Negative active material, secondary battery, and electronic device

Abstract

Provided is a negative electrode active material including a carbon-based material, a surface of a particle of the carbon-based material including an alkali metal element including a sodium element and / or a potassium element. The present application can effectively improve the quality of an SEI film by treating the surface of a carbon-based material such as a graphite material to obtain an organic substance layer similar to the SEI film on the surface of the particle, thereby improving the initial coulombic efficiency and cycle performance of a secondary battery. Also provided is a secondary battery including the negative electrode active material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to a negative electrode active material, a secondary battery and an electronic device. BACKGROUND

[0002] With the continuous expansion of the secondary battery market, the performance requirements for secondary batteries are also getting higher and higher, and accordingly the performance requirements for negative electrode active materials are also getting higher and higher. The negative electrode active material has a significant influence on the first coulomb efficiency and the cycle performance of the secondary battery, and the first coulomb efficiency of the secondary battery affects its cost and energy density, and the cycle performance directly affects its application range, especially the cycle performance is extremely high in the fields of electric vehicles, energy storage and the like. In order to meet the market demand, it is necessary to develop a negative electrode active material with high first coulomb efficiency and long cycle performance to improve the performance of the secondary battery. The existing technology usually adopts two ways of selecting single particle type and coating amorphous carbon on the particle surface to improve the first coulomb efficiency and the cycle performance, but these two ways have a large loss of energy density of the negative electrode active material. Therefore, it is necessary to propose a new technical solution to improve the cycle performance and energy density of the negative electrode active material at the same time. SUMMARY

[0003] In view of the above problems existing in the prior art, the present application provides a negative electrode active material and a secondary battery comprising the same, so as to improve the quality of the SEI film on the surface of the negative electrode active material, and further improve the first coulomb efficiency and the cycle performance of the secondary battery.

[0004] In a first aspect, the present application provides a negative electrode active material, which comprises a carbon-based material, the particle surface of the carbon-based material comprises an alkali metal element, and the alkali metal element comprises a sodium element and / or a potassium element. The present application processes the surface of the carbon-based material such as graphite material to obtain an organic substance layer similar to the SEI film on the particle surface. On the one hand, the organic matter on the particle surface can inhibit the film formation of the negative electrode active material, reduce the loss of active lithium ions, and improve the first coulomb efficiency. On the other hand, the sodium element and / or the potassium element on the particle surface can improve the electrochemical stability of the organic matter, thereby avoiding the side reaction or even decomposition of the organic matter on the particle surface of the negative electrode active material, and further improving the cycle performance of the secondary battery.

[0005] In some embodiments, a thermogravimetric test is adopted, and the mass loss ratio of the carbon-based material is S in the temperature range of 25°C to 800°C, S≥0.5%, and the exothermic peak value of the carbon-based material is T, 300°C≤T≤500°C. The conventional graphite material has stable high-temperature properties, and the mass loss ratio of the thermogravimetric test is very small. Due to the existence of the organic substance layer on the particle surface of the carbon-based material in the present application, the mass of the carbon-based material will be lost during the thermogravimetric test.

[0006] In some embodiments, 0.5%≤S≤5%. The greater the mass loss ratio S, the higher the content of organic matter on the surface of the particles, and a high content of organic matter can effectively improve the initial coulombic efficiency and cycle performance of the secondary battery. However, when S is too high, too many side reactions occur, and the generation of gas and the consumption of active lithium during electrochemical reactions are adversely affected. In some embodiments, 1%≤S≤3%.

[0007] The decomposition temperature of the organic matter on the surface of the particles of the carbon-based material is approximately 300°C to 500°C, and thus the temperature range T at which the exothermic peak (mass loss rate peak) is located is 300°C to 500°C. In some embodiments, 330°C≤T≤420°C.

[0008] In some embodiments, the atomic percentage of the alkali metal element on the surface of the particles is X, and 0.4%≤X≤3.0%. Sodium or potassium elements help form the SEI film on the surface of the negative active material, which can effectively improve the quality of the SEI film and thus improve the cycle performance of the secondary battery. However, too much sodium or potassium will make the SEI film too thick, which is not conducive to improving the cycle performance. In some embodiments, 0.6%≤X≤2.5%.

[0009] In some embodiments, the surface of the particles of the carbon-based material further includes carbon elements, and the atomic percentage of the carbon elements on the surface of the particles is C1, and C1≤96%. In some embodiments, 90%≤C1≤95%.

[0010] In some embodiments, the mass content of carbon elements in the carbon-based material is C based on the mass of the carbon-based material, and C≥98%. Because the content of the organic matter layer on the surface of the particles of the carbon-based material is low, the mass ratio of carbon atoms in the entire carbon-based particle is greater than 98%. In some embodiments, 98.5%≤C≤99.9%.

[0011] In some embodiments, Fourier infrared testing is used, and the surface of the particles of the carbon-based material contains a substance with an absorption peak in the range of 950cm -1 to 1200cm -1 . The absorption peak in the range of 950cm -1 to 1200cm -1 in the Fourier infrared test spectrum represents the vibration of chemical bonds composed of atoms such as C, H, and O. The absorption peak in this range of the carbon-based material can further indicate that the particles of the carbon-based material have components similar to the SEI film due to surface modification treatment, and thus the formation of the SEI film is reduced during the first charge and discharge process, thereby improving the initial coulombic efficiency.

[0012] In some embodiments, the surface of the particles of the carbon-based material comprises a substance having at least one functional group of hydroxyl, carboxyl, carbonyl, sulfonic acid group, phenyl, carbon-carbon double bond, or carbon-carbon triple bond.

[0013] In some embodiments, the carbon-based material has a first coulombic efficiency CE satisfying: CE≥93.0%. In some embodiments, CE≥94.0%.

[0014] In some embodiments, the carbon-based material has a particle size satisfying: Dv90 / Dv50≤3.0. The Dv90 / Dv50 within the above range can ensure that the carbon-based particle distribution is narrow, avoiding excessive small particles and large particles, thereby facilitating the improvement of the cycle performance and processing performance of the secondary battery. When the number of small particles in the carbon-based material is excessive, side reactions will increase, affecting the cycle performance of the secondary battery; when the number of large particles is excessive, the processing performance will be affected, which can cause convex points and other appearance defects of the negative electrode sheet, and even point-like lithium precipitation. In some embodiments, Dv90 / Dv50≤2.5.

[0015] In some embodiments, the carbon-based material has a specific surface area BET satisfying: 0.5m 2 / g≤BET≤5.5m 2 / g. A too large BET will increase side reactions, affecting the first coulombic efficiency, and a too small BET will cause poor wettability of the electrolyte to the negative electrode, thereby affecting the kinetic performance of the secondary battery. In some embodiments, 1.5m 2 / g≤BET≤5m 2 / g.

[0016] In some embodiments, the carbon-based material has a tap density TD satisfying: TD≥0.6g / cm 3 . The TD is related to the slurry processability of the carbon-based material, and a too low tap density will cause poor dispersion of the slurry of the carbon-based material during the preparation of the secondary battery, making the slurry prone to sedimentation, resulting in uneven coating thickness, and thereby affecting the electrical performance of the secondary battery. In some embodiments, TD≥0.8g / cm 3 .

[0017] In some embodiments, the carbon-based material has an OI value satisfying: 4≤OI≤15. The OI value of the carbon-based material represents the consistency of the orientation degree of the crystals in its particles. A larger OI value means a higher consistency of the orientation degree of the crystals, and the deintercalation direction of lithium ions in the active particles is relatively single, which will cause difficulty in deintercalation of lithium, and even lithium precipitation, thereby reducing the cycle performance of the secondary battery. In some embodiments, OI≤8.

[0018] In some embodiments, the carbon-based material comprises graphite. In some embodiments, the graphite comprises one or more of natural graphite and artificial graphite.

[0019] In some embodiments, the method for preparing the carbon-based material comprises the following steps:

[0020] S1: providing a graphite composite material;

[0021] S2: mixing the graphite composite material with an oxidizing agent and then performing an oxidation treatment to obtain an oxidized graphite composite material;

[0022] S3: mixing the oxidized graphite composite material with an organic salt of an alkali metal to obtain the carbon-based material.

[0023] In some embodiments, in S2, the oxidizing agent is selected from at least one of a hydrogen peroxide solution, a sulfuric acid solution, a nitric acid solution, or potassium permanganate. In some embodiments, the oxidizing agent is a hydrogen peroxide solution, wherein the concentration of the hydrogen peroxide solution is 3 mol / L to 7 mol / L.

[0024] In some embodiments, in S3, the organic salt of an alkali metal is selected from an organic salt having at least one functional group selected from a hydroxyl group, a carboxyl group, a carbonyl group, a sulfonic acid group, a phenyl group, a carbon-carbon double bond, or a carbon-carbon triple bond. In some embodiments, the organic salt of an alkali metal is selected from at least one of an organic acid alkali metal salt or an organic sulfonic acid alkali metal salt. In some embodiments, the organic salt of an alkali metal is selected from at least one of sodium benzoate, potassium benzoate, sodium p-toluenesulfonate, or potassium oxalate.

[0025] In some embodiments, in S3, the mass content of the organic salt of an alkali metal is 0.5% to 3% based on the mass of the oxidized graphite composite material.

[0026] In some embodiments, the providing of the graphite composite material comprises the following steps:

[0027] S11: crushing a graphite raw material, for example, to a Dv50 of 8 μm to 11 μm;

[0028] S12: performing a pre-carbonization treatment on the crushed raw material;

[0029] S13: mixing the product after the pre-carbonization treatment with pitch and granulating;

[0030] S14: performing a graphitization treatment on the granulated product to obtain the graphite composite material.

[0031] In some embodiments, the method for preparing the carbon-based material comprises: crushing artificial graphite raw materials, pre-carbonizing the crushed raw materials, adding pitch after the pre-carbonization is completed, granulating after the granulation is completed, and then performing high-temperature graphitization treatment to obtain a graphite composite material. The graphite composite material is subjected to surface modification treatment (specifically, first subjected to oxidation treatment, and then mixed with an organic salt solution of an alkali metal), to obtain a negative electrode active material.

[0032] In a second aspect, the present application provides a secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect.

[0033] In some embodiments, the compaction density P of the negative electrode satisfies: 1.3 g / cm 3 ≤ P ≤ 1.8 g / cm 3 . The compaction density of the negative electrode affects the energy density and kinetic performance of the secondary battery. When the compaction density is too low, the energy density of the secondary battery is low, and at the same time, the adhesion of the negative electrode active material particles on the current collector is poor, which can cause the negative electrode to be demolded, thereby reducing the cycle performance of the secondary battery. When the compaction density is too high, the electrolyte wettability of the negative electrode is significantly reduced, and the kinetics of the secondary battery is also reduced, and lithium precipitation is prone to occur in the secondary battery during the cycle process, thereby reducing the cycle performance of the secondary battery. In some embodiments, 1.33 g / cm 3 ≤ CD ≤ 1.68 g / cm 3 .

[0034] In some embodiments, the specific surface area capacitance M of the negative electrode satisfies: 1.0 mAh / cm 2 ≤ M ≤ 4.0 mAh / cm 2 . The specific surface area capacitance M represents the coating amount of the single-sided active material of the negative electrode. When the specific surface area capacitance M is low, the coating amount is small, which is beneficial to the rate performance of the secondary battery, but the energy density is low. When the specific surface area capacitance M is too high, the coating amount is too large, which can cause the active material layer to be too thick, thereby affecting the deintercalation of lithium ions and reducing the rate performance of the secondary battery. In some embodiments, 1.5 mAh / cm 2 ≤ M ≤ 3.5 mAh / cm 2 .

[0035] In some embodiments, the first coulombic efficiency FE of the secondary battery satisfies FE ≥ 90.0%. In some embodiments, the secondary battery satisfies a capacity retention rate ≥ 86% after 2000 cycles at 25°C, for example, ≥ 90%.

[0036] In a third aspect, the present application provides an electronic device comprising the secondary battery of the second aspect.

[0037] The application can effectively improve the quality of SEI film by treating the surface of carbon-based materials such as graphite materials to obtain an organic substance layer similar to SEI film on the surface of particles, thereby improving the first coulombic efficiency and cycle performance of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The cycle performance of lithium ion batteries of Example 1 and Comparative Example 1 of the application is shown.

[0039] Figure 2 The thermogravimetric mass loss test graph of the carbon-based material of Example 2 of the application is shown. DETAILED DESCRIPTION

[0040] Embodiments of the application will be described in detail below. Embodiments of the application should not be construed as limiting the application.

[0041] In addition, quantities, ratios, and other numerical values in the application are sometimes presented in a range format. It is to be understood that such range format is used for convenience and brevity and should be construed as having been preceded by the term "comprising at least one of" or "comprising one of" followed by a listing of individual numerical values or sub-ranges.

[0042] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "at least one of" or "one or more of" can mean any combination of individual items in the list. For example, if the list contains A and B, then "at least one of A and B" means A alone, B alone, or A and B together. In another example, if the list contains A, B, and C, then "at least one of A, B, and C" means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together. The item A can include a single element or multiple elements. The item B can include a single element or multiple elements. The item C can include a single element or multiple elements.

[0043] I. Negative active material

[0044] The negative electrode active material provided in the present application comprises a carbon-based material, the surface of the particles of the carbon-based material comprises an alkali metal element, and the alkali metal element comprises a sodium element and / or a potassium element. The present application obtains an organic substance layer similar to an SEI film on the surface of the particles of the carbon-based material, such as a graphite material, by treating the surface of the carbon-based material. On the one hand, the organic substance on the surface of the particles can inhibit the film formation on the surface of the negative electrode active material, reduce the loss of active lithium ions, and improve the initial coulombic efficiency. On the other hand, the sodium element and / or the potassium element on the surface of the particles can improve the electrochemical stability of the organic substance, thereby avoiding the side reaction and even decomposition of the organic substance on the surface of the particles of the negative electrode active material, and thereby improving the cycle performance of the secondary battery.

[0045] In the present application, the "surface of the particles of the carbon-based material" can be a region 1 μm ± 0.2 μm from the outermost side of the particles of the carbon-based material to the center of the particles of the carbon-based material. In some embodiments, the "surface of the particles of the carbon-based material" can be any 100 μm x 100 μm region in the field of view of a scanning electron microscope selected when the carbon-based material is observed by a scanning electron microscope under the condition that the acceleration voltage is 10 ± 0.5 KV and the working distance is 10 mm ± 0.5 mm.

[0046] In some embodiments, the mass loss ratio of the carbon-based material is S, S ≥ 0.5% in the temperature range of 25-800°C by thermogravimetric test, and the exothermic peak value of the carbon-based material is T, 300°C ≤ T ≤ 500°C. The conventional graphite material has stable high-temperature properties, and the mass loss ratio of the thermogravimetric test is very small. Due to the existence of the organic substance layer on the surface of the particles, the mass of the carbon-based material will be lost during the thermogravimetric test.

[0047] In some embodiments, S is 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%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or a range consisting of any two of these values. The greater the mass loss ratio S, the higher the content of the organic substance on the surface of the particles. A high content of the organic substance can effectively improve the initial coulombic efficiency and the cycle performance of the secondary battery. However, when S is too high, too many side reactions will occur, and the generation of gas and the consumption of active lithium during the electrochemical reaction will be adversely affected. In some embodiments, 0.5% ≤ S ≤ 5%. In some embodiments, 1% ≤ S ≤ 3%.

[0048] In some embodiments, T is 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, or a range consisting of any two of these values. The organic matter on the particle surface of the carbon-based material decomposes at a temperature of about 300°C to 500°C, and thus the temperature range T at which the exothermic peak (peak of mass loss rate) is located is 300°C to 500°C. In some embodiments, 330°C≤T≤420°C.

[0049] In some embodiments, the atomic percentage of the alkali metal element on the particle surface of the carbon-based material is X, and 0.4%≤X≤3.0%. In some embodiments, X is 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 a range consisting of any two of these values. The sodium element or the potassium element helps form the SEI film on the surface of the carbon-based material, can effectively improve the quality of the SEI film, and thus improve the cycle performance of the secondary battery, but too much sodium element or potassium element will make the SEI film too thick, which is not conducive to the improvement of the cycle performance. In some embodiments, 0.6%≤X≤2.5%.

[0050] The present application tests X by the following test method: under the condition of observing the carbon-based material with a scanning electron microscope, any 100 μm x 100 μm area in the field of view of the scanning electron microscope is selected, and the content of the alkali metal element is tested by EDS area scanning of the area to obtain X.

[0051] In some embodiments, the particle surface of the carbon-based material further comprises carbon element, and the atomic percentage of the carbon element on the particle surface is C1, and C1≤96%. In some embodiments, C1 is 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, or a range consisting of any two of these values. In some embodiments, 90%≤C1≤95%.

[0052] The present application tests C1 by the following test method: under the condition of observing the carbon-based material with a scanning electron microscope, any 100 μm x 100 μm area in the field of view of the scanning electron microscope is selected, and the content of the carbon element is tested by EDS area scanning of the area to obtain C1.

[0053] In some embodiments, the mass content of carbon element in the carbon-based material is C, C≥98% based on the mass of the carbon-based material. In some embodiments, C is 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or a range between any two of these values. Since the content of the organic layer on the surface of the carbon-based material particles is small, and the main body of the carbon-based material is carbon-based material, the mass ratio of carbon atoms of the carbon-based material particles as a whole is greater than 98%. In some embodiments, 98.5%≤C≤99.9%.

[0054] In some embodiments, the particle surface of the carbon-based material contains substances having absorption peaks in the range of 950cm -1 to 1200cm -1 using Fourier infrared testing. The absorption peaks in the range of 950cm -1 to 1200cm -1 in the Fourier infrared test spectrum represent the vibration of chemical bonds composed of atoms such as C, H, and O. The fact that the carbon-based material has absorption peaks in this range can further indicate that the carbon-based material, due to the surface modification treatment, has components similar to SEI film on its particles themselves, so that the formation of SEI film is reduced during the first charge and discharge process, thereby improving the first coulombic efficiency.

[0055] In some embodiments, the particle surface of the carbon-based material contains substances having at least one functional group selected from a hydroxyl group, a carboxyl group, a carbonyl group, a sulfonic acid group, a phenyl group, a carbon-carbon double bond, or a carbon-carbon triple bond.

[0056] In some embodiments, the particle surface of the carbon-based material contains substances derived from an organic salt of an alkali metal selected from an organic salt having at least one functional group selected from a hydroxyl group, a carboxyl group, a carbonyl group, a sulfonic acid group, a phenyl group, a carbon-carbon double bond, or a carbon-carbon triple bond.

[0057] In some embodiments, the organic salt of an alkali metal is selected from at least one of an organic acid alkali metal salt or an organic sulfonic acid alkali metal salt.

[0058] In some embodiments, the organic acid alkali metal salt includes at least one of a compound represented by Formula I, Formula II, or Formula III,

[0059]

[0060] wherein R1and R2are each independently selected from hydrogen or C1-C6alkyl, N is selected from sodium and / or potassium, and a is an integer between 0 and 6. In some embodiments, R1and R2are each independently selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl, and a is 0, 1, 2, 3, 4, 5, or 6.

[0061] In some embodiments, the alkali metal salt of an organic acid comprises at least one of the compounds of Formula I-1, Formula I-2, or Formula I-3,

[0062]

[0063] wherein R1is selected from hydrogen, C1-C4alkyl, or C5-C6alkyl, N is selected from sodium and / or potassium, and a is an integer between 0 and 6. In some embodiments, R1is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl, and a is 0, 1, 2, 3, 4, 5, or 6.

[0064] In some embodiments, the alkali metal salt of an organic sulfonic acid comprises at least one of the compounds of Formula IV,

[0065]

[0066] In Formula IV, R3is selected from hydrogen or C1-C6alkyl, and N is selected from sodium and / or potassium. In some embodiments, R3is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl.

[0067] In some embodiments, the alkali metal salt of an organic sulfonic acid comprises at least one of the compounds of Formula IV-1, Formula IV-2, or Formula IV-3,

[0068]

[0069] wherein R3is selected from hydrogen, C1-C4alkyl, or C5-C6alkyl, and N is selected from sodium and / or potassium. In some embodiments, R3is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl.

[0070] In some embodiments, the alkali metal salt of an organic sulfonic acid comprises at least one of the compounds of Formula IV-1, Formula IV-2, or Formula IV-3,

[0071] In some embodiments, the carbon-based material has a first coulombic efficiency CE that satisfies: CE≥93.0%, such as 93.5%, 94%, 94.5%, 95%, 95.5%, or 96%. In some embodiments, CE≥94.0%.

[0072] In some embodiments, the particle size of the carbon-based material satisfies: Dv90 / Dv50≤3.0. In some embodiments, the Dv90 / Dv50 is 1.5, 1.7, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or a range consisting of any two of these values. A Dv90 / Dv50 within the above range can ensure that the carbon-based particle distribution is narrow, avoiding excessive small particles and large particles, thereby facilitating the improvement of the cycle performance and processing performance of the secondary battery. When the number of small particles in the carbon-based material is excessive, side reactions will increase, affecting the cycle performance of the secondary battery; when the number of large particles is excessive, the processing performance will be affected, which can cause the negative electrode sheet to have convex points and other appearance defects, and in severe cases, can cause point-like lithium precipitation. In some embodiments, Dv90 / Dv50≤2.5.

[0073] In some embodiments, the Dv90 of the carbon-based material is 30 pm to 50 pm. In some embodiments, the Dv90 of the carbon-based material is 31 pm, 32 pm, 33 pm, 34 pm, 35 pm, 36 pm, 37 pm, 38 pm, 39 pm, 40 pm, 41 pm, 42 pm, 43 pm, 44 pm, 45 pm, 46 pm, 47 pm, 48 pm, 49 pm, or a range consisting of any two of these values. In some embodiments, the Dv50 of the carbon-based material is 10 pm to 15 pm. In some embodiments, the Dv50 of the carbon-based material is 10 pm, 10.5 pm, 11 pm, 11.5 pm, 12 pm, 12.5 pm, 13 pm, 13.5 pm, 14 pm, 14.5 pm, or a range consisting of any two of these values.

[0074] In some embodiments, the specific surface area BET of the carbon-based material satisfies: 0.5 m 2 / g≤BET≤5.5 m 2 / g. In some embodiments, the specific surface area BET of the carbon-based material is 0.5 m 2 / g, 1.0 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, 4.5 m 2 / g, 5 m 2 / g, or a range consisting of any two of these values. A too large BET will increase side reactions, affecting the first coulombic efficiency, and a too small BET will cause the wettability of the electrolyte to the negative electrode to be poor, thereby affecting the kinetic performance of the secondary battery. In some embodiments, 1.5 m2 / g≤BET≤5m 2 / g.

[0075] In some embodiments, the tap density TD of the carbon-based material satisfies: TD≥0.6g / cm 3 In some embodiments, TD is 0.65g / cm 3 , 0.7g / cm 3 , 0.75g / cm 3 , 0.8g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 or a range consisting of any two of these values. TD is related to the slurry processability of the carbon-based material. Too low tap density will result in poor slurry dispersibility of the carbon-based material during the preparation of secondary batteries, which will cause the slurry to settle easily, resulting in uneven coating thickness and affecting the electrical performance of the secondary battery. In some embodiments, TD≥0.8g / cm 3 .

[0076] In some embodiments, the OI value of the carbon-based material satisfies: 4≤OI≤15. In some embodiments, OI is 5, 5.5, 6, 6.5, 7, 7.5, 8, 9, 10, 11, 12, 13, 14 or a range consisting of any two of these values. The OI value of the carbon-based material indicates the consistency of the orientation degree of the crystals in its particles. A larger OI value means a higher consistency of the orientation degree of the crystals, which will result in a single direction of lithium ion deintercalation in the active particles, making it difficult to deintercalate lithium, and in severe cases, causing lithium precipitation, thereby reducing the cycle performance of the secondary battery. In some embodiments, 5≤OI≤12.

[0077] In some embodiments, the preparation method of the carbon-based material comprises the following steps:

[0078] S1: providing a graphite composite material;

[0079] S2: mixing the graphite composite material with an oxidizing agent and then performing oxidation treatment to obtain an oxidized graphite composite material;

[0080] S3: mixing the oxidized graphite composite material with an organic salt of alkali metal to obtain a carbon-based material.

[0081] In some embodiments, in S2, the oxidizing agent is selected from at least one of a hydrogen peroxide solution, a sulfuric acid solution, a nitric acid solution, or potassium permanganate. In some embodiments, the oxidizing agent is a hydrogen peroxide solution, wherein the concentration of the hydrogen peroxide solution is 3 mol / L to 7 mol / L, for example, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, or 6.5 mol / L.

[0082] In some embodiments, in S2, the temperature of the oxidation treatment is 20°C to 60°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or 55°C. In some embodiments, in S2, the time of the oxidation treatment is 4 h to 15 h, for example, 4 h, 6 h, 8 h, 10 h, 12 h, or 14 h.

[0083] In some embodiments, in S3, the organic salt of alkali metal is selected from an organic salt having at least one functional group selected from a hydroxyl group, a carboxyl group, a carbonyl group, a sulfonic acid group, a phenyl group, a carbon-carbon double bond, or a carbon-carbon triple bond. In some embodiments, the organic salt of alkali metal is selected from at least one of an organic acid alkali metal salt or an organic sulfonic acid alkali metal salt.

[0084] In some embodiments, the organic acid alkali metal salt comprises at least one of a compound represented by Formula I, Formula II, or Formula III,

[0085]

[0086] wherein R1and R2are each independently selected from hydrogen or C1-C6alkyl, N is selected from sodium and / or potassium, and a is an integer between 0 and 6. In some embodiments, R1and R2are each independently selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl, and a is 0, 1, 2, 3, 4, 5, or 6.

[0087] In some embodiments, the organic acid alkali metal salt comprises at least one of a compound represented by Formula I-1, Formula I-2, or Formula I-3,

[0088]

[0089] wherein R1is selected from hydrogen, C1-C4alkyl, or C5-C6alkyl, N is selected from sodium and / or potassium, and a is an integer between 0 and 6. In some embodiments, R1is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl, and a is 0, 1, 2, 3, 4, 5, or 6.

[0090] In some embodiments, the alkali metal salt of an organic sulfonic acid comprises at least one of the compounds shown in Formula IV,

[0091]

[0092] In Formula IV, R3is selected from hydrogen or C1-C6alkyl, and N is selected from sodium and / or potassium. In some embodiments, R3is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl.

[0093] In some embodiments, the alkali metal salt of an organic sulfonic acid comprises at least one of the compounds shown in Formula IV-1, Formula IV-2, or Formula IV-3,

[0094]

[0095] In Formula IV, R3is selected from hydrogen, C1-C4alkyl, or C5-C6alkyl, and N is selected from sodium and / or potassium. In some embodiments, R3is selected from hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, or n-hexyl.

[0096] In some embodiments, the organic salt of an alkali metal is selected from at least one of sodium benzoate, potassium benzoate, sodium p-toluenesulfonate, or potassium oxalate.

[0097] In some embodiments, in S3, the oxidized graphite composite is mixed with a solution of the organic salt of an alkali metal, such as an aqueous solution or an alcoholic solution. In some embodiments, in S3, the mixing is performed at a temperature of 40°C to 80°C, such as 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C. In some embodiments, in S3, the mixing is performed for a time period of 5h to 10h, such as 6h, 7h, or 8h.

[0098] In some embodiments, in S3, the mass content of the organic salt of an alkali metal is 0.5% to 3%, such as 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%, or 2.9%, based on the mass of the oxidized graphite composite.

[0099] In some embodiments, the graphite composite is provided by the following steps:

[0100] S11: crushing the graphite raw material, such as to a Dv50 of 8μm to 11μm;

[0101] S12: performing pre-carbonization treatment on the crushed raw material;

[0102] S13: mixing the product after pre-carbonization treatment with pitch and granulating;

[0103] S14: performing graphitization treatment on the granulated product to obtain a graphite composite material.

[0104] In some embodiments, in S11, the graphite raw material is selected from petroleum coke. In some embodiments, in S12, the pre-carbonization treatment is performed at a temperature of 800-1200°C, for example, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C or 1150°C.

[0105] In some embodiments, in S13, the pitch is added in an amount of 5-15% of the mass of the graphite raw material, for example, 6%, 8%, 10%, 12% or 14%. In some embodiments, in S13, the granulation is performed for 2-4 hours, for example, 2.5 hours, 3 hours or 3.5 hours. In some embodiments, in S13, the granulation is performed at a temperature of 200-500°C, for example, 250°C, 300°C, 350°C, 400°C or 450°C.

[0106] In some embodiments, in S14, the graphitization treatment is performed at a temperature of 2600-3100°C, for example, 2700°C, 2800°C, 2900°C or 3000°C.

[0107] In some embodiments, the method for preparing a carbon-based material comprises: crushing a synthetic graphite raw material, performing pre-carbonization treatment on the crushed raw material, adding pitch after the treatment to perform granulation, and performing high-temperature graphitization treatment after the granulation to obtain a graphite composite material. The graphite composite material is subjected to surface modification treatment (specifically, first subjected to oxidation treatment, and then mixed with an organic salt solution of an alkali metal) to obtain a carbon-based material.

[0108] Secondary battery

[0109] The secondary battery provided in the present application comprises a negative electrode, and the negative electrode comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect.

[0110] In some embodiments, the compaction density P of the negative electrode satisfies: 1.3 g / cm 3 ≤ P ≤ 1.8 g / cm 3 In some embodiments, P is 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 31.55 g / cm 3 1.6 g / cm 3 1.65 g / cm 3 1.7 g / cm 3 1.75 g / cm 3 or a range consisting of any two of these values. The compaction density of the negative electrode affects the energy density and kinetic performance of the secondary battery. When the compaction density is too low, the energy density of the secondary battery is low, and at the same time, the adhesion of the negative electrode active material particles to the current collector is poor, which can cause the negative electrode to be stripped, thereby reducing the cycle performance of the secondary battery. When the compaction density is too high, the electrolyte wettability of the negative electrode is significantly reduced, and the kinetics of the secondary battery is also reduced, and the secondary battery is prone to lithium precipitation during cycling, thereby reducing its cycle performance. In some embodiments, 1.33 g / cm 3 ≤ CD ≤ 1.68 g / cm 3 .

[0111] In some embodiments, the specific surface area of the negative electrode is 1.0 m2 / g 2 ≤ S ≤ 3.0 m2 / g 2 . In some embodiments, S is 1.5 m2 / g 2 , 2 m2 / g 2 , 2.5 m2 / g 2 , 3.0 m2 / g 2 , or 3.5 m2 / g 2 . The specific surface area S represents the coating amount of the negative electrode active material on one side of the negative electrode. When the specific surface area S is low, the coating amount is small, which is beneficial to the rate performance of the secondary battery, but the energy density is low. When the specific surface area S is too high, the coating amount is too large, which can cause the active material layer to be too thick, thereby affecting the deintercalation of lithium ions and reducing the rate performance of the secondary battery. In some embodiments, 1.5 m2 / g 2 ≤ S ≤ 3.5 m2 / g 2 .

[0112] In some embodiments, the first coulombic efficiency FE of the secondary battery satisfies FE ≥ 90.0%. In some embodiments, the secondary battery satisfies a capacity retention rate ≥ 86% after 2000 cycles at 25°C, for example, ≥ 90%.

[0113] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode current collector comprises: a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, a polymer substrate coated with a conductive metal, or any combination thereof.

[0114] In some embodiments, the negative active material layer can further include other negative active materials, such as silicon-oxygen materials, silicon-carbon materials, etc., which can further increase the energy density of the secondary battery.

[0115] In some embodiments, the negative 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0116] 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 materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0117] The secondary battery of the present application further includes a positive electrode including a positive current collector and a positive active material layer including a positive active material, a binder, and a conductive agent.

[0118] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, an aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0119] In some embodiments, the positive active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, 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 lithium manganate, spinel lithium nickel manganate, and lithium titanate. In some embodiments, the binder includes a binder polymer, such as at least one of 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, polyolefin alcohol, or polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fibers; a metal-based material, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0120] The secondary battery of the present application further includes a separator. The material and shape of the separator used in the secondary battery of the present application are not particularly limited and can be any of those known in the art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application.

[0121] For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having 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 film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0122] The surface treatment layer is provided on at least one surface of the substrate layer and can be a polymer layer or an inorganic layer, or a layer formed of a mixture of a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, 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 vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0123] The secondary battery of the present application further includes an electrolyte. The electrolyte used in the present application can be any of those known in the art.

[0124] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an optional additive. The organic solvent in the electrolyte of the present application can be any organic solvent known in the art as a solvent for an electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and can be any electrolyte known in the art. The additive of the electrolyte according to the present application can be any additive known in the art as an additive for an electrolyte. 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 an ether-based solvent, for example, including at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0125] In some embodiments, the secondary battery of the present application includes, but is not limited to, a lithium ion battery or a sodium ion battery. In some embodiments, the secondary battery includes a lithium ion battery.

[0126] III. Electronic device

[0127] The present application further provides an electronic device including the secondary battery of the second aspect of the present application.

[0128] The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a household large-sized storage battery, and a lithium ion capacitor, etc.

[0129] In the following examples and comparative examples, the reagents, materials and instruments used, unless otherwise specified, are commercially available.

[0130] Examples and Comparative Examples

[0131] Example 1

[0132] Preparation of carbon-based material

[0133] Step S1: Petroleum coke was selected as the raw material of artificial graphite, which was first crushed to Dv50 of 9 μm, then part of the small particles were removed by classification treatment, and the crushing sample yield was 80%, then the crushed material was treated at high temperature of 1000 ℃ to remove volatile matter, after the treatment was completed, pitch was added for granulation, the pitch addition amount was 4% of the mass of the material after high temperature treatment, the granulation time was controlled at 2 h, and the granulation temperature was controlled at 300 ℃. The particle size and powder compaction density were adjusted by controlling the amount of pitch added. After granulation, the graphite composite material was obtained by high temperature graphitization treatment at 2900 ℃.

[0134] Step S2: The graphite composite material was first subjected to surface oxidation treatment, and the graphite composite material was first placed in a hydrogen peroxide (H2O2) solution with a concentration of 5.0 mol / L, and soaked at 35 ℃ for 8 h, then filtered and dried to obtain the oxidized graphite composite material.

[0135] Step S3: Organic salt sodium benzoate was selected as the surface modifier, and the mass ratio of sodium benzoate to the oxidized graphite composite material was 0.9%. The sodium benzoate was dissolved in water, and the oxidized graphite composite material was added, then heated to 60 ℃ and stirred for 6 h. After the mixing and stirring were completed, the filter solid was washed with water and dried to obtain the carbon-based material.

[0136] Preparation of negative electrode sheet

[0137] The carbon-based material prepared above was used as the negative electrode active material, conductive carbon black, binder styrene-butadiene rubber (abbreviated as SBR), and thickening agent sodium carboxymethyl cellulose (abbreviated as CMC) were mixed in a weight ratio of 95.7:1.5:1.8:1, and then a proper amount of deionized water solvent was added and stirred to form a uniform negative electrode slurry. The slurry was coated on the current collector Cu foil, dried and cold-pressed to obtain the negative electrode sheet.

[0138] Preparation of positive electrode sheet

[0139] The positive electrode selects lithium iron phosphate (chemical formula: LiFePO4) as the positive electrode active material, which is mixed with conductive agent acetylene black, binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96.3:2.2:1.5 in an appropriate amount of N-methyl pyrrolidone (abbreviated as NMP) solvent, and is fully stirred to form a uniform positive electrode slurry; the slurry is coated on the current collector Al foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0140] Preparation of electrolyte

[0141] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3, then fluoroethylene carbonate and 1,3-propane sultone are added, dissolved and fully stirred, and then lithium salt LiPF6 is added, mixed uniformly to obtain the electrolyte. The mass percentage of LiPF6 is 12.5%, the mass percentage of fluoroethylene carbonate is 2%, and the mass percentage of 1,3-propane sultone is 2%, and the mass percentage of each substance is calculated based on the mass of the electrolyte.

[0142] Preparation of lithium ion battery

[0143] PE porous polymer film is selected as the separator film, the above negative electrode sheet and positive electrode sheet are wound together with the separator film, placed in an aluminum plastic film, then liquid injection, standing, and formation are carried out to prepare a lithium ion secondary battery.

[0144] Examples 2 to 15, Comparative Examples 1 to 2

[0145] Examples 2 to 15 and Comparative Examples 1 to 2 are realized on the basis of Example 1 by adjusting the mass ratio and type of organic salt. The specific adjustment measures are shown in Table a, and the detailed data are shown in Table 1.

[0146] Table a

[0147]

[0148]

[0149] Examples 16 to 23

[0150] Examples 16 to 23 are realized on the basis of Example 6 by adjusting the concentration of hydrogen peroxide solution. The specific adjustment measures are shown in Table b, and the detailed data are shown in Table 2. Adjusting the concentration of hydrogen peroxide solution can adjust the surface modification state of the negative electrode active material, change the organic salt content on the surface, and change the combination state with the composite graphite material.

[0151] Table b

[0152] Examples Concentration of hydrogen peroxide solution mol / L Example 6 5.0 Example 16 3.0 Example 17 3.6 Example 18 4.3 Example 19 4.8 Example 20 6.6 Example 21 7.0 Example 22 5.4 Example 23 6.0

[0153] Examples 24-29

[0154] Examples 24-29 are further optimization of the first coulombic efficiency and particle size of the negative active material by adjusting the mass ratio of organic salt and the particle size process on the basis of Example 23. The specific adjustment measures are shown in Table C, and the detailed data are shown in Table 3.

[0155] Table C

[0156]

[0157]

[0158] Examples 30-43

[0159] Examples 30-43 are further design and optimization of the specific surface area BET, tap density TD and powder OI value of the negative active material on the basis of Example 28. Details are shown in Table 4.

[0160] Examples 44-52

[0161] Examples 44-52 are further design and optimization of the compaction density P and the specific surface area of the negative electrode sheet on the basis of Example 42. Details are shown in Table 5.

[0162] Test method

[0163] 1. Particle size test

[0164] The particle size test method refers to GB / T 19077-2016. The specific process is to weigh 1 g of sample and mix it uniformly with 20 mL of deionized water and a small amount of dispersant, place it in an ultrasonic device for 5 min, then pour the solution into the sample system Hydro2000SM for testing. The test equipment used is Mastersizer 3000 produced by Malvern Company. During the test, when the laser beam passes through the dispersed particle sample, the particle size measurement is completed by measuring the intensity of scattered light. Then the data is used to analyze and calculate the particle size distribution that forms the scattering spectrum. The refractive index of the particles used for testing is 1.8, and each sample is tested three times. The final particle size is the average of the three tests.

[0165] 2. OI value test

[0166] The (004) face diffraction line pattern and the (110) face diffraction line pattern in the X-ray diffraction pattern of the negative electrode sheet are tested according to the People's Republic of China Machinery Industry Standard JB / T 4220-2011 "Determination of Lattice Parameters of Artificial Graphite". The test conditions are as follows: X-ray uses CuKα radiation, and the CuKα radiation is removed by a filter or a monochromator. The working voltage of the X-ray tube is (30-35) kV, and the working current is (15-20) mA. The scanning speed of the counter is 1 / 4 (°) / min. When recording the 004 diffraction line pattern, the scanning range of the diffraction angle 2θ is 53°-57°. When recording the 110 diffraction line pattern, the scanning range of the diffraction angle 2θ is 75°-79°. The peak area obtained from the (004) face diffraction line pattern is denoted as C004. The peak area obtained from the (110) face diffraction line pattern is denoted as C110. The ratio of C004 / C110 of the negative electrode sheet is calculated, that is, the OI value of the negative electrode sheet.

[0167] 3. Specific surface area test

[0168] The specific surface area test method refers to GB / T 19587-2017. The specific process is as follows: 1-8 g of sample (the sample is weighed to be at least 1 / 3 of the volume of the sphere) is placed in a 1 / 2 inch long tube with a ball bubble (the diameter of the spherical part of the tube is 12 mm), and then the sample is pretreated at 200°C for 2 h and then placed in a test device TriStar3030 (USA Mic company) for testing. The adsorption gas used is N2 (purity: 99.999%), and the test is carried out at 77K. The specific surface area is tested by the BET calculation method.

[0169] 4. Tap density test

[0170] The tap density is the mass per unit volume of the powder in the container after being vibrated under specified conditions, and the unit is g / cm 3 .

[0171] The test method is to fix a graduated cylinder containing a certain mass of powder on a mechanical vibration device. The vibration motor drives the mechanical vibration device to vibrate vertically up and down. The graduated cylinder containing the powder vibrates with the mechanical vibration device in a rhythmic manner. As the number of vibrations increases, the powder in the graduated cylinder is gradually vibrated. After the vibration number reaches the set number, the mechanical vibration device stops vibrating, and the volume of the graduated cylinder is read. According to the definition of density: mass divided by volume, the density of the vibrated powder is calculated. The specific process parameters are as follows: vibration number: 5000 times; vibration frequency: 250±15 times / min; ambient temperature: 15°C to 28°C.

[0172] 5. First coulomb efficiency CE test of carbon-based material

[0173] The first coulombic efficiency test can refer to the standard: GB / T 24533-2019. The carbon-based material is mixed, coated, rolled, punched, and dried to form a negative electrode sheet. Lithium sheet is used as the positive electrode to assemble a button cell for testing. The first coulombic efficiency of the carbon-based material is calculated by comparing the charging capacity and discharging capacity of the button cell. The carbon-based material slurry formula is as follows: negative electrode active material: CMC: SP: SBR = 94.5%: 1.5%: 1.5%: 2.5% (mass percentage, solvent is deionized water).

[0174] 6. Infrared spectroscopy (FTIR) test

[0175] Nicolet iS10 Fourier Transform Infrared (FT-IR) spectrometer is used to scan the spectrum range of 350cm -1 ~ 4000cm -1 .

[0176] 7. Mass loss ratio test of carbon-based material

[0177] Thermal gravimetric analyzer (TG-MS) is used to test the carbon-based material, with a model of STA449F3-QMS403.

[0178] Specifically: first, dry the sample in a vacuum drying oven at 80℃ for 2h, then put the dried sample into an aluminum crucible, and weigh the aluminum crucible before and after putting the sample to obtain the sample mass m1. After the sample is put in, use a special tablet press to press the crucible cover and crucible together to prevent the sample from being ejected out of the crucible by thermal decomposition gas flow or thermal decomposition projectile during heating, causing non-thermal decomposition weight loss. Then, a nitrogen protective atmosphere is introduced and heated to 800℃ at a rate of 2℃ / min. After reaching 800℃, the sample is kept for 2min. The mass change of the carbon-based material is recorded during heating, and then the remaining sample mass m2 is weighed after cooling. The mass loss ratio of the carbon-based material can be obtained by the formula (m1-m2) / m1x100%. The position of the mass loss rate peak (exothermic peak) can be obtained from the mass change curve of the carbon-based material, and the peak temperature can be obtained.

[0179] 8. Surface element atomic percentage and mass ratio test of carbon-based material particles

[0180] EDS spectrometer is used to analyze the elements on the surface of the carbon-based material particles. The surface element atomic percentage and mass ratio test method detection standard is GB / T 17359-2012, and the energy spectrum quantitative analysis method.

[0181] Detection process: under the standard experimental environment and the requirements of detection standard, the carbon-based material is placed into the scanning electron microscope sample chamber according to the standard operation process, the test position is observed under magnification using an acceleration voltage of 10 kV, and the sample is analyzed by X-ray energy spectrum analyzer for element qualitative and quantitative analysis. The surface of the carbon-based material is scanned and analyzed by selecting a region with a size of 100 μm x 100 μm, and the types and atomic percentages of elements on the surface of the carbon-based material and the mass percentage of carbon atoms can be obtained by EDS energy spectrum.

[0182] The specific device model and parameter settings are as follows:

[0183] Model: OXFORD EDS (X-max-20mm2), acceleration voltage: 10KV, working distance: 10±0.5mm, current: 2.335A, aperture: 60μm.

[0184] 9. Carbon atom mass content in carbon-based material

[0185] First, part of the sample is placed in a vacuum drying oven at 80℃ for 2h, then 1g of the dried sample is taken out and placed in a crucible. Then the crucible is placed in a muffle furnace and heated at a heating rate of 3℃ / min to 1000℃, and the mass of the residual material in the crucible is measured after 2h of heat preservation. The mass content of carbon atoms in the carbon-based material can be obtained by formula (1-m) / 1x100%.

[0186] 10. First coulomb efficiency FE test of lithium ion battery

[0187] After liquid injection, the electrode assembly is formed:

[0188] Temperature: 45℃

[0189] 1. 0.02C constant current (CC) for 10min, charge capacity C1 mAh;

[0190] 2. Standby for 10min;

[0191] 3. 0.2C CC for 60min, charge capacity C2 mAh;

[0192] 4. Standby for 10min;

[0193] 5. 0.5C CC to 3.6V, constant voltage (CV) to 0.05C, charge capacity C3 mAh;

[0194] 6. 0.5C direct current charging (DC) to 2.5V, discharge capacity D1 mAh;

[0195] The first coulomb efficiency FE of the lithium ion battery is FE=D1 / (C1+C2+C3)x100%.

[0196] 11. Lithium ion battery cycle test

[0197] Temperature: 25℃

[0198] 1. 0.5C DC to 2.5V (first discharge);

[0199] 2. Rest for 10 min;

[0200] 3. 0.5C CC to 3.6V, CV to 0.05C;

[0201] 4. Rest for 10 min;

[0202] 5. 0.5C DC to 2.5V;

[0203] 6. Repeat steps 2-5 for 2000 times;

[0204] 7. The discharge capacity of the 2000th / the discharge capacity of the second time x 100%. That is the capacity retention rate of 2000 cycles.

[0205] Test results

[0206] Table 1 shows the effect of the mass loss ratio S, the exothermic peak T and the atomic percentage X of alkali metal elements on the surface of the carbon-based particles on the performance of lithium ion batteries. Among them, the changes of S, T and X are realized by adjusting the mass content of organic salt in the oxidized graphite composite material and the type of organic salt.

[0207] Table 1

[0208]

[0209] From the data in Table 1, it can be seen that when the carbon-based particles contain sodium and / or potassium elements on the surface, the lithium ion battery can have high initial coulombic efficiency and excellent cycle performance. Further, when the carbon-based material satisfies the mass loss ratio S≥0.50%, the temperature range T of the mass loss peak is 300℃ to 500℃, the initial coulombic efficiency of the lithium ion battery can be significantly improved and its cycle performance can be improved.

[0210] Table 2 further studies the effect of the mass ratio C1 of carbon elements on the surface of the carbon-based particles and the mass content C of carbon elements in the whole carbon-based material on the performance of lithium ion batteries on the basis of Example 6. Among them, the surface modification state of the carbon-based material can be adjusted by adjusting the concentration of hydrogen peroxide solution, and the content of organic salt on the surface of the particles and the combination state with graphite can be changed.

[0211] Table 2

[0212]

[0213]

[0214] From the data in Table 2, it can be seen that when the negative active material satisfies C≥98% and C1≤96%, the first coulombic efficiency and cycle capacity retention of the lithium ion battery are further improved based on Example 6.

[0215] Table 3 further studies the influence of the first coulombic efficiency CE of the carbon-based material, Dv90 and Dv50 on the lithium ion performance based on Example 23. Among them, by controlling the mass ratio of organic salt and the crushing particle size process of raw material petroleum coke, the change of the first coulombic efficiency and particle size of the carbon-based material under discharge is realized.

[0216] Table 3

[0217]

[0218] From the data in Table 3, it can be found that when the carbon-based material satisfies one of the conditions of the first coulombic efficiency CE≥93.0% and the particle size Dv90 / Dv50≤3.0, the first coulombic efficiency and cycle capacity retention of the lithium ion secondary battery are improved, and when both conditions are satisfied, the first coulombic efficiency and cycle capacity retention are obviously improved.

[0219] Table 4 further studies the influence of the specific surface area BET, tap density TD and powder OI value of the carbon-based material on the lithium ion performance based on Example 28.

[0220] Table 4

[0221]

[0222]

[0223] From the data in Table 4, it can be seen that compared with Example 28, when the carbon-based material satisfies one or two of the conditions of 0.5m 2 / g≤BET≤5.5m 2 / g, TD≥0.6g / cm 3 and OI≤15, the first coulombic efficiency and cycle capacity retention of the lithium ion battery are improved, and when all the conditions are satisfied, the first coulombic efficiency and cycle capacity retention of the lithium ion battery are obviously improved.

[0224] Table 5 further studies the influence of the compaction density P of the negative electrode sheet and the specific capacity M per unit area of one side on the lithium ion performance based on Example 42.

[0225] Table 5

[0226]

[0227] As can be seen from the data of Table 5, when the negative electrode satisfies one of the conditions of 1.3 g / cm 3 ≤ P ≤ 1.8 g / cm 3 and 1.0 mAh / cm 2 ≤ M ≤ 4.0 mAh / cm 2 the initial coulombic efficiency and cycle capacity retention of the lithium ion battery are improved, and when all the conditions are satisfied, the initial coulombic efficiency and cycle capacity retention of the lithium ion battery are significantly improved.

[0228] Although illustrative embodiments have been shown and described, it is to be understood that the above-described embodiments are not be construed as limiting, and that changes, alternatives and modifications can be suggested as appropriate to one skilled in the art without departing from the spirit, principles and scope of the application.

Claims

1. A negative electrode active material comprising a carbon-based material, wherein the particle surface of the carbon-based material comprises an alkali metal element, wherein the alkali metal element comprises sodium and / or potassium; the atomic percentage of the alkali metal element on the particle surface of the carbon-based material is X, 0.4% ≤ X ≤ 3.0%; Thermogravimetric analysis was conducted, and within a temperature range of 25℃ to 800℃, the mass loss ratio of the carbon-based material was S, where S≥0.5%, and the peak value of the exothermic peak of the carbon-based material was T, where 300℃≤T≤500℃.

2. The negative electrode active material according to claim 1, wherein, 0.5% ≤ S ≤ 5%; and / or 330℃ ≤ T ≤ 420℃.

3. The negative electrode active material according to claim 1, wherein, 1％≤S≤3％。 4. The negative electrode active material according to claim 1, wherein, The carbon-based material satisfies at least one of the following conditions (i) to (ii): (i) The surface of the carbon-based material particles also includes carbon elements, and the mass ratio of carbon elements on the particle surface is C1, where C1 ≤ 96%; (ii) Based on the mass of the carbon-based material, the mass content of carbon element in the carbon-based material is C, and C≥98%.

5. The negative electrode active material according to claim 4, wherein, The carbon-based material satisfies at least one of the following conditions (iii) to (v): (iii) 0.6% ≤ X ≤ 2.5%; (iv) 90% ≤ C1 ≤ 95%; (v) 98.5% ≤ C ≤ 99.9%.

6. The negative electrode active material according to claim 1, wherein, Fourier transform infrared spectroscopy was used to determine the surface area of ​​the carbon-based material particles at 950 cm⁻¹. -1 Up to 1200cm -1 Substances with absorption peaks in the range; and / or The surface of the carbon-based material particles contains substances having at least one functional group selected from hydroxyl, carboxyl, carbonyl, sulfonic acid, phenyl, carbon-carbon double bond, or carbon-carbon triple bond; and / or The carbon-based material includes graphite.

7. The negative electrode active material according to claim 1, wherein, The carbon-based material satisfies at least one of the following conditions (vi) to (x): (vi) The initial coulombic efficiency CE% of the carbon-based material satisfies: CE ≥ 93.0; (vii) The particle size of the carbon-based material satisfies: Dv90 / Dv50≤3.0; (viii) The specific surface area BET of the carbon-based material satisfies: 0.5m² 2 / g≤BET≤5.5m 2 / g; (ix) The tap density TD of the carbon-based material satisfies: TD ≥ 0.6 g / cm³ 3 ; (x) The OI value of the carbon-based material satisfies: 4≤OI≤15.

8. The negative electrode active material according to claim 7, wherein, The carbon-based material satisfies at least one of the following conditions (xi) to (xv): (xi) The initial coulombic efficiency (CE) of the carbon-based material satisfies: CE ≥ 94.0%; (xii) The particle size of the carbon-based material satisfies: Dv90 / Dv50≤2.5; (xiii) The specific surface area BET of the carbon-based material satisfies: 1.5m² 2 / g≤BET≤5m 2 / g; (xiv) The tap density TD of the carbon-based material described satisfies: TD ≥ 0.8 g / cm³ 3 ; (xv) The OI value of the carbon-based material satisfies: 5≤OI≤12.

9. A secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein, The compaction density P of the negative electrode satisfies: 1.3 g / cm³ 3 ≤P≤1.8g / cm 3 ; and / or The capacitance M per unit area of ​​one side of the negative electrode satisfies: 1.0 mAh / cm² 2 ≤M≤4.0mAh / cm 2 .

11. The secondary battery according to claim 9, wherein, The compaction density P of the negative electrode satisfies: 1.33 g / cm³ 3 ≤CD≤1.68g / cm 3 ; and / or The capacitance M per unit area of ​​one side of the negative electrode satisfies: 1.5 mAh / cm² 2 ≤M≤3.5mAh / cm 2 .

12. An electronic device comprising a secondary battery as described in any one of claims 9 to 11.

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