Methods for accurate and rapid determination of purity of battery-grade silicon

Abstract

With high lithiation capacity, silicon is set to replace graphite as the active anode material in the next generation of lithium ion batteries. Si produced from various routes can contain proportions of oxide, both as a surface layer and in the bulk material. Accurate determination of Si purity is vital for anode formulation and performance testing. While there are many methods used for measuring the purity of Si, most of them are laborious, time-/resource-intensive or do not account for surface and bulk compositions. Here, we present two fast, simple and calibrated methods for the accurate determination of Si purity by using the thermogravimetric method or X-ray diffraction. The results show that by simply measuring pure Si and pure silica samples, a theoretical calibration curve can be developed for both methods, which shows excellent predictability of Si purity in real samples. Furthermore, we show that the thermal analysis was able to account for the dehydration of silica that was previously not noticed. With the increasing demand for Si for battery anodes and wider applications, this work represents a significant advance in rapidly and accurately quantifying Si purity.