Manganese-Based Tunnel-Type Cathode Materials for Secondary Li-Ion and K-Ion Batteries

The rational design of novel cathode materials remains a key pursuit in the development of (post) Li-ion batteries. Considering the relative ionic and Stokes radii and open frameworks with large tunnels, Na-based compounds can act as versatile cathodes for monovalent Li-ion and post-Li-ion batteries. Here, tunnel-type sodium insertion material Na_0.44MnO₂ is demonstrated as an intercalation host for Li-ion and K-ion batteries. The rod-shaped Na_0.44MnO₂ was synthesized by a solution combustion method assuming an orthorhombic structure (space group Pbam), which led to Na_0.11K_0.27MnO₂ (NKMO) and Na_0.18Li_0.51MnO₂ (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively, via facile electrochemical ion exchange from Na_0.44MnO₂. These new compositions, NKMO and NLMO, exhibited capacities of ∼74 and 141 mAh g^-1, respectively (at a rate of C/20), with excellent cycling stability. The underlying mechanistic aspects (structural changes and charge storage mechanism) in these cathode compositions were probed by combining ex situ structural, spectroscopy, and electrochemical tools. Tunnel-type Na_0.44MnO₂ forms a versatile cathode material for non-aqueous alkali-ion batteries.