Elucidating Lithium Alloying-Induced Degradation Evolution in High-Capacity Electrodes

Abstract

Alloy electrode materials offer high capacity in lithium-ion batteries; however, they exhibit rapid degradation resulting in particle disintegration and electrochemical performance decay. In this study, the evolution of lithium alloying-induced degradation due to electrochemomechanical interactions is examined based on a multipronged electrochemical and microstructural analysis. Copper–tin (Cu6Sn5) is chosen as an exemplary alloy electrode material. Electrodes with compositional variations were fabricated, and electrochemical performance was examined under varying conditions including voltage window, C-rate, and short- and long-term cycling. Morphology and composition analyses of pristine and cycled electrodes were conducted using micrography and spectroscopy techniques. Alloying-induced electrode microstructural evolution was probed using X-ray microtomography. The rapid capacity fading was found to be caused by mechanical degradation of the electrode. Driving the electrode to a lower potential (E ≈ 0.2 V vs Li/Li+) induced Li–Sn alloy formation and provided the characteristic large capacity; however, this led to a large volume expansion and active particle cracking and disintegration. Copper expulsion was found to be a consequence of the alloy formation; however, it was not the primary contributor to the dramatic electrochemical performance decay.

Multiscale Electrochemomechanics Interaction and Degradation Analytics of Sn Electrodes for Sodium-Ion Batteries

“…From this reconstruction, there is an apparent change in the quantity and size of Sn particles resulting from pulverization during cycling, as well as fractures in both the cross sections and three-dimensional renderings. The decrease in size of Sn particles agrees with research conducted by Juarez-Robles et al for the LIB system, which noted that increased counts of smaller particle sizes within an electrode represent the degradation of the active material by pulverization …”

“…This variation was considered acceptable due to the expected presence of subresolution voids and active materials within the regions designated as CBD . In prior work, these segmentation procedures based on variation in the grayscale values had successfully separated the different electrode components from each other depending on their attenuation. ,− As shown in Figure S1, other cycled electrodes show similar grayscale values, which enables segmentation of the Sn active material from the supporting phase regions.…”

“…The decrease in size of Sn particles agrees with research conducted by Juarez-Robles et al for the LIB system, which noted that increased counts of smaller particle sizes within an electrode represent the degradation of the active material by pulverization. 43 Phase size distributions and cumulative phase size distributions calculated using the methods of Grew et al are shown in Figure 8 for the Sn, carbon-binder domain, and macropore regions within the electrode samples. These distributions provide quantitative observations that complement the visualization provided in Figure 7.…”

Formation and Growth Mechanism of Laminar Cu6Sn5 with Ultrafine Grains on Nanocrystalline Cu by Interfacial Reaction with Sn

“…Sn/Cu interfacial reaction has been undergoing extensively studies in recent years due to its broad applications in many fields, such as electronic packaging technology, [1] battery, [2] and electrochemical reduction of CO 2 . [3] It is well known that two kinds of intermetallic compound (IMC) phases, that is, Cu 6 Sn 5 and Cu 3 Sn, generally form at Sn/Cu interface during liquidsolid reaction with scallop-like Cu 6 Sn 5 being the primary and dominant reaction product.…”

“…[29,30] Though the introduction of Cu can partially mitigate the volume expansion, it is still limited and cannot overcome mechanical degradation completely. [2] The thin laminar and fine-grained Cu 6 Sn 5 anode can further reduce internal stresses in the expansion, thereby improving the cyclic performance of the batteries. Electron beam deposition technique was used to deposit nanocolumnar structured porous thin Cu 6 Sn 5 films as the anode which exhibited a high initial discharge capacity (784.7 mA h g −1 ) with 40% Coulombic efficiency, and the Coulombic efficiency became 99.5% at 100th cycles where 300 mA h g −1 capacity was delivered by the thin film electrode.…”