Lithium-sulfur battery and electrolyte and composite additive thereof
By leveraging the synergistic effect of conjugated molecules within and outside the composite additives, the conversion efficiency of polysulfides in lithium-sulfur batteries is improved, solving the problems of low utilization of active materials and battery capacity decay caused by polysulfide shuttle, and enhancing the electrochemical performance and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2023-03-20
- Publication Date
- 2026-05-15
AI Technical Summary
The polysulfide shuttle phenomenon in lithium-sulfur batteries leads to low utilization of active materials, reduced coulombic efficiency, and battery capacity decay. Existing electrolyte additives have failed to effectively solve this problem.
Composite additives, including compounds with the structure of Formula 1 and their derivatives, as well as nitrates, are used to improve the conversion efficiency of polysulfides through conjugated intramolecular and intermolecular synergistic effects, form a stable passivation layer, and inhibit lithium dendrite growth.
It significantly improves the electrochemical performance and cycle stability of lithium-sulfur batteries, enhances their capacity and coulombic efficiency, and reduces polysulfide shuttle phenomenon.
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Figure CN116231082B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-sulfur battery technology, and more specifically to the field of lithium-sulfur batteries and their electrolytes. Background Technology
[0002] Lithium-sulfur batteries are a type of lithium battery that uses sulfur as the positive electrode and metallic lithium as the negative electrode. Elemental sulfur is abundant on Earth and is characterized by its low cost and environmental friendliness. Lithium-sulfur batteries using sulfur as the positive electrode material have high theoretical specific capacity and theoretical specific energy, reaching 1675 mAh / g and 2600 Wh / kg respectively, far exceeding the capacity of commercially widely used lithium cobalt oxide batteries (<150 mAh / g). Furthermore, sulfur is an environmentally friendly element with minimal pollution, making it a very promising lithium battery. However, due to its complex electrochemical reaction mechanism, several issues severely restrict the practical application of lithium-sulfur batteries. In ether-based electrolytes, there are typically two discharge plateaus. First, elemental sulfur is lithium-ionized to form long-chain polysulfides, Li₂S₈. Then, it is further reduced to Li₂S₆ and Li₂S₄ on the electrode surface, creating a discharge plateau at approximately 2.3V. This plateau contributes about 25% of the theoretical capacity. Next, the medium- to long-chain polysulfides further transform into solid Li₂S₂ and Li₂S, depositing on the electrode surface, with a discharge plateau at approximately 2.1V. This is because the intermediate product, the long-chain polysulfide Li₂S… X ( X =4~8) is highly soluble in ether electrolytes, resulting in low actual utilization of the positive electrode active material, causing the actual specific capacity in the first cycle to be far lower than the theoretical capacity of elemental sulfur (1675mAh / g); under the action of electric field force and concentration gradient, long-chain lithium polysulfides will diffuse to the lithium metal anode, on the one hand corroding the lithium metal anode to generate short-chain lithium polysulfides and insulating Li2S, the former will then diffuse to the positive electrode area and be oxidized to long-chain lithium polysulfides, and so on, leading to a serious reduction in coulombic efficiency and irreversible loss of active material, and the battery capacity will continue to decay.
[0003] To address the capacity decay problem in lithium-sulfur batteries, researchers have adopted numerous strategies in recent years, with electrolyte modification using additives being a key approach. Existing electrolyte additives are diverse, primarily categorized into organic and inorganic additives. Organic additives mainly include 3-methyl-1,4,2-dioxazol-5-one (CN108336405A), selenide (CN107785603A), thionyl chloride (CN109301325A), and phosphorylated chitosan (CN103515613A). Inorganic additives mainly include aluminosilicates (CN109167095A), lithium polysulfides (CN102983361A), zirconium oxynitrate (CN109088101A), and phosphorus pentasulfide (CN109148956A), among others.
[0004] Currently, during the cycling process of lithium-sulfur battery electrolytes, intermediate discharge products dissolve into the organic electrolyte, increasing its viscosity and reducing ionic conductivity. Polysulfide ions can migrate between the positive and negative electrodes, leading to the loss of active material and wasted energy. Dissolved polysulfides can diffuse across the separator to the negative electrode, reacting with it and damaging the solid electrolyte interface film. Furthermore, the amount of lithium-sulfur battery electrolyte used far exceeds industrial-scale requirements, significantly hindering the large-scale industrial production of lithium-sulfur batteries. Summary of the Invention
[0005] To address the problems of polysulfide shuttle and unsatisfactory electrochemical performance in lithium-sulfur batteries, the primary objective of this invention is to provide a composite additive that can synergistically improve polysulfide conversion efficiency, reduce shuttle, and enhance the electrochemical performance of lithium-sulfur batteries.
[0006] The second objective of this invention is to provide a lithium-sulfur battery and its electrolyte containing the aforementioned composite additive.
[0007] A compound additive comprising additive A and additive B;
[0008] The additive A is at least one of a compound having the structural formula of Formula 1 and its derived esters and salts;
[0009]
[0010] Formula 1
[0011] The n mentioned is an integer from 1 to 6;
[0012] R1 or R3 is individually a C1-C6 alkyl group or a C3-C6 alkyl group. 10 cycloalkyl, C3-C 10 Partially unsaturated cyclic groups or C4-C 20The aromatic group; wherein R2 is H, C1-C6 alkyl, C3-C6 alkyl, C4-C5 alkyl, C6 ... 10 cycloalkyl, C3-C 10 Partially unsaturated cyclic groups or C4-C 20 Aromatic groups;
[0013] The additive B is one or more of the following: lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, phosphorus sulfide, lithium bromide, lithium iodide, indium iodide, dibenzothiazole disulfide, iodonitrobenzene, and triphenylphosphine.
[0014] The present invention has found that the combination of additive A and additive B of Formula 1 can achieve synergy, improve the conversion efficiency of polysulfides, solve the polysulfide shuttle problem at its root, and help improve the performance of lithium-sulfur batteries, such as improving the capacity and cycle stability of lithium-sulfur batteries.
[0015] In this invention, the intramolecular synergy of C=N, C=C, and C=CN conjugated molecules in Formula 1 and their intermolecular synergy with additive B are key to improving polysulfide conversion efficiency, improving polysulfide shuttle, and improving the electrochemical performance of lithium-sulfur batteries.
[0016] In this invention, n in Formula 1 is an integer from 1 to 3, for example, it can be 1, 2 or 3.
[0017] In this invention, R1 and R3 are preferably aromatic groups. More preferably, the aromatic group is phenyl, naphthyl, or a substituted phenyl group; the substituent in the substituted phenyl group is at least one selected from C1-C6 alkyl, C1-C3 alkoxy, nitro, halogen, and trifluoromethyl groups.
[0018] Preferably, R2 is H.
[0019] Further preferably, Formula 1 has a structure of Formula 1-A:
[0020]
[0021] Formula 1-A
[0022] In Formula 1-A, R4 is H, a C1-C3 alkyl group, or a C1-C3 alkoxy group.
[0023] In this invention, additive A can be a free compound having the structure of Formula 1 and its derivatives, such as esters and salts. For example, the salt derived from the structure of Formula 1 in this invention can be at least one of hydrochloride, sulfate, nitrate, and organic acid salt.
[0024] In this invention, the weight ratio of additive B to additive A is 1:0.01 to 6, preferably 1:0.1 to 4, more preferably 1:0.1 to 2, and most preferably 1:0.1 to 1.5. Studies have found that at the preferred ratio, the synergistic effect of the two additives is further improved, which can further synergistically improve the electrochemical performance of lithium-sulfur batteries.
[0025] The present invention also provides a lithium-sulfur battery electrolyte, comprising a base electrolyte and the aforementioned composite additive; the base electrolyte comprises an organic solvent and a conductive lithium salt.
[0026] In this invention, the organic solvent is a polyether compound, a carbonate compound, an alkyl ester compound, a sulfone, or a sulfoxide compound; more preferably, it is one or a mixture of 1,3-dioxapentane (DOL), 1,4-dioxane (DX), ethylene glycol dimethyl ether (DME), glycol dimethyl ether (G2), polyethylene glycol dimethyl ether (G3), polyethylene glycol dimethyl ether (G4), tetrahydrofuran (THF), ethyl methyl sulfone (EMS), sulfolane (TMS), methyl isopropyl sulfone (MiPS), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).
[0027] In this invention, the conductive lithium salt can be a known conductive lithium salt in the industry, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), lithium difluorooxalateborate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), lithium dioxalateborate (LiBOB), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium nitrate (LiNO3), and lithium perchlorate (LiClO4) or more.
[0028] In the basic electrolyte, the concentration of the conductive lithium salt is 0.5–4 mol / L, preferably 1–2 M.
[0029] In the lithium-sulfur battery electrolyte of this invention, the composite additive comprises 1-15% of the weight of the base electrolyte, preferably 1.5-10%, and more preferably 1.5-4 wt.%. In a further specific embodiment, additive A comprises 0.2-8 wt.% of the weight of the base electrolyte, more preferably 0.2-2%. Additive B comprises 1-3 wt.% of the weight of the base electrolyte, more preferably 1.5-2.5%. This invention has found that, with the combined synergistic effect of the composite additives, and further combined control of the amount of composite additives added, a synergistic effect can be achieved, contributing to further improvement of the electrochemical performance of lithium-sulfur batteries.
[0030] This invention also provides an application of a lithium-sulfur battery electrolyte, used as an electrolyte in the preparation of lithium-sulfur batteries.
[0031] The present invention also provides a lithium-sulfur battery comprising the aforementioned composite additive; more preferably, it comprises the electrolyte described in the present invention.
[0032] The lithium-sulfur battery of this invention, apart from containing the composite additive described in this invention, can use conventional components, structures, and materials. For example, the lithium-sulfur battery comprises a positive electrode, a negative electrode, a separator for separating the positive and negative electrodes, and an electrolyte, wherein the electrolyte is the lithium-sulfur battery electrolyte of this invention.
[0033] The positive electrode of the lithium-sulfur battery includes a positive current collector and a positive electrode material composited on the surface of the positive current collector; the positive electrode material comprises at least one active material selected from elemental sulfur, sulfur-containing polymers, lithium sulfides, and lithium polysulfides. The negative electrode of the lithium-sulfur battery is one of lithium metal foil, lithium sheet, lithium alloy, and silicon-carbon composite.
[0034] Beneficial effects:
[0035] 1) This invention is based on the intramolecular synergy of C=N, C=C, and C=CN conjugated molecules in Formula 1 and the intermolecular synergy of additive B to improve polysulfide conversion efficiency, reduce polysulfide shuttle, and improve the electrochemical performance of lithium-sulfur batteries.
[0036] 2) The composite additives in the electrolyte can form a more stable passivation layer on the lithium anode surface. Moreover, the study found that modifying the electrolyte with functional groups, such as introducing aromatic groups, and utilizing the planar framework of aromatic groups and the interaction of π-π bonds, makes the formed SEI film more elastic, effectively suppressing the growth of lithium dendrites and further improving the cycle stability of the battery. Attached Figure Description
[0037] Figure 1 This is a cycle diagram of Example 1B;
[0038] Figure 2 This is a cycle diagram for Comparative Example 2; Detailed Implementation
[0039] The following embodiments are intended to further illustrate the content of the present invention; however, the scope of protection of the claims of the present invention is not limited by the embodiments.
[0040] Example 1
[0041] Lithium-sulfur batteries were prepared using the following method:
[0042] ① Electrolyte preparation: In a glove box under an argon atmosphere (H2O < 0.1 ppm), the organic solvent is mixed with LiTFSI (1.0 M) at a volume ratio of ethylene glycol dimethyl ether (DME): 1,3-dioxolane (DOL) = 1:1 to obtain the basic electrolyte. Additive B1 (anhydrous lithium nitrate, 2% of the weight of the basic electrolyte) and additive A1 (formula 1-A hydrochloride, and R4 = H, 0.25-10% of the weight of the basic electrolyte (see Table 1 for specific experimental groups)) are added and stirred thoroughly to obtain the lithium-sulfur battery electrolyte of the present invention.
[0043] ② Sulfur cathode preparation: Sulfur / carbon composite material (70% sulfur loading), acetylene black, and PVDF were mixed in a ratio of 90:3:7. An appropriate volume of N-methylpyrrolidone (NMP) was then added and stirred in a homogenizer for 15 minutes at a speed of 15 kr / min to form a stable and homogeneous cathode slurry. This slurry was then coated onto carbon-coated aluminum foil using a scraper and dried in an oven at 80℃ for 8 hours until the NMP had completely evaporated.
[0044] ③ Lithium-sulfur button cell assembly and testing: The prepared sulfur electrode sheets were punched into Φ13mm circular sheets and dried in an oven at 55℃ for 1 hour. Under an argon atmosphere, using lithium metal sheets as the negative electrode, a Celgard2400 polypropylene microporous membrane as the separator, and an electrolyte concentration of 15μL / mgS, CR2025 lithium-sulfur batteries were assembled sequentially. The prepared batteries were placed in a constant temperature chamber at 25℃ for 12 hours and then subjected to charge-discharge cycle testing on a Blue Electric Tester. The test conditions were constant current 0.5C charge-discharge, a potential range of 1.7–2.8V, and 100 cycles (see [link to test procedure]). Figure 1 ).
[0045] Table 1
[0046] Experimental group Additive A1 and its amount (wt.%) relative to the base electrolyte A 0.25% Additive A1 B 0.5% Additive A1 C 1% Additive A1 D 2% Additive A1 E 5% Additive A1 F 8% Additive A1 G 10% Additive A1
[0047] Example 2
[0048] Compared with Example 1, the only difference is that in the electrolyte, additive A1 accounts for 0.5% of the weight of the base electrolyte, and additive B1 accounts for 1% of the weight of the base electrolyte. Other operations, parameters, and testing methods are the same as in Example 1.
[0049] Comparative Example 1
[0050] Compared to Example 1, the only difference is that additives A1 and B1 were not added to the electrolyte; that is, the basic electrolyte was used as the lithium-sulfur battery electrolyte. Other operations, parameters, and testing methods are the same as in Example 1.
[0051] Comparative Example 2
[0052] Compared to Example 1, the only difference is that the electrolyte lacks additive A1 and only contains additive B1, and the amount added is the same as in Example 1. Other operations, parameters, and testing methods are the same as in Example 1.
[0053] Comparative Example 3
[0054] Compared to Example 1, the only difference is that the electrolyte lacks additive A1 and only contains additive B1, and its addition amount is the same as the total amount of additives A1 and B1 in Example 1, that is, additive B1 is 2.5% of the weight of the base electrolyte. Other operations, parameters, and testing methods are the same as in Example 1.
[0055] Comparative Example 4
[0056] Compared to Example 1B, the only difference is that the electrolyte lacks additive B1 and only contains additive A1, and its addition amount is the same as the total amount of additives A1 and B1 in Example 1, that is, additive A1 is 2.5% of the weight of the base electrolyte. Other operations, parameters and test methods are the same as in Example 1.
[0057] The test results of each embodiment and comparative example are the same as those of Embodiment 1.
[0058] Table 2 Test results for each embodiment and comparative example
[0059]
[0060] It is evident that by combining small amounts of additives A1 and B1, synergy can be unexpectedly achieved, resulting in excellent synergistic effects.
Claims
1. A composite additive, characterized in that, Includes additive A and additive B; The additive A is at least one of a compound having the structural formula of Formula 1 and its derived esters and salts; Formula 1 The n mentioned is an integer from 1 to 6; R1 or R3 is individually a C1-C6 alkyl group or a C3-C6 alkyl group. 10 cycloalkyl, C3~C 10 Partially unsaturated cyclic groups or C4~C 20 The aromatic group; wherein R2 is H, C1-C6 alkyl, C3-C6 alkyl, or C4-C6 alkyl. 10 cycloalkyl, C3~C 10 Partially unsaturated cyclic groups or C4~C 20 Aromatic groups; The additive B is one or more of the following: lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, phosphorus sulfide, lithium bromide, lithium iodide, indium iodide, dibenzothiazole disulfide, iodonitrobenzene, and triphenylphosphine.
2. The composite additive as described in claim 1, characterized in that, In Equation 1, n is an integer from 1 to 3.
3. The composite additive as described in claim 2, characterized in that, R1 and R3 are aromatic groups, and the aromatic group is phenyl, naphthyl or substituted phenyl; the substituent in the substituted phenyl group is at least one of C1-C6 alkyl, C1-C3 alkoxy, nitro, halogen or trifluoromethyl.
4. The composite additive as described in claim 3, characterized in that, R2 is H.
5. The composite additive as described in claim 1, characterized in that, The salt of the structure described in Formula 1 is at least one of hydrochloride, sulfate, nitrate, and organic acid salt.
6. The composite additive according to any one of claims 1 to 5, characterized in that, The weight ratio of additive B to additive A is 1:0.01~6.
7. The composite additive as described in claim 6, characterized in that, The weight ratio of additive B to additive A is 1:0.1~4.
8. The composite additive as described in claim 7, characterized in that, The weight ratio of additive B to additive A is 1:0.1~2.
9. A lithium-sulfur battery electrolyte, characterized in that, It comprises a base electrolyte and the composite additive as described in any one of claims 1 to 8; the base electrolyte comprises an organic solvent and a conductive lithium salt.
10. The lithium-sulfur battery electrolyte as described in claim 9, characterized in that, The organic solvent is a polyether compound, a carbonate compound, an alkyl ester compound, a sulfone, or a sulfoxide compound.
11. The lithium-sulfur battery electrolyte as described in claim 10, characterized in that, The organic solvent is one or more of the following: 1,3-dioxapentane, 1,4-dioxane, ethylene glycol dimethyl ether, glycol dimethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl sulfone, sulfolane, methyl isopropyl sulfone, ethylene carbonate, dimethyl carbonate, and diethyl carbonate.
12. The lithium-sulfur battery electrolyte as described in claim 9, characterized in that, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium dioxalate borate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, and lithium perchlorate.
13. The lithium-sulfur battery electrolyte as described in claim 12, characterized in that, In the basic electrolyte, the concentration of the conductive lithium salt is 0.5–4 mol / L.
14. The lithium-sulfur battery electrolyte according to any one of claims 9 to 12, characterized in that, In lithium-sulfur battery electrolytes, composite additives account for 1 to 15% of the weight of the base electrolyte.
15. The lithium-sulfur battery electrolyte as described in claim 14, characterized in that, In lithium-sulfur battery electrolytes, composite additives account for 1.5 to 10% of the weight of the base electrolyte.
16. The lithium-sulfur battery electrolyte as described in claim 14, characterized in that, In lithium-sulfur battery electrolytes, composite additives account for 1.5 to 4% of the weight of the base electrolyte.
17. A lithium-sulfur battery, characterized in that, It includes the composite additive as described in any one of claims 1 to 8.
18. The lithium-sulfur battery as described in claim 17, characterized in that, It includes the lithium-sulfur battery electrolyte according to any one of claims 9 to 16.
19. The lithium-sulfur battery as described in claim 18, characterized in that, The lithium-sulfur battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode material composited on the surface of the positive current collector.
20. The lithium-sulfur battery as described in claim 19, characterized in that, The cathode material comprises at least one active material selected from elemental sulfur, sulfur-containing polymers, lithium sulfide, and lithium polysulfide.
21. The lithium-sulfur battery as described in claim 18, characterized in that, The lithium-sulfur battery includes a negative electrode, which is one of lithium foil, lithium sheet, lithium alloy, and silicon-carbon composite.