Silicon-based anodes for lithium-ion batteries exhibit severe volumetric changes of the active material particles during (de-)lithiation, resulting in continuously occurring side reactions at the silicon/electrolyte interface over extended charge/discharge cycling. The thus formed and accumulating electrolyte decomposition products lead to a growth of the solid-electrolyte-interphase (SEI) on the silicon particles. This results not only in an ongoing loss of electrolyte but also in a significant swelling and impedance increase of silicon-based anodes which significantly compromises their cycle-life. In the present study, neutron depth profiling (NDP) is used post mortem as a non-destructive, highly lithium-sensitive technique to (i) quantify the amount of lithium-containing electrolyte decomposition products in silicon-graphite (SiG) electrodes (35 wt% silicon, areal capacity ∼1.7 mAh cm −2), (ii) monitor their distribution across the SiG electrode thickness, and (iii) determine the active material utilization across the electrode over 140 cycles. Hence, SiG negative electrodes are aged and characterized by means of galvanostatic cycling in SiG//LiFePO 4 pseudofull cells, using a capacitively oversized positive electrode and an electrolyte mixture consisting of 1 M LiPF 6 in EC:EMC with 5 wt% FEC. High-resolution cross-sectional SEM images and post-mortem characterization of the SiG electrodes with respect to changes in electrode mass thickness complement the analysis.
Due to its high specific capacity, silicon is a promising candidate to substitute conventional graphite as anode material in lithium-ion batteries. However, pure silicon-based anodes suffer from poor capacity retention, mainly due to a large volume change during cycling, which results in material pulverization and other side reactions. Therefore, alternative compositions with lowered silicon content and a similar working voltage as graphite are favored, e.g. silicon-graphite (SiG), as they can reduce these volume change and side reactions while maintaining a high capacity. Here, neutron depth profiling (NDP) offers the unique possibility to quantify non-destructively the lithium concentration profile over the depth of these electrodes. In this study, the (de-)intercalation phenomena during (de-)lithiation in SiG porous anodes with silicon contents ranging from 0 wt% to 20 wt% is investigated for the first time using ex situ NDP during the initial discharge at defined depths of discharge (DODs) states. These findings are complemented by a conventional electrochemical analysis of the first full cycle with a charge/discharge rate of C/20. While the specific capacity is observed to increase with higher silicon content, NDP directly reveals a homogeneous irreversible lithium accumulation within the entire electrode depth.
Progressing from graphite to silicon-based anodes for lithium-ion batteries increases the importance of a depth-resolved understanding of the reversible and irreversible processes across the thickness of the anode electrode. Considerable changes in electrode volume and mass loading upon (de-)lithiation make silicon electrodes more susceptible to continuous side reactions and to the isolation of active material particles, leading to non-uniform and accelerated electrode degradation. Here, we investigate the evolution of lithium concentration profiles across the thickness of porous silicon-graphite (SiG) electrodes (∼20 μm thickness, ∼1.7 mAh cm −2 ) with 35 wt% silicon nanoparticles during the first (de-)lithiation cycle. Using ex situ neutron depth profiling (NDP), we monitor depthand quantity-resolved (i) the solid-electrolyte-interphase (SEI) formation, (ii) the (de-)lithiation of the active materials, as well as (iii) the changes in the total lithium content as a function of the state-of-charge (SOC) and depth-of-discharge (DOD). The results provide depth-resolved information about reversible and irreversible processes occurring during the formation of SiG electrodes, and thus offer insight into the formation process of silicon-based electrodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.