Alpacali

This study provides comprehensive materials characterization of niobium (Nb) hydrides formed in Nb thin films as a function of fluoride chemical treatments that are commonly employed in the fabrication of superconducting qubits. This work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

Abstract

Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride-based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary-ion mass spectrometry, X-ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb₂O_5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power-independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two-level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

Graphdiyne Supercapacitors

In article number 2301118, Guang Feng and co-workers develop a multiscale modeling method to investigate the effect of pore topology and electrode metallicity on supercapacitor performance using porous graphdiynes. The reported simulations quantitively unveil the effect of image charges on energy storage in nanopores. Based on this understanding, they predict that doped porous graphdiynes can deliver both outstanding energy and power densities.

An “all-in-one” nitrocellulose (NC)/LiFSI electrolyte is developed to realize highly reversible Li deposition/dissolution. This unique electrolyte enables Li metal batteries to demonstrate remarkable electrochemical performance, i.e., stable operation under high current density up to 10 mA cm⁻². Moreover, Li|LiFePO₄ (LFP) pouch cells with 2m FM+2% NC electrolytes achieve almost 100% capacity retention after 210 cycles under a limited environment.

Abstract

Uncontrollable lithium dendrite growth and severe Li/electrolyte side reactions under high operating current densities seriously hinder the development of high-performance Li metal batteries (LMBs). To address the aforementioned critical issues, spherical Li nuclei are designed via an “all-in-one” nitrocellulose (NC)/LiFSI electrolyte to achieve high-energy/power-density and long-cycle LMBs. First, the synergistic effect of LiFSI induced LiF-rich interface and the nitro group in the NC scaffold promote uniform Li nucleation, resulting in spherical nuclei morphology instead of dendritic even under high current densities. Moreover, NC exhibits strong adsorption energy on the electrode surface, which facilitates the formation of an organic protection layer to suppress side reactions, which enables highly reversible Li cycling, even in a lean-electrolyte environment. With the assistance of the unique interphase, the Li|Li symmetric cells using NC/LiFSI electrolyte can stably run at a high current density of 10 mA cm^-2. Moreover, the assembled Li|LiFePO₄ pouch cell achieves excellent cycling stability of 210 cycles with 100% capacity retention. This finding provides a new strategy relying on electrolyte engineering to achieve high-energy/power-density and long-cycling-life LMBs.

Publication date: October 2021

Source: Energy Storage Materials, Volume 41

Author(s): Asif Mahmood, Ziwen Yuan, Xiao Sui, Muhammad Adil Riaz, Zixun Yu, Chang Liu, Junsheng Chen, Cheng Wang, Shenlong Zhao, Nasir Mahmood, Zengxia Pei, Li Wei, Yuan Chen