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Battery Encyclopedia

Everything you want to know about batteries from A to Z, curated by TWAICE experts.

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Anode, cathode, state of health, depth of discharge, end of life - read about the most important battery terms and definitions.

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Asset Manager

Energy storage

An Asset Manager is responsible for the oversight and maintenance of battery assets, ensuring they operate efficiently and reliably. This role includes monitoring performance, scheduling maintenance, and managing lifecycle costs.

AC (Alternating Current)

Battery terminology

An electric current that periodically reverses direction, used in power systems and appliances.

Aging model

Battery modeling

An aging model uses mathematical descriptions of relevant processes that predicts the degradation of lithium-ion batteries over time. It captures the effects of various factors, such as temperature, state of charge, and cycling patterns, on battery life and performance. Aging models typically consider capacity fade and increased internal resistance as primary indicators of battery aging. By predicting the battery's state of health (SoH) and estimating its remaining useful life, aging models help optimize battery management strategies, plan for maintenance or replacement, and improve the overall performance and reliability of battery-powered systems.

Ampere-hour

Battery terminology

A unit of electric charge, representing the amount of charge transferred by a steady current of one ampere flowing for one hour.

Anode

Battery cell

Electrode on which oxidation occurs – releases electrons on discharge. Usually made from graphite and binder material. Battery science and industry agreed to call it the “negative” electrode, even though oxidation and reduction process changes from discharge to charge.

Arbitrage

Energy storage

In the energy sector, arbitrage involves buying energy when prices are low and selling it when prices are high. For battery storage systems, this can mean storing energy during off-peak hours when electricity is cheaper and then selling it back to the grid during peak hours at a higher price. This practice can help balance supply and demand, stabilize grid prices, and provide a return on investment for energy storage operators.

Auto-trading

Energy storage

In the context of energy, auto-trading refers to the use of automated systems to buy and sell energy on the market. These systems can use algorithms to analyze market data, predict price trends, and make trades to maximize profits or achieve other goals, such as balancing grid demand.

Availability of Battery Energy Storage Systems (BESS)

Energy storage

Availability of Battery Energy Storage Systems (BESS) refers to the readiness and operational status of battery storage solutions to provide energy on demand. High availability ensures that these systems can reliably store and deliver electricity during peak usage times, grid outages, or when renewable energy sources are not producing. It involves maintaining optimal performance through regular maintenance, real-time monitoring, and prompt issue resolution, ensuring consistent energy supply and enhancing grid stability

BMS (battery management system)

Battery components

A BMS is an electronic system that monitors and manages the performance of a battery pack. It protects the battery from operating outside its safe voltage, temperature, and current limits, ensuring optimal performance and longevity. A BMS also provides critical information on the battery's state of charge, state of health, and other performance parameters.

BMS configuration

Battery terminology

Battery Management System (BMS) configuration entails setting up the hardware and software that monitor and control the performance, safety, and longevity of battery packs. Proper BMS configuration ensures balanced charging, protects against overcharging and deep discharge, and maintains optimal operating conditions for the battery cells

Battery Cell Side-reactions

Battery terminology

Unwanted chemical reactions within a battery cell that can degrade materials and reduce overall efficiency and lifespan.

Battery Cooling System

Battery terminology

A mechanism designed to remove excess heat from a battery pack to prevent overheating and ensure optimal performance.

Battery Fitting Process

Battery terminology

The procedure of integrating a battery into a system, ensuring optimal compatibility, performance, and safety.

Battery Pass Consortium

Battery terminology

The Battery Pass Consortium is a collaborative initiative comprising expert representatives from various fields relevant to the Battery Passport. The consortium's goal is to challenge, clarify, and translate legal Battery Passport requirements into straightforward guidelines, ensuring comprehensive and practical standards for transparency, sustainability, and regulatory compliance in the battery supply chain

Battery Passport

Battery terminology

A battery passport is a digital record containing detailed information about a battery’s materials, production, and lifecycle. It promotes transparency and accountability in battery supply chains and recycling processes. In the EU, batteries need to have a full battery passport from February 2027.

Battery Relaxation

Battery terminology

The period after charging or discharging during which a battery's internal conditions stabilize and its voltage returns to a steady state.

Battery Safety

Battery terminology

Battery safety encompasses the protocols and technologies designed to prevent accidents and ensure the safe operation of batteries. This includes measures to prevent overheating, overcharging, and physical damage, reducing risks such as fire or explosion

Battery State Estimation

Battery modeling

The process of determining key battery parameters (such as e.g. state of charge, health) through algorithms and sensor data.

Battery aging/ degradation

Battery terminology

This is the process by which a battery gradually loses its performance capabilities over time due to chemical and physical changes in the battery cells. Factors contributing to aging include cycle count, depth of discharge, temperature, and charge rate. Aging can result in reduced energy capacity, power capacity, and efficiency, and can increase the internal resistance of the battery.

Battery cell

Smallest individual electro-chemical unit that provides a certain amount of energy which depends on size, chemistry, and usage.

Battery fire

Battery terminology

Occurs when a battery overheats and causes a thermal runaway, which can result in a self-sustaining fire. Common causes include external short circuits, internal faults, mechanical abuses, poor design, or overcharging.

Battery health

Battery terminology

A measure of a battery’s current state compared to its initial state. It can be affected by factors like age, number of charge/discharge cycles, extreme temperatures, and overcharging.

Battery lifecycle

Battery terminology

This term refers to the stages a battery goes through from its creation to its disposal. It includes manufacturing, transportation, usage, maintenance, potential repurposing (like in second-life applications), and recycling or disposal at the end of its useful life.

Battery manufacturing

Battery terminology

Battery manufacturing is the process of producing batteries, from raw material processing to final assembly. Innovations in manufacturing techniques can enhance battery performance and reduce costs.

Battery modeling

Battery modeling involves the creation of mathematical representations of lithium-ion batteries using fundamental descriptions from physics, chemistry, and thermodynamics to predict their performance, behavior, and degradation. These models help engineers in various ways, among others are the enhanced design of battery management systems, optimize charging algorithms, and improve overall battery performance.

Battery module

Battery components

Modules combine 'n' number of cells to one bigger package where n is greater than 1. Usually, modules are the smallest unit of a battery pack that can be replaced during maintenance.

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Battery monitoring

Battery terminology

Battery monitoring involves continuously checking the status and performance of a battery. Effective monitoring helps identify potential issues early and ensures optimal operation

Battery pack

Battery components

Battery packs combine 'n' number of modules where n is greater than 1.

Battery performance

Battery terminology

This term encompasses various aspects of a battery's operation, mainly its electrical and thermal performances, including its capacity (how much charge it can hold), energy density (how much energy it can store in a given volume or weight), power density (how quickly it can deliver energy), charging/discharging rates, efficiency, and lifespan.

Battery recycling

Battery terminology

The process of reclaiming and reusing materials from spent batteries. Recycling helps reduce the number of batteries sent to landfills and conserves resources.

Battery size

Battery terminology

Refers to its electrical storage capacity, often measured in Watt-hours (Wh) or Ampere-hours (Ah).

Battery string

Battery components

This refers to a configuration of multiple battery cells or modules connected together in a series, parallel, or a combination of both to create a battery pack. The purpose of a battery string is to achieve the desired voltage and capacity for a specific application. In series connections, the voltage (V) adds up, while in parallel connections, the capacity (Ah) increases.

Battery swapping

Energy storage

Battery swapping is a method where depleted batteries in electric vehicles are quickly exchanged for fully charged ones. It is an alternative method to charge EVs via the ‘normal’ charging stations

Battery swelling

Battery terminology

Batteries are swelling up when Li ions are moving back and forth between cathode and anode. The swelling is dependent on the electrode chemistries used. Some electrode materials such as silicon expand by more than 300% during the intake of Li. Additionally, battery swelling can occur when gas accumulates inside a lithium-ion battery, causing it to expand. This is especially obvious for pouch cells. The gas generation can result from various factors, including overcharging, high temperatures, and manufacturing defects. Swollen batteries pose a safety risk and should be replaced promptly.

Battery system

Battery components

Battery systems combine 'n' number of packs where n is greater than or equal to 1.

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Battery technology

Battery terminology

Battery technology encompasses the development and innovation of batteries, including materials, design, and manufacturing processes. Advances in battery technology drive improvements in energy storage capacity and efficiency.

Beginning of Life (BoL)

Battery modeling

The initial state of a battery or system, indicating its performance and capacity before it undergoes any usage or degradation.

Bootstrap resampling

Battery modeling

This is a statistical technique used to estimate the distribution of a statistic (like the mean or standard deviation) by randomly sampling with replacement from the data set. In this method, numerous samples are taken, each sample is analyzed, and the results are used to form a distribution. This approach is particularly useful when the original dataset is small, as it allows for the estimation of the distribution of a statistic without the need for a large number of original observations. Bootstrap resampling is commonly used in machine learning and data analysis to assess the uncertainty of a model or to improve model accuracy.

C-rate

Battery terminology

The C-rate is a measure of a battery's charge or discharge rate relative to its capacity. A higher C-rate indicates faster charging or discharging. Batteries with high C-rates can deliver more power but may experience reduced cycle life and increased heat generation.

CAISO

Energy storage

CAISO (California Independent System Operator) is responsible for managing the electricity grid and wholesale power market in California. It plays a key role in integrating renewable energy and battery storage into the grid

Calendric aging

Battery terminology

Refers to the degradation of batteries (capacity fade and resistance increase) over time. This type of aging occurs even when the battery isn’t being charged or discharged. A predominant factor is the evolution of passivation layers.

Capacity

Battery terminology

Capacity of a cell, electrochemically speaking, is the amount of lithium ions that can be exchanged between the cathode and the anode between the upper cut-off voltage and the lower cut-off voltage. Theoretical values usually differ from the practicably achievable ones, since only a part of the lithium stored in the electrodes is available for the electrochemical reactions. In practice, the capacity is calculated by the integration of the current over time. Additional complexity arises from the fact that cathode and anode potentials change with temperature and hence influence the upper and lower cut-off voltage criteria. Thus, to define the capacity, both the current rate and temperature information are needed. Further, it must be specified if the capacity is measured during charge or during discharge.

Cell manufacturers usually provide a rated capacity value for their cells: Rated capacity means the capacity during discharge, usually measured in ampere-hours, of a cell as measured under predefined specifications. Usually, the cell manufacturer provides information to determine the rated capacity such as temperature, applied current and cut-off voltage. The influence of different parameters on the measurable capacity makes it challenging to compare tests from different parties with the same battery cell. Only if every detail is specified and agreed on, a direct comparison is possible. Therefore, there is not one true capacity, but just various ways to determine the available capacity under certain conditions.

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Cathode

Battery cell

Electrode in a battery cell in which reduction takes place, meaning the acceptance of electrons. Usually made from metal oxides, an electrically conductive powder and binder material. Battery science and industry agreed to call it the “positive” electrode.

Cell Blow-up

Battery terminology

A severe failure mode in batteries where a cell physically ruptures, often due to internal pressure build-up or thermal runaway.

Cell balancing

Battery cell

Cell balancing ensures that all cells within a battery pack charge and discharge uniformly. This process maximizes the battery's performance and lifespan by preventing individual cells from becoming overcharged or undercharged.

Cell selection

Battery cell

Cell selection is the process of choosing the appropriate battery cells based on performance, capacity, and application needs. Proper cell selection is crucial for optimizing battery pack performance and longevity. For example, in electric vehicles, manufacturers might choose high-energy-density lithium-ion cells for extended driving range, while in power tools, they might prefer high-power-density cells to deliver quick bursts of energy for demanding tasks.

Charge algorithms

Battery modeling

Charge algorithms are sets of instructions that control how a battery is charged to maximize efficiency and lifespan. These algorithms manage current, voltage, and charging duration.

Charging

Battery terminology

This is the process of adding electrical energy to a battery, allowing it to store energy for later use. Charging involves transferring electrons from an external power source into the battery, reversing the chemical reactions that occur during discharging.

Circularity

Battery terminology

Circularity in battery systems involves designing products and processes that maximize resource efficiency and minimize waste. This includes recycling, repurposing, and sustainable material sourcing.

Clamping force

Battery terminology

In the context of batteries, clamping force refers to the pressure applied to keep the components of a battery cell, particularly the electrodes and separator, firmly together. This is crucial for maintaining good electrical contact and efficient ion transport between the electrodes, as well as for the structural integrity of the cell. Inadequate clamping force can lead to increased internal resistance and uneven current distribution, which can significantly affect the performance and lifespan of a battery.

Cloud-based Battery Analytics

Battery terminology

The use of cloud computing to collect, store, and analyze battery data, enabling remote monitoring and management. Compared to the usual battery management system (BMS), battery analytics software can detect trends and anomalies early to avoid breakdowns. By analyzing historical data, the software gives you deeper insights into relevant KPIs than a BMS, providing a second layer of safety.

Commissioning

Energy storage

This is the process of installing, testing, and confirming that a battery system is functioning as intended. It involves checking the installation, ensuring safety compliance, verifying performance against specifications, and often setting up communication and control systems.

Confidence intervals

Battery modeling

Confidence intervals are a range of values, derived from the statistical analysis of data, that are believed to encompass the true value of an unknown parameter with a specified level of confidence, typically expressed in percentage terms (like 95% confidence interval). They provide an estimated range of values which is likely to include the parameter of interest and are fundamental in hypothesis testing and regression analysis. For instance, in battery performance studies, a confidence interval can indicate the reliability of the estimated average battery life.

Copper dissolution

Battery terminology

This occurs when copper from the battery's anode current collector dissolves into the electrolyte under certain conditions, such as deep discharging or high temperatures. This can lead to a reduction in the battery's capacity and lifespan, and in severe cases, internal short-circuiting.

Coulomb

Battery terminology

The standard unit of electric charge in the International System of Units (SI), equivalent to the charge transferred by a current of one ampere in one second.

Coulomb counting

Battery modeling

This is a method used to estimate the state of charge (SoC) of a battery. It involves measuring the current flowing into or out of the battery over time and summing these values (a process known as integrating the current). By knowing the total amount of charge that has moved in or out of the battery, one can estimate its current state of charge. However, this method can become inaccurate over time without recalibration, as it doesn't account for factors like efficiency losses or aging effects.

Current

Battery terminology

A flow of charged electrons or ions, typically measured in Ampere (A). In the context of batteries, it refers to the amount of charge flowing in or out of the battery.

Cycle

Battery terminology

A cycle is defined as the moment when the cell returns to the starting point after undergoing a charge and discharge process that involved both the upper and lower cut-off voltage limits as defined by the operation. Since except during cell testing (especially cell aging testing), a cycle is rarely seen, the driving profile is often characterized using equivalent full cycles:

Equivalent full cycle (EFC): It is used to classify any cycle or any charge or discharge in terms of the charge throughput of a full cycle. For example, a cycle between 50 and 100% State of charge (SoC) (so starting at 50% SoC, charging to 100% and then discharging to 50% SoC again) is equivalent to 0.5 EFC

Half cycle: The real driving profile can be broken up into a series of half cycles based on different algorithms such as the rain flow algorithm, etc. Classifications for half cycles can be quite specific such as each time the current drops to zero, a half cycle is finished. Or if the SoC signal changes direction.

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Cyclic aging

Battery terminology

Refers to the degradation of batteries (capacity fade and resistance increase) due to usage. This type of aging occurs when the battery is being charged or discharged. Mechanical strain in the electrode active materials stands out as a significant contributing element.

Cylindrical cell

Battery cell

Battery cells that have a cylindrical shape and which are the most common cell type in use today. They are widely used in various applications, including power tools and electric vehicles.

DC (Direct Current)

Battery terminology

An electric current that flows in one direction, used in batteries, electronics, and some renewable energy systems.

DCR (Direct Current Resistance)

Battery terminology

Is the resistance value calculated as the ratio of the voltage difference before and after a current pulse has been applied to the cell to the current value of the pulse in a defined time period.

Data analysis

Battery terminology

Data analysis in battery systems involves examining performance and operational data to gain insights and improve functionality. This process helps in predicting maintenance needs and optimizing system performance.

Data-driven models

Battery modeling

Models developed purely from experimental or observational data without necessarily relying on the underlying theoretical mechanisms. Machine learning algorithms are often used in this approach.

Dendrite growth

Battery terminology

Dendrite growth is a phenomenon observed primarily in lithium-ion batteries, where lithium deposits form spiky structures called dendrites during charging. These dendrites can grow long enough to break through the separator, leading to short circuits. This not only reduces the battery's efficiency and lifespan but also poses significant safety risks, as short circuits can lead to overheating or even fires. Preventing dendrite growth is a key area of research in battery technology.

Depth of discharge (DoD)

Battery terminology

Depth of Discharge (DoD) is the difference between the upper and lower State of charge (SoC) bounds of a cycle. It is sometimes referred to as cycle depth. Thus, cycling for example, between 10% and 80% SoC results in a DoD of 70% DOD. It is usually expressed as a percentage.

Digital Commissioning

Energy storage

Validate the installation and performance of a system before operation. Digital commissioning of battery energy storage systems can identify manufacturing or installation issues that were not discovered with physical commissioning.

Digital Twin

Battery modeling

A virtual model of a physical object or system, used for simulation, analysis, and control.

Discharge profiles

Battery modeling

Discharge profiles describe how a battery releases its stored energy under various conditions. Understanding discharge profiles is essential for optimizing performance and ensuring safe operation.

Discharging

Battery terminology

The process of drawing current from a battery, depleting its stored energy. During discharging, stored chemical energy is converted to electrical energy.

Driving Range

Battery terminology

The maximum distance a vehicle, especially an electric vehicle, can travel on a full charge under specific conditions.

Durability

Battery terminology

Durability refers to the ability of a battery to withstand wear, pressure, or damage over time. High durability ensures long-lasting performance and reliability.

ERCOT

Energy storage

ERCOT (Electric Reliability Council of Texas) is an organization that manages the electric grid and market in Texas. It oversees grid reliability, market operations, and integration of energy storage systems in the state

ESS / BESS / battery storage

Energy storage

ESS stands for Energy Storage System. BESS stands for Battery Energy Storage System. They are systems that store electrical energy using battery technology for use at a later time, often used for grid stabilization, renewable energy integration, and peak shaving.

Electric Vehicle

Electric vehicles

An electric vehicle (EV) is a type of vehicle that runs on electricity stored in rechargeable batteries, using electric motors for propulsion

Electric model

Battery modeling

An electric model is used to replicate the behavior of a physical battery cell. Often, the electric model uses components from electric circuits to mimic the electric response from batteries, such as resistors, capacitors or inductors. By leveraging an electric model, the electric response of a battery can be predicted based on a predefined input profile. An accurate electric model needs to take effects such as the hysteresis of batteries and also temperature-dependencies of model parameters into account.

Electrical Grid

Energy storage

A network of electrical transmission lines, substations, transformers, and more, that delivers electricity from power plants to consumers.

Electrochemical Impedance Spectroscopy

Battery modeling

A technique for characterizing the impedance of electrochemical systems, providing insights into battery health and behavior. It provides detailed information about the internal processes and mechanisms, aiding in the diagnosis of performance issues and the development of more efficient and longer-lasting batteries.

Electrochemistry

Battery terminology

Electrochemistry is the branch of chemistry that studies the chemical processes that cause electrons to move, fundamental to battery operation. It involves reactions at the anode and cathode, essential for generating electrical energy.

Electrodes

Battery cell

Thin coatings on either aluminum or copper foil made out of a mix of materials within which the electrochemical reactions take place.

Electrolyte

Battery cell

The component in the battery which allows charged particles to travel from one electrode to another and blocks the flow of electrons. In conventional batteries, the electrolyte is liquid. In solid-state batteries, the electrolyte is a solid.

Electrolyte decompositon

Battery terminology

This term refers to the chemical deterioration of the electrolyte in a battery, often caused by factors like overcharging, excessive heat, or impurities. This breakdown can lead to reduced battery efficiency, gas generation, increased internal resistance, and a decrease in overall capacity. Preventing this is crucial for maintaining battery performance and safety.

Electrons

Battery cell

Electrons are negatively charged subatomic particles that play a key role in electricity. In the context of batteries and circuits, they are the carriers of electric current, moving from the negative to the positive terminal in a circuit.

Electrothermal

Battery modeling

Pertaining to the combined electrical and thermal properties or processes, often in the context of battery operation and management.

End of life (EoL)

Battery terminology

End of Life criteria is when the cell is retired from its (first) application, usually a State of health (SoH) of 80% or an increase of the ohmic resistance up to 200% is used for automotive applications. After automotive applications, there might be a second life in stationary applications with different EoL criteria (e.g. 50% SoH) possible.

A remaining capacity of 80% might seem as like an arbitrary choice for retiring the cell from its primary application but it might have its origins in rapid cell degradation going beyond this State of health of the cell. Above 80% of the remaining capacity, the capacity fading and resistance increase is generally observed in a quasi-linear way. After the 80% to 70% crossing, capacity fading and resistance increased behave in a more non-linear way, which makes longer term forecasts more challenging. While the above characteristic parameters have been defined for cells, they are also widely used for higher levels such as for modules, systems and batteries.

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Energy

Battery terminology

Energy is the total amount of work a lithium-ion battery can perform, usually measured in watt-hours (Wh). It is a product of the battery’s voltage and capacity, determining the duration for which a battery can power a device.

Energy Storage Management System (ESMS)

Energy storage

A system that manages and optimizes the charging, discharging, and overall performance of an energy storage system, ensuring safety, longevity, and efficient operation.

Energy density

Battery terminology

Energy density is the amount of energy a battery can store per unit volume (volumetric energy density) or weight (gravimetric energy density). Higher energy density batteries can store more energy in a smaller, lighter package, making them desirable for applications such as electric vehicles and portable electronics.

Energy integration

Energy storage

Energy integration involves combining various energy sources, including batteries, to create a cohesive and efficient energy system. This approach supports the stability and sustainability of the overall energy grid.

FCR (Frequency Containment Reserve)

Energy storage

A reserve power service that helps maintain the stability of the electrical grid's frequency by quickly adjusting output.

Fast charging

Battery terminology

Fast charging refers to charging a battery at a higher current or voltage than standard charging rates, reducing the time required to reach a full charge. While fast charging can be convenient, it may generate more heat and stress the battery, potentially affecting its lifespan. There is no defined threshold for classification of fast charging. Some applications are deemed fast charging if full charging is performed within 30 mins, while others only call it fast charging if a full charge is done within 10 to 12 mins.

Flow Battery

Battery cell chemistries

A type of rechargeable battery where energy is stored and released by chemical components dissolved in liquids contained within the system.

Frequency regulation/ control

Energy storage

Frequency regulation in the context of power systems refers to the maintenance of the constant frequency of the electrical grid (e.g., 60 Hz in North America or 50 Hz in Europe). This is crucial for the stability and reliability of the grid. Batteries, especially large-scale energy storage systems, can contribute to frequency regulation by quickly absorbing excess power when the frequency is too high or releasing power when the frequency is too low, thus helping to balance supply and demand in real-time.

Graphite

Battery cell

A form of carbon used as an electrode material in many batteries, known for its electrical conductivity and ability to intercalate lithium ions.

Grid integration

Energy storage

Grid integration is the process of connecting battery systems to the electrical grid to enhance stability and efficiency. Batteries can store excess energy and supply it when demand is high, supporting renewable energy integration.

HVAC Component

Battery components

Parts of the Heating, Ventilation, and Air Conditioning system, significant for battery temperature management.

Heat-transfer-coefficients

Battery modeling

In the context of batteries, heat-transfer coefficients quantify how efficiently heat can be transferred away from the battery cells. High heat-transfer coefficients are desirable to efficiently dissipate heat and maintain optimal operating temperatures, thereby enhancing battery performance and lifespan.

Hybrid vehicle

Electric vehicles

A hybrid vehicle combines an internal combustion engine with an electric motor and battery system. This dual power system allows the vehicle to switch between or simultaneously use both power sources.

Hysteresis

Battery terminology

In the context of batteries, it refers to the different equilibrium potentials (difference in voltage between charging and discharging) at the same state of charge. The hysteresis effect can be very pronounced dependent upon the battery chemistry, requiring very accurate estimation or measurement of the terminal voltage.

IBR (Inverted Based Resources)

Battery terminology

Energy resources that use inverters to convert DC electricity to AC, enabling integration with the electrical grid.

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