Method for improving interface stability of sulfide all-solid-state battery

Abstract

The invention discloses a method for improving the interface stability of a sulfide all-solid-state battery. The method comprises the following steps: (1) mixing a positive electrode material and perfluorohexyl iodoalkane, and uniformly grinding; and (2) heating the mixture obtained in the step (1) under a vacuum condition to obtain the modified positive electrode material, (3) mixing the modified positive electrode material obtained in the step (2) with a part of sulfide solid electrolyte to obtain a composite positive electrode; and (4) assembling the composite positive electrode obtained in the step (3), the other part of sulfide solid electrolyte and a metal lithium negative electrode into an all-solid-state battery. The stability of the sulfide solid electrolyte is improved, and the cycling stability of the all-solid-state battery is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and in particular relates to a method for improving the interface stability of all-solid-state batteries. Background Art

[0002] In recent years, all-solid-state batteries based on sulfide solid electrolytes have been widely studied. All-solid-state batteries avoid safety accidents such as battery combustion and explosion that may be caused by traditional liquid electrolytes. At the same time, solid-state batteries use metallic lithium as the negative electrode, and the theoretical energy density is greatly improved compared to traditional lithium-ion batteries.

[0003] However, all-solid-state batteries face some challenges in their applications, mainly the interface stability between sulfide solid electrolytes and positive electrodes (mainly high-voltage positive electrode materials). Sulfide electrolytes are thermodynamically unstable, and when in contact with high-voltage positive electrode materials, the electrolytes are prone to irreversible decomposition, generating ionic conductive inert products such as elemental sulfur or lithium sulfide, which increase battery impedance, causing battery capacity decay or even short circuit.

[0004] To address this issue, researchers have done a lot of work: targeting the cathode interface, using magnetron sputtering, high-temperature sintering and other methods to form LiCoO 2 ,LiNi 0.7 Co 0.1 Mn 0.2 O 2 LiNbO coated on the surface of high voltage inorganic cathode materials 2 Oxides such as lithium niobate, because lithium niobate can effectively adjust the internal electric field structure of the electrolyte and enhance the electric field strength in the direction of ion transport, thereby achieving a significant increase in ionic conductivity.

[0005] Although the above method can alleviate the decomposition of sulfide electrolytes to a certain extent, the cost is too high and is not conducive to industrialization. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method for improving the interface stability of all-solid-state batteries that is simple, easy to operate, economical and environmentally friendly, which can effectively inhibit the decomposition of sulfide solid electrolytes and greatly improve the cycle stability of all-solid-state batteries based on sulfide solid electrolytes.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for improving the interface stability of a sulfide all-solid-state battery comprises the following steps:

[0009] (1) mixing the positive electrode material and perfluorohexyl iodine and grinding them evenly;

[0010] (2) Heat the mixture obtained in step (1) under vacuum conditions to obtain a modified cathode material;

[0011] (3) Mix the modified cathode material obtained in step (2) with a part of the sulfide solid electrolyte to obtain a composite cathode;

[0012] (4) Assemble the composite cathode obtained in step (3) with another part of the sulfide solid electrolyte and a lithium metal anode to form a all-solid-state battery.

[0013] As a preferred technical solution, in step (1), the cathode material is an organic cathode material or an inorganic cathode material.

[0014] As a preferred technical solution, in step (1), the cathode material is CuTCNQ or LiCoO 2 .

[0015] As a preferred technical solution, in step (1), the mass ratio of perfluorohexyl iodide to the cathode material is 2:1 - 5:1.

[0016] As a preferred technical solution, in step (2), the heating temperature is 100 - 200 °C and the heating time is 30 - 60 min.

[0017] As a preferred technical solution, in steps (3) and (4), the sulfide solid electrolyte is Li 6 PS 5 Cl, Li 10 GeP 2 S 12 , Li 7 PS 6 , Li 4 SnS 4 and Li 2 S-P 2 S 5 or several of them.

[0018] The beneficial effects of the present invention are as follows:

[0019] In the present invention, a layer of organic fluoride (perfluorohexyl iodide) is coated on the surface of the cathode material to obtain a modified cathode material. Then, the modified cathode material is compounded with the sulfide solid electrolyte. After the perfluorohexyl iodide on the surface of the modified cathode material contacts the sulfide solid electrolyte, LiF will be in-situ generated to inhibit the decomposition of the sulfide solid electrolyte, improve the stability of the sulfide solid electrolyte, and greatly improve the cycle stability of the all-solid-state battery. Description of the Drawings

[0020] In order to make the objectives, technical solutions, and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0021] Figure 1 For C 6 F 13 Schematic diagram of CuTCNQ treated by F

[0022] Figure 2 For the TEM of CuTCNQ-4 sample ( Figure 2 a), SEM ( Figure 2 b) and energy spectrum diagram ( Figure 2 c-f);

[0023] Figure 3 For the F 1s XPS diagram of CuTCNQ-4 sample ( Figure 3 a) and the F 1s XPS diagram after the combination of CuTCNQ-4 and LPSC ( Figure 3 b);

[0024] Figure 4 For the S 2p XPS diagram after the combination of CuTCNQ-0 and LPSC ( Figure 4 a) and the S 2p XPS diagram after the combination of CuTCNQ-4 and LPSC ( Figure 4 b);

[0025] Figure 5 For the rate performance diagrams of the all-solid-state batteries in Example 1 and Comparative Example 1 ( Figure 5 a-c) and cycling diagrams ( Figure 5 d);

[0026] Figure 6 For the GITT of the all-solid-state batteries in Example 1 and Comparative Example 1 ( Figure 6 a), polarization voltage ( Figure 6 b-c) and pressure test for the first 3 cycles ( Figure 6 d) and variation diagrams ( Figure 6 d-f);

[0027] Figure 7 For the cycling performance curves of the all-solid-state batteries in Example 2 and Comparative Example 2 ( Figure 7 a) and rate performance curves ( Figure 7 b). Detailed implementation manners

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments given are not intended to limit the present invention.

[0029] In the following embodiments, the sulfide solid electrolyte is Li 6 PS 5Taking Cl(LPSC) as an example, the positive electrode material is the organic positive electrode material CuTCNQ and the inorganic positive electrode material LiCoO 2 as an example.

[0030] Example 1

[0031] (1) Mix perfluorohexyl iodide C 6 F 13 I and the positive electrode material CuTCNQ in a mass ratio of 4:1, and grind them evenly;

[0032] (2) As Figure 1 shown, heat the mixture obtained in step (1) at 150 °C for 60 min under vacuum conditions to obtain a modified positive electrode material, named CuTCNQ-4;

[0033] (3) Mix CuTCNQ-4, LPSC, and Super P in a weight ratio of 2:7:1, and grind them to obtain a composite positive electrode;

[0034] (4) Use a battery mold composed of a polyether ether ketone sealing shell and a titanium alloy metal column. Put 80 mg of LPSC into the mold and cold press it at 300 MPa for 5 min; then evenly spread about 5 mg of the composite positive electrode on one side of the surface and cold press it at a pressure of 370 MPa for 5 min; subsequently, place a metal lithium sheet with a diameter of 10 mm on the other side, cold press it at a pressure of 50 MPa for 3 min and tighten the mold to assemble a all-solid-state battery.

[0035] Comparative Example 1

[0036] (1) Untreated CuTCNQ, named CuTCNQ-0;

[0037] (2) Mix CuTCNQ-0, LPSC, and Super P in a weight ratio of 2:7:1, and grind them to obtain a composite positive electrode;

[0038] (3) Use a battery mold composed of a polyether ether ketone sealing shell and a titanium alloy metal column. Put 80 mg of LPSC into the mold and cold press it at 300 MPa for 5 min; then evenly spread about 5 mg of the composite positive electrode on one side of the surface and cold press it at a pressure of 370 MPa for 5 min; subsequently, place a metal lithium sheet with a diameter of 10 mm on the other side, cold press it at a pressure of 50 MPa for 3 min and tighten the mold to assemble a all-solid-state battery.

[0039] The CuTCNQ-0 sample before treatment and the CuTCNQ-4 sample after treatment were characterized using an X-ray diffractometer and infrared spectroscopy. The charge-discharge tests were performed on the all-solid-state batteries of Example 1 and Comparative Example 1 using a charge-discharge instrument, and cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests were carried out on the batteries using an electrochemical workstation.

[0040] Figure 2 TEM images of the CuTCNQ-4 sample ( Figure 2 a), SEM images ( Figure 2 b), and energy-dispersive spectroscopy maps ( Figure 2 c-f); As can be seen from Figure 2 a, a protective amorphous layer with a thickness of about 50 nm covered the surface of the CuTCNQ after C 6 F 13 I treatment, and Figure 2 c-f show obvious distributions of F and I elements on the surface of CuTCNQ, indicating that the surface of CuTCNQ was coated with a C 6 F 13 I organic layer.

[0041] Figure 3 F 1s XPS spectra of the CuTCNQ-4 sample ( Figure 3 a) and the F 1s XPS spectra of the composite of CuTCNQ-4 and LPSC ( Figure 3 b); Figure 3 The results show that the binding energy of the C-F bond could be detected on the surface of the CuTCNQ treated with C 6 F 13 I, further indicating that the surface of CuTCNQ was coated with C 6 F 13 I; After being compounded with the sulfide solid electrolyte, Li-F could be detected on the surface, indicating that LiF was in-situ generated by the reaction of the electrolyte with C 6 F 13 I.

[0042] Figure 4 S 2p XPS spectra of the composite of CuTCNQ-0 and LPSC ( Figure 4 a) and the S 2p XPS spectra of the composite of CuTCNQ-4 and LPSC ( Figure 4 b); Figure 4 The results show that the peak of SO 4 2- was detected on the surface of the untreated CuTCNQ after being compounded with the sulfide solid electrolyte, and no SO was detected on the surface of the C 6 F 13 I-treated CuTCNQ after being compounded with the sulfide solid electrolyte.4 2- The peak indicates that the coated C 6 F 13 I-treated CuTCNQ improves the stability of the sulfide solid-state electrolyte.

[0043] Figure 5 are the rate graphs ([ Figure 5 a-c) and cycle graphs ([ Figure 5 d) of the all-solid-state batteries of Example 1 and Comparative Example 1; Figure 5 The results show that the coated C 6 F 13 I-treated CuTCNQ shows a significant improvement in the rate and cycle performance in the sulfide solid-state battery compared to the untreated CuTCNQ material.

[0044] Figure 6 are the GITT ([ Figure 6 a), polarization voltage ([ Figure 6 b-c), and pressure tests for the first 3 cycles ([ Figure 6 d) and variation graphs ([ Figure 6 d-f) of the all-solid-state batteries of Example 1 and Comparative Example 1; Figure 6 The results show that for the solid-state battery with C 6 F 13 I-treated CuTCNQ as the cathode material, the pressure change is smoother and the change in polarization voltage is smaller than that of the sulfide all-solid-state battery with the untreated CuTCNQ cathode material.

[0045] Example 2

[0046] (1) Mix perfluorohexyl iodide C 6 F 13 I and the cathode material LiCoO 2 in a mass ratio of 2:1 and grind evenly;

[0047] (2) Heat the mixture obtained in step (1) at 150 °C for 30 min under vacuum conditions to obtain a modified cathode material;

[0048] (3) Mix the modified cathode material, LPSC, and Super P in a weight ratio of 2:7:1 and grind to obtain a composite cathode;

[0049] (4) Use a battery mold composed of a polyether ether ketone sealing shell and a titanium alloy metal column. Place 80 mg of LPSC in the mold and cold press it at 300 MPa for 5 min; then evenly spread about 5 mg of the composite cathode on one side surface and cold press it at a pressure of 370 MPa for 5 min; subsequently, place a metal lithium sheet with a diameter of 10 mm on the other side, keep the pressure at 50 MPa for 3 min and tighten the mold to assemble an all-solid-state battery.

[0050] Comparative Example 2

[0051] (1) Untreated LiCoO 2 ;

[0052] (2) Mix the untreated LiCoO 2 , LPSC, and Super P in a weight ratio of 2:7:1, grind them to obtain a composite cathode;

[0053] (3) Use a battery mold composed of a polyether ether ketone sealing shell and a titanium alloy metal column. Put 80 mg of LPSC into the mold and cold press it at 300 MPa for 5 min; then evenly spread about 5 mg of the composite cathode on one side surface and cold press it at a pressure of 370 MPa for 5 min; subsequently, put a metal lithium sheet with a diameter of 10 mm on the other side, cold press it at a pressure of 50 MPa for 3 min and tighten the mold to assemble a all-solid-state battery.

[0054] Figure 7 Are the cyclic performance curves ( Figure 7 a) and rate performance curves ( Figure 7 b) of the all-solid-state batteries of Example 2 and Comparative Example 2; Figure 7 The results show that the C 6 F 13 I-treated LCO cathode has significantly improved rate and cyclic performance in sulfide solid-state batteries compared to the untreated LCO cathode.

[0055] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A method for improving the interface stability of sulfide all-solid-state batteries, characterized in that: The steps include: (1) mixing the positive electrode material and perfluorohexyl iodine and grinding them evenly; (2) heating the mixture obtained in step (1) under vacuum conditions to obtain a modified positive electrode material; (3) mixing the modified positive electrode material obtained in step (2) with a portion of the sulfide solid electrolyte to obtain a composite positive electrode; (4) Assembling an all-solid-state battery by combining the composite positive electrode obtained in step (3) with another part of the sulfide solid electrolyte and the metal lithium negative electrode.

2. The method for improving the interface stability of sulfide all-solid-state batteries according to claim 1, characterized in that: In the step (1), the positive electrode material is an organic positive electrode material or an inorganic positive electrode material.

3. The method for improving the interface stability of sulfide all-solid-state batteries according to claim 2, characterized in that: In the step (1), the positive electrode material is CuTCNQ or LiCoO2.

4. The method for improving the interface stability of sulfide all-solid-state batteries according to claim 1, characterized in that: In the step (1), the mass ratio of perfluorohexyl iodide to the positive electrode material is 2:1-5:

1.

5. The method for improving the interface stability of sulfide all-solid-state batteries according to claim 1, characterized in that: In the step (2), the heating temperature is 100-200° C. and the heating time is 30-60 min.

6. The method for improving the interface stability of sulfide all-solid-state batteries according to claim 1, characterized in that: In the steps (3) and (4), the sulfide solid electrolyte is Li6PS5Cl, Li 10 GeP2S 12 , Li7PS6, Li4SnS4 and Li2S-P2S5.

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