Defect-Engineered β-MnO2-δ Precursors Control the Structure-Property Relationships in High-Voltage Spinel LiMn1.5Ni0.5O4-δ

Aderemi B Haruna; Patrick Mwonga; Dean Barrett; Cristiane B Rodella; Roy P Forbes; Andrew Venter; Zeldah Sentsho; Philip J Fletcher; Frank Marken; Kenneth I Ozoemena

doi:10.1021/acsomega.1c03656

Defect-Engineered β-MnO_2-δ Precursors Control the Structure-Property Relationships in High-Voltage Spinel LiMn_1.5Ni_0.5O_4-δ

ACS Omega. 2021 Sep 22;6(39):25562-25573. doi: 10.1021/acsomega.1c03656. eCollection 2021 Oct 5.

Authors

Affiliations

¹ Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa.
² Brazilian Synchrotron Light Laboratory (LNLS/Brazilian Center of Energy and Materials) (CNPEM), Campinas 13083-970, São Paulo, Brazil.
³ Research and Technology Development Division, Necsa (South African Nuclear Energy Corporation) SOC Limited, Pelindaba, Pretoria 0001, South Africa.
⁴ Materials and Chemical Characterization Facility (MC), University of Bath, Claverton Down, Bath BA2 7AY, U.K.
⁵ Department of Chemistry, University of Bath, Claverton Down, Bath BA27AY, U.K.

Abstract

This study examines the role of defects in structure-property relationships in spinel LiMn_1.5Ni_0.5O₄ (LMNO) cathode materials, especially in terms of Mn³⁺ content, degree of disorder, and impurity phase, without the use of the traditional high-temperature annealing (≥700 °C used for making disordered LMNO). Two different phases of LMNO (i.e., highly P4₃32-ordered and highly Fd3̅m-disordered) have been prepared from two different β-MnO_2-δ precursors obtained from an argon-rich atmosphere (β-MnO_2-δ (Ar)) and a hydrogen-rich atmosphere [β-MnO_2-δ (H₂)]. The LMNO samples and their corresponding β-MnO_2-δ precursors are thoroughly characterized using different techniques including high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman spectroscopy, powder neutron diffraction, X-ray photoelectron spectroscopy, synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy, and electrochemistry. LMNO from β-MnO_2-δ (H₂) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO_2-δ (Ar). For the first time, defective β-MnO_2-δ has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn³⁺ content, and impurity contents without the need for conventional methods of doping with metal ions, high synthetic temperature, use of organic compounds, postannealing, microwave, or modification of the temperature-cooling profiles. The results show that the oxygen vacancy changes concurrently with the degree of disorder and Mn³⁺ content, and the best electrochemical performance is only obtained at 850 °C for LMNO-(Ar). The findings in this work present unique opportunities that allow the use of β-MnO_2-δ as viable precursors for manipulating the structure-property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.