Phase Transitions in the "Spinel-Layered" Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) Cathodes upon (De)lithiation Studied with Operando Synchrotron X-ray Powder Diffraction.

Oleg A Drozhzhin,Anastasia M Alekseeva,Dmitry Chernyshov,Evgeny V Antipov,Artem M Abakumov,Vitalii A Shevchenko

doi:10.3390/nano11061368

Abstract

“Spinel-layered” Li1+xNi0.5Mn1.5O4 (x = 0, 0.5, 1) materials are considered as a cobalt-free alternative to currently used positive electrode (cathode) materials for Li-ion batteries. In this work, their electrochemical properties and corresponding phase transitions were studied by means of synchrotron X-ray powder diffraction (SXPD) in operando regime. Within the potential limit of 2.2–4.9 V vs. Li/Li+ LiNi0.5Mn1.5O4 with cubic spinel type structure demonstrates the capacity of 230 mAh·g−1 associated with three first-order phase transitions with significant total volume change of 8.1%. The Li2Ni0.5Mn1.5O4 material exhibits similar capacity value and subsequence of the phase transitions of the spinel phase, although the fraction of the spinel-type phase in this material does not exceed 30 wt.%. The main component of Li2Ni0.5Mn1.5O4 is Li-rich layered oxide Li(Li0.28Mn0.64Ni0.08)O2, which provides nearly half of the capacity with very small unit cell volume change of 0.7%. Lower mechanical stress associated with Li (de)intercalation provides better cycling stability of the spinel-layered complex materials and makes them more perspective for practical applications compared to the single-phase LiNi0.5Mn1.5O4 high-voltage cathode material.

Highlights

IntroductionSince the discovery of extraordinary electrochemical capacity for so-called “Li-rich”
Since the discovery of extraordinary electrochemical capacity for so-called “Li-rich”oxides as positive electrodes for Li-ion batteries, materials exploiting anionic redox activity have been the subject of intense studies [1,2,3,4,5]
PXRD revealed the presence of the cubic spinel phase LiNi0.5 Mn1.5 O4

Summary

Introduction

Since the discovery of extraordinary electrochemical capacity for so-called “Li-rich”. Oxides as positive electrodes for Li-ion batteries, materials exploiting anionic redox activity have been the subject of intense studies [1,2,3,4,5]. It is worth noting that pure Li2 MnO3 was considered to be electrochemically inactive for a long time, before demonstration of reversible Li+ extraction/insertion after “activation” at ~4.5–4.7 V vs. Li/Li+ in highly dispersed powder [6]. Unlike the LiMO2 layered oxides (M—transition metal), Li2 MnO3 ( represented as Li[Li1/3 Mn2/3 ]O2 ) exhibits oxygen anion redox activity that has been confirmed by a number of experimental and computational studies [7,8,9]

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Discussion

Conclusion