In Operando magnetometry study on the charge storage mechanism of SnCo alloy lithium ion batteries

TL;DR

This study uses in situ magnetic monitoring to investigate the reversible reactions of Sn-Co alloys in lithium-ion batteries, revealing how Co content influences the alloy's electrochemical behavior and capacity.

Contribution

It introduces a real-time magnetic method to analyze the charge storage mechanism of Sn-Co alloy anodes, providing new insights into transition metal reactions during cycling.

Findings

Co particles fully recombine with Sn during delithiation at low Co content

Higher Co content leads to partial recombination and formation of cobalt-rich phases

Unreacted Co particles may hinder full lithiation, reducing capacity

Abstract

In view of the long-standing controversy over the reversibility of transition metals in Sn-based alloys as anode for Li-ion batteries, an in situ real-time magnetic monitoring method was used to investigate the evolution of Sn-Co intermetallic during the electrochemical cycling. Sn-Co alloy film anodes with different compositions were prepared via magnetron sputtering without using binders and conductive additives. The magnetic responses showed that the Co particles liberated by Li insertion recombine fully with Sn during the delithiation to reform Sn-Co intermetallic into stannum richer phases Sn7Co3. However, as the Co content increases, it can only recombine partially with Sn into cobalt richer phases Sn3Co7. The unconverted Co particles may form a dense barrier layer and prevent the full reaction of Li with all the Sn in the anode, leading to lower capacities. These critical results shed light on understanding the reaction mechanism of transition metals, and provide valuable insights toward the design of high-performance Sn alloy based anodes.