Novel solvated ionic liquid and application thereof

Abstract

The invention relates to a novel solvated ionic liquid and application thereof, and belongs to the technical field of secondary batteries, and the specific scheme is as follows: the novel solvated ionic liquid comprises an ether solvent, a lithium salt and a carboxylic ester diluent, the molar ratio of the lithium salt to the ether solvent is 1: 1-2: 1, the carboxylic ester diluent accounts for 20-60% of the total volume of the solvated ionic liquid, the molar ratio of the lithium salt to the ether solvent is 1: 1-2: 1, and the carboxylic ester diluent accounts for 20-60% of the total volume of the solvated ionic liquid. The carboxylic ester diluent comprises one or a combination of more of octyl butyrate, hexyl butyrate, amyl hexanoate, hexyl hexanoate, ethyl caprylate, hexyl caprylate and ethyl caprate. The introduced diluent is low in cost, has weak polarity, and can reduce the viscosity of the system and promote ion transmission while stabilizing the solvated structure in the solvated ionic liquid. When the novel solvated ionic liquid is applied to a sulfide solid-state battery or a halide solid-state battery, a composite positive electrode interface can be effectively wetted, the interface impedance is reduced, and the cycle performance of the solid-state battery under low voltage is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a novel solvated ionic liquid and application thereof. BACKGROUND

[0002] The solvated ionic liquid exhibits similar physicochemical properties to room temperature ionic liquids through the interaction of lithium ions and solvents, has the advantages of non-flammability and high safety, and is a green electrolyte material with great potential. In the field of solid-state batteries, due to the inherent defect of poor contact between the solid-state electrolyte and the electrode particles, the interface impedance is significantly increased, and therefore a high external pressure needs to be applied to maintain the battery performance, which greatly hinders the commercialization and large-scale application of solid-state batteries. The use of solvated ionic liquid to wet the internal pores of the composite positive electrode can construct a continuous and efficient ion transport channel, effectively reduce the interface impedance, and improve the cycle performance of the battery at low pressure, thereby providing an important idea for solving the key technical problems of solid-state batteries.

[0003] The traditional solvated ionic liquid has a large viscosity, which leads to poor wettability of the electrode, and is difficult to fully penetrate the positive electrode material, thereby affecting the interface contact quality and ion transport efficiency. Hydrofluoroether, as a commonly used high-concentration electrolyte diluent, can reduce the viscosity of the system while not destroying the solvation structure, but it has the problems of low boiling point and excessively high vapor pressure, and is easy to volatilize during the compounding process with the positive electrode powder, which not only increases the process difficulty, but also leads to the imbalance of the composition ratio, and is difficult to meet the demand. Therefore, it is of great significance to develop a novel solvated ionic liquid for promoting the industrial application of solid-state battery technology. SUMMARY

[0004] In order to solve the problems in the background art, the application provides a novel solvated ionic liquid and application thereof, and a kind of long chain carboxylic acid ester is introduced as a diluent, the number of carbon atoms of the carboxylic acid ester is 10-14, which has the characteristics of high boiling point and low vapor pressure; the long chain alkyl group gives it weak polarity, which is conducive to stabilizing the original solvation structure of the system, while reducing the viscosity, improving the ion transport efficiency and the cycle stability of the battery.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A novel solvated ionic liquid comprises an ether solvent, a lithium salt and a carboxylic acid ester diluent, wherein the molar ratio of the lithium salt to the ether solvent is 1:1-2:1, the carboxylic acid ester diluent accounts for 20%-60% of the total volume of the solvated ionic liquid, and the carboxylic acid ester diluent comprises one or a combination of octyl butyrate, hexyl butyrate, pentyl hexanoate, hexyl hexanoate, ethyl octanoate, hexyl octanoate and ethyl decanoate.

[0007] Further, the ether solvent includes a combination of one or more of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether.

[0008] Further, the lithium salt includes a combination of one or both of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide.

[0009] Application of a new type of solvated ionic liquid to a sulfide solid-state battery or a halide solid-state battery.

[0010] Further, the composite positive electrode of the sulfide solid-state battery includes 60wt%-80wt% of a positive electrode material, 15wt%-35wt% of a sulfide electrolyte or a halide electrolyte, 1wt%-5wt% of a conductive material, and 0.5wt%-5wt% of a new type of solvated ionic liquid.

[0011] Compared with the prior art, the application has the following beneficial effects:

[0012] The application innovatively introduces a long-chain carboxylate as a diluent into a solvated ionic liquid, the number of carbon atoms of the carboxylate is 10-14, compared with the hydrofluoroether diluent commonly used in high-concentration electrolyte, the carboxylate diluent has low cost, higher boiling point (> 190℃) and lower vapor pressure (< 0.2mmHg). The long-chain alkyl group makes the carboxylate have weak polarity and lower solubility of lithium salt, which can not only maintain the stability of the original solvation structure, but also effectively reduce the system viscosity. The new type of solvated ionic liquid regulated by the carboxylate diluent can be used as an interface wetting agent for a solid-state battery, fully infiltrating the internal pores of the composite positive electrode, and constructing a continuous and efficient ion transmission channel, thereby effectively reducing the interface impedance and significantly improving the cycle stability of the solid-state battery at low pressure. Tests show that the battery has no capacity decay after 125 cycles at 25Mpa and 0.5C rate, and the capacity retention rate is 90.15% after 190 cycles at 5Mpa and 0.5C rate. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The molecular structure diagram of the carboxylate diluent according to the application;

[0014] Figure 2 Fig. 1 (a) and (b) are cycle performance diagrams of solid-state batteries of Example 1 and Comparative Example 1 at 75Mpa, respectively;

[0015] Figure 3 Fig. 2 (a) and (b) are cycle performance diagrams of solid-state batteries of Example 2 and Comparative Example 2 at 25Mpa, respectively;

[0016] Figure 4 Fig. 3 is a cycle performance diagram of a solid-state battery of Example 3 at 5Mpa;

[0017] Figure 5 Figure 4 is a solid-state battery cycle performance graph of Comparative Example 3 at 5 MPa. DETAILED DESCRIPTION

[0018] The technical solutions in the present application will be described clearly and completely below in combination with the drawings and examples. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0019] Example 1

[0020] A novel solvated ionic liquid and its application, specifically comprising the following steps:

[0021] Step one: take 1 ml of triethylene glycol dimethyl ether, and then add 30 vol% of butyl octylate and lithium bis(trifluoromethanesulfonyl)imide in sequence. The molar ratio of lithium bis(trifluoromethanesulfonyl)imide to triethylene glycol dimethyl ether is 1.3:1. After sufficient stirring, a solvated ionic liquid is prepared.

[0022] Step two: take 30 mg of lithium phosphorus sulfur chloride electrolyte, 70 mg of NCM811 positive electrode material, and 1 mg of vapor phase grown carbon fiber. Add 1 wt% of the solvated ionic liquid prepared in step one and grind thoroughly to prepare a composite positive electrode powder. The electrolyte powder and the composite positive electrode powder prepared above are cold-pressed in sequence, and a solid-state battery with lithium-indium alloy as the negative electrode is assembled. The packaging pressure of the battery is 75 MPa.

[0023] The test results are shown in Figure 2 (a). After 0.2C rate activation for two cycles, 0.5C rate charging and discharging cycles are performed. The initial charge-discharge reversible capacity is 149.23 mAh / g, and the reversible capacity after 300 cycles is 152.36 mAh / g, with no capacity decay.

[0024] Example 2

[0025] A novel solvated ionic liquid and its application, specifically comprising the following steps:

[0026] Step one: take 1 ml of triethylene glycol dimethyl ether, and then add 30 vol% of butyl octylate and lithium bis(trifluoromethanesulfonyl)imide in sequence. The molar ratio of lithium bis(trifluoromethanesulfonyl)imide to triethylene glycol dimethyl ether is 1.3:1. After sufficient stirring, a solvated ionic liquid is prepared.

[0027] Step two: take 30 mg of lithium indium chloride electrolyte, 70 mg of NCM811 positive electrode material, 1 mg of vapor grown carbon fiber, and add 1 wt% of the solventated ionic liquid prepared in step one for grinding. The electrolyte powder and the above prepared composite positive electrode powder are cold pressed in sequence to assemble a solid-state battery with lithium indium alloy as the negative electrode, and the packaging pressure of the battery is 25 MPa.

[0028] The test results are shown in Figure 3 (a). After two cycles of 0.2C rate activation, the 0.5C rate is used for charge and discharge cycles, the initial charge and discharge reversible capacity is 118.11 mAh / g, and the reversible capacity is 120.88 mAh / g after 125 cycles, and the capacity does not decay.

[0029] Example 3

[0030] A new type of solventated ionic liquid and its application, specifically comprising the following steps:

[0031] Step one: take 1 ml of tetraethylene glycol dimethyl ether, and add 30 vol% of octyl hexyl ester diluent and lithium bis-trifluoromethanesulfonimide in sequence, the molar ratio of lithium bis-trifluoromethanesulfonimide to triethylene glycol dimethyl ether is 1.5:1, and the solventated ionic liquid is prepared after sufficient stirring.

[0032] Step two: take 30 mg of lithium phosphorus sulfur chloride electrolyte, 70 mg of NCM811 positive electrode material, and 1 mg of vapor grown carbon fiber, and add 1 wt% of the solventated ionic liquid prepared in step one for grinding. The electrolyte powder and the above prepared composite positive electrode powder are cold pressed in sequence to assemble a solid-state battery with lithium indium alloy as the negative electrode, and the packaging pressure of the battery is 5 MPa.

[0033] The test results are shown in Figure 4 (a). After two cycles of 0.2C rate activation, the 0.5C rate is used for charge and discharge cycles, the initial charge and discharge reversible capacity is 118.11 mAh / g, and the reversible capacity is 120.88 mAh / g after 125 cycles, and the capacity does not decay.

[0034] Comparative example 1

[0035] The difference between this comparative example and example 1 is that no solventated ionic liquid is added to the composite positive electrode of the solid-state battery, and the assembly and test method of the solid-state battery is the same as that of example 1, and the experimental results are shown in Figure 2 (b). The initial charge and discharge reversible capacity is 119.02 mAh / g.

[0036] Comparative example 2

[0037] The difference between the present comparative example and Example 2 is that no solventated ionic liquid is added in the solid-state battery composite cathode, and the assembly and testing method of the solid-state battery is the same as that of Example 2, and the experimental results are as shown in Table 1. Figure 3 As shown in Table 1, the first charge-discharge reversible capacity is 60.12 mAh / g, and the cycle stability is significantly reduced.

[0038] Comparative Example 3

[0039] The difference between the present comparative example and Example 3 is that no solventated ionic liquid is added in the solid-state battery composite cathode, and the assembly and testing method of the solid-state battery is the same as that of Example 3, and the experimental results are as shown in Table 1. Figure 5 As shown in Table 1, the first charge-discharge reversible capacity is 38.64 mAh / g, and the cycle stability is significantly reduced.

[0040] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A novel solvated ionic liquid comprising an ether solvent, a lithium salt, and a carboxylate diluent, wherein the molar ratio of the lithium salt to the ether solvent is 1:1-2:1, the carboxylate diluent accounts for 20%-60% of the total volume of the solvated ionic liquid, and the carboxylate diluent comprises one or more of octyl butyrate, hexyl butyrate, pentyl hexanoate, hexyl hexanoate, ethyl octanoate, hexyl octanoate, and ethyl decanoate.

2. A novel solvated ionic liquid according to claim 1, characterized in that: The ether solvent includes one of triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, or a combination of the two.

3. A novel solvated ionic liquid according to claim 1, characterized in that: The lithium salt includes one or a combination of bis(trifluoromethanesulfonyl)imide lithium and bis(fluorosulfonyl)imide lithium.

4. Use of the novel solvated ionic liquid according to any one of claims 1 to 3, characterized in that: The novel solvated ionic liquid is applied to sulfide solid-state batteries or halide solid-state batteries.

5. The use according to claim 4, characterized in that: The composite positive electrode of the solid-state battery includes 60wt%-80wt% of positive electrode material, 15wt%-35wt% of sulfide electrolyte or halide electrolyte, 1wt%-5wt% of conductive material and 0.5wt%-5wt% of new solvated ionic liquid.

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