A solid-state lithium metal battery negative electrode interface protection layer and preparation method thereof, solid-state lithium metal battery

Abstract

The present invention discloses a solid-state lithium metal battery negative electrode interface protection layer and a preparation method thereof, and a solid-state lithium metal battery, belonging to the technical field of solid-state lithium metal batteries. The solid-state lithium metal battery negative electrode interface protection layer of the present invention is obtained by mixing and rolling a lithium conductive material and polytetrafluoroethylene; the lithium conductive material is red phosphorus or black phosphorus, and the mass ratio of the lithium conductive material to polytetrafluoroethylene is (80-98): (2-20). The solid-state lithium metal battery obtained by assembling the solid-state lithium metal battery negative electrode interface protection layer provided by the present invention has excellent cycle stability, and the discharge capacity retention rate after 1000 cycles can still be higher than 80%, which is much higher than that of a solid-state lithium metal battery without an interface protection layer. In addition, the preparation method thereof is simple and easy, highly operable, and low-cost, and can be integrated into the existing solid-state lithium metal battery manufacturing process to achieve large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium metal batteries, and in particular to a solid-state lithium metal battery negative electrode interface protective layer and a preparation method thereof, and a solid-state lithium metal battery. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] With the rapid development of electric vehicles and large-scale energy storage technologies, lithium-ion batteries based on graphite anodes and liquid organic electrolytes have difficulty meeting the requirements of high energy density and safety simultaneously. Lithium metal batteries based on sulfide solid electrolytes significantly improve battery safety and energy density by replacing flammable and volatile organic electrolytes with inorganic solid electrolytes with high mechanical strength and thermal stability, and using lithium metal with high specific capacity as the anode material. However, the interfacial side reactions between the lithium metal anode and the sulfide solid electrolyte, high interfacial impedance, and lithium dendrite growth seriously affect the cycle life and electrochemical performance of sulfide-based solid-state lithium metal batteries.

[0004] Currently, there are two main methods for improving the interface problems between lithium metal anodes and sulfide solid electrolytes: one is to dope or coat the solid electrolyte, and the other is to modify the surface of the lithium metal anode to construct an interface buffer layer to improve the interfacial compatibility between the lithium metal anode and the solid electrolyte. Although the above strategies can alleviate the interface problems to a certain extent and promote the uniform deposition of lithium metal at the interface, at high current density, due to the insufficient lithium atom transfer rate within the lithium metal, interfacial voids are formed during the discharge process, destroying the trend of uniform deposition of lithium metal without dendrites, causing the lithium metal to begin to grow in a dendritic manner, eventually piercing the solid electrolyte, causing the battery to short circuit and the cycle performance to be slightly improved.

[0005] Therefore, how to construct an interface protection layer so that the assembled solid-state lithium metal battery still has good cycle performance at high current density is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention provides a solid-state lithium metal battery negative electrode interface protection layer and a preparation method thereof, and a solid-state lithium metal battery. The interface protection layer provided by the present invention has the characteristics of ion / electron mixed conductivity, inducing lithium metal to be uniformly deposited inside the interface layer, isolating the side reactions between lithium metal and sulfide solid electrolyte, thereby significantly improving the cycle performance of the all-solid-state battery.

[0007] In a first aspect, the present invention provides a solid-state lithium metal battery negative electrode interface protective layer, which is obtained by mixing and rolling a lithium conductive material and polytetrafluoroethylene; the lithium conductive material is red phosphorus or black phosphorus, and the mass ratio of the lithium conductive material to polytetrafluoroethylene is (80-98):(2-20).

[0008] Preferably, the mass ratio of the lithium conductive material to polytetrafluoroethylene is (85-95):(5-15).

[0009] Preferably, the molecular weight of the polytetrafluoroethylene is greater than 1,000,000 g / mol.

[0010] In a second aspect, the present invention provides a method for preparing the above-mentioned solid-state lithium metal battery negative electrode interface protective layer, comprising the following steps:

[0011] The lithium conductive material is ball-milled in an inert atmosphere, and the ball-milled lithium conductive material is ground and mixed with polytetrafluoroethylene, pressed into a film, and then rolled to a specified thickness to obtain the film.

[0012] Preferably, the grinding, mixing and pressing film-forming steps are performed under an inert atmosphere.

[0013] Furthermore, the inert atmosphere in the ball milling step and the grinding, mixing and pressing film forming step is selected from one or both of argon and nitrogen.

[0014] Preferably, the ball milling speed in the ball milling step is 200-400 rpm, the ball milling time is 8-15 hours, and the ball-to-material ratio is (20-40):1.

[0015] Preferably, the thickness is rolled to 30 to 100 μm.

[0016] In a third aspect, the present invention provides a solid-state lithium metal battery, comprising a positive electrode, a sulfide solid electrolyte layer, an interface protection layer, and a metal lithium negative electrode;

[0017] The sulfide solid electrolyte layer is arranged between the positive electrode and the metal lithium negative electrode, and the interface protection layer is arranged between the sulfide solid electrolyte layer and the metal lithium negative electrode. The interface protection layer is the above-mentioned solid-state lithium metal battery negative electrode interface protection layer.

[0018] In a fourth aspect, the present invention provides a method for preparing the above-mentioned solid-state lithium metal battery, comprising the following steps:

[0019] S1. Pressing a sulfide solid electrolyte material to obtain a sulfide solid electrolyte layer;

[0020] S2. Placing an interface protection layer and a cathode material on both sides of the sulfide solid electrolyte layer, respectively, and pressing to obtain a three-layer structure of interface protection layer-sulfide solid electrolyte layer-cathode;

[0021] S3. Place a lithium sheet on one side of the interface protective layer and press it.

[0022] Preferably, the pressing pressure in step S1 is 50-150 MPa, the pressing pressure in step S2 is 300-400 MPa, and the pressing pressure in step S3 is 150-250 MPa.

[0023] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0024] (1) The lithium-conducting material in the negative electrode interface protection layer of the solid-state lithium metal battery provided by the present invention can form Li3P that quickly conducts lithium ions after lithiation, accelerate the lithium ion transmission rate, and uniformize the lithium ion concentration; polytetrafluoroethylene, on the one hand, acts as a binder to form a film of the lithium-conducting material, and on the other hand, is reduced to form carbon and LiF when in contact with lithium metal. The carbon increases the electronic conductivity of the interface protection layer and uniformizes the electric field distribution. LiF has high interfacial energy and can inhibit the growth of lithium dendrites; thereby, the solid-state lithium metal battery assembled by the assembly has excellent cycle stability, and the discharge capacity retention rate after 1000 cycles can still be higher than 80%, which is much higher than that of a solid-state lithium metal battery without an interface protection layer (less than 30%).

[0025] (2) The preparation method of the negative electrode interface protective layer of the solid-state lithium metal battery of the present invention is simple and easy, highly operable, and low-cost, and can be integrated into the existing solid-state lithium metal battery manufacturing process to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute undue limitations thereon. It is obvious that one of ordinary skill in the art could derive other drawings based on these drawings without inventive effort.

[0027] Figure 1 The XRD patterns of the initial red phosphorus, the ball-milled red phosphorus, and the lithiated red phosphorus in Example 1 of the present invention are shown;

[0028] Figure 2 This is the critical current density curve of the solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention;

[0029] Figure 3 This is the critical current density curve of the solid-state lithium metal battery without an interface protective layer prepared in Comparative Example 1 of the present invention;

[0030] Figure 4 This is a rate diagram of a solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention;

[0031] Figure 5 This is a cycle diagram of a solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0033] The present invention provides a solid-state lithium metal battery negative electrode interface protection layer, which is obtained by mixing and rolling a lithium conductive material and polytetrafluoroethylene; the lithium conductive material is red phosphorus or black phosphorus, and the mass ratio of the lithium conductive material to polytetrafluoroethylene is (80-98):(2-20).

[0034] In the interface protective layer of the negative electrode of the solid-state lithium metal battery of the present invention, the lithium-conducting material can form Li3P that quickly conducts lithium ions after being lithiated, thereby accelerating the lithium ion transmission rate and homogenizing the lithium ion concentration. On the one hand, polytetrafluoroethylene acts as a binder to form a film of the lithium-conducting material, and on the other hand, it is reduced to form carbon and LiF when in contact with lithium metal. The carbon increases the electronic conductivity of the interface protective layer and homogenizes the electric field distribution. LiF has high interfacial energy and can inhibit the growth of lithium dendrites. However, polyvinylidene fluoride (PVDF), a common binder in batteries, is difficult to form a film using the method of the present invention. Although the non-fluorine binder polyacrylonitrile (PAN) can react with lithium metal to form Li3N and accelerate interfacial lithium ion conduction, it is still likely to form lithium dendrites at high current density due to the limited lithium atom transmission rate in lithium metal, and its cycle performance is relatively poor.

[0035] The solid-state lithium metal battery negative electrode interface protection layer of the present invention has the characteristics of ion / electron mixed conductivity, inducing lithium metal to be uniformly deposited inside the interface layer, isolating the side reactions between lithium metal and sulfide solid electrolyte, and improving the cycle performance of the all-solid-state battery.

[0036] The mass ratio of the lithium-conducting material to PTFE affects the final cycling performance of the solid-state lithium metal battery. If the PTFE content in the interface protection layer is too low, it will be difficult to form a stable conductive network, which will have an adverse effect on the battery's cycling performance. If the PTFE content in the interface protection layer is too high, lithium metal will be deposited at the interface between the interface protection layer and the solid electrolyte, and the interface protection layer will not be able to suppress lithium dendrites.

[0037] In the present invention, the mass ratio of the lithium conductive material to polytetrafluoroethylene is preferably (85-95):(5-15). Under the above mass ratio, the solid-state lithium metal battery exhibits a higher critical current density and discharge capacity retention rate.

[0038] In the present invention, the molecular weight of the polytetrafluoroethylene is 1000000 g mol -1 If the molecular weight of PTFE is too low, its film-forming property will be reduced, making it difficult to roll to a lower thickness.

[0039] The present invention also provides a method for preparing the above-mentioned solid-state lithium metal battery negative electrode interface protection layer, comprising the following steps:

[0040] The lithium conductive material is ball-milled in an inert atmosphere, and the ball-milled lithium conductive material is ground and mixed with polytetrafluoroethylene, pressed into a film, and then rolled to a specified thickness to obtain the film.

[0041] In the present invention, the grinding, mixing, and pressing film-forming steps are performed under an inert atmosphere. The inert atmosphere in the ball milling and grinding, mixing, and pressing film-forming steps is selected from one or both of argon and nitrogen, preferably argon. The inert atmosphere can prevent the lithium-conducting material from reacting with oxygen to form impurities during the ball milling and grinding, mixing, and pressing film-forming processes.

[0042] In the present invention, the ball milling speed of the ball milling step is 200-400 rpm, the ball milling time is 8-15 hours, and the ball-to-material ratio is (20-40): 1. The present invention does not impose any special restrictions on the ball milling material used in the ball milling process, and the ball milling material commonly used in the art can be used.

[0043] In the present invention, the thickness is rolled to 30 to 100 μm. Within the above thickness range, it can ensure that the interface lithium ion transmission is beneficial and at the same time ensure that the interface protection layer has a certain mechanical strength.

[0044] The present invention provides a solid-state lithium metal battery, comprising a positive electrode, a sulfide solid electrolyte layer, an interface protection layer and a metal lithium negative electrode;

[0045] The sulfide solid electrolyte layer is arranged between the positive electrode and the metal lithium negative electrode, and the interface protection layer is arranged between the sulfide solid electrolyte layer and the metal lithium negative electrode. The interface protection layer is the above-mentioned solid-state lithium metal battery negative electrode interface protection layer.

[0046] The solid-state lithium metal battery negative electrode interface protection layer of the present invention has the characteristics of ion / electron mixed conductivity, inducing metallic lithium to be uniformly deposited inside the interface protection layer, isolating the side reactions between metallic lithium and the sulfide solid electrolyte, thereby improving the cycle performance of the solid-state lithium metal battery. The discharge capacity retention rate after 1000 cycles can still be higher than 80%, which is much higher than that of the solid-state lithium metal battery without an interface protection layer (less than 30%).

[0047] The present invention does not impose any special restrictions on the positive electrode, and the positive electrode of the solid-state lithium metal battery commonly used in the art can be used. The active material in the positive electrode can be selected from one or more of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese oxide, lithium iron phosphate and lithium nickel manganese oxide. The present invention does not impose any special restrictions on the material of the sulfide solid electrolyte layer, and the sulfide solid electrolyte material commonly used in the art can be used, such as lithium sulfur phosphorus chloride fast ion conductor (Li6PS5Cl), lithium germanium phosphorus sulfur fast ion conductor (Li 10 GeP2S 12 ), lithium sulfur phosphorus fast ion conductor (Li7P3S 11 )wait.

[0048] The present invention also provides a method for preparing the above-mentioned solid-state lithium metal battery, comprising the following steps:

[0049] S1. Pressing a sulfide solid electrolyte material to obtain a sulfide solid electrolyte layer;

[0050] S2. Placing an interface protection layer and a cathode material on both sides of the sulfide solid electrolyte layer, respectively, and pressing to obtain a three-layer structure of interface protection layer-sulfide solid electrolyte layer-cathode;

[0051] S3. Place a lithium sheet on one side of the interface protective layer and press it.

[0052] In the present invention, the pressing pressure in step S1 is 50-150 MPa, the pressing pressure in step S2 is 300-400 MPa, and the pressing pressure in step S3 is 150-250 MPa.

[0053] The method for preparing the interface protective layer of the negative electrode of a solid-state lithium metal battery and the method for assembling a solid-state lithium metal battery using the same are both simple and easy to implement, low in cost, and easy to mass produce.

[0054] The technical solution of the present invention will be further described below in conjunction with specific embodiments. In the following embodiments, PTFE represents polytetrafluoroethylene.

[0055] Example 1

[0056] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0057] Step 1: Under argon atmosphere, 2.0 g of red phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0058] Step 2: Under an argon atmosphere, 950 mg of red phosphorus and 50 mg of PTFE (the mass ratio of red phosphorus to PTFE is 95:5) are continuously ground, mixed, and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protective layer; finally, it is cut into discs with a diameter of 10 mm and recorded as Li-95% RP.

[0059] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material (solid electrolyte is added to conduct lithium ions); 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-95% RP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0060] Example 2

[0061] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0062] Step 1: Under argon atmosphere, 2.0 g of red phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0063] Step 2: Under an argon atmosphere, 900 mg of red phosphorus and 100 mg of PTFE (the mass ratio of red phosphorus to PTFE is 90:10) are continuously ground, mixed, and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protective layer; finally, it is cut into discs with a diameter of 10 mm, recorded as Li-90% RP.

[0064] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-90% RP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0065] Example 3

[0066] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0067] Step 1: Under argon atmosphere, 2.0 g of red phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0068] Step 2: Under an argon atmosphere, 850 mg of red phosphorus and 150 mg of PTFE (the mass ratio of red phosphorus to PTFE is 95:5) are continuously ground, mixed, and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protective layer; finally, it is cut into discs with a diameter of 10 mm and recorded as Li-85% RP.

[0069] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-85% RP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0070] Example 4

[0071] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0072] Step 1: Under argon atmosphere, 2.0 g of black phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0073] Step 2: Under an argon atmosphere, 950 mg of black phosphorus and 50 mg of PTFE (the mass ratio of black phosphorus to PTFE is 95:5) are continuously ground, mixed and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protection layer; finally, it is cut into discs with a diameter of 10 mm, recorded as Li-95% BP.

[0074] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-95% BP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0075] Example 5

[0076] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0077] Step 1: Under argon atmosphere, 2.0 g of black phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0078] Step 2: Under an argon atmosphere, 900 mg of black phosphorus and 100 mg of PTFE (the mass ratio of black phosphorus to PTFE is 90:10) are continuously ground, mixed and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protective layer; finally, it is cut into discs with a diameter of 10 mm, recorded as Li-90% BP.

[0079] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-90% BP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0080] Example 6

[0081] This embodiment provides a method for preparing a negative electrode interface protection layer of a solid-state lithium metal battery and a method for assembling a solid-state lithium metal battery using the same.

[0082] Step 1: Under argon atmosphere, 2.0 g of black phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0083] Step 2: Under an argon atmosphere, 850 mg of black phosphorus and 150 mg of PTFE (the mass ratio of black phosphorus to PTFE is 95:5) are continuously ground, mixed and pressed in a mortar to completely bond the two materials into a film. Then, the film is rolled to a thickness of 30 μm in a roller press to obtain a solid-state lithium metal battery negative electrode interface protective layer; finally, it is cut into discs with a diameter of 10 mm and recorded as Li-85% BP.

[0084] Step 3: The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and the Li-85% BP interface protection layer obtained in step 2 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of interface protection layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the interface protection layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0085] Comparative Example 1

[0086] Compared with Example 1, this comparative example does not include the preparation of the interface protection layer.

[0087] The positive electrode active material LiCoO2 and the sulfide solid electrolyte Li6PS5Cl were weighed in a mass ratio of 70:30, and then fully ground using a mortar to obtain a composite positive electrode material; 100 mg of Li6PS5Cl sulfide solid electrolyte material was added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material was added to one side, and then pressurized at a pressure of 360 MPa to form a two-layer structure of sulfide solid electrolyte layer-positive electrode; then a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, was placed on the other side of the sulfide solid electrolyte layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0088] Comparative Example 2

[0089] Compared with Example 1, the difference is that this comparative example does not add polytetrafluoroethylene, and only uses red phosphorus as the interface protective layer. The specific steps are as follows:

[0090] Step 1: Under argon atmosphere, 2.0 g of red phosphorus material was ball-milled using zirconia balls with a diameter of 10 mm. The ball milling speed was set to 300 rpm, the ball milling time was 10 hours, and the ball-to-material ratio was 30:1.

[0091] Step 2: The positive electrode active materials LiCoO2 and Li6PS5Cl are weighed in a mass ratio of 70:30, and then fully ground in a mortar to obtain a composite positive electrode material; 100 mg of sulfide solid electrolyte material is added to an insulating outer cylinder with a diameter of 10 mm, and pressed under a pressure of 100 MPa to obtain a sulfide solid electrolyte layer; then 10 mg of the composite positive electrode material is added to one side, and 2 mg of the ball-milled red phosphorus obtained in step 1 is added to the other side, and then pressurized at a pressure of 360 MPa to form a three-layer structure of red phosphorus layer-sulfide solid electrolyte layer-positive electrode; finally, a lithium sheet with a diameter and thickness of 10 mm and 100 μm, respectively, is placed on the other side of the red phosphorus layer, and pressurized at a pressure of 200 MPa to obtain a solid-state lithium metal battery.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 1 is that polytetrafluoroethylene is replaced by polyacrylonitrile (PAN) in this comparative example.

[0094] Test example

[0095] The electrochemical performance tests were conducted on the solid-state lithium metal batteries of Examples 1 to 6 and Comparative Examples 1 to 3. The test results are shown in Table 1.

[0096] Table 1 Electrochemical properties of solid-state lithium metal batteries of Examples 1 to 6 and Comparative Examples 1 to 3

[0097]

[0098]

[0099] Note: The first-week discharge capacity in Table 1 was tested at a 1C rate, and the 1000-week discharge capacity retention was measured at a 20C rate, where 1C = 140 mAh / g.

[0100] The experimental results show that the solid-state lithium metal battery using the interface protective layer prepared by Examples 1 to 6 of the present invention has a higher critical current density and cycle stability. Compared with Comparative Example 2, the interface protective layer prepared by the present invention has the characteristics of mixed ion-electron conductivity after contact with lithium metal, can induce lithium metal to deposit in the protective layer, and has better electrochemical performance. Compared with Comparative Example 3, although PAN can react with lithium metal to form Li3N and accelerate interfacial lithium ion conduction, at high current density, it is limited by the lithium atom transfer rate in lithium metal, and lithium dendrites will still be formed.

[0101] Figure 1The XRD patterns of the red phosphorus in its initial state, after ball-milling, and after lithiating in Example 1 are shown. The lithiated red phosphorus refers to the interfacial protective layer removed from the assembled battery after 12 hours of rest, without charge-discharge testing. The figures show that upon contact with lithium metal, the red phosphorus film is lithiated to form Li3P, a fast-conducting lithium-conducting material, without requiring additional processing steps, making the process simple.

[0102] Figure 2 This is the critical current density curve of the solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention. Figure 3 The critical current density curve of the solid-state lithium metal battery without an interface protective layer prepared in Comparative Example 1 of the present invention shows that the use of the interface protective layer in Example 1 can better inhibit the formation of lithium dendrites and improve the interface stability between lithium metal and solid electrolyte.

[0103] Figure 4 This is a rate diagram of a solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention. Since the interface protection layer after lithiation has good ion and electron conductivity, the solid-state lithium metal battery using this interface protection layer exhibits excellent rate performance and can still provide 10.2 mAh g even at a rate of 50C. -1 Specific capacity. Figure 5 This is a cycle diagram of the solid-state lithium metal battery with an interface protection layer prepared in Example 1 of the present invention. It cycles stably for 1000 cycles at a rate of 20C without any short circuit.

[0104] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A solid-state lithium metal battery, characterized in that: It includes a positive electrode, a sulfide solid electrolyte layer, an interface protection layer and a metal lithium negative electrode; The sulfide solid electrolyte layer is arranged between the positive electrode and the metal lithium negative electrode, and the interface protection layer is arranged between the sulfide solid electrolyte layer and the metal lithium negative electrode; The interface protection layer is prepared by the following method: The lithium conductive material is ball-milled under an inert atmosphere, the ball-milled lithium conductive material is ground and mixed with polytetrafluoroethylene, pressed into a film, and then rolled to a thickness of 30-100 μm to obtain; The lithium conductive material is red phosphorus or black phosphorus, and the mass ratio of the lithium conductive material to polytetrafluoroethylene is (80-98):(2-20); The molecular weight of the polytetrafluoroethylene is greater than 1,000,000.

2. The solid-state lithium metal battery according to claim 1, wherein The mass ratio of the lithium conductive material to polytetrafluoroethylene is (85-95):(5-15).

3. The solid-state lithium metal battery according to claim 1, wherein The grinding, mixing and pressing film-forming steps are carried out under an inert atmosphere.

4. The solid-state lithium metal battery according to claim 3, wherein The inert atmosphere in the ball milling step and the grinding, mixing and pressing film forming step is selected from one or both of argon and nitrogen.

5. The solid-state lithium metal battery according to claim 1, wherein The ball milling speed of the ball milling step is 200-400 rpm, the ball milling time is 8-15 h, and the ball-to-material ratio is (20-40):

1.

6. The method for preparing a solid-state lithium metal battery according to any one of claims 1 to 5, characterized in that: The steps include: S1. Pressing a sulfide solid electrolyte material to obtain a sulfide solid electrolyte layer; S2. Placing an interface protection layer and a cathode material on both sides of the sulfide solid electrolyte layer, respectively, and pressing to obtain a three-layer structure of interface protection layer-sulfide solid electrolyte layer-cathode; S3. Place a lithium sheet on one side of the interface protective layer and press it.

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