Výsledky projektu Dopování 2D materiálů z koncentrovaných vodných elektrolytů

Low cycling stability is one of the most crucial issues in rechargeable batteries. Herein, we study the effects of a simple ultrasound treatment of graphite for the reversible (de)intercalation of a ClO4- anion from a 2.4 M Al(ClO4)3 aqueous solution. We demonstrate that the ultrasound-treated
graphite offers the improved reversibility of the ClO4- anion (de)intercalation compared with the untreated samples. The ex situ and in situ Raman spectroelectrochemistry and X-ray diffraction analysis of the ultrasound-treated materials shows no change in the interlayer spacing, a mild increase
in the stacking order, and a large increase in the amount of defects in the lattice accompanied by
a decrease in the lateral crystallite size. The smaller flakes of the ultrasonicated natural graphite
facilitate the improved reversibility of the ClO4
���� anion electrochemical (de)intercalation and a more
stable electrochemical performance with a cycle life of over 300 cycles

It is well-known that structural defects play a decisive role in electrochemical
behavior of atomically thin materials, where all the defects are directly accessible by the
electrolyte. However, the vast majority of experimental techniques do not allow
disentanglement of the processes at the edges/defects from those at the intact basal plane.
Therefore, to address this issue, we introduce a localized spectroelectrochemical method
featuring a microdroplet electrochemical cell with simultaneous Raman spectroscopy
monitoring. The electrochemical and spectral responses of the basal planes of monolayer
graphene samples with varying levels of disorder were compared. Two contributions,
stemming from the intact and defective areas on the surface, respectively, were discovered
both in the Raman G band shifts and cyclic voltammetry using the hexaammineruthenium
complex. Consequently, two independent electron transfer processes of slower and faster rates
coexist in one sample, but they are restricted to the defect-free and defect-rich areas,
respectively

Aqueous Zn-based batteries are promising candidates for grid energy storage due to their low cost, intrinsic
safety, and environmental friendliness. Nevertheless, they suffer from limited energy density due to the
utilization of low-voltage cathodes and electrolytes. Graphite could be a viable high-voltage cathode
material owing to its high redox potential (2.1–3.1 V vs. Zn/Zn2+). However, finding a suitable aqueous
electrolyte with high anodic stability remains a fundamental challenge. This work realizes a high-voltage
and low-cost aqueous Zn–graphite dual-ion battery based on a Zn(ClO4)2 water-in-salt electrolyte with
a wide electrochemical window of 2.80 V. The implementation of the supersaturated Zn(ClO4)2 waterin-salt electrolyte containing strong chaotropic ClO4

anions expands the oxidative stability of the
aqueous electrolyte beyond 1.65 V vs. Ag/AgCl or 2.60 V vs. Zn/Zn2+, and facilitates reversible plating/
stripping of Zn2+ with a low overpotential of <50 mV at 1 mA cm
2 and a high upper cut-off potential of
2.5 V vs. Zn/Zn2+. Consequently, the Zn–graphite dual-ion battery delivers a maximum discharge
capacity of 45 mA h g
1 at 100 mA g
1 with a mean discharge voltage of 1.95 V and cycle life of over
500 cycles.

Graphite intercalation compounds (GICs) are widely known for their remarkable multifold physicochemical properties and their numerous state-of-the-art applications, such as energy storage, sensors,
lubrication, catalysis, magneto-optics, superconductivity, etc. However, the properties of GICs largely
depend on the synthesis technique, structure, and morphology of the graphite; the size and properties of
the intercalant species and its concentration in the host material. Accordingly, in the field of electrochemical energy storage, the appearance of novel ionic systems and detailed investigations of GICs are
highly desired. In this study, two different types of graphite, natural graphite (NG) and kish graphite (KG),
were used to gain insights into the intercalation of ClO4
anion in graphite from a concentrated Al(ClO4)3
aqueous electrolyte solution through extensive electrochemical studies and various in situ and ex situ
spectroscopic characterization techniques. An analysis of cyclic voltammograms indicated the presence
of surface-controlled charge storage along with diffusion-controlled ion intercalation into the interlayer
spaces in NG and KG. Additionally, a comparative study on the electrochemical behavior of these two
types of graphite showed differences that can be correlated with their structural properties. These
findings open new perspectives for GIC formation in concentrated aqueous electrolytes and applications
in electrochemical energy storage.