What Is a Primary Cell?

A primary cell is an electrochemical cell designed to be used until its chemical reactants are largely consumed and then discarded or recycled.

Primary cells are normally:

non-rechargeable.

They convert stored:

chemical energy → electrical energy

through spontaneous redox reactions.

Common primary cells include:

• alkaline cells
• zinc-carbon cells
• primary lithium cells
• zinc-air cells
• silver oxide button cells

Primary cells are widely used because they are often:

• inexpensive
• portable
• convenient
• easy to store
• ready to use

---

Cells and Batteries

The words cell and battery are often used interchangeably in everyday language, but they have slightly different scientific meanings.

A cell is a single electrochemical unit.

A battery can contain one or more electrochemical cells connected together.

For example, an AA alkaline "battery" is technically a single:

electrochemical cell.

A larger battery may contain several individual cells.

---

How Does a Primary Cell Produce Electricity?

A primary cell contains two electrodes and an electrolyte.

At one electrode:

oxidation occurs.

At the other electrode:

reduction occurs.

These reactions transfer electrons from one substance to another.

If the electrons are forced to travel through an external circuit, they can provide:

electrical energy.

---

The Basic Energy Conversion

The overall energy transformation is:

chemical energy → electrical energy

The chemical reactants have stored chemical energy.

As the spontaneous redox reaction occurs, electrons travel through the external circuit.

These moving electrons can power devices such as:

• flashlights
• clocks
• remote controls
• toys
• smoke detectors
• calculators

---

The Anode

In a discharging primary cell, the anode is where:

oxidation occurs.

Oxidation involves:

loss of electrons.

The anode supplies electrons to the external circuit.

Remember:

AN OX

ANode = OXidation

---

The Cathode

The cathode is where:

reduction occurs.

Reduction involves:

gain of electrons.

Electrons travel through the external circuit toward the cathode.

Remember:

RED CAT

REDuction = CAThode

---

Electron Flow

During discharge, electrons move through the external circuit:

anode → device → cathode

For example, if the cell powers a flashlight:

anode → wire → lamp → wire → cathode

As electrons pass through the device, electrical energy can be converted into other forms.

In a flashlight:

electrical energy → light + thermal energy

---

What Happens Inside the Cell?

Electrons travel through the external circuit, but ions move inside the cell.

The electrolyte contains mobile ions that help:

• carry charge
• maintain electrical neutrality
• complete the internal circuit

Therefore:

electrons move through the external circuit

while:

ions move through the electrolyte.

---

Why Are Primary Cells Non-Rechargeable?

As a primary cell operates, its chemical reactants are converted into:

products.

Eventually:

• reactants become depleted
• products accumulate
• electrode materials may change
• the cell voltage decreases
• the cell can no longer provide useful electrical energy

The chemical system is designed primarily for:

discharge.

---

Irreversible Chemical Changes

In a rechargeable cell, applying an external electrical current can drive the cell chemistry back toward its original state.

In a primary cell, the discharge reactions are generally not practically reversible under normal operating conditions.

During discharge, there may be changes in:

• electrode composition
• electrode structure
• electrolyte composition
• distribution of reaction products

Simply forcing electrons backward does not reliably restore the original:

chemical system.

---

Why Can't We Just Reverse the Reaction?

It might seem that connecting a primary cell to a power supply should simply reverse the redox reaction.

In practice, unwanted reactions may occur instead.

Attempting to recharge a cell not designed for recharging can cause:

• gas production
• leakage
• overheating
• internal damage
• pressure buildup
• rupture or fire in some battery chemistries

Therefore primary cells should generally:

not be recharged unless the manufacturer explicitly states that they are rechargeable.

---

Primary vs Secondary Cells

Electrochemical cells are commonly divided into two broad categories.

Primary cells

• designed mainly for one discharge cycle
• generally non-rechargeable
• discarded or recycled after use

Secondary cells

• designed for repeated charging and discharging
• rechargeable
• reactions can be driven back toward the charged state

Examples of secondary cells include:

• lithium-ion cells
• nickel-metal hydride cells
• lead-acid cells

---

Primary Cell

During normal operation:

chemical energy → electrical energy

Once the useful reactants have been consumed:

replace or recycle the cell.

---

Secondary Cell

During discharge:

chemical energy → electrical energy

During charging:

electrical energy → stored chemical energy

This cycle can be repeated many times, although rechargeable cells also eventually:

degrade.

---

Common Primary Cells

Several different chemical systems are used in primary cells.

Important examples include:

Zinc-carbon cells

Often used in inexpensive, low-drain devices.

Alkaline cells

Common in household AA, AAA, C, D, and 9 V batteries.

Primary lithium cells

Used where long shelf life, low mass, or reliable performance is important.

Silver oxide cells

Common in small button-cell applications.

Zinc-air cells

Used in applications including many hearing aids.

Each uses a different:

electrochemical system.

---

Zinc-Carbon Cells

The zinc-carbon cell is one of the older common types of dry cell.

It typically uses:

• zinc as an important anode material
• manganese dioxide in the cathode mixture
• an electrolyte paste

Zinc-carbon cells are inexpensive and are often suitable for:

low-drain devices.

---

Why Is It Called a Dry Cell?

Early electrochemical cells often contained large amounts of liquid electrolyte.

A dry cell uses an electrolyte that is immobilized as a paste or similar material rather than a freely flowing bulk liquid.

This makes the cell:

• portable
• easier to handle
• less likely to spill

However, the term "dry" does not mean that there is:

no electrolyte present.

---

Structure of a Zinc-Carbon Cell

A typical zinc-carbon cell contains:

• zinc container
• electrolyte paste
• manganese dioxide-containing cathode mixture
• carbon rod used as a current collector
• separator
• terminals

The carbon rod helps collect current but is not simply the chemical reactant responsible for the cathode reaction.

---

Alkaline Cells

One of the most familiar primary cells is the:

alkaline cell.

Alkaline cells are commonly sold as:

• AA
• AAA
• C
• D
• 9 V batteries

They are used in many everyday devices.

---

Alkaline Cell Chemistry

A typical alkaline cell uses:

zinc

as an anode material and:

manganese dioxide

as a cathode material.

The electrolyte is usually based on:

potassium hydroxide (KOH).

Potassium hydroxide is alkaline, which gives the battery its name.

---

Energy Conversion in an Alkaline Cell

As the alkaline cell discharges:

zinc is oxidized

and:

manganese-containing species are reduced.

Electrons leave the anode and travel through the external circuit.

The overall process converts:

chemical energy → electrical energy.

---

Alkaline Cells vs Zinc-Carbon Cells

Both systems commonly use zinc and manganese dioxide chemistry, but their designs and electrolytes differ.

Compared with traditional zinc-carbon cells, alkaline cells generally provide:

• longer useful life
• better performance under moderate or higher drain
• longer shelf life
• greater capacity for many applications

However, alkaline cells are usually:

more expensive than basic zinc-carbon cells.

---

Primary Lithium Cells

Some primary cells use:

lithium metal.

These are different from the rechargeable lithium-ion cells commonly used in phones and laptops.

This distinction is important.

Primary lithium cell = normally non-rechargeable

Lithium-ion cell = rechargeable

---

Why Use Lithium?

Lithium has useful electrochemical properties.

Primary lithium cells can provide advantages such as:

• high energy density
• relatively low mass
• long shelf life
• useful performance across a range of temperatures

Different primary lithium cells use different cathode materials and therefore have different:

voltages and characteristics.

---

Coin and Button Cells

Small electrochemical cells are often manufactured in:

coin or button shapes.

They are useful where devices require compact power sources.

Examples include:

• watches
• calculators
• car key fobs
• small sensors
• medical devices

However, not all button or coin cells use the same chemistry.

Some are:

primary cells

while others may be:

rechargeable cells.

---

Silver Oxide Cells

Silver oxide primary cells are often used in small devices requiring relatively stable voltage.

Applications can include:

• watches
• calculators
• small instruments

They typically use:

zinc as an anode material

and:

silver oxide as a cathode material.

Their relatively high cost limits their use in larger everyday batteries.

---

Zinc-Air Cells

Zinc-air cells are unusual because one of the reactants comes from:

the surrounding air.

Oxygen enters the cell and participates in the cathode reaction.

Because the cell does not need to store all of this oxygen internally, more space can be used for other active materials.

---

Zinc-Air Applications

Zinc-air cells are commonly associated with:

hearing aids.

Many zinc-air batteries are activated when a protective tab is removed.

Removing the tab allows:

oxygen from the air

to enter the cell.

Once activated, the cell gradually begins functioning and should generally be used within its intended period.

---

Why Do Primary Cells Eventually Go Flat?

A cell does not contain an unlimited supply of chemical energy.

As it operates:

reactants → products

Eventually, one or more reactants become sufficiently depleted that the cell can no longer maintain a useful:

voltage and current.

We commonly say that the battery is:

dead or flat.

The matter inside the battery has not disappeared.

Instead, its:

chemical composition has changed.

---

Voltage During Discharge

A primary cell's voltage may change during use.

As discharge proceeds:

• reactant concentrations change
• products accumulate
• internal resistance may increase
• electrode surfaces may change

Eventually the voltage becomes too low to operate the device effectively.

Different battery chemistries have different:

discharge curves.

---

Capacity

The amount of electrical charge a battery can deliver is called its:

capacity.

Battery capacity is often expressed in:

ampere-hours (Ah)

or:

milliampere-hours (mAh).

For example:

2000 mAh = 2.0 Ah

Capacity is not the same thing as:

voltage.

---

Voltage vs Capacity

Imagine two cells:

Cell A:

1.5 V, 1000 mAh

Cell B:

1.5 V, 2500 mAh

They have approximately the same nominal voltage.

However, Cell B has a greater rated:

capacity.

Under suitable conditions, it can deliver more total charge before becoming discharged.

---

Energy Stored in a Battery

Battery energy depends on both:

voltage and capacity.

A useful approximate relationship is:

Energy (Wh) = Voltage (V) × Capacity (Ah)

For example, a 1.5 V cell with a capacity of 2.0 Ah has an approximate nominal energy of:

1.5 × 2.0 = 3.0 Wh

Actual usable energy depends on operating conditions.

---

Advantages of Primary Cells

Primary cells have several important advantages.

They are often:

• inexpensive initially
• simple to use
• widely available
• portable
• compact
• reliable after long periods of storage

Some primary chemistries also have:

very low self-discharge.

This makes them useful for devices that may remain unused for long periods.

---

Long Shelf Life

Shelf life describes how long a battery can be stored while retaining useful capacity.

Some primary cells have excellent shelf lives because their chemistry changes relatively slowly when the circuit is:

open.

This can make them useful for:

• emergency equipment
• smoke detectors
• backup devices
• rarely used electronics

---

Ready to Use

Primary cells normally arrive:

already charged and ready to operate.

They do not require:

• a charger
• a charging period
• charging electronics

For simple applications, this makes them very:

convenient.

---

Low Initial Cost

Many primary cells are inexpensive to purchase.

For a device used only occasionally, buying a primary cell may initially cost less than buying:

• rechargeable batteries
• a compatible charger

However, this changes when batteries must be replaced:

frequently.

---

Limitations of Primary Cells

Primary cells also have significant limitations.

They are generally:

• single-use
• not rechargeable
• replaced after discharge
• capable of producing substantial waste
• potentially more expensive over repeated use

Their suitability therefore depends on the:

application.

---

Long-Term Cost

Imagine a device that requires new batteries every week.

Using disposable primary cells repeatedly can become:

expensive.

A rechargeable battery may cost more initially but can potentially be used for many:

charge-discharge cycles.

Therefore primary cells are often less economical for:

high-use devices.

---

Environmental Impact

Used primary cells contain:

• metals
• electrolytes
• plastics
• other chemical materials

Manufacturing replacements requires additional:

• raw materials
• energy
• transportation
• packaging

Proper battery collection and recycling can help reduce some environmental impacts.

---

Battery Disposal

Battery disposal rules vary between locations and battery chemistries.

Some batteries should be taken to designated:

battery collection or recycling facilities.

This can:

• recover useful materials
• reduce waste
• prevent inappropriate disposal

Users should follow local regulations and manufacturer instructions.

---

Leakage

Some primary batteries can leak after:

• long storage
• deep discharge
• physical damage
• exposure to unsuitable conditions

Leaked electrolyte can:

• damage electronics
• corrode contacts
• irritate skin

Old batteries should therefore be removed from devices that will not be used for:

long periods.

---

Mixing Batteries

Devices commonly use several cells together.

It is generally poor practice to mix:

• old and new cells
• different battery chemistries
• different brands or capacities where manufacturers advise against it

Cells at different states of discharge may behave differently and can increase the risk of:

leakage or poor performance.

---

Choosing a Primary Cell

The best battery depends on the device.

Important factors include:

• required voltage
• required current
• capacity
• size
• mass
• shelf life
• operating temperature
• cost
• expected frequency of use

There is no single battery chemistry that is best for:

every application.

---

Example: TV Remote

A television remote control typically uses relatively little electrical energy.

It may operate for months using one set of batteries.

Primary alkaline cells can be suitable because they offer:

• convenience
• long storage life
• reasonable cost
• adequate capacity

The batteries do not need frequent replacement.

---

Example: Digital Camera

Some devices draw considerably more current.

If a device is used frequently and consumes batteries quickly, disposable primary cells may become:

expensive and wasteful.

Rechargeable secondary cells may be more appropriate.

---

Example: Smoke Detector

Some smoke detectors must operate continuously for long periods while consuming relatively little power.

A battery with a long:

shelf and service life

can be valuable.

Certain primary lithium batteries are used for applications where long operating life is particularly important.

---

Example: Emergency Flashlight

An emergency flashlight may sit unused for months.

Important battery properties include:

• long shelf life
• reliability
• low self-discharge

A suitable primary battery can therefore be advantageous even though it is:

non-rechargeable.

---

Example: Hearing Aid

A hearing aid needs a small, lightweight power source with useful energy capacity.

Zinc-air cells are widely used because oxygen comes from:

outside the battery.

This helps provide useful energy capacity in a compact package.

---

Evaluating Primary Cells

When deciding whether a primary cell is suitable, consider both:

advantages and limitations.

For occasional use:

Primary cells may offer excellent convenience.

For frequent use:

Rechargeable cells may reduce long-term cost and waste.

For long-term storage:

Some primary cells may offer excellent shelf life.

For high-energy repeated use:

Secondary cells may be more suitable.

---

Primary vs Secondary Cells

---

Worked Example 1

A battery converts stored chemical energy into electrical energy.

What type of reaction makes this possible?

A:

redox reaction.

Oxidation occurs at the anode while reduction occurs at the cathode.

Electrons travel through the external circuit.

---

Worked Example 2

Why is an alkaline AA cell considered a primary cell?

Because it is designed primarily for:

one discharge cycle

and is normally:

non-rechargeable.

---

Worked Example 3

A remote control uses one set of batteries for a year.

Would primary cells be reasonable?

Yes.

The device has relatively low energy demand, so the advantages of:

• convenience
• low initial cost
• long shelf life

may outweigh the disadvantage of being non-rechargeable.

---

Worked Example 4

A child's electronic toy requires a new set of batteries every few days.

What limitation of primary cells becomes important?

Repeated replacement causes:

• greater long-term cost
• more battery waste

A rechargeable secondary battery may be more practical for such frequent use.

---

Worked Example 5

Why does a primary cell eventually stop producing useful electricity?

Its chemical reactants are gradually:

consumed or transformed.

As the chemical system changes, the cell can no longer maintain sufficient:

voltage and current.

---

Worked Example 6

A cell has:

1.5 V

and:

2.4 Ah

Estimate its nominal energy.

Use:

Energy = Voltage × Capacity

Energy = 1.5 × 2.4

Energy = 3.6 Wh

---

Worked Example 7

Two batteries both provide 1.5 V.

One has a capacity of 1000 mAh and the other 2500 mAh.

Do they have the same capacity?

No.

They have similar nominal voltage, but the 2500 mAh cell can deliver more total:

charge under specified conditions.

---

Worked Example 8

Why might a primary lithium battery be useful in an emergency device?

Primary lithium cells can offer properties such as:

• long shelf life
• high energy density
• relatively low mass

These can be useful when a device must remain ready after long periods of:

storage.

---

Common Mistake: Primary Means First Battery

The word primary does not mean that it was the first type of battery invented.

It describes a cell intended mainly for:

non-rechargeable use.

---

Common Mistake: A Dead Battery Contains No Energy or Chemicals

A discharged battery still contains:

matter and chemical substances.

However, its chemical system has changed so that it can no longer provide useful electrical energy under normal operating conditions.

---

Common Mistake: Primary Cells Have No Electrolyte

All functioning electrochemical cells require ionic conduction.

Primary cells contain an:

electrolyte.

In many dry cells, the electrolyte is immobilized rather than existing as a large volume of free liquid.

---

Common Mistake: Electrons Move Through the Electrolyte

Electrons primarily move through the:

external circuit.

Inside the electrolyte, charge is transported mainly by:

ions.

---

Common Mistake: All Lithium Batteries Are Rechargeable

They are not.

Primary lithium batteries

are normally non-rechargeable.

Lithium-ion batteries

are designed to be rechargeable.

The words "lithium" and "lithium-ion" do not describe the same battery chemistry.

---

Common Mistake: All Primary Cells Are Identical

Primary cells can use many different chemical systems.

They can differ in:

• voltage
• capacity
• size
• shelf life
• cost
• energy density
• operating temperature

The term primary cell describes their general use category rather than one particular chemistry.

---

Common Mistake: Rechargeable Is Always Better

Rechargeable cells have important advantages, but primary cells can be more suitable for some applications.

For example, a primary cell may be preferred when:

• the device is rarely used
• long shelf life is important
• charging is inconvenient
• very low self-discharge is desirable

Battery choice depends on the:

intended application.

---

Check Your Understanding

1. Define a primary cell.

2. What energy transformation occurs in a primary cell?

3. Why are primary cells normally non-rechargeable?

4. What type of chemical reaction produces electricity in a primary cell?

5. Where does oxidation occur?

6. Where does reduction occur?

7. In which direction do electrons move through the external circuit?

8. What is the role of the electrolyte?

9. Why do primary cells eventually stop producing useful electricity?

10. Name four common types of primary cells.

11. What is a zinc-carbon cell?

12. Why is it called a dry cell?

13. What are two important materials used in an alkaline cell?

14. Why is an alkaline cell called alkaline?

15. Give three common uses of alkaline cells.

16. What is the difference between a primary lithium cell and a lithium-ion cell?

17. Give two advantages of primary lithium cells.

18. What is a silver oxide cell commonly used for?

19. How does a zinc-air cell obtain one of its reactants?

20. Why are zinc-air cells useful in hearing aids?

21. Explain the difference between voltage and capacity.

22. What unit is commonly used for battery capacity?

23. A 1.5 V cell has a capacity of 2.0 Ah. Estimate its nominal energy in Wh.

24. Give four advantages of primary cells.

25. Give four limitations of primary cells.

26. Why might primary cells be suitable for a television remote?

27. Why might rechargeable cells be more suitable for a frequently used toy?

28. Why is shelf life important for emergency equipment?

29. What is self-discharge?

30. Why should primary cells generally not be recharged?

31. What problems could occur if a non-rechargeable battery is incorrectly charged?

32. Why should old batteries be removed from devices being stored?

33. Explain why battery leakage can damage electronics.

34. Why is recycling batteries useful?

35. Explain why repeated use of primary cells can create more waste than rechargeable cells.

36. Distinguish between a cell and a battery.

37. Explain why increasing battery capacity does not necessarily increase its voltage.

38. Compare primary and secondary cells.

39. A device is used only once every few months. Explain why a primary cell might be appropriate.

40. Evaluate whether primary or secondary cells would be more suitable for a frequently used electronic device. Support your answer using cost, convenience, lifetime, and environmental impact.

---

Key Terms

• Primary cell: Electrochemical cell designed mainly for one discharge cycle and normally not rechargeable.
• Secondary cell: Electrochemical cell designed for repeated charging and discharging.
• Battery: One or more electrochemical cells used as a source of electrical energy.
• Anode: Electrode where oxidation occurs.
• Cathode: Electrode where reduction occurs.
• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.
• Redox reaction: Reaction involving both oxidation and reduction.
• Electrolyte: Material containing mobile ions that conducts charge inside an electrochemical cell.
• Dry cell: Cell in which the electrolyte is immobilized rather than present as a large amount of free-flowing liquid.
• Alkaline cell: Common primary cell using an alkaline electrolyte, typically potassium hydroxide.
• Zinc-carbon cell: Inexpensive primary dry-cell chemistry using zinc and manganese dioxide-based materials.
• Primary lithium cell: Non-rechargeable cell using lithium metal as part of its chemistry.
• Zinc-air cell: Cell that uses oxygen from the surrounding air as a reactant.
• Silver oxide cell: Primary cell commonly used in small button-cell applications.
• Capacity: Amount of electrical charge a battery can deliver under specified conditions.
• Ampere-hour: Unit commonly used to express battery capacity.
• Shelf life: Length of time a battery can be stored while retaining useful capacity.
• Self-discharge: Gradual loss of stored chemical energy while a battery is not being used.
• Discharge: Process in which a cell supplies electrical energy through a spontaneous chemical reaction.

---

Key Takeaways

• A primary cell is designed mainly for one discharge cycle and is normally non-rechargeable.
• Primary cells convert chemical energy into electrical energy.
• Electricity is produced through spontaneous redox reactions.
• Oxidation occurs at the anode and reduction occurs at the cathode.
• Electrons travel through the external circuit from anode to cathode.
• Ions move through the electrolyte to maintain charge balance.
• Primary cells become discharged because their chemical reactants are progressively transformed into products.
• Their chemistry and physical structure are generally not designed to be restored safely by electrical charging.
• Common primary cells include alkaline, zinc-carbon, primary lithium, silver oxide, and zinc-air cells.
• Alkaline cells are among the most common household primary batteries.
• Primary lithium cells should not be confused with rechargeable lithium-ion cells.
• Zinc-air cells use oxygen from the surrounding air as a reactant.
• Important advantages of primary cells include convenience, portability, availability, low initial cost, and often long shelf life.
• Important limitations include single-use operation, repeated replacement costs, resource consumption, and waste generation.
• Voltage and battery capacity are different quantities.
• A battery with greater capacity does not automatically have a greater voltage.
• Primary cells can be especially useful in low-drain, infrequently used, or long-storage applications.
• Rechargeable secondary cells are often more suitable when batteries are used and replaced frequently.
• Battery choice should consider voltage, capacity, shelf life, cost, size, operating conditions, frequency of use, and environmental impact.