Lithium metal negative electrode modified with polymer on surface, and use thereof in all-solid-state battery

Abstract

The present invention relates to a lithium metal negative electrode modified with a polymer on the surface, and the use thereof in an all-solid-state battery. A preparation method for the lithium metal negative electrode comprises: S1, polymer preparation, involving: heating a monomer solution for reaction, so as to form a polymer; and S2, preparation of a polymer-modified lithium negative electrode, involving: dispersing the polymer obtained in step S1 in a solvent to form a polymer dispersion; and coating the surface of metal lithium with the polymer dispersion, and drying same to obtain a lithium metal negative electrode modified with a polymer on the surface. By means of a reaction between the polymer and lithium, an organic / inorganic hybrid SEI film is generated, thereby improving the stability of the lithium negative electrode, and solving the problem of metal lithium dendrites; in addition, the polymer is synthesized by using a one-step solvent method in the present invention, and the preparation method is simple and easy to implement and facilitates large-scale production.

Description

Polymer-modified lithium metal anode and its application in all-solid-state batteries Technical Field

[0001] The present invention belongs to the technical field of all-solid-state batteries and relates to a polymer-surface-modified lithium metal negative electrode and its application in all-solid-state batteries. Background Art

[0002] Lithium-ion batteries with graphite as the negative electrode have a low overall energy density due to graphite's relatively low specific capacity. Compared to graphite, metallic lithium has a theoretical specific capacity approximately ten times higher. Using metallic lithium as the negative electrode can greatly improve the energy density of lithium-ion batteries. However, the use of metallic lithium also brings new problems, the most serious of which are low Coulombic efficiency and lithium dendrites. Low Coulombic efficiency causes the continuous consumption of active lithium during battery cycling, leading to battery failure after long-term cycling. All-solid-state lithium metal batteries using sulfide as the electrolyte also face the problem of violent chemical reactions between the negative electrode lithium and the electrolyte, causing aging of the interface layer and affecting battery life.

[0003] At present, there are many reports on methods to solve the above two types of problems, such as electrolyte regulation, lithium negative electrode structure regulation, lithium metal surface modification, etc. CN108365172A reported that the surface of the copper foil is uniformly coated with a natural high molecular polymer layer to achieve dendrite-free metal lithium deposition and improve the cycle life of lithium metal. However, natural high molecular agarose, tamarind seed gum and sodium alginate contain a large number of polar groups such as hydroxyl groups, which are prone to negative reactions with lithium and also cause lithium loss. CN109216652A reported that the surface of the copper foil is uniformly coated with polyacrylic acid metal salt and polymethacrylic acid metal salt to promote uniform deposition of metal lithium. The preferential deposition of metal salts is utilized to promote the adhesion between the lithium negative electrode and the polymer. However, the role played by the polymer matrix in lithium protection is not much except for the bonding effect. CN111509195A coated a polyethylene dioxythiophene polyethylene glycol copolymer solution on the surface of a metallic lithium substrate for all-solid-state battery research. However, the epoxy groups, thiophene groups, and terminal hydroxyl groups in the polyethylene dioxythiophene polyethylene glycol will attack the sulfide electrolyte, causing the battery stability to deteriorate.

[0004] Therefore, how to design and prepare a polymer coating with better affinity for lithium, improve the stability of the lithium negative electrode, and increase the limiting current density of the symmetric battery depends on the selection of the polymer.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a polymer surface-modified lithium metal anode and its application in all-solid-state batteries.

[0007] The purpose of the present invention can be achieved by the following solutions:

[0008] In a first aspect, the present invention provides a method for preparing a polymer surface-modified lithium metal anode, comprising the following steps:

[0009] S1. Polymer preparation: heating the monomer solution to react and form a polymer;

[0010] S2. Preparation of polymer-modified lithium negative electrode: dispersing the polymer obtained in step S1 in a solvent to form a polymer dispersion; coating the polymer dispersion on the surface of metallic lithium, and drying to obtain a polymer-surface-modified lithium metal negative electrode.

[0011] As an embodiment of the present invention, in step S1, the monomer includes at least one of 1,3,5-benzenetrithiol and 1,4-phenyldithiol.

[0012] As an embodiment of the present invention, in step S1, the solvent in the monomer solution includes at least one of dimethyl sulfoxide, tetrahydrothiophene, tert-dodecyl mercaptan, 2,4-dimethylsulfolane, and diethyl sulfide.

[0013] As an embodiment of the present invention, in step S1, the concentration of the monomer solution is 1-5 g / ml.

[0014] As an embodiment of the present invention, in step S1, the temperature of the heating reaction is 50-80°C, and the heating time is 10-60 minutes.

[0015] As an embodiment of the present invention, in step S1, the heating reaction is a monomer polymerization reaction, which is carried out under vacuum sealing in a quartz tube.

[0016] Furthermore, the vacuum sealing pressure is less than 5×10 -5 Pa.

[0017] As an embodiment of the present invention, in step S1, after heating reaction, the polymer is obtained by filtering and washing three times.

[0018] Furthermore, the reagent used for the washing is methanol or ethanol; the amount of methanol or ethanol used is excessive.

[0019] As an embodiment of the present invention, in step S2, the polymer is a polymer that has been vacuum-dried.

[0020] Furthermore, the polymer is vacuum dried at a temperature of 50-100° C. for 4-8 hours.

[0021] As an embodiment of the present invention, in step S2, the solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and anisole.

[0022] As an embodiment of the present invention, in step S2, the concentration of the polymer dispersion is 0.5-3 mg / ml. The polymer is uniformly dispersed by stirring at room temperature.

[0023] As an embodiment of the present invention, in step S2, the coating thickness is 5-20 μm.

[0024] As an embodiment of the present invention, in step S2, the thickness of the metallic lithium is 30-500 μm.

[0025] As an embodiment of the present invention, in step S2, the drying temperature is 50-100°C, the time is 5-24 hours, and the drying is performed in an argon environment.

[0026] In a second aspect, the present invention provides a polymer surface-modified lithium metal negative electrode obtained by the preparation method.

[0027] In a third aspect, the present invention provides an application of the polymer surface-modified lithium metal negative electrode in an all-solid-state battery.

[0028] As an embodiment of the present invention, the all-solid-state battery is a sulfide-based all-solid-state battery, and the sulfide-based battery includes an argyrodite system, a binary system, and an LGPS system.

[0029] In the present invention, the preparation method of the sulfide-based all-solid-state battery includes: grinding NCM811 and Li6PS5Cl, mixing to form a composite positive electrode; assembling a pressure battery, i.e., a sulfide-based all-solid-state battery, with a polymer-surface-modified lithium metal negative electrode, a Li6PS5Cl electrolyte, and the composite positive electrode.

[0030] In some embodiments, the mass ratio of NCM811 to Li6PS5Cl is 7:3; the grinding time is 30 min; the polymer surface-modified lithium metal negative electrode is a 10 mm diameter disc; the thickness of the Li6PS5Cl electrolyte is 700 μm; and the composite positive electrode is 10 mg.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention modifies the surface of lithium through polymers to form a stable SEI film in situ, thereby improving the stability of the lithium negative electrode and solving the technical problem of metallic lithium dendrites. In addition, compared with small molecule monomers, polymers have higher thermodynamic and chemical stability, and batteries assembled from polymer-modified lithium sheets have higher cycle stability.

[0033] (2) The present invention adopts a one-step solvent method to synthesize the polymer, which is simple and easy to implement and can be easily scaled up for production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0035] FIG1 is a flow chart of polymer surface modification of lithium;

[0036] Figure 2 is a polymer structure diagram; wherein R is 1,4-phenyldithiol and R' is 1,3,5-benzenetrithiol;

[0037] FIG3 is a scanning electron microscope image of the polymer in Example 1;

[0038] FIG4 is a charge and discharge curve of the all-solid-state battery in Comparative Example 1;

[0039] FIG5 is a charge and discharge curve of the all-solid-state battery in Example 1;

[0040] FIG6 shows the cycle stability of the all-solid-state batteries in Comparative Example 2 and Examples 1-3. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, provide detailed implementation methods and specific operating procedures, and will help those skilled in the art to further understand the present invention. It should be pointed out that the scope of protection of the present invention is not limited to the following embodiments, and a number of adjustments and improvements made under the premise of the concept of the present invention all fall within the scope of protection of the present invention.

[0042] Example 1

[0043] As shown in the surface modification flow chart of FIG1 , this embodiment provides a polymer surface-modified lithium metal anode, which specifically includes the following steps:

[0044] Step 1. Preparation of polymer: 1,3,5-benzenetrithiol (1.03 g) and DMSO (0.327 mL) were added to a 10 mL quartz tube. After the quartz tube was burned and sealed, it was heated at 50 ° C for 10 minutes. The reaction mixture was poured into a large excess of methanol, filtered, and then washed three times with methanol. The obtained polymer was dried in a vacuum at 60 ° C for 6 hours to obtain a polymer powder; wherein the vacuum sealing pressure in the quartz tube was less than 5×10 -5 The structure of the polymer is shown in Figure 2, where R is 1,4-phenyldithiol and R' is 1,3,5-benzenetrithiol; a scanning electron microscope image of the polymer is shown in Figure 3.

[0045] Step 2: Place 50 mg of the polymer powder obtained in step 1 in 25 ml of ethylene glycol dimethyl ether, and stir at room temperature to disperse evenly to obtain solution A.

[0046] Step 3: spray solution A onto a 50 μm thick surface of metallic lithium to form a polymer layer with a thickness of about 10 μm; and then dry in an argon environment at 60° C. for 10 hours.

[0047] Step 4: Preparation of the composite positive electrode for all-solid-state sulfide battery: 70 wt% NCM811 and 30 wt% Li6PS5Cl were manually ground and mixed in a mortar for 30 min.

[0048] Step 5: Cut the lithium sheet obtained in Step 3 into 10mm diameter discs as the negative electrode, use 700μm thick Li6PS5Cl as the electrolyte, and 10mg of the composite positive electrode from Step 4. A pressure cell was assembled and tested. Testing was conducted at room temperature. The charge and discharge voltage was 2.8-4.3V. After two cycles at 0.1C and 100 cycles at 0.5C (1C = 190mAh / g), the residual specific capacity was 162.5mAh / g. The charge and discharge test curves for this battery are shown in Figure 5.

[0049] Example 2

[0050] This embodiment relates to a polymer surface-modified lithium metal negative electrode, which specifically includes the following steps:

[0051] Step 1. Preparation of polymer: 1,3,5-benzenetrithiol (0.5 g), 1,4-phenyldithiol (0.5 g) and DMSO (0.327 mL) were added to a 10 mL quartz tube. After the quartz tube was burned and sealed, it was heated at 50 ° C for 10 minutes. The reaction mixture was poured into a large amount of excess methanol, filtered, and then washed three times with methanol. The obtained polymer was dried in a vacuum at 60 ° C for 6 hours to obtain a polymer powder. Among them, the vacuum sealing pressure is less than 5×10 -5 Pa.

[0052] Step 2: Place 50 mg of the polymer powder obtained in step 1 in 25 ml of ethylene glycol dimethyl ether, and stir at room temperature to disperse evenly to obtain solution A.

[0053] Step 3: spray solution A onto the surface of lithium metal with a diameter of 16 mm and a thickness of 400 μm to form a polymer layer with a thickness of about 10 μm; then dry in an argon environment at 60° C. for 10 hours.

[0054] Step 4: Preparation of the composite positive electrode for all-solid-state sulfide battery: 70 wt% NCM811 and 30 wt% Li6PS5Cl were manually ground and mixed in a mortar for 30 min.

[0055] Step 5: Cut the lithium sheet obtained in Step 3 into 10 mm diameter discs as the negative electrode, use 700 μm thick Li6PS5Cl as the electrolyte, and 10 mg of the composite positive electrode from Step 4. Assemble the pressure cell and test it at room temperature (testing method is the same as in Example 1).

[0056] Example 3

[0057] This embodiment relates to a polymer surface-modified lithium metal negative electrode, which specifically includes the following steps:

[0058] Step 1. Preparation of polymer: 1,4-phenyldithiol (1.03 g) and DMSO (0.327 mL) were added to a 10 mL quartz tube. After the quartz tube was burned and sealed, it was heated at 50 ° C for 10 minutes. The reaction mixture was poured into a large amount of excess methanol, filtered, and then washed three times with methanol. The obtained polymer was dried in a vacuum at 60 ° C for 6 hours to obtain a polymer powder. Among them, the vacuum sealing pressure is less than 5×10 -5 Pa.

[0059] Step 2: Place 50 mg of the polymer powder obtained in step 1 in 25 ml of ethylene glycol dimethyl ether, and stir at room temperature to disperse evenly to obtain solution A.

[0060] Step 3: spray solution A onto the surface of lithium metal with a diameter of 16 mm and a thickness of 400 μm to form a polymer layer with a thickness of about 10 μm; then dry in an argon environment at 60° C. for 10 hours.

[0061] Step 4: Preparation of the composite positive electrode for all-solid-state sulfide battery: 70 wt% NCM811 and 30 wt% Li6PS5Cl were manually ground and mixed in a mortar for 30 min.

[0062] Step 5: Cut the lithium sheet obtained in Step 3 into 10 mm diameter discs as the negative electrode, use 700 μm thick Li6PS5Cl as the electrolyte, and 10 mg of the composite positive electrode from Step 4. Assemble the pressure cell and test it at room temperature (testing method is the same as in Example 1).

[0063] Comparative Example 1

[0064] Step 1: Cut the untreated lithium sheet into 10 mm diameter discs as electrodes.

[0065] Step 2: Preparation of a composite positive electrode for an all-solid-state sulfide battery: 70 wt% NCM811 and 30 wt% Li6PS5Cl were manually ground and mixed in a mortar for 30 min to obtain a composite positive electrode.

[0066] Step 2: Cut the lithium sheet obtained in Step 1 into 10 mm diameter discs as the negative electrode, use 700 μm thick Li6PS5Cl as the electrolyte, and 10 mg of the composite positive electrode from Step 2. Assemble the pressure cell and test it. The test is the same as in Example 1. The test curve is shown in Figure 4. A short circuit occurs in the second cycle.

[0067] Comparative Example 2

[0068] Step 1: Place 50 mg of 1,3,5-benzenetrithiol powder in 25 ml of ethylene glycol dimethyl ether and stir at room temperature to disperse evenly to obtain solution A.

[0069] Step 2: spray solution A onto a 50 μm thick surface of metallic lithium to form a polymer layer with a thickness of about 10 μm; and then dry in an argon environment at 60° C. for 10 hours.

[0070] Step 3: Preparation of the composite positive electrode for all-solid-state sulfide battery: 70 wt% NCM811 and 30 wt% Li6PS5Cl were manually ground and mixed in a mortar for 30 min.

[0071] Step 4: Cut the lithium sheet obtained in Step 2 into 10mm diameter discs as the negative electrode, use 700μm thick Li6PS5Cl as the electrolyte, and 10mg of the composite positive electrode from Step 3. Assemble the pressure cell and test it. The test was carried out at room temperature. The charge and discharge voltage was 2.8-4.3V, and the battery was cycled for 2 cycles at 0.1C and 100 cycles at 0.5C (1C = 190mAh / g). As shown in Figure 6, the cycling stability of the battery modified with small molecule monomers in Comparative Example 2 was inferior to the performance of the battery modified with polymers in Examples 1, 2, and 3.

[0072] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a polymer surface-modified lithium metal negative electrode, characterized in that: The steps include: S1. polymer preparation: heating the monomer solution to react and form a polymer; S2. Preparation of polymer-modified lithium negative electrode: dispersing the polymer obtained in step S1 in a solvent to form a polymer dispersion; coating the polymer dispersion on the surface of metallic lithium, and drying to obtain a lithium metal negative electrode modified with the polymer surface.

2. The preparation method according to claim 1, characterized in that: In step S1, the monomer includes at least one of 1,3,5-benzenetrithiol and 1,4-phenyldithiol.

3. The preparation method according to claim 1, characterized in that: In step S1, the concentration of the monomer solution is 1-5 g / ml.

4. The preparation method according to claim 1, characterized in that: In step S1, the temperature of the heating reaction is 50-80°C, and the heating time is 10-60 minutes.

5. The preparation method according to claim 1, characterized in that: In step S1, the heating reaction is a monomer polymerization reaction, and the heating reaction is carried out in a quartz tube under vacuum sealing, and the vacuum sealing pressure is less than 5×10 -5 Pa.

6. The preparation method according to claim 1, characterized in that: In step S2, the polymer is a polymer after vacuum drying, and the temperature of vacuum drying of the polymer is 50-100° C. and the time is 4-8 hours.

7. The preparation method according to claim 1, characterized in that: In step S2, the concentration of the polymer dispersion is 0.5-3 mg / ml.

8. The preparation method according to claim 1, characterized in that: In step S2, the coating thickness is 5-20 μm; the thickness of the metal lithium is 30-500 μm.

9. A lithium metal negative electrode modified with a polymer surface obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the polymer surface modified lithium metal anode as claimed in claim 9 in an all-solid-state battery.

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