Hard carbon material and preparation method thereof, negative electrode, battery and electrical equipment

Abstract

This application provides a hard carbon material, a preparation method thereof, a negative electrode, a battery, and an electrical device. The atomic percentage of oxygen on the surface of the hard carbon material is 1 at% to 9 at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%, which is beneficial for improving the initial efficiency and reversible capacity of the battery.

Description

Technical Field

[0001] The present application relates to the technical field of electrode materials, and in particular to hard carbon materials and preparation methods thereof, negative electrodes, batteries and electrical equipment. Background Art

[0002] As a new type of secondary battery, sodium-ion batteries (SIBs) are considered one of the most suitable battery systems for large-scale energy storage due to their abundant resources, low cost, and environmental friendliness. Hard carbon, the primary anode material for SIBs, exhibits broad application prospects due to its unique amorphous carbon structure, high reversible capacity, good rate capability, and excellent cycling stability. However, the presence of groups on the surface of SIBs that undergo irreversible reactions with sodium ions results in a low initial coulombic efficiency, leading to significant irreversible capacity loss during the initial charge and discharge process, which in turn affects the performance of SIBs. Summary of the Invention

[0003] In view of this, the present application provides a hard carbon material and a preparation method thereof, a negative electrode, a battery and an electrical device.

[0004] In a first aspect, the present application provides a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1 at%-9 at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0005] Optionally, the atomic percentage of hydroxyl groups on the surface of the hard carbon material is less than 0.3 at %.

[0006] Optionally, the particle size D50 of the hard carbon material is 4 μm-10 μm.

[0007] Optionally, the particle sizes D10, D50 and D90 of the hard carbon material satisfy: 1≤(D90-D10) / D50≤2.

[0008] Optionally, the closed pore volume of the hard carbon material is 0.05 cm 3 / g-0.25cm 3 / g.

[0009] Optionally, the mass content of oxygen in the hard carbon material is 1 wt%-10 wt%.

[0010] A second aspect of the present application provides a method for preparing the hard carbon material according to the first aspect, comprising:

[0011] The carbon-containing raw material is soaked in an acid solution and then washed to obtain a first precursor;

[0012] The first precursor is carbonized to obtain a second precursor;

[0013] The second precursor is reduced to obtain a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1 at%-9 at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0014] Optionally, the temperature of the reduction treatment is 300°C-400°C.

[0015] Optionally, the reduction treatment time is 1h-3h.

[0016] Optionally, the reduction treatment includes introducing a mixed gas containing reducing gas, the volume proportion of the reducing gas in the mixed gas is 1%-10%, and the introduction speed of the mixed gas is 0.1L / min-1L / min.

[0017] Optionally, the concentration of the acid solution is 2 mol / L-9 mol / L.

[0018] Optionally, the solid-liquid ratio of the carbon-containing raw material to the acid solution is 1 g:(5-10) mL.

[0019] Optionally, the soaking time is 0.5h-3h, and the soaking temperature is 15°C-35°C.

[0020] Optionally, the acid solution contains at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid.

[0021] Optionally, the carbon-containing raw material includes a biomass raw material, and the biomass raw material includes at least one of bamboo powder, wood powder, rice husk, wheat straw, corn cob and cotton stalk.

[0022] Optionally, the carbonization treatment includes a pre-carbonization stage and a carbonization stage, the pre-carbonization stage includes heating the temperature to 400°C-650°C at a heating rate of 0.5°C / min-20°C / min and treating for 2h-5h, and the carbonization stage includes heating the temperature to 1100°C-1400°C at a heating rate of 2°C / min-5°C / min and treating for 2h-5h.

[0023] Furthermore, the preparation method further comprises:

[0024] After the first precursor undergoes the pre-carbonization stage, an intermediate precursor is obtained;

[0025] The intermediate precursor is crushed and classified and then subjected to the carbonization stage to obtain the second precursor, wherein the particle size D50 of the second precursor is 4μm-10μm, and the particle sizes D10, D50 and D90 of the second precursor satisfy: 1≤(D90-D10) / D50≤2.

[0026] In a third aspect, the present application provides a negative electrode, comprising a negative electrode current collector and a negative electrode active layer supported on the negative electrode current collector, wherein the negative electrode active layer comprises the hard carbon material described in the first aspect of the present application.

[0027] The fourth aspect of the present application provides a battery, comprising a positive electrode and the negative electrode described in the third aspect of the present application.

[0028] The fifth aspect of the present application provides an electrical device, comprising the battery described in the fourth aspect of the present application.

[0029] The hard carbon material provided in the present application has a low ratio of carbon-oxygen single bonds to carbon-oxygen double bonds on its surface and a low quinone group content. At the same time, the surface oxygen content is appropriate, which can not only reduce the occurrence of irreversible reactions between the hard carbon material and active ions, but also retain sites on the surface of the hard carbon material for reversible reactions with active ions, which is beneficial to improving its initial charge and discharge efficiency and reversible capacity, and is beneficial to improving the performance of the negative electrode, battery and electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] Figure 1 This is a flow chart of a method for preparing a hard carbon material according to one embodiment of the present application.

[0032] Figure 2 This is a flow chart of a method for preparing a hard carbon material according to another embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] Compared to graphite, hard carbon has a larger interlayer spacing, allowing active ions (such as lithium ions and sodium ions with larger ionic radii) to be rapidly intercalated and deintercalated. Furthermore, hard carbon has more defect sites and pores, which facilitate the storage of active ions. This makes hard carbon widely used in negative electrodes, particularly in sodium-ion batteries. However, the presence of groups on the surface of hard carbon that undergo irreversible reactions with active ions results in a low initial coulombic efficiency (i.e., first efficiency) of the battery, leading to significant irreversible capacity loss during the initial charge and discharge process, which affects the battery's performance.

[0035] In response to the above problems, the present application provides a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1at%-9at%, the atomic percentage ratio of carbon-oxygen single bonds (CO) to carbon-oxygen double bonds (C=O) on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5at%. Among them, CO on the surface of the hard carbon material undergoes irreversible reactions with active ions in the battery (such as sodium ions), and C=O on the surface of the hard carbon material undergoes reversible reactions with active ions in the battery. At the same time, although the quinone group has more carbon-oxygen double bonds, the high solubility of the quinone group in the battery electrolyte makes it impossible for it to be reversibly adsorbed and desorbed with the active ions, resulting in a high irreversible capacity and low first efficiency of the battery. The atomic percentage ratio of CO to C=O on the surface of the hard carbon material provided by the present application (i.e., CO / C=O) is less than 1.5, and the quinone group on the surface of the hard carbon material The atomic percentage of the base is less than 0.5at%, which can not only retain sites on the surface of the hard carbon material for reversible reactions with active ions, but also reduce the irreversible reactions between the surface of the hard carbon material and the active ions, and the atomic percentage of oxygen elements on the surface of the hard carbon material is 1at%-9at%, which can provide more slope capacity and improve the performance of the hard carbon material; in summary, the battery using this hard carbon material has high first efficiency and reversible capacity, and will not affect other performance of the battery, which is conducive to the widespread use of hard carbon materials in negative electrodes and batteries.

[0036] The present application uses an X-ray photoelectron spectroscopy (XPS) instrument to detect the atomic percentage of oxygen elements, carbon-oxygen single bonds, carbon-oxygen double bonds, and quinone groups on the surface of the hard carbon material, with the unit being at%. It is understandable that the atomic percentage of oxygen elements, carbon-oxygen single bonds, carbon-oxygen double bonds, and quinone groups on the surface of the hard carbon material can also be obtained by other means. In one embodiment of the present application, an XPS instrument can be used, using Al Kα X-rays (1486.6 eV) as an excitation source, with an energy analysis range of 0 eV to 1200 eV, to detect a surface area of ​​1 mm² of the hard carbon material, using a high-energy resolution mode for analysis, and using the Shirley background subtraction method to process the data to obtain an XPS curve, and the atomic percentage of the oxygen element is obtained from the XPS curve. The atomic percentage of different groups is obtained from the O1s XPS high-resolution spectrum, wherein the peak of 530±0.5 ev corresponds to the quinone group, the peak of 532±0.5 ev corresponds to C=O, and the peak of 533±0.5 ev corresponds to CO, thereby obtaining the atomic percentage of the quinone group and the atomic percentage ratio of CO to C=O.

[0037] In the present application, the atomic percentage of oxygen on the surface of the hard carbon material is 1 at%-9 at%, thereby ensuring the content of oxygen-containing groups on the surface of the hard carbon material and providing a higher slope capacity. Specifically, the atomic percentage of oxygen on the surface of the hard carbon material can be, but is not limited to, 1 at%, 2 at%, 3 at%, 3.5 at%, 4 at%, 4.5 at%, 5 at%, 5.5 at%, 6 at%, 7 at%, 8 at%, or 9 at%. In one embodiment of the present application, the atomic percentage of oxygen on the surface of the hard carbon material can be 1.5 at%-7 at%. In another embodiment of the present application, the atomic percentage of oxygen on the surface of the hard carbon material can be 3.5 at%-5 at%, which can enable the hard carbon material to have a higher slope capacity and also have a higher first effect and reversible capacity.

[0038] In this application, the atomic percentage ratio of CO to C=O on the surface of the hard carbon material is less than 1.5, ensuring that sites capable of reversibly reacting with active ions are retained on the hard carbon material surface. Furthermore, the number of sites capable of irreversibly reacting with active ions on the hard carbon material surface is reduced, thereby ensuring a high active ion content during battery operation and thereby improving the battery's initial efficiency and reversible capacity. In one embodiment of this application, the atomic percentage ratio of CO to C=O on the surface of the hard carbon material can be less than 1.4, further improving the battery's initial efficiency and reversible capacity.

[0039] In the present application, the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%, which avoids the irreversible capacity caused by the influence of quinone groups and can improve the initial efficiency and reversible capacity of the battery. In one embodiment of the present application, the atomic percentage of quinone groups on the surface of the hard carbon material can be less than 0.45 at%, which is beneficial to further improve the performance of the battery. In another embodiment of the present application, the atomic percentage of quinone groups on the surface of the hard carbon material can be less than 0.4 at%. In another embodiment of the present application, the atomic percentage of quinone groups on the surface of the hard carbon material can be less than 0.35 at%, which is more beneficial to the use of the battery.

[0040] In one embodiment of the present application, the mass content of oxygen in the hard carbon material is 1wt%-10wt%. This helps enhance the conductivity of the hard carbon material, provides more active ion reaction sites, and helps increase the interlayer spacing of the hard carbon material, broaden the transmission channels of active ions, reduce the diffusion and transmission resistance of active ions between layers, and thus improve the reversible capacity of the hard carbon material. In this application, the mass content of oxygen on the surface of the hard carbon material can be obtained, but is not limited to, using an elemental analyzer. Specifically, the mass content of oxygen in the hard carbon material can be, but is not limited to, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. In one embodiment of the present application, the mass content of oxygen in the hard carbon material can be 2wt%-9.5wt%, which not only helps improve the reversible capacity of the hard carbon material, but also further improves the first efficiency and reversible capacity of the battery using the hard carbon material. In another embodiment of the present application, the mass content of oxygen in the hard carbon material can be 4.5wt%-9wt%.

[0041] In one embodiment of the present application, the atomic percentage of hydroxyl groups on the surface of the hard carbon material is less than 0.3 at%, which can prevent the loss of active ions caused by irreversible reactions between hydroxyl groups and active ions, thereby improving the initial efficiency and reversible capacity of the battery. In this application, the hard carbon material can be tested using, but is not limited to, an XPS instrument. The peak at 534±0.5 eV in the O1s XPS high-resolution spectrum corresponds to the hydroxyl group, and the atomic percentage of hydroxyl groups can be obtained. In one embodiment of the present application, the atomic percentage of hydroxyl groups on the surface of the hard carbon material is less than 0.1 at%, further improving the overall performance of the hard carbon material.

[0042] In one embodiment of the present application, the interlayer spacing of the hard carbon material is 0.37 nm to 0.4 nm. The large interlayer spacing of the hard carbon material facilitates the rapid transport and storage of active ions, thereby improving the performance of the hard carbon material.

[0043] In one embodiment of the present application, the particle sizes D10, D50, and D90 of the hard carbon material satisfy the following: 1≤(D90-D10) / D50≤2. This makes the particle size distribution of the hard carbon material uniform and the morphology and structure more uniform, which is beneficial to improving the surface properties of the hard carbon material and, in turn, the performance of the negative electrode and battery. In this application, D50 is the volume median diameter, which represents the particle size value at which the cumulative distribution of the particle size distribution reaches 50%; D10 is the particle size value at which the cumulative distribution of the particle size distribution reaches 10%; and D90 is the particle size value at which the cumulative distribution of the particle size distribution reaches 90%. The particle sizes D10, D50, and D90 can be measured using a laser particle size analyzer. Specifically, the value of (D90-D10) / D50 can be, but is not limited to, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, etc.

[0044] In one embodiment of the present application, the particle size D50 of the hard carbon material is between 4 μm and 10 μm, allowing the hard carbon material to expose appropriate oxygen-containing groups, which is beneficial for improving the initial efficiency and reversible capacity of the battery. Specifically, the particle size D50 of the hard carbon material can be, but is not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0045] In one embodiment of the present application, the particle size D10 of the hard carbon material is ≤3μm. In one embodiment of the present application, the particle size D10 of the hard carbon material may be 1μm-3μm. Specifically, the particle size D10 of the hard carbon material may be, but not limited to, 1μm, 1.2μm, 1.5μm, 2μm, 2.5μm or 3μm, etc. In one embodiment of the present application, the particle size D90 of the hard carbon material is ≤15μm. In one embodiment of the present application, the D90 of the hard carbon material may be 5μm-15μm. Specifically, the particle size D90 of the hard carbon material may be, but not limited to, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm, etc.

[0046] In one embodiment of the present application, the closed pore volume of the hard carbon material is 0.05 cm 3 / g-0.25cm 3 / g, which is beneficial to the storage of active ions and ensures that the hard carbon material has a low energy storage platform, which helps to improve the energy density of the battery. In this application, the closed pore volume of the hard carbon material can be obtained by, but is not limited to, gas adsorption method. Specifically, the closed pore volume of the hard carbon material can be, but is not limited to, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.17cm 3 / g, 0.2cm 3 / g or 0.25cm 3 / g, etc.

[0047] See also Figure 1 , is a flow chart of a method for preparing a hard carbon material provided in one embodiment of the present application, comprising:

[0048] S101: The carbon-containing raw material is soaked in an acid solution and then washed to obtain a first precursor.

[0049] S102: The first precursor is carbonized to obtain a second precursor.

[0050] S103: The second precursor is subjected to reduction treatment to obtain a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1 at%-9 at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0051] In the preparation method of the present application, the surface oxygen content and oxygen-containing group content of the carbon-containing raw material can be increased after being soaked in acid, and a second precursor with a rich closed-pore structure can be obtained after carbonization treatment. After further reduction treatment, the oxygen-containing groups on its surface can be passivated, and the oxygen-containing groups that undergo irreversible reactions with active ions can be reduced as much as possible, while retaining the oxygen-containing groups that can undergo reversible reactions with active ions, thereby obtaining a hard carbon material with excellent performance.

[0052] In S101, the content of oxygen-containing groups on the surface of the carbon-containing raw material can be increased by soaking in an acid solution to obtain an oxygen-rich carbon-containing raw material, i.e., a first precursor, which is beneficial to increase the oxygen-containing groups on the surface of the hard carbon material that can reversibly react with active ions, and helps to improve the performance of the hard carbon material.

[0053] In one embodiment of the present application, the carbon-containing raw material comprises a biomass raw material. Biomass raw materials are widely available, inexpensive, minimally polluting, and continuously renewable. Furthermore, they can produce a rich pore structure after carbonization, which is beneficial for improving the electrochemical performance of hard carbon materials. Specifically, the biomass raw material may be, but is not limited to, at least one of bamboo powder, wood powder (such as pine powder), rice husks, wheat straw, corn cobs, and cotton stalks. Using biomass raw materials to prepare hard carbon materials fully utilizes the biomass raw materials and reduces the production cost of hard carbon materials, facilitating their widespread use.

[0054] In one embodiment of the present application, the acid solution has a concentration of 2 mol / L to 9 mol / L, which effectively oxidizes the carbon-containing raw material, increasing the oxygen content on its surface, thereby increasing the number of oxygen-containing groups on the surface of the carbon-containing raw material. This increases the content of oxygen-containing groups on the surface of the resulting hard carbon material that can undergo reversible reactions with active ions, thereby improving the performance of the hard carbon material. Specifically, the concentration of the acid solution can be, but is not limited to, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, or 9 mol / L.

[0055] In one embodiment of the present application, the acid solution comprises at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, and perchloric acid, which facilitates oxidation of the carbon-containing feedstock. In one example of the present application, the acid solution comprises at least two of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, and perchloric acid. Specifically, the carbon-containing feedstock can be immersed in a mixture of multiple acids, or it can be immersed in one acid solution first and then immersed in another acid solution.

[0056] In one embodiment of the present application, the solid-liquid ratio of the carbon-containing raw material to the acid solution is 1 g:(5-10) mL, which facilitates sufficient reaction between the acid solution and the carbon-containing raw material and increases the content of oxygen-containing groups on its surface. Specifically, the solid-liquid ratio of the carbon-containing raw material to the acid solution can be, but is not limited to, 1 g:5 mL, 1 g:6 mL, 1 g:7 mL, 1 g:8 mL, 1 g:9 mL, or 1 g:10 mL.

[0057] In one embodiment of the present application, the soaking time is 0.5-3 hours, and the soaking temperature is 15°C-35°C, which is conducive to sufficient mixing and reaction of the carbon-containing raw material and the acid solution to obtain a first precursor with a high oxygen content. Specifically, the soaking time can be, but is not limited to, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, and the soaking temperature can be, but is not limited to, 15°C, 18°C, 20°C, 23°C, 25°C, 27°C, 30°C, 33°C, or 35°C.

[0058] In the present application, after soaking the carbon-containing raw material in the acid solution, the carbon-containing raw material may be washed with water until neutral, but is not limited to, to remove the residual acid solution in the carbon-containing raw material before carbonization. In one embodiment of the present application, drying may also be performed after washing. Specifically, the drying process may be, but is not limited to, vacuum drying, for example, vacuum drying at 60°C for 12 hours after washing.

[0059] In S102, the first precursor is subjected to carbonization treatment to obtain a second precursor with a rich pore structure, which is conducive to obtaining a hard carbon material with good performance.

[0060] In one embodiment of the present application, the carbonization treatment includes a pre-carbonization stage and a carbonization stage. Among them, the temperature in the pre-carbonization stage is relatively low, and the temperature in the carbonization stage is relatively high, so as to obtain a hard carbon material. In the present application, the carbonization treatment is carried out in an inert gas atmosphere. Specifically, the inert gas can be, but is not limited to, argon, nitrogen, etc. In one embodiment of the present application, the pre-carbonization stage includes heating to 400°C-650°C at a heating rate of 0.5°C / min-20°C / min and treating for 2h-5h. Specifically, the heating rate in the pre-carbonization stage can be, but is not limited to, 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min in, 18°C / min, 19°C / min, or 20°C / min; the temperature of the pre-carbonization stage may be, but is not limited to, 400°C, 430°C, 450°C, 475°C, 490°C, 500°C, 525°C, 550°C, 580°C, 600°C, 610°C, 625°C, or 650°C; the treatment time of the pre-carbonization stage may be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h. In one embodiment of the present application, the carbonization stage includes heating to 1100°C-1400°C at a heating rate of 2°C / min-5°C / min and treating for 2h-5h. Specifically, the heating rate of the carbonization stage may be, but is not limited to, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min, etc.; the temperature of the carbonization stage may be, but is not limited to, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C or 1400°C, etc.; the processing time of the carbonization stage may be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc.

[0061] In S103, the second precursor is subjected to a reduction treatment to remove as much oxygen-containing groups on the surface of the second precursor that undergo irreversible reactions with active ions as possible, while retaining as much oxygen-containing groups on the surface of the second precursor that undergo reversible reactions with active ions as possible, thereby obtaining a hard carbon material with excellent performance.

[0062] In one embodiment of the present application, the temperature of the reduction treatment is 300°C-400°C, and the time of the reduction treatment is 1h-3h. In this way, the oxygen-containing groups on the surface of the second precursor can be selectively passivated, and the oxygen-containing groups that react irreversibly with active ions, such as quinone groups, hydroxyl groups, etc., can be reduced as much as possible, and the groups that react reversibly with active ions, such as carboxyl groups and ester groups containing carbon-oxygen double bonds, can be retained. In addition, the temperature of the reduction treatment can avoid the conversion of carbon-oxygen double bonds into carbon-oxygen single bonds, thereby ensuring the content of carbon-oxygen double bonds on the surface of the prepared hard carbon material that react reversibly with active ions. The ratio of the atomic percentage of surface carbon-oxygen single bonds to the atomic percentage of carbon-oxygen double bonds, the atomic percentage of surface quinone groups, and even the overall oxygen element mass content, the atomic percentage of surface oxygen elements, and the atomic percentage of surface hydroxyl groups within a certain range can be obtained, so that the hard carbon material has both excellent first effect and reversible capacity, which is conducive to the widespread use of hard carbon materials. The temperature of the reduction treatment mainly affects the selective removal of oxygen-containing groups, and the time mainly affects the overall passivation degree. If the temperature of the reduction treatment is too low or the time is too short, the oxygen-containing groups on the surface of the second precursor that undergo irreversible reaction with the active ions are limited in removal, and the first efficiency of the battery using the hard carbon material cannot be effectively improved; if the temperature of the reduction treatment is too high or the time is too long, the oxygen-containing groups on the surface of the second precursor that undergo reversible reaction with the active ions will also be removed, affecting the capacity of the hard carbon material. Specifically, the temperature of the reduction treatment can be, but is not limited to, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, and the time of the reduction treatment can be, but is not limited to, 1 hour, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 120 minutes, 135 minutes, 150 minutes, 170 minutes or 3 hours, etc.

[0063] In one embodiment of the present application, the reduction treatment includes introducing a mixed gas containing a reducing gas, and the volume proportion of the reducing gas in the mixed gas is 1%-10%, which is beneficial to passivating the oxygen-containing groups in the hard carbon material. Specifically, the volume proportion of the reducing gas in the mixed gas can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc. In one embodiment of the present application, the introduction speed of the mixed gas is 0.1L / min-1L / min, which is beneficial to the reduction treatment. Specifically, the introduction speed of the mixed gas can be, but is not limited to, 0.1L / min, 0.2L / min, 0.3L / min, 0.4L / min, 0.5L / min, 0.6L / min, 0.7L / min, 0.8L / min, 0.9L / min or 1L / min, etc. Among them, the reducing gas can be, but is not limited to, hydrogen.

[0064] See also Figure 2, is a flow chart of a method for preparing a hard carbon material provided in another embodiment of the present application, comprising:

[0065] S201: The carbon-containing raw material is soaked in an acid solution and then washed to obtain a first precursor.

[0066] S202: After the first precursor undergoes a pre-carbonization stage, an intermediate precursor is obtained.

[0067] S203: The intermediate precursor is crushed and classified and then carbonized to obtain a second precursor.

[0068] S204: The second precursor is subjected to reduction treatment to obtain a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1 at%-9 at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0069] In this embodiment, the intermediate precursor is pulverized and classified before the carbonization stage. The pulverization exposes more defects, allowing for repair during the carbonization stage, thereby improving the performance of the hard carbon material. Furthermore, the classified second precursor has a more uniform particle size and more uniform exposure of surface oxygen-containing groups, which contributes to improved performance of the hard carbon material. The intermediate precursor can be pulverized by, but is not limited to, airflow milling or impact milling.

[0070] In one embodiment of the present application, the particle sizes D10, D50, and D90 of the second precursor satisfy the following relationship: 1 ≤ (D90 - D10) / D50 ≤ 2. This results in a uniform particle size distribution and a more uniform particle structure, which facilitates control of the subsequent reduction degree, reduces over-reduction in some areas, and improves the surface properties of the resulting hard carbon material. Specifically, the value of (D90 - D10) / D50 can be, but is not limited to, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.

[0071] In one embodiment of the present application, the particle size D50 of the second precursor is 4 μm to 10 μm, which facilitates the exposure of oxygen-containing groups and defects and facilitates the subsequent use of the hard carbon material. D50 in this application refers to the volume median diameter, which can be measured using a laser particle size distribution analyzer. Specifically, the particle size D50 of the second precursor can be, but is not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0072] The carbonization stage and the reduction treatment will not have a significant impact on the particle size of the material, and there is basically no significant difference between the particle size of the second precursor and the particle size of the hard carbon material.

[0073] The present application also provides a negative electrode comprising a negative electrode current collector and a negative electrode active layer supported on the negative electrode current collector, wherein the negative electrode active layer comprises the hard carbon material of any of the above embodiments. The negative electrode comprising the hard carbon material has a high initial efficiency and good reversible capacity, which is advantageous for use in a battery.

[0074] In one embodiment of the present application, the negative electrode active layer may further include at least one of a conductive agent and a binder. The conductive agent and the binder may be any known conductive agent and binder in the art. Specifically, the conductive agent may be at least one of super carbon black, acetylene black, graphene, carbon fiber, and carbon nanotubes; and the binder may be at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, and polyacrylate.

[0075] In one embodiment of the present application, the negative electrode current collector is selected from a metal foil or an alloy foil. Among them, the metal foil includes copper, aluminum, nickel, iron or cobalt foil, and the alloy foil includes an alloy of at least one element of copper, aluminum, nickel, iron and cobalt, or stainless steel. In one embodiment of the present application, the material of the negative electrode current collector includes at least one of copper, aluminum, nickel, iron and cobalt, or stainless steel. Specifically, the negative electrode current collector can be copper foil or foam copper. In one embodiment of the present application, at least one of a binder and a conductive agent can be mixed with a hard carbon material in a solvent to form a mixed slurry, and the mixed slurry can be coated on the surface of the negative electrode current collector, and the negative electrode can be obtained after drying.

[0076] The present application provides a battery comprising a positive electrode and a negative electrode according to any of the above embodiments. The battery having the negative electrode has excellent first efficiency and reversible capacity, which facilitates battery use. Specifically, the battery may be, but is not limited to, a sodium-ion battery or a lithium-ion battery.

[0077] In one embodiment of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. In one embodiment of the present application, the positive electrode current collector is selected from a metal foil or an alloy foil. Among them, the metal foil includes copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold or silver foil, and the alloy foil includes stainless steel, or an alloy containing at least one element of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold and silver. Specifically, the positive electrode current collector can be aluminum foil. In one embodiment of the present application, the positive electrode active material layer includes at least one of a positive electrode binder and a positive electrode conductor, and a positive electrode active material. Specifically, the positive electrode active material can be a lithium battery positive electrode active material or a sodium battery positive electrode active material.

[0078] In one embodiment of the present application, the battery further comprises a separator located between the positive electrode and the negative electrode, wherein any separator known in the art can be selected as the separator of the battery of the present application.

[0079] In one embodiment of the present application, the battery further comprises an electrolyte, wherein at least a portion of the positive electrode is immersed in the electrolyte, and at least a portion of the negative electrode is immersed in the electrolyte. In one embodiment of the present application, the electrolyte comprises a solute and an organic solvent. The solute can be selected based on the type of battery. For example, the solute of the electrolyte in a sodium ion battery can be a sodium salt, and the solute of the electrolyte in a lithium ion battery can be a lithium salt.

[0080] The present application also provides an electrical device comprising the battery of any of the above embodiments. The electrical device may be, for example, an electric vehicle, a mobile phone, a tablet computer, a laptop computer, a wearable device, a digital camera, etc., and the battery may be provided in the electrical device in the form of a single cell, a battery module, a battery pack, etc.

[0081] The technical solution of this application is further illustrated below through multiple embodiments.

[0082] Example 1

[0083] The biomass feedstock (bamboo powder) and an acid solution (5 mol / L) were mixed at a solid-liquid ratio of 1 g:5 mL. After stirring at room temperature for 1 hour, the biomass feedstock was washed with water until neutral and then vacuum-dried at 60°C for 12 hours to produce the first precursor. The acid solution contained sulfuric acid and hydrochloric acid. This first precursor was pre-carbonized to produce the intermediate precursor. The pre-carbonization step involved heating the temperature to 500°C at a rate of 10°C / min for 2 hours. After crushing and screening, the intermediate precursor obtained a material with a particle size D50 of 6.60 μm, and particle sizes D10, D50 and D90 satisfying: (D90-D10) / D50 value of 1.56. The material was then heated to 1300°C at a heating rate of 5°C / min and treated for 3 hours to obtain a second precursor. The material was then cooled to 400°C and a mixed gas of hydrogen and argon was introduced at a flow rate of 0.1 L / min, in which the volume proportion of hydrogen was 10%. The material was reduced for 2 hours to obtain a hard carbon material. The particle size D50 of the hard carbon material was 6.60 μm, and the (D90-D10) / D50 value was 1.56.

[0084] Example 2-Example 15

[0085] The differences from the preparation method of Example 1 are shown in Table 1; at the same time, the biomass raw material used in Example 10 is pine wood powder.

[0086] Comparative Example 1

[0087] The differences from the preparation method of Example 1 are shown in Table 1, wherein Comparative Example 1 was not subjected to reduction treatment.

[0088] Comparative Example 2

[0089] The difference from the preparation method of Example 1 is that in Comparative Example 2, the biomass raw material is not mixed with the acid solution and is not subjected to reduction treatment.

[0090] Comparative Example 3

[0091] The difference from the preparation method of Example 1 is that the reduction temperature in Comparative Example 3 is 200° C. and the reduction time is 2 h.

[0092] Comparative Example 4

[0093] The difference from the preparation method of Example 1 is that the reduction temperature in Comparative Example 4 is 500° C. and the reduction time is 2 h.

[0094] Comparative Example 5

[0095] The difference from the preparation method of Example 1 is that in Comparative Example 5, the particle size D50 of the second precursor is 2 μm, and the value of (D90-D10) / D50 is 3.

[0096] The particle size of the second precursor in the embodiment and the comparative example was measured by a laser particle size distribution analyzer to obtain the particle size D10, D50 and D90, and the value of (D90-D10) / D50 was calculated;

[0097] Table 1 Preparation methods of Examples and Comparative Examples

[0098]

[0099] Material characterization

[0100] The hard carbon materials prepared in the above examples and comparative examples were dried in a vacuum oven at 60° C. for 12 h, and then the oxygen content of the hard carbon materials was detected using an elemental analyzer. The results are shown in the second column of Table 2 as the overall oxygen content.

[0101] The hard carbon materials prepared in the above examples and comparative examples were analyzed using an XPS instrument (Thermo Fisher K-Alpha). Al Kα X-rays (1486.6 eV) were used as the excitation source, and the energy analysis range was 0 eV to 1200 eV. The sample surface area was 1 mm², analyzed in high-energy resolution mode, and the Shirley background subtraction method was used to generate XPS curves. The atomic ratio of oxygen was determined from the XPS curves, and the atomic percentage of oxygen on the surface of the hard carbon materials was obtained. The results are shown in the third column of Table 2. In the O1s XPS high-resolution spectrum, the peak of the quinone group is at 530±0.5ev, the peak of C=O is at 532±0.5ev, the peak of CO is at 533±0.5ev, and the peak of the OH functional group is at 534±0.5ev. The atomic percentages of hydroxyl, quinone, C=O, and CO were obtained, and the atomic percentage ratio of CO to C=O (CO / C=O) was calculated. The results are shown in the fourth to sixth columns of Table 2.

[0102] The hard carbon materials prepared in the above examples and comparative examples were subjected to closed pore volume testing using a gas adsorption method. The specific testing conditions were as follows: the hard carbon materials were degassed at 150°C to 300°C and a pressure of <10 Bar to 6 Bar for 1 to 6 hours; nitrogen was then introduced at liquid nitrogen temperature, the pressure was slowly returned to atmospheric pressure, and the materials were degassed again for 10 Bar to 6 Bar. The data was recorded to obtain adsorption and desorption isotherms, and the pore volume data of the hard carbon materials were calculated using a density functional theory (DFT) model. The test results are shown in the seventh column of Table 2.

[0103] Table 2 Performance test results

[0104]

[0105] Performance Testing

[0106] The hard carbon materials prepared in the above examples and comparative examples were used to prepare batteries. The specific process included: mixing the hard carbon material, the conductive agent Super P, the binder sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 94.5:1.5:1.5:2.5, adding an appropriate amount of water and stirring to form a slurry, and then evenly coating the slurry on the current collector copper foil. After drying, the slurry was cut into circular pole pieces with a diameter of 18 mm. Under vacuum conditions, the pole pieces were dried at 80°C for about 3 hours, then vacuum dried at 80°C for 6 hours, and rolled to a surface density of 4 mg / cm 2 -7mg / cm 2 The simulated battery was assembled in an argon atmosphere glove box, using a sodium metal sheet as the counter electrode and a 1 mol / L NaPF6 solution in ethylene carbonate as the electrolyte, to form a CR2430 button cell.

[0107] The prepared battery was subjected to electrochemical performance testing, specifically, a constant current charge and discharge mode was adopted, and the charge and discharge test was carried out at a current density of 30 mA / g. The battery cyclic charge and discharge performance test was carried out under the conditions of a discharge cut-off voltage of 0 V and a charge cut-off voltage of 2.0 V. The test results are shown in Table 3;

[0108] Table 3 Battery performance results

[0109]

[0110] It can be seen that compared with the comparative example, the internal structure and surface properties of the hard carbon material are comprehensively regulated by regulating the oxidation, particle size and reduction processes in the embodiment, so that the hard carbon material has a rich closed-pore structure inside, and the proportion of groups that undergo irreversible reactions with sodium ions on the surface is reduced. At the same time, the oxygen content on the surface of the hard carbon material and the content of groups that undergo reversible reactions with sodium ions are guaranteed, so that the battery containing the hard carbon material has both high initial efficiency and reversible capacity.

[0111] The above describes the specific implementation methods in detail, but the present invention is not limited to the above specific implementation methods. Under the guidance of this application, technical personnel in this field can also make various forms of changes without departing from the scope of protection of this application, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: include: The carbon-containing raw material is soaked in an acid solution and then washed to obtain a first precursor; After the first precursor is subjected to a pre-carbonization stage, an intermediate precursor is obtained; The intermediate precursor is crushed and classified and then carbonized to obtain a second precursor, wherein the particle sizes D10, D50 and D90 of the second precursor satisfy: 1≤(D90-D10) / D50≤2; The second precursor is subjected to reduction treatment at a temperature of 300°C-400°C and a time of 1h-3h to obtain a hard carbon material, wherein the atomic percentage of oxygen on the surface of the hard carbon material is 1at%-9at%, the ratio of the atomic percentage of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface of the hard carbon material is less than 1.5, the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5at%, and the particle sizes D10, D50 and D90 of the hard carbon material satisfy: 1≤(D90-D10) / D50≤2.

2. The preparation method according to claim 1, wherein The atomic percentage of hydroxyl groups on the surface of the hard carbon material is less than 0.3 at %.

3. The preparation method according to claim 1, wherein The particle size D50 of the hard carbon material is 4 μm-10 μm; The closed pore volume of the hard carbon material is 0.05 cm 3 / g-0.25cm 3 / g; The mass content of oxygen in the hard carbon material is 1 wt%-10 wt%.

4. The preparation method according to claim 1, wherein The reduction treatment includes introducing a mixed gas containing reducing gas, wherein the volume proportion of the reducing gas in the mixed gas is 1%-10%, and the introduction speed of the mixed gas is 0.1L / min-1L / min.

5. The preparation method according to claim 1, wherein The concentration of the acid solution is 2mol / L-9mol / L; The solid-liquid ratio of the carbon-containing raw material to the acid solution is 1 g: (5-10) mL; The soaking time is 0.5h-3h, and the soaking temperature is 15°C-35°C; The acid solution comprises at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid; The carbon-containing raw material includes a biomass raw material, and the biomass raw material includes at least one of bamboo powder, wood powder, rice husk, wheat straw, corn cob and cotton stalk.

6. The preparation method according to claim 1, wherein The pre-carbonization stage includes heating to 400-650°C at a heating rate of 0.5-20°C / min and treating for 2-5 hours, and the carbonization stage includes heating to 1100-1400°C at a heating rate of 2-5°C / min and treating for 2-5 hours.

7. The preparation method according to claim 1, wherein The particle size D50 of the second precursor is 4 μm-10 μm.

8. A negative electrode, characterized in that The invention comprises a negative electrode current collector and a negative electrode active layer supported on the negative electrode current collector, wherein the negative electrode active layer comprises a hard carbon material prepared by the preparation method according to any one of claims 1 to 7.

9. A battery, characterized in that: The invention comprises a positive electrode and the negative electrode according to claim 8.

10. An electrical device, characterized in that: Comprising the battery of claim 9.

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