Design Article
Selecting the right battery
Pushek Madaan and Rajiv Badiger, Cypress
6/19/2012 8:00 AM EDT
Lithium Ion
Lithium, being the lightest metal and the one with the highest electrochemical potential, has become a common choice for battery manufacturing. However, use of lithium metal as an electrode in rechargeable batteries poses a risk of explosion. In a lithium ion battery, an electrode made out of lithium compound is used as a positive electrode and graphite as the negative. These batteries are the ones with the highest energy density and a single cell provides 3.7V to 4.2V (i.e., 3 times that of an Ni-Cd cell).
Apart from light weight and high energy density, lithium provides other advantages as well:
• Low maintenance: These batteries are hassle free because they don’t need regular maintenance like maintaining the water level in lead acid cell or complete discharging before being charged again in case of Ni-Cd batteries (memory effect).
• Low Self Discharge rate: The self discharge rate of Lithium ion battery is approx. 5-10 percent per month which is on the order of 3 times lower than NiMH batteries.
Lithium ion batteries have some significant disadvantages:
• Cell Life: An Li-ion battery requires more frequent recharging after one or two years of initial usage. This is because the charging process forms deposits inside the electrolyte which in turn increases the internal resistance and results in loss of capacity.
• Over charging and temperature: If the Li-ion battery is over charged or operated at elevated temperatures, then it loses capacity.
• Cost: As these batteries are supposed to be used at a particular voltage and temperature range, a monitoring circuit is required that shuts down the system if the voltage or temperature goes out of the range. This additional circuit increases the cost of the complete lithium ion battery charger.
Despite these disadvantages, Li-ion batteries are finding their way into more and more mobile applications because of their high energy density and light weight.
Below is table providing a summary of the different types of batteries discussed.
Editor’s note: Part 2 will discuss how to implement a battery charger using Li-Ion technology as the example.
About the authors:
Pushek Madaan is currently working with Cypress Semiconductor India Pvt. Ltd. as a Senior Application Engineer. His interests lie in designing Embedded system applications in C and assembly languages, working with analog and digital circuits, developing GUIs in C# and, above all, enjoying adventure sports. Pushek can be reached at pmad@cypress.com.
Rajiv Badiger is an applications engineer on the PSoC 1 Applications team at Cypress Semiconductor. He can be reached at rjvb@cypress.com.
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Lithium, being the lightest metal and the one with the highest electrochemical potential, has become a common choice for battery manufacturing. However, use of lithium metal as an electrode in rechargeable batteries poses a risk of explosion. In a lithium ion battery, an electrode made out of lithium compound is used as a positive electrode and graphite as the negative. These batteries are the ones with the highest energy density and a single cell provides 3.7V to 4.2V (i.e., 3 times that of an Ni-Cd cell).
Apart from light weight and high energy density, lithium provides other advantages as well:
• Low maintenance: These batteries are hassle free because they don’t need regular maintenance like maintaining the water level in lead acid cell or complete discharging before being charged again in case of Ni-Cd batteries (memory effect).
• Low Self Discharge rate: The self discharge rate of Lithium ion battery is approx. 5-10 percent per month which is on the order of 3 times lower than NiMH batteries.
Lithium ion batteries have some significant disadvantages:
• Cell Life: An Li-ion battery requires more frequent recharging after one or two years of initial usage. This is because the charging process forms deposits inside the electrolyte which in turn increases the internal resistance and results in loss of capacity.
• Over charging and temperature: If the Li-ion battery is over charged or operated at elevated temperatures, then it loses capacity.
• Cost: As these batteries are supposed to be used at a particular voltage and temperature range, a monitoring circuit is required that shuts down the system if the voltage or temperature goes out of the range. This additional circuit increases the cost of the complete lithium ion battery charger.
Despite these disadvantages, Li-ion batteries are finding their way into more and more mobile applications because of their high energy density and light weight.
Below is table providing a summary of the different types of batteries discussed.
Editor’s note: Part 2 will discuss how to implement a battery charger using Li-Ion technology as the example.
About the authors:
Pushek Madaan is currently working with Cypress Semiconductor India Pvt. Ltd. as a Senior Application Engineer. His interests lie in designing Embedded system applications in C and assembly languages, working with analog and digital circuits, developing GUIs in C# and, above all, enjoying adventure sports. Pushek can be reached at pmad@cypress.com.
Rajiv Badiger is an applications engineer on the PSoC 1 Applications team at Cypress Semiconductor. He can be reached at rjvb@cypress.com.
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Sanjib.Acharya
6/19/2012 1:21 PM EDT
This is a very nice overview of the different battery technologies.
What does the "efficiency" in the table providing a summary of the different types of batteries indicate? Efficiency of charging-discharging?
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katgod
6/20/2012 12:52 PM EDT
Good question and based on the numbers I think your guess of charge - discharge is a good one.
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Frank Eory
6/19/2012 4:19 PM EDT
Good article, but the material seems a bit dated. NiCd is in steep decline -- are those batteries even allowed in Europe anymore? And NiMH has mostly been superseded by Lithium ion for nearly all consumer portable applications.
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Hughston
6/21/2012 12:24 PM EDT
I thought Europe banned them in the mid 90s for environmental reasons.
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SimulinkJocky
6/20/2012 9:01 AM EDT
There is quite a lot of information out there pointing out that the real NICAD memory effect is largely gone in modern designs. Damage from overcharging is NOT the memory effect.
The use of a smart charger for both NI-MH and NICAD can eliminate overcharging. I hope you're going to go into that next week.
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docdivakar
6/20/2012 3:58 PM EDT
@Frank Eory & IFindNickNamesAnnoying: you are both correct, NiCd have been phased out in EU countries now, under the "batteries directive" the sale of except for medical use, alarm systems, emergency lighting, and portable power tools. This last category is to be reviewed soon.
In the US, part of the battery price charged goes toward recycling. But we all know many states are lacking in recycling e-wastes and consumers are also complicit in adhering to recycling.
MP Divakar
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Erny48
6/21/2012 2:31 AM EDT
A good article, but shouldn't it include
Lithium Iron Phosphate batteries, they seem to be the rising chemistry for a lot of applications?
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Nexing
6/21/2012 7:18 AM EDT
Another vote for the Lithium Phosphate LiFePO4 and LiPO
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elctrnx_lyf
6/21/2012 4:51 AM EDT
Li-Ion and more advanced technologies are already overtaking many applications of NiMH and NiCd also.
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Nexing
6/21/2012 7:32 AM EDT
Amazingly this article -so far- misses what probably is the most needed information; How user's usage, 1st charge and charging practices vary accordingly different battery types.
At 2012 most users have yet to learn that lithium ion batteries are best not discharged below 20-30% capacity, very different from the NiMH requirement of full discharge...
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Hughston
6/21/2012 12:57 PM EDT
Why do you leave that much reserve capacity in the battery? Is it to extend battery life? Is it because the internal impedance goes up too much? I remember when the voltage gets down near 3V, the battery is going fast.
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Nexing
7/4/2012 11:30 PM EDT
http://blog.bestlaptopbattery.co.uk/876/
Look at the inverse correlation between the level of Depth Discharge and discharging cycles at that article.
Besides, part II of this article finally did not answered most questions left unresolved here. This link http://blog.bestlaptopbattery.co.uk/ might prove to be more useful than what we are commenting into.
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Hughston
6/21/2012 12:52 PM EDT
Here are a few other good characteristics of lithium ion batteries: flat discharge curve, typical voltage just about right to linear regulate for logic, and it's easy to detect charge termination. Low self discharge is important for many low power applications.
You don't have to use CC/CV charge methods for these batteries. You can pulse charge them.
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Mike K.
6/25/2012 3:32 PM EDT
As mentioned above there are regulatory requirements to consider when selecting a battery technology. There are issues with batteries based on cadmium, lead, and lithium (and mercury, of course) in a variety of markets, not just the EU. Some are environmental, some are transport-related.
If you're going to do an article about "Selecting the right battery" in 2012, consideration of environmental performance, recyclability, potential shipping constraints, and legality are of critical importance.
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Hughston
7/9/2012 11:38 AM EDT
I was looking at my neighbor's outdoor solar lights last night and I was surprised to see NiCad batteries in what is supposed to be a green product. I assume they have the cheapest charging method, which would be trickle charge.
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Mike K.
7/9/2012 3:20 PM EDT
Hah! Who said solar anything is "green"? Most solar cells use Cd in the elements too. They lobbied for, and received, an exemption from the scope of EU RoHS.
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mcjw
6/26/2012 8:29 PM EDT
I was expecting to see what the difference is between 1000-cycle Li-ion and 300-cycle Li-ion, in cost, technology, and design. Since many products have internal batteries, this is important.
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Tim Foo
6/27/2012 9:41 AM EDT
The focus of the aricle is on recharable batteries.
There is a whole peletora of non-rechable batteries that are available off-the shelf. These includes:
Carbon Zinc 1.5V
Alkaline Manganese 1.5V
Lithium Iron Disulphide 1.5V, long shelf life, high power density
Lithium Manganese 3V, long shelf life, high power density
Lithium Thionyl Chloride 3.6V, long shelf life, very high power density
Silver Oxide 1.5V, typically button cells only
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anne-francoise.pele
7/16/2012 11:25 AM EDT
Part Two of this two-part article is now available here: http://www.eetimes.com/design/smart-energy-design/4376071/Implementing-battery-charger-using-Li-ion?Ecosystem=smart-energy-design
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anne-francoise.pele
7/16/2012 11:25 AM EDT
I invite you all to look for Part 2 next week. It will explain how to implement a battery charger using Li-Ion technology as the example.
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