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Why is this important?
Batteries are critical to powering many of our everyday technologies. Increased demand in areas such as grid transportation and storage will require longer-lasting, higher-capacity batteries. Scientific advances in batteries could meet the demand for more energy storage while ensuring these next-generation batteries are safe, cost-effective and sustainable. However, challenges remain.
Technology
What is that?
A battery is an energy storage device that consists of a chemical solution called an electrolyte and a separator that acts as a barrier between the two terminals — the anode and the cathode. During use, the electrolyte allows the flow of charged particles, such as lithium ions, from the anode to the cathode. This produces an electric current that flows from the battery to the device through an external circuit. Charging the battery reverses this process. Different applications, such as electric vehicles or grid storage, require different battery properties – such as size, weight, portability or duration of use – each of which comes with trade-offs.
Figure 1. An example of how rechargeable lithium-ion batteries work during use
Most current battery research focuses on lithium-based systems, which can store a lot of energy in a small volume and go through many charge cycles. According to the American Chemical Society, lithium-ion batteries will account for 70 percent of the rechargeable battery market by 2025. Lithium supplies should increase to meet this demand, fueling efforts to develop advanced battery technologies that use more earth-rich materials and reduce reliance on on materials of foreign production.
How does it work?
Scientists are investigating how to replace critical elements in various components of lithium-ion batteries to improve their performance and safety while using more sustainable, widely available and cost-effective materials. For example, the standard material used for the anode of lithium-ion batteries is graphite — the same flaky carbon material used in pencils. However, silicon is a cheaper and more readily available material that is safer and can potentially store 10 times more lithium by weight.
Alternative cathode materials are also being tested for lithium-ion batteries. For example, different metal oxides are commonly used in the cathode to interact with the lithium and give the battery different properties. Alternatively, lithium-sulfur batteries contain a sulfur-based cathode that reacts with lithium ions to form lithium sulfide, which could allow the cells to store 5 times more energy than a conventional lithium-ion battery. Sulfur is an abundant element that can be mined in the US. That makes it a more viable alternative to other metals commonly used in lithium-ion battery cathodes, such as cobalt, which is expensive and can come from overseas mines with controversial labor or mining practices. .
Another advance replaces the typically liquid electrolyte—which can be flammable and can ignite when overheated—with safer, more stable materials. For example, using a solid electrolyte such as a ceramic or glassy material can prevent the accumulation of lithium salt crystals that can short circuit the battery and cause a fire. These solid-state batteries have the potential to store twice as much energy as conventional lithium-ion batteries, increasing how long the battery can run before needing to be recharged.
Lithium-ion batteries are generally limited to short-term use. Rechargeable metal-air batteries and flow batteries can provide longer storage durations, which could provide advantages in storing intermittent energy produced from renewable sources for use when needed. Metal-air batteries use a metal anode paired with a porous cathode to allow oxygen to flow from the surrounding air. Because one terminal is porous, these batteries are lighter than conventional batteries. The researchers investigated various metals — such as aluminum, lithium, sodium, tin and zinc — for potential use. Each of them has different advantages and disadvantages. For example, an aluminum-air battery is light, recyclable, made from common materials, and inexpensive, but is difficult to charge due to its tendency to corrode.
Unlike standard rechargeable batteries, flow batteries store liquid electrolytes in external reservoirs. Since there is no size limit for external tanks, the storage capacity of the flow battery can be increased as needed. This makes them ideal for storing large amounts of energy for the grid, but less useful in portable applications such as electric vehicles.
Figure 2. Example of how flow batteries work for a network application
One of the most advanced flow batteries uses vanadium ions in the electrolyte. Vanadium is expensive and scarce; however, vanadium ions are stable and can pass through the battery over and over again without unwanted side reactions, theoretically providing unlimited storage. However, vanadium batteries cannot store much energy in a small volume, so they require large external reservoirs to hold enough power to be useful. Researchers are investigating different chemistries for flow batteries – including zinc-bromine, which uses cheap, readily available materials.
How ripe is it?
Advances in lithium-ion batteries are in various stages of research, but none are currently in commercial use for electric vehicles or grid storage. Batteries with sulfur-based cathodes, silicon-based anodes, and solid electrolytes are all in the pilot phase for transportation applications, with the latter two being piloted for use in electric vehicles. Batteries with silicon-based anodes are commercially available only in small electronics.
Non-rechargeable metal-air batteries can be found in devices such as hearing aids; however, currently no metal-air rechargeable battery chemistry has reached large-scale commercialization. Most research on flow battery chemistry has been conducted on a small scale in laboratories; however, flow batteries are in commercial use for several grid and storage applications—including the US, Japan, and Australia.
Possibilities
- Advanced batteries could be key to moving away from fossil fuels for transportation and electricity generation. For example, they could help the grid store larger amounts of intermittent energy from renewable sources for use during times when weather conditions do not produce enough energy or a surge of energy is needed.
- Increasing battery capacity and the number of charge cycles through advanced battery technologies can help electric vehicles travel further between charges and extend battery life.
- Advanced batteries can be designed to use materials that are more abundant or produced domestically, reducing U.S. reliance on expensive materials with potential supply chain problems or national security risks—such as lithium or vanadium.
Challenges
- The initial costs for manufacturing advanced battery technologies are high.
- Regulations can vary by jurisdiction, which presents a challenge for companies operating in multiple locations.
- Most batteries have a limited lifespan, and there is currently limited technology or infrastructure to address recycling or disposal.
Policy context and issues
- What kinds of research could policymakers encourage about the potential use of advanced battery technologies to support renewable energy sources and provide backups when energy demand is high?
- How might policymakers encourage the possible use of advanced battery technologies, including electric vehicles and grid storage?
- What steps can federal or state agencies take if they want to support the use of these technologies in multiple jurisdictions with different regulatory requirements?
- What steps could policy makers take if they want to encourage or operationalize battery recycling and reuse processes on an industrial scale?
For more information, contact Karen L. Howard at (202) 512-6888 or HowardK@gao.gov.
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