ED Sciences Chimiques
Development of an innovative method of abusive nail testing in order to be representative of an internal short circuit of a Lithium-ion element.
by Jordan SETTA (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 13h30 - Salle Campanule Institut National de l'Environnement Industriel et des Risques (INERIS), Parc technologique Alata, 5 Rue Jacques Taffanel, 60550 Verneuil-en-Halatte
in front of the jury composed of
- Dany CARLIER-LARREGARAY - Professeure des universités - Université de Bordeaux - Directeur de these
- Rémi VINCENT - Ingénieur de recherche - CEA - Rapporteur
- Sara ABADA - Ingénieure de recherche - IFP Energies nouvelles - Examinateur
- Cyril AYMONIER - Directeur de recherche - CNRS - Examinateur
- Jean-Michel VINASSA - Professeur des universités - Bordeaux INP - Examinateur
- Marcos BATISTELLA - Maître de conférences - IMT Mines Alès - Rapporteur
This thesis focuses on understanding the physical, electrical, and thermal mechanisms governing the initiation, persistence, and extinction of internal short circuits induced by nail penetration in lithium-ion batteries. This work presents a state of the art dedicated to lithium-ion batteries and internal short circuits. The different types of defects, their origins, and their thermal and safety-related consequences are detailed. A critical review of the experimental methods previously reported in the literature is also provided. In order to investigate the impact of internal short circuits on lithium-ion batteries. A dedicated nail penetration setup was designed to ensure precise control of the experimental parameters while enabling simultaneous acquisition of electrical and thermal quantities. The influence of mechanical parameters - penetration speed, nail diameter, and nail tip angle - was investigated in order to optimize test reproducibility. The results show that nail geometry strongly affects contact resistances, current intensity, and heat generation. Post-mortem analyses based on the controlled separation of electrode active materials were also developed, particularly using microscopy techniques, in order to identify contact areas and associated degradations. Experiments performed in dry stacks reveal several regimes depending on the nature of the electrodes in contact and on the local resistivity of the defect. A comparative study between different stack architectures shows that stack geometry (particularly electrode thickness) influences both short-circuit stability and thermal dissipation. The work also highlights “fuse-like” behaviors leading to spontaneous extinction of the defect, and a threshold resistivity value was experimentally estimated. Tests conducted in the presence of an electrolytic solvent without lithium salt reveal modifications of heat transfer and contact resistances, as well as cathode degradation. Finally, experiments conducted on active cells show significantly higher thermal rises due to additional electrochemical phenomena. The influence of penetration location and state of charge on defect severity was also demonstrated. This work also investigates the relative contribution of anodes, cathodes, and separators. Anodic configurations (Anode-Separator-Anode) lead to the most severe regimes, associated with high currents and significant temperature rises, while cathodic configurations (Cathode-Separator-Cathode) mainly exhibit transient “fuse-like” behavior events. Laboratory-scale electrodes were fabricated, including configurations reversing the conventional material arrangement: anodic active material coated onto an aluminum current collector, and cathodic active material coated onto a copper current collector. Experiments performed on these configurations confirm that the active material primarily governs the short-circuit dynamics, while the influence of the current collector appears as a second-order effect. Finally, morphological, thermal, and thermo-mechanical analyses of separators demonstrate that their properties play a key role in maintaining or extinguishing the short circuit by locally preserving the electrical insulation between electrodes. Overall, this work contributes to a better understanding of internal short-circuit mechanisms in lithium-ion batteries and provides key insights for improving battery safety, designing cells that are more robust against mechanical and thermal abuse, and developing strategies to prevent critical failures.
ED Sciences Physiques et de l'Ingénieur
Novel hybrid ultrafast laser sources beyond 2 μm
by Hussein TOFAILI (Laboratoire Photonique, Numérique & Nanosciences)
The defense will take place at 9h30 - Amphithéatre André Ducasse Institut d'Optique d'Aquitaine (IOA), 1 Rue François Mitterrand, 33400 Talence
in front of the jury composed of
- Eric CORMIER - Professeur des universités - Université de Bordeaux - Directeur de these
- Jacob MACKENZIE - Associate Professor - University of Southampton - Rapporteur
- Ammar HIDEUR - Professeur des universités - Université de Rouen Normandie - Rapporteur
- Philippe GRELU - Professeur des universités - Université Bourgogne Europe - Examinateur
- Alphan SENNAROGLU - Professeur des universités - Koç University - Examinateur
High-energy picosecond pulses in the 2 µm spectral region are of growing importance as pump sources for mid-infrared optical parametric chirped-pulse amplification (OPCPA) in ZnGeP₂ and related non-oxide crystals, which in turn drive applications in strong-field physics, high-harmonic generation, molecular spectroscopy, and remote sensing. This thesis investigates a hybrid fibre-bulk chirped-pulse amplification (CPA) architecture at 2050 nm based on Ho:YLF, combining gain-medium characterisation, numerical modelling, and experimental implementation up to the picosecond, tens-of-microjoules regime. After a chapter establishing the theoretical framework of ultrashort pulse propagation, dispersion, and nonlinear effects relevant to chirped-pulse amplification, the experimental work begins with the selection and characterisation of Ho:YLF as the bulk gain medium. Small-signal absorption and gain measurements are performed on two a-cut Ho:YLF crystals (1 at.% and 0.75 at.% doping) for both π and σ polarisations across the 1980–2100 nm range, and absorption and emission cross-sections are extracted via the Beer–Lambert law and the McCumber reciprocity relation. A spatially resolved, self-consistent rate-equation model of a CW double-pass Ho:YLF amplifier is then developed. It couples a 3D anisotropic heat solver, with direction-dependent photoelastic contributions to the thermal lens, to an astigmatic q-parameter beam propagation through a distributed GRIN medium. The model is validated against narrow-linewidth CW measurements and subsequently extended to a spectrally resolved broadband formulation that captures gain narrowing and spectral reshaping of pulsed seeds in the quasi-CW regime. The central experimental contribution is a hybrid CPA system combining a fibre-CPA front-end (CVBG stretcher, two Tm:Ho-codoped fibre amplifiers, fibre-pigtailed AOM pulse picker) with a two-arm Ho:YLF bulk amplifier (double-pass first arm, single-pass second arm) and a matched CVBG compressor, in a linear, regenerative-amplifier-free configuration. The system delivers 28 µJ of compressed pulse energy at 1 MHz repetition rate, corresponding to 28 W of average power, with a pulse duration of 2.95 ps (only 4 % above the Fourier-transform limit) and a peak power of approximately 8.2 MW. A dedicated study of the thermal response of the CVBG compressor identifies its dispersion drift as the dominant remaining source of compressed-pulse-duration instability. Two supporting chapters complete the work. The first describes a continuously tunable CW Tm,Ho co-doped fibre laser (1966–2117 nm, ∼210 mW at 2050 nm), built in-house and used as the seed source for the Ho:YLF crystal characterisation. The second reports preliminary results on an energy-managed soliton fibre laser adapted to a Tm–Ho co-doped large-mode-area fibre, demonstrating mode-locked operation at 2046 nm as a candidate low-repetition-rate seed architecture for future high-energy operation.