Effect and Progress of the Amorphization Process for Microscale Silicon Particles under Partial Lithiation as Active Material in Lithium-Ion Batteries

Abstract

Microscale silicon particles in lithium-ion battery anodes undergo large volume changes during (de)lithiation, resulting in particle pulverization and surface area increase concomitant with a continuous growth of the solid-electrolyte-interphase. One approach to overcome these phenomena is to operate the silicon anode under capacity-limited conditions (i.e., with partial capacity utilization). Since crystalline silicon is irreversibly transformed into amorphous phases upon lithiation, the purpose of the partial capacity utilization is to maintain a crystalline phase and thus prevent particle disintegration. Here, we investigate the amorphization process of micro-sized silicon particles in a silicon-rich anode (70 wt% silicon) over extended charge/discharge cycling in half-cells with a lithium reference electrode, varying the lower cutoff potential of the Si electrode. While the capacity of Si electrodes after formation remain constant for lithiation cutoffs of ≥170 mV vs Li+/Li, their capacity continuously increases over cycling for cutoffs of <170 mV vs Li+/Li, implying an ongoing amorphization of the crystalline phase. To quantify the ratio of the amorphous phase fraction over cycling, we employed an in-situ XRD method, utilizing the copper reflex of the current collector as internal standard. This allowed to determine the extent of amorphization over the course of cycling depending on the lithiation potentials.

Partially Lithiated Microscale Silicon Particles as Anode Material for High‐Energy Solid‐State Lithium‐Ion Batteries

“…From the second cycle, a small peak at 0.27 V versus Li/Li þ is visible in the cyclic voltammogram of the capacity-limited cell. This characteristic peak for the lithiation of a-Si [26,28,31,34] confirms that from the second cycle a-Si is lithiated in contrast to c-Si in the first cycle. Since the lithium ions reach the edge regions of the μm-Si particles and the grain boundaries in the particles best, no further lithiation of c-Si in the inner parts of the μm-Si particles takes place in the following cycles.…”

“…[21] Therefore, another concept is to only use part of the silicon capacity during cycling. [21][22][23][24][25][26] In this way, the volume change of and hence the mechanical stress in the silicon anode are reduced while still achieving higher gravimetric and volumetric capacities compared to the conventionally used graphite anode (339 mAh g À1 , 747 mAh cm À3 [4] ). [21,23,26] Applying silicon anodes in SSBs opens another approach to maintain the integrity of the anode by using high stack DOI: 10.1002/ente.202201330…”

“…These amorphous silicon domains are then cycled reversibly with reduced overall volume changes. [24,26] 2. Results and Discussion…”

“…[ 21 ] Therefore, another concept is to only use part of the silicon capacity during cycling. [ 21–26 ] In this way, the volume change of and hence the mechanical stress in the silicon anode are reduced while still achieving higher gravimetric and volumetric capacities compared to the conventionally used graphite anode (339 mAh g −1 , 747 mAh cm −3 [ 4 ] ). [ 21,23,26 ]…”

Improving Cycle Life of Silicon-Dominant Anodes Based on Microscale Silicon Particles under Partial Lithiation

“…Silicon is one of the most promising anode materials for high energy density LIB cells due to the high electrochemical capacity of Li 15 Si 4 with 3579 mAh g −1 , which is about ten times the capacity of graphite [1,2]. However, so far, the application of silicon in LIB anodes has been limited because of the huge volume expansion of Si during lithiation, which can reach up to 300% and can be ascribed to the amorphization of Si and conversion into a Li x Si y alloy with high lithium content [3][4][5]. In general, the large volume change of Si particles during lithiation and delithiation leads to three previously described challenges [4] that need to be solved for a broad market introduction of silicon-dominate anodes.…”