Hofmeister Effects in Supramolecular Chemistry for Anion-Modulation to Stabilize Zn Anode.

Aqueous Zn-ion batteries (AZIBs) are considered as promising candidates for the next-generation large-scale energy storage, which, however, is facing the challenge of instable Zn anodes. The anion is pivotal in the stability of anodes, which are not being paid enough attention to. Herein, the modulation of anions is reported using the Hofmeister series in supramolecular chemistry to boost the stability of Zn anodes. It is found that the right-side anions in the Hofmeister series (e.g., OTf-) can enhance the Zn2+ transference number, increase the Coulombic efficiency, facilitate uniform Zn deposition, reduce the freezing point of electrolytes, and thereby stabilize the Zn anodes. More importantly, the right-side anions can form strong interaction with ß-cyclodextrin (ß-CD) compared to the left-side anions, and hence the addition of ß-CD can further enhance the stability of Zn anodes in OTf--based electrolytes, showing enhancement of cycling lifespan in the Zn//Zn symmetric cells more than 45.5 times with ß-CD compared with those without ß-CD. On the contrary, the left-side anions show worse rate performance after the addition of ß-CD. These results provide an effective and novel approach for choosing anions and matching additives to stabilize the anodes and achieve high-performance AZIBs through the Hofmeister effect.

A donor-acceptor (D-A) conjugated polymer for fast storage of anions.

Organic electrode materials have attracted a lot interest in batteries in recent years. However, most of them still suffer from low performance such as low electrode potential, slow reaction kinetics, and short cycle life. In this work, we report a strategy of fabricating donor-acceptor (D-A) conjugated polymers for facilitating the charge transfer and therefore accelerating the reaction kinetics by using the copolymer (p-TTPZ) of dihydrophenazine (PZ) and thianthrene (TT) as a proof-of-concept. The D-A conjugated polymer as p-type cathode could store anions and exhibited high discharge voltages (two plateaus at 3.82 V, 3.16 V respectively), a reversible capacity of 152 mAh g-1 at 0.1 A g-1 , excellent rate performance with a high capacity of 124.2 mAh g-1 at 10 A g-1 (≈50 C) and remarkable cyclability. The performance, especially the rate capability was much higher than that of its counterpart homopolymers without D-A structure. As a result, the p-TTPZ//graphite full cells showed a high output voltage (3.26 V), a discharge specific capacity of 139.1 mAh g-1 at 0.05 A g-1 and excellent rate performance. This work provides a novel strategy for developing high performance organic electrode materials through molecular design and will pave a way towards high energy density organic batteries.

Structural Isomers: Small Change with Big Difference in Anion Storage.

Organic electrode materials are promising for batteries. However, the reported organic electrodes are often facing the challenges of low specific capacity, low voltage, poor rate capability and vague charge storage mechanisms, etc. Isomers are good platform to investigate the charge storage mechanisms and enhance the performance of batteries, which, however, have not been focused in batteries. Herein, two isomers are reported for batteries. As a result, the isomer tetrathiafulvalene (TTF) could store two monovalent anions reversibly, deriving an average discharge voltage of 1.05 V and a specific capacity of 220 mAh g-1 at a current density of 2 C. On the other hand, the other isomer tetrathianaphthalene could only reversibly store one monovalent anion and upon further oxidation, it would undergo an irreversible solid-state molecular rearrangement to TTF. The molecular rearrangement was confirmed by electrochemical performances, X-ray diffraction patterns, nuclear magnetic resonance spectra, and 1H detected heteronuclear multiple bond correlation spectra. These results suggested the small structural change could lead to a big difference in anion storage, and we hope this work will stimulate more attention to the structural design for boosting the performance of organic batteries.

A Recyclable and Scalable High-Capacity Organic Battery.

Redox organic electrode materials (OEMs) have attracted extensive attention for batteries due to the possibility to be designed with high performance. However, the practical application of OEMs requires rigor criteria such as low cost, recyclability, scalability and high performance etc. and hence seems still far away. Here, we demonstrate an OEM for high performance aqueous organic batteries. Quantification of the charge storage confirmed the storage of protons with fast reaction kinetics, thereby enabling the high performance at high mass loading. As a result, the laminated pouch cells delivered Ampere-hour-scale capacity with excellent cycling performance. Benefited from the small molecular nature and the stable both charged and discharged states, the electrodes can be recycled at any states of charge with high yields (more than 90 %). This work provides a substantial step in the practical applications of OEMs for the future sustainable batteries.

Framework Dimensional Control Boosting Charge Storage in Conjugated Coordination Polymers.

Conjugated coordination polymers (CCPs) with extended π-d conjugation, which can effectively promote long-range delocalization of electrons and enhance conductivity, are superior to traditional metal-organic frameworks (MOFs) and attracted great attention for potential applications in chemical sensors, electronics, energy conversion/storage devices, etc. However, the precise construction of CCPs is still challenging due to the complex and uncontrollable reactions of CCPs. Herein, two different framework dimensions of CCPs are controllably realized by employing the same ligand (2,3,5,6-tetraaminobenzoquinone (TABQ)) and the same metal (copper) as center ions. The manipulation of reaction leads to different valences of ligands and metal ions, different coordination geometries, and thereby 1D-CuTABQ and 2D-CuTABQ frameworks, respectively. High performance of charge storage is hence achieved involving the storage of both cations and anions, and therein, 2D-CuTABQ shows a high reversible capacity of ≈305 mAh g-1 , good rate capability and high capacity retention (≈170 mAh g-1 after 2000 cycles at 5 A g-1 with 0.01% decay per cycle), which outperforms 1D-CuTABQ and almost all of the reported MOFs as cathodes for batteries. These results highlight the delicate structural control of CCPs for high-performance batteries and other various applications.