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Rechargeable aluminum–organic batteries are of great interest as a next-generation energy storage technology because of the earth abundance, high theoretical capacity, and inherent safety of aluminum metal, coupled with the sustainability, availability, and tunabilty of organic molecules. However, the ionic charge storage mechanisms occurring in aluminum–organic batteries are currently not well understood, in part because of the diversity of possible charge-balancing cations, coupled with a wide array of possible binding modes. For the first time, we use multidimensional solid-state NMR spectroscopy in conjunction with electrochemical methods to elucidate experimentally the ionic and electronic charge storage mechanism in an aluminum–organic battery up from the atomic length scale. In doing so, we present indanthrone quinone (INDQ) as a positive electrode material for rechargeable aluminum batteries, capable of reversibly achieving specific capacities of ca. 200 mAh g–1 at 0.12 A g–1 and 100 mAh g–1 at 2.4 A g–1. We demonstrate that INDQ stores charge via reversible electrochemical enolization reactions, which are charge compensated in chloroaluminate ionic liquid electrolytes by cationic chloroaluminous (AlCl2 +) species in tetrahedral geometries. The results are generalizable to the charge storage mechanisms underpinning anthraquinone-based aluminum batteries. Lastly, the solid-state dipolar-mediated NMR experiments used here establish molecular-level interactions between electroactive ions and organic frameworks while filtering mobile electrolyte species, a methodology applicable to many multiphase host–guest systems.

Phosphorus pentoxide (P 2 O 5 ) is investigated as an acid scavenger to remove the acidic impurities in a commercial lithium hexafluorophosphate (LiPF 6 ) carbonate electrolyte to improve the electrochemical properties of Li metal batteries. Nuclear magnetic resonance (NMR) measurements reveal the detailed reaction mechanisms of P 2 O 5 with the LiPF 6 electrolyte and its impurities, which removes hydrogen fluoride (HF) and difluorophosphoric acid (HPO 2 F 2 ) and produces phosphorus oxyfluoride (POF 3 ), OF 2 P−O−PF 5 − anions, and ethyl difluorophosphate (C 2 H 5 OPOF 2 ) as new electrolyte species. The P 2 O 5 -modified LiPF 6 electrolyte is chemically compatible with a Li metal anode and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) cathode, generating a PO x F yrich solid electrolyte interphase (SEI) that leads to highly reversible Li electrodeposition, while eliminating transition metal dissolution and cathode particle cracking. The excellent electrochemical properties of the P 2 O 5 -modified LiPF 6 electrolytes are demonstrated on Li||NMC622 pouch cells with 0.4 Ah capacity, 50 μm Li anode, 3 mAh cm −2 NMC622 cathode, and 3 g Ah −1 electrolyte/capacity ratio. The pouch cells can be galvanostatically cycled at C/ 3 for 230 cycles with 87.7% retention.

No abstract

Hybrid electric storage systems that combine capacitive and faradaic materials need to be well designed to benefit from the advantages of batteries and supercapacitors. The ultimate capacitive material is graphite (GR), yet high capacitance is usually not achieved due to restacking of its sheets. Therefore, an appealing approach to achieve high power and energy systems is to embed a faradaic 2D material in between the graphite sheets. Here, a simple one-step approach was developed, whereby a faradaic material [layered double hydroxide (LDH)] was electrochemically formed inside electrochemically exfoliated graphite. Specifically, GR was exfoliated under negative potentials by Co II and, in the presence of Mn II , formed GR-CoMn-LDH, which exhibited a high areal capacitance and energy density. The high areal capacitance was attributed to the exfoliation of the graphite at very negative potentials to form a 3D foam-like structure driven by hydrogen evolution as well as the deposition of CoMn-LDH due to hydroxide ion generation inside the GR sheets. The ratio between the Co II and Mn II in the CoMn-LDH was optimized and analyzed, and the electrochemical performance was studied. Analysis of a crosssection of the GR-CoMn-LDH confirmed the deposition of LDH inside the GR layers. The areal capacitance of the electrode was 186 mF cm À 2 at a scan rate of 2 mV s À 1 . Finally, an asymmetric supercapacitor was assembled with GR-CoMn-LDH and exfoliated graphite as the positive and negative electrodes, respectively, yielding an energy density of 96.1 μWh cm À 3 and a power density of 5 mW cm À 3 .