Negative electrode composite material as well as preparation method and application thereof

Abstract

The invention provides a negative electrode composite material as well as a preparation method and application thereof. The negative electrode composite material comprises a porous carbon matrix and cobaltosic selenide distributed on the porous carbon matrix. The performance such as cycle stability and capacity of the negative electrode composite material can be improved at the same time.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a negative electrode composite material and a preparation method and application thereof. Background Art

[0002] The negative electrode material is an important component of the battery, affecting the battery's capacity and cycle stability and other performance. In the related technology, it is difficult to take into account both the stability and capacity of the negative electrode material. For example, the negative electrode of the sodium ion battery mainly uses carbon materials (such as hard carbon (HC)) or transition metal sulfide compounds. Among them, the carbon material has relatively good cycle stability, but is limited by the low theoretical capacity of the carbon material, which makes its sodium storage capacity low. Although the transition metal sulfide compound has a relatively high theoretical sodium storage capacity, it is limited by its conversion-type energy storage mechanism, which causes a more serious volume expansion during the sodium storage process, resulting in poor cycle stability. Therefore, limited by the properties of the negative electrode material such as capacity and structural stability, the battery's performance such as capacity and cycle stability is poor. Summary of the invention

[0003] The present invention provides a negative electrode composite material and a preparation method and application thereof, so as to at least solve the problem in the prior art that it is difficult to balance the cycle stability and capacity of the negative electrode composite material, and the resulting poor performance of the battery such as capacity and cycle stability.

[0004] One aspect of the present invention provides a negative electrode composite material, comprising a porous carbon matrix and tricobalt tetraselenide distributed in the porous carbon matrix.

[0005] According to one embodiment of the present invention, the specific surface area of ​​the porous carbon matrix is ​​100 m 2 / g~400 m 2 / g.

[0006] According to one embodiment of the present invention, the specific surface area of ​​the porous carbon matrix is ​​200 m 2 / g~300 m 2 / g.

[0007] According to one embodiment of the present invention, the average particle size of the tricobalt tetraselenide is 50nm~600nm.

[0008] According to one embodiment of the present invention, the average particle size of the tricobalt tetraselenide is 50 nm to 300 nm.

[0009] According to one embodiment of the present invention, the average particle size of the tricobalt tetraselenide is 100 nm to 200 nm.

[0010] According to one embodiment of the present invention, based on the total mass of the negative electrode composite material, the mass fraction of the tricobalt tetraselenide is 16% to 70%.

[0011] According to one embodiment of the present invention, the average particle size of the negative electrode composite material is greater than or equal to 10 μm.

[0012] According to one embodiment of the present invention, the tricobalt tetraselenide is distributed on the surface and inside the pores of the porous carbon matrix.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned negative electrode composite material, comprising the following steps: dispersing a cobalt source and a porous carbon matrix material in a first solvent, and then performing solid-liquid separation to obtain a porous carbon matrix material with cobalt ions attached; mixing the porous carbon matrix material with cobalt ions attached with a selenium source and performing selenization treatment to obtain the negative electrode composite material.

[0014] According to one embodiment of the present invention, the preparation process of the porous carbon matrix material includes: dissolving a carbon source and a template in a second solvent and then drying the solvent, and then carbonizing the obtained mixture to obtain the porous carbon matrix material.

[0015] According to one embodiment of the present invention, the carbon source includes one or more of glucose and sucrose; and / or the template includes one or more of NaCl, KCl and CaCl2; and / or the temperature of the carbonization treatment is 700°C~1000°C, and the time of the carbonization treatment is 1h~3h.

[0016] According to one embodiment of the present invention, the mass ratio of the porous carbon matrix material and the cobalt source is 1:2~1:20; and / or, the cobalt source includes a soluble cobalt salt, and the soluble cobalt salt includes one or more of Co(NO3)2, CoCl2, CoSO4, CoS2 and CoF2.

[0017] According to one embodiment of the present invention, the amounts of the cobalt source and the selenium source satisfy: the mass ratio of cobalt element to selenium element is (0.4~0.5):1; and / or, the selenium source includes selenium powder; and / or, the selenization treatment is carried out under an inert gas atmosphere; and / or, the temperature of the selenization treatment is 700°C~900°C, and the time of the selenization treatment is 1h~4h.

[0018] Another aspect of the present invention provides a negative electrode sheet, comprising the negative electrode composite material or the negative electrode composite material prepared according to the above preparation method.

[0019] Another aspect of the present invention provides a battery, comprising the negative electrode sheet mentioned above.

[0020] According to one embodiment of the present invention, the battery is a sodium ion battery or a lithium ion battery.

[0021] Another aspect of the present invention provides a battery pack comprising the above-mentioned battery.

[0022] Another aspect of the present invention provides an electrical device comprising the above-mentioned battery or the above-mentioned battery pack.

[0023] The negative electrode composite material provided by the present invention, and its preparation method and application, the negative electrode composite material has a porous carbon matrix, and tricobalt tetraselenide distributed on the porous carbon matrix, under such a negative electrode composite material composition system, the porous carbon matrix can improve the conductivity of the negative electrode composite material, and improve the mechanical strength and other properties of the negative electrode composite material, thereby improving the conductivity and structural stability of the negative electrode composite material, and at the same time, the tricobalt tetraselenide present on the porous carbon matrix is ​​used as an active component to improve the capacity of the negative electrode active material. Therefore, the present invention can take into account the improvement of the stability and capacity of the negative electrode composite material, thereby taking into account the improvement of the capacity and cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of a porous carbon matrix material according to an embodiment of the present invention;

[0025] Figure 2 is the SEM image of hard carbon (HC);

[0026] Figure 3 The cycle curves of the batteries of Example 2 and Comparative Examples 1 to 3 are shown;

[0027] Figure 4 is a SEM image of the negative electrode composite material of Example 1;

[0028] Figure 5 This is the XRD diagram of the negative electrode composite material of Example 1. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific implementation methods listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0030] According to the research of the inventors of this application, the cycle stability of the battery is mainly manifested in that it can still maintain a high capacity after the battery cycle. The factors affecting the capacity after the battery cycle are mainly the battery's initial charge capacity and the battery's cycle decay rate. For example, a decrease in the battery's initial charge capacity or a decrease in the battery's cycle capacity retention rate (an increase in the battery's cycle decay rate) will lead to a decrease in the battery's capacity after the cycle. Therefore, how to take into account both the battery's initial charge capacity and the battery's cycle capacity retention to increase the battery's capacity after the cycle and improve the battery's cycle stability is a technical problem that needs to be solved urgently.

[0031] In view of this, an embodiment of the present invention provides a negative electrode composite material, including a porous carbon matrix, and cobalt tetraselenide (Co3Se4) distributed in the porous carbon matrix. In the above-mentioned negative electrode composite material system, Co3Se4, as an active component of the negative electrode composite material, is the main active substance for exerting capacity, and can give the negative electrode composite material a high reversible capacity (for example, Co3Se4 can be used as the main active substance for sodium storage in the negative electrode composite material, and undergoes a conversion reaction with sodium, showing a high specific capacity, and giving the negative electrode composite material a high reversible sodium storage capacity), the porous carbon matrix is ​​used as a conductive substrate of the negative electrode composite material, which can give the negative electrode composite material good conductivity, and at the same time load Co3Se4, inhibiting the volume expansion of Co3Se4 during the battery cycle process (such as the sodium storage process), and the resulting peeling of Co3Se4 and the porous carbon matrix, Co3Se4 falling off, etc., thereby ensuring the capacity of the negative electrode composite material, improving the cycle stability and other properties of the negative electrode composite material, and then taking into account the improvement of the battery capacity and cycle capacity retention rate, and improving the battery cycle stability and other properties.

[0032] According to the research and analysis of the inventors, in the above-mentioned negative electrode composite material (Co3Se4@CN) system, the porous carbon matrix (CN) has a three-dimensional interconnected carbon network structure (carbonaceous network, CN) with a high degree of interconnection, and a large number of pores on its surface and inside can be used as attachment sites for Co3Se4. At the same time, Co3Se4 is a monoclinic structure with a high exposure ratio of its crystal surface, which can provide more surface active sites. Therefore, this composite method of Co3Se4 and porous carbon matrix is ​​conducive to the uniform distribution of Co3Se4 on the surface and in the pores of the porous carbon matrix, thereby improving the contact effect between the porous carbon matrix and Co3Se4, thereby improving the overall mechanical strength and structural stability of the negative electrode composite material, and inhibiting the volume expansion of Co3Se4 during the battery cycle process (such as the sodium storage process), and the resulting peeling of Co3Se4 from the porous carbon matrix, Co3Se4 falling off, etc., thereby ensuring the capacity of the negative electrode composite material and improving the cycle stability and other properties of the negative electrode composite material.

[0033] At the same time, in the above-mentioned negative electrode composite material, the highly interconnected porous carbon matrix has high mechanical strength, which can ensure the structural stability and other properties of the negative electrode composite material. At the same time, based on the physical restraint and other effects of the porous matrix material, the volume expansion and shedding of Co3Se4 can be suppressed, thereby ensuring the capacity and cycle stability of the negative electrode composite material.

[0034] Compared with conventional carbon materials such as hard carbon, the porous carbon matrix in the above-mentioned negative electrode composite material has a high degree of interconnection and a high specific surface area. It has a larger pore structure (generally a multi-level pore structure (mainly nanoscale pores and micron-scale pores)), which is beneficial for Co3Se4 to be distributed more in the internal pores of the porous carbon matrix material. This not only helps to increase the loading amount of Co3Se4 in the negative electrode composite material, but also helps to inhibit the volume expansion and shedding of Co3Se4 through the physical restraint of the porous matrix material, thereby ensuring the structural stability and other properties of the negative electrode composite material, and ensuring its capacity and cycle stability.

[0035] In addition, the porous carbon matrix of the embodiment of the present invention has a three-dimensional structure with a high degree of interconnection and strong integrity, which can effectively reduce the contact resistance of the porous carbon matrix, thereby reducing the contact impedance of the negative electrode composite material and ensuring that the negative electrode composite material functions as a negative electrode active material.

[0036] In addition, compared with Co3Se4, the negative electrode composite material of the embodiment of the present invention also has a higher first-cycle coulomb efficiency (first-cycle charge and discharge efficiency), which can effectively avoid the loss of positive electrode materials and improve the use efficiency of positive electrode materials.

[0037] In an embodiment of the present invention, the above-mentioned negative electrode composite material is granular, and its particle size is in the micron level. Generally, the average particle size of the negative electrode composite material may be greater than or equal to 10 μm, and may be specifically tens of microns. In the negative electrode composite material, the porous carbon matrix has an interconnection degree of tens of microns, and it is usually a multi-level pore structure (that is, the porous carbon matrix includes nanoscale pores and micron-scale pores). The presence of nanoscale pores enables the porous carbon matrix material to have a high specific surface area. The surface and a large number of pores inside the porous carbon matrix material can serve as attachment sites for Co3Se4, so that Co3Se4 is evenly distributed on the surface and in the internal pores of the porous carbon matrix, thereby improving the capacity and stability and other properties of the negative electrode composite material.

[0038] Specifically, in the negative electrode composite material, cobalt tetraselenide can be distributed on the surface and inside the pores of the porous carbon matrix, that is, cobalt tetraselenide is distributed on the surface of the porous carbon matrix particles, and the porous carbon matrix particles are porous structures, and cobalt tetraselenide is also distributed inside their pores (holes). In this way, the electrochemical reaction (such as sodium storage reaction) when Co3Se4 exerts its capacity occurs on the surface and in the pores of the porous carbon matrix, which is conducive to the capacity of Co3Se4 and further improves the performance of the negative electrode composite material such as capacity and cycle stability.

[0039] According to further research by the inventors, the specific surface area of ​​the porous carbon matrix can be 100 m 2 / g~400 m 2 / g, illustratively, the specific surface area of ​​the porous carbon matrix can be 100m 2 / g, 130 m 2 / g, 150 m 2 / g, 180 m 2 / g, 200m 2 / g, 230 m 2 / g, 250 m 2 / g, 280 m 2 / g, 300 m 2 / g, 330 m 2 / g, 350 m 2 / g, 380 m 2 / g, 400 m 2 / g or the range composed of any two of them. The specific surface area of ​​the porous carbon matrix is ​​within the above range, which is conducive to further improving the performance of the negative electrode composite material such as the cycle stability. The reason for this is that in the negative electrode composite material, the porous carbon matrix serves as the base of the negative electrode composite material, and the electrochemical reaction (such as sodium storage reaction) when Co3Se4 exerts its capacity occurs on the surface and pores of the porous carbon matrix. The smaller the specific surface area of ​​the porous carbon matrix, the less Co3Se4 particles it carries, which is not conducive to the capacity of Co3Se4 (for example, it is not conducive to the sodium storage of Co3Se4). On the contrary, the larger the specific surface area of ​​the porous carbon matrix, the smaller the The larger the surface area, the more Co3Se4 particles it carries, which is beneficial to the capacity of Co3Se4 (for example, it is beneficial to the sodium storage of Co3Se4), but it will reduce the thickness of the carbon network wall of the porous carbon matrix to a certain extent, reduce the conductive path, and reduce the conductivity of the negative electrode composite material. At the same time, too large a specific surface area will also increase the contact area between the negative electrode composite material and the electrolyte, thereby generating more SEI films, which will affect the first cycle coulomb efficiency and other performance of the battery to a certain extent. Therefore, if the specific surface area of ​​the porous carbon matrix material is too large or too small, it will affect the battery performance to a certain extent. Therefore, the specific surface area of ​​the porous carbon matrix is ​​not less than 100m 2 / g, which is conducive to loading more Co3Se4 particles and further improving the capacity and other properties of the negative electrode composite material. At the same time, the specific surface area of ​​the porous carbon matrix is ​​not higher than 400m 2 / g, which is conducive to maintaining the thickness of the carbon network wall of the porous carbon matrix, providing more conductive paths, further improving the conductivity of the negative electrode composite material, and at the same time further reducing the contact area between the negative electrode composite material and the electrolyte, forming an appropriate amount of SEI film, and further improving the battery's first-cycle coulomb efficiency and other performance.

[0040] In some preferred embodiments, the specific surface area of ​​the porous carbon matrix can be 200 m 2 / g~300 m 2 / g. The specific surface area of ​​the porous carbon matrix is ​​within the above range. By controlling the specific surface area of ​​the porous carbon matrix within the above range (200m 2 / g~300 m 2 / g), which is conducive to further improving the capacity, conductivity and stability of the negative electrode composite material, and then improving the battery's capacity, charge and discharge efficiency and cycle stability.

[0041] In the embodiment of the present invention, the Co3Se4 in the above negative electrode composite material is in granular form, that is, Co3Se4 particles are distributed on the porous carbon matrix, and the Co3Se4 particles generally include Co3Se4 nanoparticles (that is, their average particle size does not exceed 1 μm).

[0042] According to further research by the inventors, the average particle size of Co3Se4 can be 50 nm to 600 nm, for example, 50 nm, 100 nm, 130 nm, 150 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, The range of 100 nm or any two of them is conducive to improving the battery's capacity and cycle stability. The reason for this is that in the above-mentioned negative electrode composite material, Co3Se4 is used as an active component (for example, as an active material for sodium storage). During the battery cycle, it needs to undergo a conversion reaction with active ion elements (such as sodium). If the average particle size of Co3Se4 is too large, the proportion of Co3Se4 in contact with active ion elements (such as sodium) in the total amount of Co3Se4 is low, which will lead to slow reaction, easy polarization and incomplete reaction. When the Co3Se4 particles are too large, their volume expands violently during the conversion reaction, and material pulverization is prone to occur. When the average particle size of Co3Se4 is small, it is beneficial to the capacity of Co3Se4 (for example, it is beneficial to sodium storage reaction), but the sites in the porous carbon matrix that can bind to Co3Se4 are basically fixed, and the particle size of Co3Se4 is positively correlated with its loading amount on the porous carbon matrix. The smaller the particle size of Co3Se4, the less Co3Se4 is distributed in the porous carbon matrix, which makes the content of Co3Se4 in the negative electrode composite material less. Therefore, if the particle size of Co3Se4 is too small, the specific capacity of the negative electrode composite material will be affected due to the reduction of Co3Se4 content in the negative electrode composite material.

[0043] Further comprehensively considering factors such as the reaction rate, volume expansion and specific capacity of Co3Se4 in the negative electrode composite material during the battery cycle, the particle size of Co3Se4 is preferably 100nm~200nm, which is conducive to further improving the performance of the negative electrode composite material such as capacity and stability.

[0044] According to further research by the inventors, based on the total mass of the negative electrode composite material, the mass fraction of Co3Se4 (i.e., the proportion of the mass of Co3Se4 to the total mass of the negative electrode composite material) can be 16%~70%, for example, 16%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 70% or a range composed of any two of them, which is beneficial to improving the battery's capacity, cycle stability and other performance.

[0045] Specifically, in the negative electrode composite material, the porous carbon matrix has good three-dimensional interconnected physical properties and sodium (or other elements) storage methods, which can provide the negative electrode composite material with good conductivity and strong mechanical strength and other properties, while Co3Se4, as the main active component of the negative electrode composite material, is mainly used to provide capacity. When the content of Co3Se4 in the negative electrode composite material is low, the content of the porous carbon matrix is ​​relatively high, which is conducive to a more full utilization of the capacity of Co3Se4 (for example, it is conducive to a more full sodium storage of Co3Se4), and the cycle stability of the negative electrode composite material is good. However, if the content of Co3Se4 is too low, the specific capacity of the negative electrode composite material will be too low, affecting the capacity of the negative electrode composite material (for example, affecting the sodium storage effect of the negative electrode composite material); and when the content of Co3Se4 in the negative electrode composite material is too high, the content of the porous carbon matrix is ​​relatively low, which will affect the conductivity of the negative electrode composite material and is not conducive to the uniform distribution of Co3Se4 in the negative electrode composite material. For example, it will easily lead to a more serious stacking of Co3Se4 in the porous carbon matrix. In the electrochemical reaction process of the negative electrode composite material, Co3Se4 in the negative electrode composite material will fall off due to serious stacking and other factors, affecting the structural stability and cycle performance of the negative electrode composite material. Therefore, by controlling the content of Co3Se4 in the negative electrode composite material within the above range (16%~70%), it is beneficial to take into account the improvement of the battery capacity and cycle stability and other performance.

[0046] In some embodiments, based on the total mass of the negative electrode composite material, the mass fraction of Co3Se4 is 50%~65%, for example, 50%~55%. In this way, the negative electrode composite material can have a higher specific capacity. At the same time, the porous carbon matrix can ensure the good conductivity and strong mechanical strength of the negative electrode composite material, and further improve the uniformity of the distribution of Co3Se4 in the porous carbon matrix, avoiding the problem of Co3Se4 falling off during the electrochemical reaction of the negative electrode composite material, thereby improving the stability of the negative electrode composite material, and further taking into account the improvement of the battery's capacity and cycle stability and other performance.

[0047] An embodiment of the present invention also provides a method for preparing the above-mentioned negative electrode composite material, comprising the following steps: S1, dispersing a cobalt source and a porous carbon matrix material in a first solvent, and then performing solid-liquid separation to obtain a porous carbon matrix material with cobalt ions attached; S2, mixing the porous carbon matrix material with cobalt ions attached and a selenium source, and then performing selenization treatment to obtain a negative electrode composite material.

[0048] In the preparation process of the above-mentioned negative electrode composite material, Co3Se4 is in situ grown (attached) on the surface of the porous carbon matrix material by metal ion (cobalt ion) adsorption and in situ selenization method to obtain the negative electrode composite material. Specifically, in step S1, after the cobalt source and the porous carbon matrix material are dispersed in the first solvent (such as water), based on the adsorption effect of the porous carbon matrix material on cobalt ions, the cobalt source can be evenly distributed on the surface and internal pores of the porous carbon matrix material, so that the cobalt ions in the porous carbon matrix material with cobalt ions attached can be evenly distributed on the surface and internal pores of the porous carbon matrix material, and then the Co3Se4 (mainly Co3Se4 nanoparticles) formed by the selenization treatment in step S2 can be evenly grown on the surface and internal pores of the porous carbon matrix material (porous three-dimensional carbon network), avoiding uneven stacking of Co3Se4 and improving the structural stability and other properties of the obtained negative electrode material. In step S2, during the selenization treatment (selenization reaction), the cobalt ions attached to the porous carbon matrix material react with the selenium source, thereby in-situ synthesizing Co3Se4 on the surface of the porous carbon matrix material, achieving the composite of Co3Se4 and the porous carbon matrix, and obtaining the negative electrode composite material. Specifically, the solid-liquid separation can be filtration.

[0049] Specifically, in the above preparation process, the porous carbon matrix material used is in a granular form with a specific surface area of ​​100 m 2 / g~400 m 2 / g, for example 100m 2 / g, 130 m 2 / g, 150 m 2 / g, 180 m 2 / g, 200 m 2 / g, 230 m 2 / g, 250 m 2 / g, 280m 2 / g, 300 m 2 / g, 330 m 2 / g, 350 m 2 / g, 380 m 2 / g, 400 m 2 / g or any two of them, preferably 200m 2 / g~300 m 2 / g.

[0050] Through the above preparation process, after Co3Se4 is attached to the surface of the porous carbon matrix material, a negative electrode composite material is obtained. The preparation process basically does not affect the specific surface area and other characteristics of the porous carbon matrix material. That is, the specific surface area and other characteristics of the prepared negative electrode composite material (or the specific surface area of ​​the porous carbon matrix of the negative electrode composite material) are basically the same as the porous carbon matrix material used to prepare the negative electrode composite material.

[0051] According to the research of the inventors, the conductivity and mechanical properties (such as sodium storage mechanical properties) of the porous carbon matrix material are better than those of Co3Se4, and the theoretical capacity of Co3Se4 (such as the theoretical sodium storage capacity of Co3Se4 based on the conversion reaction) is much higher than that of the porous carbon matrix material. The embodiment of the present invention composites Co3Se4 and the porous carbon matrix material through the above-mentioned preparation process to obtain a negative electrode composite material, which can make the negative electrode composite material have a higher reversible capacity (such as reversible sodium storage capacity) while effectively overcoming the defects of Co3Se4, such as poor conductivity and drastic volume expansion in the process of exerting its capacity (such as sodium storage process), and irreversible structural changes caused thereby.

[0052] Thus, relative to a single porous carbon matrix material, the negative electrode composite material of the embodiment of the present invention contains high capacity (such as high sodium storage capacity) Co3Se4, so that the negative electrode composite material exhibits a higher reversible capacity; at the same time, relative to a single Co3Se4, the negative electrode composite material of the embodiment of the present invention uses a porous carbon matrix with a high degree of interconnection as a conductive substrate with high mechanical strength, so that the negative electrode composite material has higher conductivity and structural stability and other properties, and exhibits better cycle stability during the battery cycle. Thus, the embodiment of the present invention can give play to the synergistic effect of Co3Se4 and the porous carbon matrix, while improving the reversible capacity of the negative electrode composite material, enhance the structural stability of the negative electrode composite material (for example, enhance the structural stability of the negative electrode composite material for sodium storage), improve its cycle stability and other properties during the battery cycle, and thus improve the capacity of the battery (such as the sodium storage capacity of the sodium ion battery) and cycle performance, for example, after multiple cycles of the battery, the reversible capacity of the negative electrode composite material is higher than that of a single porous carbon matrix material or Co3Se4 material.

[0053] In addition, compared with directly physically mixing Co3Se4 and the porous carbon matrix material, the embodiment of the present invention in situ grows (attaches) Co3Se4 on the surface of the porous carbon matrix material through metal ion (cobalt ion) adsorption and in situ selenization method, which can improve the binding force between Co3Se4 and the porous carbon matrix material, and based on the adsorption of cobalt ions by the porous carbon matrix material, can make Co3Se4 grow uniformly in the porous carbon matrix material (specifically, it can grow on the particle surface and internal pores of the porous carbon matrix material), avoid uneven stacking of Co3Se4, thereby improving the utilization rate of Co3Se4. Among them, based on the adsorption effect of the porous carbon matrix material on cobalt ions, Co3Se4 is grown in the internal pores of the porous carbon matrix material, which can increase the loading amount of Co3Se4 in the negative electrode composite material, and can physically restrain the Co3Se4 particles in the internal pores of the porous carbon matrix material, inhibiting the volume expansion and shedding of Co3Se4, and at the same time, can improve the contact effect between the porous carbon matrix material and Co3Se4, thereby improving the mechanical strength of the prepared negative electrode composite material, improving its structural stability and other properties, and avoiding the shedding of Co3Se4 in the negative electrode composite material during the battery cycle, and the resulting poor cycle stability.

[0054] In addition, compared with other conventional carbon materials such as hard carbon, the porous carbon matrix material of the embodiment of the present invention has properties such as a porous structure and a suitable specific surface area. It has a high degree of interconnection, which is conducive to the growth of Co3Se4 in the internal pores of the porous carbon matrix material particles, thereby improving the structural stability and other properties of the obtained negative electrode composite material. At the same time, the porous carbon matrix material has a three-dimensional structure with a high degree of interconnection and strong integrity, which can effectively reduce the contact resistance of the porous carbon matrix, thereby reducing the contact impedance of the negative electrode composite material, and further ensuring the function of the negative electrode composite material as a negative electrode active material.

[0055] To give a further example, the sodium ion storage negative electrode (the negative electrode sheet of the sodium ion battery) mainly adopts hard carbon. Compared with hard carbon, the above-mentioned porous carbon matrix material adopted in the embodiment of the present invention has a three-dimensional interconnected structure and a larger specific surface area, which can effectively enhance the conductivity of the negative electrode composite material. At the same time, more Co3Se4 can be loaded in the internal pores of the porous carbon matrix material particles, thereby increasing the loading amount of Co3Se4, and protecting Co3Se4, which is the main active component of the negative electrode composite material, to avoid problems such as Co3Se4 falling off, thereby improving the capacity and stability of the negative electrode composite material, for example, improving the sodium storage performance of the negative electrode composite material.

[0056] Specifically, in step S1, the cobalt source and the porous carbon matrix material are dispersed in a first solvent. The first solvent used is a solvent that can dissolve the cobalt source, and specifically may include water.

[0057] Specifically, the cobalt source may include a soluble cobalt salt (water-soluble cobalt salt), preferably including one or more of Co(NO3)2, CoCl2, CoSO4, CoS2 and CoF2, which is beneficial to the uniform adsorption of cobalt ions on the surface and internal pores of the porous carbon matrix material, thereby improving the dispersion uniformity of Co3Se4 in the prepared negative electrode composite material, as well as the structural stability of the negative electrode composite material and other properties.

[0058] Generally speaking, in the preparation process of the above-mentioned negative electrode composite material, the greater the amount of cobalt source and selenium source used, the greater the content of Co3Se4 in the prepared negative electrode composite material, and the larger the particle size of Co3Se4 is.

[0059] In some embodiments, the mass ratio of the porous carbon matrix material to the cobalt source can be 1:2 to 1:20, for example, 1:2, 1:5, 1:8, 1:10, 1:13, 1:15, 1:18, 1:20 or a range consisting of any two of them.

[0060] Specifically, in step S2, the porous carbon matrix material with cobalt ions attached thereto and the selenium source are mixed and then subjected to selenization treatment, and Co3Se4 composited with the porous carbon matrix material is formed by the selenization treatment to obtain a negative electrode composite material.

[0061] In some embodiments, the amounts of the cobalt source and the selenium source satisfy: the mass ratio of cobalt element to selenium element is (0.4-0.5):1, which is more conducive to the reaction of the cobalt source and the selenium source to generate tricobalt tetraselenide, further improving the performance of the obtained negative electrode composite material.

[0062] Additionally, the selenium source may include selenium powder.

[0063] In addition, the selenization treatment may be performed in an inert gas atmosphere (inert atmosphere), and the inert gas includes, for example, argon gas.

[0064] In addition, the temperature of the selenization treatment can be 700°C~900°C, for example, 700°C, 750°C, 800°C, 850°C, 900°C or a range consisting of any two of them, and the time of the selenization treatment can be 1h~4h, for example, 1h, 2h, 3h, 4h or a range consisting of any two of them.

[0065] After further research, the preparation process of the porous carbon matrix material of the embodiment of the present invention may include: dissolving the carbon source and the template in a second solvent and drying, and then carbonizing the obtained mixture to obtain a porous carbon matrix material. The porous carbon matrix material obtained by this preparation process has a three-dimensional interconnected porous carbon network structure with a high degree of interconnection, which is conducive to combining the above steps S1 and S2, in-situ growth of Co3Se4 on the surface and internal pores of the porous carbon matrix material, improving the distribution uniformity of Co3Se4 in the porous carbon matrix, and obtaining the above negative electrode composite material.

[0066] Specifically, after the carbon source and the template are dissolved in the second solvent, they can be dried by freeze drying, that is, the carbon source and the template are dissolved in the second solvent and then freeze dried, and then the obtained mixture is carbonized to obtain a porous carbon matrix material. The freeze drying temperature can be -50°C to -80°C, for example -70°C.

[0067] Specifically, in the preparation process of the above-mentioned porous carbon matrix material, the porous carbon matrix material is obtained by a sacrificial template method, wherein the carbon source and the template agent are dissolved in a second solvent and then freeze-dried, so that the template agent can be crystallized and precipitated, and evenly attached to the carbon source in a certain shape. In the subsequent carbonization treatment process, the carbon source is carbonized into a carbon material, and the template agent is removed, so that the carbon material carbonized from the carbon source forms a porous carbon-carbon matrix material.

[0068] According to the inventor's research, in the preparation process of the porous carbon matrix material, after the carbon source and the template are dissolved in the second solvent, if other drying methods such as natural drying or heat drying are used, it is not conducive to the precipitation of the template, and the template maintains a relatively fixed shape, which is not conducive to the formation of the above-mentioned porous carbon matrix material with high interconnectivity. In the embodiment of the present invention, after the carbon source and the template are dissolved in the second solvent, freeze drying is used to facilitate the crystallization of the template and uniformly distribute it in the carbon source in a relatively fixed shape. After subsequent carbonization treatment and other processes, a porous carbon matrix material with high interconnectivity is obtained.

[0069] In general, the more the amount of template agent used, the more and denser the template agent crystals precipitated on the surface of the carbon source after freeze drying, and the larger the specific surface area of ​​the porous carbon matrix material obtained after subsequent carbonization treatment and other processes. Therefore, in specific implementation, the specific surface area and other characteristics of the porous carbon matrix material obtained can be regulated by regulating the amount of template agent used. In specific implementation, the appropriate amount of template agent can be selected according to the needs to obtain a porous carbon matrix material with a preset specific surface area.

[0070] Specifically, the second solvent may include a solvent capable of dissolving the template and the carbon source, and in some embodiments, the second solvent may include water.

[0071] In addition, the template may include a water-soluble template, specifically a water-soluble salt, such as a water-soluble alkali metal salt and / or alkaline earth metal salt, preferably one or more of NaCl, KCl and CaCl2, which is conducive to preparing the above-mentioned porous carbon matrix material.

[0072] Specifically, the carbon source is a water-soluble carbon source, which may specifically include one or more of glucose and sucrose, which is conducive to obtaining the porous carbon matrix material through the preparation process of the porous carbon matrix material.

[0073] In some embodiments, the mass ratio of the carbon source to the template can be 1:(2-5), such as 1:2, 1:3, 1:4, 1:5 or a range consisting of any two of them.

[0074] Specifically, the temperature of the carbonization treatment can be 700°C~1000°C, for example, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C or a range consisting of any two of them, and the time of the carbonization treatment can be 1h~3h, for example, 1h, 1.5 h, 2 h, 2.5 h, 3h or a range consisting of any two of them.

[0075] In a specific implementation, the template and the carbon source are dissolved in a second solvent and then freeze-dried. After freeze-drying and dehydration, a uniform solid mixture is obtained. The solid mixture is placed in a sintering device such as a tubular furnace for carbonization treatment. Specifically, the carbonization treatment can be carried out in a protective gas. After the carbonization treatment is completed, a carbonized product is obtained. Subsequently, the template in the carbonized product can be removed by washing with water or the like, for example, multiple washing and filtration are performed to remove the template in the carbonized product to obtain a porous carbon matrix material.

[0076] Subsequently, the porous carbon matrix material and the cobalt source can be added to the first solvent, stirred evenly, allowed to stand and filtered, and the obtained solid product is dried. The dried solid product is a porous carbon matrix material with cobalt ions attached to it. The drying temperature can be 60°C to 100°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C or a range consisting of any two thereof, and the drying time can be 6h to 24h, for example, 6h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, 24h or a range consisting of any two thereof.

[0077] Subsequently, the porous carbon matrix material with cobalt ions attached and the selenium source are mixed and then subjected to selenization treatment, that is, selenium is introduced into the porous carbon matrix material with cobalt ions attached, and tricobalt tetraselenide composited with the porous carbon matrix material is generated to obtain a negative electrode composite material. The process of selenization treatment may include: adding the porous carbon matrix material with cobalt ions attached and the selenium source to a sintering device such as a tubular furnace, heating to a selenization treatment temperature under an inert atmosphere, specifically heating to a selenization treatment temperature at a heating rate of 0.5°C / min-5°C / min, performing a selenization reaction at the selenization treatment temperature, and obtaining a negative electrode composite material after the reaction is completed.

[0078] An embodiment of the present invention further provides a negative electrode sheet, comprising the negative electrode composite material or the negative electrode composite material prepared according to the preparation method of the negative electrode composite material. The negative electrode sheet has the advantages corresponding to the negative electrode composite material, which will not be described in detail here.

[0079] Generally, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector. Specifically, the negative electrode coating can be disposed on one side of the negative electrode current collector, or on both the positive and negative sides of the negative electrode current collector.

[0080] Specifically, the negative electrode coating (negative electrode active material layer) may include negative electrode active materials, conductive agents, binders and other materials, and the negative electrode active materials include the negative electrode composite material. That is, the negative electrode composite material serves as the negative electrode active material of the negative electrode sheet.

[0081] Specifically, based on the total mass of the negative electrode coating, the mass fraction of the negative electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two of them, the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two of them, and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two of them.

[0082] In an embodiment of the present invention, the conductive agent in the negative electrode coating may be a conventional conductive material in the art, for example, the conductive agent includes one or more of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder in the negative electrode coating may be a conventional binding material in the art, for example, the binder includes one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0083] The embodiment of the present invention may use a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0084] In an embodiment of the present invention, the negative electrode sheet can be prepared by a conventional method in the art, such as by a coating method. For example, the preparation process of the negative electrode sheet includes: dispersing components such as negative electrode active materials, conductive agents, binders, etc. for forming a negative electrode coating in a third solvent, wherein the third solvent includes, for example, deionized water, to prepare a negative electrode slurry; applying the negative electrode material to the surface of the negative electrode collector, and after drying, rolling and other processes, forming a negative electrode coating on the surface of the negative electrode collector to obtain a negative electrode sheet.

[0085] An embodiment of the present invention provides a battery, including the above-mentioned negative electrode sheet. The battery has the advantages corresponding to the above-mentioned negative electrode composite material, which will not be described in detail.

[0086] Specifically, the battery can be a sodium ion battery or a lithium ion battery. Taking a sodium ion battery as an example, during the charge and discharge process of the battery, sodium ions (active ions) are deintercalated between the positive and negative electrodes, and the negative electrode composite material in the negative electrode sheet has a high reversible sodium storage capacity and good sodium storage structure stability, which avoids the shedding of Co3Se4 in the negative electrode composite material during the battery cycle and the resulting poor battery cycle stability. The problems can be taken into account to improve the performance of the sodium ion battery, such as the capacity and cycle stability.

[0087] Generally, a battery includes an electrolyte, a cell, and a package that encapsulates the cell. The electrolyte is injected into the cell in the package. The cell includes a positive electrode sheet, the negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The cell may be a laminated cell, that is, the cell is formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet.

[0088] In the embodiment of the present invention, the positive electrode sheet may be a conventional positive electrode sheet in the art, for example, the positive electrode sheet is a metal sheet. For example, when the battery is a sodium ion battery, the positive electrode sheet is a metal sodium sheet.

[0089] Alternatively, the positive electrode sheet may include a positive electrode collector and a positive electrode coating present on at least one side surface of the positive electrode collector. Specifically, the positive electrode coating may be provided on one side surface of the positive electrode collector, or the positive electrode coating may be provided on both the front and back sides of the positive electrode collector.

[0090] The positive electrode current collector may be a conventional positive electrode current collector in the art, for example, the positive electrode current collector may include copper foil, but is not limited thereto.

[0091] Among them, the positive electrode coating (positive electrode active material layer) includes a positive electrode active material, a conductive agent and a binder. The positive electrode active material can be a conventional positive electrode active material in the art. For example, when the battery is a lithium ion battery, the positive electrode active material can be a lithium-containing active material capable of deintercalating and deintercalating lithium ions; when the battery is a sodium ion battery, the positive electrode active material can be a sodium-containing active material capable of deintercalating and deintercalating sodium ions. There is no special limitation on this.

[0092] In addition, the conductive agent in the positive electrode sheet can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode sheet can include one or more of carbon black, acetylene black, Ketjen black, carbon fiber, graphene, and the like.

[0093] In addition, the binder in the positive electrode sheet can be a conventional binding material in the art. For example, the binder in the positive electrode sheet can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, etc.

[0094] Based on the total mass of the positive electrode coating, the mass fraction of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two of them, the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two of them, and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two of them.

[0095] In an embodiment of the present invention, the positive electrode sheet can be prepared by a conventional method in the art, such as by a coating method. For example, the preparation process of the positive electrode sheet includes: dispersing components for forming a positive electrode coating, such as a positive electrode active material, a conductive agent, and a binder, in a fourth solvent, wherein the fourth solvent includes, for example, N-methylpyrrolidone (NMP), to prepare a positive electrode slurry; applying the positive electrode material to the surface of the positive electrode collector, and after drying, rolling and other processes, forming a positive electrode coating on the surface of the positive electrode collector to obtain a positive electrode sheet.

[0096] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to avoid short circuit between the positive electrode sheet and the negative electrode sheet. The embodiment of the present invention can adopt conventional separators in the art. For example, the separator can include a glass fiber membrane.

[0097] The electrolyte of the embodiment of the present invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which can specifically include an organic solvent and an electrolyte salt. The organic solvent can include one or more of ethylene carbonate (EC) and dimethyl carbonate (DMC); when the battery is a sodium ion battery, the electrolyte salt can include a sodium salt, such as lithium hexafluorophosphate (NaPF6), etc. When the battery is a lithium ion battery, the electrolyte salt can include a lithium salt, such as lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0098] In the embodiment of the present invention, the battery cell may be packaged with conventional packaging (shell) materials in the art, and the battery type may be conventional battery type in the art. For example, the battery may be a button battery, but is not limited thereto.

[0099] In the embodiment of the present invention, the positive electrode sheet, the separator, the negative electrode sheet and other components can be assembled into a battery by conventional methods in the art, and there is no particular limitation on this.

[0100] An embodiment of the present invention further provides a battery pack, including the above-mentioned battery. The battery pack has the same advantages as the above-mentioned negative electrode sheet, which will not be described in detail.

[0101] Generally, a battery pack includes a plurality of the above-mentioned batteries, which are connected as single cells to form a battery pack. The batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0102] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned battery or the above-mentioned battery pack. The electrical device has the advantages corresponding to the above-mentioned negative electrode sheet, which will not be described in detail.

[0103] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in the field, such as power equipment (such as electric vehicles, electric vehicles), electronic equipment (such as mobile phones, tablet computers, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0104] In an embodiment of the present invention, after obtaining the negative electrode composite material, the specific surface area (BET) test of the porous carbon matrix in the negative electrode composite material can be performed by conventional methods in the art. In specific implementation, the cobalt tetraselenide in the negative electrode composite material can be removed by acid washing or the like to obtain a porous carbon matrix, and then the specific surface area of ​​the porous carbon matrix is ​​tested.

[0105] It can be understood that when the cobalt tetraselenide in the negative electrode composite material is removed by acid washing, the porous carbon matrix obtained is dried after acid washing and then its specific surface area is tested. Among them, the negative electrode composite material can be acid washed with a conventional inorganic acid that can dissolve cobalt tetraselenide, as long as the cobalt tetraselenide distributed on the porous carbon matrix can be washed away.

[0106] In the embodiment of the present invention, after obtaining the negative electrode composite material, the negative electrode composite material can be subjected to scanning electron microscopy (SEM) analysis to test the pores and size of the porous carbon matrix in the negative electrode composite material, and the negative electrode composite material can be subjected to transmission electron microscopy (TEM) analysis to test the particle size of Co3Se4 in the negative electrode composite material. Taking the test process of the particle size of Co3Se4 as an example, in specific implementation, after obtaining the negative electrode composite material, a TEM analysis is performed on it, and the diameters of at least 20 (for example, 20, 30, 40 or 50) Co3Se4 particles in the field of view are tested by a measuring tool, and statistics are performed based on the measurement results, and the average value of the diameters of at least 20 Co3Se4 particles measured is used as the test result (i.e., the average particle size of Co3Se4 in the negative electrode composite material).

[0107] In an embodiment of the present invention, after obtaining the negative electrode composite material, the mass fraction of Co3Se4 in the negative electrode composite material can be measured by conventional methods in the art. For example, the mass fraction of Co3Se4 in the negative electrode composite material is measured by performing thermogravimetric analysis on the negative electrode composite material. Specifically, m1 gram of the negative electrode composite material sample is taken for thermogravimetric analysis. During the thermogravimetric analysis, m1 gram of the negative electrode composite material sample is heated to burn the porous carbon matrix material therein. After the porous carbon matrix material is basically completely burned, the remaining sample is basically all Co3Se4. The mass of the remaining sample is m2, and the mass fraction of Co3Se4 in the negative electrode composite material = m2 / m1. Correspondingly, the mass fraction of the porous carbon matrix in the negative electrode composite material = (m1-m2) / m1.

[0108] In the embodiment of the present invention, after obtaining the negative electrode composite material, X-ray diffraction (XRD) analysis may be performed on the negative electrode composite material to determine the type of active component (Co3Se4) in the negative electrode composite material.

[0109] In the embodiment of the present invention, after obtaining the negative electrode composite material, the negative electrode composite material can be subjected to scanning electron microscopy (SEM) analysis to test the average particle size of the negative electrode composite material. In specific implementation, after obtaining the negative electrode composite material, SEM analysis is performed on it, and the diameters of at least 20 (for example, 20, 30, 40 or 50) negative electrode composite material particles in the field of view are tested by a measuring tool, and statistics are performed based on the measurement results, and the average value of the diameters of at least 20 negative electrode composite material particles measured is used as the test result (i.e., the average particle size of the negative electrode composite material).

[0110] In the embodiment of the present invention, when the negative electrode composite material is subjected to BET test, SEM analysis, TEM analysis and thermogravimetric analysis, the negative electrode composite material that has not been made into a negative electrode sheet or battery can be directly obtained for analysis, or the negative electrode composite material can be separated from the negative electrode sheet or battery for analysis. For example, the battery can be disassembled, the negative electrode sheet can be taken out, and the negative electrode coating can be scraped off from the negative electrode sheet, and the scraped negative electrode coating can be placed in a solvent, and the organic materials such as the binder in the negative electrode coating can be washed away by the solvent to obtain solid particles, which are mainly negative electrode composite materials, generally including a conductive agent, and the density difference between the conductive carbon and the negative electrode composite material can be used to obtain a negative electrode composite material without a conductive agent by centrifugation, and the negative electrode composite material is subjected to the above analysis to obtain corresponding test results (such as the specific surface area of ​​the negative electrode composite material, the average particle size of the negative electrode composite material, the average particle size of Co3Se4, the mass fraction of Co3Se4, the type of active component (Co3Se4) in the negative electrode composite material, etc.). Among them, the solvent used can be an organic solvent, such as N-methylpyrrolidone (NMP).

[0111] The present invention is further described below through specific examples. In the following examples and comparative examples, unless otherwise specified, porous carbon matrix materials with a preset specific surface area are prepared by adjusting the amount of template used.

[0112] Example 1

[0113] 1. Preparation of porous carbon matrix material (CN powder)

[0114] Glucose and NaCl were dissolved in water at a mass ratio of 1:4, and then freeze-dried at -70°C to obtain a solid mixture; the solid mixture was then placed in a tube furnace and carbonized at 900°C in a protective gas for 2 hours, and then washed and filtered several times to remove NaCl to obtain CN powder (porous carbon matrix material). The specific surface area of ​​the porous carbon matrix material was measured to be 200m 2 / g.

[0115] 2. Preparation of negative electrode composite material (Co3Se4@CN)

[0116] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 100 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then the obtained solid product is filtered, and the obtained solid product is dried at 80° C. for 12 hours to obtain a porous carbon matrix material with cobalt ions attached;

[0117] S2. Mix the porous carbon matrix material with cobalt ions attached obtained in step S1 with 100 parts by weight of selenium powder and place them in a tubular furnace. Heat the temperature to 800°C at a heating rate of 2°C / min in an argon environment, and then perform selenization reaction at 800°C for 2h to obtain Co3Se4@CN; wherein the amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0118] 3. Preparation of negative electrode sheet

[0119] The Co3Se4@CN prepared as above was used as the negative electrode active material, and Co3Se4@CN, acetylene black and PVDF were evenly mixed in a mass ratio of 80:10:10, and deionized water was added to prepare a negative electrode slurry; the negative electrode slurry was coated on the surface of the copper foil, vacuum dried at 120°C for more than 12 hours, and then pressed to obtain a negative electrode sheet.

[0120] 4. Assembly of sodium-ion batteries

[0121] Using metallic sodium sheets as positive electrodes and glass fiber membranes as separators, the positive electrodes, separators and negative electrodes were stacked and assembled into button-type batteries in a glove box filled with argon. The composition of the electrolyte used was as follows: the organic solvent was a mixed solution of EC and DMC in a volume ratio of 1:1, and the concentration of NaPF6 in the electrolyte was 1 mol / L.

[0122] Example 2

[0123] The difference between Example 2 and Example 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of Example 1.

[0124] In this embodiment 2, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0125] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 120 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0126] S2. Mix the porous carbon matrix material with cobalt ions attached obtained in step S1 with 120 parts by weight of selenium powder and place them in a tubular furnace. Heat the temperature to 800°C at a heating rate of 2°C / min in an argon environment, and then perform selenization reaction at 800°C for 2h to obtain Co3Se4@CN; wherein the amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0127] Example 3

[0128] 1. Referring to the preparation process of the porous carbon matrix material (CN powder) in Example 1, a specific surface area of ​​300 m 2 / g of CN powder.

[0129] 2. Preparation of negative electrode composite material (Co3Se4@CN)

[0130] S1. 20 parts by weight of CN powder (specific surface area 300 m 2 / g) and 150 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0131] S2. The porous carbon matrix material with cobalt ions attached obtained in step S1 is mixed with 150 parts by weight of selenium powder and placed in a tubular furnace. The mixture is heated to 800°C at a heating rate of 2°C / min in an argon environment, and then subjected to selenization reaction at 800°C for 2h to obtain Co3Se4@CN. The amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0132] 3. Preparation of negative electrode sheet and assembly of sodium ion battery: The difference from Example 1 is that the negative electrode active material is replaced by S3 instead of S1, and the remaining steps and conditions are the same as Example 1.

[0133] Example 4

[0134] The difference between Example 4 and Example 3 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of Example 3.

[0135] In this embodiment 4, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0136] S1. 20 parts by weight of CN powder (specific surface area 300 m 2 / g) and 240 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0137] S2. The porous carbon matrix material with cobalt ions attached obtained in step S1 is mixed with 240 parts by weight of selenium powder and placed in a tubular furnace. The mixture is heated to 800°C at a heating rate of 2°C / min in an argon environment, and then subjected to selenization reaction at 800°C for 2h to obtain Co3Se4@CN. The amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0138] The difference between Example 5 and Example 2 is that the specific surface area of ​​CN powder is 80m 2 / g (Refer to the preparation process of CN powder in Example 1, the specific surface area is 80m 2 / g of CN powder), and the other conditions were the same as in Example 2.

[0139] The difference between Example 6 and Example 2 is that the specific surface area of ​​CN powder is 150m 2 / g (refer to the preparation process of CN powder in Example 1, the specific surface area of ​​150m 2 / g of CN powder), and the other conditions were the same as in Example 2.

[0140] The difference between Example 7 and Example 2 is that the specific surface area of ​​CN powder is 350m 2 / g (refer to the preparation process of CN powder in Example 1, the specific surface area is 350m 2 / g of CN powder), and the other conditions were the same as in Example 2.

[0141] The difference between Example 8 and Example 2 is that the specific surface area of ​​CN powder is 420m 2 / g (Refer to the preparation process of CN powder in Example 1, the specific surface area is 420m 2 / g of CN powder), and the other conditions were the same as in Example 2.

[0142] Example 9

[0143] The difference between this embodiment 9 and embodiment 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of embodiment 1. In this embodiment 9, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0144] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 80 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0145] S2. The porous carbon matrix material with cobalt ions attached obtained in step S1 is mixed with 80 parts by weight of selenium powder and placed in a tubular furnace. The mixture is heated to 800°C at a heating rate of 2°C / min in an argon environment, and then subjected to selenization reaction at 800°C for 2h to obtain Co3Se4@CN. The amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0146] Example 10

[0147] The difference between this embodiment 10 and embodiment 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of embodiment 1. In this embodiment 10, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0148] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 300 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0149] S2. The porous carbon matrix material with cobalt ions attached obtained in step S1 is mixed with 300 parts by weight of selenium powder and placed in a tubular furnace. The mixture is heated to 800°C at a heating rate of 2°C / min in an argon environment, and then subjected to selenization reaction at 800°C for 2h to obtain Co3Se4@CN. The amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0150] Embodiment 11

[0151] The difference between this embodiment 11 and embodiment 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of embodiment 1. In this embodiment 11, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0152] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 50 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0153] S2. Mix the porous carbon matrix material with cobalt ions attached obtained in step S1 with 50 parts by weight of selenium powder and place them in a tubular furnace. Heat the temperature to 800°C at a heating rate of 2°C / min in an argon environment, and then perform selenization reaction at 800°C for 2h to obtain Co3Se4@CN; wherein the amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0154] Example 12

[0155] The difference between Example 12 and Example 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of Example 1. In Example 12, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0156] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 40 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0157] S2. Mix the porous carbon matrix material with cobalt ions attached obtained in step S1 with 40 parts by weight of selenium powder and place them in a tubular furnace. Heat the temperature to 800°C at a heating rate of 2°C / min in an argon environment, and then perform selenization reaction at 800°C for 2h to obtain Co3Se4@CN; wherein the amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0158] Example 13

[0159] The difference between Example 13 and Example 1 is that the negative electrode composite material (Co3Se4@CN) and its preparation process are different, and the remaining steps and conditions are the same as those of Example 1. In Example 13, the preparation process of the negative electrode composite material (Co3Se4@CN) is as follows:

[0160] S1. 20 parts by weight of CN powder (specific surface area 200 m 2 / g) and 650 parts by weight of CoCl2 are dissolved in 1000 parts by weight of water, stirred evenly, and then filtered, and the obtained solid product is dried at 80°C for 12h to obtain a porous carbon matrix material with cobalt ions attached;

[0161] S2. Mix the porous carbon matrix material with cobalt ions attached obtained in step S1 with 650 parts by weight of selenium powder and place them in a tubular furnace. Heat the temperature to 800°C at a heating rate of 2°C / min in an argon environment, and then perform selenization reaction at 800°C for 2h to obtain Co3Se4@CN; wherein the amounts of CoCl2 and selenium powder are such that the mass ratio of cobalt element to selenium element is 0.45:1.

[0162] Thermogravimetric analysis was performed on the negative electrode composite materials (Co3Se4@CN) prepared in Example 1 to Example 13, and the mass ratios (Co3Se4:CN) of Co3Se4@CN and the porous carbon matrix (CN) in each example were measured and shown in Table 1.

[0163] SEM analysis was performed on the CN powders obtained in Examples 1 to 13, and it was found that the CN powders were porous, the particle size of the CN powders was greater than 10 μm, and the CN powders exhibited a highly interconnected three-dimensional network structure. Figure 1 This is the SEM image of the CN powder of Example 1 (the test results of the other examples are similar to those of Example 1). It can be seen that the CN powder has a porous structure, the particle size of the CN powder is greater than 10 μm, and the CN powder exhibits a highly interconnected three-dimensional network structure.

[0164] In addition, the specific surface areas of the CN powders of Examples 1 to 13 (ie, the specific surface areas of the porous carbon matrix) are summarized in Table 1.

[0165] In addition, the negative electrode composite materials (Co3Se4@CN) prepared in Examples 1 to 13 were analyzed by SEM and TEM, and it was found that in Co3Se4@CN, the Co3Se4 particles were evenly distributed on the surface and in the internal pores of the CN particles. The diameters of at least 20 Co3Se4 particles in the TEM field of view were measured, and the average value was taken as the particle size of Co3Se4. The particle sizes of Co3Se4 in Co3Se4@CN of each example are shown in Table 1. For example, the SEM image of the negative electrode composite material prepared in Example 1 is shown in Figure 4 (The test results of other embodiments are similar to those of embodiment 1), Figure 4 It can be seen that in the negative electrode composite material, Co3Se4 particles are distributed on the surface and inside the pores of the carbon network.

[0166] In addition, XRD analysis was performed on the negative electrode composite materials (Co3Se4@CN) prepared in Examples 1 to 13, and it was found that the particles distributed on the porous carbon matrix were Co3Se4, which had a monoclinic structure. For example, the XRD pattern of the negative electrode composite material prepared in Example 1 is shown in FIG. Figure 5 (The test results of other embodiments are similar to those of embodiment 1), Figure 5 It can be seen that in the negative electrode composite material, the cobalt compound in the porous carbon matrix is ​​Co3Se4 ( Figure 5 The spectrum corresponding to the Co3Se4 standard card in the figure is the standard spectrum of Co3Se4).

[0167] Comparative Example 1: The difference from Example 2 is that the negative electrode active material is CN powder (specific surface area 200m 2 / g) was used to replace the Co3Se4@CN prepared in Example 2, and the remaining steps and conditions were the same as those in Example 2.

[0168] Comparative Example 2: The difference from Example 2 is that the negative electrode active material uses Co3Se4 (particle size 130 nm) to replace the Co3Se4@CN prepared in Example 2, and the remaining steps and conditions are the same as in Example 2.

[0169] Comparative Example 3: The difference from Example 2 is that the negative electrode active material uses Co3Se4@HC to replace the Co3Se4@CN prepared in Example 2, and the remaining steps and conditions are the same as those in Example 2.

[0170] In the Co3Se4@HC of Comparative Example 3, the particle size of Co3Se4 is 130nm, the particle size of HC is about 10μm, and the mass ratio of Co3Se4 to HC is 1.1:1. Figure 2 ,from Figure 2 It can be seen that HC is irregular block-shaped particles.

[0171] In Comparative Example 3, the difference between the preparation process of Co3Se4@HC and the preparation process of Co3Se4@CN in Example 2 is that in the preparation process of the negative electrode composite material, HC is used to replace CN powder to obtain Co3Se4@HC, and the remaining steps and conditions are the same as in Example 2.

[0172] Comparative Example 4: The difference from Example 13 is that Co3Se4 (particle size 130 nm) is used as the negative electrode active material to replace Co3Se4@CN prepared in Example 13, and the remaining steps and conditions are the same as those in Example 13.

[0173] Comparative Example 5: The difference from Example 13 is that the negative electrode active material uses Co3Se4@HC to replace Co3Se4@CN prepared in Example 13, and the remaining steps and conditions are the same as those in Example 13.

[0174] The charge and discharge specific capacity test of each embodiment and comparative example was tested according to the following process: the battery was set to a charge and discharge state (i.e., the working electrode deintercalated sodium), the charge and discharge current density was 0.1 A / g, the operation was stopped when the charge was charged to a cut-off voltage of 3.0 V, and the operation was stopped when the discharge was discharged to a cut-off voltage of 0.01 V. The first charge and discharge specific capacity was calculated, and the results are shown in Table 2.

[0175] Among them, the first discharge specific capacity (mAh / g) = the first sodium insertion capacity / the mass of the negative electrode active material.

[0176] Among them, the first charge specific capacity (mAh / g) = the first sodium removal capacity / the mass of the negative electrode active material.

[0177] In addition, according to the cycle process of the above charge and discharge specific capacity test, the battery was cycled 100 times (100 cycles), and the cycle curves (the relationship curve between specific capacity and cycle number) of the batteries of Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were measured. Figure 3 .

[0178] The first discharge specific capacity, first charge specific capacity, capacity retention rate after 100 cycles, and charge specific capacity after 100 cycles of the batteries of each embodiment and comparative example are shown in Table 2.

[0179] Table 1

[0180]

[0181] Table 2

[0182]

[0183] As can be seen from Table 2, compared with Comparative Examples 1 to 5, the negative electrode active materials (negative electrode composite materials) in Examples 1 to 13 include a porous carbon matrix and cobalt tetraselenide distributed in the porous carbon matrix, which can maintain a high specific charge capacity of the negative electrode active material while increasing the capacity of the battery after cycling and improving the cycle stability of the battery. For example, as can be seen from Table 2, the negative electrode active materials of Examples 1 to 4 have a higher reversible capacity than the negative electrode active material (CN powder) of Comparative Example 1, indicating that Co3Se4@CN can exhibit a higher sodium storage capacity than CN. When used as a sodium negative electrode with the same mass of positive electrode active materials, the amount of Co3Se4@CN added can be less, thereby improving the battery energy density; the negative electrode active materials of Examples 1 to 4 have a higher reversible capacity than the negative electrode active material (Co3Se4@HC) of Comparative Example 3, indicating that Co3Se4@CN has a stronger sodium storage performance than Co3Se4@HC due to the three-dimensional interconnected porous structure of the porous carbon matrix.

[0184] Further from Figure 3 It can be seen that the sodium storage capacity of the Co3Se4@CN composite material (Example 2) after 100 cycles is higher than that of single CN powder (Comparative Example 1), single Co3Se4 (Comparative Example 2) and Co3Se4@HC (Comparative Example 3). The Co3Se4@CN composite material simultaneously exhibits the good cycle stability of CN and the large sodium storage capacity of Co3Se4, which significantly improves the capacity of the battery after long cycles and improves the cycle stability of the battery.

[0185] It can be further seen from Examples 2, 5 to 8 that, relative to Examples 5 and 8, Examples 2, 6 and 7 further adopt a specific surface area of ​​100 m 2 / g~400 m 2 The porous carbon matrix in the range of 200 m / g can further improve the initial charge capacity of the battery and the capacity of the battery after a long cycle, especially in Example 2, by further using a specific surface area of ​​200 m 2 / g~300 m 2 Porous carbon matrices in the range of 100 g / cm2 can significantly improve the capacity of batteries after long cycles.

[0186] It can be further seen from Examples 1 to 2 and 9 to 13 that, relative to Examples 11 and 13, Examples 1 to 2, 9, 10 and 12 can further improve the initial charge capacity of the battery and the capacity of the battery after a long cycle by further controlling the particle size of cobalt selenide within the range of 50 nm to 300 nm. In particular, Examples 1 to 2 can more significantly improve the initial charge capacity of the battery and the capacity of the battery after a long cycle by further controlling the particle size of cobalt selenide within the range of 50 nm to 600 nm.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode composite material, characterized in that: The invention comprises a porous carbon matrix and tricobalt tetraselenide distributed in the porous carbon matrix.

2. The negative electrode composite material according to claim 1, characterized in that: The specific surface area of ​​the porous carbon matrix is ​​100 m 2 / g~400 m 2 / g.

3. The negative electrode composite material according to claim 2, characterized in that: The specific surface area of ​​the porous carbon matrix is ​​200 m 2 / g~300 m 2 / g.

4. The negative electrode composite material according to claim 1, characterized in that: The average particle size of the tricobalt tetraselenide is 50nm-600nm.

5. The negative electrode composite material according to claim 4, characterized in that: The average particle size of the tricobalt tetraselenide is 50nm-300nm.

6. The negative electrode composite material according to claim 5, characterized in that: The average particle size of the tricobalt tetraselenide is 100nm-200nm.

7. The negative electrode composite material according to claim 1, characterized in that: Based on the total mass of the negative electrode composite material, the mass fraction of the tricobalt tetraselenide is 16% to 70%.

8. The negative electrode composite material according to any one of claims 1 to 7, characterized in that: The average particle size of the negative electrode composite material is greater than or equal to 10 μm.

9. The negative electrode composite material according to any one of claims 1 to 7, characterized in that: The tricobalt tetraselenide is distributed on the surface and inside the pores of the porous carbon matrix.

10. A method for preparing the negative electrode composite material according to any one of claims 1 to 9, characterized in that: The following steps are involved: Dispersing a cobalt source and a porous carbon matrix material in a first solvent, and then performing solid-liquid separation to obtain a porous carbon matrix material with cobalt ions attached thereto; The porous carbon matrix material with cobalt ions attached thereto and a selenium source are mixed and then subjected to selenization treatment to obtain the negative electrode composite material.

11. The method for preparing the negative electrode composite material according to claim 10, characterized in that: The preparation process of the porous carbon matrix material comprises: dissolving a carbon source and a template agent in a second solvent and then drying the solvent, and then carbonizing the obtained mixture to obtain the porous carbon matrix material.

12. The method for preparing the negative electrode composite material according to claim 11, characterized in that: The carbon source includes one or more of glucose and sucrose; And / or, the template comprises one or more of NaCl, KCl and CaCl2; And / or, the temperature of the carbonization treatment is 700° C. to 1000° C., and the time of the carbonization treatment is 1 h to 3 h.

13. The method for preparing the negative electrode composite material according to claim 10, characterized in that: The mass ratio of the porous carbon matrix material to the cobalt source is 1:2 to 1:20; And / or, the cobalt source includes a soluble cobalt salt, and the soluble cobalt salt includes one or more of Co(NO3)2, CoCl2, CoSO4, CoS2 and CoF2.

14. The method for preparing the negative electrode composite material according to any one of claims 10 to 13, characterized in that: The amounts of the cobalt source and the selenium source satisfy: the mass ratio of the cobalt element to the selenium element is (0.4-0.5): 1; And / or, the selenium source includes selenium powder; And / or, the selenization treatment is performed under an inert gas atmosphere; And / or, the temperature of the selenization treatment is 700° C. to 900° C., and the time of the selenization treatment is 1 h to 4 h.

15. A negative electrode sheet, characterized in that: The negative electrode composite material comprises the negative electrode composite material according to any one of claims 1 to 9 or the negative electrode composite material prepared according to the preparation method according to any one of claims 10 to 14.

16. A battery, characterized in that: Includes the negative electrode sheet as described in claim 15.

17. The battery according to claim 16, characterized in that The battery is a sodium ion battery or a lithium ion battery.

18. A battery pack, characterized in that: A battery comprising the battery of claim 16 or 17.

19. An electrical equipment, characterized in that: Comprising the battery according to claim 16 or 17 or the battery pack according to claim 18.

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