Researchers at Pacific Northwest National Laboratory (PNNL) have developed new functional electrolytes containing multiple additives to enable Li-ion batteries (LIBs) to perform well in a wide temperature range from −40 to 60 °C. A paper on their work is published in the journal ACS Applied Materials & Interfaces.
Cells based on the optimized electrolytes show significantly enhanced discharging performance at −40 °C; long-term cycling stability at 25 °C (more than 85% of capacity retention after 1000 cycles at 1C/1C rates in 1 Ah pouch cells); as well as the obviously improved cycling stability at 60 °C.
The researchers said that the remarkable cell performances originate from the highly conductive, uniform, and compact passivating films formed on both anode and cathode surfaces by the synergistic effects of the multiple additives.
The electrolyte solutions in Li-ion batteries conduct ions between the negative electrode (anode) and positive electrode (cathode) to power the battery. Ethylene carbonate—an indispensable component of most of these solutions—helps create a protective layer, preventing further decomposition of electrolyte components when they interact with the anode.
However, ethylene carbonate has a high melting point, which limits its performance at low temperatures.
Wu Xu and colleagues showed previously that they could extend the temperature range of lithium-ion batteries by partially replacing ethylene carbonate with propylene carbonate and adding cesium hexafluorophosphate. But they wanted to improve the temperature range even further, so that lithium-ion batteries could perform well from -40 to 140 ˚F.
The researchers tested the effects of five electrolyte additives on the performance of lithium-ion batteries within this temperature range. They identified an optimized combination of three compounds that they added to their previous electrolyte solution. This new combination caused the formation of highly conductive, uniform and robust protective layers on both the anode and the cathode.
The authors acknowledge funding from the US Department of Energy.
Bin Liu, Qiuyan Li, Mark H. Engelhard, Yang He, Xianhui Zhang, Donghai Mei, Chongmin WangJi-Guang ZhangWu Xu (2019) “Constructing Robust Electrode/Electrolyte Interphases to Enable Wide Temperature Applications of Lithium-Ion Batteries” ACS Appl. Mater. Interfaces doi: 10.1021/acsami.9b03821