Porous carbon negative electrode material for potassium ion battery as well as preparation method and application of porous carbon negative electrode material

Abstract

The invention discloses a porous carbon negative electrode material for a potassium ion battery and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing and grinding glucose and MgO or CaO to obtain a uniform raw material; (2) putting the raw materials into a corundum boat, and carrying out high-temperature calcination in a protective atmosphere to obtain pyrolyzed powder; and (3) mixing and stirring the pyrolyzed powder and hydrochloric acid, and performing suction filtration and drying to obtain the porous carbon negative electrode material of the potassium ion battery. The porous carbon negative electrode material provided by the invention has rich mesoporous and macroporous structures, shows excellent potassium storage performance, has high specific capacity, excellent rate capability and long cycle stability, and is suitable for large-scale energy storage application.

Description

Technical Field

[0001] The invention belongs to the technical field of negative electrode materials for potassium ion batteries, and specifically relates to a preparation method of a porous carbon negative electrode material and an application in negative electrode materials for potassium ion batteries, and particularly relates to a carbon-based negative electrode material. Background Art

[0002] With the growth of global energy demand and the depletion of fossil fuels, the development of new energy storage technologies has become an urgent need. Lithium-ion batteries are widely used in electric vehicles and grid energy storage due to their high energy density and long cycle life. However, the scarcity and uneven distribution of lithium resources limit their large-scale application. Potassium-ion batteries have become a potential candidate to replace lithium-ion batteries due to their abundant potassium resources, low cost and similar working principles to lithium-ion batteries.

[0003] However, the development of potassium ion batteries faces many challenges, especially the negative electrode materials, which still face three problems: (1) K + The ionic radius is too large, resulting in K + The reversible embedding / de-embedding is difficult, resulting in a lower reversible capacity; (2) due to the larger K + radius, a large amount of K + Insertion / deinsertion can easily cause volume expansion of electrode materials, leading to crushing of electrode materials or even structural collapse, thus affecting their cycle stability; (3) K + The poor diffusion capacity in the electrode limits the transfer rate, resulting in K + The reaction kinetics are slow and the rate performance is poor.

[0004] In response to these three problems, researchers have proposed many methods to improve its performance. These methods can be divided into the following three directions: 1. Heteroatom doping: By doping with different elements, it is possible to introduce abundant defect sites, improve the conductivity of the material, and expand the carbon layer spacing. These modification measures help to significantly enhance the potassium storage performance of carbon materials. However, it has poor thermal stability and a complex preparation process; 2. Regulation of MOF-derived carbon: Metal organic framework (MOF) has an ordered porous skeleton, a variety of metal ions and organic ligands, so that the resulting porous carbon material not only has a high porosity and a large specific surface area, but also has rich heteroatom doping characteristics, which can effectively promote the rapid migration and efficient storage of potassium ions, and improve the rate performance of the battery. However, this method is difficult to implement and has a high cost. 3. Design of porous structure: The porous structure shortens the ion transmission path and improves the ion transmission rate during the charge and discharge process by increasing the specific surface area and pore volume of the material. For example, the template-assisted spray pyrolysis method is used to prepare porous spheres with controllable micro / mesoporous pores. The rich mesoporous structure can act as a K + transmission channel, ensuring fast K + migration rate, and the larger pore size can accommodate K + , which alleviates the volume expansion effect during charge and discharge; and the micropores can serve as K + Defect sites provide additional potassium storage capacity. However, porous materials usually have low mechanical strength and may experience structural collapse during long-term cycles, affecting cycle life.

[0005] In summary, it is necessary to rationally construct carbon-based negative electrode materials with good electrochemical properties to alleviate the problems of volume expansion, insufficient potassium storage capacity and poor cycle stability of electrode materials during the cycle of potassium ion batteries. Summary of the invention

[0006] In view of the shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for preparing a porous carbon negative electrode material for a potassium ion battery.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: Glucose and metal oxides were placed in an agate mortar and ground for 20 min to ensure that the raw materials were fully mixed; The raw material obtained in step (1) is placed in a corundum boat, and calcined at 800° C. for 2 h under a protective atmosphere to obtain a pyrolyzed powder; The pyrolyzed powder obtained in step (2) was placed in 3M HCl and stirred for 12 h, then filtered and dried in a vacuum drying oven at 60° C. for 24 h to obtain a porous carbon negative electrode material.

[0008] Preferably, the metal oxide in step (1) is CaO or MgO.

[0009] Preferably, in step (1), the mass ratio of glucose to metal oxide is 3:1.

[0010] Preferably, the protective atmosphere in step (2) is an argon atmosphere.

[0011] Preferably, the heating rate in step (2) is 5°C / min.

[0012] An application of a porous carbon negative electrode material for a potassium ion battery, wherein the porous carbon negative electrode material prepared by the above method is used to prepare an electrode sheet.

[0013] Furthermore, the electrode sheet preparation method is as follows: the porous carbon negative electrode material, the conductive agent Super P, and the binder PVDF are placed in an agate mortar and ground for 30 minutes to fully mix, and then prepared into a slurry with an appropriate amount of N-methylpyrrolidone (NMP) solvent. The slurry is evenly coated on the copper foil using a coater, and then immediately placed at 60°C to dry for 2 hours to completely volatilize the NMP. The copper foil coated with the sample is cut into discs with a diameter of 12 mm, and finally dried in a vacuum drying oven at 80°C for 12 hours to obtain an electrode sheet.

[0014] Furthermore, in terms of mass percentage, the porous carbon negative electrode material is 70%, the conductive agent is 20%, and the binder is 10%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The material has a low specific surface area and a small interlayer spacing, which makes it difficult for potassium ions to be inserted / deintercalated, and has poor capacity and rate performance. The material prepared by the CaO template has a rich mesoporous and macroporous structure with a specific surface area of ​​up to 1465.1 m 2 / g, significantly higher than traditional carbon materials. This porous structure is potassium ion (K + ) provides more storage sites and fast transmission channels, significantly improving the potassium storage capacity and rate performance of the material.

[0016] Traditional graphite materials will undergo volume expansion of up to 61% during the potassium ion embedding / de-embedding process, resulting in structural damage and rapid capacity decay. The porous structure of PCaC materials can effectively buffer the volume expansion caused by the potassium ion embedding / de-embedding process, avoid material structure collapse, and thus improve cycle stability.

[0017] The solid electrolyte interface (SEI) film of traditional carbon materials has high impedance and K + The diffusion rate is slow, resulting in poor rate performance. The porous carbon material forms a low-impedance SEI film during the cycle, which reduces the K + The transport resistance during the embedding / de-embedding process. The porous carbon material has a high diffusion coefficient and a faster K + transfer rates and better reaction kinetics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 PCaC and SEM images obtained in Example 1 of the present invention

[0019] Figure 2 This is the SEM image of PMgC obtained in Example 1 of the present invention.

[0020] Figure 3 The XRD patterns of PCaC sample of Example 1 and PMgC sample of Comparative Example 1 are shown in FIG.

[0021] Figure 4 (a) is the N of PMgC sample 1 in comparative example 2 Adsorption-desorption curve; (b) is the N of the PCaC sample in Example 1 2 Adsorption-desorption curve; (c) is the pore size distribution diagram of Example 1 and Comparative Example 1

[0022] Figure 5 The Raman images of Example 1 and Comparative Example 1 are

[0023] Figure 6 (a) is the XPS full spectrum of the prepared sample; (b) is the C and O element content distribution diagram of the prepared sample

[0024] Figure 7 It is a rate performance diagram of the sample PCaC of Example 1 and the sample PMgC of Comparative Example 1; Figure 8 is the cycle curve of the prepared sample at a current density of 100 mA / g; Fig. 9 This is the cycle curve of the prepared sample at 1000mA / g DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with embodiments

[0026] Example 1 (Synthesis of PCaC) 3g glucose and 1g CaO (mass ratio of 3:1) were placed in an agate mortar and ground for 20 minutes to fully mix the raw materials. Then, they were placed in a corundum boat and heated to 800°C at a heating rate of 5°C / min in an argon atmosphere for 2 hours. The powder obtained after pyrolysis was stirred in 3M HCl for 12 hours, then filtered and dried in a vacuum oven at 60°C overnight. The obtained sample was recorded as PCaC.

[0027] Comparative Example 1 (Synthesis of PMgC) The synthesis method of PMgC is similar to the process of Example 1. In this process, MgO is used to replace CaO and perform thermal decomposition with glucose.

[0028] Experiment 1: X-ray diffraction (XRD) was used to analyze the crystal structure and disorder degree of the prepared PMgC and PCaC

[0029] Experiment 2: The pore structures of PMgC and PCaC were further characterized by Brunauer-Emmett-Teller (BET) test.

[0030] Experiment 3: Raman spectroscopy was used to investigate the effect of different oxide templates on the structure

[0031] Experiment 4: XPS analysis of the elemental composition and existence forms of PCaC and PMgC

[0032] Experiment 5: Electrochemical performance test of PCaC and PMgC

[0033] The materials prepared in Example 1 and Comparative Example 1 are used as negative electrode materials. The battery is assembled in a glove box under an argon atmosphere, and the positive electrode shell, negative electrode sheet, electrolyte, diaphragm, electrolyte, metal potassium sheet, gasket, shrapnel, and negative electrode shell are stacked in order, and then pressed into a button battery using a sealing machine. The electrolyte can be tested only after being fully infiltrated after being left for 12 hours. The charge and discharge process, long cycle performance, and rate performance of the half-cell are tested using the NEWARE test system. The charge and discharge voltage window is set to 0.01-3V, the current density of the long cycle test is set to 1000mA / g, and the current density of the rate performance test is set to 50, 100, 200, 300, 400, 500, and 1000mA / g. After the parameters are set, the program can be started for testing, and all tests are performed at room temperature. The assembled half-cell was subjected to cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests using an electrochemical workstation with a voltage window of 0.01-3 V and a scan rate of 0.1 mV / s. The EIS frequency range was 0.01 Hz-100 kHz.

[0034] Test 1 results: According to Figure 3 From the XRD patterns of PCaC sample in Example 1 and PMgC sample in Comparative Example 1, we can see that the diffraction peaks of PCaC appear at 21.68° and 43.62°, corresponding to the (002) and (100) crystal planes. Similarly, PMgC shows obvious diffraction peaks at 22.12° and 43.19°, corresponding to the (002) and (100) crystal planes. According to the Bragg equation, the interlayer spacings of PCaC and PMgC are 0.410nm and 0.401nm, respectively, revealing the effect of different template methods on the interlayer spacing. A larger interlayer spacing is beneficial to large-sized K + In addition, the (100) crystal plane reflects the disorder of the electrode PCaC structure, indicating that it has more surface defects and active sites, which also explains why PCaC has faster electrochemical reaction kinetics.

[0035] Results of Experiment 2: According to Figure 4 N of PMgC and PCaC 2 The adsorption-desorption isotherm and the pore size distribution diagrams of Example 1 and Comparative Example 1 can be obtained according to Figure 4 (a) It can be seen that the N of the sample PMgC of Comparative Example 1 2 The adsorption-desorption curve shows an H3 hysteresis loop, indicating that it has a mixed structure of micropores and mesopores, with a specific surface area of ​​261.5 m2 / g. According to Figure 4 (b) See the N of PCaC 2 The adsorption-desorption isotherm curve is type IV, indicating that the material has a mesoporous pore structure with a specific surface area of ​​1465.1 m 2 / g. Observation Figure 4 (c) The pore size distribution of PMgC and PCaC shows that PCaC has a large number of mesoporous structures and some macroporous structures. In contrast, PMgC has only a small amount of mesoporous structures. The above results show that PCaC has abundant mesoporous-macroporous structures and a large specific surface area, which means that there is more electrolyte contact surface and abundant pore structure, which allows the electrolyte to penetrate into the electrode material more evenly, which helps K + More rapidly embedding / de-embedding in electrode materials effectively improves the battery's conductivity, cycle stability, and rate performance.

[0036] Test 3 results: Figure 5 The Raman spectra of PCaC and PMgC can be observed at 1350 cm -1 The D peak near 1580cm -1 The G peaks near the sp 3 Hybridized disordered carbon structure and sp 2 Hybrid ordered graphite structure. In addition, at 1200cm -1 The nearby T peak corresponds to the carbon atoms exposed at the edge and is located at 1470 cm -1 The nearby D" peak corresponds to the carbon defect structure that is not a six-membered ring or is doped with heteroatoms. D / A G The value of A can be used to determine the number of defects or edge active sites in the material. D / A G are 1.01 and 1.10, respectively, indicating that PMgC has more carbon defect density. However, due to the less pore structure of PMgC, K + The transport of ions leads to its slow electrochemical kinetics. In contrast, PCaC has a rich pore structure and a reasonable distribution of edge active sites, which makes it exhibit better electrochemical performance.

[0037] Test 4 results: According to Figure 6 (a) XPS full spectrum of the prepared samples We can see that PCaC and PMgC are composed of C and O elements, and the template and impurities in the synthesis process have been completely removed. Figure 6(b) The C and O element content distribution of the prepared samples shows that the C and O contents of PCaC are 94.59% and 5.41%, while the C and O contents of PMgC are 91.59% and 8.41%. Compared with PMgC, the O element content of PCaC remains basically unchanged, but slightly decreases. This difference is also reflected in the distribution of D-type and D”-type defective carbon, and the O content of PCaC corresponds to a lower defect density.

[0038] Experiment 5 results: We Figure 7 The rate performance diagram of the PCaC sample in Example 1 and the PMgC sample in Comparative Example 1 shows that the PCaC electrode material has excellent potassium storage capacity and rate performance, with capacities of 334 and 128.4 mAh / g at current densities of 50 mA / g and 1000 mA / g, respectively. Figure 8 The cycle curve of the prepared sample at a current density of 100 mA / g shows that PCaC has good cycle stability and maintains a specific capacity of 232.8 mAh / g after 100 cycles at a current density of 100 mA / g. Fig. 9 From the cycle curve of the prepared sample at 1000 mA / g, it can be seen that even after 500 cycles at 1000 mA / g, it still has a high capacity of 152.1 mAh / g, and the capacity decay rate per cycle is only 0.045%.

[0039] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed. However, as long as it is within the scope of the claims of the present application, it shall be protected by the patent law.

Claims

1. A method for preparing a porous carbon negative electrode material for a potassium ion battery, characterized in that: The following steps are involved: (1) Glucose and metal oxide were placed in an agate mortar at a mass ratio of 3:1 and ground for 20 minutes to ensure that the raw materials were fully mixed; (2) placing the raw material obtained in step (1) in a corundum boat, heating to 800° C. at a heating rate of 5° C. / min in an argon atmosphere, and calcining for 2 hours to obtain a pyrolyzed powder; (3) The pyrolyzed powder obtained in step (2) was placed in 3M HCl and stirred for 12 hours. After filtration, it was dried in a vacuum drying oven at 60° C. for 24 hours to obtain a porous carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: The metal oxide is CaO or MgO.

3. A porous carbon negative electrode material prepared according to the method according to any one of claims 1 to 2, characterized in that: The material has abundant mesoporous and macroporous structures and a specific surface area of ​​1465.1 m 2 / g, and the interlayer spacing is 0.410nm.

4. Use of the porous carbon negative electrode material according to claim 3 in a potassium ion battery, characterized in that: The material is used for preparing electrode sheets.

5. The use according to claim 4, characterized in that: The method for preparing the electrode sheet comprises the following steps: The porous carbon negative electrode material, the conductive agent Super P, and the binder PVDF were mixed in a mass ratio of 70:20:10, ground for 30 minutes, and then prepared into a slurry with N-methylpyrrolidone (NMP) solvent; the slurry was coated on a copper foil, dried at 60°C for 2 hours, cut into discs with a diameter of 12 mm, and vacuum dried at 80°C for 12 hours to obtain an electrode sheet.

6. A potassium ion battery, characterized in that: The invention comprises an electrode sheet prepared according to the method of claim 5.

7. The potassium ion battery according to claim 6, characterized in that The capacity of the porous carbon negative electrode material at current densities of 50 mA / g and 1000 mA / g is 334 mAh / g and 128.4 mAh / g respectively.

8. The potassium ion battery according to claim 6, characterized in that The capacity retention rate of the porous carbon negative electrode material is 152.1 mAh / g after 500 cycles at 1000 mA / g, and the capacity attenuation rate per cycle is only 0.045%.

9. The potassium ion battery according to claim 6, characterized in that: The porous carbon negative electrode material forms a low-impedance solid electrolyte interface (SEI) film during the cycle, which reduces the K + Transport resistance during embedding / de-embedding.

10. The potassium ion battery according to claim 6, characterized in that: The porous carbon negative electrode material can effectively buffer the volume expansion caused by the insertion / deinsertion of potassium ions and improve the cycle stability.

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