Role of the voltage window on the capacity retention of P2-Na2/3[Fe1/2Mn1/2]O2 cathode material for rechargeable sodium-ion batteries

Maider Zarrabeitia,Javier Carrasco,Oier Lakuntza,Teófilo Rojo,Francesco Nobili,Montse Casas-Cabanas,Miguel Ángel Muñoz-Márquez

doi:10.1038/s42004-022-00628-0

Abstract

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to “Z”/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading.

Highlights

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries
The results show that the phase transition occurring at high voltage has a profound impact on the electronic and ionic transport properties of P2-Na2/3[Fe1/2Mn1/2]O2 electrode, and such changes directly impact in capacity retention
The oxidation of the electrolyte and subsequent formation of the electrolyte interphase (EEI) is not expected at OCV, but a similar EEI is chemically formed before cycling, as confirmed by X-ray photoelectron spectroscopy (XPS) and in agreement with previous EEI studies of sodium-ion batteries (SIBs) electrodes[43,44,45,46]

Summary

Introduction

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. Nowadays, pushed by the increasing need for more efficient low-cost energy storage devices, sodium-ion batteries (SIBs) are becoming an alternative for large-scale applications and light electromobility[3,4,5] This is nested in the fact that sodium precursors are evenly distributed in the Earth’s crust and are cheaper and more abundant than lithium ones[6,7,8]. P2Na2/3[Fe1/2Mn1/2]O2 is one of the most promising cathode materials in terms of cost-efficiency and energy density[16] It is made from Earth abundant elements and delivers a high reversible capacity of 190 mAh g−1 when it is cycled in the voltage range of 1.5–4.3 V vs Na+/Na using metallic sodium as the counter electrode.

Methods

Results

Conclusion