Anti-Freezing Electrolytes in Aqueous Multivalent Metal-Ion Batteries: Progress, Challenges, and Optimization Strategies.

Aqueous rechargeable multivalent metal-ion batteries (ARMMBs) have attracted considerable attention due to their high capacity, high energy density, and low cost. However, their performance is often limited by low temperature operation, which requires the development of anti-freezing electrolytes. In this review, we summarize the anti-freezing mechanisms and optimization strategies of anti-freezing electrolytes for aqueous batteries (especially for Zn-ion batteries). Besides, we investigate the possible interactions and side reactions between electrolytes and electrodes. We also analyze the problems between electrolytes and electrodes at low temperature, and propose possible solutions. The research progress in the field of low temperature energy storage for aqueous Mg-ion, Ca-ion, and Al-ion batteries, and the challenges faced in their anti-freezing electrolytes are investigated in detail. Last but not least, the outlook on the energy storage applications of ARMMBs is provided to guide the future research.

Ultrafast Absorption of Polysulfides through Electrostatic Confinement by Protonated Molecules for Highly Efficient Li-S Batteries.

The lithium-sulfur battery is a promising high-energy-density storage system, which suffers from severe capacity fading due to the "shuttle effect" and low Coulombic efficiency caused by the dissolution of lithium polysulfides. At the molecular level, suppressing the shuttle effect has been greatly required for high-performance Li-S batteries. Herein, we propose a new strategy by utilizing a protonated organic absorbent (N1,N4-bis(pyridine-3-ylmethyl)butane-1,4-diammonium nitrate ([H2PBD]2+·(NO3)22-) for ultrafast absorption of polysulfides through electrostatic attractions and for fixing the polysulfides in the cathode by hydrogen-bond interactions. A lithium-sulfur battery cathode based on a commercial carbon black (CB) and an absorbent (10%) with high sulfur content (70%) exhibits a low capacity decay of 0.099% per cycle over 400 cycles at a rate of 0.5C along with 91% Coulombic efficiency. This strategy and the finding of an electrostatic absorbent offer a new alternative insight into designing cheaper lithium-sulfur batteries for their practical application in the future.

Ferroelectric Metal-Organic Framework as a Host Material for Sulfur to Alleviate the Shuttle Effect of Lithium-Sulfur Battery.

Ferroelectricity has an excellent reversible polarization conversion behavior under an external electric field. Herein, we propose an interesting strategy to alleviate the shuttle effect of lithium-sulfur battery by utilizing ferroelectric metal-organic framework (FMOF) as a host material for the first time. Compared to other MOF with same structure but without ferroelectricity and commercial carbon black, the cathode based on FMOF exhibits a low capacity decay and high cycling stability. These results demonstrate that the polarization switching behaviors of FMOF under the discharge voltage of lithium-sulfur battery can effectively trap polysulfides by polar-polar interactions, decrease polysulfides shuttle and improve the electrochemical performance of lithium-sulfur battery.

High-Performance Metal-Organic Framework-Based Single Ion Conducting Solid-State Electrolytes for Low-Temperature Lithium Metal Batteries.

Single-ionic conducting electrolytes are important for the improvement of lithium metal batteries with high energy density and safety. Herein, we propose a new strategy to anchor a large anionic group on the skeleton of metal-organic frameworks (MOFs) and achieve preeminent single-ionic conducting electrolytes. Utilizing a postsynthetic modification method, the trifluoromethanesulfonyl group is covalently coordinated to the amino groups of the UiO-66-NH2 framework. Such a single-ionic conducting solid-state electrolyte (SSE) has a high ionic conductivity (2.07 × 10-4 S cm-1 at 25 °C), a low activation energy of 0.31 eV, a wide electrochemical window up to 4.52 V, as well as a high Li+ transference number of 0.84. Simultaneously, it can effectively inhibit the formation of lithium dendrite. Solid-state batteries assembled with LiFePO4 as the cathode exhibit outstanding rate performance and cyclic stability, especially for low-temperature Li-metal batteries at 0 °C with trace amounts of propylene carbonate as wetting agents. More importantly, the corresponding all-solid-state batteries based on an MOF-based SSE also have nearly 100% Coulombic efficiency at different current densities.

Syntheses and magnetic properties of high-dimensional cucurbit[6]uril-based metal-organic rotaxane frameworks.

Three new high-dimensional cucurbit[6]-based metal-organic rotaxane frameworks [Co2(PR43)(BDC)2Cl2]·4H2O (1), [Co2(PR43)(BTC)2]·6H2O (2) and [Co2(PR43)(BPT)2]·20H2O (3) were obtained via the hydrothermal synthesis method. Compound 1 comprised a two-dimensional layered structure, while compounds 2 and 3 exhibited three-dimensional pillared structures. All the compounds showed good thermal stabilities. Furthermore, the magnetic properties of compounds 1-3 were also investigated in detail.

Guest exchange in a porous cucurbit[6]uril-based metal-organic rotaxane framework probed by NMR and X-ray crystallography.

The first CB[6]-based 3D porous metal-organic rotaxane framework is constructed by the reaction of CuCl2, terephthalic (H2BDC) and CB[6]-based [2]pseudorotaxanes ([PR44]2+·2[PF6]-) under solvothermal conditions. The structure of MORF-1 is a pillared-layer structure with 5-connected sqp topology, in which the effective free volume is 45.4% of the crystal volume. The guest molecules exchange in a single-crystal-to-single-crystal fashion, which was investigated using NMR spectroscopy and X-ray crystallography.