Characterization and electrochemical properties of Li+ ion-exchanged products of hollandite-type Ky(Mn1 − xCox)O2 for rechargeable lithium battery electrodes

Hollandite-type (K0.01Li0.42)MnO2.08 and its Co-doped (K0.04Li0.34) (Mn0.85 Co0.15)O2.07 have been synthesized by Li+ ion-exchange of α-K0.14Mn1 − xCoxO2 · zH2O (x = 0–0.15, z = 0.15–0.21) in a LiNO3/LiCl molten salt at 300 °C, and characterized by X-ray diffraction (XRD), chemical analysis, N2-sorptmetric and electrochemical measurements. XRD measurements and chemical analysis indicated that almost all the K+ ions and hydrogens of the structural waters in the [2 × 2] tunnels of the precursor α-MnO2 were exchanged by Li+ ions in the molten salt, resulting in Li+-type α-MnO2 and its Co-doped one including Li+ ions as well as Li2O in the [2 × 2] tunnels. N2-sorptmetric measurements revealed that the Li+ ion-exchanged products have a mesopore structure as well as a micropore one, in the range of 1–10 nm, and the BET surface area of the precursor α-K0.14Mn1 − xCoxO2 decreased with Li+ ion-exchanging, probably due to the incorporation of Li2O molecules in the [2 × 2] tunnels. emical diffusion coefficients of lithium for the Li+ ion-exchanged products increased by about one-order of magnitude with Li+ ion-exchanging. The Li+ ion-exchanged products provided higher initial discharge capacities and better recharge efficiencies than the parent materials, probably due to the structural stability with the existence of Li2O in the [2 × 2] tunnels.