Electrochemical fabrication and characterization of Cu/Cu₂O multi-layered micro and nanorods in Li-ion batteries

Abstract

Electrodes composed of freestanding nano- and microrods composed of stacked layers of copper and cuprous oxide have been fabricated using a straightforward one-step template-assisted pulsed galvanostatic electrodeposition approach. The approach provided precise control of the thickness of each individual layer of the high-aspect-ratio rods as was verified by SEM, EDS, XRD, TEM and EELS measurements. Rods with diameters of 80, 200 and 1000 nm were deposited and the influence of the template pore size on the structure and electrochemical performance of the conversion reaction based electrodes in lithium-ion batteries was investigated. The multi-layered Cu2O/Cu nano- and microrod electrodes exhibited a potential window of more than 2 V, which was ascribed to the presence of a distribution of Cu2O (and Cu, respectively) nanoparticles with different sizes and redox potentials. As approximately the same areal capacity was obtained independent of the diameter of the multi-layered rods the results demonstrate the presence of an electroactive Cu2O layer with a thickness defined by the time domain of the measurements. It is also demonstrated that while the areal capacity of the electrodes decreased dramatically when the scan rate was increased from 0.1 to 2 mV s(-1), the capacity remained practically constant when the scan rate was further increased to 100 mV s(-1). This behaviour can be explained by assuming that the capacity is limited by the lithium ion diffusion rate though the Cu2O layer generated during the oxidation step. The electrochemical performance of present type of 3-D multi-layered rods provides new insights into the lithiation and delithiation reactions taking place for conversion reaction materials such as Cu2O.

Lithium Trapping in Microbatteries Based on Lithium‐ and Cu2O‐Coated Copper Nanorods

“…As this amount corresponds to a deposition charge of 1.39 C while the experimental deposition charge was 1.16 C, it is clear that there also must have been lithium ions in the sample mainly due to the Cu 2 O conversion reaction (i. e. Cu 2 O + 2 Li + + 2 e − =2 Cu + Li 2 O). Since the total reduction charge for the voltammetric scan and the potential step was 2.05 C, the extra reduction charge, which mainly was associated with the large reduction peak at about 0.8 V vs. Li + /Li, was about 0.89 C. The latter is very close to the 0.9 C expected for a native Cu 2 O coating on a 50 cm 2 Cu substrate since the capacity for the Cu 2 O conversion reaction has been found to be about 5 μAh cm −2 . It can therefore be concluded that the peak at about 0.8 V vs. Li + /Li in Figure A mainly was due to the reduction of Cu 2 O.…”

“…The Li electroplating was performed on 3D Cu substrates,, featuring Cu nanorods coated with a thin native Cu 2 O oxide layer. In Figure , which shows the two‐step Li electrodeposition approach, it is seen that the potential initially was scanned from the OCP of 3.1 to −0.25 V vs .…”

“…Since the total reduction charge for the voltammetric scan and the potential step was 2.05 C, the extra reduction charge, which mainly was associated with the large reduction peak at about 0.8 V vs. Li + /Li, was about 0.89 C. The latter is very close to the 0.9 C expected for a native Cu 2 O coating on a 50 cm 2 Cu substrate since the capacity for the Cu 2 O conversion reaction has been found to be about 5 mAh cm À2 . [15] It can therefore be concluded that the peak at about 0.8 V vs. Li + /Li in Figure 1A mainly was due to the reduction of Cu 2 O. Based on the ICP-AES results it can likewise be deduced that about 20% of the Li 2 O formed in the conversion reaction failed to undergo reduction to Li during the lithium deposition step.…”

“…Based on the ICP‐AES results it can likewise be deduced that about 20% of the Li 2 O formed in the conversion reaction failed to undergo reduction to Li during the lithium deposition step. The latter can be explained by the formation of a passivating layer of Cu + Li 2 O on top of the remaining Cu 2 O in analogy with previous findings ,…”

“…The Li reference electrode was used to enable the measurement of the individual potentials of the Li/Cu and Cu 2 O /Cu electrodes and the Cu 2 O /Cu electrode was designed to be the capacity limiting electrode as the capacities of the Cu 2 O /Cu and Li/Cu electrodes were set to 0.9 and 1.0 C, respectively. It should also be noted that the Cu 2 O /Cu electrodes have been found, to exhibit a very stable cycling performance during hundreds of cycles. This means that the cycling stability of the cell rather should have been limited by the Li/Cu electrode.…”