Preparation method of biomass-derived carbon-based nano-network composite potassium negative electrode, composite potassium negative electrode and battery

Abstract

The present invention provides a preparation method of a biomass-derived carbon-based nanonetwork composite potassium anode, a composite potassium anode and a battery. The composite potassium anode is prepared by sequentially adding a biomass derivative and a polymer into an organic solvent, stirring and mixing to obtain a homogeneous polymer solution. Then, an interconnected fiber network structure is prepared by electrospinning, and a flexible carbon cloth is obtained through air pretreatment and carbonization in a high-temperature environment. The biomass derivative-modified carbon fiber composite potassium electrode can be obtained by infiltrating with molten potassium. The potassium composite electrode obtained by the present invention has a simple preparation method and low cost, and can be developed and applied on a large scale. Through the carbon fiber doped with the biomass derivative, the potassium affinity of the fiber structure is significantly improved, so that the potassium deposition / stripping process is more uniform, and the prepared potassium metal electrode is more stable.

Description

Technical Field

[0001] The present invention belongs to the field of metal electrodes, and particularly relates to a preparation method of a biomass-derived carbon-based nanonetwork composite potassium anode, a composite potassium anode, and a battery. Background Art

[0002] With the continuous development of social economy, higher requirements are put forward for energy storage devices. However, the cost of lithium-ion batteries is still at a relatively high level, and more severe challenges have been encountered in terms of resource storage capacity, etc. Therefore, more secondary batteries are needed to make up for this deficiency. Potassium-ion batteries have been widely studied because of their many characteristics similar to those of lithium-ion batteries and a wider resource storage capacity. So far, many studies have been carried out on the anode materials of potassium-ion batteries. However, the anode materials studied at the present stage still have problems such as poor cycle stability and low theoretical specific capacity. Potassium metal has become the first choice for the anode material of potassium-ion batteries because of its high theoretical specific capacity. However, it is found in practical applications that potassium metal has poor stability during cycling and is extremely prone to dendrite growth, resulting in the appearance of irreversible "dead potassium", thus leading to a low Coulombic efficiency. And uncontrollable dendrites will pierce the separator, resulting in battery short circuit. These problems greatly affect the application of potassium metal anodes.

[0003] Researchers have proposed a series of methods to solve the stability of potassium metal, including electrolyte modification, artificial SEI, and composite potassium anodes, etc. However, the existing technologies are relatively complex and costly. Therefore, exploring new materials and preparation methods to obtain potassium metal anodes with low cost and stable performance is an important research direction for the industrialization of potassium-ion batteries. Summary of the Invention

[0004] Traditional potassium composite anodes (or other similar traditional composite anodes, such as zinc composite anodes) are mostly formed by electrochemical deposition. On the one hand, the presence of other metal elements will affect the overall energy density of the battery, and on the other hand, it is difficult to form large-scale production. And more solid electrolyte interphases (SEIs) are easily formed inside the formed potassium composite anodes, thereby resulting in poor electrochemical stability and hindering the development of metal potassium anodes.

[0005] Aiming at the problems of complex preparation process and high cost of the current potassium metal composite anode, especially the low potassium affinity and too little potassium content in the formed composite electrode, resulting in difficulty in improving the overall energy density of the battery, etc.

[0006] The present invention provides a preparation method of a biomass-derived carbon-based nanonetwork composite potassium anode, which is characterized by including the following steps:

[0007] (1) Add biomass derivatives and a polymer successively into an organic solvent to obtain a homogeneous polymer solution;

[0008] (2) The above polymer solution is formed into a three-dimensional network spinning structure cross-linked with each other by electrospinning under specific voltage and pushing speed;

[0009] (3) The spinning structure prepared in step (2) is pre-oxidized in air and then obtained as a flexible self-supporting carbon cloth through high-temperature carbonization;

[0010] (4) The flexible self-supporting carbon cloth is infiltrated with molten potassium to obtain a biomass derivative-modified carbon fiber composite potassium electrode.

[0011] In the modification of potassium metal anodes, potassiumophilic current collector frameworks are generally divided into one-dimensional structures, two-dimensional structures, and three-dimensional structures. Among the above three structures, the three-dimensional self-supporting structure can combine with potassium to the greatest extent, while suppressing the growth of potassium dendrites and reducing the impact of the composite electrode on the overall energy density of the battery. Therefore, it is indispensable to select a structure with light weight and good potassium affinity in the research of potassium metal composite anodes. Carbon fibers have low density and good operability, and have been widely studied. Pure carbon fibers do not have good potassium affinity and are difficult to combine with molten potassium to form a composite anode. It is necessary to dope with potassiumophilic elements and construct the morphology. The doping of potassiumophilic elements often increases the density of the structure, which in turn leads to a decrease in the proportion of K in the composite electrode. In addition, the introduction of metal elements will increase the process cost and the complexity of the process steps. Therefore, the present invention provides a method for a suitable carbon matrix to inhibit dendrite growth and balance the energy density of the battery.

[0012] The present invention provides a method for a potassium metal composite anode with a simple process, low cost, and large-scale production. 1. By forming a homogeneous solution of a biomass derivative and a polymer, it solves the problem that a single biomass derivative is difficult to form a three-dimensional structure by electrospinning and provides a flexible current collector to expand the application of the composite electrode. 2. The overall fiber structure is modified by the biomass derivative, thereby greatly enhancing the potassium affinity of the three-dimensional structure. 3. Pure carbon materials exist as self-supporting current collectors, and biomass derivatives exist as potassiumophilic elements. Without the presence of other metal elements, the proportion of potassium in the battery anode can be significantly increased. 4. Design a stable potassiumophilic current collector to form a composite potassium anode by combining with molten potassium. This method can accommodate more potassium and exhibits good potassium affinity in the macroscopic structure. Moreover, the operation is simple, easy for industrial production, and can form a potassium composite anode with a high potassium proportion.

[0013] Preferably, in the preparation method of the present invention, the biomass derivative is cyanoethyl cellulose. As a cellulose ether widely studied in the last century, cyanoethyl cellulose is rich in sources and is used in textiles to prevent the attack of molds and bacteria. It can also be used as a high dielectric material in capacitive devices such as electronic screens; however, it has never been applied to the field of battery metal electrodes, especially there has never been a report on using ethyl cellulose as a biomass derivative in the preparation of composite potassium anodes. The present invention creatively selects cyanoethyl cellulose as the carbon fiber modification element. On the one hand, it is rich in sources, and on the other hand, it can greatly improve the potassium affinity of carbon without introducing metal elements as potassium affinity sites. As a biomass derivative, it has a low cost and a simpler electrode preparation method, and does not require a complex electrochemical deposition device to synthesize the composite electrode.

[0014] Preferably, in the preparation method of the present invention, the content of cyanoethyl cellulose is 1-20 wt%, and the content of the high molecular polymer is 5-20 wt%. By changing the ratio of cyanoethyl cellulose to the high molecular polymer in the homogeneous solution and the electrospinning parameters, the pore size and other structures of the fiber structure are controlled. And in the present invention, only biomass derivatives are used as the potassium affinity current collector modification element, without introducing high-density materials such as metal elements, which reduces the cost while not affecting the overall energy density of the battery.

[0015] Preferably, in the preparation method of the present invention, step (4) is specifically: heating metallic potassium to 80°C - 100°C in a glove box with a water oxygen value less than 0.01 ppm to make the metallic potassium form a liquid state. At this low temperature, the flexible self-supporting carbon cloth is contacted with the liquid potassium. Due to the improved potassium affinity, the high temperature of 200-300°C required for molten potassium is avoided, and the carbon cloth can be infiltrated by the liquid potassium at a safe temperature until the two are completely fused and then cooled to prepare the biomass derivative modified carbon fiber composite potassium anode.

[0016] Preferably, in the preparation method of the present invention, the high molecular polymer is one or more of polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyvinylpyrrolidone; and / or, the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone.

[0017] Preferably, in the preparation method of the present invention, the voltage of electrospinning in step (2) is 8-20 kV, the feeding speed is 0.1-2 mL / h, and the spinning time is 1-36 h. By controlling the spinning voltage and the feeding speed together, the fiber thickness and the porosity between fibers are controlled to provide more space for the binding of potassium. In addition, by controlling the spinning time, the thickness of the carbon cloth can be controlled, and further the proportion of the formed composite potassium anode in the battery can be controlled, so as to avoid waste caused by excessive potassium and achieve quantitative matching between the anode and the cathode.

[0018] Preferably, in the preparation method of the present invention, in step (3), the pre-oxidation temperature is 180-280°C, the heating rate is 1-10°C / min, and the heat preservation time is 0-10 h; the high-temperature carbonization environment is 500-1000°C, the heating rate is 1-10°C / min, and the heat preservation time is 0-10 h. The carbonization temperature of the biomass derivative can reach above 3000°C, while the present invention carbonizes the biomass derivative below 1000°C. Low-temperature carbonization can protect the structural integrity of the carbon fiber, ensure the combination of molten potassium along the fiber when forming the composite potassium negative electrode, thereby enhancing the mechanical strength and flexibility of the composite potassium negative electrode, and the technical cost required for low-temperature carbonization is relatively low, providing the possibility for large-scale production.

[0019] The present invention also provides a composite potassium negative electrode, which is prepared by the aforementioned preparation method, and the proportion of potassium in the composite potassium negative electrode is above 95%, which reduces the influence of the composite electrode on the overall energy density of the battery.

[0020] The present invention also provides a battery, which uses the aforementioned composite potassium negative electrode, and in the half-cell test, the Coulomb efficiency is stable for more than 1000 h at a current density of 0.5 mA / cm 2 ; the assembled symmetric battery is stable for more than 1100 h at a current density of 0.5 mA / cm 2 . The present invention obtains a potassium composite negative electrode and a battery with low cost, high stability and high energy density.

[0021] Compared with the prior art, the main beneficial effects and advantages of the present invention are as follows:

[0022] The present invention uses biomass derivatives with a wide range of sources, especially inexpensive cyanoethyl cellulose, to modify carbon fibers, greatly improving the potassium affinity of the fiber structure.

[0023] The present invention forms a three-dimensional potassium metal negative electrode by the method of potassium melting, which is simple in operation, easy for industrial production, and can form a potassium composite negative electrode with a high potassium proportion.

[0024] (3) The potassiumophilic three-dimensional structure formed by the present invention can effectively reduce the local current density, induce the uniform progress of the potassium deposition / stripping process, thereby inhibiting dendrite growth and preparing a highly stable potassium metal composite negative electrode. Description of the Drawings

[0025] Figure 1 Scanning electron microscope photos of Example 1 and Comparative Example 1.

[0026] Figure 2 Comparison photos before and after the preparation of the composite potassium negative electrode in Example 1.

[0027] Figure 3 Coulombic efficiency test chart of the half-cells for Example 1 and Comparative Example 1.

[0028] Figure 4 GITT test chart of the symmetric cell of Example 1 at a current density of 0.5 mA / cm 2

[0029] Figure 5 Long cycle time-voltage test chart of the symmetric cell of Example 1 at a current density of 0.5 mA / cm 2

[0030] Figure 6 Long cycle time-voltage test chart of the symmetric cell of Example 1 at a current density of 2 mA / cm 2

[0031] Figure 7 Rate and long cycle test chart of the full cell assembled with Example 1. Embodiment

[0032] In order to make the technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described below through specific examples. Those skilled in the art should understand that the described examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Example 1

[0033] (1) Dissolve 0.5 g of cyanoethyl cellulose in 10 mL of N,N-dimethylformamide and stir at room temperature for 12 h. Then dissolve 1 g of polyacrylonitrile in the above solution and stir for 12 h to prepare a spinning precursor solution.

[0034] (2) After extracting with a syringe, perform electrospinning. Set the electrospinning voltage to 12 kV, the rotational speed of the receiver roller to 100 rpm, the distance between the syringe needle and the collector to 15 cm, the feeding speed to 0.7 mL / h, and collect the electrospun membrane after 6 h.

[0035] (3) Pretreat the electrospun membrane obtained in step (2) in a tubular furnace under an air atmosphere at 200 °C for 1 h, and then carbonize it at 800 °C for 1 h under an argon atmosphere to prepare a carbon fiber thin film (NC@CNFs). This thin film can be directly combined with molten potassium (specifically, for example, heat metallic potassium to 80 °C - 100 °C in a glove box with a water oxygen value less than 0.01 ppm to make the metallic potassium in a liquid state) to obtain a potassium composite negative electrode. Comparative Example 1

[0036] (1) Dissolve 1 g of polyacrylonitrile in the above solution and stir for 12 h to prepare a spinning precursor solution.

[0037] ​​​(2) After the syringe is filled, electrospinning is carried out. The electrospinning voltage is set to 12 KV, the rotational speed of the receiver roller is 100 rpm, the distance between the syringe needle and the collector is 15 cm, the feeding speed is 0.7 mL / h, and the electrospun membrane is collected after 6 h.

[0038] (3) The electrospun membrane in step (2) is pretreated at 200 °C for 1 h in an air atmosphere in a tubular furnace, and then carbonized at 800 °C for 1 h in an argon atmosphere to prepare a carbon fiber thin film (CNFs). Example 2

[0039] The difference between Example 2 and Example 1 is that the addition amount of cyanoethyl cellulose is changed to 1 g, and other parameters remain unchanged. Example 3

[0040] The difference between Example 3 and Example 1 is that the high molecular polymer is changed from polyacrylonitrile to polyvinylpyrrolidone, and other parameters remain unchanged.

[0041] The following are the morphological characterization and electrochemical performance tests of Example 1 of the present invention.

[0042] Figure 1 (a) is a scanning electron microscope photograph of the biomass-derived carbon-based nanofibers NC@CNFs. Compared with CNFs in Comparative Example 1 ( Figure 1 (b)), after adding cyanoethyl cellulose, the fiber structure and morphology change significantly, a cross-linked structure is established between the fibers, and the surface is rougher, which is beneficial to increasing the wetting area for molten potassium.

[0043] Figure 2 It is a comparison photograph before and after the preparation of the composite potassium anode, which proves the high wettability of the carbon fiber for molten potassium and enables large-scale preparation of potassium composite electrodes. And through the mass change before and after wetting, it is obtained that the proportion of potassium in the formed potassium composite anode is about 95%, which reduces the influence of the composite electrode on the overall energy density of the battery.

[0044] Figure 3 It is a comparison chart of the Coulomb efficiency of the examples and the comparative examples. Among them, Example 1 maintains a high Coulomb efficiency cycle for more than 1000 h at a current density of 0.5 mA / cm 2 . Among them, curve 1 is NC@CNFs of Example 1, and curve 2 is CNFs of Comparative Example 1. And the nucleation voltage of NC@CNFs is 27 mV, which is much lower than the nucleation voltage of CNFs (96 mV). It shows that NC@CNFs can reduce the local current density, make the potassium deposition / stripping process more uniform, and suppress dendrite growth.

[0045] Figure 4GITT and impedance comparison diagrams before and after cycling for the symmetric batteries assembled with Example 1 and K respectively. Before cycling, the impedance of the NC@CNFs symmetric battery was slightly lower than that of the K symmetric battery. After cycling, due to the stability during the deposition / stripping process, the impedance test of the NC@CNFs symmetric battery was much lower than that of the K symmetric battery, which was consistent with the stable polarization voltage in the GITT time-voltage curve, indicating that the formed composite anode could significantly improve the electrode stability.

[0046] Figure 5 Long-term cycling stability tests were carried out on the symmetric batteries assembled with Example 1 and K respectively at a current density of 0.5 mA / cm 2 . The NC@CNFs symmetric battery could maintain a stable polarization voltage for more than 1100 h, while the polarization voltage of the K symmetric battery fluctuated significantly at 500 h of cycling, indicating severe K dendrite growth, and an obvious short-circuit occurred at 700 h of cycling, demonstrating that the composite anode could achieve long-term cycling stability of potassium deposition / stripping.

[0047] Figure 6 Long-term cycling stability tests were carried out on the symmetric batteries assembled with Example 1 and K respectively at a current density of 2 mA / cm 2 . The NC@CNFs symmetric battery could maintain a stable polarization voltage for more than 200 h, while the polarization voltage of the K symmetric battery was difficult to stabilize at a current density of 2 mA / cm 2 . This indicates that K dendrite growth existed during the cycling process, and a short-circuit occurred at 70 h of cycling. Compared with the K anode, the composite anode could stably cycle at a larger current density.

[0048] Figure 7 Potassium-ion full batteries were assembled with Example 1 and K using a cathode made of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). In the rate test, the full battery assembled with NC@CNFs had a capacity retention about 20 mAh / g higher than that of the K full battery at a current density of 1 A / g. And in the long-term cycling test at a current density of 0.1 A / g, the capacity of the K full battery was only 34.5 mAh / g (retention rate 32.2%) after 500 cycles, which was much lower than the capacity of 88.7 mAh / g (retention rate 73.9%) of the NC@CNFs full battery after 500 cycles. It was proved that the composite anode could not only improve the rate performance of the battery but also enhance the stability during long-term cycling.

[0049] Although the present invention is disclosed as above, for the ease of understanding of those skilled in the art, the above description is only the preferred embodiment of the present invention and is not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a biomass-derived carbon-based nanonetwork composite potassium anode, characterized in that, It includes the following steps: (1) Sequentially add biomass derivatives and high molecular polymers into an organic solvent to obtain a homogeneous polymer solution; the biomass derivatives are cyanoethyl cellulose; the content of cyanoethyl cellulose is 1-20 wt%, and the content of the high molecular polymer is 5-20 wt%; (2) Use electrospinning of the above polymer solution to form a three-dimensional network spinning structure that cross-links with each other under specific voltage and pushing speed; (3) Pre-oxidize the spinning structure prepared in step (2) in air and then obtain a flexible self-supporting carbon cloth through high-temperature carbonization; (4) Heat metallic potassium to 80 °C - 100 °C in a glove box where the water oxygen value is less than 0.01 ppm to make the metallic potassium form a liquid state, and infiltrate the flexible self-supporting carbon cloth with molten potassium to obtain a biomass derivative-modified carbon fiber composite potassium electrode.

2. The preparation method according to claim 1, wherein Step (4) also includes: contacting the flexible self-supporting carbon cloth with liquid potassium at this temperature until the two are completely fused and then cooling to prepare a biomass derivative-modified carbon fiber composite potassium negative electrode.

3. The preparation method according to any one of claims 1-2, characterized in that, The high molecular polymer is one or more of polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, and polyvinylpyrrolidone; and / or, the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

4. The preparation method according to any one of claims 1-2, characterized in that, In step (2), the voltage of electrospinning is 8-20 kV, the pushing speed is 0.1-2 mL / h, and the spinning time is 1-36 h.

5. The preparation method according to any one of claims 1-2, characterized in that, In step (3), the pre-oxidation temperature is 180-280 °C, the heating rate is 1-10 °C / min, and the heat preservation time is 0-10 h; the high-temperature carbonization environment is 500-1000 °C, the heating rate is 1-10 °C / min, and the heat preservation time is 0-10 h.

6. A composite potassium anode, characterized in that, The composite potassium negative electrode is prepared by the preparation method described in any one of claims 1-5.

7. The composite potassium negative electrode according to claim 6, wherein The proportion of potassium in the composite potassium negative electrode is more than 95%.

8. A battery, characterized in that, Its negative electrode is the composite potassium negative electrode described in any one of claims 6-7, and it stably cycles for more than 1000 h at a current density of 0.5 mA / cm2 in a half-cell test. The assembled symmetric cell stably cycles for more than 1100 h at a current density of 0.5 mA / cm2.

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