The high voltage battery it is one of the most important component of a battery electric vehicle (BEV). The battery parameters have a significant influence on other components and attributes of the vehicle, like:

• maximum traction motor torque
• maximum regeneration brake torque
• vehicle range
• vehicle total weight
• vehicle price

Pretty much all major aspects of a pure electric vehicle (EV) depend on the parameters of the high voltage battery.

For our electric vehicle battery design we are going to start from 4 core input parameters:

• chemistry
• voltage
• average energy consumption of the vehicle on a driving cycle
• vehicle range

A battery consists of one or more electrochemical cells (battery cells) which are converting chemical energy into electrical energy (during discharging) and electrical energy into chemical energy (during charging). The type of elements contained within a battery and the chemical reactions during discharging-charging events define the chemistry of a battery.

A battery cell consists of five major components: electrodes – anode and cathode, separators, terminals, electrolyte and a case or enclosure. For automotive applications there are different types of cells used [1]:

Individual battery cells are grouped together into a single mechanical and electrical unit called a battery module. The modules are electrically connected to form a battery pack.

There are several types of batteries (chemistry) used in hybrid and electric vehicle propulsion systems but we are going to consider only Lithium-ion cells. The main reason is that Li-ion batteries have higher specific energy [Wh/kg] and specific power [W/kg] compared with other types [2].

The voltage level of the battery determines the maximum electrical power which can be delivered continuously. Power P [W] is the product between voltage U [V] and current I [A]:

The higher the current, the bigger the diameter of the high voltage wires and the higher the thermal losses. For this reason, the current should be limited to a maximum and the nominal power obtained by having a higher voltage. For our application we are going to consider a nominal voltage of 400 V.

In the article EV design – energy consumption we have calculated the average energy consumption for propulsion E_p as being 137.8 Wh/km on WLTC drive cycle. On top of the energy needed for propulsion, the high voltage battery must supply the energy for the vehicle’s auxiliary devices E_aux [Wh/km], like: 12 V electrical system, heating, cooling, etc. Also, we have to consider the efficiency of the powertrain η_p [-] during the conversion from electrical energy to mechanical energy.

For the auxiliary devices energy consumption we are going to use data from [3], which contains the typical power requirements of some common vehicle electrical components (auxiliary loads). The prolonged electrical loads (headlights, multimedia, etc.) and intermittent loads (heater, brake lights, wipers, etc.) use on average 430 W of electrical power. The duration of the WLTC cycle is 1800 s (0.5 h), which gives an energy of 215 Wh for the auxiliary loads. If we divide it to the length of the WLTC driving cycle (23.266 km), we get an average energy consumption for the auxiliary loads E_aux of 9.241 Wh/km.

Even if Wh/km is not really energy but factorised energy, since it’s dived per unit of distance (km), for simplicity, we are going to refer to it as average energy.

The direct current (DC) supplied by the battery is converted into alternated current (AC) by the inverter. This conversion is taking place with an associated loss. Also, the electric motor and driveline have some losses which we need to consider. For this exercise we are going to use an average efficiency η_p of 0.9 from the battery to the wheel.

Replacing the values in (2) gives the average energy consumption:

The battery pack will be designed for an average energy consumption of 161.7451 Wh/km.

Battery pack architectures

All high voltage battery packs are made up from battery cells arranged in strings and modules. A battery cell can be regarded as the smallest division of the voltage.

Individual battery cells may be grouped in parallel and / or series as modules. Further, battery modules can be connected in parallel and / or series to create a battery pack. Depending on the battery parameters, there may be several levels of modularity.

The total battery pack voltage is determined by the number of cells in series. For example, the total (string) voltage of 6 cells connected in series will be the sum of their individual voltage.

In order to increase the current capability the battery capacity, more strings have to be connected in parallel. For example, 3 strings connected in parallel will triple the capacity and current capability of the battery pack.

The high voltage battery pack of Mitsubishi i-MiEV consists of 22 modules made up from 88 cells connected in series. Each module contains 4 prismatic cells. The voltage of each cell is 3.7 V and the total voltage of the battery pack 330 V.

Another example is the high voltage battery pack of Tesla Model S, which has:

• 74 cells in a parallel group
• 6 groups in series for a module
• 16 modules in series
• 7104 cells in total

Battery pack calculation

In order to chose what battery cells our pack will have, we’ll analyse several battery cells models available on the market. For this example we are going to focus only on Lithium-ion cells. The input parameters of the battery cells are summarised in table below.

Note: Since battery cells manufacturers come up with newer models continuously, it might be the case that the data used in this example is obsolete. This is less important since the aim or the article is to explain how the calculation is done. The same method can be applied for any other battery cells.

Manufacturer	Panasonic	A123-Systems	Molicel	A123-Systems	Toshiba	Kokam
Type	cylindrical	cylindrical	cylindrical	pouch	pouch	pouch
Model	NCR18650B	ANR26650m1-B	ICR-18650K	20Ah	20Ah	SLPB7570270
Source	[4]	[5]	[6]	[7]	[8]	[9]
Length [m]	0.0653	0.065	0.0652	0	0	0
Diameter [m]	0.0185	0.026	0.0186	0	0	0
Height [m]	0	0	0	0.227	0.103	0.272
Width [m]	0	0	0	0.16	0.115	0.082
Thickness [m]	0	0	0	0.00725	0.022	0.0077
Mass [kg]	0.0485	0.076	0.05	0.496	0.51	0.317
Capacity [Ah]	3.2	2.5	2.6	19.5	20	15.6
Voltage [V]	3.6	3.3	3.7	3.3	2.3	3.6
C-rate (cont.)	1	10	1	1	1	2
C-rate (peak)	1	24	2	10	1	3

Based on the cell parameters provided by the manufacturers, we can calculate the energy content, volume, gravimetric density and volumetric density for each cell.

The volume of each cell is calculated as:

• cylindrical cells, V_cc [m³]

where:
D_bc [m] – battery cell diameter
L_bc [m] – battery cell length

• pouch cells, V_pc [m³]

where:
H_bc [m] – battery cell height
W_bc [m] – battery cell width
T_bc [m] – battery cell thickness

The battery cell energy E_bc [Wh] is calculated as:

where:
C_bc [Ah] – battery cell capacity
U_bc [V] – battery cell voltage

The battery cell energy density is calculated as:

• volumetric energy density, u_V [Wh/m³]

• gravimetric energy density, u_G [Wh/kg]

where:
m_bc [kg] – battery cell mass

The energy density for each cells are summarised in the table below.

Manufacturer	Panasonic	A123-Systems	Molicel	A123-Systems	Toshiba	Kokam
Type	cylindrical	cylindrical	cylindrical	pouch	pouch	pouch
Model	NCR18650B	ANR26650m1-B	ICR-18650K	20Ah	20Ah	SLPB7570270
Energy [Wh]	11.52	8.25	9.62	64.35	46	56.16
Volume [l]	0.017553	0.034510	0.017716	0.263320	0.260590	0.171741
Energy density gravimetric [Wh/kg]	237.53	108.55	192.40	129.74	90.20	177.16
Energy density volumetric [Wh/l]	656.31	239.06	543.01	244.38	176.52	327

In order to have a better overview of the cells parameters and to compare them easier, the main parameters are displayed as bar graphs in the images below.

Image: Battery cell voltage	Image: Battery cell capacity
Image: Battery cell volumetric energy density	Image: Battery cell gravimetric energy density

With the above cell parameters and the core requirements for the battery (nominal voltage, average energy consumption and vehicle range), we calculate the main parameters of the high voltage battery.

The required battery pack total energy E_bp [Wh] is calculated as the product between the average energy consumption E_avg [Wh/km] and vehicle range D_v [km]. For this example we’ll design the high voltage battery pack for a vehicle range of 250 km.

The following calculations are going to be performed for each cell type. For this example we are going to consider that the battery pack is made up only from several strings connected in parallel.

The number of battery cells connected in series N_cs [-] in a string is calculated by dividing the nominal battery pack voltage U_bp [V] to the voltage of each battery cell U_bc [V]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

The energy content of a string E_bs [Wh] is equal with the product between the number of battery cells connected in series N_cs [-] and the energy of a battery cell E_bc [Wh].

The total number of strings of the battery pack N_sb [-] is calculated by dividing the battery pack total energy E_bp [Wh] to the energy content of a string E_bs [Wh]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

We can now recalculate the battery pack total energy E_bp [Wh] as the product between number of strings N_sb [-] and the energy content of each string E_bs [Wh].

The battery pack capacity C_bp [Ah] is calculated as the product between the number of strings N_sb [-] and the capacity of the battery cell C_bc [Ah].

The total number of cells of the battery pack N_cb [-] is calculated as the product between the number of strings N_sb [-] and the number of cells in a string N_cs [-].

The size and mass of the high voltage battery are very important parameter to consider when designing a battery electric vehicle (BEV). In this example we are going to caclulate the volume of the battery pack considering only the battery cells. In reality there are other factors to consider, like: electronic circuits, cooling circuit, battery casing, wiring, etc.

The battery pack mass (cells only) m_bp [kg] is the product between the total number of cells N_cb [-] and the mass of each battery cell m_bc [kg].

The volume of the battery pack (cells only) V_bp [m³] is the product between the total number of cells N_cb [-] and the mass of each battery cell V_cc(pc) [m³]. This volume is only used to estimate the final volume of the battery pack, since it does not take into account the auxiliary components/systems of the battery.

The volume can be also calculated function of number of strings and number of cells in a string. This calculation method is more appropriate for cylindrical cell, since the volume occupied by a cylindrical cell must take into account the air gap between cells.

The string peak current I_spc [A] is the product between the peak C-rate of the battery cell C-rate_bcp [h^-1] and the battery cell capacity C_bc [Ah].

The battery pack peak current I_bpp [A] is the product between the string peak current I_spc [A] and the number of strings of the battery pack N_sb [-].

The battery pack peak power P_bpp [W] is the product between battery pack peak current I_bpp [A] and the battery pack voltage U_bp [V].

The string continuous current I_scc [A] is the product between the continuous C-rate of the battery cell C-rate_bcc [h^-1] and the battery cell capacity C_bc [Ah].

The battery pack continuous current I_bpc [A] is the product between the string continuous current I_scc [A] and the number of strings of the battery pack N_sb [-].

The battery pack continuous power P_bpc [W] is the product between battery pack continuous current I_bpc [A] and the battery pack voltage U_bp [V].

The results of the equations (7) to (20) are summarised in the table below.

Manufacturer	Panasonic	A123-Systems	Molicel	A123-Systems	Toshiba	Kokam
# of cells in string [-]	112	122	109	122	174	112
String energy [Wh]	1290	1007	1049	7851	8004	6290
# of strings [-]	32	41	39	6	6	7
BP energy [kWh]	41.29	41.27	40.89	47.10	48.02	44.03
BP capacity [Ah]	102.4	102.5	101.4	117	120	109.2
# total cells [-]	3584	5002	4251	732	1044	784
BP mass [kg]*	173.8	380.2	212.6	363.1	532.4	248.5
BP volume [l]*	63	173	75	193	272	135
BP peak current [A]	102.4	2460	202.8	1170	120	327.6
BP peak power [kW]	40.96	984	81.12	468	48	131.04
BP continuous current [A]	102.4	1025	101.4	117	120	218.4
BP continuous power [kW]	40.96	410	40.56	46.8	48	87.36

BP – battery pack
* – taking into account only battery cells

From the table data we can see that the pouch type cell have better energy content and higher capacity compared with the cylindrical cells.

The same results can be plotted in bar graphs for an easier comparison between the different types of battery cells.

Image: Battery pack energy	Image: Battery pack capacity
Image: Battery pack total number of cells
Image: Battery pack mass (cells only)	Image: Battery pack volume (cells only)

Because of the low capacity for the cylindrical cells, compared to the pouch cells, the number of cells required for the battery pack is significant higher. A high number of cells might cause additional problems in areas of wiring, voltage monitoring, battery reliability.

The mass and volume are calculated only at cell level, taking into account the cell dimensions and mass. The battery pack which will be in the vehicle will have additional components (wires, electronic components, soldering, case, etc.), which will increase both the final volume and mass. Nevertheless by looking only at cell based volume and mass, we can estimate which model will be better compared to the other. In terms of mass and volume there is no clear distinction between cylindrical and pouch cells. However it seems that a battery pack with pouch cells is slightly heavier and bigger.

The battery cells manufactured by A123-Systems have very high maximum continuous discharge current and maximum pulse (peak) discharge current. As for energy and capacity, the pouch type cells have higher peak (continuous) current and power than cylindrical cells.

Based on the calculated data and conclusions, we can choose which battery cells are suitable for our electric vehicle battery pack. From our examples it looks like Kokam cells have the best compromise between mass, volume and energy/power density.

Cell: ANR26650M1-B Data Sheet:

Cell calculations:

Battery pack calculation

we calculation of battery we connect battery are connected in series and parallel combination cells are connected for the to required the output of 18kw there for the we assumed the 52 cells in series and 42 cells in parallel.

1. total number of cells required

total number of cells= No of celles in series * No of celles in parallel

=52*42

=2100 no's

2. voltage and current calculation of required the output of 18kw for that

a. voltage = no of celles in series * battery nominal voltage

= 52*3.3

=171.6V

total voltage of celles=171.6v

b. current = no of celles in parallel * battery nominal current (capacity)

= 42*2.4

=105.0Ah

total current of celles=105Ah

c. total output of the connection form series parallel combination of celles afret connection how much we get output

power =voltage* current

=171.6*105

=18018w

=18.018kAh

3. volume of cells: the volume of the cells are the calculation by using for of cylender the ANR26650M1-B cylendical in nature that why using.

a. each celles volume of celles=`πr^2h`

=3.14*12.925^2*65.15

=34192.07MM

b. the calculation of total volume of the battery pack.

total volume of the battery pack= volume of each cells* No of celles connections.

=34192.07*2100

=71803347MM

Total volume of battery pack is 71803347MM or 0.0718033m^3

c. the total weight of the barrery pack

total weight of battery pack= No of cells* each cells standerd weight

=2100*76

=159600g

=159.600kg

total weigth of battery pack= 159.6kg

d. energy dencity= volume * battery pack output

=0.0718033*18018

= 1293.75186 kwh/m^3

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

Battery Pack Assembly . The design of the outer package or housing of the battery depends to a great extent on the components it has to 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 - 12mm

length = 30mm

width = 30mm

weight = 5gm

Arrangement of cells in 52542P together is not the best arrangement as it will take

30mm 52 cells -1560mm For 52 cells in series

30mm 42 cells - 1260mm For 36 cells in parallel so , a total of ( 1560-1260 ) 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 battry 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 the 18KWh capacity , the application might be in a small 2 seater Electric car the area taken by the battery pack assembly is 1.56 *1.26 meters The solution for both the space required and the thermal management of battery pack is to create a module of . Arranging such 8S5P and 1S1P modules in 6S7P manner will create a 52S42P array giving 171.1V 105Ah .

While most people know what components comprise a traditional gasoline-powered automobile engine, they likely know little about the components or parts of an Electric Vehicle (EV) battery pack. This is understandable because EVs are still relatively new in the automotive marketplace, and the conception of how exactly a battery works is more difficult to understand when compared with the myriad of moving components that comprise internal combustion engines.

In reality, EV battery packs possess many traditional machine components. EV battery pack manufacturing processes, in particular, rely heavily on a variety of machine components including MISUMI components which are present at every step in the fabrication process.

To grasp this process, it’s helpful to unpack some basic terminology first. 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 co

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.