Batteries — Applications & Characteristics

Introduction 

In today’s rapidly changing era, we can’t deny that wireless electronics gadgets engulf our lives, be it a smartphone, laptop, watch, or remote. Our lives swivel around these gizmos indisputably. All most all of them are fuelled by Batteries 0r Cells as their primary power source. We wouldn’t build any wireless electronic device and rely on wired power sources only; even electric cars and space missions would not be possible without Batteries.

A battery is an electrochemical cell (or enclosed and guarded material) that can be charged electrically to supply a static potential for power or released electrical charge when needed.

A cell is a single unit bearing DC voltage in the range of 1.5V to 3V.a battery is more precisely a collection of such two or more cells connected in parallel or series or both, giving rise to higher voltage and current. Even when practically cell and battery are different things, they are used quite interchangeably.

 

Types of batteries 

The basic categorization of batteries is as follows

1. Primary batteries or Non-rechargeable batteries
2. Secondary batteries or Rechargeable batteries

 

A standard Electrochemical Cell

An electrochemical cell is a device that can generate electrical energy from the chemical reactions occurring in it, or use the electrical power supplied to it to facilitate chemical reactions in it. These devices are capable of converting chemical energy into electrical energy, or the other way around. A typical example of an electrochemical cell could be a standard 1.5-volt cell employed to power many electrical appliances like TV remotes and clocks.

Functional components of electrochemical cell

• Negative electrode
• Positive electrode
• Electrolyte
• Separator
• Current collectors

At Negative Electrode

Anode: In an electrochemical cell, the negative electrode is often metal or an alloy or hydrogen (lead metal or paste for PbA). During discharge, it gives up electrons to external circuits, is oxidized. During charge, accepts electrons from the external circuit is reduced.

During charge:   M⁺ + e^-       ( reduction is gain of electrons)

During discharge:  M^{-   -} e^-     (oxidation is loss of electrons)

 

At Positive Electrode

Cathode: In an electrochemical cell, the positive electrode is often a metallic oxide, sulfide, or oxygen (lead oxide for PbA). During discharge, accepts electrons from the circuit is reduced. During charge, gives up electrons to an external circuit, is oxidized.

During charge:     M^-     e ^-          (oxidation is loss of electrons)

During discharge: M⁺ + e^-         ( reduction is gain of electrons)

 

Electrolyte

As electrons move in the external circuit, compensating ions must move internally to the cell

• Cations are ions with a net positive charge: during discharge, they move through the electrolyte toward the positive electrode.
• Anions are ions with net negative charge: during discharge, they move through the electrolyte toward the negative electrode.

 The electrolyte offers a medium for internal ion charge transfer between the electrodes. The electrolyte is typically a solvent containing dissolved chemicals—an acid, base, or salt—providing ionic conductivity. It must be an electronic insulator to avoid self-discharge.

 

Separator & Current Collectors 

The separator electrically isolates the positive and negative electrodes to avoid short circuits and self-discharge of the cell, Often made from glass mat or fibre, or polyethylene, or a polymer.

Since electrodes are often made from powders, current collectors are metal foils—to which electrodes have adhered—that conduct electrical current to cell terminals.

 

Important Characteristics

The following are a few vital characteristics of an electrochemical cell, which define the nature, ability, and applications of these cells.

Power Capacity

It is the energy stored in a battery, which is measured in Watt-hour.

Watt-hour = V * I * hours

Units: Ah/mAh

 

Power Capability

It means the amount of energy (or current; since the voltage is usually fixed) that the battery can deliver charged or discharged. It is also known as C-rating or C-rate. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1Ah should provide 1A for one hour.

Theoretically, it is calculated as A-h divided by 1 hour.

For example: 

25000 mA hour / 1 hours      = 25000 mA = 25 A = 25 C         

 

Nominal Voltage

Nominal voltage: It is the nominal/ average voltage of the battery/ cell between its maximum and minimum values.

Units: Volts

 

Charging Current

It is the maximum current that can be applied to charge the battery.

Units: Amps

 

Charging Voltage

It is the maximum voltage that should be applied to the battery to efficiently charge a battery.
Units: Volts

 

Discharging Current

It is the current that can be drawn from the battery and is delivered to the load. If the current drawn by the load is greater than the rated discharging current, the battery drains very fast, which causes the battery to heat up quickly, which also causes the battery to explode.

Units: Amps

 

Shelf Life

Shelf life defines the time period a battery can be stay powered up and should be able to use it for a rated time period. Shelf life is mainly considered for non-rechargeable batteries.

 

Cut-off Voltage

It is the voltage at which the battery can be considered as fully discharged, after which if we still try to discharge from it, the battery gets damaged.

 

Cycle Life 

The number of cycles that a battery can charge and discharge defines the cycle life. The more the cycle life, the better will be the battery’s quality.

 

Power Density

It defines the power capacity of the battery for a given mass of volume.

Units: Wh/Kg

 

Few Prominent Battery Technologies

Lead-Acid Battery (PbA)

The lead-acid was the first rechargeable battery for commercial use, invented in 1859.

The lead-acid is not subject to memory. Leaving the battery on float charge for a prolonged time does not cause damage. The battery’s charge retention is best among rechargeable batteries.

Components:

• Positive electrode:Lead peroxide (PbO2); dark chocolate brown in color.
• Negative electrode:Sponge lead; grey in color.
• Electrolyte: Dilute Sulfuric Acid (H2SO4);31% of Sulphuric Acid.

Nickel-Cadmium Battery (Ni-Cd)

These are very rarely used; these are very cheap, and their discharge rate is very low when compared to NiMH batteries. These are available in all standard sizes like AA, AAA, C, and rectangular shapes. NiCd is a strong and silent worker. In fact, it performs well under rigorous working conditions.

A periodic full discharge is so important that, if not conducted, large crystals are formed on the cell plates (also referred to as memory), and the battery will gradually lose its performance. These contain toxic metals and is environmentally unfriendly.

Components

• Positive electrode: Nickel Hydroxide Ni(OH)2
• Negative electrode: Cadmium Cd
• Electrolyte: an alkaline Potassium Hydroxide KOH

Fig 4: Internal structure of Ni-Cd battery^[5]

^{Electrode Reactions}

Applications:

• The NiCd batteries are used where long life, high discharge rate, and economical price are important. Chief applications include two-way radios, biomedical equipment, professional video cameras, and power tools.
• The small sets of NiCd batteries are used in portable devices, electronics, and toys, while the bigger ones are employed in aircraft starting batteries, Electric vehicles, and standby power supply.
• Used in cordless phones, solar lights, etc.

Specifications:

• Specific Energy: 40-60W-h/kg
• Energy Density: 50-150 W-h/L
• Specific Power: 150W/kg
• Charge/discharge efficiency: 70-90%
• Self-discharge rate: 10%/month
• Cycle durability/life: 2000cycles
• Nominal voltage = 1.2V
• Power density = 60 Wh/Kg
• Operating temperature: -40 to 60 degree Celsius

Advantages:

• Cheap in cost
• Easy to recharge
• Can be used in all environments
• Comes in all standard sizes

Disadvantages:

• Lower power density
• Contains toxic metal
• Needs to be charged very frequently in order to avoid growth of crystals on the battery plate.

 

Nickel - Metal Hydride Battery (NiMh)

Batteries based on the NiMH chemistry are not susceptible to the “memory” effect that Nickel Cadmium (NiCd) Batteries experience. They are bulky, contain high-pressure steel canisters, and value thousands of dollars per cell. Cycling under heavy load and storage at hot temperatures reduces the service life. The NiMH suffers from high self-discharge, which is considerably greater than that of the NiCd.

Components:

• Positive electrode: Nickel Hydroxide Ni(OH)2
• Negative electrode: Hydrogen absorbing alloy; Rare-earth or nickel alloys with many metals
• Electrolyte: an alkaline Potassium Hydroxide KOH

Fig 6: Internal reactions of NiMH battery^[7]

^{Electrode Reactions}

Applications:

• Ni-MH battery packs are used in portable electronic applications such as laptop, notebook, and sub-notebook computers, cellular communication devices, and consumer electronic devices such as camcorders. 
• Used in almost all applications similar to the alkaline and Ni-Cad batteries.
• Power sources in wireless communications and mobile computing.  
• Portable computers; cellular phones;

Specification:

• Specific Energy: 60-120h/kg
• Energy Density: 140-300 Wh/L
• Specific Power: 250-1000 W/kg
• Charge/discharge efficiency: 66% - 92%
• Self-discharge rate: 1.3-2.9%/month at 20^oC
• Cycle Durability/life: 180 -2000
• Nominal voltage = 1.25 V
• Power density = 100 Wh/Kg.
• Operating temperature:  -20 to 60  degree Celsius

 

Advantages:

• Available in all standard sizes.
• High power density.
• Easy to recharge.
• A good alternative to alkaline which has almost all similarities and also it is rechargeable.

Disadvantages:

• Self-discharge is very high.
• Expensive than Ni-Cad batteries.

 

Fig 7: Ni-MH batteries in standard  sizes^[6]

 

Lithium-ion Battery (LiB)

Lithium is the lightest of all metals, has the best electrochemical potential, and provides the largest energy density per weight. Lithium-ion batteries are one of the foremost popular forms of rechargeable batteries. Lithium-ion batteries generally possess high energy density, little or no memory effect, and low self-discharge compared to other battery types. These are the best rechargeable batteries available.

Components:

• Positive electrode: lithium oxide is used as an active material.
• Negative electrode: generally,
• Electrolyte: typically, a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions.

Fig 8:  Flow of electrons in Li-ion battery while charging and discharging ^[10]

^{Electrode Reactions}

Applications:

• Li-ion batteries used in handheld electronic devices are usually based on lithium cobalt oxide (LiCoO2)
• They are found in different portable appliances, including mobile phones, smart devices, and several other battery appliances used at home.
• They also find applications in aerospace and military applications due to their lightweight nature.
• They are used in various products such as personal computers, smartphones, and tablets. You may think that nearly all LiB is used in batteries that exist around you.
• It is also widely expected as a battery for electric vehicles.

 

Specification:

• Specific Energy: 100 - 265W-h/kg
• Energy Density: 250 - 693 W-h/L
• Specific Power: 250 - 340 W/kg
• Charge/discharge percentage: 80-90%
• Cycle Durability: 400 - 1200 cycles
• Nominal cell voltage: 6/3.85V
• Operating temperature: -20 to 60 degrees Celsius
• Power density = 126 Wh/Kg

 

Advantages:

• Very light in weight.
• High C-rating.
• Power density is very high.
• Cell voltage is high.
• Stable and safe
• slow self-discharge

 

Disadvantages:

• These are a bit expensive.
• If the terminals are short circuited the battery might explode.
• Battery protection circuit is needed.

Fig 9: A 3.7 V Li-ion portable battery^[9]

 

Future of Batteries

While smartphones, smart homes, and even smart wearables are growing ever more advanced, they're still limited by power. Big technology and car companies are all too aware of the limitations of lithium-ion batteries. Here are a few significant and amazing battery technologies that could be us very soon.

• Professor Arumugam Manthiram, Walker Department of Mechanical Engineering and director of the Texas Materials Institute, and other researchers at Texas University have developed a lithium-ion battery that doesn't use Cobalt for its cathode. Instead, it is switched to a high percentage of nickel (89 percent) using manganese and aluminum for the other ingredients. Cobalt is the least abundant and most expensive component in battery cathodes. The team ensures that this will result in good battery life and an even distribution of ions. 

• Even SVOLT, based in Changzhou, China, has announced that it has manufactured cobalt-free batteries designed for the EV market. The company claims to have collaborations with European giants for the manufacturing of batteries that have a higher energy density, resulting in ranges of up to 800km (500 miles) for electric cars, while also lengthening the life of the battery and increasing the safety.

• Researchers at the University of Eastern Finland have developed a method to produce a hybrid anode, using mesoporous silicon microparticles and carbon nanotubes.They are aiming to replace graphite as the anode in batteries and use silicon, which has ten times the capacity! The hybrid material claims to improve the performance of the battery using silicone, which is produced by barley husk ash.

• Researchers at Monash University have developed a lithium-sulfur battery that can power a smartphone for five days, outperforming lithium-ion. The new battery technology is said to have a lower environmental impact than lithium-ion and lower manufacturing costs.

• IBM's researched battery is sourced from seawater, out-performs lithium-ion, and is free from heavy metals like Cobalt and nickel. It's cheaper to manufacture; it can charge faster than lithium-ion and can pack in both higher power and energy densities. All this is available in a battery with low flammability of the electrolytes. 

Fig 10: Researches in IBM Laboratory^[19]

• A team of researchers has developed a rectenna (radio wave harvesting antenna) that is only several atoms that can harvest AC power from Wi-Fi in the air and convert it to DC, either to recharge a battery or power a device directly.

• uBeam uses ultrasound to transmit electricity. Power is turned into sound waves, inaudible to humans and animals, which are transmitted and then converted back to power upon reaching the device. This discovery was made by 25-year-old astrobiology graduate Meredith Perry.

Fig 11 : Charging smartphone with uBeam^[20]

• StoreDot, a start-up born from the nanotechnology department at Tel Aviv University, has developed the StoreDot charger. It works with current smartphones and uses biological semiconductors made from naturally occurring organic compounds known as peptides. The result is a charger that can recharge smartphones in 60 seconds.

• Alcatel has developed a mobile phone with a transparent solar panel over the screen that would let users charge their phone by simply placing it in the sun.

• The Bill Gates Foundation is funding further research by Bristol Robotic Laboratory who discovered batteries that can be powered by urine. It’s efficient enough to charge a smartphone which the scientists have already shown off.

• Samsung has managed to develop "graphene balls" that are capable of boosting the capacity of its current lithium-ion batteries by 45 percent, and recharging five times faster than current batteries. Samsung says its new graphene-based battery can be recharged fully in 12 minutes, compared to roughly an hour for the current unit.

 

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