Battery Manufacturing and Cell Grades – Part 2

Battery cell grades are a classification system that manufacturers use to distinguish the benefits of capacity and runtime.

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? In part 2 of this article series we will continue where we left off and 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 I unpack that answer 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 I continue 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 batteries electrolyte per second. A milliAmp hour (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 the third longest runtime and cycle life.

Until next time Dan Hagopian www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

Battery Manufacturing and Battery Cell Grades – Part 1

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 then another?

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 then 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:

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.

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)]}.

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.

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). In part 2 of this article series I will explain what the different grades mean and how manufacturers use the different grades and what the grades mean to you and your battery.

Until next time Dan Hagopian www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

Rechargeable Batteries Can Only Be Charged 300-500 Times – Part 2

In the last two articles we addressed how and why rechargeable batteries have limited charge cycles. We reviewed in detail the effect of a charge-discharge cycle – a chemical change in a battery system that results in degradation and power loss. But there is one aspect in my last article that deserves special attention. This one factor is the basis of battery degradation. It is the reason why 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 chain of events have been discussed in depth in previous articles which you can access on my blog but what is 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 good reasons – let’s look at a few!

General 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.

Until next time Dan Hagopian www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

Rechargeable Batteries Can Only Be Charged 300-500 Times – Part 1

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 degredation?

In my last article I explained how that the simple task of charging a battery is far from easy. For example I examined 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 without question charging a battery is anything but easy.

One other thing we learned that has helped shape this article 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?

Battery Degradation and Power Loss

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 control and 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 that I write of are:

Declining capacity  – when the amount of charge a battery can hold gradually decreases due to usage, aging, and with some chemistry, lack of maintenance.

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.

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).

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 battery's self-discharges 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.

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 I will, in my next article, discuss why battery degradation occurs in the first place.

Until next time – Dan Hagopian www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.