Layered Transition Metal Oxides as Ca Intercalation Cathodes: A Systematic First‐Principles Evaluation

Abstract

to Mg, and they are much higher than Li (Ca: 4.2%, Mg: 2.3%, Li: 0.002% of Earth's crust), suggesting low materials cost and a secure supply chain. Despite the inherent advantages of Ca-based chemistry, much less research efforts have been put in Cathan in Mg-based chemistries.The emergence of Ca batteries has been hampered by the paucity of known materials functioning as electrolytes and electrodes. Recent development of electrolytes enabling facile Ca plating/ stripping [3] and fast Ca intercalation into graphite [4] sparked renewed interest in Ca-based energy storage. Recent studies found that such classes of materials as polyanionic phosphates, [5] Prussian Blue analogs, [6] and layered metal oxides [7,8] can reversibly accommodate Ca ions in nonaqueous systems; however, unlike for Mg, the design space for Ca cathode materials is still limited.In Mg ion chemistry, high-throughput computational studies discovered that the ability to modify spinel compounds by transition metal (TM) substitution results in promising Mg intercalation hosts with high voltage, energy density, and fast cation diffusion in both oxides [9] and sulfides. [10] Following these computational screening efforts, experiments demonstrated the promise of oxide spinels as cathode hosts allowing reversible Mg intercalation, [11][12][13] and ternary spinel chalcogenides even attracted interest as Mg solid electrolytes. [14] Also, the high compositional flexibility of spinel in forming TM solid solutions opens up a broader space for searching Mg cathodes. [12] However, the absence of such theory-based guidelines for Ca cathodes has hindered the development of Ca-ion batteries.Among the widely used structure types for conventional Li ion cathode materials (e.g., polyanion, layered, spinel), layered compounds with the nominal composition of CaTM 2 O 4 could be viable Ca cathode frameworks similar to spinel in Mg ion chemistry. Cabello et al. has shown that the P-type layered CaCo 2 O 4 , in which Ca cations are prismatically coordinated, can reversibly intercalate 0.35 mol of Ca and showed a capacity of 100 mAh g −1 . [7] Cushing et al. synthesized the two-layered (P2) or three-layered (P3) Ca x Co 2 O 4 at Ca concentrations x including 0.52, 0.54, 0.70, and 1, [15] indicating that partially Ca deintercalated CaCo 2 O 4 is not susceptible to chemical decomposition and maintains the original host framework. The phase diagram calculated by density functional theory (DFT) also confirmed that the partially deintercalated Ca x Co 2 O 4 (x = 0.5, 0.667, 0.7) compounds are stable. Beside the thermodynamic stability, Ca diffusivity in P3-CaCo 2 O 4 calculated by DFT using single ionic motion can be as low as 0.36 and 0.27 eV at the dilute and high Finding high-voltage Ca cathode materials is a critical step to unleashing the full potential of high-energy-density Ca-ion batteries. First-principles calculations are used to demonstrate that P-type layered calcium transition metal (TM) oxide materials (CaTM 2 O 4 ) with a range of TM substitutions (TM = Ti...

Surface Reduction Stabilizes the Single-Crystalline Ni-Rich Layered Cathode for Li-Ion Batteries

“…The conversion reaction is predicted by the density functional theory calculation to occur for a two-electron transfer per Ni ion with the intercalation of Ca ions in NiO 2 , while the intercalation reaction is predicted for a one-electron transfer. 42,43 It is possible that the reaction with CaI 2 initially proceeds as the intercalation of Ca ions, but the high diffusion barrier of Ca ions in Br-NMC impedes the diffusion of Ca ions into the particle interior, leading to the accumulation of Ca ions at the surface. The octahedral site in Br-NMC is not amenable for facile Ca-ion diffusion, which can be realized in the prismatic site.…”

“…The octahedral site in Br-NMC is not amenable for facile Ca-ion diffusion, which can be realized in the prismatic site. 43 Although there has been no report for Caion diffusion in the ternary NMC-type layered compound, computational studies of the closely related layered NiO 2 have reported a high Ca-ion diffusion barrier (>650 meV) for both charged and discharged NiO 2. 44 Once the surface concentration of Ca ions becomes sufficiently high, the conversion reaction occurs, resulting in the formation of a thin coating layer of CaO, which assumes the same cubic structure as NiO, and the displacement of Li ions into the particle interior.…”

“…The conversion reaction is predicted by the density functional theory calculation to occur for a two-electron transfer per Ni ion with the intercalation of Ca ions in NiO2, while the intercalation reaction is predicted for a one-electron transfer. 30,31 It is possible that the reaction with CaI2 initially proceeds as the intercalation of Ca ions, but the high diffusion barrier of Ca ions in To further interrogate the effect of surface modification on the electron and ion transport kinetics, PITT was employed to characterize the Li-ion diffusion and the interfacial charge transfer resistance. The analysis of the PITT result was based on a finite interfacial kinetics model 21 that accounts for both the bulk Li-ion diffusivity and the exchange current density (j0).…”

Recent Achievements in Experimental and Computational Studies of Positive Electrode Materials for Nonaqueous Ca- and Al-Ion Batteries

“…DFT calculation is an approach to the quantum mechanical many-body problem, in which the ground-state energy of an M-electron system can be treated as a function only of the electron density. There is considerable interest in utilizing DFT calculations to investigate electrode properties for battery applications. ,, Numerous key properties of electrode materials, such as equilibrium voltages and their corresponding profiles, ionic mobility, and thermal and electrochemical stabilities can be identified using these computational techniques. − The reliability of the computational results can be further used to design and develop new materials for experiments rather than the conventional trial-and-true approaches. In addition, surface and defect chemistries existing in the materials can also be projected toward achieving high-performance battery application.…”

“…As a result, Ca 3 Co 2 O 6 , CaCo 2 O 4 , and [Ca 2 CoO 3 ]­[CoO 2 ] 1.62 were successfully prepared using the Pechini method. Systematic computational studies were also performed by Zapol et al for finding suitable Ca cathode materials . They evaluated CaTM 2 O 4 materials (TM: Ti, V, Cr, Mn, Fe, Co, and Ni) in terms of their thermodynamic stability, average intercalation voltage, energy density, preference for intercalation versus conversion, synthesizability, cation mobility, and electronic structure.…”