Power/Performance Bits: May 9

Integrated battery and solar cell

Researchers from the Ulsan National Institute of Science and Technology (UNIST) in Korea developed a single-unit, photo-rechargeable portable power source based on miniaturized crystalline Si photovoltaics (c-Si PVs) and printed solid-state lithium-ion batteries (LIBs). The device uses a thin-film printing technique, in which the solid-state LIB is directly printed on the high-efficiency c-Si PV module.

According to the researchers, this single-unit PV-LIB device exhibits photo-electrochemical performance and design compactness that lie beyond those achievable by conventional PVs or LIBs alone.

In the study, the research team fabricated a solid-state LIB with a bipolar cell configuration directly on the aluminium (Al) electrode of a c-Si PV module through an in-series printing process. To enable the seamless architectural/electrical connection of the two different energy systems, the Al metal layer is simultaneously used as a current collector of the LIB, as well as an electrode for solar cells. This allows the battery to be charged without the loss of energy.

Schematic representation of the monolithically integrated SiPV–LIB device and the electrochemical performance of the bipolar LIB. (Source: UNIST)

The team connected the device to various portable electronics to explore its practical use. They fabricated a monolithically integrated smartcard by inserting the SiPV-LIB device into a pre-cut credit card. Then, electric circuits were drawn on the back of the credit card using a commercial Ag pen to connect the SiPV-LIB device with an LED lamp. The SiPV-LIB device was also electrically connected with a smartphone or MP3 player and its potential application as a supplementary portable power source was explored under sunlight illumination.

The SiPV-LIB device was capable of fully charging under sunlight illumination after 2 minutes with with a photo-electric conversion/storage efficiency of 7.61%. It also showed decent photo-rechargeable electric energy storage behavior even at a high temperature of 60°C and even at an extremely low light intensity of 8 mWcm-2, which corresponds to the intensity in a dimly-lit living room.

“This device provides a solution to fix both the energy density problem of batteries and the energy storage concerns of solar cells,” said Professor Sang-Young Lee, of Energy and Chemical Engineering at UNIST. “More importantly, batteries have relatively high power and energy densities under direct sunlight, which demonstrates its potential application as a solar-driven infinite energy conversion/storage system for use in electric vehicles and portable electronics.”

Rechargeable zinc battery

Researchers at the U.S. Naval Research Laboratory’s (NRL) Chemistry Division have developed a safer alternative to fire-prone lithium-ion batteries, which were recently banned for some applications on Navy ships and other military platforms.

The effort focused on water-based zinc batteries. The team demonstrated a breakthrough for nickel-zinc (Ni-Zn) batteries in which a three-dimensional Zn “sponge” replaces the powdered zinc anode traditionally used. With 3-D Zn, the battery provides an energy content and rechargeability that rival lithium-ion batteries while avoiding the safety issues that continue to plague lithium.

Zinc-based batteries are a standard battery for single-use applications, but are not considered rechargeable in practice due to their tendency to grow dendrites, metal conductive whiskers which can grow long enough to cause short circuits in the battery.

“The key to realizing rechargeable zinc-based batteries lies in controlling the behavior of the zinc during cycling,” said Joseph Parker of NRL. “Electric currents are more uniformly distributed within the sponge, making it physically difficult to form dendrites.”

The NRL team demonstrated Ni-3-D Zn performance in three ways: extending lifetime in single-use cells; cycling cells more than 100 times at an energy content competitive with lithium-ion batteries; and cycling cells more than 50,000 times in short duty-cycles with intermittent power bursts, similar to how batteries are used in some hybrid vehicles.

According to the researchers, the 3-D Zn sponge is ready to be deployed within the entire family of Zn-based alkaline batteries across the civilian and military sectors. “We can now offer an energy-relevant alternative, from drop-in replacements for lithium-ion to new opportunities in portable and wearable power, and manned and unmanned electric vehicles,” said Dr. Jeffrey Long of NRL, “while reducing safety hazards, easing transportation restrictions, and using earth-abundant materials.”