CN115504449A - Method and material for F-doped modified phenolic resin base - Google Patents
Method and material for F-doped modified phenolic resin base Download PDFInfo
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- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical class [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 title claims abstract description 26
- 239000000463 material Substances 0.000 title abstract description 22
- 239000005011 phenolic resin Substances 0.000 claims abstract description 27
- 229920001568 phenolic resin Polymers 0.000 claims abstract description 27
- 238000003763 carbonization Methods 0.000 claims abstract description 12
- 238000000227 grinding Methods 0.000 claims abstract description 8
- 239000000843 powder Substances 0.000 claims abstract description 7
- 239000012300 argon atmosphere Substances 0.000 claims abstract description 6
- 239000011159 matrix material Substances 0.000 claims abstract description 6
- 239000011812 mixed powder Substances 0.000 claims abstract description 5
- 238000005303 weighing Methods 0.000 claims abstract description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 239000002245 particle Substances 0.000 claims description 7
- 230000000052 comparative effect Effects 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 claims 4
- 235000013024 sodium fluoride Nutrition 0.000 claims 2
- 239000011775 sodium fluoride Substances 0.000 claims 2
- 239000002105 nanoparticle Substances 0.000 claims 1
- 229910021385 hard carbon Inorganic materials 0.000 abstract description 83
- 239000003575 carbonaceous material Substances 0.000 abstract description 51
- 239000003792 electrolyte Substances 0.000 abstract description 25
- 239000011734 sodium Substances 0.000 abstract description 14
- 230000008569 process Effects 0.000 abstract description 13
- 229910052708 sodium Inorganic materials 0.000 abstract description 12
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 abstract description 11
- 150000002148 esters Chemical class 0.000 abstract description 11
- 238000003860 storage Methods 0.000 abstract description 11
- 239000007772 electrode material Substances 0.000 abstract description 10
- 125000001153 fluoro group Chemical group F* 0.000 abstract description 10
- 238000010521 absorption reaction Methods 0.000 abstract description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 20
- 229910001415 sodium ion Inorganic materials 0.000 description 13
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 10
- 230000001351 cycling effect Effects 0.000 description 10
- 230000002441 reversible effect Effects 0.000 description 9
- 238000001228 spectrum Methods 0.000 description 9
- 230000001965 increasing effect Effects 0.000 description 8
- 239000007773 negative electrode material Substances 0.000 description 8
- 238000012360 testing method Methods 0.000 description 8
- 229910052731 fluorine Inorganic materials 0.000 description 7
- 239000011148 porous material Substances 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 238000007599 discharging Methods 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 5
- 238000009792 diffusion process Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 238000001179 sorption measurement Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000004768 lowest unoccupied molecular orbital Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 239000000523 sample Substances 0.000 description 4
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 239000011737 fluorine Substances 0.000 description 3
- 238000004770 highest occupied molecular orbital Methods 0.000 description 3
- 239000011229 interlayer Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 102000020897 Formins Human genes 0.000 description 2
- 108091022623 Formins Proteins 0.000 description 2
- 238000003917 TEM image Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000011049 filling Methods 0.000 description 2
- 238000003682 fluorination reaction Methods 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 238000009830 intercalation Methods 0.000 description 2
- 230000002687 intercalation Effects 0.000 description 2
- 230000002427 irreversible effect Effects 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 125000004436 sodium atom Chemical group 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000012876 topography Methods 0.000 description 2
- 229910016569 AlF 3 Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 238000001237 Raman spectrum Methods 0.000 description 1
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000006399 behavior Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
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- 150000001875 compounds Chemical class 0.000 description 1
- 239000013068 control sample Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 210000001787 dendrite Anatomy 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000004210 ether based solvent Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 238000002173 high-resolution transmission electron microscopy Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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- 238000001878 scanning electron micrograph Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- General Chemical & Material Sciences (AREA)
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Abstract
The invention provides a method and a material for F-doped modified phenolic resin matrix, which comprises the following steps of 1, weighing NaF with the mass fraction of 20% and alcohol-soluble phenolic resin, grinding uniformly, and putting the uniformly mixed powder into a high-temperature tube furnace filled with argon atmosphere for carbonization for 2 hours; step 2. Grind the carbonized sample to a powder, i.e. F-doped phenolic resin based and score 20% NaF-HC-1400. The invention adopts a method of doping elements with high electronegativity, such as F element, into the hard carbon electrode material, and the high electronegativity of the elements can enable the elements to play the role of electron absorption in the hard carbon. Electrons in the hard carbon material C are transferred to the doped F atoms, so that the reducibility of the electrode material is reduced, the insufficiency of the anti-reduction capability of the ester-based electrolyte is compensated, the electrolyte is prevented from reacting uncontrollably to form an over-thick SEI film in the circulating process, and finally, better sodium storage performance is obtained.
Description
Technical Field
The invention belongs to the technical field of sodium ion batteries, and particularly relates to a method and a material for modifying a phenolic resin matrix by doping F.
Background
In order to optimize the SEI film formed by the hard carbon material during charging and discharging, researchers select to use an ether-based electrolyte to match with the hard carbon negative electrode in order to obtain more excellent sodium storage performance, in addition to optimizing the hard carbon electrode. The revival of ether-based electrolyte research in sodium ion batteries stems from an encouraging discovery that sodium ions and ether-based solvent molecules can co-insert into the graphite layer, which makes graphite a possibility as a sodium ion battery negative electrode material. Finally, cao et al extended the use of ether-based electrolytes into sodium metal cathodes and found that uniform inorganic SEI films could be produced to inhibit the growth of sodium dendrites and promote good cycling stability. Bai et al have demonstrated that ether-based electrolytes are also valuable in the application of hard carbon negative electrode materials for sodium ion batteries, and in addition to improving the rate capability and cycle stability of the hard carbon materials, they also significantly improve the initial coulombic efficiency. However, many studies have been made to measure the performance of materials in sodium-ion half-cell systems. Because the ether-based electrolyte has weak oxidation resistance and cannot be matched with a high-voltage positive electrode, the ether-based electrolyte is still an ester-based electrolyte in more commercial use at present; in addition, ether-based electrolytes can form solvated intercalation compounds with sodium ions, which can cause greater volume strain in the hard carbon negative electrode material, thereby reducing the cycling stability of the material.
Comparing the ester-based electrolyte and the ether-based electrolyte, it was found that the difference in their performance was mainly caused by the large difference between the Lowest Unoccupied Molecular Orbital (LUMO) and Highest Occupied Molecular Orbital (HOMO) energy levels of the solute and the solvent, as shown in fig. 1. The LUMO of ether-based electrolytes is higher than that of ester-based electrolytes, has better reduction resistance, and can form a dense and hard inorganic SEI film. In view of this, if the reducibility of the hard carbon electrode material can be limited, it would be a better option to continue to use more commercially available ester-based electrolytes.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method and a material for modifying a phenolic resin matrix by doping F.
The invention adopts a method of doping elements with high electronegativity, such as F element, into the hard carbon electrode material, and the high electronegativity of the elements can enable the elements to play the role of electron absorption in the hard carbon. Electrons in the hard carbon material C are transferred to the doped F atoms, so that the reducibility of the electrode material is reduced, the insufficiency of the reduction resistance of the ester-based electrolyte is compensated, the electrolyte is prevented from reacting uncontrollably to form an over-thick SEI film in the circulating process, and the better sodium storage performance is finally obtained.
The invention adopts the following technical scheme:
the method for modifying the phenolic resin matrix by doping F comprises the following steps:
In the step 1, the carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ min -1 。
F doped modified phenolic resin, comparative area of carbon 2.42m 2/ g, the material is amorphous flaky particles, and contains micropores and mesopores and some narrow crack holes.
The invention has the beneficial effects that:
in the prior art, fluorine gas and argon gas are adopted for fluorination treatment at high temperature. The phenolic resin is carbonized at 600-800 ℃, the carbonization temperature is low, more oxygen and hydrogen heteroatoms are left in the phenolic resin, and the structural regularity of the obtained carbon material is poor, so that the obtained capacity is low.
In the prior art, the mixed gas of hydrogen and fluorine gas is adopted for fluorination treatment, the fluorine gas has strong etching effect on the surface of the material, and a large number of pore structures are formed on the surface of the carbon material, so that the specific surface area is increased.
The reversible capacity of the prior art is around-260 mAh/g.
The invention adjusts the reducibility of the hard carbon by doping F, thereby leading the hard carbon to show better performance in ester electrolyte.
Drawings
FIG. 1 is a graph of the difference in LUMO/HOMO energy levels between solute and solvent of ester and ether electrolytes;
FIGS. 2 (a) -2 (d) are SEM images of hard carbon material before and after F doping;
FIG. 2 (e) is a diagram of the elemental distribution of C, F, na corresponding to FIG. 2 (d);
FIG. 3 (a) is a nitrogen adsorption isotherm of HC-1400;
FIG. 3 (b) is a nitrogen adsorption isotherm of 20% NaF-HC-1400;
FIG. 3 (c) is an XRD pattern before and after F doping;
FIG. 3 (d) is a Ramman spectrum before and after doping;
FIG. 4 (a) XPS survey of 20% NaF-HC-1400;
FIG. 4 (b) is a Cls high resolution spectrum;
FIG. 4 (c) is a Ols high resolution spectrum;
FIG. 4 (d) is a schematic of F-doped phenolic resin-based hard carbon;
FIG. 5 (a) is a TEM image of HC-1400;
FIG. 5 (b) is a TEM image of 20% Na-HC-1400;
FIG. 6 (a) is a charge-discharge curve before and after F doping;
FIG. 6 (b) shows 0.1mVs before and after F doping -1 The sweep rate of (a);
FIG. 6 (c) is a graph of the rate performance before and after F doping;
FIG. 6 (d) shows 100mAg before and after F doping -1 A lower cycle performance plot;
FIG. 7 (a) is a CV curve of 20% NaF-HC-1400 electrode at different scan rates;
FIG. 7 (b) is a plot of log (scan rate) versus log (current) for b;
FIG. 7 (c) shows the pseudocapacitance contribution at 0.2mVs -1 Quantitative analysis in CV curves at scan rate;
FIG. 7 (d) is a graph showing the pseudocapacitance contribution ratio at different scan rates;
FIG. 8 (a) HC-1400 and 20% NaF-HC-1400 at 20mAg -1 Lower circulationThe subsequent EIS diagram;
FIG. 8 (b) HC-1400 and 20% NaF-HC-1400 at 20mAg -1 Low frequency zone Z' and omega after lower circulation -1/2 A relationship diagram of (1);
FIG. 8 (c) is an XPS survey spectrum;
FIG. 8 (d) shows Cls after 5 cycles of 20% NaF-HC-1400;
FIG. 8 (e) is a Ols high resolution spectrogram;
FIG. 8 (f) is a Fls high resolution spectrogram;
FIGS. 9 (a) and 9 (b) are surface topography maps of HC-1400 electrode after cycling;
FIGS. 9 (c) and 9 (d) are both surface topography maps after 20% NaF-HC-1400 electrode cycling;
FIG. 9 (e) is a graph showing an experiment of electrode folding after 20% NaF-HC-1400 cycles;
FIG. 10 is a flow chart of the steps of the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the present invention clearer and more complete, the technical solutions of the present invention are described below clearly, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 10, the method for modifying phenolic resin by doping F of the invention comprises the following steps:
The carbonization temperature in the step 1 is 1400 ℃, and the heating rate is 2 ℃ min -1 。
F doped modified phenolic resin, comparative area of carbon 2.42m 2/ g, the material is amorphous flaky particles, and contains micropores and mesopores and some narrow crack holes.
Examples of the experiments
Weighing 20% of NaF and alcohol-soluble phenolic resin by mass, uniformly grinding, and putting the uniformly mixed powder into a high-temperature tube furnace filled with argon atmosphere for carbonization for 2 hours. Wherein the carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ for min -1 . The carbonized sample was ground to a powder, i.e., F-doped phenolic resin-based hard carbon, and recorded as 20% NaF-HC-1400, the control sample was still HC-1400 as previously obtained.
Comparative example
The phenolic resin powder was carbonized for 2 hours in a high temperature tube furnace filled with argon atmosphere. The carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ for min -1 . The carbonized sample was ground to a powder to give HC-1400 ℃.
Experimental results and discussion
Influence of F doping on structure of phenolic resin-based hard carbon material
In order to prove that the F element is successfully doped into the hard carbon material, a series of characterization tests are carried out on the material before and after doping, as shown in FIGS. 2 (a) -2 (d). From fig. 2 (a), the particle morphology of HC-1400 can be seen, and from fig. 2 (b) -2 (c), it can be seen that Na-HC-1400 has obvious pores on the particle surface, which is mainly due to the corrosive nature of F element, so that the hard carbon particles are corroded during the carbonization process, which also increases the specific surface area of the hard carbon material to some extent. As shown in fig. 2 (e), the distribution of F and Na elements in the graph is relatively uniform, and the profile is almost consistent with the profile of the hard carbon particles, so that it can be preliminarily determined that F element is successfully doped into hard carbon, and the existence form of F element doped into hard carbon will be further analyzed.
In order to prove that the specific surface area of the coated material is increased, the BET specific surface area test is carried out on the F-doped hard carbon material, as shown in figures 3 (a) and 3 (b), the nitrogen adsorption curve obtained after doping is similar to that of undoped HC-1400 and is an H4 hysteresis loop, which indicates thatThe material contains micropores and mesopores and a plurality of narrow crack holes, and the specific surface area is 2.422m by testing 2 g -1 Comparative increased specific surface area of HC-1400 (0.203 m) 2 g -1 ) And is significantly increased. As shown in fig. 3 (c) and 3 (d), since the background peak of the hard carbon material itself has a larger intensity, the material is tested by using slow-scan XRD so that the background peak of the material covers the diffraction peak of NaF that may be present, and the total scanning time is 1.5 hours. However, as can be seen from fig. 3 (C), the F-doped hard carbon material does not have characteristic diffraction peak of NaF, but has C 8.6 The characteristic diffraction peak of F, corresponding to PDF card of 45-1076, means that the F element successfully penetrates into the hard carbon material and is mainly C 8.6 And F exists in a form. In addition, the diffraction peaks of (002) crystal planes of the two materials in an XRD (X-ray diffraction) pattern are slightly different from each other, the peak of the F-doped hard carbon material is slightly shifted to the right, namely the interlayer spacing of the F-doped hard carbon material is not increased, but the adjacent carbon layers of the graphite-like domain are arranged more closely due to the electron-withdrawing capability of the F-doped hard carbon material because of the strong electronegativity of the F element, specific interlayer spacing data are shown in a table 1, and as shown in a figure 3 (D), the coherent length of the graphite-like domain in the F-doped hard carbon material is shorter and more bent by calculating the ratio of the intensity of a D peak to that of a G peak.
TABLE 1 structural parameters of different hard carbon samples
XPS is also a characterization technique for analyzing the existence form of elements on the surface of a material, and as shown in fig. 4 (a) to 4 (c), it can be seen from the full spectrum (fig. 4 (a)) that the material contains elements C, O, F, na and the like. The 1s orbits of C, F elements were fitted separately to analyze their presence in hard carbon material, as shown in fig. 4 (b), 4 (c). The C1s high resolution spectra mainly have C-C bond at 284.8eV, C-O bond at 285.6 eV, and C = O/C-F bond at 289.9eV, which indicates that there is a chemical bond between the F element and the hard carbon skeleton, and the peak area is small because the content of C-F is small. However, in the high resolution spectrum of F1s, only the peak of C-F bond at 689.6eV appears, and the existence form of Na-F does not appear, which again demonstrates that the F element is successfully doped into the hard carbon material, and a schematic diagram of the F element doped phenolic resin based hard carbon material is drawn according to the previous analysis, as shown in FIG. 4 (d). The high electronegativity of the F element enables the F element to have strong electron adsorption capacity, so that electrons in the hard carbon material move to F atoms, and the reduction capacity of the hard carbon material is reduced. This will help to limit the continuous reaction of the hard carbon material with the ester-based electrolyte, thereby avoiding the continuous generation of the SEI film.
In order to more directly observe the change in the internal microstructure of the hard carbon material before and after F-doping, the present invention carried out HRTEM test on 20% NaF-HC-1400, as shown in FIG. 5 (b). The interlayer spacing of the F-doped hard carbon material did decrease to some extent compared to HC-1400 (fig. 5 (a)), consistent with the results calculated from XRD; in addition, the graphite-like domain of the F-doped hard carbon is not as long and flat as HC-1400, which is consistent with the conclusion of Raman spectrum analysis; however, it is also apparent from the figure that the F-doped hard carbon material has more nano-closed pore structure, which may also be the result of the strong electron-withdrawing ability of the F element. Based on the current researches on the sodium storage mechanism of 'adsorption-intercalation-filling', the doping of the F element brings larger reversible specific capacity to the hard carbon negative electrode material.
Influence of F doping on sodium storage performance of phenolic resin-based hard carbon material
After the materials are synthesized, the electrochemical performance of the F-doped hard carbon material is tested by the invention, for example, the first charge-discharge curve of HC-1400 and 20% NaF-HC-1400 is shown in fig. 6 (a), and the reversible specific capacity of the F-doped hard carbon material is obviously improved to 350.3mAhg -1 This is probably related to the fact that the F-doped hard carbon material contains more nano-scale closed pore structures inside. Meanwhile, the F-doped hard carbon material shows 75.2 percent of first coulombic efficiency, although sodium atoms enter the hard carbon material along with the F-doped hard carbon material to show 75.2 percent of first coulombic efficiency,although sodium atoms can enter the internal structure of the hard carbon when F is doped, and the sodium is pre-inserted to achieve the effect of pre-sodium treatment to improve the coulombic efficiency, the current obtained result is slightly lower than that of HC-1400 (77.7%), which is mainly related to the increase of the surface area of the hard carbon material after F doping, and the larger specific surface area causes the hard carbon material to have more irreversible defects, thereby reducing the first coulombic efficiency of the material. As shown in fig. 6 (b), in which the irreversible redox peak between 0.3-0.8V is not much different from that obtained from HC-1400 of fig. 6 (a), this also confirms the result that the difference in the first coulombic efficiency of the hard carbon material before and after F doping is not large. Fig. 6 (c) and 6 (d) show the rate capability and cycle capability of the material. From the rate performance graph, it can be seen that the F-doped hard carbon material has significantly higher rate capacity, 20% NaF-HC-1400 at 50, 100, 200mAg -1 Can obtain 302.1, 240.5 and 127.5mAhg at the current density of (2) -1 The reversible specific capacity of (a). Furthermore, the difference between the two samples, 20% NaF-HC-1400, is more flat than the curve for HC-1400, which has a distinct slope, is also evident from the cycle performance plot of FIG. 6 (d). The data show that the F-doped hard carbon material is at 100mAg -1 252.3mAhg can still be obtained after the charge and the discharge of the next cycle are carried out for 100 times -1 The reversible specific capacity and the single-turn capacity attenuation rate of the catalyst are only 0.15 percent, and compared with the reversible specific capacity and the single-turn capacity attenuation rate of the catalyst which only remains 114.3mAhg after HC-1400 cycles -1 The reversible specific capacity and the doping of the F element obviously improve the cycling stability of the material.
To further understand the kinetics and electrochemical reaction mechanisms of F-doped hard carbon anodes in sodium ion batteries, this study tested 20% NaF-HC-1400 at 0.1-1.2mVs -1 CV curves at different scan rates. As can be seen from fig. 7 (a) -7 (d), the shape of the CV curve remained good after the scan rate was changed. In general, the following power-exponential relationship exists for the current (i) and the scan rate (v):
i＝aν b
where a and b are variable constants. The value of b can be determined by plotting log (i) and log (v). In general, a value of b of 0.5 represents an ideal diffusion control process, while a value of b of 1.0 represents a capacitance control process. In the present invention, the current at different sweep rates at voltages of 0.5, 1.0, 1.5 and 2.0V was taken, and the fitting result is shown in fig. 7 (b). The resulting b values are all around 0.9, meaning that charge storage of Na + in F-doped hard carbon material is mainly a capacitance controlled process. Furthermore, the specific contributions of these two charge storage behaviors at a specific potential (V) can be obtained from the following formula.
Wherein k is 1 、k 2 As a fitting parameter, k 1 v is the capacitive control contribution, k 2 v 1/2 For diffusion control contribution, the ratio can be represented by k 1 、k 2 And (4) determining. The equation can be divided by v on both sides 1/2 Let the equation become:
i.e. i (V)/V 1/2 And v 1/2 The linear relation is changed, the slope is fitted, and k is obtained 1 . As shown in FIG. 7 (c), at 0.2mVs -1 20% the capacitive charge contribution calculated for the NaF-HC-1400 electrode was 55.42%. Similarly, the capacitance contribution rates at other scan rates were calculated in this manner, and the results are shown in FIG. 7 (d), with the capacitance contribution increasing with scan rate (from 0.1mVs -1 Increased to 1.2mVs -1 ) And increased to finally 1.2mVs -1 It reaches 87%. It can therefore be judged that most of the charge storage in 20% NaF-HC-1400 is related to the capacitance control process. This is distributed apart from the inherent amorphous structure of the hard carbon, and furthermore, the doping of F element also forms more defects in the hard carbon material, thereby enhancing the adsorption of Na +.
Characterization test after F-doped hard carbon material cycling
The sodium ion diffusion kinetics of 20-percent Na-HC-1400 electrode material during charging and discharging were further analyzed by EIS test. From FIG. 8 (a)It can be seen that the cell assembled with the F-doped hard carbon material exhibited a smaller charge transfer resistance after 5 cycles, but the difference in the sodium ion diffusion coefficients was not large, and the sodium ion diffusion coefficients of HC-1400 and 20% naf-HC-1400 were 3.49 × 10, respectively, as calculated according to the formula [ electrochemical kinetics formula ] -12 、3.55×10 -12 cm 2 ·s -1 。
In addition, in order to investigate the regulating effect of F doping on the SEI film formed on the surface of the hard carbon anode, the present inventors performed XPS tests on 20-vol naf-HC-1400 electrodes after cycling, as shown in fig. 8 (b) -8 (F). From the Cls high resolution spectrum, the electrode after cycling not only has the C-C bond and the C-F bond of a fresh electrode, but also has an SEI film formed on the surface of the electrode in the charging and discharging processes
And a C-H component, which can be calculated from the fitted peak area according to a Gaussian fitting calculation method to give a 20% ratio of the inorganic component in an SEI film formed during charge and discharge of the NaF-HC-1400 electrode of 41.87%. The results are in combination with AlF 3 The calculated results of the coated electrodes were not very different, which again demonstrates that the reasonable distribution of the SEI film components is critical to improve the electrical performance of the hard carbon negative electrode material. In addition, the occupation ratios of the SEI film components after 5 cycles of the hard carbon anode material before and after F doping were 87.47% (HC-1400) and 63.51% (20% naf-HC-1400) respectively, which were calculated by comparison with the Cls map after HC-1400 cycles in fig. 9 (e). It can be seen that the SEI film formed after F doping is significantly less than that formed by the undoped hard carbon material, i.e., the incorporation of F atoms into the hard carbon material achieves the intended effect. This also proves that the present invention does reduce the reducing power of the hard carbon material by moving electrons of the C skeleton in the hard carbon material toward the F atom by virtue of the strong electron-adsorbing power of the F atom to compensate for the weak reduction-resistant power of the ester-based electrolyte, thereby suppressing the continuous generation of the SEI film during the cycle. In addition, the high resolution pattern of Ols was consistent with that of the HC-1400 electrode, with a peak of C-O bond and a peak of O = C-O/C = O bond. In the F1s high resolution spectrum, na formed by the electrode and the electrolyte in the circulation process appearsF, peaks of C-F bonds of the electrode material are reserved, and the peaks indicate that chemical bonds formed with the hard carbon material when the F element is doped are not destroyed in the charging and discharging processes, and the NaF in the SEI film has higher shear modulus and better mechanical integrity, so that the strong support is provided for longer cycle life.
Disassembling the circulated battery, taking out the electrode material, washing off the electrolyte solvent attached to the pole piece by using dimethyl carbonate, drying, and performing SEM test on the pole piece to observe the surface appearance of the electrode after circulation, wherein as shown in figures 9 (a) -9 (d), cracks are obviously found in a plurality of areas of the electrode material which is not doped with F atoms, and a plurality of glass fibers are still attached to the surface of the electrode, which indicates that an SEI film on the surface of the hard carbon negative electrode and a diaphragm of the sodium ion battery are damaged to a certain extent in the circulation process. The surface of the NaF-HC-1400 electrode is clean and flat, and cracks do not appear, which also shows that an SEI film formed by the F-doped hard carbon electrode in the charging and discharging processes is more continuous and complete, thereby showing more excellent sodium storage performance. Furthermore, the present invention also carried out the folding experiment of the NaF-HC-1400 electrode 20% after cycling, and it can be seen from FIG. 9 (e) that the F-doped hard carbon electrode has strong foldability. The electrode still remains intact after three times of folding, and the problems of cracking and falling off from the current collector do not occur, so that the electrode is proved to have better mechanical stability after being subjected to the intercalation/deintercalation of sodium ions, and a basis is provided for obviously improving the cycle performance of the electrode material.
And (4) experimental conclusion:
example NaF was added to a phenolic resin to incorporate F atoms into a hard carbon negative electrode material. Due to the strong electron-withdrawing capability of F atoms, the graphite-like domain interlamellar spacing of the F-doped hard carbon material is slightly reduced, and meanwhile, the F-doped hard carbon material has more nano-scale closed pore structures. Based on the 'adsorption-embedding-filling' sodium storage model which is widely accepted by researchers at present, the increase of the closed pore structure enables the hard carbon negative electrode material to have higher reversible specific capacity.
The doping of F atoms reduces the reducibility of the hard carbon negative electrode material, compensates for the weak anti-reduction capability of the ester-based electrolyte, and thus inhibits the uncontrolled reaction of the electrolyte during the circulation process. The SEI film formed after the F-doped hard carbon negative electrode is charged and discharged for 5 times has the SEI content of only 72.6 percent of that obtained by an undoped hard carbon material, and meanwhile, the SEI film formed in the charging and discharging processes also has more inorganic components (41.87 percent).
20% after F doping the sodium storage performance of NaF-HC-1400 was significantly improved compared to HC-1400. Not only has higher reversible specific capacity of 350.3mAhg -1 Simultaneously has more excellent circulating stability and rate capability at 100mAg -1 After cycling for 100 weeks at a current density of 252.3mAhg, the capacity remained -1 And at 200mAg -1 The rate capacity of the porous material is 127.5mAhg -1 。
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (3)
- The method for doping and modifying the phenolic resin matrix 1.F is characterized by comprising the following steps:step 1, weighing NaF and alcohol-soluble phenolic resin, grinding uniformly, wherein the mass fraction of sodium fluoride is as follows: mass fraction of phenolic resin =20%:100 percent, putting the uniformly mixed powder into a high-temperature tube furnace filled with argon atmosphere for carbonization for 2 hours;step 2. Grinding the carbonized sample to a powder, i.e. an F-doped phenolic resin based, and scoring as 20% NaF-HC-1400.
- 2. The method for modifying phenolic resin matrix through F doping according to claim 1, wherein the carbonization temperature in step 1 is 1400 ℃, and the heating rate is 2 ℃ min -1 。
- 3.F doped modified phenolic resin, characterized by, as 20% NaF-HC-1400, wherein the comparative area of carbon is 2.42m 2 And/g, the nano-particles are amorphous flaky particles, contain micropores and mesopores, and contain narrow crack holes.
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