Soldiers taking enemy fire in 120-degree desert heat, carrying up to 100-pounds of gear and conducting attack operations at night are totally reliant upon battery-powered weapons, sensors and computers -- a potential scenario inspiring current Army Research Laboratory work to engineer longer-lasting, more stable and, of critical live-saving significance, less flammable Lithium-ion batteries.
Current Lithium-ion batteries, well known for their widespread use in commercial items such as laptops, are virtually indispensable to the military; they are used for a wide range of combat essential technologies, including computers, night vision, laptops, laser illuminators, radios, gun sights, night versions of gun sights, GPS units and navigational systems. However, despite their utility and crucial role supporting warfare, existing Lithium-Ion batteries are extremely heat-sensitive and subject to explosion in certain combat circumstances.
Simple desert heat, incoming enemy fire or hot flames emerging from an IED explosion or weapons attack could cause Lithium-ion batteries to malfunction, burst into flames...or even explode.
For this reason, the Army Research Office and Georgia Tech are now experimenting with new materials with which to power batteries, which can both hold more Lithium and also vastly increase safety for soldiers at war. This is because new materials, such as polymer substances now being experimented with by the ARL, can not only increase battery density for power longevity but also reduce the possibilities that battery components, such as its electrolytes, will vaporize and explode in flames.
Mobile battery power emerges from the flow of electrons from one electrode, or solid electric conductor, to another within the battery. This includes one negatively charged electrode - the anode -- and one positive electrode called the cathode. Materials called electrolytes are placed in between the anode and cathode electrodes, helping to facilitate the chemical reaction necessary for the cathode to receive the flow of electrons -- generating electricity.
"We are looking at polymeric flexible electrolytes, which could replace more dangerous liquid electrolytes. A polymer is a solid which, if you were to puncture... water and air will go in. You do have an ignition source but you do not have a readily flammable solvent," Dr. Robert Mantz, division chief, electrochemistry, Army Research Office, an element of U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, told Warrior in an interview.
The current ARL work, given this, is focused upon identifying materials and electrolytes able to produce more energy per unit, function as a better performing battery and, as Mantz put it, be “inherently more safe.”
"In most systems, carbonates are used as electrolytes. Their low viscosity and transport are faster as a liquid, but once you generate heat carbonates want to boil and generate gas. Carbonate starts coming out, which is gaseous and very flammable. Water and material react and serve as an ignition source," Mantz explained.
A wire running through the battery facilitates the flow of electrons between the cathode and anode where, Mantz added, two types of chemical reactions occur - reduction and oxidation. These reactions, as explained in an interesting essay by the Australian Academy of Science, includes the flow of electrons between the anode the cathode. Oxidation is the loss of electrons created by a chemical reaction at the anode, resulting in the generation and release of negatively charged electrons and positively charged Lithium ions.. (molecules or atoms).
“Oxidation happens at the anode, and the cathode is where reduction occurs and where the lithium would be reduced. Lithium starts as cation (positively charged ion) and is reduced at the Cathode,” Mantz said.
At the cathode, another chemical reaction occurs simultaneously that enables the electrode to pull positive Lithium ions from the electrolyte.
An essay by the U.S. Department of Energy explains this process by stating “the movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector (cathode). While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device, the opposite happens: Lithium ions are released by the cathode and received by the anode.” (U.S. Dept. of Energy, Office of Energy Efficiency & Renewable Energy)
The flow of electrons takes place between electrodes, (anode and cathode) which can be various kinds of metals or materials with conductive properties. Some batteries have used Zinc as an anode and silver as a cathode, according to the Australian essay. Some common cathode materials include Lithium Manganate, Lithium Nickel Cobalt Aluminum Oxide and Lithium Colbaltate, according to an essay from Battery University. Interestingly, the popularity of Lithium-Ion batteries have led to a circumstance wherein Cobalt and Nickel are more difficult to acquire and more expensive. As a result, part of the ARO-Georgia Tech effort involves experiments to use lower-cost "transition metal fluorides," according to an ARO paper.
“Cathodes made from iron fluoride have enormous potential because of their high capacity, low material costs and very broad availability of iron,” Gleb Yushin, a professor in Georgia Tech’s School of Materials Science and Engineering, said in an ARO statement.
The electrodes are stacked up in pairs throughout the battery, called cells, which are separated by the electrolytes. The anode called the negative electrode, and the cathode, or positive electrode, are successively stacked together throughout the battery.
“The difference in standard potential between the electrodes kind of equates to the force with which electrons will travel between the two electrodes. This is known as the cell’s overall electrochemical potential, and it determines the cell’s voltage,” the Australian essay states.
From the anode, an electron flow travels through an external wire, while positively charged Lithium ions are generated to travel through the electrolyte solution. At the anode, negatively charged electrons and positively charged ions are generated by a chemical reaction, driving a flow of negatively charged electrons through a wire in the battery. These negatively charged electrons need to be neutralized, or reduced in capacity, by the positive ions in the electrolyte materials, enabling the cathode electrode to receive the electrons -- and generate electricity.
Electrolyte possibilities, now being worked on by ARL scientists, can be liquid, gel or solid substances, inspiring the current experimentation with polymer materials.
What all of this amounts to is a chemical process, involving two simultaneous chemical reactions, through which batteries generate and store electricity. Simply put, the ARL is experimenting with how different kinds of electrolytes, including solid materials such as polymers, can extend, improve and further protect soldier missions.
"Polymer electrolytes are solid at room temperature and are a unique class of electrolytes. They have pores, so they are conductive,” Mantz told Warrior.
An interesting essay from Battery University further explains how temperature rises in Lithium-ion battery cells can “approach the melting point of Lithium, causing thermal runaway, also known as ‘venting with flame.’” An overheated anode can generate needle-like structures call dendrites which can “short out” a battery by puncturing the electrolytes.
This technical advancement, should it come to fruition, introduces new strategic advantages. Naturally, longer-lasting electronics, weapons and sensors not only increase forward-operating attack missions but also safeguard soldiers from enemy attack. It goes without saying that soldiers under enemy fire would instantly be extremely vulnerable should they lose electrical power, especially when carrying potentially flammable batteries.
Lithium-ions have been the preferred materials for years, in part because “Lithium is the lightest of all metals, has the greatest electromechanical potential and provides the largest specific energy per weight,” the Battery University essay states.
There is not a specific timeframe regarding when this emerging battery technology will be operational, yet ARL scientists do explain the program is making rapid progress.