The impact of fast and slow charging on battery life

1、 Core conclusion: Fast charging has a more significant impact on battery life

Data support:

• Laboratory cycling tests have shown that under the same number of cycles, the capacity decay of fast charging batteries is 15% -30% faster than that of slow charging.
• Tesla Model 3 actual test: After using Super Fast Charge (250kW) 500 times, the battery health (SOH) decreased to 87%, while the SOH remained at 92% after using Home Slow Charge (7kW) 500 times.

2、 Three major mechanisms of fast charging acceleration and decay

1. Lithium dendrite growth
   • Principle: During fast charging, lithium ions quickly embed into the negative electrode, and some lithium ions do not enter the layered structure, depositing on the surface to form dendrites.
   • Consequence: Dendrite piercing through the diaphragm leads to internal short circuit and accelerated capacity decay.
   • Case: Due to frequent fast charging, the battery capacity of a certain brand of electric vehicle has decayed to 75% within 2 years.
2. Polarization effect intensifies
   • Phenomenon: High current charging leads to an increase in the concentration difference at the electrode/electrolyte interface, resulting in overpotential.
   • Impact: Overpotential causes the actual voltage of the battery to exceed the cut-off voltage, accelerating electrolyte decomposition.
   • Data: During fast charging, the internal resistance of the battery increases by 20% -30%, and the heat generation increases by 40%.
3. Risk of temperature runaway
   • Thermal effect: For every doubling of fast charging power, the temperature rise of the battery increases by 8-10 ℃.
   • Critical point: When the battery temperature exceeds 45 ℃, the SEI film (solid electrolyte interface facial mask) begins to decompose, accelerating the aging.
   • Comparison: The temperature of slow charging batteries is usually controlled below 35 ℃, while fast charging may reach above 50 ℃.

3、 Three major protection mechanisms for slow charging

1. Gentle migration of lithium ions
   • Process: Low current allows sufficient time for lithium ions to embed into the negative electrode layered structure, reducing surface deposition.
   • Advantages: SEI film stabilizes growth and inhibits dendrite formation.
2. Minimize polarization effect
   • Data: During slow charging, the concentration difference at the electrode interface is less than 5%, and the overpotential is less than 0.1V, which is much lower than the 0.3-0.5V range during fast charging.
   • Result: The electrolyte decomposition rate decreased by 80%.
3. Active thermal management
   • Cooling conditions: Slow charging is usually carried out in a low-temperature environment, with low cooling pressure on the battery pack.
   • BMS intervention: Some vehicle models will activate pulse charging during slow charging to balance the temperature of the battery cells.

4、 Compromise and optimization of fast charging

1. Material improvement
   • Negative electrode modification: Using silicon carbon negative electrode (capacity increased by 10 times) or graphene coating to enhance lithium ion diffusion rate.
   • Electrolyte additives: Adding film-forming additives such as VC (ethylene carbonate) to enhance the stability of SEI film.
2. Structural innovation
   • Double layer electrode: Designed with gradient porosity to alleviate the bottleneck of lithium ion transport during fast charging.
   • CTP technology: reduces structural components and improves heat dissipation efficiency.
3. intelligent algorithms
   • Dynamic voltage regulation: Adjust the charging voltage in real-time based on the battery status to avoid overcharging.
   • Pre cooling/preheating: Before charging, the battery temperature is controlled at 25-35 ℃ through a liquid cooling system.

5、 Usage suggestion: Balance efficiency and lifespan

1. Scenario based selection
   • Daily commuting: Prioritize slow charging and use fast charging 1-2 times a week for emergency purposes.
   • Long distance travel: After fast charging, let it sit for 30 minutes before driving to avoid immediate high current discharge.
2. Temperature control
   • Summer: When fast charging, choose a cool period to avoid direct sunlight on the battery pack.
   • Winter: Start the vehicle before charging to preheat the battery and increase ion migration rate.
3. Maintenance strategy
   • Monthly deep charging and discharging: calibrate BMS power calculation to avoid false electricity.
   • Check internal resistance every six months: Use professional equipment (such as Hioki BT3563) to evaluate battery health.

6、 Future Technology: Balancing Supercharging and Long Lifespan

1. solid state battery
   • Advantages: Increased ion conductivity by 10 times, 4C fast charging temperature rise<10 ℃.
   • Progress: Toyota and QuantumScape plan to mass produce in 2027, supporting 80% filling in 10 minutes.
2. Dry electrode technology
   • Principle: Eliminate electrolyte infiltration process and reduce polarization effect.
   • Application: Tesla 4680 battery has been adopted, with a 20% increase in cycle life.
3. Wireless BMS
   • Function: Real time monitoring of the status of each battery cell and dynamic adjustment of charging strategies.
   • Effect: It can increase the fast charging cycle life to over 1500 times.

Customization of electric bicycle batteries