Organic protective layer, preparation method and application thereof, anode for lithium metal battery and lithium metal battery

Abstract

The invention relates to the technical field of electrochemistry, in particular to an organic protective layer, a preparation method and application thereof, an anode for a lithium metal battery and the lithium metal battery. The organic protective layer provided by the invention is used as an organic protective layer of anode lithium metal of the lithium metal battery, the organic protective layer is used for covering the surface of the anode lithium metal, and the organic protective layer contains lithium-7, 7, 8, 8-tetracyano p-secondary methyl benzoquinone and / or lithium-tetracyano ethylene. According to the invention, the problems of lithium deposition and dendritic growth of the existing lithium metal battery anode material can be solved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more specifically to an organic protective layer, its preparation method and application, as well as an anode for lithium metal batteries and lithium metal batteries. Background Technology

[0002] With the increasing demand for clean energy and high-performance energy storage, lithium metal has attracted widespread attention as an anode material that can be widely used in lithium metal batteries. However, the practical application of lithium metal has been limited by problems such as lithium deposition and dendritic growth, which lead to decreased performance, reduced safety, and shortened cycle life of lithium metal batteries.

[0003] Traditional liquid electrolyte lithium metal batteries are often plagued by lithium deposition and dendritic growth issues, which not only affect battery performance but also pose safety hazards. To address these problems, existing research focuses on finding new methods and materials to improve the cycle stability and safety of lithium metal batteries.

[0004] Artificial solid electrolyte interphase (SEI) layers have proven to be an effective method to limit uneven lithium deposition and dendritic lithium dendrite growth, thereby improving the performance and safety of lithium metal batteries. However, current SEI layer construction methods still have problems, and there is a need to find simpler, lower-cost, and innovative methods to further improve the performance of lithium metal anodes. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of lithium deposition and dendritic growth in existing lithium metal battery anode materials, and to provide an organic protective layer, its preparation method and application, as well as an anode for lithium metal batteries and lithium metal batteries. Using the organic protective layer of this invention can effectively improve the performance and safety of lithium metal batteries. Furthermore, the organic protective layer of this invention also has the advantages of simple preparation process, stable technology, and low cost.

[0006] To achieve the above objectives, one aspect of the present invention provides an organic protective layer, wherein the organic protective layer is used as an organic protective layer for lithium metal anode in a lithium metal battery, the organic protective layer is used to cover the surface of the anode lithium metal, and the organic protective layer contains lithium-7,7,8,8-tetracyano-p-dimethylbenzoquinone (Li-TCNQ) and / or lithium-tetracyanoethylene (Li-TCNE).

[0007] Preferably, the thickness of the organic protective layer is 5-30 nm, and more preferably 8-15 nm.

[0008] According to a second aspect of the present invention, a method for preparing an organic protective layer is provided, wherein the organic protective layer is formed by depositing 7,7,8,8-tetracyano-p-dimethylbenzoquinone (TCNQ) and / or tetracyanoethylene (TCNE) on the surface of lithium metal anode in a lithium metal battery.

[0009] Preferably, the organic protective layer is formed by depositing TCNQ and / or TCNE on the lithium metal surface of the lithium metal anode of a lithium metal battery.

[0010] Preferably, the organic protective layer is formed by depositing a solution containing TCNQ and / or TCNE onto the lithium metal surface of the lithium metal anode in a lithium metal battery.

[0011] Preferably, the concentration of solute in the solution containing TCNQ and / or TCNE is 64-408 g / L.

[0012] Preferably, the solvent of the solution containing TCNQ and / or TCNE is one or more of dimethyl ether, ethylene glycol dimethyl ether, and ethylene carbonate.

[0013] Preferably, the solution containing TCNQ and / or TCNE is prepared in an inert gas environment with an H2O content of <0.01ppm.

[0014] Preferably, the deposition results in an organic protective layer with a thickness of 5-30 nm, more preferably 8-15 nm.

[0015] Preferably, the deposition is one or more of mechanical coating, manual application, and immersion, with mechanical coating being the preferred method.

[0016] Preferably, the anode lithium metal is lithium foil, and the thickness of the lithium foil is 0.35-0.75 mm, more preferably 0.6-0.75 nm.

[0017] According to a third aspect of the present invention, an anode for a lithium metal battery is provided, comprising anode lithium metal and an organic protective layer of the first aspect of the present invention covering the surface of the anode lithium metal.

[0018] According to a fourth aspect of the present invention, a lithium metal battery is provided, wherein it includes the anode for a lithium metal battery as described in the third aspect of the present invention.

[0019] According to a fifth aspect of the present invention, the application of the organic protective layer described in the first aspect of the present invention in the preparation of an anode and a lithium metal battery is provided.

[0020] Through the above technical solutions, the organic protective layer of the lithium metal battery anode material of the present invention can effectively improve the performance and safety of lithium metal batteries, and also has the advantages of simple preparation process, stable process and low cost. Attached Figure Description

[0021] Figure 1 This represents the capacity retention rate change results of the lithium metal batteries obtained in Example 1 and Comparative Example 1 during constant current charge-discharge cycle testing.

[0022] Figure 2 This indicates that the button cell using the disk sample obtained in Example 1 as the anode... Figure 1 An anodic electron microscope image was obtained by disassembling the battery in a glove box filled with argon gas and with water and oxygen content kept below 1 ppm after 150 charge-discharge cycles.

[0023] Figure 3 This indicates that the button cell using the disk sample obtained in Comparative Example 1 as the anode... Figure 1 An anodic electron microscope image was obtained by disassembling the battery in a glove box filled with argon gas and with water and oxygen content kept below 1 ppm after 150 charge-discharge cycles. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The first aspect of the present invention provides an organic protective layer, wherein the organic protective layer is used as an organic protective layer for lithium metal anode in a lithium metal battery, the organic protective layer is used to cover the surface of the anode lithium metal, and the organic protective layer contains lithium-7,7,8,8-tetracyano-p-dimethylbenzoquinone (Li-TCNQ) and / or lithium-tetracyanoethylene (Li-TCNE).

[0026] According to the present invention, the thickness of the organic protective layer is 5-30 nm, preferably 8-15 nm, and more preferably 8-13 nm. By making the thickness of the organic protective layer within the above range, it has high-speed channels for lithium ions, and the uniform SEI surface avoids uneven precipitation of "dead lithium" and the growth of lithium dendrites. At the same time, its application in lithium metal batteries significantly improves their coulombic efficiency and stability.

[0027] According to a second aspect of the present invention, a method for preparing an organic protective layer is provided, wherein the organic protective layer is formed by depositing TCNQ and / or TCNE on the surface of lithium metal anode in a lithium metal battery.

[0028] According to the present invention, preferably, the organic protective layer is formed by depositing a solution containing TCNQ and / or TCNE onto the lithium metal surface of the lithium metal anode of a lithium metal battery. By depositing TCNQ and / or TCNE onto the lithium metal surface of the lithium metal anode of a lithium metal battery, TCNQ and / or TCNE can react with metallic lithium to generate the organic protective layer containing Li-TCNQ and / or Li-TCNE.

[0029] Specifically, a solution containing TCNQ and / or TCNE can react rapidly with lithium metal at the anode. The resulting Li-TCNQ and / or Li-TCNE can easily and quickly form a protective layer through deposition. The reaction time is usually completed within about 60-180 seconds.

[0030] According to the present invention, in order to enable the solution containing TCNQ and / or TCNE to react better with the anode lithium metal, the concentration of solute in the solution containing TCNQ and / or TCNE can be 64-408 g / L; preferably, the concentration of solute in the solution containing TCNQ and / or TCNE is 128-204 g / L.

[0031] Preferably, the solvent of the solution containing TCNQ and / or TCNE is one or more of dimethyl ether, ethylene glycol dimethyl ether, and ethylene carbonate;

[0032] Preferably, the solution containing TCNQ and / or TCNE is prepared in an inert gas environment with an H2O content of <0.01ppm.

[0033] In this invention, by formulating in an inert gas environment, the oxidation of TCNQ and / or TCNE solutions and lithium metal can be suppressed; by formulating in an environment with H2O content <0.01ppm, the reaction of TCNQ and / or TCNE solutions and lithium metal with moisture in the air can be suppressed.

[0034] According to the present invention, the thickness of the organic protective layer formed by the deposition is 5-30 nm, preferably 10-12 nm.

[0035] In this invention, the thickness of the organic protective layer is 5-30 nm, preferably 8-15 nm, and more preferably 8-13 nm. By making the thickness of the organic protective layer within the above range, it provides high-speed channels for lithium ions, and the uniform SEI surface avoids uneven deposition of "dead lithium" and the growth of lithium dendrites. Furthermore, its application in lithium metal batteries significantly improves battery performance and safety, as well as greatly enhances coulombic efficiency and stability.

[0036] According to the present invention, the deposition is one or more of mechanical coating, manual coating, and immersion, preferably mechanical coating. Specifically, when the lithium metal battery electrode is circular or square, it can be spin-coated using a spin coater.

[0037] In this invention, the anode lithium metal can be lithium foil, and the thickness of the lithium foil is 350-750 nm, preferably 600-750 nm.

[0038] According to the present invention, when the thickness of the lithium foil is within the above range, sufficient thickness can be ensured for the reaction to generate and support the organic protective film.

[0039] According to a third aspect of the present invention, an anode for a lithium metal battery is provided, comprising an anode lithium metal and an organic protective layer as described in the first aspect of the present invention covering the surface of the anode lithium metal.

[0040] In this invention, by using an anode comprising lithium metal and an organic protective layer covering the surface of the lithium metal anode, problems such as lithium-ion shuttle obstruction, uneven precipitation of "dead lithium" and growth of lithium dendrites can be avoided, thereby improving the performance and safety of lithium metal batteries.

[0041] According to a fourth aspect of the present invention, a lithium metal battery is provided, wherein it includes the anode for a lithium metal battery as described in the third aspect of the present invention.

[0042] According to a fifth aspect of the present invention, the application of the organic protective layer described in the first aspect of the present invention in the preparation of an anode and a lithium metal battery is provided.

[0043] In this invention, the application of an organic protective layer in the anode and lithium metal battery of the present invention effectively improves the problem of reduced specific capacity after charge-discharge cycles, while maintaining a stable overpotential after cycling. Furthermore, it effectively improves lithium deposition on the anode metal surface and dendritic lithium dendrite growth at the electrolyte interface. Therefore, the application of the organic protective layer of this invention in the anode and lithium metal battery of the present invention effectively improves the cycle performance and safety of lithium metal batteries.

[0044] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0045] Example 1

[0046] (1) Prepare lithium metal substrate

[0047] First, the lithium foil is cut into squares with a side length of 18mm and placed on a polymethyl methacrylate (PMMA) plate to obtain the working substrate.

[0048] (2) Preparation of organic solutions

[0049] 2.04 g of TCNQ powder was dissolved in 10 mL of DME to make the molar concentration of organic matter in the mixed solution 1 mol / L. The mixture was magnetically stirred for 60 min (magnetic stirrer, Shanghai Kexing Instrument Co., Ltd., MSP-2C) to ensure that the organic powder was mixed evenly in the solution. This step was completed entirely in a hand-operated box filled with Ar and with H2O content <0.01 ppm (four-port hand-operated box, Than Tech Innovation Co., Ltd., KK-021AS).

[0050] (3) Coating with organic solution

[0051] Deposit organic thin films on the PMMA plate with lithium metal placed in step (1), turn on the spin coater (spin coater, Rhabdos, SF-100ND), set the speed to 300 rpm, and make the PMMA plate rotate smoothly and at a constant speed.

[0052] (4) Deposition to form an organic protective film

[0053] Take 40 μL of the 1 mol / L TCNQ DME solution from step (2) and add it dropwise to deposit on the lithium foil surface to ensure uniform deposition.

[0054] (5) Drying the sample

[0055] The obtained lithium sample was dried in a vacuum chamber under manual operation for 1 hour, and then stamped into a disc sample A1 with a diameter of 12 mm. The thickness of the organic protective layer was approximately 13 nm. The thickness of the organic protective layer was determined by observing the cross-section of the disc sample using a scanning electron microscope (JEOL, JMS-7000F).

[0056] (6) The obtained disk sample was used as the anode, and LiNi was employed. 0.6 Co 0.2 Mn 0.2 Using O2 (NCM622) as the cathode, a 2032-type button cell was fabricated and assembled in a glove box filled with argon gas while maintaining water and oxygen levels below 1 ppm. Polyethylene (PE) was used as the separator. The NCM622 electrode consisted of NCM622, carbon black, and PVDF in a weight ratio of 8:1:1. An electrolyte was prepared in the glove box by dissolving 1.0 mol / L lithium hexafluorophosphate (LiPF6) in a 1:1 volume ratio in a solvent mixture of ethylene carbonate and diethyl carbonate (EC / DEC) to obtain the electrolyte for the 2032-type button cell. Finally, the cells were encapsulated using a manual button cell sealing press to prepare the lithium metal battery.

[0057] The obtained battery was tested under constant current charge-discharge cycle (Maccor, SERIES-4000), and its initial capacity was 133.6 mAh / g, with a capacity retention rate of 82% after 150 cycles.

[0058] An anodic electron microscope (AEM) image (JEOL, JMS-7000F) obtained by disassembling the battery after 150 cycles in a glove box filled with argon gas and maintaining water and oxygen content below 1 ppm. The results are as follows. Figure 2 As shown.

[0059] Electron micrographs were obtained according to the method in Example 1. Figure 2 It is known that the lithium metal anode modified with the Li-TCNQ organic protective layer has a relatively smooth surface, which avoids dendrite growth that could puncture the diaphragm and cause safety issues.

[0060] Example 2

[0061] (1) Prepare lithium metal substrate

[0062] First, the lithium foil is cut into squares with a side length of 18mm and placed on a polymethyl methacrylate (PMMA) plate to obtain the working substrate.

[0063] (2) Preparation of organic solutions

[0064] Dissolve 2.04 g of TCNQ powder in 10 mL of DME to make the molar concentration of organic matter in the mixed solution 1 mol / L. Stir magnetically for 60 min (magnetic stirrer, MSP-2C) to mix the organic powder evenly in the solution to obtain a mixed solution. This step was completed entirely in a hand-operated box (four-port hand-operated box, KK-021AS) filled with Ar and with H2O content <0.01 ppm.

[0065] (3) Coating with organic solution

[0066] In step (1), place the PMMA plate containing lithium metal to deposit an organic film. Turn on the spin coater and set the speed to 3000 rpm to make the PMMA plate rotate smoothly and at a uniform speed.

[0067] (4) Deposition to form an organic protective film

[0068] Take 20 μL of the 1 mol / L TCNQ DME solution from step (2) and add it dropwise to deposit on the lithium foil surface to ensure uniform deposition.

[0069] (5) Drying the sample

[0070] The obtained lithium sample was dried in a vacuum chamber in a hand-operated box for 1 hour, and then stamped into a disc sample A2 with a diameter of 12 mm and an organic protective layer with a thickness of about 6 nm.

[0071] (6) Using the obtained disc sample as the anode and LiNi0.6Co0.2Mn0.2O2 (NCM622) as the cathode, a 2032-type button cell was prepared. Assembly was completed in a glove box filled with argon gas, with water and oxygen content maintained below 1 ppm, and polyethylene (PE) was used as the separator. The NCM622 electrode consisted of NCM622, carbon black, and PVDF in a weight ratio of 8:1:1. 1.0 mol / L lithium hexafluorophosphate (LiPF6) was dissolved in a solvent mixture of ethylene carbonate and diethyl carbonate (EC / DEC) in a 1:1 volume ratio to prepare the electrolyte for the 2032-type button cell. Finally, the cell was encapsulated using a manual button cell sealing press to prepare the lithium metal battery.

[0072] The battery was subjected to constant current charge-discharge cycle testing, and its initial capacity was 132.7 mAh / g, with a capacity retention rate of 71% after 150 cycles.

[0073] Electron micrographs were obtained according to the method in Example 1. The electron micrographs show that the lithium metal anode modified with the Li-TCNQ organic protective layer has a relatively smooth surface, which avoids dendrite growth that could cause the membrane to puncture and lead to safety issues.

[0074] Example 3

[0075] (1) Prepare lithium metal substrate

[0076] First, the lithium foil is cut into squares with a side length of 18mm and placed on a polymethyl methacrylate (PMMA) plate to obtain the working substrate.

[0077] (2) Preparation of organic solutions

[0078] Dissolve 2.04 g of TCNQ powder in 10 mL of DME to make the molar concentration of organic matter in the mixed solution 1 mol / L. Stir magnetically for 60 min to mix the organic powder evenly in the solution to obtain a mixed solution. This step is completed in a hand-operated box filled with Ar and H2O content <0.01 ppm.

[0079] (3) Coating with organic solution

[0080] In step (1), place the PMMA plate containing lithium metal to deposit an organic film. Turn on the spin coater and set the speed to 3000 rpm to make the PMMA plate rotate smoothly and at a uniform speed.

[0081] (4) Deposition to form an organic protective film

[0082] Take 80 μL of the 1 mol / L TCNQ DME solution from step (2) and add it dropwise to deposit on the lithium foil surface to ensure uniform deposition.

[0083] (5) Drying the sample

[0084] The obtained lithium sample was dried in a vacuum chamber in a hand-operated box for 1 hour, and then stamped into a disc sample A3 with a diameter of 12 mm and an organic protective layer thickness of 24 nm.

[0085] (6) The obtained disk sample was used as the anode, and LiNi was employed. 0.6 Co 0.2 Mn 0.2 Using O2 (NCM622) as the cathode, a 2032-type button cell was fabricated and assembled in a glove box filled with argon gas while maintaining water and oxygen levels below 1 ppm. Polyethylene (PE) was used as the separator. The NCM622 electrode consisted of NCM622, carbon black, and PVDF in a weight ratio of 8:1:1. An electrolyte was prepared in the glove box by dissolving 1.0 mol / L lithium hexafluorophosphate (LiPF6) in a 1:1 volume ratio in a solvent mixture of ethylene carbonate and diethyl carbonate (EC / DEC) to obtain the electrolyte for the 2032-type button cell. Finally, the cells were encapsulated using a manual button cell sealing press to prepare the lithium metal battery.

[0086] The battery was subjected to constant current charge-discharge cycle testing, and its initial capacity was 125.5 mAh / g. After 150 cycles, the capacity retention rate was approximately 67%.

[0087] Electron micrographs were obtained according to the method in Example 1. The electron micrographs show that the lithium metal anode modified with the Li-TCNQ organic protective layer has a relatively smooth surface, which avoids dendrite growth that could cause the membrane to puncture and lead to safety issues.

[0088] Example 4

[0089] The method of Example 1 was followed, except that TCNQ powder was replaced with TCNE powder, and the same disk sample D2 was obtained, with an organic protective layer thickness of about 8 nm.

[0090] The battery was subjected to constant current charge-discharge cycle testing, and its initial capacity was 134.0 mAh / g, with a capacity retention rate of 81% after 150 cycles.

[0091] Electron micrographs were obtained according to the method in Example 1. The electron micrographs show that the lithium metal anode modified with the Li-TCNE organic protective layer has a relatively smooth surface, which avoids dendrite growth that could cause the membrane to puncture and lead to safety issues.

[0092] Comparative Example 1

[0093] The method of Example 1 was followed, except that the step of forming an organic protective layer was not performed, and the same disk sample D1 was obtained.

[0094] The battery was subjected to constant current charge-discharge cycle testing, and its initial capacity was 106.1 mAh / g, with a capacity retention rate of 22% after 150 cycles.

[0095] Electron micrographs were obtained using the same method as in Example 1. Figure 3 The electron microscope images show that the unmodified lithium metal anode has a large number of irregular dendrites on its surface.

[0096] By comparing Example 1 and Comparative Example 1, it can be seen that under a certain current density and constant charge-discharge, the modified anode exhibits excellent stability. Compared to Comparative Example 1, its capacity decay is slower, and after 150 cycles, it retains approximately 4.7 times the capacity of the battery in Comparative Example 1. This further demonstrates that by using an anode with an organic protective layer covering the lithium metal surface, problems such as lithium-ion shuttle barrier, uneven deposition of "dead lithium," and lithium dendrite growth can be avoided, thereby improving the performance and safety of lithium metal batteries.

[0097] also, Figure 2 and Figure 3 Button cells using the disk samples obtained in Example 1 and Comparative Example 1 as anodes, respectively. Figure 1 An anodic electron microscope image was obtained by disassembling the battery in a glove box filled with argon gas and with water and oxygen content kept below 1 ppm after 150 charge-discharge cycles. Figure 3 This indicates that the unmodified lithium metal anode has a large number of irregular dendrites on its surface, while Figure 2 The lithium metal anode modified with a Li-TCNQ organic protective layer has a relatively smooth surface, which avoids the growth of dendrites that could puncture the diaphragm and cause safety issues.

[0098] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An organic protective layer, characterized in that, The organic protective layer is used as an organic protective layer for the lithium metal anode of a lithium metal battery. The organic protective layer is used to cover the surface of the lithium metal anode, and the organic protective layer contains lithium-7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or lithium-tetracyanoethylene.

2. The organic protective layer according to claim 1, wherein, The thickness of the organic protective layer is 5-30 nm, preferably 8-15 nm.

3. A method for preparing an organic protective layer, characterized in that, This organic protective layer is formed by depositing 7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or tetracyanoethylene on the lithium metal surface of the lithium metal anode in a lithium metal battery.

4. The method according to claim 3, wherein, The organic protective layer is formed by depositing a solution containing 7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or tetracyanoethylene onto the lithium metal surface of the lithium metal anode in a lithium metal battery.

5. The method according to claim 4, wherein, The concentration of the solute in the solution containing 7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or tetracyanoethylene is 64-408 g / L. Preferably, the solvent of the solution containing 7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or tetracyanoethylene is one or more of dimethyl ether, ethylene glycol dimethyl ether and ethylene carbonate; Preferably, the solution containing 7,7,8,8-tetracyano-p-dimethylbenzoquinone and / or tetracyanoethylene is prepared in an inert gas environment with an H2O content of <0.01ppm; Preferably, the deposition results in an organic protective layer with a thickness of 5-30 nm; more preferably 8-15 nm.

6. The method according to any one of claims 3-5, wherein, The deposition is one or more of mechanical coating, manual application, and immersion, preferably mechanical coating.

7. The method according to any one of claims 3-5, wherein, The anode lithium metal is lithium foil, and the thickness of the lithium foil is 0.35-0.75 mm, preferably 0.6-0.75 mm.

8. An anode for a lithium metal battery, characterized in that, It includes an anode lithium metal and an organic protective layer as described in claim 1 or 2 covering the surface of the anode lithium metal.

9. A lithium metal battery, characterized in that, It includes the anode for lithium metal batteries as described in claim 8.

10. The use of the organic protective layer according to claim 1 or 2 in the preparation of the anode of a lithium metal battery and in the lithium metal battery.

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