ABSTRACT
Li-ion batteries based on high specific capacity LixSiO-Graphite anodes and LiNi0.89Co0.05 Mn0.05Al0.01O2 (NCMA) cathodes may have numerous practical applications owing to high energy density without a necessary compromise on safety. SiO, which is an attractive Li insertion anode material, offers more cycling stability than Si and a higher capacity than graphite. Therefore, a new trend has emerged for developing composite C-Si anodes, possessing the excellent cyclability of graphite coupled with high capacity SiO. The composite structure described herein prevents the volume expansion of SiO and maintains the structural integrity during prolonged cycling. However, graphite electrodes suffer from exfoliation in propylene carbonate (PC) based electrolyte solutions, which avoids well known safety benefits related to a possible use of PC based electrolyte solutions in all kinds of Li batteries. Herein, it is reported that trifluoro propylene carbonate (TFPC) is compatible with graphite anodes. New electrolyte formulations are developed and tested containing fluorinated co-solvents and compared the performance of several electrolyte solutions, including conventional alkyl carbonates-based solutions in full Li-ion cells, which included LixSiO-Graphite anodes and LiNi0.89Co0.05Mn0.05Al0.01O2 (NCMA) cathodes. Cells with new electrolyte solutions developed herein demonstrated nearly twice capacity retention in prolonged cycling experiments compared to similar reference cells containing conventional electrolyte solutions.
ABSTRACT
Redox flow batteries (RFBs) employing nonaqueous electrolytes could potentially operate at much higher cell voltages, and therefore afford higher energy and power densities, than RFBs employing aqueous electrolytes. The development of such high-voltage nonaqueous RFBs requires anolytes that are electrochemically stable, especially in the presence of traces of oxygen and/or moisture. The inherent atmospheric reactivity of anolytes mandates judicious molecular design with high electron affinity and electrochemical stability. In this study, diketopyrrolopyrrole (DPP)-based TDPP-Hex-CN4 is proposed as a stable redox-active molecule for anolytes in nonaqueous organic RFBs. We demonstrate organic RFBs using TDPP-Hex-CN4 as anolyte with unisol blue (UB) 1,4-bis(isopropylamino)anthraquinone and 1,4-di-tert-butyl-2,5-bis(2-methoxyethoxy)benzene (DBBB) as catholytes. Cyclic voltammetry measurements with scans repeated over 200 cycles were performed to establish the electrochemical stability of the redox pairs. Symmetric flow-cell studies show that TDPP-Hex-CN4 exhibits stable capacity up to 700 cycles. Redox flow cells employing TDPP-Hex-CN4 /UB and TDPP-Hex-CN4 /DBBB as redox pairs demonstrate that DPP derivatives are propitious materials for anolytes in all organic nonaqueous RFBs.