Explanation of Common Battery Technical Terms

(1) Battery CapacityIt refers to the maximum electric charge Q that a battery can store, with the unit Coulomb (C).
\(Q = Current(I) \times Time(t)\)
1 C = 1 A·s. Battery capacity is commonly measured in milliampere-hour (mAh), where 1 mAh = 3.6 C.
(2) Energy (Electric Energy)Electric energy, rather than electric charge, reflects the work capacity of a battery.
Electric Energy = Electric Power × Time = Voltage × Electric Charge
The SI unit of electric energy is Watt-hour (Wh). Due to limited battery capacity and continuous voltage drop during discharge, calculation can adopt average voltage or median voltage; average voltage delivers higher calculation accuracy evidently.
(3) Material Specific CapacityThe theoretical capacity of electrode materials (Ah/kg) can be calculated based on Faraday’s Law.
Take lithium iron phosphate (LiFePO₄) as an example: 1 mole of LiFePO₄ contains 1 mole of Li⁺. The charge carried by each mole of Li⁺ equals the elementary charge per mole, i.e., Faraday’s constant \(F = 96500\ \text{C/mol} = 26.8\ \text{Ah/mol}\). The molar mass of LiFePO₄ is 157.8 g/mol.
Specific capacity per unit mass of LiFePO₄
\(=\frac{26.8\ \text{Ah/mol}}{0.1578\ \text{kg/mol}} = 169.8\ \text{Ah/kg}\)
(4) Initial Coulombic EfficiencyInitial Efficiency = (First Discharge Capacity ÷ First Charge Capacity) × 100%
(5) Energy Density & Power DensityIt includes gravimetric energy density (Wh/kg), volumetric energy density (Wh/L); gravimetric power density (W/kg), volumetric power density (W/L).
(6) Internal ResistanceTo measure pure ohmic resistance under signal input, the AC impedance method must be adopted. For lithium-ion batteries, the real part of complex impedance obtained with a 1000 Hz AC input signal is defined as battery internal resistance. Electrolyte is regarded as ohmic resistance.
Internal resistance is a critical battery performance indicator. It directly determines energy utilization, heat generation, service life, consistency and safety of batteries. Multiple factors affect internal resistance:
Internal factors: electrode materials (particle size, specific surface area, etc.), separator, electrolyte, conductive agent, binder, additive, current collector, etc.
External factors: temperature, moisture, impurities, etc.
Nearly all links of manufacturing processes and in-process quality control exert non-negligible impacts on internal resistance.
(7) Rate CapabilityIt refers to the current acceptance capacity during charging (e.g., fast charging for electric vehicles) and current output capacity during discharging (e.g., climbing and acceleration performance of electric vehicles). Rate capability is conventionally expressed in C-rate.
Definition of C-rate: the constant current required to fully discharge a fully charged battery within 1 hour. For a specific battery, the numerical value of C equals its rated capacity.
Battery Charge/Discharge C-rate = Actual Charge/Discharge Current ÷ Battery Rated Capacity
Example: For a battery with 100 Ah rated capacity, discharge at 20 A corresponds to a 0.2 C discharge rate (20 ÷ 100).
(8) Temperature PerformanceBattery temperature performance describes operational behavior and stability under varying ambient temperatures, covering performance at high and low temperatures.High-Temperature Requirements (45°C Ambient)
Thermal Stability: Maintain stable operation without thermal runaway or explosion
Capacity Fade: Capacity degradation shall be controlled within a reasonable range, generally not lower than 100% of initial charge-discharge energy
Energy Efficiency: No less than 92%
Safety: No leakage, smoke emission, combustion or other safety hazards
Low-Temperature Requirements (-20°C Ambient)
Capacity Retention: Charge energy ≥ 80% of initial value; discharge energy ≥75% of initial value
Energy Efficiency: No less than 75%
Discharge Performance: Normal discharge output without liquid leakage, voltage cutoff or other abnormalities
Temperature Impact & Test Methods
High-Temperature Test: Expose battery to 45°C environment to test thermal stability, capacity fade and energy efficiency
Low-Temperature Test: Expose battery to -20°C environment to test capacity retention, discharge performance and energy efficiency
These tests evaluate battery adaptability across temperatures to guarantee stable operation under diverse working conditions.
(9) Cycle LifeOne complete charge followed by one complete discharge counts as one cycle. A battery is deemed end-of-life when its capacity drops to 80% of initial capacity. This industry standard originates from cumulative cycle test data: capacity will degrade rapidly to unusable levels once falling below 80% of initial capacity, so early replacement is recommended for risk mitigation.
For lithium iron phosphate batteries, rapid capacity decay may be delayed until 60% residual capacity, supporting the secondary utilization business model. For instance, retired EV power batteries with 80% residual capacity can be reused in scenarios with low energy density requirements.快速翻译更多