Affiliation:
1. Battery and Electrochemistry Laboratory (BELLA) Institute of Nanotechnology Karlsruhe Institute of Technology (KIT) Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany
2. WMG The University of Warwick Coventry CV4 7AL United Kingdom
3. BASF SE Carl-Bosch-Str. 38 67056 Ludwigshafen Germany
4. Institute of Physical Chemistry & Center for Materials Research (ZfM/LaMa) Justus-Liebig-University Giessen Heinrich-Buff-Ring 17 35392 Giessen Germany
Abstract
AbstractAs global energy storage demand increases, sodium‐ion batteries are often considered as an alternative to lithium‐ion batteries. Hexacyanoferrate cathodes, commonly referred to as Prussian blue analogues (PBAs), are of particular interest due their low‐cost synthesis and promising electrochemical response. However, because they consist of ~50 wt% cyanide anions, a possible release of highly toxic cyanide gases poses a significant safety risk. Previously, we observed the evolution of (CN)2 during cycling via differential electrochemical mass spectrometry (DEMS), but were unable to determine a root cause or mechanism. In this work, we present a systematical investigation of the gas evolution of Prussian white (PW) with different water content via DEMS. While H2 is the main gas detected, especially in hydrated PW and during overcharge (4.6 V vs. Na+/Na), the evolution of CO2 and (CN)2 depends on the electrolyte conductive salt. The use of oxidative NaClO4 instead of NaPF6 is the leading cause for the formation of (CN)2. Mass spectrometric evidence of trace amounts of HCN is also found, but to a much lower extent than (CN)2, which is the dominant safety risk when using NaClO4‐containing electrolyte, which despite being a good model salt, is not a viable option for commercial applications.
Funder
BASF
Deutsche Forschungsgemeinschaft
Horizon 2020 Framework Programme
Royal Society
Subject
Electrochemistry,Electrical and Electronic Engineering,Energy Engineering and Power Technology