CN110498413B - Method for directionally regulating and controlling pore diameter and graphitization of porous activated carbon material and application of porous activated carbon material in lithium ion capacitor - Google Patents
Method for directionally regulating and controlling pore diameter and graphitization of porous activated carbon material and application of porous activated carbon material in lithium ion capacitor Download PDFInfo
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- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
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- Y02E60/13—Energy storage using capacitors
Abstract
The invention discloses a method for directionally regulating and controlling the pore diameter and graphitization of a porous activated carbon material and application of the porous activated carbon material in a lithium ion capacitor. Carrying out coordination reaction on an organic ligand, zinc ions and cobalt ions to obtain a precursor; calcining and pickling the precursor to obtain a porous carbon material; uniformly mixing the porous carbon material and an activating agent for activation treatment to obtain a porous activated carbon material; the aperture and graphitization of the porous activated carbon material are regulated and controlled by the molar ratio of zinc ions to cobalt ions, and the porous activated carbon material which has proper aperture distribution and graphitization effect can be obtained by regulating the molar ratio of the zinc ions to the cobalt ions to be about 90% to 10%, and can be used as an anode for constructing a high-performance lithium ion capacitor.
Description
Technical Field
The invention relates to a porous activated carbon material, in particular to a method for directionally regulating and controlling the aperture and graphitization of the porous activated carbon material, a porous activated carbon material with a proper aperture and graphitization degree is synthesized by the method, and the application of the porous activated carbon material in a lithium ion capacitor is also related, belonging to the technical field of electrochemical energy storage material preparation.
Background
The lithium ion capacitor consists of a battery type cathode and a capacitance type anode, and has huge application prospect in the fields of electric automobiles, medical equipment, national power grids and aerospace and aviation due to the advantages of high energy density, high power density and long cycle stability. However, the energy density and power density of the current lithium ion capacitor are not yet ideal, and are mainly limited by the problems of mismatch of electrochemical kinetics between the negative electrode and the positive electrode and the problems of difficulty in manufacturing electrodes and difficulty in quality matching caused by the low-capacity positive electrode. Currently, activated carbon is a commonly used positive electrode material for lithium ion capacitors, although it has a large specific surface area (about 1500 m)2 g-1) However, the capacity is not ideal enough, and is less than 40mAh g-1. This is because activated carbon has a relatively narrow porosity which is detrimental to storing solvated PF6 -An anion. In order to improve the capacity of the positive electrode carbon material and promote the development of the lithium ion capacitor, corresponding researches are carried out on the aspects of surface functionalization and introduction of Faraday capacitance. The performance of the positive carbon material is based on the behavior of the electric double layer capacitance, and the fundamental reason for the influence on the electric double layer capacitance is the pore characteristics. However, many research focuses are only limited to the research on organic systems of supercapacitors, and the research on lithium ion capacitors is very little. Therefore, the search for a proper pore diameter is a key factor for improving the performance of the cathode carbon material and promoting the development of the lithium ion capacitor. In order to systematically study the influence of the pore diameter, Yury gootsi obtained a microporous carbon material by reacting chlorine gas with titanium carbide in an early stage, and the capacitance behavior of the carbon material in the tetra-ethyl-amine tetrafluoroborate electrolyte with different microporous characteristics was studied to obtain certain conclusions. However, this preparation method is dangerous and complicated to operate. In addition, currently, no report exists for systematically studying the pore size of porous carbon materials in LiPF6The capacitive behavior of the electrolyte. In addition, the graphitization effect is also a key ring influencing the performance of the carbon material, and the graphitization effect can improve the electrical conductivity of the carbon material, so that the performance of the carbon material is further improved.
Disclosure of Invention
In view of the drawbacks of the prior art, a first object of the present invention is to provide a method for simultaneously controlling the specific surface area and graphitization degree of a porous activated carbon material by designing a zinc-cobalt mixed metal coordination polymer and orienting through a zinc-cobalt mixed metal ratio.
The second purpose of the invention is to provide a porous activated carbon material with proper pore structure and graphitization degree, and the carbon material is particularly suitable for preparing a lithium ion capacitor with high energy density and good cycle performance.
The third purpose of the present invention is to provide a method for preparing a porous activated carbon material with appropriate pore structure and graphitization degree by controlling the ratio of zinc-cobalt mixed metal in a proper range, which is simple, low-cost and beneficial to industrial production.
The fourth purpose of the invention is to provide application of a porous activated carbon material with proper pore structure and graphitization degree, and the lithium ion capacitor prepared from the porous activated carbon material shows high energy density.
In order to realize the technical purpose, the invention provides a method for directionally regulating and controlling the aperture and graphitization of a porous activated carbon material, which comprises the steps of carrying out coordination reaction on an organic ligand, zinc ions and cobalt ions to obtain a precursor; calcining and pickling the precursor to obtain a porous carbon material; uniformly mixing the porous carbon material and an activating agent for activation treatment to obtain a porous activated carbon material; the aperture and graphitization of the porous activated carbon material are regulated and controlled by the molar ratio of zinc ions to cobalt ions.
Preferably, the ratio of the molar amount of the organic ligand to the total molar amount of the zinc ions and the cobalt ions is 3-5: 1. Most preferably 4: 1.
In a preferred embodiment, the organic ligand is 2-methylimidazole, benzimidazole, terephthalic acid, or 2, 5-dihydroxyterephthalic acid. Most preferred is 2-methylimidazole. The 2-methylimidazole can form a stable ZIFs topological structure with zinc ions and/or cobalt ions, and the topological structures formed by adopting monometallics and bimetals and the 2-methylimidazole are consistent. The porous activated carbon material prepared by using 2-methylimidazole as a ligand has a special ordered porous structure and has higher specific surface area and mass transfer rate.
In a preferred embodiment, the calcination treatment process comprises: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1The temperature is raised to 750-850 ℃ at the temperature raising speed, and the temperature is kept for 1-3 hours. Under the preferred calcination conditions, zinc metal volatilization can be used to make the porous carbon material microporous and to increase the degree of graphitization by cobalt catalysis. Most preferred calcination treatment process: under protective atmosphere, at 10 deg.C for min-1The temperature is raised to 800 ℃ at the temperature raising speed, and the temperature is kept for 2 hours.
Preferably, the mass ratio of the porous carbon material to the activator is 1: 0.5-1.5. Most preferably 1: 1.
In a preferred embodiment, the activator is potassium hydroxide.
In a preferred embodiment, the activation treatment process comprises: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1The temperature is raised to 750-850 ℃ at the temperature raising speed, and the temperature is kept for 1-3 hours. The pore diameter of the porous carbon material can be enlarged through activation, and partial micropores are converted into mesopores. Most preferred activation treatment process: under protective atmosphere, at 10 deg.C for min-1The temperature is raised to 800 ℃ at the temperature raising speed, and the temperature is kept for 2 hours.
In a preferred scheme, the mole percentage of cobalt ions in zinc ions and cobalt ions is increased from 0% to 100%, and the porous activated carbon material I prepared correspondinglyD/IGThe specific value is decreased progressively, the specific surface area is decreased progressively, the micropore proportion is decreased progressively, and the mesopore and macropore proportion is increased progressively. By adjusting the proportion of zinc ions and cobalt ions, the directional regulation and control of the pore structure and the specific surface area of the porous activated carbon material can be realized, and the preparation of porous carbon materials with different application requirements can be met.
In the preferred scheme, the acid washing treatment mainly adopts acid liquor to remove residual elemental metal, mainly metallic cobalt. Acids such as hydrofluoric acid are used. The acid and concentration required to dissolve the metallic cobalt are readily available to those skilled in the art.
Preferably, the protective gas is nitrogen or an inert atmosphere. An inert atmosphere such as argon.
Preferably, the zinc and cobalt ions are provided by readily soluble salts of cobalt and zinc, such as nitrates, chlorides, acetates, and the like.
The invention provides a preparation method of a porous activated carbon material, which comprises the steps of carrying out coordination reaction on an organic ligand, zinc ions and cobalt ions to obtain a precursor; calcining the precursor to obtain a porous carbon material; uniformly mixing the porous carbon material and an activating agent for activation treatment to obtain a porous carbon active material; wherein the molar ratio of the zinc ions to the cobalt ions is 95-85% to 5-15%. By controlling the ratio of the zinc ions to the cobalt ions in a preferred range, the cathode material which has the specific surface area, the pore structure and the graphitization and can most meet the application requirements of the lithium ion capacitor can be obtained. The molar ratio of zinc ions to cobalt ions is most preferably 90% to 10%.
In a preferred embodiment, the calcination treatment process comprises: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1The temperature is raised to 750-850 ℃ at the temperature raising speed, and the temperature is kept for 1-3 hours. Most preferred calcination treatment process: under protective atmosphere, at 10 deg.C for min-1The temperature is raised to 800 ℃ at the temperature raising speed, and the temperature is kept for 2 hours.
Preferably, the mass ratio of the porous carbon material to the activator is 1: 0.5-1.5. Most preferably 1: 1.
In a preferred embodiment, the activator is potassium hydroxide.
In a preferred embodiment, the activation treatment process comprises: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1The temperature is raised to 750-850 ℃ at the temperature raising speed, and the temperature is kept for 1-3 hours. Most preferred activation treatment process: heating to 800 ℃ at the heating rate of 10 ℃ min-1 under the protective atmosphere, and preserving heat for 2 hours.
In a preferable scheme, the ratio of the molar amount of the organic ligand to the total molar amount of the zinc ions and the cobalt ions is 3-5: 1; most preferably 4: 1.
In a preferred embodiment, the organic ligand is at least one of 2-methylimidazole, benzimidazole, terephthalic acid and 2, 5-dihydroxyterephthalic acid.
Preferably, the protective gas is nitrogen or an inert atmosphere. An inert atmosphere such as argon.
The invention is realized by adjusting ZThe proportion of n ions and Co ions is in a certain range, the proportion of mesopores with the aperture of 2-3nm can be improved, a certain graphitization is obtained, and the aperture of 2-3nm is PF6 -The adsorption and desorption behaviors of ions play an important role, the improvement of graphitization is favorable for improving the rate capability of the anode carbon material, and the surface capacitance behavior of the anode of the porous activated carbon material can be improved by improving graphitization and increasing the mesoporous/macroporous porosity. The porous activated carbon material prepared by the invention can be assembled to obtain a high-capacity lithium ion capacitor with high energy density and good cycle performance.
The invention also provides a porous activated carbon material which is obtained by the preparation method.
The invention also provides an application of the porous activated carbon material in a lithium ion capacitor, and the porous activated carbon material is applied as a positive electrode material of the lithium ion capacitor.
The porous activated carbon material can obtain proper pore size distribution and graphitization effect, and the assembled lithium ion capacitor shows excellent electrochemical performance, especially Zn90Co10APC (zinc ion and cobalt ion molar ratio 90%: 10% porous activated carbon material prepared) at 300W kg-1Shows up to 108Wh kg at power densities of-1The energy density of (1).
Compared with the prior art, the technical scheme of the invention has the following advantages:
1. the invention provides a method capable of simultaneously directionally regulating and controlling the pore structure and the graphitization degree of a carbon material, and provides theoretical guidance for obtaining carbon materials with different application requirements;
2. according to the invention, the pore structure and the graphitization degree of the carbon material are regulated and controlled within a certain range, so that the carbon material is particularly suitable for being used by a lithium ion capacitor, can be used as an ideal lithium ion capacitor anode material for replacing a commercial activated carbon material, and the constructed lithium ion capacitor shows excellent performance, thereby greatly promoting the application development of the lithium ion capacitor.
3. The invention prepares the graphite composite material which can obtain proper pore size distribution and graphitization effectThe lithium ion capacitor assembled by the porous activated carbon material has excellent electrochemical performance, especially Zn90Co10APC (zinc ion and cobalt ion molar ratio 90%: 10% porous activated carbon material prepared) at 300W kg-1Shows up to 108Wh kg at power densities of-1The energy density of (1).
Drawings
[ FIG. 1 ] is ZnxCo100-xExperimental XRD and simulations of ZIFs.
Fig. 2 is an XRD and Raman diagram: (a, b) ZnxCo100-xPCs and (c, d) ZnxCo100-xAPCs。
FIG. 3 is ZnxCo100-x-PCs and ZnxCo100-x-a (a, b) nitrogen desorption profile, (c, d) pore size distribution profile and (e, f) normalized cumulative pore size distribution profile of the APCs.
Fig. 4 is an HRTEM: (a, b) Zn100-PC，(c,d)Co100-PC，(e,f)Zn100APC and (g, h) Co100-APC。
FIG. 5 represents ZnxCo100-x-PCs and ZnxCo100-x-graph of the rate performance of APCs.
FIG. 6 is ZnxCo100-x-PCs and ZnxCo100-x-plot of peak current versus sweep rate for APCs.
FIG. 7 is Zn90Co10-a nitrogen desorption profile for APC (a), (b) an aperture profile, (c) a normalized cumulative aperture profile and (d) a magnification performance profile.
FIG. 8 shows PLG// Zn90Co10-cyclic voltammograms, (b) galvanostatic charge-discharge diagrams and (c) Ragon diagrams of APC LIC.
Detailed Description
The present invention will be further described with reference to the following specific examples. These examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. After reading the disclosure of the present invention, various changes or modifications made based on the principle of the present invention also fall within the scope of the present invention as defined in the appended claims.
Example 1
1. Preparation of the Material
1.1 MOFs precursors (Zn)xCo100-x-ZIFs) preparation:
monometallic ZIF-8 (Zn)100-ZIF) and ZIF-67 (Co)100-Preparation of ZIF): zn (NO)3)2·6H2O (3mmol,891mg) or Co (NO)3)2·6H2O (3mmol,873mg) was dissolved in 30mL of methanol, respectively. Next, 2-methylimidazole (984mg,12mmol) was dissolved in 30mL of methanol, respectively. Subsequently, the organic ligand solution was quickly added to the metal solution with stirring. After stirring for 15 minutes, the resulting solution was allowed to stand for 24 hours, whereby a product precipitate could be precipitated. Finally, the product obtained is washed several times with methanol and dried under vacuum at 80 ℃ for 12 hours.
Preparation of bimetallic ZIFs: the preparation of bimetallic ZIFs is very similar to the above preparation method except that Zn (NO) is changed3)2·6H2O Co(NO3)2·6H2The proportion of O. Thus, Zn75Co25-ZIF,Zn50Co50-ZIF and Zn25Co50ZIF is obtained by adjusting the Zn/Co metal ratio to 3:1, 1:1 and 1:3, respectively.
1.2 MOFs-derived porous carbon materials (Zn)xCo100-x-preparation of PCs):
zn is addedxCo100-xZIFs was placed in a tube furnace under argon atmosphere at 10 ℃ for min-1The temperature was raised to 800 ℃ and kept constant for 2 hours. And after natural cooling, washing the obtained calcined product for multiple times by using HF solution and distilled water respectively to remove residual metal impurities. Finally obtained ZnxCo100-xThe PCs product was dried under vacuum at 80 ℃ for 12 hours.
1.3 MOFs-derived porous activated carbon Material (Zn)xCo100-x-preparation of APCs):
zn prepared originallyxCo100-x-PCs and KOH powder in a mass ratio of 1:1The resulting mixture was added to 15mL of distilled water and stirred for 12 hours to obtain a uniformly mixed suspension. And then, drying the solvent, and transferring the obtained dried powder to a tube furnace for calcination under the specific conditions: 10 ℃ min-1The temperature is raised at 800 ℃ for 2 hours in an argon atmosphere. The activated sample was washed several times with dilute hydrochloric acid and distilled water. Finally, the obtained Zn is treatedxCo100-xThe APCs product was dried under vacuum at 80 ℃ for 12 hours.
2. Electrochemical testing:
taking the prepared carbon material (Zn) derived from 80 wt% MOFsxCo100-x-PCs and ZnxCo100-x-APCs) as an active material, 10 wt% of PVDF as an adhesive, 10 wt% of Super P as a conductive agent and a small amount of N-methylpyrrolidone in an agate mortar, carefully grinding until the slurry is uniform, coating the obtained slurry on an Al foil, and vacuum-drying at 80 ℃ for 12 hours to obtain the positive electrode plate to be tested. Meanwhile, the method of preparing a commercial graphite negative electrode is similar to the above-described method of preparing a carbon positive electrode: except that the slurry was mixed by grinding 70 wt% of the active material, 15 wt% of the carboxymethyl cellulose binder, 15 wt% of the Super P conductive carbon and a little distilled water, and then coated on the Cu foil.
For testing of half-cells, cut-pieces of carbon positive and graphite negative electrodes were used as working electrodes, metallic Li sheets were used as counter and reference electrodes, 1mol L-1 LiPF6The volume ratio of the electrolyte to the membrane is 1:1:1, the electrolyte is ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate, Whatman GF/C glass fiber membrane is used as a diaphragm, and a CR2016 battery shell is selected for assembly in a glove box. ) In addition, the graphite negative electrode needs to be 0.1A g in a half-cell system before being assembled into a lithium ion capacitor-1Current density was cycled 5 times.
3. Results and analysis
As is well known, ZIF-8 and ZIF-67 are isomorphs constructed from 2-methylimidazole and Zn and Co ions, respectively. In addition, the topological structure of the bimetallic ZIFs obtained after the Zn/Co metal source ratio is changed is not changed, and the crystal form of the bimetallic ZIFs is kept the same as that of the monometallic ZIF. To verify the phase and purity of the samplePrepared ZnxCo100-xFirst, XRD characterization test is carried out on ZIFs precursor, and Zn is found as the result shown in figure 1xCo100-xThe XRD patterns of the ZIFs are consistent with the computer simulation patterns, which shows that uniform precursors are obtained and the structures are consistent. As shown in fig. 2a, two peaks, clearly located at-25 ° and-44 °, are for the (002) and (001) crystal planes with carbon, respectively. Zn due to the broader and lower intensity peak characteristics100PC exhibits amorphous carbon characteristics. On the other hand, Co100The half-width of the (002) peak of PC becomes significantly narrower, which indicates that the resulting carbon is converted into graphitized carbon due to the catalytic graphitization effect of Co metal. Furthermore, as Co ions increase, ZnxCo100-xThe crystallinity of the PCs is gradually improved. Notably, Zn was present even after chemical activation with KOHxCo100-xThe APCs still retain the original ZnxCo100-xSize order of graphitization of PCs (fig. 2b) to further verify graphitization of carbon materials, Zn is appliedxCo100-x-PCs and ZnxCo100-xRaman measurements of APCs, two significant ones are located at 1350 and 1585cm, as shown in FIGS. 2c and 2d-1The peaks are assigned to the amorphous carbon D peak and the graphitized carbon G peak, respectively. Zn100-PC,Zn75Co25-PC,Zn50Co50-PC,Zn25Co75-PC and Co100-I of PCD/IGThe ratios were 1.46,1.34,1.27,1.15, and 1.05, respectively, which indicates that Zn was increased with the Co ion contentxCo100-xThe graphitization of the PCs is correspondingly enhanced. At the same time, for Zn100-APC,Zn75Co25-APC,Zn50Co50-APC,Zn25Co75APC and Co100APC of the corresponding ID/IGThe ratios are 1.86,1.51,1.37,1.31 and 1.24, respectively. Furthermore, Zn100-PC,Zn75Co25-PC,Zn50Co50-PC,Zn25Co75-PC and Co100The PC samples were each 0.1S cm-1,1.12S cm-1,5.42S cm-1,8.70S cm-1And 12.5S cm-1。Zn100-APC,Zn75Co25-APC,Zn50Co50-APC,Zn25Co75APC and Co100The conductivity of the APC sample was about 0.05S cm-1,0.89S cm-1,4.20S cm-1,6.70S cm-1And 9.5S cm-1. The above results indicate that the increase in electrical conductivity of the carbon material results from enhanced graphitization. Therefore, the graphitization of the carbon material can be directionally controlled by adjusting the molar ratio of Zn/Co ions.
ZnxCo100-x-PCs and ZnxCo100-xThe porosity characteristics of the APCs were determined by analysis after the nitrogen desorption curve, the parameters obtained being summarized in Table 1. As shown in FIG. 3a, Zn100PC exhibits a typical type I curve, indicating that it has a distinct microporous structure. And this microporous characteristic is caused by volatilization of Zn metal vapor under high temperature conditions. It is noteworthy that as the content of the Co metal source increases, ZnxCo100-xThe curve of-PCs gradually forms a H3 hysteresis loop and is between 0.45 and 1.0P/P0The gradual broadening in the range illustrates the generation of meso/macroporous regions and the formation of a broad pore size distribution. This phenomenon is mainly caused by the removal of metallic Co simple substance remaining on the carbon substrate. Research finds that ZnxCo100-xThe BET specific surface area in the system of-PCs becomes smaller and smaller in the order of Zn100-PC(957m2 g-1)>Zn75Co25-PC(524m2 g-1)>Zn50Co50-PC(370m2 g-1)>Zn25Co75-PC(367m2 g-1)>Co100-PC(332m2 g-1). The above results indicate that the specific surface area and pore size range of the carbon material can be directionally controlled by changing the Zn/Co ratio. It is well known that KOH chemical activation can increase the BET specific surface area of carbon materials and alter pore structure. Thus, ZnxCo100-xAPCs exhibit a hierarchical porous structure with increased specific surface area and rich meso/macroporous porosity (fig. 3 b). Furthermore, fig. 3c and 3d show the corresponding pore size distribution characteristics of the carbon material. To enter intoBetter evaluate the difference of pore size distribution, ZnxCo100-x-PCs and ZnxCo100-xNormalized cumulative pore profiles of APCs were analyzed in detail (fig. 3e and 3 f). This can provide more intuitive changes in pore structure to varying degrees in micropores, mesopores and macropores. In general, the average pore diameter d is often mentioned50The actual pore size distribution is not fully reflected. Thus, d25And d75The addition of (i.e., representing the pore size at 25 and 75% of the total pore volume occupied, respectively) better reflects the degree of dispersion of the pore characteristics of the carbon material. Significantly, this overall pore characteristic dispersion result provides an important parameter for the subsequent discussion of pore size distribution and capacitance behavior.
To visually observe Zn in more detail100-PC，Co100-PC，Zn100-APC，Co100Morphology of the APC, as well as pore structure changes, TEM tests were performed. FIGS. 4a-4d are Zn100-PC and Co100HRTEM image of-PC, in which Zn can be seen100PC is amorphous carbon and has a predominantly microporous structure, while Co100PC is graphitized carbon and has a large meso/macroporous pore size. After KOH activation, Zn100APC exhibits significant mesopores with a pore size of about 2 to 5nm, while Co100The mesoporous distribution of APC is more uniform and the pore size of meso/macro pores becomes smaller (fig. 4e-4 h). This result is consistent with the XRD, Raman and pore property data described above.
In order to evaluate adsorption/desorption PF of the obtained carbon material6 -The capacitance behavior of the anion is used as the anode of the lithium ion capacitor to perform half-cell test in the voltage range of 2.0-4.5V. FIGS. 5a and 5b show ZnxCo100-x-PCs and ZnxCo100-xRate capability of APCs at different current densities. Notably, Zn100PC, although having a larger BET specific surface area, exhibits the worst electrochemical performance (0.1A g)-1Only 15mAh g under current density-1Specific capacity of). This is due to Zn100The PC has a narrow and unsuitable pore size range, 80% of its pore volume being occupied by microporous featuresThereby limiting its electrochemical performance. In contrast, Co100Although the BET specific surface area of the-PC is lower, the specific capacity of the-PC is Co due to the abundant meso/macroporous porosity100PC at 0.1A g-1Can reach 40mAh g under the current density-1. As can be seen by combining FIGS. 3e and 3f, Co100The PC has a more suitable aperture range (d)50＝2.07nm～d7527.27nm), resulting in stronger adsorption and desorption PF6 -The behavior of the ions. The above results show that adsorption and desorption PF6 -The behavior of the ions is dominated by the pore size of the carbon material. Interestingly, Zn was activated by KOH100The electrochemical performance of APC is significantly improved, at 0.1A g-1Can exert 55mAh g under the current density-1The specific capacity of (A). In contrast, Co100The performance of the APC is significantly reduced. This result demonstrates Zn100APC and Co100The electrochemical performance of the APC is affected by the altered pore size distribution. Through research, Zn is found100Reduction of the pore volume fraction of APC to 49%, d thereof50And d75The pore diameters of (a) were increased to 2.12 and 2.64nm, respectively, indicating that the increased pore diameter range increased the PF6 -Adsorption and desorption behaviors of ions. Furthermore, Co100The electrochemical performance of APC is reduced due to the reduced porosity around 2 nm. At the same time, Zn75Co25D of-PC25，d50And d75The pore diameters are respectively 10.06nm,33.75nm and 51.60nm, and Zn is obtained after chemical activation75Co25APC changes were 2.11nm,2.96nm and 17.37 nm. Zn of the pores in the range of 2 to 3nm due to an increase in the pore volume fraction75Co25The electrochemical performance of APC is significantly increased. The above results show that the pore diameter is 2-3nm at PF6 -Plays an important role in the adsorption and desorption behaviors of ions. Furthermore, it is apparent that Zn is caused byxCo100-xCatalytic graphitization effect brought by Co metal in the ZIFs precursor, and the rate capability of the MOFs derived carbon material can be improved.
To better understand the obtained carbon materialFor PF6 -The adsorption and desorption behaviors of ions are tested by performing cyclic voltammetry on materials of the ions. Selecting data of peak current i and sweep speed v, and obtaining a v value according to a formula ibAnd log (i) blog (v) + loga, where a and b are variable parameters. According to the b value, the two different electrochemical energy storage behaviors can be divided, wherein the energy storage behavior is mainly dominated by the diffusion control process when the b value is closer to 0.5, and conversely, the energy storage behavior is dominated by the surface-controlled capacitance behavior when the b value is closer to 1. FIGS. 6a and 6b show ZnxCo100-x-PCs and ZnxCo100-x-the relevant fitted curve of APCs, whose corresponding b-values are also carefully calculated. Zn100-PC,Zn75Co25-PC,Zn50Co50-PC,Zn25Co75-PC and Co100B values for-PC are 0.73,0.75,0.80,0.88 and 0.94, respectively. This result demonstrates that an increase in graphitization can promote an increase in surface capacitance behavior. More importantly, Zn is chemically activated by KOH100-APC,Zn75Co25-APC,Zn50Co50-APC,Zn25Co75APC and Co100The b-value of APC was raised to 0.76,0.81,0.94,1.06 and 1.09, respectively. This result demonstrates that the enhancement of surface pseudocapacitance behavior can be achieved by increasing the meso/macroporous porosity of the carbon material. The above results confirm that the behavior of the surface capacitor of the carbon anode can be improved by promoting graphitization and increasing the mesoporous/macroporous porosity, which is helpful to provide theoretical guidance for the anode carbon material of the high-performance lithium ion capacitor better.
Carbon cathode material and adsorption/desorption PF obtained as described above6 -Conclusion of the intrinsic relationship of the capacitive behavior of the anion, Zn90Co10APC was designed and synthesized ingeniously. Zn due to proper pore size distribution and synergy of graphitization effect90Co10APC showed the most excellent electrochemical performance in all the synthesized carbon materials, at 0.1A g-1Can keep nearly 60mAh g under current density-1The reversible capacity of (FIG. 7). Commercial lithium ion capacitors are typically made of graphiteThe negative pole and the active carbon positive pole. For better evaluation of Zn prepared90Co10Excellence of-APC carbon material as positive electrode of lithium ion capacitor, Zn90Co10And assembling the APC serving as a positive electrode and a graphite negative electrode (PLG) after prelithiation into a lithium ion capacitor. Fig. 8a-8b show corresponding slightly deformed quasi-rectangular CV curves and non-completely linear constant current charging and discharging curves, which indicate that two energy storage mechanisms of faraday behavior and non-faraday behavior exist in a lithium ion capacitor system. Significantly, the assembled PLG/Zn90Co10APC lithium ion capacitor at 300W kg-1Shows up to 108Wh kg at power densities of-1And superior to the PLG// AC lithium ion capacitor (FIG. 8 c). This patent provides a method for preparing a graphitized carbon material with different pore sizes by directional adjustment, according to which Zn with proper pore size distribution and graphitization effect can be obtained90Co10Carbon material of APC, which exhibits extremely excellent electrochemical performances after its use for the construction of lithium ion capacitors.
Claims (1)
1. The application of the porous activated carbon material in the lithium ion capacitor is characterized in that: the lithium ion capacitor anode material is applied as a lithium ion capacitor anode material;
the porous activated carbon material is prepared by the following preparation method: carrying out coordination reaction on an organic ligand, zinc ions and cobalt ions to obtain a precursor; calcining the precursor to obtain a porous carbon material; uniformly mixing the porous carbon material and an activating agent for activation treatment to obtain a porous activated carbon material; wherein the molar ratio of the zinc ions to the cobalt ions is 95-85% to 5-15%;
the calcination treatment process comprises the following steps: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1Raising the temperature to 750-850 ℃ at the temperature raising speed, and preserving the heat for 1-3 hours;
the mass ratio of the porous carbon material to the activating agent is 1: 0.5-1.5; the activating agent is potassium hydroxide;
the ratio of the molar amount of the organic ligand to the total molar amount of the zinc ions and the cobalt ions is 3-5: 1;
the organic ligand is at least one of 2-methylimidazole, benzimidazole, terephthalic acid and 2, 5-dihydroxy terephthalic acid;
the activation treatment process comprises the following steps: under the protective atmosphere, at the temperature of 5-15 ℃ for min-1The temperature is raised to 750-850 ℃ at the temperature raising speed, and the temperature is kept for 1-3 hours.
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