Project 1 Mechanical design of battery pack

Answer: In this project, we are going to calculate the all parameters which are required for the build EV battery pack. We are going to use  Cell: ANR26650M1-B for our battery pack. In parameters, we will consider all electrical aspects like temperature, Depth of discharge, Operation current, Energy density, Work cycles, Battery capacity, State of Charge (SOC), State of Health (SOH), and Ampere-hour (Ah) Capacity. We also calculate all geometrical considerations like size, weight, volume, area, etc. In the end, we consider senclosureures models for our battery pack.

 

Principle;

1) To build the Battery pack for any Electric Vehicle, we have to calculate the first proportion of power then motor power, and depending on that we will model the battery pack so we know how much power we required which is 18kWh.

2) For the 18kWh battery Pack we have to calculate how many cells are parallel and how many cells are in series.

3) After calculation of series and parallel combination we have to calculate the proper Geometry and topology consideration for assembling batteries.

4) After Assembly we need to find a proper enclosure for the battery pack for thermal consideration and other physical damages.

THEORY:  

The high-voltage battery is one of the most important components 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

Pretty much all major aspects of a pure electric vehicle (EV) depend on the parameters of the high-voltage battery.

For our electric vehicle battery design we are going to start with 4 core input parameters:

• chemistry
• voltage
• average energy consumption of the vehicle on a driving cycle
• vehicle range

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, electrolytes, and a case or enclosure. For automotive applications, there are different types of cells used Individual battery cells are grouped into a single mechanical and electrical unit called a battery module. The modules are electrically connected to form a battery pack.

                           

The voltage level of the battery determines the maximum electrical power which can be delivered continuously. Power P [W] is the product between voltage U [V] and current I [A]:

                                                                                          P = U* I 

The higher the current, the bigger the diameter of the high-voltage wires and the higher the thermal losses. For this reason, the current should be limited to a maximum, and the nominal power obtained by having a higher voltage. For our application, we are going to consider a nominal voltage of 400 V.

the energy needed for propulsion, the high voltage battery must supply the energy for the vehicle’s auxiliary devices E_aux [Wh/km], like a 12 V electrical system, heating, cooling, etc. Also, we have to consider the efficiency of the powertrain η_p [-] during the conversion from electrical energy to mechanical energy.

Battery pack architecture:

All high-voltage battery packs are made up of 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 voltage.

                                  

Technical data of ANR26650M1-B 

An example is the high-voltage battery pack of the Tesla Model S, which has:

• 74 cells in a parallel-group
• 6 groups in series for a module
• 16 modules in series
• 7104 cells in total

                                                             

Battery pack production line flow chart
                                          

 

PROCEDURE:

1)  first we have to start with Cell calculation.

2) Then we will do Battery Pack assumptions.

3) After assumptions, we have to do Battery pack calculations.

4) from Cell Dimensions we calculate the surface required for a battery pack.

5) Depending upon the above calculations we build Battery Pack construction.

 

The followings are the all cell (Cell: ANR26650M1-B)  parameters for the battery pack:

                                                          

From the above all parameters we will calculate further parameters which are used for battery pack construction.

Cycle Life Performance, 100% DOD, Various Temperatures and Discharge Rates of cell:

                          

Constant Power Discharge Characteristics at 23°C of cell:

                                                             

2.5C Constant Current Discharge at Various Temperatures:

                                                                

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.

Cell dimensions:

                                       

Cell calculation:

1) Volume of the cell: For the calculation of the volume of the cell we use the formula of Volume of the cylinder.

so the formula is: πr2h">πr2hπr2h

From the Datasheet of Cell, we have 'r' and 'h' values

r=0.013m and h=0.065m =    Volume of the cell: πr2h">πr2hπr2h

                                                                      : 3.14⋅0.0132⋅0.065">3.14⋅0.0132⋅0.0653.14⋅0.0132⋅0.065

                                                                      :0.0000344929m3">m3m3

The volume of the cell is 0.0000344929m3">m3m3

The value of the volume of the cell is used to find out the total volume of the battery pack.

Cell Energy= Cell Capacity (Ah) × Cell Voltage (V)

                = 2.5 × 3.3

                = 8.25 Wh

Cell Energy is 8.25 Wh

The value of a single cell is used to calculate the total energy of the battery pack.

Single Cell Energy Density

Volumetric energy (Wh/m³) = Single Cell Energy / Volume of each cell

                                          = 8.25 Wh / 0.0000344929m³

                                          =2,39,179.6572 Wh/m³

 

Single Cell Energy Density is 2,39,179.6572 Wh/m³

 

Battery Pack Assumtions:

There are 50 cells in series and 44 cells in parallel, and as above mentioned we are going to use Cell: ANR26650M1-B this cells.

Battery pack calculation:

Now we calculated parallel and series combinations so we can now calculate the total no of cells required

Total no of cells: Series cells * parallel cells

                      :50*44

                      :2200.

The total no of cells required is 2200.

So from series and parallel combination, we can calculate the voltage of the battery pack and the current of the battery pack.

Voltage= no of cell in series* nominal voltage.

          = 50*3.3

          = 165V

The total value of voltage is 165V.

Current=No of parallel cells * cell capacity

          = 44*2.5

          =110Ah.

The total value of the Current is 110Ah 

So now we can calculate how much amount of energy this combination have the by-product of voltage and current, and check whether it will satisfy or not our requirement

Energy= Voltage * Current

         = 165 * 110

         = 18150WAh

The total value of Energy is 18150WAh.

So our calculations are satisfied the requirement that we need.

now we have the total no of cells and the volume of the single cell so we can calculate the total volume required for the battery pack

Total volume = no of cells * Volume of single cell

                  = 2200 * 0.0000344929

                  =0.07588438m3">m3m3

The total volume required for the battery pack is 0.07588438m3">m3m3

We also have single cell weight from that we can calculate the total weight of the battery pack without other mechanical and electrical connections.

Weight = No of cells * weight of the single cell.

           = 2200 * 0.076

           = 167.2kg

The weight of the battery pack is 167.2kg

Energy dencity= volume * battery pack energy

                        = 0.07588438 * 18150

                       = 1,377.301497kWh/m^3

Energy density is 1,377.301497kWh/m^3

Now we have all parameters which we need to construct the battery pack in physically.

  

The arrangement design of single-cell is shown below:

                                   

Assembly of the full battery pack with the 50s/ 44P. The arrangement of the pack is as follows:

 

Then, 

            2112 cells will have the 50S / 44P

Here I arrange the pack such that it will build a proper battery pack.

 The detailed technical specification of the 2112 battery pack is as follow:

• Package: 50S / 44P
• Capacity: 110 Ah
• Voltage: 165 V
• Weight: 167.2kg (Only Cells)
• No of Cells: 2100
• Power: 18150Wh or 18.15 kWh

                                                                

Here I also configure the battery pack into the electric vehicle's lower floor panel case, a simple layout of the battery pack in an electric vehicle is shown below:

                     

Cell holder (Bottom and Top)

 

The main function of a battery holder is to keep cells fixed in place safely and securely also it is used to keep cells in a proper arrangement so that there will be a decrease in mechanical vibration and a better thermal runway in between the cell gaps. Most of the cell holder is made up of polypropylene or nylon bodies rated for 80–100 °C.

       

                                  

Design of pack cover

The pack cover is made up of Aluminium and the reason behind is to keep the battery pack lightweight. The casing/cover thickness is 0.5 mm and the design is as shown below:

A bottom cover is shown to cover below the bottom battery holder.

                                                  

                                     

                                   

                          

Design of Lower floor case for battery pack

The lowercase is a part that is fitted in an electric vehicle for the assembly of the battery pack. A lowercase is also made up of aluminum and it has a top cover and bottom cover to battery pack from dust and environmental pollution.

Positive and Negative Clip

A positive and negative clip is used to connect the battery end cap i.e (+) and (-). The design is shown below:

                        

To make the battery pack, you have to connect the many cells using Nickel strips or thick wire. Generally, Nickel strips are widely used for this. In general two types of nickel, strips are available in the market: nickel-plated steel strips and pure nickel strips. I will suggest buying pure nickel. It is a little bit costlier than nickel-plated steel, but it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life.

Nickel strips come in different dimensions and lengths. 

                   

Joining of Cylindrical Cell Battery Pack

Cylindrical cells have improved thermal management efficiency because of their compact shape, but have low packaging efficiency because of their round cross-section. Here I use a positive and negative tab to connect multi cells.

The suitability of joining methods to build battery packs using cylindrical cells is shown below:

                       

 Different design for battery;;;

                                           

                                           

RESULT:

    

NO	Calculated Parameters	Value Get
1	Cell Volume	0.0000344929m^2
2	Cell Energy	8.25Wh
3	Cell Density	239179.6572kWh/m^2
4	Pack assumptions	50s 44p
5	Total no of cells	2200
6	Voltage	165V
7	Capacity	110Ah
8	Energy	18150WAh
9	Total volume	0.07588m^2
10	Total Density	1377.30kWh/m^2
11	Weight	167.2kg