Types of Batteries
What are batteries?
While there are several types of batteries, at its essence a battery is a device that converts chemical energy into electric energy. This electrochemistry happens through the flow of electrons from one material (electrode) to another, through an external circuit. The flow of electrons provides an electric current that can be used to do work. To balance the flow of electrons, charged ions (atoms or molecules with an electric charge) also flow through an electrolyte solution that is in contact with both electrodes. Different electrodes and electrolytes produce different chemical reactions that affect how the battery works, how much energy it can store, and its voltage.
Batteries consist of two electrical terminals called the cathode and the anode, separated by a chemical material called an electrolyte. To accept and release energy, a battery is coupled to an external circuit. Electrons move through the circuit, while ions simultaneously move through the electrolyte. Several materials can be used as battery electrodes. Different materials have different electrochemical properties, so they produce different results when assembled in a battery cell.
Batteries were invented in 1800, but their complex chemical processes are still being explored and improved. Scientists are using new tools to better understand the electrical and chemical processes in batteries to produce a new generation of highly efficient, electrical energy storage systems. While we may be more familiar with the rechargeable batteries we use every day in personal electronics, vehicles, and power tools, batteries are also essential for large-scale electricity storage to support the grid, and for storing the power generated by renewable sources. This growing need to store energy for a variety of applications has given rise to the development of several battery types, with researchers focused on ways to extend their life, expand their capacity, and reduce their costs.
What types of batteries could be used for both transportation and grid applications?
Picture a D-cell battery that once was the common perception of a battery. This kind of battery powered flashlights and toys, and had to be replaced once it was dead. Now, picture the need for lightweight, rechargeable energy storage systems that power our cars down the road or that are as large as an office building, storing energy from renewable resources so they can be used when and where they are needed on the grid. That represents the versatility of energy storage systems—better known as batteries—that scientists are developing today.
Lithium-ion: Li-ion batteries are commonly used in portable electronics and electric vehicles—but they also represent about 97 percent of the grid energy storage market. These rechargeable batteries have two electrodes: one that's called a positive electrode and contains lithium, and another called a negative electrode that's typically made of graphite. Electricity is generated when electrons flow through a wire that connects the two.
Sodium-Ion: Sodium-ion batteries are highly efficient and relatively cheap, offering promise for both grid energy storage and vehicle applications, but developing such batteries with high energy density and a long life has been a challenge. Pacific Northwest National Laboratory (PNNL) researchers are working towards making sodium a viable replacement for lithium for grid energy storage by developing a protective layer to reduce consumption of sodium ions in the battery.
What kinds of batteries are being explored for use in vehicles?
While lithium-ion and sodium-ion batteries are commonly used in consumer electronics and are commercialized for use in electric vehicles, scientists are exploring an array of other chemistries that may prove to be more effective, last longer, and are cheaper than those in use today.
Lithium-Sulfur: These lightweight batteries, which don't have any of the critical materials in positive electrodes, hold potential for electric vehicles. They can store two times the energy of batteries on today’s store shelves, but their charge is often short lived. The battery's cathode slowly disintegrates, and forms molecules called polysulfides that dissolve into the battery's electrolyte liquid. PNNL researchers have developed solutions to protect the anode and stabilize the cathode, and we're working to bring them to real-world applications.
Lithium-Metal: These batteries offer promise for powering electric vehicles that can travel further on a single charge. They are like Li-ion batteries, but with lithium metal in place of graphite anodes. These batteries hold almost twice the energy of lithium-ion batteries, and they weigh less. While promising, one challenge with high-energy lithium-metal batteries has been that they don’t last as long as their lithium-ion counterparts.
Battery technologies for grid energy storage
Next-generation batteries are needed to improve the reliability and resilience of the electrical grid in a decarbonized, electrified future. These batteries will store excess energy–including renewable energy–when it is produced and then release that electricity back into the grid when it’s needed. They also can provide backup power during or after natural disasters, like ice storms, extreme heat waves, hurricanes, and more. In addition to lithium-ion and sodium-ion batteries, the following kinds of batteries are also being explored for grid-scale energy storage.
Flow Batteries: Flow batteries provide long-lasting, rechargeable energy storage, particularly for grid reliability. Unlike solid-state batteries, flow batteries store energy in a liquid electrolyte. PNNL researchers developed an inexpensive and effective new flow battery that uses a simple sugar derivative to speed up the chemical reaction that converts energy stored in chemical bonds, releasing energy to power an external circuit. Flow batteries can serve as backup power for the electric grid and are a key pillar of a decarbonization strategy to store energy from renewable energy resources. They can be built at any scale, from the lab-bench scale, as in the PNNL study, to the size of a city block.
Vanadium-Redox Flow: These batteries integrate energy from renewable resources, such as solar and wind farms. For years, sensitivity to high temperature, high cost, and smaller storage capacity limited the widespread use of these batteries. PNNL researchers developed a new generation of vanadium flow battery with a significantly improved energy density and wider temperature window for operation, that is capable of deployment at grid scale. While there are many flow battery designs and some commercial installations, vanadium is costly and difficult to obtain. Research teams are seeking effective alternative technologies that use more common materials that are easily synthesized, stable, and nontoxic.
Zinc-Polyiodide Flow: The zinc-polyiodide redox flow battery uses an electrolyte that has more than two times the energy density, or stored energy, of the next-best flow battery—approaching the energy density of the low-end lithium-ion batteries used to power portable electronic devices and some small electric vehicles.
Organic Aqueous Flow: Early flow battery research on redox-active electrolyte materials has focused on inorganic metal ions and halogen ions. But electrolytes using organic molecules may have an advantage because of their structural diversity, customizability, and potential low cost.
Sodium-Metal Halide: Also known as ZEBRA batteries, these hold potential as stationary batteries used to store energy for the grid. PNNL researchers have developed a design that is more stable and less expensive to manufacture, with increased energy density.
Zinc-air: Several technologies and configurations employ metallic zinc as the battery anode. Zinc-air batteries generate electricity when zinc is oxidized with oxygen from the air. They have a higher energy density than lithium-ion batteries, meaning that they can store more energy in a smaller space. The small batteries used in hearing aids today are typically zinc-air batteries, but they could also be used at larger scales for industrial applications or grid-scale energy storage.
Zinc-Manganese Oxide: These easy-to-make batteries use abundant, inexpensive materials, and their energy density can exceed lead-acid batteries, while touting a better safety record than lithium-ion batteries. The challenge, though, is making zinc-manganese batteries rechargeable.
Lead-acid: Lead-acid batteries are made up of lead dioxide for the positive electrode and lead for the negative electrode. Their advantages in terms of cost-effectiveness, reliability, adaptability, energy storage capacity, and recyclability make them competitive in specific applications.
PNNL researchers are advancing batteries for a cleaner energy future
New energy storage technologies will play a foundational role in tomorrow’s cleaner, more reliable, and resilient electric power grid and the transition to a decarbonized transportation sector. Leveraging decades of experience and state-of-the-art facilities, researchers at PNNL push the boundaries of battery technology, matching the right chemistry and design with the right application, while helping to optimize their performance and lower their costs.
Researchers at PNNL are advancing energy storage solutions—testing new battery technologies, creating models to investigate new materials for more efficient and longer-lasting storage, and developing strategies so that new energy storage systems can be deployed safely and cost-effectively.
PNNL’s Battery Reliability Test Laboratory is part of its world-class battery development capability. The laboratory was established to accelerate the development of grid energy storage technologies that will help modernize the power grid. PNNL battery experts develop the evaluation tools, materials, and system designs to test emerging or existing battery technologies that support grid-scale energy storage. The facility is one of very few experimental battery manufacturing laboratories that are available to help academia and industry develop and test new batteries.
PNNL’s Advanced Battery Facility enables scientists to test different materials–including lithium-metal, sulfur, sodium, and magnesium–to make batteries last longer and store more energy. The tests are helping scientists from national laboratories, universities and industry find lower-cost replacements for today’s most common rechargeable battery, the lithium-ion battery.
A new facility called the Grid Storage Launchpad is opening on the PNNL campus in 2024. Through independent testing and validation of grid energy storage technologies, the GSL will develop and implement rigorous grid performance standards and requirements that span the entire energy storage R&D development cycle—from basic materials synthesis to advanced prototyping. The GSL will accelerate battery development and deployment by helping validate new technologies; foster collaboration among national laboratories, industry, and academia; and provide education to develop the workforce needed for this industry.