Negative active material, secondary battery, and electronic device

Abstract

Provided is a negative electrode active material, which comprises a carbon-based material, a surface of the carbon-based material comprising sodium elements and oxygen elements, an atomic percentage of the sodium elements being X, an atomic percentage of the oxygen elements being Y, wherein Y / X is greater than or equal to 3.0, and X and Y are obtained by X-ray energy spectrum analysis. By controlling the content of the sodium elements and the oxygen elements on the surface of the carbon-based material within a certain range, the quality of the SEI film can be effectively improved, and thus the secondary battery exhibits excellent cycle performance. Also provided is a secondary battery comprising the negative electrode active material.

Description

Negative electrode active materials, secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of energy storage, specifically to a negative electrode active material, a secondary battery, and an electronic device. Background Technology

[0002] As the secondary battery market continues to expand, the performance requirements are also constantly increasing, with cycle performance being a crucial indicator, especially for electric vehicles and energy storage devices where high cycle performance is essential. Considering the actual working environment and characteristics, cycle performance is critical to the lifespan of electric vehicles and energy storage devices. To meet market demands, it is necessary to develop negative electrode active materials and the negative electrode sheets composed of them with excellent cycle performance, thereby improving the cycle performance of secondary batteries. Existing technologies for improving cycle performance mainly include reducing the particle size of the active material and coating the surface of the active material with amorphous carbon. However, these two methods not only result in significant energy density loss of the negative electrode active material but also reduce the efficiency of the secondary battery. Summary of the Invention

[0003] In view of the above-mentioned problems in the prior art, this application provides a negative electrode active material and a secondary battery including the negative electrode active material to improve the quality of the SEI film on the surface of the carbon-based material, thereby improving the cycle performance of the secondary battery.

[0004] In a first aspect, this application provides a negative electrode active material comprising a carbon-based material. The surface of the carbon-based material includes sodium and oxygen elements, with the atomic percentage of sodium being X and the atomic percentage of oxygen being Y, wherein Y / X ≥ 3.0. X and Y are obtained by X-ray energy dispersive spectroscopy (EDS). Specifically, X and Y are tested using the following method: when observing the carbon-based material with a scanning electron microscope, any 100μm × 100μm area in the field of view of the scanning electron microscope is selected, and the sodium and oxygen content of this area is measured by X-ray energy dispersive spectroscopy (EDS) to obtain X and Y. The carbon-based material of this application has sodium and oxygen elements on its surface. When the carbon-based material is used as a negative electrode active material, sodium and oxygen elements are constituent elements of the SEI film, which affect the thermal stability of the SEI film on the particle surface, and the content of the two elements has a certain interactive effect on the thermal stability of the SEI. Sodium contributes to the formation of the SEI film on the surface of carbon-based materials, effectively improving the quality of the SEI film and thus enhancing the cycle performance of the secondary battery. However, excessive sodium can result in an overly thick SEI film, which is detrimental to cycle performance. Oxygen is an essential component of the SEI film, but excessive oxygen content can lead to increased side reactions, thereby affecting the storage and cycle performance of the secondary battery. This application effectively improves the quality of the SEI film by controlling the content of sodium and oxygen within the aforementioned ranges, resulting in excellent cycle performance of the secondary battery. In some embodiments, 3.5 ≤ Y / X ≤ 15.

[0005] In some embodiments, 0.2% ≤ X ≤ 4.0%. In some embodiments, the mass content of sodium is m, 0.4% ≤ m ≤ 9.0%. In this application, m is tested using the following method: When observing the carbon-based material with a scanning electron microscope, an arbitrary 100μm × 100μm region is selected in the scanning electron microscope's field of view, and the sodium content of this region is measured using EDS surface scanning to obtain m. Sodium is mainly used as an inorganic component in the SEI membrane, therefore the mass percentage of sodium should not be too small. However, if the sodium content is too high, it will affect the content of organic components in the SEI membrane, leading to a decrease in organic component content, which increases the brittleness and reduces the elasticity of the SEI membrane. Consequently, the SEI membrane is prone to cracking during cycling due to the expansion of the carbon-based material, thus affecting the cycle performance of the secondary battery. In some embodiments, 3% ≤ m ≤ 6%. In some embodiments, 0.3% ≤ X ≤ 2.5%.

[0006] In some embodiments, 2.0% ≤ Y ≤ 15.0%. Oxygen is an essential component of the SEI membrane, but excessive oxygen content can lead to increased side reactions, thereby affecting the storage and cycle performance of the secondary battery. In some embodiments, 3.0% ≤ Y ≤ 12.0%.

[0007] In some embodiments, the carbon-based material satisfies: BET / (Y×100)≤0.7, where BET m 2 / g represents the specific surface area of ​​the carbon-based material. The specific surface area of ​​carbon-based materials is affected by the oxygen content on their surface. Excessive BET (Body Surface Area) increases side reactions during secondary battery cycling, thus affecting cycle performance. This application ensures that BET / (Y×100) ≤ 0.7, maintaining a low BET level even with high oxygen content. In some embodiments, 0.2 ≤ BET / (Y×100) ≤ 0.6.

[0008] In some embodiments, the carbon-based material satisfies the following condition: 25 ≤ Dv99 - Dv10 ≤ 55, where Dv99 represents the particle size of the carbon-based material that accounts for 99% of the volumetric particle size distribution (in μm), and Dv10 represents the particle size of the carbon-based material that accounts for 10% of the volumetric particle size distribution (in μm). The value of Dv99 - Dv10 is related to the particle size distribution of the carbon-based material. A Dv99-Dv10 range ensures a narrow particle size distribution, reducing the likelihood of excessive small or large particles, thus improving the cycle performance and processing performance of the secondary battery. An excessive number of small particles in the carbon-based material increases side reactions and affects the cycle performance of the secondary battery; an excessive number of large particles affects processing performance and may lead to appearance defects such as bumps on the negative electrode, and in severe cases, may even lead to point-like lithium plating. In some embodiments, 30 ≤ Dv99 - Dv10 ≤ 40.

[0009] In some embodiments, thermogravimetric analysis (TGA) is used, and the weight loss rate of the carbon-based material is 0.2% to 5% within a temperature range of 25°C to 400°C. The weight loss rate of the carbon-based material at 400°C can represent the content of surface modification substances, and the content of surface modification substances affects the formation quality of the SEI film in subsequent formation processes. If the weight loss rate is too low, i.e., the content of modification substances is too small, it will not have the effect of improving the thermal stability of the SEI film. In some embodiments, TGA is used, and the weight loss rate of the carbon-based material is 0.5% to 2.5% within a temperature range of 25°C to 400°C.

[0010] In some embodiments, the 5t powder compaction density (PD) of the carbon-based material satisfies: 1.5 g / cm³. 3 ≤PD≤2.5g / cm 3 The compaction density of carbon-based materials used as negative electrode active materials is related to the energy density and kinetics of the secondary battery. Lower compaction density results in lower electrode compaction density, consequently reducing the energy density of the secondary battery. Excessively high compaction density reduces the kinetic performance of the secondary battery, affecting its electrical performance at high rates. In some implementations, 1.65 g / cm³ is used.3 ≤PD≤1.95g / cm 3 .

[0011] In some embodiments, the OI value of the carbon-based material is between 5 and 18. The OI value of the carbon-based material indicates the uniformity of crystal orientation within its particles. A higher OI value means that the crystal orientation is highly uniform, resulting in a more unidirectional lithium ion insertion / extraction direction in the active particles. This can lead to difficulties in lithium insertion / extraction, and in severe cases, lithium plating, thereby reducing the cycle performance of the secondary battery. In some embodiments, the OI of the carbon-based material is between 6 and 13.

[0012] In some embodiments, the carbon-based material includes graphite. In some embodiments, the graphite includes one or more of natural graphite and synthetic graphite.

[0013] In some embodiments, the preparation method of carbon-based materials includes the following steps:

[0014] S1: Provides graphite composite materials;

[0015] S2: The graphite composite material is mixed with an oxidant and then subjected to oxidation treatment to obtain the oxidized graphite composite material;

[0016] S3: The oxidized graphite composite material is mixed with an oxygen-containing sodium salt to obtain a carbon-based material.

[0017] In some embodiments, the oxidant in S2 is selected from a nitric acid (HNO3) solution. In some embodiments, the concentration of the nitric acid solution is from 2 mol / L to 5 mol / L.

[0018] In some embodiments, in S3, the oxygen-containing sodium salt is selected from at least one of inorganic sodium salts containing oxygen or organic sodium salts containing oxygen. In some embodiments, the oxygen-containing sodium salt includes carbon. In some embodiments, the oxygen-containing sodium salt is selected from at least one of sodium carbonate, sodium bicarbonate, or sodium polyacrylate.

[0019] In some embodiments, providing a graphite composite material includes the following steps:

[0020] S1: Crush the graphite raw material, for example, crush it to a Dv50 of 9μm to 11μm;

[0021] S2: Pre-carbonize the crushed raw materials;

[0022] S3: Mix the pre-carbonized product with asphalt and granulate it;

[0023] S4: The granulated product is graphitized to obtain a graphite composite material.

[0024] In some embodiments, the preparation method of carbon-based materials includes: pulverizing artificial graphite raw materials, pre-carbonizing the pulverized raw materials, adding asphalt for granulation after the pre-carbonization, and then performing high-temperature graphitization treatment to obtain a graphite composite material. The graphite composite material is then subjected to surface modification treatment (specifically including first undergoing oxidation treatment, and then mixing and ball-milling the oxidized graphite composite material with an oxygen-containing sodium salt) to obtain the carbon-based material.

[0025] In a second aspect, this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode active material of the first aspect.

[0026] In some implementations, the compaction density CD of the negative electrode sheet satisfies: 1.3 g / cm³ 3 ≤CD≤1.8g / cm 3 The compaction density of the negative electrode sheet affects the energy density and kinetic performance of the secondary battery. When the compaction density of the negative electrode sheet is too low, the energy density of the secondary battery is low, and the adhesion of the negative electrode active material particles to the negative electrode current collector becomes poor, which may cause the negative electrode active material to detach, thereby reducing the cycle performance of the secondary battery. When the compaction density of the negative electrode sheet is too high, the electrolyte wettability of the negative electrode sheet will be significantly reduced, the kinetics of the secondary battery will also decrease, and lithium plating is more likely to occur during cycling, thus leading to a decrease in its cycle performance. In some embodiments, 1.45 g / cm³ is used. 3 ≤CD≤1.75g / cm 3 .

[0027] In some embodiments, the OI value of the negative electrode is between 5 and 20. The OI value of the negative electrode represents the degree of orientation of the negative electrode active material particles on the negative electrode. When the OI value of the negative electrode is too small, it indicates that the negative electrode active material particles are randomly arranged on the surface of the negative electrode current collector, with no obvious orientation, which can easily lead to problems such as the negative electrode active material detaching. When the OI value of the negative electrode is too large, it indicates that the negative electrode active material particles are neatly arranged on the negative electrode current collector with a high degree of orientation, but this can affect the insertion and extraction of lithium ions, thereby affecting the rate performance of the secondary battery. In some embodiments, the OI value of the negative electrode is between 7 and 18.

[0028] In some embodiments, the Id / Ig ratio of the negative electrode plate satisfies: 0.1 ≤ Id / Ig ≤ 0.6, where Id represents the Raman spectrum of the negative electrode plate at 1350 cm⁻¹. -1 The peak intensity, Ig represents the Raman spectrum of the negative electrode at 1580 cm⁻¹. -1Peak intensity. The Id / Ig value represents the defect level of the negative electrode. When Id / Ig is too high, the defect level of the negative electrode is too high, which will increase side reactions and affect the cycle performance of the secondary battery. When Id / Ig is too low, the defect level of the negative electrode is low, which is not conducive to the kinetic performance of the secondary battery. In some embodiments, 0.2≤Id / Ig≤0.5.

[0029] In some implementations, the secondary battery meets the requirement of ≥90% capacity retention after 300 cycles at 45°C.

[0030] In a third aspect, this application provides an electronic device that includes the secondary battery of the second aspect.

[0031] This application effectively improves the quality of the SEI film by controlling the sodium and oxygen content on the surface of the carbon-based material within a certain range, thereby enabling the secondary battery to exhibit excellent cycle performance. Attached Figure Description

[0032] Figure 1 shows the cycle performance of the lithium-ion batteries of Embodiment 1 and Comparative Example 1 of this application. Detailed Implementation

[0033] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0034] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this application. It should be understood that such range format is for convenience and brevity, and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0035] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0036] I. Negative Electrode Active Materials

[0037] The negative electrode active material provided in this application includes a carbon-based material. The surface of this carbon-based material contains sodium and oxygen elements, with the atomic percentage of sodium being X and the atomic percentage of oxygen being Y, where Y / X ≥ 3.0. X and Y are obtained by X-ray energy dispersive spectroscopy (EDS). Specifically, X and Y are tested using the following method: While observing the carbon-based material with a scanning electron microscope (SEM), any 100μm × 100μm region within the SEM field of view is selected, and the sodium and oxygen content of this region is measured using EDS surface scanning to obtain X and Y. The carbon-based material of this application contains sodium and oxygen elements on its surface. Sodium and oxygen are constituent elements of the SEI film and affect the thermal stability of the SEI film on the particle surface, and they have a certain interaction. Sodium helps in the formation of the SEI film on the surface of the carbon-based material and can effectively improve the quality of the SEI film. When the carbon-based material is used as the negative electrode active material in a secondary battery, it can improve the cycle performance of the secondary battery. However, excessive sodium will make the SEI film too thick, which is detrimental to improving cycle performance. Oxygen is an essential component of the SEI membrane, but excessive oxygen content can lead to increased side reactions, thereby affecting the storage and cycle performance of the secondary battery. This application effectively improves the quality of the SEI membrane by controlling the content of sodium and oxygen within the aforementioned range, resulting in superior cycle performance of the secondary battery. In some embodiments, 3 ≤ Y / X ≤ 20. In some embodiments, Y / X is a range of 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 14, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, or any combination of these values.

[0038] In some embodiments, 0.2% ≤ X ≤ 4.0%. By controlling the sodium content within this range, the quality of the SEI membrane can be effectively improved, thereby enhancing the cycle performance of the secondary battery. In some embodiments, X is any value within the range of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.0%, or any combination of these values. In some embodiments, 0.3% ≤ X ≤ 2.5%.

[0039] In some embodiments, the mass content of sodium is m, where 0.4% ≤ m ≤ 9%. In this application, m is tested using the following method: While observing the carbon-based material with a scanning electron microscope (SEM), any 100 μm × 100 μm region within the SEM field of view is selected, and the sodium content of this region is measured using EDS surface scanning to obtain m. In some embodiments, m is any value within the range of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, or any combination of these values. Sodium is primarily used as an inorganic component in the construction of the SEI membrane; therefore, the mass percentage of sodium should not be too small. However, excessive sodium content can affect the organic component content in the SEI membrane, leading to a decrease in organic component content. This increases the brittleness and reduces the elasticity of the SEI membrane, making it more prone to cracking during cycling due to the expansion of the carbon-based material, thus affecting the cycle performance of the secondary battery. In some embodiments, 3% ≤ m ≤ 6%.

[0040] In some embodiments, 2.0% ≤ Y ≤ 15.0%. In some embodiments, Y is any value within a range of 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 14%, 15%, or any combination of these values. Oxygen is an essential component of the SEI membrane, but excessively high oxygen content can lead to increased side reactions, thereby affecting the storage and cycle performance of the secondary battery. In some embodiments, 3.0% ≤ Y ≤ 12.0%.

[0041] In some embodiments, the carbon-based material satisfies: BET / (Y×100)≤0.7, where BET m 2 / g represents the specific surface area of ​​the carbon-based material. The specific surface area of ​​a carbon-based material is affected by the oxygen content on its surface. Excessive BET (Body Equivalent Temperature) increases side reactions during secondary battery cycling, thus affecting cycle performance. This application ensures that BET / (Y×100) ≤ 0.7, maintaining a low BET level even with high oxygen content. In some embodiments, BET / (Y×100) is any value within the range of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or any combination of these values. In some embodiments, BET / (Y×100) ≤ 0.6.

[0042] In some embodiments, the specific surface area (BET) of the carbon-based material is 1-10, in m². 2 / g. In some embodiments, BET is a range of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or any combination of these values. Excessive BET in carbon-based materials increases side reactions during secondary battery cycling, thereby reducing cycle performance.

[0043] In some embodiments, the carbon-based material satisfies the following condition: 25 ≤ Dv99 - Dv10 ≤ 55, where Dv99 represents the particle size of the carbon-based material that accounts for 99% of the volumetric particle size distribution (in μm), and Dv10 represents the particle size of the carbon-based material that accounts for 10% of the volumetric particle size distribution (in μm). The value of Dv99-Dv10 is related to the particle size distribution of the carbon-based material. A Dv99-Dv10 range ensures a narrow particle size distribution, reducing the likelihood of excessive small or large particles, thus improving the cycle performance and processing performance of the secondary battery. An excessive number of small particles in the carbon-based material increases side reactions and affects the cycle performance of the secondary battery; an excessive number of large particles affects processing performance and may lead to appearance defects such as bumps on the negative electrode, and in severe cases, may even cause point-like lithium plating. In some implementations, Dv99-Dv10 is any value within the range of 27, 30, 33, 35, 37, 40, 43, 45, 47, 50, 53, or any combination of these values. In some implementations, 30 ≤ Dv99-Dv10 ≤ 40.

[0044] In some embodiments, the Dv99 of the carbon-based material is 20-60, in μm. In some embodiments, the Dv99 of the carbon-based material is any value within the range of 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, or any combination of these values. In some embodiments, the Dv10 of the carbon-based material is 1-10, in μm. In some embodiments, the Dv10 of the carbon-based material is any value within the range of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or any combination of these values.

[0045] In some implementations, thermogravimetric analysis (TGA) is used, and the weight loss rate of the carbon-based material ranges from 0.2% to 5% within a temperature range of 25°C to 400°C. The weight loss rate of the carbon-based material at 400°C can represent the content of surface modification substances, which in turn affects the formation quality of the SEI film in subsequent formation processes. If the weight loss rate is too low, i.e., the content of modification substances is too small, it will not have the effect of improving the thermal stability of the SEI film. In some embodiments, a thermogravimetric analysis (TGA) is employed, and the weight loss rate of the carbon-based material is 0.2%-3.0% within a temperature range of 25°C to 400°C, for example, any value within a range of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or any combination of these values. In some embodiments, a thermogravimetric analysis (TGA) is employed, and the weight loss rate of the carbon-based material is 0.5% to 2.5% within a temperature range of 25°C to 400°C.

[0046] In some embodiments, the 5t powder compaction density (PD) of the carbon-based material satisfies: 1.5 g / cm³. 3 ≤PD≤2.5g / cm 3 The compaction density of carbon-based materials used as negative electrode active materials is related to the energy density and kinetics of the secondary battery. Lower compaction density of the carbon-based material results in lower compaction density of the electrode sheet, consequently reducing the energy density of the secondary battery. Conversely, excessively high compaction density of the carbon-based material reduces the kinetic performance of the secondary battery, affecting its electrical performance at high rates. In some embodiments, the PD is 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 1.85g / cm 3 1.9g / cm 3 1.95g / cm 3 2.1g / cm 3 2.3g / cm 3 2.5g / cm 3 Or any value within a range of any two of these values. In some implementations, 1.65 g / cm³ 3 ≤PD≤1.95g / cm 3 .

[0047] In some embodiments, the OI value of the carbon-based material is less than or equal to 18. The OI value of the carbon-based material indicates the uniformity of crystal orientation within its particles. A higher OI value means higher crystal orientation uniformity, resulting in a more unidirectional lithium ion insertion / extraction direction in the active particles. This can lead to difficulties in lithium insertion / extraction, and in severe cases, lithium plating, thereby reducing the cycle performance of the secondary battery. In some embodiments, the OI value of the carbon-based material is 5-18, for example, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or any combination of these values. In some embodiments, the orientation OI value of the carbon-based material is 6 to 13.

[0048] In some embodiments, the carbon-based material includes graphite. In some embodiments, the graphite includes one or more of natural graphite and synthetic graphite.

[0049] In some embodiments, the preparation method of carbon-based materials includes the following steps:

[0050] S1: Provides graphite composite materials;

[0051] S2: The graphite composite material is mixed with an oxidant and then subjected to oxidation treatment to obtain the oxidized graphite composite material;

[0052] S3: The oxidized graphite composite material is mixed with an oxygen-containing sodium salt to obtain a carbon-based material.

[0053] In some embodiments, the oxidant in S2 is selected from a nitric acid (HNO3) solution. In some embodiments, the concentration of the nitric acid solution is from 2 mol / L to 5 mol / L, for example, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, or 4.5 mol / L.

[0054] In some embodiments, the oxidation treatment temperature in S2 is 40°C-80°C, for example, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C. In some embodiments, the oxidation treatment time in S2 is 1 hour-5 hours, for example, 2 hours, 3 hours, or 4 hours.

[0055] In some embodiments, in S3, the oxygen-containing sodium salt is selected from at least one of inorganic sodium salts containing oxygen or organic sodium salts containing oxygen. In some embodiments, the oxygen-containing sodium salt includes carbon. In some embodiments, the oxygen-containing sodium salt is selected from at least one of sodium carbonate, sodium bicarbonate, or sodium polyacrylate.

[0056] In some embodiments, the sodium salt content is 2%-8% by weight, for example, 3%, 4%, 5%, 6%, or 7%, based on the total weight of the oxidized graphite composite material and the oxygen-containing sodium salt. In some embodiments, the mixing time in S3 is 10h-24h, for example, 12h, 14h, 16h, 18h, 20h, or 22h. In some embodiments, the mixing in S3 is ball milling.

[0057] In some embodiments, providing a graphite composite material includes the following steps:

[0058] S11: Crush the graphite raw material, for example, crush it to a Dv50 of 9μm to 11μm;

[0059] S12: Pre-carbonize the crushed raw materials;

[0060] S13: Mix the pre-carbonized product with asphalt and granulate it;

[0061] S14: The granulated product is graphitized to obtain a graphite composite material.

[0062] In some embodiments, in S11, the graphite raw material is selected from petroleum coke. In some embodiments, in S12, the pre-carbonization treatment temperature is 800°C to 1200°C, for example, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, or 1150°C.

[0063] In some embodiments, in step S13, the amount of bitumen added is 5% to 15% of the mass of the graphite raw material, for example, 6%, 8%, 10%, 12%, or 14%. In some embodiments, in step S13, the granulation time is 2 hours to 4 hours, for example, 2.5 hours, 3 hours, or 3.5 hours. In some embodiments, in step S13, the granulation temperature is 200°C to 500°C, for example, 250°C, 300°C, 350°C, 4000°C, or 450°C.

[0064] In some embodiments, in S14, the temperature of the graphitization process is between 2600°C and 3100°C, for example, 2700°C, 2800°C, 2900°C or 3000°C.

[0065] In some embodiments, the preparation method of carbon-based materials includes: pulverizing artificial graphite raw materials, pre-carbonizing the pulverized raw materials, adding asphalt for granulation after the pre-carbonization, and then performing high-temperature graphitization treatment to obtain a graphite composite material. The graphite composite material is then subjected to surface modification treatment (specifically including first undergoing oxidation treatment, and then mixing and ball-milling the oxidized graphite composite material with an oxygen-containing sodium salt) to obtain the carbon-based material.

[0066] Secondary batteries

[0067] The secondary battery provided in this application includes a negative electrode sheet, which includes a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode active material of the first aspect.

[0068] In some implementations, the compaction density CD of the negative electrode sheet satisfies: 1.3 g / cm³ 3 ≤CD≤1.8g / cm 3 The compaction density of the negative electrode affects the energy density and kinetic performance of the secondary battery. When the compaction density of the negative electrode is too low, the energy density of the secondary battery is low, and the adhesion of the negative electrode active material particles to the current collector becomes poor, which may cause the negative electrode active material to detach, thereby reducing the cycle performance of the secondary battery. When the compaction density of the negative electrode is too high, the electrolyte wettability of the negative electrode will be significantly reduced, and the kinetics of the secondary battery will also decrease. The secondary battery is prone to lithium plating during cycling, which in turn leads to a decrease in its cycle performance. In some embodiments, CD is 1.35 g / cm³. 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 Or a range of any two of these values. In some implementations, 1.45 g / cm³ 3 ≤CD≤1.75g / cm 3 .

[0069] In some embodiments, the OI value of the negative electrode is between 5 and 20. The OI value of the negative electrode represents the degree of orientation of the negative electrode active material particles on the negative electrode. When the OI value of the negative electrode is too small, it indicates that the negative electrode active material particles are randomly arranged on the surface of the negative electrode current collector, with no obvious orientation, which can easily lead to the negative electrode active material detaching. When the OI value of the negative electrode is too large, it indicates that the negative electrode active material particles are neatly arranged on the negative electrode current collector with a high degree of orientation, but it will affect the insertion and extraction of lithium ions, thereby affecting the rate performance of the secondary battery. In some embodiments, the OI value of the negative electrode is 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or any combination of these values. In some embodiments, the OI value of the negative electrode is between 7 and 18.

[0070] In some embodiments, the Id / Ig ratio of the negative electrode plate satisfies: 0.1 ≤ Id / Ig ≤ 0.6, where Id represents the Raman spectrum of the negative electrode plate at 1350 cm⁻¹. -1 The peak intensity, Ig represents the Raman spectrum of the negative electrode at 1580 cm⁻¹. -1 Peak intensity. The Id / Ig value represents the defect level of the negative electrode. If Id / Ig is too high, the defect level of the negative electrode is too high, which increases side reactions and affects the cycle performance of the secondary battery. If Id / Ig is too low, the defect level of the negative electrode is low, which is detrimental to the kinetic performance of the secondary battery. In some embodiments, Id / Ig is 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, or any combination of these values. In some embodiments, 0.2 ≤ Id / Ig ≤ 0.5.

[0071] In some implementations, the secondary battery meets the requirement of ≥90% capacity retention after 300 cycles at 45°C.

[0072] In some embodiments, the negative electrode sheet further includes a negative current collector, which includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0073] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0074] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0075] The secondary battery of this application also includes a positive electrode, which includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent.

[0076] According to some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0077] According to some embodiments of this application, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate. In some embodiments, the binder includes at least one of adhesive polymers, such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyenol, or polyacrylic acid. In some embodiments, the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powder or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0078] The secondary battery of this application also includes a separator. The material and shape of the separator used in the secondary battery of this application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0079] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0080] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0081] The secondary component of this application also includes an electrolyte. The electrolyte that can be used in this application can be any electrolyte known in the prior art.

[0082] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte of this application; it can be any electrolyte known in the prior art. The additives in the electrolyte of this application can be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0083] According to some embodiments of this application, the secondary battery of this application includes, but is not limited to, lithium-ion batteries or sodium-ion batteries. In some embodiments, the secondary battery includes a lithium-ion battery.

[0084] III. Electronic Devices

[0085] This application further provides an electronic device that includes a secondary battery according to the second aspect of this application.

[0086] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are 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, large household batteries, and lithium-ion capacitors, etc.

[0087] Unless otherwise specified, all reagents, materials and instruments used in the following examples and comparative examples are commercially available.

[0088] Examples and Comparative Examples

[0089] Example 1

[0090] Preparation of carbon-based materials

[0091] Petroleum coke was selected as the raw material for artificial graphite. It was first pulverized to a Dv50 of 10.0 μm, then pre-carbonized at 1000℃. After pre-carbonization, asphalt was added for granulation at 8% of the petroleum coke content. The granulation time was controlled at 2 hours, and the granulation temperature was controlled at 300℃. The particle size and powder compaction density were adjusted by controlling the amount of asphalt added. After granulation, it underwent high-temperature graphitization at 2900℃, followed by surface modification. The graphitized material was then oxidized using a nitric acid (HNO3) solution at a concentration of 3 mol / L at 60℃ for 3 hours. After oxidization, it was washed with water and dried. Then, it was mixed with sodium polyacrylate and ball-milled at a mass ratio of 3% for 12 hours. After ball milling, the mixture was sieved to obtain the carbon-based material.

[0092] Preparation of negative electrode sheet

[0093] The carbon-based material prepared above is used as the negative electrode active material. Conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are mixed in a weight ratio of 95.7:1.5:1.8:1. The mixture is then thoroughly stirred in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry. This slurry is coated onto the current collector Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0094] Preparation of positive electrode sheet

[0095] Lithium iron phosphate (LiFePO4) is selected as the positive electrode active material. It is mixed with conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.3:2.2:1.5 in an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a uniform positive electrode slurry. This slurry is coated on current collector Al foil, dried and cold pressed to obtain the positive electrode sheet.

[0096] Preparation of electrolyte

[0097] In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. Then, fluoroethylene carbonate and 1,3-propanesulfonyl lactone were added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. The mass percentages of LiPF6, fluoroethylene carbonate, and 1,3-propanesulfonyl lactone were all 12.5% ​​and 2% respectively, calculated based on the mass of the electrolyte.

[0098] Preparation of lithium-ion batteries

[0099] PE porous polymer film is selected as the separator. The above-mentioned negative electrode and positive electrode are wound together with the separator and placed in an aluminum-plastic film. Then, liquid is injected, the film is allowed to stand, and the film is formed to produce a lithium-ion secondary battery.

[0100] Examples 2 to 10, Comparative Examples 1 to 2

[0101] Examples 2-10 and Comparative Examples 1-2 were achieved by adjusting the mass ratio of sodium salt in the mixture and the ball milling time based on Example 1. Specific adjustment measures are detailed in Table a, and detailed data are shown in Table 1.

[0102] Table a

[0103]

[0104]

[0105] Examples 11 to 18

[0106] Examples 11-18 were achieved by adjusting the amount of asphalt added and the concentration of nitric acid based on Example 6. For details of the adjustment measures, please refer to Table b, and for detailed data, please refer to Table 2.

[0107] Table b

[0108]

[0109] Examples 19 to 24

[0110] Examples 19-24 were achieved by adjusting the mass ratio of sodium salt in the mixture, the concentration of nitric acid, and the particle size of the raw materials, based on Example 14. Specific adjustment measures are detailed in Table c, and detailed data are shown in Table 3.

[0111] Table c

[0112]

[0113] Examples 25 to 30

[0114] Examples 25-30 are based on Example 20, but are achieved by adjusting the particle size of the raw materials, the amount of asphalt added, and the ball milling time. See Table 4 for details.

[0115] Examples 31 to 42

[0116] Examples 31-42 are based on Example 30, with further design and optimization of the compaction density CD, OI value, and Id / Ig of the negative electrode sheet, as detailed in Table 5.

[0117] Test methods

[0118] 1. Particle size test

[0119] The particle size distribution was determined according to GB / T 19077-2016. The specific procedure involved weighing 1g of sample and mixing it thoroughly with 20mL of deionized water and a trace dispersant. The mixture was then sonicated for 5 minutes in an ultrasonic device before being poured into a Hydro2000SM sample introduction system for testing. The testing equipment used was a Mastersizer 3000 manufactured by Malvern. During the test, the intensity of the scattered light was measured as the laser beam passed through the dispersed particle sample to determine the particle size. The data was then used to analyze and calculate the particle size distribution that formed the scattered spectrum. The refractive index of the particles used in the test was 1.8. Each sample was tested three times, and the final particle size was the average of the three tests.

[0120] 2. Powder compaction density test

[0121] The test standard for powder compaction density refers to GB / T 24533-2009 "Graphite Anode Materials for Lithium-ion Batteries". The specific test method is as follows:

[0122] Weigh 1.0000±0.0500g of carbon-based material sample and place it in the test mold (CARVER#3619 (13mm). Then place the sample in the test equipment, which is a Sansi Zongheng UTM7305 with test capacities of 0.3t, 0.5t, 0.75t, 1.0t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, and 5.0t. The pressure increase rate is 10mm / min, the pressure increase holding time is 30s, the pressure release rate is 30mm / min, and the pressure release holding time is 10s.

[0123] In this application, the compaction density of the powder is the compaction density measured after depressurization of 5t. The formula for calculating the compaction density is: Compaction density = Material mass / (Material stress area × Sample thickness).

[0124] 3. Raman test of negative electrode sheet

[0125] An area of ​​100μm × 100μm was selected on the negative electrode. The particles within this area were scanned using a laser confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division). The d-peak and g-peak of all particles within this area were obtained. The data were processed using LabSpec software to obtain the peak intensities of the d-peak and g-peak of each particle, which are Id and Ig, respectively. The frequency of Id / Ig was statistically analyzed with a step size of 0.02 to obtain a normal distribution. The (Id / Ig)max and (Id / Ig)min of these particles were statistically analyzed, and the average value of Ig / Ig was calculated, which is the Id / Ig value of the negative electrode. The laser wavelength of the Raman spectrometer can be in the range of 532nm to 785nm.

[0126] d peak: generally at 1350 cm⁻¹ -1 Nearby, from the aromatic ring sp 2 The radial breathing mode of the symmetric stretching vibration of carbon atoms causes (structural defects);

[0127] G peak: appears at 1580cm -1 Nearby, by sp 2 This is caused by the stretching vibrations between carbon atoms, which correspond to the E0 at the center of the Brillouin zone. 2g Vibrations of optical phonons (in-plane vibrations of carbon atoms).

[0128] 4. OI value test

[0129] The (004) and (110) plane diffraction patterns in the X-ray diffraction patterns of negative electrode sheets or carbon-based materials were tested according to the People's Republic of China Machinery Industry Standard JB / T 4220-2011 "Method for Determination of Lattice Parameters of Artificial Graphite". The experimental conditions were as follows: X-rays were emitted using CuKα radiation, which was removed by a filter or monochromator. The X-ray tube operating voltage was (30-35) kV, and the operating current was (15-20) mA. The counter scanning speed was 1 / 4 (°) / min. When recording the 004 diffraction pattern, the scanning range of the diffraction angle 2θ was 53°-57°. When recording the 110 diffraction pattern, the scanning range of the diffraction angle 2θ was 75°-79°. The peak area obtained from the (004) plane diffraction pattern was denoted as C004. The peak area obtained from the (110) plane diffraction pattern was denoted as C110. The ratio of C004 to C110 of the negative electrode or carbon-based material is calculated, which is the OI value of the negative electrode or carbon-based material.

[0130] 5. Specific surface area

[0131] The test method for specific surface area refers to GB / T 19587-2017. The specific procedure is as follows: weigh 1-8g of sample (the sample weight should at least cover 1 / 3 of the sphere's volume) and place it in a 1 / 2-inch long tube with a bulb (the diameter of the spherical part of the tube is 12mm). After pretreatment at 200℃ for 2 hours, the sample is placed in a TriStar3030 test device (McClone Systems, Inc., USA) for testing. The adsorbed gas used is N2 (purity: 99.999%). The test conditions are 77K, and the specific surface area is determined by the BET calculation method.

[0132] 6. Mass loss ratio of carbon-based materials

[0133] Thermogravimetric analysis (TGA) was used to test the carbon-based materials. Specifically, the sample was placed in an aluminum crucible and weighed on a balance before and after placement to obtain the sample mass m1. After the sample was placed in the crucible, the crucible lid was pressed together with the crucible using a dedicated tablet press to prevent the sample from being ejected from the crucible by thermal decomposition gas flow or thermal decomposition ejection during heating, which would cause non-thermal decomposition weight loss in the experiment. A nitrogen protective atmosphere was introduced and the temperature was raised to 400℃ and held for 10 minutes. After cooling, the remaining sample mass m2 was weighed. The mass loss ratio of the carbon-based material could then be obtained using the formula (m1-m2) / m1×100%.

[0134] 7. Element percentage and mass ratio of carbon-based materials

[0135] Test method and standard for elemental percentage and mass ratio of carbon-based materials: GB / T 17359-2012, energy dispersive spectroscopy (EDS) for quantitative analysis. Testing procedure: Under standard experimental conditions and testing standard requirements, the carbon-based material is placed in the scanning electron microscope sample chamber according to standard operating procedures. A 15kV accelerating voltage is used to magnify and observe the test location. The sample is then subjected to qualitative and quantitative elemental analysis using an X-ray energy dispersive spectroscopy (EDS) analyzer. A selected area of ​​100μm × 100μm is used for scanning analysis.

[0136] 8. Cyclic performance test

[0137] Temperature: 45℃

[0138] 1. Charge to 2.5V using 0.5C DC (not the first discharge);

[0139] 2. Let stand for 10 minutes;

[0140] 3.0.5C constant current (CC) to 3.6V, constant voltage (CV) to 0.05C;

[0141] 4. Let stand for 10 minutes;

[0142] 5.0.5C DC to 2.5V;

[0143] 6. Repeat steps 2-5 300 times;

[0144] 7. The capacity retention rate after 300 cycles is calculated as the ratio of the amount of electricity discharged on the 300th cycle to the amount of electricity discharged on the first cycle.

[0145] Test Results

[0146] Table 1 shows the effects of the atomic percentages of sodium (X) and oxygen (Y) on the surface of carbon-based materials on the cycle performance of lithium-ion batteries. The changes in X and Y were achieved by adjusting the mass ratio of sodium salt in the mixture and the ball milling time.

[0147] Table 1

[0148]

[0149] The data in Table 1 shows that when the percentage of sodium atoms X and the percentage of oxygen atoms Y on the surface of carbon-based particles satisfy Y / X≥3.0, lithium-ion batteries can exhibit excellent cycle performance.

[0150] Table 2 further investigates the effects of the specific surface area (BET value) of the carbon-based material and the sodium content (m) on the performance of lithium-ion batteries, based on Example 6. The ratio of BET to sodium content in the carbon-based material can be adjusted by changing the amount of asphalt added and the concentration of nitric acid.

[0151] Table 2

[0152]

[0153] As can be seen from the data in Table 2, when the carbon-based material satisfies BET / (Y×100)≤0.7 and 0.4%≤m≤9%, the cycle performance of the lithium-ion battery is further improved based on that in Example 6.

[0154] Table 3 further investigates the effects of particle size distribution of carbon-based materials and mass loss ratio at 400°C on lithium-ion battery performance, based on Example 14. Specifically, by adjusting the sodium salt mass ratio, nitric acid concentration, and particle size, the Dv99 and Dv10 ratios of the carbon-based materials and the mass loss ratio at 400°C can be altered.

[0155] Table 3

[0156]

[0157] The data in Table 3 show that when the carbon-based material meets at least one of the following conditions: the mass loss ratio at 400℃ is between 0.2% and 5% and 25≤Dv99-Dv10≤55, the cycle capacity retention of the lithium-ion battery is improved. When both conditions are met, the cycle capacity retention of the lithium-ion battery is significantly improved.

[0158] Table 4 further investigates the particle compaction density (PD g / cm³) of carbon-based materials based on Example 20. 3 The impact of OI value on lithium-ion battery performance.

[0159] Table 4

[0160]

[0161] As can be seen from the data in Table 4, compared to Example 20, when the carbon-based material meets the requirement of 1.5 g / cm³... 3 ≤PD≤2.5g / cm 3 When the OI value is at least one of 5 to 18, the capacity retention of lithium-ion batteries is improved. When all conditions are met, the capacity retention of lithium-ion batteries is significantly improved.

[0162] Table 5 further investigates the compaction density CD g / cm³ of the negative electrode sheet based on Example 30. 3 The impact of OI value and Id / Ig on the performance of lithium-ion batteries.

[0163] Table 5

[0164]

[0165]

[0166] As can be seen from the data in Table 5, compared to Example 30, when the negative electrode sheet meets the requirement of 1.3 g / cm³... 3 ≤CD≤1.8g / cm 3 When the OI value is in the range of 5 to 20 and one or two of the conditions of 0.1 ≤ Id / Ig ≤ 0.6, the capacity retention of lithium-ion batteries is improved. When all conditions are met, the capacity retention of lithium-ion batteries is significantly improved.

[0167] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a carbon-based material, the surface of the carbon-based material comprising sodium and oxygen elements, wherein the atomic percentage of sodium is X, and the atomic percentage of oxygen is Y, wherein... 0.2%≤X≤4.0%, 2.0%≤Y≤15.0%, Y / X≥3.0, where X and Y are obtained by X-ray energy dispersive spectroscopy; the compaction density CD of the negative electrode sheet satisfies: 1.3 g / cm³. 3 ≤CD≤1.8g / cm 3 The OI value of the negative electrode is 5 to 19.

2. The secondary battery according to claim 1, wherein, 3.5≤Y / X≤15.

3. The secondary battery according to any one of claims 1 to 2, wherein, 0.3%≤X≤2.5%; and / or 3.0%≤Y≤12.0%.

4. The secondary battery according to any one of claims 1 to 2, wherein, The carbon-based material satisfies: BET / (Y×100)≤0.7, where BET m 2 / g represents the specific surface area of ​​the carbon-based material; and / or the mass content of the sodium element is m, 0.4%≤m≤9%.

5. The secondary battery according to claim 4, wherein, 0.2≤BET / (Y×100)≤0.6; and / or 3%≤m≤6%.

6. The secondary battery according to any one of claims 1 to 2, wherein, The carbon-based material satisfies at least one of the following conditions (i) to (v): (i) 25 ≤ Dv99 - Dv10 ≤ 55, where Dv99 represents the particle size of the carbon-based material that accounts for 99% of the volumetric particle size distribution in μm, and Dv10 represents the particle size of the carbon-based material that accounts for 10% of the volumetric particle size distribution in μm; (ii) using thermogravimetric analysis, the weight loss rate of the carbon-based material is 0.2% to 5% in the temperature range of 25°C to 400°C; (iii) the 5t powder compaction density PD of the carbon-based material satisfies: 1.5 g / cm³. 3 ≤PD≤2.5 g / cm 3 (iv) The OI value of the carbon-based material is 5 to 18; (v) The carbon-based material is obtained by surface modification of graphite composite material.

7. The secondary battery according to claim 6, wherein, The carbon-based material satisfies at least one of the following conditions (vi) to (ix): (vi) 30 ≤ Dv99 - Dv10 ≤ 40; (vii) by thermogravimetric analysis, the weight loss rate of the carbon-based material is 0.5% to 2.5% in the temperature range of 25°C to 400°C; (viii) 1.65 g / cm³. 3 ≤PD≤1.95g / cm 3 (ix) The orientation degree OI value of the carbon-based material is 6 to 13.

8. The secondary battery according to any one of claims 1 to 2, wherein, The carbon-based material includes graphite.

9. The secondary battery according to claim 1, wherein, The negative electrode plate satisfies the following condition: (x) The Id / Ig ratio of the negative electrode plate satisfies: 0.1≤Id / Ig≤0.6, where Id represents the Raman spectrum of the negative electrode at 1350 cm⁻¹. -1 The peak intensity, Ig, represents the Raman spectrum of the negative electrode at 1580 cm⁻¹. -1 Peak intensity.

10. The secondary battery according to claim 9, wherein, The negative electrode sheet satisfies at least one of the following conditions (xi) to (xiii): (xi) The compaction density CD of the negative electrode sheet satisfies: 1.45 g / cm³ 3 ≤CD≤1.75g / cm 3 (xii) The OI value of the negative electrode is between 7 and 18; (xiii) The Id / Ig ratio of the negative electrode satisfies: 0.2 ≤ Id / Ig ≤ 0.5, where Id represents the value of the negative electrode at 1350 cm⁻¹. -1 The peak intensity, Ig, represents the Raman spectrum of the negative electrode at 1580 cm⁻¹. -1 Peak intensity.

11. An electronic device comprising a secondary battery according to any one of claims 1 to 10.

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