Synthesis and characterisation of Li11RE18M4O39−δ: RE = Nd or Sm; M = Al, Co or Fe

Four new phases of general formula, Li11RE18M4O39−δ: REM = NdAl, NdCo, SmCo, SmFe, have been synthesised and characterised. The NdAl phase, and probably the others, is isostructural with the NdFe analogue, but some cation disorder and partial site occupancies prevent full structural refinement of powder neutron diffraction data. The NdCo phase also forms a solid solution with variable Li content (and charge compensation by either oxygen vacancies or variable transition metal oxidation state). The NdAl phase is a modest conductor of Li+ ions whereas the other three phases are electronic conductors, attributed to mixed valence of the transition metal ions. Subsolidus phase diagrams for the systems Li2O–Nd2O3– Al2O3, ‘CoO’ have been determined and an additional new phase, LiCoNd4O8, which appears to have a K2NiF4-related superstructure, identified

A study on the influence of lithium plating on battery degradation

Within Li-ion batteries, lithium plating is considered as one of the main reasons behind the capacity fade that occurs during low temperature and fast charging conditions. Previous studies indicate that plating is influenced by the levels of loss of lithium inventory (LLI) and the loss of active material (LAM) present in a battery. However, it is not clear from the literature on how lithium plating influences battery degradation in terms of LAM and LLI. Quantifying the undesirable impacts of lithium plating can help in understanding its impact on battery degradation and feedback effects of previous lithium plating on the formation of present plating. This study aims to quantify the degradation modes of lithium plating: LLI, LAM at the electrode level. A commercial Li-ion cell was first, aged using two different cases: with and without lithium plating. Second, a degradation diagnostic method is developed to quantify the degradation modes based on their measurable effects on open-circuit voltage (OCV) and cell capacity. The results highlight that LAMNE and LLI levels under the fast charge profile are increased by 10% and 12%, respectively, compared to those under the less aggressive charge profile. Further, limitations of the degradation analysis methods are discussed

Ba₂Bi_1.4Nb_0.6O₆: A Nonferroelectric, High Permittivity Oxide

Ba₂Bi_1.4Nb_0.6O₆: A Nonferroelectric, High Permittivity Oxid

Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices

Performance assessments on miniature cylindrical cells used in Fitbit Flex 2 fitness trackers have been performed to understand the dominant ageing modes and small format implications. We utilise electrochemical testing, x-ray photoelectron Spectroscopy (XPS), x-ray computed tomography (XCT) and scanning electron microscopy (SEM), to reveal device and component structural features and changes. The cell maintains 82% cell capacity retention after 500 continuous charging and discharging cycles at 3.0–4.35 V, 0.75C rate at 20 °C. The anode shows severe delamination due to high bending stress exerted on the cell components, however this seemingly has minimum impact on the electrochemical performance if the coating is sufficiently compressed in the jelly roll with a good electrical contact. After ageing, the surface layers continue to grow, with more LiF found on the cathode and anode. The formation of LiF is discussed and we suggest the main ageing mechanism of the Fitbit cell is related to increasing charge transfer resistance due to the transportation of Li+ ions being inhibited by the thicker surface layer, which contains LiF. That preferential delamination on the inner sides of the electrode coatings was observed consistently opens up an interesting avenues for advances in cylindrical cell manufacturing at large