Project 1 Mechanical design of battery pack

1. Prepare a detailed battery pack of Cell: ANR26650M1-B, drawing along with its enclosure, and Battery pack capacity is 18kWh. State your assumptions.

ABSTRACT:

• In this project, we are going to calculate the all parameters which are required the build an 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 some enclosure models for our battery pack.

OBJECTIVE:

1) Collecting the data of Cell: ANR26650M1-B from Nano phosphate High Power Lithium-Ion Cell PDF.

2) Calculating all Electrical parameters for an 18 kWh Battery Pack.

3) Calculating all Physical dimensions for Battery Pack.

4) Consider the perfect enclosure for the dimensions that we calculated for the Battery Pack.

METHODOLOGY:

1) To build the Battery pack for any Electric Vehicle, we have to calculate the first proportion of power then motor power and ddependingon 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:

1. maximum traction motor torque
2. maximum regeneration brake torque
3. vehicle range
4. vehicle total weight
5. vehicle price
6. 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:

1. chemistry
2. voltage
3. 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:

• The 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 Eaux [Wh/km], like a 12 V electrical system, heating, cooling, etc.
• Also, we have to consider the efficiency of the powertrain ηp [-] 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 individual voltage.
• In order to increase the current capability, and 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.

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

1. 74 cells in a parallel-group
2. 6 groups in series for a module
3. 16 modules in series
4. 7104 cells in total

BATTERY PACK PRODUCTION LINE

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

From the above 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 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 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

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

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

: 3.14⋅0.0132⋅0.0653.14⋅0.0132⋅0.065

:0.0000344929m3

The volume of the cell is 0.0000344929m3

Basically, 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 ASSUMPTIONS:

• There are 50 cell 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 combinations, 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 has a by-product of voltage and current, and check 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 requirements that we need.

now we have the total no of cells and 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

The total volume required for the battery pack is 0.07588438m3

• We also have a single cell weight from which 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 density= 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,

1. 2112 cells will have the 50S / 44P.
2. 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 battery pack into electric vehicle lower floor panel case, a simple layout of the battery pack in an electric vehicle is shown below:

DESIGN OF 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

• Basically, 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

• Basically, the lowercase is a part which is fitted in an electric vehicle for the assembly of the battery pack.
• A lowercase is also made up of aluminium and it has a top cover and bottom cover to battery pack from dust and environmental pollution.

THE DESIGN OF THE LOWERCASE IS SHOWN

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 together by means of 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.

DESIGN BENEFITS

• Up to 50 per cent lighter than an equivalent steel design.
• Best-in-class mass-energy density at more than 160 watt-hours per kilogram, an extremely efficient design for OEMs and Tier 1 battery pack manufacturers.
• Accommodates all battery cell types and is designed particularly for battery electric vehicles with larger power packs such as pick-up trucks, sport utility vehicles and crossovers.
• Most cost-effective aluminium solution for mass production of electric vehicles when compared to aluminium extrusion and casting-intense designs.
• The low-price premium of $/kg saved compared to equivalent steel designs at a substantially lower weight.

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:

SOME OTHER DESIGN OPTIONS FOR BATTERY PACK CONSTRUCTIONS:

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