Silicon Nanoparticles Confined in Thin Carbon Network: The Free-Standing Anode of Lithium Ion Batteries with High Performance and Easy Recyclability

Si is a promising anode candidate of lithium ion batteries with exceptionally high theoretical capacity, however, has fatal issues including large volume expansion-induced instability and poor electrical conduction during the charging/discharging process. The stabilization of the Si anode through buffering its volume expansion meanwhile maintaining its structure/morphology integrity is currently the major strategy to overcome the issues. In this work, commercially available Si nanoparticles were confined within the network of thin graphitized carbon layer (from carbonized polydopamine, named as C-PDA) through a straightforward route, forming freestanding flexible and robust mat that can be used as anode directly. Excellent electrochemical performance, i.e., high cycled capacity (about 1750 mAh g−1 after 100 cycles at 100 mA g−1) and rate capacity (around 1600 ∼ 1700, 1200 ∼ 1300, 800 ∼ 900 and 600 ∼ 700 mAh g−1 at 200, 500, 1000 and 2000 mA g−1, respectively), was achieved after optimization due to the C-PDA thin layer that creates electron conduction pathway and the interconnected channels within the C-PDA network that offers free diffusion of electrolyte solution thus smooth transportation of Li ions. Unlike the common sense of accommodating/buffering the volume expansion of Si by carbon phase, the Si NPs collapse into smaller ones upon lithiation at the initial stage and are still trapped within the respective C-PDA frames. The C-PDA network acts as interlock to stabilize the collapsed Si, leading to good electrochemical properties. Recyclability of the used anode was also investigated in this work, implying that taking the advantage of its freestanding nature with no binder and conductive agent used, the used Si NPs with smaller size and maintained crystallinity can be easily recycled through simple solvent soaking after discharge/charge cycling. This work offers a unique and useful strategy of utilizing Si materials in an environment friendly and cost-effective way for energy storage application.