Zinc germanate / carbon composite anode materials, their preparation methods and applications

Abstract

This disclosure belongs to the field of lithium-ion battery technology and discloses a zinc germanate / carbon composite anode material, its preparation method and application. The zinc germanate / carbon composite anode material includes a substrate material and a zinc germanate wire array attached to the surface of the substrate material. The substrate material is a two-dimensional planar carbon fiber material. The zinc germanate wire array is filled with gel B and the surface of the zinc germanate wire array is covered with a coating film C.

Description

Technical Field

[0001] This disclosure belongs to the field of lithium-ion battery technology, specifically relating to a zinc germanate / carbon composite anode material, its preparation method, and its application. Background Technology

[0002] As is well known, electrode materials are one of the key factors affecting the electrochemical performance of lithium-ion batteries. Therefore, developing suitable high-performance electrode materials is an important strategy to improve the performance of lithium-ion batteries. Traditional intercalation-type graphite anode materials cannot further improve the energy density of lithium-ion batteries due to their ultra-low discharge capacity. Novel conversion-type and alloy-type anode materials have become candidate materials for the next generation of high-energy-density anodes due to their multi-electron reactions and high theoretical capacity.

[0003] Germanium, with its abundant sources, low cost, high theoretical lithium storage capacity, and suitable delithiation voltage, is one of the materials with promising commercial applications. However, unlike carbon anode materials, germanium undergoes repeated contraction and expansion during lithium insertion / extraction, which can easily lead to loss of electrical contact in the anode sheet, causing material deactivation. This may significantly reduce the application value of germanium-based anode materials. Therefore, constructing a suitable electrode system to mitigate the volume expansion and structural damage caused by lithium-ion insertion / extraction is crucial for improving its cycle stability. Summary of the Invention

[0004] This disclosure aims to at least address the technical problems existing in the prior art. To this end, this disclosure proposes a zinc germanate / carbon composite anode material, its preparation method, and its applications. By combining germanium-based anode materials with carbon materials, a stable array-type zinc germanate / carbon composite anode material is synthesized, which can provide greater capacity, higher first-pass coulombic efficiency, and greater rate performance compared to traditional graphite anode materials.

[0005] According to one aspect of this disclosure, a zinc germanate / carbon composite anode material is proposed, the zinc germanate / carbon composite anode material comprising a substrate material and an array of zinc germanate wires attached to the surface of the substrate material, the substrate material being a two-dimensional planar carbon fiber material, the zinc germanate wire array being filled with gel B, and the surface of the zinc germanate wire array being coated with a coating film C.

[0006] In some embodiments of this disclosure, the substrate material is at least one of carbon fiber membrane, carbon fiber sheet, carbon fiber felt, graphite fiber sheet, graphite fiber membrane, polymer carbonized fiber membrane, or polymer carbonized fiber sheet. Optionally, the carbon fiber membrane is a spun carbon fiber membrane, and the carbon fiber sheet is a spun carbon fiber sheet. Optionally, the substrate material is at least one of graphite fiber sheet, graphite fiber membrane, or polymer carbonized fiber membrane.

[0007] In some embodiments of this disclosure, the carbon content in the substrate material is ≥80 wt%.

[0008] In some embodiments of this disclosure, the carbon nanomaterial is selected from at least one of carbon nanofibers, carbon nanoclusters, oligowalled carbon nanotubes, single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes. As a conductive agent, the carbon nanomaterial can improve electrical conductivity.

[0009] In some embodiments of this disclosure, the lithium supplement is at least one of n-butyllithium, lithium carbonate, lithium fluoride, lithium biphenyl, lithium powder, lithium oxide, or lithium sulfide.

[0010] In some embodiments of this disclosure, the thickness of the zinc germanate / carbon composite anode material is 0.5-65 μm.

[0011] In some embodiments of this disclosure, gel B contains carbon nanomaterials. The addition of carbon nanomaterials to gel B can improve its electrical conductivity.

[0012] In some embodiments of this disclosure, the coating C contains a lithium replenishing agent. The presence of a lithium replenishing agent in the coating C improves the initial coulombic efficiency of the battery.

[0013] This disclosure also provides a method for preparing the zinc germanate / carbon composite anode material, including the following steps:

[0014] S1: The substrate material is mixed with solution A, heated to carry out the inoculation reaction, the solid and liquid are separated, and the resulting solid is washed to obtain an inoculation substrate with a zinc germanate wire array attached to the surface; the solution A is an aqueous solution of zinc formate and germanium hydroxide;

[0015] S2: Flatten the inoculation substrate, use a laser beam to translate and irradiate the surface of the zinc germanate wire array to make the thickness of the zinc germanate wire array uniform, and obtain the modified inoculation substrate after rinsing;

[0016] S3: The modified seeding substrate is placed in gel B and ultrasonically treated. Then, coating C is applied to the zinc germanate wire array surface on one side of the modified seeding substrate. After drying and cold pressing, the zinc germanate / carbon composite negative electrode material is obtained. The coating C forms the coating film C after drying.

[0017] The principle of the inoculation reaction in step S1: When heated, zinc formate hydrolyzes to produce hydroxide ions, and germanium hydroxide separates germanium ions and hydroxide ions. As the temperature increases, water molecules are removed to obtain germanium oxide. Germanium oxide and zinc ions gradually form zinc germanate particles in an alkaline environment and are deposited on the surface of the substrate material. As the dehydration time increases, germanium ions are deposited on the zinc germanate particles, gradually forming columnar zinc germanate. Due to the high concentration difference of germanium ions associated with the boundary of columnar zinc germanate, zinc germanate particles are gradually deposited on the columnar zinc germanate, turning the columnar zinc germanate into nanowire zinc germanate. The deposited zinc germanate particles are used as seeds to promote the growth of zinc germanate micro and nanowires, which slowly form long fiber zinc germanate. Multiple long fiber zinc germanate forms a filament array.

[0018] Step S2 uses the lowest point in the layer of the zinc germanate wire array as the reference point for thickness (the lowest point in the layer refers to the height of the shortest zinc germanate wire in the zinc germanate wire array). A high-power-density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the inoculation substrate. At high temperature, the zinc germanate wire array material at the contact point with the laser beam is pyrolyzed and detached. In this way, the surface of the wire array with different lengths on the inoculation substrate is modified by laser cutting, so that the thickness of the zinc germanate wire array is uniform.

[0019] In some embodiments of this disclosure, in step S1, the germanium hydroxide is at least one of germanium dihydrogen hydroxide or germanium tetrahydrogen hydroxide.

[0020] In some embodiments of this disclosure, in step S1, the thickness of the substrate material is 0.5-30 μm.

[0021] In some embodiments of this disclosure, in step S1, the molar volume ratio of zinc formate, germanium hydroxide and water in solution A is (1-3) mol: (4.5-12) mol: (10-30) L.

[0022] In some embodiments of this disclosure, in step S1, the heating temperature is 150-280°C, and the heating time is 10-30 hours. The generated gas is extracted during the heating process.

[0023] In some embodiments of this disclosure, in step S1, the washing is performed using an organic solvent, which is at least one of methanol, ethanol, acetone or ethylene glycol.

[0024] In some embodiments of this disclosure, step S1 further includes cooling with water at 0-5°C after the inoculation reaction.

[0025] In some embodiments of this disclosure, in step S2, the thickness of the zinc germanate wire array after being translated and irradiated by the laser beam is 1-95 μm.

[0026] In some embodiments of this disclosure, step S2, the rinsing, involves rinsing away excess zinc germanate wires adhering to the gaps in the zinc germanate wire array with deionized water. The excess zinc germanate wires in the gaps are those that have detached after being irradiated by the laser beam during translational irradiation.

[0027] In some embodiments of this disclosure, in step S3, the gel B is formed by mixing the nano-carbon material, the first binder and the first solvent in a mass ratio of (0.8-5):(0.1-3):(6-9).

[0028] In some embodiments of this disclosure, in step S3, the first adhesive is at least one of styrene-butadiene latex, chitosan, polyethylene glycol, or polyvinylidene fluoride.

[0029] In some embodiments of this disclosure, in step S3, the first solvent is at least one of polyacrylamide or glutaraldehyde.

[0030] In some embodiments of this disclosure, in step S3, after the ultrasonic treatment, the amount of gel B in the modified seeding substrate is 1%-12% of the mass of the modified seeding substrate.

[0031] In some embodiments of this disclosure, in step S3, the coating C comprises a second binder, a third binder, the lithium supplement agent, and a second solvent, wherein the mass ratio of the second binder, the third binder, and the lithium supplement agent is (2-6):(3-10):(0.01-0.05). Optionally, the second solvent is N-methylpyrrolidone.

[0032] In some embodiments of this disclosure, in step S3, the second adhesive is at least one of polyfurfuryl alcohol or polyethylene glycol.

[0033] In some embodiments of this disclosure, in step S3, the third adhesive is at least one selected from sodium alginate, lithium alginate, sodium carboxymethyl cellulose, carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, or lithium polyacrylate. The second and third adhesives are hydroxyl-containing and carboxyl-containing adhesives, respectively, which synergistically enhance adhesion.

[0034] In some embodiments of this disclosure, in step S3, the coating C is applied in an amount of 0.5%-2.0% of the mass of the modified inoculation substrate.

[0035] This disclosure also provides a negative electrode sheet, including a current collector and the zinc germanate / carbon composite negative electrode material disposed on the surface of the current collector.

[0036] This disclosure also provides a method for preparing the negative electrode sheet, wherein the zinc germanate / carbon composite negative electrode material is laid flat on a current collector coated with an adhesive, and then dried and cold-pressed to obtain the negative electrode sheet.

[0037] In some embodiments of this disclosure, the adhesive is at least one of sodium carboxymethyl cellulose, guar gum, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, polyimide, polyvinyl alcohol, or polyacrylonitrile.

[0038] In some embodiments of this disclosure, the amount of the adhesive is 0.8%-5% of the mass of the zinc germanate / carbon composite anode material.

[0039] According to the embodiments of this disclosure, at least the following beneficial effects are achieved:

[0040] 1. Compared with the graphite anode material obtained by mixing powdered graphite anode material with binder, the anode material with the shape of the wire array disclosed in this invention has large pores between each fiber or micro / nanowire on the seed substrate, which is conducive to electrolyte flow, wetting and retention, shortening the lithium ion transport distance, etc., and provides enough space to alleviate the volume effect during germanium alloying.

[0041] 2. This disclosure uses a rapid and precise laser cutting and modification method to ensure that each fiber or micro / nanowire on the seed substrate has a consistent length, so that the prepared wire array zinc germanate / carbon composite anode material has a consistent thickness. This makes it easier for this alloy anode material (wire array zinc germanate / carbon composite anode material) to have a consistent degree of orientation when lithiation begins at the endpoint, avoiding uneven lithiation caused by inconsistent orientation, and the occurrence of some surface areas that are not lithilated.

[0042] 3. Each micro-unit of the zinc germanate wire array disclosed herein is a micro-nano-type long rod of zinc germanate. Due to the pores between the long rods of zinc germanate, and the large amount of circumferential stress and small amount of longitudinal stress generated during the lithiation (lithiation intercalation) process, the lateral expansion dimension of the long rod of zinc germanate is much larger than the longitudinal dimension, and the outer wall expansion is greater than the inner wall expansion. The outer wall of the long rod of zinc germanate is more prone to expansion, which requires a buffer material to accommodate the release of stress. Therefore, by adding a filler gel B with low rheological properties to the zinc germanate wire array, the release of outer wall stress and the expansion stress of inner wall can be accommodated, effectively alleviating the volume change of the long rod of zinc germanate and improving the structural stability of the long rod of zinc germanate or the wire array. In addition, the filament array zinc germanate / carbon composite anode material has a lot of pores between the pores, resulting in a low compaction density of the anode sheet. This leads to a significant increase in the battery's internal resistance during charge-discharge cycles, which reduces its electrical performance. Therefore, a pore-filling gel B is left between the filament arrays to increase the density of the filament array zinc germanate / carbon composite anode material itself, thereby keeping the compaction density of the anode sheet within a reasonable range.

[0043] 4. The present invention performs a coating treatment (coating with coating C) on the surface of the wire array to form a thin film with a high viscosity modulus. This film does not undergo side reactions when in contact with the electrolyte, has high flexibility, and will not crack during the cutting of the electrode. Therefore, on the one hand, it acts as a protective layer to prevent fragments from penetrating the SEI film, separator, or excessive polarization at the negative electrode site due to material fracture during germanium alloying. On the other hand, it acts as a buffer layer for the entire wire array when it expands due to alloying, reducing the degradation of battery capacity and the reduction of battery life. Attached Figure Description

[0044] The present disclosure will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0045] Figure 1 This is a SEM image of the modified zinc germanate wire array graphite fiber membrane in step (2) of Embodiment 3 of this disclosure. Detailed Implementation

[0046] The following will describe the concept and technical effects of this disclosure clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this disclosure.

[0047] Example 1

[0048] This embodiment prepares an array-type zinc germanate / carbon composite anode material and anode sheet. The specific process is as follows:

[0049] (1) Inoculation: A two-dimensional planar graphite fiber membrane with a thickness of 18.5 μm was placed in a reaction vessel, and solution A (1 mol zinc formate, 4.5 mol germanium dihydrogen phosphate and 10 L deionized water were added. The mass ratio of solution A to graphite fiber membrane was 2:1. The reaction was carried out at 230 °C for 24 h with stirring. The membrane was cooled to room temperature with deionized water at 2 °C. After solid-liquid separation, the solid was washed with ethanol to obtain a graphite fiber membrane inoculated with zinc germanate wire array.

[0050] (2) Modification: The graphite fiber film seeded with zinc germanate wire array is flattened. The lowest point in the zinc germanate wire array layer is used as the thickness reference point. A high power density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the seeded substrate. This causes the zinc germanate wire array material to pyrolyze and fall off at the contact point with the laser beam. Then, deionized water is used to wash away the excess zinc germanate wires adhering to the gaps between the wire arrays to obtain a graphite fiber film with zinc germanate wire array of uniform thickness (modified seeded substrate).

[0051] (3) Filling with gel and coating: The zinc germanate wire array graphite fiber membrane is placed in gel B (a mixture of carbon nanofibers, styrene-butadiene latex and glutaraldehyde in a mass ratio of 2:1.5:7) and ultrasonically filled. Gel B is filled between the wire arrays. After ultrasonic treatment, the amount of gel B in the zinc germanate wire array graphite fiber membrane is 0.05 of the mass of the zinc germanate wire array graphite fiber membrane. Then, coating C (a mixture of polyfurfuryl alcohol, sodium alginate and lithium carbonate with high viscosity modulus in a mass ratio of 2:3.5:0.02, with N-methylpyrrolidone as the solvent) is coated on the surface of the zinc germanate wire array on one side of the zinc germanate wire array graphite fiber membrane. The coating amount is 0.01 of the zinc germanate wire array graphite fiber membrane. After drying and rolling at room temperature, an array-type zinc germanate / carbon composite negative electrode material with a thickness of 10 μm is obtained.

[0052] (4) Sheet preparation: The uncoated side of the array-type zinc germanate / carbon composite negative electrode material is laid flat on a current collector with adhesive (sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylonitrile are mixed in a mass ratio of 1:1.5:2.5). The amount of adhesive is 0.008 of the mass of the array-type zinc germanate / carbon composite negative electrode material. After drying, it is rolled at room temperature until the coating thickness is 5μm and then cut to obtain the array-type zinc germanate / carbon composite negative electrode sheet.

[0053] Example 2

[0054] This embodiment prepares an array-type zinc germanate / carbon composite anode material and anode sheet. The specific process is as follows:

[0055] (1) Inoculation: A two-dimensional planar graphite fiber membrane with a thickness of 18.5 μm was placed in a reaction vessel, and solution A (1.5 mol zinc formate, 6 mol germanium dihydrogen phosphate and 12 L deionized water were added. The mass ratio of solution A to graphite fiber membrane was 3:1. The reaction was carried out by heating at 245 °C for 18 h with stirring. The membrane was cooled to room temperature with deionized water at 2 °C. After solid-liquid separation, the solid was washed with ethanol to obtain a graphite fiber membrane inoculated with zinc germanate wire array.

[0056] (2) Modification: The graphite fiber film seeded with zinc germanate wire array is flattened. The lowest point in the zinc germanate wire array layer is used as the thickness reference point. A high power density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the seeded substrate. This causes the zinc germanate wire array material to pyrolyze and fall off at the contact point with the laser beam. Then, deionized water is used to wash away the excess zinc germanate wires adhering to the gaps between the wire arrays to obtain a graphite fiber film with zinc germanate wire array of uniform thickness (modified seeded substrate).

[0057] (3) Filling with gel and coating: The zinc germanate wire array graphite fiber membrane is placed in gel B (a mixture of carbon nanofibers, styrene-butadiene latex and glutaraldehyde in a mass ratio of 3:2:8) and ultrasonically filled. Gel B is filled between the wire arrays. After ultrasonic treatment, the amount of gel B in the zinc germanate wire array graphite fiber membrane is 0.08 of the mass of the zinc germanate wire array graphite fiber membrane. Then, coating C (a mixture of polyfurfuryl alcohol, sodium alginate and lithium carbonate in a mass ratio of 3:4.5:0.018, with N-methylpyrrolidone as the solvent) is coated on the surface of the zinc germanate wire array on one side of the zinc germanate wire array graphite fiber membrane. The coating amount is 0.01 of the zinc germanate wire array graphite fiber membrane. After drying and rolling at room temperature, an array-type zinc germanate / carbon composite negative electrode material with a thickness of 10 μm is obtained.

[0058] (4) Sheet preparation: The uncoated side of the array-type zinc germanate / carbon composite negative electrode material is laid flat on a current collector with adhesive (sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylonitrile are mixed in a mass ratio of 1:1.5:2.5). The amount of adhesive is 0.008 of the mass of the array-type zinc germanate / carbon composite negative electrode material. After drying, it is rolled at room temperature until the coating thickness is 5μm and then cut to obtain the array-type zinc germanate / carbon composite negative electrode sheet.

[0059] Example 3

[0060] This embodiment prepares an array-type zinc germanate / carbon composite anode material and anode sheet. The specific process is as follows:

[0061] (1) Inoculation: A two-dimensional planar graphite fiber membrane with a thickness of 18.5 μm was placed in a reaction vessel, and solution A (1.8 mol zinc formate, 6 mol germanium dihydrogen phosphate and 15 L deionized water were added. The mass ratio of solution A to graphite fiber membrane was 4:1. The reaction was carried out by heating at 175 °C for 30 h with stirring. The membrane was cooled to room temperature with deionized water at 2 °C. After solid-liquid separation, the solid was washed with ethanol to obtain a graphite fiber membrane inoculated with zinc germanate wire array.

[0062] (2) Modification: The graphite fiber film seeded with zinc germanate wire array is flattened. The lowest point in the zinc germanate wire array layer is used as the thickness reference point. A high power density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the seeded substrate. This causes the zinc germanate wire array material to pyrolyze and fall off at the contact point with the laser beam. Then, deionized water is used to wash away the excess zinc germanate wires adhering to the gaps between the wire arrays to obtain a graphite fiber film with zinc germanate wire array of uniform thickness (26 μm) (modified seeded substrate).

[0063] (3) Filling with gel and coating: The zinc germanate wire array graphite fiber membrane is placed in gel B (a mixture of carbon nanofibers, styrene-butadiene latex and glutaraldehyde in a mass ratio of 1:2.5:6.5) and ultrasonically filled. Gel B is filled between the wire arrays. After ultrasonic treatment, the amount of gel B in the zinc germanate wire array graphite fiber membrane is 0.1 of the mass of the zinc germanate wire array graphite fiber membrane. Then, coating C (a mixture of polyfurfuryl alcohol, sodium alginate and n-butyllithium in a mass ratio of 3.5:4.5:0.03, with N-methylpyrrolidone as the solvent) is coated on the surface of the zinc germanate wire array on one side of the zinc germanate wire array graphite fiber membrane. The coating amount is 0.01 of the zinc germanate wire array graphite fiber membrane. After drying and rolling at room temperature, an array-type zinc germanate / carbon composite negative electrode material with a thickness of 10 μm is obtained.

[0064] (4) Sheet preparation: The uncoated side of the array-type zinc germanate / carbon composite negative electrode material is laid flat on a current collector with adhesive (sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylonitrile are mixed in a mass ratio of 1:1.5:2.5). The amount of adhesive is 0.008 of the mass of the array-type zinc germanate / carbon composite negative electrode material. After drying, it is rolled at room temperature until the coating thickness is 5μm and then cut to obtain the array-type zinc germanate / carbon composite negative electrode sheet.

[0065] Example 4

[0066] This embodiment prepares an array-type zinc germanate / carbon composite anode material and anode sheet. The specific process is as follows:

[0067] (1) Inoculation: A two-dimensional planar polymer carbon fiber membrane with a thickness of 8.5 μm was placed in a reaction vessel, and solution A (1.0 mol zinc formate, 6 mol germanium dihydrogen phosphate and 20 L deionized water were added. The mass ratio of solution A to graphite fiber membrane was 3:1. The reaction was carried out by heating at 264 °C for 12 h with stirring. The membrane was cooled to room temperature with deionized water at 4 °C. After solid-liquid separation, the solid was washed with ethanol to obtain a graphite fiber membrane inoculated with zinc germanate wire array.

[0068] (2) Modification: The graphite fiber film seeded with zinc germanate wire array is flattened. The lowest point in the zinc germanate wire array layer is used as the thickness reference point. A high power density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the seeded substrate. This causes the zinc germanate wire array material to pyrolyze and fall off at the contact point with the laser beam. Then, deionized water is used to wash away the excess zinc germanate wires adhering to the gaps between the wire arrays to obtain a graphite fiber film with zinc germanate wire array of uniform thickness (modified seeded substrate).

[0069] (3) Filling with gel and coating: The zinc germanate wire array graphite fiber membrane is placed in gel B (a mixture of carbon nanofibers, styrene-butadiene latex and glutaraldehyde in a mass ratio of 3.5:2.5:9) and ultrasonically filled. Gel B is filled between the wire arrays. After ultrasonic treatment, the amount of gel B in the zinc germanate wire array graphite fiber membrane is 0.03 of the mass of the zinc germanate wire array graphite fiber membrane. Then, coating C (a mixture of polyfurfuryl alcohol, sodium alginate and n-butyllithium in a mass ratio of 5.5:7.5:0.042, with N-methylpyrrolidone as the solvent) is coated on the surface of the zinc germanate wire array on one side of the zinc germanate wire array graphite fiber membrane. The coating amount is 0.01 of the zinc germanate wire array graphite fiber membrane. After drying and rolling at room temperature, an array-type zinc germanate / carbon composite negative electrode material with a thickness of 10 μm is obtained.

[0070] (4) Sheet preparation: The uncoated side of the array-type zinc germanate / carbon composite negative electrode material is laid flat on a current collector with adhesive (sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylonitrile are mixed in a mass ratio of 1:1.5:2.5). The amount of adhesive is 0.008 of the mass of the array-type zinc germanate / carbon composite negative electrode material. After drying, it is rolled at room temperature until the coating thickness is 5μm and then cut to obtain the array-type zinc germanate / carbon composite negative electrode sheet.

[0071] Example 5

[0072] This embodiment prepares an array-type zinc germanate / carbon composite anode material and anode sheet. The specific process is as follows:

[0073] (1) Inoculation: A two-dimensional planar polymer carbon fiber membrane with a thickness of 8.5 μm was placed in a reaction vessel, and solution A (3 mol zinc formate, 12 mol germanium tetrahydric acid and 20 L deionized water were added. The mass ratio of solution A to graphite fiber membrane was 4.5:1. The reaction was carried out by heating at 264 °C for 12 h with stirring. The membrane was cooled to room temperature with deionized water at 4 °C. After solid-liquid separation, the solid was washed with ethanol to obtain a graphite fiber membrane inoculated with zinc germanate wire array.

[0074] (2) Modification: The graphite fiber film seeded with zinc germanate wire array is flattened. The lowest point in the zinc germanate wire array layer is used as the thickness reference point. A high power density laser beam is used to translate and irradiate the zinc germanate wire array parallel to the two-dimensional plane of the seeded substrate. This causes the zinc germanate wire array material to pyrolyze and fall off at the contact point with the laser beam. Then, deionized water is used to wash away the excess zinc germanate wires adhering to the gaps between the wire arrays to obtain a graphite fiber film with zinc germanate wire array of uniform thickness (modified seeded substrate).

[0075] (3) Filling with gel and coating: The zinc germanate wire array graphite fiber membrane is placed in gel B (made of carbon nanofibers, styrene-butadiene latex and glutaraldehyde in a mass ratio of 5:3:8.5) and ultrasonically filled. Gel B is filled between the wire arrays. After ultrasonic treatment, the amount of gel B in the zinc germanate wire array graphite fiber membrane is 0.12 of the mass of the zinc germanate wire array graphite fiber membrane. Then, coating C (made of polyfurfuryl alcohol, sodium alginate and n-butyllithium in a mass ratio of 6:8:0.5, with N-methylpyrrolidone as the solvent) is coated on the surface of the zinc germanate wire array on one side of the zinc germanate wire array graphite fiber membrane. The coating amount is 0.01 of the zinc germanate wire array graphite fiber membrane. After drying and rolling at room temperature, an array-type zinc germanate / carbon composite negative electrode material with a thickness of 10 μm is obtained.

[0076] (4) Sheet preparation: The uncoated side of the array-type zinc germanate / carbon composite negative electrode material is laid flat on a current collector with adhesive (sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylonitrile are mixed in a mass ratio of 1:1.5:2.5). The amount of adhesive is 0.008 of the mass of the array-type zinc germanate / carbon composite negative electrode material. After drying, it is rolled at room temperature until the coating thickness is 5μm and then cut to obtain the array-type zinc germanate / carbon composite negative electrode sheet.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that step (2) was not modified.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 3 is that the coating step (3) was not performed.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 3 is that the filling gel in step (3) was not performed.

[0083] Test case

[0084] 1. The array-type zinc germanate / carbon composite negative electrode sheets of Examples 1-5 and Comparative Examples 1-3 were placed in a vacuum oven for drying. In the half-cell, the dried array-type zinc germanate / carbon composite negative electrode sheet was used on the negative electrode side, and a lithium metal sheet was used as the counter electrode on the positive electrode side. The separator was Celgard 2400, and the electrolyte was 1M LiPF6 EC, DMC, and DEC (volume ratio of 1:1:1).

[0085] 2. First, the dried electrode sheets are punched, and then weighed using an electronic analytical balance with a concentration of 1 / 100,000. They are then assembled in a glove box, where the water and oxygen content is less than 0.5 ppm. The electrode sheets are first placed in the CR2025 positive electrode shell, then two drops of electrolyte are added. A 19mm diameter separator is then placed in the shell, followed by one drop of electrolyte. Next, the lithium-ion battery, spacer, and spring are placed in sequence, ensuring their centers are as close as possible to the center of the battery. Finally, the negative electrode shell is placed on top, and the preliminarily assembled battery is sealed on a battery packaging machine to complete the assembly of the coin cell.

[0086] 3. Compacted density = surface density / thickness of negative electrode sheet (excluding current collector thickness); expansion rate of negative electrode sheet = (thickness of negative electrode sheet after filling - thickness of negative electrode sheet after drying) / thickness of negative electrode sheet after drying * 100%.

[0087] 4. The charge-discharge performance of the prepared half-cell was tested at 100 mA / g using a CT2001A battery testing system.

[0088] Table 1 shows the compaction density and expansion rate of the negative electrode sheets in Examples 1-5 and Comparative Examples 1-3.

[0089] <![CDATA[Compaction density (g / cm 3 )]]> Expansion rate (%) Example 1 1.55 28.80 Example 2 1.40 28.17 Example 3 1.47 29.89 Example 4 1.60 27.72 Example 5 1.68 29.24 Comparative Example 1 1.27 31.37 Comparative Example 2 1.36 31.95 Comparative Example 3 1.19 45.38

[0090] Table 2 shows the first-efficiency and capacity retention of coin cells prepared in Examples 1-5 and Comparative Examples 1-3.

[0091]

[0092]

[0093] As shown in Tables 1 and 2, compared with Comparative Examples 1-3, Examples 1-5 exhibited higher compaction density, better initial coulombic efficiency, and better capacity retention. Furthermore, the negative electrode sheet maintained a good appearance after 500 cycles without cracking. In contrast, Example 3, lacking gel filling, resulted in higher material expansion, leading to structural damage after multiple cycles and ultimately poor cycle performance (as evidenced by the capacity retention after 500 cycles). Comparative Example 1, without modification, showed inferior initial coulombic efficiency, capacity retention, and negative electrode sheet appearance after 500 cycles compared to Examples 1-5. In conclusion, the negative electrode sheet electrical performance of Examples 1-5 was improved through modification, gel filling, and coating.

Claims

1. A zinc germanate / carbon composite negative electrode material, characterized in that, The zinc germanate / carbon composite negative electrode material comprises a substrate material and an array of zinc germanate filaments attached to the surface of the substrate material, the substrate material is a two-dimensional planar carbon fiber material, the array of zinc germanate filaments is filled with gel B, and the surface of the array of zinc germanate filaments is covered with a coating film C. The gel B is mixed by nano-carbon material, first adhesive and first solvent in a mass ratio of (0.8-5):(0.1-3):(6-9). The coating film C is formed after the coating C is dried, and the coating C comprises second adhesive, third adhesive, lithium supplement agent and second solvent. 2.The zinc germanium phosphate / carbon composite negative electrode material of claim 1, wherein, The substrate material is at least one of carbon fiber film, carbon fiber sheet, carbon fiber felt, graphite fiber sheet or graphite fiber film. 3.The zinc germanium phosphate / carbon composite negative electrode material of claim 1, wherein, The carbon content in the substrate material is ≥80wt%. 4.The zinc germanium phosphate / carbon composite negative electrode material of claim 1, wherein, The nano-carbon material is at least one of carbon nanofiber, carbon nanocluster, single-walled carbon nanotube or multi-walled carbon nanotube. 5.The zinc germanium phosphate / carbon composite negative electrode material of claim 1, wherein, The lithium supplement agent is at least one of n-butyl lithium, lithium carbonate, lithium fluoride, diphenyl lithium, lithium powder, lithium oxide or lithium sulfide. 6.The zinc germanium phosphate / carbon composite negative electrode material of claim 1, wherein, The thickness of the zinc germanate / carbon composite negative electrode material is 0.5-65μm.

7. The method of producing a zinc germanate / carbon composite negative electrode material according to any one of claims 1 to 6, characterized by, The method comprises the following steps: S1: mixing the substrate material with solution A, heating for inoculation reaction, solid-liquid separation, washing the obtained solid to obtain an inoculated substrate with an array of zinc germanate filaments attached to the surface; the solution A is an aqueous solution of zinc formate and germanium hydroxide; S2: flattening the inoculated substrate, and using a laser beam to translate and irradiate the surface of the array of zinc germanate filaments to make the thickness of the array of zinc germanate filaments uniform, and then washing to obtain a modified inoculated substrate; S3: ultrasonic treatment of the modified inoculated substrate in gel B, then coating coating C on the surface of the array of zinc germanate filaments on one side of the modified inoculated substrate, and then drying and cold pressing to obtain the zinc germanate / carbon composite negative electrode material; the coating C forms the coating film C after drying.

8. The preparation method according to claim 7, characterized in that, In step S1, the thickness of the substrate material is 0.5-30μm.

9. The preparation method according to claim 7, characterized in that, In step S1, the molar volume ratio of zinc formate, germanium hydroxide and water in the solution A is (1-3)mol:(4.5-12)mol:(10-30)L; and the mass ratio of the solution A to the substrate material is (2-5):

1.

10. The preparation method according to claim 7, characterized in that, In step S1, the heating temperature is 150-280℃, and the heating time is 10-30h.

11. The preparation method according to claim 7, characterized in that, In step S1, the washing is performed using an organic solvent, and the organic solvent is at least one of methanol, ethanol, acetone or ethylene glycol.

12. The method of claim 7, wherein, In step S2, the thickness of the array of zinc germanate filaments after the translation and irradiation of the laser beam is 1-95μm.

13. The preparation method according to claim 7, characterized in that, In step S2, the washing is to wash away the excess zinc germanate filaments adhered to the gaps between the array of zinc germanate filaments with deionized water.

14. The preparation method according to claim 7, characterized in that, In step S3, the first adhesive is at least one of styrene-butadiene latex, chitosan, polyethylene glycol or polyvinylidene fluoride.

15. The preparation method according to claim 7, characterized in that, In step S3, the first solvent is at least one of polyacrylamide or glutaraldehyde.

16. The method of claim 7, wherein, In step S3, after the ultrasonic treatment, the amount of gel B contained in the modified inoculated substrate is 1%-12% of the mass of the modified inoculated substrate.

17. The method of claim 7, wherein the method further comprises, The coating C in step S3 comprises a second binder, a third binder, a lithium supplement agent, and a second solvent, and the mass ratio of the second binder, the third binder, and the lithium supplement agent is (2-6):(3-10):(0.01-0.05).

18. The method of claim 17, wherein, The second binder in step S3 is at least one of polyfurfuryl alcohol or polyethylene glycol.

19. The method of claim 17, wherein, The third binder in step S3 is at least one of sodium alginate, lithium alginate, sodium carboxymethyl cellulose, carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, or lithium polyacrylate.

20. The method of claim 7, wherein, The coating amount of the coating C in step S3 accounts for 0.5%-2.0% of the mass of the modified inoculation substrate.

21. A negative electrode sheet characterized by comprising: The zinc germanate / carbon composite negative electrode material as claimed in any one of claims 1-6 is attached to a current collector.

22. A method of preparing the negative electrode sheet according to claim 21, characterized by, The zinc germanate / carbon composite negative electrode material is spread on a current collector with an adhesive, dried, and cold-pressed to obtain the negative electrode sheet.

23. The method of claim 22, wherein, The adhesive is at least one of sodium carboxymethyl cellulose, guar gum, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, polyimide, polyvinyl alcohol, or polyacrylonitrile.

24. The method of claim 22, wherein, The amount of the adhesive is 0.8%-5% of the mass of the zinc germanate / carbon composite negative electrode material.

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