Negative pole piece, preparation method of negative pole piece, secondary battery and electric device

Abstract

The invention relates to the technical field of secondary batteries, in particular to a negative pole piece and a preparation method thereof, a secondary battery and an electric device, and aims to solve the technical problems that in the prior art, an MOFs material is poor in structural stability, is not favorable for maintaining battery performance, and is easy to cause volume expansion and material pulverization, so that the battery performance is deteriorated. The negative pole piece comprises a negative current collector and a negative active layer which is arranged on one side of at least one surface of the negative current collector along the thickness direction of the negative current collector, wherein the negative electrode active layer has a first porous structure formed by interweaving a carbon nanofiber material, the carbon nanofiber material has a hollow tubular structure, the surface of the carbon nanofiber material has a plurality of microporous structures, and the carbon nanofiber material contains a coordination element and transition metal ions coordinated with the coordination element; transition metal ions are formed on the inner surface and the outer surface of the hollow tube of the carbon nanofiber material.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] Secondary batteries, also called rechargeable batteries, can have charge and discharge cycles of thousands to tens of thousands of times, making them more economical and practical than dry batteries.

[0003] Among secondary batteries, alkaline metal batteries such as lithium-ion batteries, sodium-ion batteries and potassium-ion batteries have developed rapidly. In these batteries, when alkaline metal ions are deintercalated in the negative electrode material, the volume of the negative electrode material changes greatly, which is not conducive to forming a stable electrochemical environment, especially for sodium-ion batteries and potassium-ion batteries with larger ion radius. In particular, active material pulverization is prone to occur on the negative electrode side, resulting in a sharp decay in battery cycle performance, which greatly limits the research and application of this type of battery.

[0004] At present, Metal Organic Framework (MOFs) compounds are used as negative electrode materials for secondary batteries due to their large specific surface area, abundant pores, diverse pore sizes, and good modifiability. However, the current research on MOFs compounds only stays at the simple coating level, that is, coating MOFs compounds on the surface of the negative electrode current collector. Although the metal ions in MOFs compounds can support and stabilize MOFs compounds and stabilize the structure of the compounds to a certain extent, as the cycle continues to deepen, the structural stability of MOFs compounds cannot be maintained, which is not conducive to maintaining battery performance and easily leads to volume expansion and material pulverization, thereby causing battery performance deterioration. Summary of the invention

[0005] Based on this, some embodiments of the present application provide a negative electrode plate and a preparation method thereof, a secondary battery and an electrical device to solve the technical problems in the related art that the structural stability of MOFs compounds is poor, which is not conducive to maintaining battery performance, and easily leads to volume expansion and material pulverization, thereby causing deterioration of battery performance.

[0006] In a first aspect, a negative electrode plate is provided, comprising:

[0007] a negative electrode current collector, and

[0008] A negative electrode active layer is disposed on at least one surface of the negative electrode current collector along the thickness direction thereof;

[0009] Among them, the negative electrode active layer has a first porous structure interwoven by carbon nanofiber material, the carbon nanofiber material is a hollow structure, and the surface of the carbon nanofiber material has multiple microporous structures, the carbon nanofiber material contains coordination elements and transition metal ions coordinated with the coordination elements, and the transition metal ions are formed on the inner surface and outer surface of the hollow tube of the carbon nanofiber material.

[0010] Optionally, the carbon nanofiber material is obtained by sequentially spinning an organic ligand of a metal organic framework compound, metal ion coordination and carbonization treatment, so that the transition metal ions are formed on the inner and outer surfaces of the hollow tube of the carbon nanofiber material.

[0011] Optionally, the carbon nanofiber material satisfies at least one of the following conditions:

[0012] (1) The porosity of the first porous structure is 50% to 80%, and the pore size of the first porous structure is 1 nm to 8 nm;

[0013] (2) The porosity of the plurality of microporous structures is 50% to 90%, and the pore size of each microporous structure is 0.1 nm to 5 nm;

[0014] (3) The transition metal ion is selected from Co 2+ , Fe 3+ 、Zn 2+ , Mn 2+ and Ni 2+ At least one of;

[0015] (4) In the negative electrode active layer, the mass proportion of the transition metal ions is 4% to 12%.

[0016] Optionally, the negative electrode active layer further comprises a carbon fiber support skeleton disposed in the hollow tube of the carbon nanofiber material, the carbon fiber support skeleton having a second porous structure, the porosity of the second porous structure is 70% to 95%, and the pore size is 0.1 nm to 1 nm.

[0017] In a second aspect, a method for preparing a negative electrode sheet is provided, comprising:

[0018] providing a negative electrode current collector;

[0019] Preparing a negative electrode active layer on at least one side of the surface of the negative electrode current collector along the thickness direction thereof;

[0020] Among them, the negative electrode active layer has a first porous structure interwoven by carbon nanofiber material, the carbon nanofiber material is a hollow tubular structure, and the surface of the carbon nanofiber material has multiple microporous structures, the carbon nanofiber material contains a coordination element and a transition metal ion coordinated with the coordination element, and the transition metal ions are formed on the inner surface and outer surface of the hollow tube of the carbon nanofiber material.

[0021] Optionally, a negative electrode active layer is prepared on at least one surface side of the negative electrode current collector along the thickness direction thereof, comprising:

[0022] preparing a first spinning solution and a second spinning solution respectively, wherein the first spinning solution comprises: an organic ligand of a metal organic framework compound and a first polymer, and the second spinning solution comprises: a second polymer, wherein the solubility of the second polymer in a first solvent is greater than the solubility of the first polymer in the first solvent;

[0023] Using a coaxial spinning process, the first spinning solution is used as a shell layer, and the second spinning solution is used as a core layer, and spinning is performed on at least one side of the surface of the negative electrode current collector along the thickness direction thereof to prepare a first fiber spinning layer;

[0024] Using a first solvent to dissolve and remove the second polymer in the first fiber spinning layer to obtain a second fiber spinning layer;

[0025] Coordinating the organic ligand of the metal organic framework compound in the second fiber spinning layer with the transition metal ion to prepare a third fiber spinning layer;

[0026] The third fiber spinning layer is carbonized by calcination to prepare the negative electrode active layer.

[0027] Optionally, the preparation method satisfies at least one of the following conditions:

[0028] (1) The organic ligand of the metal organic framework compound is selected from at least one of 2-methylimidazole, trimesic acid and terephthalic acid;

[0029] (2) the first polymer is selected from at least one of polyacrylonitrile and polymethyl methacrylate;

[0030] (3) the second polymer is at least one selected from carboxymethyl cellulose, polyvinyl pyrrolidone and polyethylene glycol;

[0031] (4) The first solvent is selected from water;

[0032] (5) The solvent used in the first spinning solution includes: an organic solvent;

[0033] (6) The solvent used in the second spinning solution includes: a polar aprotic solvent;

[0034] (7) the second spinning solution further includes: a third polymer, the solubility of the second polymer in the first solvent is greater than the solubility of the third polymer in the first solvent, and the mass ratio of the third polymer to the second polymer is 1:2 to 2:1;

[0035] When the second polymer in the first fiber spinning layer is dissolved and removed by using the first solvent, the third polymer remains;

[0036] (8) The concentration of the first spinning solution is 15 wt % to 24 wt %;

[0037] (9) The concentration of the second spinning solution is 15 wt % to 24 wt %;

[0038] (10) The spinning voltage is 16 kV ~ 22 kV, the receiving distance is 12 cm ~ 20 cm, and the propulsion speed of the spinning solution is 0.5 mL / h ~ 2.0 mL / h;

[0039] (11) placing the negative electrode current collector prepared with the first fiber spinning layer in the first solvent, and performing a first ultrasonic treatment to dissolve and remove the second polymer in the first fiber spinning layer by the first solvent; optionally, the first ultrasonic treatment has a power of 200 W to 1000 W, a frequency of 20 kHz to 50 kHz, a temperature of 23° C. to 27° C., and a time of 30 min to 60 min;

[0040] (12) using a second ultrasonic treatment to coordinate the organic ligand of the metal organic framework compound in the second fiber spinning layer with the metal ion; optionally, the power of the second ultrasonic treatment is 200 W to 1000 W, the frequency is 20 kHz to 50 kHz, the temperature is 23° C. to 27° C., and the time is 1 h to 4 h;

[0041] (13) The calcination includes: pre-calcining at a first temperature for a first time, and placing the pre-calcined product at a second temperature for a second time, wherein the first temperature is 200°C to 400°C, the first time is 2h to 4h, the second temperature is 600°C to 800°C, and the second time is 6h to 12h.

[0042] In a third aspect, a secondary battery is provided, comprising: a positive electrode sheet, a negative electrode sheet and a separator;

[0043] Wherein, the negative electrode plate is the negative electrode plate as described in the first aspect.

[0044] Optionally, the secondary battery is a potassium ion battery.

[0045] In a fourth aspect, an electrical device is provided, comprising a plurality of batteries connected in series and / or in parallel, wherein at least one battery is a secondary battery as described in the third aspect.

[0046] The beneficial technical effects of the negative electrode sheet and preparation method thereof, the secondary battery and the electric device provided by the present application are as follows:

[0047] The negative electrode active layer is interwoven with carbon nanofiber materials. Compared with the related art in which the negative electrode active layer is prepared by coating, the structural stability of the metal organic framework compound is poor, which is not conducive to the maintenance of battery performance and easily leads to material expansion and pulverization, thereby causing the battery performance to deteriorate. On the one hand, the negative electrode active layer is interwoven with carbon nanofiber materials, and mechanical stress can be used to improve the rigidity of the carbon nanofiber materials, and the structure of the carbon nanofiber materials can be supported and stabilized together with transition metal ions, which can inhibit volume expansion and reduce material pulverization, thereby reducing the deterioration of battery performance; on the other hand, the negative electrode active layer has There is a first porous structure interwoven by carbon nanofiber materials, and the first porous structure has a larger pore size, which is convenient for electrolyte infiltration, thereby promoting the transmission of alkali metal ions in the negative electrode active layer and improving the ion transmission performance; on the other hand, the surface of the carbon nanofiber material has multiple microporous structures, and the carbon nanofiber material is a hollow tubular structure. Therefore, the carbon nanofiber material has abundant pores, diverse pore sizes and a larger specific surface area, which can provide more abundant alkali metal ion storage sites, thereby further improving the alkali metal ion storage, diffusion and transmission performance, and further enhancing the electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present application;

[0049] Figure 2 A schematic flow chart of a method for preparing a negative electrode plate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0051] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as an open, inclusive meaning, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "exemplarily" or "some examples" and the like are intended to indicate that specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representation of the above terms does not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner.

[0052] Exemplary embodiments are described herein with reference to cross-sectional views and / or plan views that are idealized exemplary drawings. In the drawings, the thickness of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are conceivable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but include shape deviations due to, for example, manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0053] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0054] Herein, unless otherwise specified, "one or more" means one or more than or equal to two.

[0055] In this document, "for example", "such as", "example", "for example", etc. are used for descriptive purposes, indicating that the previous and subsequent different technical solutions are related in terms of the content covered, but should not be understood as limiting the previous technical solution, nor can they be understood as limiting the scope of protection of this document. In this document, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0056] In this article, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel options of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0057] Herein, descriptions such as "optionally contain", "optionally include", etc., mean "contain or not contain". "Optional component X" means component X exists or does not exist, or means containing or not containing the component X.

[0058] In this document, the terms "first", "second", etc. in "the first aspect", "the second aspect", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0059] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0061] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0062] In this document, "at least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multilayer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0063] Herein, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is considered to be continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to integers within the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0064] In this article, when it comes to percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0065] Herein, the term "room temperature" or "normal temperature" generally refers to 4°C to 35°C, for example, 20°C ± 5°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 10°C to 30°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 20°C to 30°C.

[0066] In view of the technical problem that the metal organic framework compounds existing in the related art have poor structural stability, are not conducive to maintaining battery performance, and easily lead to volume expansion and material pulverization, thereby causing deterioration of battery performance, the specific implementation methods of the present application are described as follows:

[0067] In a first aspect, some embodiments of the present application provide a negative electrode sheet, such as Figure 1 As shown, the negative electrode plate 10 includes: a negative electrode current collector 1, and a negative electrode active layer 2 arranged on one side of at least one surface of the negative electrode current collector 1 along the thickness direction thereof; wherein the negative electrode active layer 2 has a first porous structure interwoven with carbon nanofiber material, the carbon nanofiber material is a hollow tubular structure, and the surface of the carbon nanofiber material has a plurality of microporous structures, the carbon nanofiber material contains a coordination element and a transition metal ion coordinated with the coordination element, and the transition metal ion is formed on the inner surface and the outer surface of the hollow tube of the carbon nanofiber material.

[0068] Among them, since the negative electrode active layer 2 has a first porous structure formed by interweaving carbon nanofiber materials, the negative electrode active layer is a fiber interweaving porous structure.

[0069] The carbon nanofiber material is a hollow tubular structure, which means that the carbon nanofiber material is a hollow tubular fiber structure. Thus, a plurality of microporous structures on the surface of the carbon nanofiber material are formed on the hollow tube and can penetrate the inner and outer surfaces of the hollow tube. The carbon nanofiber material contains a coordination element and a transition metal ion coordinated with the coordination element, and the transition metal ion is formed on the inner and outer surfaces of the hollow tube of the carbon nanofiber material, which means that the transition metal ions are exposed to the outside and coordinated with the coordination element exposed on the surface of the carbon nanofiber material, and will not be embedded in the tube body of the hollow tube.

[0070] The coordinating element may be an element containing a lone pair of electrons, such as N and O.

[0071] In the negative electrode plate 10 provided in the embodiment of the present application, the negative electrode active layer 2 is interwoven with carbon nanofiber materials. Compared with the related art in which the negative electrode active layer is prepared by coating, the structural stability of the metal organic framework compound is poor, which is not conducive to the maintenance of battery performance and easily leads to material expansion and pulverization, thereby causing the battery performance to deteriorate. On the one hand, the negative electrode active layer is interwoven with carbon nanofiber materials, and mechanical stress can be used to improve the rigidity of the carbon nanofiber materials, and the structure of the carbon nanofiber materials can be supported and stabilized together with transition metal ions, which can inhibit volume expansion and reduce material pulverization, thereby reducing the deterioration of battery performance; on the other hand, On the one hand, the negative electrode active layer has a first porous structure interwoven by carbon nanofiber materials, and the first porous structure has a larger pore size, which is convenient for electrolyte infiltration, thereby promoting the transmission of alkali metal ions in the negative electrode active layer and improving the ion transmission performance; on the other hand, the surface of the carbon nanofiber material has a plurality of microporous structures, and the carbon nanofiber material is a hollow tubular structure. Therefore, the carbon nanofiber material has abundant pores, diverse pore sizes and a larger specific surface area, which can provide more abundant alkali metal ion storage sites, thereby further improving the alkali metal ion storage, diffusion and transmission performance, and further enhancing the electrochemical performance.

[0072] In some embodiments, the carbon nanofiber material is obtained by spinning organic ligands of a metal organic framework compound, metal ion coordination and carbonization treatment in sequence, so that transition metal ions are formed on the inner and outer surfaces of the hollow tube of the carbon nanofiber material.

[0073] In these embodiments, transition metal ions can be formed on the inner and outer surfaces of the hollow tube of the carbon nanofiber material as much as possible to reduce the embedding of transition metal ions, so that the structure of the hollow tube of the carbon nanofiber material can be supported and stabilized with the help of transition metal ions. At the same time, the transition metal ions can be more evenly dispersed on the inner and outer surfaces of the hollow tube of the carbon nanofiber material. The uniform distribution of transition metal ions can make the desolvation process at the interface between the electrolyte and the carbon nanofiber material more uniform, so that the alkali metal ions can be better transmitted in the hollow tube of the carbon nanofiber material, reducing the risk of alkali metal precipitation caused by uneven transmission, thereby improving the electrochemical performance of the negative electrode sheet.

[0074] In some embodiments, the porosity of the first porous structure is 50% to 80%, and the pore size of the first porous structure is 1 nm to 8 nm.

[0075] In these embodiments, the electrochemical stability of one side of the negative electrode plate can be effectively improved.

[0076] In some embodiments, the porosity of the plurality of microporous structures is 50% to 90%, and the pore size of each microporous structure is 0.1 nm to 5 nm.

[0077] In these embodiments, the wettability of the negative electrode plate can be improved, so that more electrolyte can contact the negative electrode plate, exposing more alkali metal ion desolvation sites, and facilitating the overall migration of alkali metal ions.

[0078] In some embodiments, the transition metal ion is selected from Co 2+ , Fe 3+ 、Zn 2+ , Mn 2+ and Ni 2+ At least one of .

[0079] In some embodiments, in the negative electrode active layer, the mass proportion of transition metal ions is 4% to 12%.

[0080] In these embodiments, the appropriate content of transition metal centers can effectively support the organic framework, increase active sites, and improve electrical conductivity.

[0081] In some embodiments, the negative electrode active layer also includes a carbon fiber support skeleton disposed in a hollow tube of the carbon nanofiber material, the carbon fiber support skeleton having a second porous structure, the porosity of the second porous structure is 70% to 95%, and the pore size is 0.1 nm to 1 nm.

[0082] In these embodiments, a carbon fiber support skeleton is arranged in the hollow tube of the carbon nanofiber material, and the carbon fiber support skeleton can further improve the structural stability of the carbon nanofiber material. At the same time, since the carbon fiber support skeleton has a second porous structure, the porosity of the second porous structure is 70%~95%, and the pore size is 0.1nm~1nm. Therefore, the second porous structure of the carbon fiber support skeleton can also fix transition metal ions and reduce the shedding and dissolution of transition metal ions.

[0083] In a second aspect, some embodiments of the present application provide a method for preparing a negative electrode sheet, such as Figure 2 As shown, the following steps S21 and S22 are included:

[0084] S21, providing a negative electrode current collector;

[0085] S22, preparing a negative electrode active layer on at least one surface side of the negative electrode current collector along its thickness direction;

[0086] The negative electrode active layer has a porous structure interwoven by carbon nanofiber materials. The carbon nanofiber materials are hollow structures, and the surface of the carbon nanofiber materials has multiple microporous structures. The carbon nanofiber materials contain coordination elements and transition metal ions coordinated with the coordination elements. The transition metal ions are formed on the inner and outer surfaces of the hollow tubes of the carbon nanofiber materials.

[0087] In some embodiments, S22, preparing a negative electrode active layer on at least one surface side of the negative electrode current collector along the thickness direction thereof, comprising:

[0088] S221, preparing a first spinning solution and a second spinning solution respectively, the first spinning solution comprising: an organic ligand of a metal organic framework compound and a first polymer, the second spinning solution comprising: a second polymer, and the solubility of the second polymer in the first solvent is greater than the solubility of the first polymer in the first solvent;

[0089] S222, using a coaxial spinning process, using the first spinning solution as a shell layer and the second spinning solution as a core layer, spinning on at least one side of the surface of the negative electrode current collector along its thickness direction to prepare a first fiber spinning layer;

[0090] S223, using a first solvent to dissolve and remove the second polymer in the first fiber spinning layer to obtain a second fiber spinning layer;

[0091] S224, coordinating the organic ligand of the metal organic framework compound in the second fiber spinning layer with the transition metal ion to prepare a third fiber spinning layer;

[0092] S225, carbonizing the third fiber spinning layer by calcining to prepare the negative electrode active layer.

[0093] In these embodiments, by first spinning the organic ligand of the metal organic framework compound to form the first fiber spinning layer, then coordinating the transition metal ions, and finally performing a carbonization treatment, the transition metal ions can be formed on the surface of the first fiber spinning layer as much as possible, reducing the embedding of the transition metal ions, thereby more effectively improving the structural stability of the carbon nanofiber material finally formed, and at the same time improving the uniformity of the desolvation effect between the interface of the electrolyte and the carbon nanofiber material, so that the alkali metal ions can be better transmitted in the hollow tube of the carbon nanofiber material, reducing the risk of alkali metal precipitation caused by uneven transmission. At the same time, in this process, by adding the first polymer to the organic ligand of the metal organic framework compound, the organic ligand of the metal organic framework compound can be smoothly spun; and by using the first solvent to dissolve and remove the second polymer in the first fiber spinning layer, the active sites in the first fiber spinning layer (such as the coordination elements of the organic ligand of the metal organic framework compound) can be better exposed, so that the transition metal ions can be coordinated with the coordination elements of the organic ligand of the metal organic framework compound.

[0094] In some embodiments, the organic ligand of the metal organic framework compound is selected from at least one of 2-methylimidazole, trimesic acid and terephthalic acid.

[0095] In these embodiments, suitable organic ligands facilitate the formation of the organo-metal framework.

[0096] In some embodiments, the first polymer is selected from at least one of polyacrylonitrile and polymethyl methacrylate.

[0097] In these embodiments, the first polymer can serve as a spinning matrix to improve the spinning performance of the organic ligand of the metal organic framework compound.

[0098] In some embodiments, the second polymer is selected from at least one of carboxymethyl cellulose, polyvinyl pyrrolidone and polyethylene glycol.

[0099] In these embodiments, the second polymer can be dissolved in water, so that the second polymer in the first fiber spinning layer can be dissolved and removed by water, which is non-toxic, harmless and environmentally friendly.

[0100] In some embodiments, the first solvent is selected from water, which is convenient and readily available.

[0101] In some embodiments, the solvent used in the first spinning solution includes: an organic solvent.

[0102] In these embodiments, the organic solvent can dissolve the organic ligand of the metal organic framework compound and the first polymer, so as to facilitate the preparation of the first spinning solution with excellent spinning performance.

[0103] In some embodiments, the organic solvent may include at least one of DMF, DMSO, and NMP.

[0104] The use of these organic solvents makes it easier to evenly disperse the matrix and ensure the electrospinning effect.

[0105] In some embodiments, the concentration of the first spinning solution is 15 wt %~24 wt %.

[0106] In some embodiments, the solvent used in the second spinning solution includes: a polar aprotic solvent, such as an organic solvent such as DMF, DMSP, NMP, etc.

[0107] In these embodiments, a uniformly dispersed spinning solution can be obtained, so that the reactive active sites of the resulting fiber are uniformly exposed.

[0108] In some embodiments, the concentration of the second spinning solution is 15 wt % to 24 wt %.

[0109] In some embodiments, the second spinning solution further includes: a third polymer, the solubility of the second polymer in the first solvent is greater than the solubility of the third polymer in the first solvent, and the mass ratio of the third polymer to the second polymer is 1:2 to 2:1;

[0110] When the second polymer in the first fiber spinning layer is dissolved and removed by using the first solvent, the third polymer remains.

[0111] In these embodiments, by adding the third polymer to the second spinning solution, since the solubility of the second polymer in the first solvent is greater than the solubility of the third polymer in the first solvent, when the second polymer in the first fiber spinning layer is dissolved and removed by the first solvent, the third polymer will not be dissolved and removed or will be retained. After the subsequent carbonization treatment, the third polymer can form a support inside the hollow tube of the carbon nanofiber material, thereby further improving the structural stability of the carbon nanofiber material. By controlling the mass ratio of the third polymer to the second polymer to be 1:2~2:1, a carbon fiber support skeleton can be prepared in the hollow tube of the carbon nanofiber material. The carbon fiber support skeleton has a second porous structure, and has a large porosity and pore size, which can fix transition metal ions, thereby reducing the shedding and dissolution of transition metal ions, and further improving the structural stability of the carbon nanofiber material.

[0112] In some embodiments, the spinning voltage is 16 kV to 22 kV, the receiving distance is 12 cm to 20 cm, and the propulsion speed of the spinning solution is 0.5 mL / h to 2.0 mL / h.

[0113] In some embodiments, a negative electrode current collector prepared with a first fiber spinning layer is placed in a first solvent, and the first solvent is used to dissolve and remove the second polymer in the first fiber spinning layer through a first ultrasonic treatment; optionally, the power of the first ultrasonic treatment is 200 W ~ 1000 W, the frequency is 20 kHz ~ 50 kHz, the temperature is 23 ° C ~ 27 ° C, and the time is 30 min ~ 60 min.

[0114] In these embodiments, the second polymer in the first fiber spinning layer can be effectively dissolved and removed.

[0115] In some embodiments, a second ultrasonic treatment is used to coordinate the organic ligands of the metal organic framework compound in the second fiber spinning layer with the metal ions; optionally, the second ultrasonic treatment has a power of 200 W to 1000 W, a frequency of 20 kHz to 50 kHz, a temperature of 23° C. to 27° C., and a time of 1 h to 4 h.

[0116] In these embodiments, the second ultrasonic treatment can utilize the high energy effect of ultrasound to uniformly coordinate metal ions on the surface of the organic ligands of MOFs.

[0117] In some embodiments, the calcination includes: pre-calcining at a first temperature for a first time, and placing the pre-calcined product at a second temperature for a second time, wherein the first temperature is 200°C~400°C, the first time is 2h~4h, the second temperature is 600°C~800°C, and the second time is 6h~12h.

[0118] In these embodiments, pre-calcining the product can effectively remove water, solvent and other residues from the pre-treatment process, maintain structural stability while promoting better growth of the metal organic framework compound and improving overall activity; the second calcination mainly further carbonizes the fully grown metal organic framework compound composite fibers, and finally forms a potassium ion negative electrode with suitable pore size and rich content.

[0119] In a third aspect, some embodiments of the present application provide a secondary battery, comprising: a positive electrode plate, a negative electrode plate and a separator; wherein the negative electrode plate is the negative electrode plate as described in the first aspect.

[0120] The secondary battery may be a sodium ion battery, a lithium ion battery or a potassium ion battery.

[0121] In some embodiments, the secondary battery is a potassium ion battery.

[0122] In these embodiments, the potassium ions in the potassium ion battery have a larger radius, which can effectively reduce the material pulverization and volume expansion caused by potassium ion deintercalation and improve the battery performance of the potassium ion battery.

[0123] In a fourth aspect, some embodiments of the present application provide an electrical device, comprising a plurality of batteries connected in series and / or in parallel, wherein at least one battery is a secondary battery as described in the third aspect.

[0124] The electrical devices include but are not limited to: laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0125] In order to objectively evaluate the technical effects of the embodiments of the present application, the present application will be described in detail and exemplarily through the following embodiments and comparative examples.

[0126] In the following examples and comparative examples, all raw materials can be purchased commercially, and in order to maintain the reliability of the experiment, the raw materials used in the following examples and comparative examples have the same physical and chemical parameters or are prepared by the same processing method.

[0127] Example 1

[0128] Embodiment 1 provides a negative electrode sheet, and the preparation method of the negative electrode sheet is as follows:

[0129] (1) Spinning solution preparation: 3.24 g of 2-methylimidazole was placed in 20 mL of DMF and ultrasonically pre-dispersed for 20 min. Subsequently, 20 g of polyacrylonitrile and a certain amount of DMF were added and heated and stirred for 8 h to prepare an 18 wt% spinning solution, which was recorded as solution A. Polyacrylonitrile and carboxymethyl cellulose were mixed and dissolved in DMF in a mass ratio of 1:1 to finally prepare an 18 wt% spinning solution, which was recorded as solution B.

[0130] (2) Preparation of precursor composite nanofibers: A coaxial electrospinning device was used to electrospin the stock solution A as the shell layer and the stock solution B as the core layer. The voltage setting range was 20 kV, the receiving distance was 15 cm, and the propulsion speed was 1 mL / h. Polyacrylonitrile (PAN)@carboxymethyl cellulose (CMC) composite nanofibers containing 2-methylimidazole precursor were obtained.

[0131] (3) Preparation of MOF / PAN@carboxymethyl cellulose (CMC) composite nanofibers: The precursor polyacrylonitrile (PAN)@carboxymethyl cellulose (CMC) composite nanofibers were ultrasonically dispersed in 500 mL of pure water for 40 min to remove the water-soluble CMC and expose more active sites. Then, 1.44 g Zn(NO 3 ) 2 6H 2 O was added into methanol, the ultrasonic power was 500 W, the frequency was 40 kHz, the temperature was 25 °C, and the time was 30 min, and then the composite fiber was placed in the metal solution for further ultrasonic reaction for 3 h under the same ultrasonic conditions;

[0132] (4) Preparation of carbon nanofiber material: The composite fiber in step (3) is placed in a heat-resistant mold, pre-fired in a 300°C tubular furnace for 5 hours and kept warm for 3 hours, and finally calcined in a high-temperature furnace at 700°C to finally obtain a carbon nanofiber material with a ZIF-8 carbonized skeleton as a shell layer and a carbonized PAN fiber as an inner layer, wherein the carbon nanofiber material is interwoven into a negative electrode active layer having a first porous structure, wherein the carbon nanofiber material includes a hollow tubular structure and a carbon fiber support skeleton formed in the hollow tube of the hollow tubular structure, the surface of the hollow tubular structure has a plurality of microporous structures, the carbon fiber support skeleton has a second porous structure, the porosity of the first porous structure is 68%, and the average pore size of the first porous structure is 5 nm, the porosity of the plurality of microporous structures is 75%, and the average pore size of the plurality of microporous structures is 1 nm, the porosity of the second porous structure is 89%, and the average pore size is 0.5 nm, and in the negative electrode active layer, the transition metal ion Zn 2+ The quality accounts for 8%.

[0133] Example 2

[0134] The method for preparing the negative electrode sheet provided in Example 2 is substantially the same as the method for preparing the negative electrode sheet provided in Example 1, except that:

[0135] Replacing the carboxymethyl cellulose in step (1) with polyvinyl pyrrolidone;

[0136] In the final negative electrode active layer, the porosity of the first porous structure is 70%, and the average pore size of the first porous structure is 3.5nm; the porosity of the multiple microporous structures is 83%, and the average pore size of the multiple microporous structures is 0.8nm; the porosity of the second porous structure is 89%, and the average pore size is 0.5nm.

[0137] Example 3

[0138] The method for preparing the negative electrode sheet provided in Example 3 is substantially the same as the method for preparing the negative electrode sheet provided in Example 1, except that:

[0139] Increase the amount of 2-methylimidazole added in step (1) to 6.48 g;

[0140] In the final negative electrode active layer, the porosity of the first porous structure is 67%, the average pore size of the first porous structure is 4.8nm, the porosity of the multiple microporous structures is 74%, the average pore size of the multiple microporous structures is 1.2nm, and the porosity of the second porous structure is 93%, and the average pore size is 0.3nm.

[0141] Example 4

[0142] The method for preparing the negative electrode sheet provided in Example 4 is substantially the same as the method for preparing the negative electrode sheet provided in Example 1, except that:

[0143] In step (3), Zn(NO 3 ) 2 6H 2 The amount of O added was increased to 2.88 g;

[0144] In the final negative electrode active layer, the porosity of the second porous structure is 91%, the average pore size is 0.2nm, and the transition metal ion Zn 2+ The quality accounts for 15%.

[0145] Comparative Example 1

[0146] The negative electrode provided in Comparative Example 1 is prepared by mixing 3.24 g 2-methylimidazole and 1.44 g Zn(NO 3 ) 2 6H 2 O prepared ZIF-8, and then mixed it with petroleum coke single particle artificial graphite and calcined it to obtain a negative electrode active material. Finally, the negative electrode active material was mixed with carboxymethyl cellulose (CMC) and SP conductive carbon black in a mass ratio of 97:2:1, and deionized water was used as a solvent. After stirring and mixing evenly, a slurry was made and coated on a copper foil. After being completely dried, a roller press was used to press it to 120μm.

[0147] Comparative Example 2

[0148] The preparation method of the negative electrode sheet provided in Comparative Example 2 is substantially the same as the preparation method of the negative electrode sheet provided in Example 1, except that:

[0149] In Comparative Example 2, in step (1), Zn(NO 3 ) 2 6H 2 O is added to the first spinning solution, and the composite fiber in step (3) is placed in the metal solution for further ultrasonic reaction to remove it.

[0150] Test Case

[0151] 1. The negative electrode sheets prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were prepared into button-type half-cells: button-type cells were assembled in the order of placing the negative electrode shell, potassium sheet, diaphragm, negative electrode sheet, gasket, spring sheet, and positive electrode shell. The diaphragm was a polyethylene (PE) diaphragm, and the electrolyte was a mixed solvent of EC (ethylene carbonate) and (EMC ethyl methyl carbonate) with a volume ratio of 5:5. The solute was lithium hexafluorophosphate, and the amount of electrolyte added was 80 μL. After assembly, the cells were packaged with a button cell press, and the electrochemical performance was tested after standing for 12 hours. The test results are shown in Table 1 below.

[0152] Table 1

[0153]

[0154] As can be seen from Table 1, Examples 1 to 4 of the present application have a higher initial charge and discharge efficiency, and a higher discharge capacity per gram at 0.05C, indicating that the negative electrode sheet provided in the embodiments of the present application has good ion transport properties, and can fully utilize the capacity.

[0155] 2. The above-mentioned button battery was cycled at a rate of 0.1C for 10, 30, 60 and 100 cycles respectively, and the discharge capacity after the cycle was tested. The cycle retention rate after N cycles was calculated using the formula cycle retention rate = Nth cycle discharge capacity / first discharge capacity. The calculation results are shown in Table 2 below. Wherein, N represents the number of cycles.

[0156] Table 2

[0157]

[0158] As shown in Table 2, the negative electrode sheet provided in the embodiment of the present application has a good cycle retention rate. After 100 cycles, it can still maintain a cycle retention rate of more than 76.2%, and can even maintain a cycle retention rate of more than 80%. Compared with Example 1, the cycle retention rates of Comparative Examples 1 and 2 have decreased to a large extent, indicating that the negative electrode sheet provided in the present application has a high structural stability and can reduce the deterioration of battery performance.

[0159] 3. The batteries with different cycles were disassembled and the negative electrode plates were washed three times with dimethyl carbonate (DMC). After drying, the thickness of the plates was measured and the expansion rate of the plates was recorded. The test results are shown in Table 3 below:

[0160] Table 3

[0161]

[0162] As shown in Table 3, the potassium ion battery provided in the embodiment of the present application has a low pole piece expansion rate. After 100 cycles, the pole piece expansion rate is only 0.21% at most. Compared with Example 1, the pole piece expansion rates of Comparative Examples 1 and 2 are both greatly increased, indicating that the negative pole piece provided in the present application has good structural stability and is not prone to volume expansion and material pulverization.

[0163] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A negative electrode plate, characterized in that: include: a negative electrode current collector, and A negative electrode active layer is disposed on at least one surface of the negative electrode current collector along the thickness direction thereof; Among them, the negative electrode active layer has a first porous structure interwoven by carbon nanofiber material, the carbon nanofiber material is a hollow tubular structure, and the surface of the carbon nanofiber material has multiple microporous structures, the carbon nanofiber material contains a coordination element and a transition metal ion coordinated with the coordination element, and the transition metal ions are formed on the inner surface and outer surface of the hollow tube of the carbon nanofiber material.

2. The negative electrode sheet according to claim 1, characterized in that: The carbon nanofiber material is obtained by spinning organic ligands of metal organic framework compounds, coordinating transition metal ions and carbonizing in sequence, so that the transition metal ions are formed on the inner surface and outer surface of the hollow tube of the carbon nanofiber material.

3. The negative electrode sheet according to claim 1, characterized in that: The carbon nanofiber material satisfies at least one of the following conditions: (1) The porosity of the first porous structure is 50% to 80%, and the average pore size of the first porous structure is 1 nm to 8 nm; (2) The porosity of the plurality of microporous structures is 50% to 90%, and the average pore size of the plurality of microporous structures is 0.1 nm to 5 nm; (3) The transition metal ion is selected from Co 2+ , Fe 3+ 、Zn 2+ , Mn 2+ and Ni 2+ At least one of; (4) In the negative electrode active layer, the mass proportion of the transition metal ions is 4% to 12%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The negative electrode active layer also includes a carbon fiber support skeleton arranged in the hollow tube of the carbon nanofiber material, and the carbon fiber support skeleton has a second porous structure. The porosity of the second porous structure is 70% to 95%, and the average pore size is 0.1nm to 1nm.

5. A method for preparing a negative electrode sheet, characterized in that: include: providing a negative electrode current collector; Preparing a negative electrode active layer on at least one side of the surface of the negative electrode current collector along the thickness direction thereof; Among them, the negative electrode active layer has a first porous structure interwoven by carbon nanofiber material, the carbon nanofiber material is a hollow tubular structure, and the surface of the carbon nanofiber material has multiple microporous structures, the carbon nanofiber material contains a coordination element and a transition metal ion coordinated with the coordination element, and the transition metal ions are formed on the inner surface and outer surface of the hollow tube of the carbon nanofiber material.

6. The preparation method according to claim 5, characterized in that: A negative electrode active layer is prepared on at least one surface side of the negative electrode current collector along the thickness direction thereof, comprising: preparing a first spinning solution and a second spinning solution respectively, wherein the first spinning solution comprises: an organic ligand of a metal organic framework compound and a first polymer, and the second spinning solution comprises: a second polymer, wherein the solubility of the second polymer in a first solvent is greater than the solubility of the first polymer in the first solvent; Using a coaxial spinning process, the first spinning solution is used as a shell layer, and the second spinning solution is used as a core layer, and spinning is performed on at least one side of the surface of the negative electrode current collector along the thickness direction thereof to prepare a first fiber spinning layer; Using a first solvent to dissolve and remove the second polymer in the first fiber spinning layer to obtain a second fiber spinning layer; Coordinating the organic ligand of the metal organic framework compound in the second fiber spinning layer with the transition metal ion to prepare a third fiber spinning layer; The third fiber spinning layer is carbonized by calcination to prepare the negative electrode active layer.

7. The preparation method according to claim 6, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The organic ligand of the metal organic framework compound is selected from at least one of 2-methylimidazole, trimesic acid and terephthalic acid; (2) the first polymer is selected from at least one of polyacrylonitrile and polymethyl methacrylate; (3) the second polymer is at least one selected from carboxymethyl cellulose, polyvinyl pyrrolidone and polyethylene glycol; (4) The first solvent is selected from water; (5) The solvent used in the first spinning solution includes: an organic solvent; (6) The solvent used in the second spinning solution includes: a polar aprotic solvent; (7) the second spinning solution further includes: a third polymer, the solubility of the second polymer in the first solvent is greater than the solubility of the third polymer in the first solvent, and the mass ratio of the third polymer to the second polymer is 1:2 to 2:1; When the second polymer in the first fiber spinning layer is dissolved and removed by using the first solvent, the third polymer remains; (8) The concentration of the first spinning solution is 15 wt % to 24 wt %; (9) The concentration of the second spinning solution is 15 wt % to 24 wt %; (10) The spinning voltage is 16 kV ~ 22 kV, the receiving distance is 12 cm ~ 20 cm, and the propulsion speed of the spinning solution is 0.5 mL / h ~ 2.0 mL / h; (11) placing the negative electrode current collector prepared with the first fiber spinning layer in the first solvent, and performing a first ultrasonic treatment to dissolve and remove the second polymer in the first fiber spinning layer by the first solvent; optionally, the first ultrasonic treatment has a power of 200 W to 1000 W, a frequency of 20 kHz to 50 kHz, a temperature of 23° C. to 27° C., and a time of 30 min to 60 min; (12) using a second ultrasonic treatment to coordinate the organic ligand of the metal organic framework compound in the second fiber spinning layer with the transition metal ion; optionally, the power of the second ultrasonic treatment is 200 W to 1000 W, the frequency is 20 kHz to 50 kHz, the temperature is 23° C. to 27° C., and the time is 1 h to 4 h; (13) The calcination includes: pre-calcining at a first temperature for a first time, and placing the pre-calcined product at a second temperature for a second time, wherein the first temperature is 200°C to 400°C, the first time is 2h to 4h, the second temperature is 600°C to 800°C, and the second time is 6h to 12h.

8. A secondary battery, characterized in that: include: Positive electrode sheet, negative electrode sheet and separator; Wherein, the negative electrode plate is the negative electrode plate as described in any one of claims 1 to 4.

9. The secondary battery according to claim 8, characterized in that: The secondary battery is a potassium ion battery.

10. An electrical device, characterized in that: The invention comprises a plurality of batteries connected in series and / or in parallel, wherein at least one battery is a secondary battery as claimed in any one of claims 8 to 9.

Images