Batteries/Lithium Primary/Primary Lithium Update 060520
From the 41st Power Sources Conference...
Primary Lithium Update, Part 1
by Donald Georgi
Lithium primary chemistry includes a wide variety of electrochemical processes. The 41st Power Sources Conference provided a good cross section of papers on Lithium primary batteries which, by their very nature, are used in unique applications. If there is a common thread, it may be high energy density and very long shelf life. The following are a few of the summaries of individual presentations which will be continued in later issues.
Twenty-Year Operating-Life Bobbin-Type Li/SOCl2 Cell, Tadiran Batteries Ltd. (Session 2.1)
Lithium-thyonyl chloride batteries provide long shelf life, wide storage and operating temperature performance, and high energy densities. For example, primary Zinc-carbon batteries produce less than 100 Wh/kg, primary Alkaline less than 200 Wh/kg and Lithium-thyonyl chloride batteries 730 Wh/kg. The pursuit of increased performance in both operating life and power density continues with data substantiating improvements.
In the area of operating life improvements, cell impedance and Voltage losses are minimized with a lithium anode coating of an ion conducting film which reduces the Voltage delay.
To increase the current delivered, the cell is combined with a hybrid capacitor to provide pulse currents to several Amperes from an AA size battery and AA size capacitor. Pseudo capacitance values of 615 to 820 Farads are reported for the cell in the AA configuration. Temperature performance data showed over 200 mAh at -400 and almost 300 mAh at 720 C.
Testing the Bimodal Lithium Reserve Battery Concept, Zentek Corp., SAGE Systems Tech. and ATK Power Sources Center. (Session 2.2)
The Bimodal battery is a low current device which upon demand is converted to a high power battery with the addition of a concentrated acidic electrolyte. During the low power phase of operation, the battery is called upon to provide standby power for built in test functions such as clocks or housekeeping duties. Such combinations are presently implemented with a low power battery and a second high power battery with electrolyte stored in a separate vessel and injected to activate the battery when needed. Such configuration wastes space.
The Bimodal battery combines low and high current in one structure, delivering the low power housekeeping power until modified with the addition of a high concentration electrolyte when high power is needed.
The basic cell consists of a lithium anode, separator and carbon cathode. In testing, three electrolytes were used: a neutral electrolyte, a #1 high rate electrolyte and a #2 high rate electrolyte.
The future work for the Bimodal Lithium battery will include prototype construction using various activation methods as well as a variety of shapes.
Improvements in Energizer’s L91 Li-FeS2 AA Cells, Energizer Battery Manufacturing, Inc. (Session 2.3)
As incremental improvements boost battery performance, the long term cumulative improvements are often overlooked. This is the case with Energizer’s Lithium primary cells which have been marketed since 1990. In the past 13 years, high rate capacity has gone from a nominal 1,700 mAh to over 2800 mAh, while operating temperature performance has improved to give almost 100 times the run time of a standard Alkaline cell at -200 C.
All components of the cell have shared in the continual improvements. The lithium anode has had 0.05% aluminum added to decrease impedance in elevated temperature storage and possibly will increase shelf life.
The cathode has been modified with organic and teflon binders and carbon additives for fabrication improvements, conductivity increases and better electrolyte absorption. These changes have increased capacity and rate capability simultaneously.
Separator material started out as 1 mil polypropylene and has progressed to 20 micron polyethylene with higher porosity to increase rate capability. The smaller volume also increases capacity. With the lower melting point of polyethylene, the cell has faster shutdown, increasing safety.
Electrolyte improvements have centered on the addition of a Lithium iodide-ether. As temperature drops from 600 C to -150 C, the conductivity increases by 50% contributing to low temperature performance. At 250 C this electrolyte has more than double the conductivity of the previous electrolyte, again contributing to increased capacity and power.
Manufacturing quality has been expanded to include vision systems checks and 100% checks on critical items. Each cell is subjected to Voltage and rate tests before shipping.
The Lithium primary family is being extended to include a AAA version of the cell. With the lithium primary improvements, one of these AAA cells now has about 30% greater service time at 1.5 W power draw than a standard AA Alkaline primary battery, and about 3 times more service time than a AAA Alkaline. For designers seeking smaller product profiles with greater power, the AAA may be just the right solution.
Extended Shelf Life of Energizer L91 Li-FeS2 AA Cells. Energizer Battery Manufacturing, Inc. (Session 4.1)
This is the second of two Power Sources presentations on the Lithium-iron sulfide battery. It focused on the determination of the shelf life which is elusive because of the inherently long calendar life and because electrochemical enhancements have made such determination a moving target.
Still a very scientifically thorough program was used to project the calendar life. Three different methods formed the structure of this determination.
The ambient method employs real time storage which, while not spanning all the years, does give a practical approach to shelf life. To carry out a real time test, Energizer had the luxury of using samples dating back eight years. Based on the one Amp continuous discharge data, the projections of the point where the cell capacity would drop to 80 % of its original capacity were obtained. Results were widely scattered, but averaged 57 years with a minimum determination of 31 years. Through data on production tests over the past 11 years, shelf life of 40 years are predicted.
A second method employed concentrated on elevated temperature storage to accelerate chemical aging to simulate aging. A rule of thumb was employed which assumes that each 10 OC increase in temperature will double the degradation rate. It was duly noted that elevated temperatures could introduce extraneous chemical changes, which could produce invalid data. With a variety of cells and test parameters, data showed a likelihood of shelf life to forty years.
Continuing the quest for calendar life, the program called upon microcalorimetry to provide an alternative answer. Newly built cells have a measurable exothermic reaction from the Voltage-controlling additive over the first three months, so tracking the minuscule heat loss at six months, when the cell has stabilized, gives a self discharge rate which can be a determination of the point at which the capacity drops to 80 % of original capacity. Since the real self-discharge continues to decrease with time, the six-month data will most likely produce a lesser life number. Despite such limitations, test data and interpretation produced an estimated shelf life of 26 years
BD note: It is unfortunate that a number of media analysts with limited analytical capabilities often garner the attention of the general public with statements to the effect that battery improvements do not keep pace with other technological growth. This hard data demonstrating Energizer’s continual improvements speaks for itself in showing dramatic battery life and performance improvements over the years.
Lithium-Air...the ‘Ultimate’ Battery? (part2)
by Donald Georgi
Life’s quest for the technological holy grail takes on many different aspects. To fly... to eliminate polio...to go to the moon, some of these pursuits have been achieved. But people are never satisfied and the quest continues. Battery people, utilizing technology, have their moments to hope, dream and pursue greater energy densities. Having been brought up in the era of nuclear energy, the technologist envisions the day when a battery the size of a pack of chewing gum will power a computer for years. While batteries do make modest gains in energy stored, technologies such as cell phones expand to capture the dollar of the consumer by adding features which require greater power, but result in devices with micro-sized, dim displays to match almost unuseable, tiny keyboards.
Thinking beyond the device of today, some see an ‘always-connected’ person who has the combination of computer, cell phone, PDA and entertainment center in a single device ready to make the business deal, cure the illness and make the next hotel reservation while living in a virtual reality of a galaxy far, far away. Forgetting the electronic challenges of this magic module, the energy storage device necessary to provide this power, with small package size to satisfy the user, lies within this holy grail.
As we are jolted back into the real world bounded by physical laws which encompass electrochemistry, battery people have to ask, “Where is the upper limit of energy density?” Despite extensive knowledge of chemical fundamentals, that question has not been, and may never be, completely answered because the realm of practicality must be included. The practical answer includes acceptable safety, a dependence on the application, the environment of use, the economic factors and the admission that the battery for one application may not be the best choice for another.
Just as the mountain climber would look to Mt. Everest as the pinnacle of peaks, an electrochemist, browsing the list of metals’ reduction potentials and electrochemical equivalents, sees one possibility in the combination of lithium with oxygen. Lithium metal, excluding oxygen, has the highest standard potential and electrochemical equivalence of all metals.
Between theory and practice is a reduction of that value which can be anywhere from 2:1 for Lithium-thionyl chloride to 7:1 for Lead-acid. Stated in another way, only a part of the theoretical maximum energy density can be recovered in a practical manufactured battery. The challenge is to get the most practical energy from the highest theoretical combination.
To that end, using a lithium anode with an air cathode to supply the oxygen (as is commonly done with the very popular Zinc-air hearing aid batteries) may result in the highest practical energy density possible in a metal-based battery which has an abundant air supply, environmental friendliness, and reasonable safety. Since the anode is lithium metal which reacts aggressively with water, a nonaqueous electrolyte is used with an organic polymer film separator to facilitate the supply of oxygen from the air. The cathode consists of a metal current collector surrounded by a layer of carbon which provides the platform for combining the oxygen with the lithium ion which moves from the electrolyte to form lithium peroxide or lithium oxide. Electrolytes can either be non-aqueous liquid or polymer electrolyte.3
The description of Lithium-air sounds so ideal that we might wonder why we are still stuck with the myriad of chemistries with ‘inferior’ energy densities. To better understand why it is not universally used, an understanding of the previously mentioned suitability criteria which includes the application, the environment of use, economics and practicality is needed. Much has been learned in how to build Zinc-air cells; some of this knowledge can be applied to the design of Lithium-air chemistry.
Reversability of the reaction to allow electrical recharge of Lithium-air is possible. Despite classifying the Lithium-air cell as a primary battery, the literature does include data on the performance of a rechargeable form, researched by Abraham, et. al.2 When the liquid electrolyte is replaced with a polymer electrolyte, the reaction of the lithium directly with oxygen forms lithium peroxide which can reoxidized to oxygen with externally applied current. This has been found to have major barriers in Zinc-air, so starting with the primary version of Lithium-air simplifies the goal tremendously.
As noted in the Zinc-air experience, a virtually unlimited amount of ambient air can be used to supply the oxygen, but as a result, it also adds the limitation of convenience limiting the operating life of about two weeks after exposing the cathode material to the air. Unlike Alkalines, which just ‘sit there’ when not used for days weeks or years, the Lithium-air battery cannot be put into a standby mode conveniently. The solution here is to choose the application which properly suits the continuous period after activation.
Very low power density is another constraint of the Lithium-air battery. Unlike the high power providers of chemistries such as Lead-acid, current densities of Lithium-air can be as much as 1,000 times lower in order to extract the maximum amount of energy. Low current may not be a problem if the application is tailored to the capability, but one does not look upon Lithium-air as a replacement car starting battery.
The problem of temperature range must be considered again because the performance of Lithium-air varies by a factor of 5 over the -20 0C to +40 0C range. It is important to note that the battery must be tuned to the application because Lithium-air batteries are not going to start Minnesota autos in January.
Rather than speculate on the future of Lithium-air batteries, the work being done now is a good indicator of where the technology stands and may suggest when a practical version may be built. The two presentations which describe this work were given at the 41st Power Sources Conference and are highlighted as follows:
Session 4.3 Non-aqueous Lithium-Air Batteries with an Advanced Cathode Structure. Yardney Technical Products, Inc./Lithion, Inc.
Using non-aqueous electrolytes removes the problem of self-discharge parasitic corrosion due to lithium interaction with water. Non-aqueous electrolytes also remove the production of hydrogen, thus yielding a safer cell. The next barrier to maximizing performance is the low rate of oxygen diffusion in the air cathode. Taking experience from zinc and aluminum metal air batteries, new cathode structures were fabricated using a variety of metal catalysts added to a carbon with binder and deposited on a nickel current collector.4 A teflon film was placed over the structure to repel atmospheric water but to allow oxygen diffusion. Of all the catalysts, manganese was noticeably superior, extending the specific capacity of the air cathode to 3471 mAh/g. (Note: this is for the cathode only.) The carbon material provides the reactive surface for the reduction of the oxygen gas and must have a porous structure with highly distributed catalyst materials.
Several cells were constructed and tested at constant currents at 20 0C, yielding specific capacity of 3471 mAh/g. (Ed. note. With an average potential of 2.47 Volts, this would equate to 8573 Wh/kg. Assuming practical packaging requirements to triple the mass, a real battery might produce 1157 Wh/kg, which would be a wonderful achievement.)
4.4 Temperature Performance of the Non-aqueous Lithium/Air Battery. U.S. Army Research Laboratory, Adelphi, MD
Seeking combinations of battery support for the Land Warrior has opened up the possibility of including Lithium-air batteries. If radio batteries carried by the troops have rechargeable Lithium-ion batteries, they can be recharged for the next mission by a variety of sources which might not always be a large, heavy and noisy power source.
If Lithium-ion cells had energy densities approaching 200 Wh/kg, and Lithium-air cells had energy densities of 1000 Wh/kg, then 5 field packs could be recharged from a single Lithium-air battery weighing the same as one radio battery. Extending the concept, a combination (hybrid) Lithium-air and Lithium-ion might work together so that the Lithium-ion provided the talk power, and the Lithium-air constantly kept topping off the Lithium-ion resulting in total usability time increases and reduction in pack weight to carry.
But the Army realizes that major obstacles exist for Lithium-air, especially in the area of temperature range. The present study looks at liquid electrolyte and the carbon black coated anode current collector. Over temperature ranges from -30 0C to +40 0C, the cells were discharged at constant currents from 0.05 to 0.5 mA/cm2. Cells operated at +40 0C gave nominally 10 times more specific capacity than those at -30 0C.
It is projected that the temperature affects the diffusion of oxygen through the electrolyte. It is anticipated that future work should separate the effects of oxygen solubility from oxygen diffusion. The reformulation of the electrolyte may be the way to improve low temperature operation. Until then, Lithium-air will remain in the study category for the Army.
1. Handbook of Batteries, Third Edition. pp. 1.12-1.13
2. Handbook of Batteries, Third Edition. pp.38.49-38.51
3. “A Polymer Electrolyte-Based Rechargeable Lithium/Oxygen Battery,” Abraham, K.M. J. Electrochem Soc., 1996, 143. 1-5
4. “High Capacity Cathodes for Lithium-air Batteries,” Yardney TechnicalProducts.
From the 41st Power sources Conference...
Primary Lithium, Part 3
by Donald Georgi
Part one summarized Lithium-thionyl chloride, Bimodal-lithium reserve and Lithium-ion sulfide presentations. In a second story, the Lithium-air sessions were covered, leaving this review of the last three presentations to complete the lithium primary overview.
2.4 Next Generation High Capacity LiSO2 D Cell, Saft America, Inc.
Lithium-sulfur dioxide chemistry has been a choice for military portable equipment power because of its relatively high energy density up to 260 Wh/kg,1 its wide temperature range to -40 0C long storage life, and its ability to provide high currents because of low internal resistance. Providing power for military radios in the 5590 pack is a major application of the chemistry which uses ten ‘D’ size cells.
The baseline LiSO2 cell provided 203 Wh/kg with 3.89 Wh/$. This was superceded by a Lithium-manganese dioxide (LiMnO2) battery which provided a greater 214 Wh/kg at a more economical 2.76 Wh/$.
In this project, an optimization program was developed to return the LiSO2 chemistry to a dominant position with greater energy density and value. Anode and cathode aspect ratios were evaluated along with the composition of the cathode to determine which values would lead to the dominant performance.
After a study and preliminary testing, the various combinations of aspect ratios and composition were used to build BA5590 batteries which were then tested to the military specification. The best of the configurations produced a 20% increase in capacity simultaneous with a value improvement to produce 4.78 Wh/$, a 22.9 % increase. The result was a battery with greater energy density than the LiMn O2 for the Land Warrior with less outlays of taxpayer dollars per Wh into the military budget. This is an unusual outcome of technology which normally produces evolutionary designs with expanded costs.
2.5 Advanced Lithium Oxyhalide Reserve Battery Safety Characteristics, Eagle Picher Technologies, LLC.
Military interceptor kill vehicles require that battery power remain usable after 10 years of storage while being subjected to high ambient temperatures and aggressive mechanical shock and vibration loading. Silver-zinc and thermal batteries established their abilities in missile applications, but neither has the high specific energy of Lithium-oxyhalide batteries. Unfortunately, the initial oxyhalide cells were plagued with safety problems relating to the dynamics of activation, manifold shunt currents and high required electrode surface areas. The reported program was established to design and build an oxyhalide system which would meet the safety requirements and withstand the high external heat and drop forces experienced in an operational scenario, while delivering the needed electrical energy.
The Lithium-oxyhalide battery design is based on a reserve or inactive electrolyte design in which there is a hermetic seal to separate the electrolyte (catholyte) until activated via dual redundant diaphragms. Despite being inactive for a long time, safety, after activation, is still important because the vehicle may require internal power before launch.
The net Lithium-oxyhalide design incorporated dual activation diaphragms, an integrated activation manifold, composite electrode separators, electron beam vapor deposited lithium anodes and alternate cells for pulse and power section distribution with adiabatic thermal discharge.
Batteries built with the combined improvements were shown to remain inactive to 90 0C which is 29 0C above the required maximum storage requirement. A battery heated to 110 0C was successfully discharged to End Of Life.
Separators made with glass fiber and microporous film provide excellent conduction with protection against activation fluid dynamics and assembly errors which could produce shorts. The electron beam vapor deposited lithium electrode was made thinner to limit heat and reduce the possibility of thermal runaway.
The combined test results have shown that the Lithium-oxyhalide batteries are comparable to other reserve batteries in their ability to withstand abusive conditions leading to qualifications. Over 160 batteries consisting of 2,500 cells have been activated without a safety issue.
4.2 Gassing in 8-MnO2 Cells for Land Warrior Applications, U.S. Army Research Laboratory, Adelphia
As discussed in the first summary in this overview, primary Lithium-manganese dioxide chemistry had initially provided greater energy density than primary Lithium-sulfur dioxide, but ultimately, the optimization of the Lithium-sulfur dioxide provided greater energy density along with lower cost. However, this information does not rule out Lithium -manganese dioxide chemistry as the Army has continued to fund research to better understand the gassing shortcoming of the manganese version.
The problem is that the pouch cell swells a few days after construction because of electrolyte water catalytically decomposing electrolyte solvents. The swelling can lead to rupture, which would expose both the solvent and the Lithium anode. Either could be a hazard to troops using equipment with the batteries.
A report discussing a first level research program on the identifyable cause of gassing was given. Hopefully, a solution can then be formulated, and lead to a cell which does not gas.
In working to establish the identifyable cause of gassing, two special formulations were prepared, one using Hunter’s acid wash (AW type) and another by constructing teflonated cathodes with spinel and then electrochemically charging them in a pouch cell (EC type). The experiment showed that there are apparently two mechanisms of gassing, both based on the water concentration of the cathode material. Solvent creates gas at a linear rate while electrolyte creates gas at an exponential rate. From the test results, it is projected that if a salt were selected that does not readily decompose forming hydrogen ions, the gassing in the AW cathode material could be greatly reduced. This position appears to be the beginning point for a next study which would compare the performance of various salts.
1. Handbook of Batteries, Third Edition, pp. 14.19-14.31