Pushing the Detection Limit of Static Wideline NMR Spectroscopy Using Ultrafast Frequency-Swept Pulses

We report a simple design strategy for wideband uniform-rate smooth truncation (WURST) pulses that enables ultrafast frequency sweeps to maximize the sensitivity of Carr–Purcell–Meiboom–Gill (CPMG) acquisition in static wideline nuclear magnetic resonance (NMR). Three compelling examples showcase the advantage of ultrafast frequency sweeps over currently employed WURST-CPMG protocols, demonstrating the potential of investigating materials that are typically inaccessible to static wideline NMR techniques, e.g., paramagnetic solids with short homogeneous transverse relaxation times

Pushing the Detection Limit of Static Wideline NMR Spectroscopy Using Ultrafast Frequency-Swept Pulses

We report a simple design strategy for wideband uniform-rate smooth truncation (WURST) pulses that enables ultrafast frequency sweeps to maximize the sensitivity of Carr–Purcell–Meiboom–Gill (CPMG) acquisition in static wideline nuclear magnetic resonance (NMR). Three compelling examples showcase the advantage of ultrafast frequency sweeps over currently employed WURST-CPMG protocols, demonstrating the potential of investigating materials that are typically inaccessible to static wideline NMR techniques, e.g., paramagnetic solids with short homogeneous transverse relaxation times

19F MAS NMR study on anion intercalation into graphite positive electrodes from binary-mixed highly concentrated electrolytes

Dual-graphite batteries (DGBs), which are based on anion intercalation into graphite positive electrodes, exhibit great potential for stationary energy storage due to use of more sustainable and low-cost electrode materials and processing routes. Binary-mixed highly concentrated electrolytes (HCEs) appeal highly suitable for the high operating voltages of DGBs, although the lack of sufficient insights into the formation of graphite intercalation compounds (GICs) limits the cell performance in terms of specific capacity and lifetime so far. Herein, anion intercalation from single-salt HCEs (LiPF6 and LiBF4) and an equimolar binary mixture of LiPF6/LiBF4 are studied in graphite || Li metal cells, revealing an improved performance in terms of specific capacity and Coulombic efficiency in the order LiPF6 > LiPF6/LiBF4 > LiBF4. LiBF4-based cells exhibit an increased onset potential for anion intercalation and higher area specific impedance, suggesting an ineffective interphase formation at graphite. X-ray diffraction reveals GIC formation, while a lower stage number is achieved for the LiBF4-based HCE. 19F MAS NMR spectroscopy analysis at various states-of-charge confirms no significant charge transfer between the intercalated anions and the graphite host and suggest preferred intercalation of PF6- compared to BF4- as well as a high translational and/or rotational mobility of the intercalated anions

Identification of Li x Sn Phase Transitions During Lithiation of Tin Nanoparticle-Based Negative Electrodes from Ex Situ 119 Sn MAS NMR and Operando 7 Li NMR and XRD

The lithiation mechanism of tin nanoparticle-based negative electrodes is reported and systematically studied via operando 7Li nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) combined with ex situ 119Sn magic-angle spinning (MAS) NMR. Besides the formation of the Sn-rich phases Li2Sn5 and LiSn, also the Li-richer phase Li7Sn3 is observed in good agreement with the structural evolution of the binary Li–Sn phase diagram. However, the structural investigations using ex situ 119Sn MAS NMR clearly reveal the formation of a disordered LixSn phase with increasing lithiation, possessing the structural fingerprints of Li7Sn3 with no long-range order and a body-centered cubic (bcc) packing of Sn (from XRD). Thus, in contrast to previous studies relying on 7Li NMR only, the formation of any of the Li-rich bulk crystalline Li–Sn phases, Li13Sn5, Li5Sn2, Li7Sn2, and Li17Sn4, could not be confirmed from 119Sn MAS NMR, showing that these Li–Sn phases are not formed under electrochemical operation. From a more general point of view, our approach using ex situ 119Sn MAS NMR demonstrates the possibilities of using the heavier framework ions as reporters of the local structural environments in negative electrodes. This relies on the sensitivity of the isotropic 119Sn shift with respect to the first and second atomic coordination environments, which provides a powerful source of complementary structural information to the typically performed operando 7Li NMR and XRD measurements

Carbons from biomass precursors as anode materials for lithium ion batteries: New insights into carbonization and graphitization behavior and into their correlation to electrochemical performance

We report a comprehensive and systematic study on the preparation and characterization of carbonaceous materials that are obtained from five different sustainable precursor materials and petroleum coke as reference material, particularly focusing on the correlation between the structural transformation of the precursors into carbons in dependence of heat treatment temperature (HTT) and their corresponding electrochemical characteristics as anode material in lithium ion batteries. The carbons were carbonized and graphitized in 200 °C steps, covering a broad temperature range from 800 °C to 2800 °C. So far, such a systematic synthesis approach has not been reported in literature. For biomass-derived carbons, we found a heterogeneous (discontinuous) graphitization process, i.e. a transformation from the amorphous to the graphitic phase via the turbostratic phase. A general trend was observed for the discharge capacity, i.e. a decrease of capacity from 800 °C to ≈1800–2000 °C, followed by an increase of capacity for temperatures >2000 °C. An increase of the 1st cyle Coulombic efficiency was found and could be directly correlated to the decrease of the “non-basal plane” surface area upon HTT. In addition, we found that the voltage efficiency and energy efficiency of the different carbons also increase with rising treatment temperatures

Effect of Li plating during formation of lithium ion batteries on their cycling performance and thermal safety

The presented work focuses on the effect of different applied C-rates within the formation procedure on the performance and the thermal safety of lithium ion battery cells. The formation procedure is based on constant-current constant-voltage charging and constant-current discharging. Here, two different formation procedures were used characterized by the applied current rate of either 0.2C or 2C. The cells were investigated via electrochemical, microscopic and spectroscopic methods. Applying a C-rate of 2C shortens the formation to 1.5 h compared to 10.5 h at 0.2C for one formation cycle. However, also the occurrence of Li plating with an amount corresponding to (7.8 ± 0.3) mAh g−1NMC was observed. Based on those results, thermal safety properties of cells after 0.2C or 2C formation was analyzed under quasi-adiabatic conditions in an accelerated rate calorimeter. Within the margin of error, no influence of the C-rate during formation on the thermal safety could be detected. In addition, no difference in cell cycling performance could be observed. Therefore, the here determined amount of Li plating originating solely from the formation process does not lead to significant differences in cycling performance and thermal safety behavior for the here considered lithium ion battery cells

Lithiation Mechanism and Improved Electrochemical Performance of TiSnSb-Based Negative Electrodes for Lithium-Ion Batteries

Lithium alloying materials are promising candidates to replace the current intercalation-type graphite negative electrode materials in lithium-ion batteries (LIBs) due to their high specific capacity and relatively low cost. Here, we investigate the electrochemical performance of TiSnSb regarding its charge/discharge cycling stability as a negative electrode material in LIB cells. To assess a more practical performance with respect to a limited active lithium content in LIB full-cells, we evaluate the impact of pre-lithiation for TiSnSb with respect to the cycling stability in a NCM111||TiSnSb cell setup. The observation of the individual electrode potentials reveals comprehensive insights into the ongoing cell chemistry, showing that clear performance improvements can be achieved via pre-lithiation. Furthermore, the lithiation mechanism of TiSnSb is systematically studied via ex situ7Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR), ex situ X-ray diffraction, and static ex situ119Sn wideband uniform rate smooth truncation Carr–Purcell Meiboom–Gill (CPMG) WCPMG NMR experiments. For comprehensive references regarding the isotropic 7Li shift of the Li–Sb intermetallic phases, all thermodynamically stable Li–Sb intermetallics of the binary Li–Sb systems have been synthesized and subsequently characterized by 7Li MAS NMR. Combined, our measurements for lithiated TiSnSb do not give any evidence for the formation of Li–Sn and Li–Sb intermetallics related to crystalline bulk phases (Li7Sn3, Li7Sn2, Li3Sb, and Li2Sb) as has been previously reported. In contrast, unique insights obtained from static ex situ119Sn WCPMG NMR and ex situ XRD measurements reveal the formation of ternary Li–Sb–Sn species during lithiation, which can be assigned to the intermetallic phase Li2.8SbSn0.2. Additionally, the 7Li MAS NMR measurements combined with the observed discharge capacity reveal a second Li species, which we assign to an amorphous Li–Sn phase

Exploiting the Degradation Mechanism of NCM523Graphite Lithium‐Ion Full Cells Operated at High Voltage

Layered oxides, particularly including Li[NixCoyMnz]O2 (NCMxyz) materials, such as NCM523, are the most promising cathode materials for high‐energy lithium‐ion batteries (LIBs). One major strategy to increase the energy density of LIBs is to expand the cell voltage (>4.3 V). However, high‐voltage NCMurn:x-wiley:18645631:media:cssc202002113:cssc202002113-math-0002 graphite full cells typically suffer from drastic capacity fading, often referred to as “rollover” failure. In this study, the underlying degradation mechanisms responsible for failure of NCM523urn:x-wiley:18645631:media:cssc202002113:cssc202002113-math-0003 graphite full cells operated at 4.5 V are unraveled by a comprehensive study including the variation of different electrode and cell parameters. It is found that the “rollover” failure after around 50 cycles can be attributed to severe solid electrolyte interphase growth, owing to formation of thick deposits at the graphite anode surface through deposition of transition metals migrating from the cathode to the anode. These deposits induce the formation of Li metal dendrites, which, in the worst cases, result in a “rollover” failure owing to the generation of (micro‐) short circuits. Finally, approaches to overcome this dramatic failure mechanism are presented, for example, by use of single‐crystal NCM523 materials, showing no “rollover” failure even after 200 cycles. The suppression of cross‐talk phenomena in high‐voltage LIB cells is of utmost importance for achieving high cycling stability

Investigation of Polymer/Ceramic Composite Solid Electrolyte System: The Case of PEO/LGPS Composite Electrolytes

The incorporation of inorganic lithium superionic conductors in polymer/ceramic composite electrolytes has been frequently proposed since this approach is expected to take advantage of the high ionic conductivities of the lithium superionic conductors and the elasticity of the polymer constituents of the composites. Nevertheless, the properties and mechanisms of polymer/ceramic composite electrolytes are yet to be comprehensively investigated. In this work, we systematically study sulfide-based polymer/ceramic composites from the aspects of composition dependence, electrochemical performance, and chemical stability. The composition-dependent Li-ion conduction mechanism and electrochemical behavior have been revealed for polyethylene oxide/Li10GeP2S12 composite electrolytes, highlighting the rational selection of compositions of polymer/ceramic composites toward desired functions. Furthermore, the chemical stability of the sulfide electrolyte in diverse solvent media as well as the potential internal reactions between the components of the composite electrolyte have been investigated, which underline the chemical stability consideration in the design and fabrication of the composite electrolyte. Thus, this work aims at contributing to the design and fabrication of sulfide-based polymer/ceramic composite electrolytes that enable high-performance lithium metal batteries