Investigations on the Aging-Related Lithium Loss in Lithium Ion Batteries by Using 6Li-Isotopically-Enriched Cathode Material and Post-Mortem Analysis by Means of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Abstract

In the last decades, the lithium ion battery (LIB) became the technology of choice for a huge variety of power storage applications. Nevertheless, the loss of performance caused by complex aging phenomena remains challenging. In the first electrochemical cycles, the liquid organic electrolyte is decomposed at the electrodes surfaces leading to the formation of an electrically insulating passivation layer on the anode, the solid electrolyte interphase (SEI). Although the SEI formation involves an irreversible loss of electrolyte and active lithium, it is an essential process to provide sufficient cycling stability, as it prevents the remaining electrolyte from further decomposition. In order to improve the cycle performance of LIBs a deeper understanding of the aging processes is crucial. Focusing on the SEI formation process, common techniques for lateral and/or depth resolved isotopic surface analysis are time of flight-secondary ion mass spectrometry (ToF-SIMS) and glow discharge-mass spectrometry (GD-MS), respectively. However, lateral and depth resolved isotopic imaging of whole electrodes at a reasonable time scale is only possible with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). This work features the post-mortem analysis of graphitic SEI formed in LIBs, including a 6Li-isotopically-enriched LiNi1/3Co1/3Mn1/3O2 (NMC111) cathode material, to investigate the SEI formation process and the lithium distribution in the first electrochemical cycles. Therefore, lithium isotope deposition pattern of aged anodes are investigated in lateral and depth dimension by means of LA-ICP-MS.