Negative electrode material and preparation method thereof, negative electrode plate, electrochemical device and electronic equipment

Abstract

The invention provides a negative electrode material and a preparation method thereof, a negative electrode plate, an electrochemical device and electronic equipment. The negative electrode material comprises a composite carbon material and sodium ions, wherein the sodium ions are positioned on the surface and / or inside the composite carbon material; wherein the composite carbon material comprises a carbon nanomaterial and ZnX embedded into the surface of the carbon nanomaterial, and X is selected from one or more of O, S and Se; the mass ratio of the ZnX to the carbon nanomaterial is (2-5): 1. The electrochemical device using the negative electrode material provided by the invention has relatively high specific capacity and first efficiency, and has excellent cycling stability.

Description

Technical Field

[0001] The present invention relates to a negative electrode material, a preparation method thereof, a negative electrode sheet, an electrochemical device and an electronic device. Background Art

[0002] Compared with lithium ion batteries, sodium ion batteries have the advantages of rich sodium resources, lower cost, high safety factor and environmental friendliness. Therefore, in the fields of new energy vehicles and large-scale energy storage, they show great potential in the application market.

[0003] However, sodium ion batteries still face some problems: (1) Due to the relatively large relative atomic mass of sodium element, it increases the difficulty of sodium ion insertion / extraction in the negative electrode material, and the kinetics is poor, resulting in the theoretical energy density and cycle retention rate of sodium ion batteries being lower than those of lithium ion batteries. (2) During the first charging process, active sodium ions react with the negative electrode material to form a SEI film, causing irreversible capacity loss. Therefore, a method of supplementing sodium can be adopted to make up for the loss of active sodium ions during the cycle.

[0004] Currently, there are two methods for supplementing sodium in sodium ion batteries. The first is to add sodium-rich substances to the positive electrode, and during the first cycle of charging, sodium is released through an electrochemical reaction; the second is to add sodium metal or sodium oxide to the negative electrode for direct sodium supplementation. However, the first method has low efficiency and the remaining part of the non-active substances affects the overall energy density; although the second method has a good sodium supplementation effect, the chemical properties of sodium metal and sodium oxide are extremely active. Therefore, the environmental requirements for preparing the negative electrode material are extremely harsh, and there are a series of safety hazards, making it difficult to be applied on a large scale. Therefore, there is still a need to provide a negative electrode material with good self-sodium supplementation effect, and the preparation of this negative electrode material is simple and feasible, which can meet the actual production requirements. Summary of the Invention

[0005] In order to solve the problems of low specific capacity, low first efficiency and poor cycle performance of the negative electrode material used in the existing technology for batteries, the present invention provides a negative electrode material, a preparation method thereof, a negative electrode sheet, an electrochemical device and an electronic device. The electrochemical device (especially a sodium ion battery) containing the negative electrode material of the present invention has a high specific capacity and first efficiency, and has excellent cycle stability.

[0006] The present invention mainly solves the above technical problems through the following technical solutions:

[0007] In a first aspect, the present invention provides a negative electrode material, which includes a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material;

[0008] Among them, the composite carbon material includes a carbon nanomaterial and ZnX embedded on the surface of the carbon nanomaterial, where X is selected from one or more of O, S, and Se; the mass ratio of ZnX to the carbon nanomaterial is (2-5):1.

[0009] In a second aspect, the present invention provides a method for preparing a negative electrode material, which includes the following steps: reacting a carbon nanomaterial, ZnX, and a sodium supplement agent as raw materials to obtain the negative electrode material.

[0010] In a third aspect, the present invention provides a negative electrode material prepared by the method for preparing a negative electrode material as described above.

[0011] In a fourth aspect, the present invention provides a negative electrode sheet, which includes a current collector layer and a negative electrode material layer located on the current collector layer, and the negative electrode material layer includes the negative electrode material as described above.

[0012] In a fifth aspect, the present invention provides an electrochemical device, which includes the negative electrode sheet as described above.

[0013] In a sixth aspect, the present invention provides an electronic device, which includes the electrochemical device as described above.

[0014] On the basis of conforming to common knowledge in the art, the above preferred conditions can be arbitrarily combined to obtain various preferred examples of the present invention.

[0015] The reagents and raw materials used in the present invention are all commercially available.

[0016] The positive and progressive effects of the present invention are as follows:

[0017] By introducing ZnX into the carbon nanomaterial and further introducing sodium ions, the present invention obtains a negative electrode material. The electrochemical device (especially a sodium-ion battery) using this negative electrode material has a high specific capacity and first efficiency, and has excellent cycle stability. Moreover, the conditions for the method for preparing the negative electrode material of the present invention are mild, simple and easy to implement, and can meet the actual production requirements. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the composite carbon material prepared in Example 1.

[0019] Figure 2 It is a schematic structural diagram of the composite carbon material prepared in Example 4.

[0020] Figure 3 It is a schematic structural diagram of the composite carbon material prepared in Example 7.

[0021] Reference numerals: 1: ZnX; 2: carbon nanomaterial. Detailed Embodiments

[0022] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0023] Negative electrode material

[0024] In the negative electrode material of the first aspect of the present invention: the negative electrode material includes a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material;

[0025] Among them, the composite carbon material includes a carbon nanomaterial and ZnX embedded on the surface of the carbon nanomaterial, and X is selected from one or more of O, S, and Se; the mass ratio of ZnX to the carbon nanomaterial is (2-5):1.

[0026] By embedding ZnX on the surface of the carbon nanomaterial in the present invention, the prepared composite carbon material can have a porous spatial structure and a large specific surface area. Further, sodium ions are introduced into the composite carbon material to obtain a negative electrode material capable of self-supplementing sodium. Among them, the porous spatial structure of the composite carbon material can increase the contact area between the electrolyte and the electrode, and the sodium ions, as a sodium source, increase the sodium ion content, thereby improving the transmission rate of sodium ions, enabling the sodium ion battery to have a high specific capacity, a first Coulomb efficiency, and excellent cycle stability.

[0027] In the present invention, the carbon nanomaterial has a stable structure, can effectively prevent material aggregation, and realizes uniform embedding of ZnX on its surface. The carbon nanomaterial optionally includes one or more of graphene, carbon nanotubes, and carbon spheres, preferably graphene, carbon nanotubes, or carbon spheres. Those skilled in the art are well aware that graphene has a two-dimensional honeycomb structure, a large specific surface area, excellent electrical conductivity, and can also act as a conductive agent.

[0028] Optionally, the particle size of the graphene is 200nm-1um.

[0029] Optionally, the tube diameter of the carbon nanotubes is 2-20nm.

[0030] Optionally, the particle size of the carbon spheres is 400nm-1um.

[0031] In the present invention, when X in the ZnX is selected from multiple of O, S, and Se, it means that in the composite carbon material, multiple substances such as ZnO, ZnS, and ZnSe will coexist. For example, when X is selected from O and S, it means that ZnO and ZnS coexist in the composite carbon material.

[0032] In the present invention, the sodium ions can supplement additional sodium ions during the use of the negative electrode material, and the mass of the sodium ions is not particularly limited as long as the above object can be achieved.

[0033] In some alternative embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises graphene and ZnX embedded on the surface of the graphene, and X is selected from one or more of O, S, and Se; the mass ratio of the ZnX to the carbon nanomaterial is (2-5):1; the particle size of the graphene is 200 nm - 1 μm.

[0034] In some specific embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises graphene and ZnO embedded on the surface of the graphene; the mass ratio of the ZnO to the carbon nanomaterial is 5:1.

[0035] In some specific embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon nanotubes and ZnO embedded on the surface of the carbon nanotubes; the mass ratio of the ZnO to the carbon nanomaterial is 2:1.

[0036] In some alternative embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon nanotubes and ZnX embedded on the surface of the carbon nanotubes, and X is selected from one or more of O, S, and Se; the mass ratio of the ZnX to the carbon nanomaterial is (2-5):1; the tube diameter of the carbon nanotubes is 2 - 20 nm.

[0037] In some specific embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon nanotubes and ZnS embedded on the surface of the carbon nanotubes; the mass ratio of the ZnS to the carbon nanomaterial is 2:1.

[0038] In some specific embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon nanotubes and ZnSe embedded on the surface of the carbon nanotubes; the mass ratio of the ZnSe to the carbon nanomaterial is 2:1.

[0039] In some alternative embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon spheres and ZnX embedded on the surface of the carbon spheres, and X is selected from one or more of O, S, and Se; the mass ratio of ZnX to the carbon nanomaterial is (2 - 5):1; the particle size of the carbon spheres is 400 nm - 1 μm.

[0040] In some specific embodiments, the negative electrode material comprises a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; wherein, the composite carbon material comprises carbon spheres and ZnSe embedded on the surface of the carbon spheres; the mass ratio of ZnSe to the carbon nanomaterial is 5:1.

[0041] Preparation method of negative electrode material

[0042] In the method for preparing the negative electrode material according to the second aspect of the present invention: it comprises the following steps: reacting a carbon nanomaterial, ZnX, and a sodium supplement agent as raw materials to obtain the negative electrode material.

[0043] In the present invention, the sodium supplement agent optionally comprises one or more of Na2SO4, NaNO3, NaCl, Na3PO4, and NaP, for example, Na2SO4.

[0044] In some alternative embodiments of the present invention, the method for preparing the negative electrode material adopts a one-step reaction, comprising the following steps: subjecting a mixture comprising a carbon nanomaterial, ZnX, and a sodium supplement agent to a one-step reaction to obtain the negative electrode material.

[0045] Wherein, the mass ratio of the carbon nanomaterial, ZnX, and the sodium supplement agent is optionally (60 - 83.2):(33.3 - 15):(10 - 0.2), for example, 79.2:15.8:5.

[0046] Wherein, the reaction form of the one-step reaction can be any one of hydrothermal reaction, solvothermal reaction, high-energy ball milling method, microwave-assisted method, and calcination.

[0047] Wherein, when the one-step reaction is a hydrothermal reaction, the time of the hydrothermal reaction is optionally 2 - 24 h, for example, 10 h.

[0048] Wherein, when the one-step reaction is a hydrothermal reaction, the temperature of the hydrothermal reaction is optionally 120 - 250 °C, for example, 200 °C.

[0049] Wherein, when the one-step reaction is a solvothermal reaction, the solvents used optionally include one or more of N-N-dimethylformamide, ethyl acetate, N-methylpyrrolidone, and ethanol.

[0050] Among them, when the one-step reaction is a solvothermal reaction, the time of the solvothermal reaction is optionally 2 - 24 h.

[0051] Among them, when the one-step reaction is a solvothermal reaction, the temperature of the solvothermal reaction is optionally 140 - 220 °C.

[0052] Among them, when the one-step reaction is a microwave-assisted method, ultrasonic assistance is optionally used.

[0053] Among them, when the one-step reaction is calcination, the temperature of the calcination is optionally 350 - 550 °C.

[0054] Among them, when the one-step reaction is calcination, the time of the calcination is optionally 6 - 12 h.

[0055] In some specific embodiments, it includes the following steps: mixing a carbon nanomaterial, ZnX, and a sodium supplement agent to conduct a hydrothermal reaction to obtain the negative electrode material; among them, the mass ratio of the carbon nanomaterial, the ZnX, and the sodium supplement agent is 79.2:15.8:5; the temperature of the hydrothermal reaction is 200 °C; the time of the hydrothermal reaction is 10 h.

[0056] In other alternative embodiments of the present invention, the reaction is carried out in two steps, and the method for preparing the negative electrode material includes the following steps: reacting a mixture containing the carbon nanomaterial and the ZnX to obtain a composite carbon material, and then reacting a mixture containing the composite carbon material and the sodium supplement agent to obtain the negative electrode material.

[0057] Among them, the mass ratio of the ZnX to the carbon nanomaterial is optionally (2 - 5):1.

[0058] Among them, the mass ratio of the composite carbon material to the sodium supplement agent is optionally (90 - 99.8):(0.2 - 10), preferably (90 - 95):(5 - 10), for example, 90:10 or 95:5.

[0059] Among them, the reaction forms of the first reaction and the second reaction can each independently be selected from any one of hydrothermal reaction, solvothermal reaction, high-energy ball milling method, microwave-assisted method, and calcination.

[0060] Among them, when the first reaction is a hydrothermal reaction, the time of the hydrothermal reaction is optionally 4 - 12, for example, 5 h.

[0061] Among them, when the first reaction is a hydrothermal reaction, the temperature of the hydrothermal reaction is optionally 120 - 250 °C, preferably 200 - 250 °C.

[0062] Among them, when the first reaction is a solvothermal reaction, the solvent used optionally includes one or more of N-N-dimethylformamide, ethyl acetate, N-methylpyrrolidone, and ethanol.

[0063] Among them, when the first reaction is a solvothermal reaction, the time of the solvothermal reaction is optionally 4-20 h.

[0064] Among them, when the first reaction is a solvothermal reaction, the temperature of the solvothermal reaction is optionally 150-200 °C.

[0065] Among them, when the first reaction is a microwave-assisted method, ultrasonic assistance is optionally used.

[0066] Among them, when the first reaction is calcination, the temperature of the calcination is optionally 350-550 °C, for example, 500 °C.

[0067] Among them, when the first reaction is calcination, the time of the calcination is optionally 4-10 h.

[0068] Among them, when the second reaction is a hydrothermal reaction, the time of the hydrothermal reaction is optionally 2-8 h, for example, 5 h.

[0069] Among them, when the second reaction is a hydrothermal reaction, the temperature of the hydrothermal reaction is optionally 140-180 °C, preferably 180 °C.

[0070] Among them, when the second reaction is a solvothermal reaction, the solvent used optionally includes one or more of N,N-dimethylformamide, ethyl acetate, N-methylpyrrolidone, and ethanol.

[0071] Among them, when the second reaction is a solvothermal reaction, the time of the solvothermal reaction is optionally 4-8 h.

[0072] Among them, when the second reaction is a solvothermal reaction, the temperature of the solvothermal reaction is optionally 160-180 °C.

[0073] Among them, when the second reaction is a microwave-assisted method, ultrasonic assistance is optionally used.

[0074] Among them, when the second reaction is calcination, the temperature of the calcination is optionally 140-550 °C, for example, 500 °C.

[0075] Among them, when the second reaction is calcination, the time of the calcination is optionally 2-8 h.

[0076] Among them, when the second reaction is calcination, the atmosphere of the calcination can be an inert gas, for example, nitrogen.

[0077] In some alternative embodiments, the reaction is carried out in two steps. The method for preparing the negative electrode material includes the following steps: a first reaction is carried out on a mixture containing the carbon nanomaterial and the ZnX to obtain a composite carbon material, and then a second reaction is carried out on a mixture containing the composite carbon material and the sodium supplement agent to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 120 - 250°C, preferably 200 - 250°C; the mass ratio of the ZnX to the carbon nanomaterial is (2 - 5):1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method.

[0078] In the above alternative embodiments, the mass ratio of the composite carbon material to the sodium supplement agent can be (90 - 95):(5 - 10).

[0079] In some specific embodiments, the reaction is carried out in two steps. The method for preparing the negative electrode material includes the following steps: a first reaction is carried out on a mixture containing the graphene and the ZnO to obtain a composite carbon material, and then a second reaction is carried out on a mixture containing the composite carbon material and the Na2SO4 to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200°C; the mass ratio of the ZnO to the graphene is 5:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0080] In some specific embodiments, the reaction is carried out in two steps. The method for preparing the negative electrode material includes the following steps: a first reaction is carried out on a mixture containing the graphene and the ZnO to obtain a composite carbon material, and then a second reaction is carried out on a mixture containing the composite carbon material and the Na2SO4 to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 250°C; the mass ratio of the ZnO to the graphene is 5:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0081] In some specific embodiments, the reaction is carried out in two steps. The method for preparing the negative electrode material includes the following steps: a first reaction is carried out on a mixture containing the graphene and the ZnO to obtain a composite carbon material, and then a second reaction is carried out on a mixture containing the composite carbon material and the Na2SO4 to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200°C; the mass ratio of the ZnO to the graphene is 5:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 90:10.

[0082] In some specific embodiments, the reaction is carried out in two steps. The preparation method of the negative electrode material includes the following steps: a mixture containing the carbon nanotubes and the ZnO is subjected to a first reaction to obtain a composite carbon material, and then a mixture containing the composite carbon material and the Na2SO4 is subjected to a second reaction to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200 °C; the mass ratio of the ZnO to the carbon nanotubes is 2:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0083] In some specific embodiments, the reaction is carried out in two steps. The preparation method of the negative electrode material includes the following steps: a mixture containing the carbon nanotubes and the ZnS is subjected to a first reaction to obtain a composite carbon material, and then a mixture containing the composite carbon material and the Na2SO4 is subjected to a second reaction to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200 °C; the mass ratio of the ZnS to the carbon nanotubes is 2:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0084] In some specific embodiments, the reaction is carried out in two steps. The preparation method of the negative electrode material includes the following steps: a mixture containing the carbon nanotubes and the ZnSe is subjected to a first reaction to obtain a composite carbon material, and then a mixture containing the composite carbon material and the Na2SO4 is subjected to a second reaction to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200 °C; the mass ratio of the ZnSe to the carbon nanotubes is 2:1; the first reaction is a hydrothermal reaction; the second reaction is a microwave-assisted method; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0085] In some specific embodiments, the reaction is carried out in two steps. The preparation method of the negative electrode material includes the following steps: a mixture containing the carbon spheres and the ZnO is subjected to a first reaction to obtain a composite carbon material, and then a mixture containing the composite carbon material and the Na2SO4 is subjected to a second reaction to obtain the negative electrode material; wherein, the temperature of the hydrothermal reaction is 200 °C; the mass ratio of the ZnO to the carbon spheres is 2:1; the first reaction is a hydrothermal reaction; the second reaction is calcination; the temperature of the calcination is 500 °C, and the time of the calcination is 8 h; the mass ratio of the composite carbon material to the Na2SO4 is 95:5.

[0086] In the present invention, after the first reaction, the step of drying and ball-milling the product obtained from the first reaction is further included.

[0087] In the present invention, the method for preparing the negative electrode material further includes a post-treatment step of vacuum drying and sieving the negative electrode material.

[0088] Negative electrode sheet

[0089] In the negative electrode sheet according to the fourth aspect of the present invention: it includes a current collector layer and a negative electrode material layer located on the current collector layer, and the negative electrode material layer includes the negative electrode material as described above.

[0090] In the present invention, in the negative electrode material layer, the content of the negative electrode material can be 80.0 wt% - 99.0 wt%, and the percentage is the weight percentage of the negative electrode material in the negative electrode material layer.

[0091] Optionally, the negative electrode material layer further includes one or more of a conductive agent, a binder, a dispersant, and a plasticizer.

[0092] Among them, there is no particular limitation on the conductive agent. Preferably, the conductive agent can specifically be used as follows: graphite, such as natural graphite or artificial graphite; amorphous carbon materials, such as conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc. Preferably, the conductive agent is one or more of conductive carbon black, carbon nanotubes, and graphene, and more preferably conductive carbon black.

[0093] Among them, the binder can be a binder conventionally used in the art for preparing negative electrodes. For example, the following materials can be used as the binder: polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more of them can be used.

[0094] Among them, there is no particular limitation on the dispersant. The addition of the dispersant can improve the dispersion degree of each component in the negative electrode active material layer. Generally, sodium carboxymethyl cellulose (CMC) solution can be selected.

[0095] Among them, the plasticizer is not particularly limited. The addition of the plasticizer can improve the coating crispness and edge bulging problems, and at the same time can improve the flexibility of the electrode sheet, avoid powder falling off the electrode sheet, and significantly improve the processing performance of the electrode sheet. Generally, one or more of dimethylformamide, diethyl carbonate, ethylene carbonate, propylene carbonate, 1,3-butanediol, and polyethylene glycol can be selected. For example, it is 1,3-butanediol.

[0096] In an optional embodiment of the present invention, the negative electrode material layer includes: a negative electrode material, a conductive agent, a binder, a dispersant, and a plasticizer.

[0097] In a specific embodiment of the present invention, the negative electrode material layer includes: a negative electrode material, polyacrylic acid, conductive carbon black, sodium carboxymethyl cellulose, and 1,3-butanediol.

[0098] In the embodiments of the present invention, the negative electrode current collector used in the current collector layer can be a common current collector or a composite current collector according to the actual needs of the electrochemical device. The negative electrode current collector can be used without limitation with materials that do not cause chemical changes and have electrical conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum cadmium alloy can be used, or copper, stainless steel material, or aluminum cadmium alloy surface-treated with carbon, nickel, titanium, or silver. In addition, in order to enhance the adhesion of the negative electrode active material, micro embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, or porous body, etc.

[0099] Among them, the thickness of the negative electrode current collector is, for example, 12 μm.

[0100] In the present invention, the negative electrode sheet can be prepared by a conventional method in the art. For example, the following method can be used: after mixing the negative electrode material, binder, dispersant, and plasticizer in a certain mass ratio, adding a solvent and mixing evenly to obtain a negative electrode slurry; uniformly coating the negative electrode slurry on the current collector; and then through processes such as drying, rolling, and cutting to prepare the negative electrode sheet.

[0101] Electrochemical device

[0102] In the electrochemical device of the fifth aspect of the present invention: it includes the negative electrode sheet as described above.

[0103] In the present invention, the electrochemical device can generally be a device in the art that contains the negative electrode sheet as described above, such as a secondary battery, a capacitor, etc.

[0104] In an optional embodiment of the present invention, the electrochemical device is a sodium ion battery, and the sodium ion battery includes the negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte.

[0105] In some embodiments of the present invention, a positive electrode sheet is prepared by coating a positive electrode active material including a positive electrode active substance on a positive electrode current collector. Optionally, one or more of a binder, a conductive agent, and a dispersant may be further added as needed.

[0106] For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation according to the actual needs of the electrochemical device. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can usually be used, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a mesh, or a porous body.

[0107] Among them, the thickness of the positive electrode current collector is, for example, 15 μm.

[0108] In some embodiments of the present invention, the positive electrode active substance can be a sodium ion material such as a transition metal oxide, a polyanionic compound, a Prussian blue / white compound, etc.

[0109] Optionally, the general formula of the transition metal oxide is Na x MO y , where M is selected from one or more of Ni, Co, Fe, Mn, Ru, Ir, Sn, Cr, Cu, Nb, and Mo; optionally, the value of x is 1, and optionally, the value of y is 2.

[0110] Optionally, the general formula of the polyanionic compound is NaxMy(X a O b ) z Zw, where M is selected from one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Ca, Mg, Al, and Nb; X is selected from one or more of Si, S, P, As, B, Mo, W, and Ge, and Z is selected from F and / or OH.

[0111] Optionally, the general formula of the Prussian blue / white compound is Na x M1[M2(CN)6], where M is selected from one or more of Mn, Ni, Co, Zn, Cu, and Fe; optionally, 0 < x ≤ 2.

[0112] In a specific embodiment of the present invention, the molecular formula of the positive electrode active substance is NaNi 0.34 Fe 0.33 Mn 0.33 O2.

[0113] For the conductive agent in the positive electrode active material, it can be a conductive agent conventionally used in the positive electrode in the art. For example, specifically, the following can be used: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (SP), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc.

[0114] For the binder in the positive electrode active material, it can be a binder conventionally used in the positive electrode in the art. For example, it can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used.

[0115] Among them, there is no particular limitation on the dispersant. The addition of the dispersant can improve the dispersion degree of each component in the negative electrode active material layer. Generally, sodium carboxymethyl cellulose (CMC) solution can be selected.

[0116] In some embodiments, the separator can be a polypropylene separator or a polyethylene separator.

[0117] Among them, the thickness of the separator can be 9 μm.

[0118] In a preferred embodiment, the separator is a 9 - μm polyethylene separator with a 2 - μm ceramic coating on both sides.

[0119] In some embodiments, the electrolyte can be an electrolyte conventionally used in batteries in the art, generally including a non - aqueous solvent, a sodium salt, and an additive.

[0120] Among them, the non - aqueous solvent can be a conventional non - aqueous solvent in the art, preferably an ester - based solvent, more preferably a carbonate - based solvent. The carbonate - based solvent can be selected from one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), propylene carbonate (PCA), and butylene carbonate (BC).

[0121] Among them, the additive can be selected from one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene carbonate vinylene ester (VEC), divinyl sulfate (DTD), vinylene sulfite, 1,3-propane sultone (PS), allyl sulfonic acid lactone, and 1,4-butane sultone.

[0122] Among them, the sodium salt can be a conventional sodium salt in the art, such as NaPF6.

[0123] In a specific embodiment of the present invention, the electrolyte includes NaPF6, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0124] Among them, the volume ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate is preferably 1:1:1:1.

[0125] In a specific embodiment of the present invention, the electrolyte can be prepared by the following method: Mix ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate evenly according to a volume ratio of 1:1:1:1, and then dissolve dry high-purity sodium salt NaPF6 in the above mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0126] In the present invention, the preparation method of the sodium-ion battery can be a conventional preparation method in the art. It can be winding the positive electrode sheet, the negative electrode sheet, and the separator to obtain an electric core, and then performing packaging with a packaging shell and injecting the electrolyte; or stacking the negative electrode sheet, the separator, the positive electrode sheet, and the separator in sequence to obtain an electric core, and then performing packaging with a packaging shell and injecting the electrolyte.

[0127] Electronic device

[0128] In the electrochemical device of the sixth aspect of the present invention: It includes the electrochemical device as described above.

[0129] In the present invention, the electronic device of the present invention can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, and a backup power supply, etc.

[0130] On the basis of conforming to the common knowledge in the art, the above optional conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0131] The reagents and raw materials used in the present invention are all commercially available.

[0132] Example 1

[0133] S1. Mix ZnO and graphene in a mass ratio of 5:1, add pure water solvent to obtain a mixed solution; conduct a hydrothermal reaction on the mixed solution, and after the reaction is completed, perform drying and ball milling treatments to obtain a composite carbon material (C-ZnO) with a structure as shown in Figure 1 . The particle size of graphene is 200 nm - 1 μm; the temperature of the hydrothermal reaction is 200 °C and the time is 5 h.

[0134] S2. Under ultrasonic assistance, uniformly mix the composite carbon material (C-ZnO) prepared in step S1 with a sodium supplement agent (Na2SO4). The mass ratio of the composite carbon material (C-ZnO) to the sodium supplement agent is 95:5. After vacuum drying and sieving treatments, a negative electrode material is prepared; the addition amount of the sodium supplement agent accounts for 5% of the total mass of the negative electrode material.

[0135] Example 2

[0136] The hydrothermal reaction temperature in step S1 is 250 °C, and the others are the same as in Example 1.

[0137] Example 3

[0138] The mass ratio of the composite carbon material (C-ZnO) to the sodium supplement agent (Na2SO4) in step S2 is 90:10, and the others are the same as in Example 1.

[0139] Example 4

[0140] In step S1, carbon nanotubes are used. The tube diameter of the carbon nanotubes is 2 nm - 20 nm, and the mass ratio of ZnO to the carbon nanotubes is 2:1. The others are the same as in Example 1, and the structure of the prepared composite carbon material is as shown in Figure 2 .

[0141] Example 5

[0142] In step S1, ZnS and carbon nanotubes are mixed, and the mass ratio of ZnS to the carbon nanotubes is 2:1. The others are the same as in Example 1.

[0143] Example 6

[0144] In step S1, ZnSe and carbon nanotubes are mixed, and the mass ratio of ZnSe to the carbon nanotubes is 2:1. The others are the same as in Example 1.

[0145] Example 7

[0146] S1. Mix ZnSe and carbon spheres in a mass ratio of 2:1, add pure water solvent to obtain a mixed solution; conduct a hydrothermal reaction on the mixed solution, and after the reaction is completed, perform drying and ball milling treatments to obtain a structure as shown in Figure 3The composite carbon material (C-ZnSe) shown; wherein, the particle size of the carbon spheres is 400 nm - 1 μm; the temperature of the hydrothermal reaction is 200 °C and the time is 5 h;

[0147] S2. Mix the composite carbon material (C-ZnSe) prepared in step S1 with a sodium supplement agent (Na2SO4) evenly, wherein the mass ratio of the composite carbon material (C-ZnSe) to the sodium supplement agent is 95:5, and calcine it in an N2 atmosphere at 500 °C for 8 h to obtain the negative electrode material. The structure of the obtained negative electrode material is as Figure 3 shown.

[0148] Example 8

[0149] Add ZnO, graphene and a sodium supplement agent (Na2SO4) into pure water solvent, mix them and carry out a hydrothermal reaction. The temperature of the hydrothermal reaction is 200 °C and the reaction time is 10 h. Among them, the mass ratio of ZnO, graphene and the sodium supplement agent is 79.2:15.8:5.

[0150] Comparative Example 1

[0151] The negative electrode material is a carbon composite material C-ZnO, and its preparation method is the same as that of step S1 in the example.

[0152] Comparative Example 2

[0153] The negative electrode material is ZnO.

[0154] Comparative Example 3

[0155] The mass ratio of ZnO to graphene in step S1 is 1:1, and the others are the same as in Example 1.

[0156] Comparative Example 4

[0157] The mass ratio of ZnO to graphene in step S1 is 6:1, and the others are the same as in Example 1.

[0158] The parameters of the negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-4 are shown in Table 1:

[0159] Table 1 Process parameters of the negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-4

[0160]

[0161] Effect Example

[0162] (1) Preparation of sodium-ion battery

[0163] Preparation of negative electrode sheet:

[0164] The negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-4 were used as negative electrode active materials to prepare negative electrode sheets. The preparation method adopted the following steps:

[0165] The negative electrode material, binder (PAA), conductive agent (SP), dispersant (CMC) and plasticizer (1,3-butanediol) were mixed evenly according to the mass ratio of 96.5:2:1:0.5:0.4, and then deionized water was added as a solvent to prepare a negative electrode slurry for sodium-ion batteries; the negative electrode slurry was evenly coated on a 12-μm aluminum current collector; after processes such as drying, rolling and cutting, a negative electrode sheet was prepared.

[0166] Preparation of the positive electrode sheet:

[0167] The positive electrode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) was mixed evenly with the binder (PVDF), conductive agent (SP), and dispersant according to the mass ratio of 96:2:1.5:0.5, and then N-methylpyrrolidone (NMP) was added as a solvent and stirred to disperse it evenly to obtain a positive electrode slurry for sodium-ion batteries; the positive electrode slurry was evenly coated on an aluminum current collector with a thickness of 15 μm; after drying, rolling and cutting, a positive electrode sheet was obtained.

[0168] Preparation of the electrolyte:

[0169] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and propylene carbonate (PC) were evenly mixed according to the volume ratio of 1:1:1:1, and then an appropriate amount of NaPF6 was dissolved in the above mixed solution to prepare an electrolyte with a concentration of 1 mol / L.

[0170] Preparation of the separator:

[0171] The separator was a 9-μm polyethylene separator with a 2-μm ceramic coating on both sides.

[0172] Assembly of the sodium-ion battery:

[0173] The prepared positive electrode sheet, separator, negative electrode sheet and electrolyte were assembled in sequence, so that the positive electrode sheet, separator, negative electrode sheet and separator were alternately combined, placed in an aluminum-plastic film, injected with the electrolyte, and a sodium-ion battery was obtained after formation and grading.

[0174] (2) The following tests were carried out on the sodium-ion battery:

[0175] Specific capacity: Under the condition of constant temperature at 25 °C, the battery was activated for 3 cycles at 0.2C, and then charged and discharged for 3 cycles at a current of 0.33C, with a voltage range of 1.5-3.95V. The discharge capacity of the third cycle / the mass of the collected active material was taken as the specific capacity.

[0176] Initial efficiency: In a constant temperature environment of 25 °C, the battery is activated for 3 cycles at 0.33C, and then charged and discharged at a current of 0.5C, with a voltage range of 1.5 - 3.95V, and the initial efficiency is measured.

[0177] Capacity retention rate after 200 cycles: The cycle is carried out under the same conditions as the specific capacity test. When the cycle reaches 200 cycles, the discharge capacity of the battery is measured, and the ratio to the discharge capacity of the first cycle is the capacity retention rate after 200 cycles.

[0178] The results of the above tests are listed in Table 2.

[0179] Table 2 Electrochemical performance data of sodium-ion batteries

[0180]

[0181] According to the data in Table 2, the sodium-ion batteries prepared from the negative electrode sheets containing the negative electrode materials of Examples 1 - 8 have a specific capacity of more than 123 mAh / g, an initial Coulomb efficiency of more than 87%, and a capacity retention rate of more than 95% after 200 cycles, indicating that they have a high energy density and excellent cycle stability.

[0182] The negative electrode material prepared in Comparative Example 1 is a composite carbon material, and the negative electrode material prepared in Comparative Example 2 is ZnO. The specific capacity, initial Coulomb efficiency, and capacity retention rate after 200 cycles of the sodium-ion batteries prepared from the negative electrode sheets using the negative electrode materials of Comparative Example 1 and Comparative Example 2 as the active substances are all lower than those of each example.

[0183] In the negative electrode material prepared in Comparative Example 3, the mass ratio of ZnO to graphene is too low, specifically 1:1, and the preparation method is the same as that of Example 1. In the negative electrode material prepared in Comparative Example 4, the mass ratio of ZnO to graphene is too high, specifically 6:1, and the preparation method is the same as that of Example 1. However, the specific capacity, initial Coulomb efficiency, and capacity retention rate after 200 cycles of the sodium-ion batteries prepared from the negative electrode sheets with the negative electrode materials of Comparative Example 3 and Comparative Example 4 as the active substances are all 1 lower than those of the examples. It is found that when the mass ratio of ZnX to the carbon nanomaterial is too low, it will cause excessive accumulation of the composite carbon material, thus affecting the cell capacity and increasing the cost; while when the mass ratio of ZnX to the carbon nanomaterial is too high, the conductivity of the negative electrode sheet will decrease, and the internal resistance (DCR) of the battery will increase, thus affecting the performance of the battery.

[0184] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only an example, and the protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but such changes and modifications all fall within the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that, It includes a composite carbon material and sodium ions, and the sodium ions are located on the surface and / or inside of the composite carbon material; Among them, the composite carbon material includes a carbon nanomaterial and ZnX embedded on the surface of the carbon nanomaterial, and X is selected from one or more of O, S, and Se; the mass ratio of the ZnX to the carbon nanomaterial is (2-5):

1.

2. The negative electrode material according to claim 1, characterized in that, The carbon nanomaterial includes one or more of graphene, carbon nanotubes, and carbon spheres.

3. A method for preparing the negative electrode material according to claim 1 or 2, characterized in that, It includes the following steps: using the carbon nanomaterial, ZnX, and sodium supplement agent as raw materials for reaction to obtain the negative electrode material.

4. The method for preparing the negative electrode material according to claim 3, characterized in that, The reaction is a one-step reaction, including the following steps: performing a one-step reaction on a mixture including the carbon nanomaterial, ZnX, and sodium supplement agent to obtain the negative electrode material.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, It satisfies one or more of the following conditions a-c: a. The sodium supplement agent includes one or more of Na2SO4, NaNO3, NaCl, Na3PO4, and NaP; b. The mass ratio of the carbon nanomaterial, the ZnX, and the sodium supplement agent is (60-83.2):(33.3-15):(10-0.2); c. The reaction form of the one-step reaction is selected from any one of hydrothermal reaction, solvothermal reaction, high-energy ball milling method, microwave-assisted method, and calcination.

6. The method for preparing the negative electrode material according to claim 3, characterized in that, The reaction is carried out in two steps, including the following steps: performing a first reaction on a mixture containing the carbon nanomaterial and the ZnX to obtain a composite carbon material, and then performing a second reaction on a mixture containing the composite carbon material and the sodium supplement agent.

7. The method for preparing the negative electrode material according to claim 6, characterized in that, It satisfies one or more of the following conditions a-c: a. The sodium supplement agent includes one or more of Na2SO4, NaNO3, NaCl, Na3PO4, and NaP; b. The mass ratio of the composite carbon material to the sodium supplement agent is (90-99.8):(0.2-10); c. The reaction forms of the first reaction and the second reaction are each independently selected from any one of hydrothermal reaction, solvothermal reaction, high-energy ball milling method, microwave-assisted method, and calcination.

8. A negative electrode sheet, characterized in that, It includes a current collector layer and a negative electrode material layer located on the current collector layer, and the negative electrode material layer includes the negative electrode material as described in claim 1 or 2.

9. An electrochemical device, characterized in that, It includes the negative electrode sheet as described in claim 8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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