Low-cost Zinc-Iron Flow Batteries for Long-Term and Large-Scale Energy Storage

Aqueous flow batteries are considered very suitable for large-scale energy storage due to their high safety, long cycle life, and independent design of power and capacity. Especially, zinc-iron flow batteries have significant advantages such as low price, non-toxicity, and stability compared with other aqueous flow batteries. Significant technological progress has been made in zinc-iron flow batteries in recent years. Numerous energy storage power stations have been built worldwide using zinc-iron flow battery technology. This review first introduces the developing history. Then, we summarize the critical problems and the recent development of zinc-iron flow batteries from electrode materials and structures, membranes manufacture, electrolyte modification, and stack and system application. Finally, we forecast the development direction of the zinc-iron flow battery technology for large-scale energy storage.

Double Riveting and Steric Hindrance Strategy for Ultrahigh-Loading Atomically Dispersed Iron Catalysts Toward Oxygen Reduction

Atomically dispersed iron on nitrogen doped carbon displays high intrinsic activity toward oxygen reduction reaction, and has been identified as an attractive candidate to precious platinum catalysts. However, the loading of atomic iron sites is generally limited to below 4 wt% due to the undesired formation of iron-related particles at higher contents. Herein, this work overcomes this limit by a double riveting and steric hindrance strategy to achieve monodispersed iron with a high-loading of 12.8 wt%. Systematic study reveals that chemical riveting of atomic iron in ZIF-8 framework, chelation of Fe ions with interconfined 1,4-phenylenebisboronic, and physical hindrance are essential to obtain high-loading monodispersed Fe moieties. Resultantly, designed Fe-N-C-PDBA exhibits superior catalytic activity and excellent stability over commercial platinum catalysts toward oxygen reduction reaction in both half-cells and zinc-air fuel cells (ZAFCs). This provides an avenue for developing high-loading single-atom catalysts (SACs) for energy devices.

Dendrimer Based Binders Enable Stable Operation of Silicon Microparticle Anodes in Lithium-Ion Batteries

High-capacity anode materials (e.g., Si) are highly needed for high energy density battery systems, but they usually suffer from low initial coulombic efficiency (CE), short cycle life, and low-rate capability caused by large volume changes during the charge and discharge process. Here, a novel dendrimer-based binder for boosting the electrochemical performance of Si anodes is developed. The polyamidoamine (PMM) dendrimer not only can be used as binder, but also can be utilized as a crosslinker to construct 3D polyacrylic acid (PAA)-PMM composite binder for high-performance Si microparticles anodes. Benefiting from maximum interface interaction, strong average peeling force, and high elastic recovery rate of PAA-PMM composite, the Si electrode based on PAA-PMM achieves a high specific capacity of 3590 mAh g^-1 with an initial CE of 91.12%, long-term cycle stability with 69.80% retention over 200 cycles, and outstanding rate capability (1534.8 mAh g^-1 at 3000 mA g^-1 ). This work opens a new avenue to use dendrimer chemistry for the development of high-performance binders for high-capacity anode materials.

A Bifunctional Liquid Fuel Cell Coupling Power Generation and V3.5+ Electrolytes Production for All Vanadium Flow Batteries

All vanadium flow batteries (VFBs) are considered one of the most promising large-scale energy storage technology, but restricts by the high manufacturing cost of V^3.5+ electrolytes using the current electrolysis method. Here, a bifunctional liquid fuel cell is designed and proposed to produce V^3.5+ electrolytes and generate power energy by using formic acid as fuels and V⁴⁺ as oxidants. Compared with the traditional electrolysis method, this method not only does not consume additional electric energy, but also can output electric energy. Therefore, the process cost of producing V^3.5+ electrolytes is reduced by 16.3%. This fuel cell has a maximum power of 0.276 mW cm^-2 at an operating current of 1.75 mA cm^-2 . Ultraviolet-visible spectrum and potentiometric titration identify the oxidation state of prepared vanadium electrolytes is 3.48 ± 0.06, close to the ideal 3.5. VFBs with prepared V^3.5+ electrolytes deliver similar energy conversion efficiency and superior capacity retention to that with commercial V^3.5+ electrolytes. This work proposes a simple and practical strategy to prepare V^3.5+ electrolytes.

Physicochemical Dual Cross-Linking Conductive Polymeric Networks Combining High Strength and High Toughness Enable Stable Operation of Silicon Microparticle Anodes

The poor interfacial stability and insufficient cycling performance caused by undesirable stress hinder the commercial application of silicon microparticles (µSi) as next-generation anode materials for high-energy-density lithium-ion batteries. Herein, a conceptionally novel physicochemical dual cross-linking conductive polymeric network is designed combining high strength and high toughness by coupling the stiffness of poly(acrylic acid) and the softness of carboxyl nitrile rubber, which includes multiple H-bonds, by introducing highly branched tannic acid as a physical cross-linker. Such a design enables effective stress dissipation by folded molecular chains slipping and sequential cleavage of H-bonds, thus stabilizing the electrode interface and enhancing cycle stability. As expected, the resultant electrode (µSi/PTBR) delivers an unprecedented high capacity retention of ≈97% from 2027.9 mAh g^-1 at the 19th to 1968.0 mAh g^-1 at the 200th cycle at 2 A g^-1 . Meanwhile, this unique stress dissipation strategy is also suitable for stabilizing SiO_x anodes with a much lower capacity loss of ≈0.012% per cycle over 1000 cycles at 1.5 A g^-1 . Atomic force microscopy analysis and finite element simulations reveal the excellent stress-distribution ability of the physicochemical dual cross-linking conductive polymeric network. This work provides an efficient energy-dissipation strategy toward practical high-capacity anodes for energy-dense batteries.