The development of an energy storage system with abundant elements is a key challenge for a sustainable society, and the interest of Na intercalation chemistry is extending throughout the research community. Herein, the impact of Ti integration into NaMnO ₂ in a binary system of

x

NaMnO ₂ –(

1 - x

) TiO ₂ (

0.5 \leq x \leq 1

) is systematically examined for rechargeable Na battery applications. Stoichiometric NaMnO ₂ , which is classified as an in-plane distorted O

^{'}

3-type layered structure, delivers a large initial discharge capacity of approximately 200 mAh g ^-1 , but insufficient capacity retention is observed, most probably associated with dissolution of Mn ions on electrochemical cycles. Ti-substituted samples show highly improved electrode performance as electrode materials. However, the appearance of a sodium-deficient phase, Na ₄ Mn ₄ Ti ₅ O ₁₈ with a tunnel-type structure, is observed for Ti-rich phases. Among the samples in this binary system, Na _0.8 Mn _0.8 Ti _0.2 O ₂ (

x = 0.8

), which is a mixture of a partially Ti-substituted O

^{'}

3-type layered oxide (Na _0.88 Mn _0.88 Ti _0.12 O ₂ ) and tunnel-type Na ₄ Mn ₄ Ti ₅ O ₁₈ as a minor phase elucidated by Rietveld analysis on both neutron and X-ray diffraction patterns, shows good electrode performance on the basis of energy density and cyclability. Both phases are electrochemically active as evidenced by in situ X-ray diffraction study, and the improvement of reversibility originates from the suppression of Mn dissolution on electrochemical cycles. From these results, the feasibility of Mn-based electrode materials for high-energy rechargeable Na batteries made from only abundant elements is discussed in detail.

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