Towards the realistic silicon/carbon composite for Li-ion secondary battery anode

Abstract

A practical and inexpensive method for producing Si/C composite as ready-to-use active material for Li-ion battery anode has been developed. Three-component powders (<63 µm) were synthesized by embedding micro-sized silicon (8–24 wt%) and synthetic battery-grade graphite (60–75 wt%) in a pitch-derived carbon matrix. The procedure consisted of short mechanical milling of silicon with toluene/pitch suspension followed by mixing with graphite and final heat-treatment at 1,100 °C. X-ray diffraction was applied for determining the structural characteristics of the composite and impurities present. A series of anodes were prepared by using CMC and PVDF binder. The dispersion of silicon particles in the carbon matrix and spreading of the binder into the anodic film were monitored using the SEM–EDX technique. Lithium insertion/deinsertion performance was assessed from the galvanostatic charge–discharge characteristics using a Si/C–lithium two-electrode cell. Embedding silicon in well conductive pitch coke as well as reducing the content of carbon black as percolator allowed the first cycle irreversible capacity to be decreased to 90 mAh g−1. An initial reversible capacity of 620 mAh g−1 for 12 wt% of Si in the composite, with average capacity decay of 0.3 % per cycle, was achieved thanks to a specific composite structure as well as profitable physicochemical properties of the CMC binder. Intensive press-rolling of the anodic film allowed the packing density to be increased up to 1.35 g cm−3 (9.5 mg cm−2 at thickness of 70 µm) and, as a result, an outstanding volumetric capacity up to 670 mAh cm−3 could be achieved, without changing the cycling properties.