Conjugated Microporous Polytetra(2-Thienyl)ethylene as High Performance Anode Material for Lithium- and Sodium-Ion Batteries

A Potential Polycarbonyl Polyimide as Anode Material for Lithium-Ion Batteries

Organic polymers have been considered reliable candidates for lithium storage due to their high capacity and lack of volume expansion. Compared with other organic polymers, polyimide has become a very promising electrode material for lithium-ion batteries (LIBs) because of its easy synthesis, customizable structure and structural stability. A large number of studies have confirmed that the benzene ring structure of polyimide has strong lithium storage capacity as an anode material. Hence, we designed and synthesized polyimide organic polymer (PBPAQ) for the first time. The unique spherical flower structure of this material enhances the interaction between the electrode material and the electrolyte by increasing the contact area. The PBPAQ anode has a specific discharge capacity of 738 mAh g-1 after 100 cycles at 0.1 A g-1 . The excellent lithium storage performance of this material laid a foundation for the research of the anode of LIBs in the future.

Porous Organic Polymer with Hierarchical Structure and Limited Volume Expansion for Ultrafast and Highly Durable Sodium Storage

Sustainable organic electrode materials, as promising alternatives to conventional inorganic electrode materials for sodium-ion batteries (SIBs), are still challenging to realize long-lifetime and high-rate batteries because of their poor conductivity, limited electroactivity, and severe dissolution. It is also urgent to deeply reveal their electrochemical mechanism and evolution processes. A porous organic polymer (POP) with a conjugated and hierarchical structure is designed and synthesized here. The unique molecule and structure endow the POP with electron delocalization, high ionic diffusivity, plentiful active sites, exceptional structure stability, and limited solubility in electrolytes. When evaluated as an anode for SIBs, the POP exhibits appealing electrochemical properties regarding reversible capacity, rate behaviors, and long-duration life. Importantly, using judiciously combined experiments and theoretical computation, including in situ transmission electron microscopy (TEM), and ex situ spectroscopy, we reveal the Na-storage mechanism and dynamic evolution processes of the POP, including 12-electron reaction process with Na, low volume expansion (125-106% vs the initial 100%), and stable composition and structure evolution during repeating sodiation/de-sodiation processes. This quantitative design for ultrafast and highly durable sodium storage in the POP could be of immediate benefit for the rational design of organic electrode materials with ideal electrochemical properties.

Tetrathiafulvalene-Based Metal-Organic Framework as a High-Performance Anode for Lithium-Ion Batteries

Metal-organic frameworks (MOFs) have aroused great interest as lithium-ion battery (LIB) electrode materials. In this work, we first report that a pristine three-dimensional tetrathiafulvalene derivatives (TTFs)-based zinc MOF, formulated [Zn₂(py-TTF-py)₂(BDC)₂]·2DMF·H₂O (1) (py-TTF-py = 2,6-bis(4'-pyridyl)tetrathiafulvalene and H₂BDC = terephthalic acid), can work as a high-performance electrode material for rechargeable LIBs. The TTFs-Zn-MOF 1 electrode displayed a high discharge specific capacity of 1117.4 mA h g^-1 at a current density of 200 mA g^-1 after 150 cycles along with good reversibility. After undergoing elevated discharging/charging rates, the electrode showed superior lithium storage performance in the extreme case of 20 A g^-1 and could finally recover the capability when the current rate was back to 200 mA g^-1. Particularly, specific capacities of 884.2, 513.8, and 327.8 mA h g^-1 were reached at high current densities of 5, 10, and 20 A g^-1 after 180, 175, and 300 cycles along with good reversibility, respectively. Such an excellent performance is first reported for the LIB anode materials. TTFs-Zn-MOF 2, namely, [Zn₂(py-TTF-py) (BDC)₂]·DMF·2H₂O (2), was prepared as a contrast to explore the relationship between the structures of the electrode materials and the electrochemical properties. Based on the structural analysis of 1 and 2 and ex situ X-ray photoelectron spectroscopy, the TTF moiety and the twofold TTF pillar play a key role in the excellent electrochemical performance. The full cell of MOF 1 with NMC 622 delivered the capacity of 131.9 mA h g^-1 at 100 mA g^-1 with the Coulombic efficiency of 99.45% after 70 cycles and exhibited the tolerance to high-current operation.

Exploiting Polythiophenyl-Triazine-Based Conjugated Microporous Polymer with Superior Lithium-Storage Performance

Conjugated microporous polymers (CMPs) have been heralded as promising energy-storage materials with advantages such as chemical flexibility, porous structure, and environmentally friendliness. Herein, a novel conjugated microporous polymer was synthesized by integrating triazine, thiophene, and benzothiadiazole into a polymer skeleton, and the Li⁺ -storage performance for the as-synthesized polymer anode in Li-ion batteries (LIBs) was investigated. Benefiting from the inherent large surface area, plentiful redox-active units, and hierarchical porous structure, the polymer anode delivered a high Li⁺ storage capacity up to 1599 mAh g^-1 at a current rate of 50 mA g^-1 with an excellent rate behavior (363 mAh g^-1 at 5 A g^-1 ) and a long-term cyclability of 326 mAh g^-1 over 1500 cycles at 5 A g^-1 , implying that the newly developed polymer anode offers a great prospect for next-generation LIBs.

Thiophene-embedded conjugated microporous polymers for photocatalysis

“Bottom-up” embedding of thiophene derivatives into CMPs for highly efficient heterogeneous photocatalysis is reported.

Dynamic Hierarchical Self-Assemble Small Molecule Structure Hexabenzocoronene for the High-Performance Anodes Lithium Ion Storage

This study examined the characteristics of small molecular structure nano-graphene in a dynamic hierarchical self-assembly and found that graphene is rearranged under its own pressure during dynamic aggregation and water ripples are formed by the d-spacing. The composition and structure were studied using a range of material characterization techniques. No covalent bonds were observed between molecules, and the self-assembled driving force was the only intermolecular interaction: Van der Waals' force in the intra-layer and π-π interactions between layers. The arranged-rearranged structures provided a range of lithium ion shuttle channels, including the space between layers and diffusing through the nanosheets, which decrease the diffusion distance of lithium ions remarkably and reduce the irreversible capacity of the battery.

Conjugated Microporous Polymers with Tunable Electronic Structure for High-Performance Potassium-Ion Batteries

Conjugated microporous polymers (CMPs) with π-conjugated skeletons show great potential as energy storage materials due to their porous structure and tunable redox nature. However, CMPs and the structure-performance relationships have not been well explored for potassium-ion batteries (KIBs). Here, we report the structure-engineered CMP anodes with tunable electronic structures for high-performance KIBs. The results demonstrate that the electronic structure of the CMPs plays an important role in enhancing potassium storage capability, including the lowest unoccupied molecular orbital (LUMO) distribution, LUMO energy level, and band gap, which can be finely tuned by synthetic control. It was revealed that the poly(pyrene- co-benzothiadiazole) (PyBT) with optimized structure delivers a high reversible capacity of 428 mAh g^-1 and shows an excellent cycling stability over 500 cycles. Our findings provide a fundamental understanding in the design of CMP anode materials for high-performance potassium-organic energy storage devices.

Capacitive Organic Anode Based on Fluorinated-Contorted Hexabenzocoronene: Applicable to Lithium-Ion and Sodium-Ion Storage Cells

Conducting polymer-based organic electrochemical capacitor materials have attracted attention because of their highly conductive nature and highly reversible redox reactions on the surface of electrodes. However, owing to their poor stabilities in aprotic electrolytes, alternative organic electrochemical capacitive electrodes are being actively sought. Here, fluorine atoms are introduced into contorted hexabenzocoronene (cHBC) to achieve the first small-molecule-based organic capacitive energy-storage cells that operate at high current rates with satisfactory specific capacities of ≈160 mA h g-1 and superior cycle capabilities (>400) without changing significantly. This high capacitive behavior in the P21/c crystal phase of fluorinated cHBC (F-cHBC) is caused mainly by the fluorine atoms at the end of each peripheral aromatic ring. Combined Monte Carlo simulations and density functional theory (DFT) calculations show that the most electronegative fluorine atoms accelerate ion diffusion on the surface to promote fast Li+ ion uptake and release by an applied current. Moreover, F-cHBC has potential applications as the capacitive anode in Na-ion storage cells. The fast dynamics of its capacitive behavior allow it to deliver a specific capacity of 65 mA h g-1 at a high current of 4000 mA g-1.