{ "node": { "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" ] } }, "edges": [ { "id": "edge:44", "source": "term:open-circuit-voltage", "target": "workflow:ocv-charge-balance", "type": "usedIn", "properties": { "sourceFile": "wiki-blocks.json" } }, { "id": "edge:1279", "source": "term:open-circuit-voltage", "target": "topic:topic-state", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:1280", "source": "term:open-circuit-voltage", "target": "term:ocv-soc-curve", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1281", "source": "term:open-circuit-voltage", "target": "term:relaxation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1282", "source": "term:open-circuit-voltage", "target": "term:voltage-hysteresis", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1283", "source": "term:open-circuit-voltage", "target": "term:k-value", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1284", "source": "term:open-circuit-voltage", "target": "term:internal-short-circuit", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/open-circuit-voltage/state-of-charge", "source": "term:open-circuit-voltage", "target": "term:state-of-charge", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:1286", "source": "term:open-circuit-voltage", "target": "lesson:fundamentals/cell-production/", "type": "explainedIn", "properties": { "sourceFile": "terms.json", "url": "https://lemonergy.com/learn/fundamentals/cell-production/#finishing" } }, { "id": "edge:1287", "source": "term:open-circuit-voltage", "target": "visual:voltage", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } }, { "id": "edge:1288", "source": "term:open-circuit-voltage", "target": "reference:plett-modeling", "type": "cites", "properties": { "sourceFile": "wiki-references.json", "scope": "direct technical reference" } } ], "neighbors": [ { "id": "workflow:ocv-charge-balance", "type": "Workflow", "label": "Connect SOC and voltage", "properties": { "id": "ocv-charge-balance", "title": "Connect SOC and voltage", "kind": "studio", "summary": "The battery integrates charge and combines OCV with resistance.", "steps": [ "Inspect capacity, initial SOC and OCV endpoints.", "Compare OCV with terminal voltage." ], "example": "OCV endpoints of 300 and 420 V give 360 V at 50% SOC. Charging at 10 A through 0.08 Ω adds 0.8 V.", "observe": "At unity coulombic efficiency, 10 A for 1 h adds ten percentage points to 100 Ah.", "limits": "Internal model SOC is not an estimate of an unknown physical battery. OCV is linear and resistance fixed.", "url": "https://design.lemonergy.com/cosim.html?example=charging-home", "label": "Open the Studio example", "evidence": [ "js/charging-control.js", "js/charging-scenarios.js", "docs/CHARGING_BLOCKS_SPEC.md" ] } }, { "id": "topic:topic-state", "type": "Topic", "label": "State estimation", "properties": { "id": "topic-state", "name": "State estimation", "lede": "The quantities a battery management system estimates but cannot measure directly.", "context": "Distinguish internal states from noisy measurement estimates.", "example": "Current-sensor bias accumulates in coulomb counting. Exact model SOC does not establish real estimator accuracy.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open charge balance" } }, { "id": "term:ocv-soc-curve", "type": "Term", "label": "OCV–SOC curve", "properties": { "id": "ocv-soc-curve", "name": "OCV–SOC curve", "section": "topic-state", "definition": "The characteristic relation between a cell’s open-circuit voltage and its state of charge, measured once at low current and stored in the BMS. A steep curve, as for NMC, makes SOC easy to read from voltage; LFP’s flat curve does not.", "related": [ "open-circuit-voltage", "state-of-charge", "coulomb-counting", "lfp", "voltage-plateau", "ocv-test" ], "url": "https://lemonergy.com/learn/glossary/ocv-soc-curve/", "mentions": [ "bms" ] } }, { "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": [] } }, { "id": "term:voltage-hysteresis", "type": "Term", "label": "Voltage hysteresis", "properties": { "id": "voltage-hysteresis", "name": "Voltage hysteresis", "section": "topic-charging", "definition": "The difference between the open-circuit voltage reached from charging and from discharging at the same state of charge. It is small for most lithium-ion chemistries but large for LFP and silicon, and it limits how precisely voltage can give SOC.", "related": [ "open-circuit-voltage", "ocv-soc-curve", "lfp", "silicon-anode", "energy-efficiency" ], "url": "https://lemonergy.com/learn/glossary/voltage-hysteresis/", "mentions": [ "state-of-charge" ] } }, { "id": "term:k-value", "type": "Term", "label": "K-value", "properties": { "id": "k-value", "name": "K-value", "aka": [ "OCV drop rate" ], "section": "topic-manufacturing", "definition": "The rate at which a cell’s open-circuit voltage falls during the production aging step, in millivolts per day. A high K-value signals an internal short or contamination, and such cells are scrapped before shipment.", "unit": "mV/day", "related": [ "aging-step", "self-discharge", "open-circuit-voltage", "internal-short-circuit" ], "url": "https://lemonergy.com/learn/glossary/k-value/", "mentions": [] } }, { "id": "term:internal-short-circuit", "type": "Term", "label": "Internal short circuit", "properties": { "id": "internal-short-circuit", "name": "Internal short circuit", "abbr": "ISC", "section": "topic-safety", "definition": "An unintended electronic path between the electrodes inside a cell — through a metal particle, a burr, a damaged separator or lithium deposits. It discharges the cell internally and turns its energy into local heat.", "related": [ "thermal-runaway", "dendrite", "separator", "external-short-circuit", "self-discharge", "internal-short-trigger-device" ], "lesson": "fundamentals/cell-anatomy/#short-circuit", "url": "https://lemonergy.com/learn/glossary/internal-short-circuit/", "mentions": [ "electronic-path", "burr", "metal-particle-contamination" ] } }, { "id": "term:state-of-charge", "type": "Term", "label": "State of charge", "properties": { "id": "state-of-charge", "name": "State of charge", "abbr": "SOC", "section": "topic-state", "definition": "How full a cell is, as a fraction of its available capacity. State of charge, like temperature, affects how fast a stored cell ages.", "unit": "%", "related": [ "depth-of-discharge", "ocv-soc-curve", "coulomb-counting", "state-of-health", "bms" ], "lesson": "fundamentals/battery-aging/#storage-soc", "example": { "title": "Interpret a charge inventory", "text": "If available capacity is 5 Ah and 3 Ah remains by the chosen estimator, SOC is 60%. A different estimate of available capacity changes this percentage, so compare SOC values only with the capacity convention recorded." }, "url": "https://lemonergy.com/learn/glossary/state-of-charge/", "mentions": [ "usable-capacity" ] } }, { "id": "lesson:fundamentals/cell-production/", "type": "Lesson", "label": "Lesson 3 · Cell production", "properties": { "url": "https://lemonergy.com/learn/fundamentals/cell-production/" } }, { "id": "visual:voltage", "type": "Visual", "label": "Voltage under load", "properties": { "title": "Voltage under load", "summary": "Discharge current creates an ohmic drop below open-circuit voltage.", "readout": "5 A through 20 mΩ gives 0.1 V ohmic drop.", "formula": "V_terminal = OCV − I_discharge R", "note": "Chosen OCV curve; no chemistry calibration, hysteresis or voltage cutoff.", "software": { "status": "studio", "label": "Voltage relationship in Studio", "body": "The native battery calculates terminal voltage from OCV and resistance. The curve here is an illustrative OCV relationship, not a fitted cell dataset.", "href": "https://design.lemonergy.com/cosim.html?example=charging-home" }, "html": "
Illustrative OCV and loaded voltage
Illustrative OCV and loaded voltageSOC (%) versus Voltage (V). Open circuit; Under load. Interpretation follows the graphs.1.802.42253.05503.67754.3100SOC (%)Voltage (V)
Open circuitUnder load (dashed)
" } }, { "id": "reference:plett-modeling", "type": "Reference", "label": "Extended Kalman filtering for battery management systems of LiPB-based HEV battery packs: Part 2. Modeling and identification", "properties": { "title": "Extended Kalman filtering for battery management systems of LiPB-based HEV battery packs: Part 2. Modeling and identification", "publisher": "Journal of Power Sources", "url": "https://doi.org/10.1016/j.jpowsour.2004.02.032", "type": "Research article", "scope": "Battery charge balance, open-circuit voltage, ohmic loss, polarization dynamics and model identification; parameters require cell-specific data.", "year": 2004, "authors": [ "Gregory L. Plett" ], "accessed": "2026-10-27" } } ] }