Welcome to WordPress. This is your first post. Edit or delete it, then start writing!
In the OPINCHARGE Scientific Publications series, we highlight research that deepens our understanding of battery materials and the processes that determine their performance and lifetime. This study investigates a major challenge for high-capacity silicon-based anodes — how lithium becomes trapped during cycling and how electrolyte chemistry can help prevent it.
The publication explores silicon–graphite (Si/Gr) composite anodes using solid-state nuclear magnetic resonance (NMR) spectroscopy combined with electrochemical analysis, comparing conventional EC-based and FEC-containing electrolytes.
Read the publication: https://zenodo.org/records/19729337
Silicon can store substantially more lithium than graphite, making it an attractive material for increasing the energy density of lithium-ion batteries. Combining silicon with graphite offers a promising route towards practical high-capacity anodes.
However, silicon undergoes large volume changes during lithiation and delithiation. Over repeated cycles, this can damage the electrode and its solid-electrolyte interphase (SEI) and cause lithium to become trapped in inactive silicon phases — gradually reducing the amount of lithium available for reversible battery operation.
The researchers used advanced solid-state NMR techniques to investigate lithium environments within the silicon–graphite electrode and its SEI.
A key focus was the difference between an EC-based electrolyte and one containing fluoroethylene carbonate (FEC). The analysis revealed substantially different SEI structures.
The FEC-based electrolyte produced an SEI containing a significant LiF-rich component, while the EC-based system formed a predominantly organic SEI. These structural differences influence how lithium moves across the SEI and how effectively the silicon remains protected during repeated volume changes.
The difference between the two electrolyte systems became particularly clear over longer cycling.
With the EC-based electrolyte, capacity began to decline after approximately 20 cycles. By cycle 50, discharge capacity had fallen below 750 mAh g⁻¹, compared with 1119 mAh g⁻¹ in the second cycle.
In contrast, the FEC-based electrolyte maintained stable performance, retaining 985 mAh g⁻¹ after 50 cycles, close to its second-cycle value of 1017 mAh g⁻¹.
NMR provided important insight into what was happening inside the degrading electrode.
After extended cycling with the EC-based electrolyte, the researchers detected an additional lithium environment associated with lithium trapped within the silicon. This trapped lithium is no longer fully participating in reversible charging and discharging and therefore contributes to capacity loss.
In the FEC-based system, no comparable signal from trapped Li₂Si-like environments was observed, consistent with its much better capacity retention. The study reports this as the first direct solid-state NMR evidence of Li⁺ trapping in silicon-based composite anodes.
The results demonstrate that the electrolyte does much more than simply transport lithium ions. It directly influences the chemistry and mechanical properties of the SEI — and therefore how well the silicon survives repeated expansion and contraction.
The LiF-rich SEI formed with FEC provides greater mechanical stability and helps suppress the accumulation of inactive lithium–silicon phases. By contrast, degradation in the EC-based system was linked specifically to the silicon component, while the graphite contribution remained largely stable.
Understanding exactly where capacity is lost is essential for designing better silicon-based batteries.
By connecting SEI chemistry, lithium transport, lithium trapping and electrochemical performance, this research provides new insight into why some electrolyte formulations protect silicon–graphite anodes more effectively than others.
The findings can support the development of more stable electrolytes and interfaces for high-capacity silicon-based lithium-ion batteries, helping translate silicon’s high theoretical capacity into longer-lasting real-world battery performance.
