Exploring Lithium-Cobalt-Nickel Oxide Spinel Electrodes for ≥3.5 V Li-Ion Cells

LT-LiMn0.5Ni0.5O2: a unique co-free cathode for high energy Li-ion cells

A novel LiMn_0.5Ni_0.5O₂ cathode with a predominant, partially-disordered lithiated-spinel structure has been prepared by a 'low temperature' (LT) synthesis. Li/LT-LiMn_0.5Ni_0.5O₂ cells operate between 5.0 and 2.5 V with good cycling stability, yielding a capacity of 225 mA h g^-1, principally by redox reactions on the nickel ions on distinct voltage plateaus at ∼3.6 V and ∼4.6 V.

A Comparison of Order-Disorder in Several Families of Cubic Oxides

Order-disorder on both cation and oxygen sites is a hallmark of fluorite-derived structures, including pyrochlores. Ordering can occur on long- and short-range scales and can result in persistent metastable states. In various cubic oxide systems, different types of disorder are seen. The purpose of this paper is to review and compare the types and energetics of order-disorder phenomena in several families of cubic oxides having pyrochlore, weberite, defect fluorite, perovskite, rocksalt, and spinel structures. The goal is to better understand how structure, composition, and thermodynamic parameters (enthalpy and entropy) determine the feasibility of different competing ordering processes and structures in these diverse systems.

The Effects of Trace Yb Doping on the Electrochemical Performance of Li-Rich Layered Oxides

Layered lithium-rich cathode materials are one of the most promising cathode materials owing to their higher mass energy density than the commercial counterparts. A series of trace Yb-doped lithium-rich cathode materials Li_1.2 Mn_0.54 Ni_0.13 Co_0.13-x Yb_x O₂ (0≤x≤0.050) were synthesized and the effects were investigated by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The participation of Yb ions in electrochemical reactions and the larger binding energy of Yb-O than M-O (M=Mn, Ni, Co), which expands the lithium layer spacing and stabilizes the oxygen stacking, resulted in excellent performance of materials doped with a limited Yb content (x≤0.005). However, higher doping amounts (x>0.005) significantly increased the charge-transfer impedance and led to a sharp deterioration in electrochemical performance. The reason lies in the large difference in ionic radius between the transition metals (Mn, Co, and Ni) and Yb. There is an upper limit to the amount of Yb ions in the lattice. If the amount of Yb is higher than the limit, excess Yb ions enter the Li layers instead of staying in the transition-metal layers or even segregate on the surface and form electrochemically inert oxides.

Revealing Electronic Signature of Lattice Oxygen Redox in Lithium Ruthenates and Implications for High-Energy Li-ion Battery Material Designs

Anion redox in lithium transition metal oxides such as Li2RuO3 and Li2MnO3, has catalyzed intensive research efforts to find transition metal oxides with anion redox that may boost the energy density of lithium-ion batteries. The physical origin of observed anion redox remains debated, and more direct experimental evidence is needed. In this work, we have shown electronic signatures of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O2-/(O2)n-), in charged Li2-xRuO3 after Ru oxidation (Ru4+/Ru5+) upon first-electron removal with lithium de-intercalation. Experimental Ru L3-edge high-energy-resolution fluorescence detected X-ray absorption spectra (HERFD-XAS), supported by ab-initio simulations, revealed that the increased intensity in the high-energy shoulder upon lithium de-intercalation resulted from increased O-O coupling, inducing (O-O) σ*-like states with π overlap with Ru d-manifolds, in agreement with O K-edge XAS spectra. Experimental and simulated O K-edge X-ray emission spectra (XES) further supported this observation with the broadening of the oxygen non-bonding feature upon charging, also originated from (O-O) σ* states. This lattice oxygen redox of Li2-xRuO3 was accompanied by a small amount of O2 evolution in the first charge from differential electrochemistry mass spectrometry (DEMS) but diminished in the subsequent cycles, in agreement with the more reduced states of Ru in later cycles from Ru L3-edge HERFD-XAS. These observations indicated that Ru redox contributed more to discharge capacities after the first cycle. This study has pinpointed the key spectral fingerprints related to lattice oxygen redox from a molecular level and constructed a transferrable framework to rationally interpret the spectroscopic features by combining advanced experiments and theoretical calculations to design materials for Li-ion batteries and electrocatalysis applications.

Characterization of Lithium Ion Battery Materials with Valence Electron Energy-Loss Spectroscopy

Cutting-edge research on materials for lithium ion batteries regularly focuses on nanoscale and atomic-scale phenomena. Electron energy-loss spectroscopy (EELS) is one of the most powerful ways of characterizing composition and aspects of the electronic structure of battery materials, particularly lithium and the transition metal mixed oxides found in the electrodes. However, the characteristic EELS signal from battery materials is challenging to analyze when there is strong overlap of spectral features, poor signal-to-background ratios, or thicker and uneven sample areas. A potential alternative or complementary approach comes from utilizing the valence EELS features (<20 eV loss) of battery materials. For example, the valence EELS features in LiCoO2 maintain higher jump ratios than the Li-K edge, most notably when spectra are collected with minimal acquisition times or from thick sample regions. EELS maps of these valence features give comparable results to the Li-K edge EELS maps of LiCoO2. With some spectral processing, the valence EELS maps more accurately highlight the morphology and distribution of LiCoO2 than the Li-K edge maps, especially in thicker sample regions. This approach is beneficial for cases where sample thickness or beam sensitivity limit EELS analysis, and could be used to minimize electron dosage and sample damage or contamination.

First-Principles Study of Lithium Cobalt Spinel Oxides: Correlating Structure and Electrochemistry

Embedding a lithiated cobalt oxide spinel (Li₂Co₂O₄, or LiCoO₂) component or a nickel-substituted LiCo_{1- x}Ni _xO₂ analogue in structurally integrated cathodes such as xLi₂MnO₃·(1- x)LiM'O₂ (M' = Ni/Co/Mn) has been recently proposed as an approach to advance the performance of lithium-ion batteries. Here, we first revisit the phase stability and electrochemical performance of LiCoO₂ synthesized at different temperatures using density functional theory calculations. Consistent with previous studies, we find that the occurrence of low- and high-temperature structures (i.e., cubic lithiated spinel LT-LiCoO₂; or Li₂Co₂O₄ ( Fd3̅ m) vs trigonal-layered HT-LiCoO₂ ( R3̅ m), respectively) can be explained by a small difference in the free energy between these two compounds. Additionally, the observed voltage profile of a Li/LiCoO₂ cell for both cubic and trigonal phases of LiCoO₂, as well as the migration barrier for lithium diffusion from an octahedral (O_h) site to a tetrahedral site (T_d) in Fd3̅ m LT-Li_{1- x}CoO₂, has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCo _xM_{1- x}O₂ lithiated spinel (M = Ni or Mn) structures and compositions is conducted to extend the exploration of the chemical space of Li-Co-Mn-Ni-O electrode materials. We predict a new lithiated spinel material, LiNi_0.8125Co_0.1875O₂ ( Fd3̅ m), with a composition close to that of commercial, layered LiNi_0.8Co_0.15Al_0.05O₂, which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next-generation lithium-ion batteries.

A simple, rapid and efficient flame synthesis of ultrafine LiNi0.95−xCoxTi0.05O2 (x = 0.25 and 0.30): a versatile route to synthesize Ni-rich cathode materials for Li-ion batteries

A simple, rapid, and efficient flame synthesis method was developed to fabricate LiNi_0.95−xCo_xTi_0.05O₂ (x = 0.25 and 0.30) cathode materials for Li-ion batteries.