[en] Graphical abstract: Fitted (surface) and measured degradation rates (dots) in the charge – discharge temperature space obtained from the reference cycles (R"2 = 0.92), where n is the number of cycles. Color code indicates red as conditions with a lower degradation rate and blue as conditions with a higher degradation rate. - Highlights: • Charge and discharge temperature affects differently ageing of LFP-graphite cells • Degradation rate shows quadratic relationship with Tc and linear with Td • Degradation rate presents a minimum when charge temperature is +15 °C • Cycling in the range from -20 °C to +15 °C imposes almost no degradation • Cycling at Tc = +30 °C and Td = -5 °C produces the highest degradation rate - Abstract: This work presents a systematic evaluation of the effect of dissimilar charging / discharging temperatures on the long-term performance of lithium iron phosphate / graphite based cells by using multi-factor analysis of variance. Specifically, the degradation of prototype pouch cells is presented in a range of charging and discharging temperatures from -20 °C to +30 °C, counting a total of 10 temperature combinations. In this manner, not only the effect of charging and discharging temperatures was analyzed, but also the correlations between them. Fitting of the data showed a quadratic relationship of degradation rate with charging temperature, a linear relationship with discharging temperature and a correlation between charging and discharging temperature. Cycling at the charge/discharge temperatures (+30 °C, -5 °C) produced the highest degradation rate, whereas cycling in the range from -20 °C to +15 °C, in various charge/discharge temperature combinations, created almost no degradation. It was also found that when Tc≅15 °C the degradation rate is independent of Td. When Tc < +15 °C, the higher degradation occurs at higher Td and at Tc > +15 °C lower degradation occurs at higher Td.

[en] Battery function is determined by the efficiency and reversibility of the electrochemical phase transformations at solid electrodes. The microscopic tools available to study the chemical states of matter with the required spatial resolution and chemical specificity are intrinsically limited when studying complex architectures by their reliance on two-dimensional projections of thick material. Here in this paper, we report the development of soft X-ray ptychographic tomography, which resolves chemical states in three dimensions at 11 nm spatial resolution. We study an ensemble of nano-plates of lithium iron phosphate extracted from a battery electrode at 50% state of charge. Using a set of nanoscale tomograms, we quantify the electrochemical state and resolve phase boundaries throughout the volume of individual nanoparticles. These observations reveal multiple reaction points, intra-particle heterogeneity, and size effects that highlight the importance of multi-dimensional analytical tools in providing novel insight to the design of the next generation of high-performance devices.

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[en] Highlights: • This study affords a new strategy to improve the power output of Li-O₂ cell. • FePO₄@C nanorods with exposed {010} facets are prepared and applied in O₂ cathode. • Hybrid cathode retains high energy output via ORR. • Hybrid cathode attains 8-fold increased power output via Li⁺-insertion of FePO₄. - Abstract: The aprotic lithium-oxygen (Li-O₂) battery has recently attracted the worldwide attention by virtue of its super-large energy output. However, the extremely poor power output is one of the key issues which severely restrict the commercialization of the Li-O₂ technology. In this work, we demonstrate a novel and simple strategy to address the power issue of the aprotic Li-O₂ battery. An iron phosphate/oxygen (FePO₄/O₂) hybrid cathode is proposed for the first time by simply introducing the {010}-oriented FePO₄ nanorods into a conventional O₂ cathode. The as-built hybrid cathode not only retains a high-energy output via the O₂ cathodic reaction, but also achieves an 8-fold increased power output via the Li⁺-insertion reaction of the {010}-oriented FePO₄ nanorods.

[en] In this work the limitations in using the core–shell models to simulate the operation of lithium iron phosphate electrodes are discussed and analyzed. The complications arising from the stepwise nature of the core–shell model and erroneous predictions of this model for special conditions are detailed

[en] Highlights: • Cerium containing iron phosphate based glass-ceramic waste forms were synthesized. • Main structural units of the glass-ceramics are Q⁰, Q¹ and a small amount of Q². • Good thermal stability of the glass-ceramics is obtained. • LR_Fe and LR_Ce of the glass-ceramics are 3.5 × 10⁻⁵ and 5.0 × 10⁻⁵ g m⁻² d⁻¹ respectively. • Slow cooling is a potential method to prepare iron phosphate based glass-ceramics.

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[en] Equivalent circuit model (ECM)-based state-of-charge (SOC) estimation has been considered as one of the most important aspects in battery management system (BMS). However, in case of a lithium iron phosphate (LiFePO₄) cell, because of the flatness and hysteresis effect of the open-circuit voltage (OCV) curve, there are inevitable drawbacks directly related to both erroneous SOC information and the slow SOC convergence speed caused by incorrect OCV characteristics. Therefore, this approach gives insight to the design and implementation of the ECM-based SOC estimator that is suitable for an actual LiFePO₄ cell. Two approaches for settlement in current OCV issues are as follows. Firstly, through linearization between coordinated charging and discharging OCVs, an OCV hysteresis model can be easily implemented. This model incorporating OCV measurement data is adequately applied to the model-based SOC estimator using the extended Kalman filter (EKF). Secondly, a well-adjusted measurement error covariance controlled in the EKF is used to alleviate an undesired SOC fluctuation that surely results in low BMS performance. This measurement error covariance additionally enables us to provide the fast SOC convergence speed against an inaccurate initial SOC value. This approach has been sufficiently validated by extensive experimental results conducted on LiFePO₄ cells that had a rated capacity of 14 Ah by EIG. Consequently, our validation showed the clearness of the proposed work for a reliable SOC estimator of a LiFePO₄ cell.

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No abstract available