Negative electrode active material, electrochemical device and electronic device

Abstract

To provide a negative electrode active material, an electrochemical device containing the negative electrode active material, and an electronic apparatus.SOLUTION: A negative electrode active material of the present invention contains a graphite and amorphous carbon. The negative electrode active material satisfies the equation of 1.6≤WD / WG≤2.6 by Raman examination. Here, the WD is a half value width of a D peak within a range of 1340 cm-1 to 1370 cm-1 in a Raman spectrum, satisfies the equation of 40 cm-1≤WD≤100 cm-1. The WG is a half value width of a G peak within a range of 1570 cm-1 to 1590 cm-1 in Raman spectrum, and satisfies the equation of 15 cm-1≤WG≤50 cm-1. In the negative electrode active material of the present invention, the front surface can include a defect degree of a conventional higher front surface lattice via a front surface processing, and can effectively improve a capacitance and dynamic properties per gram. In addition, an electrochemical device containing the negative electrode active material achieves both of a high energy density and an electrochemical characteristic.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of energy storage, and in particular to anode active materials and electrochemical and electronic devices including the anode active materials. [Background technology]

[0002] Electrochemical devices (e.g., lithium-ion batteries) are widely used due to their environmental friendliness, high operating voltage, large specific capacity, and long cycle life, making them the world's most promising new green chemical power source. In recent years, medium- and large-sized lithium-ion batteries with high output characteristics have been developed for use in electric vehicles (EVs) and large-scale energy storage systems (ESSs). As lithium-ion batteries become more widely used, concerns about battery life have gradually become more apparent, and improving their energy density has become an important technical challenge that must be addressed as soon as possible. Improving the active materials in the electrodes is one research direction to address these challenges.

[0003] In the prior art, the energy density of the electrode assembly is increased mainly by increasing the graphitization degree of artificial graphite or by using natural graphite to increase the capacity per gram of the negative electrode material. However, this also has a serious impact on the cycle characteristics, resulting in a trade-off between two options, making it difficult to achieve the overall performance of the lithium-ion battery. Summary of the Invention

[0004] SUMMARY OF THE INVENTION The present invention solves, at least in part, at least one problem in the related art by providing an active negative electrode material, and electrochemical and electronic devices including the active negative electrode material.

[0005] In a first aspect, the present invention provides an anode active material comprising graphite and amorphous carbon, wherein the anode active material has a Raman spectrum of 1.6≦W D / W G ≦2.6, where W Dis the Raman spectrum of 1340-1370 cm -1 is the half-width of the D peak in the range of 40 cm -1 ≦W D ≦100cm -1 and W G is the 1570 cm -1 ~1590cm -1 is the half-width of the G peak within the range of 15 cm -1 ≦W G ≦50cm -1 In the present invention, the half-width of the D peak represents the size of the surface crystal grains of the negative electrode active material, and mainly reflects the degree of defects in the surface lattice. The half-width of the G peak represents the crystallinity of the negative electrode active material. D / W G When W is in this range, the surface lattice defects of the negative electrode active material are relatively large, and such surface lattice defects are favorable for rapid insertion of active ions, thereby improving the dynamic properties of the negative electrode active material. More importantly, such surface lattice defects can store more active ions, thereby improving the capacity per gram of the negative electrode active material. In some embodiments, the negative electrode active material has a W of 1.7≦W D / W G In some embodiments, the negative electrode active material satisfies 2≦W≦2.5. D / W G Meets ≦2.5.

[0006] In some embodiments, 40 cm -1 ≦W D ≦60cm -1 In some embodiments, 15 cm -1 ≦W G ≦35cm -1 Meet the following.

[0007] In some embodiments, the negative electrode active material satisfies the relationship 0.08≦ID / IG≦1.2, where ID is the intensity of the D peak and IG is the intensity of the G peak. The ratio of ID / IG can characterize the crystal defect level of the negative electrode active material, with a higher value indicating a higher defect level. A high defect level increases the number of active ion desorption channels and improves the desorption rate of the active ions, thereby improving the kinetic properties of the negative electrode active material. However, excessive defects can lead to deterioration of the electrochemical device's performance, such as initial coulombic efficiency, cycling, and storage. When the ID / IG ratio is within this range, the electrochemical device can exhibit good kinetics without significant deterioration in performance, such as initial coulombic efficiency and cycling. In some embodiments, the ratio satisfies the relationship 0.1≦ID / IG≦1.0.

[0008] In some embodiments, when the specific surface area of ​​the negative electrode active material is B1, the specific surface area of ​​the negative electrode active material is 0. 8m 2 / g≦B1≦5. 4m 2 / g. The smaller the specific surface area of ​​the negative electrode active material, the smaller the contact area with the electrolyte, which reduces the amount of active ions consumed when the electrochemical device first forms an SEI film, resulting in a higher initial coulombic efficiency. However, if the specific surface area is too small, it becomes difficult for the electrolyte to infiltrate and the active ions to diffuse, affecting the dynamic characteristics of the electrochemical device. In some embodiments, 1. 0m 2 / g≦B1≦4. 5m 2 / g is met.

[0009] In some embodiments, the negative electrode active material includes a basal surface and an edge surface, and the ratio of the specific surface area of ​​the basal surface to the specific surface area of ​​the negative electrode active material is 40% to 70%. Lithium ions primarily intercalate through the graphite edge surfaces and some defects, and the electrolyte primarily reacts with the graphite at the edge surfaces to form an SEI film. The higher the specific surface area of ​​the basal surface, the fewer side reactions occur, improving the initial coulombic efficiency and cycling stability of the electrochemical device. However, if the basal surface ratio is too high, the dynamic characteristics will be affected. When the basal surface ratio is within the above range, the electrochemical device can exhibit good initial coulombic efficiency and cycling characteristics while maintaining good dynamic characteristics. In some embodiments, the ratio of the specific surface area of ​​the basal surface to the specific surface area of ​​the negative electrode active material is 45% to 65%.

[0010] In some embodiments, the negative electrode active material includes a base surface and an edge surface, wherein the roughness of the edge surface is greater than the roughness of the base surface.

[0011] In some embodiments, the most probable pore diameter of the negative electrode active material is 2.5 nm to 3.5 nm. The most probable pore diameter of the negative electrode active material represents the pore diameter at which the rate of change in pore volume with pore diameter is greatest. In other words, the most probable pore diameter is the pore diameter corresponding to the strongest peak on the pore diameter-pore volume differential curve. When the most probable pore diameter of the negative electrode active material of the present invention is within the above-mentioned range, it can store lithium to increase capacity and function as a lithium insertion path to improve kinetic characteristics. If the pore diameter is too large, side reactions increase. In some embodiments, the most probable pore diameter of the negative electrode active material is 2.7 nm to 3.3 nm.

[0012] In some embodiments, the proportion of the pore volume of the negative electrode active material having the most possible pore size to the total pore volume of the negative electrode active material is 3% to 8%. In some embodiments, the proportion of the pore volume of the negative electrode active material having the most possible pore size to the total pore volume of the negative electrode active material is 3.5% to 7%.

[0013] In some embodiments, the negative electrode active material satisfies the following relationship: (B2-B1) / B1×100%≦80%, where B2 is the specific surface area after applying 1 ton of pressure. When the specific surface areas of the negative electrode active material before and after applying pressure satisfy the above relationship, the structure of the negative electrode active material is stabilized, which is advantageous for improving the expansion characteristics during cycling of the electrochemical device.

[0014] In some embodiments, X-ray photoelectron spectroscopy (XPS) testing has revealed that the mass content of oxygen in the negative electrode active material is 2% to 5%. The surface oxygen content can reflect, to some extent, the degree of defects in the surface lattice of the negative electrode active material. If the surface oxygen content is too low, insufficient defects are formed on the surface, resulting in no improvement in the capacity per gram and kinetic properties of the material. If the surface oxygen content is too high, too many defects are formed, resulting in a decrease in the initial coulombic efficiency and increased electrolyte consumption. When the oxygen content is within the above range, the negative electrode active material has an appropriate degree of surface crystalline defects, achieving optimal capacity per gram and kinetic properties without affecting other properties. In some embodiments, the mass content of oxygen in the negative electrode active material is 2.2% to 4.0%.

[0015] In some embodiments, the tap density of the negative electrode active material is 0.90 g / cm 3 ~1.05g / cm 3 In some embodiments, the negative electrode active material has a powder compacted density of 1.9 g / cm at a pressure of 5 t. 3 ~2.05g / cm 3 By increasing the powder compaction density, the negative electrode active material can be used in a high-compactness electrode design, which can increase the volumetric energy density of the electrochemical device. However, if the compaction density is too high, the interlayer sliding of the negative electrode active material becomes too easy, the material becomes soft, the repulsion of the electrode pieces becomes weak, and the pores formed by the accumulation of internal particles are reduced, further hindering the infiltration of electrolyte and the diffusion of active ions, which affects the performance of the electrochemical device.

[0016] In some embodiments, the method for producing the negative electrode active material includes: S1: Providing a graphite material; S2: Mixing the graphite material in S1 with a carbonaceous precursor to obtain a graphite material coated with the carbonaceous precursor; S3: Mixing the graphite material coated with the carbonaceous precursor in S2 with bicarbonate to obtain a mixture, and heat-treating the mixture to obtain the negative electrode active material.

[0017] The method for producing an anode active material of the present invention first coats the surface of a graphite material with a carbon precursor, thereby facilitating subsequent reaction with a gas. Next, a solid capable of thermally decomposing to generate an oxidizing atmosphere is selected and mixed preferentially with the graphite material, thereby making the oxidation reaction occurring on the graphite surface more uniform and controlled. The resulting anode active material has a moderate degree of surface oxidation, and exhibits both high capacity per gram and excellent kinetic properties.

[0018] In a second aspect, the present invention provides an electrochemical device including a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material of the first aspect.

[0019] In some embodiments, the specific surface area of ​​the negative electrode active material is 4.3 5m 2 / g~5. 9m 2 / g.

[0020] In some embodiments, a charge-discharge test is performed using a button battery comprising the negative electrode and lithium metal, and the button battery satisfies C2-C1≧1, where C1 mAh / g is the reversible capacity between 0.005 V and 2 V, and C2 mAh / g is the reversible capacity between 0 V and 2 V.

[0021] In a third aspect, the present invention provides an electronic device comprising the electrochemical device of the second aspect.

[0022] In the present invention, the surface of the negative electrode active material is oxidized to have a relatively high degree of surface lattice defects, which is advantageous for rapid insertion of active ions, improving the kinetic properties of the negative electrode active material, allowing more active ions to be stored, improving the capacity per gram of the negative electrode active material, and enabling electrochemical devices including the negative electrode active material to achieve both high energy density and high electrochemical properties. [Brief explanation of the drawings]

[0023] In the following, in order to explain the embodiments of the present invention, the drawings necessary for explaining the embodiments of the present invention or the prior art will be briefly described. Obviously, the drawings described below are only a part of the embodiments of the present invention. Those skilled in the art can still obtain drawings of other embodiments based on the structures illustrated in these drawings without any creative effort. [Figure 1] FIG. 1 shows Raman spectra of the negative electrode active materials of Example 9 of the present invention and Comparative Example 1. [Figure 2] FIG. 2 shows the pore size-pore volume differential curves of the negative electrode active materials of Example 9 of the present invention and Comparative Example 1. [Figure 3] FIG. 3 shows an SEM image of the negative electrode active material of Example 9 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Examples of the present invention will be described in detail below, but the examples of the present invention should not be construed as limiting the present invention.

[0025] It should be noted that quantities, ratios, and other numerical values ​​may be expressed herein in a range format. It should be understood that such range format is used for convenience and brevity and should be understood flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges contained within that range, so long as each numerical value and subrange is explicitly specified.

[0026] In specific embodiments and claims, a list of terms connected by "at least one of," "at least one of," "at least one of," or other similar terminology can refer to any combination of the listed terms. For example, if terms A and B are listed, "at least one of A and B" means A only, B only, or A and B. In another example, if terms A, B, and C are listed, "at least one of A, B, and C" means A only, B only, C only, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Term A may include a single element or multiple elements. Term B may include a single element or multiple elements. Term C may include a single element or multiple elements.

[0027] 1. Negative electrode active material The negative electrode active material provided in the present invention includes graphite and amorphous carbon, and the negative electrode active material has a Raman scattering coefficient of 1.6≦W. D / W G ≦2.6, where W D is the 1340 cm -1 ~1370cm -1 is the half-width of the D peak in the range of 40 cm -1 ≦W D ≦100cm -1 and W G is the 1570 cm -1 ~1590cm -1 is the half-width of the G peak within the range of 15 cm -1 ≦W G ≦50cm -1 In the present invention, the half-width of the D peak represents the size of the surface crystal grains of the negative electrode active material, and mainly reflects the degree of defects in the surface lattice. The half-width of the G peak represents the crystallinity of the negative electrode active material. D / W GWhen W is in the above range, the surface lattice defects of the negative electrode active material are relatively large, and such surface lattice defects are favorable for the rapid insertion of active ions, thereby improving the dynamic properties of the negative electrode active material. More importantly, such surface lattice defects can also store more active ions, thereby improving the capacity per gram of the negative electrode active material. In some embodiments, W D / W G is 1.65, 1.75, 1.85, 1.9, 1.95, 2.0, 2.05, 2.15, 2.25, 2.35, 2.45, 2.55, or a range consisting of any two of these values. In some embodiments, 1.7≦W D / W G In some embodiments, 2≦W D / W G Meets ≦2.5.

[0028] In some embodiments, W D is 42cm -1 , 44cm -1 , 46cm -1 , 48cm -1 , 50cm -1 , 52cm -1 , 54cm -1 , 56cm -1 , 58cm -1 , 60cm -1 , 65cm -1 , 70cm -1 , 75cm -1 , 80cm -1 , 85cm -1 , 90cm -1 , 95cm -1 or a range consisting of any two of these values. -1 ≦W D ≦60cm -1 Satisfy W DIf is too high, the crystal grains on the surface of the material are too small and there are many defects, which indicates many side reactions and low initial coulomb efficiency of the electrochemical device; if is too low, it indicates that the surface treatment of the material is insufficient, there are few defects to store lithium and improve capacity, and the kinetic properties are not improved.

[0029] In some embodiments, W G is 16cm -1 , 17cm -1 , 18cm -1 , 19cm -1 , 20cm -1 , 21cm -1 , 22cm -1 , 23cm -1 , 24cm -1 , 25cm -1 , 26cm -1 , 27cm -1 , 28cm -1 , 29cm -1 , 30cm -1 , 31cm -1 , 32cm -1 , 33cm -1 , 34cm -1 , 37cm -1 , 40cm -1 , 43cm -1 , 45cm -1 , 47cm -1 or a range consisting of any two of these values. -1 ≦W G ≦35cm -1 Satisfy W G If is too high, the crystallinity of the material is poor and the crystal structure is severely destroyed, resulting in a significant decrease in the initial coulombic efficiency and a decrease in the lithium storage sites between the active material layers, which in turn reduces the capacity; if is too low, the material has good crystallinity, a high degree of graphitization, and a high capacity and initial coulombic efficiency, but poor kinetics, making the electrochemical device unstable during high-temperature cycling.

[0030] In some embodiments, the negative electrode active material satisfies the relationship 0.08≦ID / IG≦1.2, where ID is the intensity of the D peak and IG is the intensity of the G peak. The ID / IG ratio can characterize the crystal defect level of the negative electrode active material, with a higher value indicating a higher defect level. A high defect level increases the number of active ion desorption channels and improves the desorption rate of the active ions, thereby improving the kinetic properties of the negative electrode active material. However, excessive defects can lead to deterioration of the electrochemical device's properties, such as initial coulombic efficiency, cycling, and storage. When the ID / IG ratio is within the above range, the electrochemical device can exhibit good kinetics without significant deterioration in its properties, such as initial coulombic efficiency and cycling. In some embodiments, ID / IG is 0.09, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, or a range consisting of any two of these values. In some embodiments, 0.1≦ID / IG≦1.0.

[0031] In some embodiments, when the specific surface area of ​​the negative electrode active material is B1, the specific surface area of ​​the negative electrode active material is 0. 8m 2 / g≦B1≦5. 4m 2 / g. The smaller the specific surface area of ​​the negative electrode active material, the smaller the contact area with the electrolyte, which reduces the amount of active ions consumed when the electrochemical device first forms the SEI film, resulting in a higher initial Coulombic efficiency. However, if the specific surface area is too small, electrolyte infiltration and active diffusion become difficult, affecting the dynamic characteristics of the electrochemical device. In some embodiments, B1 is 0. 9m 2 / g, 1. 1m 2 / g, 1. 3m 2 / g, 1. 5m 2 / g, 1. 7m 2 / g, 2. 0m 2 / g, 2.3m 2 / g, 2. 5m 2 / g, 2. 7m 2 / g, 3. 0m 2 / g, 3. 3m 2 / g, 3. 5m 2 / g, 3. 7m 2 / g, 4. 0m 2 / g, 4. 3m 2 / g, 4. 7m 2 / g, 4. 9m 2 / g, or a range consisting of any two of these values. In some embodiments, 1. 0m 2 / g≦B1≦4. 5m 2 / g is met.

[0032] In some embodiments, the negative electrode active material includes a base surface and an end surface, and the ratio of the base surface to the specific surface area of ​​the negative electrode active material is 40% to 70%. A higher ratio of the base surface reduces side reactions, improving the initial coulombic efficiency and cycling stability of the electrochemical device. However, a too high ratio of the base surface can affect the kinetic characteristics. When the ratio of the base surface is within the above range, the electrochemical device can exhibit good initial coulombic efficiency and cycling characteristics while also maintaining good kinetic characteristics. In some embodiments, the ratio of the base surface to the specific surface area of ​​the negative electrode active material is 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, or a range consisting of any two of these values. In some embodiments, the ratio of the base surface to the specific surface area of ​​the negative electrode active material is 45% to 65%.

[0033] In some embodiments, the negative electrode active material includes a base surface and an edge surface, where the edge surface has a greater roughness than the base surface. In some embodiments, the edge surface (left side) of the negative electrode active material has a greater roughness than the base surface (right side), as shown in FIG.

[0034] In some embodiments, the maximum pore size of the negative electrode active material is 2.5 nm to 3.5 nm. The maximum pore size of a negative electrode active material refers to the pore size at which the rate of change in pore volume with pore size is greatest. When the maximum pore size of the negative electrode active material of the present invention is within the above-mentioned range, it can store lithium to increase capacity and function as a path for lithium insertion to improve dynamic characteristics. However, if the pore size is too large, side reactions increase. In some embodiments, the maximum pore size of the negative electrode active material is 2.55 nm, 2.6 nm, 2.65 nm, 2.7 nm, 2.75 nm, 2.8 nm, 2.85 nm, 2.9 nm, 2.95 nm, 3.0 nm, 3.05 nm, 3.1 nm, 3.15 nm, 3.2 nm, 3.25 nm, 3.3 nm, 3.35 nm, 3.4 nm, 3.45 nm, or a range consisting of any two of these values. In some embodiments, the negative electrode active material has a maximum pore size of 2.7 nm to 3.3 nm.

[0035] In some embodiments, the ratio of the pore volume of the negative electrode active material having the most possible pore size to the total pore volume of the negative electrode active material is 3% to 8%. In some embodiments, the ratio of the pore volume of the negative electrode active material having the most possible pore size to the total pore volume of the negative electrode active material is 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, or a range consisting of any two of these values. In some embodiments, the ratio of the pore volume of the negative electrode active material having the most possible pore size to the total pore volume of the negative electrode active material is 3.5% to 7%.

[0036] In some embodiments, the negative electrode active material satisfies the following relationship: (B2 - B1) / B1 x 100% ≦ 80%, where B2 is the specific surface area after applying 1 ton of pressure. The fact that the specific surface areas of the negative electrode active material before and after applying pressure satisfy the above-mentioned relationship indicates that the structure of the negative electrode active material is stable, which is advantageous for improving the expansion characteristics during cycling of an electrochemical device. In some embodiments, the negative electrode active material satisfies the following relationship: 10% ≦ (B2 - B1) / B1 x 100% ≦ 80%. In some embodiments, (B2 - B1) / B1 x 100% is 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a range consisting of any two of these values.

[0037] In some embodiments, the negative electrode active material is 4. 0m 2 / g≦B2≦6. 0m 2 / g. In some embodiments, B2 satisfies 4. 1m 2 / g, 4. 3m 2 / g, 4. 5m 2 / g, 4. 7m 2 / g, 5. 0m 2 / g, 5. 3m 2 / g, 5. 5m 2 / g, 5. 7m 2 / g, or a range consisting of any two of these values. In the present invention, B2 is the specific surface area after applying a pressure of 1 ton to the negative electrode active material. The method for applying pressure to the negative electrode active material is as follows: Using an electronic pressure tester (SUNS UTM7305), a powder of negative electrode active material weighing 1.0±0.05 g is placed on a mold with a diameter of 13 mm, a pressure of 1 ton is applied to the powder of negative electrode active material, and this is maintained for 5 seconds, after which the pressure is released and the powder is removed.

[0038] In some embodiments, the mass content of oxygen in the negative electrode active material is 2% to 5% as determined by X-ray photoelectron spectroscopy. The surface oxygen content can reflect, to some extent, the degree of surface lattice defects of the negative electrode active material. If the surface oxygen content is too low, insufficient defects are formed on the surface, resulting in no improvement in the capacity per gram and kinetic properties of the material. If the surface oxygen content is too high, too many defects are formed, resulting in a decrease in the initial coulombic efficiency and increased electrolyte consumption. When the oxygen content is within the above range, the degree of surface crystalline defects in the negative electrode active material is appropriate, allowing for optimal capacity per gram and kinetic properties to be achieved without affecting other properties. In some embodiments, the mass content of oxygen in the negative electrode active material is 2.1%, 2.3%, 2.5%, 2.7%, 3.0%, 3.3%, 3.5%, 3.7%, 3.9%, 4.3%, 4.5%, 4.7%, or a range consisting of any two of these values. In some embodiments, the mass content of oxygen in the negative electrode active material is 2.2% to 4.0%.

[0039] In some embodiments, the tap density of the negative electrode active material is 0.90 g / cm 3 ~1.05g / cm 3 In some embodiments, the tap density of the negative electrode active material is 0.90 g / cm 3 , 0.91g / cm 3 , 0.92g / cm 3 , 0.93g / cm 3 , 0.95g / cm 3 , 0.96g / cm 3 , 0.97g / cm 3 , 0.98g / cm 3 , 0.99g / cm 3 , 1.00g / cm 3 , 1.01g / cm 3 , 1.02g / cm 3 , 1.03g / cm 3 , 1.04g / cm 3 , or a range consisting of any two of these values.

[0040] In some embodiments, the negative electrode active material has a powder compaction density of 1.9 g / cm at a pressure of 5 t. 3 ~2.05g / cm 3 By increasing the pressed density of the powder, the negative electrode active material can be used in a high-pressure electrode piece design, thereby increasing the volumetric energy density of the electrochemical device. However, if the pressed density is too high, the interlayer sliding of the negative electrode active material becomes too easy, the material becomes soft, the repulsion of the electrode piece becomes small, and the pores formed by the accumulation of internal particles are reduced, further hindering the infiltration of the electrolyte and the diffusion of active ions, thereby affecting the performance of the electrochemical device. In some embodiments, the pressed density of the negative electrode active material at a pressure of 5 tons is 1.90 g / cm. 3 , 1.92g / cm 3 , 1.93g / cm 3 , 1.94g / cm 3 , 1.96g / cm 3 , 1.97g / cm 3 , 1.98g / cm 3 c, 1.99 g / cm 3 , 2.01g / cm 3 , 2.02g / cm 3 , 2.03g / cm 3 , 2.04g / cm 3 , or a range consisting of any two of these values.

[0041] In some embodiments, the method for producing the negative electrode active material includes: S1: Providing a graphite material; S2: Mixing the graphite material in S1 with a carbonaceous precursor to obtain a graphite material coated with the carbonaceous precursor; and S3: Mixing the graphite material coated with the carbonaceous precursor in S2 with bicarbonate to obtain a mixture, and heat-treating the mixture to obtain the negative electrode active material.

[0042] The method for producing an anode active material of the present invention first coats the surface of a graphite material with a carbon precursor, thereby facilitating subsequent reaction with a gas. Next, a solid capable of thermally decomposing to generate an oxidizing atmosphere is selected and mixed preferentially with the graphite material, thereby making the oxidation reaction occurring on the graphite surface more uniform and controlled. The resulting anode active material has a moderate degree of surface oxidation, and exhibits both high capacity per gram and excellent kinetic properties.

[0043] In some embodiments, providing the graphite material in S1 includes the steps of: mixing a graphite precursor with a binder to obtain a first mixture, subjecting the first mixture to a first heat treatment to obtain a graphite material precursor, and graphitizing the graphite material precursor to obtain the graphite.

[0044] In some embodiments, the graphite precursor is at least one selected from organic materials such as coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polybenzene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin. In some embodiments, the graphite precursor is at least one selected from petroleum coke and pitch coke. In some embodiments, the binder is at least one selected from pitch, resin, and tar. In some embodiments, the binder is high-temperature pitch. In some embodiments, the high-temperature pitch has a softening point of 200°C to 250°C, for example, 210°C, 220°C, or 240°C. In some embodiments, the ratio of graphite precursor to binder is 1:(0.1 to 1), for example, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or 1:0.9.

[0045] In some embodiments, the temperature of the first heat treatment is 450°C to 550°C, e.g., 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, or 540°C. In some embodiments, the time of the first heat treatment is 1 hour to 5 hours, e.g., 2 hours, 3 hours, or 4 hours. In some embodiments, the temperature of the graphitization treatment is 2500°C to 3200°C, e.g., 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, or 3100°C. In some embodiments, the time of the graphitization treatment is 10 hours to 200 hours, e.g., 20 hours, 40 hours, 60 hours, 80 hours, 100 hours, 120 hours, 140 hours, 160 hours, or 180 hours.

[0046] In some embodiments, the carbonaceous precursor in S2 is at least one selected from pitches, resins, and coal tar. In some embodiments, the pitch is at least one selected from coal tar, light tar oil, medium tar oil, heavy tar oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, and heavy oil. In some embodiments, the resin is at least one selected from thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenolic resins and furan resins. In some embodiments, the softening point of the pitch is 40°C to 90°C, for example, 50°C, 60°C, 70°C, or 80°C.

[0047] In some embodiments, the mixing temperature in S2 is 50° C. to 100° C., for example, 60° C., 70° C., 80° C., or 90° C. In some embodiments, the mass content of the carbonaceous precursor in S2 is 0.1% to 15%, for example, 1%, 3%, 5%, 7%, 9%, 10%, 12%, or 14%, based on the mass of the graphite material.

[0048] In some embodiments, the bicarbonate in S3 is selected from ammonium bicarbonate and / or sodium bicarbonate. In some embodiments, the mass content of the bicarbonate in S3 is 0.5% to 15%, e.g., 1%, 3%, 5%, 7%, 9%, 10%, 12%, or 14%, based on the mass of the graphite material coated with the carbonaceous precursor. In some embodiments, the temperature of the heat treatment in S3 is 50°C to 1000°C, e.g., 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 650°C, 700°C, 800°C, or 900°C. In some embodiments, the time of the heat treatment in S3 is 4 hours to 10 hours, e.g., 5 hours, 6 hours, 7 hours, 8 hours, or 9 hours. In some embodiments, the heat treatment in S3 is performed in an inert atmosphere, for example, nitrogen or argon.

[0049] 2. Electrochemical equipment The electrochemical device of the present invention includes a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material of the first aspect.

[0050] In some embodiments, the specific surface area of ​​the negative electrode active material is 4.3 5m 2 / g~5. 9m 2 / g. In some embodiments, the specific surface area of ​​the negative electrode active material is 4. 5m 2 / g, 4. 7m 2 / g, 5. 0m 2 / g, 5. 3m 2 / g, 5. 5m 2 / g, 5. 7m 2 / g, or a range consisting of any two of these values. In the present invention, the specific surface area of ​​the negative electrode active material in the electrochemical device is the specific surface area measured by discharging the voltage of the electrochemical device to 3 V, disassembling it, removing the negative electrode, and scraping off the powder on the negative electrode piece.

[0051] In some embodiments, a charge-discharge test is performed using a button battery comprising the negative electrode and lithium metal, and the button battery satisfies C2-C1≧1, where C1 mAh / g is the reversible capacity between 0.005 V and 2 V, and C2 mAh / g is the reversible capacity between 0 V and 2 V. In some embodiments, the value of C2-C1 is 1 mAh / g, 2 mAh / g, 3 mAh / g, 4 mAh / g, 5 mAh / g, 6 mAh / g, or a range consisting of any two of these values. In the present invention, the negative electrode constituting the button battery is a negative electrode that has been disassembled after an electrochemical device has been discharged to a voltage of 3 V.

[0052] In some embodiments, the electrochemical device includes a lithium ion battery, and the lithium ion battery swells less than 9% after 500 cycles at 25° C. In some embodiments, the lithium ion battery swells less than 8% or less than 7%.

[0053] In some embodiments, the negative electrode active material layer further includes an adhesive, which may include, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoroethylene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, poly(1,1-difluoroethylene), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0054] In some embodiments, the negative electrode active material layer includes a conductive material, including, but not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, or a polyphenylene derivative.

[0055] In some embodiments, the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal.

[0056] The electrochemical device of the present invention further comprises a positive electrode, and the materials, configurations and manufacturing methods that can be used for the positive electrode in the embodiments of the present invention include any techniques disclosed in the prior art.

[0057] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector.

[0058] In some embodiments, the positive electrode active material includes, but is not limited to, lithium cobalt oxide (LiCoO), lithium nickel cobalt manganese (NCM) ternary material, lithium ferrous phosphate (LiFePO), or lithium manganese oxide (LiMnO).

[0059] In some embodiments, the positive electrode active material layer further comprises an adhesive and, optionally, a conductive material. The adhesive can enhance the bonding between the positive electrode active material particles and the bonding between the positive electrode active material and the current collector.

[0060] In some embodiments, the adhesive includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoroethylene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, poly(1,1-difluoroethylene), polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0061] In some embodiments, the conductive material includes, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, and mixtures thereof. In some examples, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some examples, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, and silver. In some examples, the conductive polymer is a polyphenylene derivative.

[0062] In some embodiments, the current collector can include, but is not limited to, aluminum.

[0063] The positive electrode can be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by a method in which an active material, a conductive material, and an adhesive are mixed in a solvent to prepare an active material composition, and the active material composition is then applied to a current collector. In some embodiments, the solvent can include, but is not limited to, N-methylpyrrolidone.

[0064] The electrochemical device of the present invention further comprises an electrolyte. The electrolyte used in the embodiments of the present invention may be any known in the art.

[0065] In some embodiments, the electrolyte solution includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte solution of the present invention may be any organic solvent known in the prior art that can be used as a solvent for electrolyte solutions. The electrolyte used in the electrolyte solution of the present invention is not limited and may be any electrolyte known in the prior art. The additive of the electrolyte solution of the present invention may be any additive known in the prior art that can be used as an additive for electrolyte solutions.

[0066] 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.

[0067] In some embodiments, the lithium salt comprises at least one of an organic lithium salt or an inorganic lithium salt.

[0068] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), lithium bis(trifluoromethanesulfonyl)imide LiN(CFSO) (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SOF)) (LiFSI), lithium bis(oxalato)borate LiB(CO) (LiBOB), or lithium difluoro(oxalato)borate LiBF(CO) (LiDFOB).

[0069] In some embodiments, the concentration of the lithium salt in the electrolyte solution is 0.5 to 3 mol / L, 0.5 to 2 mol / L, or 0.8 to 1.5 mol / L.

[0070] The electrochemical device of the present invention includes a separator between the positive electrode and the negative electrode to prevent short circuits. The material and shape of the separator used in the embodiments of the present invention are not particularly limited and may be any material and shape disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic material formed from a material that is stable in the electrolyte of the present invention.

[0071] 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 having a porous structure, and the material of the substrate layer is at least one selected from 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 and used.

[0072] A surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic material.

[0073] The inorganic layer includes inorganic particles and a binder, the inorganic particles being one or more selected from alumina, silica, 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, and the binder being one or more selected from a combination of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0074] The polymer layer includes a polymer, and the polymer material is at least one selected from polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0075] In some embodiments, the electrochemical device of the present invention includes, but is not limited to, a primary battery or a secondary battery.

[0076] In some embodiments, the electrochemical device is a lithium secondary battery.

[0077] In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0078] 3.Electronic equipment The electronic device of the present invention can be any device that uses an electrochemical device according to an embodiment of the present invention.

[0079] In some embodiments, the electronic device includes, but is not limited to, a laptop computer, a pen-based computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic organizer, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor.

[0080] Hereinafter, the preparation of a lithium ion battery will be described with reference to specific examples, taking a lithium ion battery as an example. Those skilled in the art should understand that the preparation method described in the present invention is merely exemplary, and any other suitable preparation method is within the scope of the present invention.

[0081] Example 1 Preparation of Lithium-ion Batteries 1. Preparation of the negative electrode 1) Preparation of negative electrode active material S1: Petroleum coke was selected as the raw material. The petroleum coke was mixed with high-temperature pitch with a softening point of 230°C in a ratio of 1:0.15, and then the mixture was kept at 550°C for 3 hours and then graphitized at 3000°C for 150 hours to obtain graphite active material; S2: Then, the graphite active material was uniformly mixed with low-temperature pitch having a softening point of 70°C, and then heated to 80°C, where the mass ratio of the active material to the low-temperature pitch was 1:0.05, so that the pitch was uniformly coated on the surface of the graphite active material; S3: The above-mentioned pitch-coated graphite active material was mixed with ammonium bicarbonate in a weight ratio of 100:3, and placed in a box furnace with a furnace loading ratio of 50%. The mixture was heated at 300°C for 6 hours in a nitrogen atmosphere, where the furnace loading ratio is the ratio of the amount of material added to the furnace volume of the heating device, to obtain a negative electrode active material.

[0082] 2) Preparation of the negative electrode The negative electrode active material prepared above, styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were dispersed in deionized water in a weight ratio of 997.7:1.2:1.1 and thoroughly stirred to obtain a uniform mixture, forming a negative electrode slurry. Acetylene black was applied to copper foil to obtain a negative electrode current collector. The negative electrode slurry was applied to the negative electrode current collector, dried, and cold-rolled to obtain a negative electrode.

[0083] 2. Preparation of the positive electrode Lithium cobalt oxide (LiCoO2), acetylene black, and polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 96:2:2 in an appropriate amount of N-methylpyrrolidone (NMP) by thorough stirring. The mixture was then applied to an aluminum foil positive electrode current collector, dried, and cold-rolled to obtain a positive electrode.

[0084] 3. Preparation of electrolyte In a dry argon gas atmosphere, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1, and LiPF6 was added and mixed uniformly. 3 wt% fluoroethylene carbonate and 2 wt% adiponitrile were added and mixed uniformly to obtain an electrolyte solution. The LiPF6 concentration was 1.15 mol / L.

[0085] 4. Preparation of separator A 12 μm thick polyethylene (PE) porous polymer film was used as the separator.

[0086] 5. Preparation of Lithium-ion Battery The positive electrode, separator, and negative electrode were stacked in this order, and a separator was placed between the positive electrode and the negative electrode to provide isolation. The battery was then wound to obtain a bare cell. After the tabs were welded, the bare cell was placed in an aluminum laminate film exterior foil, and the above-prepared electrolyte was injected into the dried bare cell. After vacuum sealing, leaving it, molding, formation, capacity measurement, and other processes, a lithium-ion battery was obtained.

[0087] Examples 2 to 16, Comparative Examples 1 and 2 Preparation of negative electrode active material The preparation process of the negative electrode active material is the same as that of Example 1, except that the content of ammonium hydrogen carbonate in preparation step S3 (the pitch-coated graphite active material and ammonium hydrogen carbonate are added in a weight ratio of 100:x) and the heating temperature parameters are adjusted to prepare the corresponding negative electrode active material, specifically see Table 1. The negative electrode, positive electrode, electrolyte, separator, and lithium ion battery were prepared in the same manner as in Example 1.

[0088] Measurement method 1. Raman spectrum measurement method The Raman spectrum of the negative electrode active material was measured using a microscopic laser Raman spectrometer (HR Evolution). Specifically, a small amount of powder was taken, placed in the center of a sample chamber, and flattened with a glass plate. The laser parameters were set to 1800 gr / mm, 532 nm, 50%, and 2 s, and the Raman characteristic peak spectrum of the sample was measured.

[0089] 2. Method for measuring the specific surface area of ​​negative electrode active material The specific surface area of ​​the negative electrode active material was measured by the nitrogen adsorption / desorption method using a specific surface area analyzer (Tristar II 3020M). Specifically, the negative electrode active material sample was dried in a vacuum drying oven, placed in a sample tube, and measured with the analyzer. Confirming the basal plane ratio of graphite: The edge and basal planes in graphite have different gas adsorption energies, with the adsorption energy of the edge planes being 200~50 e / k, while the adsorption energy of the basal planes is generally 50~80 e / k. In the process of measuring the specific surface area, the basal plane ratio can be obtained by fitting the specific surface areas corresponding to the different adsorption energies using software.

[0090] 3. Measurement method of capacity per gram and initial coulombic efficiency of lithium-ion batteries The lithium-ion battery was discharged at 0.05C to 5.0mV, discharged at 50μA to 5.0mV, discharged at 20μA to 5.0mV, and charged at 0.1C to 2.0V. The capacity of the lithium-ion battery was recorded and used as the capacity per gram. The capacity per gram of the first charge divided by the capacity per gram of the first discharge gives the initial coulombic efficiency. 0.05C means a current value 0.05 times the designed capacity per gram, and 0.1C means a current value 0.1 times the designed capacity per gram.

[0091] 4. Measurement method for thickness expansion rate of lithium-ion batteries during cycling The thickness of the lithium-ion battery was measured at 3.95 V using a micrometer at 25°C and designated as H0. The lithium-ion battery was charged and discharged for 500 cycles at a rate of 1.5 C, during which the thickness of the lithium-ion battery was measured at a voltage of 4.45 V every 50 cycles and designated as H0. n The cycle thickness expansion rate of the lithium ion battery was calculated using the following formula. The cycle thickness expansion rate corresponding to the number of cycles = (H n -H0) / H0 × 100%.

[0092] Measurement results Table 1 shows the process parameters for the surface treatment of the negative electrode active material and the measurement results of related performance.

[0093] [Table 1]

[0094] As can be seen from Examples 1 to 4, 5 to 8, 9 to 12, and 13 to 16, at a relatively low treatment temperature of 300°C, increasing the amount of ammonium bicarbonate added increased the CO2 gas flow rate due to decomposition, resulting in a slight increase in the half-width of the D and G peaks in the Raman spectra of the negative electrode active material. This indicates an increase in the degree of disorder on the active material surface and a slight decrease in crystallinity, which is related to slight oxidation on the active material surface and destruction of the crystalline structure. The effect of gas flow rate is not clear after increasing the treatment temperature. This indicates that, provided the gas flow rate is sufficient, there is little difference in the degree of oxidation reaction on the material surface. Similar conclusions can be drawn from other performance parameters, such as the specific surface area and capacity per gram of the active material. Furthermore, as can be seen from Examples 1 to 4, the slight improvement in the initial Coulombic efficiency of the material is related to slight oxidation at low temperatures and the reduction of some -OH functional groups on the graphite surface, which are prone to side reactions with the electrolyte.

[0095] As can be seen from Examples 2, 6, 10, and 14, ensuring consistent amounts of ammonium bicarbonate significantly increased the half-width of the D and G peaks in the Raman spectra of the active materials after increasing the temperature (similar conclusions can be drawn from Examples 3, 7, 11, and 15, as well as Examples 4, 8, 12, and 16). Therefore, increasing the temperature significantly accelerated the extent of the surface oxidation reaction. Furthermore, the specific surface area and oxygen content of the active materials significantly increased with increasing temperature, indicating that after the oxidation reaction occurred on the surface of the material, some of the C in the lattice was oxidized, resulting in the formation of several pore structures. Furthermore, the decrease in the basal plane ratio indicates that most of the reaction occurred concentrated on the edge faces of the graphite, thereby increasing the specific surface area of ​​the edge faces. These pore structures can effectively store lithium, significantly improving the capacity per gram of the material. However, the increase in specific surface area also increases side reactions between the active material and the electrolyte, which overall affects the initial coulombic efficiency.

[0096] As can be seen from Comparative Examples 1 and 2, decreasing the amount of ammonium bicarbonate and the reaction temperature reduced the half-width of the G peak in the Raman spectrum of the active material. This sharpened the peak, indicating a high degree of crystallinity in the material. Furthermore, the material's small specific surface area and low capacity per gram indicated a weak oxidation reaction. After increasing the temperature and the amount of ammonium bicarbonate, the oxidation reaction of the active material became abnormally intense, and the intensity ratio of the D peak to the G peak in the Raman spectrum, which characterizes the degree of defects on the material's surface, increased significantly. While the capacity per gram improved significantly, the initial coulombic efficiency decreased significantly, which is detrimental to improving the energy density of lithium-ion batteries.

[0097] Table 2 shows the effects of the heating time and the amount of sample loaded in the heating device on the tap density, compressed density, specific surface area, button battery capacity, and cycle thickness expansion rate of the negative electrode active material in the preparation of the negative electrode active material.

[0098] The negative electrode active materials of Examples 17 to 32 were obtained based on the preparation conditions for the negative electrode active material of Example 9 by adjusting the heating time under a nitrogen atmosphere and the furnace loading rate in step S3.

[0099] The furnace loading rate is the ratio of the volume of powder actually filled to the total volume inside the furnace of the heating device.

[0100] B1 is the specific surface area of ​​the negative electrode active material before pressure is applied, and B2 is the specific surface area after a pressure of 1 ton is applied. The method for applying pressure to the negative electrode active material is as follows: Using an electronic pressure tester (SUNS UTM7305), 1.0±0.05g of negative electrode active material powder is placed on a 13mm diameter mold, a pressure of 1 ton is applied to the negative electrode active material powder, and this is maintained for 5 seconds, after which the pressure is released and the powder is removed.

[0101] B11 is the specific surface area measured by disassembling a lithium-ion battery after discharging it to 3V, removing the negative electrode piece, and scraping off the powder. C1 is the capacity per gram measured by disassembling a lithium-ion battery after discharging it to 3V, removing the negative electrode piece, and inserting the Li piece into a button cell half battery. C2 is the capacity per gram measured by discharging the lithium-ion battery to 0mV. The specific discharge procedure is as follows: discharge at 0.05C to 5.0mV or 0mV, discharge at 50μA to 5.0mV or 0mV, discharge at 20μA to 5.0mV or 0mV, and charge at 0.1C to 2.0V. The capacity of the lithium-ion battery at each stage was recorded and used as the capacity per gram. 0.05C refers to a current value 0.05 times the designed capacity per gram, and 0.1C refers to a current value 0.1 times the designed capacity per gram.

[0102] [Table 2]

[0103] Comparing Examples 17-20, 21-24, 25-28, and 29-32, it can be seen that, when the heating time is unchanged, increasing the furnace loading ratio increases the tap density of the negative electrode active material, decreases the pressed density, and decreases the C2-C1 capacity. This indicates that the degree of oxidation of the negative electrode active material is slightly weakened. This is related to insufficient contact between the powder and gas when the material loading is high. Furthermore, the cycle expansion rate of lithium-ion batteries containing this negative electrode active material also decreases slightly, indicating that the degree of oxidation affects the structural stability of the material.

[0104] Comparing Examples 17, 21, 25, and 29, 18, 22, 26, and 30, 19, 23, 27, and 31, and Examples 20, 24, 28, and 32, respectively, reveals that the compressed density of the negative electrode active material significantly improved after the reaction time was extended. However, the change in specific surface area (B2-B1) / B1 between before and after compression also increased, resulting in an increase in the expansion rate of the lithium-ion battery. Furthermore, the capacity per gram of the negative electrode active material between 5.0 mV and 0 mV significantly improved. The difference in performance of the negative electrode active material is related to the extent and location of the oxidation reaction. Vigorous oxidation reduces defects such as dislocations on the surface of the negative electrode active material, presumably making interlayer shrinkage and slippage more likely after compression, resulting in an increase in the compressed density of the negative electrode active material powder. Furthermore, these oxidation reactions react with and consume the binder between the secondary particles of the negative electrode active material, which makes the structure of the secondary particles unstable, resulting in increased expansion in the lithium ion battery.

[0105] Throughout the specification, references to "some embodiments," "some of the embodiments," "one embodiment," "another example," "an example," "a specific example," or "some of the examples" mean that at least one embodiment or example of the present invention includes the particular feature, structure, material, or characteristic described in that embodiment or example. Thus, the appearances of, for example, "some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "example" throughout the specification do not necessarily refer to the same embodiment or example of the present invention. Furthermore, particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0106] Although exemplary embodiments have been described and illustrated, those skilled in the art should understand that the above-described embodiments are not to be construed as limiting the present invention, and that modifications, substitutions, and alterations to the embodiments are possible without departing from the spirit, principle, and scope of the present invention.

Claims

1. A negative electrode active material, Contains graphite and amorphous carbon, The negative electrode active material has a Raman spectrum of 1.6≦W Ｄ / W Ｇ ≦2.6 is satisfied, W Ｄ is the 1340 cm in the Raman spectrum －１ ~1370cm －１ and the half-width of the D peak is within the range of 40 cm －１ ≦W Ｄ ≦100cm －１ Fulfilling W Ｇ is the 1570 cm in the Raman spectrum －１ ~1590cm －１ and the half-width of the G peak is within the range of 15 cm －１ ≦W Ｇ ≦50cm －１ Fulfilling When the specific surface area of ​​the negative electrode active material is B1, B1 is 1.21 m ２ / g≦B1≦3.98m ２ / g, B1 is the specific surface area of ​​the negative electrode active material before compression, a negative electrode active material, wherein the mass content of oxygen in the negative electrode active material is 2.1% to 4.0% as determined by an X-ray photoelectron spectroscopy test.

2. W Ｄ and W Ｇ However, 1.7≦W Ｄ / W Ｇ The negative electrode active material according to claim 1 , wherein the negative electrode active material satisfies the following condition: ≦2.

5.

3. The negative electrode active material is (i) W Ｄ and W Ｇ However, 2≦W Ｄ / W Ｇ ≦2.5 is satisfied, (ii) W Ｄ is 40cm －１ ≦W Ｄ ≦60cm －１ and (iii) W Ｇ is 15cm －１ ≦W Ｇ ≦35cm －１ and (iv) The negative electrode active material according to claim 1, wherein the negative electrode active material satisfies at least one of the following: 0.08≦ID / IG≦1.2, where ID is the intensity of the D peak, and IG is the intensity of the G peak.

4. The negative electrode active material is (v) the negative electrode active material has a maximum possible pore size of 2.5 nm to 3.5 nm, and the ratio of the pore volume of the maximum possible pore size of the negative electrode active material to the pore volume of the negative electrode active material is 3% to 8%; (vi) the negative electrode active material includes a base surface and an end surface, and the ratio of the specific surface area of ​​the base surface to the specific surface area of ​​the negative electrode active material is 40% to 70%; (vii) the negative electrode active material includes a base surface and an end surface, and a roughness of the end surface is greater than a roughness of the base surface.

5. The negative electrode active material is (viii) the negative electrode active material has a maximum possible pore size of 2.7 nm to 3.3 nm, and the ratio of the pore volume of the maximum possible pore size of the negative electrode active material to the pore volume of the negative electrode active material is 3.5% to 7%; (ix) the ratio of the specific surface area of ​​the base surface to the specific surface area of ​​the negative electrode active material is 45% to 65%; (x) when a specific surface area of ​​the negative electrode active material after applying a pressure of 1 t is defined as B2, B2 and B1 satisfy (B2−B1) / B1×100%≦80%.

6. The negative electrode active material is (xii) The tap density of the negative electrode active material is 0.90 g / cm ３ ~1.05g / cm ３ And, (xiii) The negative electrode active material has a powder compression density of 1.9 g / cm under a pressure of 5 tons. ３ ~2.05g / cm ３ 2. The negative electrode active material according to claim 1, wherein at least one of the following conditions is satisfied:

7. The method for producing the negative electrode active material according to claim 1, The manufacturing method includes: S1: Providing a graphite material; S2: Mixing the graphite material in S1 with a carbonaceous precursor to obtain a graphite material coated with the carbonaceous precursor; S3: mixing the graphite material coated with the carbonaceous precursor in S2 with bicarbonate to obtain a mixture, and heat-treating the mixture to obtain the negative electrode active material.

8. a negative electrode, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, An electrochemical device, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 6.

9. The specific surface area B11 of the negative electrode active material is 4.35 m ２ / g to 5.9m ２ / g, and B11 is the specific surface area measured by disassembling the electrochemical device after discharging it to 3 V, removing the negative electrode piece, and scraping off the powder on the negative electrode piece; and / or The electrochemical device according to claim 8, wherein a charge-discharge test is performed using a button battery comprising the negative electrode and lithium metal, and the button battery satisfies C2-C1≧1 when the reversible capacity at 0.005 V to 2 V is C1 mAh / g and the reversible capacity at 0 V to 2 V is C2 mAh / g.

10. An electronic device comprising the electrochemical device of claim 8.

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