Towards high-performance dual-graphite batteries using highly concentrated organic electrolytes

Abstract

Dual-ion batteries (DIBs) and dual-graphite batteries (DGBs) attract increasing attention as an alternative approach for stationary energy storage due to their environmental, cost and safety benefits over other state-of-the-art battery technologies. In order to realize an extraordinary cell performance of DGBs, it is of particular importance to stabilize the interphases between electrolyte and electrode, for both the negative and positive electrodes. In this work, we present the implementation of highly concentrated electrolytes (HCEs) in DIBs and DGBs, i.e. electrolyte formulations based on either LiPF6 or LiTFSI in dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC). A reversible cycling stability of the graphitic negative electrode is proven as well as the stability of the HCEs against oxidative decomposition at the positive electrode at a cathode potential of 5V vs. Li/Li+. Additionally, we demonstrate that the anodic dissolution of the aluminum (Al) current collector is successfully suppressed by using LiTFSI-based HCEs, which show a comparable resistivity against Al dissolution as LiPF6-based electrolytes. Furthermore, a strong dependence of concentration and onset potential of anion intercalation is observed and comprehensively discussed with respect to the thermodynamic environment of the electrolyte. Overall, the use of HCEs enables a highly reversible cycling stability, providing extraordinary high specific discharge capacities of 80–100 mAh g−1 for lithium metal-based DIBs and DGBs. The evaluation of voltage efficiency (VE) and energy efficiency (EE) reveals the highest values for the EMC/LiPF6-based electrolyte, i.e. 96% (VE) and 95% (EE). In summary, the use of HCEs is a promising strategy to further optimize the electrochemical performance of DIBs and DGBs in terms of high reversible capacity and cycling stability and decreased parasitic side reactions.