Li-ion batteries (LIBs) are currently the dominant energy storage system in portable electronic devices (EVs), electric vehicles, and energy storage systems (ESS). With the saturation of the battery market for small devices, the global Li-ion battery market has a great interest in the large energy storage system. Conventional cathode materials for Li-ion batteries are inorganic materials based on cobalt source.
For these reasons, current inorganic materials are inadequate for the post Li-ion battery market. Schematic diagram of the redox potential and specific capacity of conventional Li-ion battery electrode materials. a) Skeletal structure of AQ and PAQS, (b) Cycle performance of AQ (up) and PAQS (down). a) Schematic diagram of PTMA brush/SiO2, (b) Cyclic voltammogram (up) of PTMA film coated on the Au electrode, cyclic voltammogram (down) of PTMA brush grafted on SiO2. a) Skeletal structure of Li2TP, (b) Voltage profile and cycle performance of Li2TP. a) Skeletal structure of PTCDA, (b) SEM image of PTCDA/CNT composite, (c) Cycle performance of PTCDA and PTCDA/CNT composite with different ratios. a) Schematic diagram of S/CMK-3 composite (black: CMK-3, yellow: Sulphur), (b) Cycle performance of S/CMK-3 composite (red) and polymer coated composite (black), (c ) Elemental analysis of bare S (red), CMK-3/S composite (blue), S/CMK-3 coated with polymer (black). Galvanostatic charge-discharge curves for Li-ion batteries of (a) bare phenanthrenequinone and (b) PQ/CMK-3 for Li-ion batteries.
Introduction
Li-Ion Batteries
Typically, the cathode materials are selected as a contributor to lithium and at the same time as a lithium container. During the charging process, lithium ion came out from the cathode materials, goes through the electrolyte and then reacts with the anode materials. In contrast, lithium ion came out of anode materials during the discharge process and reintroduced into the cathode materials.
Such a cathode material that is possible to perform lithium intercalation/de-intercalation is mainly used LiCoO2 as a conventional lithium transition metal oxide material. When the battery is charged, lithium ion comes out of cathode material and enters into the interlayer of the graphite, then voltage increases. On the contrary, when the battery is discharged, lithium ion is released from the anode material and it spontaneously reacts with the cathode material.
Organic Electrode Materials
Schematic diagram of redox potential and specific capacity of electrode materials of conventional Li-ion batteries.
Strategy to Mitigate Small Molecule Dissolution
Experiment
- Synthesis
- Electrode Preparation
- Cell Preparation
- Electrochemical Characterization
- Instrumental Analysis
- DFT Calculation
Half-cell evaluation of both PQ/CMK-3 composite and bare PQ was implemented to investigate the electrochemical performance. The entire process related to cell assembly was performed in the dry box filled with inert argon gas. In the lithium ion half-cell, their electrochemical property was evaluated using 2016 coin cells, which consisted of lithium metal as anode, polyolefin bonded film separator and 1.3 M lithium bis(trifluoromethanesulfonyl) electrolyte. imide (LiTFSI) in a tetra(ethylene glycol)dimethyl ether (TEGDME) solvent (Panax Etec Co. LTD).
In DFT calculated conjugated carbonyl molecules, the electrochemical property was evaluated using 2032 coin cells. It was composed of a disk-shaped Na metal separator of the same materials used in Li-cell and electrolyte of 0.8 M sodium perchlorate (NaClO4) (≥98 %, Sigma Aldrich) in a mixed solvent of ethylene carbonate (EC )/diethyl carbonate (DEC) (v/v=1/1, Panax Etec Co. LTD). The electrochemical properties were evaluated by the galvanostatic discharge/charge measurements (WonATech WBCS 3000 battery measurement system).
After constant current experiments, the reduction potential was determined that the 5th discharge cycle of PTCDA and the second discharge cycle of other molecules were integrated and then divided into specific capacity at that cycle. High-resolution TEM samples were obtained using a high-resolution transmission electron microscope (HR-TEM, STEM, JEOL ARM-200F) with a probe Cs aberration corrector (CEOS GmbH) and an energy-dispersive X-ray spectroscopy (EDS, Oxford Instruments X-je 80 TLE) attached to the TEM . The surface areas and pore sizes of the samples were analyzed in a nitrogen adsorption experiment at -196 oC using a BEL BELSORP-Max system, and their results were calculated using the Brunauer-Emmett-Teller (BET) equation and the Barrett-Joyner-Halenda ( BJH) method.
Infrared spectra were collected by a Varian 670-IR spectrometer equipped with an Attenuated Total Reflectance (ATR) attachment. Thermal analysis was performed with a thermogravimetric analyzer (TGA, SDT Q600) at a heating rate of 5 oC min-1 in a nitrogen atmosphere. Quantitative analysis of dissolution between PQ and PQ/CMK-3 in TEGDME was performed by ultraviolet-visible (UV-VIS) spectroscopy (Varian, Cary 5000).
Nine conjugated carbonyl molecules were calculated using the density functional theory (DFT) method with the Gaussian 09 program package.
Results and Discussion
Ordered Mesoporous Phenanthrenequinone-Carbon composite
- Synthesis and Characterization
- Electrochemical Performance
In particular, the two C-H bending vibrations of PQ/CMK-3 in the low-energy region (715 and 764 cm-1) were red- and blue-shifted, respectively, compared to pure PQ (Figure 16b). This demonstrates evidence of the existence of PQ within PQ/CMK-3 due to the noncovalent force (π-π stacking interaction between PQ and CMK-3). The difference in evaporation behavior between bare PQ and PQ/CMK-3 is attributed to the strong π-π interaction between PQ and CMK-3 in PQ/CMK-3.
The different vapor pressure between pure PQ and PQ/CMK-3 is further supported by isothermal analysis (Figure 16d). In addition, the TGA graph represents the PQ content of PQ/CMK-3 in the composite range up to 31.5 wt. %. Furthermore, the 1H NMR spectra in Figure 17 showed that the NMR signal of PQ fractionated from the PQ/CMK-3 composite using the Soxhlet extraction method corresponds to bulk PQ.
It indicates that both the bare PQ and the PQ in the composite have the same chemical structure, so the infiltrated PQ is stable despite the heating up to 250 oC in air conditions. 1H NMR (CDCl3, 400 MHz, 300 K) spectra of (a) bare PQ and (b) the part collected from PQ/CMK-3 via Soxhlet extraction using chloroform. This appears to be due to the different particle size of the active material and the composition of the electrolyte.
The improved reversible capacity of the PQ/CMK-3 is therefore attributed to the improved electrical conductivity of PQ/CMK-3. Therefore, the dissolution of the PQ in the non-aqueous electrolyte was alleviated due to the confinement of the PQ in the CMK-3. The same amounts of bare PQ and PQ in PQ/CMK-3 were stored in tetra(ethylene glycol) dimethyl ether (TEGDME) with simultaneous stirring.
However, the dissolution of PQ in the composite was greatly facilitated compared to that of bare PQ, as shown in the difference in absorbance between bare PQ- and PQ/CMK-3 dissolved solvents ( Figure 20b ). It delivered approximately 113 mAh g-1 at a rate of 2 C, demonstrating that it retains 51% of the reversible capacity given at a rate of 0.1 C. -reaction mechanism of the electrochemical reduction of phenanthrenequinone. a) Cycle retention of PQ/CMK-3, (b) Quantitative UV-VIS analysis between bare PQ (blue circles) and PQ/CMK-3 (red squares) by divergent absorption according to different degree of dissolution in it same amounts of PQ in TEGDME, (c) UV-VIS spectrum of bare PQ. a) Scale ability, (b) their load-discharge curves of PQ/CMK-3.
Change in Reduction Potential via Chemical Change
- Relationship between LUMO and Reduction Potential
- Terminal Functional Group Effect
- Bridge Functional Group Effect
- Extended pi Conjugation Effect
The functional group can have an effect on aspect of inductive effect induced by sigma bond and resonance effect generated by pi bond. After these two aspects are all considered, the effect called the polar effect determines the final electron density on the benzene ring. If the electron-donating functional group is introduced into the conjugated structure, it will make it easier to release electrons as electron density in the conjugation becomes abundant.
Compared molecular structures among PTCDA, PTCDI, and BPE-PTCDI, they all have the same perylene skeleton except the terminal functional group (Figure 23b). After obtaining a voltage profile (Figure 23a), PTCDA containing an anhydride terminal functional group is correlated with PTCDI including an imide group. This allowed the phenylethyl functional group to donate electrons to the aromatic backbone, unlike the hydrogen group, resulting in the LUMO energy of BPE-PTCDI increasing with a reduced reduction potential. a) Voltage profiles in the 5th cycle of PTCDA and 2nd cycle of PTCDI and BPE-PTCDI, (b) the discharge potential and calculated LUMO energies of PTCDA, PTCDI and BPE-PTCDI.
Na-ADB, Na-CDB and Na-BPDC have a bridging functional group that exists between pi conjugation and show dramatic shift of reduction potential (Figure 25a). Furthermore, the decreased band gap is a result of an increased HOMO and a decreased LUMO, because the functional group that can affect the energy level is identical. This trend could be confirmed in molecules of Na-PTC, Na-BPDC, Na-NTC and Na-TP.
Both Na-BPDC and Na-TP have two carboxylate functional groups in one molecule and Na-BPDC has longer pi conjugation chain. This result is consistent with Na-NTC and Na-PTC having four carboxylate functional groups in one molecule. Furthermore, even though Na-NTC and Na-BPDC have a similar pi conjugation length, why the LUMO energy difference occurs is due to the number of carboxylate functional group affected in a benzene.
Most of the molecules are convinced that a lower LUMO level affects a higher electrochemical potential, except for the relationship between Na-NTC and Na-BPDC (Figure 27b).
Conclusion
P.; Dolhem, F.; Tarascon, J.-M.; Poizot, P., The lithium salt of tetrahydroxybenzoquinone: towards the development of a sustainable lithium-ion battery. ChemSusChem e) Renault, S.; Geng, J.; Dolhem, F.; Poizot, P., Evaluation of polyketones with N-cyclic structure as electrode material for electrochemical energy storage: the case of pyromellitic diimide dilithium salt. Lin, H.-C.; Li, C.-C.; Lee, J.-T., Nitroxide Polymer Brushes Grafted onto Silica Nanoparticles as Cathodes for Organic Radical Batteries.
Meng, Y.; Lu, K.; Wei, Z., An organic cathode material based on a polyimide/CNT nanocomposite for lithium ion batteries. A.; Dunn, B., Naphthalenediimide-based materials with tunable redox potential: evaluation for organic lithium-ion batteries. Song, Z.; Zhan, H.; Zhou, Y., Anthraquinone-based polymer as high-performance cathode material for rechargeable lithium batteries.
