High-specific-energy lithium-sulfur battery

Abstract

The invention relates to the technical field of lithium-sulfur batteries, and discloses a high-specific-energy lithium-sulfur battery which comprises a positive electrode material, a negative electrode material, a diaphragm and an electrolyte, the positive electrode material comprises a carbon material, elemental sulfur, a binder and a dynamic accelerator, wherein the dynamic accelerator is cobalt diselenide; the electrolyte comprises an organic solvent, an organic lithium salt and a Lewis alkaline additive, wherein the Lewis alkaline additive is triphenylphosphine. A dynamic accelerator cobalt diselenide in the positive electrode material of the lithium-sulfur battery is matched with triphenylphosphine in an electrolyte, so that the conversion kinetics of an intermediate species lithium polysulfide in the lithium-sulfur battery can be improved, and the energy density of the lithium-sulfur battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, and specifically to a high-energy-density lithium-sulfur battery. Background Technology

[0002] With the advent of the electrification era, people have placed higher demands on the usage time and range of electric devices such as computers, mobile phones, and electric vehicles. Improving the usage time and range of electric devices essentially boils down to increasing the energy density of batteries. Compared to the energy density of currently commercialized lithium-ion batteries, which is below 300Wh / kg, lithium-sulfur batteries have a theoretical energy density as high as 2600Wh / kg. Furthermore, sulfur is a widely available, inexpensive, and environmentally friendly raw material, making it a promising next-generation energy storage battery technology.

[0003] During charging and discharging, multiphase, multi-electron conversion processes occur at the positive electrode side of lithium-sulfur batteries. Taking the discharge process as an example, it involves a solid-liquid conversion process from solid elemental sulfur to soluble intermediate lithium polysulfides, and a liquid-solid conversion process from lithium polysulfides to solid lithium sulfides. The kinetic lag in these solid-liquid-solid conversion processes manifests as high positive electrode polarization and low specific capacity, which severely limits the possibility of achieving high specific energy in lithium-sulfur batteries. Based on these issues, previous researchers have mostly adopted the method of introducing positive electrode promoters to overcome the conversion kinetic lag problem, thereby constructing high-energy-density lithium-sulfur batteries.

[0004] For example, some researchers have used molybdenum disulfide as a cathode kinetic promoter, which can enhance the interaction energy between the cathode and soluble polysulfides, anchoring intermediate species on the cathode surface and thus promoting the conversion of sulfur species in the cathode. In addition, other researchers have introduced cobalt ditelluride as a kinetic promoter into the cathode, thereby promoting cathode conversion kinetics by altering the surface and interface structure and lowering the kinetic barrier for sulfur species conversion. However, during battery cycling, the kinetic promoter interacts with organic solvents and lithium salts, inducing solvent polymerization and surface gelation, thus reducing its catalytic conversion efficiency for sulfur species.

[0005] Therefore, to achieve high-energy-density lithium-sulfur batteries, while introducing kinetic enhancement, it is also necessary to eliminate surface gelation to ensure the long-term effectiveness of the enhancement. How to achieve enhanced cathode conversion kinetics while maintaining the catalytic conversion efficiency of sulfur species in lithium-sulfur batteries is a problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of low energy density in existing lithium-sulfur batteries and provide a high-energy-density lithium-sulfur battery. The kinetic promoter cobalt diselenide in the cathode material of the lithium-sulfur battery, in combination with triphenylphosphine in the electrolyte, can improve the conversion kinetics of intermediate species lithium polysulfide in the lithium-sulfur battery and increase the energy density of the lithium-sulfur battery.

[0007] To achieve the above objectives, the present invention provides a lithium-sulfur battery, wherein the lithium-sulfur battery includes a positive electrode material, a negative electrode material, a separator, and an electrolyte;

[0008] The cathode material includes carbon materials, elemental sulfur, a binder, and a kinetic promoter, wherein the kinetic promoter is cobalt diselenide;

[0009] The electrolyte comprises an organic solvent, an organic lithium salt, and a Lewis basic additive, wherein the Lewis basic additive is triphenylphosphine.

[0010] The beneficial effects achieved through the above technical solution are as follows:

[0011] The lithium-sulfur battery provided by this invention contains a kinetic promoter in its cathode material, which can improve the conversion kinetics of intermediate species and help improve the energy density and cycle performance of the lithium-sulfur battery. The electrolyte containing Lewis basic additives can interact with the Lewis acidic sites on the Lewis basic additives and kinetic promoters, reducing the ability of the kinetic promoters to interact with the solvent and lithium salts. This effectively reduces the deactivation of the kinetic promoters caused by the interaction between the kinetic promoters and the solvent in the cathode material, which induces the solvent to undergo ring-opening polymerization and form a surface gel layer. This significantly increases the efficiency of the kinetic promoters. The combination of the cathode material containing the kinetic promoters and the electrolyte containing the Lewis basic additives can continuously ensure the catalytic conversion efficiency of the kinetic promoters for intermediate species, thus constructing a high-energy-density lithium-sulfur battery. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The present invention provides a lithium-sulfur battery, wherein the lithium-sulfur battery includes a positive electrode material, a negative electrode material, a separator, and an electrolyte;

[0014] The cathode material includes carbon materials, elemental sulfur, a binder, and a kinetic promoter, wherein the kinetic promoter is cobalt diselenide;

[0015] The electrolyte comprises an organic solvent, an organic lithium salt, and a Lewis basic additive, wherein the Lewis basic additive is triphenylphosphine.

[0016] In this invention, the cathode material of the lithium-sulfur battery contains a kinetic promoter, which can improve the conversion kinetics of intermediate species. The kinetic promoter interacts with the solvent, thereby inducing the solvent to undergo ring-opening polymerization and forming a surface gel layer, which leads to the deactivation of the kinetic promoter. The Lewis basic additive in the electrolyte interacts with the acidic sites on the kinetic promoter, which can reduce the kinetic promoter's ability to react with the solvent and lithium salt, reduce the deactivation of the kinetic promoter, and continuously ensure the catalytic conversion efficiency of the kinetic promoter for intermediate species, thus helping to improve the energy density and cycle performance of the lithium-sulfur battery.

[0017] In this invention, the amounts of carbon material, elemental sulfur, and binder are not particularly limited, and those skilled in the art can adjust the amounts of each raw material according to the composition of conventional lithium-sulfur battery cathode materials.

[0018] According to the present invention, preferably, based on the total mass of the positive electrode material, the content of the kinetic promoter is 1-5 wt%, for example 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any range between the two; the content of the carbon material is 20-28 wt%, for example 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, or any range between the two; the content of elemental sulfur is 60-70 wt%, for example 60 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, or any range between the two; and the content of the binder is 5-10 wt%, for example 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any range between the two.

[0019] More preferably, based on the total mass of the cathode material, the content of the kinetic promoter is 2-4 wt%, the content of carbon material is 22-25 wt%, the content of elemental sulfur is 63-67 wt%, and the content of binder is 7-8 wt%.

[0020] In this invention, if the content of the kinetic promoter is too low, the kinetic promoter will have a poor effect on improving the conversion of intermediate species, while if the content of the kinetic promoter is too high, it will cause changes in the structure of the cathode material and lead to the problem of electrolyte denaturation.

[0021] According to the present invention, the type and source of the binder are not particularly limited, and it is a conventional battery material binder in the art, which can be commercially available or prepared using existing methods. Preferably, the binder is poly(vinylidene fluoride) and / or polytetrafluoroethylene.

[0022] According to the present invention, the type and source of the carbon material are not particularly limited, and it is a conventional carbon material in the art, which can be commercially available or prepared using existing methods. Preferably, the carbon material is selected from at least one of Ketjen black, conductive graphite, and graphene.

[0023] In this invention, the source of the elemental sulfur is not particularly limited; it can be commercially available elemental sulfur or it can be prepared from sulfur-containing substances using existing methods.

[0024] The preparation method of the positive electrode material described in this invention is not particularly limited. According to a preferred embodiment of this invention, the method includes the following steps:

[0025] Under a protective atmosphere, carbon materials, elemental sulfur, and a binder are mixed to obtain a mixture, which is then mixed with a kinetic promoter to obtain the cathode material.

[0026] In this invention, preferably, the preparation method of the cathode material is simple, the raw materials are easy to obtain, and the conditions are controllable. The obtained cathode material helps to construct high-energy-density lithium-sulfur batteries and is suitable for widespread use.

[0027] In this invention, the protective atmosphere has the conventional meaning in the art, referring to an oxygen-free atmosphere, preferably selected from at least one of argon, nitrogen, and helium.

[0028] In this invention, there are no particular limitations on the method and equipment for mixing, as long as the carbon material, elemental sulfur and binder are fully and evenly mixed. Preferably, the mixing is carried out in a glove box.

[0029] In this invention, the lithium-sulfur battery comprises a positive electrode material, a negative electrode material, a separator, and an electrolyte. By combining the positive electrode material containing a kinetic promoter and the electrolyte containing a Lewis alkaline additive, the catalytic conversion efficiency of the kinetic promoter on intermediate species can be continuously guaranteed, thus constructing a high-energy-density lithium-sulfur battery.

[0030] In this invention, the electrolyte can interact with Lewis acidic sites on Lewis basic additives and kinetic promoters, thereby reducing the kinetic promoter's ability to react with solvents and lithium salts. This effectively reduces the deactivation caused by surface gelation of the kinetic promoter in the cathode material, resulting in a significant increase in the efficiency of the kinetic promoter.

[0031] According to the present invention, preferably, the mass fraction of the Lewis alkaline additive in the electrolyte is 1-10 wt%, more preferably 2-5 wt%, for example 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or any range between the two, more preferably 3-4.5 wt%.

[0032] In this invention, the Lewis basic additive is added to the electrolyte and used in combination with the positive electrode material containing the kinetic promoter to eliminate surface gelation. However, if too much Lewis basic additive is added, it will lead to a decrease in the solubility of the electrolyte, kinetic stagnation of the positive electrode, and a decrease in the battery discharge capacity; if too little is added, it will not be able to suppress the formation of gelation and will not be able to effectively protect the positive electrode kinetic promoter and allow it to perform fully.

[0033] According to the present invention, the organic solvent can be selected from a wide range and is a conventional organic solvent in the art. Preferably, the organic solvent is ethylene glycol dimethyl ether and / or 1,3-dioxolane, more preferably 1,3-dioxolane.

[0034] In this invention, the use of the above-mentioned organic solvent can improve the solubility of organic lithium salts, increase the conductivity of lithium-sulfur battery electrolytes, provide rapid conversion reaction kinetics for the positive electrode of lithium-sulfur batteries, and achieve high energy density of lithium-sulfur batteries.

[0035] According to the present invention, the type of organolithium salt is not particularly limited, and is a conventional organolithium salt in the art. Those skilled in the art can select a suitable organolithium salt. Preferably, the organolithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0036] According to the present invention, preferably, the concentration of the organic lithium salt in the electrolyte is 300-1800 mmol / L, for example, 500 mmol / L, 600 mmol / L, 700 mmol / L, 800 mmol / L, 900 mmol / L, 1000 mmol / L, or any range between the two, preferably 500-1000 mmol / L. In the present invention, using an appropriate amount of the above-mentioned organic lithium salt can provide more active lithium ions in the electrolyte, thereby improving the cycle performance of the lithium-sulfur battery.

[0037] In this invention, the preparation method of the electrolyte is not particularly limited. According to a preferred embodiment of the present invention, the method includes the following steps: mixing an organic lithium salt, an organic solvent and a Lewis basic additive under a protective atmosphere to obtain the electrolyte.

[0038] In this invention, the type of diaphragm can be selected from a wide range, and is a conventional diaphragm in the art, preferably selected from at least one of polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation.

[0039] In this invention, the ratio of the positive electrode material and the electrolyte is not particularly limited. Those skilled in the art can adjust the amount of positive electrode material and electrolyte added to the lithium-sulfur battery according to the needs of the lithium-sulfur battery.

[0040] In this invention, the type of lithium-sulfur battery anode material is not particularly limited and can be any conventional anode material in the art. According to a preferred embodiment of this invention, the anode material is metallic lithium.

[0041] In this invention, a lithium-sulfur battery is assembled by combining a positive electrode material, a negative electrode material, an electrolyte, and a separator. Charge-discharge performance and cycle performance are tested at 25°C. In a 3Ah lithium-sulfur pouch cell, an initial energy density exceeding 400Wh / kg is achieved, and the cycle life exceeds 30 cycles when the capacity reaches 80% of the initial capacity, thus improving the cycle life and coulombic efficiency of the lithium-sulfur battery.

[0042] In this invention, there are no particular limitations on the assembly method of the positive electrode material, negative electrode material, separator and lithium-sulfur battery electrolyte of the lithium-sulfur battery. The lithium-sulfur battery can be obtained by assembling it in the conventional way in the art.

[0043] According to a particularly preferred embodiment of the present invention, a lithium-sulfur battery is provided, the lithium-sulfur battery comprising a positive electrode material, a negative electrode material, a separator, and an electrolyte;

[0044] The cathode material includes carbon materials, elemental sulfur, a binder, and a kinetic promoter, wherein the kinetic promoter is cobalt diselenide;

[0045] The electrolyte comprises an organic solvent, an organic lithium salt, and a Lewis basic additive, wherein the Lewis basic additive is triphenylphosphine.

[0046] Based on the total mass of the cathode material, the content of the kinetic promoter is 2-4 wt%, the content of carbon material is 22-25 wt%, the content of elemental sulfur is 63-67 wt%, and the content of binder is 7-8 wt%.

[0047] The mass fraction of Lewis alkaline additive in the electrolyte is 3-4.5 wt%.

[0048] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, all reagents used in the following examples and comparative examples are commercially available.

[0049] Example 1

[0050] 1) Preparation of electrolyte: In a glove box under an argon atmosphere, weigh the organic lithium salt (lithium bis(trifluoromethanesulfonyl)imide) according to the stoichiometric ratio and add it to the reagent bottle. Then, slowly add the organic solvent 1,3-dioxolane and the Lewis basic additive triphenylphosphine. Stir to fully dissolve the organic lithium salt and Lewis basic additive in the organic solvent to obtain the electrolyte. The concentration of the organic lithium salt in the electrolyte is 1000 mmol / L and the mass fraction of the Lewis basic additive is 4 wt%.

[0051] 2) Preparation of cathode material: Ketjen black, elemental sulfur, and binder poly(vinylidene fluoride) are mixed, stirred, and ground. Then, cobalt diselenide, a kinetic promoter, is added and mixed evenly to obtain cathode material. Based on the total mass of the cathode material, the mass fraction of cobalt diselenide is 3 wt%, the mass fraction of binder is 8 wt%, the mass fraction of elemental sulfur is 65 wt%, and the mass fraction of carbon material is 24 wt%.

[0052] Comparative Example 1

[0053] The method is the same as in Example 1, except that Lewis basic additives are not added in step 1) and kinetic promoters are not added in step 2). Other components and preparation processes are the same as in Example 1.

[0054] Comparative Example 2

[0055] The method is the same as in Example 1, except that Lewis basic additives are not added in step 1), while the other components and preparation process are the same as in Example 1.

[0056] Comparative Example 3

[0057] The method is the same as in Example 1, except that no kinetic promoter is added in step 2), while the other components and preparation process are the same as in Example 1.

[0058] Example 2

[0059] The method of Example 1 is followed, except that the mass fraction of the Lewis alkaline additive in step 1) is changed to 2 wt%, while the other components and preparation process remain the same as in Example 1.

[0060] Example 3

[0061] The method of Example 1 is followed, except that the mass fraction of the Lewis alkaline additive in step 1) is changed to 5 wt%, while the other components and preparation process remain the same as in Example 1.

[0062] Example 4

[0063] The method is the same as in Example 1, except that the mass fraction of cobalt diselenide in step 2) is 2 wt%, while the other components and preparation process are the same as in Example 1.

[0064] Example 5

[0065] The method is the same as in Example 1, except that the mass fraction of cobalt diselenide in step 2) is 4 wt%, while the other components and preparation process are the same as in Example 1.

[0066] Example 6

[0067] 1) Preparation of electrolyte: In an argon-atmospheric glove box, weigh the organic lithium salt (lithium bis(trifluoromethanesulfonyl)imide) according to the stoichiometric ratio and add it to the reagent bottle. Then, slowly add the organic solvent 1,3-dioxolane and the Lewis basic additive triphenylphosphine. Stir to fully dissolve the organic lithium salt and Lewis basic additive in the organic solvent to obtain the electrolyte. The concentration of the organic lithium salt in the electrolyte is 500 mmol / L and the mass fraction of the Lewis basic additive is 3 wt%.

[0068] 2) Preparation of cathode material: Ketjen black, elemental sulfur, and binder poly(vinylidene fluoride) are mixed, stirred, and ground. Then, cobalt diselenide, a kinetic promoter, is added and assembled by mechanical grinding to obtain the cathode material. The areal loading of cobalt diselenide is 4 wt%. Based on the total mass of binder, elemental sulfur, and carbon material, the mass fraction of binder is 7 wt%, the mass fraction of elemental sulfur is 67 wt%, and the mass fraction of carbon material is 22 wt%.

[0069] Test case

[0070] The lithium-sulfur battery electrolytes and cathode materials prepared in the examples and comparative examples were tested in a 3Ah lithium-sulfur pouch cell. The results of the cycle life when the energy density and capacity reached 80% of the initial capacity in the first cycle are shown in Table 1.

[0071] Lithium-sulfur pouch batteries:

[0072] The cathode material has a thickness of 180 micrometers and a sulfur surface loading of 8 mg / cm³. 2 ;

[0073] The negative electrode material is metallic lithium, with a thickness of 80 micrometers;

[0074] The diaphragm is a polypropylene diaphragm with a thickness of 25 micrometers;

[0075] The electrolyte dosage is 3 mL / g S (mL / g S (The amount of electrolyte added is based on the mass of sulfur);

[0076] Test conditions: 3Ah lithium-sulfur pouch battery, after assembly and resting for 12 hours, constant current charge and discharge at 0.05C, voltage range 1.8V-2.6V. First-cycle energy density is the first-cycle discharge energy divided by the battery mass. Stable cycle count is the number of cycles in which the capacity reaches 80% of the first-cycle capacity.

[0077] Table 1

[0078]

[0079] As shown in Table 1 above, the experimental results indicate that Comparative Example 1 and Comparative Example 1 demonstrate that the addition of a positive electrode promoter and a Lewis alkaline additive significantly improves the energy density and cycle performance of the battery. Comparative Example 1 and Comparative Examples 1 and 2 show that while the addition of a positive electrode promoter without a Lewis alkaline additive improves both energy density and cycle performance to some extent, it still falls short of the examples. This indicates that while the addition of a positive electrode promoter can promote positive electrode kinetics, the long-term effectiveness of its catalytic conversion cannot be guaranteed due to surface gelation. Comparative Example 1 and Comparative Examples 1 and 3 show that the addition of a Lewis alkaline additive without a positive electrode promoter results in virtually no improvement in energy density and cycle performance, far below the performance of the examples. This suggests that the Lewis alkaline additive's effect is only adaptable; it can only eliminate surface gelation and exert its function when used in conjunction with a positive electrode promoter. In summary, the example with both a positive electrode promoter and a Lewis alkaline additive exhibits the best energy density and cycle performance, confirming the effectiveness of the positive electrode and suitable electrolyte used in this invention.

[0080] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes a positive electrode material, a negative electrode material, a separator, and an electrolyte; The cathode material includes carbon materials, elemental sulfur, a binder, and a kinetic promoter, wherein the kinetic promoter is cobalt diselenide; The electrolyte comprises an organic solvent, an organic lithium salt, and a Lewis basic additive, wherein the Lewis basic additive is triphenylphosphine.

2. The lithium-sulfur battery according to claim 1, wherein, Based on the total mass of the cathode material, the content of the kinetic promoter is 1-5 wt%, the content of carbon material is 20-28 wt%, the content of elemental sulfur is 60-70 wt%, and the content of binder is 5-10 wt%.

3. The lithium-sulfur battery according to claim 1 or 2, wherein, Based on the total mass of the cathode material, the content of the kinetic promoter is 2-4 wt%, the content of carbon material is 22-25 wt%, the content of elemental sulfur is 63-67 wt%, and the content of binder is 7-8 wt%.

4. The lithium-sulfur battery according to any one of claims 1-3, wherein, The adhesive is poly(vinylidene fluoride) and / or polytetrafluoroethylene.

5. The lithium-sulfur battery according to any one of claims 1-4, wherein, The carbon material is selected from at least one of Ketjen black, conductive graphite, and graphene.

6. The lithium-sulfur battery according to any one of claims 1-5, wherein, The mass fraction of the Lewis alkaline additive in the electrolyte is 1-10 wt%, preferably 2-5 wt%, and more preferably 3-4.5 wt%.

7. The lithium-sulfur battery according to any one of claims 1-6, wherein, The organic solvent is ethylene glycol dimethyl ether and / or 1,3-dioxolane, preferably 1,3-dioxolane.

8. The lithium-sulfur battery according to any one of claims 1-7, wherein, The organolithium salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

9. The lithium-sulfur battery according to any one of claims 1-8, wherein, The concentration of the organic lithium salt in the electrolyte is 300-1800 mmol / L.

10. The lithium-sulfur battery according to any one of claims 1-9, wherein, The concentration of the organic lithium salt in the electrolyte is 500-1000 mmol / L.

Images