context: As illustrated in Fig. 2a, the TDAC possesses a 2π electron aromatic system that can readily undergo a single electron redox reaction to generate the corresponding TDAC radical dication. Fig. 2b presents the redox potential and solubility of TDAC salt in comparison with those of the state-of-the-art high-potential shuttle molecules. Ideally, the redox potential (protection potential) should be ∼0.2–0.3 V above the upper cut-off voltage of LIBs (normally at 4.3 V). A lower or higher potential outside the range would have the risk of escalated self-discharge during normal operation or an irreversible decomposition of battery components during overcharging. Additionally, a high solubility is desirable since it determines the maximum shuttling current. In these regards, TDAC outperforms all other shuttle candidates with the adequate redox potential of 4.55 V (vs. Li+/Li) and the highest solubility of 0.5 M (Fig. S2†). The electrolyte viscosity before and after the TDAC addition was also investigated. The concentration of 0.2 M was found to be the optimal amount. The viscosity of 0.2 M TDAC electrolyte is 2.72 mPa compared with 2.43 mPa of baseline electrolyte. The electro-kinetics of the TDAC was next investigated by cyclic voltammetry (CV) analysis as shown in Fig. 2c. Even with a high scan rate of 200 mV s−1, TDAC still exhibited a pair of well-defined redox peaks, implying a fast mass transport process within the bulk electrolyte. As shown in Fig. 2d, the diffusion coefficient of TDAC is determined to be 6 × 10−6 cm−2 s−1, which is very comparable with that of other reported shuttles. As displayed in Fig. 2e, after 1000 CV scans, the potential gap between the anodic and cathodic peaks becomes only 60 mV wider, and there is no obvious deterioration of the peak current intensity. Such excellent electrochemical stability has rarely been reported among other 4V-class shuttles. The inset photograph in Fig. 2e presents a shiny Li surface with no bubble generation after storing in TDAC-containing electrolyte solution for six months, indicating a high chemical inertness of the TDAC toward Li metal.
answer: TDAC-containing