Tang Mingxue, Dalzini Annalisa, Li Xiang, Feng Xuyong, Chien Po-Hsiu, Song Likai, Hu Yan-Yan
Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States.
National High Magnetic Field Laboratory , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.
J Phys Chem Lett. 2017 Sep 7;8(17):4009-4016. doi: 10.1021/acs.jpclett.7b01425. Epub 2017 Aug 14.
Anionic redox chemistry offers a transformative approach for significantly increasing specific energy capacities of cathodes for rechargeable Li-ion batteries. This study employs operando electron paramagnetic resonance (EPR) to simultaneously monitor the evolution of both transition metal and oxygen redox reactions, as well as their intertwined couplings in LiMnO, LiNiMnO, and LiNiMnCoO cathodes. Reversible O/O redox takes place above 3.0 V, which is clearly distinguished from transition metal redox in the operando EPR on LiMnO cathodes. O/O redox is also observed in LiNiMnO, and LiNiMnCoO cathodes, albeit its overlapping potential ranges with Ni redox. This study further reveals the stabilization of the reversible O redox by Mn and e hole delocalization within the Mn-O complex. The interactions within the cation-anion pairs are essential for preventing O from recombination into gaseous O and prove to activate Mn for its increasing participation in redox reactions. Operando EPR helps to establish a fundamental understanding of reversible anionic redox chemistry. The gained insights will support the search for structural factors that promote desirable O redox reactions.
阴离子氧化还原化学为显著提高可充电锂离子电池阴极的比能量提供了一种变革性方法。本研究采用原位电子顺磁共振（EPR）同时监测LiMnO、LiNiMnO和LiNiMnCoO阴极中过渡金属和氧氧化还原反应的演变及其相互交织的耦合。可逆的O/O氧化还原发生在3.0 V以上，这在LiMnO阴极的原位EPR中与过渡金属氧化还原明显区分开来。在LiNiMnO和LiNiMnCoO阴极中也观察到了O/O氧化还原，尽管其与Ni氧化还原的电位范围重叠。本研究进一步揭示了Mn和Mn-O络合物内电子空穴离域对可逆O氧化还原的稳定作用。阳离子-阴离子对之间的相互作用对于防止O重新组合成气态O至关重要，并被证明能激活Mn以增加其参与氧化还原反应。原位EPR有助于建立对可逆阴离子氧化还原化学的基本理解。所获得的见解将支持寻找促进理想O氧化还原反应的结构因素。
