CN115504449B - F-doped modified phenolic resin based method and material - Google Patents
F-doped modified phenolic resin based method and material 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 31
- 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 20
- 229920001568 phenolic resin Polymers 0.000 claims abstract description 20
- 230000008569 process Effects 0.000 claims abstract description 14
- 239000000843 powder Substances 0.000 claims abstract description 10
- 238000000227 grinding Methods 0.000 claims abstract description 9
- 239000012300 argon atmosphere Substances 0.000 claims abstract description 6
- 239000011812 mixed powder Substances 0.000 claims abstract description 4
- 238000005303 weighing Methods 0.000 claims abstract description 4
- 238000003763 carbonization Methods 0.000 claims description 10
- 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
- 239000011148 porous material Substances 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 5
- 230000000052 comparative effect Effects 0.000 claims description 4
- 239000011159 matrix material Substances 0.000 claims description 3
- 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
- 229910021385 hard carbon Inorganic materials 0.000 abstract description 79
- 239000003575 carbonaceous material Substances 0.000 abstract description 45
- 239000003792 electrolyte Substances 0.000 abstract description 25
- 239000011734 sodium Substances 0.000 abstract description 14
- 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 13
- 229910052708 sodium Inorganic materials 0.000 abstract description 13
- 238000003860 storage Methods 0.000 abstract description 11
- 239000007772 electrode material Substances 0.000 abstract description 10
- 150000002148 esters Chemical class 0.000 abstract description 10
- 125000001153 fluoro group Chemical group F* 0.000 abstract description 10
- 238000006243 chemical reaction Methods 0.000 abstract description 4
- 230000002829 reductive effect Effects 0.000 abstract description 4
- 230000009467 reduction Effects 0.000 abstract description 3
- 238000010000 carbonizing Methods 0.000 abstract description 2
- 230000002401 inhibitory effect Effects 0.000 abstract description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 26
- 229910001415 sodium ion Inorganic materials 0.000 description 11
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 9
- 230000001351 cycling effect Effects 0.000 description 8
- 239000010405 anode material Substances 0.000 description 7
- 238000010586 diagram Methods 0.000 description 7
- 230000002441 reversible effect Effects 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 229910052731 fluorine Inorganic materials 0.000 description 6
- 238000001179 sorption measurement Methods 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- 238000001228 spectrum Methods 0.000 description 5
- 239000011229 interlayer Substances 0.000 description 4
- 238000004768 lowest unoccupied molecular orbital Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-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
- 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
- 238000009830 intercalation Methods 0.000 description 3
- 230000002687 intercalation Effects 0.000 description 3
- 229910052757 nitrogen Inorganic materials 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
- 230000000694 effects Effects 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
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 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
- 239000007773 negative electrode material Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 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
- 238000002441 X-ray diffraction Methods 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
- 210000004027 cell Anatomy 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 150000001875 compounds Chemical class 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
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 230000003631 expected effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 238000002173 high-resolution transmission electron microscopy Methods 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 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
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Classifications
-
- 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
-
- 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
-
- 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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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Physics & Mathematics (AREA)
- Materials Engineering (AREA)
- Carbon And Carbon Compounds (AREA)
Abstract
The invention provides a method and a material for F-doped modified phenolic resin, comprising the following steps of 1, weighing 20% of NaF and alcohol-soluble phenolic resin by mass percent, uniformly grinding, and carbonizing the uniformly mixed powder in a high-temperature tube furnace filled with argon atmosphere for 2 hours; and 2, grinding the carbonized sample into powder, namely F-doped phenolic resin base, and marking the powder as 20% NaF-HC-1400. The invention adopts a method of doping high electronegativity elements, such as F element, into the hard carbon electrode material, and the high electronegativity of the high electronegativity elements can lead the high electronegativity elements to play a role of electron withdrawing 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 to compensate the insufficient reduction resistance of the ester-based electrolyte, thereby inhibiting the electrolyte from uncontrolled reaction to form an excessive thick SEI film in the circulation process, and finally obtaining better sodium storage performance.
Description
Technical Field
The invention belongs to the technical field of sodium ion batteries, and particularly relates to a method and a material for F-doped modified phenolic resin matrix.
Background
In order to optimize the SEI film formed by the hard carbon material in the charge and discharge process, researchers can select to use ether-based electrolyte to match with the hard carbon negative electrode in addition to optimizing the hard carbon electrode so as to obtain more excellent sodium storage performance. The resurgence of ether electrolyte research in sodium ion batteries stems from an encouraging finding that sodium ions can co-intercalate with ether solvent molecules into the graphite layer, which opens the possibility of graphite as a negative electrode material for sodium ion batteries. Finally, cao et al extended the application of ether-based electrolytes to sodium metal cathodes and found that a uniform inorganic SEI film could be produced to inhibit the growth of sodium dendrites and promote good cycling stability. Bai et al demonstrate that the ether-based electrolyte is also valuable in the application of the hard carbon negative electrode material of the sodium ion battery, and can improve the multiplying power performance and the cycle stability of the hard carbon material and also obviously improve the initial coulombic efficiency. However, many studies have been conducted to examine the properties of materials in sodium-ion half-cell systems. Because the ether-based electrolyte has weak oxidation resistance, the ether-based electrolyte cannot be matched with a high-voltage positive electrode, so that the ether-based electrolyte is commercially used at present; in addition, the ether-based electrolyte may form a solvated intercalation compound with sodium ions, which will cause greater volumetric strain to the hard carbon anode material, thereby reducing the cycling stability of the material.
Comparing the ester-based electrolyte and the ether-based electrolyte can find that there is a large difference in the Lowest Unoccupied Molecular Orbital (LUMO) and Highest Occupied Molecular Orbital (HOMO) energy levels of the solutes and solvents that are responsible for their performance differences, as shown in fig. 1. The LUMO of the ether-based electrolyte is higher than that of the ester-based electrolyte, so that the ether-based electrolyte has better reduction resistance and can form a compact and hard inorganic SEI film. In view of this, if the reducibility of the hard carbon electrode material can be limited, continued use of more commercially available ester-based electrolytes would be a better option.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provide a method and a material for F-doped modified phenolic resin matrix.
The invention adopts a method of doping high electronegativity elements, such as F element, into the hard carbon electrode material, and the high electronegativity of the high electronegativity elements can lead the high electronegativity elements to play a role of electron withdrawing 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 to compensate the insufficient reduction resistance of the ester-based electrolyte, thereby inhibiting the electrolyte from uncontrolled reaction to form an excessive thick SEI film in the circulation process, and finally obtaining better sodium storage performance.
The invention adopts the following technical scheme:
the F-doped modified phenolic resin based method comprises the following steps:
step 1, uniformly grinding NaF and alcohol-soluble phenolic resin with the mass fraction of 20%, wherein the mass ratio of the NaF to the phenolic resin is 20%:100%, placing the uniformly mixed powder into a high-temperature tube furnace filled with argon atmosphere for carbonization for 2 hours;
and 2, grinding the carbonized sample into powder, namely F-doped phenolic resin base, and marking the powder as 20% NaF-HC-1400.
In the step 1, the carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ min -1 。
F-doped modified phenolic resin, the comparative area of carbon is 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 and argon are adopted for fluorination treatment at high temperature. Phenolic resin is carbonized at 600-800 deg.c, and has low carbonizing temperature, high oxygen and hydrogen hetero atom residue inside, and low capacity.
In the prior art, the mixed gas of hydrogen and fluorine is adopted for fluorination treatment, the fluorine has strong etching effect on the surface of the material, and a large number of pore structures can be 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 through F doping, thereby leading the hard carbon to show better performance in the ester electrolyte.
Drawings
FIG. 1 is a LUMO/HOMO energy level difference diagram of a solute and a solvent of an ester and ether electrolyte;
FIGS. 2 (a) -2 (d) are SEM images of the 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 map;
FIG. 4 (c) is a Ols high resolution map;
FIG. 4 (d) is a schematic diagram 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) is a graph of 0.1mVs before and after F doping -1 CV curve at sweep rate of (2);
FIG. 6 (c) is a graph of the F-doping front-to-back rate performance;
FIG. 6 (d) is 100mAg before and after F doping -1 The following cycle performance graph;
FIG. 7 (a) is a CV curve of a 20% NaF-HC-1400 electrode at different scan rates;
FIG. 7 (b) is a plot of log (scan rate) versus log (current) for the b value;
FIG. 7 (c) is a graph of pseudocapacitance contribution at 0.2mVs -1 Quantitative analysis in CV curve at scan rate;
FIG. 7 (d) is a graph showing the contribution ratio of pseudocapacitance at different scan rates;
FIG. 8 (a) shows HC-1400 and 20% NaF-HC-1400 at 20mAg -1 An EIS graph after lower circulation;
FIG. 8 (b) shows HC-1400 and 20% NaF-HC-1400 at 20mAg -1 Low frequency region Z' and ω after lower cycle -1/2 Is a relationship diagram of (1);
FIG. 8 (c) is an XPS survey spectrum;
FIG. 8 (d) is 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 diagrams after HC-1400 electrode cycling;
FIGS. 9 (c) and 9 (d) are surface topography plots after cycling of 20% NaF-HC-1400 electrodes;
FIG. 9 (e) is a graph of electrode folding experiments after 20% NaF-HC-1400 cycles;
FIG. 10 is a flow chart of the steps of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 10, the method of the F-doped modified phenolic resin based of the present invention includes:
step 1, weighing NaF with the mass fraction of 20% and alcohol-soluble phenolic resin (the mass ratio of NaF to phenolic resin is 20% to 100%) and grinding uniformly, and placing the uniformly mixed powder into a high-temperature tube furnace filled with argon atmosphere for carbonization for 2 hours;
and 2, grinding the carbonized sample into powder, namely F-doped phenolic resin base, and marking the powder as 20% NaF-HC-1400.
In the step 1, the carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ min -1 。
F-doped modified phenolic resin, the comparative area of carbon is 2.42m 2/ g, the material is amorphous flaky particles, and contains micropores and mesopores and some narrow crack holes.
Experimental example
Weighing NaF with mass fraction of 20% and alcohol-soluble phenolic resin, grinding uniformly, mixing uniformly to obtain powderAnd finally, placing the mixture in 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 is ground into powder, namely F-doped phenolic resin based hard carbon, and is recorded as 20% NaF-HC-1400, and the comparison sample is still HC-1400 obtained before.
Comparative case
Phenolic resin powder was carbonized in a high temperature tube furnace filled with argon atmosphere for 2 hours. Carbonization temperature is 1400 ℃, and heating rate is 2 ℃ for min -1 . The carbonized sample is ground into powder to obtain HC-1400 ℃.
Experimental results and discussion
Influence of F doping on the Structure of phenolic resin-based hard carbon Material
To demonstrate the successful doping of F into hard carbon materials, the present invention performed a series of characterization tests on the materials before and after doping, as shown in FIGS. 2 (a) -2 (d). The particle morphology of HC-1400 can be seen in FIG. 2 (a), and the apparent pores appear on the surface of the particles of Na-HC-1400 in FIG. 2 (b) -FIG. 2 (c), mainly because the F element itself has a certain corrosiveness, so that the hard carbon particles are corroded in the carbonization process, and the specific surface area of the hard carbon material is increased to a certain extent. As shown in fig. 2 (e), the distribution of the F element and the Na element in the figure is relatively uniform, and the profile is almost consistent with that of the hard carbon particles, so that it can be primarily determined that the F element is successfully doped into the hard carbon, and the existence form of the F element doped into the hard carbon can be further analyzed.
In order to prove that the specific surface area of the coated material is increased, BET specific surface area test is carried out on the F-doped hard carbon material, as shown in fig. 3 (a) and 3 (b), the nitrogen adsorption curve obtained after doping is similar to that of undoped HC-1400, and is H4 type hysteresis, which shows that the material contains micropores and mesopores and also contains some narrow crack holes, and the specific surface area is 2.422m 2 g -1 The specific surface area of HC-1400 (0.203 m 2 g -1 ) The increase is obvious. As shown in FIG. 3 (c) and FIG. 3 (d), the hard carbon material itselfThe present invention tested the material using slow-scan XRD to avoid the background peak of the material covering the diffraction peak of the possible NaF, for a total scan time of 1.5 hours. However, as can be seen from FIG. 3 (C), the F-doped hard carbon material does not exhibit a characteristic diffraction peak of NaF, but exhibits C 8.6 F has a characteristic diffraction peak of 45-1076, which means that F element is successfully infiltrated into hard carbon material and mainly used as C 8.6 F exists in the form of a solid. In addition, the diffraction peaks of the (002) crystal face of the two materials in the XRD diagram are slightly different, the peaks of the F-doped hard carbon materials are slightly shifted to the right, namely, the interlayer spacing of the F-doped hard carbon materials is not increased, but the adjacent carbon layers of the graphite-like fields are arranged more tightly due to the electron withdrawing capability of the F-element due to the strong electronegativity, specific interlayer spacing data are shown in the table 1, and the coherence length of the graphite-like fields in the F-doped hard carbon materials can be found to be shorter and more curved by calculating the ratio of the D peak to the G peak intensity as shown in the figure 3 (D).
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 FIGS. 4 (a) -4 (c), it can be seen from the full spectrum (FIG. 4 (a)), that a material contains C, O, F, na and other elements. The 1s orbitals of C, F elements were fitted separately to analyze their presence in hard carbon materials as shown in fig. 4 (b), 4 (c). The C1s high-resolution map mainly comprises a C-C bond at 284.8eV, a C-O bond at 285.6 and a C=O/C-F bond at 289.9eV, which indicates that a chemical bond exists between the F element and a hard carbon skeleton, and the peak area is smaller because the content of C-F is smaller. However, in the high resolution spectrum of F1s, only the peak of C-F bond at 689.6eV appears, and the existence of Na-F does not appear, which again demonstrates that F element is successfully doped into the hard carbon material, and a schematic diagram of 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 makes the F element have strong electron adsorption capability to move electrons in the hard carbon material to F atoms, so that the reducing capability 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 solution, thereby avoiding continuous generation of the SEI film.
In order to more directly observe the change of the internal microstructure of the hard carbon material before and after F doping, the present invention performed 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)), which is consistent with the results calculated from XRD; in addition, the graphite-like domain of the hard carbon after F doping is not as long and straight as HC-1400, which is consistent with the conclusion of Raman spectrum analysis; however, it is also evident from the figure that the F-doped hard carbon material has a more nano-closed pore structure, which may also be a result of the strong electron withdrawing ability of the F element. Based on the consideration of the sodium storage mechanism of more 'adsorption-embedding-filling' discussed by researchers at present, the doping of F element can bring a larger reversible specific capacity for the hard carbon anode material.
Influence of F doping on sodium storage performance of phenolic resin-based hard carbon material
After the material is synthesized, the electrochemical performance after F doping is tested, as shown in a first charge-discharge curve of HC-1400 and 20% NaF-HC-1400 in a figure 6 (a), the reversible specific capacity of the hard carbon material after F doping is obviously improved to 350.3mAhg -1 This is most likely related to the fact that the F-doped hard carbon material contains more nano-scale closed pore structures inside. While the F-doped hard carbon material shows 75.2% of first coulombic efficiency, sodium atoms can enter the hard carbon material to show 75.2% of first coulombic efficiency when F is doped, while sodium atoms can enter the internal structure of the hard carbon when F is doped, the early intercalation of sodium can play a role in pre-sodium treatment to improve the coulombic efficiency, but the current result is slightly lower than HC-1400 (77.7%), which is mainly related to the increase of the surface area of the F-doped hard carbon material and the larger specific surface areaThe hard carbon material is provided with more irreversible defects, so that the first coulombic efficiency of the material is reduced. As shown in fig. 6 (b), in which irreversible redox peaks between 0.3 and 0.8V are not much different from those obtained for HC-1400 of fig. 6 (a), this also demonstrates the result that the first coulombic efficiency of the hard carbon material before and after the F doping is not much different. Fig. 6 (c) and 6 (d) show the rate performance and cycle performance of the material. The rate performance graph shows that the F-doped hard carbon material has higher rate capacity, and the 20% NaF-HC-1400 has the rate of 50 mAg, 100mAg and 200mAg -1 302.1, 240.5, 127.5mAhg can be obtained at current densities of (3) respectively -1 Is a reversible specific capacity of (a). Furthermore, it is also evident from the cycle performance chart of FIG. 6 (d) that the difference between the two samples, the 20% NaF-HC-1400 curve, is relatively straight, while HC-1400 has a significant slope. The data show that the hard carbon material doped with F is 100mAg -1 After 100 times of charge and discharge in the lower cycle, 252.3mAhg can be still obtained -1 The reversible specific capacity of (2) is only 0.15% in single-turn capacity attenuation rate, compared with the HC-1400, which only remains 114.3mAhg after circulation -1 The doping of the F element significantly improves the cycling stability of the material.
To further understand the kinetics and electrochemical reaction mechanism of F-doped hard carbon negative electrodes in sodium ion batteries, the present 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 remains good after the scan rate is changed. In general, the current (i) and the scan rate (v) exist as a power-of-the-power function:
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 b value of 0.5 indicates an ideal diffusion control process, and a b value of 1.0 indicates a capacitance control process. In the present invention, currents at different sweep rates at voltages of 0.5, 1.0, 1.5 and 2.0V were taken, and the fitting results are shown in fig. 7 (b). The resulting b values are all around 0.9, meaning that the charge storage of na+ in the F-doped hard carbon material is primarily a capacitance-controlled process. Furthermore, a specific contribution of these two charge storage behaviors at a specific potential (V) can be obtained by the following formula.
Wherein k is 1 、k 2 To fit parameters, k 1 v is the capacitive control contribution, k 2 v 1/2 Contributing to diffusion control, the ratio of which can be defined by k 1 、k 2 And (5) determining. The two sides of the equation can be divided by v 1/2 Let equation become:
i.e. i (V)/V 1/2 And v 1/2 Becomes a linear relation, and k can be obtained by fitting the slope thereof 1 . As shown in FIG. 7 (c), at 0.2mVs -1 At 20% NaF-HC-1400 electrode the calculated capacitance charge contribution was 55.42%. Similarly, the capacitance contribution rate at other scan rates was calculated in this way, and as a result, as shown in FIG. 7 (d), the capacitance contribution was increased with the increase of the scan rate (from 0.1mVs -1 Increased to 1.2mVs -1 ) And increases to a final 1.2mVs -1 When the time reaches 87%. It can be determined that most of the charge storage in 20% NaF-HC-1400 is related to the capacitive control process. This is distributed with the inherent amorphous structure of hard carbon itself, and in addition, the doping of the F element also causes more defects to form in the hard carbon material, thereby enhancing the adsorption of na+.
Characterization test of F-doped hard carbon material after circulation
Sodium ion diffusion kinetics at charge and discharge of 20% na-HC-1400 electrode material was further analyzed using EIS test. As can be seen from FIG. 8 (a), the F-doped hard carbon assembled battery exhibited less charge transfer resistance after 5 cycles, but the sodium diffusion coefficients were not greatly different, and calculated according to the formula [ electrochemical kinetics formula ], the sodium diffusion coefficients of HC-1400 and 20% NaF-HC-1400 were 3.49×10, respectively -12 、3.55×10 -12 cm 2 ·s -1 。
In addition, in order to investigate the regulation effect of F doping on SEI film formed on the surface of a hard carbon negative electrode, XPS test was performed on a 20% NaF-HC-1400 electrode after cycling, as shown in FIGS. 8 (b) -8 (F). The electrode after circulation can be found from Cls high-resolution map to have not only the C-C bond and C-F bond of fresh electrode, but also SEI film formed on the electrode surface in the charge and discharge processAnd C-H component, according to Gaussian fitting calculation method, can calculate according to peak area fitted out, the inorganic component in SEI film that 20% NaF-HC-1400 electrode forms in the charge-discharge process accounts for 41.87%. This result is compared with AlF 3 The difference of the calculated results of the coated electrodes is not large, which again demonstrates that reasonable distribution of SEI film components is a key for improving the electrical performance of the hard carbon anode material. In addition, by comparing with the Cls spectrum after HC-1400 circulation in FIG. 9 (e), the ratios of the SEI film components of the hard carbon anode material before and after F doping after 5 circulation are 87.47% (HC-1400) and 63.51% (20% NaF-HC-1400) respectively. From this, the SEI film formed after F doping is significantly less than that formed by undoped hard carbon material, i.e. the expected effect is achieved by incorporating F atoms into the hard carbon material. This also proves that the present invention does reduce the reducing ability of the hard carbon material by moving electrons of the C skeleton in the hard carbon material toward the F atoms by means of the strong electron adsorption ability of the F atoms to compensate for the weak anti-reducing ability of the ester-based electrolyte, thereby suppressing the continuous generation of the SEI film during the cycle. In addition, at the high resolution pattern of Ols, the peak of the C-O bond and the peak of the o=c-O/c=o bond were both present in agreement with the HC-1400 electrode. In the F1s high-resolution map, not only Na-F formed by the electrode and the electrolyte in the circulation process is generated, but also the peak of the C-F bond of the electrode material is reserved, which indicates that the chemical bond formed by the F element doped with the hard carbon material is not destroyed in the charge and discharge process, and the NaF in the SEI film also has higher shear modulus and better mechanical integrity, thereby providing powerful support for longer cycle life.
The electrode material was disassembled after the circulation, and after the electrolyte solvent attached to the electrode sheet was washed off with dimethyl carbonate and dried, SEM test was performed on the electrode sheet to observe the surface morphology of the electrode after the circulation, as shown in fig. 9 (a) -9 (d), it was clearly found that the electrode material without the F atoms had cracks in a plurality of regions, and that many glass fibers were still attached to the electrode surface, indicating that the SEI film on the hard carbon negative electrode surface and the sodium ion battery separator were damaged to some extent during the circulation. The surface of the NaF-HC-1400 electrode is clean and smooth, no crack appears, and the SEI film formed by the F-doped hard carbon electrode in the charge and discharge processes is more continuous and complete, so that the excellent sodium storage performance is shown. In addition, the invention also carries out folding experiments on the recycled 20% NaF-HC-1400 electrode, and the strong foldability of the F-doped hard carbon electrode can be seen from fig. 9 (e). The electrode is still intact after three folds, and the problems of cracking and falling off from a current collector are avoided, so that the electrode still has good mechanical stability after sodium ion intercalation/deintercalation, and the basis is provided for obviously improving the cycle performance of the electrode material.
Conclusion of experiment:
examples NaF was added to phenolic resins to incorporate F atoms into hard carbon anode materials. The strong electron-withdrawing capability of the F atoms slightly reduces the interlayer spacing of graphite-like domains of the F-doped hard carbon material, and simultaneously has more nanoscale closed cell structures. Based on the 'adsorption-embedding-filling' sodium storage model which is widely accepted by researchers at present, the increase of closed pore structures enables the hard carbon anode material to have higher reversible specific capacity.
The incorporation of F atoms reduces the reducibility of the hard carbon anode material, compensates for the weaker anti-reduction capacity of the ester-based electrolyte, and thus inhibits uncontrolled reaction of the electrolyte during cycling. The SEI film content formed by the F-doped hard carbon cathode after 5 times of charge and discharge is only 72.6% of that obtained by undoped hard carbon material, and meanwhile, the SEI film formed in the charge and discharge process also has more inorganic components (41.87%).
F-doped 20% NaF-HCThe sodium storage performance of 1400 is significantly improved compared with HC-1400. Not only has higher reversible specific capacity of 350.3mAhg -1 Simultaneously has more excellent cycle stability and rate capability, and is 100mAg -1 After cycling at a current density of 252.3mAhg for 100 weeks -1 And at 200mAg -1 The rate capacity at this time was 127.5mAhg -1 。
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the 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 scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (2)
1. A method of F-doping a modified phenolic resin matrix comprising:
step 1, weighing NaF and alcohol-soluble phenolic resin, and grinding uniformly, wherein the mass fraction of sodium fluoride is as follows: mass fraction of phenolic resin = 20%:100%, placing 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 into powder, namely F-doped phenolic resin base, and marking as 20% NaF-HC-1400;
in the step 1, the carbonization temperature is 1400 ℃, and the heating rate is 2 ℃ min -1 。
2. An F-doped modified phenolic resin, characterized in that it is denoted as 20% NaF-HC-1400, wherein the comparative area of carbon is 2.42m 2 And/g, which is an amorphous platelet-shaped particle comprising micropores and mesopores and comprising narrow slit pores, is obtained by the process of the F-doped modified phenolic resin-based of claim 1.
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