Batteries

What are Electrical Batteries?

Electrical batteries are electrochemical devices that convert stored chemical energy into electrical energy through redox reactions.
They consist of one or more electrochemical cells, each containing:

Parts of a battery

Anode (negative electrode): Where oxidation occurs, releasing electrons
Cathode (positive electrode): Where reduction occurs, accepting electrons
Electrolyte: Medium that allows ion flow between electrodes while preventing electron flow
Separator: Physical barrier that prevents direct contact between electrodes while allowing ion transport

When a load is connected, electrons flow from anode to cathode through the external circuit, while ions move through the electrolyte to maintain charge balance.
This creates a sustained electrical current until the chemical reactants are depleted.

Electron Flow in Cells

Traditional notation for flow of current for discharging is from +ve terminal to -ve terminal
This is called Galvanic Flow
In Electron Flow notation, the actual direction of flow of electrons is shown
During discharging, electrons flow into the +ve terminal
During charging, electrons flow into the -ve terminal

Explanation

While charging, potential difference (voltage) across terminals increases, as more and more electrons reach the -ve terminal
The +ve terminal becomes more positive as fewer and fewer electrons are present
The -ve terminal becomes more negative as more and more electrons are present
While discharging, this process is reversed, as voltage begins to drop
As more electrons reach the +ve terminal, it becomes lesser and lesser positively charged
At the -ve terminal, as more and more electrons leave, it also becomes less and less negatively charged
Potential Difference (Voltage) as a result reduces

Lead Acid Chemistry

Construction

Core Components:

Positive Electrode: Lead dioxide ( $P b O_{2}$ ) on lead grid
Negative Electrode: Spongy lead ( $P b$ ) on lead grid
Electrolyte: Sulfuric acid solution ( $H_{2} S O_{4}$ + $H_{2} O$ , specific gravity 1.25-1.28)
Separator: Microporous material AGM, gel, or liquid-flooded, see The Differences Between AGM, GEL and FLOODED Batteries
Container: Polypropylene or ABS plastic housing
Terminals: Lead alloy posts for external connections

Cell Configuration:

Voltage: 2.0V per cell
12V Battery: 6 cells connected in series
Grid Structure: Lead-antimony or lead-calcium alloy grids support active material

Working Principle

How Lead Acid Batteries Work:

Lead Acid Battery Construction & Working

When Discharging (Starting Your Car or Powering Equipment):

The battery contains lead plates - one made of pure spongy lead ( $P b$ )(negative) and one coated with lead dioxide ( $P b O_{2}$ ) (positive)
Both plates sit in sulfuric acid, which acts like a chemical soup
When you turn the key, both lead plates react with the sulfuric acid
This reaction converts both plates into the same material: lead sulfate (a white, chalky substance)
During this conversion, electrons are released and flow through your car's electrical system
The sulfuric acid gets weaker as it's used up in the reaction, and water is produced
Eventually, both plates become coated with lead sulfate and the acid becomes mostly water - the battery is "dead"

When Charging (Alternator or Battery Charger):

The charger forces electricity back into the battery, reversing everything that happened
The lead sulfate on both plates converts back to their original materials
Negative plate becomes pure lead again, positive plate becomes lead dioxide again
The weak acid and water recombine to form strong sulfuric acid
The battery is restored to its original state and ready to work again

Simple Analogy: Imagine two different colored sponges (lead plates) sitting in colored water (sulfuric acid). When you squeeze them (discharge), they both turn the same color and the water becomes clear. When you stretch them back out (charge), they return to their original colors and the water becomes colored again.

Why It Works: The beauty of lead acid batteries is that this chemical conversion is reversible hundreds of times, though eventually the plates wear out and can't convert properly anymore.

How to Tell if It's Charged:

Voltage Test: A fully charged 12V battery reads about 12.6V, while a dead one reads around 10.5V
Acid Strength: The stronger the sulfuric acid (higher specific gravity), the more charged the battery
Physical Signs: Some batteries have a built-in "magic eye" indicator that changes color based on charge level

Lead Acid Advantages:

Low cost: Economical initial investment
Robust: Tolerates overcharge and deep discharge better
Recyclable: 95%+ material recovery rate
Proven technology: Mature, well-understood chemistry
High surge current: Excellent for starting applications

Working of Lead Acid Battery & LFP Battery

Pasted image 20250607204612.png
Click on Link or Scan QR Code to view video on Lead Acid Battery & LFP Battery

Li ion Chemistry

Construction

Core Components:

Cathode: Lithium metal oxide (e.g., $L i C o O_{2}$ , $L i F e P O_{4}$ , $L i N i M n C o O_{2}$ )
Anode: Graphite ( $C_{6}$ ) with intercalated lithium
Electrolyte: Organic liquid (lithium salt in organic solvent like $L i P F_{6}$ in EC/DMC)
Separator: Microporous polymer membrane (PE/PP)
Current Collectors: Aluminum foil (cathode), Copper foil (anode)

Parts of a Li ion Battery

Pasted image 20250607205247.png

Physical Structure:

Cylindrical: Rolled electrode sheets (18650, 21700 cells)
Prismatic: Flat electrode stacks in rectangular housing
Pouch: Flexible aluminum-polymer laminate

Jelly Roll Construction of Cylindrical Cells

Pasted image 20250607205308.png

Working Principle

How Li-ion Batteries Work:

Think of a Li-ion battery like a bus shuttle system:

Construction & Working of Li ion Cell

Basic-working-principle-of-a-lithium-ion-Li-ion-battery-1.webp
When Discharging (Powering Your Device):

Lithium ions (tiny charged particles) are stored in the graphite anode, like passengers waiting at a station
When you use the battery, these lithium ions travel through the liquid electrolyte (like a highway) to reach the cathode
At the same time, electrons flow through the external wire (your device's circuit) from the negative to positive terminal
This electron flow is what powers your phone, laptop, or electric car
The process continues until most lithium ions have moved to the cathode side

When Charging:

You plug in the charger, which applies electrical pressure to push everything backwards
Lithium ions travel back from the cathode to the graphite anode through the electrolyte
The graphite anode acts like a parking garage, storing the lithium ions between its layers
Once fully charged, all the lithium ions are back in the anode, ready to make the journey again
The battery is now "reset" and ready to power your device again

Simple Analogy: Imagine a water wheel where water (lithium ions) flows from a high reservoir (anode) to a low reservoir (cathode), turning the wheel on its way down. Charging is like pumping the water back uphill to refill the high reservoir.

Li-ion Advantages:

High energy density: Compact and lightweight
No memory effect: Can be partially charged/discharged
Low self-discharge: Retains charge well during storage
Fast charging: Can accept high charge rates
Long cycle life: Thousands of charge/discharge cycles

Working Of LCO Cell

Pasted image 20250607205056.png
Click on Link or Scan QR Code to view video on Li ion LCO Battery

Comparison between Lead Acid & Lithium ion Chemistry

Parameter	Lead Acid	Lithium Ion
Energy Density	30-50 Wh/kg	150-250 Wh/kg
Cycle Life	200-300 cycles	500-2000+ cycles
Operating Temperature	-20°C to +50°C	-20°C to +60°C
Memory Effect	None	None
Depth of Discharge	50% (deep cycle)	80-100%
Initial Cost	Low ($50-150/kWh)	High ($200-600/kWh)
Maintenance	Regular (water topping)	Minimal
Safety	Hydrogen gas risk	Thermal runaway risk
Environmental Impact	Lead toxicity concern	Mining impact, recyclable
Weight	Heavy (11-18 kg/kWh)	Light (2.5-6 kg/kWh)
Voltage per Cell	2.0V	3.6-3.7V
Efficiency	70-85%	95-98%
Lifespan	3-5 years	8-15 years
Charge Estimation	Fairly Easy (Voltage - % Charge Linear relation)	More Complex (using advanced algorithms and models in BMS)

Lead Acid vs Li ion Discharge Curves

Lithium Ion Chemistry Comparison

Li ion Battery Chemistry Spider Plot

Pasted image 20250607211047.png
Please slide to the right to view all Chemistry Types in the comparison table

Chemistry	LCO	LTO	NMC	NMA	NMO	LMO	LFP
Full Name	Lithium Cobalt Oxide	Lithium Titanate	Nickel Manganese Cobalt	Nickel Manganese Aluminum	Nickel Manganese Oxide	Lithium Manganese Oxide	Lithium Iron Phosphate
Chemical Formula	$L i C o O_{2}$	$L i_{4} T i_{5} O_{12}$	$L i N i M n C o O_{2}$	$L i N i M n A l O_{2}$	$L i N i_{0.5} M n_{1.5} O_{4}$	$L i M n_{2} O_{4}$	$L i F e P O_{4}$
Nominal Voltage	3.6V	2.4V	3.6-3.7V	3.6V	4.7V	3.8V	3.2V
Energy Density	150-200 Wh/kg	70-80 Wh/kg	150-220 Wh/kg	200-260 Wh/kg	140-150 Wh/kg	100-150 Wh/kg	90-120 Wh/kg
Cycle Life	500-1000	10,000+	1000-2000	500-1000	1000+	300-700	2000-5000
Operating Temp	-20 to +60°C	-30 to +55°C	-30 to +60°C	-20 to +60°C	-20 to +60°C	-20 to +50°C	-20 to +60°C
Safety	Moderate	Excellent	Good	Good	Good	Good	Excellent
Cost	High	High	Medium	Medium	Medium	Low	Medium
Toxicity	High (Cobalt)	Low	Medium	Low	Low	Low	Very Low
Self-Discharge	2-3%/month	5%/month	3-5%/month	3-5%/month	3-5%/month	4-8%/month	3-5%/month
Fast Charging	Good	Excellent	Good	Good	Limited	Fair	Good
Applications	Smartphones, laptops, tablets	Electric buses, grid storage, fast charging	Electric vehicles, power tools, ESS	Tesla vehicles, high-energy EVs	High voltage applications, telecom	Medical devices, power tools	EV (China), home storage, marine

Additional Reading Material

Pasted image 20250607211005.png
Click on link or Scan QR Code to read MDPI research paper on types of Li-ion chemistries

Key Considerations

Energy vs Power Trade-off: Higher energy density chemistries typically have lower power density and vice versa.
Safety vs Performance: Safer chemistries like LFP and LTO often sacrifice some energy density for improved thermal stability.
Cost vs Performance: More advanced chemistries with better performance typically come at higher costs due to material composition and manufacturing complexity.
Cycle Life vs Energy: Chemistries optimized for longevity (LTO, LFP) may have lower energy density but significantly longer operational life.

Test your Knowledge!

Click here to view a sample quiz worksheet,
Check if your understanding of battery concepts are correct!

Click here to continue to Battery Pack Design & Calculations