Recharge your batteries: Study aims to understand the degradation of Li-ion batteries

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  • Published: Aug 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: Recharge your batteries: Study aims to understand the degradation of Li-ion batteries

New age

Most of us would welcome an extra hour or two’s charge, and the extra freedom it bestows to use our mobile phones and laptops on the go. Researchers from Japan and Taiwan have teamed up to probe the chemistry inside our gadgetry’s Li-ion batteries, paving the way for new and improved batteries.

Li is a new-age millennial. Like many of us, its livelihood relies on the portable energy locked within lithium ion (Li-ion) batteries. It zips from coffee shop to library to office, working, networking and playing on the go. By day Li-ion batteries are largely off the power grid, but by night phones and laptops are anchored to the mains, latching onto the steady stream of electrons. To some people, their freedom to live and work like this is entirely dependent on the capacity of their gadget’s batteries – and the bigger, the more efficient, and the more robust the better. Engineers over at Silicon Valley have taken this concept further. By packing together vast numbers of Li-ion batteries, large appliances and pieces of electrical equipment can access vast reserves of untethered electrical energy. Tesla engineers, for example, are kitting out the underbelly of their automobiles with an army of Li-ion batteries that supplies the power train. Bigger and more efficient batteries, just like our gadget’s, allows us to go on longer, further, without having to stop to power up. Research is integral to realising this goal. And that’s what researchers from the Research Institute of Electrochemical Energy of Japan and the National University of Taiwan set out to do. ‘An understanding of the reaction processes in LIBs,’ Takeda and colleagues highlight in Rapid Communications in Mass Spectrometry, ’is necessary for further improving their performance and robustness.’

Solid electrolyte interphase

Most of us, through salvaging dead batteries from the TV remote, are familiar with regular, household batteries. One end – the positively charged anode – is flat-bottomed, whilst the other – the negatively charged cathode – has a protruding point. When powering our gadgetry, electrons splinter off from lithium electrolytes down the now-completed circuitry, creating lithium ions that shuttle from the anode to the cathode in pursuit of its polar opposite.

Recent studies suggest that a solid electrolyte interphase (SEI for short) of lithium derivatives – lithium fluorides, carbonates, phosphates, ethers, alkoxides, etc. – forms where the electrodes and electrolytes meet. However, the tools used in these same studies do not provide us with all the information required to complete the overall puzzle. Nowadays Li-ion batteries, for example, use an electrolyte solution of lithium hexafluorophosphate (LiPF6) and organic carbonate solvents. Deciphering this organic chemistry is therefore vital for the whole picture.

Accordingly, the researchers from Japan and Taiwan aimed to identify the entities that emerge from the degradation of LiPF6 and organic electrolytes after 40 charge–discharge cycles at both 30 and 60°C. They sampled the battery electrolytes with LC-ESI/IT-ToF MS and, for the first time, used atmospheric solid analysis probe (ASAP)/QToF MS to explore the organic compounds that form on the electrodes.

Low-hanging fruit

Twelve products of degradation were identified in the electrolyte compartment after 40 charge–discharge cycles. Four of these were oligomers of carbonates and polyoxyethylenes, reasoned to be products resulting from the degradation of LiPF6 and carbonate electrolytes. These were always present, regardless of the temperature. The remaining eight of these twelve, however, were organophosphates that only formed at 60°C. The formation of these products also correlated with a marked decrease in battery capacity after 40 cycles. Ethyl ethylene phosphate was present within these, as deduced by comparison to a pure standard. The other seven were speculated to be derived from POF3 – formed when a component of LiPF6 reacts with water and hydrogen fluoride. In an attempt to complete the picture, Takeda and colleagues probed the SEIs for organic derivatives by ASAP-MS. In all, they found one more piece to add to the puzzle. Lingering on the anode was a compound known only by the chemical formula C4H8F2O6P2. The authors concede that this novel derivative may have been a low-hanging-fruit, and that further separation of electrode analytes may prove more fruitful. ‘Our future research,’ the paper concludes, ‘will focus on the investigation of the degradation products in LIBs under various experimental conditions by LC/ESI-MS and ASAP-MS.’

Related Links

Rapid Commun. Mass Spectrom. , 2016, 30, 1754–1762. Takeda et al.. Identification and formation mechanism of individual degradation products in lithium-ion batteries studied by liquid chromatography/ electrospray ionization mass spectrometry and atmospheric solid analysis probe mass spectrometry.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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