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Understanding the cation ordering transition in high-voltage spinel LiNi_0.5Mn_1.5O₄ by doping Li instead of Ni.

ABSTRACT: We determined how Li doping affects the Ni/Mn ordering in high-voltage spinel LiNi_0.5Mn_1.5O₄(LNMO) by using neutron diffraction, TEM image, electrochemical measurements, and NMR data. The doped Li occupies empty octahedral interstitials (16c site) before the ordering transition, and can move to normal octahedral sites (16d (4b) site) after the transition. This movement strongly affects the Ni/Mn ordering transition because Li at 16c sites blocks the ordering transition pathway and Li at 16d (4b) sites affects electrostatic interactions with transition metals. As a result, Li doping increases in the Ni/Mn disordering without the effect of Mn³⁺ ions even though the Li-doped LNMO undergoes order-disorder transition at 700 °C. Li doping can control the amount of Ni/Mn disordering in the spinel without the negative effect of Mn³⁺ ions on the electrochemical property.

SUBMITTER: Lee J

PROVIDER: S-EPMC5532243 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Understanding the cation ordering transition in high-voltage spinel LiNi0.5Mn1.5O4 by doping Li instead of Ni.

Lee Junghwa J Dupre Nicolas N Avdeev Maxim M Kang Byoungwoo B

Scientific reports 20170727 1

We determined how Li doping affects the Ni/Mn ordering in high-voltage spinel LiNi0.5Mn1.5O4(LNMO) by using neutron diffraction, TEM image, electrochemical measurements, and NMR data. The doped Li occupies empty octahedral interstitials (16c site) before the ordering transition, and can move to normal octahedral sites (16d (4b) site) after the transition. This movement strongly affects the Ni/Mn ordering transition because Li at 16c sites blocks the ordering tran ...[more]

PMID: 28751751

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Project description:The high-voltage LiNi0.5Mn1.5O4 (LNMO) spinel cathode material offers high energy density storage capabilities without the use of costly Co that is prevalent in other Li-ion battery chemistries (e.g., LiNixMnyCozO2 (NMC)). Unfortunately, LNMO-containing batteries suffer from poor cycling performance because of the intrinsically coupled processes of electrolyte oxidation and transition metal dissolution that occurs at high voltage. In this work, we use operando electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopies to demonstrate that transition metal dissolution in LNMO is tightly coupled to HF formation (and thus, electrolyte oxidation reactions as detected with operando and in situ solution NMR), indicative of an acid-driven disproportionation reaction that occurs during delithiation (i.e., battery charging). Leveraging the temporal resolution (s-min) of magnetic resonance, we find that the LNMO particles accelerate the rate of LiPF6 decomposition and subsequent Mn2+ dissolution, possibly due to the acidic nature of terminal Mn-OH groups. X-ray photoemission electron microscopy (XPEEM) provides surface-sensitive and localized X-ray absorption spectroscopy (XAS) measurements, in addition to X-ray photoelectron spectroscopy (XPS), that indicate disproportionation is enabled by surface reconstruction upon charging, which leads to surface Mn3+ sites on the LNMO particle surface that can disproportionate into Mn2+(dissolved) and Mn4+(s). During discharge of the battery, we observe high quantities of metal fluorides (in particular, MnF2) in the cathode electrolyte interphase (CEI) on LNMO as well as the conductive carbon additives in the composite. Electronic conductivity measurements indicate that the MnF2 decreases film conductivity by threefold compared to LiF, suggesting that this CEI component may impede both the ionic and electronic properties of the cathode. Ultimately, to prevent transition metal dissolution and the associated side reactions in spinel-type cathodes (particularly those that operate at high voltages like LNMO), the use of electrolytes that offer improved anodic stability and prevent acid byproducts will likely be necessary.

Dataset Information

Understanding the cation ordering transition in high-voltage spinel LiNi_0.5Mn_1.5O₄ by doping Li instead of Ni.

Publications

Understanding the cation ordering transition in high-voltage spinel LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> by doping Li instead of Ni.

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