Lead Battery Technology Highlights

70–90%

DC-DC round-trip efficiency is highest of the other battery technologies

100–500*

270 MWh

Note:
*Lead acid batteries with 5,000 cycles and 70% depth of discharge exist but are not commonplace.
** Operational capacity is based on S&P Global’s grid-connected energy storage market tracker

Lead batteries are one of the most common types of battery, found in car batteries and backup power systems, and are one of the early technologies to be used as large-scale energy storage. The mature and established technology has been around for a long time and is still used to provide bulk energy storage; however, physical, and technical limitations have resulted in it losing favor to Li-ion with most stationary energy storage developers and integrators. Most solutions refer to lead acid, but this is one of many solutions available today:

Lead acid
Known as the flooded cell and the most common battery used today. Lead acid battery systems use sulfuric acid electrolyte but are not sealed. Lead acid battery systems are not able to be left idle, as heavier molecules fall to the base of the battery and create a concentrated zone in which current can only flow in these areas. During the reaction, gases are vented, and water needs to be replaced in order to keep the lead acid cells hydrated and prevent the eventual dry-out from excessive use.

Absorbent glass mat (AGM)
AGM battery is one of two types of valve-regulated lead acid (VRLA) batteries. Sulfuric acid is absorbed into a fiberglass mat. The AGM battery is also completely sealed, giving it a safety advantage over flooded cells. Cell design allows for continuous regeneration of electrolyte, reintegration of gases produced, and results in a maintenance free system. It is used in aviation and vehicles as it benefits from reduced weight.

Gel lead acid
The other VRLA battery type was developed in the 1930s. Sulfuric acid is mixed with silica-gelling agent to form a paste or gel like substance and the battery is then sealed. Gel batteries differ from AGM batteries in that they are not able to withstand high current, which damages the paste inside; however, one benefit is durability as the gel dissipates heat, whereas the mat separator in an AGM battery acts as an insulator.

Advanced lead-carbon (ALC)
Instead of the lead and carbon electrodes being at opposite ends, the advanced lead-carbon battery has a lead-carbon combined cathode, which can prevent sulfation. In conventional lead acid systems, sulfation causes a loss of performance as the battery is only able to partially charge.

Lead Battery Technology outlook

• Despite the technology’s maturity, lead solutions have mostly been limited to off-grid or uninterruptible power supply (UPS) applications when used specifically for stationary energy storage. As new technologies are emerging—these next-generation solutions have the potential to offset the dominance of Li-ion.
• There will still be a demand for UPS systems and other backup solutions, and many customers using lead technologies today are continuing to invest in tried and tested solutions, as ultimately the battery needs to respond when required.
• Broadly speaking, lead batteries are not able to compete with Li-ion on a lifetime cost basis to provide grid energy storage.

Lead Battery Advantages

• Inexpensive and simple to manufacture, low cost per watthour
• Low self-discharge; lowest among rechargeable batteries
• High specific power, capable of high-discharge currents
• Good low- and high-temperature performance

Lead Battery Disadvantages

• Low specific energy; poor weight-to-energy ratio
• Slow charge: fully saturated charge takes 14–16 hours
• Must be stored in charged condition to prevent sulfation
• Limited cycle life: repeated deep cycling reduces battery life
• Flooded version requires watering
• Transportation restrictions on the flooded type
• Not environmentally friendly

Sodium-ion Battery Technology Highlights

80–85%

4,500–5,000

20 MWh

Note: Operational capacity is based on S&P Global’s grid-connected energy storage market tracker

Sodium batteries follow a similar historical development path to Li-ion batteries; however, owing to the atomic size of sodium ions (Na), they have a natural disadvantage when comparing energy density with Li-ion solutions. Although, it is possible through technology advancements to mitigate these natural barriers. Sodium batteries take advantage of the abundance of raw materials on the planet, which means there is no current limitations on the supply chain for any of the sodium derivatives.

This high availability also means that the building blocks for each solution are inexpensive, bringing down the overall cost of the system. The sodium space covers a variety of different solutions, summarized below:

Sodium-ion (non-aqueous)
The non-aqueous sodium-ion battery has a similar design to conventional Li-ion batteries. It comes with added benefits of being able to fully discharge without degradation and using readily available materials, for the electrolyte and electrodes.

Sodium-ion (aqueous)
The cell of an aqueous sodium-ion battery consists of an anode, cathode, electrolyte, separator, current collector, and battery housing. Construction of the battery is similar to a lead acid battery, except that the materials used are all nontoxic and environmentally friendly

Sodium-ion Battery Technology outlook

• The technology has been around for the same length of time of as Li-ion but has not seen the same level of investment, as its characteristics do not suit e-mobility. Sodium batteries tend to be heavier and require more space, making them suitable for stationary energy storage where space is not at a premium.
• Technology developers designing their systems to compete with Li-ion may struggle as like-for-like comparisons fall in favor of lithium. Developers seeking to offer a different solution, in the form of aqueous cells, may find themselves uniquely positioned to target niche markets.
• The opportunity for sodium-based batteries is limited; however, if production scale can be achieved, there is a possibility that deployment will ramp up.

Sodium-ion Battery Advantages

• Low-cost materials—Sodium battery manufacturers benefit from sodium being one of the most abundant elements on Earth and therefore priced accordingly, this means system costs are lower at the equivalent level of development compared with Li-ion.
• Depth of discharge—All sodium technologies mentioned can completely discharge without degradation to the cell.

Sodium-ion Battery Disadvantages

• Capacity—Sodium-ions are larger atoms compared with Li-ion; therefore, the level of capacity cells can store is lower. However, these challenges are being minimized in the latest cell designs/technologies.

Sodium-ion Battery Commercial Accelerators

• Safety concerns—With growing concerns around fires and thermal runaway in lithium batteries, sodium battery solutions can position themselves as a safe alternative.
• Low-cost resource—Sodium is an abundant resource and costs one-tenth of the price of lithium for the equivalent hydroxides (NaOH and LiOH).

Sodium-ion Battery Commercial Challenges

• Production capacity—As many companies are moving from the start-up phase to establishing production, volumes are still limited.
• Production line—Faradion and other manufacturers pursuing battery solutions can utilize existing production lines currently used for Li-ion battery cell manufacturing; however, it is likely that these will remain Li-ion as demand for these cells continues to increase.

NaS Battery Technology Highlights

70–80%

4,500–5,000

3,800 MWh

Note: Operational capacity is based on S&P Global’s grid-connected energy storage market tracker

The NaS cell is usually made in a cylindrical configuration. The entire cell is enclosed by a steel casing that is protected, usually by chromium and molybdenum, from corrosion on the inside.

During discharge, molten sodium donates electrons, leaving positive Na+ ions to migrate toward the cathode where they combine with molten sulfur ions, forming sodium polysulfide. The reverse reaction occurs when charging.

NaS Battery Technology outlook

• The sodium-sulfur (NaS) battery enjoyed a strong position in the market in the early days of grid battery deployment and accounted for a significant share of global installations. However, as Li-ion costs fell quickly and the market for shorter-duration applications such as frequency regulation emerged, Li-ion dislodged sodium-sulfur as the market leader.

  All sodium-sulfur systems commercially available today are designed for 6 hours of duration or more, and therefore not suitable for markets dominated by frequency regulation.

• Today, sodium-sulfur deployments are largely confined to NGK’s domestic market (Japan) as well as the United Arab Emirates, where it has engaged in a long-term partnership with local energy companies.

NaS Battery Advantages

• Low-cost materials—Sodium battery manufacturers benefit from the sodium being one of the most abundant elements on Earth and therefore priced accordingly; this means system costs are lower at the equivalent level of development compared with Li-ion.
• Depth of discharge—sodium-sulfur can completely discharge without degradation to the cell

NaS Battery Disadvantages

• Safety—As the temperature needs to be high for the battery to function, developers may have safety concerns. This may make the technology less suited to behind-the-meter (BTM) applications.
• Production capacity—NGK is currently the only recognized company producing sodium-sulfur systems in commercial volumes.

Solid-state Battery Technology Highlights

70–90%

100–500

~50 MWh

Note: Operational capacity is based on S&P Global’s grid-connected energy storage market tracker

Solid-state batteries are similar to conventional batteries in terms of components. There is still an electrode at each side and the elements in the cell are the same; however, the key difference is the electrolyte is solid instead of liquid. The function of a solid electrolyte is to act as a separator as well as carrier for electrons. This allows solid-state batteries to increase parameters such as energy/ power density while also enabling the battery to be resistant to thermal runaway.

All solid-state batteries deployed in stationary energy storage applications to date are provided by Blue Solutions, and all current efforts to further develop the technology focus around its use in electric vehicles (EV).

Solid-state Battery Technology Outlook

• Despite the technology’s immaturity, production is ramping up and the leading supplier (for ESS applications), Blue Solutions, is already selling systems to end customers. In the wider space, many leading battery manufacturers (Panasonic, Samsung SDI, LG Chem, etc.) are working toward solving the operational temperature problem.
• Once the various manufacturing challenges for solid-state batteries have been addressed, S&P Global anticipates strong potential for the technology to be adopted in EVs (where the benefits of the technology will be most valuable) and in consumer electronics. Solid-state batteries are not anticipated to play an important role in the energy storage industry.

Solid-state Battery Advantages

• Form factor—As the cell comprises solid layers instead of a mixture of solid and liquid components, for the same capacity, the size of the cell is smaller and lighter.
• Applications—As mentioned above, the advantages of a smaller and lighter storage system do allow solid-state batteries to be used in a range of solutions, from consumer electronics to transportation.

Solid-state Battery Disadvantages

• Immature technology—The technology is still under development with many leading cell manufacturers all researching different solutions. There are only a small number of commercially viable solutions on the market today, and none are in mass production.
• Cell operation—Currently, solid-state batteries need to be heated in order to perform at optimal levels. This means energy is being used internally rather than for an output, lowering the overall efficiency

Solid-state Battery Commercial Accelerators

• Applications—Smaller and lighter cells are needed to promote the transition toward higher levels of electrification in the transportation sector. It will also allow electrification of other forms of transportation as well as increasing range of electric vehicles (a key parameter that has been preventing widespread adoption).
• Funding—There has been several rounds of funding being raised to fund research and development into solid-state batteries. QuantumScape, in its most recent announcements, will be focusing on production of cells for use in e-mobility. Other leading battery manufacturers seeking to produce these cells are also receiving funding and collaborating to work toward solving the fundamental challenges.

Solid-state Battery Commercial Challenges

• Timeline to adoption—With most battery manufacturers involved in research to find a commercially viable solution (suitable for mass production and use in all sectors), S&P Global expects solid-state batteries to begin use in commercially available electric vehicles later in the 2020s. It is the view of S&P Global that solid state batteries will be deployed in premium, high-end electric vehicles and are unlikely to be used in the stationary energy sector.

Alternative/ inorganic Li-ion batteries

Alternative Li-ion batteries are taking the properties that lithium offers in terms of energy storage capabilities but addressing limitations, such as thermal runaway by creating a more stable cell and limiting side reactions, and using components that would otherwise cause localized “hot spots.” They also benefit from being able to discharge to 100% without causing internal cellular damage.

Inorganic Li-ion
Utilizes sulfur dioxide solvent to dissolve lithium salts and copper/ aluminium foil electrodes in a cylindrical cell.

Lithium sulfur
Lithium sulfur batteries use lithium metal and sulfur to passivate the lithium metal to store high levels of energy. This lightweight technology is likely to be showcased in automotive (specifically airplanes) ahead of stationary storage.

Alternative/ inorganic Li-ion Battery Technology outlook

• These technologies are still under development, and it is uncertain how they will be used in the stationary energy storage sector given the likelihood that high energy density is more of a priority in automotive applications than stationary storage.
• Inorganic lithium cells are chemically safe (unable to have thermal runaway) and can be marketed for stationary storage. Safety in the storage sector is an important topic following recent fires.

Alternative/ inorganic Li-ion Battery Advantages

• Non-flammable—No combustible components, which removes the risk of ignition and fire. Both solvents and salts used work together to provide a solution that is nonflammable and produces a higher conductivity.
• High energy density—These technologies are still in early stages of development and have reported high energy densities but are not currently commercially viable for stationary energy storage; other aviation or military applications may be more viable.
• Long life—Side reactions do not occur in the inorganic cells, which results in a predictable future capacity and limits aging. These side reactions are responsible for the formation of dendrites in typical Li-ion batteries, which hinder the ability of the cell to store energy.

Alternative/ inorganic Li-ion Battery Disadvantages

• New production process—The production processes of these technologies are still in early stages of development, and it is not clear how much investment is needed to scale production.
• No existing projects—There are no active projects using these technologies and therefore all stated data are theoretical and yet to be tested.

Liquid Metal Batteries

This technology is developed and commercialized by Ambri. The liquid metal battery uses calcium and antimony for storing energy. Liquid metal batteries are composed of a liquid calcium alloy anode, a molten salt (calcium-based) electrolyte, and a cathode comprising of solid particles of antimony.

Active materials in cells reversibly alloy and de-alloy while charging and discharging. The electrolyte is thermodynamically stable with the electrodes, avoiding unwanted side reactions such as film-formation that can degrade the performance of other cell chemistries.

The negative electrode is fully consumed when discharged, and then is reformed on every cycle, resulting in a repeatable process with no memory effect.

The cells perform optimally at an internal temperature of 500°C and generate their own heat during use, eliminating the need for external temperature control—except if the cell is completely discharged and cooled.

Liquid Metal Battery Technology outlook

• Liquid metal battery technology is in the early stages of commercialization. Ambri, the pioneer of the technology, has a contract for 250 MWh of systems. Typically, high internal temperature systems like NaS batteries have not been favored by the commercial and industrial (C&I) business owing to underlying safety concerns.
• This technology utilizes readily available materials to produce a stable and low-cost energy storage system that could prove to be disruptive in industrial locations.
• Off-grid applications that require movement of equipment may also be favorable as the battery is able to fully discharge without system degradation whereas a Li-ion cannot be transported as easily.

Liquid Metal Battery Advantages

• Complete discharge—This makes transportation of cells easier and can be activated once heated at their destination.
• Stability—Cells are also highly tolerant of overcharging or over discharging, and are not subject to thermal runaway, electrolyte decomposition, or electrolyte off-gassing.

Liquid Metal Battery Disadvantages

• Safety—Operates at extremely high internal temperatures, which can be considered a safety risk, although also considered an advantage when being used in harsh and hot climates.