Unable to submit the challenge completely due to a technical error unable to upload the images, please refer to the attached PDF below, thank you.

ANR26650M1-B, LithiumWerks Nanophosphate® 3.3V 2.5Ah Lithium Iron Phosphate Battery

ANR26650M1-B Specifications

Nominal Ratings

· Voltage: 3.3 Volts

· Capacity: 2.5 Ah

· Energy: 8.25 Wh

· Specific Power: 2600 W/kg

· Impedance (1KHz AC Typical): 6 mΩ

· Cycle Life at 1C/1C, 100% DOD: > 4000 cycles

· Cell Type: 26650 Lithium Ion Power Cylindrical Cell

Discharging

· Max Continuous Discharge: 50 A

· Max Pulse Discharge Current >50% SOC (10s): 120 A

· Minimum Voltage: 2 Volts

· Temperature Range: -30ºC to 55ºC

Charging

· Recommended Standard Charge: 2.5 Amps

· Max Charge Rate: 10 Amps

· Max Pulse Charge Current <50% SOC (10s): 25 A

· Float Voltage: 3.45 Volts

· Recommended Charge Voltage & Cut-off Current: 3.6 Volts, taper to 125mA

· Temperature Range: 0ºC to 55ºC (reduce charging current to 250mA when under 0ºC)

Mechanical

· Diameter: Ø25.96 +/- 0.5 mm (1.0")

· Length: 65.15 +/- 0.5 mm (2.6")

· Mass: 76 g

Primary Applications for Cylindrical Cells:

· Portable high power devices

· Stationary battery backup systems

· Grid stabilization energy storage systems

· Commercial truck and bus hybrid electric vehicles (HEVs)

Lithium Ion Cell Benefits:

· Power: Over 2,600 W/kg and 5,800 W/L

· Safety: Excellent abuse tolerance and environmentally friendly

· Life: Excellent calendar life, 10X cycle life vs. conventional lithium-ion

Designing an 18 KWh Battery Pack

The mathematical calculations for designing an 18 kWh battery pack are detailed below:

General Required Values for a Single Cell:

· Diameter: 0.026 m

· Length: 0.065 m

· Mass: 0.076 kg

· Single Cell Voltage: 3.3 V

· Capacity: 2.6 Ah

· Max Continuous Charge Current (C rate): 10A

· Max Pulse Charge Current (C rate): 20 A

Single Cell Calculations:

· Volume = π * r² * h

= 3.142 * (0.013)² * 0.065 = 0.03451 mm³

· Single Cell Energy = Cell Capacity * Cell Voltage

= 2.6 * 3.3 = 8.58 Wh

Calculations for High Voltage Battery:

Assume the vehicle range should be 250 Km and the nominal voltage is 250 V.

1. Average Energy per Km = 18000 / 250

= 72 Wh/Km

2. Number of Cells Connected in Series = Nominal Voltage of Series Connections / Nominal Voltage of Single Cell

= 250 / 3.3 = 75.75 or 76 Cells in series

3. Energy for Battery Pack (Wh) = Number of Cells Connected in Series * Single Cell Energy

= 76 * 8.58 = 651.96 Wh

4. Number of Cells Connected in Parallel = Battery Pack Total Energy / Energy for Battery Pack

= 18000 / 651.96 = 27.60 or 28 cells in parallel

5. Battery Pack Total Energy = Number of Cells Connected in Parallel * Energy for Battery Pack

= 28 * 651.96 = 18.255 KWh

6. Battery Pack Capacity = Single Cell Capacity * Number of Cells Connected in Parallel

= 28 * 2.6 = 72.8 Ah

7. Total Number of Cells for Battery Pack = Number of Cells in Series * Number of Cells in Parallel

= 76 * 28 = 2128 Cells

8. Mass of the Battery Pack = Total Number of Cells * Mass of Single Cell

= 2128 * 0.076 = 161.728 kg

9. Total Volume of Battery Pack = Total Number of Cells * Volume of Single Cell

= 2128 * 0.03451 = 73.3125 m³

10. Cell Peak Current (A) = Max Pulse Charge Current * Single Cell Capacity

= 20 * 2.6 = 52 A

11. Battery Pack Peak Current = Cell Peak Current * Number of Cells Connected in Parallel

= 52 * 28 = 1456 A

12. Battery Pack Peak Power (W) = Battery Pack Peak Current * Voltage of Series Connection

= 1456 * 250 = 364,000 W = 364 kW

13. Cell Continuous Current (A) = Max Continuous Charge Current * Single Cell Capacity

= 10 * 2.6 = 26 A

14. Battery Pack Continuous Current = Cell Continuous Current * Number of Cells Connected in Parallel

= 26 * 28 = 728 A

Cell Modeling

A cell typically consists of the following components: Anode, Cathode, Separator, Positive Cap, Negative Cap, and Shell.

Arrangement and Assembly of a 7S4P Cell Pack

· Configuration: 7S4P

· Capacity: 10.4 Ah

· Voltage: 23.1 V

· Cells: 28 cells

· Pack Capacity: 240.24 Wh

Assembly of the Full Battery Pack with 76S/28P

· Single Pack: 28 cells with 7S/4P

· Number of Packs: Total Cells / Cells per Pack = 2128 / 28 = 76 Modules

· Configuration: 11 modules in series and 7 modules in parallel

The battery pack is configured into the electric vehicle's lower floor panel case. A simple layout of the battery pack in an electric vehicle is shown below.

Design of Cell Holder (Bottom and Top)

The main function of a battery holder is to keep cells fixed in place safely and securely, reducing mechanical vibrations and improving thermal management. Most cell holders are made of polypropylene or nylon, rated for 80-100°C. A dimensional and 3D design is shown below.

Design of Pack Cover

The pack cover is typically made of aluminum to keep the battery pack lightweight. The casing/cover thickness is 0.5 mm. The design is shown below, with a bottom cover to protect the battery holder.

Design of Lower Floor Case Battery Pack

The lower case is fitted in an electric vehicle for the assembly of the battery pack. It is made of aluminum and has a top and bottom cover to protect the battery pack from dust and environmental pollution. The design of the lower case is shown below.

Positive and Negative Clip Design

A positive and negative clip is used to connect the battery end caps, i.e., + and -. The design is shown below.

Battery Welding Process

Battery tab welding involves joining individual batteries together with a collector plate that has tabs for the individual cells to be welded to both the positive and negative terminals. This is a critical step in the manufacturing of battery packs. Reducing the number of collector plate-to-busbar connections is essential for many packs. Various factors must be considered when selecting the appropriate welding process for battery packs, including the materials to be welded, joint shape, weld access, cycle time, and budget, as well as manufacturing flow and production needs. Proper welding is vital for a battery’s performance, range, mechanical strength, thermal efficiency, and safety. Several welding processes are used for the necessary tab-to-terminal connections (foil-to-tab, tab-to-busbar, etc.), including ultrasonic bonding, laser welding, resistance welding, and micro TIG welding. The choice of method depends on criteria such as material combinations and tab thickness.

What is a Battery Tab?

Battery tabs or terminals are the positive and negative connectors that transport electrical current through the cells. Each tab connects to a busbar (or collector plate) on the module, redistributing positive and negative current to new terminals. The battery pack is composed of several modules connected similarly. Tabs connect to current collectors or foils made of highly conductive materials like aluminum and copper inside the cell shell, carrying the current from the electrodes, both positive and negative. Battery tabs are crucial for all types of batteries, but they come in various shapes and sizes, depending on the EV battery cell type.

Tab Welding Methods

Hundreds or thousands of welds are required to connect the cells and terminals in a battery pack. Tabs and terminals connect to current collectors inside the cells as well as to busbars and collector plates. The quality of these connections is critical to the battery’s performance, with even a 1% failure rate being a major problem. Proper cleaning of surfaces, such as laser cleaning or working in a controlled environment, is necessary before welding. The appropriate welding procedure is not always clear, so each one should be considered individually.

Laser Welding: Laser welding is a high-speed procedure that joins surfaces with a highly focused light beam. Using ultrafast moving X-Y mirrors, the laser beam is directed and moved, providing versatility to weld any joint geometry and create custom weld patterns. Pulsed fiber lasers are preferred for battery welding because they produce smaller heat-affected zones, decreased porosity, and less spatter. They can weld thin or thick tabs and work with copper, aluminum, steel, nickel, and other metals. Laser welding can be used for both tab-to-busbar connections and foil-to-tab welds.

Resistance Welding: Resistance welding, or spot welding, uses copper or tungsten electrodes charged with electrical current. An electrical current passes between the electrodes as pressure is applied to the welding area, generating heat at the contact point, which bonds the two metals. Resistance welding can be used for both foil-to-tab and tab-to-busbar welds. It is a cost-effective welding method suitable for DIY battery enthusiasts and can also be mechanized.

Ultrasonic Welding: Ultrasonic bonding or welding uses ultrasounds to induce vibrations between the materials to be connected. The rapid friction between the materials generates sufficient heat to bond them almost instantly. This technology is used for foil-to-tab welding and ultrasonic wire bonding, which connects cells to busbars via wires.

Micro TIG Welding: Micro TIG welding, or pulse arc welding, creates a high-temperature plasma that melts metal in a small area using a small electrode supplied with electricity. Micro TIG welding is ideal for small battery components and works well with thick copper, suitable for tab-to-busbar welding.

Laser Cleaning for Weld Preparation

Producing high-quality joints is critical to the battery’s overall performance, reducing energy loss and heat generation during charges and discharges, and improving the battery’s lifetime and mechanical reliability. Lithium-ion batteries are the most expensive elements in electric vehicles, so avoiding recalls is crucial. Before welding, manufacturers should ensure all surfaces are completely clean. High-powered laser cleaning is effective in removing coatings, electrolytes, and oxides quickly, consistently, and precisely.

Conclusion

Based on the technical data of a single cell, an 18 kWh battery pack has been designed for an electric vehicle. The total number of cells is 2128, arranged in a 76S/28P configuration. The nominal voltage from 76 series-connected cells is 250 V, and the power capacity from 28 parallel-connected cells is 72 V. This design achieves a vehicle range of 250 km, which was the assumption for calculating the battery pack. Increasing the number of parallel cells increases power but does not achieve the desired vehicle range, hence the 76S/28P cell configuration was chosen.