Electronic changes in poly(3,4-ethylenedioxythiophene)-coated LiFeSO4F during electrochemical lithium extraction

The redox activity of tavorite LiFeSO4F coated with poly (3,4-ethylenedioxythiophene), i.e. PEDOT, is investigated by means of several spectroscopic techniques. The electronic changes and iron-ligand redox features of this LiFeSO4F-PEDOT composite are probed upon delithiation through X-ray absorption spectroscopy. The PEDOT coating, which is necessary here to obtain enough electrical conductivity for the electrochemical reactions of LiFeSO4F to occur, is electrochemically stable within the voltage window employed for cell cycling. Although the electronic configuration of PEDOT shows also some changes in correspondence of its reduced and oxidized forms after electrochemical conditioning in Li half-cells, its p-type doping is fully retained between 2.7 and 4.1 V with respect to Li+/Li during the first few cycles. An increased iron-ligand interaction is observed in LixFeSO4F during electrochemical lithium extraction, which appears to be a general trend for polyanionic insertion compounds. This finding is crucial for a deeper understanding of a series of oxidation phenomena in Li-ion battery cathode materials and helps paving the way to the exploration of new energy storage materials with improved electrochemical performances

Fiber Optic Monitoring of Composite Lithium Iron Phosphate Cathodes in Pouch Cell Batteries

- Developing techniques for real-time monitoring of the complex and dynamic environment in lithium-ion batteries is crucial for optimal use of the cells and to develop the next generation of batteries. In this work, we demonstrate the use of fiber optic evanescent wave (FOEW) sensors for monitoring lithium iron phosphate (LFP) composite cathodes in pouch cells. The fiber optic sensors were placed on top of the LFP electrodes, and the pouch cells were found to cycle well with significantly improved electrochemical performance compared to fully embedded fibers in Swagelok cells. Galvanostatic, voltammetric, and pulsed current techniques demonstrated that the optical response correlated well with the capacity, and a clear difference in sensor response was seen when the sensors were placed at the surface of composite electrodes compared to fibers embedded in the cathode. The optical response from LFP at different rates was also investigated, but no apparent influence on intensity output was found even though polarization was observed in the voltage profiles at higher currents. It was also demonstrated that the electrolyte itself functioned as a fiber cladding and that the salt concentration in the electrolyte did not influence the optical signal. In addition, given the short penetration depth of the evanescent waves, the sensor response is most likely dominated by the surface conditions of electrode particles near the sensing region. These findings provide further insight into the application and performance of FOEW sensors integrated into batteries, as well as the possibility of developing low-cost fiber optic sensors for battery monitoring under working conditions

Electrochemical quartz crystal microbalance study of polyelectrolyte film growth under anodic conditions

Coating hard materials such as Pt with soft polymers like poly-l-lysine is a well-established technique for increasing electrode biocompatibility. We have combined quartz crystal microgravimetry with dissipation with electrochemistry (EQCM-D) to study the deposition of PLL onto Pt electrodes under anodic potentials. Our results confirm the change in film growth over time previously reported by others. However, the dissipation data suggest that, after the short initial phase of the process, the rigidity of the film increases with time, rather than decreasing, as previously proposed. In addition to these results, we discuss how gas evolution from water electrolysis and Pt etching in electrolytes containing Cl− affect EQCM-D measurements, how to recognize these effects, and how to reduce them. Despite the challenges of using Pt as an anode in this system, we demonstrate that the various electrochemical processes can be understood and that PLL coatings can be successfully electrodeposited.Funding Agencies|Swedish Research Council (Vetenskapsradet)|325-2008-7537621-2007-3983|Bo Liedberg and the Molecular Physics Group at Linkoping University for access to equipment||Carl Trygger Foundation and The Swedish Foundation for Strategic Research||</p

Fiber Optical Detection of Lithium Plating at Graphite Anodes

Avoiding the plating of metallic lithium on the graphite anode in lithium-ion batteries, potentially leading to aging and the formation of dendrites is critical for long term and safe operation of the cells. In this contribution, in operando detection of lithium plating via a fiber optical sensor placed at the surface of a graphite electrode is demonstrated. The detection is based on the modulation of light at the sensing region, which is in direct contact with the graphite particles. This is first demonstrated by the intentional deposition of lithium on a copper electrode, followed by experiments with graphite electrodes in pouch cells where plating is initiated both as a result of over-lithiation and excessive cycling rates. The plating resulted in a significant loss of light from the fiber, and the findings correlated well with previous experiments on the detection of sodium plating. The modulated light is also found to correlate well with the graphite staging via changes in the optical properties of the graphite during slow (de)intercalation of lithium ions. In a practical application, the fiber optical sensor may provide a battery management system (BMS) with input to optimize the charging procedure or to warn for cell failure.Title in the list of papers of Jonas Hedman's thesis: Fiber Optic detection of Lithium Plating at Graphite Anodes</p