Advanced approaches for enhancing intercalation capacity of Na2/3Ni1/3Mg1/6Mn1/2O2: insight into the mechanism
M. Kalapsazova, R.Kukeva, E. Zhecheva, R. Stoyanova
Abstract: The sodium transition metal oxides with layered structure are in practical interests as positive electrode materials for sodium-ion batteries. However, these types of oxides have not yet reached their optimal electrochemical properties in terms of specific capacity and cycling stability. Recently, we demonstrated two different approaches for further development of the electrochemical performance of Na2/3Ni1/3Mn1/2O2 oxide. Improved cycling stability is metal substitution of transition metals with electrochemically inactive ions such as Mg2+ [1]. Improved cycling stability is obtained via metal substitution of transition metals with electrochemically inactive ions such as Mg2+ [1], while the surface modification of the layered oxide with oxygen-storage material such as CeO2 [2] and Al2O3 [3] leads to a drastic increase in the reversible capacity.
Herein we provide new data on the synergetic effect of both approaches – metal substitution in the structure and surface modification by coating. After partial substitution of the low-oxidized nickel ions for Mg2+ ions, the target Na2/3Ni1/3Mg1/6Mn1/2O2 oxide was treated with electrochemically inactive oxides, such as CeO2 and Al2O3. It is found that the coated oxides show improved electrochemical characteristics in terms of specific capacity and cycling stability in comparison with pristine Na2/3Ni1/2Mn1/2O2 and substituted Na2/3Ni1/3Mg1/6Mn1/2O2 oxides. The combined use of in-situ and exsitu analyses provided an opportunity to gain insight into the mechanism of the intercalation reaction. An in-situ XRD analysis reveals that Al2O3 coating leads to additional stabilization of the oxide structure during de/intercalation compared to uncoated and CeO2 coated oxides. An EIS technique, ex-situ XPS and EPR analyses reveals that the CeO2 and A2O3 modifier tunes the electrode–electrolyte interaction and prevent the cathode surface from hydrogen fluoride (HF) attack at upper potential limit.
References:
[1] M. Kalapsazova, P. Markov, K. Kostov, E. Zhecheva, D. Nihtianova, R. Stoyanova, Batt.&Supercaps. 3, 12 (2020) 1329-1340.
[2] M. Kalapsazova, K. Kostov, R. Kukeva, E. Zhecheva, R. Stoyanova, J. Phys. Chem. Lett. 12, 32 (2021) 7804–7811.
[3] M. Kalapsazova, R. Kukeva, S. Harizanova, P. Markov, D. Nihtianova, E. Zhecheva, R. Stoyanova, Batteries, 9 (2023) 144.
Acknowledgements: The authors thank for the financial support of the project CARiM (NSP Vihren, КП-06-ДB-6).
The authors from CARiM’s Research Team are bolded.
VIHREN-CARiM 2019 