Sodium replenishment material and preparation method therefor, positive electrode sheet and sodium ion battery

Abstract

Provided in the present application are a sodium replenishment material and a preparation method therefor, a positive electrode sheet and a sodium ion battery. The sodium replenishment material comprises a sodium replenishment agent body and a conductive carbon material, wherein the conductive carbon material comprises a first conductive portion and a second conductive portion connected to each other, the first conductive portion is located inside the sodium replenishment agent body, and the second conductive portion is exposed on the outer surface of the sodium replenishment agent body.

Description

Sodium-supplementing materials and their preparation methods, positive electrode sheets, sodium-ion batteries

[0001] Related cross-references

[0002] This application claims priority to Chinese Patent Application No. 202410916936.2, filed on July 9, 2024, entitled “Sodium Supplement Material and Preparation Method Thereof, Positive Electrode Sheet, Sodium-ion Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electrochemical technology, and in particular to a sodium-supplementing material and its preparation method, a positive electrode sheet, and a sodium-ion battery. Background Technology

[0004] Sodium-ion batteries, with their advantages of low cost, abundant sodium resources, and relatively high energy density, are expected to replace traditional lithium-ion batteries in the field of energy storage.

[0005] Adding sodium to the positive electrode using a sodium replenisher can reduce the adverse effects of sodium loss on the electrochemical performance of sodium-ion batteries. Organic sodium replenishers are environmentally friendly, low-cost, and non-toxic; however, the oxidation decomposition potential of existing organic sodium replenishers still needs improvement, which means that the cycle performance of sodium-ion secondary batteries still needs to be improved. Summary of the Invention

[0006] To address the aforementioned technical problems, this application discloses a sodium-replenishing material and its preparation method, a positive electrode sheet, and a sodium-ion battery, in order to improve the sodium-replenishing effect of the sodium-replenishing material and thereby improve the cycle performance of the sodium-ion battery.

[0007] In a first aspect, this application provides a sodium supplement material, comprising a sodium supplement body and a conductive carbon material, wherein the conductive carbon material comprises a first conductive portion and a second conductive portion connected together, the first conductive portion being located inside the sodium supplement body, and the second conductive portion being exposed on the outer surface of the sodium supplement body.

[0008] Secondly, this application provides a method for preparing the sodium-supplementing material as described in the first aspect, comprising the following steps:

[0009] Dissolve the sodium supplement in water to obtain a supersaturated solution of the sodium supplement;

[0010] An acidified conductive carbon material is added to an organic solvent to obtain a dispersion.

[0011] The supersaturated solution is added to the dispersion, and after stirring, the sodium supplement agent generates crystal nuclei around the polar functional groups of the acidified conductive carbon material for recrystallization, thus forming the sodium supplement material.

[0012] Thirdly, this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a sodium-supplementing material as described in the first aspect, or includes a sodium-supplementing material prepared by the preparation method described in the second aspect.

[0013] Fourthly, this application provides a sodium-ion battery, the sodium-ion battery comprising the positive electrode sheet described in the third aspect.

[0014] 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.

[0015] 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.

[0016] Compared with the prior art, this application has at least the following beneficial effects:

[0017] This application provides a sodium-replenishing material and its preparation method, a positive electrode sheet, and a sodium-ion battery. The sodium-replenishing material includes a sodium-replenishing agent body and a conductive carbon material. The conductive carbon material includes a first conductive portion and a second conductive portion connected together. The first conductive portion is located inside the sodium-replenishing agent body, and the second conductive portion is exposed on the outer surface of the sodium-replenishing agent body. With the above structural features, the second conductive portion of the conductive carbon material can serve as an electron transport channel, transferring external electrons to the connected first conductive portion. This promotes the transfer of external electrons into the sodium-replenishing material, accelerating the oxidative decomposition process of the sodium-replenishing agent body. This results in a lower oxidative decomposition potential for the sodium-replenishing material, thereby improving the initial sodium-replenishing effect and increasing the energy density and cycle performance of the sodium-ion battery. Attached Figure Description

[0018] 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.

[0019] Figure 1 is a cross-sectional structural diagram of a sodium supplement material according to one embodiment of this application;

[0020] Figure 2 is a cross-sectional structural diagram of a sodium supplement material according to another embodiment of this application;

[0021] Figure 3 is a structural schematic diagram of a residential energy storage system according to one embodiment of this application;

[0022] Figure 4 is a schematic diagram of the structure of an energy storage system according to one embodiment of this application;

[0023] Figure 5 is a scanning electron microscope (SEM) image of the sodium supplement material prepared in Example 10;

[0024] Figure 6 shows the SEM image of the sodium supplement material prepared in Comparative Example 1;

[0025] Figure 7 is a schematic diagram of the first charge-discharge curve of the first button cell in Example 10;

[0026] Figure 8 is a schematic diagram of the first charge-discharge curve of the first button cell in Comparative Example 3.

[0027] Figure 9 is a schematic diagram of the first charge-discharge curve of the second button cell in Example 10;

[0028] Figure 10 is a schematic diagram of the first charge-discharge curve of the second button cell in Comparative Example 3.

[0029] 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-Sodium supplement body, 20-Conductive carbon material, 201-First conductive part, 202-Second conductive part, 400-Energy storage system, 410-High voltage cable, 420-First electric power conversion device, 430-Second electric power conversion device. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] It should be noted that this application uses sodium-ion batteries as an example of secondary batteries to explain the application, but the secondary batteries in this application are not limited to sodium-ion batteries.

[0036] Organic sodium supplements are environmentally friendly, low-cost, and non-toxic; however, they still suffer from low electronic conductivity and high oxidation potential. Current modification methods typically involve directly adding conductive agents to improve the electronic conductivity of the sodium supplement material. The sodium supplement and the conductive material (e.g., conductive carbon black) are connected only through a simple physical mixing process. When this sodium supplement is added to the cathode material, the sodium supplement and the conductive agent separate, with the conductive agent dispersing within the cathode material. This significantly affects the effective utilization rate of the conductive material and limits the actual sodium supplementation effect.

[0037] In view of this, this application provides a sodium supplement material. Figure 1 is a cross-sectional structural diagram of the sodium supplement material according to one embodiment of this application, and Figure 2 is a cross-sectional structural diagram of the sodium supplement material according to another embodiment of this application. Referring to Figures 1 and 2, the sodium supplement material includes a sodium supplement body 10 and a conductive carbon material 20. The conductive carbon material 20 includes a first conductive portion 201 and a second conductive portion 202 connected together. The first conductive portion 201 is located inside the sodium supplement body 10, and the second conductive portion 202 is exposed on the outer surface of the sodium supplement body 10. That is, the conductive carbon material 20 does not completely cover the sodium supplement body 10. The second conductive portion 202 can serve as an electron transport channel, transmitting external electrons through the connected first conductive portion 201 to the sodium replenishment body 10, thereby promoting the transfer of external electrons to the sodium replenishment material. This facilitates the acceleration of the oxidative decomposition process of the sodium replenishment material, resulting in a lower oxidative decomposition potential for the sodium replenishment material. During the first charge of the sodium-ion battery, the sodium replenishment material releases additional sodium ions to compensate for the sodium ion loss caused by the formation of the negative electrode region SEI (Solid Electrolyte Interphase) and other side reactions, thereby improving the first-cycle sodium replenishment effect of the sodium replenishment material and enhancing the energy density and cycle performance of the sodium-ion battery.

[0038] In some embodiments of this application, the average number of second conductive portions in any 1600nm×1200nm region of the sodium-supplementing material SEM image is 1 to 20. For example, the average number of second conductive portions is 1, 2, 3, 5, 7, 9, 10, 12, 14, 15, 16, 18, or 20.

[0039] In this application, the sodium-supplementing material can be observed using a scanning electron microscope at a magnification of 10k to 60k to obtain an SEM image of the sodium-supplementing material. The 1600nm × 1200nm region can be any pre-selected region in the SEM image of the sodium-supplementing material; for example, it can be a rectangular region of 1600nm × 1200nm. When the selected region has the aforementioned number of second conductive portions, it is advantageous to utilize a sufficient number of second conductive portions to transfer external electrons into the sodium-supplementing material, thereby reducing the oxidative decomposition potential of the sodium-supplementing material.

[0040] In some embodiments of this application, the mass percentage of the sodium-supplementing agent is 60% to 90%, and the mass percentage of the conductive carbon material is 10% to 40%, based on the mass of the sodium-supplementing material. For example, the mass percentage of the sodium-supplementing agent is 60%, 70%, 80%, or 90%, and the mass percentage of the conductive carbon material is 10%, 20%, 30%, or 40%. By controlling the content of the sodium-supplementing agent and the conductive carbon material in the sodium-supplementing material within the above ranges, it is beneficial to control the amount of conductive carbon material portion (i.e., the second conductive portion) exposed on the surface of the sodium-supplementing agent body within the scope of this application, thereby forming a sodium-supplementing material having the structure of this application.

[0041] In some embodiments of this application, the D50 of the sodium-supplementing material is 0.8 μm to 1.8 μm. For example, the average particle size D50 of the sodium-supplementing material is 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.5 μm, 1.7 μm, or 1.8 μm. The average particle size D50 of the sodium-supplementing material represents the particle size corresponding to a cumulative particle size distribution percentage of 50%. By controlling the D50 of the sodium-supplementing material within the above range, the electron transport distance between the sodium-supplementing material particles can be effectively shortened, further promoting the oxidative decomposition process of the sodium-supplementing agent and facilitating the reduction of the oxidative decomposition potential of the sodium-supplementing material.

[0042] In some embodiments of this application, the sodium-supplementing material contains polar groups, including at least one of carboxyl and hydroxyl groups. These polar groups can be introduced from an acidified conductive carbon material. During the preparation of the sodium-supplementing material of this application, the polar functional groups such as carboxyl and hydroxyl groups in the acidified conductive carbon material adsorb sodium ions from the supersaturated solution and serve as nuclei in the subsequent recrystallization process, accelerating the recrystallization of the sodium-supplementing agent on the surface of the acidified conductive carbon material, which is beneficial for forming a sodium-supplementing material with the structure of this application. Furthermore, the presence of these polar functional groups also increases the number of recrystallization nucleation sites for the sodium-supplementing agent, thereby reducing the particle size of the sodium-supplementing material.

[0043] In some embodiments of this application, the conductive carbon material includes at least one of carbon nanotubes, carboxylated graphene, and graphene oxide, and the above-mentioned conductive carbon material has excellent electrical conductivity.

[0044] In some embodiments of this application, the carbon nanotube includes a first conductive segment and a second conductive segment connected together. The first conductive segment is located inside the sodium supplement body, and the second conductive segment is exposed outside the sodium supplement body. Although the carbon nanotube itself can improve the electronic conductivity of the sodium supplement material, the sodium supplement material with the structure of this application is different from a simple physical mixture of sodium supplement and conductive carbon material. Through the combined action of the first and second conductive segments connected together in the carbon nanotube, the exposed second conductive segment acts as an electronic conductor, and the first conductive segment deep inside the sodium supplement body acts as an electronic transport channel. This allows electrons to effectively reach the interior of the sodium supplement body, shortening the electronic transport distance between the conductive carbon material and the interior of the sodium supplement body. This promotes the stereochemical decomposition of the sodium supplement body, that is, the sodium supplement decomposes in a stereochemical decomposition form with simultaneous surface and interior decomposition. This decomposition form gives the sodium supplement material a lower oxidation decomposition potential, thereby improving the initial sodium supplementation effect of the sodium supplement material.

[0045] In some embodiments of this application, the sodium supplement is selected from at least one of Na₂C₄O₄, Na₂CO₃, CH₃COONa, C₆H₅Na₃O₇, Na₂C₂O₄, and Na₂C₆O₆. The above-mentioned sodium supplement is an organic sodium supplement, which has the advantages of being environmentally friendly, widely available, and safe and non-toxic.

[0046] It is understandable that the content of sodium supplementing agent and conductive carbon material in sodium supplementing materials is usually affected by the addition ratio of these two raw materials. Based on this, this application can control the content of sodium supplementing agent and conductive carbon material in sodium supplementing materials by adjusting the addition ratio of the raw materials.

[0047] Secondly, this application provides a method for preparing the sodium-supplementing material as described in the first aspect, comprising the following steps:

[0048] Step A: Dissolve the sodium supplement in water to obtain a supersaturated solution of the sodium supplement;

[0049] Step B: Add the acidified conductive carbon material to an organic solvent to obtain a dispersion;

[0050] Step C: Add the supersaturated solution to the dispersion. After stirring, the sodium supplement agent generates crystal nuclei around the polar functional groups of the acidified conductive carbon material and recrystallizes to form the sodium supplement material.

[0051] In step A, the sodium supplement can be a commercially available sodium supplement, but commercially available sodium supplements have the drawback of having a relatively large particle size. This application can first obtain a supersaturated solution of the sodium supplement to facilitate particle size control in subsequent steps. The water used in this application can be deionized water, pure water, distilled water, etc.

[0052] In step B, the acidified conductive carbon material includes, but is not limited to, acidified carbon nanotubes and acidified graphene oxide, preferably acidified carbon nanotubes. The acidified conductive carbon material possesses abundant polar functional groups. The acidified conductive carbon material of this application can be commercially available or prepared by the following methods:

[0053] Conductive carbon material is added to an acid solution to generate polar functional groups such as carboxyl and hydroxyl groups in the conductive carbon material. After stirring for 120 minutes, the material is filtered, washed, and dried to obtain acidified conductive carbon material. The acid solution includes, but is not limited to, a sulfuric acid solution with a mass concentration of 80%–98%, or a nitric acid solution with a mass concentration of 68%–98%, or a mixture of both.

[0054] In step C, after the supersaturated solution is added to the dispersion, on the one hand, the sodium supplement is more likely to precipitate under the driving force of supersaturation; on the other hand, the polar functional groups in the acidified conductive carbon material adsorb sodium ions in the supersaturated solution and serve as crystal nuclei in the subsequent recrystallization process, promoting the sodium supplement to generate more crystal nuclei around the polar functional groups of the acidified conductive carbon material for recrystallization. Based on these crystal nuclei, in-situ growth is carried out to form a sodium supplement material with the structure of this application, that is, a structure in which the sodium supplement body partially covers the conductive carbon material is formed.

[0055] In step C, the stirring time is 0.5 h to 3 h, which is conducive to the formation of sodium supplement material precipitate. After the sodium supplement material is formed, it exists in the liquid in the form of a precipitate. The sodium supplement material can be purified by post-processing steps such as filtration, washing, and drying, and the particle size of the sodium supplement material can be further controlled by processes such as crushing and sieving.

[0056] In some embodiments of this application, the dissolution temperature of the sodium supplement is 20℃~60℃, and the stirring time is 1h~4h. On the one hand, the dissolution temperature of the sodium supplement is controlled to regulate the supersaturation, and on the other hand, the stirring time is controlled. Thus, under the combined effect of the above process parameters, the particle size of the recrystallized particles is controlled, which is beneficial to obtaining a sodium supplement material with the particle size range of this application.

[0057] In some embodiments of this application, the organic solvent includes at least one selected from anhydrous ethanol, ethylene glycol, glycerol, diethyl ether, isopropanol, and acetone. These organic solvents are insoluble or only slightly soluble in the sodium supplement, thereby promoting the recrystallization and precipitation of the sodium supplement on the surface of the carbon material.

[0058] The method for preparing the sodium-replenishing material provided in this application is simple, uses non-toxic and safe raw materials, and produces a sodium-replenishing material with excellent sodium-replenishing performance and low cost. This improves the energy density and cycle performance of sodium-ion batteries while reducing their production cost. Furthermore, compared to sodium-replenishing materials obtained through simple physical mixing of the sodium-replenishing agent and conductive agent, the sodium-replenishing agent and conductive agent in this application do not separate, thus improving the effective utilization rate of the conductive material. Additionally, the coating structure formed by the sodium-replenishing material in this application is more uniform.

[0059] This application also provides a positive electrode sheet, including a current collector and a positive electrode active material layer disposed on at least one surface of the current collector. The positive electrode active material layer includes the sodium-supplementing material described in any of the above embodiments, or includes the sodium-supplementing material prepared by the preparation method described in any of the above embodiments.

[0060] The positive electrode active material layer of this application can be disposed on one or both surfaces of the positive electrode current collector in the thickness direction. In this application, the positive electrode active material layer is disposed on the surface of the positive electrode current collector; that is, the positive electrode active material layer can be disposed on a portion of one surface of the positive electrode current collector, or it can be disposed on the entire surface of one surface of the positive electrode current collector. This application does not have any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application; for example, it can be, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as it can achieve the purpose of this application; for example, a thickness of 8 μm to 13 μm. The thickness of the positive electrode active material layer in this application can be 150 μm to 400 μm.

[0061] In this application, the positive electrode active material layer also includes a positive electrode active material. This application does not have any particular restrictions on the positive electrode active 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 phosphate, and sodium iron pyrophosphate.

[0062] In this application, the positive electrode active 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 (CNT), Ketjen black (KB), graphene, graphene oxide, and acetylene black. The mass percentage of the conductive agent in the positive electrode active material layer is 10% to 40%. In this application, the positive electrode active 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 resin, polypropylene resin, fiber-type binder, rubber-type binder, polyimide-type binder, and polyvinylidene fluoride (PVDF).

[0063] This application also provides a sodium-ion battery, including the positive electrode sheet described in any of the above embodiments.

[0064] The sodium-ion battery of this application also includes a negative 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.

[0065] This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet typically includes a negative current collector and a negative active material layer. The negative active material layer can be disposed on the surface of the negative current collector; that is, the negative active material layer can be disposed on a portion of the surface of the negative current collector, or it can be disposed on the entire surface of the negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative current collector, as long as it achieves the purpose of this application, for example, a thickness of 4 μm to 12 μm. The thickness of the negative material layer in this application can be 70 μm to 200 μm.

[0066] In this application, the negative electrode active 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.

[0067] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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. Housing the battery within the housing increases its stability and protection, thereby 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.

[0072] 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.

[0073] 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.

[0074] Please refer to Figure 3, which is a structural schematic diagram of a residential energy storage system according to one embodiment of this application. The embodiment in Figure 3 is illustrated using a residential energy storage scenario in user-side energy storage as an example. The energy storage device in this application is not limited to residential energy storage scenarios.

[0075] 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.

[0076] Please refer to Figure 4, which is a structural schematic diagram of an energy storage system 400 according to one embodiment of this application. The embodiment in Figure 4 is illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 1 in this application is not limited to the energy storage scenario on the generation / distribution side.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Optionally, the energy storage device 1 may include, but is not limited to, a single cell, a battery module, a battery pack, and a battery system. A single cell may be a sodium-ion battery of this application; a battery module may be a battery module formed by connecting multiple sodium-ion batteries of this application in series or parallel; a battery pack may include multiple sodium-ion batteries of this application; and a battery system may be a charging and discharging system including sodium-ion batteries or a battery pack of this application.

[0081] The actual application of the energy storage device 1 provided in this application can be, but is not limited to, the listed products, and can also be other application forms. This application does not strictly limit the application form of the energy storage device 1. This application only uses a multi-cell battery as an example for illustration. When the energy storage device 1 is a single cell battery, the energy storage device 1 can be at least one of cylindrical batteries, prismatic batteries, etc.

[0082] Example

[0083] 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.

[0084] Example 1

[0085] <Preparation of Sodium-Supplying Material>

[0086] Add 36 g of commercially available sodium oxalate (Na2C4O4) powder, which is the sodium-supplying agent, into a beaker containing 80 mL of deionized water, stir for 30 min, with the dissolution temperature being 20 °C, to fully dissolve Na2C4O4 and obtain a supersaturated solution of the sodium-supplying agent; add 4 g of commercially available acidified carbon nanotubes (model: AMS11S carboxylated high-purity single-walled carbon nanotubes, product code: 31040122), which is the conductive carbon material, into a beaker containing 250 mL of absolute ethanol, and obtain a dispersion of acidified carbon nanotubes after ultrasonic dispersion for 30 min; add the supersaturated solution into the dispersion, stir for 1 h, and allow sodium oxalate to recrystallize with the acidified conductive carbon material as the crystal nucleus to form a precipitate; after filtering the obtained precipitate by suction, wash it 3 times with absolute ethanol, vacuum-dry the obtained product at 130 °C for 24 h, crush it with a crusher and sieve it to obtain the sodium-supplying material. The contents of the sodium-supplying agent and the conductive carbon material in the sodium-supplying material and the D50 of the sodium-supplying material are shown in Table 1.

[0087] Observe the prepared sodium-supplying material under a scanning electron microscope at a magnification of 10k - 60k to obtain the SEM image of the sodium-supplying material. In any 1600 nm × 1200 nm area (per unit area) in this SEM image, the average number of the second conductive parts is 3.

[0088] <Preparation of Sodium-Supplying Agent Electrode>

[0089] Mix the prepared sodium-supplying material, conductive agent Ketjenblack (KB), and binder PVDF in a mass ratio of 60:30:10, add the solvent N-methylpyrrolidone (NMP), and stir evenly to obtain a sodium-supplying agent slurry with a solid content of 60%. Then, evenly coat the sodium-supplying agent slurry on an aluminum foil with a thickness of 10 μm, with a single-sided coating thickness of 20 μm, and then vacuum-dry it at 110 °C for 12 h to obtain a sodium-supplying agent electrode. Cut the obtained sodium-supplying agent electrode into circular pieces with a diameter of 14 μm for standby. [[ID=##]] [[ID=##]]

[0090] <Preparation of NFPP Positive Electrode>

[0091] Mix the positive active material Na4Fe3(PO4)2(P2O7) (i.e., NFPP), the prepared sodium-supplying material, conductive agent Ketjenblack, and binder PVDF in a mass ratio of 60:20:10:10, then add NMP and stir evenly to obtain a positive electrode slurry with a solid content of 60%. Then, evenly coat the positive electrode slurry on an aluminum foil with a thickness of 10 μm, with a single-sided coating thickness of 20 μm, and then vacuum-dry it at 110 °C for 12 h to obtain an NFPP positive electrode. Cut the obtained NFPP positive electrode into circular pieces with a diameter of 14 μm for standby.

[0092] <Preparation of Electrolyte>

[0093] 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 NaClO4 was added and dissolved in the solvent. After thorough mixing, an electrolyte was obtained. The molar concentration of NaClO4 in the electrolyte was 1 mol / L.

[0094] <Preparation of the diaphragm>

[0095] A glass fiber membrane with a thickness of 260μm was selected as the separator.

[0096] Assembly of button batteries

[0097] Assembly of the First Button Battery

[0098] Using a circular sodium sheet with a diameter of 14 μm as the counter electrode, the circular sodium supplement electrode, the separator, and the circular sodium sheet prepared above are stacked in sequence, with the separator positioned between the circular sodium supplement electrode and the circular sodium sheet to act as a separator. Then, the prepared electrolyte is injected to assemble the first coin cell.

[0099] Assembly of the second button cell battery

[0100] Using a circular sodium sheet with a diameter of 14 μm as the counter electrode, the NFPP positive electrode, the separator, and the circular sodium sheet prepared above are stacked in sequence, with the separator positioned between the NFPP positive electrode and the circular sodium sheet to act as a separator. Then, the prepared electrolyte is injected to assemble a second coin cell.

[0101] Examples 2 to 9

[0102] Except for adjusting the dissolution temperature and stirring time of the dispersion according to Table 1 in the <Preparation of Sodium Supplement Material>, the rest is the same as in Example 1.

[0103] Examples 10 to 12

[0104] Except for the section on "Preparation of Sodium Supplement Material", where the amounts of sodium supplementing agent and conductive carbon material added are adjusted to adjust the content of sodium supplementing agent and conductive carbon material in the sodium supplement material according to Table 1, the rest is the same as in Example 7.

[0105] Examples 13 to 16

[0106] Except for adjusting the types of sodium supplementing agent and conductive carbon material according to Table 1 in the <Preparation of Sodium Supplementing Material> section, the rest is the same as in Example 7.

[0107] Comparative Example 1

[0108] Except that it is different from Example 1 in the <Preparation of Sodium Supplementing Material>, the rest is the same as Example 1.

[0109] <Preparation of Sodium Supplementing Material>

[0110] Mix 36 g of commercially available sodium oxalate (Na2C4O4) powder with 4 g of commercially available acidified carbon nanotubes (model: AMS11S carboxylated high-purity single-walled carbon nanotubes, product code: 31040122) to obtain a mixture, and this mixture is directly used as the sodium supplementing material. The contents of the sodium supplementing agent and the conductive carbon material in the sodium supplementing material and the average particle size D50 of the sodium supplementing material are shown in Table 1.

[0111] Comparative Example 2

[0112] Add 40 g of commercially available sodium oxalate (Na2C4O4) powder to a beaker containing 80 mL of deionized water, stir for 30 min, and the dissolution temperature is 60 °C to fully dissolve Na2C4O4 to obtain a supersaturated solution of the sodium supplementing agent; add the supersaturated solution to the dispersion liquid, stir for 1 h to allow sodium oxalate to recrystallize and form a precipitate; after filtering the obtained precipitate by suction, wash it 3 times with absolute ethanol, and vacuum dry the obtained product at 130 °C for 24 h. After crushing and sieving by a crusher, a sodium supplementing material is obtained, and this sodium supplementing material does not contain conductive carbon material. The D50 of the sodium supplementing material is shown in Table 1.

[0113] Comparative Example 3

[0114] Except that in the <Preparation of Sodium Supplementing Material>, the dissolution temperature is adjusted to 20 °C, the rest is the same as Comparative Example 2.

[0115] Comparative Example 4

[0116] Except that the preparation of the sodium supplementing material is not carried out, that is, the first button cell is not prepared, and the NFPP positive electrode sheet does not contain the sodium supplementing material so that the obtained second button cell also does not contain the sodium supplementing material, the rest is the same as Example 1.

[0117] <Preparation of NFPP Positive Electrode Sheet>

[0118] Mix the positive electrode active material NFPP, Ketjenblack, and PVDF in a mass ratio of 80:10:10, then add NMP and stir evenly to obtain a positive electrode slurry with a solid content of 60%. Then, uniformly coat the positive electrode slurry on an aluminum foil with a thickness of 10 μm, and the single-sided coating thickness is 20 μm. Then, vacuum dry it at 110 °C for 12 h to obtain an NFPP positive electrode sheet. Cut the obtained NFPP positive electrode sheet into circular pieces with a diameter of 14 μm for use.

[0119] Testing methods and equipment:

[0120] Testing of the number of the second conductive parts in the sodium supplementing material:

[0121] The sodium-supplementing material was observed using a scanning electron microscope at a magnification of 10k to 60k to obtain SEM images of the sodium-supplementing material. Five arbitrary 1600nm×1200nm regions were selected from the SEM images, and the number of conductive materials exposed in the sodium-supplementing agent body in the selected regions was recorded. The average value was then taken as the number of second conductive parts per unit area.

[0122] Oxidative decomposition potential test:

[0123] The first charge-discharge test of the first coin cell was carried out using the LAND test system, and the dQ / dV curve was obtained. The oxidation peak of the dQ / dV curve corresponds to the oxidation decomposition reaction of the sodium supplement material, and the potential corresponding to the oxidation peak of the dQ / dV curve is the oxidation decomposition potential of the sodium supplement material.

[0124] Material particle size testing:

[0125] The average particle size D50 of the sodium-supplementing material was measured using a laser particle size analyzer.

[0126] First charge capacity and first discharge capacity test:

[0127] The test temperature was 25℃. The coin cell battery was charged at a constant current of 0.1C to 4.5V, which is the charging stage. After resting for 10 minutes, it was discharged at a constant current of 0.1C to 2V, and then rested for 10 minutes, which is the discharging stage. The charging capacity of the first charging stage was recorded as the first-cycle charging capacity, in mAh / g; the discharging capacity of the first discharging stage was also recorded as the first-cycle discharging capacity, in mAh / g.

[0128] Cyclic performance test:

[0129] The test temperature was 25℃. The coin cell battery was charged to 4V at a constant current of 0.1C, left to stand for 10 minutes, and then discharged to 2V at 0.1C. The capacity obtained in this step is the initial discharge capacity C. i Perform 20 cycles of 0.1C charge / 0.1C discharge, and record the discharge capacity on the 20th cycle. Cycle capacity retention = (Discharge capacity on the 20th cycle / Initial discharge capacity C) i )×100%.

[0130] Table 1. Preparation parameters for each embodiment and comparative example.

[0131] In Table 1, " / " indicates that no relevant preparation parameters exist.

[0132] Table 2 Performance data of the first button cell in each embodiment and comparative example

[0133] In Table 2, " / " indicates that no relevant test parameters exist.

[0134] As can be seen from Examples 1-16 and Comparative Examples 1-3, although Comparative Example 1 exhibits a lower oxidation decomposition potential, it is because Comparative Example 1 simply physically mixes sodium squartz and carbon nanotubes. When the positive electrode is formed, the sodium squartz and carbon nanotubes separate, with the carbon nanotubes dispersed in the positive electrode active material, affecting the effective utilization rate of the carbon nanotubes. This results in a high actual oxidation decomposition potential for sodium squartz. Therefore, the first-cycle charging capacity of the second coin cell in Comparative Example 1 is only 120.3 mAh / g (see Table 3). Due to the sodium supplementation materials in Comparative Examples 2 and 3... The sodium-supplementing material only underwent recrystallization treatment, did not contain conductive carbon materials, and did not have the sodium-supplementing material structure of this application. Therefore, its sodium-supplementing material had a high oxidation decomposition potential, and the first charge capacity of the first coin cell was also relatively low. Furthermore, even though Comparative Example 2 increased the dissolution temperature, its effect on reducing the oxidation decomposition potential of the sodium-supplementing material was very limited because it did not have the sodium-supplementing material structure of this application. In contrast, the sodium-supplementing material of this application has a low oxidation decomposition potential, and the first charge capacity of the first coin cell is significantly improved, indicating that the sodium-supplementing material with the structure of this application can effectively improve the first-cycle sodium-supplementing effect.

[0135] The dissolution temperature of the sodium supplement and the stirring time during recrystallization also typically affect the performance of the sodium supplement material. As can be seen from Examples 1-3, 4-6, and 7-9, by adjusting the above preparation parameters within the scope of this application, it is beneficial to obtain a sodium supplement material with the structure of this application, thereby facilitating the production of a sodium-ion battery with a high first-cycle charging capacity.

[0136] The type and content of sodium-supplementing agents, as well as the type and content of conductive agents, typically affect the performance of sodium-ion batteries. As can be seen from Examples 10 to 16, given that the sodium-supplementing material has the structure described in this application, adjusting the aforementioned parameters within the scope of this application is beneficial for obtaining sodium-ion batteries with high first-cycle charging capacity.

[0137] Examples 1 to 16 and Comparative Examples 1 and 3 also show that, under the premise that the sodium-supplementing material has the structure of this application, by adjusting the D50 of the sodium-supplementing material within the scope of this application, it is beneficial to obtain a sodium-ion battery with a high first-cycle charging capacity.

[0138] Figure 5 is a SEM image of the sodium supplement material prepared in Example 10. As can be seen from Figure 5, the linear structure exposed on the surface of the sodium supplement body is one part of the carbon nanotube (i.e., the second conductive segment), while the other part of the carbon nanotube (i.e., the first conductive segment) is embedded inside the sodium supplement body.

[0139] Figure 6 shows the SEM image of the sodium-supplementing material prepared in Comparative Example 1. As can be seen from Figure 6, only a small portion of the carbon nanotubes (linear structures in the figure) on the surface of the sodium-supplementing agent particles are dispersed, while most of them agglomerate. When this sodium-supplementing material is applied to a sodium-ion battery system, the carbon nanotubes will separate from the conductive material and disperse in the positive electrode active material, resulting in a decrease in the local electronic conductivity of the sodium-supplementing material surface and limiting the sodium-supplementing effect.

[0140] Figure 7 is a schematic diagram of the first charge-discharge curve of the first coin cell in Example 10. As can be seen from Figure 7, the oxidation decomposition potential of Example 10 is 4.09V. Figure 8 is a schematic diagram of the first charge-discharge curve of the first coin cell in Comparative Example 3. As can be seen from Figure 8, the oxidation decomposition potential of Comparative Example 3 is 4.22V. The comparison shows that the sodium-supplementing material of this application has a lower oxidation decomposition potential.

[0141] Table 3 Performance data of the second button cell in each embodiment and comparative example

[0142] Referring to Tables 1 and 3, it can be seen from Examples 1 and Comparative Examples 1 to 4 that when the sodium supplement and conductive carbon material are simply physically mixed (e.g., Comparative Example 1), or when the sodium supplement material contains only the sodium supplement and not the conductive carbon material (e.g., Comparative Examples 2 and 3), the sodium supplement material does not have the sodium supplement material structure of this application. Furthermore, when the positive electrode does not contain the sodium supplement material (e.g., Comparative Example 4), the first-cycle charging capacity and first-cycle discharging capacity of the prepared second coin cell are both low, resulting in low first-cycle coulombic efficiency, which is detrimental to the improvement of the energy density and cycle performance of the sodium-ion battery. In contrast, the first-cycle charging capacity and capacity retention rate after 20 cycles of the second coin cell of this application are improved, and the first-cycle discharging capacity is improved or close to the first cycle capacity, which is beneficial to the improvement of the energy density and cycle performance of the sodium-ion battery.

[0143] The dissolution temperature of the sodium supplement and the stirring time during recrystallization also typically affect the performance of the sodium supplement material. As can be seen from Examples 1-3, 4-6, and 7-9, by adjusting the above preparation parameters within the scope of this application, it is beneficial to obtain a sodium supplement material with the structure of this application, thereby facilitating the production of an NFPP sodium-ion battery with a high first-cycle charging capacity.

[0144] The type and content of sodium supplementation agent, as well as the type and content of conductive agent, generally affect the performance of sodium-ion batteries. As can be seen from Examples 10 to 16, by adjusting the above parameters within the range of this application, based on the sodium supplementation material having the structure of this application, it is beneficial to obtain an NFPP sodium-ion battery with a high first-cycle charging capacity.

[0145] Examples 1 to 16 and Comparative Examples 1 and 3 also show that, based on the structure of the sodium-supplementing material in this application, by adjusting the D50 of the sodium-supplementing material within the scope of this application, it is beneficial to obtain an NFPP sodium-ion battery with a high first-cycle charging capacity.

[0146] Figure 9 is a schematic diagram of the first charge-discharge curve of the second coin cell in Example 10. As shown in Figure 9, the first-cycle charging capacity of the second coin cell in Example 10 is increased to 129.3 mAh / g, and the first-cycle discharge specific capacity is 104.6 mAh / g. Figure 10 is a schematic diagram of the first-cycle charge-discharge curve of the second coin cell in Comparative Example 3. As shown in Figure 10, the first-cycle charging capacity of the second coin cell in Comparative Example 3 is only 115.0 mAh / g, and the first-cycle discharge specific capacity is 102.0 mAh / g. Furthermore, the capacity retention rate after 20 cycles in Example 10 is also improved compared to Comparative Example 1. Therefore, the sodium-supplementing material of this application can effectively compensate for the sodium loss in the first cycle of the NFPP positive electrode sheet, demonstrating good compatibility with the NFPP positive electrode sheet, which is beneficial to improving the energy density and cycle performance of NFPP sodium-ion batteries.

[0147] The above provides a detailed description of a sodium-supplementing material, its preparation method, the positive electrode sheet, and the 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 sodium supplement material, wherein, The sodium supplement includes a sodium supplement body and a conductive carbon material, wherein the conductive carbon material includes a first conductive portion and a second conductive portion connected together, the first conductive portion being located inside the sodium supplement body, and the second conductive portion being exposed on the outer surface of the sodium supplement body.

2. The sodium supplement material according to claim 1, wherein, In any 1600nm×1200nm region of the SEM image of the sodium-supplementing material, the average number of the second conductive portions is 1 to 20.

3. The sodium supplement material according to claim 1, wherein, Based on the mass of the sodium-supplementing material, the mass percentage of the sodium-supplementing agent body is 60% to 90%, and the mass percentage of the conductive carbon material is 10% to 40%.

4. The sodium supplement material according to claim 1, wherein, The average particle size D50 of the sodium-supplementing material is 0.8 μm to 1.8 μm.

5. The sodium supplement material according to claim 1, wherein, The sodium supplement material has polar groups, including at least one of carboxyl and hydroxyl groups.

6. The sodium supplement material according to claim 1, wherein, The conductive carbon material includes at least one of carbon nanotubes, carboxylated graphene, and graphene oxide.

7. The sodium supplement material according to claim 6, wherein, The carbon nanotube includes a first conductive segment and a second conductive segment connected together. The first conductive segment is located inside the sodium supplement body, and the second conductive segment is exposed on the outer surface of the sodium supplement body.

8. The sodium supplement material according to any one of claims 1 to 7, wherein, The sodium supplement is selected from at least one of Na2C4O4, Na2CO3, CH3COONa, C6H5Na3O7, Na2C2O4, and Na2C6O6.

9. A method for preparing a sodium-supplementing material as described in any one of claims 1 to 8, wherein, Includes the following steps: Dissolve the sodium supplement in water to obtain a supersaturated solution of the sodium supplement; An acidified conductive carbon material is added to an organic solvent to obtain a dispersion. The supersaturated solution is added to the dispersion, and after stirring, the sodium supplement agent generates crystal nuclei around the polar functional groups of the acidified conductive carbon material for recrystallization, thus forming the sodium supplement material.

10. The preparation method according to claim 9, wherein, The sodium supplement is dissolved at a temperature of 20°C to 60°C, and the stirring time is 1 hour to 4 hours.

11. The preparation method according to claim 9, wherein, The organic solvent includes at least one of anhydrous ethanol, ethylene glycol, glycerol, diethyl ether, isopropanol, and acetone.

12. A positive electrode plate, wherein, The device includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a sodium-supplementing material as described in any one of claims 1 to 8, or includes a sodium-supplementing material prepared by the preparation method as described in any one of claims 9 to 11.

13. A sodium-ion battery, wherein, Includes the positive electrode sheet as described in claim 12.

14. An energy storage device, wherein, 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, wherein, The device includes the energy storage device of claim 14, which supplies power to the electrical equipment.

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