All-Aqueous Directed Assembly Strategy for Forming High-Capacity, Stable Silicon/Carbon Anodes for Lithium-Ion Batteries

Silicon (Si) particles have emerged as a promising active material for next-generation lithium-ion battery anodes. However, the large volume changes during lithiation/delithiation cycles result in fracture and pulverization of Si, leading to rapid fading of performance. Here, we report a simple, all-aqueous, directed assembly-based strategy to fabricate Si-based anodes that show capacity and capacity retention that are comparable or better than other more complex methods for forming anodes. We use a cationic surfactant, cetyltrimethylammonium bromide (CTAB), to stabilize Si nanoparticles (SiNPs) in water. This suspension is added to an aqueous suspension of para-amino benzoic acid-terminated carbon black (CB), pH 7. Charge interactions cause the well-dispersed SiNP to bind to the CB, allowing most of the SiNP to be available for lithiation and charge transfer. The CB forms a conducting network when the suspension pH is lowered. The dried SiNP/CTAB/CB anode exhibits a capacity of 1580 mAh g(-1) and efficiency of 97.3% after SO cycles at a rate of 0.1C, and stable performance at cycling rates up to SC. The directed spatial organization of the SiNP and CB using straightforward colloidal principles allows good contact between the well-dispersed active material and the electrically conducting network. The pore space in the CB network accommodates volume changes in the SiNPs. When CTAB is not used, the SiNPs form aggregates in the suspension, and do not contact the CB effectively. Therefore, the electrochemical performance of the SiNP/CB anode is inferior to that of the SiNP/CTAB/CB anode. This aqueous-based, room temperature, directed assembly technique is a new, but simple, low-cost scalable method to fabricate stable Si-based anodes for lithium-ion batteries with performance characteristics that match those made by other more sophisticated techniques.