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

Abstract

The invention provides a hard carbon material and a preparation method thereof, a negative electrode, a battery and electric equipment. The atom percentage content of oxygen element on the surface of the hard carbon material is 1-9 at%, the ratio of the atom percentage content of carbon-oxygen single bond to carbon-oxygen double bond on the surface of the hard carbon material is less than 1.5, the atom percentage content of quinonyl on the surface of the hard carbon material is less than 0.5 at%, and the first efficiency and reversible capacity of the battery can be improved.

Description

Technical Field

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

[0002] As a new type of secondary battery, sodium-ion batteries have the advantages of rich resources, low cost, and environmental friendliness, and are considered to be one of the most suitable battery systems for large-scale energy storage. As the main negative electrode material of sodium-ion batteries, hard carbon has a high reversible capacity, good rate performance, and excellent cycle stability due to its unique amorphous carbon structure, showing broad application prospects. However, there are some groups on the surface of hard carbon that undergo irreversible reactions with sodium ions, resulting in a low initial Coulombic efficiency and a large irreversible capacity loss during the first charge and discharge process, affecting the performance of sodium-ion batteries. Summary of the Invention

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

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

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

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

[0007] Optionally, the D10, D50, and D90 particle sizes 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 - 0.25 cm 3 / g.

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

[0010] In the second aspect of the present application, a preparation method of the hard carbon material as described in the first aspect is provided, including: After the carbon-containing raw material is soaked in the acid solution and then washed, a first precursor is obtained; After the first precursor is carbonized, a second precursor is obtained; The second precursor is subjected to a reduction treatment to obtain a hard carbon material. The atomic percentage content of oxygen element on the surface of the hard carbon material is 1 at% - 9 at%. The ratio of the atomic percentage content of carbon-oxygen single bond to carbon-oxygen double bond on the surface of the hard carbon material is less than 1.5. The atomic percentage content of quinone group on the surface of the hard carbon material is less than 0.5 at%.

[0011] Optionally, the temperature of the reduction treatment is 300°C - 400°C.

[0012] Optionally, the time of the reduction treatment is 1 h - 3 h.

[0013] Optionally, the reduction treatment includes introducing a mixed gas containing a reducing gas. The volume percentage of the reducing gas in the mixed gas is 1% - 10%. The introduction speed of the mixed gas is 0.1 L / min - 1 L / min.

[0014] Optionally, the concentration of the acid solution is 2 mol / L - 9 mol / L.

[0015] Optionally, the solid-liquid ratio of the carbon-containing raw material to the acid solution is 1 g:(5 - 10) mL.

[0016] Optionally, the soaking time is 0.5 h - 3 h, and the soaking temperature is 15°C - 35°C.

[0017] Optionally, the acid solution includes at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, and perchloric acid.

[0018] 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 straw.

[0019] Optionally, the carbonization treatment includes a pre-carbonization stage and a carbonization stage. The pre-carbonization stage includes heating to 400°C - 650°C at a heating rate of 0.5°C / min - 20°C / min for 2 h - 5 h. The carbonization stage includes heating to 1100°C - 1400°C at a heating rate of 2°C / min - 5°C / min for 2 h - 5 h.

[0020] Furthermore, the preparation method further includes: After the first precursor undergoes the pre-carbonization stage, an intermediate precursor is obtained; The intermediate precursor is pulverized and classified, and then undergoes the carbonization stage to obtain the second precursor. Among them, the particle size D50 of the second precursor is 4 μm - 10 μm, and the particle sizes D10, D50, and D90 of the second precursor satisfy: 1 ≤ (D90 - D10) / D50 ≤ 2.

[0021] The third aspect of the present application provides a negative electrode, which includes a negative electrode current collector and a negative electrode active layer loaded on the negative electrode current collector, and the negative electrode active layer includes the hard carbon material described in the first aspect of the present application.

[0022] The fourth aspect of the present application provides a battery, which includes a positive electrode and the negative electrode described in the third aspect of the present application.

[0023] The fifth aspect of the present application provides an electrical device, which includes the battery described in the fourth aspect of the present application.

[0024] The hard carbon material provided by the present application has a low content ratio of carbon-oxygen single bonds to carbon-oxygen double bonds on the surface and a low quinone group content, and at the same time, the surface oxygen element content is appropriate. It can not only reduce the occurrence of irreversible reactions between the hard carbon material and active ions, but also leave sites for reversible reactions with active ions on the surface of the hard carbon material, which is beneficial to improving its first charge-discharge efficiency and reversible capacity, and is beneficial to the improvement of the use performance of the negative electrode, battery and electrical device. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Figure 1 It is a flow chart of the preparation method of the hard carbon material provided by an embodiment of the present application.

[0027] Figure 2 It is a flow chart of the preparation method of the hard carbon material provided by another embodiment of the present application. Detailed Embodiments

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0029] Compared with graphite, hard carbon has a larger graphite layer spacing, enabling active ions (such as lithium ions, sodium ions with a larger ionic radius, etc.) to rapidly intercalate and deintercalate therein, and hard carbon has more defect sites and pores, which is beneficial to the storage of active ions, making hard carbon widely used in negative electrodes, especially in negative electrodes of sodium-ion batteries. However, there are some groups on the surface of hard carbon that undergo irreversible reactions with active ions, resulting in a low first Coulombic efficiency (i.e., first efficiency) of the battery, causing a large irreversible capacity loss during the first charge-discharge process and affecting the use performance of the battery.

[0030] In view of the above problems, the present application provides a hard carbon material. The atomic percentage content of oxygen element on the surface of the hard carbon material is 1 at% - 9 at%. The ratio of the atomic percentage content of carbon-oxygen single bond (C-O) to carbon-oxygen double bond (C=O) on the surface of the hard carbon material is less than 1.5, and the atomic percentage content of quinone group on the surface of the hard carbon material is less than 0.5 at%. Among them, the C-O on the surface of the hard carbon material undergoes an irreversible reaction with active ions (such as sodium ions, etc.) in the battery, and the C=O on the surface of the hard carbon material undergoes a reversible reaction 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 results in its inability to perform reversible adsorption and desorption with active ions, leading to a high irreversible capacity and a low initial efficiency of the battery. The ratio of the atomic percentage content of C-O to C=O (i.e., C-O / C=O) on the surface of the hard carbon material provided by the present application is less than 1.5, and at the same time, the atomic percentage content of the quinone group on the surface of the hard carbon material is less than 0.5 at%. This can not only retain the sites for reversible reaction with active ions on the surface of the hard carbon material, but also reduce the irreversible reaction between the surface of the hard carbon material and active ions. Moreover, the atomic percentage content of oxygen element on the surface of the hard carbon material is 1 at% - 9 at%, which can provide more sloping capacity and improve the performance of the hard carbon material. In summary, the battery using this hard carbon material has a high initial efficiency and reversible capacity, and at the same time does not affect other performances of the battery, which is conducive to the wide use of the hard carbon material in the negative electrode and the battery.

[0031] The present application detects the atomic percentage content of oxygen element, carbon-oxygen single bond, carbon-oxygen double bond, and quinone group on the surface of the hard carbon material by an X-ray photoelectron spectroscopy (XPS) instrument, with the unit of at%. It can be understood that the atomic percentage content of oxygen element, carbon-oxygen single bond, carbon-oxygen double bond, and quinone group on the surface of the hard carbon material can also be obtained by other means. In an embodiment of the present application, an XPS instrument can be used, with Al Kα X-ray (1486.6 eV) as the excitation source, the energy analysis range from 0 eV to 1200 eV, the surface area of 1 mm² of the hard carbon material is detected, analyzed in a high-energy resolution mode, and the Shirley background subtraction method is used to process the data to obtain the XPS curve. The atomic percentage content of oxygen element is obtained from the XPS curve, and the atomic percentage content of different groups is obtained from the O1s XPS high-resolution spectrogram. Among them, the peak at 530 ± 0.5 eV corresponds to the quinone group, the peak at 532 ± 0.5 eV corresponds to C=O, and the peak at 533 ± 0.5 eV corresponds to C-O, so as to obtain the atomic percentage content of the quinone group and the ratio of the atomic percentage content of C-O to C=O.

[0032] In this application, the atomic percentage content of oxygen element on the surface of the hard carbon material is 1 at% - 9 at%, so as to ensure the content of oxygen-containing groups on the surface of the hard carbon material and provide more slope capacity. Specifically, the atomic percentage content of oxygen element 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% etc. In an embodiment of this application, the atomic percentage content of oxygen element on the surface of the hard carbon material can be 1.5 at% - 7 at%. In another embodiment of this application, the atomic percentage content of oxygen element 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 initial efficiency and reversible capacity.

[0033] In this application, the ratio of the atomic percentage content of C - O to C = O on the surface of the hard carbon material is less than 1.5, so as to ensure that there are sites on the surface of the hard carbon material that can undergo reversible reactions with active ions, and there are few sites on the surface of the hard carbon material that undergo irreversible reactions with active ions, thus ensuring the content of active ions during the use of the battery, and further being beneficial to improving the initial efficiency and reversible capacity of the battery. In an embodiment of this application, the ratio of the atomic percentage content of C - O to C = O on the surface of the hard carbon material can be less than 1.4, which is beneficial to further improving the initial efficiency and reversible capacity of the battery.

[0034] In this application, the atomic percentage content of quinone groups on the surface of the hard carbon material is less than 0.5 at%, avoiding the irreversible capacity caused by the influence of quinone groups, and can improve the initial efficiency and reversible capacity of the battery. In an embodiment of this application, the atomic percentage content of quinone groups on the surface of the hard carbon material can be less than 0.45 at%, which is beneficial to further improving the performance of the battery. In another embodiment of this application, the atomic percentage content of quinone groups on the surface of the hard carbon material can be less than 0.4 at%. In yet another embodiment of this application, the atomic percentage content 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.

[0035] In an embodiment of the present application, the mass content of oxygen element in the hard carbon material is 1 wt% - 10 wt%. This is beneficial to enhancing the conductivity of the hard carbon material, having more active ion reaction sites, and at the same time helping to increase the interlayer spacing of the hard carbon material, broaden the transmission channels of active ions, reduce the diffusion transmission resistance of interlayer active ions, and is conducive to improving the reversible capacity of the hard carbon material. In the present application, the mass content of oxygen element on the surface of the hard carbon material can be obtained by, but not limited to, an elemental analyzer. Specifically, the mass content of oxygen element in the hard carbon material can be, but not limited to, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%, etc. In an embodiment of the present application, the mass content of oxygen element in the hard carbon material can be 2 wt% - 9.5 wt%, which is beneficial to improving the reversible capacity of the hard carbon material and can further improve the initial efficiency and reversible capacity of the battery using this hard carbon material. In another embodiment of the present application, the mass content of oxygen element in the hard carbon material can be 4.5 wt% - 9 wt%.

[0036] In an embodiment of the present application, the atomic percentage content of hydroxyl groups on the surface of the hard carbon material is less than 0.3 at%. This can avoid the loss of active ions caused by the irreversible reaction between hydroxyl groups and active ions, and is beneficial to the initial efficiency and reversible capacity of the battery. In the present application, the hard carbon material can be detected by, but not limited to, an XPS instrument. The peak at 534 ± 0.5 ev in the O1s XPS high-resolution spectrogram corresponds to hydroxyl groups, and the atomic percentage content of hydroxyl groups can be obtained. In an embodiment of the present application, the atomic percentage content of hydroxyl groups on the surface of the hard carbon material is less than 0.1 at%, further improving the comprehensive performance of the hard carbon material.

[0037] In an embodiment of the present application, the interlayer spacing of the hard carbon material is 0.37 nm - 0.4 nm. The larger interlayer spacing of the hard carbon material helps the rapid transmission and storage of active ions, and improves the performance of the hard carbon material.

[0038] In an embodiment of the present application, the particle sizes D10, D50 and D90 of the hard carbon material satisfy: 1 ≤ (D90 - D10) / D50 ≤ 2, making the particle size distribution of the hard carbon material uniform and the morphological structure more homogeneous, which is beneficial to improving the surface performance of the hard carbon material, and thus beneficial to improving the performance of the negative electrode and the battery. D50 in the present application is the volume median diameter, which represents the particle size value when the cumulative distribution in the particle size distribution reaches 50%; D10 is the particle size value when the cumulative distribution in the particle size distribution reaches 10%; D90 is the particle size value when the cumulative distribution in the particle size distribution reaches 90%; the particle sizes D10, D50 and D90 can be measured by a laser particle size distribution analyzer. Specifically, the value of (D90 - D10) / D50 can be, but 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.

[0039] In one embodiment of the present application, the particle size D50 of the hard carbon material is 4 μm - 10 μm, enabling the hard carbon material to expose suitable oxygen-containing groups, which is beneficial to 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, 10 μm, etc.

[0040] In one embodiment of the present application, the particle size D10 of the hard carbon material is ≤ 3 μm. In one example of the present application, the particle size D10 of the hard carbon material can be 1 μm - 3 μm. Specifically, the particle size D10 of the hard carbon material can be, but is not limited to, 1 μm, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc. In one embodiment of the present application, the particle size D90 of the hard carbon material is ≤ 15 μm. In one example of the present application, the D90 of the hard carbon material can be 5 μm - 15 μm. Specifically, the particle size D90 of the hard carbon material can be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0041] In one embodiment of the present application, the closed pore volume of the hard carbon material is 0.05 cm 3 / g - 0.25 cm 3 / g, which is beneficial to the storage of active ions, and at the same time ensures that the hard carbon material has a low energy storage platform, contributing to improving the energy density of the battery. In the present application, the closed pore volume of the hard carbon material can be obtained by, but is not limited to, the gas adsorption method. Specifically, the closed pore volume of the hard carbon material can be, but is not limited to, 0.05 cm 3 / g, 0.08 cm 3 / g, 0.1 cm 3 / g, 0.15 cm 3 / g, 0.17 cm 3 / g, 0.2 cm 3 / g or 0.25 cm 3 / g, etc.

[0042] Please refer to Figure 1 , which is a flowchart of the preparation method of the hard carbon material provided by one embodiment of the present application, including: S101: After the carbon-containing raw material is soaked in the acid solution, it is washed to obtain the first precursor.

[0043] S102: After the first precursor is carbonized, the second precursor is obtained.

[0044] S103: The second precursor is subjected to a reduction treatment to obtain a hard carbon material. The atomic percentage content of oxygen element on the surface of the hard carbon material is 1 at% - 9 at%, the ratio of the atomic percentage content 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 content of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0045] In the preparation method of the present application, after the carbon-containing raw material is soaked in acid, its surface oxygen content and oxygen-containing group content can be increased. After carbonization treatment, a second precursor with a rich closed-pore structure can be obtained. After reduction treatment, the oxygen-containing groups on its surface can be passivated, and the oxygen-containing groups that can undergo irreversible reactions with active ions can be reduced as much as possible, while the oxygen-containing groups that can undergo reversible reactions with active ions are retained, thereby obtaining a hard carbon material with excellent performance.

[0046] In S101, soaking in an acid solution can increase the oxygen-containing group content on the surface of the carbon-containing raw material, obtaining an oxygen-rich carbon-containing raw material, that is, the first precursor, which is beneficial to increasing the oxygen-containing groups on the surface of the hard carbon material that can undergo reversible reactions with active ions, and helps to improve the performance of the hard carbon material.

[0047] In one embodiment of the present application, the carbon-containing raw material includes a biomass raw material. Biomass raw materials have wide sources, low prices, low pollution and can be continuously regenerated. They can also produce a rich pore structure after carbonization treatment, which is beneficial to the improvement of the electrochemical performance of the hard carbon material. Specifically, the biomass raw material can be, but is not limited to, at least one of bamboo powder, wood powder (such as pine wood powder, etc.), rice husk, wheat straw, corn cob and cotton stalk. Using biomass raw materials to prepare hard carbon materials can make full use of biomass raw materials and reduce the preparation cost of hard carbon materials, which is beneficial to the wide use of hard carbon materials.

[0048] In one embodiment of the present application, the concentration of the acid solution is 2 mol / L - 9 mol / L, which can play a good oxidation role, increase the oxygen content on the surface of the carbon-containing raw material, and then increase the oxygen-containing groups on the surface of the carbon-containing raw material. In this way, the content of oxygen-containing groups on the surface of the prepared hard carbon material that can undergo reversible reactions with active ions can be increased, and the performance of the hard carbon material can be improved. 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, etc.

[0049] In one embodiment of the present application, the acid solution contains at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid, which is beneficial to oxidizing the carbon-containing raw material. In one example of the present application, the acid solution contains at least two of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid. Specifically, the carbon-containing raw material can be soaked in a mixed acid solution of multiple acids, or can be soaked in one acid solution first and then in another acid solution.

[0050] 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 is beneficial to the full reaction of the acid solution with the carbon-containing raw material and improves 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, etc.

[0051] In one embodiment of the present application, the soaking time is 0.5 h - 3 h, and the soaking temperature is 15°C - 35°C, which is beneficial to the full 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 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, etc., 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, etc.

[0052] After the carbon-containing raw material in the present application is soaked in the acid solution, it can be, but is not limited to, washed with water until neutral, and then carbonized after removing the residual acid solution in the carbon-containing raw material. In one embodiment of the present application, drying treatment can also be performed after washing. Specifically, the drying treatment can be, but is not limited to, vacuum drying. For example, it can also be vacuum dried at 60°C for 12 h after washing, etc.

[0053] In S102, through carbonization treatment of the first precursor, a second precursor with a rich pore structure can be obtained, which is beneficial to obtaining a hard carbon material with good performance.

[0054] In an 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 an 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, 18°C / min, 19°C / min or 20°C / min, etc.; the temperature in the pre-carbonization stage can 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, etc.; the treatment time in the pre-carbonization stage can be but is not limited to 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc. In an 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 in the carbonization stage can 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 in the carbonization stage can be but is not limited to 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C or 1400°C, etc.; the treatment time in the carbonization stage can be but is not limited to 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc.

[0055] In S103, by performing a reduction treatment on the second precursor, oxygen-containing groups on the surface of the second precursor that irreversibly react with active ions are removed as much as possible, while oxygen-containing groups on the surface of the second precursor that reversibly react with active ions are retained as much as possible, so as to obtain a hard carbon material with excellent performance.

[0056] In an 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, minimizing the oxygen-containing groups that undergo irreversible reactions with active ions, such as quinone groups and hydroxyl groups, and retaining the groups that undergo reversible reactions with active ions, such as carboxyl groups and ester groups containing carbon-oxygen double bonds. Moreover, the temperature of this reduction treatment can prevent the conversion of carbon-oxygen double bonds to carbon-oxygen single bonds, ensuring the content of carbon-oxygen double bonds on the surface of the prepared hard carbon material that can undergo reversible reactions with active ions. A hard carbon material can be obtained with a ratio of the atomic percentage content of surface carbon-oxygen single bonds to carbon-oxygen double bonds, the atomic percentage content of surface quinone groups, and even the overall oxygen element mass content, the atomic percentage content of surface oxygen elements, and the atomic percentage content of surface hydroxyl groups within a certain range, enabling the hard carbon material to have both excellent initial efficiency and reversible capacity, which is conducive to the wide use of the hard carbon material. 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 removal of oxygen-containing groups on the surface of the second precursor that undergo irreversible reactions with active ions is limited, and the initial 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 reactions with active ions will also be removed, affecting the capacity performance 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, etc., and the time of the reduction treatment can be, but is not limited to, 1h, 70min, 80min, 90min, 100min, 110min, 120min, 135min, 150min, 170min, or 3h, etc.

[0057] In an embodiment of the present application, the reduction treatment includes introducing a mixed gas containing a reducing gas, and the volume ratio 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 ratio 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 an embodiment of the present application, the introduction rate of the mixed gas is 0.1L / min - 1L / min, which is beneficial to the progress of the reduction treatment. Specifically, the introduction rate 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.

[0058] Please refer to Figure 2, is a flowchart of a method for preparing a hard carbon material provided in another embodiment of the present application, including: S201: After the carbon-containing raw material is soaked in an acid solution and then washed, a first precursor is obtained.

[0059] S202: After the first precursor undergoes a pre-carbonization stage, an intermediate precursor is obtained.

[0060] S203: After the intermediate precursor is crushed and classified, a carbonization stage is carried out to obtain a second precursor.

[0061] S204: The second precursor is subjected to a reduction treatment to obtain a hard carbon material. The atomic percentage content of oxygen elements on the surface of the hard carbon material is 1 at% - 9 at%, the ratio of the atomic percentage content 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 content of quinone groups on the surface of the hard carbon material is less than 0.5 at%.

[0062] In this embodiment, after the intermediate precursor is crushed and classified, a carbonization stage treatment is carried out; more defects can be exposed after crushing and can be repaired to a certain extent in the carbonization stage, improving the use performance of the hard carbon material. At the same time, after classification, the particle size of the second precursor is more uniform, and the exposure of surface oxygen-containing groups is more uniform, which is beneficial to the improvement of the performance of the hard carbon material. Among them, the intermediate precursor can be crushed by, but not limited to, air flow crushing, impact crushing and other methods.

[0063] In one embodiment of the present application, the particle sizes D10, D50, and D90 of the second precursor satisfy: 1 ≤ (D90 - D10) / D50 ≤ 2. The particle size distribution of the second precursor is uniform, and the particle structure is more uniform, which is beneficial to the control of the subsequent reduction degree, reducing the situation of over-reduction in some parts and under-reduction in some parts, and improving the surface performance of the prepared hard carbon material. Specifically, the value of (D90 - D10) / D50 can be, but 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.

[0064] In one embodiment of the present application, the particle size D50 of the second precursor is 4 μm - 10 μm, which is beneficial to the exposure of oxygen-containing groups and defects and the subsequent use of the hard carbon material. D50 in the present application is the volume median diameter, and D50 can be measured by a laser particle size distribution analyzer. Specifically, the particle size D50 of the second precursor can be, but not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0065] In the carbonization stage and reduction treatment, there is no obvious impact on the particle size of the material, and there is basically no obvious difference between the particle size of the second precursor and the particle size of the hard carbon material.

[0066] The present application also provides a negative electrode, which includes a negative electrode current collector and a negative electrode active layer loaded on the negative electrode current collector. The negative electrode active layer includes the hard carbon material in any of the above embodiments. The negative electrode with this hard carbon material has a high first efficiency and good reversible capacity, which is beneficial to its use in a battery.

[0067] 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. Among them, the conductive agent and the binder can be any conductive agent and binder well-known in the art. Specifically, the conductive agent can be at least one of super carbon black, acetylene black, graphene, carbon fiber, and carbon nanotube, and the binder can be at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, and polyacrylate.

[0068] In one embodiment of the present application, the negative electrode current collector is selected from metal foils or alloy foils. Among them, the metal foils include copper, aluminum, nickel, iron, or cobalt foils, and the alloy foils include alloys 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 a copper foil or a foam copper. In one embodiment of the present application, at least one of the binder and the conductive agent can be mixed with the hard carbon material in a solvent to form a mixed slurry, and the mixed slurry is coated on the surface of the negative electrode current collector and dried to obtain the negative electrode.

[0069] The present application provides a battery, which includes a positive electrode and the negative electrode in any of the above embodiments. The battery with this negative electrode has excellent first efficiency and reversible capacity, which is beneficial to the use of the battery. Specifically, the battery can be, but is not limited to, a sodium ion battery or a lithium ion battery, etc.

[0070] 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 metal foils or alloy foils. Among them, the metal foils include copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, or silver foils, and the alloy foils include stainless steel or alloys 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 an 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 conductive agent, and a positive electrode active material. Specifically, the positive electrode active material can be a positive electrode active material for a lithium battery or a positive electrode active material for a sodium battery.

[0071] In one embodiment of the present application, the battery further includes a separator located between the positive electrode and the negative electrode. Among them, any separator well-known in the art can be selected as the separator of the battery in the present application.

[0072] In an embodiment of the present application, the battery further includes an electrolyte, at least a part of the positive electrode is immersed in the electrolyte, and at least a part of the negative electrode is immersed in the electrolyte. In an embodiment of the present application, the electrolyte includes a solute and an organic solvent. Among them, the solute can be selected according to the type of the battery. For example, the solute in the electrolyte of a sodium-ion battery can be a sodium salt, and the solute in the electrolyte of a lithium-ion battery can be a lithium salt.

[0073] The present application also provides an electrical device, including the battery in any of the above embodiments. The electrical device can be, for example, an electric vehicle, a mobile phone, a tablet computer, a laptop computer, a wearable device, a digital camera, etc. The above battery can be arranged in the electrical device in the form of a single battery, a battery module, a battery pack, etc.

[0074] The technical solutions of the present application will be further described below through multiple embodiments.

[0075] Example 1 Mix the biomass raw material (bamboo powder) and the acid solution (concentration: 5 mol / L) at a solid-liquid ratio of 1 g: 5 mL. After stirring at room temperature for 1 h, wash the biomass raw material with water until neutral and vacuum dry it at 60 °C for 12 h to obtain a first precursor, wherein the acid solution contains sulfuric acid and hydrochloric acid. The first precursor is subjected to a pre-carbonization stage to obtain an intermediate precursor, wherein the pre-carbonization stage is to heat up to 500 °C at a heating rate of 10 °C / min and treat for 2 h. After the intermediate precursor is crushed and sieved, a material with a D50 particle size of 6.60 μm and the D10, D50, and D90 particle sizes satisfying: (D90 - D10) / D50 value of 1.56 is obtained. Then, heat up to 1300 °C at a heating rate of 5 °C / min and treat for 3 h to obtain a second precursor. Then, cool down to 400 °C and introduce a mixed gas of hydrogen and argon at a flow rate of 0.1 L / min, wherein the volume fraction of hydrogen is 10%, and perform a reduction treatment for 2 h to obtain a hard carbon material. The D50 particle size of the hard carbon material is 6.60 μm, and the (D90 - D10) / D50 value is 1.56.

[0076] Examples 2 - 15 The differences from the preparation method of Example 1 are shown in Table 1; meanwhile, the biomass raw material used in Example 10 is pine powder.

[0077] Comparative Example 1 The differences from the preparation method of Example 1 are shown in Table 1, wherein Comparative Example 1 does not perform a reduction treatment.

[0078] Comparative Example 2 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 no reduction treatment is performed.

[0079] Comparative Example 3 The difference from the preparation method of Example 1 is that in Comparative Example 3, the reduction temperature is 200 °C and the reduction time is 2 h.

[0080] Comparative Example 4 The difference from the preparation method of Example 1 is that in Comparative Example 4, the reduction temperature is 500 °C and the reduction time is 2 h.

[0081] Comparative Example 5 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.

[0082] Among them, the particle sizes of the second precursors in the examples and comparative examples were detected by a laser particle size distribution analyzer to obtain the particle sizes D10, D50, and D90, and the value of (D90 - D10) / D50 was calculated; Table 1 Preparation methods of examples and comparative examples

[0083] Material characterization After drying the hard carbon materials prepared in the above examples and comparative examples in a vacuum oven at 60 °C for 12 h, the mass content of oxygen element in the hard carbon materials was detected using an elemental analyzer, and the overall oxygen element content is shown in the second column of Table 2.

[0084] The hard carbon materials prepared in the above examples and comparative examples were detected using an XPS instrument (Thermo Fisher K-Alpha); among them, Al Kα X-ray (1486.6 eV) was used as the excitation source, and the energy analysis range was from 0 eV to 1200 eV. During the test, the surface area of the sample was 1 mm², and the high-energy resolution mode was used for analysis, and the Shirley background subtraction method was used to process the data to obtain the XPS curve. The atomic ratio of oxygen was obtained from the XPS curve to obtain the atomic percentage content of oxygen element on the surface of the hard carbon material, and the results are shown in the third column of Table 2 as the surface oxygen element content. In the O1s XPS high-resolution spectrogram, the peak of the quinone group is located at 530 ± 0.5 eV, the peak of C=O is located at 532 ± 0.5 eV, the peak of C-O is located at 533 ± 0.5 eV, and the peak of the O-H functional group is located at 534 ± 0.5 eV, so as to obtain the atomic percentage contents of hydroxyl group, quinone group, C=O, and C-O, and calculate the ratio of the atomic percentage contents of C-O to C=O (C-O / C=O), and the results are shown in the fourth to sixth columns of Table 2.

[0085] The obtained hard carbon materials in the above examples and comparative examples were tested for closed pore volume by gas adsorption method. The specific test conditions were as follows: The hard carbon materials were degassed at 150 °C - 300 °C and a pressure of <10 Bar - 6 Bar for 1 h - 6 h; then nitrogen gas was introduced at liquid nitrogen temperature, and after the pressure slowly returned to normal pressure, it was degassed again at 10 Bar - 6 Bar. The adsorption and desorption isotherm was recorded, and the pore volume data of the hard carbon materials was calculated according to the density functional theory (DFT) model. The test results are shown in the seventh column of Table 2; Table 2 Performance test results

[0086] Performance test Batteries were prepared using the hard carbon materials obtained from the above examples and comparative examples respectively. The specific process included: mixing the hard carbon materials, conductive agent Super P, binder sodium carboxymethyl cellulose and styrene-butadiene rubber evenly according to a mass ratio of 94.5:1.5:1.5:2.5, adding an appropriate amount of water and stirring to form a slurry, then evenly coating the slurry on the current collector copper foil, and cutting it into circular electrodes with a diameter of 18 mm after drying. Under vacuum conditions, the electrodes were dried in a blast oven at 80 °C for about 3 h, then vacuum dried at 80 °C for 6 h, and rolled to a surface density of 4 mg / cm 2 -7 mg / cm 2 , and then immediately transferred to the glove box for standby. The assembly of the simulated battery was carried out in a glove box with an argon atmosphere. A sodium metal sheet was used as the counter electrode, and 1 mol / L NaPF 6 dissolved in ethylene carbonate solution was used as the electrolyte to assemble a CR2430 button battery.

[0087] The prepared batteries were tested for electrochemical performance. Specifically, a constant current charge-discharge mode was adopted, and the charge-discharge test was carried out at a current density of 30 mA / g. The battery cycle charge-discharge performance test was carried out under the conditions that the discharge cut-off voltage was 0 V and the charge cut-off voltage was 2.0 V. The test results are shown in Table 3; Table 3 Battery performance results

[0088] It can be seen that compared with the comparative example, in the example, by regulating the oxidation, particle size and reduction processes, the internal structure and surface properties of the hard carbon material were comprehensively regulated, so that the hard carbon material had a rich closed pore structure inside, reducing the proportion of groups that irreversibly reacted with sodium ions on the surface, and at the same time ensuring the oxygen element content on the surface of the hard carbon material and the content of groups that reversibly reacted with sodium ions, making the battery with this hard carbon material have both high initial efficiency and reversible capacity.

[0089] The specific embodiments have been described in detail above, but the present invention is not limited to the above specific embodiments. Those skilled in the art can make various forms of changes without departing from the scope of protection of the present application under the inspiration of this application, and these all fall within the scope of protection of the present invention.

Claims

1. A hard carbon material, characterized in that: 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%.

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

3. The hard carbon material according to claim 1, characterized in that The particle size D50 of the hard carbon material is 4 μm-10 μm; The particle sizes D10, D50 and D90 of the hard carbon material satisfy: 1≤(D90-D10) / D50≤2; 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 1wt%-10wt%.

4. A method for preparing a hard carbon material according to any one of claims 1 to 3, characterized in that: include: The carbon-containing raw material is soaked in an acid solution and then washed to obtain a first precursor; The first precursor is subjected to carbonization treatment to obtain a second precursor; 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 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, and the atomic percentage of quinone groups on the surface of the hard carbon material is less than 0.5at%.

5. The preparation method according to claim 4, characterized in that: The temperature of the reduction treatment is 300°C-400°C, and the time of the reduction treatment is 1h-3h; The reduction treatment includes introducing a mixed gas containing a 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.

6. The preparation method according to claim 4, characterized in that: The concentration of the acid solution is 2mol / L-9mol / L; The solid-to-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 straw.

7. The preparation method according to claim 4, characterized in that: The carbonization treatment includes a pre-carbonization stage and a carbonization stage. The pre-carbonization stage includes heating to 400°C-650°C at a heating rate of 0.5°C / min-20°C / min for 2h-5h, and the carbonization stage includes heating to 1100°C-1400°C at a heating rate of 2°C / min-5°C / min for 2h-5h.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: After the first precursor is subjected to the pre-carbonization stage, an intermediate precursor is obtained; 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 4 μm-10 μm, and the particle sizes D10, D50 and D90 of the second precursor satisfy: 1≤(D90-D10) / D50≤2.

9. 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 the hard carbon material according to any one of claims 1 to 3.

10. A battery, characterized in that: It comprises a positive electrode and the negative electrode as claimed in claim 9.

11. An electrical device, characterized in that: Comprising the battery as claimed in claim 10.

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