Interfacial Phenomena/Capacities Beyond Conversion Reaction Occurring in Nano‐sized Transition‐Metal‐Oxide‐Based Negative Electrodes in Lithium‐Ion Batteries: A Review

Abstract

Nano‐sized transition‐metal oxides are of topical interest in current research towards high‐capacity negative electrodes for rechargeable lithium‐ion batteries. Schematically, an interaction with Li+ through a conversion reaction is commonly accepted. However, experimentally observed capacities often significantly exceed the correlating theoretical quantity of transferred charge carriers based on the conversion reaction. The origin of the additional capacity is under intense debate, although the indispensability of interfacial phenomena and material dimensions in the nanometer regime for concrete explanations are widely observed. Scenarios associated with additional capacities are electrode/electrolyte interphases (solid‐electrolyte interphase, polymer/gel‐like film), additional Li+ accommodation through reaction with grain boundary phases in nanostructures, interfacial Li+ accommodation along with charge separation at phase boundaries, or additional Li+ uptake in unique structural architectures with high specific surface areas that often exhibit an extensive hierarchical meso‐ and/or nanoporous system. In addition, interfacial phenomena are strongly related to battery safety, and hence a topic of highest relevance. As the number of related articles has become so intense, this Review article provides an up‐to‐date summary, and a first attempt is made to systematically classify capacity profiles of nano‐sized transition‐metal oxides that exhibit additional capacities beyond the theoretical value based on the concept of conversion reaction.

Reversible Cu4O3 Phase Formation in CuO Nanoplate Anodes for High Capacity and High Coulombic Efficiency

“…From the first charge‐discharge profiles in Figure b for both C/2 and 1C rates, it is seen that CuO nanoplates showed an initial discharge capacity of 1211 and 1176 mAh/g. The experimental capacity more than theoretical is quite common for conversion based materials and the origin of same is still under debate. The capacity far beyond the theoretical value for metal oxide anodes is mostly attributed to catalytic effect of CuO nanostructures resulting in formation of reversible gel‐like/SEI film .…”

The Role of Pilot Lines in Bridging the Gap Between Fundamental Research and Industrial Production for Lithium‐Ion Battery Cells Relevant to Sustainable Electromobility: A Review

“…Compared with pilot or industry scale, the electrolyte is often applied in excess for small lab‐made coin cells, which might have impact on the subsequent SEI formation that is based on electrolyte degradation. [ 181 ] Please note that excess electrolyte does not support lithium‐ion storage capacity, but adds weight of inactive components to the cell, which leads to a reduction in energy density. [ 182 ] Hence, especially for application‐oriented cells, an optimized amount of electrolyte regarding energy density should be determined (although varied amounts of electrolyte might be optimal for other quality parameters).…”

“…Advantageously, SEI formation for such electrodes can be controlled during the first cycle, in contrast to, for instance, transition metal oxide negative anodes, where SEI formation (and alteration) is supposed to take place over several cycles. [ 181,189 ] To reduce production costs, the preformation step should be optimized toward the quick formation of a homogenous SEI that exhibits minimal lithium consumption with sufficiently high stability but is at the same time flexible enough to accommodate electrode's swelling and shrinkage during repetitive lithium uptake and release. [ 22 ] Please note that the phrase “solid−electrolyte interphase” was introduced by Peled.…”

Production Research as Key Factor for Successful Establishment of Battery Production on the Example of Large‐Scale Automotive Cells Containing Nickel‐Rich LiNi0.8Mn0.1Co0.1O2 Electrodes

“…The resulting decomposition products can precipitate on the negative electrode and form a 3D interphase, denoted as the solid electrolyte interphase (SEI) that was found to be indispensable for proper battery operation. For electrodes based on graphite, it is assumed that SEI formation predominantly takes place at the first cycle and hence provides the possibility to be controlled during the first cycle . During the preformation process, the electrolyte filling hole is still open for large‐format, hard‐case cells, to allow for evaporation of gaseous byproducts in the process of SEI formation, after which the cell is hermetically sealed.…”