Other Factors or Risks May Bring Negative Impact to Lithium Battery for hevs

Hello, per our study on the lithium batteries used in hybrid vehicle, we optimzed the structure of the Battery Pack, and investigated the temperature characteristics of the battery pack under heating and cooling conditions. The following conclusions were obtained. (1) The temperature of the individual battery increases as the constant discharge rate increases. During the discharge process, the discharge rate is constantly changed, and the temperature of the battery varies in different discharge processes at the end of discharge. When the convective heat transfer coefficient of the battery is increased, the temperature of the battery can be reduced. When the convective heat transfer coefficient increases from 0 to 30 W/(m2·K), the Heat Dissipation effect is significant, but it becomes less obvious afterwards. (2) Through optimized design, a set of relatively good battery pack structure parameters were obtained, resulting in a 5.39 K reduction in the temperature rise of the optimized battery pack compared to the original design, and a 6.41 K decrease in the temperature difference of the battery pack. This indicates that the optimized design using ANSYS can achieve the goal of optimizing the temperature field of the battery pack.

(3) Based on the optimized battery pack, studies were conducted on both heating and cooling of the battery pack to verify the feasibility of the proposed design. The results showed that the lower the initial temperature of the battery, the longer the heating time. When the battery pack is discharged while being heated, its temperature can be rapidly raised to the appropriate temperature range. When the wind speed is higher, the time required for temperature rise is shorter, but the temperature difference of the battery pack increases. The cooling process can also control the temperature of the battery pack within a reasonable temperature range. In such conclusion, do you see other factors or risks may bring negative impact to Lithium battery for Hevs? thanks

Yes, while your study effectively addresses thermal management (a critical factor), several other interrelated factors and risks can negatively impact lithium-ion batteries in hybrid electric vehicles (HEVs). These can accelerate degradation, reduce lifespan, compromise safety, or affect performance, even in well-optimized packs.

1. Mechanical Stress and Vibration

HEVs experience constant road-induced vibrations, shocks, and impacts. These can cause:

• Structural fatigue in cells, tabs, welds, or busbars.
• Increased internal resistance and micro-cracks.
• Accelerated aging or even short circuits in severe cases.

Long-term vibration tests (simulating real-world driving) show measurable capacity fade and impedance rise. Proper pack design (dampening, secure mounting) is essential, but this risk persists over the vehicle's life.

2. Low-Temperature Effects and Lithium Plating

Your heating studies are helpful, but cold starts or operation below ~0–5°C remain challenging:

• Reduced ionic mobility and capacity.
• Lithium plating during charging/discharging (metallic lithium deposits on the anode) → permanent capacity loss, increased resistance, and higher thermal runaway risk.
• Slower chemical reactions increase internal resistance.

In HEVs with frequent shallow cycles and cold climates, this can compound if pre-heating isn't always sufficient.

3. Cycle Life, Calendar Aging, and Operating Conditions

• Frequent cycling in HEVs (even partial cycles) causes electrode degradation, SEI (solid electrolyte interphase) layer growth, and active material loss.
• Calendar aging (time-based degradation) accelerates at high temperatures, high state-of-charge (SOC), or high voltage — common if the battery sits at high SOC.
• High C-rates (even if not constant) during aggressive driving or regen braking add stress.

 Your optimization reduced temperature rise, which helps, but SOC window management (e.g., avoiding prolonged high/low SOC) is key for longevity.

4. Cell-to-Cell Imbalances and Pack-Level Issues

• Manufacturing variations or uneven aging lead to voltage/capacity mismatches.
• Poor balancing can cause some cells to overcharge/overdischarge → faster degradation or safety events.
• Optimized structure helps temperature uniformity, but electrical balancing systems (BMS) must keep up.

5. Safety Risks: Thermal Runaway Triggers

Beyond temperature control:

• Overcharge/overdischarge, internal shorts from defects/mechanical damage, or contamination.
• External factors like collisions, water ingress (especially saltwater), or manufacturing defects can initiate runaway.
• Electrolyte decomposition produces gases/toxic compounds (e.g., HF).

HEV packs are smaller than full EV packs but still carry high energy.

6. Other Environmental and Usage Factors

• Humidity/moisture/chemical contamination — can corrode components or react internally.
• Fast or improper charging (high C-rate at suboptimal temps) — exacerbates plating and heat.
• Driving style and duty cycle — high-power demands in hybrids increase stress.

Recommendations to Mitigate

• Advanced BMS for precise SOC/SOH monitoring, active balancing, and predictive maintenance.
• Robust mechanical design and vibration isolation.
• Chemistry choices (e.g., LFP for better safety/ longevity in some cases) or additives to resist plating.
• Real-world durability testing (vibration + thermal + cycling).
• Data from fleets shows modern batteries often degrade ~1–2% per year with good management, but poor conditions can worsen this significantly.

 Your ANSYS-optimized design is a strong step for thermal uniformity. Integrating these other factors into multi-physics simulations (thermal + structural + electrochemical) would further strengthen the pack.

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