21700 Lithium-Ion Cell — Overview & Specs
Dimensions: 21 mm diameter × 70 mm length
Nominal Voltage: 3.6–3.7 V; fully charged ~4.2 V
Capacity Range: ~4,000–5,000+ mAh
Energy Density: ~260–300 Wh/kg depending on chemistry
Applications & Best Fits
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Electric Vehicles (EVs): Favored by Tesla Model 3/Y and many next-gen EV platforms for higher energy per cell
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E-Bikes & Scooters: Larger capacity and higher discharge capability than 18650 make them ideal for extended range and performance
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Power Tools: Better endurance between charges, supports high-drain applications
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Energy Storage Systems: Used in large-scale battery packs for renewable storage and backup power
Chemistry & Variants
| Chemistry | Characteristic | Best Use Cases |
|---|---|---|
| ICR (Lithium Cobalt Oxide) | Highest energy density, lower safety | Capacity-focused devices, less demanding discharge |
| IMR (Lithium Manganese Oxide) | Safer, high-drain (20–35 A) | High-performance e-bikes, tools |
| INR (Nickel Manganese Cobalt Oxide) | Balanced capacity & discharge | EV packs, mid-to-high performance needs |
| IFR (LiFePO₄) | Very long cycle life, safest chemistry | Stationary storage, high-safety EV applications |
Safety & Protection
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Protected vs Unprotected Cells:
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Protected: Built-in overcharge/discharge and short-circuit safety; bulkier, ideal for consumer devices
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Unprotected: For controlled pack assembly where a BMS ensures safety
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Safety Features:
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CID and PTC to interrupt current during overheat/overload events
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Handling Guidelines:
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Avoid shorting terminals; high discharge capability means higher short-circuit risk
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Charge between 0–45 °C, discharge between -20–60 °C
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Do not charge below 0 °C — lithium plating can occur
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Cycle Life & Performance Tips
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Cycle Life: 300–800 cycles typical for cobalt blends; LiFePO₄ variants can exceed 2,000 cycles
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Storage: Store at ~40–60% charge in a cool, dry environment to prolong life
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Performance Advantage Over 18650:
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Higher capacity → fewer cells needed for the same pack size
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Lower internal resistance → more efficient power delivery
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Slightly larger size allows for higher energy density per cell
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Suggested Page Structure for Your Site
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Intro / Specs — Dimensions, Voltage, Capacity, Energy Density
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Chemistry Types — Traits & applications for ICR / IMR / INR / IFR
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Applications — EVs, bikes, tools, storage
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Safety & Handling — Temperature ranges, protection methods
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Cycle Life & Storage — Longevity and care