Project 1 Mechanical design of battery pack

Nanophosphate High Power LithiumIon Cell ANR26650M1-B : 

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 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 . 

Technical Specifications of ANR26650M1-B : 

Dishcarge Characteristics of ANR26650M1-B :

Applications :

a) COMMERCIAL SOLUTIONS -

Advanced lead acid replacement batteries for ,

- Datacenter UPS

- Telecom backup

- IT backup

- Autonomously guided vehicles (AGVs)

- Industrial robotics and material handling equipment

b) GOVERNMENT SOLUTIONS -

- Military vehicles

- Military power grids

- Soldier power

- Directed energy

c) GRID SOLUTIONS -

Versatile , flexible and proven storage solutions for grid , 

- Frequency regulation

- Renewables integration

- Reserve capacity

- Transmission and distribution

d) TRANSPORTATION SOLUTIONS -

Hybrid, plug-in hybrid and electric vehicle battery systems for ,

- Commercial vehicles

- Off-highway vehicles

- Passenger vehicles

Battery Pack of 18 kWh -

Assuming designing a vehicle of range 300 Km and nominal voltage for series connection be 200V .

Mathematical Calculations - 

Some required parameters , (considered from technical specifications) 

- Diameter = 0.02596 m ~ 0.026 m

- Length = 0.065 m

- Mass = 0.076 Kg 

- Single cell voltage = 3.3V

- Capacity = 6 Ah

- Max Continous Charge Current (C-rate) = 10 A

- Max Pulse Charge Current (C-rate) = 20 A 

Volume of Single Cell = 3.14*r^2*h = 0.0000344929 m^3 = 0.0344929 mm^3

Now Energy of Single Cell = Capacity * Cell Voltage = 2.6 Ah * 3.3 V = 8.58 Wh 

Now calculating Energy density of single cell , 

Volumetric energy (Wh/m^3) = Cell Energy / Volume of single cell  =  248,746.84 Wh/m^3  or 248.746 Wh/mm^3

Gravimetric energy (Wh/m^3) = Single Cell Energy / Single Cell Mass = 112.89 Wh/Kg 

Now to design a battery pack we have assumed a vehicle of range 300 Km . The battery pack will be of 18 kWh and nominal voltage will be 200 V .

So calculating per km average energy = Battery pack Capacity / Range of Vehicle =  60 Wh/km . 

Now number of cells connected is series = Nominal Voltage of series connection / Nominal Voltage of single Cell = 60.60 ~ 61 cells in series 

Energy of battery pack = Number of cells connected is series * Single cell energy = 523.38 Wh 

Number of legs of series connected in parallel = Battery Pack total energy / Energy for battery pack = 34.39 ~ 35 legs of  series                                                                                                                   

Battery Pack Capacity  = No of parallel connections * Single cell capacity = 91 Ah 

Total number of cells for battery pack = No of cells in series * No of parallel connections = 2135  

Total mass of battery pack = No of cells * Mass of single cell =  162.26 kg

Total Volume of Battery pack = No of cells * volume of single cell = 0.0736423415 m^3 or 73.64 mm^3 

Cell Peak Current = C-rate(Max pulse charge current) * Single cell capacity = 52 A 

So Battery Pack Peak Current = No of parallel connections * Single Cell Peak Current = 1820 A 

Battery Pack Peak Power = Battery Pack Peak Current * Nominal Voltage of cells in series = 364 kW                                                                                

Assembly of Battery Pack -

Cells Dimensions - 

Diameter = 26 +/- 0.5 mm 

Length = 65 +/- 0.5 mm 

Design of Single Cell - 

A cell basically consiste of Anode , Cathode , Seperator , Electrolyte , Positive and Negative Cap and Gasket . 

Cell Holder -

Cell holder is used to hold the cells or the cells get fixed at one place safely and makes proper arrangment . Most of the cell holders are made of Polypropylene or Nylon . The dimensions of cell holder is shown below in figure , 

Assembly of a pack -

  

The above figure shows the cell holder of cell assembly of 7S5P 

The assembly of a pack is as follows ,

Total No of cells = 2135 

So the pack will be assembled as 7S5P meane 7 cells in series and 5 parallel connection .  

Therefore number of packs will be = 2135 / (7*5) = 61 packs .  

So the detailed sepecification of 2135 cell battery pack is as follows , 

Battery Pack = 61 nos of 7S5P pack 

Total Capacity = 91 Ah 

Voltage = 200 V

Weight = 162.26 kg (only cells)

Total Power = 18 kWh  

Hence we have designed a battery pack of 18 kWh with cell sepcification of Li-ion battery ANR26650M1-B .