Ah Capacity Research Articles

Nickel–zinc accordion-fold batteries with microfibrous electrodes using a papermaking process

Thin microfibrous substrates were built using a low cost, high speed, wet lay papermaking process with nickel and copper microfibers. High quality microfiber sheets with designed thickness and void volumes were fabricated at the Center for Microfibrous Materials Manufacturing at Auburn University. Products include thin microfibrous nickel and copper substrates with or without suitable expanded metal meshes, either sandwiched inside or on the backside. An improved method for fabrication of zinc electrodes was accomplished by electro-depositing active zinc material on 6 and/or 9 μm diameter microfibrous copper substrates. These zinc electrodes with various additives were examined for shape change and tested for performance. A new structure of electrode design was employed using an accordion-fold cell. By using five individual segments sintered onto an expanded metal mesh, an accordion-fold cell (670 mAh rated capacity) was assembled and had 98.0% coulomb efficiency, 88.6% energy efficiency at 72% depth-of-discharge (DOD) and 73.2% state-of-recharge (SOR) in the 79th cycle. A Ni–Zn cell consisting of one thick nickel and one thick zinc electrode was tested for rate performance in comparison with the 670 mAh accordion-fold cell. The accordion-fold cell (1279 mAh rated capacity) was scaled-up and tested for 835 cycles at 38% DOD at a 0.3 C charge and discharge rates, and continuously operated at 38% DOD until the 1050th cycle was finished at 0.16 C charge/discharge rates. A 7115 mAh accordion-fold demonstration cell was tested at 0.28 C charge and discharge rates for 608 cycles and still had a 4.7 Ah capacity at a 0.08 C discharge rate.

Effect of sodium iodide additive on the electrochemical performance of sodium/nickel chloride cells

The effect of sodium iodide and sulfur additives on the performance of Na/β′′-alumina/NaAlCl4/NiCl2/Ni cells was investigated in quasi-sealed laboratory research cells (0.5–1.0 Ah capacity) and in sealed full-size cells (4 Ah capacity). It was found that sodium iodide additive especially in combination with sulfur in Na/NiCl2 cells significantly increases the usable capacity and reduces the impedance of the Na/NiCl2 cells. It is proposed that the use of sodium iodide enhances the energy and power performance of the NiCl2 electrode by two different mechanisms. The first mechanism, iodide ion doping of the anodically formed solid NiCl2, is dominant at potentials lower than that of iodine evolution. The doping effect of the iodide ions produces a higher-capacity, lower-impedance NiCl2 layer on the positive electrode. The second mechanism, anodic formation of very reactive iodine species, is effective when the cell is cycled through the iodine evolution potential range (2.8–3.1 V vs Na). During this process, the dissolved iodine species improve electrode kinetics through liquid-phase mass transport. Use of the sodium iodide additive is safe in sealed cells, causing no over-pressurizing problems. A maximum pressure increase of only 10 kPa was detected by a pressure sensor during severe overcharge tests.

Modeling discharge and charge characteristics of nickel–metal hydride batteries

A combined numerical and experimental study of the discharge and charge of nickel–metal hydride (Ni–MH) batteries has been performed. Numerical simulations were based on a previously developed micro–macroscopic coupled model which includes both the proton diffusion in the nickel active material and the hydrogen diffusion in metal-hydride particles. Oxygen generation and recombination, a principal mechanism to ensure safe operation of Ni–MH cells during overcharge, is also accounted for. A sealed Ni–MH cell (AA size, 1 Ah capacity) was prepared and discharge experiments were conducted at various rates. These experimental data along with other discharge and charge data available in the literature were used to validate the present model. Numerical results were presented to show the effects of oxygen evolution on battery performance, particularly on the charge acceptance, cell pressure build-up and self-discharge. This combined experimental and numerical study yields a computer-aided tool for the design and optimization of Ni–MH batteries.

Beneficial effect of carbon–PVA colloid additives for lead–acid batteries

Abstract Based on the previous success of adding ultra-fine carbon–PVA (polyvinyl alcohol) colloid solution to restore performance of weak batteries, a large scale test programme of practical batteries including those used in forklift, golf cart, taxi cab, truck and bus applications from 150 companies was carried out. More than 95% of the tested batteries exhibited excellent recovery in performance parameters including the specific gravity (S.G.), voltage and operation time (Ah capacity). The work reported here includes basic research studies to understand better the beneficial action of the carbon–PVA colloid additive.

Sukatani revisited: on the performance of nine-year-old solar home systems and street lighting systems in Indonesia

In 1988, 86 solar home systems, SHS, and 15 street lighting systems, SLS, were installed in the village of Sukatani in the province of West Java of Indonesia. The systems have a PV array of 80 Wp. In this paper we analyse the performance of these systems. For this purpose we use monitoring data and data from field surveys recorded in the period 1988–1993 and data collected in a field survey in 1997. This survey comprised both technical measurements on 62 solar home systems and interviews with 22 users of these systems. We found that, although the failure rate of street lighting systems is high, the villagers have a positive opinion about these systems. Further, we found that technically the solar home systems performed well. The users are satisfied about the performance. However, in the course of time the configuration of the SHS has changed: villagers have replaced most of the strip lights with cheap home-made candescent lamps and have replaced the initially-installed 100 Ah capacity solar batteries with cheaper locally produced 70 Ah capacity car batteries. From an analysis of monitoring data we found that the average irradiation in Sukatani is 4.2 kW/m 2/day, which is a common value for Indonesia, but more than expected in 1988 when the systems were installed (3.5 kWh/m 2/day). Furthermore, we found that daily electricity consumption per SHS can be as high as 25 Ah/day. Average values, however, range from 8.8 to 14.8 Ah/day, which is 15–50% below the daily load used in the design calculations (17.4 Ah/day). However, the average daily electricity consumption is close to the recommended value on the instruction sheets given to the users of the SHS. Because of the low demand of electricity the average performance ratio is 49%. By means of an energy loss analysis of the PV systems we found that 15% of the theoretically available energy from the array cannot be fed in the battery because it is fully charged. The replacement of 100 Ah batteries by 70 Ah batteries was justified on the grounds of the low electricity consumption of the SHS users in the period 1988–1993. On the basis of field surveys we found that the average lifetime of the 100 Ah and 70 Ah batteries is 4 and 3.5 years, respectively. The realized battery lifetime is rather long compared with other SHS projects in the world. While the average battery size in Sukatani decreased in course of time, we found on the basis of interviews with users of SHS that the average daily electricity consumption increased. We found a value of 18 Ah/day in 1997. Furthermore, the spread in the demand of electricity in 1997 and the use of other than initially-installed appliances, such as small incandesent bulbs and intercoms, indicates the need for a broad offer of system sizes and low power appliances. By means of design calculations we found that PV arrays in the range of 35–130 Wp are needed to satisfy different demand patterns. We conclude that monitoring by means of data loggers is a useful approach to allow the analysis of the long-term system performance. To increase the statistical reliability of results, monitoring should be supplemented by field measurements and interviews with users. However, due to the deviation between real and narrated experiences, interviews alone may not be sufficient to assess an SHS project.

Fabrication and evaluation of 1 Ah silver/metal hydride cells

Silver/metal hydride (Ag/MH) cells of about 1 Ah capacity have been fabricated and their discharge characteristics at different rates of discharge, faradaic efficiency, cycle life and a.c. impedance have been evaluated. These cells comprise metal–hydride electrodes prepared by employing ∼60 μm powder of an AB2-Laves phase alloy of nominal composition Zr0.5Ti0.5V0.6Cr0.2Ni1.2 with PTFE binder on a nickel-mesh substrate as the negative plates and commercial-grade silver electrodes as the positive plates. The cells are positive limited and exhibit two distinct voltage plateaus characteristic of two-step reduction of AgO to Ag during their low rates of discharge between C/20 and C/10. This feature is, however, absent when the cells are discharged at C/5 rate. On charging the cells to 100% of their capacity, the faradaic efficiency is found to be 100%. The impedance of the Ag/MH cell is essentially due to the impedance of the silver electrodes, since MH electrodes offer negligible impedance. The cells may be subjected to a large number of charge–discharge cycles with little deterioration.

Cellulosic separator applications: new and improved separators for alkaline rechargeable cells

A study has been established at Naval Surface Warfare Center, Crane Division (NAVSURFWARCENDIV) and Rutgers University to obtain material analysis data on cellulosic separator properties such as tensile strength and swelling of alkaline-soaked film samples, degree of polymerization and crystallinity, cationic and anionic diffusion and penetration rates in alkaline media, and X-ray diffraction for crystallinity. These data are then related to cycleand wet-life information from model electrochemical cells as a function of separator composition on an alkaline chemistry rechargeable cell set. The first examples used in this program are silver-zinc rechargeable cells of 28 Ah capacity, identical in every respect except for the separator composition, which are being tested in statistically significant numbers under identical temperature and relative humidity conditions, with 45% KOH as the electrolyte. The cycle-life test regime of continuous cycling is: C/5 discharge to 1.30 V, and C/30 and C/60 charge to 2.03 V, while the wet-life test regime includes a 30-day wet-stand at full charge between cycles. At the outset of the cell testing, a baseline cell was selected from each set in the matrix after the so-called formation cycling was complete, and the physical properties of crystallinity, tensile strength, and degree of polymerization were re-measured. Then, at intervals during cycleand wetlife cycling, and as cells fail the life tests, these properties will be measured again for selected cells. In this way a correlation will be established between separator life under charge/discharge conditions in actual cells and the critical physical properties of each separator film. Eight separator compositions, all cellulose-based, are being evaluated. The purpose of the study is to utilize the cycle- and wet-life data which are a function of separator composition and physical properties in the alkaline chemistry rechargeable cell set, to designate a ‘best’ separator for incorporation into actual production cells by the manufacturing community for silver/zinc rechargeable cells. The recommendations will take the form of minimum separator physical properties which are beneficial to cell performance and long life, resulting in an improvement in the assets available for Fleet use in the US Navy. This paper discusses the data available to date on cycle- and wet-life, and their relationship to separator physical properties before and at several stages during cycling.

Improved Carbon Anode Materials for Lithium-Ion Cells

ABSTRACTSeveral carbon materials have been studied for suitability as anode materials in lithium-ion cells. Carbons that have been included in this evaluation are three grades of commercially available mesophase carbon microbeads (MCMB) 6–28, 10–28 and 25–28, two specially prepared mesophase fibers (Amoco), a foreign mesophase fiber and KS-15 graphite (Lonza). Differences in cycling behavior between the three types of MCMB material are shown. Data of full lithium-ion cells demonstrate the effect that the choice of carbon material has on the cell discharge voltage and capacity. Lithium reference electrode experiments in full cells (3.0–4.0Ah capacity), elucidate the dynamics under several charge/discharge regimes and provide a comparison between the performance of carbon fiber and graphite anode materials. These test results indicate that the fibers can be charged at significantly higher rates than graphite without showing polarization at the anode. Full and half cell data also demonstrates the high coulombic efficiencies of the mesophase materials and first cycle efficiencies as compared to graphite. A comparison of two mesophase materials with different textures in full cells under strenuous cycling conditions shows significant differences in capacity retention. SEM photos of fibers showing the different textures are also presented.

Performance characterization of sintered iron electrodes in nickel/iron alkaline batteries

A nickel/iron storage battery with a porous, sintered, iron negative electrode and a nickel positive electrode is a high power system by virtue of its low internal resistance. A dry-powder sintering procedure is used to fabricate negative and positive electrodes. Negative iron electrodes are activated with various salt solutions such as CdSO 4, BaCl 2, HgCl 2 and sulfur. Positive electrodes are impregnated with nickel hydroxide by a chemical method. Tests are performed in 10 Ah capacity nickel/iron cells and two types of activated iron electrodes are used. The present work deals with electrode fabrication, charge/discharge studies, self-discharge, temperature performance and cycle life. Finally, the best iron electrodes are coupled with nickel electrodes to obtain a 1.37 V, 75 Ah nickel/iron cell. The performance of this cell is discussed.

Voltage and capacity stability of the Hubble telescope nickel-hydrogen battery

The power system of the Hubble Space Telescope includes two orbital replacement units, each containing three nickel-hydrogen (NiH 2) batteries of 88 Ah capacity. Since launch in April 1990, the batteries have completed 23 000 charge and discharge cycles and continue to meet the power demands of the satellite. The voltage, capacity, and pressure characteristics of all six batteries were analyzed to determine the state of health of the battery and to identify any signs of performance degradation. The battery pressures have changed to varying degrees. The end-of-charge pressure for battery 4 increased by 96 psi, while that for battery 3 decreased by 37 psi. The voltages of the individual cells show a decay rate of 0.69 mV per 1000 cycles, and the capacity of the batteries has apparently decreased, possibly due to the system being operated at a lower stage of charge. Autonomous battery operation involving charge termination at a preselected voltage continues to restore the energy dissipated during each orbit. The accumulated data on voltages and recharge ratios can be used to design new temperature-compensated voltage levels for similar missions that employ NiH 2 batteries.

Contribution to the development of the electric power source of the martian stations in the frame of the Mars 94 Project

In the frame of the Mars 94 Project in which the French Space Agency is involved, small stations will be used for collecting data concerning the ground and the environment. The power source of the station is constituted with both radioisotopic and electrochemical generators (which are NiCd accumulators and Li cells), the part including cells and accumulators has been taken in charge by CNES and CNRS. In the present case we will only treat of the subject concerning the accumulators and the purpose of this paper is to describe the method used for optimizing a battery when we take into account: — the current budgets — the thermal and mechanical environment constraints during the flight and the mission — the costs and the delays Due to the constraints above mentioned a first choice was in favour of NiCd elements. In a second phase, we had to determine the most adapted capacity (or range of capacities) in a purpose of obtaining the best compromise between the efficiency of the recharge and acceptable voltage losses during power consumption peaks. The last phase which allowed us to make the final choice has been devoted to appropriate tests in order to quantify the degradations of the efficiency and capacity under thermal and mechanical constraints simulating the flight conditions. This procedure oriented our choice in favour of standard NiCd cells of 0,5 Ah capacity.

Development and characterization of a high capacity lithium/thionyl chloride battery

A 30 V lithium/thionyl chloride battery with 320 Ah capacity capable of operating at currents of 14 to 75 A has been developed and tested over a temperature range from 15 to 71 °C. The 81 lb battery consists of nine series connected cylindrical cells in a three-by-three arrangement within an aluminum case. The cells are of a parallel disc electrode design with a total active surface area of 10 200 cm 2. Cells and batteries have each been tested for safety, performance and to a space environment. The battery has clearly performed in excess of the specification requirements. The cell design is very adaptable to many battery design requirements.

Totally implantable total artificial heart and ventricular assist device with multipurpose miniature electromechanical energy system.

A multipurpose miniature electromechanical energy system has been developed to yield a compact, efficient, durable, and biocompatible total artificial heart (TAH) and ventricular assist device (VAD). Associated controller-driver electronics were recently miniaturized and converted into hybrid circuits. The hybrid controller consists of a microprocessor and controller, motor driver, Hall sensor, and commutation circuit hybrids. The sizing study demonstrated that all these components can be incorporated in the pumping unit of the TAH and VAD, particularly in the centerpiece of the TAH and the motor housing of the VAD. Both TAH and VAD pumping units will start when their power line is connected to either the internal power pack or the external battery unit. As a redundant driving and diagnostic port, an emergency port was newly added and will be placed in subcutaneous location. In case of system failure, the skin will be cut down, and an external motor drive or a pneumatic driver will be connected to this port to run the TAH. This will minimize the circulatory arrest time. Overall efficiency of the TAH without the transcutaneous energy transmission system was 14-18% to deliver pump outputs of 4-9 L/min against the right and left afterload pressures of 25 and 100 mm Hg. The internal power requirement ranged from 6 to 13 W. The rechargeable batteries such as NiCd or NiMH with 1 AH capacity can run the TAH for 30-45 min. The external power requirement, when TETS efficiency of 75% was assumed, ranged from 8 to 18 W. The accelerated endurance test in the 42 degrees C saline bath demonstrated stable performance over 4 months. Long-term endurance and chronic animal studies will continue toward a system with 5 years durability by the year 2000.

Mixed Ether Electrolytes for Secondary Lithium Batteries with Improved Low Temperature Performance

Tetrahydrofuran (THF): 2‐methyl‐tetrahydrofuran mixed solutions, despite their lower conductivity, have allowed significantly better low temperature performance in cells than have . 13C NMR data suggest that this may be related to the structurally disordered Li+‐solvates that exist in the mixed ether solutions. High cycling efficiencies for the Li electrode in solutions have been achieved by the use of 2Me‐F as an additive. A 5 Ah capacity cell has been cycled more than 100 times at 100% depth‐of‐discharge, with the cell capacity remaining at over 3 Ah at the 100th cycle.

Interpretation of Sodium‐Sulfur Cell Characteristics Using an Alternating Current Resistance Technique

An alternating current (ac) resistance technique for sodium‐sulfur cells is described. The method has been applied to central sodium and central sulfur cells with between 16 and 650 Ah capacity. The shape of the ac charge resistance‐capacity plot has been correlated with resistive layer composition. Anomalies in direct current (dc) resistances for oriented‐mat sulfur electrode cells are explainable in conjunction with ac analysis. The increased sensitivity of ac compared to dc measurements has been utilized to identify incipient electrolyte failure and sodium electrode problems not discernable by the latter technique.

Direct calculation of the sulphur electrode resistance in sodium-sulphur cells

A simple model is used to compute the resistance of the sulphur electrode as a function of charge. It is shown that the general network used for the simulation of the behaviour of the sulphur electrode can be simplified because of the relatively small value of the polarization resistance. Reasonable assumptions concerning the distribution of reactants and products are discussed. The model is able to assess the contribution of the sulphur electrode to the total cell resistance for a 16 Ah capacity cell.