Battery Life Cycles n Grades

8/3/2019 Battery Life Cycles n Grades

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Rechar geable Batteries Can Only Be Charged 300-500 Times

A charge-discharge cycle involves draining or using your battery to where there is for all intensive

purposes, no charge left, and then subsequently charging the battery with a power adapter to 100%

capacity. This process of charging and discharging (charge cycling) can only be done between 300-500

times. The question that we want to address is why? Why is it that lithium batteries can only be charged

less than 500 times? Why does a battery over time degrade and eventually stops working and what if any

does the reduction of the battery's active material and subsequent causes of chemical changes effect battery

degradation?

Examine how a battery, a device that converts chemical energy into electrical energy, has two internal

electrodes - an anode (the negative end) and a cathode (the positive end), and that between the two electrodes

runs an electrical current caused primarily from a voltage differential between the anode and cathode. We

learned that batteries are made up of plates of reactive chemicals (Li-ion, Li-Po, NiMH, NiCD) separated by an

electrolyte barrier (which can be either be in a liquid, solid, or gel state), and subsequently polarized so all the

electrons gather on one side. We looked at how electricity is produced through a chemical change inside the

battery system. We also learned that batteries require electricity to produce electricity and that the

introduction of electricity involves replenishing the electrons in the lithium chemical and this chemical

process is called intercalation, which, is the joining of a molecule between two other molecules. So withoutquestion charging a battery is anything but easy.

One other thing is that a charge-discharge cycle involves draining or using your battery to where there

is for all intensive purposes, no charge left, and then subsequently charging the battery with a power adapter

to 100% capacity. This process of charging and discharging (charge cycling) can only be done between

300-500 times. The question that we want to address is why is it that lithium batteries can only be charged

less than 500 times?

B a t t e r y D eg r a d a t i o n a n d P o w e r L o s s

A battery over time degrades and eventually stops working, this is no surprise, but why this occurs is

really a fascinating yet technical process. These reasons are complex issues that are way beyond user controland are wholly contained within your battery and within your device! These technical processes are a result

of the reduction of the battery’s active material and subsequent causes of chemical changes.

The chemical changes are:

a) Declining Capacity - when the amount of charge a battery can hold gradually decreases due to

usage, aging, and with some chemistry, lack of maintenance.

b) The Loss of Charge Acceptance of the Li-ion/polymer batteries is due to cell oxidation. Cell

oxidation is when the cells of the battery lose their electrons. This is a normal process of the battery

discharge process. In fact every time you use your battery a loss of charge acceptance occurs (the

charge loss allows your battery to power your device by delivering electrical current to your device).Capacity loss is permanent. Li-ion/polymer batteries cannot be restored with cycling or any other

external means. The capacity loss is permanent because the metals used in the cells run for a specific

time only and are being consumed during their service life.

c) Internal Resistance , known as Impedance, determines the performance and runtime of a battery.

It is a measure of opposition to a sinusoidal electric current. A high internal resistance curtails the

flow of energy from the battery to a device. The aging of the battery cells contributes, primarily, to

the increase in resistance, not usage. The internal resistance of the Li -ion batteries cannot be

improved with cycling (recharging). Cell oxidation, which causes high resistance, is non-reversible

and is the ultimate cause of battery failure (energy may still be present in the battery, but it can no

longer be delivered due to poor conductivity).

d) All batteries have an inherent Elevated Self-Discharge . The self-discharge on nickel-based

batteries is 10 to 15 percent of its capacity in the first 24 hours after charge, followed by 10 to 15



percent every month thereafter. Li-ion batteries self-discharge about five percent in the first 24 hours

and one to two percent thereafter in the following months of use. At higher temperatures, the

self-discharge on all battery chemistry increases. The self-discharge of a battery increases with age

and usage. Once a battery exhibits high self-discharge, little can be done to reverse the effect.

e) Premature Voltage Cut-Off - some devices like PDAs do not fully utilize the low-end voltage

spectrum of a battery. The PDA device itself, for example cuts off before the designated

end-of-discharge voltage is reached and battery power remains unused. For example, a PDA that is

powered with a single-cell Li-ion battery and is designed to cut-off at 3.7V may actually cut-off at

3.3V. Obviously the full potential of the battery and the device is lost (not utilized).

Now that we have looked at how the chemical changes in a battery effect battery degradation and power

loss and contribute to the eventual total loss of the battery, now let’s see why battery degradation occurs in the

first place.

Due to battery degradation, batteries can never just keep going and going and going. The fact is, is that all

batteries degrade and lose power because there is a reduction in the battery’s active material.

We know that a battery is a device that converts chemical energy into electrical energy. In order to convert

chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of

electrical energy. The key to the creation of electricity is that in batteries electrical energy is produced from

two chemicals in a solution. After discharging you recharge the battery via a charger. The charge process

involves intercalation: the joining of a molecule (or molecule group) between two other molecules (or groups).

Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is

one of the chemical components used to create electrical energy in batteries. Lithium compounds have

minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current.

Ionizing lithium loads the crystal planes to the point where they are forced into a current flow. Intercalation

replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive

property. You could say if you use it you will lose it!

Why then is lithium used as the chemical to create electricity in batteries? There are a number of goodreasons - let’s look at a few!

Genera l Characteristics of Lithium

• Name: lithium

• Symbol: Li

• Atomic number: 3

• Atomic weight: [6.941 (2)] g m r

• CAS Registry ID: 7439-93-2

• Group number: 1

• Group name: Alkali metal

• Period number: 2

• Block: s-block

• Standard state: solid at 298 K

• Color: silvery white/grey

• Classification: Metallic

Lithium is one of the metals in the alkali group (the other metals include Sodium, Potassium, Rubidium,

Cesium, and Francium). Lithium is a highly reactive metal. Lithium has only one electron in its outer shell

(two electrons in its inner shell), which makes it chemically “ready” to lose that one electron in ionic bonding

with other elements. Lithium is used as a battery anode material (due to its high electrochemical potential).

Electrochemical potential is the sum of the chemical potential and the electrical potential. The higher the

electrochemical potential the better the electrical current yields. In some lithium-based cells the

electrochemical potential can be five times greater than an equivalent-sized lead-acid cell and three times

greater than alkaline batteries. One other core advantage that lithium has is that it is soft and bendable which



allows for tight configurations in small cell designs (PDAs. Laptops, Cameras etc…).

Lithium, even with all of its good chemical properties will eventually, however, react to the point where

the electrochemical potential will yield a charge that is simply not enough to create current to pass to power a

device.

Battery Manufacturing and Cell Grades

What is involved when a battery is manufactured? What materials are needed to manufacture a battery?

What are battery cell grades? What do battery grades mean? How do the different grades affect the quality

of a battery? How can you know what battery grade you have? And is any one grade more important than

another?

To understand battery cell grades we have to understand how batteries are manufactured. Battery

manufacturing involves the collection of raw material, the development and setting of design specifications,

and the assembly of an individual battery pack. On a very high level that is ultimately what is involved when

a battery is made. Furtherore battery manufacturers utilize manufacturing principles, much like

manufacturers of other products, to get the batteries made efficiently and effectively.

When it comes to the collection of raw materials manufacturers have to collect very specific material to

be used in the assembly of battery packs. This material includes the following:

a) The Casing - for enclosing and hermetically sealing a battery body – is manufactured in one, two,

or three layers that include for example polyethylene terephthalate layers, a polymer layer, and a

polypropylene layer.

b) The Chemistry which is often times Lithium - based for its high electrochemical potential. An

example could be a

Solution of Lithium hexaflourophosphate (LiPF6) - a mixture of Organic Solvents: [Ethylene Carbonate (EC)

+ DiEthyl Carbonate (DMC) + DiEthyl Carbonate (DEC) + Ethyl Acetate (EA)].

c) The Electrolyte -The actual conversion of chemical energy into electrochemical energy can only be

done if an electron flow passes between two electrodes, an anode (the negative end) and a cathode(the positive end). The battery’s electrical current (electron flow) runs from one electrode to another

through a conductive chemical called an electrolyte solution.

d) The battery’s Specialized Hardware that includes: the connector, the fuse, the charge and

discharge FETs, the Cell Pack, the Sense Resistor (RSENSE), the Primary and Secondary protection

ICs, the Fuel-Gauge IC, the Thermistor, the PC Board, the EEPROM or Firmware for the

Fuel-Gauge IC.

Now part of the manufacturing process is the categorization of battery cells. Categorizing battery cells are

done in grades (Grade A, Grade B, and Grade C).

What are battery cell grades? How do manufacturers use cell grades in the manufacturing of batteries?

How do the different grades affect the quality of a battery? Now let’s look at the battery cell grade classification

system that battery manufacturers use during the process of collecting raw battery material, developing design

specifications, and assembling packs for various consumer and industrial applications.

Battery cell grades are a classification system that manufacturers use to distinguish the benefits of

capacity and runtime. Before that we need to understand that battery grades are not a measure of quality!

Battery grades do not imply that one grade is “better” than another but a reflection of capacity and internal

resistance at different price points. Before continuing with cell grades it is important to understand Capacity

and Internal Resistance.

Battery Capacity quantifies the total amount of energy stored within a battery. Battery capacity is rated

in Ampere-hours (AH), which is the product of: AH= Current x Hours to Total Discharge. Battery capacity is

measured in Amperes, which is the volume of electrons passing through the battery’s electrolyte per second.

A milli-AmpHour (mAh) is the most commonly used notation system for consumer electronic batteries. Note

that 1000 mAh is the same as 1 Ah. (Just as 1000mm equals 1 meter). In essence more capacity equals



longer runtime between battery charges.

Internal Resistance , known as Impedance, determines the performance and runtime of a battery. It

is a measure of opposition to a sinusoidal electric current. A high internal resistance curtails the flow of

energy from the battery to a device. Internal resistance is caused primarily from the opposition of current

by the electrolyte that resides between a battery’s two electrodes.

Now battery cell grading is a process of categorizing cells into grades (Grade A, Grade B, and Grade C).

Every grade is important to the manufacturer, meaning there is not one grade that is better than another. In

fact every manufacturer wants to make and sell each cell grade because of the unique differences of each

grade and because each cell grade has a specific market and device segment.

As mentioned above cells are always categorized to be graded A, B and C but there is not a single

manufacturing standard for categorizing cells; each manufacturing factory may have their own standard so

thus cell grade categorization is not necessarily scientific.

For example, Li-ion cell 053450, some companies may categorize the cell as follows:

Grade A Capacity above 1000mAh, Internal Resistance below 60mΩ

Grade B Capacity 900 to 1000mAh, Internal Resistance 60mΩ to 80mΩ

Grade C Capacity below 900mAh, Internal Resistance above 80mΩ

But for some companies with better production lines and capability, they may have higher capacity cells

so they may categorize cell 053450 as follows:

Grade A Capacity above 1100mAh, Internal Resistance below 60mΩ

Grade B Capacity 1000 to 1100mAh, Internal Resistance 60mΩ to 80mΩ

Grade C Capacity below 1000mAh, internal resistance above 80mΩ

One generally accepted conclusion can be drawn from these two examples and that is grade A cells have

the longest runtime and cycle life, grade B has the second longest runtime and cycle life and grade C has thethird longest runtime and cycle life.

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Battery Life Cycles n Grades