Batteries and Fuel Cells
3. Rechargeable Batteries
Learning outcomes
- I can explain how rechargeable batteries store and release energy.
- I can describe the operation of lithium-ion batteries.
- I can compare different rechargeable battery technologies.
- I can evaluate factors affecting battery performance.
- I can discuss the environmental impacts of battery use and disposal.
What Is a Rechargeable Battery?
A rechargeable battery is an electrochemical energy-storage device that can be charged, discharged, and then charged again many times.
Rechargeable batteries contain one or more:
secondary cells.
During discharge, stored chemical energy is converted into electrical energy:
chemical energy → electrical energy
During charging, an external source supplies electrical energy that drives chemical changes inside the battery:
electrical energy → chemical energy
This allows the battery to store energy for later use.
How Does a Battery Store Energy?
A battery does not simply "store electricity."
Instead, energy is stored in the:
chemical state of the materials inside the battery.
During charging, an external power source drives chemical changes that increase the chemical potential energy of the system.
The battery can then release this stored energy during:
discharge.
A useful way to think about the process is:
Charging: electrical energy → stored chemical energy
Discharging: stored chemical energy → electrical energy
What Happens During Discharge?
When a rechargeable battery powers a device, spontaneous:
redox reactions
occur inside its cells.
At the anode during discharge:
oxidation occurs.
Electrons are released.
At the cathode:
reduction occurs.
Electrons are accepted.
Electrons travel through the external circuit:
anode → device → cathode
As they pass through the device, they transfer:
electrical energy.
What Happens Inside the Battery?
Electrons travel through the external circuit, but they cannot simply travel through the electrolyte.
Inside the battery, charge is transported mainly by:
ions.
Therefore:
electrons move through the external circuit
while:
ions move through the electrolyte.
Both movements are necessary for the battery to continue operating.
What Happens During Charging?
When a rechargeable battery is connected to an appropriate charger, electrical energy is supplied to the cell.
The charger drives chemical reactions in the opposite direction from normal discharge.
In simplified form:
Discharge:
Charged materials → discharged materials + electrical energy
Charging:
Discharged materials + electrical energy → charged materials
Charging therefore restores the battery toward a:
higher-energy chemical state.
Charging Is Not Perfectly Reversible
The reactions in rechargeable batteries are designed to be:
substantially reversible.
However, they are never perfectly reversible.
During repeated charging and discharging:
- side reactions can occur
- electrode structures can change
- electrolyte can degrade
- active materials can be lost
- internal resistance can increase
This is why rechargeable batteries eventually:
lose capacity and performance.
Lithium-Ion Batteries
One of the most important rechargeable battery technologies is the:
lithium-ion battery.
Lithium-ion batteries are used in:
- smartphones
- laptops
- tablets
- wireless headphones
- cameras
- power tools
- electric bicycles
- electric vehicles
- energy-storage systems
They are popular because they can store a relatively large amount of energy while remaining:
compact and lightweight.
Structure of a Lithium-Ion Battery
A simplified lithium-ion cell contains:
- a negative electrode
- a positive electrode
- an electrolyte
- a separator
- current collectors
The negative electrode commonly contains:
graphite.
The positive electrode contains a:
lithium-containing material.
Many different positive-electrode chemistries exist.
The Electrolyte
The electrolyte allows:
lithium ions
to move between the electrodes.
The electrolyte conducts ions but is not intended to provide a direct electronic pathway between the electrodes.
Electrons instead travel through the:
external circuit.
The Separator
The separator is positioned between the positive and negative electrodes.
Its job is extremely important.
It:
- prevents direct electrical contact between the electrodes
- allows ions to move through the cell
- helps prevent an internal short circuit
If the electrodes make direct electrical contact, a large current may flow internally and produce:
dangerous heating.
Lithium-Ion Discharge
During discharge, lithium ions move through the electrolyte from the negative-electrode side toward the positive-electrode side.
At the same time, electrons travel through the external circuit.
The electrons can power a device before reaching the positive electrode.
Therefore two movements occur simultaneously:
Lithium ions → through electrolyte
Electrons → through external circuit
Lithium-Ion Charging
During charging, an external power source forces the electrochemical processes in the opposite direction.
Lithium ions move back toward the negative-electrode material.
Electrons are also driven through the external circuit in the corresponding direction.
The battery returns toward its:
charged chemical state.
Energy is stored as:
chemical potential energy.
Charging and Discharging
A simplified cycle is:
CHARGING
Electrical energy enters battery
↓
Chemical changes occur
↓
Energy stored chemically
↓
DISCHARGING
Chemical reactions occur
↓
Electrons flow through external circuit
↓
Electrical energy powers device
↓
Battery returns toward discharged state
The cycle can then begin again.
Lithium Ions vs Lithium Metal
The name lithium-ion battery is important.
Lithium-ion cells operate mainly through the movement of:
Li⁺ ions
between electrode materials.
This is different from many primary lithium batteries, which can contain lithium metal.
Therefore:
primary lithium battery ≠ lithium-ion battery
Primary lithium batteries are generally non-rechargeable.
Lithium-ion batteries are:
rechargeable.
Why Is Lithium Useful?
Lithium is useful in battery technology because it is:
- a very light element
- highly electropositive
- capable of contributing to high cell voltages
- suitable for battery systems with high energy per unit mass
These characteristics help lithium-ion batteries achieve high:
energy density.
Energy Density
Energy density describes how much energy can be stored relative to the battery's mass or volume.
A battery with high energy density can store a large amount of energy without becoming excessively:
large or heavy.
This is especially important for:
- smartphones
- laptops
- drones
- electric vehicles
where mass and space are important design considerations.
Specific Energy
When energy storage is compared with mass, we often use:
specific energy.
It can be expressed in:
watt-hours per kilogram (Wh/kg).
For example, if a battery stores 200 Wh and has a mass of 1 kg:
specific energy = 200 Wh/kg
A larger value means more energy is stored for each kilogram of battery.
Battery Capacity
Battery capacity describes how much electrical charge a battery can deliver under specified conditions.
It is commonly measured in:
ampere-hours (Ah)
or:
milliampere-hours (mAh).
For example:
5000 mAh = 5.0 Ah
Capacity and voltage are different quantities.
Estimating Battery Energy
Battery energy can be estimated using:
Energy (Wh) = Voltage (V) × Capacity (Ah)
Suppose a battery is rated:
3.7 V and 5.0 Ah
Then:
Energy = 3.7 × 5.0
Energy = 18.5 Wh
The nominal stored energy is approximately:
18.5 Wh.
Voltage Is Not Capacity
Consider two batteries.
Battery A:
3.7 V, 2.0 Ah
Battery B:
3.7 V, 5.0 Ah
Both have the same nominal voltage.
Battery B has a greater:
capacity.
Its approximate energy is also greater:
Battery A:
3.7 × 2.0 = 7.4 Wh
Battery B:
3.7 × 5.0 = 18.5 Wh
Different Rechargeable Battery Technologies
Lithium-ion is not the only rechargeable battery technology.
Other important types include:
- lead-acid
- nickel-metal hydride
- nickel-cadmium
- sodium-ion
- several specialized rechargeable systems
Each battery chemistry has different advantages and limitations.
Lead-Acid Batteries
Lead-acid batteries have been used for more than a century.
They contain:
- lead
- lead dioxide
- sulfuric acid electrolyte
They are widely used in:
- cars
- motorcycles
- backup power systems
- uninterruptible power supplies
Advantages of Lead-Acid Batteries
Lead-acid batteries can:
- provide very large currents
- be manufactured relatively inexpensively
- operate reliably
- be recycled through established systems
This makes them particularly useful for:
starting vehicle engines.
Limitations of Lead-Acid Batteries
Lead-acid batteries are:
- heavy
- relatively low in energy density
- made using toxic lead
- based on corrosive sulfuric acid
They are therefore less suitable than lithium-ion batteries for many lightweight portable devices.
Nickel-Metal Hydride Batteries
Nickel-metal hydride (NiMH) batteries are rechargeable cells commonly available in:
AA and AAA sizes.
They are used in:
- toys
- cameras
- flashlights
- game controllers
- household electronics
- some hybrid vehicles
Advantages of NiMH Batteries
NiMH batteries can offer:
- good capacity
- repeated rechargeability
- common household battery sizes
- useful performance in moderately high-drain devices
They can replace many disposable alkaline cells in compatible devices.
Limitations of NiMH Batteries
Compared with lithium-ion cells, NiMH batteries generally have:
- lower energy density
- lower cell voltage
- greater mass for a given amount of stored energy
Some types also experience noticeable:
self-discharge.
Nickel-Cadmium Batteries
Nickel-cadmium (NiCd) batteries are another rechargeable technology.
They can provide:
- high currents
- good cycle performance
- reliable operation
However, cadmium is:
toxic.
Environmental concerns and regulations have reduced their use in many consumer applications.
Sodium-Ion Batteries
Sodium-ion batteries operate using principles similar in some ways to lithium-ion batteries, but charge is transported using:
sodium ions (Na⁺).
Sodium is relatively abundant.
Sodium-ion technology is being developed and commercialized for applications where factors such as:
- material availability
- cost
- safety
- stationary storage
may be important.
Its characteristics differ from lithium-ion, so it is not simply a direct replacement in every application.
Comparing Rechargeable Technologies
| Characteristic | Lithium-Ion | Lead-Acid | NiMH |
|---|---|---|---|
| Rechargeable | Yes | Yes | Yes |
| Energy density | High | Low | Moderate |
| Mass | Relatively low | High | Moderate |
| Cell voltage | Relatively high | Moderate | Lower |
| High current capability | Good | Very good | Good |
| Common application | Phones, laptops, EVs | Cars, backup systems | Rechargeable AA/AAA |
| Major concern | Heat and degradation | Lead and mass | Lower energy density |
| Recycling importance | High | Very high | High |
The exact performance varies considerably between individual battery designs.
What Determines Battery Performance?
Battery performance is affected by many factors.
Important examples include:
- temperature
- charge rate
- discharge rate
- age
- number of cycles
- depth of discharge
- state of charge
- battery chemistry
- internal resistance
These factors can affect:
- capacity
- power
- efficiency
- lifetime
- safety
Temperature
Temperature can strongly affect rechargeable batteries.
At low temperatures:
- chemical reactions may proceed more slowly
- internal resistance can increase
- available power may decrease
- usable capacity may temporarily decrease
At high temperatures:
- reactions may proceed faster
- degradation may accelerate
- unwanted side reactions may increase
Very high temperatures can create:
serious safety problems.
Why Does Your Phone Battery Perform Differently in the Cold?
At low temperatures, electrochemical processes inside the battery become less effective.
The battery may temporarily:
- provide less current
- show reduced available capacity
- experience greater voltage drop under load
This does not necessarily mean that all of the stored chemical energy has permanently disappeared.
Performance can improve when the battery returns to an appropriate:
operating temperature.
Charge Rate
Charging a battery quickly can be convenient.
However, very rapid charging can increase:
- heating
- electrochemical stress
- unwanted side reactions
Modern charging systems therefore carefully control:
current and voltage.
The safe charging rate depends on the battery chemistry and design.
Discharge Rate
How quickly energy is removed also affects battery performance.
A high-power device demands a large:
current.
High discharge rates can cause:
- greater internal heating
- larger voltage drops
- reduced usable capacity in some systems
Battery designers therefore distinguish between:
energy requirements and power requirements.
Energy vs Power
These terms are related but different.
Energy
describes how much work can ultimately be done.
Power
describes how quickly energy is transferred.
A battery may store a large amount of energy but be unable to release it safely at an extremely high:
power.
Internal Resistance
Real batteries have:
internal resistance.
When current flows, some energy is converted into heat inside the battery.
The power lost internally can be described by:
P = I²R
where:
P = power converted to heat
I = current
R = internal resistance
Because current is squared, high currents can cause substantial:
heating.
Battery Age
Rechargeable batteries gradually change even if they are not used heavily.
This is called:
calendar aging.
Factors contributing to aging can include:
- time
- temperature
- state of charge
- chemical side reactions
Therefore a rechargeable battery can lose capacity simply through:
aging.
Cycle Aging
Using and recharging a battery also causes degradation.
This is called:
cycle aging.
Repeated cycling can cause:
- loss of active material
- electrode structural changes
- electrolyte degradation
- increased internal resistance
Eventually the battery can no longer store its original amount of:
energy.
Cycle Life
Cycle life describes how many charge-discharge cycles a battery can complete before its capacity falls to a specified level.
A battery's cycle life depends on:
- chemistry
- temperature
- charging conditions
- discharge conditions
- depth of discharge
Therefore there is no single cycle-life value that applies to all rechargeable batteries.
Depth of Discharge
Depth of discharge (DoD) describes the percentage of usable battery capacity that has been removed.
For example:
A battery begins at 100%.
It is used until 40% remains.
The depth of discharge is approximately:
60%.
For some battery systems, repeated deep discharge contributes to faster degradation.
State of Charge
State of charge (SoC) describes how much usable charge remains.
For example:
100% SoC = fully charged
50% SoC = approximately half charged
0% SoC = discharged to its defined lower operating limit
State of charge and depth of discharge are related but opposite ideas.
Battery Management Systems
Large or sophisticated rechargeable batteries often use a:
battery management system (BMS).
A BMS can monitor:
- voltage
- current
- temperature
- state of charge
- individual cells in a battery pack
It can help protect the battery from:
- overcharging
- excessive discharge
- overheating
- excessive current
Why Battery Packs Need Management
A large battery pack may contain hundreds or thousands of individual cells.
Small differences can develop between cells.
One cell might become:
- more charged
- less charged
- hotter
- more degraded
than neighboring cells.
A BMS helps keep the battery pack operating within appropriate:
limits.
Electric Vehicle Batteries
Electric vehicles require batteries capable of storing large amounts of energy while also providing high power.
Important EV battery characteristics include:
- energy density
- power density
- charging speed
- cycle life
- temperature performance
- mass
- cost
- safety
Lithium-ion technology is widely used because it provides a useful balance of these properties.
Regenerative Braking
Electric and hybrid vehicles can recover some energy while slowing down.
Normally, braking converts kinetic energy into:
thermal energy.
With regenerative braking, the electric motor can operate as a generator.
The energy transformations are approximately:
kinetic energy → electrical energy → chemical energy
Some of this recovered energy is stored in the battery.
Renewable Energy Storage
Rechargeable batteries can also store energy generated by:
- solar panels
- wind turbines
- other electricity sources
For example:
During sunny conditions:
solar energy → electrical energy → chemical energy
Later:
chemical energy → electrical energy
This allows energy generated at one time to be used:
later.
Environmental Benefits of Rechargeable Batteries
Rechargeable batteries can reduce the number of batteries that must be manufactured and discarded.
One rechargeable battery may replace many single-use batteries over its useful life.
Potential benefits include:
- less repeated battery waste
- reduced packaging
- fewer replacement batteries
- support for renewable-energy storage
- electrification of transportation
However, rechargeable batteries still have:
environmental impacts.
Raw Materials
Battery manufacturing requires raw materials.
Depending on battery chemistry, these can include:
- lithium
- nickel
- cobalt
- manganese
- graphite
- copper
- aluminum
- lead
Mining and processing these materials can require:
- energy
- water
- land
- transportation
and can create environmental and social impacts.
Mining Impacts
Mining can potentially affect:
- habitats
- water resources
- soil
- local ecosystems
- surrounding communities
The severity depends on factors such as:
- material being mined
- mining method
- location
- environmental controls
- energy sources
- waste management
Therefore battery sustainability must consider the entire:
life cycle.
Manufacturing
Battery manufacturing also requires energy.
Important processes can include:
- refining materials
- producing electrode materials
- manufacturing cells
- assembling battery packs
- transporting components
If manufacturing energy comes from fossil fuels, this can increase the battery's:
carbon footprint.
Battery Use
The environmental impact during use depends partly on where the charging electricity comes from.
For example, electricity could be generated from:
- solar
- wind
- hydroelectric power
- nuclear power
- natural gas
- coal
Therefore the environmental impact of operating a rechargeable battery depends partly on the:
electricity system supplying it.
End of Life
Eventually rechargeable batteries lose enough performance that they are no longer suitable for their original application.
At this stage they may be:
- reused
- repurposed
- recycled
- disposed of according to local regulations
Proper management is important because batteries contain:
valuable and potentially hazardous materials.
Battery Recycling
Battery recycling can recover materials for future use.
Depending on the process and battery chemistry, recoverable materials can include:
- lithium
- nickel
- cobalt
- copper
- aluminum
- lead
Recycling can reduce:
- demand for newly mined material
- waste sent for disposal
- loss of valuable resources
Lead-Acid Battery Recycling
Lead-acid batteries have well-established recycling systems in many regions.
Materials that can be recovered include:
- lead
- plastics
- other components
Because lead is toxic, responsible collection and recycling are particularly:
important.
Lithium-Ion Recycling
Lithium-ion battery recycling is increasingly important as the number of:
- electric vehicles
- portable electronics
- energy-storage systems
increases.
Recycling technologies aim to recover valuable battery materials so that they can potentially be returned to:
manufacturing supply chains.
Second-Life Batteries
An electric vehicle battery may eventually lose enough capacity that it is no longer ideal for transportation.
However, it may still have useful capacity for less demanding applications.
Possible second-life applications can include:
stationary energy storage.
This can extend the useful life of the battery before final:
recycling.
A Battery Life Cycle
The life cycle of a rechargeable battery can be represented as:
Raw material extraction
↓
Material processing
↓
Battery manufacturing
↓
Transportation
↓
Battery use
↓
Reuse or second life
↓
Recycling
↓
Recovered materials
↓
New products
A more circular system attempts to keep useful materials in circulation rather than treating used batteries simply as:
waste.
Comparing Environmental Impacts
Rechargeable batteries are not automatically environmentally harmless.
A complete comparison should consider:
- raw material extraction
- manufacturing
- transportation
- number of uses
- charging electricity
- lifespan
- recycling
- disposal
A rechargeable battery used hundreds of times may have advantages over repeatedly replacing primary batteries, particularly when it is:
properly recycled.
Safety and Lithium-Ion Batteries
Lithium-ion batteries store a large amount of energy in a relatively small space.
If a battery is:
- physically damaged
- internally short-circuited
- severely overheated
- improperly charged
rapid heating can occur.
In severe cases, this can lead to:
thermal runaway.
Thermal Runaway
Thermal runaway occurs when heat-producing reactions cause the battery temperature to rise, which then causes further heat-producing reactions.
This creates a dangerous positive feedback cycle:
temperature rises → reactions accelerate → more heat → temperature rises further
Battery design includes multiple safety systems intended to reduce this risk.
Battery Safety Systems
Safety measures can include:
- separators
- protective circuits
- temperature sensors
- current limits
- voltage limits
- battery management systems
- thermal management
These systems are especially important in:
large lithium-ion battery packs.
Comparing Battery Technologies
When evaluating a battery, there is rarely one technology that is "best" in every category.
A useful comparison should consider:
Energy density
How much energy can it store for its mass or volume?
Power
How quickly can it provide energy?
Cycle life
How many times can it be charged and discharged?
Cost
How expensive is the battery?
Safety
How does it behave under abnormal conditions?
Mass
How heavy is it?
Temperature performance
How well does it operate in hot or cold environments?
Environmental impact
What materials and processes are required?
Choosing a Battery for a Smartphone
Important characteristics include:
- low mass
- small size
- high energy density
- rechargeable operation
- useful cycle life
Lithium-ion technology is well suited to these requirements.
A lead-acid battery would be impractical because it would be:
far too heavy and bulky for comparable portable use.
Choosing a Battery for Starting a Car
A starter battery must provide a very large:
current
for a short period.
Lead-acid batteries can provide high currents relatively inexpensively.
Therefore they remain widely used for:
vehicle starting systems.
Choosing Rechargeable AA Batteries
For frequently used household devices, NiMH batteries can be useful.
For example:
- game controllers
- cameras
- toys
- flashlights
Instead of repeatedly purchasing disposable alkaline batteries, the same NiMH cells can be:
recharged and reused.
Choosing a Battery for Grid Storage
For large stationary energy-storage systems, battery mass may be less important than it is for smartphones or electric vehicles.
Important considerations can include:
- cost
- cycle life
- safety
- material availability
- efficiency
- lifetime
This means technologies that are not ideal for portable electronics may still be useful for:
stationary storage.
Worked Example 1
A phone battery is rated:
3.8 V, 4000 mAh
Convert capacity:
4000 mAh = 4.0 Ah
Calculate approximate nominal energy:
Energy = V × Ah
Energy = 3.8 × 4.0
Energy = 15.2 Wh
Worked Example 2
A battery stores 60 Wh and has a mass of 0.30 kg.
Calculate its specific energy.
Specific energy = energy ÷ mass
= 60 ÷ 0.30
= 200 Wh/kg
Worked Example 3
A battery begins at 100% state of charge and is used until 25% remains.
Depth of discharge:
100% − 25% = 75%
Therefore:
DoD = 75%.
Worked Example 4
A rechargeable battery originally has a capacity of:
5000 mAh
After several years it can store only:
4000 mAh
Percentage of original capacity remaining:
4000 ÷ 5000 × 100
= 80%
The battery retains approximately:
80% of its original capacity.
Worked Example 5
Why might a battery become warmer when supplying a large current?
Some electrical energy is converted into thermal energy because of:
internal resistance.
Since:
P = I²R
increasing current can greatly increase internal heating.
Worked Example 6
Why are lithium-ion batteries useful in electric vehicles?
They provide a useful combination of:
- high energy density
- high power capability
- rechargeability
- relatively low mass
- useful cycle life
Vehicle designers must still manage cost, degradation, temperature, and safety.
Worked Example 7
Why might lead-acid be preferred over lithium-ion for some applications?
Lead-acid batteries can offer:
- low initial cost
- high current capability
- mature technology
- established recycling
If mass and energy density are less important, these advantages can make lead-acid suitable.
Worked Example 8
A student says:
"Rechargeable batteries are environmentally friendly because they create no waste."
This statement is:
incomplete.
Rechargeable batteries can reduce waste through repeated use, but they still require:
- raw materials
- manufacturing
- electricity
- eventual recycling or disposal
Their full environmental impact must be evaluated across the battery's:
life cycle.
Common Mistake: Batteries Store Electricity
Batteries primarily store:
chemical energy.
During discharge, this chemical energy is converted into electrical energy.
Common Mistake: Lithium Ions Travel Through the Wire
Lithium ions move mainly through the:
electrolyte.
Electrons move through the:
external circuit.
Keeping these two charge movements separate is essential for understanding lithium-ion batteries.
Common Mistake: Rechargeable Means Unlimited Use
Rechargeable batteries have a finite:
cycle life.
Chemical and physical degradation gradually reduces their performance.
Common Mistake: Higher Capacity Means Higher Voltage
Capacity and voltage are different.
A battery can have:
greater capacity but the same voltage.
Capacity describes available charge.
Voltage describes electrical potential difference.
Common Mistake: Fast Charging Has No Effect
Fast charging can be convenient, but it may increase:
- heat
- chemical stress
- degradation
Battery and charger design determine how rapidly charging can occur safely.
Common Mistake: Cold Permanently Destroys All Capacity
Cold temperatures can temporarily reduce battery performance because electrochemical processes slow and internal resistance increases.
Some performance may return when the battery warms to an appropriate operating temperature.
Extreme temperatures, however, can contribute to:
permanent damage.
Common Mistake: Rechargeable Batteries Have No Environmental Impact
Rechargeable batteries require:
- mining
- processing
- manufacturing
- transportation
- electricity
- end-of-life management
Their environmental benefits and costs must be evaluated across their entire:
life cycle.
Common Mistake: All Rechargeable Batteries Are the Same
Different battery technologies have very different characteristics.
The best battery depends on the required balance of:
energy, power, cost, mass, safety, lifetime, and environmental impact.
Check Your Understanding
- What type of energy is primarily stored in a rechargeable battery?
- What energy transformation occurs during discharge?
- What energy transformation occurs during charging?
- What type of chemical reactions occur during battery operation?
- Why can secondary batteries be recharged?
- Where do electrons travel during discharge?
- What carries charge through the electrolyte?
- Name the major components of a lithium-ion cell.
- What is the purpose of the separator?
- What happens to lithium ions during discharge?
- What happens to lithium ions during charging?
- Why is a lithium-ion battery different from a primary lithium battery?
- Define battery capacity.
- What units are commonly used for capacity?
- Define energy density.
- Why is high energy density important for smartphones?
- Calculate the energy of a 3.7 V, 2.5 Ah battery.
- Name three rechargeable battery technologies.
- Give two common applications of lead-acid batteries.
- Why are lead-acid batteries suitable for starting vehicles?
- Give two applications of NiMH batteries.
- Give two advantages of lithium-ion batteries.
- Give two limitations of lithium-ion batteries.
- What is sodium-ion battery technology?
- Define self-discharge.
- Define cycle life.
- Explain the difference between calendar aging and cycle aging.
- What is depth of discharge?
- What is state of charge?
- Explain how temperature can affect battery performance.
- Why can high current cause battery heating?
- What is internal resistance?
- What does a battery management system do?
- Why are battery management systems particularly important in large battery packs?
- Explain how regenerative braking can recharge an electric vehicle battery.
- Explain how rechargeable batteries can support renewable-energy systems.
- Identify three environmental impacts associated with battery production.
- Explain why battery recycling is important.
- What is meant by a second-life battery?
- What is thermal runaway?
- Why can damaged lithium-ion batteries present a safety hazard?
- A 12 V battery has a capacity of 8 Ah. Calculate its approximate energy in Wh.
- A 100 Wh battery has a mass of 0.5 kg. Calculate its specific energy.
- A battery originally stored 3000 mAh but now stores 2400 mAh. What percentage of its original capacity remains?
- Compare lithium-ion, lead-acid, and NiMH batteries in terms of energy density, mass, applications, and environmental considerations.
- Explain why no single rechargeable battery technology is ideal for every application.
- Evaluate which battery characteristics are most important for a smartphone.
- Evaluate which characteristics are most important for an electric vehicle.
- Explain why environmental comparisons should consider the entire battery life cycle.
- Describe the complete energy-storage cycle of a rechargeable battery from charging through discharge and recharging.
Key Terms
Rechargeable battery: Battery containing secondary cells designed for repeated charging and discharging.
Chemical energy: Energy stored in the chemical state and arrangement of substances.
Discharge: Process in which stored chemical energy is converted into electrical energy.
Charging: Process in which electrical energy drives chemical changes that restore stored chemical energy.
Lithium-ion battery: Rechargeable battery in which lithium ions move between electrode materials.
Electrolyte: Material through which ions move inside an electrochemical cell.
Separator: Material that prevents direct electronic contact between electrodes while allowing ionic movement.
Capacity: Amount of electrical charge a battery can deliver under specified conditions.
Energy density: Amount of energy stored per unit volume or, more broadly in common usage, relative to battery size.
Specific energy: Energy stored per unit mass, commonly measured in Wh/kg.
Cycle life: Number of charge-discharge cycles a battery can undergo before reaching a specified performance limit.
State of charge: Measure of how much usable charge remains in a battery.
Depth of discharge: Percentage of usable battery capacity that has been removed.
Self-discharge: Gradual loss of stored charge while a battery is not being used.
Internal resistance: Resistance within a battery that contributes to voltage loss and heating when current flows.
Battery management system: Electronic system used to monitor and control battery operation.
Regenerative braking: Recovery of some kinetic energy during vehicle braking for storage in the battery.
Thermal runaway: Self-accelerating heating process that can occur in a severely failing battery.
Battery recycling: Recovery and processing of materials from used batteries.
Key Takeaways
- Rechargeable batteries store energy mainly as chemical energy.
- During discharge, chemical energy is converted into electrical energy.
- During charging, electrical energy is converted into stored chemical energy.
- Rechargeable batteries use electrochemical reactions that are sufficiently reversible for repeated operation.
- Lithium-ion batteries move Li⁺ ions through the electrolyte while electrons move through the external circuit.
- The separator prevents direct electrical contact between the electrodes while allowing ions to move.
- Lithium-ion batteries offer high energy density and are widely used in portable electronics and electric vehicles.
- Lead-acid batteries are heavier but inexpensive, capable of high currents, and widely recycled.
- NiMH batteries are useful in rechargeable household cells and some vehicle applications.
- Battery performance depends on temperature, charge rate, discharge rate, age, internal resistance, state of charge, and cycling.
- Capacity, voltage, energy, and power describe different aspects of battery performance.
- Rechargeable batteries gradually lose capacity because their chemistry is not perfectly reversible.
- Battery management systems help control voltage, current, temperature, and other operating conditions.
- Rechargeable batteries can support renewable energy and electric transportation.
- Battery production requires raw materials and energy and therefore has environmental impacts.
- Environmental evaluation should consider the entire battery life cycle, not only its use.
- Reuse, second-life applications, and recycling can reduce waste and recover valuable materials.
- Different battery technologies involve trade-offs between energy density, power, cost, mass, safety, lifespan, and environmental impact.