Battery Chemistry Definitions & Glossary has quite a lot of overlap with the Cell Glossary. Hence apologies for any repeats, although some are required.
3rd Electrode or Reference Electrode is added to a battery cell so that the anode and cathode potentials can be referenced against a known point.
Active Material Loading – The mass of active electrode material applied per unit area of current collector foil, expressed in g/cm² or mAh/cm². Higher loading increases cell energy density but can impair ion transport through thicker electrodes, requiring careful balance with porosity and tortuosity during electrode design.
Ah – Ampere-hour is the unit of cell capacity.
Alloying Reaction – An electrode reaction in which the active material forms a metallic alloy with lithium (or another working ion) rather than intercalating it into a host lattice, as seen in silicon, tin and antimony anodes.
Alloying-Type Anode – An anode material, such as silicon, tin, antimony, bismuth or germanium, that stores lithium by alloying reaction instead of intercalation, giving high capacity at the cost of large volume expansion on cycling.
All-Solid-State Battery (ASSB) – A battery cell in which the liquid electrolyte is replaced entirely with a solid ionic conductor. ASSBs eliminate flammable liquid electrolytes, potentially enabling lithium metal anodes and higher voltage cathodes, but face challenges in interfacial resistance and manufacturing scalability. See: Solid State Battery
Aluminium Air – high energy density and low cost. The aluminium anode and air cathode along with an aqueous electrolyte, generate power through the oxidation of aluminium by oxygen from the air.
Aluminium Ion – the aluminium metal anode can exchange three electrons during the electrochemical process, hence can deliver a high theoretically high volumetric and gravimetric capacity.
Anode – the negative or reducing electrode that releases electrons to the external circuit and oxidizes during and electrochemical reaction.
Anode-Cathode – in chemistry, we define Cathode as the electrode where reduction takes place and Anode the electrode where oxidation occurs. Both, during the discharge and recharge electrons move from the Anode to the Cathode. {Anode and Cathode swap places}.
Anode Free – a battery cell where the Anode is formed during the cell formation cycles.
Aqueous Battery – battery based on an electrolyte dissolved in water.
ARC – Accelerated Rate Calorimetry (thermal runaway testing)
Area Specific Resistance (ASR) This is the resistance of the electrode normalised by the active area. It includes both electronic and ionic contributions.
Argyrodite A family of Li6PS5X-type (X = Cl, Br, I) sulfide solid electrolytes prized for very high room-temperature ionic conductivity, though sensitive to moisture.
Binder – something that holds the active materials together.
Biomimetics – inspired by nature and can include materials and structures that mimic biological processes.
Button Cell – otherwise known as a coin cell, used a lot in early stage cell chemistry development.
Calendar Ageing – the capacity loss of the battery with time and without cycling.
Calendaring – in the calendaring process the dried anode and cathode are run separately between rollers to compress the active layer. This brings the thickness and porosity to a given dimension.
CAM -Cathode Active Material
Capacity – battery capacity is expressed in ampere-hours.
Capacity Fade – the general term for the gradual, permanent loss of usable capacity in a cell over its lifetime, whatever the underlying mechanism.
Capacity per Gram – the capacity of the anode or cathode material per unit mass.
Carbon Nanotubes – added to both anodes and cathodes to improve electrical and thermal performance, also add mechanical stability. Can be an enabler for Si anodes.
Cathode – the positive electrode, at which electrochemical reduction takes place. As current flows, electrons from the circuit and cations from the electrolytic solution in the device move towards the cathode.
Catholyte / Anolyte – In flow batteries, the catholyte is the liquid electrolyte circulated through the positive (cathode) half-cell, and the anolyte circulates through the negative (anode) half-cell. The two electrolytes are separated by a membrane that permits ion transfer while preventing mixing.
Charge – the process of electrical energy being converted into chemical energy.
Coating – the process of applying the active materials to the backing electrodes.
Coating Density – the mass of cathode or anode material applied per unit area.
Coin Cell – used a lot in early stage cell chemistry development as it is normally the simplest bilayer.
Conversion Anode – An anode material that stores lithium through a chemical conversion reaction rather than intercalation. Metal oxides, sulfides, and phosphides are typical conversion-type materials, offering high theoretical capacity but often exhibiting large volume changes and poor reversibility.
Conversion Cathode – a cathode material, such as a metal fluoride or sulfide, that reacts by fully breaking and reforming chemical bonds rather than by intercalation.
Conversion Reaction – an electrode reaction mechanism in which the active material undergoes a full chemical transformation, breaking down into new phases rather than simply hosting inserted ions.
Coulomb – unit of electric charge. One coulomb (1C) equals one ampere-second (1As).
Coulombic Efficiency (CE) – The ratio of charge extracted on discharge to charge input during the preceding charge cycle, expressed as a percentage. First-cycle coulombic efficiency (also called Initial Coulombic Efficiency, ICE) is particularly important as it quantifies lithium consumed in forming the SEI and is a key metric for silicon anodes and new chemistries.
Cracking / Particle Fracture – Mechanical degradation of electrode active material particles caused by the repeated stress of lithium insertion and extraction. Particle fracture exposes fresh surfaces to electrolyte, consuming lithium inventory in renewed SEI formation and accelerating capacity fade. A significant degradation mechanism in high-nickel cathodes and silicon anodes.
C rate – the Ampere current in charge or discharge divided by the Ah capacity of the cell.
Cryo-Electron Microscopy (Cryo-EM) – an imaging technique that freezes a sample to preserve delicate structures, increasingly used to study the solid electrolyte interphase and lithium metal morphology.
Cutoff Voltage – specified closed circuit voltage at which a cell is terminated.
Cycle Ageing – the capacity loss in a battery through charge and discharge repeated cycling.
Cycle Life – the number of charge and discharge cycles that a battery can complete before losing performance.
DC Internal Resistance (DCIR) – The effective resistance of a cell measured from the voltage response to a step current pulse, typically at 10 seconds. DCIR captures both ohmic and kinetic contributions and is widely used in cell characterisation, BMS power limit calculations, and ageing assessment.
Deintercalation – the process of removing ions from a host electrode structure, the reverse of intercalation, occurring at the cathode during discharge or the anode during charge.
Dendrite – A needle-like filament of metallic lithium that can grow from the anode surface during charging, particularly at high rates or low temperatures. Dendrites can penetrate the separator and cause an internal short circuit, leading to thermal runaway. Dendrite suppression is a central challenge in lithium metal and solid-state battery development. See: Lithium Plating
Differential Capacity Analysis (dQ/dV) – A characterisation technique that plots the derivative of capacity with respect to voltage (dQ/dV vs V). Peaks in the dQ/dV plot correspond to electrochemical phase transitions in the electrode materials; tracking peak positions and heights over cycles reveals active material degradation and lithium inventory loss.
Differential Electrochemical Mass Spectrometry (DEMS) – an analytical technique that identifies and quantifies gases evolved from a cell in real time during cycling.
Discharge – the process of chemical energy being converted into electrical energy.
Disordered Rock Salt (DRS) – An emerging class of cathode materials in which lithium and transition metal cations are randomly distributed on a face-centred cubic oxygen lattice. DRS cathodes can achieve high capacity without cobalt but require fluorine substitution and careful design to achieve adequate lithium diffusion.
Dual-Ion – battery technology that offers a low cost solution for grid based storage. Cations and anions both participate in the intercalation and deintercalation processes using graphite as both cathode and anode material.
Dry Electrode – eliminating the solvents in the processing and coating of the electrodes has a number of benefits.
Dry Room – typically aim for a dew point of -30°C or lower, equivalent to less than 1% relative humidity (RH).
Dry Separator – the separator is produced without solvents being used in the process.
Effective Ionic Conductivity Depends on how much electrolyte is present and how well ions can move through the open pore structure.
EL Cell
Electrical Double Layer The arrangement of ions and charge that forms at the interface between an electrode and the electrolyte, central to understanding interfacial charge-transfer kinetics.
Electrochemical Impedance Spectroscopy (EIS) – A characterisation technique that applies a small sinusoidal voltage or current perturbation across a range of frequencies and measures the resulting impedance. EIS deconvolutes the contributions of ohmic resistance, charge transfer, and diffusion, enabling detailed diagnosis of degradation mechanisms and SEI evolution.
Electrochemical Stability Window – The voltage range over which an electrolyte is thermodynamically stable — i.e., it does not oxidise at the cathode or reduce at the anode. Electrolytes operating outside this window decompose, though kinetic stabilisation by the SEI and CEI can extend practical operating voltages beyond thermodynamic limits. See: Electrochemical Potential Window
Electrode – the electrical part of a cell and consists of a backing metallic sheet with active material printed on the surface.
Electrolyte – the medium that allows ionic transport between the electrodes during charging and discharging of a cell.
Electrolyte Additives – used for a number of functions, including:
- improved SEI formation
- reduce irreversible capacity loss and gas generation
- enhance thermal stability of LiPF6
- protect the cathode material from dissolution and overcharge
- improve the physical properties of the electrolyte
Electrolyte Decomposition – The breakdown of electrolyte molecules through oxidation at the cathode or reduction at the anode. Decomposition products form the SEI on the anode and the CEI on the cathode. Excessive decomposition consumes lithium inventory and electrolyte, contributing to gas evolution and capacity fade.
Faraday Constant – the electric charge carried by one mole of electrons (or singly-ionized ions).
First Cycle Loss (FCL) – The irreversible capacity consumed during the first charge cycle, primarily through formation of the SEI and CEI. Expressed as a percentage of first-charge capacity, FCL represents lithium permanently removed from the active inventory. Prelithiation strategies are used to compensate for this loss. See: Prelithiation
Flow Battery – An electrochemical energy storage system in which the energy-storing electrolytes are held in external tanks and pumped through an electrochemical cell stack during charge and discharge. Power and energy are independently scalable, making flow batteries attractive for large-scale stationary storage. See: Battery Energy Storage Systems
Foil – or Electrode is the backing metallic sheet (current collector) with active material printed on the surface.
Formation – the process of initially charging and discharging the cell after it has been assembled. So named because this process “forms” the electrochemical system.
Fluoride-Ion – seen as a replacement for lithium and possibly the post-lithium technology with “up to 7x the Wh/kg” of current Lithium technology.
Fluorinated Electrolyte – An electrolyte formulation in which some or all carbonate solvents are replaced with fluorinated analogues (e.g. fluoroethylene carbonate, FEC; difluoroethylene carbonate, DFEC). Fluorinated electrolytes improve the quality of the SEI on silicon anodes, extend the oxidative stability window for high-voltage cathodes, and improve low-temperature performance.
Fluoroethylene Carbonate (FEC) – A fluorinated cyclic carbonate commonly used as an electrolyte additive in silicon-anode cells. FEC preferentially decomposes to form a thinner, more mechanically stable SEI that better accommodates silicon’s large volume changes, improving capacity retention and initial coulombic efficiency.
Galvanostatic Intermittent Titration Technique (GITT) – measures the transient voltage change and open circuit voltage (OCV) change during the charging and discharging processes using only a constant current supply and specified cut-off intervals.
Gas Evolution / Gassing – The production of gases (CO₂, CO, H₂, O₂, and others) within a cell, typically from electrolyte decomposition or cathode oxygen release. Gassing occurs mainly during formation and early cycles but can continue with ageing. In sealed cells it causes swelling; unvented accumulation increases internal pressure and safety risk.
GED – Gravimetric Energy Density
Graphene Aluminium Ion – graphene cathode and aluminium anode, high charge rate battery technology.
Graphite – amorphous form of carbon, made of carbon atoms bound hexagonally in sheets.
Hard Carbon – A disordered, non-graphitisable form of carbon used as the dominant anode material in sodium-ion batteries. Hard carbon stores sodium in nanopore voids and between graphene-like layers, offering adequate capacity at a low potential plateau. Its disordered structure prevents the large volume changes that would occur with graphite. See: Sodium-Ion Battery
HF — Hydrogen Fluoride (critical thermal runaway gas hazard)
High Nickel – Cathode chemistry with a nickel content above 80% (e.g. NMC 811, NMC 9.5.5, NCA). High-nickel cathodes deliver greater specific capacity and energy density than mid-nickel formulations but are more prone to structural instability, surface reactivity, and thermal runaway at elevated state of charge. See: NMC
HOMO-LUMO – the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the electrolyte.
Humidity – typically a dry room with a dew point of -30°C or lower is equivalent to less than 1% relative humidity (RH).
Impedance – The total opposition a cell presents to alternating current, encompassing ohmic (resistive), capacitive, and inductive components. Impedance increases with ageing as the SEI thickens, active material degrades, and lithium inventory is lost. Often characterised by EIS and used as a state-of-health indicator in BMS algorithms.
Initial Coulombic Efficiency (ICE) – The ratio of first-discharge capacity to first-charge capacity, expressed as a percentage. ICE quantifies irreversible lithium consumed in SEI and CEI formation during the initial cycle. A high ICE (close to 100%) is desirable; silicon additives and novel cathode materials typically exhibit lower ICE than conventional graphite/NMC cells.
Instrumenting Cells – if you are going to instrument a cell you need to be able to do this reliably and robustly. The process flow diagram illustrates the experimental stages employed for cell instrumentation and includes: sensor fabrication, cell modification and sensor insertion. The diagram highlights the different verification stages for assessing LIB performance, operation and ageing.
Intercalation / Deintercalation – The reversible insertion (intercalation) and extraction (deintercalation) of lithium ions into and out of a host electrode material without fundamentally altering the host crystal structure. Intercalation underpins the operation of graphite anodes and layered oxide cathodes, providing the reversibility essential for rechargeable lithium-ion cells.
Internal Resistance – The resistance within a cell that opposes current flow, comprising ohmic resistance (current collectors, electrolyte, electrode conductivity) and non-ohmic contributions from electrochemical kinetics and diffusion. Higher internal resistance increases heat generation and reduces power capability. Measured by DCIR or EIS.
Ionic Conductivity – The ability of an electrolyte to transport ions, expressed in S/cm (Siemens per centimetre). Liquid electrolytes typically achieve ~10 mS/cm at room temperature; solid electrolytes must approach this value to be viable. Ionic conductivity decreases at low temperatures, limiting cell rate capability in cold climates. See: Electrolyte
Jahn-Teller Distortion – A structural distortion driven by Mn3+ ions that contributes to capacity fade in manganese-rich cathode materials.
Knee Point – describes a sudden change in the gradient of a cell cycling curve.
Also called:
- rollover failure
- nonlinear aging
- sudden death
- saturation
- second-stage degradation
- two-phase degradation
- capacity plunge
- drop-off
LATP / LLZO / LGPS – Three leading classes of inorganic solid electrolyte materials: LATP (lithium aluminium titanium phosphate, NASICON-type), LLZO (lithium lanthanum zirconium oxide, garnet-type), and LGPS (lithium germanium phosphorus sulfide, sulfide-type). Each offers different trade-offs of ionic conductivity, electrochemical stability window, and processability. See: Solid State Battery
Lattice Oxygen Release – The irreversible loss of oxygen from a cathode’s crystal structure at high states of charge, a key degradation pathway in nickel-rich and lithium-rich cathodes.
Layered Oxide – A structural family of cathode materials (including NMC, NCA, and NCMA) in which lithium ions occupy layers between sheets of transition metal oxides in an alpha-NaFeO₂-type crystal structure. Layered oxides deliver high specific capacity and are the dominant cathode family in high energy density lithium-ion cells. See: NMC
LCA – Life Cycle Analysis
LCO — Lithium Cobalt Oxide
LFP – Lithium Iron Phosphate, a lithium ion cathode material with graphite used as the anode. This cell chemistry is typically lower energy density than NMC or NCA, but is also seen as being safer.
LiPF6 – Lithium hexafluorophosphate
Lithium Dendrite – Filamentary metallic lithium growth that can pierce the separator and cause an internal short circuit, distinct from the more general phenomenon of lithium plating.
Lithium Plating – This is the deposition of metallic lithium on the surface of the graphite anode. This is one of the most significant degradation mechanisms.
Lithium Air – promised as the beyond lithium ion technology with unrivaled energy density.
Lithium Rich Manganese – high specific capacity because of both cationic and anionic redox activity and are expected to be developed and applied as cathode materials for a new generation of high-energy density lithium-ion batteries.
Lithium Sulfur – perhaps the most mature of the beyond Li-ion’ battery chemistries with a potential energy density of >600Wh/kg.
LMB – Lithium Metal Battery
LMFP – Lithium manganese iron phosphate.
LMO – Lithium Manganese Oxide
LMR = Lithium Manganese Rich
LNMO – Lithium Nickel Manganese Oxide
Loss of Active Material (LAM) – A degradation mode in which electrode material becomes electrochemically inactive due to particle isolation, cracking, or structural transformation. LAM reduces the cell’s capacity ceiling and shifts the balance between anode and cathode capacity. Together with Loss of Lithium Inventory (LLI), LAM forms the standard two-axis degradation taxonomy.
Loss of Lithium Inventory (LLI) – A degradation mode in which cyclable lithium is permanently removed from active service, typically through SEI growth, lithium plating, or reactions with electrolyte decomposition products. LLI is the dominant early-life degradation mechanism in most lithium-ion cells and is tracked through coulombic efficiency measurements.
LRM – Lithium Rich Manganese has a high specific capacity because of both cationic and anionic redox activity
LTMO – Layered Transition Metal Oxide
LTO – Lithium Titanate / Lithium Titanium Oxide
M3P – CATL’s trade name for their own developed variation on LFP.
Magnesium-Ion – function is very similar to lithium-ion batteries, comparable energy density to lithium-ion along with potential for improvement as there are double the electrons for every individual magnesium ion.
Memory Effect – phenomenon in which a cell, operated in successive cycles to the same, but less than a full, depth of discharge experiences a depression of its discharge voltage and temporarily loses the rest of its capacity at normal voltage levels.
Mid Nickel – chemistry with a Nickel content of 40% to 60%.
Na Ion – Sodium Ion battery cell.
NCA – Lithium Nickel Cobalt Aluminium Oxide — a layered oxide cathode material widely used in cylindrical cells (e.g. Tesla/Panasonic applications). Aluminium substitution improves structural stability and thermal safety versus NMC at comparable nickel content. NCA cells deliver high specific energy but require careful thermal management.
NCMA – Nickel Cobalt Manganese Aluminium cathodes are more stable than NMC.
NED – Normalised Energy Density
Negative Electrode – the anode.
Nernst Equation – the fundamental equation relating an electrode’s potential to the concentrations of reactants and products, underpinning most electrochemical analysis.
Nickel Cadmium – rechargeable battery that uses nickel oxide hydroxide and metallic cadmium as electrodes. Today it is the technology of choice for several highly demanding industrial applications. This is due to: superior resistance to mechanical and electrical stress able to operate at extreme temperatures and a frequently cycling temperature.
Nickel Hydrogen – has the positive electrode of nickel oxide from the nickel-cadmium cell, and a hydrogen negative electrode from the hydrogen-oxygen fuel cell. The energy density is low at ~60Wh/kg, cost high, but cycle life can be ~200,000 and hence find a niche application in space craft.
Nickel Iron – the NiFe battery, nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide.
NMC – Lithium Nickel Manganese Cobalt Oxides are a family of mixed metal oxides of lithium, nickel, manganese and cobalt. Nickel is known for its high specific energy, but poor stability. Manganese has low specific energy but offers the ability to form spinel structures that allow low internal resistance.
N/P Ratio – refers to the ratio between the effective capacity of the anode (negative electrode, N) and the cathode (positive electrode, P). In simple terms, it compares how much lithium the anode can store versus how much the cathode can provide.
Olivine Structure – A crystal structure adopted by LFP (LiFePO₄) and LMFP in which phosphate (PO₄) groups form a robust three-dimensional framework around iron and lithium sites. The strong P–O covalent bonds provide excellent structural and thermal stability, underpinning the safety characteristics of LFP chemistry. See: LFP
Open Circuit Voltage (OCV) – is the potential difference between the positive and negative terminals when no current flows and the cell is at rest.
Operando X-ray Diffraction – a structural characterization technique performed on a cell while it is actively charging or discharging, revealing phase changes in real time.
Overpotential – The deviation of electrode potential from its equilibrium (thermodynamic) value when current flows. Overpotential has three components: ohmic (IR drop), activation (charge transfer kinetics), and concentration (diffusion limitations). Total cell overpotential determines the gap between charge voltage and discharge voltage, directly affecting round-trip efficiency.
Particle Size Distribution (PSD) – The PSD of active materials directly impacts their tap density and compactibility—two critical factors that determine how densely an electrode can be packed during calendaring. A higher tap density allows for denser coatings, which is essential when aiming for higher energy density in cells.
PbA – abbreviation of lead acid battery.
PBA – Prussian Blue Analogues
Polarisation – The shift in cell voltage from its equilibrium OCV when a current is applied, arising from ohmic, kinetic, and diffusion overpotentials. Polarisation increases at higher currents, low temperatures, and with ageing. It causes charge voltage to rise and discharge voltage to fall relative to OCV, reducing usable energy.
Polysulfide Shuttle Effect – The core degradation mechanism in lithium-sulfur cells, where soluble polysulfide intermediates migrate between electrodes and cause continuous capacity loss.
Porosity – The fraction of electrode volume occupied by void space (pores), expressed as a percentage. Porosity determines the volume available for electrolyte impregnation and directly affects ion transport through the electrode. Higher porosity aids ion diffusion but reduces volumetric energy density; calendaring is used to tune electrode porosity to specification.
Positive Electrode – the cathode.
Potassium Ion – potential to be a low cost storage based chemistry, but large large change of ~60% of graphite with the insertion of K ions puts high strain on lattice and so limits cycling.
Precursor Cathode Active Material (pCAM) – a powder-like substance critical to manufacture lithium-ion batteries. It contains materials such as: Nickel, Cobalt, Manganese.
Prelithiation – introduces extra active lithium ions through various lithium sources. These extra lithium ions contribute to the formation of the solid electrolyte interphase (SEI), hence improving the delivered energy density of the cell.
Primary Cell – a cell that can only be discharged once.
PVDF -Polyvinylidene Fluoride
Redox Couple – The paired oxidized and reduced forms of a chemical species that exchange electrons at an electrode, the basic building block of every battery and flow battery reaction.
Redox Mediator – A soluble species used to shuttle charge to or from an otherwise poorly conductive solid active material, used in semi-solid flow and metal-air battery designs.
Redox Reaction – A coupled electrochemical reaction in which one species is oxidised (loses electrons) and another is reduced (gains electrons). In a lithium-ion cell, transition metal ions in the cathode are reduced on discharge and oxidised on charge, while lithium is intercalated and deintercalated. The difference in redox potentials between anode and cathode determines cell voltage.
Reference Electrode or 3rd Electrode is added to a battery cell so that the anode and cathode potentials can be referenced against a known point.
Secondary Cell – a rechargeable battery cell.
Self Discharge – the capacity loss per month given a percentage of the nominal capacity. Typically this is declared at room temperature.
Separator – material that separates the anode and cathode electrically whilst allowing ions to pass through.
SHE – Standard Hydrogen Electrode
Silicon Anode – as an additive to graphite anodes it is seen as a drop-in to increase the efficiency and energy storage capacity of lithium-ion batteries. However, the downsides have been increased expansion and hence material degradation reducing cycle life.
Silicon Oxide Anode (SiOx) – A silicon-based anode material in which silicon is partially oxidised to form a silicon oxide matrix (SiOₓ, x ≈ 1). SiOx offers higher specific capacity than graphite with better cycling stability than pure silicon, because the oxide matrix buffers volume expansion. Used in commercial cells, often blended with graphite, as a step toward full silicon anodes. See: Silicon Anode
Slurry – The wet mixture of active material, conductive additive (e.g. carbon black), and binder (e.g. PVDF) dispersed in a solvent (typically NMP for cathodes, water for graphite anodes) that is coated onto the current collector foil. Slurry formulation — solid content, viscosity, and particle dispersion — directly determines electrode microstructure and cell performance.
Solid Electrolyte Interphase – is formed on electrode surfaces from decomposition products of electrolytes. The SEI allows Li+ transport and blocks electrons in order to prevent further electrolyte decomposition and ensure continued electrochemical reactions.
Solid State – anode, cathode and electrolyte are solid.
Solvation Shell / Desolvation – the cluster of solvent molecules surrounding an ion in solution, and the process of shedding that shell before the ion can intercalate into an electrode, a key step governing fast-charging and low-temperature performance.
Spinel Structure – A cubic crystal structure adopted by LMO (LiMn₂O₄) and LNMO (LiNi₀.₅Mn₁.₅O₄). The three-dimensional lithium diffusion pathways in spinel structures enable fast charge rates. LNMO operates at ~4.7 V vs Li/Li⁺, making it attractive for high-voltage applications but demanding on electrolyte stability.
Standard Electrode Potentials – every electrochemical couple has a characteristic tendency to gain or give up electrons. The standard electrode potential, E°, puts a number on that tendency so that different half-reactions can be ranked on one scale. It is the starting point for estimating the voltage of any battery chemistry, and for understanding why some materials make good anodes while others make good cathodes.
Standard Hydrogen Electrode (SHE) – a reference point for measuring electrode potentials. Defined as a potential of 0V under standard conditions (298 K, 1 atm pressure, 1 M concentration).
Superionic Conductor – A solid material with unusually high ionic conductivity approaching that of liquid electrolytes (>1 mS/cm at room temperature). Superionic conductors such as LGPS and certain LLZO compositions are candidate solid electrolytes for all-solid-state batteries, combining high ionic conductivity with the mechanical rigidity to suppress lithium dendrite penetration. See: Solid State Battery
Ternary Battery – battery chemistry that integrates a cathode composed of three metallic elements, such as nickel, cobalt and manganese
Third Electrode – electrode used in cells to establish the potential of the anode and cathode independently.
Tin Anode (Sn) – An alternative anode material offering a theoretical specific capacity of 993 mAh/g through alloying with lithium (vs 372 mAh/g for graphite). Like silicon, tin suffers from large volume changes (~260%) during lithiation, leading to particle fracture and capacity fade. Tin is used in small quantities as an additive and in thin-film configurations.
Tortuosity – A measure of the complexity of the ion transport path through an electrode’s pore network, defined as the ratio of the effective path length to the straight-line thickness. Higher tortuosity increases effective electrolyte resistance within the electrode, limiting rate capability. Tortuosity is influenced by particle morphology and the arrangement of pores created during electrode manufacturing.
Transference Number – The fraction of total ionic current carried by the lithium cation (Li⁺) in the electrolyte. A transference number close to 1.0 means Li⁺ carries nearly all the current, minimising concentration gradients across the cell. Typical liquid electrolytes have Li⁺ transference numbers of ~0.3–0.4; single-ion conducting solid or polymer electrolytes aim for values approaching 1.0. See: Electrolyte
Vanadium Redox Flow Battery (VRFB) – A flow battery that uses vanadium ions in different oxidation states (V²⁺/V³⁺ on the negative side, VO²⁺/VO₂⁺ on the positive side) dissolved in sulfuric acid electrolyte. Using vanadium on both sides eliminates cross-contamination degradation. VRFBs are established in large-scale stationary storage due to their long cycle life and independent power and energy scaling. See: Battery Energy Storage Systems
VED – Volumetric Energy Density
Voltage Fade – A degradation phenomenon observed in lithium-rich (LMR) cathode materials in which the average discharge voltage decreases with cycling, even when capacity is maintained. Voltage fade arises from irreversible structural changes in the cathode — specifically, the progressive conversion of layered domains to a spinel-like phase — and reduces the practical energy delivered by the cell. See: Lithium Rich Manganese
Warburg Impedance – the low-frequency tail on a lithium-ion cell’s Nyquist plot is not just the last stretch of the same curve as the semicircles before it, it is the signature of a different physical process. It represents lithium ions diffusing through the solid electrode material, and it is normally described using a Warburg element.
Wet Separator – the separator is produced using solvents.
Zebra Battery – Sodium-Nickel-Chloride Molten Salt Battery
Zinc Air – perhaps the most promising metal-air battery technology. Typically it has a zinc anode, an oxygen permeable cathode, a separator, and a caustic alkaline electrolyte. Promising low cost, high stability and high energy density.
Zinc Bromine – promising flow battery technology.
Zinc Carbon – a primary battery chemistry, commonly used in batteries for radios, toys and household goods.
See also: Abbreviations and Jargon