Ionic liquid electrolyte suitable for sulfurized polyacrylonitrile and long-life energy storage battery thereof

Abstract

The invention discloses an ionic liquid electrolyte suitable for sulfurized polyacrylonitrile (SPAN) and a long-life energy storage battery thereof. As a lithium (Li)-free positive electrode, the SPAN energy storage battery needs to pre-lithiate the positive electrode or the negative electrode, and meanwhile, since the SPAN has relatively high irreversible capacity in the first week, the Li needs to be excessive to a certain extent, so that the battery has relatively high energy density and relatively long cycle life. However, excessive Li can bring risks of lithium precipitation and short circuit to the battery. The invention provides an ionic liquid electrolyte. The ionic liquid electrolyte is characterized by comprising one or more ionic liquids, one or more organic carbonate solvents and one or two or more lithium salts. Wherein the ionic liquid has high electrochemical stability, thermal stability and ionic conductivity, not only can protect the lithium negative electrode and prevent the lithium negative electrode from forming harmful lithium dendrites in the cycle process, but also can improve the thermal stability of the battery, so that the cycle stability and safety of the SPAN energy storage battery are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium-sulfur batteries, and particularly relates to an ionic liquid electrolyte suitable for sulfonated polyacrylonitrile (SPAN) and a long-life energy storage battery thereof BACKGROUND

[0002] With the rapid development of the times, the global demand for energy is also rapidly growing, and the energy density of traditional lithium-ion batteries has almost reached the theoretical limit, thus promoting the development of the next generation of high-energy-density rechargeable batteries. Emerging lithium-sulfur batteries have attracted much attention from the scientific community due to their ultra-high theoretical specific energy (2600 Wh Kg -1 ), environmental protection, low cost, and abundant sulfur resources, and are considered to be one of the next generation of high-energy-density rechargeable batteries. However, lithium-sulfur batteries face many challenges in practical applications, such as polysulfide shuttle effect. Sulfonated polyacrylonitrile (SPAN) as an important branch of lithium-sulfur batteries not only has high sulfur content and high energy density, but also has a unique solid-phase reaction mechanism that can avoid the polysulfide "shuttle effect" of traditional sulfur cathodes, thus becoming an effective way to solve the "shuttle effect" of traditional sulfur cathodes. As a lithium (Li)-free cathode, SPAN energy storage batteries need to be pre-lithiated on the cathode or anode, and due to the high irreversible capacity of SPAN in the first week, the first coulombic efficiency is only 75-80%, which means that 20-25% of the active Li is irreversibly consumed in the first cycle, directly limiting the energy density of the full battery. Therefore, Li needs to be excessive to some extent to ensure a high energy density and a long cycle life of the battery. However, the excess Li also brings the risk of lithium precipitation and short circuit, which can be avoided by replacing the Li metal anode with a stable anode (graphite or silicon-carbon) to avoid the problem of lithium dendrites. In addition, existing technologies still have many bottlenecks, and traditional organic electrolytes (such as EC / DEC-based systems) still have problems such as high-temperature volatilization, flammability, and poor compatibility with the anode. Although ionic liquids (ILs) have the advantages of high thermal stability and non-flammability, single ionic liquid systems have the disadvantages of high viscosity and insufficient interface compatibility with SPAN. Therefore, it is urgent to develop a composite electrolyte that has wide temperature performance and high interface stability. SUMMARY

[0003] The purpose of the present application is to address the fact that existing sulfonated polyacrylonitrile (SPAN) batteries must use excess lithium in pre-lithiation to achieve practical energy density and life requirements due to their unique lithium-free properties and high first-cycle irreversible capacity, but this introduces serious safety hazards (lithium precipitation / dendrites / short circuit). Traditional organic electrolytes cannot effectively resolve this core contradiction. Therefore, an ionic liquid electrolyte suitable for sulfonated polyacrylonitrile (SPAN) and a long-life energy storage battery thereof are proposed.

[0004] To achieve the above object, the application adopts the following technical scheme:

[0005] Provided are an ionic liquid electrolyte suitable for sulfidized polyacrylonitrile (SPAN) and a long-life energy storage battery thereof, characterized in that the ionic liquid electrolyte is composed of one or more ionic liquids, one or more organic carbonate solvents, and one or more lithium salts.

[0006] The ionic liquid comprises one or more of N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI), N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide (PP13FSI), N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), and N-methyl-N-butylpyrrolidinium bis(fluorosulfonyl)imide (Py14FSI).

[0007] The organic carbonate solvent comprises one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), and vinylene carbonate (VC).

[0008] The lithium salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium tetrafluoroborate (LiBF4).

[0009] The ionic liquid is preferably N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI) and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), and accounts for 5-50% of the total mass of the electrolyte solvent, preferably 10-30%.

[0010] The carbonate solvent is preferably a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), and diethyl carbonate (DEC), and accounts for 50-95% of the total mass of the electrolyte solvent, preferably 70-90%.

[0011] The lithium salt is preferably a mixture of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB), wherein the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte is 0.1-1.5 mol / kg, and the concentration of lithium difluoro(oxalato)borate (LiDFOB) in the electrolyte is 0.1-1 mol / kg.

[0012] The application also comprises a preparation method of the ionic liquid electrolyte suitable for the sulfurized polyacrylonitrile (SPAN), comprising the following steps: mixing the carbonate solvent and the lithium salt at room temperature in a glove box containing inert gas and the water oxygen content is less than 0.1 ppm, then adding the ionic liquid, and shaking uniformly to obtain the ionic liquid electrolyte of the lithium-sulfur battery.

[0013] The application also comprises a sulfurized polyacrylonitrile (SPAN) battery, comprising a positive electrode, a negative electrode and a separator, and the ionic liquid electrolyte suitable for the sulfurized polyacrylonitrile.

[0014] The positive electrode active material is one of the sulfurized polyacrylonitrile (SPAN), sulfur-carbon composite and sulfur-containing polymer, preferably the sulfurized polyacrylonitrile (SPAN);

[0015] The negative electrode active material is one of the lithium metal, graphite, silicon-carbon (SiC) composite and alloy lithium, preferably one of the graphite, silicon-carbon composite and alloy lithium.

[0016] The solution based on the ionic liquid electrolyte provided by the application directly solves the core safety problem caused by the characteristics of SPAN by utilizing the unique high electrochemical stability (inhibiting dendrites), high thermal stability (improving thermal safety) and high ionic conductivity (ensuring performance) of the ionic liquid, while ensuring the high energy density potential and long cycle life of the battery. Therefore, the ionic liquid electrolyte provided by the application has the advantages and positive effects as follows:

[0017] (1) The ionic liquid can anchor polysulfides through electrostatic interaction due to its high polarity and special cation-anion synergistic effect, thereby inhibiting the shuttle effect.

[0018] (2) On the surface of the battery negative electrode, the ionic liquid participates in the formation of a solid electrolyte interface film (SEI) with high ionic conductivity. Unlike the inorganic SEI film generated by the traditional electrolyte, the ionic liquid can promote the formation of a stable organic-inorganic composite SEI layer, which is rich in LiF and Li3N and organic sulfides and other components, has higher mechanical flexibility and electrochemical stability, and significantly inhibits the growth of lithium dendrites.

[0019] (3) The ionic liquid also has good oxidation stability and conductivity, which can effectively prolong the cycle life of the battery.

[0020] (4) The non-flammability and high thermal stability of the ionic liquid significantly reduce the flammability of the electrolyte, thereby improving the high-temperature performance and safety of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1A cycle performance graph of a SPAN||SiC battery of Example 1 and Comparative Example 1 according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0022] In order to make the technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be described clearly and completely below. The described embodiments are not all the embodiments of the present application, but only some of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by adjustment and improvement of those skilled in the art based on the concept of the present application are within the scope of protection of the present application.

[0023] The 2025 type button cell is tested on a blue light tester, and the full cell of SPAN positive electrode against SiC negative electrode is assembled using the ionic liquid electrolyte of the present application. The following are the examples and comparative examples of SPAN||SiC battery.

[0024] Example 1

[0025] The present embodiment provides an ionic liquid electrolyte suitable for a sulfidized polyacrylonitrile (SPAN) battery and a long-life energy storage battery.

[0026] Preparation of the ionic liquid electrolyte: In an argon-filled glove box (moisture is below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) are mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro(oxalato)borate (LiDFOB) are slowly added to the mixed solvent, and after fully shaking to dissolve the lithium salt, a proper amount of vinylene carbonate (VC) is added, accounting for 1% of the total weight of the solvent, and finally a certain amount of ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI) and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) are added, accounting for 10% and 10% of the total weight of the solvent respectively, and it is left overnight to obtain the ionic liquid electrolyte of the present embodiment.

[0027] Battery assembly and test: In the glove box, the sulfurized polyacrylonitrile (SPAN) was taken as the positive electrode, the polypropylene film with a diameter of 16 mm was taken as the separator, the silicon carbon (SiC) or graphite or alloy lithium was taken as the negative electrode, and the above obtained ionic liquid electrolyte was assembled into a button cell. The N / P ratio of the battery was about 1.1-1.2. After the battery was assembled, it was placed for 24 hours, and then the charge-discharge cycle test was carried out on the blue electricity tester. The charge-discharge conditions were as follows: first, 0.2C charge-discharge for two weeks, then 0.5C cycle, and the voltage interval was 1-3V or 1-2.5V.

[0028] Example 2

[0029] Preparation of ionic liquid electrolyte: In the argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro oxalate borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, a proper amount of vinyl carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl) imide salt (PP13TFSI) was added, accounting for 20% of the total weight of the solvent. The mixture was left overnight to obtain the ionic liquid electrolyte of this example.

[0030] Battery assembly and test same as example 1.

[0031] Example 3

[0032] Preparation of ionic liquid electrolyte: In the argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro oxalate borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, a proper amount of vinyl carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl) imide salt (PP13TFSI) was added, accounting for 20% of the total weight of the solvent. The mixture was left overnight to obtain the ionic liquid electrolyte of this example.

[0033] Battery assembly and test same as example 1.

[0034] Example 4

[0035] Preparation of the ionic liquid electrolyte: In an argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro(oxalato)borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, an appropriate amount of vinylene carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI) and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) were added, accounting for 15% and 15% of the total weight of the solvent, respectively. The mixture was left overnight to obtain the ionic liquid electrolyte of the present example.

[0036] The battery was assembled and tested as in Example 1.

[0037] Example 5

[0038] Preparation of the ionic liquid electrolyte: In an argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro(oxalato)borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, an appropriate amount of vinylene carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI) was added, accounting for 30% of the total weight of the solvent. The mixture was left overnight to obtain the ionic liquid electrolyte of the present example.

[0039] The battery was assembled and tested as in Example 1.

[0040] Example 6

[0041] Preparation of the ionic liquid electrolyte: In an argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro(oxalato)borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, an appropriate amount of vinylene carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) was added, accounting for 30% of the total weight of the solvent. The mixture was left overnight to obtain the ionic liquid electrolyte of the present example.

[0042] The battery was assembled and tested as in Example 1.

[0043] Comparative Example 1

[0044] Preparation of the ionic liquid electrolyte: In an argon-filled glove box (moisture below 0.1 ppm), organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a weight ratio of 2:5:2:1, then 1 mol / kg of lithium hexafluorophosphate (LiPF6) and 0.1 mol / kg of lithium difluoro(oxalato)borate (LiDFOB) were slowly added to the mixed solvent. After the lithium salt was fully dissolved by shaking, an appropriate amount of vinylene carbonate (VC) was added, accounting for 1% of the total weight of the solvent. Finally, a certain amount of ionic liquid N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) was added, accounting for 30% of the total weight of the solvent. The mixture was left overnight to obtain the ionic liquid electrolyte of the present example.

[0045] The battery was assembled and tested as in Example 1.

[0046] The battery data tested according to the above examples and comparative examples are shown in Table 1.

[0047] Table 1: Performance of SPAN|SiC batteries cycled for 1000 cycles at 0.5C rate

[0048]

Claims

1. An ionic liquid electrolyte suitable for Sulfurized Polyacrylonitrile (SPAN) and its long life energy storage battery, characterized in that The ionic liquid electrolyte is composed of one or more ionic liquids, one or more organic carbonate solvents, and one or more lithium salts; The ionic liquid comprises one or more of N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI), N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide (PP13FSI), N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), and N-methyl-N-butylpyrrolidinium bis(fluorosulfonyl)imide (Py14FSI). The organic carbonate solvent comprises one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), and vinylene carbonate (VC). The lithium salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium tetrafluoroborate (LiBF4).

2. The ionic liquid electrolyte for sulfidized polyacrylonitrile (SPAN) according to claim 1, characterized in that, The ionic liquid is preferably N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP13TFSI) and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), accounting for 5-50% of the total mass of the electrolyte solvent, preferably 10-30%.

3. The ionic liquid electrolyte for sulfidized polyacrylonitrile (SPAN) according to claim 1, characterized in that, The carbonate solvent is preferably a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), and diethyl carbonate (DEC), accounting for 50-95% of the total mass of the electrolyte solvent, preferably 70-90%.

4. The ionic liquid electrolyte for sulfidized polyacrylonitrile (SPAN) according to claim 1, characterized in that, The lithium salt is preferably a mixture of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB), wherein the concentration of lithium hexafluorophosphate in the electrolyte is 0.1-1.5 mol / kg, and the concentration of lithium difluoro(oxalato)borate in the electrolyte is 0.1-1 mol / kg.

5. A process for the preparation of an ionic liquid electrolyte for sulphurized polyacrylonitrile (SPAN) according to any one of claims 1-4, characterized in that, The method comprises the following steps: mixing the carbonate solvent with the lithium salt at room temperature in a glove box containing an inert gas and having a water and oxygen content of less than 0.1 ppm, then adding the ionic liquid, and shaking thoroughly to obtain the ionic liquid electrolyte for lithium-sulfur batteries.

6. A long-life energy storage battery, characterized by, The sulfurized polyacrylonitrile (SPAN) battery comprises a positive electrode, a negative electrode, a separator, and the ionic liquid electrolyte of sulfurized polyacrylonitrile (SPAN) according to any one of claims 1-5.

7. The long-life energy storage battery according to claim 6, wherein the positive electrode is one of sulfurized polyacrylonitrile, sulfur-carbon composite, and sulfur-containing polymer, preferably sulfurized polyacrylonitrile (SPAN). The negative electrode is one of lithium metal, graphite, silicon-carbon composite, and alloyed lithium, preferably one of graphite, silicon-carbon composite, and alloyed lithium.

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