Intercalation-type positive electrode materials for nonaqueous calcium-ion batteries

Abstract

Calcium-ion batteries (CIBs) are among the promising alternatives to overcome the limitation of lithium-ion batteries in current use. Compared with lithium, calcium is environmentally friendly, reliable, safe, and abundant in resources. Despite the development of intercalation-type cathode materials for CIBs in its infancy, the number of newly discovered materials has remarkably increased in the last few years. In this Review, we present the recent accomplishments and challenges in the development of cathode materials for nonaqueous CIBs, classified by the constituent anion type: oxides, polyanions, and others (chalcogenides, fluorides, and nitrides), and further subdivided based on Ca diffusion dimensionality (one-, two-, and three-dimensions). Each of the materials is presented, emphasizing structural aspects, electrochemical properties, intercalation mechanisms during cycling, and problems to be solved. Finally, this Review concludes by providing overview and perspectives on each type of materials. To date, the observed capacities are still far below the theoretically expected doubled capacity due to the divalency of calcium. Nevertheless, the research progress during the past few years suggests that unexplored opportunities for discovering new cathode materials with improved performances are wide open. This Review will help researchers easily grasp the overall accomplishments and challenges of the CIB cathode materials, stimulating further development.

Impact of Differential Ca2+ Coordination in Borohydride-Based Electrolyte Blends on Calcium Electrochemistry and SEI Formation

“…Given concerns about the supply and sustainability of lithium (Li) ion battery components, there is growing interest in developing a beyond-Li materials basis for rechargeable batteries. , Divalent batteries based on calcium (Ca) have received growing attention due to the ∼2000-fold higher concentration of Ca than Li in the earth’s crust, lower cost than Li, and attractive theoretical cell-level metrics if Ca is used as the metallic anode (−2.87 V vs SHE, 1337 mAh/g, 2073 mAh/cm 3 ). − However, technological development of Ca batteries has been hindered by a lack of viable electrolytes for pairing with Ca anodes as well as a lack of suitable cathode materials . In nonaqueous liquid electrolytes, large coordination shells form around Ca 2+ that can include upward of 8 solvating species (compared to ∼4 for Li + ) and significant ion pairing, ,, which increases energy barriers of dissociation and/or desolvation and hinders Ca 2+ transport.…”

“…3−6 However, technological development of Ca batteries has been hindered by a lack of viable electrolytes for pairing with Ca anodes 7 as well as a lack of suitable cathode materials. 8 In nonaqueous liquid electrolytes, large coordination shells form around Ca 2+ that can include upward of 8 solvating species (compared to ∼4 for Li + ) and significant ion pairing, 3,6,9 which increases energy barriers of dissociation and/or desolvation and hinders Ca 2+ transport. At the solid electrolyte interphase (SEI), solid-state Ca 2+ migration is impeded by the cation's large ionic radius as well as poor Ca 2+ ionic conductivity of the SEI phases.…”

(NH4)2V7O16 as a Cathode Material for Rechargeable Calcium-Ion Batteries: Structural Transformation and Co-Intercalation of Ammonium and Calcium Ions

“…Given these advantages, one key to successful CIB development is using positive electrode materials exhibiting high theoretical capacity. However, CIB cathode material development is still in its infancy; only a few materials have been reported to reversibly insert calcium ions in dried nonaqueous electrolytes to date; the mechanism of Ca insertion into host materials remains poorly understood …”

“…However, CIB cathode material development is still in its infancy; only a few materials have been reported to reversibly insert calcium ions in dried nonaqueous electrolytes to date; the mechanism of Ca insertion into host materials remains poorly understood. 12 Examination of the CIB host materials reported thus far suggests that sufficiently wide pathways should be ensured for facile migration of Ca ions. 13 Accordingly, most known cathode materials have a layered structure with wide interlayer spacing and structural flexibility.…”