Negative electrode material, secondary battery, and electronic device

Abstract

Provided is a negative electrode material including a carbon-based material, wherein, through a thermogravimetric test, the negative electrode material has an exothermic peak in a temperature range of 600 DEG C to 800 DEG C in an air atmosphere. The negative electrode material of the present application has excellent kinetic performance, which can effectively improve the discharge rate performance of a secondary battery including the negative electrode material.

Description

TECHNICAL FIELD

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

[0002] With electrochemical devices such as lithium ion batteries becoming widely used energy systems, there are more and more sub-directions, one of which is the fast charging and discharging application. Therefore, the development of energy systems with superior charging and discharging performance is crucial for their large-scale application in transportation, power grid, wind and solar systems.

[0003] However, fast charging and discharging of the battery can cause some problems, such as when charging and discharging at a large rate, due to the existence of the internal resistance of the battery itself, the temperature rises rapidly during charging and discharging, affecting the rate and safety performance. The existing technology improves the battery impedance mainly by reducing the coating thickness of the pole piece and reducing the particle size of the negative active material, but this way will significantly reduce the energy density of the battery, reduce the endurance of the battery and the cost is higher. SUMMARY

[0004] In view of the above problems existing in the prior art, the present application provides a negative electrode material and a secondary battery comprising the same to improve the kinetics of the carbon-based negative electrode material and thus improve the discharge rate performance of the secondary battery comprising the same.

[0005] In a first aspect, the present application provides a negative electrode material comprising a carbon-based material, wherein the negative electrode material has an exothermic peak in the temperature range of 600-800°C in air atmosphere by thermogravimetric test. The exothermic peak of the negative electrode material in the temperature range of 600-800°C is related to the reactivity of the negative electrode material with active ions such as lithium ions, and the exothermic peak of the negative electrode material of the present application in the above range can react faster with lithium ions, which is beneficial to improve the rate performance of the secondary battery. In some embodiments, the negative electrode material has an exothermic peak in the temperature range of 650-750°C.

[0006] In some embodiments, the preparation method of the carbon-based material comprises: sequentially preparing a graphite composite material, spheroidizing treatment, coating treatment and carbonization treatment for a graphite material, wherein the graphite material comprises at least one of natural graphite or artificial graphite.

[0007] In some embodiments, the preparation process of the graphite composite material comprises: dissolving one or more of natural graphite and artificial graphite and polymethyl methacrylate (PMMA) in N-N dimethylformamide (DMF) at the same time, stirring at a temperature of 50-80°C for 10-14h, collecting the precipitate by filtration, washing with deionized water and ethanol for 2-4 times, and completely drying at a temperature of 60-90°C to obtain a graphite composite material precursor; heating the graphite composite material precursor in a tube furnace to 1000-1200°C at a heating rate of 8-16°C / min, then introducing CH4 / C2H2 / H2 mixed gas (proportions are 5-10:5-10:80-85, respectively) into the tube furnace, maintaining for 8-12h, and then naturally cooling to room temperature, thereby obtaining the graphite composite material.

[0008] In some embodiments, the spheroidization process comprises: applying continuous impact force, compression force and shearing force between the particles from the rotating disc, the inner wall and the particles to the mixture containing the graphite composite material and the dispersant solution, so that the graphite composite material is spheroidized. In some embodiments, the spheroidization time is 10-20min. In some embodiments, the mixture is subjected to collision, friction, shearing and bending folding by applying impact force, compression force and shearing force to the mixture using a spheroidization device, thereby removing the corners of the graphite composite material while achieving the effect of fixing the fine powder to the large particles. In some embodiments, the spheroidization device is a mixer granulator. In some embodiments, the rotating speed of the spheroidization device is 30-50Hz. In some embodiments, the dispersant solution is an aqueous solution of carboxymethyl cellulose (CMC). In some embodiments, the mass content of carboxymethyl cellulose in the dispersant solution is 0.5-2%. In some embodiments, the mass content of the dispersant solution is 5-20% based on the mass of the graphite material.

[0009] In some embodiments, the coating process comprises: coating the spheroidized graphite composite material with pitch. In some embodiments, the mass content of pitch is 2-15% based on the mass of the spheroidized graphite composite material. In some embodiments, the carbonization treatment temperature is 900-1500°C.

[0010] In some embodiments, the negative electrode material satisfies 0.2≤Id / Ig≤0.5 by Raman test, where Id is the intensity of the 1350cm -1 peak in the Raman spectrum, and Ig is the intensity of the 1580cm -1The intensity of the peak. The Id / Ig ratio can represent the defect degree of the negative electrode material, and the larger the value, the higher the defect degree. High defect degree can increase the deintercalation channel of active ions, improve the deintercalation speed of active ions, and thus improve the kinetic performance of the negative electrode material. However, too many defects can reduce the initial efficiency, cycle, storage and other performances of the secondary battery. When the Id / Ig ratio is in the above range, the secondary battery can exhibit good kinetics, and the initial efficiency, cycle and other performances will not be significantly reduced. In some embodiments, 0.3≤Id / Ig≤0.5.

[0011] In some embodiments, the negative electrode material satisfies: 0.002 cm 3 / g≤S≤0.035 cm 3 / g by nitrogen adsorption desorption test, wherein S is the adsorption volume of the pores with a pore size of 3 nm to 35 nm in the negative electrode material. The adsorption volume of the pores can represent the amount of mesopores in the structure of the negative electrode material. The larger the adsorption volume, the higher the proportion of mesopores, and the more pores in the negative electrode material, which can increase the adsorption and intercalation of lithium of active ions and improve the capacity of the negative electrode material. However, too many pores can adversely affect the initial efficiency, cycle and other performances of the secondary battery. The adsorption volume of the pores with a pore size of 3 nm to 35 nm in the negative electrode material of the present application is in the above range, and the secondary battery has high energy density and its initial efficiency, cycle and other performances will not be significantly reduced. In some embodiments, 0.004 cm 3 / g≤S≤0.03 cm 3 / g.

[0012] In some embodiments, the ratio of the diffraction peak area C004 of the 004 crystal face to the diffraction peak area C110 of the 110 crystal face of the negative electrode material satisfies 1≤C004 / C110≤6 by X-ray diffraction method. The ratio of C004 / C110 is a parameter reflecting the degree of crystal orientation of the negative electrode material, and the larger the value of C004 / C110, the higher the degree of crystal orientation, and the more limited the deintercalation of active ions in the negative electrode material. The smaller the C004 / C110, the lower the degree of crystal orientation, and the active ions can deintercalate in multiple directions of the negative electrode material. The C004 / C110 of the negative electrode material of the present application is in the above range, and the active ions can quickly deintercalate in the negative electrode material, thereby further improving the discharge rate performance of the secondary battery. In some embodiments, 1≤C004 / C110≤3.

[0013] In some embodiments, the negative electrode material has a diffraction peak a in the range of 2θ of 43° to 44° and a diffraction peak b in the range of 2θ of 45° to 47° in the X-ray diffraction spectrum by X-ray diffraction method, wherein the peak intensity of the diffraction peak a is I a , the peak intensity of the diffraction peak b is I b , and 2≤I a / I b The diffraction peak a and the diffraction peak b of the negative electrode material are related to the rhombohedral (3R) graphene layer stacking sequence in graphite. The diffraction peak a and the diffraction peak b appear in the negative electrode material of the application, and the peak intensity of the diffraction peak a is higher than that of the diffraction peak b, which represents that the rhombohedron structure exists in the formed graphite, and the lithium deintercalation can be more easily carried out. The ratio of the peak intensity of the diffraction peak a to the peak intensity of the diffraction peak b in the negative electrode material of the application is within the above range, and the direct current resistance of the negative electrode material is significantly reduced, thereby further improving the discharge rate performance of the secondary battery.

[0014] In some embodiments, the specific surface area of the negative electrode material is 4 cm 2 / g to 20 cm 2 / g. The smaller the specific surface area of the negative electrode material, the smaller the area of the negative electrode material in contact with the electrolyte, thereby reducing the active ions consumed by the secondary battery when the SEI film is formed for the first time, and increasing the initial efficiency. However, when the specific surface area is too small, the electrolyte infiltration and active diffusion become difficult, thereby affecting the kinetic performance of the secondary battery. The specific surface area of the negative electrode material of the application is within the above range, and the secondary battery has high initial efficiency and kinetic performance is not significantly reduced. In some embodiments, the specific surface area of the negative electrode material is 4 cm 2 / g to 10 cm 2 / g.

[0015] In some embodiments, the Dv50 of the negative electrode material satisfies: 5 μm ≤ Dv50 ≤ 25 μm. The larger the Dv50 of the negative electrode material, the larger the corresponding gram capacity, but too large will affect the kinetic performance. The Dv50 of the negative electrode material of the application is within the above range, which can ensure that the negative electrode material has a relatively high gram capacity and the kinetic performance is not significantly reduced. In some embodiments, 10 μm ≤ Dv50 ≤ 20 μm.

[0016] In some embodiments, the graphitization degree of the negative electrode material is 94% to 96%. The graphitization degree of the negative electrode material is within the above range, and the negative electrode material has high capacity and high compaction density, which can further improve the gram capacity of the negative electrode material. In some embodiments, the graphitization degree of the negative electrode material is 94.5% to 96%.

[0017] In a second aspect, the application provides a secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material of the first aspect.

[0018] In some embodiments, the negative electrode further comprises an electrically conductive coating layer between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the electrically conductive coating layer comprises at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotube and graphene. The electrically conductive coating layer can play a role of conducting electrons, and the charge transfer impedance is significantly reduced, thereby further improving the kinetic performance of the secondary battery. In some embodiments, the thickness of the electrically conductive coating layer is 0.5 μm to 1.2 μm.

[0019] In a third aspect, the present application provides an electronic device comprising the secondary battery of the second aspect.

[0020] The present application improves the discharge rate performance of the secondary battery comprising the negative electrode material comprising the carbon-based material by improving the kinetic performance of the negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The thermogravimetric curve of the negative electrode material of Example 1 and Comparative Example 1 of the present application.

[0022] Figure 2 The capacity retention rate curve of the lithium ion battery of Example 1 and Comparative Example 1 of the present application at different rates is shown. DETAILED DESCRIPTION

[0023] For the sake of brevity, the present application discloses only some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or single numerical value can itself serve as a lower limit or upper limit to combine with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0024] In the description of the present application, unless otherwise specified, "above", "below" include the number itself.

[0025] Unless otherwise defined, the terms used in the present application have the commonly understood meanings as understood by those skilled in the art. Unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various measuring methods commonly used in the art (for example, can be tested according to the methods given in the examples of the present application).

[0026] The list of items connected by “at least one of,” “at least one,” “at least one of the items in,” or other similar phrases can mean any combination of the listed items. For example, if A and B are listed, the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if A, B, and C are listed, the phrase “at least one of A, B, and C” means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0027] The present application is further illustrated by the following specific embodiments. It is to be understood that these embodiments are merely illustrative of the present application and do not limit the scope of the present application.

[0028] I. Negative electrode material

[0029] The negative electrode material provided by the present application includes a carbon-based material, and through thermogravimetric testing, the negative electrode material has an exothermic peak in the temperature range of 600-800°C in an air atmosphere. The exothermic peak of the negative electrode material in the temperature range of 600-800°C is related to the reactivity of the negative electrode material with active ions such as lithium ions, and the exothermic peak of the negative electrode material of the present application is in the above range, which can more easily react with lithium ions, and is beneficial to improve the rate performance of the secondary battery. In some embodiments, the negative electrode material has an exothermic peak at 610°C, 620°C, 630°C, 640°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 760°C, 770°C, 780°C, 790°C, or a range consisting of any two of these values. In some embodiments, the negative electrode material has an exothermic peak in the temperature range of 650-750°C. In the present application, the negative electrode material has an exothermic peak in the temperature range of 600-800°C means that the peak temperature of the exothermic peak is in the temperature range of 600-800°C.

[0030] In some embodiments, the method for preparing the carbon-based material includes sequentially performing graphite composite material preparation, spheroidization treatment, coating treatment, and carbonization treatment on one or more materials of natural graphite and artificial graphite.

[0031] In some embodiments, the preparation process of the graphite composite material comprises dissolving one or more of natural graphite and artificial graphite and polymethyl methacrylate (PMMA) in N-N dimethylformamide (DMF) at the same time, stirring at a temperature of 50-80 °C for 10-14 h, collecting the precipitate by filtration, washing with deionized water and ethanol for 2-4 times, and completely drying at a temperature of 60-90 °C to obtain a graphite composite material precursor. The graphite composite material precursor is heated to 1000-1200 °C in a tube furnace at a heating rate of 8-16 °C / min, then a CH4 / C2H2 / H2 mixed gas (proportions of 5-10:5-10:80-85, respectively) is introduced into the tube furnace, and maintained for 8-12 h before naturally cooling to room temperature, thereby obtaining the final graphite composite material.

[0032] In some embodiments, the spheroidization process comprises applying continuous impact force, compression force and shearing force from the rotating disc, the inner wall and the particles to the mixture comprising the graphite composite material and the dispersant solution, so that the graphite composite material is spheroidized. In some embodiments, the spheroidization time is 10-20 min, for example 12 min, 14 min, 16 min or 18 min. In some embodiments, the mixture is subjected to collision, friction, shearing and bending folding by applying impact force, compression force and shearing force to the mixture using a spheroidization device, thereby removing the corners of the graphite composite material while achieving the effect of fixing the fine powder to the large particles. In some embodiments, the spheroidization device is a mixing granulator. In some embodiments, the rotational speed of the spheroidization device is 30-50 Hz, for example 35 Hz, 40 Hz or 45 Hz.

[0033] In some embodiments, the dispersant solution is an aqueous solution of carboxymethyl cellulose (CMC). In some embodiments, the mass content of carboxymethyl cellulose in the dispersant solution is 0.5-2%, for example 0.7%, 1.0%, 1.3%, 1.5% or 1.7%. In some embodiments, the mass content of the dispersant solution is 5-20% based on the mass of the graphite material, for example 7%, 10%, 13%, 15%, 17% or 19%.

[0034] In some embodiments, the coating process comprises: coating the spheroidized graphite composite with pitch. In some embodiments, the content of pitch is 2% to 15% by mass, for example 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or 14% based on the mass of the spheroidized graphite composite. In some embodiments, the carbonization temperature is 900°C to 1500°C, for example 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C or 1450°C. In some embodiments, the carbonization time is 3h to 10h, for example 4h, 5h, 6h, 7h, 8h or 9h.

[0035] In some embodiments, the negative electrode material satisfies: 0.2≤Id / Ig≤0.5 by Raman test, wherein Id is the intensity of the 1350cm -1 peak in the Raman spectrum, and Ig is the intensity of the 1580cm -1 peak in the Raman spectrum. The Id / Ig ratio can represent the defect degree of the negative electrode material. The larger the value, the higher the defect degree. High defect degree can increase the deintercalation channel of active ions, improve the deintercalation speed of active ions, and thus improve the kinetic performance of the negative electrode material. However, too many defects will reduce the performance of the secondary battery such as initial efficiency, cycle, storage, etc. When the Id / Ig ratio is within the above range, the secondary battery can exhibit good kinetics, and its performance such as initial efficiency and cycle will not be significantly reduced. In some embodiments, Id / Ig is 0.23, 0.25, 0.27, 0.29, 0.33, 0.35, 0.37, 0.4, 0.43, 0.45, 0.47 or a range formed by any two of these values. In some embodiments, 0.3≤Id / Ig≤0.5.

[0036] In some embodiments, the negative electrode material satisfies: 0.002cm 3 / g≤S≤0.035cm 3 / g by nitrogen adsorption-desorption test, wherein S is the adsorption volume of pores with a pore size of 3nm to 35nm in the negative electrode material. The adsorption volume of pores can represent the amount of mesopores in the structure of the negative electrode material. The larger the adsorption volume, the higher the proportion of mesopores, and the more pores in the negative electrode material, which can increase the adsorption and intercalation of lithium of active ions, and thus improve the capacity of the negative electrode material. However, too many pores will adversely affect the performance of the secondary battery such as initial efficiency and cycle. The adsorption volume of pores with a pore size of 3nm to 35nm in the negative electrode material of the present application is within the above range, and the secondary battery has high energy density and its performance such as initial efficiency and cycle will not be significantly reduced. In some embodiments, S is 0.006cm 3 / g, 0.008cm3 / g, 0.01 cm 3 / g, 0.011 cm 3 / g, 0.012 cm 3 / g, 0.013 cm 3 / g, 0.014 cm 3 / g, 0.015 cm 3 / g, 0.016 cm 3 / g, 0.017 cm 3 / g, 0.018 cm 3 / g, 0.019 cm 3 / g, 0.02 cm 3 / g, 0.021 cm 3 / g, 0.022 cm 3 / g, 0.023 cm 3 / g, 0.024 cm 3 / g, 0.025 cm 3 / g, 0.026 cm 3 / g, 0.027 cm 3 / g, 0.028 cm 3 / g, 0.029 cm 3 / g, 0.031 cm 3 / g, 0.032 cm 3 / g, 0.033 cm 3 / g, 0.034 cm 3 / g or a range consisting of any two of these values. In some embodiments, 0.004 cm 3 / g < S < 0.03 cm 3 / g.

[0037] In some embodiments, X-ray diffraction tests are performed to determine that the ratio of the diffraction peak area C004 (004 crystal plane) to the diffraction peak area C110 (110 crystal plane) of the negative electrode material satisfies 1 ≤ C004 / C110 ≤ 6. The C004 / C110 ratio is a parameter reflecting the crystal orientation degree of the negative electrode material. A larger C004 / C110 value indicates a higher crystal orientation degree, and a more limited intercalation / deintercalation surface for active ions in the negative electrode material. Conversely, a smaller C004 / C110 value indicates a lower crystal orientation degree, and active ions can intercalate / deintercalate in multiple directions within the negative electrode material. In some embodiments, C004 / C110 is a range of 1.2, 1.4, 1.6, 1.8, 2.3, 2.5, 2.7, 3.0, 3.3, 3.5, 3.7, 4.0, 4.3, 4.5, 4.7, 5.0, 5.3, 5.5, 5.7, or any combination of these values. In this application, the C004 / C110 ratio of the negative electrode material is within the aforementioned range, allowing active ions to rapidly intercalate and deintercalate within the negative electrode material, thereby further improving the discharge rate performance of the secondary battery. In some embodiments, 1 ≤ C004 / C110 ≤ 3.

[0038] In some embodiments, X-ray diffraction testing reveals that the negative electrode material exhibits diffraction peak a in the range of 43° to 44° at 2θ, and diffraction peak b in the range of 45° to 47° at 2θ, wherein the peak intensity of diffraction peak a is I. a The peak intensity of diffraction peak b is I b ,2≤I a / I b ≤6. In some implementations, I a / I b The values ​​are 2.3, 2.5, 2.7, 3.0, 3.3, 3.5, 3.7, 4.0, 4.3, 4.5, 4.7, 5.0, 5.3, 5.5, 5.7, 5.9, or any combination of these values. The diffraction peaks a and b of the negative electrode material are related to the rhombic (3R) graphene layer stacking sequence in the graphite. The negative electrode material of this application exhibits diffraction peaks a and b, and the peak intensity of diffraction peak a is higher than that of diffraction peak b, indicating the presence of an orthorhombic hexahedral structure in the formed graphite, which facilitates lithium insertion / extraction. In the negative electrode material of this application, the ratio of the peak intensity of diffraction peak a to that of diffraction peak b is within the above range, significantly reducing the DC internal resistance of the negative electrode material, thereby further improving the discharge rate performance of the secondary battery.

[0039] In some embodiments, the specific surface area of ​​the negative electrode material is 4 cm². 2 / g to 20cm 2 / g. The smaller the specific surface area of the negative electrode material, the smaller the area of the negative electrode material in contact with the electrolyte, thereby reducing the active ions consumed by the secondary battery when forming the SEI film for the first time, and increasing the initial efficiency. However, when the specific surface area is too small, the electrolyte is difficult to infiltrate and the active diffusion is difficult, thereby affecting the kinetic performance of the secondary battery. The specific surface area of the negative electrode material in the present application is within the above range, and the secondary battery has high initial efficiency and the kinetic performance is not significantly reduced. In some embodiments, the specific surface area of the negative electrode material is 5 cm 2 / g, 5.5 cm 2 / g, 6 cm 2 / g, 6.5 cm 2 / g, 7 cm 2 / g, 7.5 cm 2 / g, 8 cm 2 / g, 8.5 cm 2 / g, 9 cm 2 / g, 9.5 cm 2 / g, 10.5 cm 2 / g, 11 cm 2 / g, 12 cm 2 / g, 13 cm 2 / g, 14 cm 2 / g, 15 cm 2 / g, 16 cm 2 / g, 17 cm 2 / g, 18 cm 2 / g, 19 cm 2 / g, or a range consisting of any two of these values. In some embodiments, the specific surface area of the negative electrode material is 4 cm 2 / g to 10 cm 2 / g.

[0040] In some embodiments, the Dv50 of the negative electrode material satisfies: 5 μm≤Dv50≤25 μm. The larger the Dv50 of the negative electrode material, the larger the corresponding gram capacity, but too large will affect the kinetic performance. The Dv50 of the negative electrode material in the present application is within the above range, which can ensure that the negative electrode material has a relatively high gram capacity and the kinetic performance is not significantly reduced. In some embodiments, the Dv50 is 6 μm, 8 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 21 μm, 22 μm, 23 μm, 24 μm, or a range consisting of any two of these values. In some embodiments, 10 μm≤Dv50≤20 μm. In the present application, Dv50 represents that 50% of the particles in the negative electrode material have a particle size less than the value on a volume basis.

[0041] In some embodiments, the graphitization degree of the negative material is 94% to 96%. The negative material has a high capacity and a high compaction density, and the graphitization degree of the negative material is within the above range, which can further improve the gram capacity of the negative material. In some embodiments, the graphitization degree of the negative material is 94.3%, 94.7%, 95%, 95.3%, 95.5%, or 95.7%. In some embodiments, the graphitization degree of the negative material is 94.5% to 96%

[0042] Secondary battery

[0043] The secondary battery provided in the present application comprises a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative material of the first aspect.

[0044] In some embodiments, the negative electrode further comprises a conductive coating layer between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the conductive coating layer comprises at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotube, and graphene. The conductive coating layer can play a role in conducting electrons, and the charge transfer impedance is significantly reduced, thereby further improving the kinetic performance of the secondary battery. In some embodiments, the thickness of the conductive coating layer is 0.5 μm to 1.2 μm. In some embodiments, the thickness of the conductive coating layer is 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, or a range consisting of any two of these values.

[0045] In some embodiments, the negative electrode current collector comprises a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0046] In some embodiments, the negative electrode active material layer further comprises a binder and a conductive agent. In some embodiments, the binder comprises, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon, etc.

[0047] In some embodiments, the conductive agent comprises, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0048] The secondary battery of the present application further includes a cathode including a cathode current collector and a cathode active material layer including a cathode active material, a binder, and a conductive agent.

[0049] According to some embodiments of the present application, the cathode current collector can employ 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 base material.

[0050] According to some embodiments of the present application, the cathode 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, polyolefin, 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 fiber; a metal-based material such as a metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0051] The secondary battery of the present application further includes a separator film. The material and shape of the separator film used in the secondary battery of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer or inorganic material formed of a material stable to the electrolyte of the present application, etc.

[0052] For example, the separator film can include a base layer and a surface treatment layer. The base layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base 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 non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0053] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing 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).

[0054] The secondary battery according to the present application further includes an electrolyte. The electrolyte used in the present application can be any electrolyte known in the art.

[0055] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and an optional additive. The organic solvent used in the electrolyte according to the present application can be any organic solvent known in the art that can be used 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 used in the electrolyte according to the present application can be any additive known in the art that can be used 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, such as 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.

[0056] According to some embodiments of the present application, 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.

[0057] III. Electronic device

[0058] The present application further provides an electronic device comprising the secondary battery of the second aspect of the present application.

[0059] 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 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, an illuminating appliance, a toy, a game machine, a timepiece, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0060] In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0061] Examples and Comparative Examples

[0062] Example 1

[0063] Preparation of anode material

[0064] 95 g of artificial graphite was selected and dissolved in 100 mL of N-N dimethylformamide (DMF) with 5 g of polymethyl methacrylate (PMMA) at 70°C for 12 h. The precipitate was collected by filtration, and the precipitate was washed with deionized water and ethanol for 2 times, and completely dried at 80°C to obtain a graphite composite precursor. The graphite composite precursor was heated to 1100°C at a heating rate of 10°C / min in a tube furnace, and then CH4 / C2H2 / H2 mixed gas (proportions are 5:10:85, respectively) was introduced into the tube furnace, and maintained for 10 h, and then naturally cooled to room temperature, thereby obtaining the final graphite composite material. The graphite composite material was mixed with a 10% proportion of a 1% solid content CMC aqueous solution, and spheroidized in a spheroidization device at a rotation speed of 40 Hz for 15 minutes. After spheroidization, 5% pitch was used for coating treatment, and finally the coated mixture was heated to 1000°C at a rate of 5°C / min, and maintained for 5 h, and then naturally cooled to room temperature, thereby obtaining a carbon-based material, i.e. an anode material.

[0065] Preparation of anode

[0066] The negative electrode material prepared above, a binder styrene-butadiene rubber (abbreviated as SBR), and a thickening agent sodium carboxymethyl cellulose (abbreviated as CMC) are mixed in a weight ratio of 97:1.5:1.5 with a proper amount of deionized water as a solvent, and stirred to form a uniform negative electrode slurry. The slurry is coated on a current collector Cu foil with a conductive coating thickness of 1 μm, dried, and cold-pressed to obtain a negative electrode sheet.

[0067] Preparation of a positive electrode

[0068] Lithium cobalt oxide (chemical formula: LiCoO2) is selected as a positive electrode active material, which is mixed with a conductive agent acetylene black and a binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96.3:2.2:1.5 in a proper amount of N-methyl pyrrolidone (abbreviated as NMP) solvent, and stirred to form a uniform positive electrode slurry. The slurry is coated on an Al foil current collector, dried, and cold-pressed to obtain a positive electrode sheet.

[0069] Preparation of an electrolyte

[0070] In a dry argon glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC=2:2:3:3, followed by addition of fluoroethylene carbonate and ethylene sulfate. After dissolution and sufficient stirring, lithium salt LiPF6 is added, and the mixture is uniformly mixed to obtain an electrolyte. The mass percentage of LiPF6 is 12.5%, the mass percentage of fluoroethylene carbonate is 4%, and the mass percentage of ethylene sulfate is 2%. The mass percentages of the substances are calculated based on the mass of the electrolyte.

[0071] Preparation of a lithium ion battery

[0072] The positive electrode, a separator (a porous polyethylene polymer film), and the negative electrode are sequentially stacked with the separator between the positive electrode and the negative electrode to play a role of isolation, and then wound to obtain an electrode assembly. After welding of the tab, the electrode assembly is placed in an outer packaging foil aluminum plastic film, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum packaging, standing, formation, shaping, capacity testing, and other processes, a soft-pack lithium ion battery is obtained.

[0073] Examples 2 to 10 and Comparative Examples 1 and 2

[0074] Preparation of a negative electrode material

[0075] The negative electrode material is prepared in a similar manner to Example 1, except that the ratio of carbon-based material to PMMA, the rotation speed of the spheroidization equipment, the carbonization temperature, and the holding time are adjusted to prepare the corresponding negative electrode material. The specific preparation parameters are shown in Table a.

[0076] Table A

[0077]

[0078] Preparation of positive electrode, electrolyte and lithium ion battery is the same as Example 1.

[0079] Examples 11-20

[0080] Preparation of negative electrode material

[0081] The preparation process of the negative electrode material is similar to Example 1, except that the Id / Ig value of the negative electrode material is adjusted by adjusting the residual carbon ratio of the coated pitch. In the preparation process of Examples 11-20, the residual carbon ratio of the coated pitch is distributed as 8%, 11%, 2%, 15%, 5%, 14%, 12.5%, 3.5%, 6.5%, 9.5%.

[0082] Preparation of positive electrode, electrolyte and lithium ion battery is the same as Example 1.

[0083] Examples 21-30

[0084] Preparation of negative electrode material

[0085] The preparation process of the negative electrode material is similar to Example 16, except that the 3-35 nm cumulative pore volume value of the negative electrode material is adjusted by adjusting the heating rate of the carbonization process. In the preparation process of Examples 21-30, the heating rate of the carbonization process is distributed as 2.5℃ / min, 9.5℃ / min, 8℃ / min, 9℃ / min, 6.5℃ / min, 5℃ / min, 1.5℃ / min, 8.5℃ / min, 10℃ / min, 2.5℃ / min.

[0086] Preparation of positive electrode, electrolyte and lithium ion battery is the same as Example 16.

[0087] Examples 31-40

[0088] The preparation process of the negative electrode material is similar to Example 23, except that the C004 / C110 value of the negative electrode material is adjusted by adjusting the solid content of the CMC solution, the I a / I b value of the negative electrode material is adjusted by adjusting the spheroidization time, and the specific surface area value of the negative electrode material is adjusted by adjusting the pitch coking value.

[0089] Preparation of positive electrode, electrolyte and lithium ion battery is the same as Example 23.

[0090] Test method

[0091] 1. Thermogravimetric test of negative electrode material

[0092] The negative electrode material powder is placed in a thermal gravimetric tester, the temperature range is set to 20-1000℃, the heating rate is 10℃ / min, and the gas atmosphere is air.

[0093] 2. Raman test of negative electrode material

[0094] The negative electrode material is scanned by a laser microscopic confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Co., Ltd.) to obtain the g peak and g peak of all particles in the area range. The data are processed by LabSpec software to obtain the peak intensity of the d peak and g peak of each particle, which are Id and Ig, respectively. The frequency of Id / Ig is counted with a step size of 0.02 to obtain a normal distribution graph. The (Id / Ig)max, (Id / Ig)min of these particles are counted, and the average value of Id / Ig is calculated, which is the Id / Ig value of the negative electrode active material. The laser wavelength of the Raman spectrometer can be in the range of 532-785 nm.

[0095] d peak: generally at 1350 cm -1 , caused by the symmetric stretching vibration mode of sp2 carbon atoms in the aromatic ring (structural defects);

[0096] g peak: appears at 1580 cm -1 , caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of E2g optical phonon at the center of the Brillouin zone (in-plane vibration of carbon atoms).

[0097] 3. Pore size distribution test of negative electrode material

[0098] 1) 20-30g of negative electrode material sample is weighed and pressed into a tablet. After pressing, 1.5-3.5g is weighed and loaded into the test sample tube;

[0099] 2) The sample is degassed at 200℃ for 2h;

[0100] 3) Then high-purity nitrogen is introduced, and the sample is adsorbed with nitrogen at a liquid nitrogen temperature environment until adsorption saturation;

[0101] 4) The obtained N2 adsorption-desorption curve is extracted according to the BJH model to obtain the BJH cumulative pore size volume distribution curve. The adsorption volume corresponding to the pores in different pore size ranges can be calculated.

[0102] 4. Particle size (Dv50) test of negative electrode material

[0103] The particle size test method refers to GB / T 19077-2016. The specific process is to weigh 1g of negative electrode material sample, mix it uniformly with 20mL of deionized water and a small amount of dispersant, place it in an ultrasonic device for 5min, then pour the solution into the sample injection system Hydro2000SM for testing. The testing equipment used is Mastersizer 3000 produced by Malvern Company. During the test, when the laser beam passes through the dispersed particle sample,

[0104] 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 of the particles forming the scattering spectrum. In the volume-based particle size distribution of the negative electrode material, the particle size reaching 50% of the volume accumulation from the small particle size side is the Dv50 of the negative electrode material. The particle refractive index used for testing is 1.8. One sample is tested three times, and the final particle size is the average of the three tests.

[0105] 5. Specific surface area of negative electrode material

[0106] The specific surface area test method refers to GB / T 19587-2017. The specific process is to weigh 1-8g of negative electrode material sample (the sample weighs at least 1 / 3 of the volume of the sphere) and place it in a 1 / 2 inch long tube with a ball bubble (the diameter of the spherical part of the tube is 12mm). After pretreatment at 200°C for 2h, it is placed in the testing equipment TriStar3030 (USA Mike 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.

[0107] 6. Graphitization degree of negative electrode material

[0108] High-purity silicon powder is used as a standard sample. The negative electrode material sample and the silicon standard sample are mixed in a weight ratio of 5:1. The 002 peak of the negative electrode material and the 111 peak of silicon are tested. The 002 peak of the tested negative electrode material is calibrated. The graphitization degree of the negative electrode material is indirectly calculated by the calibrated 002 interlayer spacing d002. The calculation formula is 0.3440 represents the interlayer spacing of completely non-graphitized carbon, and 0.3354 represents the interlayer spacing of ideal graphite. Both units are nm.

[0109] 7. XRD test of negative electrode material

[0110] The X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) is used to test the negative electrode material to obtain the XRD test curve. The target is Cu Kα, the voltage / current is 40KV / 40mA, the scanning angle range is 5° to 80°, the scanning step is 0.00836°, and the time for each step is 0.3s.

[0111] wherein the a peak is located at a diffraction angle 2Q in the range of 43°-44°, the b peak is located at a diffraction angle 2Q in the range of 45°-47°, Ia and Ib are the highest intensity values of the diffraction peak a and the diffraction peak b, respectively. a and Ia / Ib b wherein Ia and Ib are the highest intensity values of the diffraction peak a and the diffraction peak b, respectively.

[0112] The diffraction peak of the (004) plane (004 peak in the XRD pattern of the negative electrode material) is located at a diffraction angle 2Q in the range of 52°-57°, and the diffraction peak of the (110) plane (110 peak in the XRD pattern of the negative electrode material) is located at a diffraction angle 2Q in the range of 75°-80°. The peak area value of the 004 peak is calculated by integration and is denoted as C004, and the peak area value of the 110 peak is calculated by integration and is denoted as C110, so as to calculate the ratio of C004 / C110 of the negative electrode material.

[0113] La and Lc are calculated using the half-height peak width of the (110) crystal plane and the (002) diffraction peak in the XRD pattern of the negative electrode material in combination with the Scherrer formula. The Scherrer formula is D = Kλ / (βcosθ), wherein K is a constant; λ is the X-ray wavelength; β is the half-height width of the diffraction peak; and θ is the diffraction angle. In the above formula, the value of the constant K is related to the definition of β. When β is the half-height, K is 0.89; and when β is the integral width, K is 1.0.

[0114] 8. Gravimetric capacity and initial efficiency test

[0115] (1) Preparation of button cell: the negative electrode prepared in the above examples, lithium sheet, separator, electrolyte, steel sheet, foamed nickel and button cell shell are assembled together to obtain a button cell, which is statically placed for 6 h before testing.

[0116] (2) The button cell is placed on a blue cell tester for testing. The test procedure is as follows: discharged to 5 mV at 0.05 C, statically placed for 5 min, discharged to 5 mV at 0.05 mA, discharged to 5 mV at 0.01 mA, charged to 2.0 V at 0.1 C to obtain the charge capacity, and finally divided by the weight of the active material to obtain the gravimetric capacity of the negative electrode material. The charge capacity ratio of the above discharge capacity can obtain the initial efficiency.

[0117] 9. Lithium ion battery DCR direct current impedance test

[0118] 1) The test temperature is 25°C;

[0119] 2) Static for 60 min;

[0120] 3) 0.5 C CC (constant current) to 4.43 V, CV (constant voltage) to 0.025 C;

[0121] 4) Static for 10 min;

[0122] Discharge, temperature 25°C

[0123] 5) 0.1 C DC to 3 V;

[0124] 6) Rest for 10 min;

[0125] 7) 0.5 C CC to 4.43 V, CV to 0.025 C;

[0126] 8) Rest for 1 h;

[0127] 9) 0.1 C DC to 10 s;

[0128] 10) 1 C DC to 1 s;

[0129] 11) Rest for 1 h;

[0130] 12) 0.5 C DC to 6 min;

[0131] 13) If voltage < 2.5 V, go to step 15;

[0132] 14) Cycle steps 8 to 13 for 26 times;

[0133] 15) Rest for 10 min;

[0134] 16) 0.5 C CC to 3.95 V, CV to 0.025 C;

[0135] 17) Rest for 10 min;

[0136] Take the impedance DCR of the battery at 70% SOC, end of test.

[0137] 10. Discharge capacity retention test

[0138] 1) Test temperature is 25°C;

[0139] 2) Rest for 30 min;

[0140] 3) 0.5 C DC to 3 V;

[0141] 4) Rest for 5 min;

[0142] 5) 0.5 C CC to 4.43 V, CV to 0.025 C;

[0143] 6) Rest for 5 min;

[0144] 7) Rate XX DC to 3 V

[0145] Rate XX = {0.2 C, 0.5 C, 0.7 C, 1 C, 1.5 C, 2 C};

[0146] 8) Stand for 5 min;

[0147] 9) Cycle step 5 to step 8, test all the rate in turn according to the rate condition;

[0148] 10) Stand for 5 min;

[0149] The 2C discharge capacity retention rate of the lithium ion battery is calculated by the following formula: 2C discharge capacity retention rate = 2C discharge capacity / 0.2C discharge capacity x 100%.

[0150] Test results

[0151] Table 1 shows the influence of the exothermic peak temperature in the thermogravimetric test of the negative electrode material on the performance of the lithium ion battery. In Table 1, the Id / Ig of the examples and the comparative examples is 0.254, the cumulative pore volume of 3 nm to 35 nm is 2.18 x 10 -3 cm 3 / g, the C004 / C110 is 4.77, and the I a / I b is 1.89.

[0152] Table 1

[0153]

[0154] From the data in Table 1, it can be seen that when the negative electrode material in the lithium ion battery meets the combustion in the air atmosphere at 500°C to 1000°C, and the exothermic peak peak is between 600°C to 800°C, the secondary battery shows good 2C discharge rate capacity retention rate. It is speculated that because the reaction activity of the graphite negative electrode material with lithium ions with this feature is significantly improved, it is beneficial for the rapid release of lithium ions during discharge, so that the 2C discharge rate capacity retention rate is large, and the kinetic performance is improved.

[0155] Table 2 further studies the influence of the Id / Ig value of the negative electrode material on the performance of the lithium ion battery on the basis of Example 1.

[0156] Table 2

[0157] Examples Id / Ig ratio 2C discharge capacity retention rate / % Example 1 0.254 96.3 Example 11 0.389 97.1 Example 12 0.423 97.3 Example 13 0.349 96.4 Example 14 0.470 97.8 Example 15 0.382 97.1 Example 16 0.467 97.6 Example 17 0.464 97.4 Example 18 0.375 96.6 Example 19 0.386 97.1 Example 20 0.419 97.2

[0158] From the data in Table 2, it can be seen that Examples 11 to 20 all show better discharge rate performance. It is speculated that because the Id / Ig value of the negative electrode material is in a suitable range, the surface has more defects, the lithium ion reaction activity is stronger, the diffusion rate increases, the kinetic performance of the active material is good, and then the lithium ion battery shows good discharge rate performance.

[0159] Table 3 further investigates the influence of the 3nm to 35nm cumulative pore volume of the negative electrode material on the performance of the lithium ion battery based on Example 16.

[0160] Table 3

[0161]

[0162]

[0163] From the data in Table 3, it can be seen that when the cumulative pore volume of the negative electrode material is in the range of 4x10 -3 cm 3 / g to 30x10 -3 cm 3 / g, the specific capacity Cap of the negative electrode material is ≥350mAh / g, and the 2C discharge capacity retention of the lithium ion battery can be further improved.

[0164] Table 4 further investigates the influence of the C004 / C110, I a / I b , BET, Dv50 and graphitization degree of the negative electrode material on the performance of the lithium ion battery based on Example 23. Among them, the peak intensity of the diffraction peak of the negative electrode material in the XRD pattern at 2θ of 43° to 44° is I a , and the peak intensity of the diffraction peak at 2θ of 45° to 47° is I b .

[0165] Table 4

[0166]

[0167] From the comparison of Example 31, Example 32 and Example 23, it can be seen that when the C004 / C110 of the negative electrode material is in the range of 1 to 3, the lithium ion battery has lower impedance.

[0168] Examples 33-34 are negative electrode active material Ia / Ib in the range of 2-6, and the impedance DCR is also reduced to a certain extent compared with Example 26.

[0169] Examples 35-36 are negative electrode active material BET in the range of 4-10m2 / g, and the initial efficiency of these examples is improved, and the discharge rate performance is also improved to a certain extent.

[0170] Examples 37-38 are negative electrode material Dv50 in the range of 10-20μm, and the discharge capacity retention of these examples is also increased to a certain extent compared with Example 26

[0171] Examples 39-40 are negative electrode material graphitization degree in the range of 94.5-96%, and the discharge capacity retention of these examples is also improved.

[0172] This shows that the above-mentioned limiting conditions for the active material can further improve the performance of lithium ion batteries.

[0173] While the illustrative embodiments have been demonstrated and described, it should be understood that the above-described embodiments are not to be considered limitations on the present application, and that changes, alternatives, and modifications can be suggested to one skilled in the art without departing from the spirit, principles, and scope of the present application.

Claims

1. A negative electrode material comprising a carbon-based material, wherein, The negative electrode material has an exothermic peak in a temperature range of 600-800°C in a thermogravimetric test in an air atmosphere, wherein the negative electrode material satisfies at least one of the following conditions (i) to (ii): (i) the ratio of the 004 crystal face diffraction peak area C004 to the 110 crystal face diffraction peak area C110 of the negative electrode material satisfies 1≤C004 / C110≤6 in a test by X-ray diffraction method; (ii) X-ray diffraction testing revealed that the negative electrode material exhibits diffraction peak a in the range of 43° to 44° at 2θ, and diffraction peak b in the range of 45° to 47° at 2θ, wherein the peak intensity of diffraction peak a is I. a The peak intensity of the diffraction peak b is I. b ,2≤I a / I b ≤6.

2. The negative electrode material of claim 1, wherein, the negative electrode material has an exothermic peak in a temperature range of 650-750°C.

3. The negative electrode material of claim 1, wherein, The negative electrode material satisfies, by Raman testing, 0.2 ≤ Id / Ig ≤ 0.5, where Id is the intensity of a peak at 1350 cm -1 in the Raman spectrum, and Ig is the intensity of a peak at 1580 cm -1 in the Raman spectrum.

4. The negative electrode material of claim 3, wherein, 0.3≤Id / Ig≤0.

5.

5. The negative electrode material according to claim 1 or 2, wherein The negative electrode material satisfies, through nitrogen adsorption-desorption testing: 0.002 cm 3 / g≤S≤0.035 cm 3 / g, wherein S is the adsorption volume of pores with a pore size of 3 nm to 35 nm in the negative electrode material.

6. The negative electrode material of claim 5, wherein, 0.004 cm 3 / g ≤ S ≤ 0.03 cm 3 / g.

7. The negative electrode material according to claim 1 or 2, wherein The negative electrode material satisfies at least one of the following conditions (iii) to (v): (iii) the specific surface area of the negative electrode material is 4 cm 2 / g to 20 cm 2 / g; (iv) the Dv50 of the negative electrode material satisfies: 5μm≤Dv50≤25μm; (v) the graphitization degree of the negative electrode material is 94%-96%.

8. The negative electrode material according to claim 1 or 2, wherein The raw material for preparing the carbon-based material comprises artificial graphite and / or natural graphite. 9.A secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material according to any one of claims 1-8. 10.An electronic device comprising the secondary battery according to claim 9.

Images