Project 1 Mechanical design of battery pack

Mechanical design of ANR26650M1-B cell to convert it into 18KWh battery pack

Cell:

It consist of a anode and cathode seperated by electrolyte. A battery is made of more cells. 

Battery Pack:

More battery module are arranged in series and parallel to provide the required electric energy for teh elctrical and electronic device used in the system. Mostly Lithium ion battery is used due to its high power density in EV application.

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 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

Performance Charactersitics of this cell is :

This LFP battery has high power and energy density with excellent life cycle in lighter weight. Also the impedance growth also incresases in a slow rate as age progressses. Wide SOC can be used with high energy.

Application of ANR26650M1-B cell:

COMMERCIAL SOLUTIONS
Advanced lead acid replacement batteries for:
+ Datacenter UPS
+Telecom backup
+IT backup
+Autonomously guided vehicles (AGVs)
+ Industrial robotics and material handling equipment

GOVERNMENT SOLUTIONS
+ Military vehicles
+ Military power grids
+Soldier power
+ Directed energy

GRID SOLUTIONS
+ Frequency regulation
+ Renewables integration
+ Reserve capacity
+ Transmission and distribution

TRANSPORTATION SOLUTIONS
Hybrid, plug-in hybrid and electric vehicle battery systems for:
+Commercial vehicles
+ Off-highway vehicles
+Passenger vehicles

Design overview:

Factors that decide the design of battery pack:

Capacity and voltage:

Capacity and voltage of each cell will decide the battery packs capacity and voltage. Higher battery volateg is acheived by adding o=more number cells in series. Also battery capacity is increases by adding more parallel legs.

Cell voltage is fixed by the manufacturer. Cell capacity depends on surface area of the elctrode and volume of electrolyte. Parallel cells should be avoided so that fewer cells will require fewr electronics.

CELL CONFIGURATION:

Shap and dimenesion of battery pack is governed by the application we are going to use for. Cylindrical cells are simpler option for cooling in case of high power application. Pouch cells are more compact.

Battery Electronics:

Besides the cells many battery packs now incorporate associated electronic circuits. These may be protection devices and circuits, monitoring circuits, charge controllers, fuel gauges, and indicator lights. Electronics for high power multi-cell packs also include cell balancing and communications functions.

 The packs may also be designed to deliver more than one voltage from the basic cell combination, although applications requiring multiple voltage sources are more likely to make provision for this within the application.

 In addition to the basic battery support electronics the battery pack may include other functions such as heaters to extend the lower working temperature or solar cells to keep the battery fully charged. These circuits in turn have their own control circuits. Space, fixing points and methods and interconnections need to be allocated for all these electronic circuits.

 Software:

Sofware is a major component of Lithium batteries, particularly for automotive applications . Control systems are required to keep the cells within their specified operating range and to protect them from abuse. Fuel gauging needs complex algorithms to estimate the state of charge (SOC). Communications with other vehicle systems are needed for monitoring the battery status and controlling energy flows.

Internal connection :

Low power cells are connected using nickel strips which is welded to the cell terminals.Electronic components are mounted over it as PCB.

Thermal design:

Thermal management system is one the main thing in case of high power battery pack. Air or water cooling ducts , pumps or fans and heat exchagers are used to avoid cells to go to thermal run away.The cells shuould be convective to avoid heat flow between the cells.

Battery Packaging:

Cell packaging designs and their combinations in modules and battery packs are offered in a huge variety, for primary and secondary batteries, and for different applications.The wording “battery module” is usually only used associated with high-power batteries. It denotes an assembly of cell packages, safety features like temperature,voltage and chargemonitoring, as well as a battery management system (BMS),cooling / heating system and a base plate or housing.

Especially Liion cell configurations must contain electronic safety circuitry to prevent damage to the user. Since the overall capacity and voltage of a module are defined by the
weakest cell in the configuration, it is wise to monitor state of charge (SOC) and state of health (SOH), amongst other parameters already on cell level. Battery Management
Systems provide this, combined with communication features to levelize charging and discharging, or even bypass bad cells. Tesla Motors, for example, use standard 18650 cells for their modules and put all their efforts of optimization into the BMS, rather than optimizing the cells. A BMS protects the battery by preventing it from running outside safe operation mode, such as over-current, over-voltage (during charging), under-voltage (during discharging), over-heating, undercooling, or overpressure. It is therefore a very important part of the module. 

Although highly desireable for cost-effective production, a lot of production steps today still require manual handling, as indicated above. This is partly due to the precision required, partly a lack of measurement tecchnology, and partly an
economical issue. On top of the mechanical automation, there is still a lack of automation on the information technology side, from data mining up to Manufacturing Execution Systems (MES). To set up this line integration, connecting single machines to highly automated turn-key lines must be a goal for the entire industry and poses a huge opportunity to the production equipment makers in the medium term. Whereas clean room conditions and dry environment are an essential prerequisite in electrode and cell production, it is workplace safety in module and pack assembly that plays an important role for the production environment.Clearly shows the
high voltages up to 600 Volts that occur during all assembly steps.

BATTERY PACK DESIGN:

Cell radius = 0.013m

Cell height = 0.065m

cell capacity = 2.5Ah

Weight of cell = 76g

Nominal voltage = 3.3V

Power = 2600W/kg

Therefore,

cell volume = pi * cell redius * cell height

                   = 3.14*0.013*0.065

                  = 2.653 x (10^-3) m^3

Cell Energy = cell voltage * cell capacity = 3.3 * 2.5 = 8.25KW

As per the question capacity is 18kWh

So let us consider,

Battery pack voltage = 600V

Total battery capacity = total battery pack energy/total battery pack voltage = 18000/600 = 30 Ah

Total Battery pack capacity = 30Ah

So battery pack is 600V and 30Ah

Total number of cells required to produce the amount of energy:

No.of cells in parallel = battery pack capaciy/nominal cell capacity = 30/2.5 = 12

No.of cells in parallel = 12 cells

No.of cells in series = battery pack capaciy/nominal cell voltage  = 600/3.3   =181.81 = 182 cels

No.of cells in series = 182 cells

Our battery pack will be a combination of 182s 12p cell

Therfore,

Total number of cells = 182*12 = 2160 cells

Total number of cells in battery pack = 2160 cells

Therefore, our battery pack will contain total of 2160 ANR26650M1-B cells which will produce 18000Wh of Energy.

Calculation of dimension of battery pack:

Length of battery pack = no.of cells in series * cell Diameter = 182*0.026 = 4.732 m

Length of the battery pack = 4.732m

Width of battery pack = no.of cells in parallel * cell Diameter = 12*0.026 = 0.312m

Width of battery pack = 0.312m

Height of battery pack = height of each cell = 0.065m

Height of battery pack = 0.065m

Therfore,

Area of Battery pack = Length of battery pack * Width of battery pack    =    4.732 * 0.312 = 1.47m^2

Area of Battery pack = 1.47m^2

Volume of battery pack = Area of Battery pack * Height of  battery pack  =  1.47*0.065 =0.09596 m^3

Volume of battery pack = 0.09596 m^3

Total weight of battery pack = total number of cells * weight of each cell = 2160 * 0.076 = 164.16kg

Total weight of battery pack = 164.16 kg