Flow batteries are promising for renewable energy storage due to their safety and scalability. Zinc/bromine flow batteries (Zn/Br) are popular due to their high energy densities and inexpensive electrolytes. However, they have a poor service life and lead to environmental harm as a result of the generated corrosive and volatile Br 2 . Here we introduce a Br 2 scavenger to the catholyte, reducing the Br 2 concentration to an acceptable level (~7 mM). The scavenger, sodium sulfamate (SANa), reacts rapidly with Br 2 to form a mild product, N -bromo sodium sulfamate (Br-SANa; Br + ). Additionally, the two-electron transfer reaction of Br-SANa/Br − (Br + /Br − ) increases the energy density. We have developed a Zn/Br flow battery, paired with a Zn anode, that outperforms traditional Zn/Br flow batteries in energy density (152 Wh l −1 versus 90 Wh l −1 ) and cycle life (>600 versus 30 cycles), using a sulfonated polyetheretherketone membrane. We assembled a 5-kW stack that operated stably for over 700 cycles (~1,400 h). Using this reaction, we have built a large-scale battery system.
Xueting Huang,Jiaxin Wen,Jinglei Lei,Guangsheng Huang,Fusheng Pan,Lingjie Li
A cost-effective and highly efficient electrolyte with a wide electrochemical window, high reversibility of Mg plating/stripping, non-/low-corrosivity, good compatibility with cathode materials, and tolerance of trace water and impurity is crucial for the commercialization of rechargeable magnesium batteries. In this work, a novel boron-centered non-nucleophilic electrolyte that meets all the above requirements is prepared via a facile and economic approach from the raw materials B(TFE)3/MgCl2/CrCl3/Mg (BMCM). The as-prepared BMCM electrolyte is mainly composed of tetracoordinated anions [B(TFE)4]− and solvated cations [Mg2(μ-Cl)2(DME)4]2+. The BMCM electrolyte demonstrates attractive electrochemical performance, with a low overpotential (∼139 mV), a high Coulombic efficiency (∼97%), a high anodic stability (∼3.5 V vs Mg/Mg2+), and a long-term (more than 500 h) cycling stability. Moreover, BMCM shows good compatibility with the CuS cathode material. The CuS|BMCM|Mg full cell delivers a discharge specific capacity of 231 mAh g–1 (at 56 mA g–1), which can retain ∼88% even after 100 cycles. Importantly, the BMCM electrolyte is cost-effective and tolerant of trace impurity and water, which has great potential to be commercialized. This work is expected to promote the development of practical rechargeable magnesium batteries.
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