{ "node": { "id": "term:relaxation", "type": "Term", "label": "Relaxation", "properties": { "id": "relaxation", "name": "Relaxation", "aka": [ "rest" ], "section": "topic-charging", "definition": "The slow recovery of a cell’s voltage towards open-circuit voltage after current stops, as concentration gradients inside the electrodes level out. It takes minutes to hours, which is why OCV measurements need a rest period.", "related": [ "open-circuit-voltage", "polarization", "diffusion", "hppc", "voltage-relaxation-analysis" ], "url": "https://lemonergy.com/learn/glossary/relaxation/", "mentions": [] } }, "edges": [ { "id": "edge:129", "source": "term:relaxation", "target": "workflow:hppc", "type": "usedIn", "properties": { "sourceFile": "wiki-blocks.json" } }, { "id": "edge:1136", "source": "term:relaxation", "target": "topic:topic-charging", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:1137", "source": "term:relaxation", "target": "term:open-circuit-voltage", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1138", "source": "term:relaxation", "target": "term:polarization", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1139", "source": "term:relaxation", "target": "term:diffusion", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1140", "source": "term:relaxation", "target": "term:hppc", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1141", "source": "term:relaxation", "target": "term:voltage-relaxation-analysis", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1142", "source": "term:relaxation", "target": "visual:rc", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "workflow:hppc", "type": "Workflow", "label": "Inspect pulse characterization", "properties": { "id": "hppc", "title": "Inspect pulse characterization", "kind": "protocol", "summary": "HPPC alternates pulses, moves SOC and includes long rests.", "steps": [ "Open HPPC pulse characterization.", "Compare immediate voltage change and recovery." ], "example": "0.2 V change after a 10 A step gives 20 mΩ by ΔV/ΔI on the same cell/pack basis.", "observe": "Long rests differ from the immediate resistive jump.", "limits": "The estimate depends on timing, temperature and state; this is not AC impedance spectroscopy.", "url": "https://design.lemonergy.com/", "label": "Open Design → Protocol bench", "evidence": [ "js/test-protocol.js" ] } }, { "id": "topic:topic-charging", "type": "Topic", "label": "Charging and discharging", "properties": { "id": "topic-charging", "name": "Charging and discharging", "lede": "How current goes in and comes out, and the limits that stop it.", "context": "Separate regulation from availability.", "example": "The same CC–CV law can operate overnight or during a short depot stop.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open charging quantities" } }, { "id": "term:open-circuit-voltage", "type": "Term", "label": "Open-circuit voltage", "properties": { "id": "open-circuit-voltage", "name": "Open-circuit voltage", "abbr": "OCV", "section": "topic-state", "definition": "The voltage across a cell’s terminals when no current flows and the cell has rested long enough for the voltage to settle. It depends on state of charge and temperature, and a cell whose open-circuit voltage falls unusually fast in storage may have an internal short.", "unit": "V", "related": [ "ocv-soc-curve", "relaxation", "voltage-hysteresis", "k-value", "internal-short-circuit" ], "lesson": "fundamentals/cell-production/#finishing", "url": "https://lemonergy.com/learn/glossary/open-circuit-voltage/", "mentions": [ "state-of-charge" ] } }, { "id": "term:polarization", "type": "Term", "label": "Polarization", "properties": { "id": "polarization", "name": "Polarization", "aka": [ "overvoltage" ], "section": "topic-charging", "definition": "The gap between a cell’s terminal voltage under load and its open-circuit voltage. It has ohmic, charge-transfer and concentration parts, grows with current and falling temperature, and is where delivered energy is lost.", "unit": "V", "related": [ "overpotential", "ir-drop", "concentration-polarization", "open-circuit-voltage", "polarisation-curve" ], "url": "https://lemonergy.com/learn/glossary/polarization/", "mentions": [ "voltage", "closed-circuit-voltage" ] } }, { "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": "term:hppc", "type": "Term", "label": "Hybrid pulse power characterisation", "properties": { "id": "hppc", "name": "Hybrid pulse power characterisation", "abbr": "HPPC", "section": "topic-testing", "definition": "A test that applies a short discharge pulse and a short charge pulse at each state of charge, from which resistance and power capability are read as a function of SOC. It is the standard source of equivalent-circuit parameters.", "related": [ "equivalent-circuit-model", "state-of-power", "internal-resistance", "dcir", "pulse-test" ], "url": "https://lemonergy.com/learn/glossary/hppc/", "mentions": [ "state-of-charge" ] } }, { "id": "term:voltage-relaxation-analysis", "type": "Term", "label": "Voltage relaxation analysis", "properties": { "id": "voltage-relaxation-analysis", "name": "Voltage relaxation analysis", "aka": [ "rest-voltage analysis", "relaxation voltage", "rest voltage diagnostics" ], "section": "topic-testing", "definition": "Extracting diagnostic information from the way a cell’s voltage settles during a rest. After fast charging, a plateau in the relaxing voltage — a peak in dV/dt — reveals plated lithium re-entering the graphite; features of the relaxation curve also track capacity fade, and a rest voltage that keeps drifting down points to self-discharge.", "related": [ "relaxation", "lithium-plating", "open-circuit-voltage", "fast-charging", "state-of-health", "k-value" ], "url": "https://lemonergy.com/learn/glossary/voltage-relaxation-analysis/", "mentions": [ "graphite", "self-discharge", "capacity-fade" ] } }, { "id": "visual:rc", "type": "Visual", "label": "Voltage response and relaxation", "properties": { "title": "Voltage response and relaxation", "summary": "One time constant completes about 63% of a first-order voltage change.", "readout": "At τ = 20 s, 63.2% of the step response is complete; a relaxation retains 36.8%.", "formula": "τ = RC; step response = 1 − e^(−t/τ)", "note": "Two separate analytical experiments; normalized voltage, not measured data.", "software": { "status": "reference", "label": "Reference concept", "body": "An analytical RC response explains polarization and relaxation. It is not an identified RC network or a native Studio battery capability.", "href": "../chapter-1/" }, "html": "
First-order voltage response
First-order voltage responseTime (s) versus Fraction of voltage change. Step response; Separate relaxation experiment. Interpretation follows the graphs.000.263450.525900.7881351.05180Time (s)Fraction of voltagechange
Step responseSeparate relaxation experiment (dashed)
" } } ] }