Negative active material, method for preparing the same, negative electrode sheet, and secondary battery

Abstract

The application provides a negative electrode active material and a preparation method thereof, a negative electrode sheet and a secondary battery. The negative electrode active material comprises a hard carbon material; the hard carbon material comprises micropores and ultramicropores, the pore size of the micropores is < 2 nm, the pore size of the ultramicropores is < 0.7 nm, the proportion of the pore volume of the micropores in the total pore volume is 95% to 100%, and the pore volume of the ultramicropores is 0.01 cm 3 / g to 0.2 cm 3 / g, and the proportion of the pore volume of the ultramicropores in the total pore volume is 80% to 99%. The negative electrode active material provided by the application has a stable low potential platform, a high gram capacity and a high reversible capacity. When the negative electrode active material is applied to a secondary battery, the energy density of the secondary battery can be improved, and the cycle performance of the secondary battery can be improved.

Description

[0001] This application is a divisional application of Chinese patent application filed on April 7, 2023, with application number 202310369251.6 and invention title "Negative electrode active material and preparation method thereof, negative electrode sheet and secondary battery". Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electronic device. Background Technology

[0003] Secondary batteries have outstanding advantages such as high energy density, low self-discharge rate, long cycle life, and stable discharge performance, and are widely used in industrial production and people's daily lives.

[0004] Current capacity development for graphite anode active materials has reached its limit, approaching its theoretical capacity of 372 mAh / g. This makes it difficult to further improve the energy density of lithium-ion batteries using graphite as the anode active material, and commercially available graphite cannot be directly applied to sodium-ion batteries. Among the many anode active materials under development, hard carbon materials have attracted considerable attention due to their high theoretical specific capacity, low volume expansion, and fast charge / discharge characteristics. Furthermore, hard carbon materials can be used as anode active materials for both lithium-ion and sodium-ion batteries, showing broad application prospects. However, existing hard carbon materials have low actual specific capacity, high irreversible capacity, and lack a stable charge / discharge platform. Their application in rechargeable batteries offers very limited improvement in energy density, failing to meet the demands of practical applications. Summary of the Invention

[0005] The purpose of this application is to provide a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electronic device to improve the energy density of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of this application provides a negative electrode active material, which includes a hard carbon material; the hard carbon material comprises micropores and ultramicropores, wherein the pore size of the micropores is <2 nm and the pore size of the ultramicropores is <0.7 nm; the pore volume of the micropores accounts for 95% to 100% of the total pore volume, and the pore volume of the ultramicropores is 0.01 cm³. 3 / g to 0.2cm 3 / g, the pore volume of the micropores accounts for 80% to 99% of the total pore volume. By controlling the proportion of micropore pore volume to total pore volume, the proportion of micropore pore volume to total pore volume, and the micropore pore volume within the above range, the negative electrode active material can have a stable low potential plateau, high specific capacity, and high reversible capacity. Applying the negative electrode active material of this application to secondary batteries can improve the energy density of secondary batteries and improve their cycle performance.

[0007] In some embodiments of this application, the hard carbon material comprises carbon and oxygen, with the oxygen content in the hard carbon material being 2% to 7% by mass. Hard carbon materials comprising carbon and oxygen, with the oxygen content within the aforementioned range, facilitate the adsorption of active metal ions in micropores and the intercalation / deintercalation within ultramicropores, thereby improving the specific capacity of the negative electrode active material.

[0008] In some embodiments of this application, the oxygen element in the hard carbon material exists in the form of carbonyl groups and carboxyl groups, and the mass of oxygen element in the carbonyl groups and carboxyl groups accounts for 60% to 99% of the total mass of oxygen element in the hard carbon material. The presence of oxygen element in the hard carbon material in the above-mentioned forms and the regulation of its content within the above-mentioned range are more conducive to the redox reaction of active metal ions, thereby further improving the specific capacity of the negative electrode active material.

[0009] In some embodiments of this application, the hard carbon material further comprises element A, which includes at least one of N or S; the mass percentage of element A is 0.05% to 2% based on the mass of the hard carbon material. The inclusion of element A within the aforementioned range and the control of its content within this range in the hard carbon material helps to expand the carbon interlayer spacing, promotes the intercalation and deintercalation of active metal ions within the hard carbon material, and enables the negative electrode active material to have a low potential plateau and high reversible capacity.

[0010] In some embodiments of this application, the hard carbon material satisfies 0.8 ≤ I D / I G ≤1.5, I D I represents the peak area of ​​peak D in the Raman spectrum of hard carbon materials. G The peak area of ​​the G peak in the Raman spectrum of the hard carbon material is shown. This indicates that the hard carbon material has a suitable degree of defect, which can promote ion adsorption and binding while reducing irreversible capacity loss caused by high defect degree, thus helping to improve the specific capacity of the negative electrode active material.

[0011] In some embodiments of this application, Li / Li ratios are used at voltages ranging from 0V to 2.5V. + Within the potential range, the total lithium storage capacity of hard carbon materials ranges from 300 mAh / g to 700 mAh / g; the delithiation energy of hard carbon materials is E1 Wh, the delithiation capacity is C1 Ah, and the average delithiation potential is E1 / C1 V, with 0.13 ≤ E1 / C1 ≤ 0.28; within the Li / Li ratio range of 0 V to 0.1 V... + Within the potential range, the specific capacity of hard carbon materials accounts for 30% to 65% of the total lithium storage capacity; in the Li / Li ratio from 0V to 0.8V... +Within the potential range, the specific capacity of hard carbon materials accounts for 70% to 96% of the total lithium storage capacity. This indicates that hard carbon materials have high total lithium storage capacity and low average delithiation potential. Using hard carbon materials with these characteristics as negative electrode active materials in lithium-ion batteries is beneficial to improving the energy density of lithium-ion batteries.

[0012] In some embodiments of this application, Na / Na is used at 0V to 2.5V. + Within the potential range, the total sodium storage capacity of hard carbon materials ranges from 250 mAh / g to 400 mAh / g; the sodium removal energy of hard carbon materials is E2 Wh, the sodium removal capacity of hard carbon materials is C2 Ah, and the average sodium removal potential of hard carbon materials is E2 / C2 V, 0.2 ≤ E2 / C2 ≤ 0.4; within the Na / Na range of 0 V to 0.5 V... + Within the potential range, the specific capacity of hard carbon materials accounts for 76% to 91% of the total specific capacity of sodium storage; in the Na / Na ratio of 0V to 0.8V... + Within the potential range, the specific capacity of hard carbon materials accounts for 89% to 95% of the total sodium storage capacity. This indicates that hard carbon materials have high total sodium storage capacity and low average sodium removal potential. Using hard carbon materials with these characteristics as the negative electrode active material in sodium-ion batteries is beneficial to improving the energy density of sodium-ion batteries.

[0013] In some embodiments of this application, the electrical conductivity of the hard carbon material is from 0.5 S / cm to 10 S / cm. By controlling the electrical conductivity of the hard carbon material within the above range, it is beneficial to improve the capacity and rate performance of the secondary battery, as well as the cycle performance of the secondary battery.

[0014] The second aspect of this application provides a method for preparing the negative electrode active material of the first aspect of this application, wherein the method for preparing the hard carbon material includes the following steps:

[0015] (1) After the precursor is crushed and screened, it is placed in a closed reactor and the gas in the closed reactor is replaced by a first gas; the precursor includes at least one of lignin, cellulose, alkali lignin, asphalt, epoxy resin or phenolic resin, and the first gas includes any one of oxygen, air and carbon dioxide.

[0016] (2) After sealing the closed reactor, place it in a nitrogen atmosphere for one calcination, and heat it to 700℃ to 900℃ at a rate of 0.5℃ / min to 5℃ / min for 1h to 4h for pre-carbonization. After cooling, the pre-carbonized material is obtained.

[0017] (3) The pre-carbonized material is placed in a nitrogen atmosphere for secondary calcination. The temperature is increased to 1000℃ to 1500℃ at a rate of 0.5℃ / min to 5℃ / min for 1h to 8h. After cooling, the carbonized material is obtained. Then the carbonized material is classified according to particle size.

[0018] (4) Heat the material after grading in step (3) to 700°C to 1200°C, introduce a mixture of reducing gas and argon, and keep it for 0.1h to 12h before replacing it with nitrogen. Then cool to obtain hard carbon material. The reducing gas includes at least one of acetylene or methane, and the mass percentage of the reducing gas is 5wt% to 20wt% based on the mass of the mixture.

[0019] The negative electrode active material prepared by the method provided in the second aspect of this application has a stable low potential plateau, high specific capacity and high reversible capacity. When used as the negative electrode sheet of a secondary battery, it can improve the energy density of the secondary battery and improve its cycle performance.

[0020] A third aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material provided in the first aspect of this application or a negative electrode active material prepared according to the preparation method provided in the second aspect of this application. The negative electrode sheet provided in the third aspect of this application has high capacity. When applied to a secondary battery, it can improve the energy density of the secondary battery and enhance its cycle performance.

[0021] In some embodiments of this application, the compaction density of the negative electrode active material layer is 0.8 g / cm³. 3 Up to 1.2 g / cm 3 By adjusting the compaction density of the negative electrode active material layer within the aforementioned range, the content of negative electrode active material per unit area can be increased, thereby improving the energy density of the secondary battery.

[0022] A fourth aspect of this application provides a secondary battery, which includes the negative electrode provided in the third aspect of this application. The secondary battery provided in the fourth aspect of this application has high energy density and good cycle performance.

[0023] The fifth aspect of this application provides an electronic device that includes the secondary battery provided in the fourth aspect of this application. The secondary battery provided in the fourth aspect of this application has high energy density and good cycle performance, thereby providing the electronic device provided in the fifth aspect of this application with a long service life.

[0024] The beneficial effects of this application are:

[0025] This application provides a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electronic device. The negative electrode active material includes a hard carbon material; the hard carbon material comprises micropores and ultramicropores, wherein the pore size of the micropores is <2 nm, the pore size of the ultramicropores is <0.7 nm, the pore volume of the micropores accounts for 95% to 100% of the total pore volume, and the pore volume of the ultramicropores is 0.01 cm³. 3 / g to 0.2cm3 / g, the pore volume of the micropores accounts for 80% to 99% of the total pore volume. By controlling the proportion of micropore pore volume to total pore volume, the proportion of micropore pore volume to total pore volume, and the micropore pore volume within the above range, the negative electrode active material can have a stable low potential plateau, high specific capacity, and high reversible capacity. Applying the negative electrode active material of this application to secondary batteries can improve the energy density of secondary batteries and improve their cycle performance.

[0026] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0028] Figure 1 Scanning electron microscope images of the hard carbon materials prepared in Examples 1-5;

[0029] Figure 2 Pore ​​size distribution diagrams of the hard carbon materials prepared in Examples 1-5 based on nitrogen adsorption-desorption;

[0030] Figure 3 The hard carbon materials of Examples 1-5 at Li / Li ratios from 0V to 2.5V. + The charge-discharge curves within the potential range;

[0031] Figure 4 The hard carbon material of Comparative Example 2 was tested at Li / Li ratios from 0V to 2.5V. + The charge-discharge curves within the potential range;

[0032] Figure 5 The hard carbon material of Example 2-1 is subjected to Na / Na at 0V to 2.5V. + The charge-discharge curves within the potential range;

[0033] Figure 6 The Raman spectra of the hard carbon materials prepared in Examples 1-5;

[0034] Figure 7 The X-ray diffraction patterns are those of the hard carbon materials prepared in Examples 1-5. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0036] It should be noted that, in the specific embodiments of this application, lithium-ion batteries and sodium-ion batteries are used as examples of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries and sodium-ion batteries.

[0037] The first aspect of this application provides a negative electrode active material, which includes a hard carbon material; the hard carbon material comprises micropores and ultramicropores, wherein the pore size of the micropores is <2 nm and the pore size of the ultramicropores is <0.7 nm; the pore volume of the micropores accounts for 95% to 100% of the total pore volume, and the pore volume of the ultramicropores is 0.01 cm³. 3 / g to 0.2cm 3 / g, the pore volume of ultramicropores accounts for 80% to 99% of the total pore volume. For example, the pore volume of micropores can account for 95%, 96%, 97%, 98%, 100% of the total pore volume, or any range of two values ​​therein. The pore volume of ultramicropores can be 0.01 cm³. 3 / g, 0.04cm 3 / g, 0.08cm 3 / g, 0.12cm 3 / g, 0.15cm 3 / g, 0.17cm 3 / g, 0.2cm 3 / g or a range consisting of any two of these values, the percentage of the pore volume of the micropores to the total pore volume can be 80%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 97%, 99% or a range consisting of any two of these values. In this application, the total pore volume refers to the sum of the pore volumes of all pores in the hard carbon material, the pore volume of the micropores refers to the sum of the pore volumes of all micropores in the hard carbon material, and the pore volume of the micropores refers to the sum of the pore volumes of all micropores in the hard carbon material.

[0038] The negative electrode active material provided in this application includes a hard carbon material. The hard carbon material has abundant micropores and ultramicropores, allowing active metal ions (such as lithium ions and sodium ions) to be stored within these pores. Therefore, the abundant micropores and ultramicropores within the hard carbon material enhance its specific capacity and provide a stable low-potential plateau. Simultaneously, the high proportions of micropore volume to total pore volume and ultramicropore volume within the hard carbon material minimize the formation of mesopores (pore size 2nm to 50nm) and macropores (pore size greater than 50nm) due to overactivation, thus not affecting the initial coulombic efficiency and irreversible capacity. By controlling the proportions of micropore volume to total pore volume, ultramicropore volume to total pore volume, and ultramicropore volume within the aforementioned ranges, the negative electrode active material can exhibit a stable low-potential plateau, high specific capacity, and high reversible capacity. Applying the negative electrode active material of this application to secondary batteries can improve the energy density and cycle performance of the secondary batteries.

[0039] In some embodiments of this application, the hard carbon material comprises carbon and oxygen elements, and the mass percentage of oxygen in the hard carbon material is 2% to 7%, for example, the mass percentage of oxygen in the hard carbon material can be 2%, 3%, 4%, 5%, 6%, 7%, or a range consisting of any two of these values. Hard carbon materials containing carbon and oxygen elements with an oxygen mass percentage within the above range facilitate the intercalation and deintercalation of active metal ions in micropores and ultramicropores, thereby improving the specific capacity of the negative electrode active material.

[0040] In some embodiments of this application, the oxygen element in the hard carbon material exists in carbonyl and carboxyl groups, with the mass of oxygen in the carbonyl and carboxyl groups accounting for 60% to 99% of the total mass of oxygen in the hard carbon material. For example, the percentage of oxygen in the carbonyl and carboxyl groups in the total mass of oxygen in the hard carbon material can be 60%, 70%, 75%, 80%, 90%, 99%, or a range of any two of these values. Besides carbonyl and carboxyl groups, the oxygen element in the hard carbon material also includes ether groups. Compared to ether groups, carbonyl and carboxyl groups have stronger electronegativity and are more conducive to the binding of ions (such as lithium ions and sodium ions). The presence of oxygen in the hard carbon material in the above-mentioned forms and the regulation of the mass content of oxygen in the carbonyl and carboxyl groups within the above-mentioned range further facilitates the redox reaction of active metal ions, thereby further improving the specific capacity of the negative electrode active material.

[0041] In some embodiments of this application, the hard carbon material further comprises element A, which includes at least one of N or S; based on the mass of the hard carbon material, the mass percentage content of element A is from 0.05% to 2%, for example, the mass percentage content of element A can be 0.05%, 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.7%, 2%, or a range consisting of any two of these values. The hard carbon material comprising element A within the aforementioned range and controlling its content within this range helps to expand the interlayer spacing of the hard carbon material, promotes the insertion and extraction of active ions within the hard carbon material, and enables the negative electrode active material to have a low potential plateau and high reversible capacity.

[0042] In some embodiments of this application, the hard carbon material satisfies 0.8 ≤ I D / I G ≤1.5. I D I represents the peak area of ​​peak D in the Raman spectrum of hard carbon materials. G This represents the peak area of ​​the G peak in the Raman spectrum of hard carbon materials. For example, I... D / I G The value can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or a range of any two of these values. This indicates that the hard carbon material has a suitable degree of defect, which can promote ion adsorption and binding while reducing irreversible capacity loss caused by high defect degree, thereby helping to improve the specific capacity of the negative electrode active material.

[0043] In some embodiments of this application, Li / Li ratios are used at voltages ranging from 0V to 2.5V. + Within the potential range, the total lithium storage capacity of hard carbon materials ranges from 300 mAh / g to 700 mAh / g; the delithiation energy of hard carbon materials is E1Wh, the delithiation capacity is C1Ah, and the average delithiation potential is E1 / C1 V, with 0.13 ≤ E1 / C1 ≤ 0.28. For example, in the Li / Li ratio range of 0V to 2.5V... + Within the potential range, the total lithium storage capacity of the hard carbon material is 300 mAh / g, 400 mAh / g, 500 mAh / g, 600 mAh / g, 700 mAh / g, or any two of these values. The E1 / C1 value can be 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, or any two of these values. This indicates that the hard carbon material has a high total lithium storage capacity and a low average delithiation potential. Using hard carbon materials with these characteristics as the negative electrode active material for lithium-ion batteries is beneficial to improving the energy density of lithium-ion batteries. In this application, the total lithium storage capacity refers to the Li / Li ratio within the range of 0V to 2.5V. + The total gram capacity of lithium storage in hard carbon materials within the potential range.

[0044] In some embodiments of this application, Li / Li ratios are used at 0V to 0.1V. + Within a given potential range, the specific capacity of hard carbon materials accounts for 30% to 65% of the total lithium storage capacity, for example, in the Li / Li ratio from 0V to 0.1V. + Within the potential range, the specific capacity of hard carbon material as a percentage of the total lithium storage capacity can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or any combination of two of these values. This indicates that hard carbon material has a low average delithiation potential. Using hard carbon material with these characteristics as the negative electrode active material in lithium-ion batteries is beneficial for improving the energy density of lithium-ion batteries.

[0045] In some embodiments of this application, Li / Li ratios are used at 0V to 0.8V. + Within a given potential range, hard carbon materials account for 70% to 96% of the total lithium storage capacity, for example, in the Li / Li ratio from 0V to 0.8V. + Within the potential range, the specific capacity of hard carbon materials as a percentage of the total lithium storage capacity can be 70%, 75%, 80%, 85%, 90%, 95%, 96%, or any combination of two of these values. This indicates that hard carbon materials have a low average delithiation potential. Using hard carbon materials with these characteristics as the negative electrode active material in lithium-ion batteries is beneficial for improving the energy density of lithium-ion batteries.

[0046] In some embodiments of this application, Na / Na is used at 0V to 2.5V. + Within the potential range, the total sodium storage capacity of hard carbon materials ranges from 250 mAh / g to 400 mAh / g; the sodium removal energy of hard carbon materials is E2Wh, the sodium removal capacity is C2Ah, and the average sodium removal potential is E2 / C2 V, where 0.2 ≤ E2 / C2 ≤ 0.4. For example, in the Na / Na range from 0V to 2.5V... + Within the potential range, the total sodium storage capacity of the hard carbon material is 250 mAh / g, 300 mAh / g, 325 mAh / g, 350 mAh / g, 400 mAh / g, or any combination of two such values. The E2 / C2 value can be 0.2, 0.25, 0.3, 0.35, 0.4, or any combination of two such values. This indicates that the hard carbon material has a high total sodium storage capacity and a low average sodium removal potential. Using hard carbon materials with these characteristics as the negative electrode active material for sodium-ion batteries is beneficial for improving the energy density of sodium-ion batteries. In this application, the total sodium storage capacity refers to the Na / Na ratio within the range of 0V to 2.5V. + The total sodium storage capacity of hard carbon materials within the potential range.

[0047] In some embodiments of this application, Na / Na is used at 0V to 0.5V. + Within the potential range, the specific capacity of hard carbon materials accounts for 76% to 91% of the total specific capacity of sodium storage. For example, in the Na / Na… + Within the potential range, the specific capacity of hard carbon material as a percentage of the total sodium storage capacity can be 76%, 80%, 83%, 85%, 88%, 91%, or any combination of two of these values. This indicates that hard carbon material has a low average sodium removal potential. Using hard carbon material with these characteristics as the negative electrode active material in sodium-ion batteries is beneficial for improving the energy density of sodium-ion batteries.

[0048] In some embodiments of this application, Na / Na is used at 0V to 0.8V. + Within the potential range, the specific capacity of hard carbon materials accounts for 89% to 95% of the total specific capacity of sodium storage. For example, in the Na / Na ratio from 0V to 0.8V... + Within the potential range, the specific capacity of hard carbon material as a percentage of the total sodium storage capacity can be 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any combination of two of these values. This indicates that hard carbon material has a low average sodium removal potential. Using hard carbon material with these characteristics as the negative electrode active material in sodium-ion batteries is beneficial for improving the energy density of sodium-ion batteries.

[0049] In some embodiments of this application, the electrical conductivity of the hard carbon material is from 0.5 S / cm to 10 S / cm. For example, the electrical conductivity of the hard carbon material can be 0.5 S / cm, 1 S / cm, 3 S / cm, 5 S / cm, 7 S / cm, 9 S / cm, 10 S / cm, or a range of any two of these values. By controlling the electrical conductivity of the hard carbon material within the above range, the internal resistance of the secondary battery can be reduced, which is beneficial to improving the capacity and rate performance of the secondary battery, as well as improving the cycle performance of the secondary battery.

[0050] The second aspect of this application provides a method for preparing the negative electrode active material of the first aspect of this application, wherein the method for preparing the hard carbon material includes the following steps:

[0051] (1) After the precursor is crushed and screened, it is placed in a closed reactor and the gas in the closed reactor is replaced by a first gas; the precursor includes at least one of lignin, cellulose, alkali lignin, asphalt, epoxy resin or phenolic resin, and the first gas includes any one of oxygen, air and carbon dioxide.

[0052] (2) After sealing the closed reactor, place it in a nitrogen atmosphere for one calcination, and heat it to 700℃ to 900℃ at a rate of 0.5℃ / min to 5℃ / min for 1h to 4h for pre-carbonization. After cooling, the pre-carbonized material is obtained.

[0053] (3) The pre-carbonized material is placed in a nitrogen atmosphere for secondary calcination. The temperature is increased to 1000℃ to 1500℃ at a rate of 0.5℃ / min to 5℃ / min for 1h to 8h. After cooling, the carbonized material is obtained. Then the carbonized material is classified according to particle size.

[0054] (4) Heat the material after grading in step (3) to 700°C to 1200°C, introduce a mixture of reducing gas and argon, and keep it for 0.1h to 12h before replacing it with nitrogen. Then cool to obtain hard carbon material. The reducing gas includes at least one of acetylene or methane, and the mass percentage of the reducing gas is 5wt% to 20wt% based on the mass of the mixture.

[0055] The negative electrode active material prepared by the method provided in the second aspect of this application has a stable low potential plateau, high specific capacity and high reversible capacity. When used as the negative electrode sheet of a secondary battery, it can improve the energy density of the secondary battery and improve its cycle performance.

[0056] This application does not specifically limit the grading method in step (3) above, as long as it can achieve the purpose of this application. For example, the calcined negative electrode active material precursor can be crushed and graded using a grading crusher. This application does not specifically limit the closed reactor, and those skilled in the art can select one according to actual needs, as long as it can achieve the purpose of this application. For example, the closed reactor can include, but is not limited to, a closed graphite reactor, a closed corundum reactor, a closed nickel crucible, a closed iron crucible, etc. In this application, the particle size Dv99 of the material after grading in step (3) above can be 30 μm to 50 μm. In this application, the particle size Dv50 of the hard carbon material is 3 μm to 20 μm. The particle size Dv99 of the hard carbon material can range from 30 μm to 50 μm. Dv50 refers to the particle size that reaches 50% of the volume cumulative in the particle size distribution based on the volume of the material. Dv99 refers to the particle size that reaches 99% of the volume cumulative in the particle size distribution based on the volume of the material.

[0057] Generally, the precursor mass, initial calcination time, initial calcination temperature, vapor deposition time, and secondary calcination time all affect the proportions of micropore volume and ultramicropore volume in hard carbon materials. With increasing precursor mass, these proportions initially increase and then decrease. With prolonged initial calcination time, both proportions decrease; conversely, with shorter initial calcination times, they increase. With increasing initial calcination temperature, both proportions increase; conversely, with decreasing initial calcination temperature, they decrease. With increasing vapor deposition time, the proportions of micropore volume and ultramicropore volume in the total pore volume increase; conversely, with decreasing vapor deposition time, these proportions decrease. Furthermore, with increasing secondary calcination temperature, the proportions of micropore volume and ultramicropore volume in the total pore volume decrease; conversely, with decreasing secondary calcination temperature, these proportions increase. In this application, carbonized materials of different particle sizes can be selected by grading the carbonized material according to particle size.

[0058] A third aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material provided in the first aspect of this application or a negative electrode active material prepared according to the preparation method provided in the second aspect of this application. The negative electrode sheet provided in the third aspect of this application has high capacity. When applied to a secondary battery, it can improve the energy density of the secondary battery and enhance its cycle performance.

[0059] In some embodiments of this application, the compaction density of the negative electrode active material layer is 0.8 g / cm³. 3 Up to 1.2 g / cm 3 For example, the compaction density of the negative electrode active material layer can be 0.8 g / cm³. 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 This could be a range consisting of any two of these values. By adjusting the compaction density of the negative electrode active material layer within the above range, the content of negative electrode active material per unit area can be increased, thereby improving the energy density of the secondary battery.

[0060] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, wherein the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, and poly(p-phenylene terephthalate). In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 130 μm. In this application, the negative electrode active material layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the term "surface" here can refer to the entire area of ​​the negative electrode current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. Optionally, the negative electrode active material includes a thickener, which may include, but is not limited to, sodium carboxymethyl cellulose. The negative electrode active material layer of this application may also include a conductive agent and a binder.

[0061] This application does not impose any particular limitations on the aforementioned conductive agents and binders, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, carbon materials, metals, or conductive polymers. Carbon materials may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, natural graphite, artificial graphite, flake graphite, carbon dots, or graphene. Metals may include metal powders or fibers of copper, iron, aluminum, etc. Conductive polymers may include at least one of polythiophene, polypyrrole, polyaniline, polyphenylene, and polyphenylenevinyl chloride. The adhesive may include, but is not limited to, at least one of the following: polyacryl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, waterborne acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0062] A fourth aspect of this application provides a secondary battery, which includes the negative electrode provided in the third aspect of this application. The secondary battery provided in the fourth aspect of this application has high energy density and good cycle performance.

[0063] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil may be aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer located on at least one surface of the polymer material base layer. For example, the material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. The polymer material base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, or polyethylene. The positive active material layer of this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application.

[0064] In some embodiments, the secondary battery is a lithium-ion battery, and the positive electrode active material may include lithium transition metal oxides, which may include, but are not limited to, lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In other embodiments, the secondary battery is a sodium-ion battery, and the positive electrode active material may include at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. Sodium transition metal oxides may include Na... 1-x Cu h Fe k Mn l M 1 m O 2-y Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, Na a Li b Ni c Mn d Fe e O2, where M 1 It is at least one of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, or Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;M 2is at least one of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn or Ba, 0 < z ≤ 0.1; 0.67 < a ≤ 1, 0 < b < 0.2, 0 < c < 0.3, 0.67 < d + e < 0.8, b + c + d + e = 1. The polyanionic compound may include but is not limited to: A 1 f M 3 g (PO4) i O j X 1 3-j , Na n M 4 PO4X 2 , Na p M 5 q (SO4)3, Na s Mn t Fe 3-t (PO4)2(P2O7), where A 1 is at least one of H, Li, Na, K or NH4, M 3 is at least one of Ti, Cr, Mn, Fe, Co, Ni, V, Cu or Zn, X 1 is at least one of F, Cl or Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2; M 4 is at least one of Mn, Fe, Co, Ni, Cu or Zn, X 2 is at least one of F, Cl or Br, 0 < n ≤ 2; M 5 is at least one of Mn, Fe, Co, Ni, Cu or Zn, 0 < p ≤ 2, 0 < q ≤ 2; 0 < s ≤ 4, 0 ≤ t ≤ 3. The Prussian blue compounds may include but are not limited to at least one of Na2Fe[Fe(CN)6], Na2Mn[Fe(CN)6] or Na2Mn[Mn(CN)6].

[0065] This application does not particularly limit the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. In this application, the positive electrode active material layer may be provided on one surface in the thickness direction of the positive electrode current collector, or may be provided on both surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here may be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector. This application does not particularly limit it, as long as the purpose of this application can be achieved. The positive electrode active material layer of this application may further contain the above-mentioned conductive agent and the above-mentioned binder.

[0066] The secondary battery of this application also includes an electrolyte. In one embodiment, the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one selected from LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. In another embodiment, the electrolyte includes a sodium salt and a non-aqueous solvent. The sodium salt may include at least one selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. This application does not impose any particular limitation on the concentration of the sodium salt in the electrolyte, as long as the purpose of this application is achieved. The aforementioned non-aqueous solvents are not particularly limited, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0067] The secondary battery of this application also includes a separator for separating the positive and negative electrode plates, preventing internal short circuits, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide (PI) membranes, polyamide (PA) membranes, spandex, or aramid membranes. The type of separator can be, but is not limited to, at least one of woven membranes, nonwoven membranes (non-woven fabrics), microporous membranes, composite membranes, rolled membranes, or spun membranes. The diaphragm of this application may have a porous structure, with a porous layer disposed on at least one surface of the diaphragm. The porous layer comprises inorganic particles and a binder. The inorganic particles may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder may include at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not particularly limit the pore size of the porous structure, as long as it achieves the purpose of this application; for example, the pore size may be from 0.01 μm to 1 μm. In this application, the thickness of the diaphragm is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness may be from 5 μm to 500 μm.

[0068] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0069] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0070] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0071] The fifth aspect of this application provides an electronic device that includes the secondary battery provided in the fourth aspect of this application. The secondary battery provided in the fourth aspect of this application has high energy density and good cycle performance, thereby providing the electronic device provided in the fifth aspect of this application with a long service life.

[0072] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0073] Example

[0074] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0075] Test methods and equipment

[0076] Raman test

[0077] The Raman spectra of hard carbon materials were measured using a Raman spectrometer. Hard carbon material powder was used for testing. A 200 μm × 500 μm area was selected for the test, and more than 200 points were measured at equal intervals within this area, with each point measured over 1000 cm⁻¹. -1 Up to 2000cm-1 Between; recorded at 1320cm -1 Up to 1370cm -1 The peak that appears between these points is the D peak, located at 1570 cm⁻¹. -1 Up to 1620cm -1 The peaks that appear between them are called G peaks, and the I values ​​at each point are statistically analyzed. D / I G The intensity ratio is then calculated, and the average value of multiple points is taken as the final I. D / I G The strength ratio.

[0078] X-ray diffraction (XRD) test

[0079] The X-ray diffraction pattern of hard carbon material was tested using an X-ray powder diffractometer (XRD, instrument model Bruker D8 ADVANCE), and the position of the XRD 002 peak of hard carbon material was obtained by analysis.

[0080] Scanning electron microscopy (SEM) test

[0081] The hard carbon material particles were observed using a scanning electron microscope (ZEISSSEM) and SEM images were taken.

[0082] Powder particle size test

[0083] The particle size distribution of hard carbon materials was tested using a Malvern particle size analyzer (Master Sizer 2000). In the volumetric particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the volumetric accumulation was defined as Dv50, and the particle size reaching 99% of the volumetric accumulation was defined as Dv99.

[0084] Pore ​​size distribution test

[0085] Hard carbon material powder was placed in a sample tube and degassed under vacuum at 100℃ for 12 hours. The adsorption capacity of the hard carbon material for carbon dioxide under different pressures was measured using an ASAP2460 physical adsorption analyzer, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the shape of the hysteresis loop. The pore size distribution curve of the micropores was fitted using a DFT model, and the pore volumes of the ultramicropores, micropores, and total pore volume in the hard carbon material were calculated. The proportion of micropore volume to total pore volume = micropore volume / total pore volume; the proportion of ultramicropore volume to total pore volume = ultramicropore volume / total pore volume.

[0086] Elemental analysis test

[0087] X-ray photoelectron spectroscopy (ThermoESCALAB250XI) was used to determine the proportion and content of C, O, N, and S elements in hard carbon materials. Three different parts of the same material were selected to test the content of the above elements and calculate their mass percentage.

[0088] The percentage of oxygen in carbonyl and carboxyl groups relative to the total oxygen mass in hard carbon materials was determined using X-ray photoelectron spectroscopy. Peak fitting of the O1s peak in the X-ray photoelectron spectrum was performed, and the peaks near 530.8 eV and 533.9 eV corresponded to carbonyl oxygen and carboxyl oxygen, respectively. The proportion of oxygen in carbonyl and carboxyl groups relative to the total oxygen mass in the hard carbon materials was obtained by dividing the corresponding peak area by the total area of ​​the O1s peak.

[0089] Conductivity test

[0090] The conductivity of hard carbon materials was tested using a four-probe powder conductivity meter (Suzhou Crystallographic ST2742B). The test pressure was 5 MPa, the temperature was 25℃, and the humidity was 65%. Each sample was tested three times and the average value was taken.

[0091] Total lithium storage capacity and initial efficiency test of hard carbon materials

[0092] The initial reversible specific capacity of hard carbon material from 0V to 2.5V can be obtained by the following test method: Hard carbon material, styrene-butadiene rubber binder, and sodium carboxymethyl cellulose thickener are mixed in a mass ratio of 97:1.5:1.5, and then deionized water is added as a solvent to prepare a slurry with a solid content of 40wt%. The slurry is coated on one side of the negative electrode current collector copper foil to obtain a negative electrode sheet. The negative electrode sheet is cut into a disc with a diameter of 14mm and used as the working electrode. Then, a lithium sheet is used as the counter electrode, and a porous polyethylene membrane (provided by Celgard) is used as the separator. After injecting electrolyte, a button cell is assembled. The button cell is first discharged to 0V with a small current in three stages of 0.05C / 0.01C / 0.005C, and the initial discharge capacity of the button cell is recorded. Then, it is charged to 2.5V with a constant current of 0.1C and the initial charge capacity of the button cell is recorded. The mass of hard carbon material in the negative electrode was calculated based on the coating weight and area of ​​the slurry during the electrode preparation process described above. Initial efficiency = (initial charge capacity / initial discharge capacity) × 100%; the initial reversible specific capacity of the hard carbon material from 0V to 2.5V, i.e., the total lithium storage capacity Q = initial charge capacity / mass of hard carbon material, in mAh / g. Li / Li ratio from 0V to 0.1V... + The specific capacitance of hard carbon materials within the potential range is denoted as Q1; Li / Li ratio from 0V to 0.8V. + The specific capacity of hard carbon materials within the potential range is denoted as Q2.

[0093] The electrolyte consists of a base solvent and a lithium salt. The base solvent is obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a mass ratio of 1:1. The lithium salt is LiPF6 with a concentration of 1 mol / L.

[0094] The total lithium storage capacity and initial efficiency of the graphite in Comparative Example 1 were tested using the same methods as those used for the hard carbon materials described above.

[0095] Total sodium storage capacity and initial efficiency test of hard carbon materials

[0096] The testing methods for sodium storage capacity and initial efficiency of hard carbon materials are the same as those for the total lithium storage capacity and initial efficiency of the aforementioned hard carbon materials, except that sodium sheets are used instead of lithium sheets as the counter electrode, aluminum foil is used as the negative electrode current collector, and sodium salt NaPF6 is used instead of lithium salt. (Na / Na...) + The total sodium storage capacity of hard carbon materials within the potential range is denoted as R; the Na / Na ratio from 0V to 0.5V is... + The specific capacitance of hard carbon materials within the potential range is denoted as R1; Na / Na ratio from 0V to 0.8V. + The specific capacity of carbon materials within the potential range is denoted as R2.

[0097] Test of compaction density of negative electrode active material

[0098] Take a fully discharged lithium-ion battery, disassemble the negative electrode sheet, clean and dry it. Weigh the negative electrode sheet with an area of ​​S using an electronic balance, and record the weight as W1. Measure the thickness T1 of the negative electrode sheet using a micrometer. Wash away the negative electrode active material layer with the solvent DMC, dry it, and measure the weight of the negative electrode current collector, recording it as W2. Measure the thickness T2 of the negative electrode current collector using a micrometer. Calculate the weight W0 and thickness T0 of the negative electrode active material layer on the side of the negative electrode current collector, as well as the compaction density of the negative electrode active material layer, using the following formula: W0 = W1 - W2, T0 = T1 - T2, then compaction density = W0 / (T0 × S).

[0099] Energy density (ED) test

[0100] In an environment of 25℃, lithium-ion or sodium-ion batteries are charged at a constant current of 0.2C to a voltage of 4.48V or 3.95V, and then charged at a constant voltage; followed by discharge at a constant current of 0.2C to a voltage of 2V. This is recorded as one cycle, and the discharge capacity C and discharge energy E of the first cycle are recorded. The length, width, and height of the battery at 50% charge are measured to obtain the battery volume V. m Average discharge voltage U = E / C; Energy density ED = E / V m .

[0101] Example 1-1

[0102] <Preparation of Negative Electrode Active Materials>

[0103] A 20g precursor of alkali lignin (m) was placed in a 500mL covered graphite crucible in a reactor. The gas in the reactor was replaced with air as the first gas. After sealing the reactor, it was transferred to a box furnace for primary calcination under nitrogen protection. The temperature was increased at a rate of 5℃ / min to the primary calcination temperature T1 = 700℃, and the primary calcination time t1 was 2h. The temperature was then lowered. The pre-carbonized material powder in the reactor was then transferred to a nitrogen atmosphere furnace for secondary calcination. The temperature was increased at a rate of 2℃ / min to the secondary calcination temperature T2 = 1100℃, and carbonized for 2h. The temperature was then lowered, and the carbonized material was obtained. The material was crushed to obtain powder, which was then classified according to particle size. The particle size of the classified powder was controlled at Dv99 to be 40μm and Dv50 to be 10μm. The graded powder was then transferred to a nitrogen atmosphere-protected furnace and heated to the vapor deposition temperature T3 = 900℃ at a heating rate of 5℃ / min. The gas atmosphere was then replaced with a mixture of reducing gases, methane and argon, for a vapor deposition time of t3 = 2 hours. After vapor deposition, the mixed gas was disconnected and replaced with nitrogen. After cooling to room temperature, a hard carbon material with a Dv50 of 18 μm, i.e., the negative electrode active material, was obtained. Based on the mass of the mixed gas, the mass percentage of the reducing gas methane was 20%.

[0104] <Preparation of Negative Electrode Sheets>

[0105] The aforementioned anode active material (hard carbon), binder (styrene-butadiene rubber), and thickener (sodium carboxymethyl cellulose) were mixed in a mass ratio of 97:1.5:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 40 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the anode active material layer, with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 76.6 mm × 875 mm.

[0106] <Preparation of the positive electrode>

[0107] Lithium cobalt oxide (CCO) as the positive electrode active material, conductive carbon black (Super P) as the conductive agent, and PVDF as the binder were mixed at a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous, resulting in a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil used as a positive electrode current collector, and dried at 85 °C to obtain a single-sided coated positive electrode sheet with a positive electrode active material layer thickness of 80 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85 °C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0108] <Preparation of Electrolyte>

[0109] In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1. Fluorinated ethylene carbonate was then added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the lithium salt content was 12.5%, the fluoroethylene carbonate content was 3.5%, and the remainder was the base solvent.

[0110] <Preparation of the diaphragm>

[0111] A 7μm thick polyethylene film (supplied by Celgard) was used as the separator.

[0112] <Preparation of Lithium-ion Batteries>

[0113] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, degassing, and shaping processes.

[0114] Examples 1-2 to Examples 1-14

[0115] Except for adjusting the preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0116] Table 1

[0117]

[0118] Example 2-1

[0119] <Preparation of Negative Electrode Active Materials>

[0120] Except for adjusting the secondary calcination temperature T2 to 1300℃, the rest is the same as in Examples 1-5.

[0121] <Preparation of Negative Electrode Sheets>

[0122] Except for the use of the above-prepared negative electrode active material, styrene-butadiene rubber binder, and sodium carboxymethyl cellulose thickener mixed in a mass ratio of 97:2:1, and aluminum foil replacing copper foil as the negative electrode current collector, the rest is the same as in Examples 1-5.

[0123] <Preparation of the positive electrode>

[0124] In addition to using copper-nickel-iron-manganese oxide (NaCu) as the positive electrode active material 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 Except for replacing the positive electrode active material lithium cobalt oxide with O2, the rest is the same as in Examples 1-5.

[0125] <Preparation of Electrolyte>

[0126] In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a mass ratio of 50:50. Then, fluoroethylene carbonate was added, dissolved, and thoroughly stirred. Sodium salt NaPF6 was then added and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the sodium salt had a mass percentage of 12.5%, the fluoroethylene carbonate had a mass percentage of 3.5%, and the remainder was the base solvent.

[0127] <Preparation of the diaphragm>

[0128] PVDF and alumina ceramic were mixed at a mass ratio of 9:1, and deionized water was added as a solvent to prepare a slurry with a solid content of 12wt%. The slurry was stirred evenly and then uniformly coated on one surface of a 9μm thick porous polyethylene (provided by Celgard). After drying, a diaphragm with a 2μm alumina ceramic layer coated on one side was obtained.

[0129] <Preparation of Sodium-ion Batteries>

[0130] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the sodium-ion battery is obtained through vacuum sealing, settling, formation, degassing, and shaping processes.

[0131] Example 2-2

[0132] <Preparation of Negative Electrode Active Materials>

[0133] Except for adjusting the secondary calcination temperature T2 to 1300℃, the rest is the same as in Examples 1-7.

[0134] The preparation of the negative electrode, positive electrode, electrolyte, separator, and sodium-ion battery are the same as in Example 2-1.

[0135] Example 2-3

[0136] <Preparation of Negative Electrode Active Materials>

[0137] Except for adjusting the secondary calcination temperature T2 to 1300℃, the rest is the same as in Examples 1-8.

[0138] The preparation of the negative electrode, positive electrode, electrolyte, separator, and sodium-ion battery are the same as in Example 2-1.

[0139] Examples 2-4

[0140] Except for adjusting the secondary calcination temperature T2 to 1300℃, the rest is the same as in Examples 1-10.

[0141] The preparation of the negative electrode, positive electrode, electrolyte, separator, and sodium-ion battery are the same as in Example 2-1.

[0142] Comparative Example 1

[0143] Except for replacing the negative electrode active material prepared in the <Preparation of Negative Electrode Active Material> with artificial graphite, the rest is the same as in Example 1-1.

[0144] Comparative Example 2

[0145] Except for the negative electrode active material prepared by the following <Preparation of Negative Electrode Active Material>, the rest is the same as in Example 1-1.

[0146] <Preparation of Negative Electrode Active Materials>

[0147] 20g of the precursor alkali lignin was placed in a box furnace and calcined twice under a nitrogen atmosphere. The temperature was increased to the secondary calcination temperature T2 = 1100℃ at a heating rate of 2℃ / min, and carbonized for 2 hours. After cooling, the carbonized material was obtained, crushed to obtain powder, and then the powder was classified according to particle size, with the particle size Dv99 controlled at 40μm and Dv50 controlled at 10μm. The classified powder was then transferred to a nitrogen atmosphere furnace and heated to the vapor deposition temperature T3 = 900℃ at a heating rate of 5℃ / min. Subsequently, the gas atmosphere was changed to a mixture of reducing gases methane and argon, and the vapor deposition time t3 = 2 hours. After the vapor deposition was completed, the mixed gas was disconnected and replaced with nitrogen. After cooling to room temperature, a hard carbon material with a Dv50 of 18μm was obtained, which is the negative electrode active material. Based on the mass of the mixed gas, the mass percentage of reducing gas methane was 20%.

[0148] Comparative Example 3

[0149] Except for the negative electrode active material prepared by the following <Preparation of Negative Electrode Active Material>, the rest is the same as in Example 1-1.

[0150] <Preparation of Negative Electrode Active Materials>

[0151] 20g of the precursor alkali lignin was placed in a 500mL covered graphite reactor, and the gas in the reactor was replaced with air as the first gas. After sealing the reactor, it was transferred to a box furnace for primary calcination under nitrogen protection. The temperature was increased to the primary calcination temperature T1700℃ at a heating rate of 5℃ / min, and the primary calcination time t1 was 2h. The temperature was then lowered. The powder after primary calcination was crushed and classified, and the particle size Dv99 was controlled to be 40μm and Dv50 to be 10μm. The classified powder was then transferred to a nitrogen atmosphere protected furnace and heated to the vapor deposition temperature T3 = 900℃ at a heating rate of 5℃ / min. The gas atmosphere was then changed to a mixture of reducing gases methane and argon, and the vapor deposition time t3 = 2h. After the vapor deposition was completed, the mixed gas was disconnected and replaced with nitrogen. After cooling to room temperature, a hard carbon material with a Dv50 of 18μm was obtained, which is the negative electrode active material. Based on the mass of the gas mixture, the mass percentage of the reducing gas methane is 20%.

[0152] Comparative Example 4

[0153] <Preparation of Negative Electrode Active Materials>

[0154] Except for adjusting the secondary calcination temperature T2 to 1300℃, the rest is the same as Comparative Example 2.

[0155] The preparation of the negative electrode, positive electrode, electrolyte, separator, and sodium-ion battery are the same as in Example 2-1.

[0156] The relevant parameters and performance tests of each embodiment and comparative example are shown in Tables 2 to 4. In Tables 2 to 4 below, the proportion of micropore volume to total volume is abbreviated as micropore percentage, the proportion of ultramicropore volume to total volume is abbreviated as ultramicropore percentage, and X is the percentage of the mass of oxygen element in carbonyl and carboxyl groups to the total mass of oxygen element in hard carbon material.

[0157]

[0158]

[0159] As can be seen from Examples 1-1 to 1-14 and Comparative Examples 1 to 3, the negative electrode active material includes hard carbon material. Within the scope of this application, the micropore ratio, ultramicropore ratio, and pore volume of the ultramicropores in the hard carbon material are larger, with Q1 and Q2 values ​​being comparable to those of graphite material. The hard carbon material exhibits a lower average delithiation potential, and simultaneously has a higher total lithium storage capacity Q and higher initial efficiency in the 0V to 2.5V range. This indicates that the negative electrode active material provided in this application has a stable low-potential platform, higher specific capacity, and reversible capacity. Lithium-ion batteries incorporating the negative electrode active material of this application have higher energy density and capacity retention, thus demonstrating that the lithium-ion batteries provided in this application have higher energy density and better cycle performance.

[0160] The mass percentage of oxygen, the mass percentage of element A (N+S), the value of X, and I in hard carbon materials D / I G The values ​​of the dielectric constant and the conductivity of hard carbon materials typically affect the performance of the negative electrode active material, such as the average delithiation potential, specific capacity, and initial efficiency, thereby influencing the cycle performance and energy density of the lithium-ion battery. As can be seen from Examples 1-1 to 1-14, when the above parameters are within the range of this application, the negative electrode active material exhibits a stable low-potential plateau, high specific capacity, and reversible capacity, resulting in a lithium-ion battery with high energy density and capacity retention. This demonstrates that the lithium-ion battery provided in this application has high energy density and good cycle performance.

[0161] The compaction density of the negative electrode active material layer typically affects the cycle performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1 to 1-14, when the compaction density of the negative electrode active material layer is within the range specified in this application, the resulting lithium-ion battery exhibits high energy density and capacity retention, thus demonstrating that the lithium-ion battery provided in this application possesses high energy density and good cycle performance.

[0162] As can be seen from Examples 2-1 to 2-4 and Comparative Example 4, the negative electrode active material, including the hard carbon material, has a higher proportion of micropores, a higher proportion of ultramicropores, and a larger pore volume of ultramicropores within the scope of this application. Furthermore, the values ​​of R1 and R2 are larger, and the values ​​of R1 / R and R2 / R are also larger. The hard carbon material exhibits a lower average sodium removal potential, and simultaneously has a higher total sodium storage capacity R and a higher initial efficiency in the 0V to 2.5V range. This indicates that the negative electrode active material provided in this application has a stable low-potential plateau, higher specific capacity, and reversible capacity. Sodium-ion batteries incorporating the negative electrode active material of this application have higher energy density and capacity retention, thus demonstrating that the sodium-ion batteries provided in this application have higher energy density and better cycle performance.

[0163] Table 3 shows the positions of the 002 peaks in the XRD diffraction patterns of the hard carbon materials in Examples 1-5, 1-11, and 1-12. The 002 peak positions of the hard carbon materials in these examples are between 21.2° and 21.8°, indicating that the large interplanar spacing of the hard carbon materials is beneficial for lithium ion intercalation between the layers. Table 3 also shows the oxygen content and electrical conductivity of the hard carbon materials in these examples. It can be seen that the oxygen content is greatly affected by the type of the first gas. Specifically, when the first gas is CO2, air, and O2 in that order, the oxygen content increases sequentially, and the electrical conductivity of the hard carbon materials decreases sequentially.

[0164] Table 4 shows the positions of the 002 peaks in the XRD diffraction patterns of the hard carbon materials in Examples 2-1 to 2-4. The positions of the 002 peaks in the hard carbon materials of the above examples are between 23.3° and 24.9°, indicating that the interplanar spacing of the hard carbon materials is large, which is conducive to the intercalation of sodium ions between the layers of the hard carbon materials.

[0165] Figure 1 Scanning electron microscope images of the hard carbon materials prepared in Examples 1-5 are shown. The hard carbon materials are irregular blocks, and there are no obvious pore structures on the surface of the particles, indicating that there are no large pores on the surface of the hard carbon materials. Figure 2 The diagram shows the pore size distribution of the hard carbon materials prepared in Examples 1-5 based on nitrogen adsorption-desorption. It can be seen that the hard carbon materials are mainly composed of micropores with a pore size of less than 2 nm, while ultramicropores with a pore size of less than 7 nm can be clearly observed. Furthermore, no mesopores or macropores are present in the hard carbon materials.

[0166] from Figure 3 It can be seen that the Li / Li ratios are [values] in the ranges of 0V to 0.1V, 0V to 0.8V, and 0V to 2.5V. + Within the potential range, the specific capacities of the hard carbon materials in Examples 1-5 were 285 mAh / g, 401 mAh / g, and 465 mAh / g, respectively, indicating that the hard carbon materials in Examples 1-5 possessed high specific capacity and low delithiation potential. Figure 4It can be seen that the Li / Li ratios are [values] in the ranges of 0V to 0.1V, 0V to 0.8V, and 0V to 2.5V. + Within the potential range, the specific capacities of the hard carbon material in Comparative Example 2 were 144 mAh / g, 276 mAh / g, and 300 mAh / g, respectively, indicating that the hard carbon material in Comparative Example 2 has a lower specific capacity and a higher delithiation potential. Combined with... Figure 3 and Figure 4 It can be seen that, compared with Comparative Example 2, the hard carbon materials of Examples 1-5 have higher specific capacity and lower delithiation potential.

[0167] from Figure 5 It can be seen that the charge-discharge curves of hard carbon materials exhibit distinct plateaus at Na / Na ratios between 0V and 0.5V, 0V and 0.8V, and 0V and 2.5V. + Within the specified potential range, the specific capacities of the hard carbon material in Example 2-1 were 274 mAh / g, 293 mAh / g, and 315 mAh / g, respectively. This indicates that the hard carbon material in Example 2-1 exhibits a high specific capacity and a low desodiumization potential.

[0168] Figure 6 The Raman spectra of the hard carbon materials prepared in Examples 1-5 are shown. Figure 6 In the middle, located at 1320cm -1 Up to 1370cm -1 The peak area of ​​peak D is 58213, located at 1570 cm⁻¹. -1 Up to 1620cm -1 The peak area of ​​peak G between them is 51976, and I can be calculated. D / I G =1.12. This indicates that a suitable degree of defects in hard carbon materials is beneficial to improving the specific capacity of hard carbon materials.

[0169] from Figure 7 It can be seen that the 002 peak position of the hard carbon materials in Examples 1-5 is at 21.8°, indicating that the interplanar spacing of the hard carbon materials is large, which is conducive to the intercalation of lithium ions between the layers of the hard carbon materials.

[0170] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0171] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0172] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A negative electrode active material, wherein, The negative electrode active material includes hard carbon material; the hard carbon material comprises micropores and ultramicropores, wherein the pore size of the micropores is <2 nm and the pore size of the ultramicropores is <0.7 nm; the pore volume of the micropores accounts for 95% to 100% of the total pore volume, and the pore volume of the ultramicropores is 0.01 cm³. 3 / g to 0.2cm 3 / g, wherein the pore volume of the ultramicropores accounts for 80% to 99% of the total pore volume; The hard carbon material contains carbon and oxygen elements, and the mass percentage of oxygen in the hard carbon material is 2% to 7%. The oxygen element in the hard carbon material exists in carbonyl and carboxyl groups, and the mass of oxygen element in carbonyl and carboxyl groups accounts for 60% to 99% of the total mass of oxygen element in the hard carbon material.

2. The negative electrode active material according to claim 1, wherein, The hard carbon material satisfies 0.8≤I D / I G ≤1.5, I D I represents the peak area of ​​peak D in the Raman spectrum of the hard carbon material. G The peak area of ​​the G peak in the Raman spectrum of the hard carbon material is given.

3. The negative electrode active material according to claim 1, wherein, The hard carbon material further comprises element A, which includes at least one of N or S; the mass percentage of element A is 0.05% to 2% based on the mass of the hard carbon material.

4. The negative electrode active material according to claim 1, wherein, The hard carbon material satisfies at least one of the following characteristics (a) or (b): (a) The pore volume of the micropores is 0.04 cm. 3 / g to 0.2cm 3 / g; (b) The oxygen content in the hard carbon material is 2.54% to 6% by mass.

5. The negative electrode active material according to claim 3, wherein, Based on the mass of the hard carbon material, the mass percentage of element A is 0.1% to 1.7%.

6. The negative electrode active material according to claim 1, wherein, Li / Li from 0V to 2.5V + Within the potential range, the total lithium storage capacity of the hard carbon material is 300 mAh / g to 700 mAh / g; the delithiation energy of the hard carbon material is E1Wh; the delithiation capacity of the hard carbon material is C1Ah; and the average delithiation potential of the hard carbon material is E1 / C1V, 0.13≤E1 / C1≤0.

28. Li / Li at 0V to 0.1V + Within the potential range, the specific capacity of the hard carbon material accounts for 30% to 65% of the total lithium storage capacity; in the Li / Li ratio range of 0V to 0.8V... + Within the potential range, the specific capacity of the hard carbon material accounts for 70% to 96% of the total lithium storage capacity.

7. The negative electrode active material according to claim 1, wherein, Na / Na from 0V to 2.5V + Within the potential range, the total sodium storage capacity of the hard carbon material is 250 mAh / g to 400 mAh / g; the sodium removal energy of the hard carbon material is E2Wh, the sodium removal capacity of the hard carbon material is C2Ah, and the average sodium removal potential of the hard carbon material is E2 / C2V, 0.2≤E2 / C2 ≤0.4; Na / Na at 0V to 0.5V + Within the potential range, the specific capacity of the hard carbon material accounts for 76% to 91% of the total sodium storage capacity; in the Na / Na ratio range of 0V to 0.8V... + Within the potential range, the specific capacity of the hard carbon material accounts for 89% to 95% of the total specific capacity of sodium storage.

8. The negative electrode active material according to claim 1, wherein, The electrical conductivity of the hard carbon material is from 0.5 S / cm to 10 S / cm.

9. A method for preparing a negative electrode active material according to any one of claims 1 to 8, wherein, The preparation method of hard carbon materials includes the following steps: (1) After the precursor is crushed and screened, it is placed in a closed reactor and the gas in the closed reactor is replaced by a first gas; the precursor includes at least one of lignin, cellulose, alkali lignin, asphalt, epoxy resin or phenolic resin, and the first gas includes any one of oxygen, air and carbon dioxide. (2) After sealing the closed reactor, place it in a nitrogen atmosphere for a first calcination, and heat it to 700°C to 900°C at a rate of 0.5°C / min to 5°C / min for 1h to 4h for pre-carbonization. After cooling, the pre-carbonized material is obtained. (3) The pre-carbonized material is placed in a nitrogen atmosphere for secondary calcination, and the temperature is increased to 1000℃ to 1500℃ at a rate of 0.5℃ / min to 5℃ / min for 1h to 8h. After cooling, the carbonized material is obtained, and then the carbonized material is classified according to particle size. (4) The material after grading in step (3) is heated to 700°C to 1200°C, a mixture of reducing gas and argon is introduced, and the mixture is kept for 0.1h to 12h before being replaced with nitrogen. The material is then cooled to obtain the hard carbon material. The reducing gas includes at least one of acetylene or methane, and the mass percentage of the reducing gas is 5wt% to 20wt% based on the mass of the mixture.

10. A negative electrode plate, wherein, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes the negative active material according to any one of claims 1 to 8 or the negative active material prepared by the preparation method according to claim 9.

11. The negative electrode sheet according to claim 10, wherein, The compaction density of the negative electrode active material layer is 0.8 g / cm³. 3 Up to 1.2 g / cm 3 .

12. A secondary battery, wherein, The secondary battery includes the negative electrode sheet as described in claim 10 or 11.

13. An electronic device, wherein, The electronic device includes the secondary battery as described in claim 12.

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