Tailored SiNx-Based Anode Processing for Li-Ion Batteries
Authors: Bapat Shalmali , Oezcan Fatih , Kilian Stefan Oliver , Wiggers Hartmut , Segets Doris 
Published: May 2020

Silicon, due to its high abundance and high theoretical specific capacity (~4200 mAh/g) compared to conventional graphite, has emerged as the most attractive candidate for anodes of lithium ion batteries [1]. However, commercial use of silicon-based electrodes is hindered by several degradation problems resulting mainly from high volume expansion during cycling [2], [3]. One promising approach for resolving these issues focuses on stabilizing the cycle life of the anode material by introducing electrochemically inactive components on the nanoscale. This can be achieved by a new type of Si-based nanoparticles (SiNx) that undergo irreversible conversion reactions upon cycling, producing active domains of silicon finely dispersed in an inactive matrix with high cycling stability [4].

While there is an extensive research on electrochemical reaction mechanism, there is less knowledge on electrode formulation and processing. A typical formulation of electrode systems is comprised of an active material (in this case SiNx), a binder, a conductive additive and usually a solvent mixture. Besides the composition, the energy and time input of employed dispersing techniques affect the nanoscale interactions within electrode systems. The resulting particle interactions that are responsible for observed differences in dispersibility govern macroscopic properties such as electrode microstructures, electrode slurry stability and rheology. This in turn, influences the final device manufacturing and ultimately the electrochemical performance [5].

In this work, we examined a set of probe solvents based on the concept of Hansen solubility parameters (HSP) [6], [7]. The dispersibility of solvents was measured from their settling behavior with an analytical centrifuge (AC). With this approach, it was possible to rapidly identify suitable solvents and their composition for optimal anode formulation. The effects of different dispersion methods on stability and homogeneity of the electrode slurries, the nanoscale interactions and the resulting electrode morphology were studied by AC in combination with microscopy and contact angle measurement techniques.

In conclusion, processes for tailored anodes and unraveling the underlying process-structure-property relationships allows a realistic assessment of influential parameters on the final battery performance. This is key towards a knowledge-based process development of new SiNx-based lithium ion batteries with enhanced electrical and electrochemical performance.

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