# Evaluation of Alternative Lithium Salts for Li Ion Batteries With SiO x ‐Containing Anodes: Characteristic Failure Mechanisms and Different Impacts of the Fluoroethylene Carbonate Additive

## TL;DR

This paper explores how different lithium salts and additives can improve the cycle life of lithium-ion batteries with silicon oxide anodes.

## Contribution

The study reveals a novel 'self-healing' mechanism via FEC and LiDFOB that reactivates lost capacity in SiOx anodes.

## Key findings

- Replacing LiPF6 with LiBOB or LiDFOB improves cycle life in SiOx-containing anodes.
- FEC suppresses failure cascades and reduces active lithium loss.
- LiDFOB enables active lithium generation through oxidation of soluble SEI species.

## Abstract

Incorporating silicon‐based active materials, e.g., SiO
x
, into the negative electrodes can increase the gravimetric/volumetric energy of Li ion batteries. Nevertheless, SiO
x
shortens cycle life due to the large volume expansion during charge/discharge cycling. The mechanical stress on the solid electrolyte interphase (SEI) necessitates continuous SEI repair, which accelerates active lithium loss (ALL) over cycling. In this work, the impact of common lithium salts is investigated in electrolytes for LiNi0.5Co0.2Mn0.3O2 (NCM 523) || 10%SiO
x
‐graphite Li ion pouch cells. The end‐of‐life (EOL) with LiPF6 can be enhanced by anode passivation via fluoroethylene carbonate (FEC), which not only decreases ALL but also suppresses failure cascades (e.g., electrode crosstalk) initiated by HF over the course of SiO
x
reactions with LiPF6. Though ALL remains similar when adding FEC to lithium bis(oxalato)borate (LiBOB), it enhances the generation of active Li through oxidation reactions at the cathode, likely due to the inverse crosstalk of partly soluble SEI species. This “self‐healing” or “recovery” mechanism reactivates the apparently “wasted SEI” and formerly lost capacity, thereby enhancing cycle life. This positive effect is even more pronounced with LiDFOB. However, the accompanying gassing of the oxalato‐based salts remains an obstacle to practical applicability.

(a) The cycle life of Li ion batteries with SiO
x
‐containing anodes can be extended by replacing the state‐of‐the‐art LiPF6 salt with LiBOB or LiDFOB, and by further employing FEC as an electrolyte additive. (b) When employing LiDFOB‐based electrolyte, long cycle life is partly by active lithium generation from the oxidation of soluble SEI species that diffuses from the anode toward the cathode and/or the LiDFOB salt itself.© 2026 WILEY‐VCH GmbH