Work Performed and Main Results
The project's journey began with an extensive literature review and meticulous planning of activities, including year one planning and risk assessment (D5.1 and D5.2).
Synthesis of Bio-Waste Derived Hard Carbon:
We initiated the scientific endeavor with the preparation of bio-waste derived hard carbon. Hazelnut shells from a local source were ball-milled to achieve a fine powder with a size distribution of 10 to 100 microns. Subsequent steps involved a two-step synthesis process, involving citric acid digestion at 200°C for 14 hours and pyrolysis at 1000°C. Variations in acid concentration and temperature yielded notable structural variations, impacting electrochemical performance. More than 10 samples were synthesized and tested in half sodium cells, with the standout performer named C05-1100.
Period at HZB, Berlin, Germany:
The following six months saw a crucial phase at HZB, Berlin, Germany. Replicating the performance achieved in Rome, we optimized electrode preparation for angular resolved X-ray fluorescence (XRF) measurements. Ex-situ XRF analysis on aged electrodes provided insights into SEI evolution during cycling. Furthermore, a custom test cell, tailored for ultra-high vacuum experiments such as High-Resolution X-ray Fluorescence (HRXRF), was developed. A 500 nm SiN window facilitated low-energy X-ray penetration. The subsequent operando experiments elucidated key aspects, including X-ray damage, electrochemical stability, X-ray penetration depth, and angular resolution. These tests furnished reliable measurements of SEI dynamics during cycling, revealing Na accumulation, nucleation, and solid-phase transitions.
Second Year Planning and Risk Assessment
During this phase, the project adhered to the second-year planning and risk assessment (D5.3 and D5.4). Internal seminars and an international conference on sodium-ion batteries organized by Prof. Adelhelm at HZB allowed the dissemination of preliminary results within the research community.
Last 8 Months at La Sapienza:
In the final eight months, comprehensive data extraction, processing, and result evaluation took place. The methodological procedure was validated through experiments, including impedance and SEM at the Helmholtz Institute Ulm. The PI presented research findings at international conferences, including E-MRS in Strasbourg (May 2023) and the Italian School of Synchrotron Light Facilities (SILS) in Rome (August 31, 2023). The culmination was a final seminar at La Sapienza on September 21, 2023.
Summary of Results:
The project yielded remarkable results that push the boundaries of current scientific knowledge:
1. In-depth investigation of synthetic parameters' impact on material structure.
2. Advanced characterization of C05-1100 compared to HC-com using SAXS, SEM, and WAXS.
3. Dynamic bulk behavior of Na+ insertion observed through operando SAXS.
4. Ex-situ analysis of electrodes stopped at different state-of-charge.
5. HRXRF characterization of aged electrodes (up to 100 cycles).
6. Operando HRXRF analysis of C05-1100 and the benchmark for the first two cycles.
These results represent a significant advancement beyond the current state of the art, particularly in the field of operando characterization.
