An expanded graphite-silver composite negative electrode material and its preparation method

Abstract

The present invention provides an expanded graphite-silver composite negative electrode material and a preparation method thereof, which relates to the technical field of energy storage materials. The preparation method comprises the following steps: preparing expanded graphite; dispersing the expanded graphite in a mixed solvent to obtain a dispersion; adding silver nitrate to the dispersion to obtain a first reaction mixture; adding an aqueous sodium hydroxide solution to the first reaction mixture to obtain a second reaction mixture; dropwise adding an aqueous hydroxylamine solution to the second reaction mixture to obtain a third reaction mixture; centrifuging the third reaction mixture, washing the product with deionized water until neutral, and performing vacuum drying on the washed product to obtain the expanded graphite-silver composite negative electrode material. The preparation method of the expanded graphite-silver composite negative electrode material provided by the present invention has the advantages of simple operation, low cost, and wide applicability; the silver in the composite negative electrode material can reduce the nucleation energy of lithium, avoid the growth of lithium dendrites on the side of metallic lithium, and reduce potential safety hazards.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and particularly relates to an expanded graphite-silver composite anode material and a preparation method thereof. Background Art

[0002] Metallic lithium has a high theoretical specific capacity (3860 mAh g -1 ) and a low electrochemical potential (-3.04 V), and is currently a widely used anode for high-energy density solid-state batteries. However, metallic lithium is prone to side reactions with electrolytes, resulting in a decrease in the Coulombic efficiency of the battery, a shortening of the cycle life, and even serious safety accidents such as combustion and explosion. The fundamental reasons for affecting performance and causing safety accidents are that during the discharge process of lithium metal batteries, the uneven deposition of metallic lithium leads to the growth of lithium dendrites on one side of the metallic lithium. The lithium dendrites pierce the separator, causing battery short-circuiting and triggering safety problems, presenting safety hazards and hindering the commercial application of lithium metal batteries. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to solve the problem that lithium dendrites are prone to grow on one side of metallic lithium during the discharge process of existing lithium metal batteries. The present invention provides an expanded graphite-silver composite anode material and a preparation method thereof. This preparation method utilizes the characteristic that silver can reduce the nucleation energy of lithium to promote the uniform deposition of metallic lithium, solve the problem that lithium dendrites are prone to grow on one side of metallic lithium during the discharge process of existing lithium metal batteries, and thus improve the performance of solid-state batteries.

[0004] The technical solution adopted by the present invention to solve its technical problems is:

[0005] A preparation method of an expanded graphite-silver composite anode material, comprising the following steps:

[0006] S1: Using inorganic acid and flake graphite as raw materials, prepare expanded graphite;

[0007] S2: Disperse the expanded graphite in a mixed solvent of ethanol and water to obtain a dispersion;

[0008] S3: Add silver nitrate to the dispersion, stir and react at room temperature to obtain a first reaction mixture;

[0009] S4: Add an aqueous sodium hydroxide solution to the first reaction mixture, stir and react at room temperature to obtain a second reaction mixture;

[0010] S5: Dropwise add an aqueous hydroxylamine solution to the second reaction mixture, stir and react at room temperature to obtain a third reaction mixture;

[0011] S6: Centrifuge the third reaction mixture, collect the product, and wash the product with deionized water until it is neutral to obtain the washed product;

[0012] S7: Vacuum dry the washed product to obtain the expanded graphite-silver composite anode material.

[0013] Optionally, step S1 includes: adding flake graphite to a mixed acid composed of sulfuric acid and nitric acid, heating to 50 °C, and stirring for reaction; after the reaction, centrifuge to collect the product, wash it until neutral, and dry it to obtain expandable graphite; keep the expandable graphite at 500-1100 °C for 1-15 min to obtain expanded graphite.

[0014] Optionally, the volume ratio of sulfuric acid to nitric acid in the mixed acid is 8:(1-4); the mass of the flake graphite in each milliliter of the mixed acid is 100-500 mg.

[0015] Optionally, the stirring reaction time in step S1 is 4-12 hours; the drying temperature is 80 °C.

[0016] Optionally, the volume ratio of water to ethanol in the mixed solvent is 12:(0-4); the addition amount of the expanded graphite in each milliliter of the mixed solvent is 10-100 mg.

[0017] Optionally, the mass ratio of the expanded graphite to the silver nitrate is 4:(1-3).

[0018] Optionally, the concentration of the sodium hydroxide aqueous solution is 4 mM, and the volume ratio of the sodium hydroxide aqueous solution to the mixed solvent is (1-4):10.

[0019] Optionally, the concentration of the hydroxylamine aqueous solution is 5 mM, and the volume ratio of the hydroxylamine aqueous solution to the mixed solvent is (0.1-0.3):10.

[0020] Optionally, the stirring reaction time in step S3 is 1-8 hours; the stirring reaction time in step S4 is 20-60 min; the stirring reaction time in step S5 is 4-10 hours.

[0021] Another object of the present invention is to provide an expanded graphite-silver composite anode material prepared by the preparation method of the expanded graphite-silver composite anode material as described above.

[0022] The beneficial effects of the present invention are:

[0023] The preparation method of the expanded graphite-silver composite negative electrode material provided by the present invention has the advantages of simple operation, low cost and wide applicability; during the preparation process, expanded graphite is used as the carbon matrix and silver nitrate is used as the silver source to prepare a lithium-free silver-carbon negative electrode material, that is, an expanded graphite-silver composite negative electrode material. The silver in the composite negative electrode material can reduce the nucleation energy of lithium, thereby promoting the uniform deposition of metallic lithium during the discharge process of the lithium metal battery, avoiding the growth of lithium dendrites on one side of the metallic lithium, reducing potential safety hazards and improving the performance of the solid-state battery; moreover, the carbon material in the composite negative electrode material can, on the one hand, promote the uniform dispersion of silver nanoparticles, prevent the aggregation of silver during charge and discharge, and on the other hand, can serve as a three-dimensional host for the deposition of metallic lithium, further improving the uniformity of metallic lithium deposition, thereby further reducing potential safety hazards and improving the performance of the solid-state battery. Brief Description of the Drawings

[0024] The present invention will be further described below with reference to the drawings and embodiments.

[0025] Figure 1 It is a scanning electron microscope image of flake graphite in Example 1 of the present invention;

[0026] Figure 2 It is a scanning electron microscope image of expanded graphite in Example 1 of the present invention;

[0027] Figure 3 It is a scanning electron microscope image of the expanded graphite-silver composite negative electrode material in Example 1 of the present invention;

[0028] Figure 4 It is a cyclic performance diagram of the solid-state full battery of the expanded graphite-silver composite negative electrode material in Example 1 of the present invention;

[0029] Figure 5 It is a cyclic performance diagram of the solid-state full battery of the expanded graphite-silver composite negative electrode material in Example 3 of the present invention;

[0030] Figure 6 It is a cyclic performance diagram of the solid-state full battery of the expanded graphite-silver composite negative electrode material in Example 4 of the present invention;

[0031] Figure 7 It is a cyclic performance diagram of the solid-state full battery of the expanded graphite-silver composite negative electrode material in Example 6 of the present invention. Detailed Embodiments

[0032] The present invention will now be described in further detail. The following described embodiments are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0033] To solve the problem that lithium dendrites tend to grow on the side of metallic lithium during the discharge process of lithium metal batteries in the prior art, the present invention provides a method for preparing an expanded graphite-silver composite negative electrode material, and the preparation method includes the following steps:

[0034] S1: Using inorganic acid and flake graphite as raw materials, prepare expanded graphite;

[0035] S2: Disperse the expanded graphite in a mixed solvent of ethanol and water to obtain a dispersion;

[0036] S3: Add silver nitrate to the dispersion, stir and react at room temperature to obtain a first reaction mixture;

[0037] S4: Add an aqueous sodium hydroxide solution to the first reaction mixture, stir and react at room temperature to obtain a second reaction mixture;

[0038] S5: Dropwise add an aqueous hydroxylamine solution to the second reaction mixture, stir and react at room temperature to obtain a third reaction mixture;

[0039] S6: Centrifuge the third reaction mixture, collect the product, and wash the product with deionized water until neutral to obtain a washed product;

[0040] S7: Vacuum-dry the washed product to obtain an expanded graphite-silver composite negative electrode material.

[0041] The method for preparing the expanded graphite-silver composite negative electrode material provided by the present invention has the advantages of simple operation, low cost, and wide applicability; during the preparation process, expanded graphite is used as the carbon matrix and silver nitrate is used as the silver source to prepare a lithium-free silver-carbon negative electrode material, that is, an expanded graphite-silver composite negative electrode material. The silver in the composite negative electrode material can reduce the nucleation energy of lithium, thereby promoting the uniform deposition of metallic lithium during the discharge process of lithium metal batteries, avoiding the growth of lithium dendrites on the side of metallic lithium, reducing potential safety hazards, and improving the performance of solid-state batteries; moreover, the carbon material in the composite negative electrode material can, on the one hand, promote the uniform dispersion of silver nanoparticles, prevent the aggregation of silver during charge and discharge, and on the other hand, can serve as a three-dimensional host for lithium metal deposition, further improving the uniformity of lithium metal deposition, and further reducing potential safety hazards and improving the performance of solid-state batteries.

[0042] During the preparation process of the expanded graphite-silver composite negative electrode material of the present invention, after silver nitrate and expanded graphite are fully mixed in a mixed solvent, silver nitrate is uniformly distributed between the layers of expanded graphite, and then an aqueous sodium hydroxide solution and an aqueous hydroxylamine solution are successively added to react with silver nitrate, so that nano-silver can be in-situ generated in the interlayer structure of expanded graphite, thereby ensuring that nano-silver can be uniformly distributed in the interlayer structure of expanded graphite, and improving the structural stability and uniformity of the expanded graphite-silver composite negative electrode material.

[0043] In addition, for existing lithium-containing anode materials, since metallic lithium is relatively soft, hot pressing is required when using it in lithium metal batteries, which increases the production complexity and cost and limits the commercial application of lithium metal batteries. At the same time, the excessive use of metallic lithium in lithium metal batteries will reduce the energy density of the batteries, further hindering the commercial application of lithium metal batteries. However, the expanded graphite-silver composite anode material provided by the present invention does not contain metallic lithium, has a simple application process, low cost, and will not reduce the energy density of the batteries during use, thus contributing to the commercial application of lithium metal batteries.

[0044] In the present invention, the inorganic acid is preferably a mixed acid of sulfuric acid and nitric acid, so as to facilitate the use of the strong oxidation of sulfuric acid and nitric acid to form an intercalation compound layered structure of graphite. Specifically, preferably step S1 includes: adding flake graphite into the mixed acid composed of sulfuric acid and nitric acid, heating to 50 °C, and stirring and reacting; after the reaction ends, centrifugally collecting the product, washing until neutral, and drying to obtain expandable graphite; further loading the expandable graphite into a crucible and putting it into a muffle furnace at 500-1100 °C, keeping warm for 1-15 min to obtain expanded graphite.

[0045] To ensure the comprehensive performance of the expanded graphite-silver composite anode material, the volume ratio of sulfuric acid to nitric acid in the mixed acid is preferably 8:(1-4) in the present invention; the mass of flake graphite in each milliliter of the mixed acid is 100-500 mg.

[0046] To ensure the full progress of the reaction while taking into account the reaction efficiency, the stirring reaction time in step S1 is preferably 4-12 hours in the present invention; the drying temperature is 80 °C.

[0047] The volume ratio of water to ethanol in the mixed solvent is preferably 12:(0-4) in the present invention; and further preferably, the addition amount of expanded graphite in each milliliter of the mixed solvent is 10-100 mg; adding water in the mixed solvent can ensure the full dissolution of silver nitrate, and ethanol has lipophilicity, which can ensure the full infiltration of expanded graphite and the solution.

[0048] To ensure the electrochemical performance of the expanded graphite-silver composite anode material, the mass ratio of expanded graphite to silver nitrate is preferably 4:(1-3) in the present invention, and the stirring reaction time in step S3 is preferably 1-8 hours.

[0049] The concentration of the sodium hydroxide aqueous solution is preferably 4 mM in the present invention, and the volume ratio of the sodium hydroxide aqueous solution to the mixed solvent is preferably (1-4):10, and the stirring reaction time in step S4 is preferably 20-60 min.

[0050] The concentration of the hydroxylamine aqueous solution is preferably 5 mM in the present invention, and the volume ratio of the hydroxylamine aqueous solution to the mixed solvent is preferably (0.1-0.3):10, and the stirring reaction time in step S5 is preferably 4-10 hours.

[0051] Another object of the present invention is to provide an expanded graphite-silver composite negative electrode material, which is prepared by the preparation method of the expanded graphite-silver composite negative electrode material as described above.

[0052] The expanded graphite-silver composite negative electrode material provided by the present invention uses expanded graphite as the carbon matrix and silver nitrate as the silver source. Silver can reduce the nucleation energy of lithium, thereby promoting the uniform deposition of metallic lithium during the discharge process of the lithium metal battery, avoiding the growth of lithium dendrites on one side of the metallic lithium, reducing potential safety hazards, and improving the performance of the solid-state battery. Moreover, on the one hand, the carbon material in the composite negative electrode material can promote the uniform dispersion of silver nanoparticles and prevent the aggregation of silver during charge and discharge. On the other hand, it can serve as a three-dimensional host for the deposition of metallic lithium, further improving the uniformity of metallic lithium deposition, further reducing potential safety hazards, and improving the performance of the solid-state battery.

[0053] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0054] Example 1

[0055] This example provides a preparation method of an expanded graphite-silver composite negative electrode material, and the preparation method includes the following steps:

[0056] S1: Add 4 g of flake graphite to 20 mL of a mixed acid of sulfuric acid and nitric acid (the volume ratio of sulfuric acid to nitric acid is 8:1), stir at 50 °C for 8 h, after the reaction ends, centrifuge to collect the product, wash it with deionized water until neutral, and dry it in a blast dryer at 80 °C to obtain expandable graphite; put the expandable graphite into a crucible and place it in a muffle furnace at 800 °C, keep it warm for 15 min to obtain expanded graphite;

[0057] S2: Weigh 2 g of the expanded graphite synthesized in the previous step, disperse it in 20 mL of a mixed solvent of water and ethanol (the volume ratio of water to ethanol is 12:2), and ultrasonicate until it is uniformly dispersed to obtain a dispersion;

[0058] S3: Add 0.5 g of silver nitrate to the dispersion, stir and react at room temperature for 1 h to obtain a first reaction mixture;

[0059] S4: Add an aqueous sodium hydroxide solution (4 mM, 3 mL) to the first reaction mixture, stir and react at room temperature for 30 min to obtain a second reaction mixture;

[0060] S5: Dropwise add an aqueous hydroxylamine solution (5 mM, 300 μL) to the second reaction mixture, stir and react at room temperature for 4 h to obtain a third reaction mixture;

[0061] S6: Centrifuge the third reaction mixture, collect the product, and wash the product with deionized water until neutral to obtain the washed product.

[0062] S7: Vacuum dry the washed product at 80 °C to obtain the expanded graphite-silver composite negative electrode material.

[0063] See Figures 1 to 3 As shown, perform scanning electron microscopy detection on the flake graphite, expanded graphite, and expanded graphite-silver composite negative electrode material in this example; it can be seen from the figure that the expanded graphite has an obvious layered structure compared with the flake graphite, and nano-silver is loaded in the expanded graphite-silver composite negative electrode material.

[0064] Preparation of the negative electrode sheet:

[0065] Uniformly mix the obtained expanded graphite-silver composite negative electrode material with conductive carbon (Super P) and binder (polyvinylidene fluoride) under the condition of a mass ratio of 8:1:1, add 800 μL of N-methylpyrrolidone, stir at room temperature for 6 h, then uniformly coat the obtained suspension on the copper foil (the coating amount per square centimeter of copper foil is about 1.5 mg), and dry it in a blast oven at 80 °C for 10 h; cut the obtained electrode sheet into circular pieces with a diameter of 12 mm using a manual slicing machine to obtain the negative electrode sheet.

[0066] Preparation of the positive electrode sheet: Uniformly mix lithium iron phosphate with conductive carbon (Super P) and binder (polyvinylidene fluoride) under the condition of a mass ratio of 8:1:1, add N-methylpyrrolidone, and stir at room temperature for 6 h; after stirring, uniformly coat the obtained suspension on the aluminum foil (the coating amount per square centimeter of aluminum foil is about 4 mg), and dry it in a blast oven at 80 °C for 12 h to obtain the positive electrode sheet of the solid-state lithium metal battery.

[0067] Preparation of the solid electrolyte: Uniformly mix PEO and lithium bis(trifluoromethanesulfonyl)imide under the condition of a mass ratio of 5:2, add acetonitrile, stir at room temperature for 10 h, and after stirring, place the obtained suspension in a polytetrafluoroethylene mold to dry into a film; after drying, take out the film and cut it into circular pieces with a diameter of 20 mm to obtain the solid electrolyte.

[0068] In this example, the battery adopts a standard full-cell configuration. The battery case is a CR2030 type stainless steel button battery case, and the electrolyte is a mixed solution of 1 M LiPF6 in dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 1:1). When assembling the full cell, the mass ratio of the positive and negative active materials is 2.3:1. 10 μL of the electrolyte is respectively dropped near the separator on the positive and negative electrodes. The test voltage range is 0.01 - 3 V, and the test current is 80 mAg -1 , and the test is carried out using a LAND CT2001A type battery test system.

[0069] See Figure 4 As shown, when using the expanded graphite-silver composite anode material prepared in this example, the discharge and charge specific capacities of the solid-state full cell in the first cycle are 64 and 7 mAh g -1 respectively, and the reversible specific capacity after 20 cycles reaches 30 mAh g -1 . After cycling, the battery was disassembled and the anode was observed, and no lithium dendrites were deposited.

[0070] Example 2

[0071] The difference between this example and Example 1 is that the volume ratio of water to ethanol in step S2 is 12:1.

[0072] For the test process in this example, refer to the relevant content in Example 1.

[0073] After testing, when using the expanded graphite-silver composite anode material prepared in this example, the reversible specific capacity of the solid-state full cell after 20 cycles reaches 30 mAh g -1 . After cycling, the battery was disassembled and the anode was observed, and no lithium dendrites were deposited.

[0074] Example 3

[0075] The difference between this example and Example 1 is that the volume ratio of water to ethanol in step S2 is 12:0.

[0076] For the test process in this example, refer to the relevant content in Example 1.

[0077] After testing, see Figure 5 As shown, when using the expanded graphite-silver composite anode material prepared in this example, the discharge and charge specific capacities of the solid-state full cell in the first cycle are 88 and 56 mAh g -1 respectively, and the reversible specific capacity after 20 cycles reaches 54 mAh g -1 . After cycling, the battery was disassembled and the anode was observed, and local lithium dendrites were deposited.

[0078] Example 4

[0079] The difference between this example and Example 1 is that the volume ratio of sulfuric acid to nitric acid in step S1 is 8:2.

[0080] For the test process in this example, refer to the relevant content in Example 1.

[0081] After testing, see Figure 6 As shown, when using the expanded graphite-silver composite anode material prepared in this example, the discharge and charge specific capacities of the solid-state full cell in the first cycle are 19 and 10 mAh g -1 respectively, and the reversible specific capacity after 20 cycles reaches 44 mAh g-1 After cycling, the battery was disassembled and the negative electrode was observed. No lithium dendrites were precipitated.

[0082] Example 5

[0083] The difference between this example and Example 1 is that in step S1, the volume ratio of sulfuric acid to nitric acid is 8:2, and in step S2, the volume ratio of water to ethanol is 12:1.

[0084] For the testing process in this example, refer to the relevant content in Example 1.

[0085] After testing, when the expanded graphite-silver composite negative electrode material prepared in this example was used, the reversible specific capacity of the solid-state full battery reached 31 mAh g after 20 cycles -1 After cycling, the battery was disassembled and the negative electrode was observed. No lithium dendrites were precipitated.

[0086] Example 6

[0087] The difference between this example and Example 1 is that in step S1, the volume ratio of sulfuric acid to nitric acid is 8:2, and in step S2, the volume ratio of water to ethanol is 12:0.

[0088] For the testing process in this example, refer to the relevant content in Example 1.

[0089] After testing, as shown in Figure 7 When the expanded graphite-silver composite negative electrode material prepared in this example was used, the discharge and charge specific capacities of the solid-state full battery in the first cycle were 94 and 22 mAh g, respectively -1 , and the reversible specific capacity reached 42 mAh g after 20 cycles -1 After cycling, the battery was disassembled and the negative electrode was observed. Lithium dendrites were locally precipitated.

[0090] Example 7

[0091] The difference between this example and Example 1 is that in step S1, the volume ratio of sulfuric acid to nitric acid is 8:3.

[0092] For the testing process in this example, refer to the relevant content in Example 1.

[0093] After testing, when the expanded graphite-silver composite negative electrode material prepared in this example was used, the reversible specific capacity of the solid-state full battery reached 37 mAh g after 20 cycles -1 After cycling, the battery was disassembled and the negative electrode was observed. No lithium dendrites were precipitated.

[0094] Example 8

[0095] The difference between this example and Example 1 is that in step S1, the volume ratio of sulfuric acid to nitric acid is 8:3, and in step S2, the volume ratio of water to ethanol is 12:1.

[0096] For the test process in this embodiment, refer to the relevant content in Embodiment 1.

[0097] After testing, when using the expanded graphite-silver composite negative electrode material prepared in this embodiment, the reversible specific capacity of the solid-state full battery reaches 34 mAh g -1 after 20 cycles. After cycling, the battery was disassembled and the negative electrode was observed, and no lithium dendrites were precipitated.

[0098] Embodiment 9

[0099] The difference between this embodiment and Embodiment 1 is that the volume ratio of sulfuric acid to nitric acid in Step S1 is 8:3, and the volume ratio of water to ethanol in Step S2 is 12:0.

[0100] For the test process in this embodiment, refer to the relevant content in Embodiment 1.

[0101] After testing, when using the expanded graphite-silver composite negative electrode material prepared in this embodiment, the reversible specific capacity of the solid-state full battery reaches 32 mAh g -1 after 20 cycles. After cycling, the battery was disassembled and the negative electrode was observed, and no lithium dendrites were precipitated.

[0102] Embodiment 10

[0103] The difference between this embodiment and Embodiment 1 is that the addition amount of silver nitrate in Step S3 is 1.5 g.

[0104] For the test process in this embodiment, refer to the relevant content in Embodiment 1.

[0105] After testing, when using the expanded graphite-silver composite negative electrode material prepared in this embodiment, the discharge and charge specific capacities of the solid-state full battery in the first cycle are 66 and 8 mAh g respectively -1 , and the reversible specific capacity reaches 32 mAh g after 20 cycles -1 After cycling, the battery was disassembled and the negative electrode was observed, and no lithium dendrites were precipitated.

[0106] Embodiment 11

[0107] The difference between this embodiment and Embodiment 1 is that the addition amount of silver nitrate in Step S3 is 1 g.

[0108] For the test process in this embodiment, refer to the relevant content in Embodiment 1.

[0109] After testing, when using the expanded graphite-silver composite negative electrode material prepared in this embodiment, the discharge and charge specific capacities of the solid-state full battery in the first cycle are 64 and 8 mAh g respectively -1 , and the reversible specific capacity reaches 31 mAh g after 20 cycles -1After the cycle, the battery was disassembled and the negative electrode was observed, and no lithium dendrites were deposited.

[0110] Comparative Example 1

[0111] This comparative example provides a method for preparing an expanded graphite-silver composite negative electrode material, the preparation method comprising the following steps:

[0112] S1: Add 4 g of flake graphite to 20 mL of a mixed acid of sulfuric acid and nitric acid (the volume ratio of sulfuric acid to nitric acid is 8:1), stir at 50° C. for 8 h, collect the product by centrifugation after the reaction is completed, wash with deionized water until neutral, and dry with air at 80° C. to obtain expandable graphite; put the expandable graphite into a crucible, put it into a muffle furnace at 800° C., and keep it warm for 15 min to obtain expandable graphite;

[0113] S2: Add 0.5 g of silver nitrate to 20 mL of a mixed solvent of water and ethanol (the volume ratio of water to ethanol is 12:2), stir at room temperature for 1 h to obtain a dispersion;

[0114] S3: adding sodium hydroxide aqueous solution (4 mM, 3 mL) to the dispersion, stirring at room temperature for 30 min to obtain a first reaction mixture;

[0115] S4: adding hydroxylamine aqueous solution (5 mM, 300 μL) dropwise to the first reaction mixture, stirring at room temperature for 4 h to obtain a second reaction mixture;

[0116] S5: Weigh 2 g of expanded graphite, disperse it in the second reaction mixture, and perform ultrasonication until the mixture is uniformly dispersed to obtain a third reaction mixture;

[0117] S6: centrifuging the third reaction mixture to collect the product, and washing the product with deionized water until it is neutral to obtain a washed product;

[0118] S7: The washed product is vacuum dried at 80° C. to obtain an expanded graphite-silver composite negative electrode material.

[0119] The test process in this comparative example refers to the relevant content in Example 1.

[0120] The test shows that when the expanded graphite-silver composite negative electrode material prepared in this comparative example is used, the discharge and charge specific capacities of the solid-state full battery in the first cycle are 55 and 6 mAh g, respectively. -1 After 20 cycles, the reversible specific capacity reaches 7 mAh g -1 After the cycle, the battery was disassembled and the negative electrode was observed, and lithium dendrites appeared over a large area.

[0121] The difference between this comparative example and Example 1 is that the preparation process was replaced while the raw material composition remained unchanged; by comparing the test results of this comparative example with those of Example 1, it was found that the electrochemical performance of the composite negative electrode material prepared in this comparative example was far worse than that of Example 1, and a large number of lithium dendrites appeared after cycling, and the safety performance was poor.

[0122] Comparative Example 2

[0123] This comparative example provides a method for preparing an expanded graphite-silver composite negative electrode material, the preparation method comprising the following steps:

[0124] S1: Weigh 2 g of flake graphite, disperse it in 20 mL of a mixed solvent of water and ethanol (the volume ratio of water to ethanol is 12:2), and perform ultrasonic treatment until the dispersion is uniform to obtain a dispersion;

[0125] S2: Add 0.5 g of silver nitrate to the dispersion, stir and react at room temperature for 1 h to obtain a first reaction mixture;

[0126] S3: adding sodium hydroxide aqueous solution (4 mM, 3 mL) to the first reaction mixture, stirring at room temperature for 30 min to obtain a second reaction mixture;

[0127] S4: adding hydroxylamine aqueous solution (5 mM, 300 μL) dropwise to the second reaction mixture, stirring at room temperature for 4 h to obtain a third reaction mixture;

[0128] S5: centrifuging the third reaction mixture to collect the product, and washing the product with deionized water until it is neutral to obtain a washed product;

[0129] S6: The washed product is vacuum dried at 80° C. to obtain a graphite-silver composite negative electrode material.

[0130] The test process in this comparative example refers to the relevant content in Example 1.

[0131] The test shows that when the graphite-silver composite negative electrode material prepared in this comparative example is used, the discharge and charge specific capacities of the solid-state full battery in the first cycle are 56 and 6 mAh g, respectively. -1 After 20 cycles, the reversible specific capacity reaches 15 mAh g -1 After the cycle, the battery was disassembled and the negative electrode was observed, and lithium dendrites appeared over a large area.

[0132] The difference between this comparative example and Example 1 is that flake graphite is directly used as the carbon source; by comparing the test results of this comparative example with those of Example 1, it is found that the electrochemical performance and safety performance of the composite negative electrode material prepared in this comparative example are far inferior to those of Example 1.

[0133] Taking the ideal embodiments of the present invention described above as an inspiration, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A preparation method of an expanded graphite-silver composite anode material, characterized in that, It includes the following steps: S1: Using inorganic acid and flake graphite as raw materials, prepare expanded graphite; S2: Disperse the expanded graphite in a mixed solvent of ethanol and water to obtain a dispersion; S3: Add silver nitrate to the dispersion, stir and react at room temperature to obtain a first reaction mixture; S4: Add an aqueous sodium hydroxide solution to the first reaction mixture, stir and react at room temperature to obtain a second reaction mixture; S5: Dropwise add an aqueous hydroxylamine solution to the second reaction mixture, stir and react at room temperature to obtain a third reaction mixture; S6: Centrifuge the third reaction mixture, collect the product, and wash the product with deionized water until neutral to obtain the washed product; S7: Vacuum-dry the washed product to obtain an expanded graphite-silver composite negative electrode material; Step S1 includes: Add flake graphite to a mixed acid composed of sulfuric acid and nitric acid, heat up to 50 °C, and stir and react; After the reaction, centrifuge to collect the product, wash until neutral, and dry to obtain expandable graphite; Keep the expandable graphite at 500 - 1100 °C for 1 - 15 min to obtain expanded graphite.

2. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, characterized in that, The volume ratio of sulfuric acid to nitric acid in the mixed acid is 8:(1 - 4); The mass of the flake graphite in each milliliter of the mixed acid is 100 - 500 mg.

3. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, wherein, The stirring reaction time in step S1 is 4 - 12 hours; The drying temperature is 80 °C.

4. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, characterized in that, The volume ratio of water to ethanol in the mixed solvent is 12:(0 - 4); The addition amount of the expanded graphite in each milliliter of the mixed solvent is 10 - 100 mg.

5. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, characterized in that, The mass ratio of the expanded graphite to the silver nitrate is 4:(1 - 3).

6. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, characterized in that, The concentration of the aqueous sodium hydroxide solution is 4 mM, and the volume ratio of the aqueous sodium hydroxide solution to the mixed solvent is (1 - 4):10 in terms of the addition amount.

7. The preparation method of the expanded graphite-silver composite negative electrode material according to claim 1, characterized in that, The concentration of the aqueous hydroxylamine solution is 5 mM, and the volume ratio of the aqueous hydroxylamine solution to the mixed solvent is (0.1 - 0.3):10 in terms of the addition amount.

8. The preparation method of the expanded graphite-silver composite negative electrode material according to any one of claims 1 to 7, characterized in that, The stirring reaction time in step S3 is 1 - 8 hours; The stirring reaction time in step S4 is 20 - 60 min; The stirring reaction time in step S5 is 4 - 10 hours.

9. An expanded graphite-silver composite negative electrode material, characterized in that, It is prepared by the preparation method of the expanded graphite-silver composite negative electrode material according to any one of claims 1 - 8.

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