Electronics 101: Lesson-10 Battery Technologies

Introduction:

This tutorial will mainly focus on the most often used batteries in our D.I.Y Mechatronics projects as there are quite a number of different battery technologies on the market today. We shall cover a number of things concerning batteries which include but not limited to the following; the different types of batteries, the defining characteristics and terminologies used in batteries, and how they are charged and discharged.

Battery defining characteristics and terminologies;

Shape;
Batteries come in different shapes and sizes. You’ve probably heard of “AA” and “AAA” batteries, these refer to the specific shapes and sizes of these batteries.

Nominal cell voltage;
This is basically the average voltage a cell/battery outputs when fully charged and it depends on the chemical reaction behind it. A coin cell battery will output 3V whereas a lead-acid car battery will output 12V. The actual measured voltage on a battery will decrease as it discharges.

Capacity;
This refers to the amount of power a battery can store. When it’s fully charged, the capacity is the amount of power it contains and often time batteries of the same type will be rated by the amount of current they can output over time which is measured in (mAh) for-example 5500mAh.

Energy density;
The energy density of any battery can be calculated by combining capacity with its shape and size. Different battery technologies allow different densities for-instance, lithium-ion batteries are capable of storing more power in a given volume as compared to alkaline or coin cell batteries.

Internal discharge rate;
This is basically the rate at which a battery discharges itself over time. Batteries always discharge when sitting on the shelf or when unused. A typical example of this is trying to start a motor vehicle that has been sitting in your back-yard for some time, chances are it will not start.

Primary Vs Secondary;
Primary batteries are also referred to as disposable batteries and these once fully-drained, can’t be recharged. This means they have a lower discharge rate, so they last longer but they can also be less economical than their counterparts. A typical example of primary batteries are alkaline AA or AAA batteries.

Secondary batteries are also known as rechargeable batteries and these require another power source to fully charge back up and also they’re capable of fully charging and discharging many times over their life-span. They have a higher discharge rate but they are economical. A typical example of secondary batteries are Lithium-ion batteries

BMS (Battery Management System);
This is basically an intelligent electronic component responsible for monitoring and managing a battery pack. It’s the brain behind the battery responsible for its performance, charge rates, longevity and its levels of safety by protecting the battery from operating outside its safe operating area.

Discharge Protection Circuit:
This prevents the battery from discharging below a certain voltage level to prevent damage to the battery.

C-Rating:
This is the measure of the rate at which a battery is being charged or discharged. A 1C-rate means a fully charged battery with a capacity of 100Ah should be able to provide 100Amps for one hour.

Battery Life:
Battery life or better known as battery lifetime has two meanings for rechargeable batteries but only one for non-rechargeables. For rechargeables, it can mean either the length of time a device can run on a fully charged battery or the number of charge/discharge cycles possible before the cells fail to operate satisfactorily. For a non-rechargeable these two lives are equal since the cells last for only one cycle by definition.

 

Types of Batteries;

1. Coin Cell batteries;

These are small round-shaped very cheap batteries, majority of which are not rechargeable and are a good choice for very small, low power projects such as illuminating LEDs. They are often times used in remote controls, digital wrist watches and in lots of small disposable devices.

Some coin cell batteries are alkaline with a nominal voltage of 1.5V whereas others are lithium with a nominal voltage of 3V.

Coin cell batteries come in different categories such as different sizes and each with a specific code name to indicate the size and chemistry. Lithium coin cells are all prefixed with a “C” for-example the popular “CR2032” is a lithium battery with a nominal voltage of 3V whereas Alkaline coin cell batteries all start with an “L” for-example an “LR1154” (LR44) is an alkaline battery with a nominal voltage of 1.5V.

 

2. Alkaline batteries;

These are by-far the most common type of battery that you can get anywhere. They are safe-to-use due to their alkaline chemistry and are very cheap but unfortunately they’re not rechargeable.

Typical examples of alkaline batteries are the AA, AAA and 9V non-rechargeable batteries. AA and AAA have an output nominal voltage of 1.2V (but usually are around 1.5V when first used). Because of their low voltage, they are often combined in packs of 3 or 4 to run a 3.3V or 5V system. As for the 9V batteries, they are usually 9V nominally and they are great choice to make a project portable though they don’t last long since the capacity of a 9V battery is pretty low.

These batteries are a great choice for newbies as they are readily available almost anywhere in the world.

One thing that should be noted however is that if these batteries are attached backwards, they might heat up but you don’t have to worry too much as this causes little damage.

 

3. Lithium Ion (li-ion) and Lithium Polymer batteries (Li-Po);

The main difference between these two types of batteries is this;

Lithium-ion batteries are a type of rechargeable battery in which lithium ions move from the positive electrode through an electrolyte to the negative electrode during charging and back when discharging. They use an interlaced lithium compound as the material at the positive electrode and typically graphite at the negative electrode. They are known to have a high energy density, no memory effect and low self-discharge.

 

Whereas Lithium Polymer batteries or sometimes called Lithium-ion polymer batteries are a type of rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. These batteries provide higher specific energy than other lithium battery types.

These batteries are used in a number of applications where weight is a critical feature such as in mobile devices, laptop computers, power banks, media players, power tools, radio-controlled equipment like cars and aircraft and in some electric vehicles.

The capacity of the battery you choose depends on the intended run time of your project, size constraints and other factors.

 

Almost all Li-Po batteries have a small safety circuit built into the top of the cell that will shut off the battery if the voltage drops below a certain threshold (usually 3V) and they also have a very low internal discharge rate which makes them a good candidate for projects that have low power requirements and need to run for many days or months. Not forgetting that they pack a lot of juice which can source multiple amps continuously.

Nominal Voltage;

A given Li-Po cell has a nominal voltage of 3.7V and when its fully charged, you’ll see nearly 4.3V but it’ll quickly drop to 3.7V under normal use. If you need 5V or more, you’ll need to combine two or three Li-Pos in series to create a 7.4V or 11.1V pack and regulate it down to your requirement.

Charging and discharging;

Most Li-Po batteries come terminated with various 2-pin connectors which prevents the battery from being plugged in the wrong way.

Before charging a Li-ion or Li-Po battery, ensure that you are aware of the battery capacity and the charge current supplied by the charger. A Li-Po battery can be harmed by overcharging, so use a specifically designed Li-Po charger for a given battery like the one showed above. They are usually low-cost and use USB to charge the battery.

 

Other examples of Lithium Ion Batteries;

4. High discharge lithium Ion Batteries;

These are most commonly used in powering RC robots, UAVs and portable projects that need a small battery with a lot of juice.

These have a nominal voltage of 7.4V and they don’t have a built protection circuit just like the Li-Po batteries seen above. So this means, we must be extremely careful when charging and discharging these batteries.

As seen in the image above, these batteries do have a charge connector which is a 3-pin JST-XH charge plug and discharge is via the Dean’s connector discharge leads.

For charging and discharging this type of battery, a special balance-charger is needed since they are typically dual cell battery packs, they are not compatible with single cell chargers.

 

5. High capacity lithium Ion Batteries;

These are often round in shape but are often bigger than the “AA” non-rechargeable alkaline batteries. A typical example of this type of battery is the famous 18650 rechargeable Li-Ion battery found in most laptop batteries. These too pack a lot of power/juice and they are easy to use for your DIY projects.

These batteries also carry a nominal voltage of 3.7V and just like the high discharge Li-Po batteries above, they too don’t have a protection circuit built-in just like we saw in the flat Li-Po batteries before.

These batteries can be used in your DIY projects by using specific battery holders and they are also a good candidate when it comes to building your own battery packs for your homemade electric bikes and scooters.

Special attention should be given to these batteries when charging and discharging them since there is no protection circuit on these batteries so you must account for the possibility of overcharging or under charging.

An intelligent universal charger can be used in this case as shown above.

 

6. Lithium Ion Phosphate batteries (LiFePO4);

This is a type of Lithium-ion battery that uses the Lithium-ion phosphate as the cathode material and a graphitic carbon electrode with a metallic backing as the anode.

This type of battery technology is finding a number of applications in electric vehicle use, utility scale stationary applications and backup power in solar systems because of its high discharge rates needed for acceleration, lower weight, low cost, low toxicity, well-defined performance, and long-term stability.

The main drawback of this type of battery is its low electrical conductivity.

LiFePO4 batteries have a nominal voltage of 3.2V and can easily be charged with a li-ion phosphate charger that is programmed with the appropriate voltage limits. Combining 4 cells in series gives a nominal voltage of 12.8V which is close to the nominal voltage of six-cell lead-acid batteries. This makes them a good potential replacement for lead-acid batteries in applications such as automotive and solar applications.

The other thing you should put into consideration when working with this type of battery is that, the cells must be balanced initially before the pack is assembled and a protection system (BMS) must also be added to the battery pack to ensure no cell can be discharged below a voltage of 2.5V or severe damage will occur in most instances.

 

7. Nickel Metal Hydride (Ni-MH) & Nickel Cadmium (Ni-Cd) batteries;

A nickel metal hydride battery (abbreviated as NiMH or Ni-MH) is a type of a rechargeable battery whose chemical reactions at the positive electrode are somewhat similar to the sealed Nickel Cadmium (Ni-Cd) batteries in that it utilizes a Nickel based positive electrode (the cathode) that is the nickel oxide hydroxide (Ni-OOH) but however the negative electrodes use a hydrogen-absorbing alloy instead of cadmium (Cd).

NiMH batteries are often cheaper than other chemistries and can have two to three times the capacity of Ni-Cd batteries of the same size with significantly higher energy density although much less than Lithium-ion batteries and they are typically used as an alternative for similarly shaped non-rechargeable alkaline batteries since they feature a slightly lower but mostly compatible cell voltage and are also resistant against leaking and explosion.

NiMH batteries are often found in low cost electronic devices such as cordless shavers and toothbrushes where the output voltage is less of a concern.

Each NiMH or Ni-Cd cell has a nominal voltage of 1.2V which is close to alkaline batteries of the same size that output 1.5V. Combining 4 NiMH or Ni-Cd batteries will give you a 4.8V pack which should run most 5V systems.

 

NiMH batteries have no discharge protection circuits and because of their similarity to regular consumer AA batteries, charging them is often done with chargers that plug into the wall. When fast-charging, it is advisable to charge the NiMH cells with a smart battery charger to avoid overcharging which can damage the cells.

Nickel–metal hydride (NiMH) batteries are the newest, and most similar, competitor to Ni–Cd batteries. Compared to Ni–Cd batteries, NiMH batteries have a higher capacity and are less toxic, and are now more cost effective. However, a Ni–Cd battery has a lower self-discharge rate (for example, 20% per month for a Ni–Cd battery, versus 30% per month for a traditional NiMH under identical conditions).

 

8. Lead-Acid (Deep Cycle, AGM, Gel & VRLA) batteries;

The lead-acid battery is the first type of rechargeable battery ever created. It was invented by a French physicist Gaston Plante in 1859. A lead-acid battery is basically composed of lead at the positive and negative plates and diluted sulfuric acid as the electrolyte.

Lead-acid batteries are often times used in automobiles specifically for starting, lighting and ignition or provide high current required by starter motors. They’re mostly preferred for this application because of their relatively low cost as compared to newer technologies, low energy density and easy to maintain among other reasons.

Charging and Discharging;

When its fully charged (Charged State), the chemical energy of the battery is stored in the potential difference between the pure lead at the negative side and the Lead dioxide (PbO2) on the positive side plus the electrolyte solution with higher concentrations of aqueous sulfuric acid which stores most of the chemical energy.

When discharged (Discharged State), both the positive and negative plates become lead (ii) sulfate (PbSO4) and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water.

Over charging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water which bubbles out and is lost. Some types of lead-acid batteries are designed to allow the electrolyte levels to be inspected and topped up with pure water to replace any that has been lost. We’re pretty sure you’ve probably done this on your 12V lead-acid battery in your car.

 

Deep-Cycle Batteries;

These are lead-acid batteries with a different geometry for their positive electrodes. The positive electrode is not a flat plate but a row of lead-oxide cylinders or tubes strung side by side so their geometry is called tubular or cylindrical. This increases the surface area in contact with the electrolyte with higher discharge and charge currents than a flat-plate cell of the same volume and depth-of-charge.

These have a higher power density than flat-plate cells which makes them suitable for high-current applications with weight or space limitations and also in applications where they’re regularly discharged such as in electric vehicles (golf carts, forklifts, and electric cars), photovoltaic systems, uninterruptible power supplies, among other applications.

 

Absorbent-Glass Mart (AGM) batteries;

AGM batteries are lead-acid batteries with a glass fiber mat soaked in electrolyte to act as the separator between the plates as it is in the flooded design. There is only enough electrolyte in the mat to keep it wet and if the battery is punctured, the electrolyte will not flow out of the mats.

The primary reason for this design is to substantially increase the gas transport through the separator, hydrogen and oxygen gas produced during overcharge or charge is able to freely pass through the glass mat and reduce or oxidize the opposing plate respectively. The mat also prevents the vertical motion of the electrolyte within the battery.

 

Gel batteries;

These batteries are composed of a mixture of a silica gelling agent into the electrolyte. This converts the formerly liquid interior of the cells into a semi-stiff paste providing many of the same advantages of the AGM batteries. They have lower freezing and higher boiling points than the liquid electrolytes used in conventional wet cells and AGMs which makes them suitable for use in extreme conditions.

Gel batteries are less susceptible to evaporation and are often used in situations where little or no periodic maintenance is possible. Gel batteries are most commonly used in energy storage applications like off-grid systems.

However, gel batteries have a downside where the gel prevents rapid motion of the ions in the electrolyte which reduces carrier mobility and thus surge current capability.

 

Valve Regulated Lead-Acid (VRLA) batteries;

In a VRLA battery, the hydrogen and oxygen produced in the cells largely recombine into water. Leakage is minimal although some electrolyte still escapes if the recombination cannot keep up with gas evolution. Since these batteries do not require regular checking of the electrolyte levels, they are often referred to as Maintenance free batteries. However, this is always not the case, as the electrolyte is lost, the VRLA cells dry out and lose capacity and this can be detected by taking regular internal resistance, conductance or impedance measurements.

VRLA batteries are most commonly used in motorcycles because the acid electrolyte is absorbed into the separator so it cannot spill and this also helps them better withstand vibrations while in motion. They’re also applied in stationary applications such as telecommunication devices due to their small foot print and installation flexibility.

 

Conclusion:

You probably have a clear distinction of the different battery technologies out there. We’ve looked at the different battery terminologies, their internal chemistries, nominal voltages, how to charge and discharge them and their different applications in the real world.


 

 

Tum Kurtzman
Author: Tum Kurtzman

Computer Engineer, Ugandan Life Hacker, Tech Blogger, YouTuber, Founder & Lead Engineer at SONALABS.ORG... Tum completed his BSc. in Computer Engineering from Makerere University and you can reach him via e-mail at tum@sonalabs.org.

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