Project 1 Mechanical design of battery pack

Objective:

battery pack capacity=18 kwh

cell= ANR 26650M1-B

prepare a detailed battery pack drawing along with its enclosure. State your assumption.

Nano phosphate High Power Lithium-Ion Cell: ANR 26650M1-B

A123 high-performance Nano phosphate 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 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.

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 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.

1.COMMERCIAL SOLUTIONS:

• Data center UPS
• Telecom backup
• IT backup
• Autonomously guided vehicles
• Industrial robotic and material handling equipment

2.GOVERNMENT SOLUTIONS:

• Military vehicles
• military power grids
• soldier power
• directed energy

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 graph 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:

Cell:

The Lithium Works ANR26650M1-B is the next generation of A123 Systems' pioneering 26650 cylindrical cell, now with greater power and energy density and lower impedance. This versatile lithium-ion cell is suitable for a wide variety of applications and system designs.

Module:

A battery management system (BMS) is any electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment.

Battery pack:

A battery pack is a set of any number of (preferably) identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density.

battery pack calculation:

The high voltage battery it is one of the most important component of a battery electric vehicle (BEV). The battery parameters have a significant influence on other components and attributes of the vehicle, like:

• maximum traction motor torque
• maximum regeneration brake torque
• vehicle range
• vehicle total weight
• vehicle price

different type of cell lithium-ion battery cell:

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.

Battery pack architectures:

All high voltage battery packs are made up from battery cells arranged in strings and modules. A battery cell can be regarded as the smallest division of the voltage.

Individual battery cells may be grouped in parallel and / or series as modules. Further, battery modules can be connected in parallel and / or series to create a battery pack. Depending on the battery parameters, there may be several levels of modularity.

The total battery pack voltage is determined by the number of cells in series. For example, the total (string) voltage of 6 cells connected in series will be the sum of their individual voltage.

In order to increase the current capability the battery capacity, more strings have to be connected in parallel. For example, 3 strings connected in parallel will triple the capacity and current capability of the battery pack.

Battery dimensions:

• Length of casing:

length = number of cells x (cell diameter + margin at both side of cells ) + clearance at side

L = 100 x (26 + 4) + 60 = 3060 mm

• Breadth of the casing (B):

Breadth = number of cells x (cell diameter + margin at both side of cell) + clearance at side

B = 22 x (26 +4) + 60 = 720 mm

• Height of casing (H):

Height = Height of cell + margin for wiring

H = 65+35 = 100 mm

Volume of each cell:

cylindrical cells, V_cc 〖[m〗^3]=  (〖πD〗_bc^2)/4  .L_bc 
where:
Dbc [m] – battery cell diameter
Lbc [m] – battery cell length

rom the datasheet D_bc=26mm=0.026m & L_bc= 65mm= 0.065m

V_cc 〖[m〗^3]=  (π*0.026*0.026)/4*0.065
V_cc=3.5×10^(-5) 〖[m〗^3]

Battery cell energy Ebc [Wh]:

Ebc = Cbc * Ubc

where:

Cbc [Ah] – battery cell capacity = 2.5 Ah

Ubc [V] – battery cell voltage = 3.3 V

Ebc = 2.5 * 3.3 = 8.25 Wh

Battery cell energy density:

volumetric energy density = uV=  E_bc/V_(cc(bc)) 

uV=  8.25/(3.5×10^(-5) )=235714.5 Wh/m^3

gravimetric energy density = uG=  E_bc/m_bc 
uG=  8.25/0.076=108.55 Wh/kg

Number of battery cells connected in series:

calculated by dividing the nominal battery pack voltage Ubp [V] to the voltage of each battery cell Ubc [V]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

Let us assume that the battery pack voltage which is required to be 330V and the nominal voltage of the battery as per the datasheet is given as 3.3V.

N_CS=  U_bp/U_bc =  330/3.3=100

Energy Content of a string:

The product between the number of battery cells connected in series and the energy of a battery cell.

E_bs= N_CS 〖*E〗_bc=100*825=825 Wh

The total number of strings of the battery pack:

calculated by dividing the battery pack total energy Ebp [Wh] to the energy content of a string Ebs [Wh]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

N_sb=  E_bp/E_bs =  18000/825  =21.818

22 string is connected in parallel.

Battery pack capacity:

Is the calculated as the product between the number of strings Nsb and the capacity of the battery cell Cbc [Ah].

C_bp= N_sb 〖*C〗_bc=22*2.5=55Ah

Total number of cells of the battery pack:

Is calculated as the product between the number of strings Nsb [-] and the number of cells in a string Ncs.

N_cb= N_sb 〖*N〗_cs=22*100=2200

Mass of the battery pack:

Is the product between the total number of cells Ncb and the mass of each battery cell mbc [kg].

m_bp= N_cb 〖*m〗_bc=2200*0.076=167.2 kg

Volume of the battery pack:

It is the product of the total number of cells Ncb and the mass of each battery cell Vcc(pc). This volume is only used to estimate the final volume of the battery pack since it does not take into account the auxiliary components/systems of the battery.

V_bp= N_cb 〖*V〗_(cc(pc))=2200*3.5×10^(-5)=  0.077m^3  
The total volume of the battery pack is 77000 〖mm〗^3.

String peak Current:

Is the product between the peak C-rate of the battery cell C-rate bcp and the battery cell capacity Cbc [Ah].

From the datasheet, the battery pack peak C-rate is 24 and the nominal capacity is 2.5Ah.

I_spc= 〖C-rate〗_bcp 〖*C〗_bc
I_spc=24*2.5=60A

Battery pack peak current:

is the product between the string peak current Ispc [A] and the number of strings of the battery pack Nsb.

I_bpp= I_spc 〖*N〗_sb=60*22=1320A

Battery pack peak power:

Is the product between battery pack peak current Ibpp [A] and the battery pack voltage Ubp [V].

P_bpp= I_bpp 〖*U〗_bp=1320*330=435600=435.6 kw

String continuous current:

is the product between the continuous C-rate of the battery cell C-rate bcc and the battery cell capacity Cbc [Ah].

From the datasheet, the battery pack continuous C-rate is 10 and the nominal capacity is 2.5Ah.

P_bpp= 〖C-rate〗_bcc 〖*C〗_bc=10*2.5=25A

Battery pack continuous current:

is the product between the string continuous current Iscc and the number of strings of the battery pack Nsb.

I_bpc= I_scc 〖*N〗_sb=25*22=550A

Battery pack continuous power:

Is the product between battery pack continuous current Ibpc [A] and the battery pack voltage Ubp [V].

P_bpc= I_bpc 〖*U〗_bp=550*330=181500
The battery pack continuous power will be 181.5 kW

Manufacture	A123 - Systems
Number of cells in the string	100
String energy	825 Wh
Number of string	22
battery pack energy	55 Ah
Total number of cells	2200
Battery pack mass	167.2kg
battery pack volume	0.077 m^3
Battery pack peak current	1320A
Battery pack peak power	435.6kW
battery pack continuous current	550A
Battery pack continuous power	181.5kw

Component of the battery pack:

• 2200 cells
• Nickel strip
• PVC heat sink film
• spot welder
• Connected
• Cell holder
• Solder

1) The first step is to start snapping the square cell holder together. One can use the cell terminal block but they will take more space than a hexagonal block.

2)Placing the cells in the holder matrix. Place all the cells in the holder and put the second holder in the place.

3) Now we will be connecting the cells with nickel strips using the spot welding process. The series connection will be made by connecting the positive terminal of the cells to the negative terminal. The parallel connection will be made by connecting the same terminal.

4) Connecting the heat sink to the battery pack

5) Connect the balancing wire pin to the battery management system.

6) Final battery pack:

Conclusion: The calculation of battery pack and designing of battery pack is successfully implemented with ANR26650M1-B datasheet.