Engineering topics

Koirala, Krishna P.

Publications and source records attributed to Koirala, Krishna P..

4 records

DOE OSTI2024

Lithicone‐Protected Lithium Metal Anodes for Lithium Metal Batteries with Nickel‐Rich Cathode Materials

The high energy density advantage of lithium (Li) metal batteries (LMBs) makes them increasingly desirable; however, problems such as strong reactivity and dendrite growth of Li metal anode limit their practical uses. In this work, a novel Li‐containing glycerol (LiGL) or lithicone protection layer on a 50 μm thick Li metal anode is employed for improving the performance of LMBs. This LiGL layer was accurately deposited via a molecular layer deposition (MLD) process at 150 °C, using lithium tert‐butoxide and glycerol as precursors. The as‐formed LiGL coating layer is highly tunable in its thickness by simply adjusting MLD cycles and shows a good stability and outstanding ionic transport properties. The LiGL layer is found to effectively mitigate side reactions and enhance cycling stability in both symmetric cells and full cells. Specifically, the LMBs with LiGL@Li anode of 400 MLD cycles and LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathode enable a capacity retention of ≈87%, much higher than ≈35% of the cells with bare Li after 200 cycles at a charge/discharge current density of 2.1 mA cm −2 . This work paves a feasible way for practical LMBs with improved capacity and stability through applying an innovative protection layer on Li metal anodes.

25 ENERGY STORAGE↗

DOE OSTI2024

Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes in a Localized High‐Concentration Electrolyte

Abstract Lithium (Li)‐rich transition metal oxide cathodes with a cation disordered rock salt structure (DRX) are increasingly gaining popularity for advanced Li batteries as they offer high capacity and cost benefits over the commonly used layered Li transition metal oxide cathodes. However, the performance of DRX cathodes and their applications are limited by severe side reactions between the cathode and the state‐of‐the‐art carbonate‐based electrolytes at high voltage of 4.8 V, transition metal dissolution, and structural instability of the cathode particles. In this work, an advanced localized high‐concentration electrolyte (LHCE) is developed to form a stable cathode‐electrolyte interphase and mitigate structural instability of the Li 1.13 Mn 0.66 Ti 0.21 O 2 (LMTO) DRX during electrochemical cycling. Li||LMTO half cells with the LHCE demonstrate increased capacity, cycling stability, and superior rate capability compared with cells containing a conventional carbonate electrolyte. For instance, the Li||LMTO cells cycled in LHCE show a higher initial capacity of 205.2 mAh g −1 and a better capacity retention of 72.5% after 200 cycles at a current density of 20 mA g −1 than those with the conventional electrolyte (initial capacity of 187.7 mAh g −1 and capacity retention of 19.9%). This work paves the way to the development of practical DRX cathode‐based high‐energy Li batteries.

25 ENERGY STORAGE↗

DOE OSTI2023

Epitaxial growth of hexagonal BaNi O 3–δ thin films on SrTi O 3 (111) substrates

Transition metal oxides containing nickel species in oxidation states higher than 3+ often exhibit high catalytic activity, which makes them promising for applications as advanced electrocatalysts for water splitting and fuel cells. Here, we examine the structure and properties of BaNiO 3 (BNO) thin films, containing formally Ni 4+ , grown on SrTiO 3 (111) substrates using oxygen-plasma–assisted molecular beam epitaxy. X-ray diffraction and scanning transmission electron microscopy measurements reveal that BNO films have a hexagonal structure with $c$- and $a$-axes of mixed textures showing epitaxial relationships BNO (0001) ∥ SrTiO 3 (111) and BNO (10$\overline{1}$0) ∥ SrTi O 3 (111), respectively. The formation of the $a$-axis texture is dominant due to the smaller lattice mismatch with the substrate. Here, density functional theory calculations confirm that the hexagonal BNO film with the $a$-axis texture is energetically more favorable than the competing $c$-axis texture. Detailed spectroscopy data analysis indicates that hexagonal BNO films contain mixtures of Ni 2+ , Ni 3+ , and Ni 4+ species, with Ni 4+ being dominant. Our study provides insights into stabilizing Ni 4+ in complex oxides, which is important for further exploration of the potential of materials containing Ni 4+ .

36 MATERIALS SCIENCE↗

DOE OSTI2022

Alternate Synthesis Method for High-Performance Manganese Rich Cation Disordered Rocksalt Cathodes

Cation-disordered rocksalt (DRX) cathodes have recently emerged as a promising class of cobalt-free, high-capacity cathodes for lithium-ion batteries. To facilitate their commercialization, the development of scalable synthesis techniques providing control over composition and morphology is critical. To this end, a sol-gel synthesis route to prepare Mn-rich DRX cathodes with high capacities is presented here. Several compositions with varied Mn content and nominal F doping are successfully prepared using this technique. In-situ X-ray diffraction measurements demonstrate that DRX formation proceeds at moderate temperature (800 °C) through the sol-gel route, which enables intimate mixing among reactive intermediate phases that form at lower temperatures. All synthesized compositions possess cation short-range order, as evidenced by neutron pair distribution function and electron diffraction analysis. These DRX materials demonstrate promising electrochemical performance with reversible capacities up to 275 mAh g. Compared to the baseline oxide (Li 1.2 Mn 0.4 Ti 0.4 O 2 ), the Mn-rich compositions exhibit improved cycling stability, with some showing an increase in capacity upon cycling. Finally, this study demonstrates the feasibility of preparing high-capacity DRX cathodes through a sol-gel based synthesis route, which may be further optimized to provide better control over the product morphology compared to traditional synthesis methods.

25 ENERGY STORAGE↗