Project 1 Mechanical design of battery pack

AIM:Prepare a detailed battery pack drawing along with its enclosure.

GIVEN:

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

EXPLANATION:

Nanophosphate® Lithium-ion battery technology offers stable chemistry, faster charging, consistent output, excellent cycle life and superior cost performance. It 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 lithium-ion chemistries.

ANR26650M1-B Specifications
Nominal Ratings
Voltage: 3.3 Volts
Capacity: 2.56 Ah
Energy: 8.5 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 Discharage: 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

Certifications
Transportation: UN 3480 (UN38.3), CIQ
Safety: UL 1642, IEC 62133

The LithiumWerks ANR26650M1-B is the next generation of A123 Systems’ pioneering 26650 cylindrical cell, now with greater power and energy density and lower impedance. This versatile lithium ion cell is suitable for a wide variety of applications and system designs. Proven performance in the toughest conditions, combining durability, reliability, and safety, the ANR26650 cell offers an excellent combination of price-performance.

Cylindrical Cell Primary Applications:

• Portable high power devices
• Stationary battery backup systems
• Grid stabilization energy storage systems
• Commercial truck and bus hybrid electric vehicles (HEVs)

Lithium Ion Cell Benefits:

• Power: Over 2,600 W/kg and 5,800 W/L
• Safety: Excellent abuse tolerance and environmentally friendly
• Life: Excellent calendar life, 10X cycle life vs. conventional lithium ion

Battery packs become the key component in electric vehicles (EVs). The main costs of which are battery cells and assembling processes. The battery cell is indeed priced from battery manufacturers while the assembling cost is dependent on battery pack designs. Battery pack designers need overall cost as cheap as possible, but it still requires high performance and more safety. Material selection and assembly method as well as component design are very important to determine the cost-effectiveness of battery modules and battery packs. Therefore, this work presents Decision Matrix, which can aid in the decision-making process of component materials and assembly methods for a battery module design and a battery pack design.

The aim of this study is to take the advantage of incorporating Architecture Analysis method into decision matrix methods by capturing best practices for conducting design architecture analysis in full account of key design components critical to ensure efficient and effective development of the designs. The methodology also considers the impacts of choice-alternatives along multiple dimensions. Various alternatives for materials and assembly techniques of battery pack are evaluated, and some sample costs are presented. Due to many components in the battery pack, only seven components which are positive busbar and Z busbar are represented in this paper for using decision matrix methods

Assumptions:

We are assuming the overall voltage required to operate the motor and other acessories of electric vehicle as 400V.

So we have construct the battery pack of 18KWh for a 400 V input voltage motor.

Construction of battery pack:

To construct a battery pack initially we have to estimate the voltage requirement of the overall load of vehicle.

We had assumed as 400V as mentioned above.

Then the battery modules should be created in such a way that the overall voltage is matched with the load requirement voltage.

The modules can be created in series/parallel connections of individual cells.Then every modules should be connected in series/parallel to construct final battery pack.

In series connecction-Voltage added and Current remains same.

In Parallel connection-Voltage remains same and Current gets added.

Here in our case single cell voltage is 3.3V and a capacity of 2.56Ah.Energy provided from sigle cell is give 8.5Wh.

So,for 18KWh battery pack we need approximately(18000/8.25=2182 cells).

We have to create a single module to produce 400V for our load requirement.

So to obtain 400 V output ,cells are connected in series where voltage become added and current remains same.

To obtain 400V ,no of cells required is approximately(400/3.3=122 cells).

Thus single module gives as 400V from 122 cells but energy of one module is not enough to run the vehicle as motor power rating is higher.The energy generated from

single module is (122*8.25Wh=1006.5Wh).

So to construct a battery pack with 18KWh with not exceeding 400V the modules are connected in parallel.In this parallel connections the currents are getting added and

voltage remains same as 400V.As current increases the power of battery pack increase to run the motor load of high power rating.

Now we have to find how many similar modules should be connected in parallel to acheive 18KWh battery pack.

This can be calculated as (18KWh/1006.5Wh =17.88),which gives as nearly 18 similar modules should be connected in pararallel to acheive 18KWh battery pack.

Thus the battery model is said to be 122S18P configuration(122 series and 18 parallel connections),which gives us (122*18 =2196 cells).From this we have created overall capacity of battery pack as (2196*8.25Wh=18117Wh) which is slightly higher than 18KWh.

The overall Capacity(Ah) of battery pack is given as (2.5Ah * 18 = 45Ah).

Which means it provided 45 A of current continuously for one hour to full discharge.

Thus 18 modules should be arranged in a way as battery pack to fit in an EV chasis.

Enclosure construction:

To find overall enclosure volume we have to find the volume of single module volume consist of 122 cells in series connection and multiplied with 18 parallel connected module volume.

Single module,

Let as assume 122 cells(single module) are divided into 2 modules of 61+61 cells.

The length of the module=No.of cell in row*(Cell dia + Margin at both side of cells) + clearance at side(2(cell dia + margin)).

=61*(26+4) +60 =1890mm.

The bredth of the module=(cell dia +Margin of both side of cells + clearance)

=26+4+60 =90mm.

Height of the module=Height of cell + connectiing strip thickness,wires say 35mm

=65+35 =100 mm.

Thus the volume required for single module is 1.8*0.09*0.1 = 0.0162 m3.

Total number of modules assumed are 18*2 =36 modules,since single module is divided into two modules.

Therefore total volume required for battery pack of 122S18P configuration construction is 0.0162*36 = 0.583 m3.

Thus from the above results it is assumed approximately 1m3 of volume should be used for EV battery pack with additional ventilation spaces for pack.

We can assume that two modules are combained into one cabinet. So 18 cabinets should be connected to form final battery pack.

Materials and process in battery pack construction:

Battery pack constructions consist of three major levels of processings namely cell level,module level,pack level constructions.

The electrodes are combined with electrolyte to various cell models as cylindrical,prismatic,pouch type cells.

After case sealing cells are combained to form module level construction.Finally these modules are combained to form pack level constructions.

Joining technologies of cells:

The interconnections between cells/modules are practised by various welding techniques.Some of them are,

• Ultrasonic metal welding.
• Resistance welding.
• Laser beam welding.
• Wire bonding.
• Mechanical Jooining.

Ultrasonic metal welding-

Ultrasonic metal welding or UMW, is a solid-state welding technique which forms a bond by applying moderate static pressure and an ultrasonic oscillation of about 20 kHz between two

parts of metal. The solid-state weld is formed through the high frequencymotion between the parts causing continuous shearing and plastic deformation, while also removing any oxide layers

or contaminants.

Most metals can be ultrasonically welded and the method is excellent for welding together thin foils, as well as thicker sheets with spot or seam welds and also wires.

The four types of materials welded in this process can be seen as,

a)Aluminium wire welding on copper.

b)Copper and aluminium welding.

c)Multilayered copper foil welding.

d)Ultrasonic seam welding.

Resistance spot welding-

One of the oldest welding methods is resistance spot welding (RSW).RSW is a technique where two or more metal sheets are welded together through the application of an electrical current

and pressure between two electrodes. The electrical resistance of the material at the interface results in the generation of heat and melts the materials together without the use of

filler material or gases.

The temperature increases in the affected area, the interface, and eventually reaches the material’s melting point. A weld nugget forms in the affected area after cooling.

This is a small volume of the material which has melted and then fused together.

Laser beam welding-

Laser beam welding or LBW is a welding technique in which a laser beam provides a concentrated heat source that fuses the materials together.

LBW is commonly performed using keyhole mode welding in which the extreme power density of the laser beam causes the metal to melt and evaporate.

As the metal atoms evaporate from the surface, forces in the opposite direction of the evaporation causes a local vapor pressure. The vapor pressure creates a hole which is known as the

keyhole by depressing the molten metal.

Here below shown the welding of busbars to cylindrical battry cans.

Enclosures:

Cells in series connection-

When you connect cells together in series, it doesn’t change the amps or the capacity, it only raises the voltage of the pack. Hooking them up in series means that you connect the positive end

of one cell (or P-group) to the negative end of the other as shown below.

Cells in Parallel connections-

If you take several cells and connect their same-type electrodes in parallel, they all will act as though they are one large cell. Also, when you first connect them to each other,

they must be at the same level of charge.

Cell houlders-

These houlders are used for houlding the individual cells in a better posture without mis-assemble.The connections can be made accordingly to make series connections and

parallel connections to form the required module dimensions.

After installind the cells in a individual module the entire maximum positive terminal and maximum negative terninal are made under single pair of

terminals as shown below.

Here shown the cells are arranged and welded without using cell houlders as,

They are just covered by polimer sheet after the interconnections are made. Mostly connections with cell holders should be recommanded for better

safety concerns.

Battery Cabinet arrangements-

Each modules are interconnected in series or parllel according to the requirement and packed as a single large cabinet pack as shown below.

Battery pack arrangement:

Finally the overall battery pack after the arrangement of all cabinet connections with enclosure looks like this as shown below,

Vents holes are present with enclosure for cooling/heating the battery pack temperature according to its environment conditions.

Different cell types are used by different manufacturers of EV such as Cylindrical,Prismatic,Pouch types.

The pack constructions are different for every manufacturers.

Below shown the battery pack constructios process of Tesla,BMW and Nissan Leaf.

.

This is 4S4P battery pack of capacity 3kWh with Cell: ANR26650M1-B

The Battery Cell is a small, rectangular component roughly the geometry of a paperback book. These battery cells are assembled together in frames to form Battery Modules. These modules are then linked together via a myriad of electrical connections and enclosed in the Battery Pack which is assembled directly to the automobile frame. The following arrow diagram below is a compass to understand the process terminology.

Battery Cells -> Battery Modules -> Battery Pack

The process outlined in this article will begin with taking the battery cells out of packaging. This article will discuss the fabrication process using the battery cells as the “raw material” in the battery pack fabrication process. These small individual cells are typically manufactured at other, specialized facilities and arrive at the automobile fabrication plant as completed products. This workflow is the vision for the vaulted Tesla Gigafactory in Nevada which will produce all the battery cells required for the Tesla’s automotive assembly facilities.

The individual battery cells are simply metallic cartridges that contain an anode, cathode, and separator immersed in an electrolyte fluid.

The machine components that unpack the battery cells from packaging are comprised of many components such as power cables, roller conveyors, rotary shafts, and linear ball bushings.

The fixtures that check the battery cells are also comprised of dozens of components such as aluminum extrusions, configurable mounting plates, timing belt/pulley systems, circular cordsets, and circular connectors.

The next step in the process involves assembling the battery cells into battery modules. Typically, there are about 12 battery cells per battery module, but this varies across automotive make and model. The modules stack within a metallic frame. This frame comprises the module housing and protects the cells from physical shock loads.

This assembly process is highly automated and involves many MISUMI configurable machine components. The most visible of these components are the timing and conveyor belts which run the workpieces through the process.

Conveyor Timing Belt

The last step in battery pack fabrication is assembling the modules into the battery pack housing. This step involves a significant number of electrical hookups and fine-tuning. For example, the Nissan Leaf EV contains 48 battery modules which are all connected together via electrical monitoring equipment. These modules are typically picked and placed by an automated robotic assembly arm into the battery pack housing. After all the modules are placed into the housing they are manually connected together by an automotive technician. After all connections have been made, the battery pack housing cover is placed manually; finally, an automated robot arm is typically used to drill all screws thus completing the battery pack fabrication process.

Nissan Leaf
Tennen-Gas, CC BY-SA 3.0, via Wikimedia Commons

The MISUMI components that are typically employed in this final step involve control and instrumentation cables, sensor cordsets, angle brackets, locating pins, shims and spacers, and pressure gauges.

From this step, the completed battery pack is ready to be assembled into the automotive frame. Indeed, each EV battery pack could not be fabricated without the critical manufacturing functions performed by dozens of machined components including MISUMI components.

CONCLUSION:

Hence we have prepared the detailed battery pack of capacity: 18 kWh ans cell Cell: ANR26650M1-BNanophosphate® Lithium-ion drawing along with its enclosure.