Lithium-ion vs. Lead Acid Batteries: Degradation, Safety, and Applications

Posted on Dec 17, 2024 in Electronics

Lithium-ion Battery Degradation

Lithium-ion battery degradation has two primary effects:

  • Decrease in rated capacity
  • Reduction in the ability to deliver power

Calendar Life

Avoid storing batteries fully charged or discharged. A State of Charge (SOC) of around 40% at 3-8 degrees Celsius is optimal.

Cycle Life

High and low temperatures accelerate cell aging. Avoid charging in extreme temperatures.

High Depth of Discharge (DoD) also contributes to cell aging.

High discharge currents degrade the cell more rapidly.

Always adhere to the cell manufacturer’s recommended limits.

Inside the Lithium-ion Cell

Aging causes: Cell operating factors or conditions that trigger battery degradation, enabling any of the aging mechanisms.

Aging or degradation mechanisms: Physical phenomena occurring in battery cell components (electrodes and electrolyte) causing deterioration. These can be mechanical or chemical.

Degradation modes: A method to group degradation mechanisms based on their impact on the kinetic and thermodynamic behavior of the cell.

Degradation effects: Consequences of the mechanisms directly observable in cell performance, primarily capacity fade and power fade.

Side reactions occur where ions are irreversibly lost and no longer participate in the chemical reaction.

Internal resistance increases as lithium ions are lost and become trapped in the Solid Electrolyte Interphase (SEI) layer. As this layer thickens, ion movement becomes more difficult, reducing power output.

Safety Considerations for Lithium-ion Batteries

Undervoltage: Can lead to copper dissolving into the electrolyte.

Overvoltage: Can cause the formation of lithium dendrites.

Undertemperature: May result in cathode damage, short circuits, and lithium plating.

Overtemperature: Leads to capacity loss, contact between anode and electrolyte, decomposition, gas release, fire, and thermal runaway.

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Lithium-ion Battery Form Factors

  • Mechanical stability: Prismatic ≈ Cylindrical > Pouch
  • Energy density: Pouch > Prismatic > Cylindrical

Lithium-ion Battery Cathode Materials

  • High energy density: NCA, NMC
  • Safety, lifespan, and power: LFP
  • Performance, safety, and lifespan: LTO

Lead Acid Batteries

General Characteristics

  • Both flooded and sealed lead acid batteries share similar materials and cyclability.
  • The primary difference lies in maintenance requirements.

Flooded Lead Acid Batteries

  • Require frequent water addition, periodic equalization, and electrolyte specific gravity checks.
  • Generate hydrogen, necessitating an active ventilation system.

Sealed Lead Acid Batteries

  • Maintenance-free.
  • Shorter lifespan compared to flooded batteries due to the inability to perform maintenance.

Composition

Positive electrode: PbO2

Negative electrode: Pb

Electrolyte: H2O + H2SO4

The cathode, a solid lead dioxide plate, is inserted into a separator envelope made of microporous polyethylene, which acts as an ionic conductor. The battery container is typically made of polypropylene, a material resistant to sulfuric acid.

Lead Acid vs. Deep Cycle Lead Acid Batteries

Deep cycle batteries are more expensive.

  • Lead acid: High power output for a short duration.
  • Deep cycle lead acid: Lower power output for an extended duration.

Deep cycling a regular lead acid battery can accelerate aging due to mechanical stress. Deep cycle batteries incorporate improvements to mitigate this.

Lead Acid Battery Degradation

Corrosion and shedding: Cannot be entirely avoided but can be limited by:

  • Reducing the depth of discharge (DoD).
  • Avoiding overcharging.
  • Controlling the operating temperature, avoiding high temperatures.

Sulfation: Formation of small crystals on the negative plates, reducing active material content. Occurs when the battery is not fully charged. Maximize charging time to 14-16 hours when possible. If crystals have formed, a controlled overcharge (15-16 volts for 12-volt batteries) at 50-60°C can help dissolve them.

Stratification: Unequal acid concentration in the battery. Can be addressed by gently shaking or tipping the battery.

Lead Acid Battery Maintenance

Flooded Batteries

  • Use distilled or de-ionized water, adding it when the battery is charged. Tap water may be suitable in some regions.
  • Equalize cells and check the electrolyte’s specific gravity periodically.
  • Never allow the electrolyte level to drop below the top of the plates. Exposed plates can sulfate and become inactive. Add water to cover exposed plates before charging, and fill to the correct level after charging.
  • Never add acid, as this can raise the specific gravity excessively, leading to corrosion.

Sealed Batteries

  • Always keep lead acid batteries charged. Avoid storage below 2.07V/cell.
  • Allow a full saturation charge of 14-16 hours.
  • Avoid deep discharges. Deeper discharges shorten battery life.
  • If sulfation occurs, a controlled overcharge can help, but be cautious as it can also lead to corrosion.

Lithium-ion vs. Lead Acid: Applications

Lead Acid Battery Applications

  • Where volume and weight are not critical.
  • Low power applications without high charge/discharge rates (C-rates).
  • Where DoD is not high, even with deep cycle batteries.
  • Where the number of cycles is not very high.
  • Suitable for grid support and UPS systems.

Lithium-ion Battery Applications

  • Where volume and weight are crucial.
  • Fast charging and discharging are required.
  • High DoDs are necessary.
  • Longer lifespans are needed.
  • Ideal for electric vehicles (EVs), trains, buses, and marine applications where autonomy is essential. Also suitable for power tools where heavy lead acid batteries are impractical.
  • Grid applications demanding high-power peaks.

Choosing Between Lead Acid Battery Types

For grid support, flooded batteries offer longer life with maintenance, while sealed AGM batteries provide a maintenance-free option. For mobile applications like golf carts or scooters, sealed GEL batteries are preferred due to their resistance to movement.

Choosing Between Lithium-ion Battery Types

  • NMC or NCA cathodes: When energy density is paramount.
  • LFP cathodes: When safety and lifespan are prioritized over energy density.
  • Titanate anode: When safety, high charging power, and very long lifespans are the highest priorities, despite the higher cost.

Key Characteristics: Lithium-ion vs. Lead Acid

Almost every characteristic favors lithium-ion technology over lead acid. However, lead acid remains relevant due to its lower cost and established safety record. Lead acid technology is mature, and the cost of a lithium-ion battery with the same capacity is roughly double that of a lead acid battery.

Wh/L and Wh/kg are significantly higher for lithium-ion batteries.

Lithium-ion batteries maintain capacity across various C-rates, while lead acid batteries experience a significant capacity reduction at higher C-rates (Peukert effect).

Cycle life is considerably longer for lithium-ion batteries.

Battery Testing in a Laboratory

Reception Tests

Consist of 5 consecutive charge/discharge cycles at a low C-rate (0.5-1C) to verify normal cell operation. Capacity is measured after these cycles.

Open Circuit Voltage (OCV) Measurement

Methods include:

  • Linear interpolation: Charging/discharging at a very low current across the entire SOC range.
  • Voltage relaxation: Charging/discharging to specific SOC points and allowing the cell to reach equilibrium voltage.

Calendar Aging Tests

SOC and temperature significantly impact calendar aging. A test matrix evaluates cell aging under various SOC and temperature conditions. Capacity is measured during the degradation process.

Cycling Aging Tests

SOC range (DoD) and C-rate influence cycling aging. A test matrix assesses cell aging under different conditions. Capacity is measured throughout the degradation process.