Lithium-sulfur battery electrolyte with long cycle life, preparation method and application thereof, and lithium-sulfur battery

Abstract

The invention relates to the technical field of lithium-sulfur batteries, and discloses a long-cycle-life lithium-sulfur battery electrolyte, a preparation method and application thereof, and a lithium-sulfur battery, the electrolyte comprises an ether solvent, an organic lithium salt and a cycle protective additive; and the cyclic protective additive is (2, 2, 3, 3, 4, 4-hexafluoro-1, 5-pentanediol) dinitrate. The electrolyte can generate a protective solid electrolyte interface film rich in LiF on the surface of a lithium metal negative electrode, so that the lithium metal negative electrode is protected, and the cycle life of the high-energy-density lithium-sulfur battery is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium-sulfur batteries, and particularly relates to a lithium-sulfur battery with long cycle life, a preparation method and application thereof, and a lithium-sulfur battery. BACKGROUND

[0002] A large amount of energy consumption and the continuous growth of energy demand of human society promote the innovation and development of energy storage technology and devices. Lithium-sulfur batteries have extremely high theoretical energy density (2600 Wh / kg), and sulfur raw materials are widely available and low in cost, so they are considered as one of the most promising energy storage conversion devices. However, the limited cycle life seriously restricts the practical process of lithium-sulfur batteries.

[0003] During the charging and discharging process of lithium-sulfur batteries, soluble intermediate products polysulfides will diffuse to the negative electrode and react irreversibly with the lithium negative electrode, causing serious lithium metal corrosion and generating a large amount of dendrites and non-active lithium, which makes the metal lithium negative electrode fail rapidly, resulting in reduced cycle life of the battery.

[0004] The side reaction of lithium metal negative electrode and lithium polysulfide is significantly affected by the solid electrolyte interface film (SEI) of the lithium negative electrode. Recently, researchers have regulated SEI through strategies such as surface modification of metal lithium and electrolyte additives to inhibit the side reaction of polysulfides and metal lithium, thereby improving the stability of the lithium metal negative electrode. Some researchers have prepared artificial SEI on the surface of metal lithium in vitro, such as Nafion film, LiF protective layer, etc., to block the side reaction of polysulfides and metal lithium to protect the lithium metal negative electrode. Some researchers have introduced active additives such as lithium nitrate and trioxane into the electrolyte to form SEI rich in beneficial components to inhibit the side reaction of polysulfides and metal lithium, thereby improving the stability of the lithium metal negative electrode. However, the current protection strategies for lithium metal negative electrode are not sufficient, and the cycle life improvement effect is not significant.

[0005] Therefore, how to effectively construct SEI to inhibit polysulfide side reactions and achieve high-energy long-cycle lithium-sulfur batteries is a problem that needs to be solved urgently. SUMMARY

[0006] The purpose of the present application is to overcome the poor protection effect of the lithium metal negative electrode and the short cycle life of the lithium-sulfur battery in the prior art, and to provide a lithium-sulfur battery with long cycle life, a preparation method and application thereof, and a lithium-sulfur battery. The electrolyte can generate a protective solid electrolyte interface film rich in LiF on the surface of the lithium metal negative electrode, protect the lithium metal negative electrode, and improve the cycle life of high-energy density lithium-sulfur batteries.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a lithium-sulfur battery electrolyte, wherein the electrolyte comprises an ether solvent, an organic lithium salt and a cycle protection additive.

[0008] The cycle protective additive is (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate.

[0009] Preferably, the ether solvent is ethylene glycol dimethyl ether and / or 1,3-dioxolane, preferably ethylene glycol dimethyl ether and 1,3-dioxolane.

[0010] Preferably, the volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane in the ether solvent is 1:0.5-5, preferably 1:0.8-2.

[0011] Preferably, the volume fraction of the cycle protective additive in the electrolyte is 2-10%, preferably 3-10%.

[0012] Preferably, the organic lithium salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0013] Preferably, the concentration of the organic lithium salt in the electrolyte is 300-1800 mmol / L.

[0014] Preferably, the concentration of the organic lithium salt in the electrolyte is 500-1000 mmol / L.

[0015] The second aspect of the present application provides a preparation method of the lithium-sulfur battery electrolyte of the first aspect, wherein the method comprises the following steps:

[0016] Mixing the organic lithium salt, the ether solvent and the cycle protective additive under a protective atmosphere to obtain the lithium-sulfur battery electrolyte.

[0017] The third aspect of the present application provides an application of the lithium-sulfur battery electrolyte of the first aspect in a lithium-sulfur battery.

[0018] The fourth aspect of the present application provides a lithium-sulfur battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte;

[0019] The electrolyte is the lithium-sulfur battery electrolyte of the first aspect.

[0020] Through the above technical solution, the following beneficial effects are obtained:

[0021] In this invention, a cycle-protective additive (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate is added to the electrolyte of a lithium-sulfur battery. In combination with organic lithium salts and ether solvents, a protective solid electrolyte interface film rich in LiF can be generated on the surface of the lithium metal anode. This promotes uniform lithium-ion transport to induce uniform lithium metal deposition, suppresses side reactions between polysulfides and lithium metal, thereby protecting the lithium metal anode and improving the cycle life of high-energy-density lithium-sulfur batteries. Detailed Implementation

[0022] 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.

[0023] The first aspect of the present invention provides a lithium-sulfur battery electrolyte, wherein the electrolyte comprises an ether solvent, an organic lithium salt, and a cycle-protective additive;

[0024] The cyclic protective additive is (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate.

[0025] In this invention, a cycle-protective additive (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate is added to the electrolyte of a lithium-sulfur battery. In combination with organic lithium salts and ether solvents, a protective solid electrolyte interface film rich in LiF can be generated on the surface of the lithium metal anode. This promotes uniform lithium-ion transport to induce uniform lithium metal deposition, suppresses side reactions between polysulfides and lithium metal, thereby protecting the lithium metal anode and improving the cycle life of high-energy-density lithium-sulfur batteries.

[0026] According to the present invention, preferably, the ether solvent has a wide range of options and is a conventional ether-containing solvent in the art. The ether solvent is ethylene glycol dimethyl ether and / or 1,3-dioxolane, preferably ethylene glycol dimethyl ether and 1,3-dioxolane.

[0027] According to the present invention, preferably, the volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane in the ether solvent is 1:0.5-5, for example 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:2, 1:3, 1:4, 1:5, or any range between the two, preferably 1:0.8-2.

[0028] In this invention, the ether solvent is prepared according to the above volume ratio. The organic lithium salt has higher solubility in the ether solvent, which can improve the conductivity of the lithium-sulfur battery electrolyte. At the same time, it can ensure the full solubilization of polysulfides in the electrolyte, provide rapid conversion reaction kinetics for the positive electrode of the lithium-sulfur battery, and improve the energy density of the lithium-sulfur battery.

[0029] According to the present invention, preferably, the volume fraction of the cyclic protective additive in the electrolyte is 2-10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between the two, preferably 3-10%. In the present invention, the content of the cyclic protective additive satisfying the above range can promote the formation of a protective solid electrolyte interface film, promote uniform lithium ion transport to induce uniform lithium metal deposition, and suppress side reactions between polysulfides and lithium metal.

[0030] In this invention, preferably, if the amount of the cyclic protective additive used is too low, it will not be able to effectively form a protective solid electrolyte interface film and will not be able to suppress the side reaction between lithium polysulfide and lithium metal; while if the amount of the cyclic protective additive added is too high, it will reduce the reactivity of lithium metal and reduce the energy density of lithium-sulfur batteries.

[0031] 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.

[0032] According to the present invention, preferably, the concentration of the organic lithium salt in the electrolyte is 300-1800 mmol / L, for example, 300 mmol / L, 400 mmol / L, 500 mmol / L, 600 mmol / L, 700 mmol / L, 800 mmol / L, 900 mmol / L, 1000 mmol / L, 1200 mmol / L, 1500 mmol / L, 1800 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.

[0033] In this invention, the lithium-sulfur battery electrolyte has the above-mentioned composition. The composition is simple, consisting of organic lithium salt, ether solvent, and cycle protection additive. It is suitable for conventional lithium-sulfur batteries in the field and has excellent cycle stability and high energy density. The organic lithium salt improves the ionic conductivity, the ether solvent solubilizes lithium polysulfides, thereby enabling the lithium-sulfur battery to be charged and discharged, and the cycle protection additive forms a protective LiF solid electrolyte interface film on the surface of the lithium metal anode, promoting uniform lithium ion transport and uniform lithium metal deposition, suppressing side reactions between lithium metal and lithium polysulfides, and thus improving the cycle stability of the lithium metal anode and the cycle life of the lithium-sulfur battery.

[0034] A second aspect of the present invention provides a method for preparing the lithium-sulfur battery electrolyte described in the first aspect, wherein the method includes the following steps:

[0035] Under a protective atmosphere, an organic lithium salt, an ether solvent, and a cyclic protective additive are mixed to obtain the lithium-sulfur battery electrolyte.

[0036] In this invention, preferably, the preparation method of the lithium-sulfur battery electrolyte is simple and the conditions are controllable. The organic lithium salt, ether solvent, and cyclic protective additive are mixed evenly under a protective atmosphere to obtain the lithium-sulfur battery electrolyte.

[0037] 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.

[0038] In this invention, the method and equipment for mixing are not particularly limited, as long as the organolithium salt is fully dissolved in the ether solvent. Preferably, the mixing is performed in a glove box. Preferably, the mixing is carried out under stirring conditions. The stirring rate is not particularly limited, as long as the electrolyte is mixed uniformly.

[0039] According to a preferred embodiment of the present invention, the preparation method includes the following steps:

[0040] 1) Under a protective atmosphere, an organolithium salt is mixed with an ether solvent to obtain an intermediate electrolyte;

[0041] 2) Mix the intermediate electrolyte described in step 1) with the cycle protection additive to obtain the lithium-sulfur battery electrolyte.

[0042] In this invention, the organic lithium salt and ether solvent are first mixed evenly, and then mixed with the cycle protection additive. The resulting lithium-sulfur battery electrolyte has more uniform mixing of the components and better system stability.

[0043] The third aspect of this invention provides an application of the lithium-sulfur battery electrolyte described in the first aspect in a lithium-sulfur battery.

[0044] In this invention, the lithium-sulfur battery electrolyte has strong applicability and can be widely used in conventional lithium-sulfur batteries in the field, maintaining the high energy density advantage of lithium-sulfur batteries while improving their cycle stability. The cycle-protective additives introduced into the lithium-sulfur battery electrolyte, in combination with organic lithium salts and ether solvents, promote the formation of a protective solid electrolyte interface film, effectively suppressing side reactions between polysulfides and metallic lithium, and improving the stability of the lithium metal anode.

[0045] A fourth aspect of the present invention provides a lithium-sulfur battery, the lithium-sulfur battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte;

[0046] The electrolyte is the lithium-sulfur battery electrolyte described in the first aspect.

[0047] In this invention, the types of positive and negative electrodes of the lithium-sulfur battery are widely selectable, including conventional lithium-sulfur battery positive and negative electrode materials in the art. Those skilled in the art can adjust the types of positive and negative electrode materials according to the performance requirements of the lithium-sulfur battery and the adaptability of experimental conditions. The following is an illustrative description of one embodiment, but it does not limit the scope of the invention.

[0048] According to a preferred embodiment of the present invention, the positive electrode is a carbon-sulfur composite positive electrode. The negative electrode is metallic lithium. Both can be commercially available or prepared using existing methods.

[0049] 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.

[0050] In this invention, the lithium-sulfur battery electrolyte is assembled with a positive electrode, a negative electrode, and a separator to obtain a lithium-sulfur battery. Charge-discharge performance and cycle performance are tested at 25°C. In a 3Ah lithium-sulfur pouch battery, an initial energy density of over 370Wh / kg can be achieved, and the cycle life exceeds 50 cycles when the capacity reaches 80% of the initial capacity, thus improving the cycle life and coulombic efficiency of the lithium-sulfur battery.

[0051] In this invention, there are no particular limitations on the assembly method of the positive electrode, negative electrode, separator and the lithium-sulfur battery electrolyte. The lithium-sulfur battery can be obtained by assembling it in a conventional manner in the art.

[0052] According to a particularly preferred embodiment of the present invention, a lithium-sulfur battery electrolyte comprises an ether solvent, an organic lithium salt, and a cycle-protective additive.

[0053] The cyclic protective additive is (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate;

[0054] The volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane in the ether solvent is 1:0.8-2;

[0055] The volume fraction of the cyclic protective additive in the electrolyte is 3-10%;

[0056] The organic lithium salt is lithium bis(trifluoromethylsulfonyl)imide.

[0057] 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.

[0058] Example 1

[0059] 1) In an argon-atmospheric glove box, weigh out the organic lithium salt (lithium bis(trifluoromethanesulfonyl)imide) according to the stoichiometric ratio and add it to the reagent bottle. Add the ether solvent ethylene glycol dimethyl ether and 1,3-dioxolane, and stir to fully dissolve the organic lithium salt in the ether solvent. The volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane is 1:1.

[0060] 2) Add (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate to the solution obtained in step 1) and stir until no solid precipitates to obtain lithium-sulfur battery electrolyte.

[0061] The concentration of organic lithium salt in the lithium-sulfur battery electrolyte is 1000 mmol / L, and the volume fraction of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate is 5%.

[0062] Example 2

[0063] The electrolyte was prepared according to the method of Example 1, except that the amount of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate added in step 2) was changed to obtain a lithium-sulfur battery electrolyte, such that the volume fraction of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate in the lithium-sulfur battery electrolyte was 2%, and other conditions were the same as in Example 1.

[0064] Example 3

[0065] The electrolyte was prepared according to the method of Example 1, except that the amount of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate added in step 2) was changed to obtain a lithium-sulfur battery electrolyte, such that the volume fraction of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate in the lithium-sulfur battery electrolyte was 10%, and other conditions were the same as in Example 1.

[0066] Example 4

[0067] 1) In an argon-atmospheric glove box, weigh out the organic lithium salt (lithium bis(fluorosulfonyl)imide) according to the stoichiometric ratio and add it to the reagent bottle. Add the ether solvent ethylene glycol dimethyl ether and 1,3-dioxolane, and stir to fully dissolve the organic lithium salt in the ether solvent. The volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane is 1:2.

[0068] 2) Add (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate to the solution obtained in step 1) and stir until no solid precipitates to obtain lithium-sulfur battery electrolyte.

[0069] The concentration of organic lithium salt in the lithium-sulfur battery electrolyte is 500 mmol / L, and the volume fraction of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate is 5%.

[0070] Comparative Example 1

[0071] The electrolyte was prepared according to the method of Example 1, except that the cyclic protective additive (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate was not added in step 2), and the other conditions were the same as in Example 1.

[0072] Comparative Example 2

[0073] The electrolyte was prepared according to the method of Example 1, except that (1,5-pentanediol) dinitrate was added in step 2) to obtain the lithium-sulfur battery electrolyte, so that the volume fraction of (1,5-pentanediol) dinitrate in the lithium-sulfur battery electrolyte was 5%, and other conditions were the same as in Example 1.

[0074] Comparative Example 3

[0075] The electrolyte was prepared according to the method of Example 1, except that (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) diacetate was added in step 2) to obtain the lithium-sulfur battery electrolyte, so that the volume fraction of (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) diacetate in the lithium-sulfur battery electrolyte was 5%, and other conditions were the same as in Example 1.

[0076] Test case

[0077] The lithium-sulfur battery electrolytes prepared in the examples and comparative examples were tested in 3Ah lithium-sulfur pouch cells. The results of the first-cycle energy density and cycle life when the capacity reached 80% of the initial capacity are shown in Table 1.

[0078] Lithium-sulfur pouch batteries:

[0079] The cathode is a carbon-sulfur composite cathode with a sulfur content of 63 wt% and a sulfur surface loading of 7.2 mg / cm³. 2 ;

[0080] The negative electrode is metallic lithium, with a thickness of 80 micrometers;

[0081] The diaphragm is a polypropylene diaphragm with a thickness of 25 micrometers;

[0082] 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.

[0083] Table 1

[0084]

[0085]

[0086] As can be seen from the results in Table 1, the lithium-sulfur soft-pack battery assembled using the lithium-sulfur battery electrolyte provided in the embodiments of the present invention exhibits more stable cycle performance and higher energy density in battery performance testing.

[0087] 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 electrolyte, characterized in that, The electrolyte comprises ether solvents, organic lithium salts, and cycle-protective additives; The cyclic protective additive is (2,2,3,3,4,4-hexafluoro-1,5-pentanediol) dinitrate.

2. The electrolyte according to claim 1, wherein, The ether solvent is ethylene glycol dimethyl ether and / or 1,3-dioxolane, preferably ethylene glycol dimethyl ether and 1,3-dioxolane.

3. The electrolyte according to claim 1 or 2, wherein, The volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane in the ether solvent is 1:0.5-5, preferably 1:0.8-2.

4. The electrolyte according to any one of claims 1-3, wherein, The volume fraction of the cyclic protective additive in the electrolyte is 2-10%, preferably 3-10%.

5. The electrolyte according to any one of claims 1-4, wherein, The organolithium salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

6. The electrolyte according to any one of claims 1-5, wherein, The concentration of the organic lithium salt in the electrolyte is 300-1800 mmol / L.

7. The electrolyte according to any one of claims 1-6, wherein, The concentration of the organic lithium salt in the electrolyte is 500-1000 mmol / L.

8. The method for preparing the lithium-sulfur battery electrolyte according to any one of claims 1-7, characterized in that, The method includes the following steps: Under a protective atmosphere, an organic lithium salt, an ether solvent, and a cyclic protective additive are mixed to obtain the lithium-sulfur battery electrolyte.

9. The application of the lithium-sulfur battery electrolyte according to any one of claims 1-7 in lithium-sulfur batteries.

10. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The electrolyte is the lithium-sulfur battery electrolyte according to any one of claims 1-7.

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