One of today’s most challenging tasks in energy production and storage is to find a means to store energy for use at peak times when power is most expensive. Batteries are often paired with renewables to store energy produced at wind and solar farms and to stabilize the difference between demand and supply. The biggest problem with conventional batteries, however, is that developing a commercially-viable battery from readily available and cheap materials has proved an elusive goal for many a researcher.
Now (2017), scientists at Stanford University have designed a battery made with urea, commonly found in fertilizers and mammal urine, which could provide a low-cost way of storing energy produced through solar power or other forms of renewable energy for consumption during off-peak hours. The battery is nonflammable and contains electrodes made from abundant aluminum and graphite. Its electrolyte’s main ingredient, urea, is already industrially produced by the ton for plant fertilizers. The new battery design scored 99.7% on the Coulombic efficiency rating, which was extremely high.
This new battery uses some of the cheapest and most abundant materials you can find on Earth and has a very good performance. The scientists claimed that the battery may be a good replacement for lithium-ion batteries, which are currently used as an energy storage battery. However, these batteries are expensive and do have a short lifespan.
The battery was especially designed for grid storage of electricity from renewable energy sources, such as wind and solar. It is an updated version of a first-of-its-kind aluminium-ion battery introduced in 2015 by Stanford professor, Hongjie Dai, and his team. The original version used a chemical mixture known as EMIC (1-ethyl-3-methylimidazolium chloride) as its main electrolyte ingredient, which when mixed with aluminium chloride makes a liquid salt, or ionic liquid. This high-performance aluminum battery was fast-charging, long-lasting, and inexpensive. Researchers believed that the new technology offered a safe alternative to many commercial batteries. An aluminum-ion battery consisted of two electrodes: a negatively charged anode made of aluminum and a positively charged cathode. For the experimental battery, the Stanford team placed the aluminum anode and graphite cathode, along with an ionic liquid electrolyte, inside a flexible polymer-coated pouch. The advantage of this battery was that, in contrast to conventional aluminum batteries developed at other laboratories which usually died after just 100 charge-discharge cycles, the Stanford battery was able to withstand more than 7,500 cycles without any loss of capacity. Another feature of the aluminum battery is flexibility, as it can bent and folded, so it has the potential for use in flexible electronic devices. Aluminum is also a cheaper metal than lithium.
At the same time (2017), the same scientists developed a secondary Al battery system based on the reversible deposition/stripping of aluminum at the Al negative electrode and reversible intercalation/deintercalation of chloroaluminate anions at the graphite positive electrode in a non-flammable 1-ethyl-3-methylimidazolium chloroaluminate (EMIC-AlCl3) IL electrolyte (7, 8). During charging, Al2Cl7- was reduced to deposit aluminum metal, and AlCl4−ions intercalated (to maintain neutrality) in graphite as carbon was oxidized. During discharge, this battery exhibited a cathode specific capacity of∼70 mAh g−1 with a Coulombic efficiency (CE) of 97–98%, and ultrahigh charge/discharge rate (up to 5,000 mA g−1) for over 7,000 cycles.
One of the main advantages of the new urea battery is that it consists of some of the cheapest and most abundant materials you can find on Earth. So, the cost of producing this battery is low, its efficiency is high and it has a long cycle life. The Coulombic efficiency for this battery is high – 99.7 percent. Today’s batteries, like lithium-ion or lead acid batteries, are costly and have limited lifespans. In comparison to lithium-ion batteries, the new urea battery is non-flammable and therefore less risky.
To meet the demands of grid storage, a commercial battery would have to be designed that could last at least ten years. Understanding the chemical processes inside the battery will surely play an important role in extending its lifetime. The outlook is promising. In the lab, urea-based aluminium ion batteries can go through about 1,500 charge cycles with a 45-minute charging time. In the future they might even reach higher capacities.