(April 2003) Advancements in battery rapid-testing
How accurate is AC conductance?
Not just a concept to provide greater information about battery charge conditions, Electrochemical Impedance Spectroscopy (EIS) now provides data to show superior performance. The electrochemical characteristics of a battery are determined by applying an AC potential at varying frequencies and measuring the current response of the electrochemical cell. Written by our Expert, Isidor Buchmann
(April 2003) Q: What factors affect Charging at high and
Q:Whats the role of the Supercapacitor?
Q: Will the reusable Alkaline battery have a future?
Q? Can the Lead-acid battery compete in modern times?
(July 2002) Q: What are the chraracteristics of Nickel-based batteries, its dominance and the future?
Q: Whats the best battery?
Battery novices often brag about phantom battery
systems that offer very high energy densities, deliver
1000 charge/discharge cycles and are paper-thin. These attributes are indeed achievable but not on the same battery pack.
A certain battery may be designed for small size and long runtime, but this pack has a limited cycle life. Another battery may be built for durability but is big and bulky. A third pack may have high energy density and long durability but is too expensive for the commercial consumer.
Battery manufacturers are aware of customer needs and offer packs that best suit the application. The cell phone industry is an example of this clever adaptation. Here, small size and high energy density reign in favor of longevity. Short service life is not an issue because a device is replaced before the battery fails.
Lets briefly examine various battery designs. A prismatic Nickel-metal-hydride battery is made for slim geometry. Its energy density is a meager 60Wh/kg and the cycle count is limited to around 300. In comparison, a cylindrical Nickel-metal-hydride offers 80Wh/kg and higher. Still, the cycle count is moderate to low. High durability Nickel-metal-hydride for industrial use and electric vehicles is packaged in large cylindrical cells. Surprisingly, the energy density on these cells is a modest 70Wh/kg.
Similarly, Lithium-ion batteries for defense applications are being produced that far exceed the energy density of the commercial equivalent. These super-high capacity Lithium-ion batteries are not approved for the commercial market for safety reasons.
Lets examine the strength and limitations of todays popular battery systems. Although energy density is paramount, other viral attributes are service life, load characteristics, maintenance requirements, self-discharge and operational costs. Since Nickel-cadmium remains a standard against which batteries are compared, we evaluate alternative chemistries against this classic battery type.
· Nickel-cadmium mature but has moderate energy density. Nickel-cadmium is used where long life, high discharge rate and a extended temperature range are important. Main applications are two-way radios, biomedical equipment and power tools. Nickel-cadmium contains toxic metals.
· Nickel-metal-hydride has a higher energy density compared to Nickel-cadmium at the expense of reduced cycle life. There are no toxic metals. Applications include mobile phones and laptop computers.
· Lead-acid most economical for larger power applications where weight is of little concern. This battery is the preferred choice for hospital equipment, wheelchairs, emergency lighting and UPS systems.
· Lithium-ion fastest growing battery system; offers high-energy density and low weight. Protection circuits are needed to limit Voltage and current for safety reasons. Applications include notebook computers and cell phones.
· Lithium-ion-polymer Similar to Lithium-ion, this system enables slim geometry and simple packaging at the expense of higher cost per Watt/hours. Main applications are cell phones.
· Reusable Alkaline Its limited cycle life and low load current is compensated by long shelf life, making this battery ideal for portable entertainment devices and flashlights.
Table 1 on page 13 summarizes the characteristics of the common batteries. The figures are based on average ratings at time of publication. Note that Nickel-cadmium has the shortest charge time, delivers the highest load current and offers the lowest overall cost-per-cycle but needs regular maintenance.
In subsequent columns I will describe the strength and limitation of each chemistry in more detail. We will also examine charging techniques and explore methods to get the most of these batteries.
Table 1: Characteristics of commonly used rechargeable batteries.
|Gravimetric Energy Density (Wh/kg)
|Internal Resistance (includes peripheral circuits) in mW
||100 to 2001 6V pack
||200 to 3001 6V pack
||<1001 12V pack
||150 to 2501 7.2V pack
||200 to 3001 7.2V pack
||200 to 20001 6V pack
|Cycle Life (to 80% of initial capacity)
||300 to 5002,3
||200 to 3002
||300 to 5003
||300 to 500
||503 (to 50% capacity)
|Fast Charge Time
||2 to 4h
||8 to 16h
||2 to 4h
||2 to 4h
||2 to 3h
|Self-discharge/Month (room temperature)
|Cell Voltage (nominal)
|Load Current peak best result
||5C 0.5C or lower
||>2C 1C or lower
||>2C 1C or lower
||0.5C 0.2C or lower
|Operating Temperature8 (discharge only)
||Minus 20 to 60°C
||Minus 20 to 60°C
||Minus 20 to 60°C
||Minus 20 to 60°C
||0 to 60°C
||0 to 65°C
||30 to 60 days
||60 to 90 days
||3 to 6 months9
|Typical Battery Cost10 (US$, reference only)
|Cost per Cycle (US$)11
|Commercial use since
1 Internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. Protection circuit of Lithium-ion and Lithium-ion-polymer adds about 100mW.
2 Cycle life is based on a battery receiving regular maintenance. Failing to apply periodic full discharge cycles may reduce the cycle life by a factor of three.
3 Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.
4 The discharge is highest immediately after charge, and then tapers off. The capacity of Nickel-cadmium decreases 10% in the first 24h, then declines about 10% every 30 days thereafter. Self-discharge increases with higher temperature.
5 Internal protection circuits typically consume 3% of the stored energy per month.
6 1.25V is the open cell Voltage. 1.2V is commonly used as a method of rating.
7 Capable of high current pulses.
8 Applies to discharge only; charge temperature range is more confined.
9 Maintenance may be in the form of equalizing or topping charge.
10 Cost of battery for commercially available portable devices.
11 Derived from the battery price divided by cycle life. Does not include the cost of electricity and chargers.
Isidor Buchmann, CEO, Cadex Electronics, Inc.
Q: When was the battery invented?(04-02 BD73-13)
One of the most important discoveries in the last 400 years has been electricity. You may ask, Has electricity been around that long? The answer is yes, and perhaps much longer. But electricity only became useful in the late 1800s.
The earliest methods of generating electricity were by creating a static charge. Alessandro Volta (1745-1827) invented the so-called electric pistol by which an electrical wire was placed in a jar filled with methane gas. By sending an electrical spark through the wire, the jar would explode.
Volta then thought of using this invention to provide long distance communications, albeit only one Boolean bit. An iron wire supported by wooden poles was to be strung from Como to Milan, Italy. At the receiving end, the wire would terminate in a jar filled with methane gas. On command, an electrical spark would be sent by wire that would cause a detonation to signal a coded event. This communications link was never built.
| Figure 1: Voltas experimentations at the French National Institute in November of 1800 in which Napoleon Bonaparte was present.
Ó Cadex Electronics Inc.
The next stage of generating electricity was through electrolysis. Volta discovered in 1800 that a continuous flow of electrical force was possible when using certain fluids as conductors to promote a chemical reaction between metals. Volta discovered further that the Voltage would increase when Voltaic cells were stacked. This led to the invention of the battery.
No longer were experiments limited to a brief display of sparks that lasted a fraction of a second. A seemingly endless stream of electric current was now available.
At this time, France was approaching the height of scientific advancements and new ideas were welcomed with open arms to support the political agenda. By invitation, Volta addressed the Institute of France in a series of lectures in which Napoleon Bonaparte was present. Napoleon himself helped with the experiments, drawing sparks from the battery, melting a steel wire, discharging an electric pistol and decomposing water into its elements. New discoveries were made when Sir Humphry Davy installed the largest and most powerful electric battery in the vaults of the Royal Institution of London. He connected the battery to charcoal electrodes and produced the first electric light. As reported by witnesses, his Voltaic arc lamp produced the most brilliant ascending arch of light ever seen. In 1802, Dr. William Cruickshank designed the first electric battery capable of mass production. Cruickshank arranged square sheets of copper soldered at their ends, intermixed with sheets of zinc of equal size. These sheets were placed into a long rectangular wooden box that was sealed with cement. Grooves in the box held the metal plates in position. The box was filled with an electrolyte of brine, or watered down acid.
Until now, all batteries were primary cells, meaning that they could not be recharged. In 1859, the French physicist Gaston Planté invented the first rechargeable battery. This secondary battery was based on Lead-acid chemistry, a system that is still used today.
The third method of generating electricity was discovered relatively late electricity through magnetism. In 1820, André-Marie Ampère (1775-1836) had noticed that wires carrying an electric current were at times attracted to one another, while at other times they were repelled. In 1831, Michael Faraday (1791-1867) demonstrated how a copper disc was able to provide a constant flow of electricity when revolved in a strong magnetic field. Faraday and his research team succeeded in generating an endless electrical force as long as the movement between a coil and magnet continued.
In 1899, Waldmar Jungner from Sweden invented the Nickel-cadmium battery. In 1947, Neumann succeeded in completely sealing the cell. These advances led to the modern sealed Nickel-cadmium battery.
Research of the NiMH system started in the 1970s, but the metal hydride alloys were unstable in the cell environment. New hydride alloys were developed in the 1980s that improved the stability. NiMH became commercially available in the 1990s.
The first primary Lithium batteries appeared in early 1970s. Attempts to develop rechargeable lithium batteries followed in the 1980s but failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, the Lithium ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first Lithium-ion battery.
As awkward and unreliable the early batteries may have been, our descendants may one day look at todays technology in a similar way to how we view our predecessors clumsy experiments of 200 years ago.
History of Battery Development
1600 Gilbert (England) Establishment of electrochemistry study 1791 Galvani (Italy) Discovery of animal electricity
1800 Volta (Italy) Invention of the Voltaic cell
1802 Cruickshank (England) First electric battery capable of mass procduction
1820 Ampère (France) Electricity through magnetism
1833 Faraday (England) Announcement of Faradays Law
1836 Daniell (England) Invention of the Daniell cell
1859 Planté (France) Invention of the Lead-acid battery
1868 Leclanché (France) Invention of the Leclanché cell
1888 Gassner (USA) Completion of the dry cell
1899 Jungner (Sweden) Invention of the Nickel-cadmium battery
1901 Edison (USA) Invention of the Nickel-iron
1932 Shlecht & Ackermann (Germany) Invention of the sintered pole plate
1947 Neumann (France) Successfully sealing the Nickel-cadmium battery
Mid 1960 Union Carbide (USA) Development of primary Alkaline battery
Mid 1970 Development of valve regulated Lead-acid battery
1990 Commercialization Nickel-metal hydride battery
1992 Kordesch (Canada) Commercialization reusable Alkaline battery
1999 Commercialization Lithium-ion polymer
2002 Limited production of proton exchange membrane (PEM) fuel cell
Figure 2: History of battery development. The battery may be much older. It is believed that the Parthians who ruled Baghdad (ca. 250 BC) used batteries to electroplate silver. The Egyptians are said to have electroplated antimony onto copper over 4,300 years ago.
(03-02 BD72-14)Batteries Digest Newsletter has asked me to write a monthly column of battery issues that are of interest to people. Practical, down to earth information on batteries is sometimes hard to find. Battery manufacturers are often too optimistic in their promises.
I have a background in radio communications and studied the behavior of rechargeable batteries in practical, everyday applications for several decades. When testing batteries for performance and longevity, I soon noticed that the manufacturers specifications do not always agree with the performance when in the hands of the common users. I wrote several articles addressing the strength and limitations of the battery. These articles have been published in various trade magazines in the USA, Canada and Europe. I later compiled the material and created my first book entitled Batteries in a Portable World A Handbook on Rechargeable Batteries for Non-Engineers.
The 88-page first edition book appeared in 1997 and covered such topics as the memory effect of Nickel-cadmium batteries and how to restore them. Some readers commented that I favored the Nickel-cadmium over the Nickel-metal-hydride. Perhaps this observation is valid and I have taken note. Having been active in the mobile radio industry for many years, much emphasis is placed on battery longevity, a quality that is true of the Nickel-cadmium. Todays battery users prefer small size and maximum runtime. Longevity is less important, especially in the consumer market.
The second edition Batteries in a Portable World was published in 2001. With 18 Chapters and 300 pages, this book has been extended to answer most questions battery users would ask. Much emphasis is placed on new battery technologies and their field applications.
In May 2001, I created the Battery Information Website www.buchmann.ca and made the contents of the book available to everyone. New battery articles have also been added. A search engine helps the readers in finding issues of interest.
Out of sheer curiosity, I did a statistical analysis at the end of the year to find out which battery topics are being requested most often. The five winning chapters are:
Number 1. Getting the Most from your Batteries Chapter 10
Number 2. Proper Charge Methods Chapter 4
Number 3. Internal Battery Resistance Chapter 9
Number 4. Choosing the Right Battery Chapter 8
Number 5. The Smart Battery Chapter 7
With Getting the Most from your Batteries as first choice, it is evident that people want good runtime and dependable service. Proper Charge Methods is also very much in the hearts of the battery users. A surprise was Internal Battery Resistance in third position. This subject is of growing concern with digital equipment that puts high demands on the battery. A seemingly good battery often fails to deliver the heavy current bursts because of elevated internal resistance caused by aging and high cycle count.
Batteries in a Portable World is written for the non-engineer. It addresses the use of the battery in the hands of the general public, far removed from the protected test lab environment of the manufacturer. Some information contained in this book was obtained through tests performed in Cadex laboratories; other knowledge was gathered by simply talking to diverse groups of battery users. Not all views and opinions expressed in the book are based on scientific facts. Rather, they follow opinions of the general public, who use batteries. Some difference of opinion with the reader cannot be avoided. I will accept the blame for any discrepancies, if justified.
The monthly columns, which will appear in Batteries Digest Newsletter, will be based on the book, Batteries in a Portable World. I will address such issues as the choice of battery chemistries, physical battery packs, charge and discharge methods, runtime concerns, the smart battery, internal battery resistance and much more. I hope you will find these columns helpful.
About the Author
Go back to Ask the Experts
Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC. Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decade
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