Neutron and X-ray Diffraction Investigation of Crystal Structure and Phase Transition for Na2/3[NiyMnzAl1-y-z]O2 as a Cathode Material for Sodium-ion Batteries

TL;DR

This study investigates how adding aluminum to a sodium-ion battery material affects its structure and performance, aiming to improve battery stability.

Contribution

The paper reveals how different aluminum substitution strategies impact crystal structure and phase transitions in sodium-ion battery cathodes.

Findings

Aliovalent Al substitution disrupts Na/vacancy ordering but not transition metal ion ordering.

Operando XRD shows reduced structural mismatch during phase transition due to Al substitution.

Aluminum substitution improves cycling stability by altering crystal structure and phase evolution.

Abstract

Sodium-ion batteries promise to provide low cost and environmentally friendly energy storage as an alternative to lithium-ion batteries. The P2 layered structured Na2/3[Ni1/3Mn2/3]O2 material offers a high theoretical capacity but suffers rapid fade in capacity due to the P2 to O2 structure transition. Partial substitution of the transition metal ions with aluminum ions has been demonstrated to improve its cycling stability, yet, it is unclear how different substitution strategies (aliovalent vs. isovalent substitution) affects the crystal structure and the phase evolution of this material. Using joint X-ray and neutron powder diffraction methods, we have elucidated how different aluminum substitution strategies affect the Na/vacancy and Ni/Mn orderings. The aliovalent Al substitution disrupts the Na/vacancy ordering but not the transition metal ion ordering. Operando XRD revealed a reduced structural mismatch during the phase transition as a result of Al substitution.