Electrochemical intercalation and deintercalation of NaxMnO2 bronzes

Various NaxMnO2 bronzes have been electrochemically deintercalated. Na0.40MnO2 has a channel structure which is maintained for a large intercalation range (0.30 ≤ × ≤ 0.58). In order to explain the upper intercalation limit, an ordered sodium distribution between two types of Na+ sites is proposed. Na0.70MnO2 and α-NaMnO2 have lamellar structures of P2 and 0′3 types. During intercalation the original P2 type is maintained for 0.45 ≤ × ≤ 0.85 while two reversible structural transitions are observed from α-NaMnO2. A similar behavior occurs during the deintercalation of the high-temperature β-NaMnO2 variety. In each case of the structural transition the double octahedral layers remain unchanged. Electronic localization (increased by Mn3+ Jahn—Teller effect) tends to trap the Na+ ions and therefore increases the relaxation time of the investigated materials.