Engineering topics

Yan, Yingying

Publications and source records attributed to Yan, Yingying.

4 records

DOE OSTI2021

Carbon decorated Li 3 V 2 (PO 4 ) 3 for high-rate lithium-ion batteries: Electrochemical performance and charge compensation mechanism

Fast charging and high-power delivering batteries are highly demanded in mobile electronics, electric vehicles and grid energy storage, but there are full of challenges. The star-material Li 3 V 2 (PO 4 ) 3 is demonstrated as a promising high-rate cathode material meeting the above requirements. Herein, we report the carbon decorated Li 3 V 2 (PO 4 ) 3 (LVP/C) cathode prepared via a facile method, which displays a remarkable high-rate capability and long-term cycling performance. Briefly, the prepared LVP/C delivers a high discharge capacity of 122 mAh g -1 (~93% of the theoretical capacity) at a high rate up to 20 C and a superior capacity retention of 87.1% after 1000 cycles. Importantly, by applying a combination of X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering, we clearly elucidate the structural and chemical evolutions of LVP upon various potentials and cycle numbers. Furthermore, we show unambiguous spectroscopic evidences that the evolution of the hybridization strength between V and O in LVP/C as a consequence of lithiation/delithiation is highly reversible both in the bulk and on the surface during the discharge-charge processes even over extended cycles, which should be responsible for the remarkable electrochemical performance of LVP/C. Our present study provides not only an effective synthesis strategy but also deeper insights into the surface and bulk electrochemical reaction mechanism of LVP, which should be beneficial for the further design of high-performance LVP electrode materials.

25 ENERGY STORAGE↗

DOE OSTI2019

Quantification of Anionic Redox Chemistry in a Prototype Na-Rich Layered Oxide

Harnessing anionic redox reactions is of prime importance for boosting the capacity of sodium-ion batteries (NIBs). However, quantifying the cyclability of anionic redox reactions is still challenging. Herein, we conduct a qualitative and quantitative investigation of the cationic and anionic redox reactions of a prototype Na-rich layered oxide, namely, Na 3 RuO 4 , by a combination of bulk-sensitive X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering. We unequivocally reveal that both Ru cations and oxygen anions are involved in the charge compensation process of Na 3 RuO 4 . Ru redox is highly reversible over extended electrochemical cycles, while the cyclability of lattice oxygen redox gradually decreases with the retention of only 36% after 30 cycles, which is mainly responsible for the capacity fading of Na 3 RuO 4 . Finally, our findings provide deeper insights into the complex oxygen redox mechanism, which plays a decisive role for designing high-energy Na-rich electrode materials for NIBs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Elucidation of Anionic and Cationic Redox Reactions in a Prototype Sodium-Layered Oxide Cathode

The ever-increasing demand for large-scale energy storage has driven the prosperous investigation of sodium-ion batteries (NIBs). As a promising cathode candidate for NIBs, P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 (NaNMO), a prototype sodium-layered oxide, has attracted extensive attention because of its high operating voltage and high capacity density. Although its electrochemical properties have been extensively investigated, the fundamental charge compensation mechanism, that is, the cationic and anionic redox reactions, is still elusive. In this report, we have systematically investigated the transition metal and oxygen redox reactions of NaNMO nanoflakes using bulk-sensitive soft X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering from an atomic-level view. We show that the bulk Mn 3+ /Mn 4+ redox couple emerges from the first discharge process with the increment of inactive Mn 3+ upon cycling, which may have a negative effect on the cyclability. In contrast, the bulk Ni redox mainly stems from the Ni 2+ /Ni 3+ redox couple, in contrast to the conventional wisdom of the Ni 2+ /Ni 4+ redox couple. The quantitative analysis provides unambiguous evidence for the continuous reduction of the average valence state of Mn and Ni over extended cycles, leading to the voltage fading. In addition, we reveal that the oxygen anions also participate in the charge compensation process mainly through irreversible oxygen release rather than reversible lattice oxygen redox. Such understanding is vital for the precise design and optimization of NaNMO electrodes for rechargeable NIBs with outstanding performance.

25 ENERGY STORAGE↗

DOE OSTI2019

Deciphering the Reaction Mechanism of Lithium–Sulfur Batteries by In Situ/Operando Synchrotron-Based Characterization Techniques

Lithium-sulfur (Li-S) batteries have received extensive attention as one of the most promising next-generation energy storage systems, mainly because of their high theoretical energy density and low cost. Yet, the practical application of Li-S batteries has been hindered by technical obstacles arising from the polysulfide shuttle effect and poor electronic conductivity of sulfur and discharge products. Therefore, it is of critical significance for understanding the underlying reaction mechanism of Li-S batteries to circumvent these problems and improve the overall battery performance. Advanced characterization techniques, especially synchrotron-based X-ray techniques, have been widely applied to the mechanistic understanding of Li-S batteries. Specifically, in situ/operando synchrotron-based techniques allows chemical and structural evolution to be directly observed under real operation conditions. Here, current progress in the understanding of the operating principles of Li-S batteries based on in situ/operando synchrotron-based techniques, including X-ray absorption spectroscopy, X-ray diffraction, and X-ray microscopy, is reviewed. The aim of this progress report is to provide a comprehensive treatise on in situ/operando synchrotron-based techniques for mechanism understanding of Li-S batteries, and thereby provide guidance for optimizing their overall electrochemical performances.

25 ENERGY STORAGE↗