“Voltage/capacity/energy density: understand the three most critical parameters of lithium batteries, you can really see the battery performance!”
I. Voltage: the “blood pressure” of the battery, determining the limit of energy output
【Core Concepts】
Voltage: the potential difference generated by the movement of the unit charge inside the battery, which directly affects the power supply capacity of the device
Nominal voltage: the voltage of the battery in normal operation (such as 3.7V lithium)
Discharge cut-off voltage: the lowest voltage at which the battery can be safely discharged (usually 2.5-3.0V)
[Fatal Misconceptions]
Higher voltage = more energy?
→ Wrong! Voltage only reflects the strength of single discharge, actual energy = voltage × capacity (Wh)
→ Comparison: 5V/2000mAh=10Wh VS 3.7V/5000mAh=18.5Wh
[Real Case].
A brand drone crash accident in 2019:
→ The nominal voltage of the battery was falsely labeled to 4.2V (standard 3.7V), and the continuous discharge caused the electrolyte to boil and explode
II.The capacity: the battery's “meal”, the essence of the decision to extend the duration of time
Core formula
Capacity (mAh) = discharge current (mA) × time (h)
In-depth analysis
Capacity test standard:
0.5C discharge: discharge at half of the rated capacity to the cut-off voltage (e.g. 1000mAh battery discharged with 500mA)
Low-temperature capacity degradation: -20℃ lithium iron phosphate capacity decreases by 40%, while lithium ternary only decreases by 15%.
The “false label” trap
A treasure pop-up charging treasure actual test:
→ nominal 20000mAh, the actual 0.5C discharge only 6300mAh output (false labeling rate of 63%)
→ Key indicators: check whether the label “mAh@2A” or “20W output”.
III.The consumer must see the parameter selection guide
Cell phone/tablet:
Prioritize 4000mAh or above + 3.8V or above voltage
Be wary of below 20000mAh + below 3.2V (mostly low-end batteries)
E-bikes:
Focus on energy density above 60Wh/kg (new national standard requires ≥50Wh/kg)
Choose 18650 battery cell
Charging treasure:
Calculate the actual energy: capacity (mAh) × voltage (V)/1000 → 20000mAh/3.7V = 74Wh
Civil aviation restrictions in 2023: ≤100Wh can be directly boarded, 100-160Wh requires airline approval
Voltage is the “vital signs” of lithium batteries, capacity is the “amount of food”, energy density is the “size”. Understanding these three parameters, you will be able to see through the business publicity tactics, to make a more informed choice. When solid-state batteries break through the energy density bottleneck, perhaps we will witness a real energy revolution - after all, who can master the balance of these three parameters, who will hold the lifeblood of the science and technology industry in the next decade.
Post time: Mar-20-2025