The new LiDFOB electrolyte for lithium-ion batteries is cost-effective, highly conductive, and stable, offering a better alternative to traditional lithium salts. It improves battery performance and sustainability, and simplifies production and recycling processes.
Scientists have created a very low-concentration electrolyte for lithium-ion batteries.
Lithium salts boost battery power but also raise costs. A new electrolyte with a very low concentration of the lithium salt LiDFOB could provide a more affordable and sustainable choice.
Cells using these electrolytes and standard electrodes have demonstrated high performance, as reported by a research team to the journal Angewandte Chemie. Additionally, the electrolyte could aid in both battery production and recycling.
Challenges with Traditional Electrolytes
Lithium-ion batteries (LIBs) power smartphones, tablets, electric vehicles, and electricity storage at power plants. Most LIBs consist of lithium cobalt oxide (LCO) cathodes, graphite anodes, and liquid electrolytes that carry mobile ions for the separated cathode and anode reactions.
These electrolytes influence the properties of the interphase layer that forms on the electrodes, affecting battery cycling performance. However, current electrolytes are mainly based on a system formulated over 30 years ago: 1.0 to 1.2 mol/L lithium hexafluorophosphate (LiPF) in carboxylic acid esters (“carbonate solvent”).
In the last decade, high-concentration electrolytes (> 3 mol/L) have been developed, enhancing battery performance by promoting the formation of strong inorganic-dominated interphase layers. However, these electrolytes have high viscosity, poor wetting ability, and inferior conductivity.
The large amounts of lithium salts needed also make them very expensive, often a critical factor for feasibility. To reduce costs, research has also started on ultra-low-concentration electrolytes (< 0.3 mol/L). However, the downside has been that the battery cell decomposes more solvent than the few salt anions, leading to an organic-dominated and less stable interphase layer.
Breakthrough with LiDFOB Electrolyte
A team led by Jinliang Yuan, Lan Xia, and Xianyong Wu at Ningbo University (China) and the University of Puerto Rico-Rio Piedras Campus (USA) has now developed an ultra-low-concentration electrolyte that may be suitable for practical use in lithium-ion batteries: LiDFOB/EC-DMC.
LiDFOB (lithium difluoro(oxalato)borate) is a common additive and significantly cheaper than LiPF. EC-DMC (ethyl carbonate/dimethyl carbonate) is a commercial carbonate solvent.
The electrolyte has a potentially record-breaking low salt content of 2 weight percent (0.16 mol/L) but a sufficiently high ionic conductivity (4.6 mS/cm) to operate a battery. Additionally, the properties of the DFOB– anions enable the formation of a strong inorganic-dominated interphase layer on LCO and graphite electrodes, resulting in excellent cycling stability in half and full cells.
While the LiPF in current use decomposes when it comes into contact with moisture and releases highly toxic and corrosive hydrogen fluoride gas (HF), LiDFOB is stable when exposed to water and air. Instead of needing strictly dry room conditions, lithium-ion batteries with LiDFOB can be manufactured under normal conditions, which also saves costs. Recycling would also be significantly less problematic and lead to more sustainability.
Reference: “An Ultralow-concentration and Moisture-resistant Electrolyte of Lithium Difluoro(oxalato)borate in Carbonate Solvents for Stable Cycling in Practical Lithium-ion Batteries” by Zhishan Liu, Wentao Hou, Haoran Tian, Qian Qiu, Irfan Ullah, Shen Qiu, Wei Sun, Qian Yu, Jinliang Yuan, Lan Xia and Xianyong Wu, 14 March 2024, Angewandte Chemie International Edition.
DOI: 10.1002/anie.202400110
The study was funded by the National Natural Science Foundation of China, the Zhejiang Provincial Natural Science Foundation of China, the Ningbo Science & Technology Innovation 2025 Major Project, and the NSF Center for the Advancement of Wearable Technologies.
