Storing energy to smooth the intermittency of wind and solar power can be accomplished in a number of ways, including mechanical (pumped hydro, flywheels, compressed air and others), thermochemical (phase-change materials and molten salts, for example), chemical (conversion of electricity to hydrogen) and electrical (ultracapacitors and others). Because of their flexibility, efficiency and energy density, electrochemical approaches (in the form of rechargeable batteries) are likely to play a dominant role in the future of grid-energy storage. This one-page reference outlines the main battery chemistries for electrical-grid-energy storage applications, along with their strengths and weaknesses.
Lithium-ion batteries
Driven by innovation and cost reduction in portable electronics and electric vehicle applications, lithium-ion batteries (LIBs) have emerged as a critical technology for grid-energy storage. LIBs operate by shuttling Li+ ions between anode and cathode, through a porous electrolyte membrane that permits Li+ ions to pass, but prevents contact between electrodes (Figure 1). During discharge, Li+ ions move from anode to cathode and generate a flow of electrons through the external circuitry. For charging, an external power source drives Li+ ions from the cathode to the anode (usually graphite), where they insert themselves between layers of carbon.
FIGURE 1. In lithium-ion batteries, Li+ ions move between a cathode and anode through a membrane
In grid-energy storage, LIBs have several advantages, along with several limitations.
Advantages. LIBs have high specific energy (watt-hours per kilogram), high power density and high round-trip efficiency (90–95%) [1]. Round-trip efficiency refers to the percentage of energy put into the battery during charging that can be retrieved during discharge. They also have low self-discharge rates.
Disadvantages. LIBs have a high initial cost, due in part to expensive raw materials that can present supply-chain challenges. However, for LIBs, the levelized cost of storage (total lifetime cost of a storage system divided by the total electricity it delivers), is often more competitive [2]. Over time, LIBs can degrade, giving them a limited service life. They can also have safety issues, due to the loss of thermal stability as the batteries age.
Because of their characteristics, LIBs are more suitable for shorter-duration (6–8 h) storage. Cost and degradation make them less ideal for long-duration (12–100 h storage).
LFP versus NMC
The types of LIBs are categorized by their cathode material. Two of the most common LIB chemistries are those using lithium iron phosphate (LFP) and lithium nickel manganese cobalt oxide (NMC) cathodes. While both cathode types have been effective, LFP is considered to safer, lower cost and longer-lasting, while NMC provides higher energy density [3].
NMC batteries are more dependent on certain critical metals (such as Mn and Co), making them more susceptible to supply-chain issues.
Metal-air and flow batteries
Aside from LIBs, other battery chemistries are being explored for grid-scale applications. Here are brief descriptions of two prominent types:
Redox flow batteries. In a flow battery, electrolytes contained in external reservoirs are pumped through a stack of positive and negative electrodes in an electrochemical cell, with two half-cells that are separated by an ion-exchange membrane. Flow batteries differ from conventional batteries in that conventional batteries have energy stored in the electrodes, while flow batteries have it stored in the electrolytes. Chemical energy from the electrolytes is converted into electricity during discharge, and ion exchange occurs at the membrane to complete the circuit.
Flow batteries are considered a promising technology for grid-scale energy storage because they offer the potential for long lifetimes, low self-discharge rates and cost-effectiveness due to their design.
Among the types of redox flow batteries are polysulfide bromine, vanadium redox and zinc-bromine redox flow batteries. The specific energy of flow batteries ranges from 10 to 35 Wh/kg, with specific power of 100–166 W/kg, round-trip efficiency of 65–85%, service life of 15 years, and self-discharge rate of ~0 [1, 4].
Metal-air batteries (iron-air). Iron-air batteries operate by the formation of iron oxide (rust) from the reaction of oxygen from air with iron metal. In the discharge (periods of high power demand and low production), this reaction releases energy. To recharge the battery (when production of electricity is high), the rust is converted to iron and oxygen is released.
There are a few major advantages that have led to iron-air being of interest for grid storage. One is long-duration energy storage. Iron-air batteries are capable of storing energy for several days, longer than LIBs in grid applications. Also, because they rely on lower-cost materials, iron-air batteries are cost-effective for large-scale applications.
Their limitations include lower round-trip efficiency (~60%) and slower response time in applications requiring faster charge-discharge.
References
1. Kebede, A.A., Kalogiannis, T., Van Mierlo, J. and Berecibar, M., A comprehensive review of stationary energy storage devices for large-scale renewable energy sources grid integration, Renewable and Sustainable Energy Reviews, vol. 159, May 2022.
2. Ngoy, K., Lukong, V., Yoro, K. and others, Lithium-ion batteries and the future of sustainable energy, Renewable and Sustainable Energy Reviews, vol. 223, November 2025.
3. Evro, S., Ajumobi, A., Mayon, D. and Tomomewo, O., Navigating battery choices: A comparative study of lithium iron phosphate and nickel manganese cobalt battery technologies, Future Batteries, vol. 4, December 2024.
4. Stauffer, N.W., Flow batteries for grid-scale energy storage, Energy Futures, MIT Energy Initiative, Winter 2023.
4. Ngoy, K., Lukong, V., Yoro, K. and others, Lithium-ion batteries and the future of sustainable energy, Renewable and Sustainable Energy Reviews, vol. 223, November 2025.