to construct a sulfur-based battery based on a solid-solid sulfur conversion mechanism.

[0068] In some specific embodiments, the DN value of the main solvent is 0-15, including but not limited to any point value of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any range value between two of them. This indicates that the main solvent has a weak polarity.

[0069] In some specific embodiments, the main solvent includes at least one of cyclopentyl methyl ether, 1,1-dimethoxycyclopentane, tetraethyl silicate and dicyclopentyldimethoxysilane, or two, three or more thereof.

[0070] In some specific embodiments, the organic reagent capable of complexing with polysulfide includes at least one of thiuram additives, sulfide additives (such as dimethyl sulfide, diethyl sulfide) and thiol additives (such as ethanethiol, 1,2-ethanedithiol), or two or three thereof. The use of the above-mentioned types of additives is conducive to further improving the reaction kinetics of solid-phase sulfur species, thereby further improving the rate performance of sulfur-based batteries.

[0071] In some specific embodiments, the thiuram additive has the following molecular structure:

[0072] Wherein, x≥1, R1, R2, R3, R4 are each independently an alkyl group CH3-(CH2) n -, n≥0. Among them, S x refers to x S atoms, for example, when x=2, S x That is -SS-. Wherein, n includes but is not limited to any point value of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range value between any two of them.

[0073] In some specific embodiments, the molar concentration of the additive in the weakly solvated electrolyte is ≤1 mol / L, including but not limited to any point value of 0.8 mol / L, 0.7 mol / L, 0.6 mol / L, 0.5 mol / L, 0.4 mol / L, 0.3 mol / L, 0.2 mol / L, 0.1 mol / L, 0.01 mol / L or any range value between two thereof; preferably ≤0.2 mol / L. By controlling the molar concentration of the additive, it is beneficial to improve the rate performance of the sulfur-based battery.

[0074] In some specific embodiments, the weakly solvated electrolyte further comprises a co-solvent, which can reduce the viscosity of the electrolyte and improve the wettability of the electrolyte to the electrode.

[0075] In some specific embodiments, the dielectric constant of the co-solvent is 0 to 10, including but not limited to any point value of 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10 or any range value between two of them. The dielectric constant can be used to describe the ability to dissolve lithium salts. The low dielectric constant prevents the co-solvent from participating in the dissociation of the electrolyte salt and lithium polysulfide, ensuring the slight solubility of the electrolyte on lithium polysulfide. In some specific embodiments, the DN value of the co-solvent is 0 to 10, including but not limited to any point value of 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10 or any range value between two of them. The low DN value prevents the co-solvent from participating in the dissociation of the electrolyte salt and lithium polysulfide, ensuring the slight solubility of the electrolyte on lithium polysulfide.

[0076] In some specific embodiments, the volume of the co-solvent accounts for 5 to 95% of the total volume of the weakly solvated electrolyte, including but not limited to any point value of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90% or any range value between two of them.

[0077] It is understood that the main solvent dissolves the electrolyte salt; the co-solvent does not participate in dissolving the electrolyte salt, but is miscible with the main solvent. Therefore, even if the main solvent content is very low, it is still the main solvent.

[0078] In some specific embodiments, the solubility of the co-solvent in the electrolyte salt is ≤1 mmol / L.

[0079] In some specific embodiments, the co-solvent includes at least one of hydrofluoroether, aromatic hydrocarbon, tetrahydrothiophene and alkane.

[0080] In terms of functionality, the electrolyte salt can be dissolved by the main solvent to provide ionic conductivity to the electrolyte; the cation of the electrolyte salt should be the same as the element of the metal negative electrode.

[0081] In some specific embodiments, the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, calcium salt, aluminum salt and iron salt.

[0082] In some specific embodiments, the molar concentration of the electrolyte salt in the weakly solvated electrolyte is 0.1 to 4 mol / L, including but not limited to any point value of 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L or any range value between two thereof. This ensures that the electrolyte has sufficient cations, thereby ensuring ionic conductivity.

[0083] In some specific embodiments, the anion in the electrolyte salt includes at least one of perchlorate, dioxalatoborate, difluorooxalatoborate, trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, bisfluoromethanesulfonyl imide, hexafluorophosphate, borate, tetrafluoroborate and hexafluoroarsenate.

[0084] In a second aspect, the present invention provides a sulfur-based battery, comprising the weakly solvated electrolyte.

[0085] The present invention further develops a sulfur-based battery system based on a weakly solvated electrolyte, which has the advantages of high energy density, high rate, long cycle, high safety and no self-discharge.

[0086] The sulfur-based battery based on a weakly solvated electrolyte provided by the present invention has very excellent electrochemical performance from an electrochemical point of view. First, from the positive electrode side, the solubility of polysulfides in a weakly solvated electrolyte is extremely low, so the shuttling effect of polysulfides can be fundamentally eliminated, and the coulombic efficiency and cycle life of the battery are significantly improved; secondly, from the negative electrode side, in a weakly solvated electrolyte, the coordination effect between metal cations and anions is strong, so that the lowest unoccupied orbital energy level (LUMO) of the anion is reduced, so the anion is more easily electrochemically reduced on the negative electrode surface. As a result, in a weakly solvated electrolyte, a layer of SEI film with a higher proportion of inorganic elements will be enriched on the surface of the metal negative electrode, and the SEI film is conducive to the smooth deposition of the metal negative electrode and reduces the possibility of dendrites.

[0087] Taking lithium-sulfur batteries as an example, in a weakly solvated electrolyte constructed with cyclopentyl methyl ether and lithium bis(trifluorosulfonyl)imide, the solubility of Li2S4 is only 8 mmol / L.

[0088] Specifically, the sulfur-based battery based on a weakly solvated electrolyte provided by the present invention has very excellent cycle stability. In a weakly solvated electrolyte, since the sulfide positive electrode realizes a solid-solid reaction, the coulombic efficiency (more than 99.99%) and cycle stability of the sulfide battery are greatly improved; at the same time, the additive can significantly promote the electrochemical redox reaction of polysulfides, reduce the passivation of sulfur species (elemental sulfur, polysulfides, sulfides), and improve the utilization rate of active substances in the sulfur electrode. Taking lithium-sulfur batteries as an example, the battery life in a weakly solvated electrolyte can reach more than 600 cycles.

[0089] The sulfur-based battery based on a weakly solvated electrolyte provided by the present invention has excellent rate characteristics. For sulfur-based batteries, in conventional electrolytes, metal negative electrodes generally have high reactivity, while sulfur species (elemental sulfur, polysulfide, sulfide) have high reaction inertness, and the reaction rate of the sulfur electrode is slow, so the sulfur electrode is the key to restricting the cycle life and rate of sulfur-based batteries. The electrolyte additives in the present invention can complex with sulfur species, enhance the diffusion and charge transfer of sulfur species on the positive electrode side, and greatly enhance the reaction kinetics of the sulfur electrode, so that the metal-sulfur-based battery has excellent rate characteristics.

[0090] The sulfur-based battery based on the weakly solvated electrolyte provided by the present invention can be stored for a long time without self-discharge. The high solubility of polysulfides is an important reason for the serious self-discharge phenomenon of sulfur batteries. The weakly solvated electrolyte provided by the present invention can greatly inhibit the dissolution and shuttling of polysulfides, and the active substances of the sulfur positive electrode can be very well maintained in the positive electrode itself. Therefore, the self-discharge phenomenon of the battery is well suppressed and can be stored for a long time without power decay. Taking the sodium-sulfur battery as an example, the battery can be stably stored for more than 3 years using the weakly solvated electrolyte in the present invention.

[0091] The sulfur-based battery based on a weakly solvated electrolyte provided by the present invention has low cost. The positive electrode of the sulfur-based battery includes sulfur, which is a byproduct of the chemical process, is cheap and abundant in resources; and the negative electrode of the sulfur-based battery also has the characteristics of abundant reserves and low price. Therefore, the battery in the present invention has the advantage of low material cost and has great application prospects in the field of large-scale energy storage. For example, the cost of lithium-sulfur batteries is US$9.9 / kWh, and the cost of sodium-sulfur batteries is US$1.4 / kWh, which is much lower than the US$83.2 / kWh of lithium-ion batteries (lithium cobalt oxide positive electrode).

[0092] In some specific embodiments, the positive electrode in the sulfur-based battery is a sulfur positive electrode, and the sulfur active material in the sulfur positive electrode includes at least one of elemental sulfur, lithium sulfide, sulfur-containing polymers and sulfur-containing small molecules. Among them, the sulfur-containing polymer is a sulfurized polymer material, such as sulfurized polyacrylonitrile, sulfurized polyvinylidene fluoride, sulfurized rubber, etc. The sulfur-containing small molecule is a non-polymer material, and the sulfur-containing small molecule includes but is not limited to selenium disulfide, selenium polysulfide, dimethyl disulfide, sulfur-phosphorus compounds, sulfide metals (such as molybdenum trisulfide, iron disulfide, ferrous sulfide, titanium disulfide, etc.), etc.

[0093] In some specific embodiments, the negative electrode of the sulfur-based battery includes at least one of lithium metal, graphite, hard carbon, silicon, silicon-carbon composite materials, sodium metal, potassium metal, magnesium metal, calcium metal, aluminum metal and iron metal.

[0094] In some specific embodiments, the addition amount of the weakly solvated electrolyte in the sulfur-based battery is 0.5 to 20 ul / mg, including but not limited to any point value of 0.5 ul / mg, 1 ul / mg, 2 ul / mg, 3 ul / mg, 4 ul / mg, 5 ul / mg, 6 ul / mg, 8 ul / mg, 10 ul / mg, 13 ul / mg, 15 ul / mg, 17 ul / mg, and 20 ul / mg, or a range value between any two of them.

[0095] It can be understood that the uL in the above unit ul / mg refers to the volume of the weakly solvated electrolyte, and mg refers to the mass of the active substance sulfur.

[0096] In the ether electrolytes commonly reported / applied, the reaction dissolution-deposition mechanism of the sulfide positive electrode requires the dissolution effect of the electrolyte, so the amount of electrolyte used is generally high, which is not conducive to building a high energy density battery.

[0097] The sulfur-based battery based on a weakly solvated electrolyte provided by the present invention can effectively reduce the amount of electrolyte used and improve the energy density of soft-pack batteries. In a weakly solvated electrolyte, the sulfur electrode is a solid-solid reaction mechanism, and the electrochemical redox reaction of sulfur no longer depends on the amount of electrolyte used. Therefore, the amount of weakly solvated electrolyte used in this application can be greatly reduced. Low electrolyte usage is conducive to reducing the proportion of inactive substances in the battery (<30%, calculated based on soft-pack batteries), which is crucial to improving the mass energy density of the battery.

[0098] In some specific embodiments, the positive electrode is made of the sulfur active material, a sulfur carrier, a conductive agent and a binder.

[0099] In some specific embodiments, the sulfur carrier includes at least one of Ketjen black, activated carbon, carbon nanotubes, graphene, carbon fiber, mesoporous carbon and microporous carbon.

[0100] In some specific embodiments, the conductive agent includes at least one of carbon nanotubes, graphene, acetylene black, activated carbon and carbon fiber.

[0101] In some specific embodiments, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, LA133, LA132 and styrene-butadiene rubber, wherein LA133 and LA132 are a kind of acrylonitrile multi-polymer, which is the main component of a water-based binder.

[0102] In a third aspect, the present invention provides an electrical device comprising the sulfur-based battery.

[0103] It can be understood that the above-mentioned electrical equipment includes any device and equipment containing the above-mentioned sulfur-based battery.

[0104] The sulfur-based battery provided by the present invention has a long cycle life, high rate characteristics and extremely high energy density (>300Wh / kg), and has broad application prospects, such as in power batteries, portable devices, large energy storage power stations, especially in the field of drones, but not limited thereto.

[0105] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0106] Example 1

[0107] The weak solvation electrolyte provided in this embodiment is composed of: cyclopentyl methyl ether (main solvent, with a dielectric constant of 4.76) and lithium bis(trifluoromethanesulfonyl)imide (electrolyte salt), and the additive is tetramethylthiuram disulfide (i.e., thiuram additive). The molar concentration of the electrolyte salt in the weak solvation electrolyte is 1 mol / L; the molar concentration of the additive in the weak solvation electrolyte is 10 mmol / L.

[0108] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 8 mmol / L, calculated as sulfur atom.

[0109] This embodiment also provides a sulfur-based battery, using the weakly solvated electrolyte prepared in this embodiment, wherein the sulfur positive electrode is composed of elemental sulfur (sulfur active material), Ketjen black (sulfur carrier), graphene (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 56:14:20:10:1. The negative electrode of the sulfur-based battery is metallic lithium. The assembly steps of the sulfur-based battery are: in an argon-protected glove box, a sulfur-Ketjen black-polyvinylidene fluoride electrode is used as the positive electrode, a Celgard 2500 diaphragm, a metallic lithium negative electrode, a 2032 battery shell, and a sulfur loading of 2.5 mg / cm 2 , the electrolyte dosage is 10μL / mg.

[0110] The sulfur-based battery prepared in this embodiment was subjected to constant current charge and discharge test and cycle performance test at a test temperature of 25°C. The test results are as follows: Figure 1 and Figure 2 As shown, it can be seen that the lithium-sulfur battery exhibits a higher discharge specific capacity (1230 mAh / g) at a rate of 0.1C, and the reversible discharge capacity of the battery after 50 cycles is maintained at 995 mAh / g, with a capacity retention rate of 80.9%.

[0111] Example 2

[0112] The weak solvation electrolyte provided in this embodiment is composed of tetraethyl silicate (main solvent, with a dielectric constant of 4.1) and lithium bis(fluoromethanesulfonyl)imide (electrolyte salt), and the additive is tetramethylthiuram monosulfide (i.e., thiuram additive). The molar concentration of the electrolyte salt in the weak solvation electrolyte is 1 mol / L; the molar concentration of the additive in the weak solvation electrolyte is 50 mmol / L.

[0113] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 10 mmol / L, calculated as sulfur atom.

[0114] This embodiment also provides a sulfur-based battery, using the weakly solvated electrolyte prepared in this embodiment, wherein the sulfur positive electrode is composed of elemental sulfur (sulfur active substance), multi-walled carbon nanotubes (sulfur carrier), activated carbon (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 49:21:20:10. The negative electrode of the sulfur-based battery is metallic lithium. The assembly steps of the sulfur-based battery are as follows: in an argon-protected glove box, a sulfur-multi-walled carbon nanotube-polyvinylidene fluoride electrode is used as the positive electrode, an Al2O3-coated PE diaphragm, a metallic lithium negative electrode, a 2032 battery shell, and a sulfur loading of 2.5 mg / cm 2 , the electrolyte dosage is 6μL / mg.

[0115] The sulfur-based battery prepared in this embodiment was subjected to constant current charge and discharge test and cycle performance test at a test temperature of 25°C. The test results are as follows: Figure 3 and Figure 4 As shown, it can be seen that the lithium-sulfur battery exhibits a very high discharge specific capacity (1144 mAh / g) at a rate of 0.1C, and the reversible discharge capacity of the battery after 50 cycles is maintained at 893 mAh / g, with a capacity retention rate of 78.1%.

[0116] Example 3

[0117] The weak solvation electrolyte provided in this embodiment is composed of: 1,1-dimethoxycyclopentane (main solvent) and lithium bis(trifluoromethanesulfonyl)imide (electrolyte salt), and the additive is tetramethylthiuram disulfide (i.e., thiuram additive). The molar concentration of the electrolyte salt in the weak solvation electrolyte is 2 mol / L; the molar concentration of the additive in the weak solvation electrolyte is 50 mmol / L.

[0118] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 50 mmol / L, calculated as sulfur atom.

[0119] This embodiment also provides a sulfur-based battery, using the weakly solvated electrolyte prepared in this embodiment, wherein the sulfur positive electrode is composed of elemental sulfur (sulfur active substance), mesoporous carbon (sulfur carrier), carbon fiber (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 64:16:10:10. The negative electrode of the sulfur-based battery is metallic lithium. The assembly steps of the sulfur-based battery are: in an argon-protected glove box, a sulfur-mesoporous carbon-polyvinylidene fluoride electrode is used as the positive electrode, Celgard 2500 diaphragm, metallic lithium negative electrode, 2032 battery shell, and the sulfur loading is 3.5 mg / cm 2 , the electrolyte dosage is 5μL / mg.

[0120] The sulfur-based battery prepared in this embodiment was subjected to constant current charge and discharge tests at a test temperature of 25°C. The test results are as follows: Figure 5As shown. It can be seen that the lithium-sulfur battery exhibits a very high discharge capacity (1192 mAh / g) at a rate of 1C, and the discharge capacity of the lithium-sulfur battery at a rate of 5C is as high as 1043 mAh / g. It can be seen that in the weakly solvated electrolyte of the present invention, the lithium-sulfur battery exhibits excellent rate performance.

[0121] Example 4

[0122] The composition of the weakly solvated electrolyte provided in this embodiment is substantially the same as that of Embodiment 1, except that the additive is replaced by a thioether additive, dimethyl sulfide.

[0123] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 8 mmol / L, calculated as sulfur atom.

[0124] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 1 using the weakly solvated electrolyte prepared in this example.

[0125] Example 5

[0126] The composition of the weakly solvated electrolyte provided in this embodiment is substantially the same as that of Embodiment 1, except that the additive is replaced by ethanethiol, a thiol additive.

[0127] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 8 mmol / L, calculated as sulfur atom.

[0128] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 1 using the weakly solvated electrolyte prepared in this example.

[0129] Example 6

[0130] The composition of the weak solvating electrolyte provided in this embodiment is basically the same as that in Example 1, except that it also includes a co-solvent, which is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (hydrofluoroether), and its dielectric constant is 6.21. The volume of the co-solvent accounts for 50% of the total volume of the weak solvating electrolyte.

[0131] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 7 mmol / L, calculated as sulfur atom.

[0132] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 1 using the weakly solvated electrolyte prepared in this example.

[0133] Example 7

[0134] The composition of the weak solvation electrolyte provided in this embodiment is basically the same as that in embodiment 1, except that: it also includes a co-solvent, which is benzene, and its dielectric constant is 2.3 and DN value is 0.1. In this embodiment: the molar concentration of the electrolyte salt in the weak solvation electrolyte is 2 mol / L; the molar concentration of the additive in the weak solvation electrolyte is 100 mmol / L; the volume of the co-solvent accounts for 70% of the total volume of the weak solvation electrolyte.

[0135] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 4 mmol / L, calculated as sulfur atom.

[0136] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 1 using the weakly solvated electrolyte prepared in this example.

[0137] Example 8

[0138] The composition of the weakly solvated electrolyte provided in this embodiment is substantially the same as that of Embodiment 1, except that the electrolyte salt is replaced by lithium bis(fluorosulfonyl)imide.

[0139] At 25°C, the solubility of polysulfide in the weakly solvated electrolyte is 9 mmol / L, calculated as sulfur atom.

[0140] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 1 using the weakly solvated electrolyte prepared in this example.

[0141] The sulfur-based batteries prepared in Examples 4 to 8 were subjected to constant current charge and discharge tests and cycle performance tests, respectively, at a test temperature of 25° C. The test results are shown in Table 1.

[0142] Table 1 Electrochemical performance test results of Examples 4 to 8

[0143]

[0144]

[0145] Comparative Example 1

[0146] The composition of the electrolyte provided in this comparative example is substantially the same as that of Example 3, except that it does not contain any additives.

[0147] A sulfur-based battery was prepared according to the preparation method of the sulfur-based battery in Example 3 using the electrolyte prepared in this comparative example.

[0148] The sulfur-based battery prepared in this comparative example was subjected to constant current charge and discharge tests at a test temperature of 25°C. The test results are as follows: Figure 6As shown. It can be seen that the discharge capacity of the lithium-sulfur battery at 1C rate is 1167mAh / g, and the discharge capacity of the lithium-sulfur battery at 5C rate is 697mAh / g. That is, in an electrolyte without additives, the rate performance of the lithium-sulfur battery is poor.

[0149] Comparative Example 2

[0150] The electrolyte provided in this comparative example is a typical ether electrolyte, whose main solvents are 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1), the concentration of lithium bistrifluoromethanesulfonyl imide (electrolyte salt) in the electrolyte is 1 mol / L, and the concentration of lithium nitrate (additive) in the electrolyte is 2 wt%.

[0151] The ether electrolyte prepared in this comparative example was used to prepare a sulfur-based battery according to the preparation method of the sulfur-based battery in Example 1, but the amount of the ether electrolyte used was 20 μL / mg.

[0152] The sulfur-based battery prepared in this comparative example was subjected to constant current charge and discharge test and cycle performance test at a test temperature of 25°C. The test results are as follows: Figure 7 and Figure 8 It can be seen that the discharge capacity of the battery at 0.1C is about 1377mAh / g, and the remaining capacity of the battery after 50 cycles is 476mAh / g, and the capacity retention rate is only 34.6%.

[0153] In summary, the weakly solvated electrolyte provided by the present invention can effectively improve the cycle stability and rate characteristics of sulfur-based batteries such as lithium-sulfur batteries.

[0154] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A weakly solvated electrolyte, characterized in that: including a main solvent, an electrolyte salt and additives; The main solvent includes an organic solvent containing heteroatoms, and the dielectric constant of the main solvent is 0 to 5; The additive includes an organic agent capable of complexing with the polysulfide; The solubility of the polysulfide in the weakly solvated electrolyte is ≤0.5 mol / L in terms of sulfur atom.

2. The weakly solvated electrolyte according to claim 1, characterized in that: The heteroatom in the main solvent includes at least one of O, S, N, Si, P, and F; Preferably, the main solvent includes at least one of cyclopentyl methyl ether, 1,1-dimethoxycyclopentane, tetraethyl silicate and dicyclopentyldimethoxysilane.

3. The weakly solvated electrolyte according to claim 1, characterized in that: The organic reagent capable of complexing with polysulfide comprises at least one of thiuram additives, thioether additives and mercaptan additives; Preferably, the thiuram additive has the following molecular structure: Wherein, x≥1, R1, R2, R3, R4 are each independently an alkyl group CH3-(CH2) n -, n≥0.

4. The weakly solvated electrolyte according to claim 1, characterized in that: The molar concentration of the additive in the weakly solvated electrolyte is ≤1 mol / L, preferably ≤0.2 mol / L.

5. The weakly solvated electrolyte according to claim 1, characterized in that: The weakly solvating electrolyte further includes a co-solvent; Preferably, the dielectric constant of the co-solvent is 0 to 10; Preferably, the volume of the co-solvent accounts for 5 to 95% of the total volume of the weakly solvated electrolyte; Preferably, the co-solvent comprises at least one of hydrofluoroethers, aromatic hydrocarbons, tetrahydrothiophene and alkanes.

6. The weakly solvated electrolyte according to claim 1, characterized in that: The electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, calcium salt, aluminum salt and iron salt; Preferably, the molar concentration of the electrolyte salt in the weakly solvated electrolyte is 0.1 to 4 mol / L; Preferably, the anions in the electrolyte salt include at least one of perchlorate, dioxalatoborate, difluorooxalatoborate, trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, bisfluoromethanesulfonyl imide, hexafluorophosphate, borate, tetrafluoroborate and hexafluoroarsenate.

7. A sulfur-based battery, characterized in that: It comprises the weakly solvated electrolyte as claimed in any one of claims 1 to 6.

8. The sulfur-based battery according to claim 7, characterized in that: The positive electrode in the sulfur-based battery is a sulfur positive electrode, and the sulfur active material in the sulfur positive electrode includes at least one of elemental sulfur, lithium sulfide, a sulfur-containing polymer and a sulfur-containing small molecule; Preferably, the negative electrode of the sulfur-based battery comprises at least one of lithium metal, graphite, hard carbon, silicon, silicon-carbon composite material, sodium metal, potassium metal, magnesium metal, calcium metal, aluminum metal and iron metal; Preferably, the addition amount of the weakly solvated electrolyte in the sulfur-based battery is 0.5-20 ul / mg.

9. The sulfur-based battery according to claim 8, characterized in that: The positive electrode is made of the sulfur active material, the sulfur carrier, the conductive agent and the binder: Preferably, the sulfur carrier comprises at least one of Ketjen black, activated carbon, carbon nanotubes, graphene, carbon fiber, mesoporous carbon and microporous carbon; Preferably, the conductive agent comprises at least one of carbon nanotubes, graphene, acetylene black, activated carbon and carbon fiber; Preferably, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, LA133, LA132 and styrene-butadiene rubber.

10. An electrical device, characterized in that: Comprising the sulfur-based battery as claimed in any one of claims 7 to 9.

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