Sam Stimson, a Global Supplier Quality Engineer with Dell Computer had an important message to share with the attendees at Power 2002 on Lithium-ion safety. Sam’s presentation, “Statistical Control of Critical Processes to Improve Lithium-ion Cell Safety Reliability,” describes a need being fulfilled in the industry. With all the redundant safety devices in and outside of the cell pack, Sam says , “It’s what goes on inside the cell that actually gets you in big trouble.” Not only has the power density of a cell risen since 1995, but the number of defective parts per million (dppm) - cell faults in the field - have also escalated. In the 1999-2000 time frame, the battery community was seeing about one dppm; what that means, Sam explained, is that you have a one in a million chance of something happening to the cell that could create a dramatic happening. Such a happening could be a cell fully venting. Referring to Mr. Takashita’s data in an earlier conference session, Sam mentioned that with 740 million cells produced last year, there could be the probability of having 740 “happenings” that are “not very nice.” Yes, there are standards such as UL, CSA and TUV that various manufacturers are using in their testing, but the industry needs to set their own standards which have even stricter parameters.
Sam Stimson, (left) Presenter at Power 2002 and Senior Consultant at Dell on batteries, and Ralph Brodd, President and Consultant of Broddarp of Nevada, Inc., share ideas at the Power 2002 conference.
Sam has been the “battery guy” at Dell for 11 years. His experience goes back to the development of Nickel-cadmium. He can remember when a Ni-cad battery weighed 7 pounds, almost as much as the total notebook of today equipped with its very light Lithium-ion battery.
Sam emphasized the critical importance for the industry to begin monitoring some variables. He commented on how notebook systems are taking more power so the cylindrical cell power needs to increase. As the 18650 cell size capacity is increased from 1.8 Ah to 2.0 Ah, the people in the computer industry began to see “happenings” in the field. (See Figure 1.) Seeing cells beginning to vent is a dramatic event where cells encapsulated in plastic in a battery pack have “stuff” coming out at 300 0C. Those concerned with batteries and portables want to investigate a regimented process so that this type of venting doesn’t occur.
Safety Concern for all batteries
Perhaps the word Lithium carries more safety concerns than other chemistries because its chemical composition has a known potential for flammability, but batteries of all chemistries need to be surrounded with safety, both in manufacturing the cells as well as in design application in a product. In September 2002, Nikon, Inc. voluntarily recalled 9,100 Coolpix 2000 digital cameras imported into the United States because of a “possible short circuit and overheating in the battery compartment.” These Coolpix cameras are supplied with AA-Alkaline batteries. A similar recall of digital cameras (Model DC5000) was made by Eastman Kodak Company. The recall read, “Kodak received 12 reports, including six in the U.S., of consumers who experienced an electrical shock while changing batteries, or installing or removing the memory card or USB cable.” Unfortunately, to the general public, the blame for any incident is attributed to the battery, regardless of chemistry, rather than the over all design of the product.
Most recently, in September, Siemens AG ran into a difficult situation with pirated aftermarket nickel-based rechargeables for their C-25 mobile phone sold in Europe. As a result of a recent case causing damage, mobile phone maker Siemens issued a warning against the use of non-licensed and non-approved third party batteries. The company stated, “ These, for the most part, technically inferior products can, in extreme cases, explode when on charge for long periods in the home or in car chargers since some of these batteries have no safety functions to protect against overcharging....Dangerous pirate copies such as batteries are predominately offered at flea markets, street markets and over the internet.”
At this point, the IEEE Project Number P1625 work will be limited to Lithium-ion and Lithium-ion polymer. However, additional standards may need to developed for other battery chemistries in the future.
Safety in Cell Manufacturing
The following is a list of the ten key considerations and tests that the IEEE committee has felt to be critical in the cell manufacturing process:
- PTC Impedance -XbarR chart - Take many samples to check to see that each cell remains well within the design limits.
- CID Pressure -X bar R chart - Protect the cell from outside forces causing massive current draining so that the cell will not get too hot - possibly vent.
-Nickel plating thickness - Accurate measurements are important because if the plating isn’t heavy enough, it can start chipping off -containments then get in and cause internal shorts.
- Contamination levels in raw material - X bar R chart and
- Contamination levels in mixed material - XBarR chart Lithium cobalt oxide has to be free of iron. Lithium salts and iron do not work well together; in combination they can cause dangerous contamination levels in the mixed materials.
- Yield at Insulation (HiPot) test - Once the jelly roll has been put together, these tests tell you whether you have imperfections in the separator. If such occurs, the anode and cathode can short.
- Electrolyte Weight -XbarR chart - The electrolyte must be measured accurately.
- Plot of Cpk at OCV Test -XbarR - At least three or four Open circuit Voltage (OCV) tests need to taken as the cell is aging.
- Plot of Cpk at IR Test -XbarR chart - The IR will rise if there is contamination
- Plot of Platinum Yield - P Chart - If yields are below 96 percent, something is wrong with the process; there may be contamination.
IEEE Leads Way to Create Battery Safety Standards
The Stationary Batteries Committee of the Institute of Electrical and Electronics Engineers (IEEE) is creating the IEEE P1625TM, “Standard for Rechargeable Batteries for Portable Computers.” The Laptop Battery Working Group draws upon battery suppliers, original development manufacturers and computer systems manufacturers, including Dell, HP IBM, Panasonic Compaq, Quanta, Sony, Sanyo and Toshiba.
The IEEE P1625 standard will focus on system management and control, battery pack communications, energy density and reliability. The standard anticipates smarter battery system designs, including self-monitored charge, disccharge and environmental conditions. It is also addressing redundant protections needed to assure system reliability.
“The standard will reflect real mobile user profiles and the growing demand for ever more reliable power in mobile computing applications,” says Bruce Riggs, IEEE P1625 Working Group Chairman and Vice President of Dell’s Operations and Quality for Client Product Group. “We expect laptop power demand to accelerate as increasingly powerful mobile processors, wireless solutions and advanced graphics capability become more prevalent in mobile computing. We’ve also seen increasing battery duty cycles as the average daily use of mobile computers continues to climb.”
IEEE was chosen as the preferred organization for three reasons. Bruce Riggs listed them as follows:
1) Functioning as an organization-only working group will enable the group’s participants to fast track their efforts.
2) Because IEEE is the largest organization of its kind, there is access to a huge pool of computer, battery and other technology-oriented companies.
3) IEEE can offer a broad range of support services that can help the group stay focused and make the task more efficient.
For more information see http://www.standards.ieee.org
A draft standard should be ready for final balloting in
These aren’t the ‘Ten Commandments,’ but they are critical areas that need to be monitored by all of the suppliers. Suuppliers give Dell monthly reports on Lot parameters to make sure there are not any variations in cell quality.
Lithium-ion batteries - a review of recalls due to safety concerns
Dell has taken positive action for Lithium-ion safety based on their knowledge and experiences. In October 2000 in cooperation with the U.S. Consumer Product Safety Commission (USPSC), the company voluntarily recalled 27,000 Lithium-ion batteries, manufactured by Sanyo Electric Co. Ltd., and sold in notebook computers. In the same year, Dell had a recall of 284,000 batteries which had been shipped to customers from January 7, 2000 through March 21, 2001. In November of 2001, they made a similar recall of 13,000 batteries because of the possibility of overcharge during recharging, causing them to overheat, smoke and possibly catch fire.
Compaq also recalled Lithium-ion batteries shipped to customers in Asia/Pacific and Japan in October 2000. The recall involved 55,000 notebook batteries manufactured by Sony Corp. According to Masami Kato, a spokesperson for Sony, “...the battery defect is not with the battery cell, but the circuit board that controls the recharge and discharge process.”1 Nevertheless, a proactive move was made to recall the battery.
Although not computer-related, a recent Lithium-ion battery recall with the USPSC was in September 2002 when EV Global Motors Company announced the recall of 2,000 batteries in their Mini E electric bicycles. EV Global Motors received five reports of the batteries overheating, three of which caught fire, though no injuries were reported.
Sam suggested using a Cell Manufacturing FEMA Analysis which encompasses all areas of cell manufacturing (Mechanical Process, Control and Qualification, Test Process and Containments). In review of manufacturing processes for induced cell failures found in the field, one can examine the various areas to lessen any potential of error in a specific point of process. For example, in reviewing the Mechanical Process (including winding, welding, slitting, cutting and assembly) one might need to examine if any dust was found beyond the electrode as a result of slitting. This is a guide for the team at the cell factory; it pinpoints areas which can uncover potential problems.
Figure 1. Currently Dell is using 2.2 Ah cells in their 66 Wh packs (4S, 2P) and they are sampling 2.4 Ah packs. They will be offering 9 and 12 cell packs in a few months. (Reprint permission is courtesy of Dell Computer.)
Pack Design Initiatives
There are basically six “rules” to consider in creating safe battery packs.
1. Isolate the BMU board
2. Limit the number of wires if possible.
3. Use plenty of tape where soldering can burn insulation of the can.
4. Verify each tab weld.
5. Don’t mix cell batch and test OCV/IR before use. This is a very important point. Once cells leave the cell manufacturing site they go to the pack site and can be there for as long as 30 to 45 days before the pack operation begins. There is going to be a certain amount of degradation in Voltage of the packs, so one needs to be sure that the degradation seen is not more than that which can be attributed to the shipping process. If it is too low, there is internal contamination. Obviously, those cells should not be used at all because their internal resistance is increasing.
6. Keep meticulous records. Be able to track cells all the way back to the batch of materials from which the cells were made.
The battery technologies covered in IEEE P1625 are limited to Lithium-ion and Lithium-ion polymer, but future versions of this document may include technologies that are not in general use at present. Also included are: battery pack electrical and mechanical construction; system, pack and cell level charge and discharge controls; and battery status communications.
Measurement methods are provided for:
- Qualification Process and Requirements
- Manufacturing Process Control Requirements
- Energy Capacity and Demand Management
- Levels of management and control in battery systems
-Current and planned lithium-based battery chemistries and packaging technologies
The pack should protect the cells. This includes inhibiting charge when cells are full and inhibiting charge/discharge when ambient temperature is too high. The pack design should also protect cells in distress resulting from cell Voltage imbalance and cell over-temperature. Finally, the pack should be isolated from improper conditions such as excessive charge Voltage and current and also excessive discharge current. In the pack design, remember the cell is the critical element.
Asian countries such as Japan and Korea already have 50% of their PCs as mobile units. Quality batteries having optimum safety specifications and testing are vital. (Data from interview of Intel Corp.’s Asia Pacific regional manager, Melissa McVicker, - “Global mobile PC sales to outpace desktops” by Won Choon Mei, Reuters (Kuala Lumpur) 10/22/02
Working for Industry Standards
The IEEE P1625 committee sees their Standards development as being all encompassing. Their purpose is “to reduce the incidence of user problems.” Their statement reads, “The portable computer and battery industries need standardized criteria for qualification of rechargeable systems and for verifying the quality and reliability of those batteries.” Through their work they will utilize the current UL, CSA and TUV testing protocols, but they will also provide for failure analysis, establish uniform safety qualification testing and ultimately enhance the customer experience. As Sam reported...” If you look at the various suppliers of lithium rechargeables today, everyone does things a little bit differently when it comes to safety qualifications. “Some test very rigorously, but others do not do so.” The IEEE standard development was described by Sam as a big planar wrapper or umbrella whereby all manufacturers do all of the necessary process control in the same way. One reason Dell, competetors and the major battery manufacturers are putting forth diligent efforts for standardization is to avoid real problems; as Sam says, “the last thing the industry needs is to have a battery vent on an airplane.”
A New Non-combustible Battery Additive
Bridgestone Corporation, Japan’s largest maker of tires, states that it has developed the world’s first battery electrolyte additive that will make Lithium-ion batteries non-combustible. This additive in no way should be a detriment to the power or capabilities of the battery. Next year, Bridgestone will be testing the product with manufacturers. This announcement was made in the Nihon Keizai Shimbun Daily in Tokyo in early November. To BD’s knowledge, it was not mentioned at the Power 2002 Conference.
Thus, a seal of approval that the battery, its pack and total design in a product meets approvals such as the IEEE standards is a necessary step for the industry. Name brand companies want to keep a “five star rating” for the cells, the battery packs and ultimately their the battery-operated products. Perhaps the industry can never say definitely that “an event” with a Lithium-ion battery will never happen. But, in making remarks about the Standards committee, Sam said, “What we want to try to do is move from one ppm to one ppb (part per billion), and we feel that can happen.” And, if an event does happen, at least there will be a monitoring tool in place so that its origin can be traced. That’s something that the industry doesn’t have in place today.
(Reprint permission is courtesy of Dell Computer.)
Elements of Cell Level Control
PTC Device (Positive Temperature Coefficient)
> Limits current to a cell in the event of higher than expected temperature or external current draw.
> Recoverable PTC will recover when current and temperature return to specified limits.
CID (Circuit Interrupt Device)
> Interrupts charging current to the cathode when internal gas pressure in a cell exceed specified limits.
> Non-Recoverable Gas pressure deforms the CID and permanently interrupts charge.
> Opens in response to a sudden increase in cell pressure and allows gas to escape.
> Non-Recoverable but with significant contributions to the customer’s product safety.
(Editor’s note: BD has been promoting Lithium-ion safety since 1997. For some of our articles, see the following issues with hyphenated page numbers: 20-2, 30-4, 32-16, 35-8, 36-14, 39-5, 39-11, 43-11, 49-14, 50-14, 59-2, 65-15, and 77-6.)