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The present work focuses on the state‐of‐charge (SOC) estimation of a lithium‐ion battery in terms of a second‐order extended Kalman filter (EKF). First, an equivalent circuit model is introduced to describe the performance of lithium‐ion batteries. The model parameters are then identified through hybrid pulse power characterization experiments conducted over a wide range of temperatures (−10 to 55°C). A two‐dimensional mathematical relationship is established with respect to the SOC and temperature based on a dual‐fifth polynomial expression. The main effects and sensitivities of the SOC and temperature on the parameters are analysed according to the principle of variance analysis and partial derivatives. An estimation algorithm is developed, which combines the two‐dimensional parameter model and second‐order EKF. Finally, the proposed approach is validated compared to other estimation schemes through discharge experiments under extreme temperatures and dynamic loading profiles, which yields experimental results that estimate the SOC with an absolute error of less than 4.5% under harsh conditions. This not only demonstrates that it can characterize dependency of the model parameters on the operating conditions and address the uncertainty of model parameters, but also verifies the advantage of present method at low temperatures especially at sub‐zero temperatures.

Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling performance. The FePO4-coated sample exhibits capacity retention of 82 % after 100 cycles at 0.5 °C between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge–discharge condition. The electrochemical impedance spectroscopy (EIS) results indicate that this improved cycling performance could be ascribed to the presence of FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mn0.54]O2 particle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.

Seismic monitoring data for the past 50 years in the Three Gorges Reservoir area show that the reservoir head area is a typical weak seismic region with low seismicity before impoundment and that the epicenters were concentrated in the east and west sides of the Zigui Basin, most of which were natural tectonic earthquakes. After impoundment, the seismic activity shifted to the segment between Badong and Zigui along the Yangtze River, mainly within 5 km of the reservoir bank. The seismogenesis was categorized into four types; Karst collapse earthquakes, earthquakes caused by Karst gas explosion, mining tunnel collapse earthquakes, and rock (terrane) slip earthquakes, all of which are related to the lithology, structure, and tectonics of near-surface geological bodies of the area. Compared with the seismicity before impoundment, the seismic frequency increase was remarkable, with most of the magnitudes below M s2. 0. Therefore, the intensity of the earthquakes remained at a low level. On November 22, 2008, a magnitude 4. 1 earthquake, the largest earthquake recorded since impoundment, occurred in Quyuan Town, Zigui County. The intensity and PGA of reservoir-induced earthquakes are higher than those of tectonic earthquakes with equal magnitude, but the peak intensity of reservoir-induced earthquakes is not likely to go beyond that of the estimated range from earlier studies.