Project 1 Mechanical design of battery pack

Aim: Design a mechanical battery pack.

Objective:

Cell: ANR26650M1-B

Battery Pack Capacity: 18 kWh

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.

10S1P battery

Lithium-ion batteries are popular power sources for cell phones and other electronics but are problematic in extreme heat or cold.

Most batteries will operate, with varying degrees of effectiveness in the 5- 35 °C range so are fine for the autumn and spring operating months, however, if you want a battery that will also operate efficiently in winter and summer you need to understand how temperature has an effect on batteries operating capabilities.

The ambient weather temperatures have a large impact on the performance and on the life of most batteries and unfortunately, it’s a characteristic that isn’t often talked about.

The optimum temperature for most batteries to operate at is around 25°C and this is the temperature all battery testing is performed at. When temperatures vary, either up or down there is an effect on the performance and life of most batteries.

Depending on the chemistry of the battery different batteries will only operate optimally within a limited temperature range, so it’s important to understand this when purchasing or upgrading your battery for energy storage.

When the temperature starts to fall below about 15°C, depending on the battery's chemistry, the electrochemistry of the battery becomes sluggish and doesn’t perform as well. In fact, very few batteries operate below 0°C. This is relevant in many countries in Europe, the USA or Canada but not as relevant in most of Australia.

What is relevant to the Australian market is the other end of the scale with the hot weather temperatures, particularly those of 40°C or above. Over 35°C, again depending on the battery chemistry, the battery will not operate and will start to degrade. For this reason, many batteries need to be kept in an air-conditioned environment which adds to the ongoing running costs of the battery and is something that needs to be taken into account when considering the LOC or lifetime cost of a battery. In the past, many installations have installed extra batteries, just to keep the air-conditioning running to keep the batteries cool.

Keeping a battery within its safe operating range is critical in the case of certain battery technologies as some batteries will catch fire if they get too hot. This is one reason those certain batteries have a BMS or battery operating system included to make sure that the battery can’t overheat. However, if this BMS fails or there is no power for an extended period of time there is the possibility of batteries catching fire or exploding. (Just another thing to take into consideration.)

The FIAMM Sodium Nickel Chloride or SoNick batteries are the only batteries that will really work reliably in temperatures over 40°C and these temperatures don’t cause the SoNick battery to deteriorate so won’t have a detrimental effect on the battery’s longevity. This is particularly important in hot areas of Australia or in bushfire prone areas.

Lithium-ion batteries power the lives of millions of people each day. From laptops and cell phones to hybrids and electric cars, this technology is growing in popularity due to its lightweight, high energy density, and ability to recharge.

The basic internal structure.

THE BASICS

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.

ENERGY DENSITY VS. POWER DENSITY

The two most common concepts associated with batteries are energy density and power density. Energy density is measured in watt-hours per kilogram (Wh/kg) and is the amount of energy the battery can store with respect to its mass. Power density is measured in watts per kilogram (W/kg) and is the amount of power that can be generated by the battery with respect to its mass. To draw a clearer picture, think of draining a pool. Energy density is similar to the size of the pool, while power density is comparable to draining the pool as quickly as possible.

Nanaophospate high Poer Lithium Ion 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 sate 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.

Procedure for the Calculation:

The capacity of the battery pack is set to be 18kWh.

For making a high voltage battery pack many cells are arranged in a particular pattern and sequence to improve the voltage and the power rating.

Individual battery cells may be grouped in parallel and/or series as modules. Further, battery modules can be connected in parallel and/or in 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 of 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.

Now for calculating our required battery pack on the cell manufacture data provided.

The calculation for the battery pack is as follows:

1. Volume of each cell

Cylindrical volume V_c [m³]

From the datasheet we have D_bc = 26mm = 0.026m and L_bc = 65mm = 0.065m

Therefore, V_Cc = π * 0.025² * 0.065/4 = 3.5 * 10^-5 m³

The volume of each cell is 35 mm³

2. Battery Cell Energy

we have,

C_bc = 2.5 Ah

U_bc = 3.3 V

Substituting the values in the above equation we get

E_bc = 2.5 * 3.3 = 8.25 Wh

3. Battery cell energy density

• Volumetric energy density

Substituting the value

• Gravimetric energy density

Substituting the above-calculated values in the equation, we get,

4. Total number of the battery pack

The total energy of the battery pack which is required is given as 18 kWh

E_bp = 18000Wh

5. Number of cells connected in series

It is calculated by dividing the nominal battery pack voltage U_bc [V] by the voltage of each battery cell U_bc [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.

The total number of cells in series is 100

6. 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 * 8.25 = 825 Wh

7. Number of strings in the battery pack

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

Substitute the above value

All the 22 strings will be connected in parallel

8. Battery pack Capacity

It is calculated as the product between the number of strings N_sb [-] and the capacity of the battery cell C_bc [Ah].

C_bp = N_sb * C_cb = 22 * 2.5 = 55Ah

9. Total number of cells of the battery pack

It is calculated as the product between the number of strings N_sb [-] and the number of cells in a string N_cs [-].

N_cb = N_sb * N_cs = 22 * 100 = 2200

The total number of cells required for the design pack is 2200.

10. Mass of the battery pack

It is the product of the total number of cells N_cb [-] and the mass of each battery cell m_bc [kg].

m_bp = N_cb * m_bc = 2200 * 0.076 = 167.2 kg

11. Volume of the battery pack

It is the product of the total number of cells N_cb [-] and the mass of each battery cell V_cc(pc) [m³]. 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.

12. String peak Current

Is the product between the peak C-rate of the battery cell C-rate_bcp [h^-1] and the battery cell capacity C_bc [Ah].

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

I_spc = 24 * 2.5 = 60A

13. Battery pack peak power

Is the product between the string peak current I_spc [A] and the number of strings of the battery pack N_sb [-].

Substituting the above values

I_bpp = 60 * 22 = 1320 A

14. Battery pack peak power

Is the product between battery pack peak current I_bpp [A] and the battery pack voltage U_bp [V].

Substituting the above values

P_bpp = 1320 * 330 = 435600 W = 435.60kW

15. String continuous current

It is the product between the continuous C-rate of the battery cell C-rate_bcc [h^-1] and the battery cell capacity C_bc [Ah].

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

I_scc = 10 * 2.5 = 25 A

16. Battery Pack Continuous Current

It is the product between the string continuous I_scc [A] and the number of strings of the battery pack N_sb [-].

I_bpc = 25 * 22 = 550 A

17. Battery Pack Continuous Power

It is the product between the string continuous I_ppc [A] and the battery pack voltage U_bp [V].

P_bpc = 550 * 33 = 181500 W

The battery pack's continuous power will be 181.5 kW

All the above parameters that are calculated are in the table below.

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	167.2 kg
Battery Pack Volume	0.077 m^3
Battery Pack Peak Current	1320 A
Battery Pack Peak Power	435.6 kW
Battery Pack Continuous Current	550 A
Battery Pack Continuous Power	181.5 kW

Battery dimensions:

1. Length of casing length = number of cells * (cell diameter + margin at both sides of cells) + clearance at side

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

2. Breadth of the casing (B)

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

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

3. Height of casing (H)

Height = Height of cell + margin for wiring

H = 65 + 35 = 100 mm

Assembly of the battery pack

Component of the battery pack

1. 2200 cells
2. Nickel strip
3. PVC heat sink film
4. Spot welder
5. Connected
6. Cell holder
7. Solder

Step 1-

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

This is the cell holder block

This image shows the insulate gasket

Step 2-

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

Step 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.

Connecting the complete matrix of the cell together.

Step 4-

Connecting the heat sink to the battery pack

Now we will be soldering the battery wire

Now the internal structure of the battery pack is assembled and all the terminals are connected as per the connections.

Step 5-

Connect the balancing wire pin to the battery management system.

Step 6-

After the battery management system, the next and final step is to place the enclosure for the battery pack.

This is the final battery pack model created.

CONCLUSION

The design calculation for the battery pack was carried out and calculated and a table has been made for the same. The steps involved in the making of the battery pack have been listed.

Thank you...