On the Reliability of Half-Cell Tests for Monovalent (Li⁺, Na⁺) and Divalent (Mg²⁺, Ca²⁺) Cation Based Batteries

Abstract

A comprehensive study is reported entailing a comparison of Li, Na, K, Mg, and Ca based electrolytes and an investigation of the reliability of electrochemical tests using half-cells. Ionic conductivity, viscosity, and Raman spectroscopy results point to the cationsolvent interaction to follow the polarizing power of the cations, i.e. Mg 2+ > Ca 2+ > Li + > Na + > K + and to divalent cation based electrolytes having stronger tendency to form ion pairs -lowering the cation accessibility and mobility. Both increased temperature and the use of anions with delocalized negative charge, such as TFSI, are effective in mitigating this issue. Another factor impeding the divalent cations mobility is the larger solvation shells, as compared to those of monovalent cations, that in conjunction with stronger solvent -cation interactions contribute to slower charge transfer and ultimately a large impedance of Mg and Ca electrodes. An important consequence is the non-reliability of the pseudo-reference electrodes as these present both significant potential shifts as well as unstable behaviors. Finally, experimental protocols in order to achieve consistent results when using half-cell set-ups are Although the lithium-ion battery is currently being considered as the most promising technology for electric vehicle propulsion, the development of alternative and complementary battery chemistries and technologies is of great importance, especially aiming at large-scale applications, i.e. the grid for which the cost in $/kWh and sustainability are crucial indicators. Indeed, the implementation of lithium based technology at large scale faces a significant challenge, since the controversial debates on lithium availability and cost cannot be overlooked. Amongst several chemistries possible the most appealing alternatives involve the use of sodium (Na), magnesium (Mg) or calcium (Ca) for mainly two reasons. The prime is the abundance of the raw materials, i.e. Na, Mg, and Ca being the 6 th , 8 th , and 5 th most abundant elements in the Earth's crust, vs. 25 th for Li, making them 20 to 50 times cheaper than Li, e.g. $5000/ton, $135-165/ton, $265/ton, and $100/ton for Li 2 CO 3 , Na 2 CO 3 , MgO 2 , and CaCO 3 , 1 respectively. Performance wise, the low cost alternatives of Na, Mg, and Ca technologies would also benefit from high standard reduction potentials, ca. −2.71, −2.37, and −2.87 V vs. SHE for Na, Mg, and Ca, respectively, as compared to −3.04 V for Li, and large theoretical electrochemical capacities, both gravimetric and volumetric, for the metal electrodes (Fig. 1).Sodium metal anodes are already used in the liquid state (m.p. ∼97• C) in the Na/S technology 2 and room-temperature Na-ion technology is currently intensively investigated with hundreds of papers appearing per year, with progress being summarized in several review papers amongst which 3-5 are the most recent. For Mg and Ca metal anodes, the situation is radically different. For the Mg battery technology, proof-of-concept was achieved as late as in 2000, 6 although i...

Calcium‐Ion Batteries: Current State‐of‐the‐Art and Future Perspectives

“…b) CVs (0.1 mV s −1 ) obtained in three‐electrode Swagelok cells with 0.45 m Ca(BF 4 ) 2 in EC 0.5 :PC 0.5 using Ca. Adapted with permission . Copyright 2017, Electrochemical Society.…”

“…In addition, large scale energy storage in support of intermittent renewable energy production from solar and wind power is needed to provide reliable, sustainable green energy for the developed world. Cost‐effective storage is needed to stabilize the energy supply and prevent the variability of the renewable energy from affecting the quality of the power supply from the electricity grid …”

“…This finding makes it potentially feasible to use multivalent metallic anodes in place of the graphite anodes used in lithium‐ion batteries, resulting in a significant increase in the anode gravimetric and volumetric capacity. This promises increased energy density for these multivalent battery systems compared to lithium‐ion batteries[4,17b,19b] ( Figure ). The use of multivalent ions also leads to a possible increase in the electrochemical capacity of intercalation electrodes and hence to a significant increase in the energy density of cells utilizing these electrodes compared to Li‐ion cells.…”

On the viability of Mg extraction in MgMoN2: a combined experimental and theoretical approach

“…Lithium was also used as reference electrode, as it has proved to be much more reliable than other mono valent and divalent metals. 30 The All the electrochemical cells were Swagelok type and assembled in Ar-filled dry box. Al and stainless steel current collectors were used for the working and reference/counter electrodes, respectively.…”

Discovery of Calcium‐Metal Alloy Anodes for Reversible Ca‐Ion Batteries

“…[4] Also, Ca 2+ diffusion is observed to be extremely sluggish through the as-formed solid electrolyte interphase (SEI) between the calcium metal anode and the electrolyte. [27,28] TM oxide (i.e., V 2 O 5 ) [29] based anodes have been shown to be effective at storing Ca-ions; however, the high calciation potential (≈2.8 V) of this material significantly reduces the overall output voltage of the whole cell. [17] Alloying-type anodes, widely studied for Li-ion batteries, show great promise for reversible CIBs.…”