CARiM event 2025: Poster presentation by Dr. Mariya Kalapsazova

Effective approaches for enhancing electrochemical performance of layered NaTMO2 oxides

M. Kalapsazova, E. Zhecheva аnd R. Stoyanova

Abstract: Among all positive electrode materials for sodium-ion batteries, the sodium transition metal oxides (NaTMO2) with layered structure are in practical interests. However, these types of oxides have not yet reached their optimal electrochemical properties in terms of specific capacity and cycling stability.

Within the framework of the CARiM project, over the last few years, we have developed several different and effective approaches to improve the electrochemical performance of these electrode materials. One of the approaches we have adopted is to stabilize the bulk of the P3-Na2/3Ni1/2Mn1/2O2 structure by introducing electrochemically inactive ions, i.e. Mg2+ and Ti4+ ions were used through partial replacement of low- and high-oxidized nickel ions, respectively: Na2/3Ni1/3Mg1/6Mn1/2O2 and Na2/3Ni1/3Ti1/6Mn1/2O2 [1,2]. Furthermore, the metal-substituted oxides were surface modified by an oxygen storage material, such as CeO2 [3,4]. The results show, that Ti-substituted oxide displays moderate cycling stability and poor rate capability [3,4]. Contrary to Ti4+, the Mg2+ substituents mainly influence the nickel redox activity and suppress the deposition of MnF2, all of them contributing to the exceptional cycling stability and rate capability [2,3,4]. The CeO2 modifier has a much stronger effect on the oxygen redox activity than that of metal substituents; thus, the highest specific capacity is attained [3,4].Taking into account these results, in the next stage we modified the surface of Na2/3Ni1/3Mg1/6Mn1/2O2 with another electrochemically inactive oxides, i.e. Al2O3. It is found that better electrochemical performance is achieved, in terms of specific capacity and cycling stability, when Al2O3 is used instead of CeO2.

References:

1. M. Kalapsazova, P. Markov, K. Kostov, E. Zhecheva, D. Nihtianova and R. Stoyanova, Batt.&Supercaps. 3, 12 (2020) 1329-1340.

2. M. Kalapsazova, K. Kostov, E. Zhecheva, R. Stoyanova, Frontiers in Chemistry, 8 (2020) 600140.

3. M. Kalapsazova, K. Kostov, R. Kukeva, E. Zhecheva and R. Stoyanova, J. Phys. Chem. Lett. 12, 32 (2021) 7804–7811.

4. M. Kalapsazova, R. Kukeva, E. Zhecheva, R. Stoyanova, Batteries, 8, 6, (2022) 56.

Acknowledgements: The authors thank for the financial support of the project CARiM (NSP Vihren, КП-06-ДB-6/16.12.2019).

The authors from CARiM’s Research Team are bolded.