Impact of Mg and Ti doping in O3 type NaNi_1/2Mn_1/2O₂ on reversibility and phase transition during electrochemical Na intercalation

Abstract

O3 type NaNi1/2Mn1/2O2 materials with Mg and Ti co-substitution demonstrate better capacity capability with an initial discharge capacity of 200 mA h g−1 in non-aqueous Na cells without any capacity loss due to substitution.

Using High-Entropy Configuration Strategy to Design Na-Ion Layered Oxide Cathodes with Superior Electrochemical Performance and Thermal Stability

“…Then, binary TM oxides (e.g., NaNi 0.5 Mn 0.5 O 2 ) were explored, and even though slightly encouraging results were obtained; phase transitions among O3, O’3, P3 and P’3 during charge still appear, causing deteriorated cycle performance . Subsequently, multi-substitution was tried; for instance, the substitution of Mn 4+ by Sn 4+ or Ti 4+ , dual substitution of Ni 2+ and Mn 4+ by Cu 2+ and Ti 4+ or Mg 2+ and Ti 4+ , and simultaneous substitution of Ni 2+ and Mn 4+ by Fe 3+ were widely used to alleviate the structural degradation and increase the redox voltage. − However, these cathodes suffer from phase impurity when using the traditional solid-state sintering method and experience heterogeneous surface reconstruction, TM dissolution, and generation of intragranular cracks during repeated cycling. , …”

Transition metal oxides as a cathode for indispensable Na-ion batteries

“…The structure of NaNi 1/2 Mn 1/2 O 2 is O3 type layered oxide and it is same as a-NaFeO 2 , has drawn interest as a cathode material for SIBs due to its larger reversible capacity of 200 mA h g À1 . 59 The O3 type NaNi 1/2 Mn 1/2 O 2 materials with Ti or Mg substitution show good capacity, and co-substituted Ti and Mg material shows a discharge capacity of 200 mA h g À1 with no loss of capacity owing to substitution. Replacement of Ti 4+ and Mg 2+ , (bigger ions than Mn 4+ or Ni 2+ ), outcomes a greater inplane lattice of the O3 type structure, this could postpone the transition of phase in charging.…”

Multiphase layered transition metal oxide positive electrodes for sodium ion batteries

“…Electrochemically induced irreversible phase transitions, oxygen release, reaction with electrolyte, and transition metal migration to the sodium layer adversely affect the performance of the electrode. Consequently, the practical capacity of O3‐type positive electrodes is often significantly less than the theoretical capacity because the voltage range must be limited 33–36 . In contrast to O3‐type materials, P‐type materials often demonstrate excellent power performance but can be limited by their low theoretical capacity and suffer from similar degradation mechanisms as O3‐type materials 37–48 .…”

“…Consequently, the practical capacity of O3-type positive electrodes is often significantly less than the theoretical capacity because the voltage range must be limited. [33][34][35][36] In contrast to O3-type materials, P-type materials often demonstrate excellent power performance but can be limited by their low theoretical capacity and suffer from similar degradation mechanisms as O3-type materials. [37][38][39][40][41][42][43][44][45][46][47][48] Other than electrochemical degradation, a significant barrier to the practical application of LTMOs is their vulnerability to degradation resulting from exposure to air.…”