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Activation of anion redox in P3 structure cobalt-doped sodium manganese oxide via introduction of transition metal vacancies

DOI: 10.1016/j.jpowsour.2020.229010 DOI Help

Authors: Eun Jeong Kim (University of St Andrews; The Faraday Institution) , Kenza Mofredj (University of St Andrews) , David M. Pickup (University of Kent) , Alan V. Chadwick (University of Kent) , John T. S. Irvine (University of St Andrews; The Faraday Institution) , A. Robert Armstrong (University of St Andrews; ALISTORE-ERI; The Faraday Institution)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Power Sources , VOL 481

State: Published (Approved)
Published: November 2020
Diamond Proposal Number(s): 14239

Abstract: Additional capacity delivered by oxygen redox activity may in principle represent a means of enhancing the electrochemical performance of layered sodium transition metal oxides. However, irreversible structural changes occurring during cycling typically cause significant capacity fade with limited reversibility of oxygen redox processes. Here, P3-structure Na0.67Co0.2Mn0.8O2 was synthesised under two different reaction conditions. Both materials exhibit very stable cycling performance in the voltage range 1.8–3.8 V where the redox couples of transition metals entirely dominate the electrochemical reaction. For the compound prepared under more oxidising conditions, anion redox activity is triggered in the wider voltage window 1.8–4.4 V in a reversible manner with exceptionally small voltage hysteresis (20 mV). The presence of vacancies in the transition metal layers is shown to play a critical role not only in generating unpaired O 2p states but also in stabilising the crystal structure in the high voltage region.

Journal Keywords: Sodium ion batteries; Layered oxides; Oxygen redox; Transition metal vacancies; P3 structure

Subject Areas: Chemistry, Materials, Energy

Instruments: B18-Core EXAFS