TY - JOUR

T1 - Activation of anion redox in P3 structure cobalt-doped sodium manganese oxide via introduction of transition metal vacancies

AU - Kim, Eun Jeong

AU - Mofredj, Kenza

AU - Pickup, David

AU - Chadwick, Alan

AU - Irvine, John Thomas Sirr

AU - Armstrong, Robert

N1 - EJK would like to thank the Alistore ERI for the award of a studentship. This work was supported by the Faraday Institution (grant number FIRG018).

PY - 2021/1/1

Y1 - 2021/1/1

N2 - 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.

AB - 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.

KW - Sodium ion batteries

KW - Layered oxides

KW - Oxygen redox

KW - Transition metal vacancies

KW - P3 structure

U2 - 10.1016/j.jpowsour.2020.229010

DO - 10.1016/j.jpowsour.2020.229010

M3 - Article

VL - 481

JO - Journal of Power Sources

JF - Journal of Power Sources

SN - 0378-7753

M1 - 229010

ER -