The Value of Light Element Imaging Using FIB-SIMS for Material Characterization at Nanometer Scales

Le résumé fourni par la source

In the midst of the electrification revolution, driven by rapid expansion of the lithium containing battery market, the imaging of light-mass elements such as lithium is critical to support development of new materials and battery structures [1, 2] However, the scarcity of instruments with the necessary sensitivity and resolution poses a significant obstacle to lithium ion imaging. The work described here was carried out using a new generation of the fibTOF secondary ion mass spectrometer (SIMS) from TOFWERK, designed as a detector for FIB-SEM microscopes. Covering all elements and their isotopes, starting from hydrogen and spanning the entire periodic table, the fibTOF seamlessly integrates cutting-edge TOF and FIB technologies. This integration enables swift (within minutes) 3D chemical imaging, offering unparalleled spatial resolution and sensitivity [3, 4]. This paper presents examples focused on (but not limited to) the imaging of light-mass elements relevant to industry, including battery technology and metallurgy. The first example is an investigation of the solid-electrolyte interphase (SEI) composition and transition metal (TM) dissolution in lithium-ion battery cells, in particular for cells with LiNiₓMnyCo1-x-yO₂ cathodes, and the impact of molecular additives on improving the SEI properties and preventing TM shuttling [5], Such interphases are very important as they determine the capacity and lifetime of the battery cells [6]. Interphase is considered a dynamic medium because its composition changes during battery galvanostatic cycling. This study focused on investigating the SEI composition of the graphite anode in LiNi0.6Mn0.2Co0.2O2, NMC622 artificial graphite cell chemistry as well as the TM dissolution of the cathode and deposition on the anode during galvanostatic cycling. This work includes the investigation of six different graphite anodes, one pristine, four cycled to the end of their life (50% state of health) in the presence of the additives, and one control sample cycled without any additive. The measurement of Mn and Ni at the anode surface confirmed irreversible phase changes and metal dissolution of the cathode. Li+, F-, Li2O+, and Li2F+ distributions were studied, with Li+ and Li2F showing similar distributions, and Li2O mainly originating from a thinner top layer. The second FIB-SIMS imaging example is of an M3 high-speed steel alloy characterized by a microstructure comprising primary carbides (MC and M6C) and MnS dispersed within a martensitic Fe matrix [7]. The study correlated FIB-SIMS imaging results with nanoindentation-derived hardness maps. Certain phases identified chemically as carbides exhibited traces of hydrogen, and revealed a correlation with softer regions in the hardness map, suggesting a potential link to hydrogen embrittlement. It is noteworthy that the presented case studies were conducted using elevated ion currents, showcasing how fibTOF effectively handles heightened signals and highlighting the advantageous applications of this measurement technique. Moreover, these studies underscore the versatility and reliability of fibTOF in analyzing diverse materials and complex microstructures. FIB-SIMS analysis of a graphite anode from a NMC622 Li ion battery cycled to 50% of state of health without any additives. FIB current was a 30keV, 1nA 69Ga beam and the field of view was 20 µm. Measurements were taken on a FIB-SEM microscope in combination with a TOFWERK fibTOF mass spectrometer. a) Secondary electron FIB image, b-d) chemical map projected from above (top projection TP), e-g) chemical map projected from the side (front projection FP).

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