Hard carbon composite materials and their preparation methods, negative electrode sheets, sodium-ion batteries

Abstract

This application provides a hard carbon composite material and its preparation method, a negative electrode sheet, and a sodium-ion battery. The hard carbon composite material includes spherical hard carbon material, and the surface of the hard carbon material has a coating layer formed by soft carbon material. The hard carbon material is formed by etching a precursor material by molten salt electrolysis. The precursor material is formed by carbonizing a spherical thermosetting resin. The hard carbon material has a three-dimensional network porous structure, and the interlayer spacing of the hard carbon composite material is 0.390 nm to 0.402 nm.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a hard carbon composite material and its preparation method, a negative electrode sheet, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have advantages such as low cost, abundant sodium resources, and relatively high energy density, and are expected to replace traditional lithium-ion batteries in the field of energy storage.

[0003] Hard carbon materials provide sufficient space for the storage and deintercalation of sodium ions, maintaining good stability during the sodium ion deintercalation process, making them more suitable as anode materials for sodium-ion batteries. However, in practical applications, the rate performance and cycle performance of sodium-ion batteries still need improvement when hard carbon materials are used as anode materials. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses a hard carbon composite material and its preparation method, a negative electrode sheet, and a sodium-ion battery, in order to improve the rate performance and cycle performance of sodium-ion batteries.

[0005] In a first aspect, this application provides a hard carbon composite material comprising spherical hard carbon material, the surface of which has a coating layer formed of soft carbon material;

[0006] The hard carbon material has a three-dimensional network porous structure, and the interlayer spacing of the hard carbon composite material is 0.390 nm to 0.402 nm. The hard carbon material is formed by etching a precursor material by molten salt electrolysis, and the precursor material is formed by carbonizing a spherical thermosetting resin.

[0007] In some embodiments of this application, the specific surface area of ​​the hard carbon composite material is 3 m². 2 / g~4m 2 / g.

[0008] In some embodiments of this application, the tap density of the hard carbon composite material is 0.75 g / cm³. 3 ~0.85g / cm 3 .

[0009] In some embodiments of this application, based on the mass of the hard carbon composite material, the hard carbon material is the core layer of the hard carbon composite material, the diameter of the core layer is 0.2 μm to 16 μm, and the thickness of the coating layer is 0.01 μm to 0.2 μm.

[0010] In some embodiments of this application, the thermosetting resin includes at least one of phenolic resin, epoxy resin, and phenolic epoxy resin.

[0011] Secondly, this application provides a method for preparing a hard carbon composite material as described in the first aspect, comprising the following steps:

[0012] Preparation of spherical thermosetting resin: Spherical thermosetting resin was prepared by spray drying method;

[0013] First carbonization treatment: The spherical thermosetting resin is subjected to a first carbonization treatment under an inert gas atmosphere to obtain a spherical precursor material;

[0014] Electrolytic etching: The precursor material is pressed into a sheet and used as the electrolytic anode. Electrolytic etching is performed at a voltage of 3V to 4V for 10 to 15 minutes to obtain the hard carbon material.

[0015] Second carbonization treatment: The soft carbon material is mixed with the hard carbon material and then subjected to a second carbonization treatment under an inert gas atmosphere to obtain the hard carbon composite material.

[0016] In some embodiments of this application, the preparation method further includes: the inlet air temperature of the spray drying is 150℃~180℃, the feed rate is 20mL / min~50mL / min, and the outlet air temperature is 80℃~110℃.

[0017] In some embodiments of this application, the temperature of the first carbonization treatment is 700℃~900℃, the heating rate is 3℃ / min~7℃ / min, and the holding time is 1h~3h.

[0018] In some embodiments of this application, the reaction vessel for electrolytic etching is a corundum crucible, the electrolyte is anhydrous sodium carbonate, the gas atmosphere is an inert gas, and the electrolytic cathode is a graphite carbon rod.

[0019] In some embodiments of this application, the processing temperature of the second carbonization treatment is 1250℃~1350℃, the heating rate is 1℃ / min~3℃ / min, and the holding time is 3h~5h.

[0020] In some embodiments of this application, in the second carbonization step, the mass ratio of the soft carbon material to the hard carbon material is 1:10 to 20.

[0021] Thirdly, this application provides a negative electrode sheet, including a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, wherein the negative electrode material layer includes the hard carbon composite material described in the first aspect, or includes a hard carbon composite material prepared by the preparation method described in the second aspect.

[0022] Fourthly, this application provides a sodium-ion battery, the sodium-ion battery comprising the negative electrode sheet described in the third aspect.

[0023] Fifthly, this application provides an energy storage device, including a housing and at least one sodium-ion battery as described in the fourth aspect, the sodium-ion battery being housed within the housing.

[0024] In a sixth aspect, this application provides an electrical device including the energy storage device described in the fifth aspect, wherein the energy storage device supplies power to the electrical device.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] This application provides a hard carbon composite material, its preparation method, a negative electrode sheet, and a sodium-ion battery. The hard carbon composite material includes spherical hard carbon materials with a three-dimensional network porous structure. The hard carbon material is formed by electrolytic etching of a precursor material using molten salt. The precursor material is formed by carbonizing a spherical thermosetting resin. This hard carbon composite material exhibits high structural consistency and a suitable interlayer spacing of 0.390 nm to 0.402 nm. It also possesses a rich pore structure, providing abundant active sites for sodium ions, thereby increasing sodium storage capacity and facilitating rapid insertion and extraction of sodium ions, thus improving the rate performance of the hard carbon composite material. Furthermore, the three-dimensional network porous structure of this application not only forms a three-dimensional network current path for rapid electron transport but also serves as a stable mechanical framework, thereby improving the conductivity and cycle stability of the hard carbon composite material. Additionally, the surface of the hard carbon material has a coating layer formed by soft carbon materials, which reduces the specific surface area and surface defects of the hard carbon composite material. Sodium-ion batteries with the hard carbon composite material of this application show significantly improved performance in terms of reversible capacity, rate capability, and cycle stability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the cross-sectional structure network of a hard carbon composite material in one embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application;

[0030] Figure 3 This is a schematic diagram of the energy storage system according to one embodiment of this application.

[0031] Explanation of reference numerals in the attached drawings: 1-Energy storage device, 2-Electric power conversion device, 3-First user load, 4-Second user load, 10-Hard carbon material, 20-Clad layer, 400-Energy storage system, 410-High voltage cable, 420-First electric power conversion device, 430-Second electric power conversion device. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0034] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0035] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0036] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0037] This application provides a hard carbon composite material, such as Figure 1As shown, the hard carbon composite material includes spherical hard carbon material 10, which has a three-dimensional network porous structure. This three-dimensional network porous structure is formed by etching a precursor material through molten salt electrolysis. The precursor material is formed by carbonizing spherical thermosetting resin. (Reference) Figure 1 The three-dimensional network porous structure is distributed in a sponge-like manner in the hard carbon composite material, thus forming abundant closed pores, mesopores, and micropores, which is beneficial to increasing the sodium storage capacity. The hard carbon composite material of this application has high structural consistency and a suitable interlayer spacing of 0.390 nm to 0.402 nm, and possesses a rich pore structure, which can provide abundant active sites for sodium ions, thereby increasing the sodium storage capacity and facilitating the rapid insertion and extraction of sodium ions, thereby improving the rate performance of the hard carbon composite material. Furthermore, the three-dimensional network porous structure can not only form a three-dimensional network current path for rapid electron transport, but also serve as a stable mechanical framework, thereby improving the conductivity and cycle stability of the hard carbon composite material. The hard carbon composite material of this application has a core-shell structure. The core of the core-shell structure is a spherical hard carbon material 10, and the shell includes a coating layer 20 formed of soft carbon material, which can reduce the specific surface area and surface defects of the hard carbon composite material, which is beneficial to improving the first-pass efficiency of the hard carbon composite material. Moreover, the coating layer formed of soft carbon material is beneficial to improving the conductivity of the hard carbon composite material. Sodium-ion batteries with the hard carbon composite material of this application show significantly improved reversible capacity, rate performance, and cycle stability.

[0038] In this application, interlayer spacing refers to the distance between the atomic layers of carbon in a hard carbon composite material. The interlayer spacing can be determined by analyzing the diffraction pattern of the hard carbon composite material using X-ray diffraction.

[0039] In some embodiments of this application, the specific surface area of ​​the hard carbon composite material is 3m². 2 / g~4m 2 / g. For example, a specific surface area of ​​3m². 2 / g, 3.5m 2 / g, 3.7m 2 / g or 4m 2 / g. By controlling the specific surface area of ​​the hard carbon composite material within the above range, it is beneficial to provide abundant active sites and reaction area for sodium ions, improve the utilization rate of the negative electrode material, and thus enable sodium-ion batteries to exhibit high rate capability and high reversible capacity.

[0040] In some embodiments of this application, the tap density of the hard carbon composite material is 0.75 g / cm³. 3 ~0.85g / cm 3 For example, the tap density is 0.75 g / cm³. 3 0.77g / cm3 0.80g / cm 3 0.83g / cm 3 Or 0.85g / cm 3 By controlling the tap density of the hard carbon composite material within the aforementioned range, it is beneficial to improve the volumetric energy density of sodium-ion batteries.

[0041] In some embodiments of this application, the hard carbon material is the core layer of the hard carbon composite material, and the diameter of the core layer is 0.2 μm to 16 μm, for example, the diameter of the core layer is 0.2 μm, 0.5 μm, 1 μm, 10 μm or 16 μm; the thickness of the coating layer is 0.01 μm to 0.2 μm, for example, the thickness of the coating layer is 0.01 μm, 0.05 μm, 0.1 μm or 0.2 μm. By controlling the diameter of the core layer and the thickness of the coating layer within the above ranges, it is beneficial to balance the high sodium storage capacity of the core layer and the stability of the coating layer, which can both suppress electrolyte decomposition and improve the initial efficiency, and increase the capacity of the material, thereby improving its cycle performance and rate performance. It is understood that the diameter of the core layer is mainly affected by the particle size of the precursor material. Based on this, the diameter of the core layer can be controlled by controlling the particle size of the precursor material; the thickness of the coating layer is mainly affected by the addition ratio of the soft carbon material. Based on this, the thickness of the coating layer can be controlled by controlling the addition ratio of the soft carbon material.

[0042] In some embodiments of this application, based on the mass of the hard carbon composite material, the mass percentage of hard carbon material is 90%–95%, and the mass percentage of the coating layer is 5%–10%. When the relative content of hard carbon material is too high, the relative content of the coating layer is too low, which is detrimental to improving the conductivity of the hard carbon composite material. Furthermore, a large number of unclosed pores will consume excessive electrolyte during cycling, leading to lower first-time efficiency and poorer cycle performance. Conversely, when the relative content of hard carbon material is too low, the relative content of the coating layer is too high, which is detrimental to improving the capacity of the hard carbon composite material. This application, by controlling the mass percentages of hard carbon material and coating layer within the above-mentioned ranges, is beneficial to obtaining a hard carbon composite material with good conductivity and high capacity.

[0043] In some embodiments of this application, the thermosetting resin includes at least one of phenolic resin, epoxy resin, and phenolic epoxy resin. Because the molecular structures of the aforementioned thermosetting resins are relatively simple and controllable, and the relevant molecular structures can be designed as needed to precisely construct adjustable pore structures and active sites at the molecular level, hard carbon materials exhibit better rate capability and cycling stability. Furthermore, the hard carbon materials prepared from the aforementioned thermosetting resins have high specific capacity, good electrochemical performance, and good consistency, demonstrating significant performance advantages. Therefore, this is beneficial for forming precursor materials with high structural consistency, thereby facilitating the formation of hard carbon composite materials with high structural consistency.

[0044] This application does not impose any particular limitation on soft carbon materials, as long as they can achieve the purpose of this invention. For example, soft carbon materials include at least one of anthracite, mesophase carbon microspheres, residual oil, and bitumen.

[0045] This application also provides a method for preparing the hard carbon composite material according to any of the above embodiments, comprising the following steps:

[0046] Preparation of spherical thermosetting resin: Spherical thermosetting resin was prepared by spray drying method;

[0047] First carbonization treatment: The spherical thermosetting resin is subjected to a first carbonization treatment under an inert gas atmosphere to obtain a spherical precursor material;

[0048] Electrolytic etching: The precursor material is pressed into a sheet and used as the electrolytic anode. Electrolytic etching is performed at a voltage of 3V to 4V for 10 to 15 minutes to obtain hard carbon material.

[0049] Second carbonization treatment: After mixing soft carbon materials and hard carbon materials, a second carbonization treatment is carried out under an inert gas atmosphere to obtain a hard carbon composite material.

[0050] In the first carbonization step, before the first carbonization process, the product obtained by spray drying can be cured at 130℃~170℃ for 15h~25h, which is more conducive to obtaining spherical precursor materials, thereby facilitating the formation of the hard carbon composite material structure of this application.

[0051] In the electrolytic etching step, this application does not have a particular limitation on the electrolysis temperature, as long as it is sufficient to melt the electrolyte. For example, the electrolysis temperature is 850°C to 870°C. The product after electrolytic etching can be rinsed with deionized water to remove residual molten salt, and then dried at a low temperature (about 50°C) to obtain spherical precursor material.

[0052] In the second carbonization step, the precursor material can be ball-milled to deagglomerate, sieved, and then the treated precursor material, asphalt, and ethanol are ball-milled together and dried. This process disperses the precursor material, preventing agglomeration and facilitating the production of precursor materials with the desired particle size.

[0053] In some embodiments of this application, the preparation method further includes: an inlet air temperature of 150°C to 180°C, for example, 150°C, 170°C, or 180°C; a feed rate of 20 mL / min to 50 mL / min, for example, 20 mL / min, 30 mL / min, 40 mL / min, or 50 mL / min; and an outlet air temperature of 80°C to 110°C, for example, 70°C, 80°C, 90°C, or 110°C. The D50 of the spherical thermosetting resin can be 2 μm to 25 μm. D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%. By controlling the inlet air temperature, feed rate, and outlet air temperature of the spray dryer within the above ranges, it is beneficial to obtain hard carbon composite materials with the desired specific surface area and tap density.

[0054] In some embodiments of this application, the temperature of the first carbonization treatment is 700℃ to 900℃, for example, the treatment temperature is 700℃, 800℃, or 900℃; the heating rate is 3℃ / min to 7℃ / min, for example, the heating rate is 3℃ / min, 5℃ / min, or 7℃ / min; and the holding time is 1h to 3h, for example, the holding time is 1h, 2h, or 3h. By adjusting the above parameters of the first carbonization treatment within the scope of this application, it is beneficial to obtain precursor materials with high structural consistency.

[0055] In some embodiments of this application, the reaction vessel for electrolytic etching is a corundum crucible, the electrolyte is anhydrous sodium carbonate, the gas atmosphere is an inert gas, and the electrolytic cathode is a graphite carbon rod. The electrode reaction can be represented as follows:

[0056] Anode reaction: C + 2O 2- →CO2 + 4e -

[0057] C+2CO3 2- →3CO2 + 4e -

[0058] Cathode reaction: CO3 2- +4e - →C+3O 2-

[0059] Overall reaction: CO3 2- →CO2+O 2-

[0060] This application involves electrolytic etching of a spherical precursor material sheet under an applied electric field. This process removes a portion of the carbon atoms from the surface to the interior of the spherical precursor material. During this process, due to the migration of carbon atoms (i.e., the etching of carbon atoms) and the erosion of molten salt, the prepared hard carbon material forms many pore structures, thereby obtaining a sponge-like three-dimensional network porous structure.

[0061] This application does not impose any particular restrictions on the inert gas; for example, it may be at least one of inert gases such as argon and nitrogen.

[0062] In some embodiments of this application, the processing temperature of the second carbonization treatment is 1250℃ to 1350℃, for example, 1250℃, 1300℃, or 1350℃; the heating rate is 1℃ / min to 3℃ / min, for example, 1℃ / min, 2℃ / min, or 3℃ / min; and the holding time is 3h to 5h, for example, 3h, 4h, or 5h. By adjusting the above parameters of the second carbonization treatment within the scope of this application, it is beneficial to obtain the hard carbon material of this application.

[0063] In some embodiments of this application, the temperature of the second carbonization treatment is higher than that of the first carbonization treatment, and the heating rate of the second carbonization treatment is lower than that of the first carbonization treatment. This is because excessively rapid heating is not conducive to the formation of the pore structure of the soft carbon material coating layer, and it also leads to poor interfacial bonding between the soft carbon material and the hard carbon material, making it susceptible to damage during electrode fabrication and negatively impacting the cycle performance of the hard carbon composite material. Therefore, a higher second carbonization treatment temperature and a lower second carbonization treatment heating rate are beneficial for pore closure and reducing open pores, thus improving the sodium storage capacity of the hard carbon composite material.

[0064] In some embodiments of this application, in the second carbonization step, the mass ratio of soft carbon material to hard carbon material is 1:10 to 20, for example, a mass ratio of 1:10, 1:15 or 1:20, which is beneficial to improving the electrical conductivity of the hard carbon composite material.

[0065] The method for preparing hard carbon composite materials provided in this application is based on thermosetting resin and molten salt electrolytic etching. It has the advantages of wide availability of raw materials and simple preparation process. Furthermore, the prepared hard carbon composite material has excellent performance and low cost, thereby improving the reversible capacity, initial coulombic efficiency, rate performance and cycle stability of sodium-ion batteries while reducing the production cost of sodium-ion batteries.

[0066] This application also provides a negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer includes the hard carbon composite material described in any of the above embodiments, or includes the hard carbon composite material prepared by the preparation method described in any of the above embodiments.

[0067] The negative electrode material layer of this application can be disposed on one or both surfaces of the negative electrode current collector in the thickness direction. In this application, the negative electrode material layer is disposed on the surface of the negative electrode current collector; that is, the negative electrode material layer can be disposed on a portion of one surface of the negative electrode current collector, or it can be disposed on the entire surface of one surface of the negative electrode current collector. This application does not have any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application; for example, it can include, but is not limited to, copper foil, copper alloy foil, or aluminum foil. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application; for example, the thickness can be 4μm to 12μm. The thickness of the negative electrode material layer in this application can be 70μm to 200μm.

[0068] In this application, the negative electrode material layer may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, it may include at least one of acrylate, polyamide, polyimide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0069] This application also provides a sodium-ion battery, including the negative electrode sheet described in any of the above embodiments.

[0070] The sodium-ion battery of this application also includes a positive electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode and plays a role in isolation.

[0071] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet typically includes a positive current collector and a positive electrode material layer. The positive electrode material layer can be disposed on one surface or two surfaces in the thickness direction of the positive current collector. In this application, the positive electrode material layer is disposed on the surface of the positive current collector, that is, the positive electrode material layer can be disposed on a portion of a surface of the positive current collector or on the entire surface of a surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application, it can be, for example, including but not limited to aluminum foil, aluminum alloy foil, or copper foil. In this application, there is no particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application, for example, a thickness of 8μm to 13μm. The thickness of the positive electrode material layer in this application can be 150μm to 400μm.

[0072] In this application, the positive electrode material layer also includes a positive electrode material. This application does not have any particular restrictions on the positive electrode material, as long as it can achieve the purpose of this application. For example, it may include at least one of sodium nickel manganate, sodium nickel iron manganate, sodium iron sulfate, sodium vanadium phosphate, sodium copper iron manganate, sodium iron pyrophosphate, and sodium iron pyrophosphate.

[0073] In this application, the positive electrode material layer may further include a positive electrode conductive agent. This application does not impose any particular limitation on the positive electrode conductive agent, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, acetylene black, and graphene. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. In this application, the positive electrode material layer may further include a positive electrode binder. This application does not impose any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of fluorinated resins, polypropylene resins, fiber-type binders, rubber-type binders, or polyimide-type binders.

[0074] This application does not impose any particular restrictions on the diaphragm; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the diaphragm material can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular restrictions. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular restrictions.

[0075] The sodium-ion battery of this application also includes an electrolyte. This application does not impose any particular limitation on the electrolyte; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), or fluoroethylene carbonate (FEC) can be mixed in a certain mass or volume ratio to obtain a non-aqueous organic solvent, and then a sodium salt can be added to dissolve and mix evenly. This application does not limit the type of sodium salt, as long as the purpose of this application is achieved. For example, the sodium salt may include at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium p-toluenesulfonate. This application does not impose any particular limitation on the concentration of the sodium salt in the electrolyte, as long as the purpose of this application is achieved. For example, the concentration of the sodium salt is 1.0 mol / L to 2.0 mol / L.

[0076] The sodium-ion battery of this application also includes a casing. This application does not impose any particular limitations on the casing, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the casing may include an aluminum-plastic film.

[0077] This application does not impose any particular limitation on the preparation method of sodium-ion batteries. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of sodium-ion batteries includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and winding and folding them as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a sodium-ion battery.

[0078] This application also provides an energy storage device, including a housing and at least one sodium-ion battery as described in any of the above embodiments, the sodium-ion battery being housed within the housing. The energy storage device with this sodium-ion battery exhibits excellent performance, which is beneficial for its use. Housed within the housing, the sodium-ion battery is secured and protected, thus extending the lifespan of the energy storage device. It is understood that the energy storage device may contain one or more sodium-ion batteries, and when the energy storage device contains multiple sodium-ion batteries, the multiple sodium-ion batteries can be connected in at least one manner, such as parallel or series connection.

[0079] This application also provides an electrical device including the energy storage device in any of the above embodiments, which is beneficial to improving the product competitiveness and performance of the electrical device. In an optional embodiment, the electrical device includes an electrical device body, and the energy storage device is used to supply power to the electrical device body. In an optional embodiment, the electrical device body includes a positive electrode and a negative electrode, the positive electrode of the sodium-ion battery in the energy storage device is used to electrically connect to the positive electrode of the electrical device body, and the negative electrode of the sodium-ion battery in the energy storage device is used to electrically connect to the negative electrode of the electrical device body, so as to supply power to the electrical device.

[0080] The electrical equipment covered by this application may include, but is not limited to: containers, household energy storage systems, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0081] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application, and this application... Figure 2 The implementation plan is illustrated using the residential energy storage scenario in user-side energy storage as an example. The energy storage device in this application is not limited to the residential energy storage scenario.

[0082] This application provides a residential energy storage system, which includes a power conversion device 2 (photovoltaic panel), a first user load 3 (streetlight), a second user load 4 (e.g., household appliances such as air conditioners), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 1 is used to store this electrical energy and supply it to streetlights and household appliances during periods of high electricity prices, or to provide power during power outages / power failures.

[0083] Please see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 400 according to one embodiment of this application, and this application Figure 3 The implementation plan is illustrated using the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1 in this application is not limited to the power generation / distribution side energy storage scenario.

[0084] This application provides an energy storage system 400, which includes a high-voltage cable 410, a first power conversion device 420, a second power conversion device 430, and the energy storage device 1 provided in this application. During power generation, the first power conversion device 420 and the second power conversion device 430 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable 410 and supplied to the power consumption side of the distribution network. When the power load is low and the first power conversion device 420 and the second power conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1, along with the high-voltage cable 410, in a grid-connected mode to supply power to the power consumption side. This provides various services such as peak shaving, frequency regulation, and backup for the power grid operation, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0085] Optionally, the first power conversion device 420 and the second power conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0086] The number of energy storage devices 1 can be multiple, and these devices can be connected in series or in parallel. The multiple energy storage devices 1 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" refers to two or more. An energy storage box can also be provided outside the energy storage device 1 to house it.

[0087] Optionally, the energy storage device 1 may include, but is not limited to, battery modules, battery packs, and battery systems. The battery module may be a battery module formed by connecting multiple sodium-ion batteries of this application in series or parallel; the battery pack may be a battery pack formed by connecting multiple sodium-ion batteries of this application in series or parallel; and the battery system may be a charging and discharging system including the battery modules or battery packs of this application. The actual application form of the energy storage device 1 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 1. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 1 includes a single cell battery, the energy storage device 1 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0088] Example

[0089] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0090] Example 1

[0091] <Preparation of spherical thermosetting resins>

[0092] Phenolic resin powder was dispersed in deionized water to prepare a 3wt% phenolic resin dispersion, which was then spray-dried at an inlet temperature of 150℃, a feed rate of 30mL / min, and an outlet temperature of 100℃. The mixture was then cured at 150℃ for 20h to obtain spherical phenolic resin.

[0093] <First Carbonization Process>

[0094] Under an argon atmosphere, 50g of the obtained spherical phenolic resin was placed in a tube furnace for the first carbonization treatment: the temperature was increased to 700℃ at a heating rate of 5℃ / min, and then held for 2h to obtain spherical precursor material.

[0095] Electrolytic Etching

[0096] 30g of precursor material was pressed into a 0.2cm thick sheet as the electrolytic anode. An alumina crucible was used as the reaction vessel, analytical grade anhydrous sodium carbonate as the electrolyte, and argon (99.9% purity) as the protective gas. A graphite carbon rod (99.9% purity) was used as the electrolytic cathode. The precursor material was electrolyzed at 3.5V for 10 minutes at 860℃. The product obtained after electrolysis was removed, soaked and rinsed with deionized water to remove residual molten salt, and then dried at 50℃ for 24 hours to obtain hard carbon material.

[0097] <Second carbonization treatment>

[0098] The obtained hard carbon material was ball-milled and depolymerized. After passing through a 400-mesh sieve, 20g of hard carbon material was ball-milled and mixed with 2g of asphalt and 10g of ethanol (the mass ratio of asphalt to hard carbon material was 1:10). After drying, it was placed in a tube furnace under an argon atmosphere for a second carbonization treatment: the temperature was raised to 1300℃ at a heating rate of 2℃ / min, and then held for 4h to obtain the hard carbon composite material.

[0099] Examples 2 to 5

[0100] Except for adjusting the relevant process parameters of electrolytic etching according to Table 1 in <Electrolytic Etching>, the rest is the same as in Example 1.

[0101] Examples 6 to 7

[0102] Except for adjusting the relevant process parameters of the first carbonization treatment according to Table 1 in the <First Carbonization Treatment>, the rest is the same as in Example 1.

[0103] Examples 8 to 11

[0104] Except for adjusting the relevant process parameters and the mass ratio of soft carbon to hard carbon materials according to Table 1 in the <Second Carbonization Process>, the rest is the same as in Example 1.

[0105] Comparative Examples 1 to 4

[0106] Except for adjusting the relevant process parameters of electrolytic etching according to Table 1 in <Electrolytic Etching>, the rest is the same as in Example 1.

[0107] Comparative Example 5

[0108] Except for not electrolytically etching the precursor material, i.e., directly using the precursor material mixed with asphalt to prepare the hard carbon composite material, everything else is the same as in Example 1.

[0109] Comparative Example 6

[0110] Except for not coating the hard carbon material with asphalt, that is, directly using the hard carbon material obtained after electrolytic etching as a hard carbon composite material, everything else is the same as in Example 1.

[0111] Table 1. Preparation parameters of hard carbon composite materials for each embodiment and comparative example.

[0112]

[0113]

[0114] In Table 1, " / " indicates that the relevant preparation parameters are not included.

[0115] Test methods and equipment:

[0116] Tests on specific surface area, tap density, interlayer spacing, and particle size D50 of hard carbon composite materials:

[0117] The test was conducted according to the test methods in the national standard GB / T 24533 2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0118] Electrical conductivity testing of hard carbon composite materials:

[0119] The four-probe method was used, with the four probes of the resistivity meter in contact with the hard carbon composite powder sample. Current and voltage were measured, and the resistivity of the powder under different pressures was calculated. Conductivity = 1 / resistivity, with units of S / cm. The conductivity data in Table 2 are all test results at a pressure of 25 MPa.

[0120] Table 2. Physicochemical parameters of hard carbon composite materials in each embodiment and comparative example.

[0121]

[0122]

[0123] Button cell battery performance test:

[0124] To test the effectiveness of the hard carbon composite material described in the above embodiments and comparative examples in sodium-ion battery materials, this application prepared a 2032-type coin cell by using the hard carbon composite material as the negative electrode of a half-cell, and tested and evaluated its effectiveness. In practical applications, this hard carbon composite material can be used as the negative electrode material for sodium-ion batteries.

[0125] The method for manufacturing button cells includes the following steps:

[0126] Preparation of the negative electrode sheet: The hard carbon composite material, carboxymethyl cellulose (CMC) thickener, conductive carbon black (Super-P) conductive agent, and styrene-butadiene rubber (SBR) binder prepared in the various examples and comparative examples were mixed in a mass ratio of 95:2:1.5:1.5. Deionized water was added and the mixture was stirred evenly to obtain a negative electrode slurry with a solid content of 30%. The negative electrode slurry was uniformly coated on one surface of a copper foil, and then vacuum dried. After rolling and stamping, a circular negative electrode sheet was obtained.

[0127] Electrolyte preparation: In an argon-atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1. Then, sodium salt NaPF6 was added and dissolved in the solvent. After thorough mixing, the electrolyte was obtained. The molar concentration of NaPF6 in the electrolyte was 1 mol / L.

[0128] Assembly of coin cell: The circular sodium sheet, the separator (glass fiber membrane with a thickness of 260μm), and the circular negative electrode sheet prepared above are stacked in sequence, with the separator positioned between the circular sodium sheet and the negative electrode sheet to act as a separator. Then, the prepared electrolyte is injected to assemble the coin cell.

[0129] After the assembled button cells were left to stand for 12 hours, the following charge and discharge tests were performed using a Blue Battery testing system (model CT2001A):

[0130] Reversible capacity, discharge capacity and first-efficiency testing:

[0131] The test temperature was 25℃. After standing for 10 minutes, the battery was discharged at a constant current of 0.1 times (C) to 0.005V, and then discharged at a constant current of 0.05C to 0.005V. After standing for 10 minutes, this was the discharge stage. The battery was then charged at a constant current of 0.1C to 2V, which was the charging stage. The initial efficiency was calculated as: (charge capacity during charging stage / discharge capacity during discharging stage) × 100%.

[0132] Ratio performance test:

[0133] The test temperature was 25℃. The coin cell was discharged at 0.1C to 0.005V; then discharged at 0.05C to 0.005V; after resting for 10 minutes, it was charged at a constant current of 0.1C to 2V; after resting for 10 minutes, the coin cell was discharged at 0.1C to 0.005V; after resting for 10 minutes, it was charged at a constant current of 0.1C to 2V. The capacity obtained in this step is the 0.1C discharge capacity, denoted as C1. After resting for 10 minutes, the coin cell was discharged at 3C to 0.005V; after resting for 10 minutes, it was charged at a constant current of 0.1C to 2V. The capacity obtained in this step is the 3C discharge capacity, denoted as C2. Rate performance = (discharge capacity C2 / discharge capacity C1) × 100%.

[0134] Cyclic performance test:

[0135] The test temperature was 25℃. The coin cell battery was discharged at 0.2C to 0.005V, allowed to stand for 10 minutes, and then charged at a constant current of 0.2C to 2V. The capacity obtained in this step was taken as the initial discharge capacity C0. A 0.2C charge / discharge cycle test was performed 200 times, and the discharge capacity of the 200th cycle was recorded. Cycle capacity retention rate = (Discharge capacity of the 200th cycle / Initial discharge capacity C0) × 100%.

[0136] Table 3 Performance parameters of the button cells in each embodiment and comparative example

[0137]

[0138] Combining Tables 2 and 3, it can be seen from Examples 1-5 and Comparative Examples 1-6 that when the electrolytic etching voltage is too low (e.g., Comparative Example 1), the interlayer spacing of the hard carbon composite material is small, resulting in low sodium storage capacity and affecting the reversible capacity, rate performance, and cycle performance of the sodium-ion battery. When the electrolytic etching voltage is too high (e.g., Comparative Example 2), the initial efficiency, rate performance, and cycle performance of the sodium-ion battery are low. This may be because excessively high voltage leads to too many defects in the hard carbon composite material, forming too many openings, resulting in an excessively large specific surface area of ​​the hard carbon composite material. Even after subsequent asphalt coating and second carbonization treatment, a large number of pores cannot be closed. The hard carbon composite material will consume too much electrolyte during battery cycling, which is not conducive to improving the performance of the sodium-ion battery. When the electrolytic etching time is too short (e.g., Comparative Example 3), the interlayer spacing of the hard carbon composite material is small, resulting in low sodium storage capacity and affecting the reversible capacity, rate performance, and cycle performance of the sodium-ion battery. When the electrolytic etching time is too long (e.g., Comparative Example 3), the interlayer spacing of the hard carbon composite material is small, resulting in low sodium storage capacity and affecting the reversible capacity, rate performance, and cycle performance of the sodium-ion battery. As in Comparative Example 4), the initial efficiency, rate performance, and cycle performance of the sodium-ion battery are relatively low. This may be because excessively long electrolytic etching time leads to too many defects in the hard carbon composite material, which is detrimental to improving the performance of the sodium-ion battery. When electrolytic etching is not performed (e.g., Comparative Example 5), the reversible capacity, rate performance, and cycle performance of the sodium-ion battery are relatively low. This may be because this hard carbon composite material does not have a sponge-like three-dimensional network porous structure, resulting in smaller interlayer spacing, fewer defects, fewer sodium storage active sites, and the inability to form a three-dimensional network current path inside the hard carbon composite material, leading to a lower sodium storage capacity and a worse rate performance of the sodium-ion battery. When the hard carbon material is not coated with soft carbon (e.g., Comparative Example 6), the initial efficiency, rate performance, and cycle performance of the sodium-ion battery are relatively low. This may be because this hard carbon material does not have the core-shell structure of this application, and a large number of pores are not closed, which will consume too much electrolyte during cycling, resulting in a lower initial efficiency and a worse cycle performance of the hard carbon material. The hard carbon composite material of this application forms a sponge-like three-dimensional network porous structure through the electrolytic etching process of this application, and has a coating layer formed by soft carbon material. Under the combined effect of the two, the conductivity and other properties of the hard carbon composite material are significantly improved, which significantly improves the reversible capacity, initial coulombic efficiency, rate performance and cycle stability of sodium-ion batteries.

[0139] The processing temperature and holding time of the first carbonization treatment, the processing temperature and holding time of the second carbonization treatment, and the mass ratio of soft carbon to hard carbon materials during coating also typically affect the performance of hard carbon composite materials. As can be seen from Examples 1 and 6-11, based on the structure of the hard carbon composite material in this application, by adjusting the above parameters within the range of this application, the conductivity and other properties of the hard carbon composite material are significantly improved. The resulting sodium-ion battery exhibits good reversible capacity, initial coulombic efficiency, rate performance, and cycle stability.

[0140] The above provides a detailed description of a hard carbon composite material, its preparation method, negative electrode sheet, and sodium-ion battery disclosed in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A hard carbon composite material, characterized in that, The hard carbon composite material includes spherical hard carbon material, the surface of which has a coating layer formed of soft carbon material; The hard carbon material has a three-dimensional network porous structure, and the interlayer spacing of the hard carbon composite material is 0.390 nm to 0.402 nm. The hard carbon material is formed by etching a precursor material by molten salt electrolysis, and the precursor material is formed by carbonizing a spherical thermosetting resin.

2. The hard carbon composite material according to claim 1, characterized in that, The specific surface area of ​​the hard carbon composite material is 3m². 2 / g~4m 2 / g.

3. The hard carbon composite material according to claim 1, characterized in that, The tap density of the hard carbon composite material is 0.75 g / cm³. 3 ~0.85g / cm 3 .

4. The hard carbon composite material according to claim 1, characterized in that, The hard carbon material is the core layer of the hard carbon composite material, the diameter of the core layer is 0.2 μm to 16 μm, and the thickness of the coating layer is 0.01 μm to 0.2 μm.

5. The hard carbon composite material according to claim 1, characterized in that, The thermosetting resin includes at least one of phenolic resin, epoxy resin, and phenolic epoxy resin.

6. A method for preparing a hard carbon composite material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Preparation of spherical thermosetting resin: Spherical thermosetting resin was prepared by spray drying method; First carbonization treatment: The spherical thermosetting resin is subjected to a first carbonization treatment under an inert gas atmosphere to obtain a spherical precursor material; Electrolytic etching: The precursor material is pressed into a sheet and used as the electrolytic anode. Electrolytic etching is performed at a voltage of 3V to 4V for 10 to 15 minutes to obtain the hard carbon material. Second carbonization treatment: The soft carbon material is mixed with the hard carbon material and then subjected to a second carbonization treatment under an inert gas atmosphere to obtain the hard carbon composite material.

7. The preparation method according to claim 6, characterized in that, The inlet air temperature for spray drying is 150℃~180℃, the feed rate is 20mL / min~50mL / min, and the outlet air temperature is 80℃~110℃.

8. The preparation method according to claim 6, characterized in that, The temperature of the first carbonization treatment is 700℃~900℃, the heating rate is 3℃ / min~7℃ / min, and the holding time is 1h~3h.

9. The preparation method according to claim 6, characterized in that, The reaction vessel for the electrolytic etching is a corundum crucible, the electrolyte is anhydrous sodium carbonate, the gas atmosphere is an inert gas, and the electrolytic cathode is a graphite carbon rod.

10. The preparation method according to claim 6, characterized in that, The second carbonization treatment is carried out at a temperature of 1250℃~1350℃, with a heating rate of 1℃ / min~3℃ / min and a holding time of 3h~5h.

11. The preparation method according to claim 6, characterized in that, In the second carbonization process, the mass ratio of the soft carbon material to the hard carbon material is 1:10 to 20.

12. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes a hard carbon composite material as described in any one of claims 1 to 5, or includes a hard carbon composite material prepared by the preparation method as described in any one of claims 6 to 11.

13. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 12.

14. An energy storage device, characterized in that, It includes a housing and at least one sodium-ion battery as described in claim 13, the sodium-ion battery being housed within the housing.

15. An electrical appliance, characterized in that, The device includes the energy storage device of claim 14, which supplies power to the electrical equipment.

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