Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, 8010, Graz, Austria.
Institute for Analytical Chemistry and Food Chemistry, Graz University of Technology, Stremayrgasse 9, 8010, Graz, Austria.
Angew Chem Int Ed Engl. 2017 Dec 4;56(49):15728-15732. doi: 10.1002/anie.201709351. Epub 2017 Nov 2.
Aprotic sodium-O batteries require the reversible formation/dissolution of sodium superoxide (NaO ) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO , a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Herein we show that singlet oxygen ( O ) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in- and ex-situ via a O trap that selectively and rapidly forms a stable adduct with O . The O formation mechanism involves proton-mediated superoxide disproportionation on discharge, rest, and charge below ca. 3.3 V, and direct electrochemical O evolution above ca. 3.3 V. Trace water, which is needed for high capacities also drives parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.
非质子钠离子-O 电池需要在循环过程中可逆地形成/溶解超氧化钠 (NaO )。较差的循环寿命与电解质和电极与 NaO 的反应性有关，NaO 是一种强亲核试剂和碱。然而，其反应性不能始终如一地解释副反应和不可逆性。在此，我们表明单线态氧 ( O ) 在循环的所有阶段都会形成，并且它是寄生化学的主要驱动力。通过 O 陷阱在原位和异位检测到了它，O 陷阱选择性且快速地与 O 形成稳定的加合物。 O 的形成机制涉及在放电、休息和低于约 3.3 V 时通过质子介导的超氧化物歧化反应，以及在高于约 3.3 V 时直接电化学 O 演化。痕量水对于高容量也是必需的，也会引发寄生化学。因此，控制高反应性的单线态氧对于实现高度可逆的电池操作至关重要。
