Calcium Ion

Calcium ion battery (CIB) chemistry is viewed as greener with a more resource-secure future. Calcium is the fifth most abundant element in the Earth’s crust (accounting for approximately 41,500 ppm, compared to lithium’s 200 ppm) and benefits from a well-established global supply chain through the limestone and cement industries.

  • calcium’s standard reduction potential of -2.87 V versus the standard hydrogen electrode (SHE)
    • remarkably close to lithium’s -3.04 V
    • high cell voltages between 3.0 V and 3.5 V
  • calcium ion (Ca2+) is a divalent cation, it transfers two electrons per ion, which theoretically doubles its volumetric capacity compared to monovalent ions
    • metallic calcium anode provides a theoretical volumetric capacity of 2073 mAh/cm³
      • compared to lithium metal theoretical volumetric capacity of 2062 mAh/cm³
  • calcium paradox: Despite carrying twice the charge of Li+, Ca2+ has a larger ionic radius (100 pm) than other multivalent ions like magnesium (72 pm), resulting in a much lower charge density.
    • a lower charge density weakens electrostatic interactions with host lattices and reduces desolvation energy barriers at the electrolyte-electrode interface, granting calcium faster diffusion kinetics and making it a highly viable candidate for high-power applications
  • inherently safer: calcium metal possesses a significantly higher melting point 842 °C vs. lithium’s 180.5 °C
  • calcium is less prone to the dendritic growth that can cause internal short circuits and fires

Despite these advantages there are a number of challenges that need to be solved to enable a commercial battery chemistry. These include:

  • in conventional electrolytes, calcium tends to decompose the solution and form a Solid Electrolyte Interphase (SEI) layer comprised of compounds like CaCO3​ or CaF2​
    • these decomposition products are virtually impermeable to the larger, divalent Ca2+ ions, this resistive layer effectively passivates the electrode and shuts down the battery
  • the strong electrostatic interaction between Ca2+ and the anions in conventional metal-oxide lattices often leads
    • sluggish diffusion kinetics
    • structural instability
    • poor rate performance during the intercalation and extraction phases

References

  1. Andrii Kachmar, Petru Apostol, Robert Markowski, Taniya Purkait, Darsi Rambabu, Da Tie, Roy Heyns, Jan Fransaer, Koen Binnemans, Alexandre Ponrouch and Alexandru Vlad, A fluorine-free electrolyte for calcium metal batteries, EES Batteries, 2026, 2,138
  2. Xu ZL, Park J, Wang J, Moon H, Yoon G, Lim J, Ko YJ, Cho SP, Lee SY, Kang K. A new high-voltage calcium intercalation host for ultra-stable and high-power calcium rechargeable batteries. Nat Commun. 2021 Jun 7;12(1):3369.

See also: Ammonium-Ion Battery, Fluoride Ion