Effect of Al-doping on the Electrochemical Performances of O3-type NaNMC Cathode Material for Sodium Ion Batteries

Ghosh, Shuvajith and Martha, Surendra Kumar (2019) Effect of Al-doping on the Electrochemical Performances of O3-type NaNMC Cathode Material for Sodium Ion Batteries. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

O3-type layered NaNMC is considered as one of the most promising cathode materials for sodium-ion batteries (SIBs). NaNi0.5Mn0.3Co0.2O2, synthesized by using simple solution combustion method followed by thermal treatment delivers an initial discharge capacity of 135 mAh g-1 at C/10 rate, which indicates a reversible insertion of more than 50% sodium. However, it loses 37% of the initial capacity after 100 cycles due to structural deformation during sodiation/de-sodiation. The irreversible phase transition due to structural deformation leads to sluggish kinetics, rapid capacity fade and poor rate performance; thereby limit its wide practical applications. The partial substitution of Co3+ (0.545 Å) by Al3+ (0.535 Å) ions in the transition-metal layer to synthesize NaNi0.5Mn0.3Co0.2-xAlx (x=0.01, 0.02, 0.05) by solution combustion technique is an effective strategy to address the issue of structural deformation and thus to improve the performance of NaNi0.5Mn0.3Co0.2O2. The O3-type structure of the synthesized material with R-3m space group was confirmed from XRD analysis. The synthesized materials show a morphology of hexagonal plate-like primary structures aggregated to form secondary clusters. The galvanostatic charge-discharge studies carried out at C/10 rate in the voltage range of 2.0-4.0 V shows that the composition with an overall 2% Al doping (x=0.02) delivers much better capacity retention (~20% improvement than pristine NaNMC) even after 100 cycles than the other compositions studied (1% (x=0.01) and 5% (x=0.05) Al doping). Moreover, the NaNi0.5Mn0.3Co0.18Al0.02O2 shows good capacity of around 80 mAhg-1 even at high C-rate of 5C rate, which is almost 72% of the initial capacity at C/10 rate. The improved electrochemical performance of the Al-substituted NaNMC is attributed to the enhanced structural stability of the sodium layered transition metal oxide achieved after the partial substitution of Co3+ by Al3+ ion.

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