CN112072075A - Negative electrode film and preparation method and application thereof - Google Patents
Negative electrode film and preparation method and application thereof Download PDFInfo
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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Abstract
The invention discloses a negative electrode film and a preparation method and application thereof. Wherein, the preparation method comprises the following steps: mixing needle coke and a binder, heating, and performing calendaring treatment and carbonization treatment to obtain a carbon film; cooling the carbon film, performing calendaring exhaust treatment, and then heating for graphitization treatment to obtain a graphite film; and carrying out calendaring pore-forming treatment and/or transverse stretching pore-forming treatment on the graphite film so as to obtain the flexible negative electrode film with the surface and the interior provided with three-dimensional channels for lithium ion transmission, intercalation and intercalation. The preparation method does not need solvent, and can obtain the flexible negative electrode film with a complete heat conduction channel and a three-dimensional channel for lithium ion transmission, intercalation and intercalation, so that the negative electrode film has higher heat conductivity coefficient, conductivity, mechanical strength and electrochemical activity capacity.
Description
Technical Field
The invention belongs to the field of lithium batteries, and particularly relates to a negative electrode film and a preparation method and application thereof.
Background
With the continuous progress of society, the demand of human beings to the high energy density of lithium cell increases gradually, forces lithium cell manufacturer to reach this purpose through constantly compressing the mass flow body thickness, and the mass flow body heat conduction that nevertheless the attenuation has received very big restriction, hardly conducts the heat that produces inside the battery to the battery surface fast, causes the battery thermal runaway and then arouses the incident easily. In view of the above problems, there is a high necessity for a carrier having electrochemical activity and high thermal conductivity. Furthermore, the graphite cathode used at present is obtained by using copper foil as a current collector and coating graphite with electrochemical activity by a wet method, point-point contact is formed among graphite particles obtained by coating, the movement of heat conduction phonons is inhibited by a plurality of interfaces, the heat conduction is seriously influenced, and the wet coating process is long in time and is not environment-friendly. Therefore, the preparation process of the graphite negative electrode still needs to be further improved.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, an object of the present invention is to propose an anode film, a method for producing the same, and applications thereof. The preparation method does not need solvent, and can obtain the flexible negative electrode film with a complete heat conduction channel and a three-dimensional channel for lithium ion transmission, intercalation and intercalation, so that the negative electrode film has higher heat conductivity coefficient, conductivity, mechanical strength and electrochemical activity capacity.
The present invention is proposed based on the following findings of the inventors:
at present, a graphite cathode film is prepared by graphitizing polyimide, and has a continuous heat conduction channel so as to obtain higher heat conductivity, however, the graphite cathode film cannot be applied to a cathode because no lithium ion transmission channel exists in the graphite cathode film and lithium ions cannot be stored. Therefore, the inventor imagines that a membrane material with complete heat conduction channels can be prepared by using easily graphitized raw materials, and three-dimensional channels for lithium ion transmission, intercalation and intercalation can be obtained by using graphite interlayer defects and anisotropic characteristics of graphite layers.
To this end, according to a first aspect of the present invention, the present invention proposes a method of producing a negative electrode film. According to an embodiment of the invention, the method comprises:
mixing needle coke and a binder, heating, and performing calendaring treatment and carbonization treatment to obtain a carbon film;
cooling the carbon film, performing calendaring exhaust treatment, and then heating for graphitization treatment to obtain a graphite film;
and carrying out calendaring pore-forming treatment and/or transverse stretching pore-forming treatment on the graphite film so as to obtain the flexible negative electrode film with the surface and the interior provided with three-dimensional channels for lithium ion transmission, intercalation and intercalation.
According to the method for preparing the cathode film, the carbon film is subjected to rolling and exhausting, so that the porosity and the gas pore diameter in the carbon film can be obviously reduced, the density of the carbon film is improved, and the graphitization treatment efficiency and the graphitization degree are further improved; and further carrying out calendaring and/or stretching treatment on the graphite film after graphitization, and forming a three-dimensional channel for lithium ion transmission, intercalation and intercalation on the surface and inside of the graphite film by using residual small bubbles in the graphite film. Therefore, the preparation method does not need a solvent, and can obtain a flexible negative electrode film with a complete heat conduction channel and a three-dimensional channel for lithium ion transmission, intercalation and intercalation, so that the negative electrode film has higher heat conductivity coefficient, electric conductivity, mechanical strength and electrochemical activity capacity, specifically, the heat conductivity coefficient of the negative electrode film can reach 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, the electrochemical capacity at the discharge rate of 0.1C at normal temperature can reach 360mAh/g or even higher, when the negative electrode film is used as a negative electrode sheet in a battery, the negative electrode sheet is not only beneficial to battery assembly, but also can obviously improve the cycle life, energy density and safety of the battery, and greatly reduce the probability of thermal runaway of the battery.
In addition, the method of manufacturing a negative electrode film according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the present invention, the method of preparing a negative electrode film satisfies at least one of the following conditions: the temperature of the calendering treatment is 300-500 ℃, and the pressure is 1-100 MPa; the carbonization treatment is carried out at 850-1300 ℃; the temperature of the calendering exhaust treatment is not higher than 50 ℃, and the pressure is 0.01-10 MPa; the temperature of the graphitization treatment is 2500-3000 ℃; the temperature of the calendaring pore-forming treatment and/or the transverse stretching pore-forming treatment is not higher than 500 ℃; the pressure of the calendering pore-forming treatment is 0.01-100 MPa, and the tension of the transverse stretching pore-forming treatment is 0.01-1000N; the transverse stretching pore-forming treatment is realized by adopting uniaxial stretching or biaxial stretching.
In some embodiments of the present invention, the temperature of the calendering and/or transverse stretching pore-forming treatment is 300 to 500 ℃.
In some embodiments of the invention, the binder is pitch, and the needle coke and the pitch are present in a mass ratio of 100: (5-100).
In some embodiments of the present invention, the thickness of the negative electrode film is 0.5 to 1000 μm.
In some embodiments of the invention, the degree of graphitization of the negative electrode film is not less than 99%.
According to a second aspect of the present invention, a negative electrode film is provided. According to the embodiment of the invention, the negative electrode film is obtained by adopting the method for preparing the negative electrode film. Compared with the prior art, the negative electrode film integrates three functions of a negative electrode current collector, a negative electrode active substance and a heat conductor, not only has a complete heat conduction channel, and the surface and the inside of the lithium ion battery also have three-dimensional channels for lithium ion transmission, intercalation and intercalation, and have higher thermal conductivity, electrical conductivity, mechanical strength and electrochemical activity capacity, particularly, the heat conductivity coefficient of the negative electrode film can reach 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, the electrochemical capacity at the discharge rate of 0.1C at normal temperature can reach 360mAh/g or even higher, when the negative electrode film is used as a negative electrode plate in a battery, the negative plate has the advantages that the cycle life, the energy density and the safety of the battery can be obviously improved, the probability of thermal runaway of the battery is greatly reduced, and the negative plate is flexible and can be wound, so that the battery is more favorably assembled.
According to a third aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the above negative electrode film or the negative electrode film obtained by the above preparation method. Compared with the prior art, the battery has the advantages of convenience in assembly, good cycle stability, high energy density and high safety, and the probability of thermal runaway events is lower.
In some embodiments of the present invention, the lithium battery is a liquid lithium ion battery, a quasi-solid state lithium ion battery, or a solid state lithium ion battery.
In some embodiments of the present invention, the lithium battery is a button battery, a pouch battery, a cylindrical battery, or a square battery.
In some embodiments of the invention, the negative electrode film and the tab are bonded by conductive silver glue or conductive carbon glue.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a flowchart of a method of manufacturing a negative electrode film according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
According to a first aspect of the present invention, a method of manufacturing a negative electrode film is proposed. According to an embodiment of the invention, the method comprises: mixing needle coke and a binder, heating, and performing calendaring treatment and carbonization treatment to obtain a carbon film; cooling the carbon film, performing calendaring exhaust treatment, and then heating for graphitization treatment to obtain a graphite film; and carrying out calendaring pore-forming treatment and/or transverse stretching pore-forming treatment on the graphite film so as to obtain the flexible negative electrode film with three-dimensional channels for lithium ion transmission, intercalation and intercalation in the surface and the interior. The preparation method does not need solvent, and can obtain a flexible negative electrode film with a complete heat conduction channel and a three-dimensional channel for lithium ion transmission, intercalation and intercalation, so that the negative electrode film has higher heat conductivity coefficient, electric conductivity, mechanical strength and electrochemical activity capacity, specifically, the heat conductivity coefficient of the negative electrode film can reach 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, the electrochemical capacity at the discharge rate of 0.1C at normal temperature can reach 360mAh/g or even higher, when the negative electrode film is used as a negative electrode sheet in a battery, the negative electrode film is not only beneficial to battery assembly, but also can obviously improve the cycle life, energy density and safety of the battery, and greatly reduce the probability of thermal runaway of the battery.
The method of manufacturing the negative electrode film of the above embodiment of the present invention will be described in detail with reference to fig. 1.
S100: mixing needle coke and binder, heating, performing calendaring and carbonization treatment to obtain the carbon film
According to one embodiment of the present invention, the needle coke selected for use in the present invention is readily graphitized relative to other graphitizing raw materials. In addition, the kind of the binder in the present invention is not particularly limited, and those skilled in the art can select the binder according to actual needs. Preferably, the binder may be pitch, and the mass ratio of the needle coke to the pitch may be 100: (5-100), such as 100/5, 100/10, 100/15, 100/25, 100/35, 100/45, 100/60, 100/80 or 100/100, etc., the inventor finds that the use of asphalt as a binder is not only beneficial to high-temperature molding and carbonization of needle coke, but also does not introduce excessive other impurities; further, if the amount of the asphalt is too small, it is difficult to form a uniform and dense film layer during the calendaring process, and if the amount of the asphalt is too large, the conductivity and the negative electrode capacity of the negative electrode film are adversely affected due to relatively poor high-temperature graphitization degree of the asphalt. According to the invention, the asphalt is selected as the binder, and the mass ratio of the asphalt to the needle coke is controlled within the range, so that the graphitization degree, the thermal conductivity coefficient, the electric conductivity, the mechanical strength and the electrochemical activity capacity of the finally prepared cathode film can be further improved, for example, the graphite degree of the cathode film is not lower than 99%, the thermal conductivity coefficient reaches 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, and the electrochemical capacity at 0.1C discharge rate at normal temperature reaches 360mAh/g or even higher.
According to another embodiment of the present invention, the temperature of the calendering process may be 300 to 500 ℃, for example, 300 ℃, 340 ℃, 380 ℃, 420 ℃, 460 ℃ or 500 ℃, etc., and the inventors found that the above temperature condition is more favorable for the uniform mixing and molding of the needle coke and the asphalt, preferably, the calendering process is performed at 300 to 400 ℃; further, the pressure of the calendering process may be 1 to 100MPa, for example, 1MPa, 5MPa, 10MPa, 15MPa, 25MPa, 35MPa, 50MPa, 65MPa, 80MPa or 100MPa, and the inventors found that if the pressure of the calendering process is too low, stable molding of the needle coke is difficult to achieve, the carbon film obtained after molding carbonization has poor uniformity and surface morphology, and may have local depressions or protrusions and holes, and if the pressure of the molding process is too high, carbonization efficiency may be affected.
According to another embodiment of the present invention, the carbonization treatment may be performed at 850 to 1300 ℃, for example, the carbonization treatment temperature may be 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1100 ℃ or 1300 ℃, and the inventors found that the carbon film obtained by carbonization is more stable in this temperature range. Preferably, the temperature of the carbonization treatment may be 850 to 950 ℃.
According to yet another embodiment of the present invention, the needle coke and pitch may be blended in a ratio of 100: (5-100), stirring, ball-milling, rolling and molding at 300-500 ℃, and carbonizing at 850-1300 ℃ to obtain the carbon film with the predetermined thickness.
S200: cooling the carbon film, rolling, exhausting, heating for graphitization to obtain graphite film
According to the embodiment of the invention, the carbonized carbon film is relatively fluffy, pores or cracks may exist in the carbonized carbon film, and the porosity and gas pore diameter in the carbon film can be obviously reduced and the density of the carbon film can be improved by further carrying out calendaring and exhausting treatment on the carbon film, so that the efficiency and the graphitization degree of subsequent graphitization treatment are improved.
According to an embodiment of the present invention, the temperature of the rolling degassing treatment may be not higher than 50 ℃, for example, the carbon film may be cooled to room temperature and then subjected to the rolling degassing treatment, and the pressure of the rolling treatment may be 0.01 to 10MPa, for example, 1MPa, 5MPa, 10MPa, 15MPa, 25MPa, 35MPa, 50MPa, 65MPa, 80MPa, or 100MPa, thereby further improving the density of the carbon film. Further, the temperature of the graphitization treatment is 2500-3000 ℃, so that the carbon film can be further ensured to have higher graphitization degree, for example, the graphite degree of the finally obtained negative electrode film can be not less than 99%, and the conductivity of the negative electrode film is greatly improved.
S300: carrying out calendering pore-forming treatment and/or transverse stretching pore-forming treatment on the graphite film to obtain the flexible negative electrode film with three-dimensional channels for lithium ion transmission, intercalation and intercalation in the surface and inside
According to the embodiment of the invention, small pores exist in the graphite film obtained by graphitizing the carbon film, and by further performing calendaring and/or stretching treatment on the graphite film, three-dimensional channels for lithium ion transmission, intercalation and intercalation can be formed on the surface and in the graphite film by using residual small bubbles in the graphite film, so that the electrochemical activity of the finally obtained flexible negative electrode film is remarkably improved; in addition, the inventors found that the calendering process is performed along the length direction of the graphite film, the arrangement of the graphite layers in the graphite film along the length direction is dense, and only longitudinal stretching of the graphite film cannot form effective three-dimensional channels for lithium ion transmission, intercalation and intercalation on and in the graphite film, so that the obtained negative electrode film has low electrochemical activity and low electrochemical capacity, and transverse stretching of the graphite film can significantly improve the electrochemical activity and electrochemical capacity of the negative electrode film. In the present invention, the longitudinal stretching means stretching along the longitudinal direction of the graphite film, and the transverse stretching means stretching along the width direction of the graphite film.
According to one embodiment of the present invention, the temperature of the calendering and/or transverse stretching pore-forming treatment may be not higher than 500 ℃, for example, at room temperature, or at 50 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃ or 500 ℃; preferably, calendering pore-forming treatment and/or transverse stretching pore-forming treatment can be carried out at 300-500 ℃, and at the moment, the thermal motion of graphite molecules is faster, so that a three-dimensional channel for lithium ion transmission, intercalation and intercalation can be formed on the surface and in the graphite film. Further, the pressure of the calendering pore-forming treatment may be 0.01 to 100MPa, for example, 1MPa, 5MPa, 10MPa, 15MPa, 25MPa, 35MPa, 50MPa, 65MPa, 80MPa, or 100 MPa; the tension of the transverse stretching pore-forming treatment can be 0.01-1000N, for example, 1N, 5N, 10N, 25N, 50N, 100N, 200N, 500N, 800N or 1000N, and the inventors found that if the pressure of the calendaring pore-forming treatment or the tension of the transverse stretching pore-forming treatment is too low, it is not favorable for forming uniform and stable three-dimensional channels in and on the surface of the graphite film, and if the pressure of the calendaring pore-forming treatment or the tension of the transverse stretching pore-forming treatment is too high, the compactness of the graphite film is too high, and effective three-dimensional channels are difficult to form.
According to another embodiment of the present invention, the manner of implementing the transverse stretching pore-forming treatment in the present invention is not particularly limited, and those skilled in the art can select the method according to actual needs, for example, uniaxial stretching or biaxial stretching can be used to implement the transverse stretching pore-forming treatment. Further, after the graphitization treatment, the graphite film may be subjected to a rolling pore-forming treatment in advance, and then the pore-forming is continued by uniaxial stretching or biaxial stretching, so as to obtain a three-dimensional pore channel for lithium ion transmission.
According to another embodiment of the present invention, the thickness of the negative electrode film in the present invention is not particularly limited, and can be selected by those skilled in the art according to actual needs, for example, the thickness of the negative electrode film can be 0.5 to 1000 μm, and further can be 0.5 μm, 1 μm, 5 μm, 15 μm, 30 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, or 1000 μm, etc.
In summary, according to the method for preparing the cathode film of the embodiment of the invention, by performing calendering and exhausting on the carbon film, the porosity and gas pore size in the carbon film can be significantly reduced, the density of the carbon film is improved, and further the graphitization treatment efficiency and graphitization degree are improved; and further carrying out calendaring and/or stretching treatment on the graphite film after graphitization, and forming a three-dimensional channel for lithium ion transmission, intercalation and intercalation on the surface and inside of the graphite film by using residual small bubbles in the graphite film. Therefore, the preparation method does not need a solvent, and can obtain a flexible negative electrode film with a complete heat conduction channel and a three-dimensional channel for lithium ion transmission, intercalation and intercalation, so that the negative electrode film has higher heat conductivity coefficient, electric conductivity, mechanical strength and electrochemical activity capacity, specifically, the heat conductivity coefficient of the negative electrode film can reach 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, the electrochemical capacity at the discharge rate of 0.1C at normal temperature can reach 360mAh/g or even higher, when the negative electrode film is used as a negative electrode sheet in a battery, the negative electrode sheet is not only beneficial to battery assembly, but also can obviously improve the cycle life, energy density and safety of the battery, and greatly reduce the probability of thermal runaway of the battery.
According to a second aspect of the present invention, a negative electrode film is provided. According to the embodiment of the invention, the negative electrode film is obtained by adopting the method for preparing the negative electrode film. Compared with the prior art, the negative electrode film integrates three functions of a negative electrode current collector, a negative electrode active substance and a heat conductor, can be directly used as a negative electrode plate, not only has a complete heat conduction channel, but also has a three-dimensional channel for lithium ion transmission, intercalation and intercalation on the surface and inside, has higher heat conductivity coefficient, electric conductivity, mechanical strength and higher electrochemical activity capacity, particularly, the heat conductivity coefficient of the negative electrode film can reach 1800W/(m.K) or even higher, the electric conductivity is not lower than 1200S/cm, the electrochemical capacity at the discharge rate of 0.1C at normal temperature can reach 360mAh/g or even higher, when the negative electrode film is used as the negative electrode plate in a battery, the cycle life, the energy density and the safety of the battery can be obviously improved, the probability of thermal runaway of the battery is greatly reduced, and the negative electrode plate has flexibility, can be wound, and is more beneficial to the assembly of the battery. It should be noted that the features and effects described for the above method for preparing the negative electrode film are also applicable to the negative electrode film, and are not described in detail herein.
According to a third aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the above negative electrode film or the negative electrode film obtained by the above preparation method. Compared with the prior art, the battery has the advantages of convenience in assembly, good cycle stability, high energy density and high safety, and the probability of thermal runaway events is lower. It should be noted that the type of the lithium battery in the present invention is not particularly limited, and those skilled in the art can select the lithium battery according to actual needs, for example, the lithium battery may be a liquid lithium ion battery, a quasi-solid lithium ion battery, or a solid lithium ion battery; further, the lithium battery can be a button battery, a soft package battery, a cylindrical battery or a square battery.
According to one embodiment of the present invention, the inventors found that the negative electrode film of the present invention is difficult to connect the tab by using a common ultrasonic welding process, and the bonding between the negative electrode film and the tab can be achieved by conductive silver paste or conductive carbon paste.
It should be noted that the features and effects described for the above-mentioned negative electrode film and the method for preparing the negative electrode film are also applicable to the lithium battery, and are not described in detail herein.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:10, then carrying out high-temperature rolling molding, carbonizing at 1300 ℃ to obtain a 10-micron carbon film, cooling, rolling, heating to 3000 ℃ for graphitizing, then carrying out cold rolling at room temperature, wherein the rolling pressure is 10MPa, and thus obtaining the cathode film with electrochemical activity. The heat conductivity coefficient of the obtained negative electrode film is 1950W/(m.K), the electric conductivity is 1340S/cm, and the electrochemical capacity at the normal temperature is 156mAh/g at the discharge rate of 0.1C.
Example 2
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:10, then carrying out high-temperature rolling forming, carbonizing at 1300 ℃ to obtain a 10-micron carbon film, cooling, rolling, heating to 3000 ℃ for graphitizing, and then transversely stretching at room temperature with the prestress of 30N to obtain the cathode film with electrochemical activity. The heat conductivity coefficient of the obtained negative electrode film is 850W/(m.K), the electric conductivity is 1250S/cm, and the electrochemical capacity at normal temperature is 112mAh/g at the discharge rate of 0.1C.
Example 3
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:10, then carrying out high-temperature rolling molding, carbonizing at 1200 ℃ to obtain a 5-micron carbon film, cooling, rolling, heating to 2500 ℃ for graphitization, and then carrying out cold rolling at room temperature under the rolling pressure of 50MPa to obtain the cathode film with electrochemical activity. The heat conductivity coefficient of the obtained negative electrode film is 1850W/(m.K), the conductivity is 1280S/cm, and the electrochemical capacity at the normal temperature is 312mAh/g at the discharge rate of 0.1C.
Example 4
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:15, then carrying out high-temperature rolling molding, carbonizing at 1100 ℃ to obtain a carbon film with the thickness of 11 microns, cooling, rolling, heating to 2800 ℃ for graphitizing, then carrying out cold rolling at room temperature, wherein the rolling pressure is 15MPa, and then carrying out transverse stretching with the prestress of 20N to obtain the cathode film with electrochemical activity. The heat conductivity coefficient of the obtained negative electrode film is 1150W/(m.K), the electric conductivity is 1200S/cm, and the electrochemical capacity at normal temperature is 358mAh/g at the discharge rate of 0.1C.
Comparative example 1
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:10, then carrying out high-temperature rolling molding, carbonizing at 1300 ℃ to obtain a 10-micron carbon film, cooling, rolling, heating to 3000 ℃ and graphitizing to obtain the negative electrode film. The heat conductivity coefficient of the obtained negative electrode film is 2100W/(m.K), the electric conductivity is 1600S/cm, and the electrochemical capacity at the normal temperature is 34mAh/g at the discharge rate of 0.1C.
Comparative example 2
Stirring and ball-milling needle coke and asphalt according to the mass ratio of 100:10, then carrying out high-temperature rolling forming, carbonizing at 1300 ℃ to obtain a 10-micron carbon film, cooling, rolling, heating to 3000 ℃ for graphitizing, and then longitudinally stretching at room temperature with the prestress of 30N to obtain the cathode film with electrochemical activity. The heat conductivity coefficient of the obtained negative electrode film is 1780W/(m.K), the conductivity is 1080S/cm, and the electrochemical capacity at normal temperature is 22mAh/g at the discharge rate of 0.1C.
The negative electrode films obtained in examples 1 to 4 and comparative examples 1 to 2 were used for battery assembly and cycle performance test, respectively, under the same conditions:
assembling the battery: injecting a commercial electrolyte into a ternary material LiNi0.8Co0.1Mn0.1O2In the soft package lithium ion battery which is a positive electrode and takes the negative electrode film prepared in the above embodiment or the comparative example as a negative electrode, the battery is charged for 1h at a constant current of 0.05C, then charged to 4.0V at a constant current of 0.2C, and charged to 4.2V at 0.05C, and finally the battery is put into an oven at 55 ℃ for aging for 24h, and discharged to 3.0V at a constant current of 0.2C.
And (3) testing the cycle performance: the lithium ion battery after formation was charged to 4.4V at a constant current of 1C and a cut-off current of 0.01C, then discharged to 3.0V at a constant current of 1C, and the cycle performance was evaluated by repeating the 1C charge/1C discharge cycle 200 times. The cycle performance was calculated from the capacity retention of the formula:
capacity retention (%) × (discharge capacity at 200 th cycle/initial discharge capacity) × 100%.
The lithium ion battery is subjected to cycle test at normal temperature and high temperature of 45 ℃ respectively, and the test results are shown in table 1.
TABLE 1 negative electrode film and Battery test results
Results and conclusions:
as can be seen from table 1, further performing calendering or transverse stretching treatment on the graphite film after the graphitization treatment can significantly improve the electrochemical activity of the negative electrode film, so that the negative electrode film has a higher electrochemical capacity; particularly, after graphitization treatment, the graphite film is rolled in advance and then transversely stretched, so that the electrochemical activity and the electrochemical capacity of the negative electrode film can be further improved, and the battery can have better cycling stability at normal temperature and high temperature when the graphite film is used for preparing the battery. And the electrochemical activity of the negative electrode film cannot be improved by longitudinally stretching the graphite film after the graphitization treatment. In summary, the negative electrode film obtained by the preparation method of the embodiment of the invention has good thermal conductivity, electrical conductivity and electrochemical activity, and can be widely used in the battery field as a negative electrode sheet.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A method of making a negative electrode film, comprising:
mixing needle coke and a binder, heating, and performing calendaring treatment and carbonization treatment to obtain a carbon film;
cooling the carbon film, performing calendaring exhaust treatment, and then heating for graphitization treatment to obtain a graphite film;
and carrying out calendaring pore-forming treatment and/or transverse stretching pore-forming treatment on the graphite film so as to obtain the flexible negative electrode film with the surface and the interior provided with three-dimensional channels for lithium ion transmission, intercalation and intercalation.
2. The method of claim 1, wherein at least one of the following conditions is satisfied:
the temperature of the calendering treatment is 300-500 ℃, and the pressure is 1-100 MPa;
the carbonization treatment is carried out at 850-1300 ℃;
the temperature of the calendering exhaust treatment is not higher than 50 ℃, and the pressure is 0.01-10 MPa;
the temperature of the graphitization treatment is 2500-3000 ℃;
the temperature of the calendaring pore-forming treatment and/or the transverse stretching pore-forming treatment is not higher than 500 ℃;
the pressure of the calendering pore-forming treatment is 0.01-100 MPa, and the tension of the transverse stretching pore-forming treatment is 0.01-1000N;
the transverse stretching pore-forming treatment is realized by adopting uniaxial stretching or biaxial stretching.
3. The method according to claim 2, wherein the temperature of the calendering pore-forming treatment and/or the transverse stretching pore-forming treatment is 300-500 ℃.
4. The method according to any one of claims 1 to 3, wherein the binder is asphalt, and the mass ratio of the needle coke to the asphalt is 100: (5-100).
5. The method according to claim 1, wherein the thickness of the negative electrode film is 0.5 to 1000 μm.
6. The method of claim 1, wherein the degree of graphitization of the negative electrode film is no less than 99%.
7. A negative electrode film characterized by being produced by the method according to any one of claims 1 to 6.
8. A lithium battery comprising the negative electrode film according to claim 7 or the negative electrode film produced by the method according to any one of claims 1 to 6.
9. The lithium battery of claim 8, wherein the lithium battery is a liquid lithium ion battery, a quasi-solid state lithium ion battery, or a solid state lithium ion battery.
10. The lithium battery according to claim 8 or 9, wherein the lithium battery is a button cell battery, a pouch cell battery, a cylindrical battery or a square battery,
optionally, the negative electrode film is bonded with the tab through conductive silver glue or conductive carbon glue.
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