Project 1 Mechanical design of battery pack
AIM: To Build a Battery pack of capacity 18 kWh for a Cell Model: ANR26650M1-B. Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
As Per Question:
Battery pack capacity: 18 kWh
Cell: ANR26650M1-B
Calculations are made with some assumptions.
In this project, we are going to calculate all parameters which are required for the build EV battery pack. We are going to use the 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), Ampere-hour (Ah) Capacity. We also calculate all geometrical considerations like size, weight, volume, area, etc. In the end, we consider some enclosures model for our battery pack.
OBJECTIVE:
· Collecting the data of Cell: ANR26650M1-B from Nano-phosphate High Power Lithium-Ion Cell PDF ( https://a123batteries.com/anr26650m1-b-lithiumwerks-nanophosphate-3-3v-2-5ah-lithium-iron-phosphate-battery/ )
· Calculating all Electrical parameters for 18 kWh Battery Pack
· Calculating all Physical dimensions for Battery Pack
· Consider perfect enclosure for dimensions that we calculated for the Battery Pack
Here we are taking A123 systems Cell Model: ANR26650M1-B to study and build a battery pack of capacity 18 kwh.
Cell Specifications of Model ANR26650M1-B
Here we are using the cell of chemistry type LiFePO4(Lithium iron phosphate).so, the characteristics of LiFePO4 is quite different than other cell chemistries which are explained in detail.
Lithium iron phosphate has a cathode of iron phosphate and an anode of graphite. It has a specific energy of 90/120 watt-hours per kilogram and a nominal voltage of 3.20V or 3.30V. The charge rate of lithium iron phosphate is 1C and the discharge rate of 1-25C.
Structure and performance of the LiFePO4 cathode material: from the bulk to the surface
Abstract
Currently, LiFePO4 is one of the most successfully commercialized cathode materials in the rechargeable lithium-ion battery (LIB) system, owing to its excellent safety performance and remarkable electrochemical properties and is expected to have a broader market soon. Although it is widely recognized that the crystalline structure of a cathode material largely dictates its electrochemical properties (e.g., capacity, cycle life and rate capabilities), this intrinsic connection in LiFePO4 has not been systematically reviewed. Different from the previous reviews, which mainly focus on the improvement of electrochemical performance by all kinds of techniques, in this review, the relationship between its electrochemical performance and bulk/surface structure is reviewed and discussed. First, it is revealed that the intra-particle Li+ transfer is influenced by several properties of the bulk, including crystalline structures, antisite defects and electronic structures. Next, it is demonstrated that the surface/interfacial structures of LiFePO4, which can be reconstructed artificially or spontaneously, also have great impacts on the performances. Lastly, the intrinsic connection between the structure and performance is preliminarily established, showing brand-new perspectives on the strategy for further improvement and contributing to a comprehensive understanding of LiFePO4.
What is Lithium Nanophosphate?
Nanophosphate is a registered trademark for a Lithium Iron Phosphate battery technology that maximizes the performance of the standard technology. The three main areas where Lithium Nanophosphate has distinct advantages over other Lithium Iron Phosphate batteries are listed below.
Power is a positive electrode material of remarkable rate capability, critical to high power systems.
High power products can pulse at discharge rates as high as 100C and deliver superior power by weight or volume in a cost-effective solution. With their low impedance and thermally conductive design, high power cells can be continuously discharged at a 35C rate, a marked improvement over other rechargeable battery alternatives, and have consistent power over a wide state of charge (SOC) range.
Safety begins with chemistry and Nanophosphate is stable chemically, which provides the foundation for safe systems while meeting the most demanding customer requirements.
Multiple layers of protection are employed at the chemistry, cell and system level to achieve an energy storage solution with superior safety and abuse tolerance compared to metal oxide lithiumion chemistries.
Life
Nanophosphate technology delivers exceptional calendar and cycle life. At low rates our cells can deliver thousands of cycles at 100% depth of discharge (DOD), a feat unmatched by most commercial lithium ion cells. Even when cycled at 10C discharge rates, cells deliver more than 1,000 full DOD cycles. Not only does the technology retain its energy, but it also retains its power capability. Not all lithium-ion technologies behave the same. The nanoscale structure of the Nanophosphate chemistry, for example, enables battery systems with higher power, increased abuse tolerance, longer life, and the greater ability to maintain consistent power over a wide range of state-of-charge (SOC) as compared with competing lithium-ion and other chemistries.
Understanding the fundamental chemical differences between Nanophosphate and other technologies is necessary to develop a complete and accurate assessment of the optimal advanced battery system that will deliver the best performance for a given application.
Discharge characteristics of LiFePO4 (Lithium iron phosphate cell )
ANR26650M1-B Specifications
Nominal Ratings
Voltage: 3.3 Volts
Capacity: 2.5 Ah
Energy: 8.25 Wh
Specific Power: 2600 W/kg
Impedance (1KHz AC Typical) 6 mΩ
Cycle Life at 1C/1C, 100% DOD: > 4000 cycles
Cell Type: 26650 Lithium-Ion Power Cylindrical Cell
Discharging
Max Continuous Discharge: 50 A
Max Pulse Discharge Current >50% SOC (10s): 120 A
Minimum Voltage: 2 Volts
Temperature: -30ºC to 55ºC
Charging
Recommended Standard Charge: 2.5 Amps
Max Charge Rate: 10 Amps
Max Pulse Charge Current <50% SOC (10s): 25 A
Float Voltage: 3.45 Volts
Recommended charge V & Cut-off Current: 3.6 Volts, taper to 125mA
Temperature
(reduce charging current to 250mA when under 0ºC): 0ºC to 55ºC
Mechanical
Diameter: Ø25.96 +/- 0.5 mm (1.0")
Length: 65.15 +/- 0.5 mm (2.6")
Mass: 76 g
Calculation as per assumptions: - 18kWh Battery Pack
calculation for designing an 18kWh battery pack, basically 18kWh is energy require to achieve the vehicle its proper range. It is depending upon the voltage (V) parameter and ampere-hour or capacity (Ah).
Here ,we design a high voltage battery pack for an electric vehicle to achieve its range up to 220 km. For this calculation, I assumed 145.2 V a nominal voltage for series connection.
Basically, the value of the volume of the cell is used to find out the total volume of the battery pack.
- Single Cell Energy (Wh)
= Cell Capacity (Ah) x Cell Voltage (V)
= 2.6 x 3.3
= 8.58 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/m^3) = Single Cell Energy / Volume of each cell
= 8.58 Wh / 0.03451 m^3
= 248.62 Wh/m^3
Gravimetric energy (Wh/kg) = Single Cell Energy / Single Cell Mass
= 8.58 Wh / 0.076 kg
= 112.89 Wh/kg
Calculation of High Voltage Battery Pack
For design and calculation of battery pack here, I assume a vehicle to achieve 250 km in 18 kWh battery pack. Also, I assume 145.2 nominal voltage for series connection.
So,
Vehicle Range = 250 KM (assumed)
Battery Pack capacity = 18.121 kWh or 18120.96 Wh (For better and accurate calculation here I change kWh)
Now,
We will calculate per km average energy = 18120.96 / 250
= 72.483 Wh/km
Therefore,
Battery Pack total energy = Average energy x km
= 72.483 x 250
= 18120.96 Wh or 18.120 kwh
Let’s assume Nominal voltage for series connection = 145.2 V, Basically, this depends upon the motor power, We can decide the value according to the motor.
- Number of cells connected in series
= Nominal voltage of series connection / Nominal voltage of a single cell
=145.2 V / 3.3 V
= 44
44 Cells will be connected in a series connection to provide a proper voltage.
- Energy for battery pack (wh)
= No. of cells connected in series x Single-cell energy
= 44 x 8.58 wh
= 377.52 wh
- Number of cells connected in parallel
= Battery pack total energy (wh) / Energy for battery pack (wh)
=18120.96/377.52
= 48
48 cells will be connected in parallel to provide a proper capacity power.
- Battery pack total energy (wh)
= No. of cells connected in parallel x Energy for battery pack (wh)
= 48 x 377.52
= 18120.96 wh or 18.120 kWh
- Battery pack capacity
= No. of cells connected in parallel x Single cell capacity (Ah)
= 48 x 2.6 Ah
= 124.8 Ah
The value of battery pack capacity is used for the total power required by the vehicle.
- Total number of cells for battery pack
= No. of cells connected in parallel x No. of cells connected in series
=48x44
= 2112
2112 Cells will be used to make a complete battery pack.
- Mass of battery pack
= Total no. of cells for batter pack x Mass of single cell
= 2112 x 0.076 kg
= 160.512 kg
it is the total weight of cells connected in parallel and series.
- Total volume of the battery pack
= Total no. of cells for batter pack x Volume of single cell
= 2112 x 0.0345
= 72.89 m^3
This is the volume of2112 cells which are used in the battery pack system.
- Cell peak current (A)
= C rate (Max Pulse Charge Current) x Single cell capacity
= 20 x 2.6
= 52 A
- Battery pack peak current (A)
= Cell peak current x No. of cells connected in parallel
=52X48
= 2496 A
It is used for the operation of the battery pack. By this way, a vehicle will decide how much power is required to move.
- Battery pack peak power (W)
= Battery pack peak current x Voltage of series connection
= 2496 A x 145.2
= 3624192 or 362.42 W
- Cell continuous current (A)
= Crate (Max Continuous Charge Current) x Single cell capacity
= 10 x 2.6
= 26 A
- Battery pack continuous current (A)
= Cell continuous current x No. of cells connected in parallel
= 26 x 48
= 1248 A
This is the power which is supply continue to the whole battery pack system.
- Battery pack continuous power (W)
= Battery pack continuous current x Voltage of series connection
=1248 x145.2
= 18120.96 or 18.120 Kwh
detailed battery pack drawing along with its enclosure.
BATTERY HOLDER ,SPACE For CELL CYLINDRICAL LI-ION
Nickel Strips
Nickel strip is generally used in battery building. Its due to its efficiency of usage in spot welding and soldering its high corrosion resistance as well over time. It has good properties and excellent resistance to many corrosive environments. The pure nickel will never get rust after it applied to battery packs. It won’t affect the current transfer between batteries.
Pure nickel strips are the material you want, but many vendors swap out it for nickel-plated steel strips, which are poorer and have greater resistance – not suitable for most battery projects.
100% pure nickel strip. verify all of our strips to assure that you are getting the high-quality pure nickel. It also solder incredibly quickly, so you can weld them onto your existing busbar connections to raise the supply of current you can pull through the busbars. The benefits are nearly limitless!
Battery enclosure
Design Benefits
• Up to 50 percent 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 aluminum solution for mass
production electric vehicles when compared to
aluminum extrusion and casting-intense designs.
• Low price premium on $/kg saved compared
to equivalent steel designs at substantially
lower weight.
https://www.novelis.com/automotive/electric-vehicle-battery-enclosure/
As we know now
Power (p)= Voltage (v) * Current (i) kw
p= v * i
3.3 *2.5 =8.25 kw
To get 18kwh, we are assuming 48s 48p.
i.e., 48*48 =2304 cells
series connection gives 48*3.3 =158.4 v
parallel connection gives 48* 2.5 =120 A
from this we can get
158.4* 120 =19.008 kwh energy or capacity.
we design battery pack for 48s and 48p cell along with battery spacers to hold cells and for their connection nickel strip is used.
when cells are connected by nickel strip spot welding should be used so that cell does not get damage.
Battery Pack Assembly:
The design of the outer package or housing of the battery depends to a great extent on the components it must accommodate and the physical protection it has to provide for them. These components are not just the cells, but also protection devices, electronic circuits, interconnections, and connectors which must all be specified before the final battery case can be designed. For high-power, high-energy batteries robust packaging is required for safety reasons.
Cell holder dimensions:
Height = 10mm
length = 29mm
width = 29mm
weight = 5gm
Arrangement of cells in 60S30P together is not the best arrangement as it will take:
29mm*60 cells =1740mm for 60 cells in series
29mm*36 cells =1044mm for 36 cells in parallel so, a total of (1740*1044) space required and all the cells in a single matrix will lead to poor thermal management as we are employing the air-cooled technique in the battery pack the ventilators will not be able to cool the inner cells as the air will not reach till the inner cells.
Also, according to the18KWh capacity, the application might be in a small 2-seater Electric car the area taken by the battery pack assembly is 1.74*1.04 meters.
The solution for both the space required and the thermal management of battery pack is to create a module of 10S6P. This will create 33V 15Ah module. Arranging such 10S6P modules in 6S6P manner will create a 60S36P array giving 198V 90Ah.
Step 1: Arrange all the cell holders in 10S6P manner.
Step 2: Arrange all the cells in cell holders in 10S6P manner.
Step3: Add cell holders on the upper side of cells and add nickel strips for series and parallel connections.
Now one module is complete and such 36 modules are required for 6 series and 6 parallel connections. The below image shows the arrangement of 36 such modules this completes the battery pack assembly with the required combination of cells.
Thermal Design:
Thermal management is a major issue in high power designs, particularly for automotive applications. See details in the Thermal Management section. As part of the battery system, it may be necessary to provide air- or water-cooling ducts, pumps or fans and heat exchangers for high temperature working or heaters for operating in low temperature environments. The layout of the cells should be conducive to managing heat flows within the pack.
We have used Air-Cooling Technique in the battery pack assembly.
Passively air-cooled batteries like those in early Nissan LEAF cars have demonstrated unacceptable hot weather performance, even when using a lower energy, thermally tolerant battery chemistry. Clearly, Tesla will need robust temperature control for Model 3 batteries as they have for the batteries in Models S/X.
Cooling (and heating) the battery cells by circulating air within the sealed battery pack through a heat exchanger connected to the car's HVAC system, and then over the cells can achieve the same or even better thermal control as Tesla's current liquid cooling scheme. The difficulty is that quite large volumes of air must be moved past the cells, and that requires large cooling passages and much larger battery modules to hold a given number of cells.
This air-cooled battery module is sized for extreme Supercharging.
Air-Cooled Module Is Different
Air-cooled battery modules offer several advantages and some shortcomings when compared with liquid cooled modules such as Tesla currently uses. The Air-cooled module is much simpler because air being an electrical insulator can be in direct contact with the cells without short circuiting the battery. Water-glycol liquid coolant is electrically conductive so special thermally conductive and electrically insulating materials must always separate battery cells and coolant.
Liquid-cooled modules require coolant tubes, fittings, insulating coverings and the like to channel coolant amongst the cells. Air, on the other hand, can be routed through the array of cells by nothing more than simple passages molded into the plastic module housing.
The drawback is that air being less dense requires larger channels between cells making the air-cooled module substantially larger.
We will consider only battery modules containing lots of little round cells because that is the type of cell Tesla has committed to, unlike legacy carmakers who mostly prefer using fewer, bigger flat prismatic or pouch cells. Incidentally, we will in a bit, see once again, why Tesla's is the right choice.
In a Tesla style battery module, cells are connected in parallel to form cell groups, and these groups are then connected in series. Small gage wires connect each cell's positive and negative terminal to a bus-bar that connects the cell to other cells in its parallel cell group. By arranging the air-cooled module with each group of parallel cells in single-file and spacing the cell groups apart to form cooling air passages, the buss-bars can be aligned with the cooling air passages as illustrated below.
In the air-cooled battery module, groups of parallel connected cells are lined-up single file with air passages between cell groups. Buss-bars connecting cells in parallel are then placed above or below the air passages. - Author
By taking advantage of the wide air-cooling passages to locate the buss-bars, two important advantages are gained. First, because the bus-bars can run between rows of cells the buss-bars can be in the same plane as the cell ends. With Tesla's dense, liquid cooling scheme, cells are so close together that the bus-bar must be positioned above/below the cells, with small 'access holes' through which the cell connecting wires run. This allows the overall height of the air-cooled modules to be slightly less, or the cells to be slightly longer.
There is a second, more significant advantage that comes with placing buss-bars beside rather than above/below the cells. It is that with buss-bars beside rather than above the cells, a single cell within the pack can be removed and replaced without having to break the wiring to all the other cells connected to a bus-bar.
Battery Packing:
The battery casing must provide the mechanical and electrical interfaces to the product it is designed to power as well as to contain all the components outlined above. This is how the battery pack will be which is manufactured by the companies and employed in an Electric Vehicle.
REFERENCES:
· https://datasheetspdf.com/pdf/1424845/A123Systems/ANR26650M1-B/1
· https://a123batteries.com/anr26650m1-b-lithiumwerks-nanophosphate-3-3v-2-5ah-lithium-iron-phosphate-battery/
· https://youtu.be/EgqrT5EA3ag
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