Negative electrode materials, secondary batteries and electronic devices

Abstract

Provided is a negative electrode material comprising a carbon-based material, wherein the X-ray diffraction spectrum of the negative electrode material has a diffraction peak a in the range of 43° to 44° at 2θ, and a diffraction peak b in the range of 45° to 47° at 2θ, wherein the peak intensity of the diffraction peak a is I a , the peak intensity of diffraction peak b is I b , I a / I b >1. The negative electrode material of the present application has excellent kinetic properties, thereby effectively reducing the internal resistance of the secondary battery containing the negative electrode material and improving the overall performance of the secondary battery. A secondary battery containing the negative electrode material is also provided.

Description

Technical Field

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

[0002] As electrochemical devices such as lithium-ion batteries become widely used energy systems, their applications are becoming increasingly diverse, with fast charge and discharge being a key area. Therefore, developing energy systems with superior charge and discharge performance is crucial for their large-scale application in transportation, power grids, and wind and solar energy systems.

[0003] However, rapid charging and discharging will bring some problems. For example, when lithium-ion batteries are charged and discharged at high rates, the temperature rises rapidly during the charging and discharging process due to the internal resistance of the battery itself. As a result, the battery is in a high-temperature environment, which causes great damage to its cycle and safety performance. Therefore, the consumer market has an urgent demand for batteries with lower internal resistance, and batteries with lower internal resistance need to be developed. The existing technology improves battery impedance mainly by reducing the coating thickness of the electrode and reducing the particle size of the negative electrode active material, but this method will significantly reduce the energy density of the battery, reduce the battery's endurance, and is costly. Therefore, it is very necessary to develop negative electrode materials with low internal resistance and other moderate properties. Summary of the Invention

[0004] In view of the above-mentioned problems existing in the prior art, the present application provides a negative electrode material and a secondary battery comprising the negative electrode material, so as to improve the kinetic performance of the negative electrode material, thereby reducing the internal resistance of the secondary battery and improving the overall performance of the secondary battery.

[0005] In a first aspect, the present application provides a negative electrode material comprising a carbon-based material, wherein the X-ray diffraction spectrum of the negative electrode material has a diffraction peak a in the range of 43° to 44° at 2θ, and a diffraction peak b in the range of 45° to 47° at 2θ, wherein the peak intensity of the diffraction peak a is I a , the peak intensity of diffraction peak b is I b , I a / I b >1. The diffraction peak a and diffraction peak b of the negative electrode material are related to the stacking sequence of rhombic (3R) graphene layers in graphite. The diffraction peak a and diffraction peak b appear in the negative electrode material of the present application, and the peak intensity of diffraction peak a is higher than the peak intensity of diffraction peak b, indicating that there is an unstable rhombohedral structure in the formed graphite, which can more easily carry out lithium insertion and extraction, thereby reducing the internal resistance of the battery. In some embodiments, 2≤I a / I b ≤6.

[0006] In some embodiments, 400≤I a≤2500. In some embodiments, 0≤I b ≤600.

[0007] In some embodiments, the ratio of the diffraction peak area C004 of the 004 crystal plane of the negative electrode material to the diffraction peak area C110 of the 110 crystal plane satisfies 1≤C004 / C110≤4 when tested by X-ray diffraction. The ratio of C004 / C110 is a parameter reflecting the crystal orientation of the negative electrode material. The larger the C004 / C110 value, the higher the crystal orientation, and the more limited the surface of the active ions in the negative electrode material for deintercalation. The smaller the C004 / C110 value, the lower the crystal orientation, and the active ions can be deintercalated in multiple directions of the negative electrode material. When the C004 / C110 of the negative electrode material of the present application is within the above range, the active ions can be quickly deintercalated in the negative electrode material, thereby further improving the kinetic performance of the secondary battery. In some embodiments, 1≤C004 / C110≤3.

[0008] In some embodiments, the average stacking thickness of the negative electrode material along the a-axis is La, as measured by X-ray diffraction, and is 100nm≤La≤160nm. In some embodiments, the average stacking thickness of the negative electrode material along the c-axis is Lc, as measured by X-ray diffraction, and is 18nm≤Lc≤30nm. La represents the average size of the negative electrode material crystals along the a-axis, and Lc represents the thickness of the negative electrode material microchips stacked along the c-axis perpendicular thereto. The values ​​of La and Lc can characterize the degree of graphitization of the negative electrode material. The larger the La and Lc, the higher the gram capacity of the negative electrode material. However, when the Lc and La values ​​are too high, although the gram capacity of the negative electrode material increases, its cycle performance will decrease. When the Lc and La values ​​of the negative electrode material of the present application are within the above range, the negative electrode material has a high gram capacity while the cycle performance is not significantly reduced. In some embodiments, 110nm≤La≤160nm. In some embodiments, 20nm≤Lc≤30nm.

[0009] In some embodiments, the negative electrode material has a Dn10 value ≥ 0.4 μm. Dn10 can indicate the content of fine powder in the negative electrode material, with a lower value indicating a higher content of fine powder. Excessive fine powder content can cause the negative electrode material to consume more lithium ions during initial lithium insertion, leading to reduced initial efficiency. In some embodiments, the negative electrode material has a Dn10 value ≥ 0.5 μm.

[0010] In some embodiments, the Dv10 and Dv90 of the negative electrode material satisfy: 5≤Dv90 / Dv10≤25. Dv90 / Dv10 represents the concentration of the particle size distribution in the negative electrode material. The larger the value, the more dispersed the material particle size distribution, and vice versa. When the volume fraction of the negative electrode material is the same, the larger the particle size and the wider the distribution, the lower the viscosity of the corresponding negative electrode slurry, which can increase the solid content and reduce the difficulty of coating. At the same time, when the particle size distribution is wider, small particles can fill the gaps between large particles, which helps to increase the compaction density of the electrode sheet and improve the volume energy density of the secondary battery. In addition, the particle morphology will also have a significant impact on the rate performance and low temperature performance of the secondary battery. When the Dv90 / Dv10 of the negative electrode material of the present application is within the above range, the secondary battery including the negative electrode material has a high energy density, and its electrical properties such as rate performance and low temperature performance will not be reduced. In some embodiments, 5≤Dv90 / Dv10≤15.

[0011] In some embodiments, the negative electrode material has a Dv90 of 30 μm to 65 μm. In some embodiments, the negative electrode material has a Dv10 of 2 μm to 8 μm. Excessively large particles of the negative electrode material can impair slurry processing, while too small particles can reduce initial efficiency. In some embodiments, the Dv90 is 30 μm to 60 μm. In some embodiments, the Dv10 is 3 μm to 7 μm.

[0012] In some embodiments, the 5t powder compaction density of the negative electrode material is C, 1.5g / cm 3 / ≤C≤2.5g / cm 3 The powder compaction density represents the degree to which the negative electrode material can be compressed during pressing. The larger the value, the more it can be compressed during pressing, and the higher the volume energy density of the corresponding secondary battery. The powder compaction density of the negative electrode material of the present application is within the above range, and the secondary battery including the negative electrode material has a high energy density. In some embodiments, 1.8 g / cm 3 / ≤C≤2.1g / cm 3 .

[0013] In some embodiments, the carbon-based material includes graphite, and the graphite includes one or more of natural graphite and artificial graphite. In some embodiments, the method for preparing the carbon-based material includes: preparing a graphite composite material from one or more of natural graphite and artificial graphite, spheroidizing, coating, and carbonizing.

[0014] In some embodiments, the preparation process of the graphite composite material includes dissolving one or more of natural graphite and artificial graphite and polymethyl methacrylate (PMMA) in NN dimethylformamide (DMF) at the same time, stirring at a temperature of 50°C to 80°C for 10h to 14h, filtering and collecting the precipitate, washing with deionized water and ethanol 2 to 4 times, and completely drying at a temperature of 60°C to 90°C to obtain a graphite composite material precursor; heating the graphite composite material precursor to 1000°C to 1200°C in a tube furnace at a heating rate of 8°C / min to 16°C / min, and then introducing a CH4 / C2H2 / H2 mixed gas (in ratios of 5-10:5-10:80-85, respectively) into the tube furnace, keeping for 8h to 12h, and then naturally cooling to room temperature to obtain a graphite composite material.

[0015] In some embodiments, the spheroidization process includes: applying continuous impact force, compression force and shear force from the turntable, inner wall and between 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 minutes to 20 minutes. In some embodiments, the mixture is subjected to impact force, compression force and shear force by using a spheroidization device, thereby causing the mixture to collide, rub, shear and bend and fold, thereby removing the sharp corners of the graphite composite material and achieving the effect of fixing the micropowder to the large particles. In some embodiments, the spheroidization device is a mixing granulator. In some embodiments, the rotation speed of the spheroidization device is 30Hz to 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% to 2%. In some embodiments, the mass content of the dispersant solution is 5% to 20% based on the mass of the graphite composite material.

[0016] In some embodiments, the coating process includes coating the spheroidized graphite composite material with pitch. In some embodiments, the mass content of the pitch is 2% to 15% based on the mass of the spheroidized graphite composite material. In some embodiments, the carbonization temperature is 900° C. to 1500° C.

[0017] In a second aspect, the present 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 includes a conductive coating positioned between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the conductive coating comprises at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotubes, and graphene. The conductive coating can conduct electrons, significantly reducing charge transfer impedance, thereby further improving the dynamic performance of the secondary battery. In some embodiments, the conductive coating has a thickness of 0.5 μm to 12 μm.

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

[0020] This application helps to reduce the particle size of the graphite material by spheroidizing, coating and carbonizing the graphite material, transforming the irregular morphology into a regular spherical morphology, thereby significantly improving the kinetic performance of the negative electrode material, thereby further reducing the internal resistance of the secondary battery and improving the overall performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 and 2 are XRD diagrams of the negative electrode materials of Example 1 and Comparative Example 1 of the present application.

[0022] Figure 2 The DCR curves of the lithium-ion batteries of Example 1 and Comparative Example 1 of the present application are shown. DETAILED DESCRIPTION

[0023] For the sake of clarity, this application only specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0024] In the description of the present application, unless otherwise specified, “above” and “below” include the number.

[0025] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

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

[0027] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0028] 1. Anode Materials

[0029] The negative electrode material provided in the present application includes a carbon-based material. The X-ray diffraction spectrum of the negative electrode material has a diffraction peak a in the range of 43° to 44° at 2θ, and a diffraction peak b in the range of 45° to 47° at 2θ, wherein the peak intensity of the diffraction peak a is I a , the peak intensity of diffraction peak b is I b , I a / I b >1. The diffraction peak a and diffraction peak b of the negative electrode material are related to the stacking sequence of rhombic (3R) graphene layers in graphite. The diffraction peak a and diffraction peak b appear in the negative electrode material of the present application, and the peak intensity of diffraction peak a is higher than the peak intensity of diffraction peak b, indicating that the formed graphite has a rhombohedral structure, which can be more easily deintercalated and deintercalated with lithium, and has a higher specific capacity. In some embodiments, I a / I b 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, 5.9 or a range consisting of any two of these values. In some embodiments, 2≤1 a / I b ≤6.

[0030] In some embodiments, 400≤I a ≤2500. In some embodiments, I a1 is 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400 or a range consisting of any two of these values. In some embodiments, 0≤1 b ≤600. In some embodiments, I b is 50, 100, 150, 200, 300, 350, 400, 450, 500, 550 or a range consisting of any two of these values. a It is the highest intensity value of the diffraction peak a in the range of 43° to 44° at 2θ. b It is the maximum intensity value of the diffraction peak b in the range of 45° to 47° at 2θ.

[0031] In some embodiments, as tested by X-ray diffraction, the ratio of the diffraction peak area C004 of the 004 crystal plane of the negative electrode material to the diffraction peak area C110 of the 110 crystal plane satisfies 1≤C004 / C110≤4. The C004 / C110 ratio is a parameter reflecting the crystal orientation of the negative electrode material. The larger the C004 / C110 value, the higher the crystal orientation, and the more limited the plane of deintercalation of the active ions in the negative electrode material. The smaller the C004 / C110 value, the lower the crystal orientation, and the active ions can be deintercalated in multiple directions of the negative electrode material. When the C004 / C110 ratio of the negative electrode material of the present application is within the above range, the active ions can be quickly deintercalated in the negative electrode material, thereby further improving the kinetic performance of the secondary battery. In some embodiments, C004 / C110 is 1.2, 1.4, 1.6, 1.8, 2.3, 2.5, 2.7, 3.0, 3.3, 3.5, 3.7, or a range consisting of any two of these values. In some embodiments, 1≤C004 / C110≤3.

[0032] In some embodiments, the average stacking thickness of the negative electrode material along the a-axis direction is La as measured by X-ray diffraction, and 100 nm ≤ La ≤ 160 nm. In some embodiments, La is 100 nm, 103 nm, 105 nm, 107 nm, 110 nm, 113 nm, 115 nm, 117 nm, 120 nm, 123 nm, 125 nm, 127 nm, 130 nm, 143 nm, 145 nm, 147 nm, 150 nm, 153 nm, 155 nm, 157 nm, or a range consisting of any two of these values. In some embodiments, the average stacking thickness of the negative electrode material along the c-axis direction is Lc as measured by X-ray diffraction, and 18 nm ≤ Lc ≤ 30 nm. In some embodiments, Lc is 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or a range consisting of any two of these values. La represents the average size of the negative electrode material crystals along the a-axis direction, and Lc represents the thickness of the negative electrode material microchips stacked along the c-axis direction perpendicular thereto. The values ​​of La and Lc can characterize the degree of graphitization of the negative electrode material. The larger the La and Lc, the higher the gram capacity of the negative electrode material. However, when the Lc and La values ​​are too high, although the gram capacity of the negative electrode material increases, its cycle performance will decrease. When the Lc and La values ​​of the negative electrode material of the present application are within the above range, the negative electrode material has a high gram capacity while the cycle performance will not be significantly reduced. In some embodiments, 110 nm ≤ La ≤ 160 nm. In some embodiments, 20 nm ≤ Lc ≤ 30 nm.

[0033] In some embodiments, the negative electrode material has a Dn10 of ≥ 0.4 μm. Dn10 can indicate the content of fine powder in the negative electrode material, with a smaller value indicating a higher content of fine powder in the negative electrode material. Excessive fine powder content can cause the negative electrode material to consume more lithium ions during initial lithium insertion, resulting in reduced initial efficiency. In some embodiments, Dn10 is 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1.0 μm, 1.05 μm, 1.1 μm, 1.15 μm, 1.2 μm, 1.25 μm, 1.3 μm, 1.35 μm, 1.4 μm, 1.45 μm, 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm, 1.85 μm, 1.9 μm, 1.95 μm, 2.0 μm, or a range consisting of any two of these values. In some embodiments, the negative electrode material has Dn10 ≥ 0.5 μm. In this application, Dn10 indicates that 10% of the particles in the particle size distribution of the negative electrode material on a number basis have a particle size smaller than this value.

[0034] In some embodiments, Dv10 and Dv90 of the negative electrode material satisfy: 5≤Dv90 / Dv10≤25. Dv90 / Dv10 represents the concentration of the particle size distribution in the negative electrode material. The larger the value, the more dispersed the material particle size distribution, and vice versa. The volume fraction of the negative electrode material is the same. The larger the particle size and the wider the distribution, the lower the viscosity of the corresponding negative electrode slurry, which can increase the solid content and reduce the difficulty of coating. At the same time, when the particle size distribution is wider, small particles can fill the gaps in the large particles, which helps to increase the compaction density of the electrode and improve the volume energy density of the secondary battery. In addition, the particle morphology will also have a significant impact on the rate performance and low temperature performance of the secondary battery. When the Dv90 / Dv10 of the negative electrode material of the present application is within the above range, the secondary battery including the negative electrode material has a high energy density, and its electrical properties such as rate performance and low temperature performance will not be reduced. In some embodiments, Dv90 / Dv10 is 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 20, 22, 24, or a range consisting of any two of these values. In some embodiments, 5≤Dv90 / Dv10≤15.

[0035] In some embodiments, the Dv90 of the negative electrode material is 30μm to 65μm. In some embodiments, the Dv10 of the negative electrode material is 2μm to 8μm. If the particles of the negative electrode material are too large, their slurry processing performance will deteriorate, and if they are too small, their first efficiency will be reduced. In some embodiments, Dv90 is 32μm, 34μm, 36μm, 38μm, 40μm, 43μm, 45μm, 47μm, 50μm, 52μm, 55μm, 57μm, 59μm, 62μm, 64μm, or a range consisting of any two of these values. In some embodiments, Dv90 is 30μm to 60μm. In some embodiments, Dv10 is 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, or a range consisting of any two of these values. In some embodiments, Dv10 is 3μm to 7μm. In this application, Dv10 means that in the volume-based particle size distribution of the negative electrode material, 10% of the particles have a particle size smaller than this value. Dv90 means that in the volume-based particle size distribution of the negative electrode material, 90% of the particles have a particle size smaller than this value.

[0036] In some embodiments, the 5t powder compaction density of the negative electrode material is C, 1.5g / cm 3 ≤C≤2.5g / cm 3The powder compaction density represents the degree to which the negative electrode material can be compressed during pressing. The larger the value, the more it can be compressed during pressing, and the higher the volume energy density of the corresponding secondary battery. The powder compaction density of the negative electrode material of the present application is within the above range, and the secondary battery including the negative electrode material has a high energy density. In some embodiments, C is 1.6 g / cm 3 , 1.7g / crm 3 , 1.85g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.05g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 Or any two of these values. In some embodiments, 1.8 g / cm 3 / ≤C≤2.1g / cm 3 .

[0037] In some embodiments, the carbon-based material includes graphite, and the graphite includes one or more of natural graphite and artificial graphite. In some embodiments, the method for preparing the carbon-based material includes: preparing a graphite composite material from one or more of natural graphite and artificial graphite, spheroidizing, coating, and carbonizing.

[0038] 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), stirring at a temperature of 50°C to 80°C for 10 to 14 hours, collecting the precipitate by filtration, washing it with deionized water and ethanol 2 to 4 times, and completely drying it at a temperature of 60°C to 90°C to obtain a graphite composite material precursor. The graphite composite material precursor is heated to 1000°C to 1200°C in a tube furnace at a heating rate of 8°C / min to 16°C / min, and then a CH4 / C2H2 / H2 mixed gas (ratios of 5-10:5-10:80-85, respectively) is introduced into the tube furnace, maintained for 8 to 12 hours, and then naturally cooled to room temperature to obtain the final graphite composite material.

[0039] In some embodiments, the spheroidization process comprises: applying continuous impact force, compression force and shear force from the turntable, inner wall and between 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 minutes to 20 minutes, for example, 12 minutes, 14 minutes, 16 minutes or 18 minutes. In some embodiments, the mixture is subjected to magnetic collision, friction, shearing and bending folding by using a spheroidization device, thereby removing the sharp 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 rotation speed of the spheroidization device is 30 Hz to 50 Hz, for example, 35 Hz, 40 Hz or 45 Hz.

[0040] 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% to 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% to 20%, for example, 7%, 10%, 13%, 15%, 17%, or 19%, based on the mass of the graphite composite.

[0041] In some embodiments, the coating process includes: coating the spheroidized graphite composite material with pitch. In some embodiments, the mass content of the pitch is 2% to 15%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or 14%, based on the mass of the spheroidized graphite composite material. In some embodiments, the temperature of the carbonization treatment 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.

[0042] 2. Secondary batteries

[0043] The secondary battery provided in the present application includes a negative electrode, which 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, wherein the negative electrode active material layer includes the negative electrode material of the first aspect.

[0044] In some embodiments, the negative electrode further includes a conductive coating located between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the conductive coating includes at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotubes, and graphene. The conductive coating can conduct electrons, significantly reducing the charge transfer impedance, thereby further improving the dynamic performance of the secondary battery. In some embodiments, the thickness of the conductive coating is 0.5 μm to 1.2 μm. In some embodiments, the thickness of the conductive coating 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: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

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

[0047] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, 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 positive electrode, which includes a positive electrode current collector and a positive electrode active material layer, which includes a positive electrode active material, a binder, and a conductive agent.

[0049] According to some embodiments of the present application, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0050] According to some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In some embodiments, the binder includes a binder polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, 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 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 also includes a separator. The material and shape of the separator used in the secondary battery of the present application are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.

[0052] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film may be used.

[0053] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0054] The secondary of the present application also includes an electrolyte. The electrolyte that can be used in the present application can be an electrolyte known in the prior 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 in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no restriction on the electrolyte used in the electrolyte according to the present application, and it may be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. 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 solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (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(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate 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] 3. Electronic Devices

[0058] The present application further provides an electronic device, which includes the secondary battery according to the second aspect of the present application.

[0059] The electronic devices or devices of the present application are not particularly limited. In some embodiments, the electronic devices of the present application include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

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

[0061] Examples and Comparative Examples

[0062] Example 1

[0063] Anode material preparation

[0064] 95g of artificial graphite was selected and dissolved with 5g of polymethyl methacrylate (PMMA) in 100mL of NN dimethylformamide (DMF), and stirred at 70℃ for 12h; the precipitate was collected by filtration, washed twice with deionized water and ethanol, and completely dried at 80℃ to obtain a graphite composite material precursor; the mixture was heated to 1100℃ at a heating rate of 10℃ / min in a tube furnace, and then a CH4 / C2H2 / H2 mixed gas (ratio of 5:10:85) was introduced into the tube furnace, kept for 10h and then naturally cooled to room temperature to obtain a graphite composite material; the graphite composite material was mixed with a 10% CMC aqueous solution with a solid content of 1%, spheroidized for 15 minutes at a spheroidization equipment speed of 40Hz, and coated with 5% asphalt after spheroidization. Finally, the coated mixture was heated to 1000℃ at a rate of 5℃ / min, kept warm for 5h, and naturally cooled to room temperature after keeping warm to obtain a carbon-based material, i.e., a negative electrode material.

[0065] Preparation of negative electrode

[0066] The above-prepared negative electrode material, binder styrene-butadiene rubber (abbreviated as SBR), and thickener sodium carboxymethyl cellulose (abbreviated as CMC) are mixed in a weight ratio of 97:1.5:1.5, and then fully stirred and mixed in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry; this slurry is coated on the current collector Cu foil, dried, and cold pressed to obtain the negative electrode sheet.

[0067] Preparation of positive electrode

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

[0069] Preparation of electrolyte

[0070] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 1:3:2:4. Fluorinated ethylene carbonate and vinylene carbonate were then added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain an electrolyte. The mass percentage of LiPF6 was 12.5%, the mass percentage of fluoroethylene carbonate was 3%, and the mass percentage of vinylene carbonate was 1%. The mass percentages of each substance were calculated based on the mass of the electrolyte.

[0071] Preparation of lithium-ion batteries

[0072] The positive electrode, separator (polyethylene porous polymer film), and negative electrode are stacked in order, with the separator placed between the positive and negative electrodes to serve as an isolation, and then wound to obtain an electrode assembly; after welding the tabs, 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, Comparative Example 1

[0074] Anode material preparation

[0075] The preparation process of the negative electrode material is similar to that of Example 1, except that the corresponding negative electrode material is prepared by adjusting the parameters such as the ratio of carbon-based material to PMMA, the rotation speed of the spheroidizing equipment, the residual carbon ratio of the coating pitch, and the carbonization temperature during the preparation process. The specific preparation parameters are shown in Table a:

[0076] Table a

[0077]

[0078] The preparation of the positive electrode, electrolyte and lithium ion battery is the same as that in Example 1.

[0079] Example 11 to Example 20

[0080] Anode material preparation

[0081] The preparation process for the negative electrode material was similar to that of Example 5, except that the C004 / C110 ratio of the negative electrode material was adjusted by adjusting the solid content of the CMC solution. During the preparation of Examples 11 to 20, the solid content of the CMC solution was 0.8%, 0.6%, 1.2%, 1.0%, 1.6%, 0.4%, 0.2%, 1.8%, 2.0%, and 1.4%.

[0082] The preparation of the positive electrode, electrolyte and lithium ion battery is the same as that in Example 5.

[0083] Example 21 to Example 30

[0084] Anode material preparation

[0085] The preparation process of the negative electrode material was similar to that of Example 14, except that the La and Lc values ​​of the negative electrode material were adjusted by adjusting the heating rate of the carbonization process. In the preparation processes of Examples 21-30, the heating rates of the carbonization process were 2.5°C / min, 6.5°C / min, 9.5°C / min, 10°C / min, 1.5°C / min, 4.5°C / min, 5°C / min, 8°C / min, 8.5°C / min, and 9°C / min.

[0086] The preparation of the positive electrode, electrolyte and lithium ion battery is the same as that in Example 14.

[0087] Example 31 to Example 40

[0088] The preparation process of the negative electrode material was similar to that of Example 25, except that the particle size of the negative electrode material was adjusted by adjusting the spheroidization time. In the preparation process of Examples 31-40, the spheroidization time distribution was 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, and 20 min.

[0089] The preparation of the positive electrode, electrolyte and lithium ion battery is the same as that in Example 25.

[0090] Example 41 to Example 45

[0091] Anode material preparation

[0092] The preparation process of the negative electrode material is the same as that of Example 35.

[0093] Anode preparation

[0094] The preparation process of the negative electrode is similar to that of Example 35, except that a conductive coating is added.

[0095] The preparation of the positive electrode, electrolyte and lithium-ion battery is the same as in Example 35.

[0096] Test Method

[0097] 1. XRD test of negative electrode materials

[0098] The negative electrode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) to obtain an XRD test curve, wherein the target material was Cu Kα, the voltage / current was 40 kV / 40 mA, the scanning angle range was 5° to 80°, the scanning step was 0.00836°, and the time per step was 0.3 s.

[0099] Among them, the a peak is located at the diffraction angle 2θ range of 43°-44°, the b peak is located at the diffraction angle 2θ range of 45°-47°, I a and I b are the highest intensity values ​​of diffraction peak a and diffraction peak b, respectively.

[0100] The diffraction peak of the (004) plane (the 004 peak in the XRD pattern of the negative electrode material) is located at a diffraction angle 2θ of 52°-57°, and the diffraction peak of the (110) plane (the 110 peak in the XRD pattern of the negative electrode material) is located at a diffraction angle 2θ of 75°-80°. The peak area value of the 004 peak is integrated and recorded as C004, and the peak area value of the 110 peak is integrated and recorded as C110. The C004 / C110 ratio of the negative electrode material is calculated based on this.

[0101] 2. Powder compaction density test

[0102] The test standard for powder compaction density refers to GB / T 24533-2009 "Graphite-based negative electrode materials for lithium-ion batteries". The specific test method is:

[0103] Weigh 1.0000±0.0500g of the negative electrode material sample and place it in a test mold (CARVER#3619 (13mm), and then place the sample in the test equipment. The test equipment is Sansi Zongheng UTM7305 with test tonnages of 0.3t, 0.5t, 0.75t, 1.0t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, and 5.0t. The pressure rise rate is 10mm / min, the pressure rise holding time is 30s, the pressure relief rate is 30mm / min, and the pressure relief holding time is 10s.

[0104] In this application, the compacted density of powders is the compacted density measured at a test tonnage of 5 tons. The compacted density is calculated as follows: compacted density = material mass / (material load area × sample thickness).

[0105] 3. Particle size (Dv10, Dv90 and Dn10) test

[0106] The particle size test method follows GB / T 19077-2016. The specific process involves weighing 1g of the negative electrode material sample, mixing it with 20mL of deionized water and a trace amount of dispersant. The solution is then ultrasonicated for 5 minutes, then poured into a sample injection system (Hydro 2000SM) for testing. The testing instrument used is a Malvern Mastersizer 3000. During the test, the particle size is measured by measuring the intensity of the scattered light as a laser beam passes through the dispersed particle sample. The data is then used to analyze and calculate the particle size distribution of the scattering spectrum. The Dv10 of the negative electrode material is the particle size at which the cumulative volume percentage of the negative electrode material, starting from the smallest particle size, reaches 10% of the total volume. The Dy99 of the negative electrode material is the particle size at which the cumulative volume percentage of the negative electrode material, starting from the smallest particle size, reaches 99% of the total volume. The Dn10 of the negative electrode material is the particle size at which 10% of the particles in the number-based particle size distribution fall below this value. The refractive index of the particles used in the test was 1.8. One sample was tested three times, and the particle size was finally taken as the average value of the three tests.

[0107] 4. Gram capacity test

[0108] (1) Preparation of button cells: The negative electrode, lithium sheet, separator, electrolyte, steel sheet, nickel foam and button cell shell prepared in the above embodiment were assembled together to obtain a button cell, which was left to stand for 6 h before testing.

[0109] (2) Place the button cell on a blue battery tester for testing. The test process is to discharge to 5mV at 0.05C, let it stand for 5 minutes, discharge to 5mV at 0.05mA, discharge to 5mV at 0.01mA, and charge to 2.0V at 0.1C to obtain the charging capacity. Finally, divide it by the weight of the active material to obtain the gram capacity of the negative electrode material.

[0110] 5. Lithium-ion battery DCR DC impedance test

[0111] 1) The test temperature is 25°C;

[0112] 2) Let it stand for 60 minutes;

[0113] 3) 0.5C CC (constant current) to 4.43V, CV (constant voltage) to 0.025C;

[0114] 4) Let it stand for 10 minutes;

[0115] Discharge, temperature 25℃

[0116] 5) 0.1C DC to 3V;

[0117] 6) Let stand for 10 minutes;

[0118] 7) 0.5C CC to 4.43V, CV to 0.025C;

[0119] 8) Let stand for 1 hour;

[0120] 9) 0.1C DC to 10s;

[0121] 10) 1C DC to 1s;

[0122] 11) Let stand for 1 hour;

[0123] 12) 0.5°C DC to 6 minutes;

[0124] 13) If the voltage is ≤2.5V, go to step 15;

[0125] 14) Repeat steps 8 to 13 26 times;

[0126] 15) Let stand for 10 minutes;

[0127] 16) 0.5C CC to 3.95V, CV to 0.025C;

[0128] 17) Let stand for 10 minutes;

[0129] Take the battery impedance DCR at 70% SOC and the test ends.

[0130] Test results

[0131] Table 1 shows the effect of the ratio of the peak intensity Ia of the diffraction peak at 2θ of 43° to 44° to the peak intensity Ib of the diffraction peak at 2θ of 45° to 47° in the XRD pattern of the negative electrode material on lithium-ion battery performance. In Table 1, Lc is 10.7 nm, La is 102 nm, and the C004 / C110 ratio is 4.71 for the Examples and Comparative Examples.

[0132] Table 1

[0133]

[0134] From the data in Table 1, it can be seen that the negative electrode material has diffraction peaks at 43° to 44° and 45° to 47° in the XRD spectrum, and the diffraction peak intensity I a The diffraction peak intensity I b When the ratio is 2 to 6, the lithium-ion battery has a lower DCR impedance.

[0135] Table 2 further studies the effect of the C004 / C110 value of the negative electrode material on the performance of lithium-ion batteries based on Example 5.

[0136] Table 2

[0137]

[0138] It can be seen from the data in Table 2 that when the C004 / C110 of the negative electrode material powder is in the range of 1-3, the active material has good isotropy and the lithium-ion battery can exert good dynamic performance.

[0139] Table 3 further studies the effects of the La and Lc values ​​of the negative electrode material on the performance of lithium-ion batteries based on Example 14.

[0140] Table 3

[0141]

[0142] It can be seen from the data in Table 3 that when La is 110nm to 160nm and Lc is 20nm to 30nm, the gram capacity Cap of the negative electrode material is ≥350mAh / g, and the impedance DCR of the lithium-ion battery can also be further improved.

[0143] Table 4 further studies the effect of the particle size and distribution of the negative electrode material on the performance of the lithium-ion battery based on Example 25.

[0144] Table 4

[0145]

[0146] The data in Table 4 shows that when the negative electrode material's Dn10 is ≥ 0.5 μm, the initial efficiency of the lithium-ion battery can be improved to a certain extent, while its DCR is correspondingly reduced. When the negative electrode material meets the conditions of 5 ≤ Dv90 / Dv10 ≤ 15, Dv90 is between 30 μm and 60 μm, and Dv10 is between 2 μm and 8 μm, the impedance DCR of the lithium-ion battery is also improved to a certain extent.

[0147] Table 5 further studies the effects of the thickness and type of the conductive coating in the negative electrode on the performance of lithium-ion batteries based on Example 35.

[0148] Table 5

[0149]

[0150] It can be seen from the data in Table 5 that when the thickness of the conductive coating is in the range of 0.5 μm to 1.2 μm, the DCR internal resistance of the lithium-ion battery is low.

[0151] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments 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 X-ray diffraction spectrum of the negative electrode material has a diffraction peak a in the range of 43° to 44° at 2θ and a diffraction peak b in the range of 45° to 47° at 2θ, wherein: The peak intensity of the diffraction peak a is I a , the peak intensity of the diffraction peak b is I b , 2.56≤I a / I b ≤7.2; The carbon-based material includes graphite.

2. The negative electrode material according to claim 1, wherein 2.56≤I a / I b ≤6。 3. The negative electrode material according to claim 1 or 2, wherein 400≤I a ≤2500; and / or 0≤I b ≤600.

4. The negative electrode material according to claim 1 or 2, wherein The negative electrode material satisfies at least one of the following conditions (i) to (vi): (i) as tested by X-ray diffraction, the ratio of the diffraction peak area C004 of the 004 crystal plane to the diffraction peak area C004 of the 110 crystal plane of the negative electrode material satisfies 1≤C004 / C110≤4; (ii) as measured by X-ray diffraction, the average stacking thickness of the negative electrode material along the a-axis is La, 100 nm ≤ La ≤ 160 nm, and the average stacking thickness of the negative electrode material along the c-axis is Lc, 18 nm ≤ Lc ≤ 30 nm; (iii) Dn10 of the negative electrode material is ≥ 0.4 μm; (iv) Dv10 and Dv90 of the negative electrode material satisfy the following conditions: 5≤Dv90 / Dv10≤25; (v) the Dv90 of the negative electrode material is 30 μm to 65 μm, and the Dv10 of the negative electrode material is 2 μm to 8 μm; (vi) The compacted density of 5t powder of the negative electrode material is C, 1.5g / cm 3 / ≤C≤2.5g / cm 3 .

5. The negative electrode material according to claim 4, wherein The negative electrode material satisfies at least one of the following conditions (vii) to (xii): (vii) 1≤C004 / C110≤3; (viii)110nm≤La≤160nm, 20nm≤Lc≤30nm; (ix) Dn10 ≥ 0.5 μm; (x)5≤Dv90 / Dv10≤15; (xi) Dv90 of 30 μm to 60 μm and Dv10 of 3 μm to 7 μm; (xii)1.8g / cm 3 / ≤C≤2.1g / cm 3 。 6. The negative electrode material according to claim 1 or 2, wherein The method for preparing the carbon-based material comprises: preparing a graphite composite material from a graphite material, subjecting the graphite material to a spheroidization treatment, a coating treatment, and a carbonization treatment. 7 . 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 claim 1 .

8. The secondary battery according to claim 7, wherein The negative electrode further includes a conductive coating layer located between the negative electrode active material layer and the negative electrode current collector.

9. The secondary battery according to claim 8, wherein The conductive coating comprises at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotubes and graphene; and / or The conductive coating has a thickness of 0.5 μm to 1.2 μm.

10. An electronic device comprising the secondary battery according to any one of claims 7 to 9.

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