Project 1 Mechanical design of battery pack
Aim:-
Battery pack capacity: 18 kWh
Cell:ANR26650M1-B
Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
THEORY:-
Any number of (ideally similar) batteries or individual battery cells may be combined to form a battery pack. To offer the necessary voltage, capacity, or power density, they may be set up in series, parallel, or a combination of the two configurations. The phrase "battery pack" is often used in connection with battery-operated cars, radio-controlled hobby toys, and cordless power equipment.
Individual batteries or cells and the interconnects that allow for electrical conduction between them are included in battery packs' components. A temperature sensor is often found in rechargeable battery packs, and the battery charger utilises this sensor to determine when charging is complete. Batteries have interconnects as well since they are the component that links each cell, even though they are often only placed in series strings.
There are several wire layouts that take the electrical balance of the circuit into mind when a pack has groups of cells in parallel. Battery regulators are occasionally employed to maintain each cell's voltage below its maximum level while charging, allowing the weaker batteries to completely charge and restoring balance to the whole pack. Battery balancers are also capable of active balancing, transferring energy in real time from strong cells to weak ones for improved balance. A balanced pack has a longer shelf life and performs better.
The market for electric vehicles is steadily expanding, as we all know. The popularity of lithium-ion batteries is growing along with the popularity of electric vehicles. Cells that are cylindrical are used to store the energy source for electric vehicles.
High power may be delivered using lithium-ion batteries. Aerospace, automotive electric vehicles, mobile gadgets, medical devices, and other electronic equipment based on these cells all employ lithium-ion batteries. The battery pack is put in the bottom floor of the electric vehicle to provide optimal centre of gravity maintenance and equal weight distribution.
One of any electric vehicle's most vital parts is the high voltage battery pack. An electric vehicle's traction battery must do the following:
provide the traction motors their maximum torque
Range of a vehicle in kilometres
To ensure that a battery has the necessary life cycle
An electric vehicle's battery pack often has a series or parallel configuration. Multiple cell modules are used to create huge battery packs, which are made up of several cells that are maintained close to one another. In essence, a parallel connection is utilised for compound current capacity whereas a series connection is used to compound voltage. Five main parts make up a battery cell: electrodes (anode and cathode), separators, terminals, electrolyte, and container.
Battery pack's mechanical design:
The two most important factors for big battery packs are safety and dependability. We must adhere to a few technical standards while building the mechanical components of a big battery pack to prevent battery failure.
Mechanical jolts should be reduced
adjusting for a strong impact force
more effective thermal runway for cooling
Availability for use and recycling
Here, we utilise the ANR26650M1B Lithium-Ion Cell as our basis model to create an 18 kWh battery pack. The lithium iron phosphate (LiFePO4) chemistry of the ANR26650M1B cell makes it ideal for usage in a variety of temperatures and environments. The following capabilities of the lithium ion cell ANR26650M1B are possible:
In this as we can see that by changing the charging and discharging cases as shown its performance characteristics changed her (+) represents charging and (-) represents discharging. By changing the temperatures its performance change.
Design of the ANR26650M1-B cell with dimensions as shown below,
We all know that any object's safety, design, size, and other factors are crucial to its manufacture, transportation, and other operations. These characteristics of lithium-ion cell batteries make it challenging to transport the battery due to vibrations, exposure to strong forces, and thermal runaway. Robust mechanical designs are required to prevent all these too tiny issues. Here, mechanical designs are crucial before being used in vehicles or other machines because if there is a problem at the design stage, it could damage the battery or cause a serious issue in the circuit. Battery packaging is designed to provide better protection against several of these.
The basic structure of the cells
A battery module is an integrated mechanical and electrical structure made up of various battery cells. A battery pack is created by electrically connecting the modules.
We will only discuss lithium-ion cells, though hybrid and electric vehicle propulsion systems use a variety of battery (chemistry) types. The primary factor is that Li-ion batteries outperform other types in terms of specific energy [Wh/kg] and specific power [W/kg].
During discharging, a battery's electrochemical cells (also known as battery cells) transform chemical energy into electrical energy and electrical energy back into chemical energy (during charging).
The chemistry of a battery is determined by the kind of components it contains and the chemical processes that take place during charging and discharging cycles.
Electrodes (anode and cathode), separators, terminals, electrolyte, and a container or enclosure are the five main parts of a battery cell.
A battery module is a collection of individual battery cells that functions as a single mechanical and electrical unit.
A battery pack is created by electrically connecting the modules.
We will only discuss lithium-ion cells, while hybrid and electric car propulsion systems utilise a variety of battery (chemical) types. The primary factor is that Li-ion batteries outperform other varieties in terms of specific energy [Wh/kg] and specific power [W/kg].
Ev primarily employs three different cell types: cylindrical, prismatic, and pouch.
Calculations:-
To make the battery pack, we have to first finalize the nominal voltage and capacity of the pack. Either it will be in term of Volt, mAh/ Ah or Wh.
Total required Battery pack capacity is 18 kWh = 18000 wh
The individual Cell: ANR26650M1-B has
Nominal voltage = 3.3 V
Current Capacity = 2.5 Ah
So, let us assume that for 18 kwh battery pack we need supply voltage of 200 V and 90 Ah
200 V = 3.3 * Cell in series
Cell in series = 200/3.3 = 60
Now, as we know that battery pack capacity (Wh) = Total current * Total voltage = (2.5* cell in parallel) * 200
18000 = (2.5* cell in parallel) * 200
Cell in Parallel = 18000/ (2.5*200) = 36
Module capacity:-
The required battery pack combination is 60S36P
For this we decided to choose 5 series and 3 parallel module connection.
Each 5S3P configuration Module Voltage capacity = 5*3.3 = 16.5 V
Each 5S3P configuration Current Module capacity = 3*2.5 = 7.5 Ah
So, total capacity of 1 module is = 16.5 * 7.5 = 123.75 Wh
Total Cells:
Total number of cells = cell in 1 module * 144
Total number of cells = (5*3) *144
Total number of cells = 2160
1 cell capacity = 3.3* 2.5 = 8.25 Wh
So, total cell capacity = 2160*8.25
Total cells capacity = 17820 Wh = 17.82 KWh (almost 18 KWh)
We should always target more KWH than required considering the losses and connection limitations.
Weight of one cell = 76 g = 0.076kg
So, Battery pack cell weight = 0.076*2160 = 164.16 kg
Module Connection:-
For 18 KWh of total 200 V and 90 Ah battery pack capacity we need 18000/123.75 = 145.45 modules.
For Simplicity of configuration, we took 12*12= 144 modules of 5S3P.
We have to connect the cells in parallel to reach the desired capacity (mAh) and connect such parallel groups in series to achieve the nominal voltage (Volt).
In this way, to achieve 200 V battery voltage, number of 5S3P configuration in series connected modules are = 200/16.5 = 12.12 = 12.
For 90 Ah battery current, now we connected 12(90/7.5 = 12) times such (series of 12 module of 200 V) in parallel to get 90 A current from this battery pack.
Here we got the battery sizes its weight, no of cells and modules, pack size with its accessories like wires etc.
The Battery Management System (BMS) is connected to the cells modules and battery which is used to identify the critical situations like the voltage, temperature, battery capacity values at the running of the battery time. It is mainly used for the monitoring purpose and balancing of the cells in the battery pack. By this we can operate with out and damages which leads to explode at critical situations. The outlook of the BMS with the cells look like as shown.
shrinking machine is used to shrink the battery pack with certain heated temperature in the form of air in the closed loop. The code printing and the aging machine are used to print he code value of the battery cell like ANR26650M1-B and life time of the battery be calculated respectively.
The testers are used to confirm the cell total parameters like voltage, capacity, temperature, pressure, BMS, chemicals etc.
Welding of battery pack:-
Making the Correct Battery Strip Selections and Spot Welding the Nickel Strips
There are two ways to combine the ANR26650M1-B cells:
Soldering
A Spot Weld
Spot welding is always the best option, but it is much more expensive than a good soldering iron.
The ANR26650M1-B cells must be connected to one another using thick wire or nickel strips in order to create the battery pack.
Nickel strips are frequently used for this.
There are typically two types of nickel strips on the market: pure nickel strips and nickel-plated steel strips.
Although pure nickel is slightly more expensive than nickel-plated steel, it has significantly less resistance. Low resistance results in less heat being produced during charging and discharging, extending the useful life of the battery.
References:-
https://x-engineer.org/ev-design-battery-calculation/
https://www.batteryspace.com/prod-specs/6610.pdf
https://sklc-projects-2021.s3.amazonaws.com/projects/2021/53263/59106.txt