A hard carbon negative electrode material, a hard carbon negative electrode sheet and a sodium-ion secondary battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a hard carbon negative electrode material, a hard carbon negative electrode sheet and a sodium-ion secondary battery. The hard carbon negative electrode material comprises first hard carbon particles, second hard carbon particles and third hard carbon particles; the first hard carbon particles are multi-angled hard carbon particles, the second hard carbon particles are few-angled or non-angled hard carbon particles, and the third hard carbon particles are obtained by heating treatment of the first hard carbon particles, the second hard carbon particles, a carbon source and a hot melt salt. The application uses different types of hard carbon particles to obtain the hard carbon negative electrode material, enhances the close contact of different hard carbon negative electrode materials in the hard carbon negative electrode sheet and the particle slip during cold pressing, reduces the rebound after cold pressing of the composite hard carbon negative electrode sheet, improves the compaction density of the composite hard carbon negative electrode sheet, and thus improves the volume energy density of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a hard carbon anode material, a hard carbon anode sheet, and a sodium-ion secondary battery. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used in electric vehicles and portable electronic products due to their high energy density, long cycle life, and mature industrial manufacturing. However, the low reserves and uneven distribution of lithium resources hinder the continued development of LIBs, especially in large-scale power grid applications. Therefore, there is an urgent need to develop new energy storage technologies to replace LIBs in certain fields. Sodium, an alkali metal element adjacent to lithium on the periodic table, has similar physicochemical properties. Therefore, sodium-ion batteries (SIBs) have attracted considerable attention as a potential alternative to LIBs due to the widespread availability of sodium precursors and their low cost.

[0003] Among them, hard carbon anodes in sodium-ion batteries are low-cost, renewable, environmentally friendly, and abundant carbon sources from various biomass or synthetic polymers. However, for the practical application of hard carbon anode materials, there are still significant problems: due to the microporous structure and high porosity of hard carbon anode materials (HC), they are prone to slippage and rebound when pressure is applied. Therefore, their compaction density (≤0.90 g / cm³) is low during cold pressing of the anode sheet. 3 The low compaction density of the negative electrode sheet significantly affects the volumetric energy density of the battery, thus significantly slowing down the application of HC. Summary of the Invention

[0004] The present invention aims to solve the above problems and provides a hard carbon anode material, a hard carbon anode sheet and a sodium-ion secondary battery. By enhancing the close contact of different hard carbon anode materials in the hard carbon anode sheet and the particle slippage during cold pressing, the rebound of the composite hard carbon anode sheet after cold pressing is reduced, thereby improving the compaction density of the composite hard carbon anode sheet.

[0005] According to the technical solution of the present invention, the hard carbon anode material comprises,

[0006] The first hard carbon particle is a multi-faceted hard carbon particle.

[0007] The second hard carbon particle is a hard carbon particle with few or no sharp edges.

[0008] The third hard carbon particle includes a hard carbon particle core and a carbon source covering the hard carbon particle core. The hard carbon particle core includes a first hard carbon particle and a second hard carbon particle. The carbon source contains molten salt.

[0009] Specifically, the term "no sharp edges" refers to a surface without protrusions, presenting as a curved or flat surface; the specific shape of the second hard carbon particle can be spherical, quasi-spherical, ellipsoidal, etc.; the third hard carbon particle is spherical, quasi-spherical, or irregular polygonal block.

[0010] Furthermore, the first hard carbon particles are hard carbon particles obtained by carbonizing and crushing starch, coconut shell, walnut shell, olive shell, camellia shell, tung oil shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw, wood, etc.

[0011] The second hard carbon particles are obtained by carbonizing (obtaining hard carbon) starch, coconut shell, walnut shell, olive shell, camellia shell, tung oil shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw, wood, etc., and then crushing them, followed by ball milling and carbon coating to remove the surface edges.

[0012] Furthermore, the carbonization temperature is 1000-1600℃;

[0013] The carbon source used for carbon coating is a polymer carbon source, selected from one or more of polyacrylonitrile, polyaniline, polypropylene, polyethylene, etc., and the amount of carbon source used is 1-8 wt% of hard carbon; the carbon coating method is heat treatment at 1000-1500℃ for 1-5 hours.

[0014] Furthermore, the hard carbon anode material satisfies at least one of the following conditions:

[0015] The median particle size Dv50 of the first hard carbon particle is less than that of the second hard carbon particle and less than that of the third hard carbon particle, which is less than or equal to 60 μm.

[0016] The mass ratio of the first hard carbon particle, the second hard carbon particle, and the third hard carbon particle is (1-10):(1-10):(1-5).

[0017] Furthermore, the third hard carbon particle satisfies at least one of the following conditions:

[0018] The carbon source is selected from one or more of needle coke, pitch tar, petroleum coke and isomorphous coke;

[0019] The hot molten salt is selected from one or more of sodium chloride, potassium chloride, magnesium chloride, lithium chloride, sodium nitrate, potassium nitrate, lithium nitrate, and magnesium nitrate;

[0020] In the preparation of raw materials, the mass ratio of the first hard carbon particles, the second hard carbon particles, the carbon source and the hot molten salt is (1-10):(1-20):(0.1-1):(0.01-3).

[0021] Furthermore, the third hard carbon particle is obtained by heating the first hard carbon particle, the second hard carbon particle, the carbon source, and the hot molten salt.

[0022] Furthermore, the temperature of the heat treatment is 300-1200℃, and the heat treatment time is 1-8h.

[0023] Furthermore, the process includes cooling and washing steps after the heat treatment.

[0024] A second aspect of the present invention provides a hard carbon anode sheet, which uses the above-mentioned hard carbon anode material as the anode active material.

[0025] Furthermore, the hard carbon negative electrode sheet includes a porous current collector and a negative electrode coating; the negative electrode coating fills the pores of the porous current collector and / or covers at least one side surface of the porous current collector; the negative electrode coating comprises the aforementioned hard carbon negative electrode material.

[0026] Specifically, the negative electrode coating fills the pores of the porous current collector, or covers at least one side surface of the porous current collector, or fills the pores of the porous current collector and covers at least one side surface of the porous current collector; the active material of the negative electrode coating adopts the above-mentioned hard carbon negative electrode material.

[0027] When the negative electrode coating fills the pores of the porous current collector and covers at least one side surface of the porous current collector, the negative electrode coating includes an inner negative electrode coating on the porous current collector and an outer negative electrode coating on the surface of the porous current collector.

[0028] Furthermore, at least one of the following conditions must be met:

[0029] The thickness of the hard carbon negative electrode sheet is 35-620 μm;

[0030] The thickness of the porous current collector is 5-180 μm;

[0031] The pore size of the porous current collector is 3-90 μm.

[0032] Furthermore, the porous current collector is made of copper, nickel, aluminum, nickel-plated copper, copper-nickel, copper-aluminum, nickel-aluminum, etc.

[0033] Furthermore, the thickness of the external negative electrode coating (i.e., the negative electrode coating outside the single-sided surface of the porous current collector) is 30-220 μm.

[0034] A third aspect of the present invention provides a method for preparing the above-mentioned hard carbon negative electrode sheet, comprising the following steps:

[0035] S1: Add water to the mixture of hard carbon anode material, conductive agent and binder, and mix well to obtain anode coating, wherein the hard carbon anode material is the above-mentioned hard carbon anode material;

[0036] S2: The negative electrode coating is applied to at least one side of the porous current collector, and after drying and cold pressing, the hard carbon negative electrode sheet is obtained.

[0037] Furthermore, at least one of the following conditions must be met:

[0038] a. In step S1, the mixing method is to stir under vacuum for 180-560 minutes;

[0039] b. In step S1, the mass percentages of the hard carbon anode material, conductive agent, and binder in the mixture are 85.0-99.6 wt%, 0.2-7.0 wt%, and 0.2-8.0 wt%, respectively.

[0040] c. In step S1, the fineness of the negative electrode coating is ≤0.08mm;

[0041] d. In step S1, the mass percentage of hard carbon anode material in the anode coating is 32-70%.

[0042] e. In step S2, the transmission side pressure of the cold press is 10-90T;

[0043] f. In step S2, the cold pressing includes a first cold pressing and a second cold pressing. After the first cold pressing, the compaction density of the electrode sheet is 0.60-0.89 g / cm³. 3 The compaction density of the electrode sheet after secondary cold pressing (i.e., the hard carbon negative electrode sheet) is 0.90-1.30 g / cm³. 3 .

[0044] Furthermore, the conductive agent is at least one of conductive carbon black, acetylene black, graphite, graphene, carbon microwires, carbon nanowires, carbon microtubes, and carbon nanotubes.

[0045] The adhesive is at least one of polyvinylidene fluoride, polyimide, polyurethane, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyacrylate, styrene-butadiene rubber, and sodium alginate.

[0046] Furthermore, the viscosity of the negative electrode coating is 0.5-9.0 Pa·s.

[0047] Furthermore, in step S2, the drying temperature is 75-115℃.

[0048] A fourth aspect of the present invention provides a sodium-ion secondary battery comprising the above-described hard carbon negative electrode sheet, or a hard carbon negative electrode sheet prepared by the above-described preparation method.

[0049] Furthermore, the sodium-ion secondary battery also includes a positive electrode and a separator.

[0050] The positive electrode material in the positive electrode sheet is at least one of sodium nickel manganate, sodium nickel copper manganate, sodium nickel iron manganate, sodium nickel cobalt manganate, sodium nickel iron titanate, sodium hexacyanoferrate, sodium hexacyanomanganate, sodium hexacyanocobalt ferrate, sodium hexacyanonickel ferrate, sodium iron manganese phosphate, and sodium fluorophosphate.

[0051] The separator is a polymer separator made of at least one of polyethylene, polypropylene, polysulfonyl, polyvinyl alcohol, polyvinylidene fluoride, and polymalonic acid.

[0052] The technical solution of the present invention has the following advantages compared with the prior art:

[0053] 1. This invention involves mixing a first hard carbon particle with multiple angular edges, a second hard carbon particle with fewer or no angular edges, and a third hard carbon particle with a larger particle size. The first and second hard carbon particles fill the third hard carbon particle, reducing the gaps between particles caused by the single multi-angular, few-angular, or non-angular hard carbon particles, and improving the bonding between hard carbon particles. At the same time, the multi-angular first hard carbon particles hold the non-angular second and third hard carbon particles in place, reducing slippage between hard carbon particles during cold pressing.

[0054] 2. The third hard carbon particle of the present invention is obtained by mixing the first hard carbon particle, the second hard carbon particle with a carbon source and hot molten salt and then treating it at high temperature. The low melting point salt of the hot molten salt is used as the reaction medium. A liquid phase will appear during the synthesis process. The salt reactants diffuse in the carbon source to a certain extent. When the temperature is raised, the solid-solid reaction is transformed into a solid-liquid reaction, which accelerates the carbonization and crystallization process of hard carbon (first hard carbon particle and second hard carbon particle). It also helps to reduce the contact gap between the first hard carbon particle and the second hard carbon particle in the third hard carbon particle, and the bonding is tighter, which helps to improve the compaction density of the negative electrode sheet.

[0055] 3. The hard carbon negative electrode sheet of the present invention can improve the compaction effect of the negative electrode sheet by using different types of hard carbon particles in combination and then coating it. The preparation process is simple and easy to implement and has great practical application value.

[0056] 4. The hard carbon negative electrode sheet of the present invention adopts a porous current collector. The high mechanical strength of the porous skeleton (porous current collector) can slow down the rebound of the negative electrode coating after cold pressing and reduce the rebound thickness of the negative electrode sheet. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the structure of the first hard carbon particle and the second hard carbon particle in the hard carbon anode material of the present invention.

[0058] Figure 2 This is a schematic diagram of the structure of the third hard carbon particle in the hard carbon anode material of the present invention.

[0059] Figure 3This is a schematic diagram of the porous current collector in the hard carbon negative electrode of the present invention.

[0060] Figure 4 This is a schematic diagram of the hard carbon negative electrode sheet of the present invention.

[0061] Explanation of reference numerals in the attached figures: 1-First hard carbon particle, 2-Second hard carbon particle, 3-Third hard carbon particle, 4-Porous current collector, 5-Internal negative electrode coating, 6-External negative electrode coating. Detailed Implementation

[0062] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0063] This invention provides a hard carbon anode material, comprising a first hard carbon particle 1, a second hard carbon particle 2, and a third hard carbon particle 3 in a mass ratio of (1-10):(1-20):(0.1-1):(0.01-3). The median particle size Dv50 of the first hard carbon particle is less than or equal to the median particle size Dv50 of the second hard carbon particle, and the median particle size Dv50 of the third hard carbon particle is less than or equal to 60 μm.

[0064] like Figure 1 As shown, the first hard carbon particle 1 is a hard carbon particle with multiple edges and corners, and the second hard carbon particle 2 is a hard carbon particle with few edges or no edges and corners (it is quasi-spherical in the figure, but it can also be spherical, ellipsoidal, etc.).

[0065] The first hard carbon particles can be obtained by carbonizing and crushing at a high temperature of 1000-1600℃ from at least one of the following: starch, coconut shell, walnut shell, olive shell, camellia shell, tung oil shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw, and wood.

[0066] The first and second hard carbon particles can be obtained by carbonizing at high temperature (to obtain hard carbon) and crushing at least one of the following: starch, coconut shell, walnut shell, olive shell, camellia shell, tung oil shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw, wood, etc., followed by ball milling and carbon coating to remove surface sharp edges. The specific carbon coating process involves adding 1-8 wt% of a polymer carbon source by weight of the hard carbon, and heat-treating at 1000-1500℃ for 1-5 hours. The polymer carbon source is selected from one or more of polyaniline, polypropylene, polyethylene, etc.

[0067] The third hard carbon particle 3 is obtained by heating the first hard carbon particle 1, the second hard carbon particle 2, a carbon source, and a hot molten salt in a mass ratio of (1-10):(1-20):(0.1-1):(0.01-3). The resulting product has the following morphology: Figure 2 As shown.

[0068] The carbon source is selected from one or more of needle coke, pitch tar, petroleum coke and isomorphous coke.

[0069] The hot molten salt is selected from one or more of sodium chloride, potassium chloride, magnesium chloride, lithium chloride, sodium nitrate, potassium nitrate, lithium nitrate, and magnesium nitrate;

[0070] The heat treatment temperature is 300-1200℃, and the heat treatment time is 1-8 hours; after heat treatment, cooling and washing are carried out.

[0071] The obtained hard carbon anode material can be used to prepare hard carbon anode sheets, and its preparation method is as follows:

[0072] S1: Place 85.0-99.6wt%, 0.2-7.0wt%, and 0.2-8.0wt% of hard carbon anode material, conductive agent, and binder in the mixing tank of a mixer, and add water (such as deionized water) until the mass percentage of hard carbon anode material is 32-70% and the viscosity is 0.5-9.0 Pa·s. Stir under vacuum for 180-560 min, and control the fineness to ≤0.08 mm to obtain the anode coating.

[0073] S2: The obtained negative electrode coating is coated on at least one side of the porous current collector 4, dried at 75-115°C, and then cold-pressed to obtain the hard carbon negative electrode sheet.

[0074] Cold pressing includes a single cold pressing, with a pressure of 10-90T on the drive side. After the single cold pressing, the compacted density of the electrode sheet is 0.60-0.89 g / cm³. 3 ;as well as

[0075] The secondary cold pressing involves a pressure of 10-90T on the transmission side, resulting in a compaction density of 0.90-1.30 g / cm³ for the electrode sheet (i.e., the hard carbon negative electrode sheet). 3 .

[0076] The conductive agent is at least one of conductive carbon black, acetylene black, graphite, graphene, carbon microwires, carbon nanowires, carbon microtubes, and carbon nanotubes.

[0077] The binder is at least one of polyvinylidene fluoride, polyimide, polyurethane, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyacrylate, styrene-butadiene rubber, and sodium alginate.

[0078] The thickness of the porous current collector is 5-180 μm, and the pore size is 3-90 μm (the pores can be tortuous / through the porous current collector, such as...). Figure 3 As shown), its materials are copper, nickel, aluminum, nickel-copper plated, copper-nickel plated, copper-aluminum plated, nickel-aluminum plated, etc.

[0079] During the coating process, the negative electrode coating enters the pores of the porous current collector, ultimately forming an internal negative electrode coating 5 on the porous current collector 4 and an external negative electrode coating 6 on the surface of the porous current collector 4 (e.g., ...). Figure 4 (as shown);

[0080] The thickness of the external negative electrode coating on one side ranges from 30 to 280 μm.

[0081] The thickness of the resulting negative electrode sheet is 35-620 μm, for example, it can be 35-50 μm, 50-60 μm, 60-70 μm, 70-80 μm, 80-100 μm, 100-120 μm, 120-150 μm, 150-180 μm, 180-200 μm, 200-230 μm, 230-250 μm, 25-300 μm, 300-350 μm, 350-400 μm, 400-450 μm, 450-500 μm, 500-600 μm, 600-620 μm, or any other value within the above range.

[0082] It can be used to prepare sodium-ion secondary batteries.

[0083] In sodium-ion secondary batteries, the positive electrode material in the positive electrode sheet can be at least one of sodium nickel manganate, sodium nickel copper manganate, sodium nickel iron manganate, sodium nickel cobalt manganate, sodium nickel iron titanate, sodium hexacyanoferrate, sodium hexacyanomanganate, sodium hexacyanocobalt ferrate, sodium hexacyanonickel ferrate, sodium iron manganese phosphate, and sodium vanadium fluorophosphate.

[0084] The separator can be a polymer separator made of at least one of polyethylene, polypropylene, polysulfonyl, polyvinyl alcohol, polyvinylidene fluoride, and polymalonic acid.

[0085] Example 1

[0086] This embodiment provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0087] S1: 97wt% hard carbon anode material, 1.2wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 1.8wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% sodium polyacrylate) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 48% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 2.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0088] Among them, the hard carbon anode material is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles in a mass ratio of 5:3:2.

[0089] The first hard carbon particle has a Dv50 of 7.4μm and is obtained by high-temperature carbonization and crushing of coconut shells;

[0090] The second hard carbon particles have a Dv50 of 11.1 μm and are spherical. They are obtained by carbonizing coconut shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyacrylonitrile by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0091] The third hard carbon particle has a Dv50 of 28.6 μm. It was obtained by treating the first hard carbon particle, the second hard carbon particle, needle coke and potassium chloride in a mass ratio of 5:5:0.2:0.05 at 900℃ for 3 h, followed by cooling and washing.

[0092] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector, 60μm thick, 35μm pore size), and dried at 105℃; the drive-side pressure during a single cold press is 27T, and the compaction density of the electrode sheet is 0.83g / cm³. 3 The secondary cold pressing process involves a transmission-side pressure of 29T to obtain a hard carbon negative electrode sheet with a compaction density of 0.99 g / cm³. 3 The thickness is 161μm.

[0093] Example 2

[0094] This embodiment provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0095] S1: 97wt% hard carbon anode material, 1.2wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 1.8wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% sodium polyacrylate) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 52% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 3.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0096] Among them, the hard carbon anode material is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles in a mass ratio of 5:3:2.

[0097] The first hard carbon particle has a Dv50 of 7.4μm and is obtained by high-temperature carbonization and crushing of coconut shells;

[0098] The second hard carbon particles have a Dv50 of 11.1 μm and are spherical. They are obtained by carbonizing coconut shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyacrylonitrile by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0099] The third hard carbon particle has a Dv50 of 28.6 μm. It was obtained by treating the first hard carbon particle, the second hard carbon particle, needle coke and potassium chloride in a mass ratio of 5:5:0.3:0.05 at 900℃ for 3 h, followed by cooling and washing.

[0100] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector, 60μm thick, 35μm pore size), dried at 105℃, and subjected to a single cold pressing at a transmission side pressure of 27T, resulting in a compaction density of 0.84g / cm³. 3 The transmission side pressure during secondary cold pressing is 30T, and the compaction density of the hard carbon negative electrode sheet is 1.01g / cm³. 3 The thickness is 158μm.

[0101] Example 3

[0102] This embodiment provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0103] S1: 97wt% hard carbon anode material, 1.2wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 1.8wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% polyacrylamide) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 53% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 3.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0104] The hard carbon anode material is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles in a mass ratio of 5:3.5:1.5.

[0105] The first hard carbon particle has a Dv50 of 6.5μm and is obtained by high-temperature carbonization and crushing of camellia shells;

[0106] The second hard carbon particles have a Dv50 of 10.2 μm and are nearly spherical. They are obtained by carbonizing camellia shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyacrylonitrile by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0107] The third hard carbon particle has a Dv50 of 28.6 μm. It is obtained by treating the first hard carbon particle, the second hard carbon particle, needle coke and potassium nitrate in a mass ratio of 5:5:0.2:0.06 at 800℃ for 3 hours, followed by cooling and washing.

[0108] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector, 60μm thick, 35μm pore size), dried at 105℃, and subjected to a single cold pressing at a transmission side pressure of 28T. The compaction density of the hard carbon negative electrode sheet is 0.84g / cm³. 3The transmission side pressure during secondary cold pressing is 31T, and the compaction density of the hard carbon negative electrode sheet is 1.02 g / cm³. 3 The thickness is 156μm.

[0109] Example 4

[0110] This embodiment provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0111] S1: 96.8 wt% hard carbon anode material, 1.2 wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 2.0 wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% polyacrylamide) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 54% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 4.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0112] The hard carbon anode material is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles in a mass ratio of 5:3.5:1.5.

[0113] The first hard carbon particle has a Dv50 of 6.5μm and is obtained by high-temperature carbonization and crushing of camellia shells;

[0114] The second hard carbon particles have a Dv50 of 10.2μm and are nearly spherical. They are obtained by carbonizing camellia shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyethylene by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0115] The third hard carbon particle has a Dv50 of 28.6 μm. It is obtained by treating the first hard carbon particle, the second hard carbon particle, needle coke and potassium nitrate in a mass ratio of 5:5:0.3:0.06 at 800℃ for 3 hours, followed by cooling and washing.

[0116] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector, thickness 60μm, pore size 35μm), dried at 105℃, and subjected to a single cold pressing at a transmission side pressure of 27T. The compaction density of the hard carbon negative electrode sheet is 0.83g / cm³. 3 The transmission side pressure during secondary cold pressing is 31T, and the compaction density of the hard carbon negative electrode sheet is 1.01g / cm³. 3 The thickness is 157μm.

[0117] S3: The sodium nickel copper manganese oxide positive electrode, polyethylene polymer separator, and hard carbon negative electrode are sequentially bonded, wound, and ultrasonically welded to obtain a bare cell. The insulation of the bare cell is tested. The bare cell is placed in the battery case, laser welded and sealed, vacuum baked at 100°C, electrolyte is injected into the aluminum-plastic film case, packaged, and aged and tested to obtain a 2.8Ah secondary battery.

[0118] Example 5

[0119] This embodiment provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0120] S1: 96.8 wt% hard carbon anode material, 1.2 wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 2.0 wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% polyacrylamide) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 56% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 4.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0121] The hard carbon anode material is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles in a mass ratio of 5:3.5:1.5.

[0122] The first hard carbon particle has a Dv50 of 6.5μm and is obtained by high-temperature carbonization and crushing of camellia shells;

[0123] The second hard carbon particles have a Dv50 of 10.2μm and are nearly spherical. They are obtained by carbonizing camellia shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyethylene by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0124] The third hard carbon particle has a Dv50 of 28.6 μm. It is obtained by treating the first hard carbon particle, the second hard carbon particle, needle coke and potassium nitrate in a mass ratio of 5:5:0.5:0.06 at 800℃ for 3 hours, followed by cooling and washing.

[0125] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector, thickness 60μm, pore size 35μm), dried at 105℃, and subjected to a single cold pressing at a transmission side pressure of 28T. The compaction density of the hard carbon negative electrode sheet is 0.84g / cm³. 3 The transmission side pressure during secondary cold pressing is 32T, and the compaction density of the hard carbon negative electrode sheet is 1.03g / cm³. 3 The thickness is 153μm.

[0126] Comparative Example 1

[0127] This comparative example provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0128] S1: 97wt% hard carbon anode material, 1.2wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 1.8wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% sodium polyacrylate) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 48% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 2.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0129] Among them, the hard carbon anode material is the first hard carbon particle with a Dv50 of 7.4μm, which is obtained by high-temperature carbonization and crushing of coconut shell;

[0130] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector thickness is 60μm, pore size is 35μm), dried at 105℃, and subjected to a single cold pressing with a transmission side pressure of 26T. The compaction density of the hard carbon negative electrode sheet is 0.80g / cm³. 3 The transmission side pressure during secondary cold pressing is 31T, and the compaction density of the hard carbon negative electrode sheet is 0.87g / cm³. 3 The thickness is 171μm.

[0131] Comparative Example 2

[0132] This comparative example provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0133] S1: 97wt% hard carbon anode material, 1.2wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 1.8wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% sodium polyacrylate) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 48% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 2.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0134] Among them, the hard carbon anode material is the second hard carbon particle with a Dv50 of 11.1μm. It is spherical and is obtained by carbonizing coconut shell at high temperature (to obtain hard carbon), crushing it, adding 4% of hard carbon by weight of polyacrylonitrile, mixing it, and heat-treating it at 1300℃ for 2 hours to coat the surface edges.

[0135] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector thickness is 60μm, pore size is 35μm), dried at 105℃, and subjected to a single cold pressing with a transmission side pressure of 26T. The compaction density of the hard carbon negative electrode sheet is 0.80g / cm³. 3 The transmission side pressure during secondary cold pressing is 31T, and the compaction density of the hard carbon negative electrode sheet is 0.87g / cm³. 3The thickness is 171μm.

[0136] Comparative Example 3

[0137] This comparative example provides a hard carbon negative electrode sheet, the preparation method of which is as follows:

[0138] S1: 96.8 wt% hard carbon anode material, 1.2 wt% conductive agent (composed of 90% conductive carbon black and 10% carbon nanotubes), and 2.0 wt% binder (composed of 60% styrene-butadiene rubber, 20% sodium carboxymethyl cellulose and 20% polyacrylamide) are placed in the mixing tank of a mixer. Deionized water is added until the mass of hard carbon anode material in the container accounts for 54% of the total mass. The mixture is stirred for 3 hours and 40 minutes under a vacuum of -0.085 MPa until the viscosity is 4.0 Pa·s, and the fineness is controlled to be ≤0.08 mm to obtain the anode coating.

[0139] The hard carbon anode material is composed of a mixture of first hard carbon particles and second hard carbon particles in a mass ratio of 5:3.5.

[0140] The first hard carbon particle has a Dv50 of 7.4μm and is obtained by high-temperature carbonization and crushing of coconut shells;

[0141] The second hard carbon particles have a Dv50 of 11.1 μm and are spherical. They are obtained by carbonizing coconut shells at high temperature (to obtain hard carbon), crushing them, adding 4% polyacrylonitrile by weight of hard carbon, mixing them, and then heat-treating them at 1300℃ for 2 hours to coat the surface edges.

[0142] S2: The negative electrode coating is applied to a porous current collector (copper-based porous current collector thickness is 60μm, copper-based porous current collector pore size is 35μm), dried at 105℃, and subjected to a single cold pressing with a transmission side pressure of 26T. The compaction density of the hard carbon negative electrode sheet is 0.78g / cm³. 3 The transmission side pressure during secondary cold pressing is 30T, and the compaction density of the hard carbon negative electrode sheet is 0.88g / cm³. 3 The thickness is 169μm.

[0143] Results analysis:

[0144] The hard carbon anode sheets in the examples and comparative examples were tested, and the results are shown in Table 1. The test items included anode sheet thickness, compaction density rebound, and secondary battery volumetric energy density, as detailed below:

[0145] (1) Rebound of negative electrode thickness and compaction density

[0146] The middle part of the hard carbon negative electrode sheet of the examples and comparative examples was cut into a rectangular negative electrode sheet of 100*40mm. The negative electrode sheet was placed in a room temperature environment with humidity <10% for 48h. The initial thickness after the second cold pressing, the thickness of the negative electrode sheet after 24h and 48h was measured with a micrometer, and the corresponding compaction density was calculated.

[0147] (2) Volumetric energy density of secondary batteries

[0148] The hard carbon negative electrode sheets used in the examples and comparative examples were prepared into batteries using the following methods:

[0149] A 132 μm thick sodium nickel copper manganate positive electrode (Na2Ni) was sequentially applied. 0.55 Mn 0.4 Cu 0.05 O2 (content of 96.5wt%), polyethylene polymer separator, hard carbon negative electrode sheet are bonded, wound, and ultrasonically welded to obtain bare cells. The bare cells are placed in the battery case, laser welded to seal, vacuum baked at 100℃, electrolyte is injected into the aluminum-plastic film case, encapsulated, aged and tested to obtain a 2.8Ah secondary battery.

[0150] The volume of the secondary batteries in the examples and comparative examples was measured, and the discharge energy from fully charged to 3.95V and then discharged to 1.5V was recorded. The volumetric energy density = discharge energy / secondary battery volume.

[0151] Table 1

[0152]

[0153] The results showed that, compared with Examples 1-5, the hard carbon anode sheets of Comparative Examples 1, 2, and 3 only contained first hard carbon particles, second hard carbon particles, and first hard carbon particles and second hard carbon particles. Under similar pressures during the first and second cold pressing, the initial compaction density was still low. The thickness of the hard carbon anode sheet rebounding after 24 hours and 48 hours was still large. Moreover, the compaction density decreased even more after 24 hours and 48 hours of cold pressing. The low compaction density resulted in a low volumetric energy density of the secondary battery. Therefore, the hard carbon anode sheet obtained by mixing the first hard carbon particles with second hard carbon particles with few or no edges and third hard carbon particles with larger particle sizes has a higher initial compaction density after cold pressing. The thickness change of the hard carbon anode sheet rebounding after 24 hours and 48 hours is smaller, and the volumetric energy density of the secondary battery is higher.

[0154] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A hard carbon anode material, characterized in that, It is composed of a mixture of first hard carbon particles, second hard carbon particles and third hard carbon particles; The first hard carbon particle is a multi-faceted hard carbon particle; The second hard carbon particle is a hard carbon particle with few or no sharp edges; The third hard carbon particle is spherical, near-spherical, or irregularly polygonal, and includes a hard carbon particle core and a carbon source covering the hard carbon particle core. The hard carbon particle core includes a first hard carbon particle and a second hard carbon particle, and the carbon source contains molten salt. The median particle size Dv50 of the first hard carbon particle < the median particle size Dv50 of the second hard carbon particle < the median particle size Dv50 of the third hard carbon particle ≤ 60 μm; the carbon source is selected from one or more of needle coke, pitch tar, petroleum coke and isoform coke; the hot molten salt is selected from one or more of sodium chloride, potassium chloride, magnesium chloride, lithium chloride, sodium nitrate, potassium nitrate, lithium nitrate and magnesium nitrate.

2. The hard carbon anode material as described in claim 1, characterized in that, The mass ratio of the first hard carbon particle, the second hard carbon particle, and the third hard carbon particle is (1-10):(1-10):(1-5).

3. The hard carbon anode material as described in claim 1, characterized in that, The third hard carbon particle is obtained by heating the first hard carbon particle, the second hard carbon particle, the carbon source, and the hot molten salt. The heat treatment temperature is 300-1200℃, and the heat treatment time is 1-8h.

4. The hard carbon anode material as described in claim 1 or 3, characterized in that, In the preparation of raw materials, the mass ratio of the first hard carbon particles, the second hard carbon particles, the carbon source and the hot molten salt is (1-10):(1-20):(0.1-1):(0.01-3).

5. A hard carbon negative electrode sheet, characterized in that, The hard carbon anode material according to any one of claims 1-4 is used as the anode active material.

6. The hard carbon negative electrode sheet as described in claim 5, characterized in that, The hard carbon negative electrode sheet includes a porous current collector and a negative electrode coating; the negative electrode coating fills the pores of the porous current collector and / or covers at least one side surface of the porous current collector; the negative electrode coating comprises the hard carbon negative electrode material according to any one of claims 1-4.

7. The hard carbon negative electrode sheet as described in claim 6, characterized in that, At least one of the following conditions must be met: The thickness of the hard carbon negative electrode sheet is 35-620 μm; The thickness of the porous current collector is 5-180 μm; The pore size of the porous current collector is 3-90 μm.

8. A method for preparing a hard carbon negative electrode sheet according to any one of claims 5-7, characterized in that, Includes the following steps, S1: Add water to the mixture of hard carbon anode material, conductive agent and binder, and mix well to obtain anode coating, wherein the hard carbon anode material is the hard carbon anode material according to any one of claims 1-3; S2: The negative electrode coating is applied to at least one side of the porous current collector, and after drying and cold pressing, the hard carbon negative electrode sheet is obtained.

9. The preparation method according to claim 8, characterized in that, At least one of the following conditions must be met: a. In step S1, the mixing method is to stir under vacuum for 180-560 minutes; b. In step S1, the mass percentages of the hard carbon anode material, conductive agent, and binder in the mixture are 85.0-99.6 wt%, 0.2-7.0 wt%, and 0.2-8.0 wt%, respectively. c. In step S1, the fineness of the negative electrode coating is ≤0.08mm; d. In step S1, the mass percentage of hard carbon anode material in the anode coating is 32-70%. e. In step S2, the transmission side pressure of the cold press is 10-90T; f. In step S2, the cold pressing includes a first cold pressing and a second cold pressing. After the first cold pressing, the compaction density of the electrode sheet is 0.60-0.89 g / cm³. 3 The compaction density of the electrode sheet after secondary cold pressing is 0.90-1.30 g / cm³. 3 .

10. A sodium-ion secondary battery, characterized in that, Includes the hard carbon anode sheet according to any one of claims 5-7, or the hard carbon anode sheet prepared by the preparation method according to claim 8 or 9.

Images