Preparation method of negative electrode active material, negative electrode active material, battery and equipment

Abstract

The embodiment of the invention provides a preparation method of a negative electrode active material, the negative electrode active material, a battery and equipment. Fluorine-containing gas is used as discharge gas, and discharge current is introduced into a plasma treatment device in the process of performing vibration dispersion treatment on a porous carbon substrate through the plasma treatment device; the fluorine-containing gas is used for carrying out plasma discharge treatment on the porous carbon matrix, so that the fluorine element provided by the fluorine-containing gas can react with carbon atoms on the surface of the porous carbon matrix to form chemical bonding, and the chemical bonding uniformity between the fluorine element and the carbon atoms on the surface of the porous carbon matrix can be improved; and the preparation cost of the negative electrode active material can be reduced, and the preparation efficiency of the negative electrode active material is improved, so that the battery capacity and the cycle performance of a secondary battery prepared from the negative electrode active material disclosed by the embodiment of the invention can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a method for preparing a negative electrode active material, a negative electrode active material, a battery and a device. Background Art

[0002] With the continuous expansion of the application scope of secondary batteries, the specific capacity of secondary batteries using graphite as the negative electrode active material is too low (372 mAh / g), making it difficult to meet the growing energy storage demand.

[0003] In related technologies, silicon-carbon porous materials are generally used as the negative electrode active material of secondary batteries to improve the specific capacity of secondary batteries; however, in actual application scenarios, the mechanical strength of silicon-carbon porous materials is relatively low. As the secondary battery undergoes continuous charge and discharge cycles, the fragmentation and pulverization of the negative electrode active material will cause the solid electrolyte interface (SEI) formed on the surface of the negative electrode sheet to break and reform repeatedly. This process continuously consumes lithium ions and electrolyte in the secondary battery, resulting in a decrease in the capacity and cycling performance of the secondary battery. Summary of the Invention

[0004] Embodiments of the present application provide a method for preparing a negative electrode active material, a negative electrode active material, a battery and a device, so as to solve the problems in related technologies that the capacity and cycling performance of secondary batteries decrease due to the low mechanical strength of the negative electrode active material.

[0005] To solve the above problems, the present application is implemented through the following technical solutions:

[0006] The present application provides a method for preparing a negative electrode active material, the method comprising:

[0007] Loading a porous carbon matrix into a plasma treatment device;

[0008] Introducing a fluorine-containing gas into the plasma treatment device;

[0009] Performing a vibration dispersion treatment on the porous carbon matrix through the plasma treatment device;

[0010] During the vibration dispersion treatment of the porous carbon matrix, a discharge current is introduced into the plasma treatment device to perform a plasma discharge treatment on the porous carbon matrix using the fluorine-containing gas, thereby obtaining a negative electrode active material; the negative electrode active material includes the porous carbon matrix and fluorine elements provided by the fluorine-containing gas, and the fluorine elements are chemically bonded to carbon atoms on the surface of the porous carbon matrix.

[0011] Further, in the method, in the plasma processing device, the gauge pressure of the fluorine-containing gas is 0.02 MPa to 0.05 MPa.

[0012] Further, in the method, during the process of vibrating and dispersing the porous carbon matrix by the plasma processing device, the motor speed of the plasma processing device is 750 r / min to 1100 r / min.

[0013] Further, in the method, the discharge current is 0.4 A to 3 A.

[0014] Further, in the method, the duration of the plasma discharge treatment on the porous carbon matrix is 15 min to 60 min.

[0015] Further, in the method, the vibrating and dispersing treatment of the porous carbon matrix by the plasma processing device includes:

[0016] When the duration of the vibrating and dispersing treatment of the porous carbon matrix by the plasma processing device reaches the first duration, the porous carbon matrix is subjected to a static treatment;

[0017] When the duration of the static treatment of the porous carbon matrix reaches the second duration, the porous carbon matrix is vibrated and dispersed by the plasma processing device until the total duration of the vibrating and dispersing treatment of the porous carbon matrix by the plasma processing device reaches the preset duration.

[0018] Further, in the method, the porous carbon matrix includes a biomass porous carbon material.

[0019] The present application also provides a negative electrode active material, which is prepared by the preparation method of the negative electrode active material as described above.

[0020] The present application also provides a secondary battery, which includes a positive electrode plate and a negative electrode plate; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material prepared by the preparation method of the negative electrode active material as described above.

[0021] The present application also provides an electrical device, which includes the secondary battery as described above, and the secondary battery serves as the power supply of the electrical device.

[0022] Compared with the related art, the embodiments of the present application have the following advantages:

[0023] The preparation method of the negative electrode active material provided by the embodiment of the present application uses a fluorine-containing gas as the discharge gas. During the vibration dispersion treatment of the porous carbon matrix by a plasma treatment device, a discharge current is introduced into the plasma treatment device to perform plasma discharge treatment on the porous carbon matrix with the fluorine-containing gas, so that the active fluorine atoms and fluorine-containing free radicals generated by the ionization of the fluorine-containing gas can uniformly bombard the surface of the porous carbon matrix, improving the reaction activity of carbon atoms on the surface of the porous carbon matrix, which is beneficial to the reaction between the fluorine element provided by the fluorine-containing gas and the carbon atoms on the surface of the porous carbon matrix to form chemical bonds. Thus, by means of the "force-electricity-thermal" multi-field coupling effect formed by vibration dispersion treatment, high-energy electron bombardment of discharge plasma, and thermal effect of discharge plasma, not only can the uniformity of chemical bonding between the fluorine element and the carbon atoms on the surface of the porous carbon matrix be improved, but also the preparation cost of the negative electrode active material can be reduced and the preparation efficiency of the negative electrode active material can be improved; further, during the charge and discharge cycle of the secondary battery including the negative electrode active material prepared by the embodiment of the present application, the fluorine element chemically bonded to the surface of the porous carbon matrix can combine with lithium ions in the secondary battery to form lithium fluoride, so that the solid electrolyte interface film formed on the surface of the negative electrode active material contains lithium fluoride. And there is a strong electrostatic attraction between lithium ions and fluorine ions in lithium fluoride, which can form a stable ionic lattice, promoting the formation of a dendrite-free and dense film-forming morphology of the solid electrolyte interface film, being beneficial to improving the stability and mechanical strength of the solid electrolyte interface film, reducing the probability of the solid electrolyte interface film breaking and pulverizing during the charge and discharge cycle, reducing the number of reconstructions of the solid electrolyte interface film, and further reducing the consumption of lithium ions and electrolyte in the secondary battery during the reconstruction process of the solid electrolyte interface film, improving the battery capacity and cycle performance of the secondary battery.

[0024] It should be understood that the above general description and subsequent detailed description are only exemplary and explanatory, and cannot limit the present application. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 is a flowchart of the steps of a preparation method of a negative electrode active material provided by the present application;

[0027] Figure 2 is a scanning electron microscope image of the negative electrode active material obtained through Example 4 provided by the present application;

[0028] Figure 3 is the scanning electron microscope image of the negative electrode active material obtained through Example 5 provided by this application;

[0029] Figure 4 is the scanning electron microscope image of the biomass porous carbon material provided by this application;

[0030] Figure 5 is the X-ray photoelectron spectroscopy curve of the negative electrode active material obtained through Example 4 provided by this application;

[0031] Figure 6 is the X-ray photoelectron spectroscopy curve of the negative electrode active material obtained through Comparative Example 1 provided by this application;

[0032] Figure 7 is the atomic force microscope image of the negative electrode sheet obtained through Example 4 provided by this application;

[0033] Figure 8 is the atomic force microscope image of the negative electrode sheet obtained through Comparative Example 1 provided by this application. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

[0035] To make the above objects, features, and advantages of this application more obvious and understandable, the following further details this application in conjunction with the drawings and specific implementation manners.

[0036] In the related art, a silicon-carbon porous material is used as the negative electrode active material of a secondary battery, which can theoretically improve the specific capacity of the secondary battery; however, in actual application scenarios, due to the low mechanical strength of the silicon-carbon porous material, as the cyclic charge and discharge process of the secondary battery continues, the negative electrode active material with low mechanical strength continuously breaks and pulverizes, resulting in the repeated rupture and reformation of the solid electrolyte interface film formed on the surface of the negative electrode sheet. This process continuously consumes lithium ions and electrolyte in the secondary battery, leading to a decrease in the capacity and cycle performance of the secondary battery; further, during the cyclic charge and discharge process of the secondary battery, the breakage and pulverization of the negative electrode active material will also cause the negative electrode active material to fall off from the negative electrode sheet and be unable to participate in the electrochemical reaction, gradually reducing the reversible capacity of the secondary battery and further deteriorating the cycle performance.

[0037] Furthermore, the preparation process of the silicon-carbon porous material is generally as follows: First, a porous carbon matrix framework material is prepared; then, nanosilicon particles are deposited on the surface and inside of the porous carbon matrix by silane cracking; finally, carbon coating is performed on the outer layer of the above material by methane pyrolysis, resulting in a cumbersome preparation process and high cost of the silicon-carbon porous material.

[0038] In order to solve the above problems, an embodiment of the present application provides a method for preparing a negative electrode active material. Referring to Figure 1 , a step flowchart of a method for preparing a negative electrode active material provided by an embodiment of the present application is shown. The method includes the following steps:

[0039] Step S101: Load the porous carbon matrix into a plasma processing device.

[0040] Step S102: Introduce a fluorine-containing gas into the plasma processing device.

[0041] Step S103: Perform vibration dispersion treatment on the porous carbon matrix through the plasma processing device.

[0042] Step S104: During the vibration dispersion treatment of the porous carbon matrix, introduce a discharge current into the plasma processing device to perform plasma discharge treatment on the porous carbon matrix with the fluorine-containing gas to obtain a negative electrode active material.

[0043] The negative electrode active material prepared by the method for preparing a negative electrode active material provided by an embodiment of the present application includes a porous carbon matrix and fluorine elements provided by the fluorine-containing gas, and the fluorine elements are chemically bonded to the carbon atoms on the surface of the porous carbon matrix.

[0044] Among them, the plasma processing device is a device with a powder vibration function and a plasma discharge treatment function; exemplarily, the plasma processing device can be a plasma vibration ball mill, and the model of the ball mill can be selected as Plasma-BM-S.

[0045] The plasma processing device includes a plasma generation chamber; specifically, the plasma generation chamber is a sealed container for accommodating the discharge gas, electrodes, and porous carbon matrix during the plasma generation process, where the number of electrodes is 2. The main function of the plasma generation chamber is to provide a stable electric field environment through the electrodes so that the discharge gas molecules are broken down by the electric field to form discharge plasma. Exemplarily, when the plasma processing device is a plasma vibration ball mill, the plasma generation chamber is the ball milling tank of the plasma vibration ball mill.

[0046] In step S101, the porous carbon matrix can be loaded into the plasma generation chamber of the plasma processing device, and the plasma generation chamber can be sealed. Exemplarily, when the plasma generation chamber is the ball milling tank of a plasma vibration ball mill, in step S101, the porous carbon matrix can be loaded into the ball milling tank, and vacuum sealant can be applied at the end cap rubber ring and the electrode rod shoulder rubber ring of the ball milling tank to complete the encapsulation of the ball milling tank.

[0047] Among them, the porous carbon matrix can be a porous carbon negative electrode material commonly used in the field of secondary batteries. Exemplarily, the porous carbon matrix can include, but is not limited to, activated carbon materials, mesoporous carbon materials, silicon-carbon porous materials, etc. In some embodiments, the porous carbon matrix exists in the form of solid powder.

[0048] In step S102, the plasma generation chamber of the plasma processing device is evacuated, and then a fluorine-containing gas is introduced into the evacuated plasma generation chamber. The above evacuation process and the operation of introducing the fluorine-containing gas are repeated n times to clean the impurity gases in the plasma generation chamber, prevent the influence of components such as nitrogen (N2) and oxygen (O2) in the air on the plasma discharge process in step S104, and improve the purity and quality of the negative electrode active material obtained through step S104.

[0049] Among them, n is an integer greater than 0.

[0050] The fluorine-containing gas can include sulfur hexafluoride (SF6). In the embodiments of the present application, as the discharge gas in the plasma discharge process, the fluorine-containing gas can be broken down under the action of the electric field in the plasma generation chamber to form fluorine element plasma.

[0051] In step S103, the motor of the plasma processing device can be started, and the motor is used to drive the plasma processing device to perform vibration dispersion processing on the porous carbon matrix in the plasma generation chamber.

[0052] During the vibration dispersion treatment of the porous carbon matrix in step S103, step S104 is simultaneously performed to introduce a discharge current into the plasma treatment device, so as to perform plasma discharge treatment on the porous carbon matrix with the fluorine element plasma formed by the breakdown of the fluorine-containing gas under the action of an electric field, and obtain the negative electrode active material. Specifically, the fluorine element plasma includes active fluorine atoms and fluorine-containing radicals; through plasma discharge treatment, the fluorine-containing gas is broken down and ionized under the action of an electric field to generate a large number of active fluorine atoms. These active fluorine atoms have strong oxidizing and reactive activities. When the active fluorine atoms come into contact with the surface of the porous carbon matrix, they will react with the carbon atoms on the surface of the porous carbon matrix to form carbon-fluorine chemical bonds (C-F); the active fluorine atoms generated by the ionization of the fluorine-containing gas also have relatively high energy, and this energy can break the chemical bonds on the surface of the porous carbon matrix to generate some active sites. At the same time, particles such as electrons and ions in the active fluorine atoms interact with the surface of the porous carbon matrix to promote the adsorption and bonding of the active fluorine atoms at these active sites; further, the fluorine-containing gas is broken down and ionized under the action of an electric field to also generate fluorine-containing radicals, such as CF3·, F·, etc. These radicals have high reactive activities and can undergo radical reactions with the carbon atoms on the surface of the porous carbon matrix to form C-F chemical bonds. For example, the CF3· radical can combine with the carbon atoms on the surface of the porous carbon matrix to form a C-CF3 bond.

[0053] It can be understood that step S103 and step S104 are carried out simultaneously. By performing vibration dispersion treatment on the porous carbon matrix in step S103, the uniformity of the dispersion of the porous carbon matrix in the plasma generation chamber is improved. At the same time, step S104 is performed to introduce a discharge current into the plasma treatment device, so as to perform plasma discharge treatment on the porous carbon matrix in a dispersed state in the plasma generation chamber with the fluorine element plasma formed by the breakdown of the fluorine-containing gas under the action of an electric field. Not only can the negative electrode active material be obtained, but also the uniformity of the chemical bonding between the fluorine element and the carbon atoms on the surface of the porous carbon matrix can be improved, that is, the uniformity of the dispersion of the fluorine element on the surface of the porous carbon matrix in the negative electrode active material can be improved, so that the role of the negative electrode active material in improving the battery capacity and cycle performance of the secondary battery can be fully exerted.

[0054] Specifically, in step S104, by introducing a discharge current into the plasma treatment device, a discharge voltage can be applied between two electrodes in the plasma generation chamber to form an electric field between the two electrodes; as the electric field strength increases, the strong electric field formed between the electrodes will accelerate electrons and collide with the fluorine-containing gas molecules in the plasma generation chamber, resulting in the breakdown and ionization of the fluorine-containing gas molecules under the action of the electric field; as the ionization region expands, the ion and electron densities in the fluorine-containing gas reach a certain threshold, making the entire region filled with charged particles, and the fluorine-containing gas is completely broken down to generate fluorine element plasma.

[0055] In the embodiment of the present application, when fluorine element plasma is generated from a fluorine-containing gas, the fluorine element plasma moving at high speed in the plasma generation chamber bombards the surface of the porous carbon matrix, increasing the thermal stress and strain in the micro-region of the porous carbon matrix surface, thereby forming a "thermal explosion" phenomenon on the porous carbon matrix surface, improving the reaction activity of carbon atoms on the porous carbon matrix surface, promoting the chemical reaction between the fluorine element plasma and the carbon atoms on the porous carbon matrix surface, enabling the fluorine element to chemically bond with the carbon atoms on the porous carbon matrix surface, and obtaining the negative electrode active material provided by the embodiment of the present application.

[0056] It should be noted that when steps S103 and S104 are carried out simultaneously, the total duration of the vibration dispersion treatment of the porous carbon matrix is equal to the duration of the plasma discharge treatment of the porous carbon matrix.

[0057] The preparation method of the negative electrode active material provided by the embodiment of the present application uses a fluorine-containing gas as the discharge gas. During the process of vibration dispersion treatment of the porous carbon matrix by a plasma treatment device, a discharge current is introduced into the plasma treatment device to perform plasma discharge treatment on the porous carbon matrix using the fluorine-containing gas, so that the active fluorine atoms and fluorine-containing free radicals generated by the ionization of the fluorine-containing gas can uniformly bombard the surface of the porous carbon matrix, improving the reaction activity of carbon atoms on the porous carbon matrix surface, facilitating the reaction between the fluorine element provided by the fluorine-containing gas and the carbon atoms on the porous carbon matrix surface to form chemical bonds. Thus, by means of the "force-electricity-thermal" multi-field coupling effect formed by the vibration dispersion treatment, the high-energy electron bombardment of the discharge plasma, and the thermal effect of the discharge plasma, not only can the uniformity of the chemical bond between the fluorine element and the carbon atoms on the porous carbon matrix surface be improved, but also the preparation cost of the negative electrode active material can be reduced and the preparation efficiency of the negative electrode active material can be increased; further, during the charge and discharge cycle of a secondary battery including the negative electrode active material prepared in the embodiment of the present application, the fluorine element chemically bonded to the porous carbon matrix surface can combine with lithium ions in the secondary battery to form lithium fluoride, such that the solid electrolyte interface film formed on the negative electrode active material surface contains lithium fluoride, and there is a strong electrostatic attraction between the lithium ions and fluorine ions in lithium fluoride, which can form a stable ionic lattice, promoting the formation of a dendrite-free and dense film-forming morphology of the solid electrolyte interface film, being beneficial to improving the stability and mechanical strength of the solid electrolyte interface film, reducing the probability of the solid electrolyte interface film breaking and pulverizing during the charge and discharge cycle. When the stability and mechanical strength of the solid electrolyte interface film are improved, the degree of breakage and pulverization of the negative electrode active material during the charge and discharge cycle can be reduced, the number of reconstructions of the solid electrolyte interface film can be reduced, and further, the consumption of lithium ions and electrolyte in the secondary battery during the reconstruction process of the solid electrolyte interface film can be reduced, being beneficial to improving the battery capacity and cycle performance of the secondary battery.

[0058] Furthermore, when the stability and mechanical strength of the solid electrolyte interface film are improved and the degree of fragmentation and pulverization of the negative electrode active material during the charge and discharge cycles of the secondary battery is reduced, the amount of the negative electrode active material detached from the negative electrode plate can also be decreased, which is beneficial to further improving the battery capacity and cycle performance of the secondary battery.

[0059] In some embodiments, the porous carbon matrix includes a biomass porous carbon material. The biomass porous carbon material is a carbon material with a porous structure prepared from biomass (such as wood, straw, fruit shells, etc.) through processes such as pyrolysis, carbonization, and activation.

[0060] The preparation method of the negative electrode active material provided by the embodiments of the present application not only has a simple operation process and high repeatability, but also can use a biomass porous carbon material with a lower preparation cost as the porous carbon negative electrode material, which is beneficial to reducing the preparation cost of the negative electrode active material while improving the battery capacity and cycle performance of the secondary battery through the negative electrode active material. The preparation method of the negative electrode active material provided by the embodiments of the present application is more environmentally friendly, does not produce environmentally destructive waste liquid, and does not require high-temperature treatment, saving more electric energy, and is suitable for large-scale industrial production.

[0061] Optionally, in the preparation method of the negative electrode active material provided by the embodiments of the present application, the gauge pressure of the fluorine-containing gas introduced into the plasma processing device through step S102 is 0.02 MPa to 0.05 MPa; specifically, in the plasma processing device, the gauge pressure of the fluorine-containing gas can be one of 0.02 MPa, 0.03 MPa, 0.035 MPa, 0.04 MPa, and 0.05 MPa or any range value between any two of them. Within this range, it is beneficial to increase the quantity and stability of the fluorine element plasma formed by the breakdown of the fluorine-containing gas under the action of the electric field, and increase the probability of chemical bonding between the fluorine element plasma and the carbon atoms on the surface of the porous carbon matrix, so that the role of the negative electrode active material including the fluorine element in improving the battery capacity and cycle performance of the secondary battery can be fully exerted.

[0062] It can be understood that in the plasma processing device, the gauge pressure of the fluorine-containing gas refers to the gauge pressure of the fluorine-containing gas in the plasma generation chamber of the plasma processing device.

[0063] Optionally, during the vibration dispersion treatment of the porous carbon matrix by the plasma processing device in step S103, the motor speed of the plasma processing device is 750 r / min to 1100 r / min; specifically, during the vibration dispersion treatment of the porous carbon matrix by the plasma processing device, the motor speed of the plasma processing device can be one of 750 r / min, 800 r / min, 850 r / min, 950 r / min, 1000 r / min, and 1100 r / min or the range value of any two of them. Within this range, the uniformity of the dispersion of the porous carbon matrix in the plasma generation chamber of the plasma processing device can be improved, which is beneficial to improving the uniformity of the plasma discharge treatment of the porous carbon matrix in step S104 and the uniformity of the distribution of fluorine elements on the surface of the porous carbon matrix in the negative electrode active material prepared in step S104. Furthermore, it is beneficial to improve the uniformity of lithium fluoride in the solid electrolyte interface film, and improve the stability and mechanical strength of the solid electrolyte interface film.

[0064] Optionally, during the vibration dispersion treatment of the porous carbon matrix by the plasma processing device in step S103, the vibration frequency of the plasma generation chamber in the plasma processing device is 10 Hz to 20 Hz. Within this range, the uniformity of the dispersion of the porous carbon matrix in the plasma generation chamber of the plasma processing device can be improved, which is beneficial to improving the uniformity of the plasma discharge treatment of the porous carbon matrix in step S104 and the uniformity of the distribution of fluorine elements on the surface of the porous carbon matrix in the negative electrode active material prepared in step S104. Furthermore, it is beneficial to improve the uniformity of lithium fluoride in the solid electrolyte interface film, and improve the stability and mechanical strength of the solid electrolyte interface film.

[0065] Optionally, in step S104, the discharge current introduced into the plasma processing device is 0.4 A to 3 A; specifically, the discharge current introduced into the plasma processing device can be one of 0.4 A, 1 A, 1.5 A, 2 A, 2.2 A, 2.8 A, and 3 A or the range value of any two of them. Within this range, the activity and quantity of fluorine element plasma generated by the fluorine-containing gas can be improved, and then the effect of the plasma discharge treatment on the porous carbon matrix can be improved.

[0066] Optionally, in step S104, the duration of the plasma discharge treatment on the porous carbon matrix is 15 min to 60 min; specifically, the duration of the plasma discharge treatment on the porous carbon matrix can be any value within the range of 15 min to 60 min or the range value of any two of them. Within this range, it can promote the full contact and reaction between the fluorine element plasma and the carbon atoms on the surface of the porous carbon matrix, so as to improve the chemical bonding effect between the fluorine element in the negative electrode active material and the carbon atoms on the surface of the porous carbon matrix, and the content of the fluorine element in the negative electrode active material.

[0067] It should be noted that the duration of the plasma discharge treatment on the porous carbon matrix is equal to the duration of passing the discharge current into the plasma treatment device.

[0068] The total duration of the vibration dispersion treatment on the porous carbon matrix in step S103 is equal to the duration of the plasma discharge treatment on the porous carbon matrix in step S104. When the duration of the plasma discharge treatment on the porous carbon matrix in step S104 is 15 min to 60 min, the total duration of the vibration dispersion treatment on the porous carbon matrix in step S103 is also 15 min to 60 min.

[0069] Optionally, step S103 of performing the vibration dispersion treatment on the porous carbon matrix through the plasma treatment device includes:

[0070] Step S1031: When the duration of the vibration dispersion treatment on the porous carbon matrix through the plasma treatment device reaches the first duration, perform a static treatment on the porous carbon matrix.

[0071] Step S1032: When the duration of the static treatment on the porous carbon matrix reaches the second duration, perform the vibration dispersion treatment on the porous carbon matrix through the plasma treatment device until the total duration of the vibration dispersion treatment on the porous carbon matrix through the plasma treatment device reaches the preset duration.

[0072] In an embodiment of the present application, during the process of vibrating and dispersing a porous carbon matrix by means of a plasma processing device, the vibrating and dispersing process of the porous carbon matrix can be carried out in a "interval operation, timed shutdown" mode through the operations corresponding to step S1031 and step S1032. That is, after the first duration of vibrating and dispersing the porous carbon matrix by the plasma processing device, it is necessary to control the plasma processing device to stop the vibrating and dispersing process of the porous carbon matrix to achieve the static treatment of the porous carbon matrix. And after the second duration of static treatment of the porous carbon matrix, the vibrating and dispersing process of the porous carbon matrix is continued by the plasma processing device until the total duration of vibrating and dispersing the porous carbon matrix by the plasma processing device reaches a preset duration. It can be understood that while the porous carbon matrix is being vibrated and dispersed, step S104 for performing plasma discharge treatment on the porous carbon matrix needs to be executed simultaneously. When the total duration of vibrating and dispersing the porous carbon matrix by the plasma processing device reaches the preset duration, it indicates that the duration of plasma discharge treatment on the porous carbon matrix through step S104 also reaches the preset duration, thereby obtaining the negative electrode active material provided by the embodiment of the present application.

[0073] For the preparation method of the negative electrode active material provided by the embodiment of the present application, during the process of vibrating and dispersing a porous carbon matrix by means of a plasma processing device, the vibrating and dispersing process of the porous carbon matrix is carried out in a "interval operation, timed shutdown" mode through the operations corresponding to step S1031 and step S1032. This can enable the heat generated during the vibrating and dispersing process and the plasma discharge process of the porous carbon matrix to be dissipated during the static treatment process, preventing problems such as phase change, decomposition or agglomeration of the negative electrode active material due to overheating, which is beneficial to improving the quality of the negative electrode active material prepared by the embodiment of the present application. In addition, the embodiment of the present application can also reduce the continuous operation time of the plasma processing device, which is then beneficial to reducing the internal wear of the plasma processing device, extending the service life of the plasma processing device, and reducing the maintenance cost of the plasma processing device.

[0074] In an embodiment of the present application, the first duration and the second duration can be equal or unequal, and the values of the first duration and the second duration can be determined according to the motor speed of the plasma processing device and the discharge current introduced into the plasma processing device. Specifically, the first duration is negatively correlated with the motor speed and the discharge current of the plasma processing device, that is, the greater the motor speed and / or the discharge current of the plasma processing device, the shorter the first duration; the second duration is positively correlated with the motor speed and the discharge current of the plasma processing device, that is, the greater the motor speed and / or the discharge current of the plasma processing device, the longer the second duration.

[0075] As an example, the first duration is 3 min and the second duration is also 3 min; in step S103, when the duration of the vibration dispersion treatment of the porous carbon matrix by the plasma processing device reaches 3 min, the porous carbon matrix is subjected to a static treatment; when the duration of the static treatment of the porous carbon matrix reaches 3 min, the porous carbon matrix is subjected to a vibration dispersion treatment by the plasma processing device until the total duration of the vibration dispersion treatment of the porous carbon matrix by the plasma processing device reaches a preset duration.

[0076] In the embodiments of the present application, the preset duration can be determined according to the chemical bonding effect of fluorine elements on the surface of the porous carbon matrix and the content of fluorine elements chemically bonded on the surface of the porous carbon matrix in step S104; wherein, the content of fluorine elements chemically bonded on the surface of the porous carbon matrix can be reasonably determined according to the requirements for the battery capacity and cycle performance of the secondary battery, and the embodiments of the present application do not make specific limitations on the content of fluorine elements chemically bonded on the surface of the porous carbon matrix.

[0077] In some embodiments, the upper limit value of the content of fluorine elements chemically bonded on the surface of the porous carbon matrix is a fluorine coating layer formed on the surface of the porous carbon matrix by the fluorine elements chemically bonded on the surface of the porous carbon matrix.

[0078] The present application also provides a negative electrode active material, and the negative electrode active material is prepared by the preparation method of the negative electrode active material as described above.

[0079] For the above embodiments of the negative electrode active material, it is prepared by the preparation method of the negative electrode active material as described above and can achieve the same technical effects. To avoid repetition, it will not be described in detail here, and the relevant parts can be referred to the partial description of the embodiments of the preparation method of the negative electrode active material.

[0080] The present application also provides a secondary battery, wherein the secondary battery includes a positive electrode plate and a negative electrode plate; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material prepared by the preparation method of the negative electrode active material as described above.

[0081] For the above embodiments of the secondary battery, it includes the above negative electrode active material and can achieve the same technical effects. To avoid repetition, it will not be described in detail here, and the relevant parts can be referred to the partial description of the embodiments of the negative electrode active material.

[0082] The present application also provides an electrical device, wherein the electrical device includes the secondary battery as described above, and the secondary battery serves as the power supply of the electrical device.

[0083] For the above-mentioned embodiments of the electrical equipment, it includes the above-mentioned secondary battery and can achieve the same technical effects. To avoid repetition, it will not be elaborated here. For relevant parts, refer to the partial description of the secondary battery embodiments.

[0084] To make the invention objectives, technical solutions, and beneficial effects of this application clearer, the following further describes this application in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application.

[0085] The following details this application through embodiments.

[0086] Embodiment 1

[0087] (1) Preparation of the negative electrode active material

[0088] (i) Load the biomass porous carbon material into the ball milling tank of the plasma vibration ball mill, and apply vacuum sealant at the rubber rings of the end cover of the ball milling tank and the shoulder of the electrode rod to complete the encapsulation of the ball milling tank. Among them, the model of the plasma vibration ball mill is Plasma - BM - S, the material of the ball milling tank is tungsten carbide hard alloy, and the volume of the ball milling tank is 0.2L.

[0089] (ii) Evacuate the ball milling tank through the ball milling tank vacuum valve, then fill it with sulfur hexafluoride gas with a gauge pressure of 0.05MPa, and repeat 3 times. Finally, make the gauge pressure of sulfur hexafluoride gas in the ball milling tank 0.05MPa. Among them, the purity of the sulfur hexafluoride gas is 99.9%.

[0090] (iii) Install and fix the ball milling tank on the plasma vibration ball mill, turn on the power supply of the plasma vibration ball mill and start it. Set the method of vibration dispersion treatment for the biomass porous carbon material as follows: when the duration of vibration dispersion treatment for the biomass porous carbon material reaches 3min, perform a static treatment on the biomass porous carbon material, and when the duration of static treatment for the biomass porous carbon material reaches 3min, perform vibration dispersion treatment on the biomass porous carbon material through the plasma vibration ball mill until the total duration of vibration dispersion treatment for the biomass porous carbon material reaches 15min. Among them, during the vibration dispersion treatment of the biomass porous carbon material, the motor speed of the plasma vibration ball mill is 960r / min.

[0091] (iv) During the vibration dispersion treatment of the biomass porous carbon material, introduce a discharge current into the plasma vibration ball mill to perform plasma discharge treatment on the biomass porous carbon material with a fluorine - containing gas to obtain the negative electrode active material. Among them, the discharge current is 1A, and the duration of plasma discharge treatment for the biomass porous carbon material is 15min.

[0092] (2) Preparation of the negative electrode sheet

[0093] First, the negative electrode active material binder sodium carboxymethyl cellulose (Carboxymethyl Cellulose Sodium, CMC) prepared in step (1) and the conductive agent Super C45 are uniformly mixed at a mass ratio of 8:1:1. Using deionized water as the solvent, a negative electrode slurry is prepared through a high-speed stirring and defoaming mechanism. Then, the prepared negative electrode slurry is uniformly coated on the surface of a battery-grade copper foil with a coating thickness of 250 μm to obtain a coated negative electrode sheet. Finally, the coated negative electrode sheet is dried to obtain the negative electrode sheet.

[0094] (3) Preparation of the secondary battery

[0095] The negative electrode sheet prepared in step (2) is punched into circular sheets with a diameter of less than 20 mm, and the circular sheets are transferred to a glove box with a high-purity argon environment for the assembly of CR20 series button cells to obtain button cells. Specifically, the water and oxygen content in the glove box is lower than 0.01 ppm. In the button cell, a lithium metal sheet is used as the counter electrode of the negative electrode sheet. The electrolyte includes lithium hexafluorophosphate, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate, and the concentration of lithium hexafluorophosphate is 1 mol / L. The volume ratio of ethylene carbonate to diethyl carbonate is 1:2, and the mass percentage of fluoroethylene carbonate in the electrolyte is 10 wt%.

[0096] Examples 2 - 3

[0097] The differences between Examples 2 - 3 and Example 1 are as follows:

[0098] In step (1)(iii), the total duration of the vibration dispersion treatment of the biomass porous carbon material is 30 min and 60 min respectively. Correspondingly, in step (1)(iv), the duration of the plasma discharge treatment of the biomass porous carbon material is 30 min and 60 min respectively.

[0099] Examples 4 - 5

[0100] The differences between Examples 4 - 5 and Example 1 are as follows:

[0101] In step (1)(ii), the gauge pressure of sulfur hexafluoride gas in the ball milling tank is 0.02 MPa and 0.03 MPa respectively.

[0102] Example 6

[0103] The difference between Example 6 and Example 4 is as follows:

[0104] In step (1)(iii), the total duration of the vibration dispersion treatment of the biomass porous carbon material is 30 min; correspondingly, in step (1)(iv), the duration of the plasma discharge treatment of the biomass porous carbon material is 30 min.

[0105] Examples 7-8

[0106] The differences between Examples 7-8 and Example 1 are as follows:

[0107] In step (1)(iii), during the vibration dispersion treatment of the biomass porous carbon material, the motor speeds of the plasma vibration ball mill are 750 r / min and 1100 r / min, respectively.

[0108] Examples 9-10

[0109] The differences between Examples 9-10 and Example 1 are as follows:

[0110] In step (1)(iv), the discharge currents are 0.4 A and 3 A, respectively.

[0111] Comparative Example 1

[0112] The differences between Comparative Example 1 and Example 1 are as follows:

[0113] In step (1), a silicon-carbon material in the art is used as the negative electrode active material.

[0114] The preparation process parameters of the negative electrode active materials in each example are shown in Table 1.

[0115] Table 1

[0116]

[0117] Testing method:

[0118] (1) Scanning Electron Microscope (SEM) test of the negative electrode active material: Use SEM to characterize the surface morphology of the negative electrode active material and the biomass porous carbon material obtained through the above examples, and the magnification range is 500 times to 30,000 times.

[0119] (2) X-ray photoelectron spectroscopy test: Use the X-ray photoelectron spectrometer (XPS) of Thermo Scientific K-Alpha Nexs to detect the elemental composition and chemical bonding state on the surface of the negative electrode active material, and use the C1s peak at 284.8 eV as a reference.

[0120] (3) Atomic force microscopy test of the negative electrode plate: First, perform the first charge-discharge cycle on the secondary battery obtained through the above-mentioned examples or comparative examples; then, disassemble the secondary battery after the first charge-discharge cycle; finally, use an atomic force microscope (AFM, Bruker Dimension Icon) to measure the surface mechanical modulus strength of the disassembled negative electrode plate. Among them, the conditions for the first charge-discharge cycle are: set the nominal specific capacity of the secondary battery 1C to 1800 mAh / g; discharge process: the first stage discharges at a rate of 0.1C, the first discharge cut-off voltage is 0.005V, and after standing for 5 minutes, the second stage of discharge is carried out; the second stage discharges at a rate of 0.02C, the second discharge cut-off voltage is 0.005V; after standing for 5 minutes, the third stage of discharge is carried out; the third stage discharges at a rate of 0.01C, the third discharge cut-off voltage is 0.005V; then charge, the first stage charges at a rate of 0.1C, the first charge cut-off voltage is 0.8V, then the second stage of charging is carried out, the second stage charges at a rate of 0.1C, and the second charge cut-off voltage is 1.5V; then discharge, the first stage discharges at a rate of 0.1C, the first discharge cut-off voltage is 0.005V, and after standing for 5 minutes, the second stage of discharge is carried out; the second stage discharges at a rate of 0.02C, the second discharge cut-off voltage is 0.005V; after standing for 5 minutes, the third stage of discharge is carried out; the third stage discharges at a rate of 0.01C, the third discharge cut-off voltage is 0.005V.

[0121] (4) Cycling performance test of the secondary battery: In an environment of 25 ± 3°C, perform a constant current charge-discharge test under the following conditions on a LAND CT2001A battery test system: set the nominal specific capacity of the secondary battery 1C to 1800 mAh / g; the first stage discharges at a rate of 0.1C, the first discharge cut-off voltage is 0.005V, and after standing for 5 minutes, the second stage of discharge is carried out; the second stage discharges at a rate of 0.02C, the second discharge cut-off voltage is 0.005V; after standing for 5 minutes, the third stage of discharge is carried out; the third stage discharges at a rate of 0.01C, the third discharge cut-off voltage is 0.005V; then charge, the first stage charges at a rate of 0.1C, the first charge cut-off voltage is 0.8V, then the second stage of charging is carried out, the second stage charges at a rate of 0.1C, and the second charge cut-off voltage is 1.5V; thereafter, perform the same charge-discharge test cycle as the above steps on the secondary battery within the voltage range of 0.005V to 1.5V, and stop the charge-discharge when the number of cycles is equal to 1000.

[0122] Test results:

[0123] (1) Scanning electron microscopy test of the negative electrode active material: The negative electrode active materials obtained through the above-mentioned Example 4 and Example 5, as well as the biomass porous carbon material, were subjected to scanning electron microscopy tests, and the test results are as Figures 2 to 4 shown; compared with the scanning electron microscopy image of the biomass porous carbon material shown in Figure 4 , the negative electrode active materials obtained through the plasma discharge treatment of Example 4 (refer to Figure 2 ) and the negative electrode active materials obtained through the plasma discharge treatment of Example 5 (refer to Figure 3 ) have basically no surface damage, indicating that the plasma discharge treatment of the embodiments of the present application will not cause excessive damage to the surface structure of the negative electrode active material.

[0124] (2) X-ray photoelectron spectroscopy test: The negative electrode active materials obtained through the above-mentioned Example 4 and Comparative Example 1 were subjected to the above-mentioned X-ray photoelectron spectroscopy test, and the test results are as Figure 5 and Figure 6 shown. Referring to Figure 5 , there is a signal of C-F related chemical bonds on the surface of the negative electrode active material obtained through Example 4, indicating that fluorine elements have been successfully compounded onto the surface of the biomass porous carbon material in a chemically bonded manner. Referring to Figure 6 , there is no signal of C-F related chemical bonds on the surface of the negative electrode active material obtained through Comparative Example 1.

[0125] (3) Atomic force microscopy test of the negative electrode plate: The negative electrode plates obtained through the above-mentioned Example 4 and Comparative Example 1 were subjected to the above-mentioned atomic force microscopy test, and the test results are as Figure 7 and Figure 8 shown. The elastic modulus range of the negative electrode plate obtained through Example 4 is 5.2 GPa to 12.9 GPa, while the elastic modulus range of the negative electrode plate obtained through Comparative Example 1 is 2.0 GPa to 5.1 GPa. It can be seen that the mechanical strength of the negative electrode plate prepared based on the negative electrode active material provided in the embodiments of the present application has been significantly improved.

[0126] (4) Cycle performance test of the secondary battery: The secondary batteries obtained through the above-mentioned Examples 1 to 10 and Comparative Example 1 were subjected to the above-mentioned cycle performance test, and the test results are shown in Table 2.

[0127] Table 2

[0128]

[0129] According to the test data in Table 2, the initial discharge specific capacity of the secondary battery obtained through the embodiment of the present application is increased by more than 0.65% compared with the initial discharge specific capacity of 922.39 mAh / g of the secondary battery obtained through Comparative Example 1; the secondary discharge specific capacity of the secondary battery obtained through the embodiment of the present application is increased by more than 63% compared with the secondary discharge specific capacity of 50.37 mAh / g of the secondary battery obtained through Comparative Example 1; the discharge specific capacity retention rate of the secondary battery after 1000 cycles obtained through the embodiment of the present application is increased by more than 13.97% compared with the discharge specific capacity retention rate of 5.37% of the secondary battery after 1000 cycles obtained through Comparative Example 1; thus, it can be seen that both the battery capacity and the cycling performance of the secondary battery prepared based on the negative electrode active material provided by the embodiment of the present application are significantly improved.

[0130] In summary, for the preparation method of the negative electrode active material provided by the embodiment of the present application, a fluorine-containing gas is used as the discharge gas. During the process of vibration dispersion treatment of the porous carbon matrix by a plasma treatment device, a discharge current is introduced into the plasma treatment device to perform plasma discharge treatment on the porous carbon matrix using the fluorine-containing gas, so that the active fluorine atoms and fluorine-containing free radicals generated by the ionization of the fluorine-containing gas can uniformly bombard the surface of the porous carbon matrix, improving the reaction activity of the carbon atoms on the surface of the porous carbon matrix, which is beneficial to the reaction between the fluorine element provided by the fluorine-containing gas and the carbon atoms on the surface of the porous carbon matrix to form chemical bonding. Therefore, by means of the "force-electricity-thermal" multi-field coupling effect formed by vibration dispersion treatment, high-energy electron bombardment of the discharge plasma, and the thermal effect of the discharge plasma, not only can the uniformity of the chemical bonding between the fluorine element and the carbon atoms on the surface of the porous carbon matrix be improved, but also the preparation cost of the negative electrode active material can be reduced and the preparation efficiency of the negative electrode active material can be improved; further, during the charge and discharge cycle process of the secondary battery including the negative electrode active material prepared by the embodiment of the present application, the fluorine element chemically bonded to the surface of the porous carbon matrix can combine with lithium ions in the secondary battery to form lithium fluoride, so that the solid electrolyte interface film formed on the surface of the negative electrode active material contains lithium fluoride. The lithium ions and fluoride ions in lithium fluoride have strong electrostatic attraction, which can form a stable ionic lattice, promoting the formation of a dendrite-free and dense film formation morphology of the solid electrolyte interface film, being beneficial to improving the stability and mechanical strength of the solid electrolyte interface film, reducing the probability of the solid electrolyte interface film being broken and pulverized during the charge and discharge cycle process, reducing the number of reconstructions of the solid electrolyte interface film, and further reducing the consumption of lithium ions and electrolyte in the secondary battery during the reconstruction process of the solid electrolyte interface film, thereby improving the battery capacity and cycling performance of the secondary battery.

[0131] Although the preferred embodiments of the embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the claims are intended to be construed as including the preferred embodiments as well as all changes and modifications that fall within the scope of the embodiments of the present application.

[0132] The above has introduced in detail a method for preparing a negative electrode active material, a negative electrode active material, a battery, and a device provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for preparing a negative electrode active material, characterized in that, The method includes: Loading a porous carbon matrix into a plasma processing device; Introducing a fluorine-containing gas into the plasma processing device; Performing a vibration dispersion treatment on the porous carbon matrix through the plasma processing device; During the vibration dispersion treatment of the porous carbon matrix, introducing a discharge current into the plasma processing device to perform a plasma discharge treatment on the porous carbon matrix with the fluorine-containing gas, obtaining a negative electrode active material; the negative electrode active material includes the porous carbon matrix and fluorine elements provided by the fluorine-containing gas, and the fluorine elements are chemically bonded to carbon atoms on the surface of the porous carbon matrix.

2. The method according to claim 1, characterized in that In the plasma processing device, the gauge pressure of the fluorine-containing gas is 0.02 MPa to 0.05 MPa.

3. The method according to claim 1, characterized in that During the process of performing the vibration dispersion treatment on the porous carbon matrix through the plasma processing device, the motor speed of the plasma processing device is 750 r / min to 1100 r / min.

4. The method according to claim 1, wherein The discharge current is 0.4 A to 3 A.

5. The method according to claim 1, characterized in that, The duration of the plasma discharge treatment on the porous carbon matrix is 15 min to 60 min.

6. The method according to claim 1, characterized in that The performing the vibration dispersion treatment on the porous carbon matrix through the plasma processing device includes: When the duration of the vibration dispersion treatment on the porous carbon matrix through the plasma processing device reaches a first duration, performing a static treatment on the porous carbon matrix; When the duration of the static treatment on the porous carbon matrix reaches a second duration, performing a vibration dispersion treatment on the porous carbon matrix through the plasma processing device until the total duration of the vibration dispersion treatment on the porous carbon matrix through the plasma processing device reaches a preset duration.

7. The method according to claim 1, characterized in that, The porous carbon matrix includes a biomass porous carbon material.

8. A negative electrode active material, characterized in that, The negative electrode active material is prepared by the preparation method of the negative electrode active material according to any one of claims 1 to 7.

9. A secondary battery, characterized in that, It includes a positive electrode plate and a negative electrode plate; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material prepared by the preparation method of the negative electrode active material according to any one of claims 1 to 7.

10. An electrical device, characterized in that, It includes a secondary battery according to claim 9, and the secondary battery serves as a power supply for the electrical device.

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