{ "node": { "id": "term:chronoamperometry", "type": "Term", "label": "Chronoamperometry", "properties": { "id": "chronoamperometry", "name": "Chronoamperometry", "aka": [ "potentiostatic hold", "potential step" ], "section": "topic-testing", "definition": "Stepping an electrode to a fixed potential and recording how the current decays with time. A diffusion-limited current falls with the inverse square root of time, the Cottrell relation, which yields diffusion coefficients; long holds measure leakage currents from electrolyte oxidation or self-discharge, and a staircase of small steps is PITT.", "formula": "i(t) = n·F·A·c·√(D / (π·t))", "related": [ "pitt", "potentiostat", "diffusion-coefficient", "self-discharge-test", "chronopotentiometry" ], "example": { "title": "Compare a diffusion-controlled current at two times", "text": "In the ideal Cottrell regime i ∝ 1/√t. If the current is 2 mA at 1 s, the model gives 1 mA at 4 s. This applies only while the assumed planar semi-infinite diffusion and potential-step conditions hold." }, "url": "https://lemonergy.com/learn/glossary/chronoamperometry/", "mentions": [ "electrode", "electrolyte", "self-discharge", "oxidation", "diffusion" ] } }, "edges": [ { "id": "edge:5342", "source": "term:chronoamperometry", "target": "topic:topic-testing", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:5343", "source": "term:chronoamperometry", "target": "term:pitt", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5344", "source": "term:chronoamperometry", "target": "term:potentiostat", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5345", "source": "term:chronoamperometry", "target": "term:diffusion-coefficient", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5346", "source": "term:chronoamperometry", "target": "term:self-discharge-test", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5347", "source": "term:chronoamperometry", "target": "term:chronopotentiometry", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/chronoamperometry/electrode", "source": "term:chronoamperometry", "target": "term:electrode", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/chronoamperometry/electrolyte", "source": "term:chronoamperometry", "target": "term:electrolyte", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/chronoamperometry/self-discharge", "source": "term:chronoamperometry", "target": "term:self-discharge", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/chronoamperometry/oxidation", "source": "term:chronoamperometry", "target": "term:oxidation", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/chronoamperometry/diffusion", "source": "term:chronoamperometry", "target": "term:diffusion", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:5353", "source": "term:chronoamperometry", "target": "visual:cottrell", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-testing", "type": "Topic", "label": "Testing methods", "properties": { "id": "topic-testing", "name": "Testing methods", "lede": "The measurements and test procedures that characterise a cell or pack, from capacity and pulse tests to abuse and environmental tests.", "context": "Record specimen, state, instrument, temperature and timing.", "example": "Resistance immediately after a current step can differ from a ten-second value because slower polarization contributes.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open capacity measurements" } }, { "id": "term:pitt", "type": "Term", "label": "Potentiostatic intermittent titration technique", "properties": { "id": "pitt", "name": "Potentiostatic intermittent titration technique", "abbr": "PITT", "section": "topic-testing", "definition": "The voltage-step counterpart of GITT: the potential is stepped and the decaying current recorded, giving the diffusion coefficient from the current transient. It needs a potentiostat rather than a cycler.", "related": [ "gitt", "diffusion-coefficient", "potentiostat" ], "url": "https://lemonergy.com/learn/glossary/pitt/", "mentions": [ "diffusion" ] } }, { "id": "term:potentiostat", "type": "Term", "label": "Potentiostat", "properties": { "id": "potentiostat", "name": "Potentiostat", "aka": [ "galvanostat" ], "section": "topic-testing", "definition": "An instrument that controls the potential of an electrode against a reference and measures the current, or the reverse as a galvanostat. It is the tool for electrochemical impedance spectroscopy and three-electrode experiments.", "related": [ "cycler", "electrochemical-impedance-spectroscopy", "three-electrode-cell", "reference-electrode", "cyclic-voltammetry" ], "url": "https://lemonergy.com/learn/glossary/potentiostat/", "mentions": [ "impedance", "electrode" ] } }, { "id": "term:diffusion-coefficient", "type": "Term", "label": "Diffusion coefficient", "properties": { "id": "diffusion-coefficient", "name": "Diffusion coefficient", "abbr": "D", "aka": [ "diffusivity" ], "section": "topic-transport", "definition": "The proportionality constant D in Fick’s first law, in m²/s. It sets how fast a species spreads for a given concentration gradient.", "unit": "m²/s", "related": [ "ficks-first-law", "solid-state-diffusion", "gitt", "diffusion" ], "lesson": "transport/ficks-first-law/#law", "url": "https://lemonergy.com/learn/glossary/diffusion-coefficient/", "mentions": [ "concentration-gradient" ] } }, { "id": "term:self-discharge-test", "type": "Term", "label": "Self-discharge test", "properties": { "id": "self-discharge-test", "name": "Self-discharge test", "section": "topic-testing", "definition": "Charging a cell to a set state, storing it, and measuring either the OCV drop over days or the capacity lost over weeks. In production it is the K-value check; in the laboratory a potentiostatic hold measures the leakage current directly in hours.", "related": [ "self-discharge", "k-value", "open-circuit-voltage", "internal-short-circuit" ], "url": "https://lemonergy.com/learn/glossary/self-discharge-test/", "mentions": [ "chronoamperometry" ] } }, { "id": "term:chronopotentiometry", "type": "Term", "label": "Chronopotentiometry", "properties": { "id": "chronopotentiometry", "name": "Chronopotentiometry", "aka": [ "galvanostatic measurement", "constant-current measurement" ], "section": "topic-testing", "definition": "Applying a constant current and recording the electrode potential over time — the principle behind ordinary galvanostatic cycling and GITT. On lithium metal it measures Sand’s time, when the salt concentration at the surface reaches zero and dendrites begin to grow.", "related": [ "gitt", "constant-current", "chronoamperometry", "dendrite", "concentration-polarization" ], "url": "https://lemonergy.com/learn/glossary/chronopotentiometry/", "mentions": [ "electrode", "electrode-potential" ] } }, { "id": "term:electrode", "type": "Term", "label": "Electrode", "properties": { "id": "electrode", "name": "Electrode", "section": "topic-components", "definition": "A solid conductor where the cell’s reaction happens, in contact with the electrolyte. A lithium-ion cell has a negative electrode and a positive electrode, each a porous coating on a metal foil.", "related": [ "negative-electrode", "positive-electrode", "porous-electrode", "current-collector" ], "lesson": "fundamentals/cell-anatomy/#components", "example": { "title": "Two transport paths", "text": "Electrons need connected solid paths to the collector; ions need electrolyte paths to reaction sites. More of one constituent displaces others at fixed volume." }, "url": "https://lemonergy.com/learn/glossary/electrode/", "mentions": [ "electrolyte", "coating" ] } }, { "id": "term:electrolyte", "type": "Term", "label": "Electrolyte", "properties": { "id": "electrolyte", "name": "Electrolyte", "section": "topic-electrolytes", "definition": "The ion-conducting medium between the electrodes. In a liquid-electrolyte cell it fills the pores of both electrodes and the separator, so it is not a separate structural layer.", "related": [ "lithium-salt", "carbonate-solvent", "electrolyte-additive", "ionic-conductivity", "solid-electrolyte", "ionic-liquid-electrolyte" ], "lesson": "fundamentals/cell-architecture/#electrolyte", "example": { "title": "Ions and electrons", "text": "Electrolyte carries ions between electrodes; the external circuit carries electrons. The two paths serve different roles." }, "url": "https://lemonergy.com/learn/glossary/electrolyte/", "mentions": [ "separator" ] } }, { "id": "term:self-discharge", "type": "Term", "label": "Self-discharge", "properties": { "id": "self-discharge", "name": "Self-discharge", "section": "topic-charging", "definition": "The slow loss of stored charge while a cell is not in use. An unexpected rise can signal a leakage path or a soft internal short.", "unit": "%/month", "related": [ "internal-short-circuit", "calendar-aging", "k-value", "calendar-life", "self-discharge-test" ], "lesson": "fundamentals/battery-aging/#check-yourself", "url": "https://lemonergy.com/learn/glossary/self-discharge/", "mentions": [] } }, { "id": "term:oxidation", "type": "Term", "label": "Oxidation", "properties": { "id": "oxidation", "name": "Oxidation", "section": "topic-electrochemistry", "definition": "Loss of electrons by a species. On discharge the negative electrode is oxidised as lithium leaves it as Li⁺, which is why that electrode is called the anode.", "related": [ "reduction", "anode", "redox-reaction" ], "url": "https://lemonergy.com/learn/glossary/oxidation/", "mentions": [ "electrode", "negative-electrode" ] } }, { "id": "term:diffusion", "type": "Term", "label": "Diffusion", "properties": { "id": "diffusion", "name": "Diffusion", "section": "topic-transport", "definition": "The net movement of a species from where it is concentrated to where it is scarce, driven by random thermal motion. In a cell lithium diffuses through the electrolyte in the pores and, far more slowly, through the solid particles themselves.", "related": [ "ficks-first-law", "diffusion-coefficient", "solid-state-diffusion", "concentration-gradient", "migration" ], "lesson": "transport/ficks-first-law/#in-a-cell", "url": "https://lemonergy.com/learn/glossary/diffusion/", "mentions": [ "electrolyte" ] } }, { "id": "visual:cottrell", "type": "Visual", "label": "Diffusion-limited current decays as 1/√t", "properties": { "title": "Diffusion-limited current decays as 1/√t", "summary": "An ideal potential-step experiment gives a decreasing diffusion-limited current.", "readout": "With n = 1 and area = 1 cm², current at 1 s is 0.1721 mA.", "formula": "i(t) = nFAc √(D/(πt))", "note": "Planar semi-infinite diffusion, constant D and bulk concentration, fast reaction and no convection or double-layer transient. Starts at 0.1 s because the ideal expression is singular at zero.", "software": { "status": "reference", "label": "Reference concept", "body": "This analytical Cottrell curve explains chronoamperometry. It does not fit a diffusion coefficient or distinguish leakage current from a measured experiment.", "href": "../chapter-1/" }, "html": "
Cottrell current after a potential step
Cottrell current after a potential stepTime (s) versus Current (mA). Diffusion-limited current. Interpretation follows the graphs.00.10.1362.580.2725.050.4087.530.54410Time (s)Current (mA)
Diffusion-limited current
" } } ] }