An interfacial wetting agent for halide solid state electrolytes

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to an interface wetting agent for halide solid electrolyte. Raw materials for preparing the interface wetting agent include a solvent and a lithium salt, the solvent is one or both of n-butyl ether or isobutyl ether, and the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide. The interface wetting agent provided by the application has the advantages of wide electrochemical window and stability with the halide solid electrolyte. When used in a solid-state battery, the interface wetting agent can improve electrode density, improve the electrical conductivity between solid-solid interfaces, reduce the impedance of the solid-solid interface, and thus improve the performance of the solid-state battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to an interface wetting agent for halide solid electrolyte. BACKGROUND

[0002] Solid-state batteries have high safety performance, high energy density (expected to reach 300-400 Wh / kg or even higher), long cycle life (expected to avoid the problems of SEI film formed by liquid electrolyte in the charging and discharging process and lithium dendrite piercing the separator), wide working temperature range (good needle and high temperature stability), high production efficiency, good flexibility and other advantages, so solid-state batteries have become one of the mainstream directions of future battery development.

[0003] The development of solid-state electrolyte is one of the most critical steps for solid-state batteries. The solid-state electrolytes currently studied mainly include polymers, oxides, sulfides and halides. Halides have high ionic conductivity, stable chemical / electrochemical stability, good plasticity, high oxidation stability potential (-4.2 V) (Adv. Mater. 2018, 1803075), and good compatibility with lithium cobalt oxide positive electrode materials, ternary positive electrode materials and lithium-rich manganese-based positive electrode materials. Therefore, halide solid-state electrolyte is the most potential electrolyte for application in solid-state batteries.

[0004] However, the interface problem between the solid-state electrolyte and the electrode is the main factor restricting its large-scale commercial application. Compared with traditional liquid batteries, solid-state batteries have positive electrode-electrolyte interface, negative electrode-electrolyte interface and interface between inorganic particles. The migration of lithium ions on these interfaces determines the overall conductivity of the solid-state electrolyte and the overall performance of the battery (Joule 2, 1-25, October 17, 2018). So far, the interface wetting agent in the prior art applied to halide solid-state electrolyte has the problem of low oxidation potential, which cannot be effectively applied.

[0005] In view of the problem that the interface wetting agent for halide solid-state electrolyte in the prior art is not ideal, the application provides an interface wetting agent specially used for halide solid-state electrolyte. The raw materials for preparing the wetting agent include a solvent and a lithium salt, the solvent is one or both of n-butyl ether or isobutyl ether; and the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide.

[0006] The application finds that the interface wetting agent prepared by using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a lithium salt and n-butyl ether or isobutyl ether as a solvent has the advantages of high oxidation potential and stable performance after mixing with halide solid-state electrolyte in the process of being applied to halide solid-state electrolyte.

[0007] Preferably, the lithium salt has a concentration of 2-3 mol / L in the solvent.

[0008] Preferably, the lithium salt further comprises lithium bisfluorosulfonylimide (LiFSI).

[0009] Preferably, the lithium salt is a mixture of lithium bistrifluoromethanesulfonylimide and lithium bisfluorosulfonylimide, and the molar percentage of lithium bistrifluoromethanesulfonylimide is greater than or equal to 50%. After adding lithium bisfluorosulfonylimide, the electrochemical window of the material will be reduced to a certain extent, but within the above-mentioned addition amount, it will not have a significant impact on the electrochemical window, and the subsequent application range can be expanded.

[0010] Preferably, the chemical composition formula of the halide solid-state electrolyte is Li a M b X c , wherein M comprises at least one selected from metal elements and semi-metal elements other than Li, and X comprises at least one selected from F, Cl, Br and I.

[0011] The application also protects a preparation method of the interfacial wetting agent described in the application, comprising the following steps:

[0012] In an argon-filled glove box, the lithium salt is weighed and added to the solution until it is completely dissolved.

[0013] The application also protects a lithium ion battery or lithium battery of the interfacial wetting agent described in the application.

[0014] Preferably, the lithium ion battery or lithium battery is a halide solid-state electrolyte-high nickel positive electrode material system or a lithium-rich manganese-based high-voltage positive electrode material system.

[0015] The application has the following beneficial effects:

[0016] The interfacial wetting agent provided by the application has the advantages of wide electrochemical window, stability with halide solid-state electrolyte, etc. When used in a solid-state battery, it can improve electrode density, improve the electrical conductivity between solid-solid interfaces, reduce solid-solid interface impedance, and thus improve the performance of the solid-state battery. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 XRD pattern after the halide solid-state electrolyte is mixed with the interfacial wetting agent and left for 1 day;

[0018] Figure 20.1C initial charge-discharge curves of the battery without the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6) and the battery with the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6+ interfacial wetting agent);

[0019] Figure 3 0.1C cycle curves of the battery without the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6) and the battery with the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6+ interfacial wetting agent);

[0020] Figure 4 Cycle impedance comparison curves of the battery without the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6) and the battery with the interfacial wetting agent (Li-In / Li3InCl6+ Li10GeP2S12 / LiNiCoMn+ Li3InCl6+ interfacial wetting agent); DETAILED DESCRIPTION

[0021] The following examples are intended to illustrate the present application but not to limit the scope of the present application.

[0022] The following examples are intended to illustrate the present application but not to limit the scope of the present application.

[0023] Unless otherwise specified, the experimental reagents and materials used in the examples of the present application are commercially available.

[0024] Unless otherwise specified, the technical means used in the examples of the present application are conventional means known to those skilled in the art.

[0025] Example 1

[0026] According to the ratio of 0.02 mol LiTFSI to 10 mL n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent. The conductivity of the interfacial wetting agent was tested using a conductivity tester. Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0027] Example 2

[0028] According to the ratio of 0.026 mol LiTFSI to 10 mL of n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; a Li-stainless steel sheet button cell was assembled to test the electrochemical window of the interfacial wetting agent.

[0029] Example 3

[0030] According to the ratio of 0.030 mol LiTFSI to 10 mL of n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; a Li-stainless steel sheet button cell was assembled to test the electrochemical window of the interfacial wetting agent.

[0031] Example 4

[0032] According to the ratio of 0.02 mol LiTFSI to 10 mL of isobutyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; a Li-stainless steel sheet button cell was assembled to test the electrochemical window of the interfacial wetting agent.

[0033] Example 5

[0034] According to the ratio of 0.02 mol LiFSI / LiFSI, wherein the molar ratio of LiFSI to LiFSI is 1:1, to 10 mL of n-butyl ether, LiFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; a Li-stainless steel sheet button cell was assembled to test the electrochemical window of the interfacial wetting agent.

[0035] Example 6

[0036] The interfacial wetting agent in Example 1 was subjected to TG-DSC testing to test its thermal stability.

[0037] Example 7

[0038] Li3InCl6 was soaked in the interfacial wetting agent prepared in Example 2 for 1 day, and part of the solid-state electrolyte was taken out and dried in a vacuum drying box. XRD and ionic conductivity were tested.

[0039] Example 8

[0040] In an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), ordinary LiNiCoMo was used as the positive electrode material. The positive electrode material: Li3InCl6: conductive agent: interfacial wetting agent electrode additive material was mixed in a ratio of 59.85:25.65:4.5:10 (mass ratio). The mixing process was carried out in the glove box. A thin lithium-indium alloy was used as the negative electrode, and Li3InCl6 was used as the electrolyte material. 70 mg of Li3InCl6 was placed in the inner container of the mold battery with a cross-sectional area of 0.785 cm 2 . The tablet was pressed at a pressure of 150 MPa. 30 mg of Li 10 GeP2S 12 was added to one side of the electrolyte layer, and the tablet was pressed again at a pressure of 150 MPa. The positive electrode layer and the electrolyte layer were pressed together. 12 mg of Li 10 GeP2S 12 was placed on one side of the Li3InCl6, and a Li-In sheet was used as the negative electrode layer. After the entire process was completed, the inner container was placed in the mold battery, and the screw was tightened to seal it. After sealing, a full-solid-state Li-In / Li3InCl6+Li 10 GeP2S 12 / LiNiCoMn+Li3InCl6+C+interfacial wetting agent secondary battery was obtained.

[0041] Comparative Example 1

[0042] In an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), LiTFSI was weighed according to a ratio of 0.02 mol LiTFSI to 10 mL of ether. Then, ether was added to the LiTFSI, and the mixture was stirred for 30 minutes. The lithium salt was completely dissolved to obtain the interfacial wetting agent. TG-DSC testing was performed.

[0043] Comparative Example 2

[0044] In an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), LiTFSI was weighed according to a ratio of 0.02 mol LiTFSI to 10 mL of isopropyl ether. Then, isopropyl ether was added to the LiTFSI, and the mixture was stirred for 30 minutes. The lithium salt was completely dissolved to obtain the interfacial wetting agent. TG-DSC testing was performed.

[0045] Comparative Example 3

[0046] According to the proportion of 0.02 mol LiTFSI and 10 mL of n-pentyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-pentyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester.

[0047] Comparative Example 4

[0048] According to the proportion of 0.02 mol LiTFSI and 10 mL of n-pentyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-pentyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester.

[0049] Comparative Example 5

[0050] According to the proportion of 0.02 mol LiFSI and 10 mL of isopropyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then isopropyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0051] Comparative Example 6

[0052] According to the proportion of 0.02 mol LiFSI and 10 mL of n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0053] Comparative Example 7

[0054] According to the proportion of 0.02 mol LiFSI and 10 mL of n-pentyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-pentyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0055] Comparative Example 8

[0056] According to the proportion of 0.02 mol LiFSI and 10 mL of n-hexyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-hexyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0057] Comparative Example 9

[0058] According to the proportion of 0.02 mol LiPF6 and 10 mL of n-butyl ether, LiPF6 was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, heated and stirred at 60°C for 2 hours, and the lithium salt was not completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester.

[0059] Comparative Example 10

[0060] According to the proportion of 0.02 mol LiBOB and 10 mL of n-butyl ether, LiBOB was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, heated and stirred at 60°C for 2 hours, and the lithium salt was not completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester.

[0061] Comparative Example 11

[0062] According to the proportion of 0.02 mol LiDFOB and 10 mL of n-butyl ether, LiDFOB was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, heated and stirred at 60°C for 2 hours, and the lithium salt was not completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester.

[0063] Comparative Example 12

[0064] According to the proportion of 0.015 mol LiTFSI and 10 mL of n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; Li-stainless steel sheet button cells were assembled, and the electrochemical window of the interfacial wetting agent was tested.

[0065] Comparative Example 13

[0066] According to the ratio of 0.036 mol LiTFSI to 10 mL n-butyl ether, LiTFSI was weighed in an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), and then n-butyl ether was added thereto, stirred for 30 minutes, and the lithium salt was completely dissolved to obtain the interfacial wetting agent; the conductivity of the interfacial wetting agent was tested using a conductivity tester; and a Li-stainless steel sheet button cell was assembled to test the electrochemical window of the interfacial wetting agent.

[0067] Comparative Example 14

[0068] In an argon-filled glove box (moisture 1 ppm, oxygen 1 ppm), ordinary LiNiCoMn was used as the positive electrode material. The positive electrode material: Li3InCl6: conductive agent was mixed in a ratio of 66.5:28.5:5 (mass ratio), and the mixing process was carried out in the glove box. A thin lithium-indium alloy was used as the negative electrode, and Li3InCl6 was used as the electrolyte material. 70 mg of Li3InCl6 was placed in the inner container of the mold battery with a cross-sectional area of 0.785 cm 2 , and was pressed into a tablet at a pressure of 150 MPa. 30 mg of Li 10 GeP2S 12 was added to one side, and was evenly spread and pressed into a tablet at a pressure of 150 MPa for the second time to obtain an electrolyte layer; 12 mg of positive electrode powder was added to one side of the Li3InCl6, and was evenly spread and pressed into a tablet at a pressure of 350 MPa to press the positive electrode layer and the electrolyte layer together; and a Li-In sheet was placed as the negative electrode layer on the Li 10 GeP2S 12 . After the entire process was completed, the inner container was placed in the mold battery, and was tightly pressed and screwed to seal. After sealing, a full-solid-state Li-In / Li3InCl6+Li 10 GeP2S 12 / LiNiCoMn+Li3InCl6+C secondary battery was obtained.

[0069] The performance of the batteries in the examples and comparative examples was tested, and the results are shown in Tables 1-6.

[0070] Table 1 Comparison table of conductivities of interfacial wetting agents with different solvents of lithium salt LiTFSI

[0071]

[0072]

[0073] Table 2 Comparison table of electrochemical windows of different interfacial wetting agents

[0074]

[0075] Table 3 Comparison table of thermal decomposition temperatures of different interfacial wetting agents

[0076]

[0077] Table 4 Comparison table of conductivity of different lithium salt interfacial wetting agent

[0078]

[0079] Table 5 Comparison table of conductivity of different concentration of LiTFSI interfacial wetting agent

[0080]

[0081] Table 6 Ionic conductivity of interfacial wetting agent mixed with halide solid state electrolyte in Example 7

[0082]

[0083] It is found from Table 1 that when the C chain is greater than 4, the conductivity of the interfacial wetting agent is very low and cannot be used in solid-state batteries, so an ether solvent with a C chain less than or equal to 4 is selected.

[0084] It is found from Table 2 that compared with LiTFSI, when LiFSI is used as the lithium salt in the interfacial wetting agent, the oxidation potential will decrease, which is lower than 4.0V (when LiFSI is a single lithium salt), and is not suitable for halide solid state electrolyte-high nickel, lithium-rich manganese-based and other high-voltage positive electrode material systems with a wide voltage range; it is found from Table 4 that LiPF6, LiBOB and LiDFOB are not soluble in ether solvents; therefore, LiTFSI is selected as the lithium salt.

[0085] It is found from Table 3 that when the C chain is less than or equal to 3 (such as diethyl ether, isopropyl ether), the thermal decomposition stability of the interfacial wetting agent is low and the safety is poor, which limits its use in the battery coating process; in combination with Table 2, it is concluded that when the C chain is 4 (i.e. n-butyl ether or isobutyl ether), the interfacial wetting agent has the best performance.

[0086] It is found from Table 5 that when the concentration of LiTFSI is between 2-3 mol / L, the conductivity of the interfacial wetting agent is relatively high; as the concentration of LiTFSI increases, the conductivity of the interfacial wetting agent first increases and then decreases; therefore, the concentration range of LiTFSI is selected to be 2-3 mol / L.

[0087] It is found from Table 6 that after the halide solid state electrolyte is soaked in the interfacial wetting agent, the conductivity retention rate is 78.3%; it is found that after the halide solid state electrolyte is soaked in the interfacial wetting agent for 1 day, the structure does not change; therefore, the interfacial wetting agent and the halide solid state electrolyte can exist stably. Figure 1

[0088] Figure 2 ​It is known that the first discharge specific capacity of the halide solid electrolyte-high nickel positive electrode material system battery is increased from 166.9 mAh / g to 209.4 mAh / g after adding the interface wetting agent.

[0089] Figure 3 It is known that the capacity retention rate after 50 cycles of the halide solid electrolyte-high nickel positive electrode material system battery is increased from 26.2% to 83.4% after adding the interface wetting agent.

[0090] Figure 4 It is known that the interface impedance of the halide solid electrolyte-high nickel positive electrode material system battery is obviously reduced after adding the interface wetting agent.

[0091] Although the present application has been described in detail with general description, specific embodiments and experiments, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of the present application claimed.

Claims

1. An interfacial wetting agent for halide solid state electrolytes, characterized in that, The raw materials for preparing the interfacial wetting agent include a solvent and a lithium salt, the solvent is one or both of n-butyl ether or isobutyl ether; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide or a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; The chemical composition formula of the halide solid-state electrolyte is Li a M b X c , wherein M includes at least one selected from metal elements and semi-metal elements other than Li, and X includes at least one selected from F, Cl, Br, and I. The concentration of the lithium salt in the solvent is 2-3 mol / L.

2. The interface wetting agent of claim 1, wherein, The lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide, and the mole percentage of lithium bis(trifluoromethanesulfonyl)imide is greater than or equal to 50%.

3. The method for producing an interfacial wetting agent according to claim 1 or 2, characterized by, The method comprises the following steps: In an argon-filled glove box, the lithium salt is weighed and added to the solution and completely dissolved.

4. A lithium-ion or lithium battery comprising an interfacial wetting agent, characterized in that, The lithium ion battery or lithium battery comprises the interfacial wetting agent according to claim 1 or 2.

5. The lithium-ion or lithium battery according to claim 4, characterized in that The lithium ion battery or lithium battery is a halide solid electrolyte-high nickel positive electrode material system or a lithium-rich manganese-based high-voltage positive electrode material system.

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