Negative electrode plate, secondary battery and electrical device

Abstract

A negative electrode plate 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 a negative electrode active material, the negative electrode active material comprising graphite, wherein the negative electrode plate satisfies the following equation: 1.0×10-3≤(|La1-La2| / Lax) / (VOI×DV50)≤3.0×10-3;in the equation, La1 is an average crystal size in the a-axis direction of the negative electrode plate obtained by XRD measurement, and the unit is nm, La2 is an average crystal size in the a-axis direction of the negative electrode plate obtained by Raman spectroscopy measurement, and the unit is nm, Lax is a larger value of La1 and La2, VOI is a ratio of a peak intensity I004 of a (004) crystal plane to a peak intensity I110 of a (110) crystal plane of the negative electrode plate obtained by XRD measurement, and DV50 is a particle size corresponding to the time when a cumulative volume distribution percentage of the negative electrode active material reaches 50%, and the unit is µm.;

Description

BACKGROUNDTechnical FieldThe disclosure relates to the technical field of batteries, and more particularly to a negative electrode plate, a secondary battery, and an electric device.Description of the Prior ArtIn recent years, as electric vehicles increasingly replace the fuel-powered vehicles, people's demand for the performance of batteries for electric vehicles has become increasingly high: not only a higher energy density is required to improve the range, but also a faster charging speed to shorten the charging time. Therefore, the question of how to improve the charging speed of the battery is one of the problems to be solved urgent.Lithium ion batteries have advantages of high energy density, long life, and environmental friendliness, and are widely used in the field of electric vehicles. At present, the improvement of the rapid charging performance of lithium ion batteries mainly depends on the development and improvement of the materials for the negative electrodes. Among the materials, graphite negative electrodes are the most important negative electrode materials for power batteries at present because of their good cycle and rate performance as well as their good selectivity to the electrolyte. However, conventional graphite-based negative electrode materials have a limited diffusion rate for lithium ions and tend to precipitate metallic lithium within a very short number of cycles, resulting in a short cycle life, so that it is difficult to meet the requirements for rapid charging and cycle life of electric batteries.Therefore, the improvement of the charging speed and the life of the battery has become a technical problem that must be solved urgent by those skilled in the art.SUMMARYThe purpose of the disclosure is to overcome the deficiencies of the prior art and to provide a negative electrode plate, a secondary battery, and an electrical device, the disclosure promoting rapid storage and release of lithium ions from the negative electrode plate by reasonably limiting the crystal size and orientation value of the negative electrode plate and the particle size of the negative electrode active material, so that the battery including the negative electrode plate has excellent rapid charging performance and cycle life. The invention is defined by the features of the independent claims. Advantageous embodiments are the subject of the dependent claims.In order to achieve the above-mentioned purpose, in the first aspect of the disclosure, the disclosure provides a negative electrode plate including: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 a negative electrode active material;wherein the negative electrode active material comprises graphite;wherein the negative electrode plate satisfies an equation as follows: wherein La1 is the average crystal size in the a-axis direction of the negative electrode plate obtained by XRD measurement, and the unit is nm,La2is the average crystal size in the a-axis direction of the negative electrode plate obtained by Raman spectroscopy measurement, and the unit is nm,Lax is the larger value of La1 and La2,V OI is the ratio of the peak intensity I 004 of the (004) crystal plane to the peak intensity I 110 of the (110) crystal plane of the negative electrode plate obtained by XRD measurement, D V50 is the particle size corresponding to the time point at which the cumulative volume distribution percentage of the negative electrode active material reaches 50%, and the unit is μm.In an alternative embodiment of the disclosure, the negative electrode plate satisfies the following equation: 1.2×10-3≤(|La1-La2| / Lax) / (V OI×D V50) ≤2.5×10-3.In an alternative embodiment of the disclosure, the range of La1is 30 to 70 nm.In an alternative embodiment of the disclosure, the range of La2is 50 to 80 nm.In an alternative embodiment of the disclosure, the range of La1is 45 to 60 nm and the range of La2is 65 to 75 nm.In an alternative embodiment of the disclosure, the range of V OI is 10 to 35.In an alternative embodiment of the disclosure, the range of V OI is 11 to 15.In an alternative embodiment of the disclosure, the range of D V50 is 5 to 20 μm.In an alternative embodiment of the disclosure, the range of D V50 is 8 to 15 μm.In an alternative embodiment of the disclosure, the porosity P of the negative electrode plate is 20 to 45%.In an alternative embodiment of the disclosure, the porosity P of the negative electrode plate is 30 to 40%.In the second aspect of the disclosure, the disclosure provides a secondary battery including a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the negative electrode plate is the above-mentioned negative electrode plate.In the third aspect of the disclosure, the disclosure provides an electric device including the above-mentioned secondary battery.The disclosure has the following positive effects:The disclosure promotes rapid storage and release of lithium ions from the negative electrode plate by reasonably limiting the crystal size and orientation value of the negative electrode plate and the particle size of the negative electrode active material, so that the battery including the negative electrode plate has excellent rapid charging performance and cycle life.BRIEF DESCRIPTION OF THE DRAWINGSFor a better understanding of the invention, reference may be made to the exemplary embodiments illustrated in the following drawings. The components in the drawings are not necessarily to scale and related elements may be omitted, or in some cases, the proportions may be exaggerated, to emphasize and clearly illustrate the features described herein. Moreover, related elements or components may be arranged differently as is known in the art. In addition, in the drawings, like reference numerals designate corresponding parts throughout the several views. For a better understanding of the invention, reference may be made to the exemplary embodiment illustrated in the following drawings. The components in the drawings are not necessarily to scale and related elements may be omitted or in some cases the proportions may be exaggerated. FIG. 1 is an XRD pattern of a negative electrode plate prepared in Example 2 of the disclosure. FIG. 2 is a Raman spectrum of the negative electrode plate prepared in Example 2 of the disclosure.DESCRIPTION OF THE EMBODIMENTSIn order to clarify the purpose, the technical solutions, and the advantages of the embodiments of the disclosure, the technical solutions in the embodiments of the disclosure will be clearly and fully described below. Of course, the described embodiments are only a part of the embodiments of the disclosure, and not all embodiments. Based on the embodiments of the disclosure, all other embodiments obtained by those skilled in the art without any user's activity fall within the scope of the disclosure.In the disclosure, the technical features described in the open specification include both closed technical solutions consisting of the listed features and open technical solutions having the listed features.In the disclosure, unless otherwise stated, numerical ranges are considered to be continuous and include the minimum and maximum values of the range, as well as any value between the minimum and maximum values. If the range refers to an integer, it also includes any integer between the minimum value and the maximum value of the range. When multiple regions are specified to describe a feature or property, the regions may also be merged. In other words, unless otherwise specified, all the ranges disclosed herein are to be understood as including all the sub-ranges included therein.In the disclosure, there are no particular restrictions on the specific dispersion and stirring methods.The reagents or instruments used in the disclosure are commercially available products, which are commercially available, without the manufacturer's instructions.Negative electrode plateOne aspect of the disclosure provides a negative electrode plate including:.A negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector are provided, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite.The negative electrode plate satisfies the following equation.1.0×10 -3 ≤(|La1-La2| / Lax) / (V OI × D V50) ≤3.0×10 -3, and a description of the equation is as follows.La 1 is the average crystal size in the a-axis direction of the negative electrode plate obtained by XRD measurement, and the unit is nm.La2is the average crystal size in the a-axis direction of the negative electrode plate obtained by Raman spectroscopy measurement, and the unit is nm.Lax is the larger value of La1 and La2.V OI is the ratio of the peak intensity I 004 of the (004) crystal plane to the peak intensity I 110 of the (110) crystal plane of the negative electrode plate obtained by XRD measurement.D V50 is the particle size corresponding to the time point at which the cumulative volume distribution percentage of the negative electrode active material reaches 50%, and the unit is μm.The La1 value of the negative electrode plate can be obtained by an X-ray diffraction (XRD) test calculated by the Scherer formula, and the conditions of the XRD test can be the same as the known methods. The La2 value of the negative electrode is examined by Raman spectroscopy and calculated according to the following formula: La2=2.4×10 -10 ×λ 4 × (A D / A G)-1, where λ is the incident laser wavelength of the Raman spectrum, A D is the peak area of the D peak (located in the wavelength range of 1320 to 1380 cm -1) in the Raman spectrum, and A G is the peak area of the G peak (located in the wavelength range of 1560 to 1600 cm -1) in the Raman spectrum.In negative electrode active materials containing graphite, the change in the average crystal size La is influenced by the degree of graphitization. When hetero atoms or molecules are inserted between the surface layers of the graphite, the average crystal size La changes. Since the graphitization process is a nonlinear, continuous and erratic process, the physical and chemical structure of the graphite is not uniform. If conditions such as pretreatment temperature and pressure are varied, new components having different degrees of graphitization may coexist. When the components having different degree of graphitization reach a specific content, the Raman parameters for evaluating the degree of ordering may deviate from the development curve of the XRD parameters. Therefore, there are specific differences between the La1 value and the La2 value of the same negative electrode plate.The inventors have found that the difference between La1measured by XRD and La2measured by Raman spectroscopy can be used to comprehensively evaluate the degree of graphitization of the negative electrode plate and the degree of deterioration of the graphite by heteroatoms. In the disclosure, the difference rate between La 1 and La 2 is expressed by the ratio of |La 1-La 2| to Lax. The larger the difference between the two values, the more internal defects are present in the graphite. The difference rate between La1 and La2 affects on the one hand the rapid charging performance of the battery and on the other hand the high temperature resistance of the battery. The inventors have found that when the difference rate between La1 and La2 is within an appropriate range so that the negative electrode plate satisfies the above-mentioned equation, the battery has both excellent rapid charging performance and high temperature performance and has a high cycle life under rapid charging or high temperature conditions.The V OI of the negative electrode plate represents the orientation index of the material. The V OI can be determined by the following method. The prepared negative electrode plate is directly placed in an X-ray diffractometer, the peak intensity I 004 of the (004) crystal plane diffraction peak, and the peak intensity I 110 of the (110) crystal plane diffraction peak of the negative electrode active material in the negative electrode plate are obtained by X-ray diffractometry. The V OI of the negative electrode plate is I 004 / I 110.D V50 is the particle size obtained when the cumulative volume distribution percentage of the negative electrode active material reaches 50%. The disclosure does not limit the method for detecting D V50. It is possible for the person skilled in the art to determine the D V50 of the negative electrode active material using conventional technical means. For example, the D V50 is determined with a laser particle measurement device.The inventors of the disclosure have found through extensive research that, for negative electrode plates containing negative electrode active materials, V OI × D V50 can comprehensively judge the morphological characteristics of the negative electrode active materials such as orientation and particle size. By further combining the ratio of |La1-La2| to Lax, the grain size of the negative electrode plate and the morphology properties of the negative electrode active material are appropriately controlled, thereby improving the rapid charging performance and the cycle life of the lithium ion battery.In one embodiment, the negative electrode plate satisfies the following equation: 1.2×10 -3 ≤(|La1-La2| / Lax) / (V OI D V50) ≤2.5×10 -3. When the negative electrode plate satisfies the range of the equation, the overall performance of the negative electrode plate is relatively better, so that the fast charging performance and the cycle life of the lithium ion battery are relatively more balanced. In some embodiments, for example, the value of (|La1-La2| / Lax) / (V OI × D V50) of the negative electrode plate is 1.2×10 -3, 1,3×10 -3, 1,5×10 -3, 1,8×10 -3, 2,0×10 -3, 2,3×10 -3 or 2.5×10 -3.In one embodiment, the range of La1is 30 to 70 nm, e.g., 32 nm, 37 nm, 41 nm, 45 nm, 52 nm, 58 nm, 60 nm, or 67 nm.In one embodiment, the range of La2is 50 to 80 nm, e.g., 55 nm, 59 nm, 65 nm, 67 nm, 69 nm, 72 nm, 75 nm, or 79 nm.In one embodiment, the range of La1is 45 to 60 nm and the range of La2is 65 to 75 nm.La 1 and La 2 of the negative electrode plate can be controlled by graphitising the negative electrode active material under various conditions such as temperature, time, and pressure. When the value of La 1 or La 2 of the negative electrode plate is too small, the crystallinity of the negative electrode active material is relatively low and the capacity is small, which restricts the improvement in the energy density of the lithium ion battery. When the value of La1or La2of the negative electrode plate is too large, the diffusion distance of lithium ions after being embedded in the negative electrode active material layer increases, resulting in an increase in diffusion resistance, and lithium precipitates may occur during charging and discharging at high rates, thereby decreasing the cycle life of the battery.In one embodiment, the range of V is OI10 to 35, for example, 10.5, 11.4, 12.7, 13.5, 15.9, 17.1, 24.4, 27.5 or 33.9.In an alternative embodiment, V OI is in the range of 11 to 15.The V OI- value of the negative electrode plate can be controlled by methods such as adjustment of the density of the negative electrode plate or adjustment of the V OI- value of the negative electrode active material. If the V OI- value of the negative electrode plate is small, the negative electrode active material is more perpendicular to the current collector direction, which direction promotes the storage and release of lithium ions, and the rapid charging performance of the battery can be improved significantly; if the V OI- value is too small, the negative electrode plate tends to be folded during charging, thereby impairing the cycle performance of the battery.In one embodiment, the range of D is V50 5 to 20 μm, for example 7 μm, 8 μm, 10 μm, 11 μm, 13 μm, 15 μm or 18 μm.In an alternative embodiment, the range of D is V50 8 to 15 μm.When the D V50 of the negative electrode active material is small, the route of solid phase lithium ion transfer is relatively shorter, which contributes to improvement of the rapid charging performance of the battery. However, D V50 should not be too small, which makes the processing of the negative electrode active material layer difficult and leads to a low density of the negative electrode active material and deterioration of the electrochemical performance of the battery.In one embodiment, the porosity P of the negative electrode plate is in a range of 20 to 45%, e.g., 20%, 25%, 30%, 35%, 40% or 45%.In an alternative embodiment, the porosity P of the negative electrode plate is in a range of 30 to 40%.In general, the porosity of the negative electrode plate indirectly reflects the liquid phase diffusion resistance of lithium ions within the pores of the negative porous electrode. The larger the porosity, the lower the diffusion resistance in the liquid phase, which improves the rapid charging performance of the battery. However, if the porosity is too high, the electronic conductivity of the negative electrode decreases, thereby degrading the electrochemical performance of the battery. The inventors have found that, on the basis that the above equation is satisfied, when the porosity of the negative electrode plate of the disclosure is in a range of 20 to 45%, particularly in a range of 30 to 40%, the rapid charging performance and the cycle life of the battery including the negative electrode plate are relatively better.The graphite in the negative electrode active material of the disclosure may include natural graphite and / or artificial graphite. The negative electrode active material of the disclosure may be prepared by using needle coke, pitch coke, or petroleum coke at least as raw material.As for the negative electrode plate, there are no particular restrictions on the negative electrode current collector in the disclosure as long as the current collector has high conductivity and does not cause adverse chemical changes in the battery. For example, the following materials may be used: copper, stainless steel, aluminum, nickel, titanium, fired carbon; copper or stainless steel surface treated with carbon, nickel, titanium or silver; or an aluminum-cadmium alloy.The negative electrode active material layer of the negative electrode plate may include a conductive agent and a binder in addition to the negative electrode active material.The conductive agent plays a role in improving the conductivity of the negative electrode active material layer. The disclosure does not include any particular restrictions on the conductive agent. For example, carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; graphite powders such as natural graphite or artificial graphite; conductive fibers such as carbon fibers or metal fibers; or conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers may be used.The binder helps improve the adhesion between the conductive agent, the negative electrode active material, and the negative electrode current collector. The disclosure does not include any particular restrictions on the binder. For example, the following materials may be used: polymeric materials such as fluororesin binders, rubber binders, cellulose binders, polyol binders, polyolefin binders, polyimide binders, polyester binders or silane binders.Moreover, the negative electrode active material layer may further include a thickener, and carboxymethyl cellulose may be used as the thickener.It should be noted that the method for preparing the negative electrode plate in the disclosure is not particularly limited, and those skilled in the art can prepare a negative electrode plate according to conventional methods.The method for preparing the negative electrode plate is, for example, as follows.The negative electrode current collector may be coated with a negative electrode slurry prepared by dissolving or dispersing the negative electrode active material and optionally a binder and a conductive agent in a solvent, followed by rolling or drying.Alternatively, the method for preparing the negative electrode plate may be as follows. The negative electrode slurry is cast on a separate support, and then the film layer separate from the support is laminated on the negative electrode current collector.Secondary BatteryOne aspect of the disclosure provides a secondary battery including a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the negative electrode plate is the above-mentioned negative electrode plate.The positive electrode plate of the disclosure includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and may further include a conductive agent and / or a binder.The disclosure includes no particular restrictions on the positive electrode current collectors as long as the current collector has high conductivity and does not cause adverse chemical changes in the battery. For example, the following materials may be used: copper, stainless steel, aluminum, nickel, titanium, fired carbon; copper or stainless steel surface treated with carbon, nickel, titanium or silver; or an aluminum-cadmium alloy. The positive electrode current collector may be identical to or different from the negative electrode current collector of the disclosure.The positive electrode active material is a compound capable of reversibly depositing and releasing lithium. For example, the positive electrode active material may include a lithium composite metal oxide, and the lithium composite metal oxide includes lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al). Specifically, the positive electrode active material may include at least one of Li(Ni 0,6 Mn 0,2 Co 0,2) O 2, Li(Ni 0,7 Mn 0,2 Co 0,10) O 2, Li(Ni 0,8 Mn 0,1 Co0,1)O2, Li(Ni0,8Co0,15Al0,05)O2, Li(Ni 0,86 Mn 0,07 Co 0,05 Al 0,02) O 2, and Li(Ni 0,9 Mn 0,05 Co 0,05) O 2.The conductive agent plays a role in improving the conductivity of the positive electrode active material layer, and the disclosure has no particular limitation on the conductive agent. The conductive agent in the positive electrode plate may be identical to or different from the conductive agent in the negative electrode plate of the disclosure.The binder plays a role in improving the adhesion between the conductive agent, the positive electrode active material, and the positive electrode current collector. The disclosure does not include any particular restrictions on the binder. The binder in the positive electrode plate may be identical to or different from the binder in the negative electrode plate of the disclosure.Note that the method for preparing the positive electrode plate in the disclosure is not particularly limited, and those skilled in the art can prepare a positive electrode plate according to conventional methods.The method for preparing the positive electrode plate is exemplified as follows.The positive electrode current collector may be coated with a positive electrode slurry prepared by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive agent in a solvent, followed by rolling or drying.Alternatively, the method for preparing the positive electrode plate may be as follows. The positive electrode slurry is cast on a separate support, and then the film layer separate from the support is laminated on the positive electrode current collector.The electrolyte of the disclosure may be any electrolyte solution suitable for prior art electrochemical energy storage devices. The electrolyte solution includes an electrolyte and a solvent. The electrolyte may generally comprise a lithium salt. More specifically, the lithium salt may be an inorganic lithium salt and / or an organic lithium salt. The solvent in the electrolyte solution is typically a non-aqueous solvent. In particular, the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate / methylethyl carbonate or halogenated derivatives thereof.The secondary battery may further include a separator. The separator is disposed between the positive electrode plate and the negative electrode plate, and serves to separate the positive electrode plate and the negative electrode plate to prevent the positive electrode plate and the negative electrode plate from contacting each other and causing a short circuit. The separator may be made of any material suitable for use as a separator for electrochemical energy storage devices in the prior art. In particular, the separator comprises at least one of the following materials: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.Electrical DeviceOne aspect of the disclosure provides an electric device including the above-mentioned secondary battery. The secondary battery serves as a power supply for the electric device.The disclosure is described in more detail below with reference to specific embodiments.Example 1This configuration provides a lithium ion battery, and the specific preparation method is as follows.(1) Preparation of Negative Electrode PlateThe needle coke raw material was crushed and sieved to obtain graphite powder; then the graphite powder was graphitized at 2650° C. for 6 hours under an inert atmosphere; and after cooling, crushing and sieving, a negative electrode active material having a D V50 of 10.5 μm was obtained.The negative electrode active material, the binder (sodium carboxymethylcellulose), and the conductive agent (acetylene black) were mixed in a mass ratio of 98:1.5:0.5 and processed into a slurry by wet process, which was applied to the upper and lower surfaces of the negative electrode current collector (copper foil), and then the negative electrode plate was obtained after drying (at a temperature of 85° C., for 5 hours), rolling, and slitting.(2) Preparation of positive electrode plateThe positive electrode active material Li(Ni 0,8 Mn 0,1 Co 0,1) O 2, binder (polyvinylidene fluoride), and conductive agent (acetylene black) were mixed in a mass ratio of 98:1:1, N-methylpyrrolidone (NMP) was added, stirred under the action of a vacuum stirrer until the mixed system became a positive electrode slurry having uniform flowability; the positive electrode slurry was uniformly applied to the positive electrode current collector (aluminum foil) to a thickness of 9-12 μm; and then the positive electrode plate was obtained after drying (at a temperature of 120° C., for 8 hours), rolling, and slitting(3) Preparation of the electrolyte solutionThe electrolyte solution was a 1 mol / L LiPF 6- solution, and the solvent was a mixed solvent of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC, and DEC was 1:1:1.(4) Preparation of SeparatorA polyethylene (PE) separator coated with ceramics and polyvinylidene fluoride was used.(5) Preparation of the batteryThe positive electrode plate, the separator, and the negative electrode plate prepared above were wound to obtain a bare battery core without liquid injection; the bare battery core was placed in an outer packaging film, the prepared electrolyte solution was injected into the dried bare battery core, and a lithium ion battery was obtained according to processes such as vacuum packaging, standing, forming, shaping, and sorting.Example 2This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the needle coke raw material was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 2500° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 10 μm was obtained.Example 3This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 310° C. for 8 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 10.7 μm was obtained.Example 4This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 2900°C for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 15.1 μm was obtained.Example 5This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 4, while the difference was as follows.In the preparation of the negative electrode plate, the rolling pressure was adjusted so that the porosity of the prepared negative electrode plate was 45%.Example 6This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 4, while the difference was as follows.In the preparation of the negative electrode plate, the rolling pressure was adjusted so that the porosity of the prepared negative electrode plate was 22%.Example 7This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 280 °C for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 8.2 μm was obtained.Example 8This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the needle coke raw material was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 3000° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 11.2 μm was obtained.Example 9This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the needle coke raw material was crushed and sieved to obtain graphite powder, then graphitization of the graphite powder was carried out at 310° C. for 10 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 5 μm was obtained.Example 10This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, then graphitization of the graphite powder was carried out at 2500° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 19.6 μm was obtained.Configuration 11This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the asphalt coke raw material was crushed and sieved to obtain graphite powder, then graphitization of the graphite powder was carried out at 280 °C for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 10.2 μm was obtained.Example 12This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the needle coke raw material was crushed and sieved to obtain graphite powder, and then the graphite powder was graphitized at 3300° C. for 10 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 9.1 μm was obtained.Example 13This embodiment provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the asphalt coke raw material was crushed and sieved to obtain graphite powder, then the graphite powder was graphitized at 2500° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 18.2 μm was obtained.Comparative Example 1This comparative example provided a lithium ion battery, the specific preparation method was substantially the same as in Example 1, while the difference was as follows.In the preparation of the negative electrode plate, the needle coke raw material was crushed and sieved to obtain graphite powder, and then the graphite powder was graphitized at 280 °C for 4 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 17.3 μm was obtained.Comparative Example 2This comparative example provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, the difference being as follows.In the preparation of the negative electrode plate, the asphalt coke raw material was crushed and sieved to obtain graphite powder, and then the graphite powder was graphitized at 3000° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 6.1 μm was obtained.Comparative Example 3This comparative example provided a lithium ion battery, the specific preparation method was substantially the same as in Example 1, while the difference was as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, and then the graphite powder was graphitized at 3300° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 15.6 μm was obtained.Comparative Example 4This comparative example provided a lithium ion battery, the specific preparation method being substantially the same as in Example 1, while the difference was as follows.In the preparation of the negative electrode plate, the raw material petroleum coke was crushed and sieved to obtain graphite powder, and then the graphite powder was graphitized at 2650° C. for 6 hours under an inert atmosphere. After cooling, crushing and sieving, the negative electrode active material having a D V50 of 6.8 μm was obtained.The negative electrode active materials, the negative electrode plates, and the lithium ion batteries prepared in Examples and Comparative Examples were each tested, and the specific test items and methods were as follows.(1) La1La1 of the negative electrode plate was obtained by testing and analyzing it with Rigku Ultima IV X-ray diffractometer of Rigaku Corporation of Japan. The XRD was calibrated by the internal silicon standard method, and La1was calculated by the Scherer formula. The conditions for XRD analysis were: Cu target, scan voltage of 40 KV, current of 40 mA, and scan range of 5° to 90°. In order to reduce the error in the spectrum matching, the instrument measurement pitch was 0.02° and the scanning speed was 5° / min.(2) La2The La2of the negative electrode plate was obtained by testing and analyzing with the Thermo Fisher Raman spectrometer. La2was calculated according to the following formula: La2=2.4×10-10×λ 4 ×(A D / A G)-1, where λ is the incident laser wavelength of the Raman spectrum, A D is the peak region of the D peak (located in the waveband region 1320 to 1380cm -1) in the Raman spectrum, and A G is the peak region of the G peak (located in the waveband region 1560 to 1600cm -1) in the Raman spectrum. The analysis conditions for the Raman spectroscopy tests were: at room temperature and normal atmospheric pressure, using a laser with a wavelength of 785 nm and a spot size of less than 1 μm 2.(3) VOIV OI of the negative electrode plate can be obtained by means of an X-ray diffractometer. According to the general rules of X-ray diffraction analysis and the method for determining the lattice parameters of graphite JIS K 0131-1996 and JB / T4220-2011, the X-ray diffraction spectrum of the negative electrode plate was obtained. According to the formula V OI= I 004 / I 110, the OI value of the negative electrode plate was calculated, wherein I 004 is the peak intensity of the 004 diffraction characteristic peak and I 110 is the peak intensity of the 110 diffraction characteristic peak. The conditions for XRD analysis were: Cu target, scan voltage of 40 KV, current of 40 mA, and scan range of 5° to 90°. In order to reduce the error in the spectrum matching, the instrument measurement pitch was 0.02° and the scanning speed was 5° / min.(4) DV50The D V50 of the negative electrode active material was measured by the laser particle size test method and the Malvern particle size tester. The test steps were as follows. The sample to be tested was dispersed in deionized water containing a dispersant (e.g., 0.03 wt % nonylphenol polyoxyethylene ether) to form a mixture. The mixture was sonicated for 2 minutes and then placed in a particle size tester for testing.(5) Porosity PorosityThe porosity of the negative electrode plate was measured with a vacuum density meter. Specifically, a tens of thousandths of micrometer (accuracy: 0.0001 mm) was used to measure the apparent volume of the electrode sheet. Apparent volume = Sample thickness × Sample length × Sample width. The actual volume of the sample was measured with a vacuum density meter, and the porosity = (apparent volume - actual volume) / apparent volume.(6) Performance of Lithium PrecipitationFor the test, the BTSDA test system was used, the test temperature was 25°C, and the cycle test was performed as follows. The battery was charged to 4.45 V at 3 C constant current and charged to 0.05 C at constant voltage, held for 10 minutes and then discharged to 2.8 V at 1 C, held for 10 minutes, and this charging and discharging procedure was repeated for 200 cycles. The battery of Figure 200. Cycle was taken out and decomposed, it was observed whether there were lithium precipitates on the negative electrode plate, and the ratio of the area of lithium precipitate to the entire area of the negative electrode plate was estimated. When the ratio of the area of lithium excretion to the total area of the electrode sheet was less than 20%, it was easy to precipitate lithium, and when the ratio of the area of lithium excretion to the total area of the electrode sheet was 20% or more, it was strong to precipitate lithium.(7) Lifetime Life SpanThe fast charge cycle life was tested as follows. A battery charge and discharge tester was used to perform the charge and discharge cycle test on the lithium ion battery at 25° C. The charging and discharging system was as follows: The battery was charged with a constant current from 3C to 4.25V and charged with a constant voltage until the current fell to 0.02C, allowed to stand for 5 minutes, and then discharged with a constant current from 1C to 2.5V; this was one cycle. As the battery was cyclically charged, the capacity of the battery decreased further. When the capacity decreased to 80% of the initial discharge capacity, the number of cycles experienced was recorded as the rapid charge cycle life of the battery.The high temperature life was tested as follows. With a battery charge and discharge tester, the lithium ion battery was tested at 60° C. The charging and discharging system was as follows: The battery was charged to 4.25 V with a constant current of 1 C and charged to constant voltage until the current dropped to 0.02 C; it was continued for 5 minutes and then discharged to 2.5 V with a constant current of 1 C; this was one cycle. As the battery was cyclically charged, the capacity of the battery decreased further. When the capacity decreased to 80% of the initial discharge capacity, the number of cycles experienced was recorded as the life of the battery at high temperatures.The XRD spectrum and the Raman spectrum of the negative electrode plate prepared in Example 2 are shown in FIG. 1 and FIG. 2, respectively, and other specific test results are shown in Table 1. Table 1 Table 1Example 16074, 611, 210, 51.66E-0338No lithium precipitation39501980Example 258, 969, 412, 6101.20E-0335No lithium precipitation38202050Example 353, 9671510, 71.22E-0338No lithium precipitation39701970Example 44863, 111, 415, 11.39E-0338No lithium precipitation39151960Example 548, 563, 312, 515, 11.24E-0345No lithium precipitation36201905Example 648,63,1115,1.43E-22None of them were3685192022103Lithium PrecipitationExample 745, 460, 212, 18,22.48E-0331No lithium precipitation38401985Example 8637715, 211, 21.07E-0333No lithium precipitation35201810Example 969, 58010, 152.60E-0331No lithium precipitation35501835Example 10405612, 919, 61.13E-0338No lithium precipitation35201850Example 1131, 850, 234, 610, 21.04E-0339No lithium precipitation35051830Example 1273, 285, 515, 29,11.04E-0335No lithium precipitation35001800Example 1327, 545, 32018, 21.08E-0338No lithium precipitation34901805Comparative Example 161, 1761817, 30.63E-0332Slight Lithium Precipitation29801560Comparative Example 235, 254, 910, 56,15.60E-0335No lithium precipitation29701320Comparative Example 355, 768, 11415, 68.34E-0435No lithium precipitation29301580Comparative Example 442, 157, 611, 36,83.50E-0335Slight Lithium Precipitation29401420From the test results in Table 1, it is understood that the negative electrode plate satisfies the equation: 1.0×10 -3 ≤(|La1-La2| / Lax) / (V OI ×D V50) ≤3.0×10 -3, the prepared lithium ion batteries have a good fast charging cycle life and a high temperature cycle life, and no lithium precipitation occurs under fast charging conditions. Specifically, when the negative electrode plate satisfies the equation: 1.2×10 -3 ≤(|La1-La2| / Lax) / (V OI ×D V50) ≤2.5×10 -3, the fast charge cycle life and the high temperature cycle life of the prepared lithium ion batteries are relatively higher. At the same time, according to the test results of Comparative Examples 1 to 4, the cycle life and the rapid charge cycle performance of the lithium ion batteries including the negative electrode plate are significantly reduced when the calculated value of (|La1-La2| / Lax) / (V OI ×D V50) of the negative electrode plate is less than 1.0×10 -3 or more than 3.0×10 -3.Based on the negative electrode plate satisfying that the calculated value of (|La1-La2| / Lax) / (V OI ×D V50) is in a range of 1.0×10 -3 to 3.0×10 -3, the inventors have further studied and found that the prepared lithium ion battery has better rapid charging performance and cycle life when the porosity of the negative electrode plate is in a range of 30% to 40%.

Claims

A negative electrode plate, 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 a negative electrode active material, wherein the negative electrode active material comprises graphite, wherein the negative electrode plate satisfies the following equation: 1.0×10 -3 ≤(|La1-La2| / Lax) / (V OI ×D V50) ≤3.0×10 -3; in the equation, La1 is an average crystal size in an a-axis direction of the negative electrode plate obtained by XRD measurement, and the unit is nm, La 2 is an average crystal size in the a-axis direction of the negative electrode plate obtained by Raman spectroscopy measurement, and the unit is nm, Lax is a larger value of La 1 and LA 2, V OI is a ratio of a peak intensity I 004 of a (004) crystal plane to a peak intensity I 110 of a (110) crystal plane of the negative electrode plate obtained by XRD measurement, and D V50 is a particle size corresponding to the time when a cumulative volume distribution percentage of the negative electrode active material reaches 50%, and the unit is μm.The negative electrode plate according to claim 1, wherein the negative electrode plate satisfies the following equation: 1.2×10 -3 ≤(|La1-La2| / Lax) / (V OI × D V50) ≤2.5×10 -3.The negative electrode plate according to any preceding claim, wherein the range of La1 is 30 to 70 nm.The negative electrode plate according to any preceding claim, wherein a range of La2 is 50 to 80 nm.The negative electrode plate according to any preceding claim, wherein the range of La1 is 45 to 60 nm, and a range of La2 is 65 to 75 nm.The negative electrode plate according to any preceding claim, wherein a range of V is OI10 to 35.The negative electrode plate according to any preceding claim, wherein a range of V is OI11 to 15.The negative electrode plate according to any one of the preceding claims, wherein a range of D is V50 5 to 20 μm.The negative electrode plate according to any one of the preceding claims, wherein a range of D is V50 8 to 15 μm.The negative electrode plate according to any one of the preceding claims, wherein a porosity of the negative electrode plate is 20 to 45%.The negative electrode plate according to any one of the preceding claims, wherein a porosity of the negative electrode plate is 30 to 40%.The negative electrode plate according to any one of the preceding claims, wherein the graphite comprises natural graphite and / or artificial graphite.The negative electrode plate according to any one of the preceding claims, wherein the graphite is natural graphite.The negative electrode plate according to any one of the preceding claims, wherein copper, stainless steel, aluminum, nickel, titanium, fired carbon or an aluminum-cadmium alloy is used for the negative electrode current collector.The negative electrode plate according to any one of the preceding claims, comprising a conductive agent and a binder in addition to the negative electrode active material.The negative electrode plate according to claim 15, wherein the conductive agent comprises carbon powder, graphite powder, conductive fibers, or conductive whiskers.The negative electrode plate of claim 15 or 16, wherein the binder comprises a polymer material.The negative electrode plate according to any one of the preceding claims, wherein the negative electrode active material layer comprises a thickener, e.g. carboxymethylcellulose.A secondary battery, in particular a lithium ion battery, comprising: a positive electrode plate, a negative electrode plate and an electrolyte or electrolyte solution, wherein the negative electrode plate is the negative electrode plate according to any one of claims 1 to 18.The secondary battery according to claim 19, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material.The secondary battery according to any one of claims 19 or 20, wherein copper, stainless steel, aluminum, nickel, titanium, fired carbon, or an aluminum-cadmium alloy is used for the positive electrode current collector.The secondary battery according to any one of claims 19 to 21, wherein the positive electrode current collector is identical to or different from the negative electrode current collector.The secondary battery according to any one of claims 20 to 22, wherein the positive electrode active material comprises a lithium composite metal oxide containing lithium and at least one metal selected from the group consisting of Ni, Co, Mn, Fe and Al.The secondary battery according to any one of claims 20 to 23, wherein the positive electrode active material comprises at least one(s) of the following compounds: Li(Ni 0,8 Mn 0,1 Co 0,1) O 2, Li(Ni 0,8 Co 0,15 Al 0,05) O 2 and Li(Ni 0,86 Mn 0,07 Co0,05Al0,02)O2.The secondary battery according to any one of claims 20 to 24, wherein the positive electrode active material comprises at least one(s) of the following compounds Li(Ni 0,6 Mn 0,2 Co 0,2) O 2 and Li(Ni 0,7 Mn 0,2 Co 0,10) O 2.The secondary battery according to any one of claims 20 to 25, wherein the positive electrode active material comprises at least the following compound Li(Ni 0,9 Mn 0,05 Co 0,05) O 2.The secondary battery according to any one of claims 19 to 26, wherein the positive electrode plate comprises a conductive agent.The secondary battery according to claim 27, wherein the conductive means of the positive electrode plate is identical to or different from a / the conductive means of the negative electrode plate.The secondary battery according to any one of claims 19 to 28, wherein the positive electrode plate comprises a binder.The secondary battery according to claim 29, wherein the binder of the positive electrode plate is identical to or different from a / the binder of the negative electrode plate.The secondary battery according to any one of claims 19 to 30, wherein the electrolyte solution comprises an electrolyte and a solvent.The secondary battery of any one of claims 19 to 31, wherein the electrolyte comprises a lithium salt.The secondary battery of claim 32, wherein the lithium salt is an inorganic lithium salt and / or an organic lithium salt.The secondary battery according to any one of claims 31 to 33, wherein the solvent is a nonaqueous solvent.The secondary battery according to any one of claims 31 to 34, wherein the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylethyl carbonate, and a halogenated derivative thereof, respectively.The secondary battery according to any one of claims 19 to 35, comprising a separator between the positive electrode plate and the negative electrode plate.The secondary battery of claim 36, wherein the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.A secondary battery according to any one of claims 19 to 37 for use in an electric vehicle.An electrical device comprising the secondary battery according to any one of claims 19 to 38.The electrical device according to claim 39, wherein the secondary battery serves as a power supply for the electrical device.An electric vehicle comprising an electric device according to claim 39 or 40, or a secondary battery according to any one of claims 19 to 38.

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