Thin‐Film Electrode Design for High Volumetric Electrochemical Performance Using Metal Sputtering‐Combined Ligand Exchange Layer‐by‐Layer Assembly

Abstract

The design of electrode with high volumetric performance in energy storages still remains as a significant challenge because it simultaneously requires a high packing density of active materials for high energy density and a conductive porous structure for facile charge transfer. Here, a novel assembly process is introduced for thin-film anodes for Li-ion battery with a high volumetric energy density and rate performance by systematically controlling the interfacial structure between metal-oxide nanoparticles and/ or metal clusters. For this study, oleic-acid-stabilized Fe 3 O 4 nanoparticles are layer-by-layer assembled with small organic molecules through a ligand exchange reaction, which enable a high packing density. During layer-by-layer deposition, periodic Pt-sputtering onto multilayers significantly reduces the internal resistance of the electrodes but maintains the nanopores formed among the nanoparticles. The resulting anode exhibits an extremely high volumetric capacity of ≈3195 mA h cm −3 and rate performance, which are far superior to that reported for Li-ion battery anodes. Additionally, all components in the electrodes have a stable covalent bond network between the metal atom and the amine group of organic molecule linker, allowing good cycle retention. This approach can be widely applied to the fabrication of various nanoparticle-based electrodes, enabling maximum charge storage performance in confined volumes.

Nanoparticle‐Based Electrodes with High Charge Transfer Efficiency through Ligand Exchange Layer‐by‐Layer Assembly

“…Recently, Cho and co-workers reported novel types of LbL selfassembly for functional NPs based on the in situ ligand exchange reaction between the hydrophobic ligands of NP and amine (NH 2 )-functionalized organic linkers in organic media. [50][51][52][53][54][55][56][57]104] In this process, the high affinity of amine moieties to metal surfaces (via covalent bonds) [105][106][107][108] effectively induces the replacement of insulating hydrophobic ligands of NPs with hydrophilic incoming ligands (i.e., HN 2 -functionalized dendrimers), showing dramatic changes in the surface chemistry (Figure 3a). As the deposition time of the NH 2 -dendrimer layer increased, the characteristic peaks originating from the hydrophobic ligand (i.e., PA) gradually disappeared, and new peaks arising from the hydrophilic moiety NH 2 were observed, indicating the complete removal of insulating ligands from the NPs.…”

“…[55,[128][129][130][131][132] That is, by simply increasing the bilayer number (n), the thickness and mass of NP-based multilayers are regularly increased without significant NP agglomeration, which can be expanded up to a micrometer-scale thickness irrespective of substrate size and shape ( Figure 3e). [104] The scalability of this approach is highly advantageous in achieving high volumetric and areal energy densities, which are considered valuable performance factors in practical and commercial energy storage systems. [133] Additionally, this approach can be easily applied to automatic spray or roll-to-roll LbL deposition processes, [134,135] enabling fast and large-scale fabrication of flexible or wearable energy electronics.…”

“…These possibilities were systematically demonstrated by the ligand‐engineering‐ (or ligand exchange reaction)‐induced LbL assembly of hydrophobic Fe 3 O 4 NPs (i.e., stabilized by OA) with consecutive insertion of metal (platinum, Pt) NPs using flash sputtering processes ( Figure a). [ 104 ] In this case, the bulky OA ligands of Fe 3 O 4 NPs were effectively replaced by NH 2 ‐functionalized small organic ligands (i.e., tris(2‐aminoethyl)amine, TREN)) during LE‐LbL assembly in organic media. This approach allowed dense packing of Fe 3 O 4 NPs in the formed Fe 3 O 4 NP/TREN multilayers (mass density of ≈3.5 vs ≈5.2 g cm −3 for the bulk) because of the absence of electrostatic repulsion between neighboring Fe 3 O 4 NPs as well as insulating polymer binders, indicating a significant reduction in interparticle distance that can facilitate electron transport between adjacent NPs.…”

Interfacial Design and Assembly for Flexible Energy Electrodes with Highly Efficient Energy Harvesting, Conversion, and Storage

“…In the typical sputtering process, continuously deposited metal atoms on the surface of the substrate simultaneously form nanoclusters through the nucleation and growth mechanism. [80][81][82] Such enlarged or aggregated metal nanoclusters can create well-connected conducting networks that act as electron pathways. However, at the same time, this growth mechanism of metal clusters can block the pores of the substrate, thereby significantly decreasing the ion penetration kinetics into the inner region of the porous material-based electrodes.…”

Layer‐by‐Layer Self‐Assembled Nanostructured Electrodes for Lithium‐Ion Batteries

“…To further optimize electrode performances of LbL self‐assembled LIBs, Cho group purposed the use of small molecules rather than the conventional high‐molecular‐weight polyelectrolytes to facilitate electron transport by minimizing the spacing between the electron conducting phase and the Li + intercalating phase. [ 27 ] However, the small molecule has been only demonstrated to assemble particles smaller than 10 nm [ 27–28 ] which is significantly smaller than the particle size of traditional battery materials (ranging from hundreds of nanometers to micrometers). Such small particle size is known to result in charge storage in a pseudocapacitive manner rather than the intercalative manner for traditional battery materials.…”