Quantification of Lithium Inventory Loss in Micro Silicon Anode Via Titration-Gas Chromatography

Abstract

Enabling silicon as an anode material for LIBs has been largely impeded by the severe volume changes it undergoes during cell operation, causing continuous Li inventory loss . Therefore, It is important to understand and quantify various sources of capacity fade in order to design effective mitigation strategies. In this work, we used a method based on Titration Gas Chromatography (TGC) to show a non-linear volume expansion in µSi anode during the electrochemical lithiation process. The severe volume expansion towards the end of lithiation leads to the accelerated SEI formation and thus leading to the conductive pathway loss, which results in a large amount of trapped Li-Si alloy accumulation. This TGC method was also applied to study μSi anodes with two different binders namely: Sodium Carboxymethyl Cellulose (CMC-Na) and Polyacrylic Acid (PAA). The main reason for capacity loss for the anode with CMC-Na binder was the trapped Li-Si alloy, which was reduced by using a more mechanically robust PAA binder. The concept of State of Charge (SoC) control was also investigated in µSi-LFP full cells with both the binders by tuning the N/P ratios from 1.5 to 3. The results showed that binder robustness is important for mitigating the trapped Li-Si alloy accumulation in µSi anode. Additionally, the effect of particle size of active material on trapped Li-Si accumulation was also investigated using the TGC method Figure: Cycle performance of µSi- CMC-Na-LFP full-cell with various N/P ratios (b) Cycle performance of µSi-PAA-LFP full-cell with various N/P ratios (c) TGC Data for Lithium inventory loss of full cell after 1st cycle for various N/P ratios (d) TGC Data for Lithium inventory loss of full cell after 10 cycles for various N/P ratios Figure 1