Project 1 Mechanical design of battery pack

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

ANR26650M1-B cell with lithium iron phosphate (LiFePO4) battery technology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. The cells have low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge (SOC) range, allowing our systems to meet end-of-life power and energy requirements with minimal pack oversizing.

Key Features and benefits

-Excellent abuse tolerance and superior cycle life from A123's patented Nanophosphate lithium ion Chemistry
-High power with over 2,600W/kg and 5,800 W/L, 10 seconds, 50%SOC
-High usable energy over a wide state of charge (SOC) range

APPLICATIONS

COMMERCIAL SOLUTIONS

Advanced lead acid replacement batteries for: Datacenter UPS, Telecom backup, IT backup, Autonomously guided vehicles (AGVs), Industrial robotics and material handling equipment, Medical devices

GOVERNMENT SOLUTIONS

Military vehicles, Military power grids, Soldier power, Directed energy

GRID SOLUTIONS

Versatile, flexible and proven storage solutions for the grid:

TRANSPORTATION SOLUTIONS

Hybrid, plug-in hybrid and electric vehicle battery systems for: Commercial vehicles, Off-highway vehicles, Passenger vehicles

The technical specifications of the cell is

The discharge characterestics of the cell with cycle life at different operating temperatures are as follows

The voltage characterestics at different discharge rates are as shown below.

Assumptions

We will assume that the voltage requirement for the battery pack is 360V.

Battery pack Calculations

Total capacity required 18kWh.

Operating voltage is 360V

From the data sheet for a single cell, voltage is 3.3V and energy is 8.3Wh

The modules can be created in series/parallel connections of individual cells.Then every modules should be connected in series/parallel to construct final battery pack.

In series connecction-Voltage added and Current remains same.

In Parallel connection-Voltage remains same and Current gets added.

• Number of cells connected in series:

The number of cells connected in series to get 360V = 360/3.3 =109.1 ~ 110 cells

Now 110 cells are connected in series to create a module which will have 360V and 2.56Ah.

• Number of cells connected in parallel:

The total energy of the module = 110*8.3=913Wh

Total energy for the pack is 18kWh.

So no of modules to be connected in parellel = 18000/913=19.7 ~ 20 cells

• Battery pack capacity

Battery pack capacity = no. of cells connected in parellel * single cell capacity

=20*2.5 =50Ah

The battery pack will be 110S20P.

• Total number of cells in battery pack:

The total no of cells in pack =110*20=2200 cells

The total energy =2200*8.3=18260Wh=18.2kWh

• Cell peak current:

cell peak current = `C r a t e`(maximum pulse charge current) * single cell capacity

=20*2.5 =50A

• Battery pack peak current:

Battery pack peak current = cell peak current * number of cells connected in parallel

= 50*49= 2450A

So Now the cell arrangement in the pack is completed. Next we need to design the enclosure for the battery pack.

Weight of battery pack = (Total no. of cells in the battery pack) * (Cell Weight)

= (2200 * 0.076) =167.2kg

Length of battery pack = (No. of cells in series) * (Cell Diameter)

= 110 * 0.026 = 2.86 m

Width of battery pack = (No. of cells in parallel) * (Cell Diameter)

= 20 * 0.026 = 0.52 m

Area of battery pack = (Length of battery pack) * (Width of battery pack)

= 2.86 * 0.52 = 1.487 m2

Materials and process in battery pack construction:

Battery pack constructions consist of three major levels of processings namely cell level,module level,pack level constructions.

The electrodes are combined with electrolyte to various cell models as cylindrical,prismatic,pouch type cells.

After case sealing cells are combained to form module level construction.Finally these modules are combained to form pack level constructions.

Joining technologies of cells:

The interconnections between cells/modules are practised by various welding techniques.Some of them are,

• Ultrasonic metal welding.
• Resistance welding.
• Laser beam welding.
• Wire bonding.
• Mechanical Jooining.

Ultrasonic metal welding-

Ultrasonic metal welding or UMW, is a solid-state welding technique which forms a bond by applying moderate static pressure and an ultrasonic oscillation of about 20 kHz between two

3112parts of metal. The solid-state weld is formed through the high frequencymotion between the parts causing continuous shearing and plastic deformation, while also removing any oxide layers or contaminants.

Most metals can be ultrasonically welded and the method is excellent for welding together thin foils, as well as thicker sheets with spot or seam welds and also wires.

The four types of materials welded in this process can be seen as,

a)Aluminium wire welding on copper.

b)Copper and aluminium welding.

c)Multilayered copper foil welding.

d)Ultrasonic seam welding.

Resistance spot welding-

One of the oldest welding methods is resistance spot welding (RSW).RSW is a technique where two or more metal sheets are welded together through the application of an electrical current

and pressure between two electrodes. The electrical resistance of the material at the interface results in the generation of heat and melts the materials together without the use of

filler material or gases.

The temperature increases in the affected area, the interface, and eventually reaches the material’s melting point. A weld nugget forms in the affected area after cooling.

This is a small volume of the material which has melted and then fused together.

Laser beam welding-

Laser beam welding or LBW is a welding technique in which a laser beam provides a concentrated heat source that fuses the materials together.

LBW is commonly performed using keyhole mode welding in which the extreme power density of the laser beam causes the metal to melt and evaporate.

As the metal atoms evaporate from the surface, forces in the opposite direction of the evaporation causes a local vapor pressure. The vapor pressure creates a hole which is known as the

keyhole by depressing the molten metal.

Here below shown the welding of busbars to cylindrical battry cans.

Enclosures:

Cells in series connection-

When you connect cells together in series, it doesn’t change the amps or the capacity, it only raises the voltage of the pack. Hooking them up in series means that you connect the positive end

of one cell (or P-group) to the negative end of the other as shown below.

Cells in Parallel connections-

If you take several cells and connect their same-type electrodes in parallel, they all will act as though they are one large cell. Also, when you first connect them to each other,

they must be at the same level of charge.

Cell houlders-

These houlders are used for houlding the individual cells in a better posture without mis-assemble.The connections can be made accordingly to make series connections and

parallel connections to form the required module dimensions.

After installind the cells in a individual module the entire maximum positive terminal and maximum negative terninal are made under single pair of

terminals as shown below.

Here shown the cells are arranged and welded without using cell houlders as,

They are just covered by polimer sheet after the interconnections are made. Mostly connections with cell holders should be recommanded for better

safety concerns.

Battery Cabinet arrangements-

Each modules are interconnected in series or parllel according to the requirement and packed as a single large cabinet pack as shown below.

Battery pack arrangement:

Finally the overall battery pack after the arrangement of all cabinet connections with enclosure looks like this as shown below,

Vents holes are present with enclosure for cooling/heating the battery pack temperature according to its environment conditions.

Different cell types are used by different manufacturers of EV such as Cylindrical,Prismatic,Pouch types.

The pack constructions are different for every manufacturers.