February/March 2021

RESEARCH 7 www.power-mag.com Issue 1 2021 Power Electronics Europe lower temperature is on the heat pipe. Additionally, with the same GHP diameter and length, the temperature on the heater decreases by improving the thermal conductivity of GF. This observation implies that improving thermal designed. In particular, thermal conductivity of container was set as 400, 900, and 1400 W m -1 K -1 to figure out the contribution from the container in a GHP. Similar to the experimental results, it was found that the shorter GHP, the conductivity of the container would effectively promote heat dissipation of GHP. A commercial copper heat pipe with the same diameter (CHP, Spread Fast AB, 6 mm) was used as a reference to evaluate the thermal dispassion behavior of GHP. In the CHP, copper and sintered copper powder works as container and wick structure (Figure 2G). Similar temperature distribution and start-up behavior are observed from GHP and CHP, as shown in Figure 3H. While compared to CHP, the start-up time of GHP decreases 35 %. Such improvement maybe because the rough and flexible surface property of GF, which decrease contact resistance between the heat pipe and heat source. Moreover, the GHP shows a significant advantage on specify thermal transfer coefficient (Figure 2I). A standard 90 mm GHP weights 2.1 g while the weight of the same diameter CHP is 12.9 g. The specific thermal transfer coefficient of GHP is improved by 3.5 times compared to that of the CHP. Therefore, such a high specific thermal transfer coefficient makes GHP an ideal candidate for thermal management on lightweight applications such as in spacecraft, avionics, automotive and consumer systems where performance versus weight is of great concern. Literature A lightweight and high thermal performance graphene heat pipe https://doi.org/10.1002/nano.202000195 Heat dissipation performance of a 6 mm GHP (A, B, C, temperature distribution along GHP with lengths of 90, 130, and 150 mm; D, specific thermal transfer coefficient of GHP with length of 90, 130, and 150 mm (R 2 = 0.98607, 0.96344, 0.84614); E, temperature distribution on heater with 90, 130, and 150 mm GHP under 10 W input; F, start-up times of 90 mm GHP under various heat loading; G, cross?section SEM image of CHP; H, start-up times of GHP and CHP with 10 W heat loading; I, specific thermal transfer coefficient of GHP and CHP) ¶ Hot Salt Rechargeable Battery Using salt as a key ingredient, Chinese and British researchers have designed a new type of rechargeable battery that could accelerate the shift to greener electric transport. Many electric vehicles (EV) are powered by rechargeable lithium-ion batteries, but they can lose energy and power over time. Under certain conditions, such batteries can also overheat while working or charging, which can also degrade battery life and reduce miles per charge. To solve these issues, the University of Nottingham is collaborating with six scientific research institutes across China to develop an innovative and affordable energy store with the combined performance merits of a solid-oxide fuel cell and a metal-air battery. The new battery could significantly extend the range of electric vehicles, while being fully recyclable, environmentally-friendly, low-cost and safe. A solid-oxide fuel cell converts hydrogen and oxygen into electricity as a result of a chemical reaction. While they are highly- efficient at extracting energy from a fuel, durable, low-cost and greener to produce, they are not rechargeable. Meanwhile, metal-air batteries are electrochemical cells that uses a cheap metal such as iron and the oxygen present in air to generate electricity. During charging, they emit only oxygen into the atmosphere. Although not very durable, these high-energy dense batteries are rechargeable and can store and discharge as much electricity as lithium-ion batteries, but much more safely and cheaply. In the early research phases, the research team explored a high-temperature, iron-air battery design that used molten salt as a type of electrolyte - activated by heat - for electrical conductivity. Cheap and inflammable, molten salts help to give a battery impressive energy storage and power capability and a lengthy lifecycle. Key nano-technology However, molten salts also possess adverse characteristics. University of Nottingham study lead, Prof. George Chen said: “In extreme heat, molten salt can be aggressively corrosive, volatile and evaporate or leak, which is challenging to the safety and stability of battery design. There was an urgent need to fine-tune these electrolyte characteristics for better battery performance and to enable its future use in electric transport.” The researchers have now improved the technology by turning the molten salt into soft-solid salt, using solid oxide nano- powders. The novel quasi-solid-state (QSS) electrolyte, consisting of the molten eutectic mixture of Na2CO3-K2CO3 and nanoparticles of yttrium stabilized zirconia (YSZ) in a mass ratio of 1:1. The QSS electrolyte has relatively lower volatility in comparison with the pristine molten Na2CO3-K2CO3 eutectic, and therefore significantly suppresses the evaporation of molten salts, thanks to a strong interaction at the interface between molten salt and YSZ nanoparticles at high temperatures. The QSS electrolyte was used to construct an iron-air battery that performed excellently in charge-discharge cycling with high columbic and energy efficiencies. Also a redox mechanism at the three-phase interlines in the negative electrode appears. These findings can help establish a simpler and more efficient approach to designing low-cost and high-performance molten salt metal-air batteries with high stability and safety. Prof. Jianqiang Wang, from the Shanghai