Freeze battery - defrost helps to store electricity for many months

Scientists develop a new type of battery to store electricity for a long time with low materials cost, about 23 USD per kWh.

A team of scientists at the US Department of Energy's Pacific Northwest National Laboratory (PNNL) has developed a "freeze-defrost" battery with the ability to "freeze" energy for later use. The new study was published online in the journal Cell Reports Physical Science on March 23.

The battery prototype is about the size of a hockey puck, but has enormous potential. In the future, the new battery model will help store energy from intermittent sources such as sun and wind for a long time.

First, the battery is charged by heating it to 180 degrees Celsius, causing ions to flow through the liquid electrolyte to generate chemical energy. The battery is then cooled down to room temperature, locking in its energy. The electrolyte becomes solid and the energetic ions are almost stationary. When needed, the battery is reheated and energy flows.

Freezing - defrosting occurs thanks to the battery electrolyte, which is molten salt. This material is a liquid at high temperature but a solid at room temperature.

Freezing - defrosting technology helps avoid a familiar problem for those who have "left behind" their car for a long time, which is the battery that self-discharges when inactive. Discharge rates as fast as those found in most cars or laptops would be problematic for batteries designed to store energy for months. PNNL's freeze-thaw battery holds up to 92% capacity over 12 weeks.

The team avoided rare, expensive, and reactive materials. Instead, they use common and readily available materials. The anode and cathode electrodes are made of aluminum and nickel, respectively. Experts also add sulfur, a cheap and common element, to the electrolyte to enhance the battery's ability to store energy. In addition, they eliminated the ceramic separator between the anode and the cathode, replacing it with fiberglass. This reduces costs and makes the battery last longer through the freeze-thaw cycle.

The battery's energy is stored at a material cost of about $23 per kWh. The team is working on using iron, a cheaper material, in the hope of reducing the cost of the material to about $6 per kWh, about 15 times less than the material cost of today's lithium-ion batteries. The theoretical energy density of the battery is 260 Wh per kg - higher than that of a lead acid battery.

Batteries designed to store electricity seasonally can only charge and discharge once or twice a year, the team says. Unlike batteries for electric cars, laptops or other consumer devices, batteries that store electricity do not need to go through hundreds or thousands of charge and discharge cycles.