Hybrid solid electrolytes for "all-solid" batteries: Formulation and multi-scale characterization of ionic transport

Lithium-ion batteries, widely present in our daily lives, have revolutionized portable applications and are now used in electric vehicles. The development of new generations of batteries for future applications in transport and storing electricity from renewable sources is therefore vital to mitigating climate change. Lithium-ion technology is generally considered as the preferred solution for applications requiring high energy density, while sodium-ion technology is particularly attractive for applications requiring power.

However, the intrinsic instability of liquid electrolytes results in safety issues. Faced with the requirements concerning the environment and safety, solid-state batteries based on solid electrolytes can provide an effective solution while meeting battery energy storage needs. The barriers to overcome allowing the development of all-solid-state battery technology consist mainly in the research of new chemically stable solid electrolytes with good electrical, electrochemical and mechanical performance. For this goal, this thesis project aims to develop “polymer/polymer” and “ceramic/polymer” composite solid electrolytes with high performance and enhanced safety. Characterizations by electrochemical impedance spectroscopy (EIS) will be carried out in order to understand the cation dynamics (by Li+ or Na+) at the macroscopic scale in composite electrolytes, while the local dynamics will be probed using advanced techniques of Solid-state NMR (23Na / 7Li relaxation, 2D NMR, in-situ NMR & operando). Other characterization techniques such as X-ray and neutron diffraction, XPS, chronoamperometry, GITT ... will be implemented for a perfect understanding of the structure of electrolytes as well as aging mechanisms at the electrolyte / electrolyte and electrolyte/electrode interfaces of the all-solid battery.

Key words: composite solid electrolyte, all-solid-state battery, interfaces, multiscale characterization, dynamics of Li + and Na + ions, electrochemical performance, solid-state NMR, X-ray / neutron diffraction.

Development of new anode materials for potassium-ion batteries

Classic Li-ion batteries are composed of a graphite anode and a cathode containing a lithiated layered oxide (formula LiNixMnyCozO2). The development and the generalization of the electric automobile market will generate stress on certain chemical elements source, especially for lithium, nickel, cobalt and copper. In addition, the production method consumes a lot of energy (multiple calcinations) and several solvents/products used are not respectful of the environment (NMP, ammonia).
The thesis aims to develop a battery technology based on potassium without using any critical element in order to significantly decrease the ecological footprint.
The insertion of potassium ion inside the graphite structure has been reported as an advantage in front of Na-ion batteries. However, due to the potassium size, the graphite structure expands (60%) and can limit the batterie cycle life.
The final target of the PhD thesis is to solve this issu following two approches : 1/ Find the link beetween graphites specifications and the resulting electrochemical performances in order to select the best graphite grade 2/ Develop new anode materials for K-ion application.

Physics-based ageing model of Li-ion batteries

In recent years, Li-ion batteries have become the benchmark technology for the global battery market, supplanting the older Nickel-Cadmium and Alkaline technologies. Although slightly inferior to fossil fuels in terms of massic energy capacity, Li-ion batteries have a major advantage for the development of electric vehicles: their exceptional lifespan. It has recently been demonstrated that particular electric vehicle technologies can exceed one million km. Beyond the promising performance of ideal prototypes, the question of battery lifespan is linked to industrial, economic and environmental issues that are crucial to the ecological transition and energy sovereignty of our country.

One of the major challenges in developing these long-life batteries is to anticipate and control the various internal degradation phenomena that occur during actual use. Although most degradation phenomena have been identified in laboratory on common battery materials, the question of their kinetics in a battery pack in real use remains open, as does the prediction of the battery's state of health and end-of-life.

CEA's teams draw on a unique expertise combining experimental data and modeling to build a predictive physico-chemical model of Li-ion battery degradation. As part of this thesis, you will design and carry out basic characterization experiments on battery degradation mechanisms in the laboratory, using a wide range of advanced experimental techniques (electrochemical titration, impedance spectroscopy, operando gas measurements, DRX, etc.). Your work will also involve integrating your results into aging models, and studying the predictions and validation of these models.

In situ Magic Angle spinning NMR analysis of Li-ion batteries

In situ solid-state Nuclear Magnetic Resonance (ssNMR) is a valuable characterization tool to decipher the electrochemical phenomena during battery operation. However, the broad signal lineshapes acquired from the sample static condition often retrain from the full potential of ssNMR characterization. Ex situ ssNMR experiments, using Magic-Angle sample Spinning (MAS), are often necessary to interpret the in situ data. As in any ex situ characterizations, the analyses do not always represent the real electrochemistry because of unwanted artifacts from the ex situ sample preparation, i.e., cell dismantling and electrode separations. Consequently, in situ ssNMR applications have been limited. The PhD student will address this limitation by developing a spinning battery cell for acquiring high-resolution ssNMR data under MAS for in situ study, including a new method of spatially-resolved ssNMR spectroscopy. Combining in situ, MAS, and localized spectroscopy would lead to an unprecedented in situ ssNMR tool for deciphering fundamental insights into battery chemistry, which the student will emphasize by studying phenomena such as interfaces and dendrite formation in operating Li-ion batteries.