Pyroelectric energy conversion to boost battery life

The heat your computer generates could help increase battery life by a fifth with a nanostructured thin film technology that turns that waste warmth into electricity.

The thin film converts heat into electricity using what is called pyroelectrics and it could be just 50 nanometres thick. Pyroelectric energy conversion makes use of a property of some materials where heat induces an electrical charge. This means the thin film has no moving parts, the very structure of the material attains a charge as it absorbs the heat. The captured energy could be used to recharge the battery during a computer’s use. According to Lawrence Berkeley National Laboratory, nearly 70 percent of the energy produced in the United States each year is wasted as heat.

“The idea would be to effectively extend your battery life by 10-20% more by grabbing some of that wasted energy,” said Lane Martin, an associate professor of materials science and engineering at Lawrence Berkeley National Laboratory. Much of the waste heat emitted by household and industrial electronics is less than 100 degrees Celsius and does not present a problem for capture by pyroelectric materials. His research team may one day spin out a company to commercially exploit the thin films or work with an established firm.

Pyroelectrics is not a phenomenon new to science, but the Lawrence Berkeley work claims new records for the levels of energy conversion. The team has achieved an energy density of 1.06 Joules per cubic centimetre and a power density of 526 Watts per cubic centimetre. This may be sufficient for commercial applications. The effectiveness of converting heat into power is called the Carnot efficiency, named after 19th century French physicist Nicolas Leonard Sadi Carnot. Martin said their thin film is 19% efficient.

“A significant contribution of [our] new study is to demystify that [pyroelectric] process and improve the understanding of pyroelectric physics,” Martin explains. Understanding that physics also means more accurate measurements of the thin films’ pyroelectric properties. Martin and his colleagues have designed a thin film that allows the temperature and electrical currents created to be measured, to test its power generation capabilities.

The Lawrence Berkeley work will continue, and as Martin explains, it will attempt to answer the question, “what are the limits of such technologies when it comes to energy conversion?” Different materials might have higher efficiency levels and the researchers already know that no one single material will be applicable to all forms of electronics. Martin added that: “Another thing that is important to know in this regard is what waste heat stream somebody wants to harvest. This sets the temperatures, it sets the material, it sets the ways we can control and manipulate it.” The expectation is that researchers could “tune” a material for a specific waste heat stream.

Converting that heat into electricity is a large part of the solution, but then how is that energy fed back into the battery or electronic circuit? Martin explains that circuitry might need, “conditioning hardware,” to allow the battery to be fed this power. “There is a group at the United States [US] Army Research Laboratory working on this problem.” And Martin’s research was supported, in part, by grants from the US Army Research Office and the US government’s National Science Foundation.

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