Reference

Battery terms and definitions

Battery and energy storage terms: how cells work, the chemistries in use and in development, performance and safety testing, manufacturing, grid storage, thermal and mechanical storage, raw materials and recycling. These are general reference definitions, not tied to any one report.

218 terms · Updated 21 Oct 2026

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A

Accelerating rate calorimetry (ARC, heat-wait-seek): A safety test that heats a cell in steps, waits and watches for self-heating, a method called heat-wait-seek. It reveals the temperature at which the cell begins to run away.
Active material (electrode active material): The material in an electrode that actually stores and releases charge, as opposed to binders, conductive additives and foils. Cathode active material is usually the most expensive part of a lithium-ion cell.
Ampere-hour (Ah, amp-hour, mAh): A unit of electric charge: one ampere flowing for one hour. Cell capacity is given in ampere-hours; multiplying by voltage gives energy in watt-hours.
Ancillary services (grid services): Grid support services beyond selling energy, such as frequency regulation, reserves and voltage support. They are often the first profitable market for new storage.
Anode (negative electrode): The negative electrode of a battery during discharge, where the stored material gives up electrons. Graphite is the standard anode in lithium-ion cells; silicon, lithium metal and hard carbon are alternatives.
Anode-free cell (anode-less): A cell built with no anode material: lithium from the cathode plates directly onto the copper foil on first charge. It saves weight and cost but makes cycle life even harder to achieve.

B

Battery: A device that stores energy chemically and releases it as electricity, built from one or more electrochemical cells. In industry use, the word often means a whole pack or storage system.
Battery categories (EU) (portable battery, LMT battery, light means of transport battery, industrial battery, EV battery): The EU Battery Regulation sorts batteries into five types, each with its own rules. See the table
Battery energy storage system (BESS, battery storage, grid battery): A stationary installation of batteries, inverters, controls and safety equipment that stores electricity for later use. Most new grid-scale systems use LFP cells in shipping-container units.
Battery management system (BMS): The electronics and software that monitor a battery's cells and keep them within safe limits. It estimates state of charge and health, balances cells and controls charging.
Battery module (module): A group of cells wired together in a frame with sensors and connections, which in turn is assembled into a pack. Many newer packs skip modules altogether.
Battery pack (pack): The complete battery as installed in a vehicle or product: cells or modules plus housing, cooling, wiring and a battery management system. Pack-level energy density is always lower than cell-level.
Battery passport (digital battery passport): A digital record, linked by QR code, of a battery's origin, materials, carbon footprint and condition. The EU requires one for EV, light-transport and large industrial batteries from 18 February 2027.
Battery swapping (battery swap): Replacing a vehicle's depleted battery with a charged one at a station, instead of charging it in place. It takes minutes but needs standardized packs and costly station networks.
Battery-grade (battery grade): Material refined to the very high purity cell makers require, such as nickel sulfate, cobalt sulfate or lithium hydroxide. Purity, not mining, is often the supply bottleneck.
Behind-the-meter and front-of-meter (behind-the-meter, front-of-the-meter, BTM, FTM, utility-scale storage): Behind-the-meter storage sits on a customer's side of the utility meter, such as home or factory batteries. Front-of-meter storage connects directly to the grid and sells services to it.
Bill of materials (BOM): The list and cost of every material and part in a product. In batteries the cathode, anode, electrolyte, separator and foils make up most of it.
Binder (PVDF, polyvinylidene fluoride): A polymer that holds electrode particles together and to the foil. PVDF, a fluoropolymer processed with a toxic solvent, is standard for lithium-ion cathodes; water-based binders are used for many anodes.
Black mass: The dark powder left after spent lithium-ion batteries are discharged, shredded and screened. It contains the valuable cathode and anode materials, such as lithium, nickel, cobalt and graphite, and is the main traded recycling intermediate.
Brushless DC motor (BLDC, brushless motor)In Aerospace: An electric motor that switches current electronically instead of through brushes, making it efficient and durable. Nearly all small drones use brushless motors with permanent magnets.
Burst containment: The housing that captures fragments if a flywheel rotor fails at speed. It adds mass and cost, and below-ground vaults are often used for safety.

C

C-rate (C rate): Charge or discharge current expressed relative to capacity. At 1C a full battery discharges in one hour; at 2C in 30 minutes; at C/2 in two hours.
Calendar life (calendar aging): How long a battery lasts with age alone, regardless of use. Heat and high state of charge speed calendar aging, so stored batteries degrade even when idle.
Calendering (roll-pressing): Pressing coated electrodes between heavy rollers to a precise thickness and density. It sets how much active material fits in a cell.
Capacity (usable capacity, energy capacity): How much charge or energy a battery can store, given in ampere-hours or watt-hours. Usable capacity is less than nameplate capacity because some is held back to protect the cells.
Capacity factor: A plant's actual output over a period divided by what it would produce running at full power the whole time. Solar typically reaches ≈10–25%; storage owners use it to describe utilization.
Capacity fade (capacity loss, degradation): The gradual loss of a battery's usable capacity with cycling and age, caused by side reactions, lost lithium and electrode damage.
Capacity utilization (utilization rate, utilisation): Actual output divided by nameplate capacity. Low utilization across an industry signals overcapacity and price pressure.
Capital and operating costsIn Finance: Capital costs (capex) are the upfront spending to build or expand a project, such as the plant, equipment and mine development. Operating costs (opex) are the recurring costs of running it, often quoted per tonne of ore or per unit of product.
Carbon footprint declaration (battery carbon footprint): A statement of the life cycle greenhouse gas emissions of a battery, required under EU battery rules for EV and some industrial batteries, followed by performance classes and maximum limits.
Carnot limit (Carnot efficiency): The theoretical maximum share of heat that any engine can turn into work, set by its hot and cold temperatures. It caps how much electricity a heat store can return.
Cathode (positive electrode): The positive electrode of a battery during discharge, where electrons are taken up. In lithium-ion cells the cathode chemistry, such as LFP or NMC, largely sets energy density, cost and the metals needed.
Cathode active material (CAM): The finished cathode powder, such as LFP or NMC, sold to cell makers. It is made from precursor and lithium compounds and is the largest single cost in most lithium-ion cells.
Cell cost (cell cost per kWh): The cost of producing one kilowatt-hour of cell capacity, given in $/kWh. Materials make up most of it, so metal prices move it as much as factory efficiency does.
Cell voltage (nominal voltage, open-circuit voltage, OCV): The electrical potential difference between a cell's electrodes, set mainly by its chemistry. Nominal lithium-ion voltages are ≈3.2 V for LFP and ≈3.6–3.7 V for NMC; sodium-ion cells sit near 3 V.
Cell-to-pack (CTP, cell-to-body, CTB, cell-to-chassis): A pack design that places cells directly in the pack without modules, raising the share of pack mass and volume that stores energy. Cell-to-body designs go further and make the pack part of the vehicle structure.
Closed-loop recycling (closed loop): Recycling in which recovered materials go back into the same product, such as new battery cells.
CLTC (China Light-duty Vehicle Test Cycle): The China light-duty vehicle test cycle, used to rate electric-vehicle range in China. It gives higher range figures than the European WLTP or US EPA cycles for the same car.
Cobalt-free: Describes cathodes that use no cobalt, such as LFP, LMFP and some high-nickel or manganese-rich designs. Removing cobalt cuts cost and reliance on mining in the Democratic Republic of the Congo.
Coefficient of performance (COP): Heat delivered by a heat pump divided by the electricity it uses. Values of ≈3–4 are typical; resistive heating has a value of 1.
Compressed air energy storage (CAES): Storing energy by compressing air into caverns or tanks and later expanding it through turbines. Heat lost in compression lowers efficiency unless it is captured and reused.
Coulombic efficiency: The share of charge put into a cell that comes back out on discharge. Small losses compound over hundreds of cycles, so even 99.9% efficiency matters for long-life cells.
Cradle-to-graveIn Sustainability: A lifecycle boundary that runs from raw material extraction or cultivation through processing and use to final disposal or combustion. For fuels the equivalent term is well-to-wheel.
Critical mineral (critical material)In Finance: A mineral or material considered essential to economic or national security whose supply is at risk of disruption. Governments publish official lists, such as the US Geological Survey critical minerals list.
Critical Raw Materials Act (CRMA, Regulation (EU) 2024/1252): The 2024 EU law, Regulation (EU) 2024/1252, on securing critical raw materials. Its 2030 benchmarks call for EU extraction of 10%, processing of 40% and recycling of 25% of EU needs, and no more than 65% from any one non-EU country.
Current collector (copper foil, aluminum foil): The metal foil on which electrode material is coated and through which current flows out of the cell. Lithium-ion anodes need copper; sodium-ion cells can use cheaper, lighter aluminum on both sides.
Curtailment (curtailed electricity): Deliberately reducing output from wind or solar plants because the grid cannot use or carry the power. Curtailed electricity is cheap or free to store.
Cycle life (cycle count): The number of full charge-discharge cycles a battery delivers before its capacity falls to a set threshold, commonly 80% of the original. Test conditions such as depth of discharge and temperature change the result.
Cylindrical, prismatic and pouch cells (cylindrical cell, prismatic cell, pouch cell, 21700, 2170, 4680): The three main cell formats. Cylindrical cells are wound in metal cans, such as the 21700 or 4680 sizes; prismatic cells are rectangular cans; pouch cells are stacked layers sealed in soft foil.

D

Defense Production Act Title III (DPA Title III, Defense Production Act)In Aerospace: A US authority that lets the Defense Department fund, lend to or guarantee domestic production of materials and components critical to national defense.
Dendrite (lithium dendrite, dendrites): A needle-like metal growth that can form on an anode during charging, especially with lithium metal or at high charge rates. Dendrites can pierce the separator and short-circuit the cell.
Depth of discharge (DoD): The share of a battery's capacity used in a cycle. Deeper discharges extract more energy per cycle but usually shorten cycle life, so warranties often state cycles at a given depth.
Design for disassembly (design-for-disassembly, design for recyclability, design-for-recyclability): Designing a product so it can be taken apart easily for repair, reuse or recycling, for example with removable fasteners instead of glue.
Direct recycling (direct cathode recycling, relithiation): Recovering cathode material with its crystal structure intact and restoring it, rather than breaking it down to metals. It could save energy and cost but must handle many cathode chemistries.
District heating: A network of insulated pipes that carries hot water or steam from central plants to heat many buildings. Large heat stores can charge from cheap electricity and feed these networks.
DO-311A (RTCA DO-311A)In Aerospace: An RTCA standard for the performance and safety of rechargeable lithium batteries installed in aircraft, including tests that a cell fire stays contained.
Dry room: A production room kept at extremely low humidity, because moisture damages lithium-ion and especially sulfide solid-state materials. Running it is a major energy cost.
Dry-electrode process (dry electrode, dry coating): Making electrodes from dry powder pressed into film, without a liquid solvent. It removes drying ovens and toxic solvent recovery, but is hard to run at scale.
Dual-chemistry pack (hybrid pack, mixed-chemistry pack): A battery pack that combines two cell chemistries, such as sodium-ion and LFP, so each covers the other's weakness, for example cold-weather power and energy density.
Dual-use (dual-use technology, dual-use goods)In Aerospace: Describes goods, software and technology with both civilian and military uses, such as drones, machine tools and some chips. They are controlled under regimes such as the EAR and the Wassenaar Arrangement.
Duration (storage duration): How long a storage system can deliver its full rated power: energy rating divided by power rating. Most grid batteries offer 2–4 hours.

E

Earnshaw's theorem: A physics result showing that static magnets alone cannot hold an object in stable levitation. Magnetic bearings therefore need active control, superconductors or a mechanical touchdown bearing.
Electrochemical cell (cell, battery cell, galvanic cell): The basic unit of a battery: two electrodes separated by an electrolyte, in which chemical reactions move electrons through an outside circuit. Cells are joined in series to raise voltage and in parallel to raise capacity.
Electrode: A conductor through which current enters or leaves a cell. In batteries it is usually a thin coating of active material on a metal foil.
Electrode coating (slurry coating, wet coating, roll-to-roll): Spreading a slurry of active material, binder and solvent onto metal foil and drying it, usually on fast roll-to-roll lines. Coating speed, uniformity and drying energy drive cost.
Electrolysis (electrolytic hydrogen)In Sustainability: Splitting water into hydrogen and oxygen with electricity, using about 55 kWh per kilogram of hydrogen. Its footprint is set by the power source.
Electrolyte: The medium inside a cell that lets ions move between the electrodes while blocking electrons. Lithium-ion cells normally use a flammable liquid of lithium salt in organic solvents; solid-state cells use a solid.
Electrolyte filling (electrolyte injection): Injecting liquid electrolyte into an assembled cell and letting it soak into the electrodes before sealing.
Electronic speed controller (ESC)In Aerospace: The circuit that drives an electric motor on a drone, switching current to set its speed on commands from the flight controller.
Embodied emissionsIn Sustainability: Emissions released in making equipment and infrastructure, such as tractors, refineries and pipelines, spread over their useful life.
End of life (EOL, T80): The point at which a battery is judged no longer fit for its first use, often when capacity falls to 70–80% of new. End-of-life batteries go to second-life use or recycling.
Energy arbitrage (arbitrage, time-shifting): Charging storage when electricity is cheap and discharging when it is expensive, earning the price difference minus losses.
EU Battery Regulation (Regulation (EU) 2023/1542, Batteries Regulation): Regulation (EU) 2023/1542, which replaced the 2006 Battery Directive and covers batteries across their life cycle in the EU. It sets battery passports, carbon footprint rules, recycling targets, recycled content minimums and supply-chain due diligence, now due from August 2027.
eVTOL (electric vertical takeoff and landing)In Aerospace: An electric aircraft that takes off and lands vertically, usually with several battery-powered rotors. eVTOLs are being developed as air taxis, cargo carriers and military vehicles. Battery energy limits their range and payload.
Extended producer responsibility (EPR, producer responsibility organization): A policy that makes producers pay for collecting and recycling their products at end of life, usually through producer responsibility organizations.

F

Fast charging (fast charge, ultra-fast charging): Charging a battery much faster than usual, typically at 2C or more, or from 10% to 80% in under ≈20 minutes. It stresses cells through heat and lithium plating.
Flow battery (redox flow battery, vanadium flow battery, vanadium redox flow battery, VRFB, zinc-bromine flow battery): A battery that stores energy in liquid electrolytes held in external tanks and pumped through a cell stack. Energy and power can be sized separately, which suits long-duration grid storage, but energy density is low.
Flywheel energy storage (FESS, flywheel): Storing energy in a spinning rotor and recovering it with a motor-generator. Flywheels respond almost instantly and last for many cycles, but lose energy within hours, so they suit short bursts.
Foreign entity of concern (FEOC): A US legal category for companies tied to China, Russia, Iran or North Korea, used to bar them from clean-energy tax credits. The 2025 OBBBA law added broader prohibited foreign entity rules for most remaining credits.
Formation and aging (formation, cell formation, degassing): The first controlled charge cycles of a new cell, which build its protective SEI layer, followed by storage to screen out defective cells and, for pouch cells, degassing. It can take days and is a large share of factory floor space and energy.
Frequency regulation (frequency response, frequency containment): Fast adjustments to power output that keep grid frequency at its target, 50 Hz or 60 Hz. Batteries and flywheels respond in milliseconds, which suits this service.

G

GB 38031 (GB 38031-2025): China's mandatory safety standard for electric-vehicle traction batteries. Its 2025 edition, in force from 1 July 2026, requires that a single cell's thermal runaway cause no fire or explosion of the pack.
Gigafactory (giga-factory, gigascale): A battery cell factory with annual output measured in gigawatt-hours (GWh). Capacity is quoted in GWh per year; one GWh is enough for ≈15,000 electric cars with ≈65 kWh packs.
Graphite anode (natural graphite, synthetic graphite, spherical graphite): The standard lithium-ion anode, made of natural graphite mined and purified, or synthetic graphite made by heating petroleum coke or pitch to ≈3,000 °C. China dominates both supply chains.

H

Halide electrolyte (halide solid electrolyte): A solid electrolyte based on lithium metal chlorides or other halides. It combines good conductivity with stability at high voltage, but is still at an early stage.
HAPS (high-altitude platform station, high-altitude platform system, high-altitude pseudo-satellite)In Aerospace: An aircraft, airship or balloon that holds position in the stratosphere, ≈20 km up, to provide communications, sensing or navigation over a region. The ITU defines high-altitude platform stations as operating at 20–50 km. Solar power and weather limit their payload and endurance.
Hard carbon: A disordered form of carbon, made by heating biomass, resins or coal, that serves as the standard sodium-ion anode. Graphite does not hold sodium well, so hard carbon supply is a key sodium-ion bottleneck.
Heat as a Service (HaaS): A business model in which a provider owns and runs a heating system and sells the customer heat at an agreed price, instead of selling the equipment.
Heat pump: A device that moves heat from a cooler place to a warmer one using electricity, delivering several units of heat for each unit of power used.
Heat-to-heat and power-to-power efficiency (heat-to-heat efficiency, power-to-power efficiency, electric-to-electric efficiency): Heat-to-heat efficiency counts heat delivered against energy put in; power-to-power counts electricity returned. Thermal stores score highly on the first but far lower on the second, a common source of confusion.
High-nickel cathode (high-nickel, nickel-rich cathode): A nickel-based cathode with roughly 80% or more nickel among its metals, such as NMC811 or NCA. It raises energy density and cuts cobalt use, but is harder to make and less stable.
Hydrometallurgy (hydrometallurgical recycling, hydromet): Recovering metals by dissolving them in acid and separating them chemically. It recovers lithium as well as nickel and cobalt at high purity and is now the dominant recycling route.

I

IEA (International Energy Agency)In Sustainability: The Paris-based intergovernmental energy analysis body.
IEC 62660: The international standards series for testing the performance and reliability of lithium-ion cells used in electric vehicles.
Inflation Reduction Act (IRA): The 2022 US law that created or expanded clean-energy tax credits, including Sections 45X, 30D and 48E. The 2025 OBBBA law cut back many of them.
Intercalation: The reversible insertion of ions into the gaps of a host material's crystal structure without breaking it. Lithium-ion and sodium-ion batteries work by intercalation in both electrodes.
Internal resistance: The opposition to current flow inside a cell, which turns some energy into heat. It rises as a cell ages or gets cold, which limits power and fast charging.
Internal short circuit (internal short): A direct electrical connection between a cell's electrodes inside the cell, from separator failure, dendrites, damage or manufacturing defects. It is a leading trigger of thermal runaway.
Inverter: A power electronic device that converts direct current (DC) from batteries or solar panels into alternating current (AC). Inverter losses and size are part of every storage system's cost.
Ionic conductivity (mS/cm): How easily ions move through an electrolyte, in millisiemens per centimetre (mS/cm). Liquid electrolytes reach ≈10 mS/cm; solid electrolytes must approach that to allow fast charging.
IPCEI (Important Project of Common European Interest): Important Project of Common European Interest, an EU state-aid route that lets member states fund large cross-border industrial projects, such as battery value chains, beyond normal aid limits.
Iron-air battery (iron air): A battery that stores energy by reversibly rusting iron with oxygen from the air. It is very cheap per kilowatt-hour but heavy and inefficient, which suits multi-day grid storage.
Isostatic pressing (warm isostatic press): Compressing a part evenly from all sides with pressurized fluid or gas. Solid-state cell makers use warm isostatic presses to bond electrolyte and electrode layers without voids.

J

Joule heating (resistive heating, resistance heating): Heating by passing an electric current through a resistive material. Electric thermal stores use it to charge, converting electricity to heat at nearly 100% efficiency.

L

Latent heat storage (latent heat, phase-change material, PCM): Storing heat in a material as it melts or changes phase, at a nearly constant temperature. It packs more energy into less space than sensible storage.
Layered oxide cathode (layered transition-metal oxide, NaxTMO₂): A cathode built of stacked sheets of transition-metal oxide, such as copper, iron or manganese oxides for sodium-ion. It gives the highest sodium-ion energy density but is sensitive to moisture.
Leaching (acid leaching, bioleaching): Dissolving metals out of a solid, such as black mass or ore, with acid or another solution. It is the first chemical step in hydrometallurgy.
Lead-acid battery (lead acid, AGM, absorbent glass mat): The oldest rechargeable battery, using lead electrodes in sulfuric acid. It is cheap and almost fully recycled but heavy and short-lived; it still starts most combustion vehicles.
Levelized cost of storage (LCOS): The lifetime cost of a storage system divided by the energy it delivers, in $/MWh. It folds in capital cost, efficiency, cycle life and operating costs for comparing technologies.
LFP (lithium iron phosphate, LiFePO₄): Lithium iron phosphate, a lithium-ion cathode chemistry. It uses no nickel or cobalt, is cheap, long-lived and thermally stable, but stores less energy per kilogram than nickel-based cathodes.
Life cycle (lifecycle)In Sustainability: All the stages of a product's existence, from raw materials to end of life. A lifecycle emission figure adds up every stage inside the chosen boundary.
Life cycle assessment (LCA)In Sustainability: The standardized method, set out in ISO 14040 and 14044, for totaling the environmental impacts of a product across its life cycle. It can be run on an attributional or consequential basis.
Lithium carbonate (Li₂CO₃): A lithium compound that is the main traded form of lithium and the usual feed for LFP cathodes. Lithium prices are often quoted per tonne of battery-grade lithium carbonate.
Lithium carbonate equivalent (LCE): A common unit for comparing lithium content across compounds, expressed as the mass of lithium carbonate that would contain the same lithium. One tonne of lithium metal equals ≈5.3 tonnes LCE.
Lithium hydroxide (LiOH, lithium hydroxide monohydrate): A lithium compound preferred for high-nickel cathodes because it reacts at lower temperatures. It is usually made from spodumene or converted from lithium carbonate.
Lithium plating: Deposition of metallic lithium on the anode surface instead of inside it, typically when charging fast or in the cold. It reduces capacity and can lead to dendrites.
Lithium-ion battery (Li-ion, LIB, lithium-ion, lithium-ion cell): A rechargeable battery in which lithium ions move between a graphite or silicon anode and a metal-oxide or phosphate cathode. It dominates electric vehicles, electronics and grid storage.
Lithium-manganese-rich cathode (LMR, LMR-NMC, lithium-rich manganese): A cathode family with extra lithium and manganese that can store more charge than standard NMC while using less nickel and cobalt. Voltage fade over cycling has slowed its adoption.
Lithium-metal anode (lithium metal, Li-metal): An anode made of pure lithium foil, giving the highest possible energy density. Dendrites and short cycle life have kept it mostly out of liquid-electrolyte cells; solid-state designs aim to make it practical.
Lithium-polymer battery (LiPo, Li-Po, lithium polymer): A lithium-ion battery using a gel or polymer electrolyte, usually in a soft pouch. Common in drones and phones, it allows thin, light, flexible shapes.
Lithium-sulfur battery (Li-S, lithium sulfur): A battery pairing a lithium-metal anode with a sulfur cathode. It promises very high specific energy at low cost, but the cathode dissolves over cycling, which limits life.
LLZO (garnet electrolyte, Li₇La₃Zr₂O₁₂): Lithium lanthanum zirconium oxide, a garnet-structured ceramic solid electrolyte. It is stable against lithium metal but is brittle and needs sintering at ≈1,000 °C or more.
LMFP (lithium manganese iron phosphate): Lithium manganese iron phosphate, a variant of LFP with manganese added to raise cell voltage. It gains ≈15–20% energy density over LFP while keeping most of its cost and safety advantages.
Long Duration Storage Shot: A US Department of Energy goal, set in 2021, to cut the cost of grid storage lasting more than 10 hours by 90% within the decade.
Long-duration energy storage (LDES, long-duration storage, multi-day storage, seasonal storage): Storage that can deliver power for many hours to days, to cover gaps that daily batteries cannot. Definitions vary: the US Department of Energy uses more than 10 hours. Flow, iron-air, thermal and pumped hydro compete here.

M

Magnetic bearing (active magnetic bearing, AMB, superconducting magnetic bearing, passive magnetic bearing): A bearing that supports a rotor with magnetic fields instead of contact, reducing friction to nearly zero. Active types use controlled electromagnets; passive and superconducting types need less power.
Manufacturing scrap (production scrap): Electrodes and cells rejected during battery production. It has been the largest source of recycling feed so far, because few electric-vehicle batteries have yet reached end of life.
Manufacturing yield (yield, first-pass yield): The share of cells or electrodes made that pass quality tests. New lines often start with low yields; reaching ≈90% or more is a key test of a factory ramp.
Material assistance (material assistance cost ratio, MACR): Under US tax law since 2025, the share of a facility's or component's direct costs that comes from prohibited foreign entities. Projects exceeding set thresholds, which tighten each year, lose clean-energy credits.
Mechanical pre-processing (pre-processing, shredding): The first recycling steps: discharging, dismantling, shredding and separating batteries into black mass, metals and plastics.
Megajoule (MJ)In Sustainability: A unit of energy equal to one million joules. A litre of diesel holds about 36 MJ; a kilowatt-hour equals 3.6 MJ.
Microgrid: A local grid with its own generation and storage that can run connected to the main grid or alone, in island mode. Ports, campuses and remote sites use microgrids for resilience.
Molten salt storage (molten salt, solar salt): Thermal storage using a mixture of nitrate salts, kept liquid at ≈290–565 °C. Concentrated solar power plants use it to keep generating after sunset.

N

Nameplate capacity: A factory's rated maximum annual output, in GWh for battery plants. Actual output is usually lower because of ramp-up time, yield and demand.
NASICON (NASICON-type): A family of phosphate ceramic ion conductors whose name comes from sodium superionic conductor. Variants serve as solid electrolytes for lithium and as cathode frameworks for sodium batteries.
NCA (nickel cobalt aluminum, NMCA): Nickel cobalt aluminum oxide, a high-nickel lithium-ion cathode. It gives high energy density and is used mainly in some electric vehicle cylindrical cells.
NEC Article 706 (National Electrical Code Article 706): The part of the US National Electrical Code that covers wiring and installation of energy storage systems, including home batteries.
NFPA 855: The US National Fire Protection Association standard for installing stationary energy storage systems. It sets size limits, spacing, ventilation and fire protection, and is widely adopted into local codes.
Nickel sulfate and cobalt sulfate (nickel sulfate, cobalt sulfate, manganese sulfate): The dissolved-metal chemicals from which NMC and NCA cathode precursors are made. Manganese sulfate plays the same role for manganese.
NMC (nickel manganese cobalt, NCM, NMC811, NMC622, NMC532, NMC111): Nickel manganese cobalt oxide, the main high-energy lithium-ion cathode family. Grades are named by metal ratio: NMC811 is 8 parts nickel to 1 manganese to 1 cobalt. Higher nickel raises energy density but reduces stability.

O

OBBBA (One Big Beautiful Bill Act)In Sustainability: The 2025 U.S. budget law that amended Section 45Z, excluding ILUC for fuel produced after 2025 and restricting feedstocks to North America.
Offtake (offtake agreement)In Sustainability: A contract in which a buyer commits in advance to purchase a share of a producer's future output, often for several years. Offtakes give lenders confidence to finance a plant.
Oxide electrolyte (oxide solid electrolyte, ceramic electrolyte): A solid electrolyte made of ceramic oxides, such as garnet LLZO or NASICON-type phosphates. Oxides are stable in air but brittle and need high temperatures to process.

P

Pack price (battery pack price, volume-weighted average pack price): The average price of a complete battery pack per kilowatt-hour, the standard benchmark of battery costs. BloombergNEF's annual survey is the most cited series.
Peak shaving (peak-shaving, demand charge management): Using stored energy to cut the highest points of a site's or grid's demand, which lowers demand charges and delays grid upgrades.
Peak watt (Wp, kWp, MWp, watt-peak): The rated output of a solar panel under standard test conditions. A 3 MWp solar array produces 3 MW only in ideal sunlight.
Pilot line (pilot plant, demonstration line): A small production line used to prove a cell design and process before full-scale manufacturing. Pilot output is far too small to show whether costs will fall at scale.
Polyanionic cathode (polyanion cathode, NVPF, NFPP): A cathode built around phosphate or similar groups, such as NVPF or NFPP for sodium-ion, or LFP for lithium-ion. Strong chemical bonds give long life and stability at some cost in energy density.
Polymer electrolyte (PEO, polyethylene oxide electrolyte, solid polymer electrolyte): A solid electrolyte made of a polymer, typically polyethylene oxide, with a dissolved lithium salt. It is easy to process but conducts ions well only when warm, ≈60–80 °C.
Polysulfide shuttle (shuttle effect): The main failure mode of lithium-sulfur cells: sulfur compounds dissolve into the electrolyte, drift to the anode and react there, wasting capacity on every cycle.
Power conversion system (PCS, bidirectional inverter): The inverters and related equipment that convert a battery's direct current to grid alternating current and back.
Power rating and energy rating (MW/MWh, power capacity, energy rating): A storage system's power rating, in MW, is how fast it can deliver energy; its energy rating, in MWh, is how much it holds. A 100 MW / 400 MWh system can run at full power for 4 hours.
Precursor (pCAM, cathode precursor): An intermediate compound from which cathode active material is made, such as mixed nickel-manganese-cobalt hydroxide. It is mixed with a lithium compound and fired to form the finished cathode.
Primary and secondary batteries (primary battery, secondary battery, rechargeable battery): A primary battery is used once and discarded, like an alkaline battery. A secondary battery is rechargeable, like lithium-ion and lead-acid batteries.
Process heat (industrial heat): Heat used in industrial production, such as drying, cooking, chemical reactions and steelmaking. It is a large and hard-to-electrify share of industrial energy use.
Prohibited foreign entity (PFE, specified foreign entity, foreign-influenced entity): A US tax-law category created in 2025 covering specified foreign entities, such as companies controlled by China, and foreign-influenced entities tied to them. It bars or limits clean-energy credits, including for batteries.
Prussian blue analogue (PBA, Prussian blue, Prussian white): A family of low-cost cathode materials related to the pigment Prussian blue, with an open framework that lets sodium ions move easily. Prussian white is a sodium-rich form used in commercial cells.
Pumped hydro storage (pumped storage, pumped hydro, PSH): Storing energy by pumping water to an upper reservoir and releasing it through turbines when needed. Worldwide it holds far more stored energy than batteries do.
Pyrometallurgy (pyrometallurgical recycling, smelting): Recovering metals by smelting at high temperature. It handles mixed feed robustly and recovers nickel, cobalt and copper, but loses lithium and aluminum to slag and uses much energy.

R

Rankine and Brayton cycles (Rankine cycle, Brayton cycle): The two main heat-engine cycles for generating power. The Rankine cycle boils water into steam to drive a turbine; the Brayton cycle heats compressed gas, as in gas turbines.
Recovery rate (material recovery rate): The share of a given metal in recycling feed that is recovered in usable form. Recyclers often quote rates of 95% or more for nickel and cobalt; lithium rates are usually lower.
Recycled content (recycled content minimums): The share of a product's material that comes from recycling. EU rules require new industrial and EV batteries to contain set minimums of recycled cobalt, lithium, nickel and lead from August 2031. See the table
Recycling efficiency: Under EU battery rules, the share by weight of a waste battery that a recycling process turns into usable output. For lithium-based batteries the target was 65% by the end of 2025.
Redox reaction (redox, oxidation and reduction): A chemical reaction in which one substance loses electrons (oxidation) and another gains them (reduction). Every battery's discharge is a controlled redox reaction.
Ride-through: The ability of equipment to keep running through a brief power dip or outage, often supplied by batteries or flywheels until backup generation starts.
Rocking-chair battery (rocking chair intercalation): A battery in which ions shuttle back and forth between two intercalation electrodes during charge and discharge. Lithium-ion and sodium-ion cells both work this way.
Rotational kinetic energy (moment of inertia, E = ½Iω²): The energy stored in a spinning body: half its moment of inertia times its angular speed squared. Doubling a flywheel's speed stores four times the energy, so rotor strength limits capacity.
Round-trip efficiency (RTE): The share of energy put into storage that comes back out. Lithium-ion batteries return ≈85–95%; pumped hydro ≈70–80%; heat stores converted back to electricity far less.

S

SAE J2464: An SAE practice for abuse-testing electric-vehicle batteries, such as crush, penetration, overcharge and fire exposure.
Sample stages (A-sample, B-sample, C-sample, A-samples, B-samples, C-samples): The automotive qualification stages for new cells. A-samples are early prototypes, B-samples are near-final designs from pilot lines, and C-samples come from production-intent lines for vehicle validation.
Sand battery (sand-based thermal storage): A marketing name for thermal storage that heats sand or crushed rock with electricity to several hundred degrees Celsius and later releases the heat. It mainly supplies district heating and industrial heat.
Scrap rate: The share of material or cells discarded during production. High scrap rates raise costs and supply manufacturing scrap to recyclers.
Second-life battery (second life, second-life): A retired electric-vehicle battery reused in a less demanding role, such as stationary storage, before recycling. Testing, warranties and mixed pack designs limit the market.
Section 30D (30D, clean vehicle credit): The US clean vehicle tax credit of up to $7,500 for new electric vehicles, with battery sourcing rules. The 2025 OBBBA law ended it for vehicles acquired after 30 September 2025.
Section 45X (45X, advanced manufacturing production credit): The US advanced manufacturing production credit. For batteries it pays $35 per kWh of cells and $10 per kWh of modules made and sold in the US, phasing down from 2030 to zero after 2032.
Section 48E (48E, clean electricity investment credit, investment tax credit, ITC): The US clean electricity investment tax credit, which also covers energy storage technology. Since 2025 it carries prohibited foreign entity and material assistance limits.
Self-discharge (standby losses, self-discharge rate): The gradual loss of stored energy while a battery or other storage device sits unused. Lithium-ion cells lose a few percent a month; flywheels and thermal stores can lose energy far faster.
Semi-solid battery (semi-solid-state, quasi-solid, hybrid solid-liquid battery, solid-liquid battery): A battery that mixes solid electrolyte with a smaller amount of liquid or gel electrolyte. A December 2025 draft Chinese national standard drops the term and calls such cells hybrid solid-liquid batteries.
Sensible heat storage (sensible heat): Storing heat by raising a material's temperature without changing its state. The heat stored equals mass × specific heat × temperature rise.
Separator (separator film): A thin porous film, usually polyethylene or polypropylene, that keeps a cell's electrodes from touching while letting ions pass through. A separator failure can cause an internal short circuit.
Shore power (cold ironing, onshore power supply): Supplying electricity from land to a docked ship so it can switch off its engines. It cuts port emissions but needs large grid connections at the berth.
Silicon anode (silicon-anode, silicon-carbon anode, silicon composite anode): An anode that uses silicon, alone or blended with graphite, because silicon can hold about ten times more lithium per gram. Silicon swells up to ≈300% when charged, which cracks particles and shortens life.
SLI battery (starting, lighting and ignition battery, starter battery): A battery that powers starting, lighting and ignition in combustion vehicles, traditionally lead-acid. EU battery rules treat it as its own category.
Soda ash (sodium carbonate, Solvay process): Sodium carbonate, a common industrial chemical made mostly by the Solvay process or mined as trona. It is the main sodium source for sodium-ion cathodes.
Sodium-ion battery (Na-ion, SIB, sodium-ion): A rechargeable battery that uses sodium ions instead of lithium. Sodium is abundant and cheap, and cells work well in the cold, but energy density is lower than LFP.
Solid electrolyte (solid-state electrolyte, inorganic electrolyte): A solid material that conducts ions between a battery's electrodes. The main families are sulfides, oxides, polymers and halides, each trading conductivity against stability and ease of manufacture.
Solid electrolyte interphase (SEI, SEI layer): A thin layer that forms on the anode surface during a cell's first charges, as electrolyte breaks down. A stable layer protects the cell; continued growth consumes lithium and causes capacity loss.
Solid-state battery (SSB, solid-state lithium battery, SSLB, all-solid-state battery, ASSB): A battery that uses a solid electrolyte instead of a flammable liquid one. It could allow lithium-metal anodes, higher energy density and better safety, but making large cells cheaply remains unproven.
Solvent extraction (SX): Separating dissolved metals by mixing a water solution with an organic liquid that selectively picks up one metal. It is used both in battery recycling and in rare earth refining.
Specific capacity (mAh/g, gravimetric capacity): The charge an electrode material can store per unit mass, in milliampere-hours per gram (mAh/g). It is the main yardstick for comparing anode and cathode materials.
Specific energy (gravimetric energy density, Wh/kg): Energy stored per unit mass, in watt-hours per kilogram (Wh/kg), at cell or pack level. It sets range in vehicles and endurance in aircraft and drones.
Specific power (power density, W/kg, kW/kg): Power a battery can deliver per unit mass, in watts per kilogram (W/kg). High-power cells sacrifice some energy density to deliver bursts for takeoff, acceleration or grid support.
Spinning reserve (contingency reserve, operating reserve): Generating or storage capacity that is online and ready to supply power within minutes if a plant or line fails.
Spodumene (spodumene concentrate, SC6): A hard-rock lithium mineral mined chiefly in Australia and refined, largely in China, into lithium chemicals. It is sold as concentrate, often around 6% lithium oxide.
Stack pressure: The external pressure that holds a solid-state cell's layers in contact. Many designs need several megapascals of pressure, which adds weight and complexity at pack level.
State of charge (SOC, SoC): How full a battery is, as a percentage of its usable capacity. Battery management systems estimate it continuously; operators often avoid keeping cells near 0% or 100% to slow wear.
State of health (SOH, SoH): A battery's present condition compared with when it was new, usually its remaining capacity as a percentage of original capacity. It decides warranty claims, resale value and second-life use.
Stranded assetIn Finance: An asset that loses much of its value before the end of its expected life because of regulation, new technology or changing markets. Fossil fuel reserves that cannot be developed under tighter climate policy are a frequently cited example.
Sulfide electrolyte (sulfide solid electrolyte, argyrodite, LGPS, Li₆PS₅Cl): A solid electrolyte based on lithium sulfur compounds, such as LGPS or argyrodites. It conducts ions about as well as liquids but reacts with moisture to release toxic hydrogen sulfide, so it needs dry-room production.

T

Technology readiness level (TRL)In Aerospace: A 1–9 scale, developed at NASA, for how mature a technology is, from basic principles observed to proven in operation. Agencies and investors use it to judge development risk. See the table
Thermal energy storage (TES, heat storage, heat battery): Storing energy as heat or cold in materials such as sand, brick, molten salt or water, for later use as heat or electricity. It is far cheaper than batteries for delivering heat.
Thermal management (battery thermal management, BTMS): Keeping battery cells in their best temperature range, typically ≈15–35 °C, with air, liquid or immersion cooling and heating. It affects life, safety, power and charging speed.
Thermal propagation (propagation, cell-to-cell propagation): The spread of thermal runaway from one cell to its neighbors. Pack designs use spacing, barriers and cooling to stop one failed cell from igniting the whole pack.
Thermal runaway: A self-heating chain reaction in which a failing cell releases heat faster than it can shed it, often ending in venting, fire or explosion. Causes include internal shorts, overcharging, damage and overheating.
Thermophotovoltaics (TPV, thermophotovoltaic): Turning heat directly into electricity with photovoltaic cells tuned to the infrared light that glowing hot materials emit. It could let very hot heat stores return power without turbines.
Tipping fee (gate fee): A fee a recycler or disposal site charges to accept waste. Recyclers charge tipping fees for low-value batteries such as LFP, whose metals do not cover processing costs.

U

UL 1973: A UL safety standard for batteries used in stationary storage, light electric rail and similar applications. It covers the battery system itself, not the full installation.
UL 9540: The UL safety standard for complete energy storage systems, including batteries, inverters and controls. US building and fire codes commonly require listing to it.
UL 9540A: A UL test method that measures how fire spreads from a cell in thermal runaway to modules, units and the installation. Its results set spacing and fire protection under NFPA 855.
UN 38.3 (UN38.3): The UN test series that lithium cells and batteries must pass before being shipped, covering altitude, temperature, vibration, shock, short circuit and overcharge. It sits in the UN Manual of Tests and Criteria.
UN 3480 and UN 3481 (UN3480, UN3481, UN 3480, UN 3481, Class 9 dangerous goods): The UN shipping numbers for lithium-ion batteries shipped alone (UN 3480) and packed with or in equipment (UN 3481). They fall in Class 9 dangerous goods. For air transport, many shipments must be at no more than 30% state of charge.
Urban mining: Recovering metals from discarded products such as batteries and electronics instead of mining ore.

V

Value stacking: Earning several revenue streams from one storage asset, such as arbitrage, reserves and backup power, to make it pay.
Voltaic pile: The first practical chemical battery, built by Alessandro Volta in 1800 from stacked zinc and copper discs separated by cloth soaked in salt water. It gave a steady current, which made early electrochemistry possible.
Volumetric energy densityIn Sustainability: Energy per litre of fuel. HVO holds about 34 MJ per litre against about 36 for fossil diesel, so slightly more litres are needed for the same work.

W

Watt-hour (Wh, kWh, MWh, GWh, kilowatt-hour, megawatt-hour, gigawatt-hour): A unit of energy equal to one watt for one hour, or 3,600 joules. Batteries are sized in watt-hours, kilowatt-hours (kWh), megawatt-hours (MWh) and gigawatt-hours (GWh).
Windage (windage loss): Drag on a fast-spinning rotor from the surrounding air. Flywheels spin in a vacuum to reduce it.

Z

Zero-volt storage (zero-volt transport): The ability of a cell to be fully discharged to 0 V for storage or shipping without damage. Sodium-ion cells can do this because they use aluminum current collectors, which do not corrode at 0 V.