Power/Performance Bits: Sept. 23

Improved liquid battery
Researchers at MIT, led by a materials chemistry professor, have improved a proposed liquid battery system that could enable renewable energy sources to compete with conventional power plants.

Professor Donald Sadoway and some colleagues have already started a company to produce electrical-grid-scale liquid batteries, with layers of molten material that automatically separate due to their differing densities, but a new formula substitutes different metals for the molten layers used in a battery previously developed by the team.

The new formula allows the battery to work at a temperature more than 200 degrees Celsius lower than the previous formulation, which should simplify the battery’s design and extend its working life in addition to the lower operating temperature. Also, this new formulation will be less expensive to make.

The liquid-battery system promises 70% efficiency, and with further refinements may be able to do better. And unlike pumped hydro systems — which are only feasible in locations with sufficient water and an available hillside — the liquid batteries could be built virtually anywhere, and at virtually any size, the team noted.

A physical model of the liquid metal battery at room temperature, in a glass container. The bottom layer is the positive electrode. In the real battery this is an alloy of antimony and lead, represented here by mercury. The middle layer is the electrolyte — in reality, a mixed molten salt; here, a solution of salt in water. The top layer is the current collector of the negative electrode, a metal mesh of iron-nickel alloy. (Source: MIT)

This work also opens up whole new avenues of research, and the researchers will continue to search for other combinations of metals that might provide even lower-temperature, lower-cost, and higher-performance systems.

Liquid ink for better solar cells
A diverse team of UCLA scientists from the California NanoSystems Institute is improving the efficiency of new film materials that they said are revolutionizing solar cell technology.

The researchers have recently shown how they increased the power conversion efficiency of the materials kesterite and perovskite for making highly efficient and low-cost solar cells.

Kesterite is an inorganic substance made from abundant materials such as copper, zinc, tin and sulfur. The UCLA team developed a way to increase the conversion of sunlight to electricity by controlling the composition and dispersion of kesterite nanocrystals in an ink that’s used to create the film used in solar cells.

Perovskite is an organic and inorganic hybrid material that combines carbon and lead and was first used as solar cell material five years ago, but improvements have advanced its power conversion efficiency to nearly 20%.

Perovskite begins as a liquid ink, and the UCLA researchers delicately controlled the dynamics of the material during its growth, which is done in air at low temperatures. This makes manufacture of large-area perovskite devices with high performance levels inexpensive. The improved technique can be used in perovskite-based devices of such differing applications as light-emitting diodes, field-effect transistors, and sensors.

Diagram showing elemental layers of kesterite (CZTS, left) and perovskite.
(Source: UCLA)