KR102425006B1 - Negative electrode active material using organic solid solution and manufacturing negative electrode for lithium or sodium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an anode active material using an organic solid solution and a negative electrode for a lithium or sodium secondary battery comprising the same, comprising a mixed solid solution of hexabenzocoronene and fluorinated hexabenzocoronene It is possible to provide a high-performance lithium or sodium secondary battery including an anode active material.

Description

Negative electrode active material using organic solid solution and manufacturing negative electrode for lithium or sodium secondary battery comprising the same

The present invention relates to an anode active material using an organic solid solution and to a lithium or sodium secondary battery negative electrode comprising the same.

Functional organic materials have attracted considerable interest as electrode active materials for next-generation rechargeable Li/Na-ion batteries due to their structural diversity, rapid redox reaction with Li- or Na- ions, and cost effectiveness. Among recent organic electrode materials, conjugated carbonyl compounds are quinones, organosulfurs and organic salts. Strategic design of molecules is a multi-electron redox reaction that provides high capacity and fast kinetics. has significant advantages in

However, one major problem with functional organic active materials is their high solubility in aprotic electrolytes. This is due to the strong interaction between the functional groups of the organic material and the solvent increasing the solubility of the active material during battery operation, resulting in unacceptable cycling performance with low coulombic efficiency. To solve this problem, various methods have been recently proposed to alleviate the dissolution problem, such as polymerization, the use of a conductive scaffold for immobilizing the active material, or the use of PEO / LISICON solid electrolyte. There are problems in that the total weight of the inactive cell is greatly increased and the total energy density is reduced.

In addition, another major problem of the organic active material is that the conductivity is not good due to the large HOMO-LUMO gap, and a fairly large amount of 15-40 wt% of the conductive material is required to provide an appropriate rate-limiting performance. This ultimately has a problem in reducing the energy density of the battery.

On the other hand, a solid solution compound can form a continuum quasi-isostructural compound with new properties due to the strong interrelationship between two individual components. By forming a solid solution with a transition metal-based inorganic material, Significant improvements in energy storage and device properties have been reported with efficient bandgap engineering of semiconductor materials. However, due to strict prerequisites for forming a homogeneous solid solution, studies on functional organic solid solutions in energy storage materials have not been conducted.

Therefore, there is a need for research on an anode material having high conductivity, high energy density, and high output density using an organic solid solution.

1. J. Phys. Chem. C 2014, 118, 51, 29517-29524 (published on November 26, 2014)

An object of the present invention is to provide an anode active material for a lithium and sodium secondary battery having high performance and an anode for a secondary battery including the same.

In addition, another object of the present invention is to provide a method for manufacturing a negative electrode for a secondary battery including the negative active material for lithium and sodium secondary batteries having the above high performance.

In order to achieve the above object, the present invention provides an anode active material including a mixed solid solution of hexabenzocoronene and fluorinated-hexabenzocoronene.

In addition, the present invention provides a negative electrode for a secondary battery comprising the negative active material.

In addition, the present invention comprises the steps of: a) preparing a solid solution by mixing hexabenzocoronene and fluorinated hexabenzocoronene; b) preparing a negative electrode by coating the solid solution of step a) on a metal and annealing; It provides a method for manufacturing a negative electrode for an interest battery comprising a.

Since the organic solid solution according to the present invention has high electrical conductivity, there is no need to separately mix a conductive material, so it is possible to significantly lower the manufacturing cost and significantly improve the lifespan of the existing organic negative electrode battery.

In addition, the organic cHBC / FcHBC solid solution exhibits excellent reversible capacity, excellent rate performance, excellent Coulombic efficiency, and excellent cycle stability in lithium and sodium ion secondary batteries, and thus can be usefully used as an anode of lithium or sodium secondary batteries.

1 is a schematic diagram showing the molecular structures of cHBC and FcHBC and a solid solution of similar isostructural cHBC and FcHBC molecules.
Figure 2 shows A) FcHBC, cHBC / FcHBC mixing ratio B) 3: 7, C) 5: 5 and D) 7: 3, E) SEM images of cHBC (scale bars are 20 μm and 2 μm (inset)), F) Nyquist plots of various electrodes in a Li metal half-cell structure, G) R _SEI + R _CT values corresponding to Nyquist plots, H) 2D GIWAXS 1D diffraction traces of electrodes.
3 shows A) constant current charge-discharge profiles of cHBC, FcHBC and cHBC/FcHBC solid solution electrodes with mixing ratios of 3:7 and 5:5, B) 1D diffraction traces of lithiated cHBC/FcHBC electrodes, C) 10% XRD patterns of cHBC/FcHBC electrodes successively obtained per lithiation process, and D) F 1s XPS spectra of cHBC/FcHBC electrodes successively obtained per 20% lithiation process, E) [010], [001] and [100] It is a diagram showing the P2 ₁ / n crystal phase of cHBC / FcHBC solid solution according to the direction (cHBC and FcHBC molecules are shown in gray and yellow, fluorine is shown in red).
4 is a diagram showing the 1D diffraction profile of a lithiated cHBC/FcHBC (5:5) solid solution electrode after 400 cycles.
5 is A) cHBC / FcHBC electrode mixed with a molar ratio (mol: mol) of 3: 7 (green) and 5: 5 (red) according to the current density in the range of 0.1 A g ^-1 to 7.0 A g ^-1 Rate performance, B) CV profile of a 5:5 electrode at various voltage sweep rates from 0.03 to 1.0 mV s ⁻¹ , C) log-log plot of sweep rate ( _ν ) versus peak current (ip ) , D) 0.4 mV CV profile at sweep rate of s ⁻¹ (shaded region represents capacity contribution to total stored charge ( k ₁ ν)), E) P2 ₁ / n crystalline phase with Li-ions as a function of Li-ion number (n) Formation energy of cHBC/FcHBC solid solution, F) Inset of experimental (black line) and calculated (red line) voltage profiles (F): optimized cHBC with 12, 24 and 36 Li-ions along the [010] direction / Projection of FcHBC solid solution), G) A diagram showing the long-term cycle stability and Coulombic efficiency of the cHBC / FcHBC electrode (5: 5) at a current density of 5.0 A g ^-1 .
6 is a diagram showing a P2 ₁ / n crystalline cHBC / FcHBC solid solution having a connolly surface (blue) along the [010], [001] and [100] directions (cHBC and FcHBC molecules are shown in gray and yellow, respectively; Fluorine atoms are shown in red).
7 is a view showing the P2 ₁ / n crystal phase of a cHBC / FcHBC solid solution containing lithium ions along the [010], [001] and [100] directions (cHBC molecules, FcHBC molecules, aromatic rings of cHBC and FcHBC molecules) The interposed Li ion, the Li ion between the aromatic ring of the cHBC molecule and the fluorine of the FcHBC molecule, and the Li ion of the aromatic ring of the cHBC and FcHBC molecule are shown in gray, yellow, purple, magenta and blue, respectively, and the fluorine atom in red. ).
8 is an enlarged view of the adsorption site of Li ions in the optimized structure of P2 ₁ / n crystalline cHBC / FcHBC solid solution containing Li ions; A) Lithium ion interposed between the aromatic ring of cHBC and FcHBC molecule (site I, purple), B) Lithium ion between the aromatic ring of cHBC and fluorine of FcHBC (site II, magenta), C) Lithium of the aromatic ring of FcHBC molecule Ions (site III, blue) (cHBC and FcHBC molecules are shown in gray and yellow, fluorine atoms are shown in red, and Li ions are in close contact with orange dotted lines).
9 is A) Nyquist plot of cHBC (black), FcHBC (grey) and cHBC / FcHBC (5:5) electrodes (red) in Na metal half-cell structure, B) Current density of 0.1A g ^-1 voltage value of cHBC/FcHBC electrode in, C) formation energy of P2 ₁ /n crystalline cHBC/FcHBC solid solution with Na-ion as a function of Na-ion number (n), D) experimental (black line) and calculated (red line) Line) Inset of voltage profile (D): Projection of an optimized cHBC/FcHBC solid solution with 12, 20 and 24 Na- ions along the [010] direction), E) 0.1A g ^-1 to 3.0 A g ^-1 It is a diagram showing the rate-limiting performance at a current density of F) and cycle stability at a current density of 0.5 A g ^-1 .
10 is a view showing the P2 ₁ / n crystal phase of a cHBC / FcHBC solid solution containing sodium ions along the [010], [001] and [100] directions (cHBC molecules, FcHBC molecules, aromatic rings of cHBC and FcHBC molecules) The interposed Na ion, the Na ion between the aromatic ring of the cHBC molecule and the fluorine of the FcHBC molecule, and the Na ion of the aromatic ring of the FcHBC molecule are shown in gray, yellow, purple, magenta and blue, respectively, and the fluorine atom in red).
11 is a cyclic voltammetry analysis result of cHBC/FcHBC (5:5) solid solution electrode in Na-ion battery, A) CV profile at various scan rates from 0.1 mV s ⁻¹ to 0.4 mV s ⁻¹ , B) sweep Log-log plot of velocity (ν) versus peak current ( i _p ), C) C) CV profile at sweep rate of 0.4 mV s ⁻¹ (shaded area represents capacity contribution ( k ₁ ν) to total stored charge) the drawing shown.

Hereinafter, the present invention will be described in detail.

The present inventors have prepared a solid solution anode active material having a crystal structure using hexabenzocoronene molecules, which are organic polycyclic aromatic hydrocarbons, which have excellent reversible capacity, excellent rate performance, The present invention was completed by revealing that it can be usefully used as a negative electrode of a secondary battery by showing excellent coulombic efficiency and excellent cycle stability.

The present invention provides an anode active material comprising a mixed solid solution of hexabenzocoronene and fluorinated-hexabenzocoronene.

At this time, the solid solution is a curved hexabenzocoronene (contorted hexabenzocoronene; cHBC) and curved fluorinated hexabenzocoronene (fluorinated-contorted hexabenzocoronene; FcHBC) is uniformly mixed (Fig. 1) monoclinic P2 ₁ / n crystal can have a structure.

In addition, the hexabenzocoronene and the fluorinated hexabenzocoronene are mixed in a molar ratio (mol:mol) of (3 to 7): (7 to 3) to form a solid solution, preferably It may be mixed in a molar ratio of 5: 5, but is not limited thereto.

In addition, the present invention provides a negative electrode for a secondary battery comprising the negative active material.

In this case, the secondary battery is characterized in that it is a lithium ion or sodium ion secondary battery, but is applicable to the negative electrode of a conventional secondary battery without limitation.

In the lithium ion or sodium ion battery of the present invention, the negative electrode or positive electrode may be prepared by including an active material, a binder and a solvent on a current collector, and the current collector, the binder and the solvent in addition to the negative active material are lithium ion or sodium Any one commonly used for manufacturing ion batteries may be used without limitation. In addition, the lithium ion or sodium ion battery of the present invention may further include a separator.

Specifically, the lithium ion or sodium ion battery of the present invention can be manufactured by injecting an electrolyte solution for a lithium ion or sodium ion battery into an electrode structure comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In this case, the separator may be used without limitation as long as it is conventionally used for manufacturing a lithium ion or sodium ion battery.

In addition, the present invention comprises the steps of: a) preparing a solid solution by mixing hexabenzocoronene and fluorinated hexabenzocoronene; and b) coating the solid solution of step a) on a metal, and annealing to prepare an anode; It provides a method for manufacturing a negative electrode for an interest battery comprising a.

At this time, the solid solution is a monoclinic P2 ₁ / n crystal structure in which curved hexabenzocoronene (cHBC) and curved fluorinated-contorted hexabenzocoronene (FcHBC) are uniformly mixed. Characterized, the hexabenzocoronene and the fluorinated hexabenzocoronene may be mixed in a molar ratio (mol:mol) of (3 to 7): (7 to 3) to form a solid solution.

In addition, the annealing treatment comprises the steps of: a) THF-steam annealing of the solid solution coated on the metal; b) a) subjecting the treated solid solution to thermal annealing at a temperature of 300 to 400° C.; and c) b) subjecting the treated solid solution to an electrolyte vapor annealing.

At this time, in the THF-steam annealing treatment, the solid solution slurry according to the present invention is applied on top of a copper foil and dried to prepare a negative electrode, and then the prepared negative electrode is placed in a closed system (eg, vial, etc.) with THF solvent puddle (4 mL) in THF By leaving it out of contact with the puddle, the THF vapor changes the crystal structure of the material on the surface of the anode, there is no direct contact between the cathode and THF, the cathode material is insoluble in the THF material, and agglomerated or agglomerated through the THF vapor annealing step. It is not destroyed.

In addition, the electrolyte solution is a lithium salt or sodium salt; and a carbonate-based solvent.

Here, the electrolyte is LiPF ₆ , LiClO ₄ , NaPF ₆ , a lithium salt or sodium salt of NaClO ₄ and ethylene carbonate (EC), diethyl carbonate (DEC), 1-10 wt% fluoroethylene A solvent of carbonate (fluoroethylene carbonate; FEC) may be used, but is not limited thereto.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention in more detail, and it is to those of ordinary skill in the art to which the present invention pertains that the scope of the present invention is not limited by these examples according to the gist of the present invention. it will be self-evident

<Reference example> Experimental material

cHBC and FcHBC molecules were synthesized according to the procedure in a previous report ( J Mater Chem A 2018 , 6 , 12589, Adv Sci 2018 , 5 , 1801365). N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone; NMP) and tetrahydrofuran (THF) were purchased from Aldrich Korea and used without purification. The 2032-type coin cell, electrolyte and polyethylene (PE) separator (Celgard 2400) used for electrochemical performance measurement were purchased from Wellcos Co., Korea and Celgard®, respectively.

< Example 1> Manufacture of working electrode

cHBC, FcHBC and cHBC / FcHBC mixed solid solution slurry was prepared by mixing cHBC, FcHBC or cHBC / FcHBC mixed powder with PVDF binder (powder (active material) / binder weight ratio = 95/5) in NMP solvent. Using a doctor blade (Wellcos Co., Korea), the slurry of 100 to 300 μm in height was coated on 18 μm copper foil, and then dried in a vacuum oven at 120° C. overnight to remove any residual solvent and moisture. The prepared electrodes were subjected to THF-steam annealing and thermal annealing at a temperature of 300 to 400°C. In the THF-steam annealing, the prepared cathode is placed in a closed system (eg, a vial, etc.) with a pool of THF solvent (4 mL) so that the THF vapor changes the crystal structure of the material on the surface of the anode. Then, electrolyte vapor annealing was performed by placing the electrode pieces in an 80 ml vial with 10 ml of battery electrolyte in an Ar-filled glove box at 50° C. and room temperature for 2 hours and 6 hours, respectively. The annealing electrolyte is LiPF ₆ , LiClO ₄ , NaPF ₆ , NaClO ₄ Solutes and ethylene carbonate (EC), diethyl carbonate (DEC), 1-10 wt% fluoroethylene carbonate; FEC) was used.

< Example 2> Characteristics analysis of working electrode

The surface morphology of the electrodes was analyzed using SEM (S-4800, Hitachi). The detailed crystal structures of various electrodes were analyzed by XRD (Rigaku D / MAX2500V / PC power diffractometer, Cu Kα radiation, λ=1.5418 Å) and 2D-GIWAXS. GIWAXS (grazing angle incident X-ray scattering) measurements were performed using the 6D UNIST-Pohang Accelerator Laboratory (PAL) line of Pohang University of Science and Technology. GIWAXS samples were prepared following the same procedure as the above working electrode preparation except that they were glued onto a Si wafer with a 300 nm SiO ₂ layer, subjected to THF-steam annealing and thermal annealing, monochromated X with a fixed incidence angle of 0.12°. The samples were analyzed by irradiating them with a -line (λ = 1.07216 Å). Chemical information for the cHBC / FcHBC electrode was obtained through XPS analysis (Model ESCALAB 250XI, Thermo Fisher Scientific) with Al Kα radiation (1486.6 eV) under ultra-high vacuum.

< Example 3> Electrochemical analysis of working electrode

For the electrochemical analysis, the 2032-type coin cell was assembled with various working electrodes (cHBC, FcHBC or cHBC / FcHBC mixed), PE separator, and Li or Na foil as counter electrodes. For Li- or Na- ion storage cells, 10 wt % FEC and EC / DEC (30/70 vol) solvent, 1 M LiPF ₆ solute or 4 wt % FEC and EC / DEC (50/50 vol) solvent and 1.3 M NaPF ₆ solute electrolyte was used respectively. For XPS analysis, an electrolyte containing EC / DEC (volume ratio 50/50) solvent and 1 M LiClO ₄ was used. EIS and CV measurements were performed using a multi-channel potentiostat (BioLogic VSP-300). Nyquist plots were measured in the frequency range from 2 × 10 ⁵ Hz to 1 × 10 ⁻¹ Hz with an amplitude voltage of 10 mV. CV was measured at various sweep rates over a voltage range of 1.2 V to 0.01 V. Constant current charge-discharge measurements at various current densities were performed using a battery tester (Wonatech, WBCS3000S) in a voltage range of 2.00 to 0.01 V (vs Li / Li ⁺ or Na / Na ⁺ ).

< Experimental example 1> cHBC and FcHBC Solid solution formation between molecules

cHBC, FcHBC solid solution negative electrode was prepared according to <Example 1> above for manufacturing a high energy density electrode without using a separate conductive material.

As can be seen from the scanning electron microscope (SEM) images of FIGS. 2A-2E , the cHBC and FcHBC solid solutions mixed at various molar ratios (mol: mol) showed different morphologies. Specifically, the cHBC:FcHBC mixing ratios of 3:7 (Fig. 2B) and 5:5 (Fig. 2C) showed microcrystals with an average diameter of 4 μm at the surface, whereas the 7:3 sample (Fig. 2D) had a small number of microcrystals and showed a flat morphology. This is because the miscibility of the cHBC and the FcHBC semiconductor material at a specific mixing ratio affects the crystal morphology, resulting in a change in the characteristics of the crystal.

Ethylene carbonate / diethyl carbon (EC / DEC volume ratio = 30 / 70), 10 wt% fluorinated ethylene carbonate (FEC) to measure the electrochemical properties of the mixed cHBC / FcHBC film working electrode compared to cHBC and FcHBC A half-cell structure was constructed using 1 M lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte and Li metal as a counter electrode. 2F and 2G are Nyquist plots and charge transfer resistance (R _CT ) values corresponding to cHBC / FcHBC electrodes mixed with FcHBC, cHBC, and various molar ratios (mol: mol) without the use of a separate conductive material. showed As a result, we found low R _CT values of 30 and 159 Ω cm ^-2 according to the blend ratio of 5: 5 and 3: 7 in the Nyquist plot, which is the same mixing ratio as observed with microcrystals through SEM. (Fig. 2B, 2C). In addition, the low R _CT values are due to the well-developed molecular level assembly between the semiconducting cHBC and FcHBC molecules, which indicates that the relatively lower LUMO of the FcHBC molecules enhances electron transfer in the mixed solid solution film, resulting in organic co-crystal (co-crystal) ) because it is similar to

0.49 Å^-1)와 cHBC (q

0.69 Å^-1)의 두 가지 피크가 새로운 피크의 생성 없이 점진적으로 다양한 몰비(mol : mol)의 혼합 필름에서 이동함을 보여주었다. 또한, 결정질 혼합 필름의 1D 회절은 FcHBC 및 cHBC 성분의 결정 격자 사이의 상관관계를 보여주었다. 이로써 혼합된 cHBC / FcHBC 필름은 하나의 결정구조를 두개의 물질이 공유함으로써 d-spacing 이 바뀌게 되어 x-선 산란에서의 피크 이동이 나타났으며, cHBC, FcHBC의 고용체(solid solution) 형성이 이루어짐을 확인하였다.Figure 2H shows GIWAXS patterns obtained from FcHBC, cHBC and mixed cHBC/FcHBC films. Compared with FcHBC, cHBC, the 1D diffraction trace result in FIG. 2H shows that FcHBC (q

0.49 Å ^-1 ) and cHBC (q

0.69 Å ⁻¹ ) showed that the two peaks gradually shifted in the mixed film of various molar ratios (mol: mol) without the generation of new peaks. In addition, 1D diffraction of the crystalline mixed film showed a correlation between the crystal lattice of FcHBC and cHBC components. As a result, in the mixed cHBC / FcHBC film, as two materials share one crystal structure, d-spacing is changed, peak shift in x-ray scattering, and solid solution of cHBC and FcHBC is formed. was confirmed.

< Experimental example 2> cHBC and FcHBC Characterization of the solid solution

Electrochemical analysis was further performed by preparing a half-cell structure with solid solution electrodes of cHBC, FcHBC, and 3: 7 and 5: 5 molar ratios (mol: mol). As can be seen from the charge-discharge voltage curve with a current density of 0.1 A g ⁻¹ in FIG. 3A , the solid solution electrode with a mixing ratio of 5: 5 exhibited the highest reversible capacity of 350 mA hg ⁻¹ , which cHBC negative electrode reversible capacity (80 mA hg ^-1 ) was about 4 times higher than the higher. These results indicate that solid solution formation at a certain mixing ratio enhances the reversible capacity, which is in good agreement with the SEM and electrochemical impedance spectroscopy (EIS) results in FIG. 2 .

0.51 Å^{- 1}에서 이동된 1 차 피크와 q

0.69 Å^-1에서 사라진 회절을 발견하였는데, 이는 초기 리튬화 동안 고용체 필름의 결정상이 완전히 변형되었음을 나타낸다. 또한, 변형된 결정상은 추가 사이클링에 의해 현저하게 변화되지 않았으며, 이는 비가역적인 상 전이가 첫 번째 사이클에서 발생하고, 배터리 사이클링 동안 유지된다는 것을 의미한다(도 4). 이는 cHBC / FcHBC 고용체 전극이 초기 리튬화 공정 동안 분자 구조를 안정화시킴을 시사한다.In order to investigate the reason for the high capacity in the solid solution electrode with a ratio of 5: 5, lithium ions were completely lithiated at a current density of 0.1 A g ^-1 , and then GIWAXS analysis was performed. Figure 3B shows the 1D GIWAXS pattern of a lithiated 5:5 solid solution electrode. As a result, q

1st peak shifted at 0.51 Å ^{- 1} and q

A diffraction that disappeared at 0.69 Å ⁻¹ was found, indicating that the crystalline phase of the solid solution film was completely transformed during initial lithiation. In addition, the strained crystalline phase was not significantly changed by further cycling, meaning that an irreversible phase transition occurs in the first cycle and is maintained during battery cycling (Fig. 4). This suggests that the cHBC/FcHBC solid solution electrode stabilizes the molecular structure during the initial lithiation process.

To further understand the detailed crystal phase changes of the cHBC/FcHBC (5:5) solid solution, the continuous XRD pattern of the cHBC/FcHBC electrode from the initial lithiation process was measured. As can be seen from Fig. 3C, the diffraction portion at 2θ = 7.2 ° in the cHBC / FcHBC electrode during every 10% lithiation process was significantly improved at the 60% point of the discharge capacity, showing that it gradually increased to 100% of the discharge capacity. .

Detailed chemical state information from ex-situ XPS (X-ray photoelectron spectroscopy) can further explain the phase change of cHBC/FcHBC electrodes. For XPS analysis, a fluorine-free electrolyte (1M LiClO ₄ in EC/DEC, 50/50 volume ratio) was used to eliminate the possibility of decomposition of LiPF ₆ or FEC components. The F 1s spectrum in Fig. 3D showed that the LiF characteristic peak of 684.9 eV at the time point of the 60% lithiation process increased rapidly, and increased with the gradual increase of the discharge capacity. This, together with the XRD results in Fig. 3C, was confirmed to indicate the formation of a surface layer in which the presence of LiF during the lithiation process resulted in a change in the crystal layer.

In addition, after the lithiation process, the changed crystal structure of cHBC/FcHBC solid solution was further analyzed by computational screening of various solid solution structures sampled through a Monte Carlo simulation annealing process. As a result of comparing the GIWAXS pattern of the solid solution structure with the simulated XRD pattern, the cHBC / FcHBC solid solution showed an energetically stable P2 ₁ / n crystal phase, and it was found that the cHBC and FcHBC molecules were most uniformly mixed at the molecular level ( Figure 3E). This means that the formation of cHBC/FcHBC solid solution is thermodynamically favored over phase separation of cHBC and FcHBC. When cHBC and FcHBC are thoroughly mixed, a clear molecular junction is formed between cHBC and FcHBC molecules with different HOMO/LUMO energy levels, confirming that each cHBC (FcHBC) molecule is surrounded by eight FcHBC (cHBC) molecules. This molecular junction in solid solution will contribute to the enhancement of charge transport in semiconducting organic co-crystals.

< Experimental example 3> in lithium ion batteries cHBC / FcHBC Electrochemical performance of solid solution

P2 ₁ / n crystal phase cHBC / FcHBC 3: 7 and 5: using a solid solution electrode having a mixed molar ratio (mol: mol) of 5, without adding a conductive material, the rate characteristics were analyzed at various current densities. 5A shows the capacity retention performance of 3:7 and 5:5 solid solution electrodes at various current densities of 0.1 A g ^-1 to 7.0 A g ^-1 . In the 5:5 solid-solution electrode, the cell exhibited a reversible capacity of 350 mA hg ^-1 at a current density of 0.1 A g ^-1 , and maintained about 100 mA hg ^-1 at a high current density of 7.0 A g ^-1 . Thereafter, it was confirmed that when the discharge rate returned to 0.5 A g ^-1 , the capacity was mostly recovered. The reason for the high capacity even at such high current rates is the unique crystal structure of the cHBC/FcHBC solid solution. In addition, cHBC/FcHBC solid solution provides sufficient charge transport even at low voltage hysteresis due to the formation of molecular junctions between cHBC and FcHBC, which generates effective vacant sites for Li ion access with good reversibility.

In addition, cyclic voltammetry (CV) analysis was performed at various scan rates of 0.03 to 1.0 mV s ^-1 with a voltage in the range of 1.2 to 0.01 V. As can be seen in FIG. 5B, two peaks of positive and negative reactions were shown at 0.2 and 0.4 V, respectively, as a result of the current reaction, which is related to the discharge and charge potentials of FIG. 3A.

In addition, the reaction kinetics of the 5:5 solid-solution electrode because the b value calculated from the slope of log( i _p ) versus log (ν) indicates capacitive (b = 1) or battery (b = 0.5) behavior. _{To analyze} the ^positive and negative _ _ Cathodic reaction peaks were compared as a function of scan rate. Consequently, the observed b values of 0.69 and 0.64 for the positive and negative reaction peaks, respectively, indicate that the 5:5 solid-solution electrode dominates the battery behavior (Fig. 5C). However, it is additionally capacitive using the equation i ( V ) = k ₁ ν + k ₂ ν ^0.5 (where ^k ₁ ν and k ₂ ν ^0.5 are due to capacitive and diffusion-limited processes, respectively ⁾ . The behavioral contribution was calculated. As shown in Fig. 5D, the film with a 5:5 mixing ratio exhibited a capacitive area of about 30% in the CV profile at a scan rate of 0.4 mV s ^-1 , which was in good agreement with the calculated b value in Fig. 5C. This capacitive moiety could be derived from the FcHBC molecules in the solid solution film, probably because, as previously reported on FcHBC electrodes, the strong negative electrostatic potential of the fluorine atom ultimately increases the Li ion accessibility.

To understand the Li ion storage mechanism of the P2 ₁ /n crystalline cHBC/FcHBC solid solution electrode, we theoretically construct a void for Li ions by first constructing a Connolly surface using a probe with a radius of 0.76 Å (i.e., lithium ion radius). was analyzed (FIG. 6). As a result, most of the empty space was at the edge of each molecule due to the curved shape of the cHBC and FcHBC molecules. Also, there were accessible voids between the aromatic rings, which were caused by the stacked structure of molecules with similar curvatures.

Specific Li ion storage locations were analyzed using Monte Carlo simulations and density functional theory (DFT) calculations. Considering the various Li ion storage positions, the formation energy of the cHBC / FcHBC solid solution crystal phase using Li ions was calculated (Fig. 5E). The energy convex hull, defined as the lowest formation energy for each concentration of Li ions, showed that the crystalline phase of the cHBC/FcHBC solid solution became unstable when more than 36 Li ions were stored. Its theoretical capacity is 379 mA hg ^-1 , which is consistent with the experimental capacity with a value of 350 mA hg ^-1 . The crystal phase composition of the cHBC/FcHBC solid solution with Li ions and the voltage profile calculated along the convex hull are shown in FIGS. 5F and 7 . First, Li ions (denoted as site I) are inserted into the vacancy between the fringe aromatic ring of the cHBC molecule and the FcHBC molecule (Fig. 8A). These are the most thermodynamically stable sites due to their sandwich structure and cation-π interactions. Next, additional Li ions (represented by site II) are adsorbed to the vacancy between the edge of the aromatic ring in the cHBC molecule and the fluorine in the FcHBC molecule, which is due to the interaction between the π electron of the aromatic carbon and the electronegative fluorine atom. (Fig. 8B). Finally, an additional Li ion (denoted site III) is located in the other aromatic ring of cHBC with a relatively large-spaced FcHBC molecule, forming a cation-π interaction (Fig. 8C). As a result, all 36 Li- ions were adsorbed to the cation-π interaction site, where 8 Li ions (22%) were located around the fluorine of the FcHBC molecule (site II). The negative electrostatic potential of the fluorine atom could accelerate the ion diffusion and promote a fast redox reaction. Thus, lithium ion adsorption at site II may be responsible for the experimentally observed 30% capacitive behavior (Fig. 5D).

In addition, the cycling stability of the 5: 5 solid solution electrode was monitored, and it was observed that the stable capacity retention rate of 200 mA hg ^-1 at a current density of 5.0 A g ^-1 was observed. As can be seen in FIGS. 5G and 4 , a 99.8% coulombic efficiency retention rate was exhibited without significant crystal phase change even after 400 cycles.

Therefore, it was confirmed that the cHBC / FcHBC solid solution can not only improve the reversible specific capacity to 350 mA hg ^-1 but also maintain the high specific capacity at high current density.

< Experimental example 4> in sodium ion batteries cHBC / FcHBC electrochemical performance

The electrochemical properties of a 5:5 solid solution electrode for Na-ion batteries were further analyzed. Half-cells were prepared with Na metal and 1.3 M sodium hexafluorophosphate (NaPF ₆ ) in EC/DEC (volume ratio 50/50) using 4 wt % of FEC electrolyte.

Figure 9A shows the EIS results of cHBC, FcHBC 5: 5 solid solution film without a conductive material in a Na ion battery. The low R _CT value of the 5:5 solid-solution electrode in the Nyquist plot is consistent with the results of the Li-ion cell in Fig. 2F.

In addition, Fig. 9B shows the constant current discharge and charge curves of the 5: 5 solid solution electrode. As a result, the specific capacity of 250 mA hg ^-1 at a current density of 0.1 A g ^-1 is that FcHBC is used as a negative electrode ( Adv Sci 2018 , 5 , 1801365) was confirmed to be about 2 times higher. Based on the crystal structure of the solid solution electrode, this high specific capacity is due to the reversible vacant sites for Na ions generated in solid solution formation.

DFT calculations were performed to investigate the Na ion storage mechanism of P2 ₁ / n crystalline cHBC / FcHBC solid solution. The calculated formation energy for the crystalline phase of cHBC/FcHBC solid solution with Na ions indicated that up to 24 Na ions could be stored (Fig. 9C). The calculated voltage profile was correlated with the experimental results as shown in FIGS. 9D and 10 , confirming that the theoretical capacity (ie, 253 mA hg ^{−1 )} was similar to that of 250 mA hg ⁻¹ . As demonstrated in the Li ion case of <Experimental Example 3>, the Na ion storage mechanism also exhibited similar site preference. Na ions were first inserted at the most thermodynamically stable vacancy between the marginal aromatic rings in the cHBC and FcHBC molecules. Subsequently, additional Na ions were stored in the vacancy between the fringe aromatic ring of the cHBC molecule and the fluorine of the FcHBC molecule. As additional Na ions were inserted, they were finally adsorbed to the aromatic ring of the FcHBC molecule where there was an accessible space. As a result, 8 Na ions out of a total of 24 Na ions were adsorbed around the fluorine in the FcHBC molecule.

The contribution of the capacitive behavior for Na ions (33%) was observed to be greater than for Li ions (22%). This is because the aromatic ring sites accessible by Na ions are reduced due to the larger ionic radius of Na ions than Li ions. The values related to this were in good agreement with the calculated cathodic/anodic reaction b values. The negative / positive reaction b value of the cHBC / FcHBC negative electrode for Na ion storage was 0.75 / 0.77, and the k ₁ ν region showed a value of about 45% corresponding to the capacitive process (Fig. 11). This capacitive characteristic of the current response at a scan rate of 0.4 mV s ⁻¹ is 1.5 times higher than that of the Li ion storage cell, probably because the large size of Na ions (1.02 Å) improves the capacitive characteristics.

80 mA h g^-1을 나타냈으며, 이는 초기 용량의 약 32 % 이다.9E shows the rate-limiting performance at a current density of 0.1 to 3.0 A g ^-1 . The 5: 5 solid-solution electrode has a high current density of 2.0 A g ^-1

80 mA hg ^-1 , which is about 32% of the initial dose.

In addition, very reliable cycle stability was confirmed at a current density of 0.5A g ^-1 with a coulombic efficiency of 99% over 200 cycles (FIG. 9F), indicating that the cHBC / FcHBC solid solution anode is also advantageous for high-performance Na ion storage cells. indicates that

100 mA h g^-1을 나타내었으며, 99.8 % 이상의 쿨롱 효율로 400 회 이상의 사이클 안정성을 보여주었다. 이러한 높은 전기 화학적 성능은 주로 cHBC / FcHBC 고용체의 고유한 P2 ₁ / n 결정상에 의해 발생하며, 이는 GIWAXS 및 심층적인 계산 분석에 의해 확인되었다. In conclusion, we have effectively fabricated organic solid-solution electrodes for high-performance Li- and Na- ion storage cells. The semiconductor cHBC/FcHBC solid solution showed an excellent reversible capacity of 350 mA hg ⁻¹ for the Li ion storage cell. In addition, the cHBC/FcHBC solid solution electrode also showed good performance and cycle stability. Li ion storage cell at 7.0 A g ^-1

It exhibited 100 mA hg ^-1 , and showed stability over 400 cycles with a coulombic efficiency of 99.8% or more. This high electrochemical performance is mainly caused by the intrinsic P2 ₁ /n crystal phase of cHBC/FcHBC solid solution, which was confirmed by GIWAXS and in-depth computational analysis.

In addition, when a cHBC / FcHBC solid solution electrode is applied to a Na ion storage cell, reliable cycle stability with a specific capacity of 250 mA hg ^-1 at a current density of 0.1 A g ^-1 and a coulombic efficiency of 99% over 200 cycles showed

Therefore, it was confirmed that the cHBC / FcHBC solid solution is a useful active material for manufacturing high-performance organic active electrodes for Li and Na ion storage cells.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (10)

Containing a mixed solid solution of hexabenzocoronene and fluorinated hexabenzocoronene,
The hexabenzocoronene and the fluorinated hexabenzocoronene are mixed in a molar ratio of (3 to 7): (7 to 3) (mol: mol) to form a solid solution. According to claim 1,
The solid solution is characterized in that curved hexabenzocoronene (cHBC) and curved fluorinated-contorted hexabenzocoronene (FcHBC) are uniformly mixed to have a monoclinic P2 ₁ / n crystal structure. anode active material. delete A negative electrode for a secondary battery comprising the negative active material according to claim 1 . 5. The method of claim 4,
The secondary battery is a secondary battery negative electrode, characterized in that the lithium ion or sodium ion secondary battery. a) preparing a solid solution by mixing hexabenzocoronene and fluorinated-hexabenzocoronene; and
b) preparing a negative electrode by coating the solid solution of step a) on a metal and annealing; including,
The hexabenzocoronene and the fluorinated hexabenzocoronene are mixed in a molar ratio (mol:mol) of (3 to 7): (7 to 3) to form a solid solution,
The annealing treatment is
i) subjecting the solid solution coated on the metal to THF-steam annealing;
ii) i) thermal annealing the treated solid solution at a temperature of 300 to 400° C.; and
iii) ii) A method of manufacturing a negative electrode for a secondary battery, comprising the step of annealing the solid solution treated in step ii) by an electrolyte vapor annealing treatment. 7. The method of claim 6,
The solid solution is characterized in that curved hexabenzocoronene (cHBC) and curved fluorinated-contorted hexabenzocoronene (FcHBC) are uniformly mixed to have a monoclinic P2 ₁ / n crystal structure. A method of manufacturing a negative electrode for a secondary battery. delete delete 7. The method of claim 6,
The electrolyte may be a lithium salt or a sodium salt; and
A method for manufacturing a negative electrode for a secondary battery, comprising a carbonate-based solvent.

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