Thermal adhesives in lithium-ion battery packs

Thermal adhesives - Thermal management in lithium-ion battery packs

Thermal adhesives play a crucial role in lithium-ion battery packs, especially in electric vehicles (EVs), by facilitating efficient heat dissipation and maintaining optimal operating temperatures. Here's a breakdown of their applications in lithium cell connections.

1. Cell-to-Cell Bonding:

• Heat Dissipation: Lithium-ion cells generate heat during operation due to internal resistance. Thermal adhesives between cells create a thermally conductive pathway, allowing heat to spread evenly and dissipate more effectively. This prevents localized hot spots that can accelerate battery degradation and compromise safety.

• Structural Support: Adhesives provide mechanical bonding between cells, enhancing the structural integrity of the battery pack. This is particularly important in cell-to-pack designs where individual cells are directly integrated into the battery pack structure.

• Electrical Insulation: While primarily designed for thermal conductivity, these adhesives offer electrical insulation, preventing short circuits between adjacent cells.

2. Cell-to-Cooling Plate Bonding:

• Efficient Heat Transfer: Thermal adhesives bond cells to cooling plates or heat sinks, which are essential components of the battery thermal management system. The adhesive facilitates efficient heat transfer from the cells to the cooling system, maintaining optimal operating temperatures.

• Uniform Contact: The adhesive ensures uniform contact between the cell and the cooling plate, maximizing the heat transfer area and efficiency.

3. Module-to-Pack Bonding:

• Thermal Management at the Module Level: Battery packs with modular designs, and thermal adhesives are used to bond individual modules to the pack structure. This helps manage heat dissipation at the module level, further enhancing overall thermal management.

• Structural Integrity: Adhesives contribute to the structural integrity of the battery pack by bonding modules together and to the pack housing.

Key Considerations for Thermal Adhesives:

• Thermal Conductivity: The primary requirement is high thermal conductivity to ensure efficient heat transfer.

• Adhesion Strength: The adhesive provides strong bonding to maintain contact between components under various operating conditions.

• Electrical Insulation: The adhesive should be electrically insulating to prevent short circuits.

• Chemical Compatibility: The adhesive must be chemically compatible with the cell materials and other components in the battery pack.

• Long-Term Reliability: The adhesive must maintain its properties over a wide temperature range and throughout the battery's lifespan.

In conclusion, thermal adhesives are essential for effective thermal management in lithium-ion battery packs. They facilitate heat dissipation, enhance structural integrity, and contribute to the overall safety and performance of the battery system.

 

VECU vs ECU

ECU

ECU and VECU stand for:

• ECU: Electronic Control Unit  
• VECU: Vehicle Control Unit

While both are electronic control units within a vehicle, they serve different purposes and are found in different types of vehicles.  

ECU (Electronic Control Unit)

• Function: An ECU is a generic term for any electronic control unit in a vehicle. It can control various systems like the engine (engine control unit), transmission (transmission control unit), brakes (anti-lock braking system control unit), airbags, and more. In traditional gasoline or diesel vehicles, the primary ECU is often the engine control unit, which manages engine performance.  

• Vehicle Type: Found in conventional fuel vehicles (gasoline, diesel).  

• Focus: Primarily focuses on managing the specific system it is designed for, such as optimizing engine performance for fuel efficiency and emissions.  

VECU (Vehicle Control Unit)

VECU



• Function: The VECU is the central control unit in electric vehicles (EVs) and some hybrid vehicles. It manages the overall operation of the electric powertrain, including the battery, electric motors, regenerative braking, and other EV-specific systems. It also coordinates with other ECUs in the vehicle.  

• Vehicle Type: Found in electric vehicles (EVs) and some hybrid vehicles.  

• Focus: Manages the overall energy flow and efficiency of the electric powertrain, maximizing range and performance. It handles functions like regenerative braking, battery management, and coordinating the electric motors.  

Key Differences:

Below is a table summarizing the key differences:

Feature	ECU	VECU
Vehicle Type	Conventional fuel vehicles	Electric and hybrid vehicles
Primary Function	Manages a specific system (e.g., engine)	Manages the electric powertrain and overall vehicle operation
Energy Focus	Emissions and fuel efficiency	Energy efficiency and range
Key Functions	Engine control, transmission control, etc.	Battery management, regenerative braking, motor control

What is VECU in Electric Vehicles?

 

VECU of an Electric Vehicle

The VECU is a complex technology, and it's important to understand its functions thoroughly. 

1. Power Flow Management: (Energy Management)

• Battery to Motor: When accelerating, the VECU receives the signal from the accelerator pedal. It then determines the optimal amount of power to draw from the battery and deliver to the motor controllers. This involves complex calculations considering factors like:
  • Desired acceleration
  • Battery state of charge and temperature
  • Motor temperature and efficiency
  • Driving mode (e.g., Eco, Sport)
   
• Motor to Battery (Regenerative Braking): During deceleration or braking, the VECU reverses the motor's function, turning it into a generator.

    It controls the amount of regenerative braking to:

1. Maximize energy recovery.
2. Provide smooth and stable deceleration.
3. Prevent overcharging the battery.

Coordination with Other Systems: The VECU also communicates with other ECUs in the vehicle, such as the Battery Management System (BMS) and the Motor Control Unit (MCU), to ensure seamless power flow and prevent conflicts.

2. System Monitoring and Control:  (Performance and Safety)

• Battery Management: The VECU works closely with the BMS to monitor:
  • Individual cell voltages and temperatures.
  • Overall battery state of charge and health.
  • Cooling system performance.
  • It uses this information to optimize charging and discharging rates, prevent damage to the battery, and estimate the remaining range.
• Motor Control: The VECU monitors the motor's:
• Temperature.
• Speed and torque.
• Efficiency.
• It adjusts the motor's operation to maintain optimal performance and prevent overheating.   

• Thermal Management: The VECU plays a key role in managing the thermal systems of the EV, including:
  • Battery cooling and heating.
  • Motor cooling.
  • Cabin climate control.
  • It optimizes the operation of these systems to ensure efficient operation and passenger comfort.

3. Regenerative Braking: (Maximizing Efficiency)

• Blending with Friction Brakes: The VECU seamlessly blends regenerative braking with traditional friction brakes to provide consistent and effective stopping power.
• Optimizing Energy Recovery: It dynamically adjusts the amount of regenerative braking based on driving conditions, such as:
  • Speed
  • Road grade
  • Traffic
  • This maximizes energy recovery and improves overall efficiency.

4. Safety and Diagnostics: (Ensuring Reliability)

• Fault Detection and Management: The VECU constantly monitors all systems for faults and anomalies. If a problem is detected, 

          It takes appropriate action, such as:

• Triggering warning lights on the dashboard
• Limiting vehicle performance
• Storing diagnostic trouble codes (DTCs) for later analysis

 Functional Safety: The VECU is designed with safety in mind, adhering to strict functional safety standards (e.g., ISO 26262). This ensures that the vehicle operates safely even in the event of a component failure.

In summary, the VECU is a sophisticated and essential component in modern EVs. It acts as the central intelligence, managing power flow, monitoring systems, optimizing efficiency, and ensuring safety. Its complex algorithms and real-time control capabilities are crucial for delivering the performance, range, and reliability that EV owners expect.

DFMEA Process in Lithium ion battery?

DFMEA Cycle

DFMEA is a structured approach to identifying and assessing potential failure modes in a product or process design. 

By proactively identifying and addressing these potential failures, organizations can improve product reliability, reduce costs, and enhance customer satisfaction.

Key Steps in a DFMEA:

1. Define the System: Clearly outline the system or product being analyzed, including its functions and intended use.
2. Identify Function: List the primary functions of the system or product.
3. Identify Potential Failure Modes: For each function, brainstorm potential ways in which it could fail.
4. Identify Potential Effects: Determine the consequences of each failure mode on the system or product and the customer.
5. Assess Severity: Assign a severity rating to each potential effect, indicating the seriousness of its impact.
6. Identify Potential Causes: For each failure mode, identify the root causes that could lead to its occurrence.
7. Assess Occurrence: Assign an occurrence rating to each potential cause, indicating the likelihood of it happening.
8. Assess Detection: Determine the likelihood of detecting each failure mode before it reaches the customer. Assign a detection rating.
9. Calculate Risk Priority Number (RPN): Multiply the severity, occurrence, and detection ratings to obtain the RPN. A higher RPN indicates a higher risk.
10. Develop Action Plans: Prioritize the highest-risk failure modes and develop action plans to mitigate or eliminate them.
11. Implement Corrective Actions: Execute the action plans to address the identified risks.
12. Re-evaluate: Periodically review the DFMEA to identify new risks and update the analysis as necessary.

Benefits of DFMEA:

• Proactive Risk Management: Identifies potential failures early in the design phase.
• Improved Product Quality: Reduces the likelihood of product failures and defects.
• Enhanced Customer Satisfaction: Delivers more reliable and durable products.
• Cost Reduction: Prevents costly recalls and field repairs.
• Regulatory Compliance: Helps meet industry standards and regulatory requirements.
• Continuous Improvement: Fosters a culture of continuous improvement and risk mitigation.

By systematically applying DFMEA, organizations can significantly improve their products and processes quality and reliability.

Lithium-ion battery DFMEA Analysis (Design Failure Mode and Effects Analysis)

Here's how the DFMEA process is applied to lithium-ion batteries:

1. Define the Scope:

• Clearly define the system or subsystem being analyzed (e.g., the entire battery pack, a single cell, the battery management system (BMS), etc.).
• Identify the functions and requirements of the system.

2. Identify Potential Failure Modes:

• List all potential ways in which the battery or its components could potentially fail. Examples include:
  • Cell Level: Internal short circuit, electrolyte leakage, thermal runaway, capacity fade, overcharge, over-discharge.
  • Pack Level: Poor thermal management, inadequate electrical connections, BMS failure, mechanical damage.
  • Material Level: Degradation of electrodes, separator breakdown, current collector corrosion.

3. Determine the Effects of Each Failure Mode:

• Describe the consequences of each failure mode on the battery's performance, safety, and reliability. Examples include:
  • Reduced capacity, loss of power, overheating, fire, explosion, shortened lifespan.

4. Assign Severity Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each failure mode based on the severity of its effects. A higher rating indicates a more severe consequence. 

5. Identify Potential Causes of Each Failure Mode:

• List all the possible causes that could lead to each failure mode. Examples include:
  • Manufacturing defects, material impurities, improper handling, extreme temperatures, mechanical stress, and electrical abuse (overcharge/over-discharge).

6. Assign Occurrence Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each cause based on the likelihood of it occurring. A higher rating indicates a higher probability of occurrence. 

7. Identify Prevention Controls:

• Describe any existing design features or controls that are in place to prevent or detect the failure modes. Examples include:
  • Safety vents, thermal fuses, BMS functions (overcharge/over-discharge protection, temperature monitoring), and quality control measures.

8. Assign Detection Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each control based on its ability to detect the failure mode before it has a significant effect. A higher rating indicates a lower probability of detection.

9. Calculate the Risk Priority Number (RPN):

• For each failure mode, calculate the RPN by multiplying the severity, occurrence, and detection ratings:
  • RPN = Severity x Occurrence x Detection
   
• The RPN provides a quantitative measure of the risk associated with each failure mode.

10. Develop Recommended Actions:

• For failure modes with high RPNs, develop and implement corrective actions to reduce the risk. These actions may include:
  • Design changes, material selection, process improvements, and additional controls.
     

11. Take Action and Re-evaluate:

• Implement the recommended actions and then re-evaluate the RPNs to ensure that the risk has been adequately reduced.

Lithium Batteries Failure Cause and Effects:

                                                             Lithium-ion battery DFMEA Analysis (Design Failure Mode and Effects Analysis)

Can we use 250KW charger to charge a 20KW EV battery Vehicle ?

Yes, We can generally use a 250kW charger for a 20kW EV battery, but with some important thing need to remember :

Key Considerations

• Battery Management System (BMS): The car's BMS is crucial. It communicates with the charger to regulate the charging process. It will ensure that the battery receives the appropriate voltage and current, preventing damage from overcharging or excessive heat.

• Charging Rate Limit: Every EV battery has a maximum charging rate it can safely handle. Even if you plug into a 250kW charger, the BMS will limit the charging rate to the battery's maximum capacity. With a 20kW battery, the maximum charge rate will likely be significantly lower than 250kW.

• Charging Pattern: EV batteries don't charge at a constant rate. They typically charge faster initially and then gradually slow down as they approach full capacity. This is known as the charging curve. The BMS manages this process to optimize charging speed and battery health. 

What to Expect: 

• Faster Initial Charging: You might experience a faster initial charging rate compared to using a lower-powered charger, but this will quickly taper off as the battery gets closer to full.

• No Damage to the Battery: If your EV and its BMS are functioning correctly, using a higher-powered charger will not damage the battery. The BMS will act as a protector.

• Not Necessarily the Fastest Charge: While you can use a 250kW charger, it doesn't mean your 20kW battery will charge incredibly fast. The limiting factor is the battery's capacity and its maximum charging rate.

Example:

Take the case of the TATA Nexon Vehicle, The battery pack is 320V & 90AH Capacity, Energy is 28.8KWh.

The maximum energy the Nexon battery accepts for charging depends upon the BMS inside the battery pack and the nominal charging ampere of a 90AH battery is 45Amps, 

The 55KW charger can charge the 28.8KW Pack of Nexon Car with a maximum of 16.4KW , 

How. Since the Lithium cell's maximum voltage is 3.65v and we multiply 3.65*100 Cells is 365v. then multiply 365v*45A (Nominal Charging Current ) which is 16.4KW.

Note:

There are different types of chargers available,

1. Slow Chargers.

2. Fast Chargers.

3. Ultra Fast Chargers or rapid chargers.

To learn more about the types of chargers, click the below post...

The charging speed and time depend on the power supplied by each type of charger and also depend on the capacity of the battery.

In Summary

Using a 250kW charger with a 20kW EV battery is generally safe, thanks to the BMS. However, don't expect a dramatically faster charging time compared to a lower-powered charger. The battery's limitations will determine the actual charging speed.