Prussian Blue MgLi Hybrid Batteries

Abstract

The major advantage of Mg batteries relies on their promise of employing an Mg metal negative electrode, which offers much higher energy density compared to graphitic carbon. However, the strong coulombic interaction of Mg2+ ions with anions leads to their sluggish diffusion in the solid state, which along with a high desolvation energy, hinders the development of positive electrode materials. To circumvent this limitation, Mg metal negative electrodes can be used in hybrid systems by coupling an Li+ insertion cathode through a dual salt electrolyte. Two “high voltage” Prussian blue analogues (average 2.3 V vs Mg/Mg2+; 3.0 V vs Li/Li+) are investigated as cathode materials and the influence of structural water is shown. Their electrochemical profiles, presenting two voltage plateaus, are explained based on the two unique Fe bonding environments. Structural water has a beneficial impact on the cell voltage. Capacities of 125 mAh g−1 are obtained at a current density of 10 mA g−1 (≈C/10), while stable performance up to 300 cycles is demonstrated at 200 mA g−1 (≈2C). The hybrid cell design is a step toward building a safe and high density energy storage system.

Monoclinic Sodium Iron Hexacyanoferrate Cathode and Non-Flammable Glyme-Based Electrolyte for Inexpensive Sodium-Ion Batteries

“…36 The other peaks at 1619, 3445 and 3611 cm −1 are attributable to structural water present, with the 1619 cm −1 peak corresponding to the O-H bending band and the broader peaks at high wavenumbers to the O-H stretching bands. 25,36 The weight loss of about 10 wt% indicates that about 2 moles of water were present per mole of the material. Hence, based on ICP-OES, EDX, CHN and TGA analyses, the stoichiometry of this material could be stated as Na 2 Fe 2 (CN) 6 .2H 2 O highlighting the Na rich nature and lack of vacancies resulting from our synthesis protocol.…”

“…41 To ascertain which Fe partakes in the low (3.0-3.3 V) and high (4.0 V) voltage plateaus witnessed during galvanostatic cycling, ex-situ FTIR measurements were conducted at relevant states of charge and discharge to follow the cyanide stretching vibration band as it is a sensitive indicator of the Fe oxidation state in such PBAs. 25,[45][46][47] Within the 3.9-2.0 V window, the cyanide stretching bands shift from 2072 cm −1 for the pristine state to 2078 cm −1 for the cathode charged to 3.9 V and then it shifts back to 2072 cm −1 when discharged to 2.0 V (see Figure 3d). The stretching band at 2078 cm −1 agrees well with the band at 2076 cm −1 reported for Na 0.75 Fe 2.08 (CN) 6 , indicating that one of the Fe 2+ has been oxidized to Fe 3+ .…”

“…This arrangement leaves eight sub-cube units within each unit cell where alkali ions such as Na + and/or interstitial water molecules may reside. [24][25][26][27] Most of the PBAs which have been reported to store sodium have less Na content in the as-synthesized compounds (0 ≤ x ≤ 1) demonstrating a cubic structure with a space group Fm-3m. [28][29][30][31][32][33] This may become a disadvantage in a full cell formulation against a suitable anode as a full cell relies on the cathode supplying Na during the first charging (sodium extraction from cathode and insertion into the anode).…”

A concentrated electrolyte for zinc hexacyanoferrate electrodes in aqueous rechargeable zinc-ion batteries

“…The capacity gradually increased during the initial cycles in both electrolytes. The reason for this phenomenon is unclear at present and a detailed interpretation is beyond the scope of this work, but it may be related to activation or conditioning effects [20,21,26].…”

“…In particular, PBAs are notable potential cathode materials for application in ARZIBs owing to their superior characteristics, such as structural stability, large channels, and ease of synthesis [9,18]. Additionally, these materials have large open sites (4.6 Å in diameter) and <100> channels (3.2 Å in diameter), which enable the rapid diffusion of various hydrated metal ions, including zinc ions [19][20][21]. However, the electrochemical performance of these materials has to be improved, as they exhibit relatively low capacities and capacity reduction during the initial cycles.…”