They always say that heat can be detrimental to your smartphone; keep it out of elevated temperatures, don’t let your phone overheat and don’t throw your phone in the oven. One reason is because heat could cause damage to your battery. Heat actually causes a battery’s fluid to evaporate, meaning the loss of electrolytes; leading to permanent internal damage. Increased temperatures make for an increased rate of chemical reactions. While it may seem as through you are getting better performance due to these faster reactions, you actually cause the self-discharge rate to double with each 10°C increase in temperature.
After reading that, you may think it’s not so hot being so hot. Over at the Massachusetts Institute of Technology, researchers have been working on a way to tap into ambient heat and convert it into usable electrical power. They’ve developed a button sized battery, that self-charges using low heat; roughly between 20°C and 60°C. This means the battery could charge while sitting in your pocket; perhaps faster if it’s in your back pocket, after you’ve eaten a burrito.
Dr Gang Chen, head of the mechanical engineering department at MIT, who led the work, said the technology could lead to new mobile phone batteries that can be charged without needing to be plugged in.
He said: ‘It is a self-powered device and may be attractive for places without electric grid.
‘To generate enough power for practical applications (such as in mobile phones), better material and system designs are needed, and we are working on it.
‘With further development, there is potential to use such batteries to convert low grade heat into electricity at an attractive cost for broader applications. It uses inexpensive materials. It may have potential application for harvesting thermal energy from the environment, especially in remote areas.’
The team took advantage of the thermally regenerative electrochemical cycle relationship, allowing for their ¾ of an inch battery to be charged at a high temperature and ability to deliver the energy at a lower temperature. This is a breakthrough, as the team was earlier able to harvest heat energy between 60°C and 100°C. The only downside to this charging technology is the very thing it harnesses, temperature. The idea is that the battery would cool down when removed from the pocket; if the room temperature matches body temperature, the charging method becomes less efficient.
Currently, their prototype can achieve a heat to electricity conversion rate of a mere 2%. It’s Dr Chen’s hope that they can increase that rate to 12%.
‘Tremendous low-grade heat is stored in industrial processes and the environment. Efficient and low-cost utilization of the low-grade heat is critical to imminent energy and environmental challenges.The upper limit of efficiency for harvesting heat is proportional to the temperature difference between hot source and cold source - room temperature. For low temperature heat sources, this temperature difference is small, so that upper limit of efficiency is already low. It takes some temperature difference to transfer heat into the heat engines, which further reduces the temperature range the heat engine works.’