Investigation of silicon nanoparticle size on specific capacity of Li-ion battery via electrochemical impedance spectroscopy

Silicon is an attractive anode material in Li-ion batteries due to its high specific capacity, but the stability of silicon limits its industrial-scale application. To avoid this, the particle size reduction below 150 nm (critical radius) showed improved reactivity and cycle life but still below the benchmark for industrial-scale application. In this work, we applied the impedance analysis to understand the physicochemical processes occurring at the anode (Si electrode)/electrolyte interface. For this, we fabricated three samples of Si anode with 50 nm, 150 nm, and a mixture of 50 and 150 nm particles in equal ratios. The small particle size sample showed low charge transfer resistance, showing the highest activity towards lithiation and delithiation reaction, but high SEI formation hampers the overall capacity of the device. On the other hand, the 150 nm sample showed the low SEI formation but high charge transfer resistance due to low surface area. Finally, the mixed sample showed the compromise between the charge transfer reaction and SEI formation showing the lowest polarisation resistance after 50 cycles. Thus, the mixed sample having the advantage of intermediate surface area and intermediate SEI formation gives the highest capacity.