Search NASA⌕ Search

Engineering topics

McCloskey, Bryan D.

Publications and source records attributed to McCloskey, Bryan D..

61 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Role of Redox-Inactive Transition-Metals in the Behavior of Cation-Disordered Rocksalt Cathodes

Owing to the capacity boost from oxygen redox activities, Li-rich cation-disordered rocksalts (LRCDRS) represent a new class of promising high-energy Li-ion battery cathode materials. Redox-inactive transition-metal (TM) cations, typically d 0 TM, are essential in the formation of rocksalt phases, however, their role in electrochemical performance and cathode stability is largely unknown. In the present study, the effect of two d 0 TM (Nb 5+ and Ti 4+ ) is systematically compared on the redox chemistry of Mn-based model LRCDRS cathodes, namely Li 1.3 Nb 0.3 Mn 0.4 O 2 (LNMO), Li 1.25 Nb 0.15 Ti 0.2 Mn 0.4 O 2 (LNTMO), and Li 1.2 Ti 0.4 Mn 0.4 O 2 (LTMO). Although electrochemically inactive, d 0 TM serves as a modulator for oxygen redox, with Nb 5+ significantly enhancing initial charge storage contribution from oxygen redox. Further studies using differential electrochemical mass spectroscopy and resonant inelastic X-ray scattering reveal that Ti 4+ is better in stabilizing the oxidized oxygen anions (O n- , 0 < n < 2), leading to a more reversible O redox process with less oxygen gas release. As a result, much improved chemical, structural and cycling stabilities are achieved on LTMO. Detailed evaluation on the effect of d 0 TM on degradation mechanism further suggests that proper design of redox-inactive TM cations provides an important avenue to balanced capacity and stability in this newer class of cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material

Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO 2 and O 2 evolution, ~90% and ~100% respectively, during the first charge up to 4.8 V vs. Li +/0 . CO 2 suppression is related to Li 2 CO 3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance compared to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation (“O-redox”) during Li + removal by a novel ex-situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region around 4.5 V. X-ray photoelectron spectra and Mn -L X-ray absorption spectra of the cathode powders reveal a Li + deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, our O K-edge resonant inelastic X-ray scattering shows the lattice O-redox behavior largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation.

25 ENERGY STORAGE↗
DOE OSTI2020

Definition of Redox Centers in Reactions of Lithium Intercalation in Li 3 RuO 4 Polymorphs

Cathodes based on layered LiMO 2 are the limiting components in the path toward Li-ion batteries with energy densities suitable for electric vehicles. Introducing an over-stoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. However, the role and fate of the oxide ligands in such intriguing additional capacity remain unclear. This reactivity was predicted in Li 3 RuO 4 , making it a valuable model system. For this study, a comprehensive analysis of the redox activity of both Ru and O under different electrochemical conditions was carried out, and the effect of Li/Ru ordering was evaluated. Li 3 RuO 4 displays highly reversible Li intercalation to Li 4 RuO 4 below 2.5 V vs Li + /Li 0 , with conventional reactivity through the formal Ru 5+ -Ru 4+ couple. In turn, it can also undergo anodic Li extraction at 3.9 V, which involves O states to a much greater extent than Ru. This reaction competes with side processes such as electrolyte decomposition and, to a much lesser extent, oxygen loss. Although the associated capacity is reversible, reintercalation unlocks a different, conventional pathway also involving the formal Ru 5+ -Ru 4+ couple despite operating above 2.5 V, leading to chemical hysteresis. This new pathway is both chemically and electrochemically reversible in subsequent cycles. This work exemplifies both the challenge of stabilizing highly depleted O states, even with 4d metals, and the ability of solids to access the same redox couple at two very different potential windows depending on the underlying structural changes. It highlights the importance of properly defining the covalency of oxides when defining charge compensation in view of the design of materials with high capacity for Li storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrahigh power and energy density in partially ordered lithium-ion cathode materials

There is an intensive search for high-performance cathode materials for rechargeable batteries. In this work the authors report that oxyfluorides with partial spinel-like cation order, made from earth-abundant elements, display both exceptionally high energy and power. The rapid market growth of rechargeable batteries requires electrode materials that combine high power and energy and are made from earth-abundant elements. In this paper we show that combining a partial spinel-like cation order and substantial lithium excess enables both dense and fast energy storage. Cation overstoichiometry and the resulting partial order is used to eliminate the phase transitions typical of ordered spinels and enable a larger practical capacity, while lithium excess is synergistically used with fluorine substitution to create a high lithium mobility. With this strategy, we achieved specific energies greater than 1,100 Wh kg -1 and discharge rates up to 20 A g -1 . Remarkably, the cathode materials thus obtained from inexpensive manganese present a rare case wherein an excellent rate capability coexists with a reversible oxygen redox activity. Our work shows the potential for designing cathode materials in the vast space between fully ordered and disordered compounds.

25 ENERGY STORAGE↗
DOE OSTI2020

How Bulk Sensitive is Hard X-ray Photoelectron Spectroscopy: Accounting for the Cathode–Electrolyte Interface when Addressing Oxygen Redox

Sensitivity to the `bulk' oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes, Li 2 MnO 3 , Li-rich NMC, and NMC 442, that shows no clear link to oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High-Capacity P2-Type Na x Li 0.25 Mn 0.75 O 2 Cathode Enabled by Anionic Oxygen Redox

Sodium-ion battery technology has attracted significant attention due to its substantial cost advantage and similar operating mechanism to Li-ion batteries. P2-type sodium manganese oxide cathode is one of the most promising candidates, demonstrating both high capacity and good cycling stability. Here, we explore the lattice oxygen activity in layered sodium transition metal oxides. We synthesize a series of sodium lithium manganese oxides, NaxLi 0.25 Mn 0.75 O2 (x = 0.75 – 0.833), to optimize Na content. We further investigate the charge compensation mechanism for the best performing Na 0.75 Li 0.25 Mn 0.75 O 2 over an extensive electrochemical cycling window. The large charge and discharge capacity is enabled by reversible lattice oxygen redox in the high voltage region (≥2.5 V), along with Mn redox at the voltages below 2.5 V. Additionally, we reveal a small amount of oxygen gas evolution, 0.04% of the total oxygen in Na 0.25 Li 0.25 Mn 0.75 O 2 . This initial study will trigger an interest in the lattice oxygen activity in layered sodium metal oxide cathode, therefore, leading to better understanding of its correlation with crystal structure and electrochemical performance.

25 ENERGY STORAGE↗