Battery Storage Schemes Employ Freeze-Thaw Approach and More
Offering novel approaches to battery energy storage, a trio of research efforts are using electronic technologies and materials science to tackle energy storage challenges.
For renewable energy, the effective storage of electric power is imperative. That’s because many sources produce power at a rate that is environmentally dependent. For instance, solar panels produce a lot of power while in direct sunlight, but not as much on a rainy day.
These renewable energy applications all require batteries to be able to hold more charge, over a longer period of time, and these requirements are pushing researchers to the cutting-edge of electronics and materials science.
In this article, we’ll examine three such battery storage research efforts unveiled this year.
Overcoming the Performance Decline Problem
Earlier this year, a group of researchers at the US Department of Energy’s (DoE) Argonne National Laboratory announced a novel method for overcoming the decline that occurs with repeated charge-discharge cycling of batteries in the cathode.
Transition electron microscopic image (left) of synthesized cathode material. Schematic (right) shows strain and stress induced into the layered cathode structure. Image used courtesy of Argonne National Laboratory
While currently lithium-ion batteries are used in most situations, the research team at Argonne Lab sees promise in the sodium-ion structure. This is due to many factors, such as the abundance of sodium on Earth, bringing down materials cost. Because of the battery’s ability to cycle at a high voltage (4.5 V for example), a sodium-ion battery has a much higher energy density as compared to lithium-ion.
While these batteries have many advantages, the research team discovered defects in the material that form during the preparation of the cathode. These defects, found by X-ray probing and transmission electron microscopy, according to the group’s paper, destroy the lifetime of the battery as they eventually lead to a structural earthquake in the cathode.
These defects on the material arise during the cathode synthesis, where the temperature of the material is raised to a very high temperature, held there, and then dropped rapidly. The rapid drop causes strain, which the team discovered by noticing the surface becoming less smooth at this time.
This becomes the precursor to more serious strain leading to eventual breakdown during cathode cycling. The lifetime is found to be especially degraded when the cathode experiences high strain by cycling in high temperature environments or when fast charging is applied.
This kind of research allows teams to combat this in the manufacturing process, allowing sodium-ion batteries to be as robust as they are energy dense and low-cost.
Molten-salt Battery Has “Freeze-Thaw” Capability
Another new battery technology specifically applicable in renewable energy storage has been developed at the DoE’s Pacific Northwest National Laboratory (PNNL). In April, PNNL announced a novel molten-salt battery that developed with a “freeze-thaw” capability. This capability allows the battery to freeze its energy use and thaw it for use when needed.
As this animation shows, a long-duration battery can be charged with renewable energy, then discharge that energy when it’s needed months in the future. Image used courtesy of the DoE’s PNNL (Click to open animated gif)
For current flow, the battery must be heated up to 180 °C for the electrolyte to become a liquid allowing ion movement, while at room temperature the electrolyte becomes solid and the ions nearly stop moving.
This process allows one to control when to use energy and when to conserve it. That’s due to the fact that the solid electrolyte does not self-discharge when idle because it is capable of retaining 92.3% of its capacity over a span of 12 weeks, according to the team’s paper published in Cell Reports.
The battery anode and cathode are made of aluminum and nickel respectively, which are abundant on Earth, as well as sulfur—another low-cost material. Meanwhile, the component of the battery known as the separator, which is usually made of an expensive ceramic material, is made from simple fiberglass.
Increasing Thermal Conductivity Using Boron Nitride
Last, but not least, a research team led by Yingying Lu of Zhejiang University in China has developed a method of ultrafast battery heat dissipation. As explained in their research paper, in high energy density and fast charging applications, heat can cause a variety of safety concerns. Normal air and liquid cooling will not suffice in applications such as this.
Shown here is an h-BN/PW composite with ordered and interconnected thermal network that is derived from an ice template combined freeze-drying method. Image used courtesy of Yingying Lu and coauthors (Click to enlarge)
With that in mind, many look into phase-change materials. One of particular interest is paraffin wax due to its high latent heat capacity and low cost. However, the thermal conductivity of paraffin wax is low, hindering the material’s ability to transfer heat efficiently from the battery.
The team was able to find a way to increase the thermal conductivity eightfold by introducing a highly ordered hexagonal boron nitride network, resulting in a thermal conductivity of 1.86 Wm-1K-1. This material change resulted in the surface temperature of the battery being lowered by 6.9 °C, an improvement of the bare material by 2 °C to 5 °C during the continuous charge-discharge process.
Big Steps Toward More Effective Batteries
Collectively, these advances in battery technology have the capability of creating our batteries smaller, more cost-effective, more capable of storing energy for a long period of time, and easier to cool. These are large steps toward batteries that are able to sustain the green future we have planned.