• Energy Research

Rechargeable aluminum batteries (AlBs), which represent cost‐effective energy‐storage devices due to the abundance of natural aluminum resources, have emerged as promising candidates for the next generation of rechargeable batteries. Although the electrochemical deposition of aluminum in ionic liquids (ILs) is well investigated for aluminum refining, the reversible electrochemical deposition/dissolution behavior of aluminum ions is not trivial. More specifically, the dendrite growth issue, which is common in Li metal anodes, is scarcer or vague. Herein, the electrochemical stability of the aluminum metal anode in IL electrolytes is investigated and the failure mechanism is discussed. It is confirmed that the inorganic anion of ILs mainly affects the electrochemical stability, whereas the organic cation influences the aluminum metal degradation. X‐ray computed tomography results further identify deterioration of the surface morphology of the aluminum metal. The formation of “dead aluminum” is further confirmed, which indeed causes cell failure with repeated cycles. Finally, using the predeposited aluminum graphene paper as an alternative anode candidate for AlBs is further demonstrated.

Since aluminum is the third most abundant element in Earth’s crust, developing rechargeable aluminum-ion offers1 a golden opportunity for delivering a high energy-to-price ratio. Nevertheless, finding appropriate host electrodes for inserting aluminum (complex) ion remains a fundamental challenge. Here, we demonstrate2 a new strategy for designing active materials for rechargeable aluminum batteries. This strategy entails the use of redox-active triangular phenanthrenequinone-based macrocycles which form layered superstructures resulting in the reversible insertion and extraction of cationic aluminum complex. This architecture exhibits an outstanding electrochemical performance with a reversible capacity of 110 mAh g–1 along with a superior cyclability of up to 5000 cycles. Furthermore, we prepared a hybrid electrode by blending the macrocycle with graphite flakes, featuring homogeneous stacking of both macrocycle and graphite flake. These findings lay the groundwork for future design and operation of aluminium-ion batteries and represent a promising starting point for developing affordable large-scale energy storage applications. References M. -C. Lin, et al. Nature 2015, 520 , 324–328. D. J. Kim, D.-J. Yoo, M. T. Otley, A. Prokofjevs, C. Pezzato, M. Owczarek, S. J. Lee, J. W. Choi, and J. F. Stoddart, Nat. Energy, 2019, 4, 51–59. Figure 1

Anode‐free lithium metal batteries (AFLMBs) show promise as a means of further enhancing the energy density of current lithium‐ion batteries, as they do not require conventional graphite anodes. The anode‐free configuration, however, suffers from inferior chemical stability of the solid electrolyte interphase (SEI) layer and experiences inhomogeneous lithium deposition during charge/discharge processes, resulting in rapid capacity fading. To address these issues, a carbonized polydopamine (CPD) coating is applied to the copper current collector. The CPD‐coated copper current collector promotes highly efficient and reversible lithium plating and stripping processes, resulting in a densely packed lithium deposition that significantly improves cycling stability. The anode‐free full cell, consisting of CPD‐coated copper current collector and a LiFePO4 cathode, demonstrates significantly improved electrochemical performance, with a capacity retention of more than 63% after 100 cycles at a current rate of 0.3C. The stability of the SEI layer and the presence of lithiophilic sites are verified through a range of techniques, including optical microscopy, Raman spectroscopy, X‐ray photoelectron spectroscopy, chronoamperometry, and electrochemical impedance spectroscopy. Based on these collective findings, it can be inferred that the use of CPD coating provides a simple way to enhance the electrochemical performance of AFLMBs.