Silicon-carbon composites (Si/C) are considered as one of the most promising candidates for anode active materials in high energy lithium-ion batteries. This research activity aims to develop scalable manufacturing processes of novel Si/C-based anode materials for lithium-ion batteries. To achieve anodic active material with high cycling stability, silicon nanoparticles are encapsulated into a protective carbon layer. The encapsulation process is done via a low-cost deposition and thermally activated transformation of an abundant and sustainable carbon source. For slurry production, silicon-carbon composites are mixed with a conductive agent and a suitable binder to form a water-based slurry. Standard electrochemical testing is performed in 2-electrode (coin cells) and 3-electrode (EL-Cell PAT-Cell) arrangements.
Si/C-based electrodes show a high initial capacity of up to 3300 mAh/gSi in half-cells. To improve cycling performance, several binders for aqueous slurries were evaluated. It was found that the choice of the binder has a tremendous impact on capacity retention during cycling, ranging from full capacity loss after < 20 cycles to capacity retention > 1500 mAh/gSi over several hundred cycles. The high specific capacities and high cycling stability of the battery cells presented in this work, show that silicon anode-related challenges such as volume expansion, particle fragmentation and lithium losses through continuous SEI formation can be controlled.
Full-cells with electrochemically pre-lithiated Si/C anodes and LiNi0.6Co0.2Mn0.2O2 (NMC 622) cathodes show high initial coulombic efficiencies of > 85% during formation and exceed 99,9% after the first charge and discharge cycle. C-rate tests were performed at 0.5C, 1C, 2C and 4C, achieving > 85% state of charge during constant current (CC) phase at 4C, as shown in the attachment.
Attachment: cell voltage vs. state of charge of pre-lithiated Si/C NMC 622 battery full cell at 0.5C, 1C, 2C and 4C