Preparation method of low-cost high-pressure-resistant water / organic two-phase electrolyte

Abstract

The application discloses a kind of low-cost, high-pressure-resistant water / organic two-phase electrolyte preparation method in the technical field of secondary battery high-performance electrolyte, comprising the following steps: first, prepare water-phase high-concentration double-salt electrolyte;Second, prepare organic phase electrolyte;Finally, when assembling lithium metal battery, water-phase high-concentration double-salt electrolyte is compounded with organic phase fluorinated electrolyte, that is, low-cost, high-pressure-resistant water / organic two-phase electrolyte is obtained, the application can be applied to lithium metal battery, improve the energy density, rate performance and safety of battery, and simultaneously reduce cost.

Description

Technical Field

[0001] This invention relates to the field of high-performance electrolyte technology for secondary batteries, and particularly to a method for preparing an electrolyte. Background Technology

[0002] To meet the demands of portable electronic devices, electric vehicles, and grid energy storage, the development of lithium-ion batteries that combine high safety with low cost is crucial. Aqueous electrolytes for lithium-ion / lithium metal batteries offer higher safety compared to non-aqueous organic electrolytes; however, the narrower electrochemical range of aqueous electrolytes leads to lower energy density in lithium-ion batteries (Suo, L. et al. “Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries. Science 350, 938-943 (2015)). To address this challenge, researchers developed a high-concentration salt-phase electrolyte, successfully extending the electrochemical window from 1.23 V to 3.0 V by forming a LiF-rich solid electrolyte interface at the negative electrode and simultaneously adsorbing hydrophobic anions at the positive electrode. The study shows that the high-concentration aqueous salt electrolyte outperforms carbonate-based non-aqueous electrolytes (4.2 V vs Li|Li). + It has a higher oxidation limiting potential (4.9 V vs Li|Li) + However, the aqueous high-concentration salt electrolyte at 1.9 V (vs Li|Li) + The reduction process generates gas, which limits the reversibility of graphite and lithium metal anodes.

[0003] The limited reducing stability of the aqueous electrolyte can be increased to some extent by adding ethylene glycol, dimethyl sulfoxide (DMSO), and urea [CO(NH2)2]. These additives, when dissolved in the aqueous electrolyte, can alter the Li... + The solvation structure reduces water and forms a nanoscale inorganic-organic composite solid electrolyte interface. However, the lowest reduction potential limit achieved to date is only 1.3 V (vs Li|Li + (Xie, J., Liang, Z. & Lu, Y.-C. Molecular crowding electrolytes for high-voltage aqueous batteries. Nat. Mater. 19, 1006–1011(2020)). The use of a two-phase electrolyte design is attractive for extending the reduction limit potential of aqueous electrolytes. However, current high-efficiency Li-ion batteries in both the liquid phase and interface of two-phase electrolytes... + Transportation remains an unresolved challenge. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-cost, high-pressure-resistant method for preparing a water / organic two-phase electrolyte, thus solving the problems in the background technology.

[0005] The objective of this invention is achieved as follows: a low-cost, high-pressure-resistant method for preparing a water / organic two-phase electrolyte, comprising the following steps:

[0006] Step 1: In an argon-filled glove box, take 5-20 g of organic lithium salt and place it in a glass bottle. Add ultrapure water dropwise and start magnetic stirring to form a uniform ionic liquid solution, so that water molecules are coated by lithium salt molecules to form a "salt-in-water" solution system. The molar ratio of ultrapure water to organic lithium salt is in the range of 1:4 to 1:20.

[0007] Step 2: After the lithium salt in the above system is completely dissolved, add two or more inorganic lithium salts and stir continuously to dissolve the newly added inorganic lithium salts in the ionic liquid obtained in Step 1. After the lithium salt is completely dissolved, an aqueous high-concentration dual-salt electrolyte is obtained. The molar ratio of the total amount of inorganic lithium salt to the organic lithium salt in Step 1 is in the range of 1:10 ~ 1:5.

[0008] Step 3: Add the crown ether as a lithium ion carrier to the aqueous high-concentration dual-salt electrolyte system obtained in Step 2. The crown ether has a higher binding free energy to lithium ions than Li. + -Free energy of the hydrated structure of H2O;

[0009] Step 4: In an argon-filled glove box, take 1-5g of organic lithium salt and place it in a glass bottle. Slowly add the fluorinated organic solution drop by drop while continuously stirring to form a uniform organic electrolyte. The molar concentration of the organic lithium salt in the fluorinated solvent should be controlled between 0.1mol / L and 2mol / L.

[0010] Step 5: Dissolve the crown ether as a lithium ion carrier in the fluorinated organic electrolyte obtained in Step 4, and form Li₂ atoms with a size of 2-10 nm in the fluorinated organic electrolyte. + -CE lithium-ion carrier nanoclusters;

[0011] Step 6: When assembling lithium metal batteries, the aqueous high-concentration dual-salt electrolyte obtained in step 3 is combined with the fluorinated organic electrolyte obtained in step 5 to obtain an aqueous / organic biphase electrolyte.

[0012] Furthermore, the organic lithium salt in step 1 includes at least one of lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, lithium mono-5-sulfon-1,3-phenylenediate, and lithium tetrafluoroborate.

[0013] Furthermore, the inorganic lithium salt in step 2 includes at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate.

[0014] Furthermore, in step 3, the mass ratio of the crown ether to the aqueous high-concentration dual-salt electrolyte ranges from 1:10 to 1:20.

[0015] Furthermore, the organolithium salt in step 4 includes at least one of lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, lithium mono-5-sulfo-1,3-phenylenediate, and lithium tetrafluoroborate.

[0016] Furthermore, the fluorinated organic solvent in step 5 includes at least one of 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, methyl trifluoroacetate, methyl pentafluoropropionate, methyl heptafluorobutyrate, methyl trifluoroethyl carbonate, difluoroethyl acetate, and ethyl difluoroacetate.

[0017] Furthermore, in step 5), the mass ratio of crown ether to fluorinated electrolyte is in the range of 1:20 to 1:25.

[0018] Compared with existing technologies, the advantages of this invention are as follows: This invention uses crown ether as a lithium ion carrier, and constructs a unique biphase electrolyte system by combining it with ultrapure water, lithium salt, and fluorinated organic solvent. In the non-aqueous phase, the hydrophobic fluorinated ether serves as the solvent, and the crown ether reacts with Li... + A stable [Li(CE)] is formed. + The complex excludes water molecules from the Li through strong coordination. + Beyond the first solvation layer. Meanwhile, TFSI - Anions and Li + It forms contact ion pairs and charged aggregates, creating nanoclusters with sizes of 2-10 nm in fluorinated solvents, whose Li + Achieved through a "vehicle-type transmission" mechanism, room temperature Li + The conductivity reaches 0.33 mS / cm. The aqueous electrolyte uses a high-concentration "dual-salt" electrolyte, and the TFSI in this aqueous electrolyte... - Anions can form a hydrophobic adsorption layer on the cathode surface, raising the oxidation limit to 4.9 V. The addition of crown ethers significantly reduces the activity of free water in the aqueous phase, thereby increasing electrolyte stability. Through the dynamic equilibrium of the lithium-ion support between the two phases, Li... + It can quickly cross the interface, thereby significantly reducing the interfacial impedance of the two-phase electrolyte and promoting rapid desizing of the electrode interface.

[0019] This invention can be applied to lithium metal batteries to improve the battery's energy density, rate performance, and safety, while simultaneously reducing costs. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 The impedance spectrum test results of the electrolyte of this invention at different temperatures are shown.

[0022] Figure 2 The results are the electrochemical window test results for the electrolyte of this invention.

[0023] Figure 3 The results show the test results of assembling a Li|LFP full cell using the electrolyte of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] A low-cost, high-pressure resistant water / organic two-phase electrolyte preparation method includes the following steps:

[0027] a. Preparation of a highly concentrated aqueous dual-salt electrolyte:

[0028] Step 1: In an argon-filled glove box, take 4 g of lithium trifluoromethanesulfonate and 1 g of lithium bis(trifluoromethanesulfonyl)imide and place them in a glass bottle. Slowly add ultrapure water dropwise and start magnetic stirring to form a uniform ionic liquid solution, so that water molecules are coated by lithium salt molecules to form a "salt-in-water" solution system. The molar ratio of ultrapure water to the total amount of the two organic lithium salts is in the range of 1:20.

[0029] Step 2: After the lithium salt in the above system is completely dissolved, add lithium perchlorate and lithium tetrafluoroborate in equal molar amounts. Continue stirring to dissolve the newly added inorganic lithium salt in the ionic liquid obtained in Step 1. After the lithium salt is completely dissolved, an aqueous high-concentration dual-salt electrolyte is obtained. The molar ratio of the total molar amount of lithium perchlorate and lithium tetrafluoroborate to the total amount of organic lithium salt in Step 1 is 1:10.

[0030] Step 3: Add 18-crown ether 6, with a mass ratio of 1:10 to the aqueous high-concentration dual-salt electrolyte, as a lithium ion carrier to the aqueous high-concentration dual-salt electrolyte system obtained in Step 2, and continue stirring until the 18-crown ether 6 is completely dissolved to obtain an aqueous high-concentration dual-salt electrolyte containing a lithium ion carrier.

[0031] b. Preparation of organic phase electrolyte:

[0032] Step 4: In an argon-filled glove box, take 1 g of lithium trifluoromethanesulfonate and place it in a glass bottle. Slowly add dropwise a mixture of methyl trifluoroethyl carbonate and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane in a fluorinated organic solution with a molar ratio of 1:4. Continue stirring to form a homogeneous organic electrolyte. The molar concentration of the organic lithium salt in the fluorinated solvent is controlled at 0.5 mol / L.

[0033] Step 5: Dissolve 18-crown ether 6 as a lithium ion carrier in the fluorinated organic electrolyte obtained in step 4, and form lithium ion carrier nanoclusters with a size of 2-10 nm in the fluorinated electrolyte. The mass ratio of 18-crown ether 6 to fluorinated electrolyte is 1:20.

[0034] c. Finally, during the assembly of lithium metal batteries, the aqueous high-concentration dual-salt electrolyte is combined with the organic fluorinated electrolyte phase to obtain a low-cost, high-voltage-resistant aqueous / organic dual-phase electrolyte. + This is achieved through a "vehicle-based transmission" mechanism, Li + The electrical conductivity reaches 0.33 mS / cm ( Figure 1 ).

[0035] Example 2

[0036] A low-cost, high-pressure resistant water / organic two-phase electrolyte preparation method includes the following steps:

[0037] a. Preparation of a highly concentrated aqueous dual-salt electrolyte:

[0038] Step 1: In an argon-filled glove box, take 10 g of lithium trifluoromethanesulfonate and place it in a glass bottle. Add ultrapure water dropwise and start magnetic stirring to form a uniform ionic liquid solution, so that water molecules are coated by lithium salt molecules to form a "salt-in-water" solution system. The molar ratio of ultrapure water to the organic lithium salt is in the range of 3:20.

[0039] Step 2: After the lithium salt in the above system is completely dissolved, add a mixture of lithium tetrafluoroborate and lithium hexafluoroarsenate in a molar ratio of 2:3. Continue stirring to dissolve the newly added inorganic lithium salt in the ionic liquid obtained in Step 1. After the lithium salt is completely dissolved, an aqueous high-concentration dual-salt electrolyte is obtained. The molar ratio of the total amount of inorganic lithium salt to the organic lithium salt in Step 1 is in the range of 1:8.

[0040] Step 3: Add 12-crown ether 4 as a lithium ion carrier to the aqueous high-concentration dual-salt electrolyte system obtained in Step 2. The mass ratio of 12-crown ether 4 to the aqueous high-concentration dual-salt electrolyte is in the range of 1:15.

[0041] b. Preparation of organic phase electrolyte:

[0042] Step 4: In an argon-filled glove box, take 5g of organolithium salt and place it in a glass bottle. Slowly add ethyl difluoroacetate and 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane in a fluorinated organic solution with a molar ratio of 1:1. Stir continuously to form a homogeneous organic electrolyte. The molar concentration of organolithium salt in the fluorinated solvent is controlled at 0.1 mol / L.

[0043] Step 5: Dissolve 12-crown ether 4 as a lithium ion carrier in the fluorinated organic electrolyte obtained in step 4, and form lithium ion carrier nanoclusters with a size of 2-10 nm in the fluorinated electrolyte. The mass ratio of 12-crown ether 4 to fluorinated electrolyte is 1:23.

[0044] c. Finally, during the assembly of lithium metal batteries, the aqueous high-concentration dual-salt electrolyte is combined with the organic fluorinated electrolyte to obtain a low-cost, high-voltage resistant aqueous / organic biphase electrolyte.

[0045] Linear sweep voltammetry measurements were performed on a CHI760E electrochemical workstation to determine the oxidation potential limit of aqueous electrolytes and that of organic and biphase electrolytes at 25 ± 0.05 μm. oElectrochemical window under C. A three-electrode cell was used, with the two outer electrodes as working electrodes and the middle electrode as a reference electrode, to measure the ESW of the aqueous solution. Using Ti and Al foils as working electrodes and Ag|AgCl as the reference electrode, the reduction limit potential and oxidation limit potential of the aqueous electrolyte were tested. In the reduction limit potential test, Ti foil was used as the working electrode and Al foil as the counter electrode. In the oxidation limit potential test, Al foil was used as the working electrode and Ti foil as the counter electrode. Using Cu and Al foils as working electrodes and Li metal as the reference electrode, the reduction limit potential and oxidation limit potential of organic electrolytes and biphase electrolytes were tested in a coin cell. In the reduction limit potential test, copper foil was used as the working electrode and aluminum foil as the counter electrode. In the oxidation limit potential test, aluminum foil was used as the working electrode and copper foil as the counter electrode. The electrochemical window range of the biphase electrolyte was measured to be 0~4.7V. Figure 2 ).

[0046] Example 3

[0047] A low-cost, high-pressure resistant water / organic two-phase electrolyte preparation method includes the following steps:

[0048] a. Preparation of a highly concentrated aqueous dual-salt electrolyte:

[0049] Step 1: In an argon-filled glove box, take 20 g of the organolithium salt 5-sulfon-1,3-benzenedicarboxylic acid monolithium and place it in a glass bottle. Add ultrapure water dropwise and start magnetic stirring to form a uniform ionic liquid solution, so that water molecules are coated by lithium salt molecules to form a "salt-in-water" solution system. The molar ratio of ultrapure water to the organolithium salt is in the range of 1:4.

[0050] Step 2: After the lithium salt in the above system is completely dissolved, add lithium hexafluorophosphate and stir continuously to dissolve the newly added inorganic lithium salt in the ionic liquid obtained in Step 1. After the lithium salt is completely dissolved, an aqueous high-concentration dual-salt electrolyte is obtained. The molar ratio of the total amount of inorganic lithium hexafluorophosphate to the organic lithium salt 5-sulfonyl-1,3-phenylenediamine monolithium in Step 1 is 1:5.

[0051] Step 3: Add 9-crown ether 3 as a lithium ion carrier to the aqueous high-concentration dual-salt electrolyte system obtained in Step 2. The mass ratio of 9-crown ether 3 to the aqueous high-concentration dual-salt electrolyte is 1:20.

[0052] b. Preparation of organic phase electrolyte:

[0053] Step 4: In an argon-filled glove box, take 5g of the organolithium salt 5-sulfon-1,3-phthalic acid monolithium and place it in a glass bottle. Slowly add dropwise a mixed fluorinated organic solution of methyl trifluoroacetate and ethyl difluoroacetate in a molar ratio of 1:5. Stir continuously to form a homogeneous organic electrolyte. The molar concentration of the organolithium salt 5-sulfon-1,3-phthalic acid monolithium in the fluorinated solvent is controlled at 0.2 mol / L.

[0054] Step 5: Dissolve 9-crown ether 3 as a lithium ion carrier in the fluorinated organic electrolyte obtained in step 4, and form lithium ion carrier nanoclusters with a size of 2-10 nm in the fluorinated electrolyte. The mass ratio of 9-crown ether 3 to fluorinated electrolyte is 1:25.

[0055] c. Finally, during the assembly of lithium metal batteries, the aqueous high-concentration dual-salt electrolyte is combined with the organic fluorinated electrolyte to obtain a low-cost, high-voltage resistant aqueous / organic biphase electrolyte.

[0056] For assembling CR2032 coin-shaped batteries, the positive electrode is placed in the middle of the positive electrode shell. 50 μL of a monomer precursor aqueous electrolyte is filled to the positive side of the battery, covering the positive electrode and its shell. Then, in-situ gelation is performed under ultraviolet light. The gelled positive electrode is transferred to a glove box, covered with a glass fiber separator, and then 50 μL of a fluorinated organic electrolyte is added. After covering with a lithium metal or graphite-based electrode, pressure sealing is performed. The Li-LFP full cell assembled using the low-cost, high-pressure resistant aqueous / organic biphase electrolyte configured in this invention achieves a capacity of 155 mAh / g. Figure 3 ).

[0057] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A low-cost, high-pressure-resistant method for preparing a water / organic two-phase electrolyte, characterized in that, Includes the following steps: Step 1: In an argon-filled glove box, take 5-20 g of organic lithium salt and place it in a glass bottle. Add ultrapure water dropwise and start magnetic stirring to form a uniform ionic liquid solution, so that water molecules are coated by lithium salt molecules to form a "salt-in-water" solution system. The molar ratio of ultrapure water to organic lithium salt is in the range of 1:4 to 1:

20. Step 2: After the lithium salt in the above system is completely dissolved, add two or more inorganic lithium salts and stir continuously to dissolve the newly added inorganic lithium salts in the ionic liquid obtained in Step 1. After the lithium salt is completely dissolved, an aqueous high-concentration dual-salt electrolyte is obtained. The molar ratio of the total amount of inorganic lithium salt to the organic lithium salt in Step 1 is in the range of 1:10 ~ 1:

5. Step 3: Add the crown ether as a lithium ion carrier to the aqueous high-concentration dual-salt electrolyte system obtained in Step 2. The crown ether has a higher binding free energy to lithium ions than Li. + The free energy of the -H2O hydration structure, and the mass ratio of crown ether to aqueous high-concentration dual-salt electrolyte ranges from 1:10 to 1:20; Step 4: In an argon-filled glove box, take 1-5g of organic lithium salt and place it in a glass bottle. Slowly add the fluorinated organic solution drop by drop while continuously stirring to form a uniform organic electrolyte. The molar concentration of the organic lithium salt in the fluorinated solvent should be controlled between 0.1mol / L and 2mol / L. Step 5: Dissolve the crown ether as a lithium ion carrier in the fluorinated organic electrolyte obtained in Step 4, and form Li₂ atoms with a size of 2-10 nm in the fluorinated organic electrolyte. + -CE lithium ion carrier nanoclusters, with a crown ether to fluorinated electrolyte mass ratio ranging from 1:20 to 1:25; Step 6: When assembling lithium metal batteries, the aqueous high-concentration dual-salt electrolyte obtained in step 3 is combined with the fluorinated organic electrolyte obtained in step 5 to obtain an aqueous / organic biphase electrolyte.

2. The method for preparing a low-cost, high-pressure resistant water / organic two-phase electrolyte according to claim 1, characterized in that, The organic lithium salt in step 1 includes at least one of lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, lithium mono-5-sulfon-1,3-phthalic acid, and lithium tetrafluoroborate.

3. A method for preparing a low-cost, high-pressure resistant water / organic two-phase electrolyte according to claim 1 or 2, characterized in that, The inorganic lithium salt in step 2 includes at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate.

4. A method for preparing a low-cost, high-pressure resistant water / organic two-phase electrolyte according to claim 1 or 2, characterized in that, The organic lithium salt in step 4 includes at least one of lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, lithium mono-5-sulfon-1,3-phthalic acid, and lithium tetrafluoroborate.

5. A method for preparing a low-cost, high-pressure resistant water / organic two-phase electrolyte according to claim 1 or 2, characterized in that, The fluorinated organic solvent in step 5 includes at least one of 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, methyl trifluoroacetate, methyl pentafluoropropionate, methyl heptafluorobutyrate, methyl trifluoroethyl carbonate, difluoroethyl acetate, and ethyl difluoroacetate.

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