2. Outline
• Why is this important?
• Brief history of batteries
• Basic chemistry
• Battery types and characteristics
• Case study: ThinkPad battery technology
3. The Electrochemical Series
Most wants to reduce
(gain electrons)
• Gold
• Mercury
• Silver
• Copper
• Lead
• Nickel
• Cadmium
• Iron
• Zinc
• Aluminum
• Magnesium
• Sodium
• Potassium
• Lithium
Most wants to oxidize
(lose electrons)
But, there’s a reason
it’s a sodium drop
4. Battery Characteristics
• Size
– Physical: button, AAA, AA, C, D, ...
– Energy density (watts per kg or cm3
)
• Longevity
– Capacity (Ah, for drain of C/10 at 20°C)
– Number of recharge cycles
• Discharge characteristics (voltage drop)
5. Further Characteristics
• Cost
• Behavioral factors
– Temperature range (storage, operation)
– Self discharge
– Memory effect
• Environmental factors
– Leakage, gassing, toxicity
– Shock resistance
6. Primary (Disposable) Batteries
• Zinc carbon (flashlights, toys)
• Heavy duty zinc chloride (radios, recorders)
• Alkaline (all of the above)
• Lithium (photoflash)
• Silver, mercury oxide (hearing aid,
watches)
• Zinc air
7. Standard Zinc Carbon Batteries
• Chemistry
Zinc (-), manganese dioxide (+)
Zinc, ammonium chloride aqueous electrolyte
• Features
+ Inexpensive, widely available
– Inefficient at high current drain
– Poor discharge curve (sloping)
– Poor performance at low temperatures
8. Heavy Duty Zinc Chloride Batteries
• Chemistry
Zinc (-), manganese dioxide (+)
Zinc chloride aqueous electrolyte
• Features (compared to zinc carbon)
+ Better resistance to leakage
+ Better at high current drain
+ Better performance at low temperature
9. Standard Alkaline Batteries
• Chemistry
Zinc (-), manganese dioxide (+)
Potassium hydroxide aqueous electrolyte
• Features
+ 50-100% more energy than carbon zinc
+ Low self-discharge (10 year shelf life)
± Good for low current (< 400mA), long-life use
– Poor discharge curve
12. Lithium Manganese Dioxide
• Chemistry
Lithium (-), manganese dioxide (+)
Alkali metal salt in organic solvent electrolyte
• Features
+ High energy density
+ Long shelf life (20 years at 70°C)
+ Capable of high rate discharge
– Expensive
15. Nickel Cadmium Batteries
• Chemistry
Cadmium (-), nickel hydroxide (+)
Potassium hydroxide aqueous electrolyte
• Features
+ Rugged, long life, economical
+ Good high discharge rate (for power tools)
– Relatively low energy density
– Toxic
16. NiCd Recharging
• Over 1000 cycles (if properly maintained)
• Fast, simple charge (even after long storage)
C/3 to 4C with temperature monitoring
• Self discharge
10% in first day, then 10%/mo
Trickle charge (C/16) will maintain charge
• Memory effect
Overcome by 60% discharges to 1.1V
20. NiMH Recharging
• Less prone to memory than NiCd
• Shallow discharge better than deep
Degrades after 200-300 deep cycles
Need regular full discharge to avoid crystals
• Self discharge 1.5-2.0 more than NiCd
• Longer charge time than for NiCd
To avoid overheating
25. Lead Acid Batteries
• Chemistry
Lead
Sulfuric acid electrolyte
• Features
+ Least expensive
+ Durable
– Low energy density
– Toxic
26. Lead Acid Recharging
• Low self-discharge
– 40% in one year (three months for NiCd)
• No memory
• Cannot be stored when discharged
• Limited number of full discharges
• Danger of overheating during charging
27. Lead Acid Batteries
• Ratings
CCA: cold cranking amps (0F for 30 sec)
RC: reserve capacity (minutes at 10.5v, 25amp)
• Deep discharge batteries
Used in golf carts, solar power systems
2-3x RC, 0.5-0.75 CCA of car batteries
Several hundred cycles
28. Lithium Ion Batteries
• Chemistry
Graphite (-), cobalt or manganese (+)
Nonaqueous electrolyte
• Features
+ 40% more capacity than NiCd
+ Flat discharge (like NiCd)
+ Self-discharge 50% less than NiCd
– Expensive
32. Discharge Rates
Type Voltage Peak
Drain
Optimal
Drain
Alkaline 1.5 0.5C < 0.2C
NiCd 1.25 20C 1C
Nickel metal 1.25 5C < 0.5C
Lead acid 2 5C 0.2C
Lithium ion 3.6 2C < 1C
33. Recharging
Type Cycles
(to 80%)
Charge
time
Discharge
per month
Cost per
kWh
Alkaline 50 (50%) 3-10h 0.3% $95.00
NiCd 1500 1h 20% $7.50
NiMH 300-500 2-4h 30% $18.50
Li-ion 500-1000 2-4h 10% $24.00
Polymer 300-500 2-4h 10%
Lead acid 200-2000 8-16h 5% $8.50
34. Lithium-ion Batteries in
Notebooks
• Lithium: greatest electrochemical potential,
lightest weight of all metals
– But, Lithium metal is explosive
– So, use Lithium-{cobalt, manganese, nickel}
dioxide
• Overcharging would convert lithium-x
dioxide to metallic lithium, with risk of
explosion
