Julien Fullenwarth

NiP3: a promising negative electrode for Li- and Na-ion batteries

Due to the abundance and low cost of sodium-containing precursors ambient temperature sodium ion batteries are promising for large scale grid storage. The low melting point of Na (97.7 °C) compared to 180.6 °C for Li represents a significant safety hazard for the use of Na metal anodes at ambient temperatures, which emphasizes the need for scientists and engineers to identify, design and develop new negative electrodes for Na-ion batteries. The identification of a suitable negative electrode is a crucial challenge for any further successful development of new cells, and to date efficient and competitive negative electrodes for NaB are still very rare. In this work we demonstrate that NiP3 could be a good challenger for this purpose. NiP3 based electrodes are evaluated as negative electrode materials for Li-ion batteries (LiB) and Na-ion batteries (NaB). The study of the reaction mechanism reveals the formation of a phase of composition close to Li3P and Na3P embedding Ni nanoparticles as the final reaction product after a full discharge. While the direct conversion of NiP3 into Na3P is identified for the reaction versus Na, it is still unclear whether an amorphous phase exists during the first discharge for the reaction versus Li before the conversion. Furthermore, thanks to the carboxymethyl cellulose/carbon black (CMC/CB) electrode formulation, the NiP3 electrode possesses a very promising capacity with a reversible storage capacity higher than 1000 mA h g−1 after 50 cycles for LiB and 900 mA h g−1 after 15 cycles for NaB, which represents one of the highest capacities ever sustained in Na-ion batteries.

TiSnSb a new efficient negative electrode for Li-ion batteries: mechanism investigations by operando-XRD and Mössbauer techniques

We report the electrochemical study of TiSnSb towards Li, as a negative electrode for Li-ion batteries. TiSnSb can reversibly take up more than 5 lithiums per formula unit leading to reversible capacities of 540 mA h g−1 and 4070 mA h cm−3 at 2 C rate. From complementary operandoXRD and Mossbauer spectroscopy measurements, it was shown that during the first discharge the TiSnSb undergoes a conversion process leading simultaneously to the formation of Li–Sb and Li–Sn alloys. At the end of the discharge, Li3Sb and Li7Sn2 were identified. Once the first discharge is achieved, both phases were shown to form Ti–Sn or Ti–Sb or Ti–Sn–Sb nanocomposites. The cycling performance of TiSnSb was shown to be excellent with maintaining 90% of the specific capacity during 60 cycles at 2 C rate. The good electrochemical performance of TiSnSb (compared to Sn and Sb) seems to be a consequence of the presence of the non-active metal. The comparative study of Ti/Sn/Sb composite demonstrated that the structural feature of the pristine material clearly impacts both the mechanism involved during the cycling and the corresponding performance.

The Quest for Polysulfides in Lithium–Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study

Confocal Raman spectra of a lithium-sulfur battery electrolyte are recorded operando in a depth-of-discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.

Pioneer study of SiP2 as negative electrode for Li- and Na-ion batteries

For the first time it is demonstrated that a dense SiP2 pyrite-type obtained by a very simple ball milling method delivers outstanding capacity in both lithium and sodium batteries with up to 1000 mA h g−1 and 572 mA h g−1 sustained after 30 and 15 cycles respectively.