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Anion Reactivity in Cation‐Disordered Rocksalt Cathode Materials: The Influence of Fluorine Substitution
Advanced Energy Materials ( IF 27.8 ) Pub Date : 2020-08-02 , DOI: 10.1002/aenm.202001500
Matthew J. Crafton 1, 2 , Yuan Yue 2 , Tzu‐Yang Huang 1, 2 , Wei Tong 2 , Bryan D. McCloskey 1, 2
Affiliation  

The demand for high energy‐density, mass‐producible cathode materials has spurred the exploration of new material structures and compositions. Lithium‐excess, cation‐disordered rocksalt (DRX) materials are a new class of transition metal oxides that display high capacity and environmental friendly composition. These materials achieve their high capacities partially through oxygen redox, which leads to oxygen loss and detrimental reactivity with the electrolyte. It has previously been shown that oxygen loss can be suppressed by partial substitution of the lattice oxygen for fluorine, but the explicit mechanism behind this effect remains unknown. In this work, differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry are used to quantify the primary electrochemical reactions occurring during the first cycle in DRX materials. Comparing a DRX oxide and a DRX oxyfluoride, it is shown that fluorination limits oxygen redox and suppresses oxygen loss. Additionally, DEMS is coupled with fluoride‐scavenging to demonstrate that small amounts of fluorine dissolve from DRX oxyfluorides during the first cycle. Finally, these techniques are extended over the first several cycles, demonstrating that CO2 evolution persists and fluoride dissolution continues to a diminishing extent during the first few cycles. These findings motivate surface modifications to control interfacial reactivity and improve long‐term cycling.

中文翻译:

阳离子无序岩盐阴极材料中的阴离子反应性:氟取代的影响

对高能量密度,可大量生产的阴极材料的需求刺激了对新材料结构和成分的探索。锂过量,阳离子无序的岩盐(DRX)材料是一类新型的过渡金属氧化物,具有高容量和环保的成分。这些材料部分地通过氧还原来实现其高容量,这导致氧损失和与电解质的有害反应性。先前已经表明,可以通过用晶格氧部分取代氟来抑制氧损失,但是这种作用背后的明确机理仍然未知。在这项工作中 差示电化学质谱法(DEMS)和滴定质谱法用于量化DRX材料在第一个循环中发生的主要电化学反应。比较DRX氧化物和DRX氟氧化物,氟化作用限制了氧的氧化还原并抑制了氧的损失。此外,DEMS与除氟技术相结合,证明在第一个循环中少量氟从DRX氟氧化物中溶解。最终,这些技术扩展到了最初的几个周期,证明了CO在最初的几个循环中,继续有2放出物,氟化物的溶解继续减少。这些发现促使表面改性以控制界面反应性并改善长期循环。
更新日期:2020-09-15
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