Impact of Charging and Charging Rate on Thermal Runaway Behaviors of Lithium-Ion Cells

The present work carries out a series of thermal runaway experiments to explore the impact of charging and charging rate on the thermal runaway behaviors of lithium-ion cells, in which five charging rates (0C, 0.5C, 1C, 2C and 4C) and three initial states of charge (SOC), i.e. 25%, 50% and 75% are included. The thermal runaway process of 18650 lithium-ion cells induced by over-heating usually consists of seven stages, and is accompanied with high-temperature, fire and toxicity risks. The internal morphology of cells and the micro features of cell materials are seriously damaged after thermal runaway. Charging aggravates the thermal runaway behavior of cells, which is further exhibited as the earlier occurrence of safety vent opening, gas releasing and thermal runaway. Moreover, the severity deteriorates as the charging rate increases (the larger the charging rate, the earlier and more severe the thermal runway), which may be ascribed to the growth of cell SOC and the decline of cell stability under charging. This phenomenon is especially apparent for the cell with a high initial SOC where a more dramatic-rising α (the advancement ratio of critical times for thermal runaway due to charging) is observed.

Melting Enhancement in a Triple-Tube Latent Heat Storage System with Sloped Fins

Due to the potential cost saving and minimal temperature stratification, the energy storage based on phase-change materials (PCMs) can be a reliable approach for decoupling energy demand from immediate supply availability. However, due to their high heat resistance, these materials necessitate the introduction of enhancing additives, such as expanded surfaces and fins, to enable their deployment in more widespread thermal and energy storage applications. This study reports on how circular fins with staggered distribution and variable orientations can be employed for addressing the low thermal response rates in a PCM (Paraffin RT-35) triple-tube heat exchanger consisting of two heat-transfer fluids flow in opposites directions through the inner and the outer tubes. Various configurations, dimensions, and orientations of the circular fins at different flow conditions of the heat-transfer fluid were numerically examined and optimized using an experimentally validated computational fluid-dynamic model. The results show that the melting rate, compared with the base case of finless, can be improved by 88% and the heat charging rate by 34%, when the fin orientation is downward–upward along the left side and the right side of the PCM shell. The results also show that there is a benefit if longer fins with smaller thicknesses are adopted in the vertical direction of the storage unit. This benefit helps natural convection to play a greater role, resulting in higher melting rates. Changing the fins’ dimensions from (thickness × length) 2 × 7.071 mm2 to 0.55 × 25.76 mm2 decreases the melting time by 22% and increases the heat charging rate by 9.6%. This study has also confirmed the importance of selecting the suitable values of Reynolds numbers and the inlet temperatures of the heat-transfer fluid for optimizing the melting enhancement potential of circular fins with downward–upward fin orientations.

Studies on the Performance of Two Dimensional AlSi as the Anodes of Li Ion Battery

Recently, two-dimensional (2D) materials have been rapidly developed and they provided a wide application on the anode of the batteries, reducing the adverse effect of traditional ion batteries including low capacity, short cycle life, low charging rate and poor safety mainly coming from the use of graphite anode. The current report investigates the anode performances of AlSi, a new 2D material exfoliated from NaAlSi, for Li ion batterys (LIBs) through density functional theory (DFT) calculations and gives quantitative discussions on the Li ion valences, binding energies and open-circuit voltages of 2D AlSi anode. The results indicate that 2D AlSi performs great as a novel anode due to the moderate adhesion to Li and low barrier for ion diffusion. Furthermore, our research results illustrate a broad application prospect on the new anode inventions as well as reducing useless consumption on the batteries by the practice of AlSi anode.

Stability and performance analysis of wireless powered communication networks

In RF-based wireless powered communication networks (WPCNs), the wireless charging rate at a device is usually low or unstable because of health concerns or time-varying characteristics of wireless channels. Under a low charging rate, the data backlog at a wireless device may be continuously increasing, leading to system performance degradation and data loss. To keep a wireless powered device stable and preserve a finite data backlog, the upper limit of data arrival/acquisition rate at a wireless powered device must be solved under the given data transmission rate and wireless charging rate. Hence, in this paper a novel two-dimensional continuous-time Markov chain model was proposed for analyzing the stability condition of a wireless powered device with a finite energy storage buffer. The average number of data packets, average packet delay, and energy shortage probability at a wireless powered device were analyzed as well. Additionally, simulations were conducted to validate the analytic results and demonstrate that the obtained stability condition is necessary and sufficient for the wireless device.

Design and Implementation of Buck Converter for Fast Charging with Fuzzy Logic

This research presents a battery charger design that can charge faster than using a PWM type solar charge controller (SCC). SCC is often operated when the battery capacity is 80% so that the charging current that can be provided is only 10% to 20% of the battery capacity. The battery charging method applied in this study uses the principle of fast charging by adjusting the value of the current and the output voltage value of the buck converter. Fast charging has its own characteristic, obviously, the charging rate that is greater than the usual charging method, which is up to 1C of the battery capacity. The principle of fast charging in this study uses the constant current / constant voltage method. This converter is designed with the ability to produce current by the charging rate of 1C from a 12Ah battery capacity of 12 A and an output voltage of 16.8 V. To ensure that the output of the converter matches the setpoint, the duty cycle value is adjusted using fuzzy control. Based on the results obtained from the simulation, the control of this study obtained an output current 12 Amperes with error ripple current around 8.3%. The SOC on this battery increased by 75.74% in 45 minutes.

Numerical and experimental investigation of melting of paraffin in a hemicylindrical capsule

Phase change of paraffin in a hemicylindrical storage unit is investigated numerically and experimentally. The predicted findings are confirmed by comparison with the experimental results of the present work. Good agreements are achieved between the two approaches. The influence of the hot wall temperatures of 80, 85 and 90 °C is examined. The conduction mechanism is dominant only during the initial periods of the charging process, while buoyancy-driven convection is prevalent at later stages. The charging rate and stored energy both increased, whereas the melting time is reduced as the wall temperature increases. The Nusselt number increases sharply at the initial period of the fusion process, followed by a decaying trend with time until it stabilizes when the charging process is terminated. Increasing the cell diameter from 20 to 40 cm will raise the melting time by 300% for the wall temperature of 90 °C. In addition, under the same operating conditions, the melting of the PCM inside the hemicylindrical cell is faster than that observed in a rectangular one with equivalent volume. Savings in melting time due to using hemicylindrical container instead of a rectangular one of equivalent PCM volume are about 7.1, 8.3 and 11.7% for hot-wall temperatures of 65, 75 and 85 °C, respectively.