Challenge

Project 1 Mechanical design of battery pack

MMohammed Asad Ali17 Feb 2023

DESIGN

AIM:

Design a mechanical battery pack.

OBJECTIVE:

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

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

INTRODUCTION

As electric vehicles are increasing in the market is gradually increasing, there is considerable growth in the production of lithium-ion batteries. As it is the electrical source for the EV.

A lithium-ion battery or Li-ion battery is a type of rechargeable battery in which lithium ions move from the negative electrodes through an electrolyte to the positive electrode during discharge, and back when charging. Li-ion batteries use an intercalated lithium compound as the material at the positive electrode and typically graphite at the negative electrode.

Lithium-ion batteries are made use of various different electrodes. The most common material use is lithium cobalt oxide and graphite which are most commonly found in portable electronic devices such as cellphones and laptops. Lithium manganese oxide and lithium iron phosphate are also used as cathode materials.

The basic internal structure

A battery is made up of an anode, cathode, separator, electrolyte, and two current collectors (positive and negative). The anode and cathode store the lithium. The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector. The electrical current then flows from the current collector through a device being powered (cell phone, computer, etc.) to the negative current collector. The separator blocks the flow of electrons inside the battery.

CHARGE/DISCHARGE
While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device, the opposite happens: Lithium ions are released by the cathode and received by the anode.

Nanaophosphate High Power LithiumIon Cell ANR26650M1-B

A123’s high-performance Nanophosphate® 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. Our cells have a 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.

Applications of the battery.

There are various applications of Lithium-ion cells

1. COMMERCIAL SOLUTIONS

This is a large-scale application for the battery where high power is required.

Datacenter UPS
Telecom backup
IT backup
Autonomously guided vehicles
Industrial robotic and material handling equipment

2. GOVERNMENT SOLUTIONS

Military vehicles
military power grids

3. GRID SOLUTIONS

Frequency regulation
Renewable integration
REverse capacity
Transmission and distribution

4. TRANSPORTATION SOLUTIONS

Plug-in hybrid vehicles, hybrid cars, electric vehicles
Commercial vehicles
Off-highway vehicles
passenger vehicles.

The performance of the cell is given in the datasheet that is referred to for this project.

These images show the power discharge, current discharge, and the life cycle of the cells used for the battery pack.

Here you can see the voltage capacity of the battery for different power ratings.

DESIGN CALCULATION

All the parameters of this calculation are taken from the datasheet

Calculation :

This calculation is to determine how much space of volume the cell will take in the to have the capacity of 18kw.

Cell energy=Nominal volatge * niminal cell capacity

Cell energy=3.3*2.5

=8.25Wh

so each cell has the energy of 8.25 wh.

Cell Volume=π *r*r*h

=3.14*0.013*0.13*0.065

=0.0344929 m^3

So now we have to calculate how much Watt per volume the cell can produce:

Cell energy density=cell energy/cell volume

=8.25/0.0344929 Wh/m^3

=239.17 wh/m^3

Now we have to assume the battery pack:

To get 18 kw as a output power we have to conside serises and paraller cells to be connected to create the battery pack module of the required capacity.

let us consider 58 cells connected in series a and 38 cells connected in parallel.

So the toatal number of cells required =58*38=2204 cells

Voltage of the pack=Nominal volatge *cell connecetd in series

=3.3*58

=191.4

current capacity of the battery pack=Cell capacity*Cells conned in parallel

=38*2.5

=95Ah

The total energy of the battery pacck=Volatage *current capacity

=191.4*95

=18.18KW

Now we know the total number of cells which are required in the battery pack we can now calaculate the energy density,volume and weight of the enitre batery pack.

Total volume =Cell volume*Total no of cells

=0.0344929*2204

=76.022m^3

And total weight of the battery=Total no of cells*Weight of each cell

=2204*0.076 kg

=167.504 Kg is the total weight of the battery

Now we know the weight and volume of the battery pack of 18kw .So, we will consturct the battery pack.
Battery Pack:

A battery consists of one or more electrochemical cells (battery cells) which are converting chemical energy into electrical energy (during discharging) and electrical energy into chemical energy (during charging).
The type of elements contained within a battery and the chemical reactions during discharging-charging events define the chemistry of a battery.A battery cell consists of five major components: electrodes – anode and cathode, separators, terminals, electrolyte and a case or enclosure
Individual battery cells are grouped together into a single mechanical and electrical unit called a battery module.
The modules are electrically connected to form a battery pack.
There are several types of batteries (chemistry) used in hybrid and electric vehicle propulsion systems but we are going to consider only Lithium-ion cells. The main reason is that Li-ion batteries have higher specific energy [Wh/kg] and specific power [W/kg] compared with other types.

Ev uses mainly 3 types of cells:Cylindrical,prismatic and pouch.

Battery Pack construction:

There are 3 steps for the construction of the battery pack.

Battery holding and providing the spacing between the battries.
Connecting the battries with the strips (Series or Parallel)
Making and manifacturing the battery enclosure housing with the thermal managment system and BMS

1. Holding and spacing:

Each of the cells are now need to be connected so that it could form a big battery module.
So this holdes are very importatnt to provide the gapping between the battery and holding the battries in the correct manner.
The cells has a vent at the end cap of the cell.and should not be covered by any mechinical means.Blocking the cell vent and then sufficiently abusing the cell so as to built the pressure in cell.There must be minimum of 1mm spacing between each cells to allow the vent to open under the fault condition.
Holders will make it easy to palcethe contact plate between the cells.

2. Connecting the cells:

When the cells are plalced in the holders ,then the cells need to be connect in the proper manner in series or parallel to get the desired results.
Ususally a nickle strip is used between the cells to make the conatct.

Nickel strip is generally used in battery building.
Its due to its efficiency of usage in spot welding and soldering as well its high corrosion resistance over time.
It has good properties and excellent resistance to many corrosive environments.
The pure nickel will never get rust after it applied to battery packs.
It won’t affect the current transfer between batteries.Pure nickel strips are the material you want, but many vendors swap out it for nickel-plated steel strips, which are poorer and have greater resistance – not suitable for most battery projects. 100% pure nickel strip.
verify all of our strips to assure that you are getting the high-quality pure nickel. It also solder incredibly quickly, so you can weld them onto your existing busbar connections to raise the supply of current you can pull through the busbars. The benefits are nearly limitless!

3. Battery enclosure and thermal managment of battery and BMS

The battery encolsure is the final protection of the battery.
So the battery enclose must be very strong and light in weight.
In the case of any accident the batteries has the tendentcy of catch fire if it get leaked during the car crash,so the battery modle is enclose in a very strong encolsure due to the safety.
The weight should be less so we can get the best pssible range.
In this metal housing there is a temperature managment system provided to cool and heat the battries when there is a need to get the best performace of the battries.
There a several numbers of models connected in series and parallel to build a entire battry pack.