> []# Futuretron EV Course_CHAPTER4

# CHAPTER 4: Batteries

## 4.1 Batteries
Battery is a device which is used to store electrical energy in the form of chemical energy and to transform this chemical energy into electrical energy. The construction of battery consists of electrochemical cells, which consists of two electrodes, negative and positive electrode and an electrolyte in the centre. When the two electrodes are connected by a wire, electrons will flow from negative electrode to positive electrode. This flow of electrons is called electricity.The cell is called dead whenever the electrons on the positive and negative electrodes are equivalent to the electrons produced by chemical reactions and in batteries several different chemical reactions are used For instance, the disposable batteries, is a non-rechargeable energy storage device which once dead must be disposed, example Alkaline batteries. Thus, rechargeable batteries are used so regular replacement is not required. The power stored in battery is used to run the electric motor and other electronic units in an electric vehicle. The batteries are recharged from the dedicated charging unit

## 4.2 Battery Fundamentals

1. Volt - The unit of measurement of electromotive force, or difference of potential, which will cause a current of one ampere to flow through a resistance of one ohm.

#### How to measure the voltage in a cell?

* Set the multimeter to measure DC voltage measuring mode. 2] Connect the probes into the multimeter.
* Connect the positive probe to the positive terminal of the cell and the negative probe to the negative cell terminal.
* The voltage value of the cell will be displayed.

2. Ampere: An Ampere or an Amp is a unit of measurement for an electrical current. One amp is the amount of current produced by an electromotive force of one volt acting through the resistance of one ohm.

3. Ampere-Hour: A unit of measurement of a battery's electrical storage capacity. Current multiplied by time in hours equals ampere-hours. One ampere hour is equal to a current of one ampere flowing for one hour. Also, 1 ampere-hour is equal to 1,000 mAh.

4. Watt - A measurement of total power. It is amperes multiplied by volts.

5. Watt-Hour: A Watt Hour is a unit of measurement for power over a period of time. One watt- hour is equal to one Watt of average power flow over an hour. One Watt over two hours would be two Watt-Hours of power.

6. Cell - An electrochemical device, composed of positive and negative plates and electrolyte, which is capable of storing electrical energy. It is the basic “building block” of a battery.
7. Capacity - The capacity of a battery is a measure of the amount of energy that it can deliver in a single discharge. Battery capacity is normally listed as amp-hours (or milli amp-hours) or as watt-hours.
8. Direct Current (DC) – The unidirectional flow of electric charge. It is the type of electrical current that a battery can supply. One terminal is always positive and the other is always negative.
9. Cycle - One sequence of charge and discharge.
10. Charge - The conversion of electric energy, provided in the form of a current, into chemical energy within the cell or battery.
11. Discharge - The conversion of the chemical energy of the battery into electric energy.
12. Battery-Charge Rate - The current expressed in amperes (A) or milli amps (mA) at which a battery is charged.
13. Cycle Life - For rechargeable batteries, the total number of charge/discharges cycles the cell can sustain before its capacity is significantly reduced. End of life is usually considered to be reached when the cell or battery delivers only 80% of rated ampere- hour capacity. The cycle of a battery is greatly influenced by the type depth of the cycle (deep or shallow) and the method of recharging. Improper charge cycle cut-off can greatly reduce the cycle life of a battery.
14. Depth of Discharge - The amount of energy that has been removed from a battery (or battery pack). Usually expressed as a percentage of the total capacity of the battery. For example, 80% DOD means that eighty percent of the energy has been discharged, so the battery now holds only 20% of its full charge.
15. Energy Density: The volumetric energy storage density of a battery, expressed in Watt-hours per litre (Wh/l).
16. Power Density: The volumetric power density of a battery, expressed in Watts per litre (W/l).
17. State of Charge [SOC]: SOC refers to the remaining charge in a cell as a percentage of the charge contained by the cell when it is full. We cannot accurately determine the charge remaining in the cell without fully discharging it first, so the calculation for SOC is usually performed by subtracting the charge removed from the cell so far from the charge contained when it was last charged to 100% SOC.
18. State of Health [SOH]: The change in the amount of charge that the cells can hold as they age. In case of Electric Vehicle, the capacity of the cells in the battery pack is the important parameter in determining the range which can be achieved in one charge.
Hence State of Health of an Electric Vehicle battery pack, that is SOHe, which is the amount of charge the cells in the battery pack can hold as they age.

Over a succeeding number of cycles of cells, the capacity of a lithium-ion cell will drop owing to a number of factors including loss of lithium inventory and failing of the electrodes inside the cell. Hence when an aged cell is charged and discharged to its maximum and minimum voltage values respectively, the charge obtained will be lower than charge obtained when the cell was new.

19. C RATE: C rate of the battery is the rate at which the capacity of the battery is charged or discharged to the load. C rating is important in applications which draw high amounts of current.
Maximum Current Draw = Capacity (Ah) x C-Rate
Example, a 3S 2.5Ah 5C LiPo battery pack will draw a maximum safe current of
2500mAh x 5C = 12.5A

Discharging a battery too quickly is not good considering the health of the battery. Due to which internal resistance (IR) will increase than discharging within the battery’s limit.
The battery capacity is generally rated at 1C, which means that the fully charged battery rated at 2Ah must provide 2A for 1 hour. The same battery if rated at 0.5C should provide 1A for 2 hours. Same battery rated at 2C should provide 4A for 30minutes.

C/10 = C10 = which means C amount of discharge current flowing for 10 hours
C/5 = C5
C/0.5 = C0.5 = 2C
20C = The discharge current the battery is capable of discharging is 20 times C

The higher quality batteries are capable of handling higher charge rates with minimum or no degradation but the lower quality batteries have higher possibility of getting overheat at higher charge rates. Its always suggested to charge at 1c or follow the recommendations from battery manufacturer regarding high performance and long battery life.

## 4.3 Mathematical Calculations

#### • Average Battery Current
IB=C/N
IB = Average battery current
C= Capacity in Ah
N= No of hours of discharge

Example:
For 10Ah of battery and 10hours of discharge
IB=30Ah/10h = 3A
It means that 30Ah of battery is capable of supplying 3Ah of average current to the load up-to 10hours. Though due to losses 30Ah battery can supply 3A average current for less than 10 hours.

#### • Continuous Discharge
2500mah battery with 5C rating
Continuous Discharge Amperage = (mAh/1000) x C Rate)
= (2500 /1000) x5=12.5A

#### • Run Time for Safe Continuous Discharge
2500mah battery with 5C rating
Run Time = (60min/C-Rate) = (60min/5) = 12min
Therefore, Discharge 25A for 12min

## 4.4 Types of Batteries

The types of rechargeable batteries used in Hybrid Electric Vehicles and Other Electric Vehicles [EV] are
1. Lead-Acid battery.
2. Nickel-Cadmium Battery (NiCd or NiCad)
3. Nickel Metal Hydride [NiMH] battery.
4. Lithium-ion [Li-ion] battery.

Each battery type has its own set of advantages and disadvantages selection of these batteries depends on where it is used so that maximum benefit can be obtained.
#### 1. LEAD ACID BATTERIES
It was invented by Gaston Plante, a French Physician in 1859. To convert chemical energy to electrical energy sponge metallic lead and lead peroxide are used in Lead Acid batteries. It is the oldest and the first rechargeable batteries made available.
Some of its advantages are low cost, long life cycle, and can withstand slow, fast and overcharging, it is available in all sizes and shapes, wide capacity range, low self-discharge- which is lowest among rechargeable batteries, high discharge rate, can be recycled and reused in new batteries.
Some of its disadvantages are energy density is low, poor weight-to-energy ratio, not environmental friendly, as it employs harmful chemicals transportation restrictions on flooded lead acid, limited number of full discharge cycles.

#### 2. NICKEL-CADMIUM BATTERY (NiCd or NiCad) BATTERIES:
Waldemar Jungner invented Nickel-Cadmium battery in 1899. The rechargeable NiCd battery is composed of nickel hydroxide in the positive electrode, cadmium in the negative and potassium hydroxide as electrolyte. A typical lead-acid battery has cell voltage of roughly 2V, which then steadily comes down as it is depleted whereas NiCad batteries will maintain a steady voltage of 1.2v per cell up till it is nearly completely depleted.
Some of the advantages are low internal resistance, wide range of sizes and performance options are available, high charge and discharge rate, lighter, more compact and higher energy density than lead acid batteries, self-discharge rate is lower than NiMH batteries.
Some of the disadvantages are expensive than lead acid, extremely toxic-causes environmental pollution, high self-discharge, low energy densities compared to newer systems.

#### 4. NICKEL METAL HYDRIDE[NiMH] BATTERIES:
The Nickel Metal Hydride Battery was patented by Standford Ovshinsky, founder of Ovonics. Hydrogen absorbing alloys are used as the active element at the negative electrode and Nickel
-hydroxide at the positive electrode.
Some of the advantages are higher capacity than NiCd, environmentally friendly no toxicity issue, wide operating temperature range, transportation and storage is simple.
Some of the disadvantages are load discharge is high, generates heat during fast charge, sensitive to overcharge.

#### 4. Lithium Ion Battery
NiMH and Li-ion came into view in 1990s and Li-ion became the most promising and the fastest growing battery system. Lithium offers the largest energy density and is the lightest of all the metals. Due to safety issues, attempts at developing Lithium-rechargeable batteries failed. Thus, there was a shift from Lithium to Lithium-ion, it is safer but lower energy density than Lithium metal. The Sony Corporation in 1991 commercialized the first Lithium-ion battery. The electrodes are made of lightweight lithium and carbon. The Lithium-ion has energy density twice that of Ni-Cad Batteries.
One of the reasons for the rapid growth in the development of Li-ion batteries is a huge acceptance of these batteries in cell phones, laptops, and computers. Out of all battery types Li-ion provides the highest density and thus electronic manufacturers prefer these over other battery technologies. The applications are categorized into automotive, medical, aerospace, military, consumer electronics and so on. They are also used in renewable energy areas for energy storage purposes. Other advantages such as long lifespan, low self-discharge, high charge, and discharge cycles have added to the growth of lithium-ion battery market.
The subclass of the lithium-ion battery market is Lithium-Iron-Phosphate [LiFePO4], Lithium- Nickel-Manganese-Cobalt-Oxide [NMC], Lithium-Manganese-Oxide [LMO], Lithium- Nickel-Cobalt-Aluminium-Oxide [NCA], and Lithium-Cobalt-Oxide [LCO] batteries.
3.6 V 2400mAh Lithium-Ion battery has Typical end-of-discharge of 2.8V - 3V and maximum charge voltage of 4.2V 2400mAh. 3.2V 6000mAh LiFePO4 can be charged up to 3.7V and has cut off voltage of 2.7V.

Lithium iron phosphate is used for high power applications. Due to the long cycle life, good thermal stability, upgraded safety, and tolerance features and constant voltage the market demand is increasing in consumer electronics and also in EV sectors.
Due to the high energy density, long life span, and thermal stability, the Lithium-Nickel- Manganese-Cobalt-Oxide [NMC] battery market is predicted to witness the highest growth rate. Researchers are working towards reducing the Cobalt content which would further increase the demand.
Lithium Cobalt Oxide [LCO] is one of the most widely used batteries in applications such as cell-phones, laptops, cameras and so on. Hence has increased the global lithium-ion market share.
One of the developing trends in battery technology is Lithium-Sulphur. Some of the aspects of Lithium Sulphur are sulphur is less expensive compared to Nickel, Aluminium, and Cobalt. They are expected to have high densities compared to other battery technologies.
With the rapid growth in the EV industry, the need for a power revolution is always on topic.

#### OTHER BATTERY TECHNOLOGIES

##### 1. Solid state battery:

The difference between a conventional Li-ion battery and a solid-state battery is the electrolyte material. The Solid-state battery employs a solid material for its electrolyte and replaces the liquid or polymer electrolyte. The battery pack thus obtained possess higher energy density and hence reduces the cost per Kw in terms of commercialization purpose. It also has higher durability, longer life and higher charging capabilities.
To find a suitable solid-state material that can conduct electricity efficiently at large scale is a key challenge in this battery tech. The solid state of the electrolyte makes them less conductive than liquid electrolytes as the conductivity of a material is mainly temperature dependant. There are chances of energy density of solid-state batteries to decrease more in cold temperatures when compared to that of a liquid electrolyte battery. Hence, lot of research are being carried out in this technology to overcome such challenges.

#### 2. Aluminium-air battery:

The flow of electrons in this battery is produced due to the reaction of oxygen in the air with aluminium. These batteries possess one of the highest energy densities among all the batteries. An EV equipping such batteries can offer up to eight times the range of an EV with a conventional lithium-ion battery while occupying significantly less space.
These are primary cells, i.e., non-rechargeable. Once the aluminium in the anode is consumed due to the reaction with oxygen at the cathode forming hydrated aluminium oxide, the battery will be incapable of producing electricity and hence require replacement of Anode material. The cost of replacement of the anode material is very high and electrolyte replacement is challenging if conventional electrolytes are used.

**Battery chemistry comparison – The Lithium family**

Fig:Hexagonal spider graph of Lithium Family

The Hexagonal spider graph gives a brief summary of the performance and other characteristics of the Li-ion family.

**Specific energy**
It is the amount of energy that a particular type of cell can store per unit volume. Higher the specific energy graph reads, higher the amount of energy it can store in a particular volume. NCA, NMC and LMO cells have very good specific energy values.

**Safety**
It is one of the most important parameter that is considered before opting a particular battery chemistry. LFP cells are most preferred for applications that require high safety applications although LTO cells rank as the safest choice amongst all they are not a popular choice as they fail to deliver on other crucial parameters.

**Life span**
This refers to the number of charge cycles a particular battery pack can sustain and deliver its rated capacity. One cycle refers to one complete charge and discharge of the battery cell. NCA, LTO and LFP cells are the top performers in this category.

An ideal battery chemistry must have good performance in all categories and the spider graph should be of hexagonal shape. NMC and LFP battery pack performance characteristics match to that of hexagonal graph shape. Hence, NMC & LFP are a popular choice for various applications.

## 4.5 Battery Pack

#### The following parameters are considered while opting for a battery pack:

Life span: This is a crucial parameter considered while opting for a battery pack for an EV. High life cycle batteries are generally expensive but the initial cost breaks even as it offers high life cycle. Generally, the battery pack of an EV has a life cycle of 8 years or 160,000 Km.

Safety: The range offered by a modern day EV is comparatively higher and hence a very high capacity battery is employed for the same. A safe operation must be ensured by carefully designing a proper BMS for the rated application and insulating the pack from being influenced by external parameters such as weather conditions or dust particles.

Cost: A major disadvantage for EV’s is the cost is much higher than that of an ICE vehicle. The cost of a high capacity battery pack could be equivalent to that of a small ICE vehicle. The cost of the battery pack has considerably come low but it is still a few years away from becoming competitive for an ICE vehicle alone.

Specific energy: The energy density is a measure of battery capacity in weight (Wh/kg) and the amount of energy stored per unit mass. Higher specific energy ensures that a very high capacity battery can be packed in a smaller dimension and weighs much lower.

## 4.6 Series and Parallel Connection

A battery pack consists of set of identical individual battery cells. They may be configured in parallel, series or combination of both to produce the desired voltage, capacity, or power density rating.

Connecting in series, parallel and in series-parallel depends on the requirement, that is to increase the voltage the cells must be connected in series, to increase the ampere-hour rating the cells must be connected in parallel. Therefore, connecting cells depends on the requirement of the systems.

The required operating voltage and current for any application is got by connecting number of cells in series and parallel connection.

Three types of Connection

* Series Connection
* Parallel Connection
* Series-Parallel Connection

### SERIES CONNECTION
In series connection voltages gets added and current remains constant.

Two cells are connected in series by connecting positive (+) terminal of the battery to the negative (-) terminal of the other battery and negative terminal (-) to positive (+) terminal as in the figure below.

Series Connection

In a series connection each cell adds its voltage keeping the same amperage rating (Amp- Hours).
For instance, two 3.6V 2400mAh batteries connected in series(2s)

3.6V+3.6V=7.2V
Thus forming, 7.2V & 2400mAh.

### PARALLEL CONNECTION

In parallel connection increases the current rating keeping the same voltage rating.
Two cells are connected in parallel by connecting positive terminal (+) of battery to positive terminal (+) of the other battery and negative terminal (-) to negative (-) terminal of the other as in figure below.

Parallel connection

For instance, two 3.6V 2400mAh batteries connected in parallel(2p)

2400mAh+2400mAh = 4800 mAh
Thus, 3.6V & 4800mAh

### SERIES-PARALLEL CONNECTION:
By connecting two pairs of two batteries in series and then parallel, then this configuration is called Series-Parallel configuration.

Series-Parallel connection

Some battery packs comprise of a grouping of series and parallel connections as per the application requirement.
For instance, to satisfy the requirement 7.2V and 4800mAh, cells must be connected in 2s2p format where each cell value is 3.6V 2400mah, meaning 2 cells in series (7.2V) and 2 cells in parallel(4800mah).

3.6+3.6=7.2V (2S connection)
2400+2400=4800mAh (2P connection)
Thus, 7.2V & 4.8Ah (2S2P)

It is very important to ensure that the same battery category with equivalent capacity (Ah) and voltage (V) and never to group different battery type and sizes. A weaker cell in the pack will cause an imbalance that is a weaker cell may not break down instantly but there is a chance of getting drained rapidly than the strong cells when connected to the load.

### Battery Calculation

**1. Design a NMC battery pack of 12V and 20Ah. Consider the nominal voltage of NMC to be 3.6V with a capacity of 2600 mAh each.**

Solution:
The cells that should be connected in series :
Series = Req. volt / Nominal volt = 12/3.6 = 3.33
Therefore 4s (4 cells in series connection)

The cells to be connected in parallel:
Parallel = Req. current/ Rated capacity = 20/2.6= 7.68
Therefore 8P (8 cells in parallel connection)

The cell configuration is 4S8P.

**2. Design a LFP battery pack of 36V and 30Ah. Consider the nominal voltage of LFP to be 3.2V and a capacity of 6000 mAh each.**

Solution:
The cells that should be connected in series :
Series = Req. volt / Nominal volt = 36/3.2= 11.25
Therefore 12s (12 cells in series connection)

The cells to be connected in parallel:
Parallel = Req. current/ Rated capacity = 30/6= 5
Therefore 5P (5 cells in parallel connection)

The cell configuration is 12S5P.

**3. Design a NMC battery pack to run a motor of 48V and 3000W for 1 hour.**

Solution:
From the given data, the current drawn by the motor is, I = P/V = 3000/48= 62.5A
Consider the nominal voltage of NMC is 3.6volt , capacity is 2.6Ah each

The cells that should be connected in series :
Series = Req. volt / Nominal volt = 48/3.6 = 13.33
Therefore 14s (14 cells in series connection).

The cells to be connected in parallel:
Parallel = Req. current/ Rated capacity = 62.5/2.6= 24.03
Therefore 24P (24 cells in parallel connection).

The cell configuration is 14S24P.

**4. Design a LFP battery pack to run a 2KW, 48V BLDC motor for 1 hour.**

Solution:

From the given data, the current drawn by the motor is, I = P/V = 2000/48= 41.66A
Consider the nominal voltage of LFP to be 3.2V and a rated capacity of 6Ah each.

The cells that should be connected in series :
Series = Req. volt / Nominal volt = 48/3.2 = 15
Therefore 15s (15 cells in series connection).

The cells to be connected in parallel:
Parallel = Req. current/ Rated capacity = 41.66/6= 6.94
Therefore 7P (7 cells in parallel connection).

The cell configuration is 15S7P.

## 4.7 Insulation and types of insulation

Proper insulation of a battery pack is important to shield the battery from high and low temperatures respectively. These extreme temperatures can shorten the lifespan of the battery. Proper insulation also ensures that the system is not affected by external factors such as weather, dust or moisture. This not only prolongs the lifespan of the battery cells but also ensures safety.

**Cell holders**
Battery cell holders are often used to provide rigid support to the battery pack structure. These are not necessary but are used by hobbyists and amateurs to help them master the art of assembly and welding the battery pack.

Battery cell holders

**Barley sheet**
Barley Paper can be used for insulation. Barley paper insulation provides high insulation, shielding and anti-interference. Proper maintenance of a battery extends its life and prevents the battery from failing.
Barley sheet insulation

**Shrink wraps**
Common methods of sealing the battery packs are using heat shrink wraps or putting the battery pack in some hardcase. Shrink wraps are available in multiple dimensions to suit different configurations. The shrink wraps are selected based on their width; the wraps must be wide enough to not only accommodate the battery pack but instead should be a little wider than the battery width to allow for the shrinking when it is exposed to the heat of the heat gun. This shrinking method ensures that the pack is tightly sealed and there is no gap left for moisture or dust particles to enter.

PVC shrink wrap