CN115838170A - Modified graphite, preparation method thereof, and secondary battery and electric device containing modified graphite - Google Patents
Modified graphite, preparation method thereof, and secondary battery and electric device containing modified graphite Download PDFInfo
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- CN115838170A CN115838170A CN202210209678.5A CN202210209678A CN115838170A CN 115838170 A CN115838170 A CN 115838170A CN 202210209678 A CN202210209678 A CN 202210209678A CN 115838170 A CN115838170 A CN 115838170A
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- modified graphite
- graphite
- petroleum coke
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application relates to a preparation method of modified graphite, which comprises the following steps of S1: mixing and crushing the high-volatility petroleum coke and a compound containing a doping element M, and then mixing the mixture with a solution of a surfactant to obtain a dispersion liquid of a doped high-volatility raw material A; s2: crushing and heat treating the low volatile petroleum coke to obtain a low volatile raw material B; s3: adding the low-volatile component raw material B obtained in the step S2 into the solution of the doped high-volatile component raw material A obtained in the step S1, drying, and carrying out preheating treatment to obtain a precursor; s4: and (4) graphitizing the graphite precursor obtained in the step (S3) to obtain the modified graphite. The present application also relates to a secondary battery and an electric device comprising the modified graphite. The preparation method is simple and low in cost, and the obtained modified graphite improves the quick charging capacity and the storage performance of the battery.
Description
Technical Field
The application relates to the technical field of lithium ion secondary batteries, in particular to a preparation method of modified graphite. Further, the present application relates to a secondary battery comprising the modified graphite prepared by the method, and an electric device comprising the secondary battery.
Background
In recent years, with the wider application range of lithium ion secondary batteries, lithium ion secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. As lithium ion secondary batteries have been greatly developed, higher requirements are placed on the quick charging capacity and the storage capacity thereof.
At present, graphite carbon cathode active materials are mainly adopted as the cathode active materials of the lithium ion secondary battery, and the cathode active materials have the advantages of low and stable lithium intercalation potential, high first coulombic efficiency, good cycling stability, low cost and the like, and become ideal cathode active materials in the application of the lithium ion secondary battery at present. However, in the prior art, the graphite material is generally prepared by using low-sulfur low-volatile tar, and performing the processes of crushing, spheroidizing, graphitization and subsequent carbonization. These processes often have problems of high raw material cost and complicated process.
Therefore, the preparation method of the modified graphite needs to be further improved, and the quick charging capacity needs to be further improved.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing modified graphite and modified graphite obtained by the production method, which can reduce production costs and simplify processes, and can improve the quick charge capacity and storage performance of a lithium ion secondary battery.
In order to achieve the above object, a first aspect of the present application provides a method for preparing modified graphite, comprising the steps of:
s1: mixing and crushing the high-volatility petroleum coke and a compound containing a doping element M, and then mixing the mixture with a solution of a surfactant to obtain a dispersion liquid of a doped high-volatility raw material A;
s2: crushing and heat treating the low volatile petroleum coke to obtain a low volatile raw material B;
s3: adding the low-volatile raw material B obtained in the step S2 into the solution of the doped high-volatile raw material A obtained in the step S1, drying, and carrying out preheating treatment to obtain a graphite precursor;
s4: and (4) graphitizing the graphite precursor obtained in the step (S3) to obtain the modified graphite.
In the method, modified graphite with more surface defects can be obtained by adopting differentiated graphite raw materials (a high-volatility raw material A and a low-volatility raw material B) and doping modification of the graphite raw materials, so that the quick charge capacity and the storage performance of the lithium ion secondary battery are effectively improved; meanwhile, the method avoids using a coating agent and performing a subsequent carbonization process, and has the advantages of low raw material cost, simple process and the like.
In any embodiment, in step S1, the high volatiles petroleum coke comprises an S content of 6 to 12 wt.% and a volatile component content of 2 to 5 wt.% based on the weight of the high volatiles petroleum coke. The method is favorable for forming the uniformly coated carbon coating layer, reduces or prevents the formation of long-range ordered crystal lattices in the carbon coating layer, generates more structural defects on the surface of the modified graphite, and promotes the de-intercalation of lithium ions.
In any embodiment, in step S1, the high volatile petroleum coke is obtained by coking green petroleum coke, the coking being carried out at < 900 ℃, optionally from 300 to 600 ℃. Thus, high volatile petroleum coke is obtained.
In any embodiment, in said step S1, said compound containing a doping element M is selected from magnesium oxide and/or aluminum oxide, and the doping element M is selected from magnesium and/or aluminum; the weight ratio of the doping element M to the high volatile petroleum coke is (0.03-0.20): 1, and optionally (0.10-0.16): 1. By improving the doping element of the high-volatile petroleum coke, the surface micropores and lithium embedding paths can be increased on the carbon coating layer, so that the surface defects can be increased, and the subsequent carbonization process can be avoided.
In any embodiment, in step S2, the low volatiles petroleum coke comprises an S content of 6 to 12 wt.% and a volatiles content of less than 1 wt.% based on the weight of the low volatiles petroleum coke. The low-volatile petroleum coke is adopted as a raw material, so that a carbon core with a graphite crystal structure is formed.
In any embodiment, in step S2, the low volatile petroleum coke is heat treated at 1000 to 1500 ℃. This facilitates the formation of a uniformly coated carbon coating layer, enhancing kinetics.
In any embodiment, in step S1, the volume median particle diameter Dv50 of the doped high volatile raw material a is 0.5 to 1.2 μm, and the volume median particle diameter Dv50 of the low volatile raw material B is 6 to 12 μm. This facilitates the adhesion of the doped high-volatile material a to the surface of the low-volatile material a, improving the uniform coverage.
In any embodiment, in the step S3, the weight ratio of the doped high volatile raw material a to the low volatile raw material B is 1 (3-15), and optionally 1 (4-10). Thereby the doped high volatile raw material A is completely or mostly adhered on the surface of the raw material B.
In any embodiment, the preheating treatment in step S3 adopts a stepwise temperature rise, and includes at least 2 temperature-programmed stages, and optionally 2 to 4. Therefore, the doped high-volatility raw material A is gradually softened from a solid state to a liquid state, and uniform coating on the low-volatility raw material B is facilitated.
A second aspect of the present application provides modified graphite obtained by the production method of the present application, wherein the graphite has a structure in which La is in the range of 80 to 160nm, lc is in the range of 27 to 37nm, and the lattice spacing d 002 In the range of 0.360 to 0.365 nm. The lithium ion secondary battery prepared from the modified graphite has obviously improved quick charging capacity and storage performance.
In any embodiment, the modified graphite comprises a carbon core and a carbon coating layer in an amount of greater than 0 to 5 wt% based on the weight of the carbon core. This is advantageous in improving the quick charge capability of the lithium ion secondary battery.
In any embodiment, the particles of the modified graphite have a volume median particle diameter Dv50 of 7 to 14 μm, optionally 9 to 13 μm. This is advantageous for reducing the lithium ion solid phase diffusion path in the modified graphite.
In any embodiment, the modified graphite has a degree of graphitization of 88 to 98%. Therefore, the graphite has a good layered structure, is beneficial to the extraction and the insertion of lithium ions, and improves the conductivity.
A third aspect of the present application provides a secondary battery comprising the modified graphite obtained by the production method according to the first aspect of the present application.
A fourth aspect of the present application provides an electric device including the secondary battery described in the third aspect of the present application.
This application is through the graphite raw and other materials that adopt the differentiation and the preparation method that carries out doping modification to graphite raw and other materials, obtains the modified graphite of this application including carbon kernel and carbon coating, the carbon kernel is graphite crystal structure, the carbon coating is the carbon structure that is soft to one side. The lithium ion secondary battery containing the modified graphite has obviously improved quick charge capacity, storage performance and cycle performance.
Drawings
FIG. 1 is an X-ray powder diffraction (XRD) pattern of the modified graphite of example 1;
fig. 2 is a schematic view of a secondary battery according to an embodiment of the present application.
Fig. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 2.
Fig. 4 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.
Description of reference numerals:
1 a secondary battery; 11 a housing; 12 an electrode assembly; 13 a top cover assembly.
Detailed Description
Hereinafter, embodiments of the modified graphite of the present application, a method for producing the same, a secondary battery including the modified graphite, and an electric device using the secondary battery will be specifically disclosed with reference to the drawings. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.
Hereinafter, embodiments of the modified graphite of the present application, preparation thereof, a secondary battery comprising the modified graphite, and an electric device using the secondary battery will be specifically disclosed with reference to the accompanying drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.
The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Further, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.
All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.
All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.
All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.
The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.
In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).
The graphite material has the advantages of low and stable lithium intercalation potential, high first coulombic efficiency, good cycling stability, low cost and the like, so that the graphite material becomes an ideal negative active material in the application of the lithium ion secondary battery at present. Graphite materials are generally classified into natural graphite and artificial graphite according to their raw materials and processing techniques. For artificial graphite, a surface coating treatment is generally employed to achieve further improvement in its electrical properties. For example, by secondary coating of graphite, a coating agent such as asphalt or other high molecular polymer needs to be added during the coating process, and carbonization needs to be performed after graphitization, so that the preparation process is complicated and high in cost. Or, the homologous graphite is adopted as the coating layer, but in the coating process, adhesion is easy to occur under the stirring state, the particle size control is not facilitated, and the obtained modified graphite is not obviously improved in the aspect of quick charging capability.
Therefore, the application provides a preparation method of modified graphite, which aims to solve the technical problems of complex preparation process and high cost of the graphite material in the prior art, and simultaneously realizes the obvious improvement of the quick charge capacity of the lithium ion secondary battery and the obvious improvement of the storage performance of the lithium ion secondary battery.
The application provides a method for preparing modified graphite, which comprises the following steps:
s1: mixing and crushing the high-volatility petroleum coke and a compound containing a doping element M, and then mixing the mixture with a solution of a surfactant to obtain a dispersion liquid of a doped high-volatility raw material A;
s2: crushing the low volatile petroleum coke, and performing heat treatment to obtain a low volatile raw material B;
s3: adding the low-volatile component raw material B obtained in the step S2 into the solution of the doped high-volatile component raw material A obtained in the step S1, drying, and carrying out preheating treatment to obtain a graphite precursor;
s4: graphitizing the graphite precursor obtained in the step S3 to obtain the modified graphite.
Further, the graphite precursor having the a raw material adhered to the surface of the B raw material is obtained from the step S3.
In the present application, the volatile component is a volatile component, and means a material volatilized at a temperature of less than 1300 ℃, such as low molecular weight alkanes and aromatics, water, ash, and the like, which are known to those skilled in the art.
In this application, the high volatile petroleum coke refers to petroleum coke having a volatile content of greater than 2 wt% and a sulfur content of greater than 5 wt%, based on the weight of the high volatile petroleum coke; the low volatile petroleum coke refers to petroleum coke with a volatile content of less than 2 wt%, based on the weight of the low volatile petroleum coke.
Therefore, the method obtains the modified graphite by adopting the doped high-volatility raw material A and the doped low-volatility raw material B, performing heat treatment on the low-volatility raw material B in advance, and performing preheating treatment after mixing the two raw materials and before graphitizing. The modified graphite has more surface defects, such as more micropores, more and shorter lithium ion deintercalation paths, and thus can effectively improve the quick charge capacity and the storage performance of a lithium battery. In addition, the method avoids using a coating agent and carrying out a subsequent carbonization process, and has the advantages of low raw material cost, simple process and the like.
In some embodiments, in step S1, the high volatile petroleum coke comprises an S content of 6 to 12 wt.% and a volatile component content of 2 to 5 wt.%, based on the weight of the high volatile petroleum coke.
By adopting the high-volatile petroleum coke, the raw material A with high sulfur content and high volatile content can be obtained after the high-volatile petroleum coke is mixed with a compound containing a doping element M, wherein the raw material A has high sulfur content, so that the doped high-volatile raw material A is favorably adhered to the surface of the low-volatile raw material B in the preheating treatment process of the step S3, the aim of uniform covering is further fulfilled, and a uniformly-coated carbon coating layer is formed on a carbon core; the raw material A has high volatile content, and the volatile components can generate gas escape at high temperature, so that the formation of long-range ordered crystal lattices in the carbon coating layer can be reduced or prevented, more structural defects are generated on the surface of the modified graphite, and the deintercalation of lithium ions is facilitated.
In some embodiments, in step S1, the high volatile petroleum coke is obtained by coking petroleum green coke, said coking being carried out at < 900 ℃, optionally at 300 to 600 ℃. Further, the coking time is 2 to 4 hours.
In the process of the petroleum coke with high volatile content, if the coking temperature is higher than 900 ℃, the petroleum coke is subjected to full forging; if the temperature is lower than 300 ℃, the petroleum green coke cannot be in a micro-molten state.
In some embodiments, in step S1, the compound containing a doping element M is selected from magnesium oxide and/or aluminum oxide, and the doping element M is selected from magnesium and/or aluminum; the weight ratio of the doping element M to the high volatile petroleum coke is (0.03-0.20): 1, and optionally (0.10-0.16): 1. The mass of the doping element M is based on the compound containing the doping element M.
Further, the surfactant is selected from ammonium lauryl bromide and/or sodium stearate.
Modifying the high volatile petroleum coke, such as doping with M, thereby producing the doped high volatile feedstock A. This is advantageous for increasing surface micropores and lithium intercalation paths on the carbon coating layer by gasifying the compound doped with the element at the graphitization stage of step S4, thereby increasing surface defects, forming a coating layer with a soft carbon-like structure, effectively improving the quick charging capability of graphite, and avoiding the subsequent carbonization process.
In some embodiments, in step S2, the low volatiles petroleum coke comprises an S content of 6 to 12 wt.% and a volatiles content of less than 1 wt.% based on the weight of the low volatiles petroleum coke. By low volatile matter petroleum coke preparation hangs down volatile matter raw materials B to form the carbon kernel of this application modified graphite, can guarantee that the graphitization degree of carbon kernel is higher, and the capacity can promote.
Further, in the step S2, the low volatile petroleum coke is obtained by coking crude petroleum coke, the coking is carried out at 500-700 ℃ for 8-12 h.
In some embodiments, in step S2, the low volatile petroleum coke is heat treated at 1000-1500 ℃ for 4 to 8 hours. Therefore, the dangling bonds of the low-volatile matter raw material B are increased, so that the adsorption capacity of the low-volatile matter raw material B and the doped high-volatile matter raw material A is improved, the formation of a uniformly coated carbon coating layer is promoted, and the kinetics is improved.
As used herein, the term "dangling bond" means a carbon-carbon double bond or single bond at the edge of graphite is broken in a high-temperature environment, and has an unsaturated property and is liable to adsorb other atoms.
In some embodiments, in step S1, the volume median particle diameter Dv50 of the doped high-volatile feedstock a is in the range of 0.5 to 1.2 μm, and the volume median particle diameter Dv50 of the low-volatile feedstock B is in the range of 6 to 12 μm. This facilitates the adhesion of the doped high volatile material a to the surface of the low volatile material B, improving the uniformity of the coating.
Further, the crushing operation is as follows: crushing by using a mechanical mill or a roller mill, wherein the feeding frequency can be 10 Hz-60 Hz, such as 25 Hz-35 Hz, and the crushing frequency can be 20 Hz-50 Hz, such as 35 Hz-45 Hz, and obtaining crushed aggregate after the treatment; then, the obtained aggregate is placed in a shaping machine for shaping and fine powder removal, wherein the grading frequency can be 20Hz to 50Hz, such as 40Hz to 50Hz, and the induced air frequency can be 30Hz to 55Hz, such as 35Hz to 45Hz. Specifically, in step S1, crushing is carried out at a classification frequency of 45Hz and an induced air frequency of 50Hz, resulting in particles having a volume median particle diameter Dv50 of 0.5-1.0 μm and a distribution width (Dv 90-Dv 10)/Dv 50 in the range of 1.15-1.25; in step S2, crushing is carried out at a classification frequency of 25Hz and an induced air frequency of 35Hz to obtain particles with a volume median particle diameter Dv50 of 6-11 μm and a distribution width (Dv 90-Dv 10)/Dv 50 of 1.10-1.3; thereby achieving a higher consistency of particle size.
In some embodiments, the weight ratio of the doped high volatile material A to the low volatile material B in the step S3 is 1 (3-15), optionally 1 (4-10). Thereby adhering the doped high volatile material A on the surface of the material B.
In some embodiments, the pre-heating process in step S3 employs a stepwise temperature increase, comprising at least 2 temperature-programmed stages, optionally 2-4. Therefore, the doped high volatile material a is gradually softened from a solid state to a liquid state at a phase transition point, and the fluidity is low and the adhesiveness is increased in the process of gradual softening. This facilitates uniform coating on the low volatile material B to form a uniformly coated carbon coating layer.
Further, in step S3, a horizontal or vertical reaction kettle is used for heat treatment, and the reaction kettle is heated to a certain temperature and kept at the same temperature for a certain period of time, so as to obtain the modified graphite of the present application with a desired particle size distribution by arranging a plurality of (for example, 2 to 4) temperature programming platforms in the temperature raising process. Further, the preheating treatment comprises heating to 200 ℃ and holding for 2 hours, and then heating to 500 ℃ and holding for 5 hours.
Further, in step S4, graphitization of the graphite precursor with a carbon coating layer obtained from step S3 can be performed using equipment known in the art, such as a graphitization furnace, alternatively, such as an acheson graphitization furnace. The graphitization temperature is 2500 to 3500 ℃.
A second aspect of the present application provides a modified graphite obtained by the process of the first aspect of the present application, the modified graphite having a structure such that La is in the range of 80 to 160nm, optionally 110 to 150nm, lc is in the range of 27 to 37nm, optionally 30 to 36 nm, lattice spacing d 002 In the range of 0.360 to 0.365 nm. Such as the XRD pattern shown in figure 1 and tables 1-2.
In the present application, "La" is used to indicate the average size of graphite in the direction of the a-axis; "Lc" represents the thickness of the graphite sheet stacked in the direction perpendicular to the c-axis. In the prior art, graphite generally has a La of 170 to 180nm, an lc of about 40nm, and a lattice spacing d 002 About 0.3660nm.
The inventors have unexpectedly found that by the preparation method of the present application, using differentiated graphite raw materials and doping modification of the graphite raw materials, the modified graphite of the present application comprising a carbon core and a carbon coating layer can be obtained, wherein the carbon core is of a graphite crystal structure and the carbon coating layer is of a softer carbon structure. The modified graphite with the structure obviously improves the quick charge capacity, the storage performance and the cycle performance of the lithium ion secondary battery.
In some embodiments, the modified graphite comprises a carbon core and a carbon coating layer in an amount of greater than 0 to 5 wt% based on the weight of the carbon core. If the weight of the coating layer is more than 5 wt%, this results in a significant deterioration in storability of the modified graphite when used as a negative electrode active material.
Further, in the modified graphite, the carbon coating layer contains magnesium and/or aluminum in an amount of 0 to 20 wt%, optionally 5 to 12 wt%, based on the total weight of the modified graphite. Too high a content of the doping element reduces gram capacity of the lithium ion secondary battery and poses safety risks.
Further, the content of the S element in the modified graphite is 0 to 2 wt%, and optionally 0 to 1 wt%, based on the total weight of the modified graphite.
In some embodiments, the particles of the modified graphite have a volume median particle diameter Dv50 of 7 to 14 μm, optionally 9 to 13 μm; the distribution width (Dv 90-Dv 10)/Dv 50, which is a measure of the width of the particle size distribution of the sample, is from 1.0 to 1.5, optionally from 1.1 to 1.4. The particle size of the modified graphite is controlled in a proper range, so that a smaller lithium ion solid phase diffusion path is obtained.
In some embodiments, the modified graphite has a degree of graphitization of 88 to 98%.
The carbon material is generally composed of graphite crystals and amorphous carbon, and the graphitization degree is the proportion of the graphite crystals to the whole. The graphitization degree is calculated by the following calculation:
degree of graphitization
Wherein the interlayer spacing of the ideal crystal is 0.3354nm; the interlayer spacing of the amorphous carbon is 0.334nm, d 002 Is the measured interlayer spacing.
Interlayer spacing (d) 002 ) Gradually decreases with increasing graphitization degree.The higher the graphitization degree is, the graphite has a good layered structure, which is beneficial to the de-intercalation of lithium ions and improves the conductivity.
It should be understood that the modified graphite of the present application can be used not only for lithium batteries, but also for any other batteries and electric devices thereof, which require improved storage performance.
Secondary battery and electric device
The secondary battery of the present application and an electric device using the same are explained below with reference to the drawings.
Secondary battery
In one embodiment of the present application, there is provided a secondary battery, wherein the negative electrode tab comprises the modified graphite provided in the first aspect of the present application.
In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.
[ Positive electrode sheet ]
The positive pole piece comprises a positive pole current collector and a positive pole film layer arranged on at least one surface of the positive pole current collector.
As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.
In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the positive active material may employ a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) 2 ) Lithium nickel oxides (e.g., liNiO) 2 ) Lithium manganese oxide (e.g., liMnO) 2 、LiMn 2 O 4 ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) 1/3 Co 1/3 Mn 1/3 O 2 (may also be abbreviated as NCM) 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (may also be abbreviated as NCM) 523 )、 LiNi 0.5 Co 0.25 Mn 0.25 O 2 (may also be abbreviated as NCM) 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (may also be abbreviated as NCM) 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (may also be abbreviated as NCM) 811 ) Lithium nickel cobalt aluminum oxides (e.g., liNi) 0.85 Co 0.15 Al 0.05 O 2 ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) 4 (may also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) 4 ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.
In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.
[ negative electrode sheet ]
The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, the negative pole rete includes the modified graphite of the aforesaid this application.
As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two surfaces opposite to the negative electrode current collector.
In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the negative active material is a modified graphite of the present application.
In some embodiments, the anode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
In some embodiments, the negative electrode film layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.
In some embodiments, the negative electrode sheet can be prepared by: dispersing the components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the negative electrode pole piece.
[ electrolyte ]
The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of the electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution).
In some embodiments, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.
In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium perchlorate (LiClO) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium dioxaoxalato borate (LiBOB), lithium difluorophosphates (LiP)O 2 F 2 ) One or more of lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
In some embodiments, the solvent may be selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), butylene Carbonate (BC), fluoro Ethylene Carbonate (FEC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS), and diethylsulfone (ESE).
In some embodiments, the electrolyte may further optionally include an additive. For example, the additive can comprise a negative electrode film forming additive, can also comprise a positive electrode film forming additive, and can also comprise an additive capable of improving certain performances of the battery, such as an additive capable of improving the overcharge performance of the battery, an additive capable of improving the high-temperature performance of the battery, an additive capable of improving the low-temperature performance of the battery, and the like.
[ separator ]
In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.
In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.
In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.
In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and electrolyte.
In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 2 is a secondary battery 1 of a square structure as an example.
In some embodiments, referring to fig. 3, the overpack may include a housing 11 and a lid 13. The housing 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 11 has an opening communicating with the accommodating chamber, and a cover plate 13 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 12 through a winding process or a lamination process. An electrode assembly 12 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 12. The number of the electrode assemblies 12 included in the secondary battery 1 may be one or more, and those skilled in the art can select them according to the actual needs.
The application also provides an electric device, the electric device includes the secondary battery that the application provided. The secondary battery may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.
Fig. 4 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like.
As another example, the device may be a cell phone, tablet, laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.
Examples
Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
1. Preparation examples
Example 1: preparation of modified graphite
Step S1, preparation of high-volatile component raw material A doped with aluminum
Coking the crude petroleum coke at 450 ℃ for 3h to obtain high volatile petroleum coke (called A coke) with high sulfur element content; then mixing 1000g A coke with 200g of aluminum oxide, crushing at the crushing frequency of 40Hz, shaping and subdividing at the classification frequency of 45Hz and the induced air frequency of 50Hz to obtain the high-volatile matter raw material A (called as A particles) doped with aluminum; the A Jiao Zhongbao mass fraction of sulfur element was determined to be 8%, and the mass fraction of volatile components was determined to be 4%, based on the total weight of A coke.
Then, 200g of the a particles were added to an aqueous solution of dodecylammonium bromide (cationic surfactant) with a mass fraction of 1% (based on the weight of the solution), and mixed with rapid stirring to obtain an a solution having uniformly dispersed a particles.
Step S2, preparation of low-volatile component raw material B
Coking petroleum green coke at 600 deg.C to obtain low volatile petroleum coke (called B coke) with high sulfur content, then performing heat treatment at 1200 deg.C under inert gas atmosphere for 6h, then pulverizing with 30Hz pulverizing frequency, then shaping and subdividing at grading frequency of 25Hz and induced air frequency of 35Hz to obtain B particles.
Wherein the B Jiao Zhongbao contains 8% of sulfur element by mass and 0.5% of volatile component by mass based on the total weight of the B coke.
Step S3, preparation of precursor
Adding the B particles (1000 g) obtained from step S2 to the 5L of A solution (containing 200g A particles) obtained from step S1, continuing stirring and mixing, and vacuum drying at 120 ℃; and then carrying out preheating treatment, heating to 200 ℃, preserving heat for 2h, heating to 500 ℃, preserving heat for 5h, and obtaining a precursor with particles A adhered to particles B.
Step S4, preparation of modified graphite
Graphitizing the precursor obtained in the step S3 at 3000 ℃ to obtain the modified graphite of the application.
The XRD pattern of the obtained modified graphite is shown in FIG. 1
Examples 2 to 3:
the procedure of example 1 was repeated except that: in step S1, the temperature of coking is changed; or changing the weight of the added aluminum oxide;
examples 4 to 5
The procedure of example 1 was repeated except that: in step S2, the time of the heat treatment is changed.
Examples 6 to 7
The procedure of example 1 was repeated except that: in step S3, the weight of the raw material a particles is changed; i.e. the weight ratio of particles a to particles B is varied.
Relevant process parameters for examples 1-7 are shown in Table 1.
Comparative example
Comparative examples 1 to 2
Comparative examples 1-2 the procedure of example 1 was repeated except that: in step S1, the temperature of coking is changed.
Comparative examples 3-4 the procedure of example 1 was repeated except that: in step S1, the weight of the added alumina is changed.
Comparative examples 5 to 6
Comparative examples 5-6 the procedure of example 1 was repeated except that: in step S1, the crushing frequency was 60Hz in comparative example 5 and 10Hz in comparative example 6 to obtain A particles of different Dv 50.
Comparative examples 7 to 8
Comparative examples 7-8 the procedure of example 1 was repeated except that: in step S3, the weight of the raw material a particles is changed.
Comparative example 9
Comparative example 9 the procedure of example 1 was repeated except that: in step S1, alumina is not added, but added during the graphitization in step S4.
Comparative example 10
Comparative example 9 the procedure of example 1 was repeated except that:
step S1 is not performed; and the precursor of step S3 is prepared as follows:
adding the B particles (200 g) obtained in step S2 to 5L of an aqueous solution of 1% by mass (based on the weight of the solution) of dodecylammonium bromide (cationic surfactant), rapidly stirring and mixing, and vacuum-drying at 120 ℃; and then carrying out preheating treatment, heating to 200 ℃, preserving heat for 2h, and then heating to 500 ℃, preserving heat for 5h to obtain a precursor.
The relevant process parameters for comparative examples 1-10 are shown in table 2.
Test method
1. Method for testing sulfur content and volatile component content
Petroleum coke volatile matter determination is carried out according to the petrochemical industry standard (SH/T0026-90) of the people's republic of China.
2.D V 50、D V 10 and D V 90 test method
This was determined using a laser particle Size analyzer (Malven Master Size 3000) according to the standard GB/T19077.1-2016.
XRD test methods (La and Lc data)
The degree of graphitization of the negative active material is a well-known meaning in the art and can be tested using methods known in the art: the D can be determined by testing using an X-ray diffractometer (e.g. Bruker D8 iscover) according to JIS K0131-1996, JB/T4220-2011 002 Then according to the formula G = (0.344-d) 002 )/(0.344-0.3354)×100% is calculated to obtain the degree of graphitization, wherein d 002 Is the interlayer spacing in the graphite crystal structure expressed in nanometers (nm). According to the data measured by XRD, using Bravais lattice equation to calculate according to [110]And [002]Peak calculation the dimensions of each axis (La and Lc):
wherein FWHM [110] is the full width at half maximum of the [110] peak; pos [110] is the peak position of the [110] peak; FWHM [002] is the full width at half maximum of the [002] peak; pos [002] is the peak position of the [002] peak; "" denotes an arithmetic symbol multiplication sign "x".
In the X-ray diffraction analysis test, a copper target is used as an anode target, cuK alpha rays are used as a radiation source, and the wavelength of the rays is
The angle range of the scanning 2 theta is 20-80 degrees, and the scanning speed is 4 degrees/min. />
2. Application examples
1. Preparing a negative pole piece: uniformly mixing the modified graphite prepared by the method, a conductive agent Super P and a binder (PVDF) with a solvent NMP (N-methyl pyrrolidone) according to a mass ratio of 91.6; coating the prepared slurry on a copper foil current collector, drying in an oven and then cold pressing for later use, wherein the compaction density is 1.5g/cm 3 ；
2. Positive pole piece: a metal lithium sheet is taken as a counter electrode;
3. preparing an electrolyte: a Polyethylene (PE) film is used as a separation film; ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) were mixed in a volume ratio of 1 6 Uniformly dissolving the electrolyte in the solution to obtain electrolyte, and preparing the electrolyte: wherein LiPF 6 The concentration of (A) is 1mol/L;
4. preparing a secondary battery: the above parts were assembled into CR2430 button cells in an argon-protected glove box.
Test method
(a) Battery quick charge performance (0-80% SOC)
The secondary batteries prepared in examples and comparative examples were constant-current charged at 25 ℃ to 4.25V at 1C (i.e., a current value at which the theoretical capacity was completely discharged within 1 h), followed by constant-voltage charging to a current of 0.05C, standing for 5 minutes, and then constant-current discharged at 1C to 2.8V, and the actual capacity was recorded as C0. Then, the battery is sequentially charged to 4.25V or 0V negative pole cut-off potential (based on the first reaching) by 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, 4.5C0 at constant current, after charging is completed, 1C0 is required to be discharged to 2.8V, the negative pole potential corresponding to charging to 10%, 20%, 30% … … 80 and SOC (State of Charge) under different charging magnifications is recorded, magnification-negative pole potential curves under different SOC states are drawn, after linear fitting, the charging magnification corresponding to the negative pole potential under different SOC states being 0V is obtained, the charging magnification is the charging window under the SOC, which is respectively marked as C20% SOC, SOC C30% SOC, C40% SOC, C50%, C60% SOC, C70% SOC, C80% SOC, C60% SOC (60 + C60 + 60C 60/60C 60), and the charging time is calculated from the equation of charging time of 10/60 + C60 + SOC (T + C60 + C + 60/60C + 60). The shorter the time, the more excellent the quick charging performance of the battery.
(b) Battery storage performance testing
The secondary batteries prepared in examples and comparative examples were constant-current charged at 25 ℃ to a charge cut-off voltage of 4.25V at 0.33C, followed by constant-voltage charging to a current of 0.05C, standing for 5 minutes, and then constant-current discharged at 0.33C to a discharge cut-off voltage of 2.8V, and the initial capacity thereof was recorded as C0. Then stored at a constant temperature in an environment of 60 ℃ until the cycle capacity retention rate (Cn/C0 × 100%) is 80%, and the storage days are recorded. The more days of storage, the better the storage life of the battery.
(c) Battery cycling performance (decay to 80% of initial reversible capacity)
The secondary batteries prepared in examples and comparative examples were charged at a constant current of 0.33C to a charge cut-off voltage of 4.25V at 25C, followed by constant-voltage charging to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, and the initial capacity thereof was recorded as C0. The discharge capacity Cn was then recorded for each cycle as 2C charge, 1C discharge, until the cycle capacity retention (Cn/C0 × 100%) was 80%, the number of cycles was recorded. The greater the number of cycles, the better the cycle life of the battery.
TABLE 3 results of the performance test of each example and comparative example
From the above results, it is understood that examples 1 to 7 all achieve good effects in improving the quick charge performance, the storage performance and the cycle performance of the secondary battery, as compared with comparative examples 1 to 10.
The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.
Claims (15)
1. The preparation method of the modified graphite is characterized by comprising the following steps:
s1: mixing and crushing the high-volatility petroleum coke and a compound containing a doping element M, and then mixing the mixture with a solution of a surfactant to obtain a dispersion liquid of a doped high-volatility raw material A;
s2: crushing and heat treating the low volatile petroleum coke to obtain a low volatile raw material B;
s3: adding the low-volatile component raw material B obtained in the step S2 into the solution of the doped high-volatile component raw material A obtained in the step S1, drying, and carrying out preheating treatment to obtain a graphite precursor;
s4: and graphitizing the graphite precursor obtained in the step S3 to obtain the modified graphite.
2. The method of claim 1, wherein in step S1, the high volatile petroleum coke comprises an S content of 6 to 12 wt% and a volatile component content of 2 to 5 wt%, based on the weight of the high volatile petroleum coke.
3. The method of claim 1 or 2, wherein in step S1 the high volatile petroleum coke is obtained by coking petroleum green coke, said coking being carried out at < 900 ℃, optionally at 300 to 600 ℃.
4. The process according to any one of the preceding claims 1 to 3, characterized in that, in said step S1, said compound containing a doping element M is selected from magnesium oxide and/or aluminium oxide, the doping element M being selected from magnesium and/or aluminium; the ratio of the mass of the doping element M to the mass of the high volatile petroleum coke is (0.03-0.20): 1, and optionally (0.10-0.16): 1.
5. The method of any of the preceding claims 1-4, wherein in step S2, the low volatile petroleum coke comprises S content of 6-12 wt% and volatile components content of less than 1 wt% based on the weight of the low volatile petroleum coke.
6. The method according to any one of the preceding claims 1 to 5, wherein in step S2, the low volatile petroleum coke is heat treated at 1000 to 1500 ℃.
7. The method according to any one of the preceding claims 1 to 6, wherein in step S1, the volume median particle diameter Dv50 of the doped high-volatile feedstock A is in the range of 0.5 to 1.2 μm, and the volume median particle diameter Dv50 of the low-volatile feedstock B is in the range of 6 to 12 μm.
8. The method according to any one of the preceding claims 1 to 7, wherein the weight ratio of the doped high volatile material A to the low volatile material B in step S3 is 1 (3-15), optionally 1 (4-10).
9. Preparation method according to any one of the preceding claims, characterized in that the pre-heating treatment of step S3 employs a stepwise temperature increase, comprising at least 2 temperature-programmed stages, optionally 2-4.
10. A modified graphite obtained by the production method according to any one of claims 1 to 9, wherein the graphite has a structure in which La is in the range of 80 to 160nm, lc is in the range of 27 to 37nm, and a lattice spacing d 002 In the range of 0.360 to 0.365 nm.
11. The modified graphite of claim 10, wherein the modified graphite comprises a carbon core and a carbon coating layer, the carbon coating layer having a weight of greater than 0 to 5 wt% or less, based on the weight of the carbon core.
12. Modified graphite according to claim 10 or 11, wherein the particles of the modified graphite have a volume median particle diameter Dv50 of 7-14 μ ι η, optionally 9-13 μ ι η.
13. The modified graphite of any one of claims 10 to 12, wherein the degree of graphitization of the modified graphite is 88-98%.
14. A secondary battery comprising a positive electrode tab, a negative electrode tab, a separator and an electrolyte, wherein the negative electrode tab comprises the modified graphite prepared by the process of any one of claims 1-9, or the modified graphite of any one of claims 10-13.
15. An electric device comprising the secondary battery according to claim 13.
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