Negative electrode active material, secondary battery, and electronic device

Abstract

A negative electrode active material, a secondary battery, and an electronic device. The negative electrode active material comprises graphite, and Dn10, Dv50, and Dv90 of the negative electrode active material satisfy: D=(Dv90-Dn10) / Dv50, wherein 0.8≤D≤1.5; the Dn10 of the negative electrode active material is 1 μm to 5 μm; in an X-ray diffraction pattern of the negative electrode active material, the peak intensity ratio of a characteristic peak C004 to a characteristic peak C110 is I; and the negative electrode active material satisfies: 2≤I / D≤4. The negative electrode active material can be used to improve the cycle performance of a secondary battery.

Description

Negative electrode active material, secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on August 11, 2023, with application number 202311017464.9 and invention name “A negative electrode active material, negative electrode plate, secondary battery and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a negative electrode active material, a secondary battery, and an electronic device. Background Art

[0003] As a supporting industry and key driver of energy restructuring, the energy storage industry holds broad application prospects across diverse sectors, including traditional power generation, transmission and distribution, power demand, ancillary services, and new energy. Currently, energy storage primarily relies on secondary batteries, such as lithium-ion batteries. These batteries, with their high energy density, low self-discharge rate, long cycle life, and stable discharge performance, are widely used in industrial production and daily life.

[0004] The negative electrode active material in the negative electrode plate of lithium-ion batteries is one of the key factors affecting the performance of lithium-ion batteries. The cycle performance of traditional artificial graphite as a negative electrode active material needs to be improved. At present, natural graphite, which is low in cost and has huge reserves, has problems of cycle expansion and low cycle capacity retention rate, which also affects the cycle performance of lithium-ion batteries.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a negative electrode active material, a secondary battery, and an electronic device to improve the cycle performance, expansion performance, and rate performance of the secondary battery. The specific technical solution is as follows:

[0007] The first aspect of the present application provides a negative electrode active material comprising graphite, wherein Dn10, Dv50, and Dv90 of the negative electrode active material satisfy the following conditions: D = (Dv90 - Dn10) / Dv50, 0.8 ≤ D ≤ 1.5; Dn10 of the negative electrode active material is between 1 μm and 5 μm; in the X-ray diffraction pattern of the negative electrode active material, the peak intensity ratio of characteristic peak C004 to characteristic peak C110 is 1; and the negative electrode active material satisfies the following conditions: 2 ≤ I / D ≤ 4. By regulating the values ​​of D, Dn10, and I / D within the above-mentioned ranges, the resulting negative electrode active material has a suitable and narrow particle size distribution, can reduce the tortuosity of diffusion of active ions in the electrode sheet, and simultaneously has strong isotropic properties. Application of the above-mentioned negative electrode active material to the negative electrode sheet of a secondary battery can improve the cycle performance, expansion performance, and rate performance of the secondary battery.

[0008] In some embodiments of the present application, 2≤1≤6. This indicates that the negative electrode active material not only has a narrow particle size distribution and strong isotropic properties, but also can take into account the diffusion path of active ions and the deformation of the negative electrode sheet during the charge and discharge process of the secondary battery, further improving the cycle performance and expansion performance of the secondary battery.

[0009] In some embodiments of the present application, the negative electrode active material satisfies at least one of the following conditions: (1) Dn10 is 2 μm to 4 μm; (2) Dv90 is 14 μm to 30 μm; (3) Dv50 is 8 μm to 15 μm; and (4) 2 ≤ 1 ≤ 4. The negative electrode active material satisfies at least one of the above conditions (1) to (4), and its application to the negative electrode sheet of a secondary battery can improve the cycle performance, expansion performance, and rate performance of the secondary battery.

[0010] In some embodiments of the present application, the sphericity of the negative electrode active material is C=4πA / P 2 , 0.5≤C≤1, A is the area of ​​the orthographic projection of the negative electrode active material particle, and P is the perimeter of the orthographic projection of the negative electrode active material particle; the negative electrode active material satisfies the following: 1.8≤D / C+1≤4. When the sphericity C and D / C+1 of the negative electrode active material are within the above ranges, the negative electrode active material has an appropriate sphericity and a narrow particle size distribution. The sphericity and particle size are well matched, which can further improve the cycling performance and expansion performance of the secondary battery, while also providing the secondary battery with a high energy density and good rate performance.

[0011] In some embodiments of the present application, the negative electrode active material satisfies at least one of the following conditions: (a) the tap density TD of the negative electrode active material is 0.8 g / cm 3 to 1.2g / cm 3 (b) the degree of graphitization G of the negative electrode active material is 90% to 96%; and (c) the gram capacity W of the negative electrode active material is 344 mAh / g to 358 mAh / g. Negative electrode active materials that meet at least one of the above conditions (a) to (c) and are used in negative electrode sheets of secondary batteries can improve the cycling performance, expansion performance, and rate performance of the secondary battery.

[0012] In some embodiments of the present application, 0.8≤D≤1.3.

[0013] In some embodiments of the present application, 2.4≤I / D≤3.5.

[0014] In some embodiments of the present application, the peak intensity ratio of the d peak to the g peak in the Raman spectrum of the negative electrode active material, Id / Ig, is 0.1 to 0.3. When the Id / Ig value of the negative electrode active material is within the above range, the negative electrode active material has an appropriate defectivity and a narrow particle size distribution, which can further improve the cycle performance and expansion performance of the secondary battery while also having good rate performance.

[0015] In some embodiments of the present application, the graphite includes natural graphite and artificial graphite. Natural graphite can provide high specific capacity and better kinetics, and artificial graphite can provide good cycle performance. When both graphites are used, the cycle performance and rate performance of the secondary battery can be further improved.

[0016] The second aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode collector and a negative electrode material layer arranged on at least one surface of the negative electrode collector, and the negative electrode material layer includes the negative electrode active material in any of the above embodiments.

[0017] In some embodiments of the present application, the negative electrode sheet satisfies at least one of the following conditions: (i) the porosity of the negative electrode sheet is 25% to 40%; (ii) the OI value of the negative electrode sheet is 8 to 15. A negative electrode sheet that satisfies at least one of the above conditions (i) or (ii) and is used in a secondary battery is beneficial for improving the cycling performance and expansion performance of the secondary battery.

[0018] A third aspect of the present application provides an electronic device comprising the secondary battery in any one of the above embodiments.

[0019] Beneficial effects of this application:

[0020] The present application provides a negative electrode active material comprising graphite, wherein Dn10, Dv50, and Dv90 of the negative electrode active material satisfy the following conditions: D = (Dv90 - Dn10) / Dv50, 0.8 ≤ D ≤ 1.5; Dn10 of the negative electrode active material is 1 μm to 5 μm; in an X-ray diffraction pattern of the negative electrode active material, the peak intensity ratio of characteristic peak C004 to characteristic peak C110 is 1; and the negative electrode active material satisfies the following conditions: 2 ≤ I / D ≤ 4. The negative electrode active material provided herein can improve the cycle performance of a secondary battery.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0023] FIG1 is an electron microscope photograph of the negative electrode active material in Example 1-1;

[0024] FIG2 is an X-ray diffraction pattern of the negative electrode active material in Examples 1-3;

[0025] FIG3 is an X-ray diffraction pattern of the negative electrode sheet in Example 1-3;

[0026] FIG4 is a graph showing the change in cycle capacity retention rate of the lithium ion batteries in Example 1-1 and Comparative Example 1-1;

[0027] FIG5 is a graph showing thickness expansion rate changes of the lithium-ion batteries in Example 1-1 and Comparative Example 1-1;

[0028] FIG6 is a Raman spectrum of the negative electrode active material in Example 1-3. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0030] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0031] The first aspect of the present application provides a negative electrode active material, which includes graphite, and the Dn10, Dv50, and Dv90 of the negative electrode active material satisfy: D = (Dv90-Dn10) / Dv50, 0.8≤D≤1.5. In some embodiments of the present application, 0.8≤D≤1.3. For example, the value of D can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two values ​​therein. The Dn10 of the negative electrode active material is 1 μm to 5 μm; in some embodiments of the present application, the Dn10 of the negative electrode active material is 2 μm to 4 μm. For example, the Dn10 of the negative electrode active material can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range consisting of any two values ​​therein. In the X-ray diffraction pattern of the negative electrode active material, the peak intensity ratio of the characteristic peak C004 to the characteristic peak C110 is 1; the negative electrode active material satisfies the following conditions: 2≤I / D≤4. In some embodiments of the present application, 2.4≤I / D≤3.5. For example, the value of I / D can be 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, or a range consisting of any two of these values.

[0032] The inventors discovered that the D value and Dn10 can characterize the particle size distribution of the negative electrode active material. When the D value is too small, for example, less than 0.8, the particle size distribution of the negative electrode active material is too narrow, and the fine powder content is significantly reduced. This can deteriorate the conduction of electrons between particles, affect the conductive network, and thus affect the cycle performance and rate performance of the secondary battery. When the D value is too large, for example, greater than 1.5, the particle size distribution of the negative electrode active material is relatively wide, which can extend the diffusion path of active ions such as lithium ions in the negative electrode plate containing the negative electrode active material, increase the diffusion impedance of the active ions, and affect the cycle performance and rate performance of the secondary battery. When I / D is within the above range, it indicates that the particle size distribution of the negative electrode active material is moderate, which can reduce the tortuosity of the diffusion of active ions in the plate. In addition, the negative electrode active material has strong isotropic properties, which is conducive to improving the cycle performance and expansion performance of the secondary battery. By regulating the values ​​of D, Dn10, and I / D within the above ranges, the resulting negative electrode active material has a suitable and narrow particle size distribution, which can reduce the tortuosity of the diffusion of active ions in the electrode sheet. At the same time, the negative electrode active material has strong isotropic properties. Applying the above negative electrode active material to the negative electrode sheet of a secondary battery can improve the cycle performance, expansion performance, and rate performance of the secondary battery. In this application, active ions refer to active ions that participate in the charge and discharge electrochemical reactions during the charge and discharge process of the secondary battery, and can specifically be lithium ions or sodium ions.

[0033] In some embodiments of the present application, 2≤1≤6. In some embodiments of the present application, 2≤1≤4. For example, the value of I can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range consisting of any two of these values. This indicates that the negative electrode active material not only has a narrow particle size distribution and strong isotropic properties, but also can balance the diffusion path of active ions and the deformation of the negative electrode sheet during the charge and discharge process of the secondary battery, further improving the cycle performance and expansion performance of the secondary battery.

[0034] In some embodiments of the present application, the Dv90 of the negative electrode active material is 14μm to 30μm. For example, the Dv90 of the negative electrode active material can be 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, or a range consisting of any two of these values. Under the premise that the negative electrode active material meets the above-mentioned ranges of D, Dn10, and I / D, the Dv90 of the negative electrode active material is within the above-mentioned range, indicating that the negative electrode active material has a suitable particle size and particle size distribution and a narrow particle size distribution, which can reduce the tortuosity of the diffusion of active ions in the electrode sheet. At the same time, the negative electrode active material has strong isotropic properties. Applying the above-mentioned negative electrode active material to the negative electrode sheet of a secondary battery can improve the cycle performance, expansion performance, and rate performance of the secondary battery.

[0035] In some embodiments of the present application, the Dv50 of the negative electrode active material is 8μm to 15μm. For example, the Dv50 of the negative electrode active material can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or a range consisting of any two of these values. Under the premise that the negative electrode active material meets the above-mentioned ranges of D, Dn10, and I / D, the Dv50 of the negative electrode active material is within the above-mentioned range, indicating that the negative electrode active material has a suitable particle size and particle size distribution and a narrow particle size distribution, which can reduce the tortuosity of the diffusion of active ions in the electrode sheet. At the same time, the isotropic properties of the negative electrode active material are strong. Applying the above-mentioned negative electrode active material to the negative electrode sheet of the secondary battery can improve the cycle performance, expansion performance and rate performance of the secondary battery.

[0036] In some embodiments of the present application, the sphericity of the negative electrode active material is C=4πA / P 2, 0.5 ≤ C ≤ 1, A is the area of ​​the orthographic projection of the negative electrode active material particle, and P is the perimeter of the orthographic projection of the negative electrode active material particle. The negative electrode active material satisfies the following: 1.8 ≤ D / C + 1 ≤ 4. For example, the value of C can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a range consisting of any two values ​​therein; the value of D / C + 1 can be 1.8, 2, 2.2, 2.5, 2.7, 3, 3.3, 3.5, 3.8, 4, or a range consisting of any two values ​​therein. When the sphericity C value of the negative electrode active material is within the above range, it indicates that the negative electrode active material has an appropriate sphericity, which is beneficial for both the diffusion of active ions and the insertion and extraction of active ions, further improving the cycle performance of the secondary battery. Furthermore, the negative electrode active material particles can be densely packed, and the negative electrode electrode sheet has a high compaction density, which is conducive to obtaining a secondary battery with a higher energy density. Therefore, under the premise that the negative electrode active material meets the above ranges of D, Dn10, and I / D, and the sphericity C and D / C+1 of the negative electrode active material are within the above ranges, the negative electrode active material has an appropriate sphericity and particle size distribution, and the particle size distribution is relatively narrow. The sphericity and particle size are well matched, which can further improve the cycle performance and expansion performance of the secondary battery, while also providing the secondary battery with a high energy density and good rate performance.

[0037] In some embodiments of the present application, the tap density TD of the negative electrode active material is 0.8 g / cm 3 to 1.2g / cm 3 For example, the tap density of the negative electrode active material TD can be 0.8 g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 Or a range consisting of any two of the values. When the tap density of the negative electrode active material is within the above range, less dispersant is required during the slurrying process, the prepared slurry is more stable, less prone to sedimentation, and the particles in the negative electrode sheet can be in close contact, thereby improving electronic conductivity and active ion diffusion rate, and improving the cycle performance of the secondary battery. Therefore, under the premise that the negative electrode active material meets the above ranges of D, Dn10, and I / D, the TD of the negative electrode active material is within the above range, the negative electrode active material has a suitable tap density and particle size distribution, and the particle size distribution is narrow, which can improve the cycle performance, expansion performance, and rate performance of the secondary battery, while also improving the processing performance of the secondary battery.

[0038] In some embodiments of the present application, the degree of graphitization G of the negative electrode active material is 90% to 96%. For example, the degree of graphitization G of the negative electrode active material can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, or a range consisting of any two values ​​therein. The degree of graphitization G being within the above range indicates that the degree of graphitization of the negative electrode active material is low, which is beneficial to improving the cycle performance and expansion performance of the secondary battery. Therefore, under the premise that the negative electrode active material meets the above ranges of D, Dn10, and I / D, the degree of graphitization of the negative electrode active material is within the above range, the negative electrode active material has a suitable degree of graphitization and particle size distribution, and the particle size distribution is narrow, which can further improve the cycle performance and expansion performance of the secondary battery, while having good rate performance.

[0039] In some embodiments of the present application, the gram capacity W of the negative electrode active material is 344 mAh / g to 358 mAh / g. For example, the gram capacity W of the negative electrode active material can be 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 353 mAh / g, 354 mAh / g, 355 mAh / g, 356 mAh / g, 357 mAh / g, 358 mAh / g or a range consisting of any two values ​​therein. The gram capacity W of the negative electrode active material is within the above range, indicating that it has a higher gram capacity. Thus, under the premise that the negative electrode active material meets the above-mentioned ranges of D, Dn10, and I / D, the negative electrode active material has a higher gram capacity, a suitable particle size distribution, and a narrow particle size distribution, which can improve the cycle performance and expansion performance of the secondary battery, while having good rate performance and a higher energy density.

[0040] In some embodiments of the present application, in the Raman spectrum of the negative electrode active material, the peak intensity ratio of the d peak and the g peak Id / Ig is 0.1 to 0.3. For example, the value of Id / Ig can be 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3 or a range consisting of any two values ​​therein. The value of Id / Ig is within the above range, indicating that the surface of the negative electrode active material has a suitable degree of defectivity, which is beneficial to improving the cycle performance and expansion performance. Thus, under the premise that the negative electrode active material meets the above-mentioned ranges of D, Dn10, and I / D, its Id / Ig value is within the above range, has a suitable degree of defectivity and particle size distribution, and has a narrow particle size distribution, which can further improve the cycle performance and expansion performance of the secondary battery, while having good rate performance.

[0041] In the present application, at least one of the characteristics I, Dv90, sphericity C, tap density TD, degree of graphitization G, gram capacity W, and Id / Ig of the above-mentioned negative electrode active material can be combined with the characteristics "D, Dn10, I / D", and the embodiments covered by the above combinations are all within the scope of protection of this application.

[0042] In some embodiments of the present application, graphite includes natural graphite and artificial graphite. Natural graphite refers to graphite made from flakes produced from natural ores. The origin, properties, and types of natural graphite used in the embodiments of the present application are not particularly limited. Artificial graphite refers to graphite that is prepared by artificial methods and is close to complete graphite crystals. Artificial graphite can be obtained by graphitization, coating and carbonization processes of precursor raw material coke such as petroleum coke, coal coke, asphalt coke, etc. In some embodiments of the present application, the two types of graphite can be distinguished by observing the cross-sectional morphology of the negative electrode sheet along the thickness direction or observing the negative electrode active material powder through a scanning electron microscope. Graphite particles with irregular shapes and flat shapes are artificial graphite particles, and graphite particles with rounded surfaces and higher sphericity are natural graphite particles. There are no special restrictions on the types of precursors, graphitization methods, carbonization methods, and other processes of the artificial graphite used in the embodiments of the present application.

[0043] The present application does not particularly limit the preparation method of the negative electrode active material, as long as it can achieve the purpose of the present application. For example, the preparation method of the negative electrode active material may include but is not limited to the following preparation steps:

[0044] S1: Provide natural graphite pellets with a particle size of 6μm to 23μm and a purity of more than 95%;

[0045] S2: providing raw coke with a particle size of 8 μm to 15 μm as an artificial graphite precursor component;

[0046] S3: Provide high coking value asphalt as adhesive;

[0047] S4: mixing a natural graphite component, an artificial graphite precursor component, and an adhesive in a mass ratio of (10 to 90):(10 to 90):(2 to 10) to obtain a mixed raw material, and adding the mixed raw material into a reactor;

[0048] S5: heat treating the reactor at a temperature T1 of 300° C. to 800° C. for a heat treatment time t1 of 2 h to 8 h, melting the adhesive to bond the natural graphite and the artificial graphite precursor components together, and then cooling to room temperature to obtain a sample;

[0049] S6: placing the sample into a crucible and performing low-temperature graphitization treatment to obtain a treated sample, wherein the temperature T2 of the low-temperature graphitization treatment is 1800° C. to 2600° C. and the time t2 is 36 h to 48 h;

[0050] S7: Classifying and shaping the treated sample to obtain the desired particle size distribution and sphericity;

[0051] S8: Then sieve and demagnetize to obtain the negative electrode active material.

[0052] The present application does not specifically limit the raw coke in S2, as long as the objectives of this application can be achieved. For example, the raw coke may include, but is not limited to, at least one of petroleum coke, asphalt coke, and coal coke. The high coking value asphalt in S3 refers to asphalt with a coking value of 30% to 80%. The present application does not specifically limit the classification and shaping in S7, or the screening and demagnetization in S8; these are conventional steps known in the art.

[0053] Generally, the Dn10, Dv50, and Dv90 of the negative electrode active material can be controlled by regulating the parameters of grading, shaping, and screening, thereby regulating the value of D. The sphericity C and tap density of the negative electrode active material can also be regulated by regulating the parameters of grading, shaping, and screening. The value of I can be regulated by regulating the mass proportion of the binder in the mixed raw material. For example, the smaller the mass proportion of the binder in the mixed raw material, the greater the value of I; the larger the mass proportion of the binder in the mixed raw material, the smaller the value of I. The degree of graphitization G can be regulated by regulating the temperature and time of the low-temperature graphitization treatment. For example, the higher the temperature and the longer the time of the low-temperature graphitization treatment, the greater the graphitization degree G; the lower the temperature and the shorter the time of the low-temperature graphitization treatment, the smaller the graphitization degree G. The gram capacity W can be regulated by regulating the ratio of natural graphite and artificial graphite precursor in this application. For example, the lower the ratio of artificial graphite precursor in this application, the greater the gram capacity W; the higher the ratio of artificial graphite precursor in this application, the smaller the gram capacity W. The value of Id / Ig can be controlled by regulating the temperature of the low-temperature graphitization treatment or the mass proportion of the binder in the mixed raw materials. For example, the lower the temperature of the low-temperature graphitization treatment or the higher the mass proportion of the binder in the mixed raw materials, the greater the value of Id / Ig; the higher the temperature of the low-temperature graphitization treatment or the lower the mass proportion of the binder in the mixed raw materials, the smaller the value of Id / Ig.

[0054] A second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises the negative electrode active material of any of the aforementioned embodiments. The secondary battery of the present application has good cycle performance, expansion performance, and rate performance.

[0055] The phrase "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" herein can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in this application, as long as the objectives of this application can be achieved.

[0056] In some embodiments of the present application, the porosity of the negative electrode sheet is 25% to 40%. For example, the porosity of the negative electrode sheet can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or a range consisting of any two of these values. This indicates that the negative electrode sheet has a higher porosity, which is conducive to the transmission and diffusion of active ions, thereby improving the cycle performance, expansion performance, and rate performance of the secondary battery.

[0057] In some embodiments of the present application, the OI value of the negative electrode plate is 8 to 15. For example, the OI value of the negative electrode plate can be 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. Negative electrode plates with OI values ​​within the above ranges have good ion diffusion properties. Application of such negative electrode plates in secondary batteries can improve the cycling performance and expansion performance of the secondary batteries.

[0058] In the present application, the negative electrode active material may also include other negative electrode active materials known in the prior art. For example, other negative electrode active materials may include but are not limited to mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon materials, silicon-oxygen materials, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys. This application does not limit the content of other negative electrode active materials, as long as the purpose of this application can be achieved.

[0059] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a polymer substrate coated with a conductive metal, etc. Among them, the conductive metal includes but is not limited to copper, nickel or titanium, and the material of the polymer substrate includes but is not limited to at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene naphthalate or poly(p-phenylene terephthalamide). In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 12μm, and the thickness of the single-sided negative electrode material layer is 50μm to 200μm.

[0060] The negative electrode material layer in the present application may also include at least one of a conductive agent, a binder or a thickener. The present application does not particularly limit the types of conductive agents and binders, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. For example, the binder may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer. Those skilled in the art may select the appropriate thickener based on actual needs, as long as the objectives of the present application are achieved.

[0061] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.

[0062] The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0063] The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include a metal foil or a composite current collector, etc. For example, the metal foil may be an aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer located on at least one surface of the polymer material base layer. The material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver or silver alloy. The polymer material base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene or polyethylene. The positive electrode material layer of the present application contains a positive electrode active material. The present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material includes lithium cobalt oxide, lithium nickel cobalt manganese oxide (NCO2), ... 0.95 C 0.05 M 0.05 , NCM811, NCM622, NCM523, NCM111), at least one of lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide or lithium titanate.

[0064] The present application has no particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. The thickness of the single-sided positive electrode material layer is 50μm to 300μm. The positive electrode material layer of the present application may also contain the above-mentioned binder and the above-mentioned conductive agent. The present application has no particular restrictions on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0065] In the present application, the electrolyte includes a lithium salt and an organic solvent. The lithium salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB) or lithium difluorooxalatoborate (LiDFOB). The present application has no particular restrictions on the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the above-mentioned organic solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvent. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound or a cyclic carbonate compound. The above-mentioned chain carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or methyl ethyl carbonate. The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate, propylene carbonate, butylene carbonate or vinyl ethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The electrolyte may further include additives, which may include, but are not limited to, at least one of fluoroethylene carbonate, 1,3-propane sultone, or adiponitrile.

[0066] The secondary battery of the present application may further include a diaphragm to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, as long as it can achieve the purpose of the present application. For example, the material of the diaphragm may include but is not limited to polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin diaphragms, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films, polyamide films, spandex or aramid films, etc. At least one of the types of diaphragms may include but is not limited to woven films, non-woven films (non-woven fabrics), microporous films, composite films, rolled films or spun films, etc. The diaphragm of the present application may have a porous structure, and the porous layer is provided on at least one surface of the diaphragm, and the porous layer includes inorganic particles and a binder. The inorganic particles may include 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 or barium sulfate. The binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the size of the pore size of the porous structure, as long as the purpose of the present application can be achieved, for example, the size of the pore size can be 0.01 μm to 1 μm. In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness can be 3 μm to 30 μm.

[0067] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0068] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one embodiment of the present application, the secondary battery may include, but is not limited to, a lithium ion battery or a sodium ion battery.

[0069] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0070] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In certain embodiments, electronic equipment can include but is not limited to laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, 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-scale household batteries and lithium-ion capacitors, etc.

[0071] Example

[0072] The following describes the present invention in more detail using lithium-ion batteries as examples and comparative examples. Various tests and evaluations were performed using the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0073] Test methods and equipment:

[0074] Sampling method for negative electrode sheets and negative electrode active materials:

[0075] The lithium-ion battery was discharged at a constant current of 1C to a voltage of 3.0V, then disassembled. The negative electrode was removed and soaked in dimethyl carbonate (DMC) for 20 minutes, followed by a rinse with DMC and then acetone. The negative electrode was then placed in an oven and baked at 80°C for 12 hours to obtain a treated negative electrode sample. The negative electrode samples used in the following porosity test were sampled using this method.

[0076] The negative electrode material layer on the negative electrode sheet was scraped off with a scraper. The powder was then heat-treated in a tube furnace at 400°C for 4 hours under argon to remove the binder adhering to the surface of the negative electrode active material. This yielded a powder sample of the negative electrode active material. The negative electrode active material samples used in the following particle size, sphericity, X-ray diffraction (XRD), tap density, Raman spectroscopy, and scanning electron microscopy tests were all sampled using this method.

[0077] Powder particle size test:

[0078] The powder particle size test method follows GB / T 19077-2016. The specific procedure involves weighing 1g of sample and mixing it with 20mL of deionized water and a trace amount of dispersant. The mixture 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 scattered light as a laser beam passes through the dispersed particle sample. The data is then used to analyze and calculate the powder particle size distribution, which forms the scattering spectrum. The particles used in the test have a refractive index of 1.8. Each sample is tested three times, and the particle size Dn10, Dv50, and Dv90 values ​​are calculated as the average of these three measurements. Dn10 represents the particle size at which the cumulative number of particles reaches 10% of the total number of particles, measured from the smallest particle size. Dv50 represents the particle size at which the cumulative volume of particles reaches 50% of the total volume of particles, measured from the smallest particle size. Dv90 indicates the particle size at which 90% of the volume is accumulated, measured from the smallest particle size in the volume-based particle size distribution.

[0079] Sphericity test:

[0080] Using a particle shape image analysis device, the particles of the dynamically flowing sample were continuously focused and photographed, obtaining 50 particle images. The plane projection area A and projection perimeter P of each particle in the image were obtained through image processing software, and the sphericity C = 4πA / P was then calculated. 2 , take the average value of the sphericity of all particles as the final result.

[0081] XRD test:

[0082] According to the international standard JJS K 0131-1996, "General Rules for X-ray Diffraction Analysis," an X-ray diffractometer (Bruker D8 ADVANCE) was used, using Cu Kα radiation at a voltage of 40 kV and a current of 40 mA. The test angle ranged from 20° to 80°, with a step time of 0.3 s. The negative electrode active material powder was scanned to obtain an XRD spectrum. The peak values ​​of the (004) crystal plane diffraction peak and the (110) crystal plane diffraction peak were analyzed and the ratio of the (004) crystal plane diffraction peak to the (110) crystal plane diffraction peak was calculated to obtain the peak intensity ratio (I) of the negative electrode active material powder characteristic peak C004 to characteristic peak C110.

[0083] The negative electrode piece was scanned to obtain an XRD spectrum, and the peak values ​​of the (004) crystal plane diffraction peak and the (110) crystal plane diffraction peak were obtained by analysis. The OI value of the negative electrode piece was obtained by calculating the ratio of the peak values ​​of the (004) crystal plane diffraction peak and the (110) crystal plane diffraction peak.

[0084] An X-ray diffractometer (Bruker D8ADVANCE) was used, using Cu Kα radiation, a voltage of 40 kV, a current of 40 mA, a test angle of 52° to 58°, and a step time of 0.3 s. A silicon standard containing a carbon-silicon standard ratio of C:Si=5:1 (mass ratio) was used as a reference sample for scanning testing. The XRD pattern of the negative electrode active material powder was processed to obtain the interplanar spacing d at the (002) peak position of the negative electrode active material. 002 By calculating the graphitization degree of the negative electrode active material G = (3.44-d 002 ) / (3.44-3.354)×100%.

[0085] Tap density test:

[0086] The tap density of a powder sample (50 ± 0.2 g) was measured using a GeoPyc 1365 instrument from McMurtry's National Standard GB / T 5162-2006, "Determination of Tap Density of Metal Powders," at a vibration frequency of 250 times / min.

[0087] Raman testing:

[0088] The Raman spectrum of the negative electrode active material was tested using a laser microconfocal Raman spectrometer (HR Evolution, manufactured by HORIBA, France). The laser wavelength of the Raman spectrometer can be in the range of 532nm to 633nm. The negative electrode active material powder was tested. During the test, a 100μm×100μm range was scanned. The particles within this area were scanned and 100 points were tested at equal intervals. The test range of each point was 0.02cm. -1 to 0.05cm-1 Between. Recorded at 1300cm -1 to 1400cm -1 The peak between is the d peak, at 1500cm -1 to 1600cm -1 The peak between the two peaks is the g peak. The La Spec software is used to process the data to obtain the peak intensities of the d peak and the g peak of the particles, which are recorded as I d and I g , count the I of each point d / I g The intensity ratio of the 100 points is then calculated as the average value of the final I d / I g strength ratio.

[0089] Scanning electron microscope (SEM) test:

[0090] The JEOL JSM-6360LV scanning electron microscope and its supporting X-ray spectrometer were used to analyze the morphology and structure of the negative electrode active material samples, observe the morphological characteristics of the samples and take scanning electron microscope photos.

[0091] Pole piece porosity test:

[0092] The negative electrode was prepared into a 10 cm diameter disc. 30 samples were tested for each example or comparative example, and the volume of each sample was about 0.35 cm. 3 According to the national standard GB / T24586-2009 “Determination of apparent density, true density and porosity of iron ore”, the porosity of the negative electrode material layer was tested using an AccuPycⅡ1340 true density meter, and helium was used as the test gas.

[0093] Rate performance test:

[0094] At 25°C, the lithium-ion battery is charged to 3.6V at a constant current of 0.2C, then charged to 0.05C at a constant voltage of 3.6V, left to stand for 5 minutes, and then discharged to 2.5V at a rate of 0.2C to obtain a 0.2C discharge capacity. Then, it is charged to 3.6V at a constant current of 0.2C, charged to 0.05C at a constant voltage of 3.6V, left to stand for 30 minutes, and then discharged to 2.5V at a rate of 3C to obtain a 3C discharge capacity. The 3C / 0.2C rate performance of the lithium-ion battery = 3C discharge capacity / 0.2C discharge capacity × 100%.

[0095] Cyclic performance test:

[0096] The lithium-ion battery was placed in a constant temperature box at 25℃±1℃ for 30 minutes. The cycle process was as follows: charging to 3.6V at a constant current of 0.5C, then charging to 0.02C at a constant voltage of 3.6V, and then standing for 15 minutes. Then, it was discharged to 2.5V at a rate of 0.5C and stood for 30 minutes. This was a charge and discharge cycle process. The thickness H0 and the first cycle discharge capacity C0 of the lithium-ion battery were recorded. After that, the above cycle process was repeated for 3000 cycles. At the 100th, 200th, and 300th cycles, the battery was charged to 2.5V at a rate of 0.5C. Small-rate capacity recovery was performed at 400, 500, every 200 cycles from 501 to 1500, and every 500 cycles from 1501 to 3000. The small-rate capacity recovery charge and discharge process was as follows: the lithium-ion battery was placed in a constant temperature chamber at 25°C ± 1°C for 30 minutes. The cycle process was as follows: constant current charge at 0.2C to 3.6V, constant voltage charge at 3.6V to 0.02C, rest for 15 minutes, and then discharge at 0.2C to 2.5V and rest for 30 minutes. The thickness H1 and cyclic discharge capacity C1 of the lithium-ion battery at the 3000th cycle were recorded.

[0097] 3000 cycle capacity retention rate = C1 / C0×100%.

[0098] Thickness expansion rate after 3000 cycles = (H1-H0) / H0×100%.

[0099] Example 1-1

[0100] <Preparation of negative electrode active material>

[0101] Natural graphite (particle size of 8μm, purity of 99.5%), artificial graphite precursor component petroleum coke (particle size of 10μm), and adhesive asphalt (coking value of 70%) are mixed evenly in a mass ratio of x:y:z=48:48:4, and then put into a reactor. Heat treatment is carried out at a heating rate of 4℃ / min to T1=500℃, and the heat treatment time is t1=4h. The heat-treated sample is placed in a crucible and then subjected to low-temperature graphitization treatment under an argon atmosphere. The low-temperature graphitization treatment temperature is T2=2200℃ and the time is t2=24h. Then it is cooled to room temperature, graded, shaped, sieved, and demagnetized by an electromagnetizer to obtain the negative electrode active material.

[0102] The Dn10, Dv50, Dv90, I, sphericity C, and tap density TD of the negative electrode active materials are shown in Table 1.

[0103] <Preparation of negative electrode sheet>

[0104] The negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) prepared above were mixed in a mass ratio of 97.4:1.5:1.5. Deionized water was then added as a solvent and stirred thoroughly to prepare a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was evenly coated on one surface of a 6 μm thick negative electrode current collector copper foil and dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided negative electrode material layer and a coating thickness of 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After cold pressing (cold pressing pressure of 15T), cutting, and slitting, the negative electrode sheet was obtained with a specification of 76.6 mm × 875 mm.

[0105] <Preparation of positive electrode sheet>

[0106] The positive electrode active material, lithium iron phosphate, the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 96.3:2.2:1.5. N-methylpyrrolidone (NMP) was added as a solvent and stirred thoroughly to prepare a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on one surface of a 13 μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a single-sided positive electrode material-coated positive electrode sheet with a thickness of 130 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode material-coated positive electrode sheet. After cold pressing, cutting, and slitting, the resulting positive electrode sheet had a size of 74 mm x 867 mm.

[0107] <Preparation of Electrolyte>

[0108] In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. Fluorinated ethylene carbonate and 1,3-propane sultone were then added, dissolved, and stirred uniformly. The lithium salt LiPF6 was then added and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of the lithium salt was 12.5%, the mass percentage of fluoroethylene carbonate was 2%, the mass percentage of 1,3-propane sultone was 2%, and the balance was the base solvent.

[0109] <Diaphragm>

[0110] A polyethylene film with a thickness of 7 μm (supplied by Celgard) was used as a separator.

[0111] <Preparation of lithium-ion batteries>

[0112] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an insulator, and then wound to form an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in an 80°C vacuum oven to dry for 12 hours to remove moisture, and then injected with the prepared electrolyte. After vacuum packaging, standing, formation (temperature 45°C, 0.1C constant current charging, end time 1800s, then 0.5C constant current charging to 3.6V), degassing, and trimming, a lithium-ion battery is obtained.

[0113] Example 1-2 to Example 1-18

[0114] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0115] Example 2-1 to Example 2-6

[0116] Except for adjusting the parameters according to Table 2, the rest is the same as Example 1-3.

[0117] Comparative Example 1-1 to Comparative Example 1-4

[0118] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0119] Comparative Examples 1-5

[0120] Except that the natural graphite in Example 1-1 is directly used as the negative electrode active material to prepare the negative electrode sheet, the rest is the same as Example 1-1.

[0121] The relevant parameters and performance tests of each embodiment and each comparative example are shown in Tables 1 and 2.

[0122] Table 1

[0123] It can be seen from Examples 1-1 to 1-18 and Comparative Examples 1-1 to 1-5 that when the D value and I / D value of the negative electrode active material are within the range of the present application, the obtained lithium ion battery has a higher cycle capacity retention rate and a lower thickness expansion rate, indicating that the lithium ion battery of the present application has better cycle performance and expansion performance.

[0124] From Example 1-1 to Example 1-18, it can be seen that Dn10, Dv50, Dv90, C, and TD of the negative electrode active material are interrelated and influence each other, which in turn affect the value of D, the value of I, the value of I / D, and the value of D / C+1, and the values ​​of the above characteristics are all within the scope of the present application. The porosity and OI value of the obtained negative electrode sheet are also within the scope of the present application. The lithium-ion batteries have a higher cycle capacity retention rate and a lower cycle thickness expansion rate, which indicates that the lithium-ion batteries have good cycle performance and expansion performance.

[0125] Specifically, as shown in Figure 1, which is an electron micrograph of the negative electrode active material in Example 1-1, it can be seen that the negative electrode active material has a relatively uniform particle size, which is beneficial for improving lithium ion diffusion and electronic conductivity, thereby improving the cycle performance and rate performance of the lithium-ion battery. Figure 2 is an XRD pattern of the negative electrode active material in Example 1-3. As can be seen from the figure, the peak area corresponding to the characteristic peak C004 at 54.56° is 3021.82, and the peak area corresponding to the characteristic peak C110 at 77.41° is 712.44. The peak area ratio I of the characteristic peak C004 to the characteristic peak C110 is 4.2. Figure 3 is the XRD pattern of the negative electrode sheet in Example 1-3. It can be seen from the figure that the peak area corresponding to the (004) crystal plane diffraction peak at 54.65° is 2665.10, and the peak area corresponding to the (110) crystal plane diffraction peak at 77.49° is 222.09, so the OI value of the negative electrode sheet is 12. Figures 4 and 5 are graphs showing the cycle retention rate and thickness expansion rate of the lithium-ion batteries in Example 1-1 and Comparative Example 1-1 as a function of the number of cycles. It can be seen from the figures that the cycle capacity retention rate of Example 1-1 is always higher than that of Comparative Example 1-1, and the thickness expansion rate is always lower than that of Comparative Example 1-1.

[0126] Table 2

[0127] It can be seen from Examples 1-3 and 2-1 to 2-6 that the values ​​of the degree of graphitization G, gram capacity W and Id / Ig of the negative electrode active material vary with the changes in the preparation parameters, and there is a correlation and influence between the degree of graphitization G, gram capacity W and Id / Ig of the negative electrode active material. When the values ​​of the above characteristics are all within the scope of this application, the porosity and OI value of the obtained negative electrode sheet are also within the scope of this application, and the lithium-ion batteries have higher cycle capacity retention and lower cycle thickness expansion rate, which means that when the degree of graphitization G, gram capacity W and Id / Ig of the negative electrode active material are within the scope of this application, the lithium-ion batteries have better cycle performance and expansion performance.

[0128] Specifically, FIG6 is a Raman spectrum of the negative electrode active material in Example 1-3, the peak intensity corresponding to the d peak is 89.52, the peak intensity corresponding to the g peak is 710.92, and the Id / Ig of the negative electrode active material is 0.13.

[0129] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0130] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. A negative electrode active material comprising graphite, wherein Dn10, Dv50 and Dv90 of the negative electrode active material satisfy: D = (Dv90 - Dn10) / Dv50, 0.8 ≤ D ≤ 1.5; The Dn10 of the negative electrode active material is 1 μm to 5 μm; In the X-ray diffraction spectrum of the negative electrode active material, the peak intensity ratio of the characteristic peak C004 to the characteristic peak C110 is 1; The negative electrode active material satisfies: 2≤I / D≤4.

2. The negative electrode active material according to claim 1, wherein 2≤I≤6。 3. The negative electrode active material according to claim 1 or 2, wherein The negative electrode active material satisfies at least one of the following conditions: (1) Dn10 is 2 μm to 4 μm; (2) Dv90 is 14 μm to 30 μm; (3) Dv50 is 8 μm to 15 μm; (4)2≤I≤4； (5) The graphite includes natural graphite and artificial graphite.

4. The negative electrode active material according to any one of claims 1 to 3, wherein The sphericity of the negative electrode active material is C=4πA / P 2 , 0.5≤C≤1, A is the area of ​​the positive projection of the negative electrode active material particle, and P is the perimeter of the positive projection of the negative electrode active material particle; The negative electrode active material satisfies: 1.8≤D / C+1≤4.

5. The negative electrode active material according to any one of claims 1 to 4, wherein The negative electrode active material satisfies at least one of the following conditions: (a) The tap density TD of the negative electrode active material is 0.8 g / cm 3 Up to 1.2g / cm 3 ; (b) the graphitization degree G of the negative electrode active material is 90% to 96%; (c) The gram capacity W of the negative electrode active material is 344 mAh / g to 358 mAh / g.

6. The negative electrode active material according to any one of claims 1 to 5, wherein 0.8≤D≤1.3。 7. The negative electrode active material according to any one of claims 1 to 6, wherein 2.4≤I / D≤3.

5.

8. The negative electrode active material according to any one of claims 1 to 7, wherein In the Raman spectrum of the negative electrode active material, the peak intensity ratio Id / Ig of the d peak and the g peak is 0.1 to 0.

3.

9. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode collector and a negative electrode material layer disposed on at least one surface of the negative electrode collector, wherein the negative electrode material layer comprises the negative electrode active material according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein The negative electrode sheet satisfies at least one of the following conditions: (i) the porosity of the negative electrode sheet is 25% to 40%; (ii) The OI value of the negative electrode plate is 8 to 15. 11 . An electronic device comprising the secondary battery according to claim 9 or 10.

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