Energy storage
The electricity we use is traditionally generated just moments before it is consumed. It is a challenge for today's energy industry to plan for variable demand. With future energy needs driven by electric mobility, for example, and with renewable energy coming from weather-dependent sources such as wind, sun and waves, balancing supply and demand will become even more challenging.
More efficient energy storage technologies enable the integration of larger quantities of renewable energy into the energy system, helping to replace fossil fuels.. A wide range of energy storage technologies are currently at various stages of development.
Key technology categories include mechanical storage such as pumped hydropower storage and compressed gas; thermal storage using water, solids or steam accumulators; and electrochemical solutions including batteries, which can be complemented by technologies such as supercapacitors.
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Electrochemical energy storage (batteries and supercapacitors)
Electrochemical inventions (e.g. batteries) account for 88% of all patenting activity in the field of electricity storage, far exceeding electrical (9%), thermal (5%) and mechanical (3%) solutions. Growth in the markets for electric vehicles and stationary electricity storage make electrochemical solutions even more important for the future.
According to the Sustainable Development Scenario outlined by the International Energy Agency (IEA) in 2020, close to 10 000 gigawatt-hours of battery and other forms of energy storage will be required annually across the energy system by 2040; and only around 200 GWh are available today.
Patenting activity has been increasing for a range of inventions including lead acid, redox flow and nickel-based batteries. However, innovation in the field has been spearheaded by lithium-ion (Li-ion) batteries, with a patenting activity rate of 45% versus a mere 7.3% for other chemistries, and the remainder in manufacturing and engineering.
Nickel manganese cobalt cathode material
While traditionally lithium cobalt oxide was used, concerns related to cost and supply have now shifted the focus towards nickel- and/or manganese-containing materials (together with lithium iron phosphate or LFP).
Lithium nickel cobalt oxide with aluminium or magnesium (NCA-Mg) cathode material
Sodium-ion batteries
Sodium-ion batteries are among the candidates with the potential to meet high-performance battery technology requirements in areas such as electromobility. Further candidates include lithium-metal solid-state, lithium-sulphur and even lithium-air batteries. Compared with more conventional Li-ion batteries, all of these could represent an improvement in terms of cost, density and lifecycle, as well as wider availability. Moreover, sodium-ion batteries rely on readily available base materials and, as such, offer potentially unlimited capacity.
Supercapacitors
Supercapacitors can complement Li-ion batteries by addressing specific needs. Supercapacitors can be charged and discharged within seconds. However, unlike batteries, they cannot store electricity in such large quantities. Their ability to provide bursts of power makes them valuable in combination with other higher-capacity battery types in electric cars, for example.
Inorganic solid-state batteries
Much of today's major innovation in solid-state electrolytes is geared towards finding alternatives to the liquid or polymer gel electrolytes currently used in Li-ion batteries, which pose a flammability risk. In addition to providing improved safety, solid-state electrolytes can offer a high level of specific energy coupled with a high degree of stability and durability.
Redox flow batteries
For some applications, redox flow batteries can provide a safer, more durable and scalable alternative to Li-ion batteries. Redox flow batteries use porous electrodes, in which an ion-exchange membrane separates the active materials in the form of positive and negative liquid solutions containing redox-active species.
Redox flow batteries can be based on different chemistries, with vanadium being the most commonly used redox-active cation. Their scalability makes them particularly interesting for residential and large-scale stationary applications.
Battery circularity
Battery circularity refers to a systemic approach to designing, using and managing batteries so that the value of their materials is retained across multiple lifecycles. It involves minimising material losses and enabling the recovery of materials across the full lifecycle of batteries, from initial design through use to end-of-life. In practice, this includes designing batteries for durability and easier disassembly, enabling reuse or repurposing in second-life applications and ensuring effective recycling processes that recover valuable materials for reintegration into new production.
In a broader context, battery circularity is increasingly important for securing access to critical raw materials that are otherwise geographically concentrated and subject to supply risks. By reducing dependence on primary extraction and mitigating the environmental and social impact of mining, circular approaches strengthen supply chain resilience while supporting climate and industrial policy goals. As demand for batteries continues to grow rapidly, circularity is therefore not only a waste management strategy but also a key pillar of sustainable and secure energy transitions. The process of recycling items by transforming them back into critical raw materials is also called “urban mining”.
- Pre-processing
Pre-processing includes all the handling steps between collection and the main recycling processes. It focuses on making batteries safe, testing them and getting them into a form suitable for reuse, repair or further treatment.
Controlled electrical discharge
Controlled discharge safely drains the remaining electrical energy from a used battery, using dedicated circuits or resistors, for example. It avoids dangerous shortcuts which can cause overheating, fires and internal damage that complicates subsequent recycling.
Isolation and immobilisation
Isolation and immobilisation keep used batteries separated from each other and from conductive objects that could cause short circuits. To this end, items such as non-conductive packaging, terminal covers and packing materials that stop batteries moving around in boxes or containers are used.
Remote handling
Remote handling involves the use of robots or long-reach tools so workers do not have to directly handle risky batteries. Activities such as cutting, opening, or moving damaged devices can therefore be performed while keeping people at a safe distance in case of shocks, fires or gas releases.
Testing for safety
Pre-processing tests are used to check batteries or battery waste materials before full treatment. Testing may measure remaining voltage, temperature, gas build-up or basic composition. Devices and materials can then be routed to the right processing line and unsafe items can be identified early.
Characterisation of battery type
It is important to establish aspects such as the battery’s chemistry, size, shape and internal design. This information guides safe handling, sorting, and the choice of the most efficient recycling or reuse path.
State-of-health analytics
State-of-health analytics estimate how much useful life a used battery still has left. These analytics combine measurements (relating to capacity and internal resistance, for example) as well as usage history in some cases, to decide whether a battery should be reused, repaired or fully recycled.
Storage solutions
Storage solutions keep batteries safe during collection and processing. They can include fire-resistant containers, separation by chemistry and condition, and sometimes cooled or monitored rooms to reduce fire risk.
Repurposing
Repurposing gives used batteries a “second life”, instead of directly recycling them. Ôld electric-vehicle packs, for example, can be reused in stationary energy storage, where lower-performance units are still of use.
Tracking
Tracking technologies include barcodes, radio-frequency identification (RFID) tags and digital product passports. They enable a battery to be tracked from its manufacture to recycling. This makes it easier to establish what is inside each battery, where it came from and how it should be handled and processed.
- Conditioning
Conditioning is about processing steps that restore or upgrade battery components so they can be reused instead of having to be fully broken down. The focus is on activities such as repairing cells, cleaning collectors and rejuvenating active materials.
Cell repair / replacement
Cell repair and replacement involve identifying weak or failed batteries in a pack and fixing or swapping them. This can extend the service life of packs and modules, delaying the need for energy-intensive recycling.
Relithiation and crystal repair
Relithiation and crystal repair aim to “heal” used cathode materials instead of dissolving them. By restoring lost lithium and fixing damaged crystal structures, the treated material can largely regain its original properties.
Repackaging for stationary applications
Once tested and conditioned, cells can be reassembled into new packs for stationary applications such as home or grid storage. As these applications are less demanding than electric vehicles, cells with reduced capacity can remain useful for many years.
Conditioning of current collector
Current collectors are thin copper and aluminium foils that carry electrical current inside the battery. Conditioning them involves the removal of coatings and contaminants so that the metals can be reused directly or sold on.
Graphite recovery
Recovering and upgrading the graphite from battery anodes can be achieved by removing binder and electrolyte residues. The aim is to provide graphite that is sufficiently pure for reuse in new batteries.
- Sorting and separating
Sorting and separating focus on splitting mixed battery waste into cleaner streams. Better separation leads to higher-quality recovered materials and more efficient downstream chemical processing.
Binder and electrolyte removal
This involves the use of chemicals to dissolve the polymer binder in the battery that glues active powders to metal foils. Chemicals can also help to wash out the electrolyte. Powders and foils subsequently separate more easily, enabling cleaner metal and active-material streams.
Extraction using supercritical CO2
Supercritical carbon dioxide - a fluid state of carbon dioxide where it behaves simultaneously like a gas and a liquid - can penetrate battery materials and extract organic solvents and some salts. It facilitates the controlled removal of electrolyte materials from the battery and enables solvent to be recovered without burning it.
Dismantling
Taking battery packs and modules apart, often by undoing screws, welds and connectors, can produce cleaner streams, as housings, busbars and cells are separated. However, the process tends to be slow and hard to automate.
Mechanical comminution
Comminution is the general term for breaking batteries into smaller pieces by shredding, milling or crushing. It liberates metals, plastics and powders, but also mixes them, so it must be followed by additional separation steps. The fine shredding of batteries results in what is often called “black mass”, a dark granular material that may contain lithium, cobalt, nickel, manganese and graphite. This mass of material can subsequently be transformed to yield separate metals.
- Chemical transformation
This concept covers processes that convert used batteries / battery parts or “black mass” into purified raw materials. These processes produce metal salts, alloys or refined powders of these raw materials, such as lithium, graphite, nickel, cobalt or manganese, that can be used to produce new batteries or for other applications.
Hydrometallurgy
Hydrometallurgic processes use liquid chemicals – often acids with oxidants – to dissolve metals from shredded battery material. Metals like lithium, cobalt, nickel and manganese are then separated and purified, typically by means of precipitation and solvent extraction.
Pyrometallurgy
Pyrometallurgy is a process whereby mixed battery waste is melted at high temperatures together with additives that promote melting and help to separate metals from impurities, forming metal alloys and slag. The process is well-suited to mixed feedstocks and requires relatively simple pre-treatment. However, it is also energy-intensive and can lead to the loss of some elements in the slag.
Electrochemical extraction
Electrochemical extraction is a process that recovers metals from solutions by causing them to precipitate onto electrodes. The method can be used to selectively extract valuable metals, reducing the need for further chemical separation.
- Enabling technologies
Enabling technologies are devices, measures and design choices that make battery collection, separation and recycling safer and more efficient. These technologies include better product design, safety systems and process controls.
Circularity-friendly design of batteries and processes
The aim here is to consider the reuse and recycling of materials from the outset. Circularity-friendly design can include standardising device formats, avoiding hard-to-remove glues, clearly labelling chemistries and designing process layouts that facilitate disassembly.
Emission control
Many lithium-ion batteries contain fluorine in their electrolytes, which can form highly corrosive acids, such as hydrofluoric acid, when heated or in the event of a fire. Controlling these acids and other volatile components involves ventilation, scrubbing systems and resistant materials to safely capture or neutralise them.
Fire and gas hazard mitigation
Early detection, ventilation and suppression systems can be used to address the issues of thermal runaway and gas release. The aim is to prevent a single faulty battery from causing a larger fire or explosion and to protect air quality.
Mechanical energy storage
Electrical energy can be converted into various forms of mechanical energy, such as gravitational potential energy and kinetic energy. It can also be used to compress a gas such as air. Some of these forms of energy are suitable for large-scale, long-duration energy storage (LDES). Mechanical energy systems tend to have large environmental footprints and often require a favourable geological setting to be viable in the first place.
Pumped-storage hydroelectricity (PSH)
PSH is a type of gravitational energy storage whereby water is pumped from a lower elevation reservoir to a higher elevation. When electricity is needed, e.g. for load balancing, the stored water is released through turbines to produce electric power. This currently represents some 90% of existing electric grid storage. Existing PSH could also play a larger role in balancing supply and demand in other renewable energy generation technologies.
Liquid air energy storage (LAES)
LAES is a type of cryogenic energy storage: it involves storing air in liquid form at a very low temperature but near-ambient pressure. To generate electricity, the liquid air is heated to a gas, which is then used to drive a turbine.
Liquid air energy storage - full result set
Compressed air energy storage (CAES)
CAES systems store pressurised air underground in cavities or above ground in tanks. Some CAES systems also store the heat that is generated when the air is compressed. CAES has been widely discussed as a potential grid-scale energy storage option, but faces significant hurdles for deployment at scale, including high costs.
Pumped thermal electricity storage (PTES)
These systems use a heat pump to turn electricity into heat. The heat is subsequently stored in a medium, such as water, gravel or sand, inside a thermally insulated tank. Using a heat engine, the heat is then turned back into electricity when needed.
Pumped thermal electricity storage - full result set
Dry gravity energy storage (GES)
GES systems use an electric motor to lift a mass, such as a very heavy rock mass, so that it acquires potential energy. This energy is then released by lowering the mass and using the motor as a generator of electricity.
Dry gravity energy storage - full result set
Flywheel energy storage (FES)
These systems accelerate a rotor (flywheel) to a high-speed using a motor, such that rotational kinetic energy is stored in the system. When energy is required, the rotational speed of the flywheel is reduced as electricity is generated.
Thermal energy storage
Thermal energy storage (TES) means storing energy as heat. Energy stored in this way can be used on a short-term, daily basis, or on a longer-term basis, including seasonal storage whereby summer heat is stored in a given medium and then re-used to heat buildings in winter. Materials can also be stored at a lower temperature for air-conditioning purposes.
Alternatively, energy can be absorbed or released during the phase transition of water or another medium, such as a salt or polymer, for the purposes of latent heat storage or release.
Thermochemical (chemical reaction, adsorption, absorption)
Thermochemical heat storage relies on a reversible exothermic/endothermic chemical reaction involving thermochemical materials (TCM) such as potassium oxide, calcium hydroxide or nitrosyl chloride. Depending on the reactants, this technique can yield an even higher storage capacity than latent heat storage. Exothermic/endothermic adsorption of water vapour by zeolites, for example, may provide a practical method of heat storage with a potentially unlimited lifetime.
Thermochemical (chemical reaction, adsorption, absorption) - full result set
Liquid (hot water, molten salt)
Water has a relatively high heat capacity and is the obvious choice for liquid heat storage. However, molten salt may be stored at up to 1 400°C for the purposes of energy storage or molten salt energy storage (MSES). It can then be used on demand e.g. for the generation of superheated steam, which can, in turn, drive turbine generators that produce electricity. The following smart search focuses on liquid heat storage mediums used to store renewable energy.
Liquid (hot water, molten salt) - full result set
Solid (pebble, stone, concrete, metal)
Hot rocks, stone and concrete - potentially in the form of granular packed beds - can provide a low-cost but high-volume means of energy storage that can withstand high temperatures. Their use may be enhanced by means of heat pumps, for example, to store and extract the heat. Metals (including alloy combinations) can also offer a means of storage that is conducive to rapid heat transfer. The following smart search focuses on the heat storage mediums used to store renewable energy.
Solid (pebble, stone, concrete, metal) - full result set
Latent (phase change material)
Phase change materials include salts, polymers, gels and alloys. Their different melting points enable tailored use for sensible heat storage according to demand. Ice-based technologies are also used for cooling purposes. These are often used in combination with heat pump exchange systems. The following smart search focuses on phase change materials used in conjunction with renewable energy.
Steam power plants with steam or heat accumulators
Steam accumulators use a combination of water and steam and can be applied on an industrial scale. The steam that is used to drive steam turbines can also be used for storage purposes if it is allowed to partially condense, creating a certain latent heat capacity. Steam power plants may also be combined with local heat storage using other technologies. The following smart search focuses on heat storage for steam power plants used in combination with renewable energy generation.
Steam power plants with steam or heat accumulators - full result set
Solar thermal power plants with heat storage
Solar thermal power plants may incorporate heat storage facilities to overcome the variability of solar (and wind) energy. This can be achieved by generating and accumulating steam, or even through thermal energy storage using molten salt (or molten salt energy storage (MSES)). Electricity can then be generated accordingly on demand.