Mg-Ion Battery Electrode: An Organic Solid’s Herringbone Structure Squeezed upon Mg-Ion Insertion

Abstract

We report that crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), an organic solid, is highly amenable to host divalent metal ions, i.e., Mg and Ca, in aqueous electrolytes, where the van der Waals structure is intrinsically superior in hosting charge-dense ions. We observe that the divalent nature of Mg causes unique squeezing deformation of the electrode structure, where it contracts and expands in different crystallographic directions when hosting the inserted Mg-ions. This phenomenon is revealed experimentally by ex situ X-ray diffraction and transmission electron microscopy, and is investigated theoretically by first-principles calculations. Interestingly, hosting one Mg ion requires the coordination from three PTCDA molecules in adjacent columns of stacked molecules, which rotates the columns, thus reducing the (011) spacing but increasing the (021) spacing. We demonstrate that a PTCDA Mg-ion electrode delivers a reversible capacity of 125 mA h g, which may include a minor contribution of hydronium storage, a good rate capability by retaining 75 mA h g at 500 mA g (or 3.7 C), and a stable cycle life. We also report Ca storage in PTCDA, where a reversible capacity of over 80 mA h g is delivered.

Molecular Design Strategies for Electrochemical Behavior of Aromatic Carbonyl Compounds in Organic and Aqueous Electrolytes

“…[59][60][61][62] Such a molecular structure is not only present in an organic solution battery, it also has great value in an aqueous solution battery. However, in the coordination theory of multivalent cations, the size of the ionic radius is not the only factor that affects the electrochemical reaction.…”

“…Although aqueous solution batteries are still in their infancy, various cationic batteries in an aqueous electrolyte with nucleophilic addition reaction of the carbonyl are discussed, such as those of H + , [165] NH 4 + , [65] Li + , [166,167] K + , [168,169] Na + , [170][171][172] Mg 2+ , [62] Zn 2+ , [173][174][175] and Ca 2+ . Improving the conductivity and binding in the active material, and the selection of a solid electrolyte and gel electrolyte, could alleviate the side effects.…”

“…[62] During the discharge process, Mg 2+ and oxygen anion combine to form an OMg bond. [62] During the discharge process, Mg 2+ and oxygen anion combine to form an OMg bond.…”

Cyclohexanehexone with Ultrahigh Capacity as Cathode Materials for Lithium‐Ion Batteries

“…Themethod can be seen in Figure 1a-c. First, we use DFT calculations to investigate several C n O n (n = 4, 5, 6,7,8,9) which have the potential to exhibit the highest theoretical capacity (957 mA hg À1 )a mong all carbonyl-based organic cathode materials based on the formula in Figure 1a. Compared with other cyclic ketones (C n O n , n = 4, 5,7,8,9), C 6 O 6 shows the highest theoretical working voltage (Figure 1b and Figure S1 in the Supporting Information).…”

“…[11] In addition, ap revious work has revealed that the activity and structural evolution of aC 6 O 6 analogue (Na 2 C 6 O 6 )i ss ensitive to the selection of electrolyte. b) Calculated average working voltage and energy gap between HOMO and LUMO of C n O n (n = 4, 5, 6,7,8,9). a) The formula to calculate the theoreticalcapacity of different electrode materials.…”