[LiCl₂]⁻ Superhalide: A New Charge Carrier for Graphite Cathode of Dual‐Ion Batteries

Abstract

New acceptor‐type graphite intercalation compounds (GICs) offer candidates of cathode materials for dual‐ion batteries (DIBs), where superhalides represent the emerging anion charge carriers for such batteries. Here, the reversible insertion of [LiCl2]− into graphite from an aqueous deep eutectic solvent electrolyte of 20 m LiCl + 20 m choline chloride is reported. [LiCl2]− is the primary anion species in this electrolyte as revealed by the femtosecond stimulated Raman spectroscopy results, particularly through the rarely observed H–O–H bending mode. The insertion of Li–Cl anionic species is suggested by 7Li magic angle spinning nuclear magnetic resonance results that describe a unique chemical environment of Li+ ions with electron donors around. 2H nuclear magnetic resonance results suggest that water molecules are co‐inserted into graphite. Density functional theory calculations reveal that the anionic insertion of hydrated [LiCl2]− takes place at a lower potential, being more favorable. X‐ray diffraction and the Raman results show that the insertion of [LiCl2]− creates turbostratic structure in graphite instead of forming long‐range ordered GICs. The storage of [LiCl2]− in graphite as a cathode for DIBs offers a capacity of 114 mAh g−1 that is stable over 440 cycles.

Ultrafast Spectroscopies of Nitrophenols and Nitrophenolates in Solution: From Electronic Dynamics and Vibrational Structures to Photochemical and Environmental Implications

“…Raman spectroscopy provides a unique spectral toolset to structurally characterize the site-specific vibrations of small molecules in aqueous solution. In particular, no solvent deuteration (i.e., D 2 O) is needed, as the HOH bending mode, despite being dominant around 1650 cm –1 in IR spectroscopy, displays minimal Raman intensity [ 69 ]. A recent development in Raman methodology, termed femtosecond stimulated Raman spectroscopy (FSRS) [ 54 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ], is a powerful technique that can resonantly enhance the typically weak Raman scattering signal while allowing for certain species to be isolated by strategically tuning the Raman pump wavelength to desired regions [ 54 , 75 ], either in the electronic ground [ 79 ] or excited states [ 43 , 80 ] depending on the laser pulse combination and sequence used.…”

Recent Advancements in Devising Computational Strategies for Dual‐Ion Batteries

“…[59] Another recent work has introduced the reversible intercalation of superhalide LiCl 2 À into graphite from an aqueous electrolyte. [60] They could obtain a capacity of 110 mAh g À 1 and proved the successful intercalation of hydrated LiCl 2 À into graphite using DFT. There have also been other reports of DIBs based on TFSI with Li or K cations, which show extraordinary electrochemical performance close to LIBs with output voltages > 4.5 V. [61][62][63] Another theoretical report worth mentioning has proposed that intercalation of Al 3 + in carbon nanotubes can give a cell voltage as high as around 12 V utilizing the noncovalent cation-π interactions between Al 3 + and π cloud of CNT.…”

“…In this context, a DIB of TFSI is found to perform better than DIBs involving BF 4 and CF 3 SO 3 anions [59] . Another recent work has introduced the reversible intercalation of superhalide LiCl 2 − into graphite from an aqueous electrolyte [60] . They could obtain a capacity of 110 mAh g −1 and proved the successful intercalation of hydrated LiCl 2 − into graphite using DFT.…”

Spreading the Landscape of Dual Ion Batteries: from Electrode to Electrolyte

“…demonstrated the reversible intercalation conversion of [ICl 2 ] − within the graphite, which can reach a high capacity of 291 mAh g −1 [205] . Recently, Ji and co‐workers demonstrated through a series of characterizations that [LiCl 2 ] − embedded in graphite did not form graphite intercalation compounds but offered a turbulent layer structure, and that [LiCl 2 ] − storage in graphite as the cathode of the DIB provided a capacity of 114 mAh g −1 that remained stable over 440 cycles [206] . Both illustrate that there is a distinct future for halogen‐embedded conversion DIBs.…”