Suppression of Aluminum Current Collector Dissolution by Protective Ceramic Coatings for Better High‐Voltage Battery Performance

Abstract

Batteries based on cathode materials that operate at high cathode potentials, such as LiNi Mn O (LNMO), in lithium-ion batteries or graphitic carbons in dual-ion batteries suffer from anodic dissolution of the aluminum (Al) current collector in organic solvent-based electrolytes based on imide salts, such as lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). In this work, we developed a protective surface modification for the Al current collector by applying ceramic coatings of chromium nitride (Cr N) and studied the anodic Al dissolution behavior. By magnetron sputter deposition, two different coating types, which differ in their composition according to the CrN and Cr N phases, were prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and their electronic conductivity. Furthermore, the anodic dissolution behavior was studied by cyclic voltammetry and chronocoulometry measurements in two different electrolyte mixtures, that is, LiTFSI in ethyl methyl sulfone and LiTFSI in ethylene carbonate/dimethyl carbonate 1:1 (by weight). These measurements showed a remarkably reduced current density or cumulative charge during the charge process, indicating an improved anodic stability of the protected Al current collector. The coating surfaces after electrochemical treatment were characterized by means of SEM and XPS, and the presence or lack of pit formation, as well as electrolyte degradation products could be well correlated to the electrochemical results.

Perspective on Performance, Cost, and Technical Challenges for Practical Dual-Ion Batteries

“…Electrolytes which are not able to form a passivation layer on Al, such as certain imide salt-based electrolytes, may suffer from strong dissolution and pit formation of the Al current collector. 53,103 In general, a decrease of the C eff (%100%) might not only be related to SEI (re-) formation at the anode, but also to instability and degradation of the electrolyte components and of the Al current collector, as well as enhanced selfdischarge reactions, 26 in particular at a high SOC of the DIB cell. The basic electrolyte properties (ionic conductivity, viscosity, etc.)…”

“…Therefore, suitable strategies for stabilization at extreme cycling conditions (high operating voltage and high temperatures [60 C]) have to be pursued, e.g., by electrolyte additives or protective coatings. 53,103 The graphite cathode experiences significant electrode thickness changes due to the volume changes of graphite during anion intercalation/de-intercalation 45,112,113 and, therefore, the electrode's mechanical stability needs to be controlled by suitable measures, e.g., optimized binders and cell concepts. Furthermore, the electrode porosity may be tailored according to the volume changes of the graphite cathode particles during anion uptake and release.…”

Enabling High Performance Potassium‐Based Dual‐Graphite Battery Cells by Highly Concentrated Electrolytes

“…Compared to prior measurements reported in literature (e. g. for LiTFSI/Pyr 14 TFSI or LITFSI/ethyl methyl sulfone (EMS) electrolytes), both the changed cation as well as the different anion that was used may be the driving force for the decreased electrochemical stability of the ACC. Especially FSI‐based electrolytes are known to show severe Al dissolution compared to other imide‐based electrolytes (such as TFSI or FTFSI), as previously reported by Beltrop et al .…”

“…In particular, it also needs to be considered that the salt concentration will be reduced during each charge step as cations and anions are removed from the electrolyte, i. e ., an enhanced Al dissolution at the positive electrode will take place at the highest state‐of‐charge. However, if protective coatings or other current collector materials such as TiN were applied the cycling performance may be further improved . Next to this, an initial “activation process” for the C Eff is noteworthy, i. e., the C Eff increases from ≈85 % to ≈95 % over cycling (Figure b).…”

“…To overcome the drawbacks related to the ACC, different strategies could be applied. Those include the use of protective coatings or the exchange of the current collector to other materials such as TiN, which shows a much higher oxidative stability . Kravchyk et al.…”