On the Beneficial Impact of Li_2CO_3 as Electrolyte Additive in NCM523 ‖ Graphite Lithium Ion Cells Under High-Voltage Conditions

摘要

Lithium ion battery cells operating at high-voltage typically suffer from severe capacity fading, known as 'rollover' failure. Here, the beneficial impact of Li2CO3 as an electrolyte additive for state-of-the-art carbonate-based electrolytes, which significantly improves the cycling performance of NCM523 parallel to graphite full-cells operated at 4.5 V is elucidated. LIB cells using the electrolyte stored at 20 degrees C (with or without Li2CO3 additive) suffer from severe capacity decay due to parasitic transition metal (TM) dissolution/deposition and subsequent Li metal dendrite growth on graphite. In contrast, NCM523 parallel to graphite cells using the Li2CO3-containing electrolyte stored at 40 degrees C display significantly improved capacity retention. The underlying mechanism is successfully elucidated: The rollover failure is inhibited, as Li2CO3 reacts with LiPF6 at 40 degrees C to in situ form lithium difluorophosphate, and its decomposition products in turn act as 'scavenging' agents for TMs (Ni and Co), thus preventing TM deposition and Li metal formation on graphite.