Porous Zinc Electrodes Research Articles

Surface Characterization and Optimization of Porous Zinc Anodes to Improve Cycle Stability by Mitigating Dendritic Growth

Zinc-based batteries are a scalable and safe alternative to Lithium-ion batteries due to the nature of abundance, low cost and easy to process. In this work, we have successfully synthesized porous zinc electrodes (PZEs) via a gel-binder method that can stably charge and discharge for over 700 h at 1 mA cm−2 before showing signs of failure. We compared PZEs synthesized from small (60 nm), intermediate (10 μm), and large (150 μm) zinc particles to determine which surface features are best suited to mitigate dendritic growth and to improve electrolyte stability. The zinc deposits on the large PZE shows a stable and flat morphology, which does not form the hexagonal close-packed (HCP) crystal structure that is typically seen on planar zinc anodes. The intermediate PZE has an increased affinity to deposit onto the glass microfiber separator leading to a decrease of active material on the anode that causes instability during galvanostatic cycling. Both planar zinc and small PZE show HCP deposits that are normal to the surface, which result in very poor electrochemical performance. As the particle size increases, the deposits transition from HCP crystals to flat amorphous metal deposits, increasing cyclic stability.

A high areal capacity solid-state zinc-air battery via interface optimization of electrode and electrolyte

Solid-state zinc-air batteries (SZABs) are regarded as a promising energy source for next-generation wearable electronic devices due to their high theoretical energy density and reliability. However, practical development of solid-state zinc-air batteries is hindered by the low specific areal capacity and poor contact between solid-state electrolyte and electrode caused by zinc passivation and electrolyte aging. Herein, we report a new strategy for optimizing the solid-state electrolyte/electrode interface coupling by combining porous zinc electrode and thermal-sensitive solid-state electrolyte F127 to improve the areal-capacity of solid-state zinc-air batteries. The porous Zn anode prepared by zinc electrodeposition on the zinc substrate is used to alleviate zinc passivation and improve the specific area capacity of SZAB. In addition, to enhance the contact between the solid-state electrolyte and the zinc anode, the F127 surfactant is selected as the solid-state electrolyte due to its fluidity at low temperatures. Benefiting from the porous structure and excellent contact, the SZAB using porous zinc anode and the solid-state electrolyte F127 exhibits high areal capacity of 133 mAh cm−2 at the current density of 4 mA cm−2, which is 100 times higher than that of the solid zinc-air battery using zinc foil as the anode. Moreover, the results show that the use of porous zinc electrodes is conducive to achieving high current discharge, which is critical for the practical application of solid-state zinc-air batteries.

Morphological Evolution in Rechargeable Alkaline Zinc Anodes

Dendrites, passivation, and shape changes are the common suspects to blame in the failures of rechargeable zinc anodes. The formation of porous zinc is not, or rarely discussed in the context of zinc batteries. We show that when starting with an electrode made of ZnO powder, the charging and then discharging cycles to a certain depth will make it partially a porous zinc electrode. This morphological evolution has important implications to the structural stability, as it reshapes the electronic conductivity, the specific area, the structural uniformity, and the geometrical path of the electrochemical reactions. By carefully dissecting some forty coin cells, we show step by step how the morphological evolution takes place and progresses, and how it may affect the cycle life.

Cold Sintering as a Cost-Effective Process to Manufacture Porous Zinc Electrodes for Rechargeable Zinc-Air Batteries

Zinc-air batteries (ZABs) offer a sustainable and safe pathway to low-cost energy storage. Recent research shows that thermally-sintered porous Zn electrodes with a three-dimensional network structure can enhance the performance and lifetime of ZABs, but they are expensive and energy-intensive to manufacture. In this work, monolithic porous Zn electrodes fabricated through an efficient cold sintering process (CSP) were studied for rechargeable ZABs. Electrochemical studies and extended charge-discharge cycling show good Zn utilization with no observable performance degradation when compared to Zn foil. Post-mortem analysis after 152 h of cycling reveals that the cold-sintered electrodes retain their original structure. A techno-economic assessment of the cold sintering process confirms significant reductions in both the time and energy required to manufacture Zn electrodes compared to a comparable thermal sintering process.

Improving zinc porous electrode for secondary alkaline batteries: Toward a simple design of optimized 3D conductive network current collector

The internal migration of zinc within the thickness of porous composite negative electrodes for rechargeable zinc batteries causes detrimental shape change of the zinc electrode. It depends on various parameters linked to the electron conduction in the electrode: electronic percolation, conductive additives, primary current collector. This study highlights a simple solution, that drastically enhances the electrochemical performance of thick and porous zinc electrodes, by rethinking their architecture. Using a multiplicity of thin current collectors enables to create a 3D network of electronic percolation and a better repartition of the current lines within the electrode; as a result, the formation of multiple active zinc cores in the electrode volume is better controlled. This strategy allows to improve the management of zinc migration within the electrode structure, leading to minimal densification of each zinc core, and overall enables higher reversibility of zinc oxidation/reduction upon discharge/charge. It finally mitigates the initial drastic capacity fading observed on standard type calcium zincate negative electrode.

Failure Analysis of the Rechargeable Porous Zinc Electrode in Alkaline Electrolyte

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, earth abundant metal. It has a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg|HgO) in concentrated alkaline electrolyte, a high gravimetric discharge capacity of 820 mAh/g, and a high volumetric discharge capacity of 5850 mAh/mL. During discharge, Zn oxidizes and forms a dissolved complex known as the zincate ion, Zn(OH)4 2-, from which zinc oxide (ZnO) precipitates as a solid. On charge, Zn(OH)4 2- is reduced to metallic Zn. Motivation to study the Zn electrode in rechargeable batteries is driven by a target overall battery energy density of 200 Wh/L that is sustainable for 500 or more charge-discharge cycles. This corresponds to a Zn electrode volumetric capacity of 650 mAh/mL. The cycle life of the porous Zn electrode in concentrated alkaline electrolyte is observed to decrease with increasing percentage of discharge capacity of Zn accessed. The percentage of discharge capacity of Zn accessed is known as the depth of discharge (DOD). Zn electrodes were cycled in the range of 1% to 15% Zn DOD in zinc-manganese dioxide (Zn-MnO2) batteries and in the range of 15% to 30% Zn DOD for zinc-nickel (Zn-Ni) batteries. Additives were incorporated into the zinc electrodes for the tests done on Zn-Ni batteries. Additives used were surfactant cetyltrimethylammonium bromide (CTAB), bismuth oxide (Bi2O3), synthetic layered silicate Laponite, and calcium hydroxide (Ca(OH)2). The potential values of the Zn electrodes vs. Hg|HgO reference electrodes were recorded. During healthy galvanostatic discharge, Zn electrodes displayed a nearly constant potential vs. Hg|HgO at approximately -1.35 V. Tests that failed due to Zn exhibited a shift from this equilibrium potential that corresponded to a loss of cell voltage. This shift may be attributed to a concentration overpotential as ZnO is precipitated, thereby inhibiting the hydroxide ions from reaching the reacting metal interface. The shift may also be due to formation of a passivated layer on the electrode which effectively blocks the remaining active material. There are multiple regimes observed in the potential curves of the Zn electrode vs. Hg|HgO prior to cell failure. Beyond the healthy plateau at -1.35 V, a sloping potential is observed. This is followed by an additional plateau. The second plateau shifts with increasing cycle number and precedes cell death. See the attached figure for discharge curves of a Zn electrode cycled at 11.3% Zn DOD. After the second plateau a steep slope is observed in the potential for later cycles, which is believed to be due to passivation of the Zn electrode. The additives were observed to modify the discharge potential curve of the Zn electrode vs. Hg|HgO. Figure 1

Failure Analysis of the Rechargeable Porous Zinc Electrode in Alkaline Electrolyte

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, earth abundant metal. It has a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg/HgO) in concentrated alkaline electrolyte and a high gravimetric discharge capacity of 820 mAh/g. During discharge, Zn oxidizes and forms a dissolved complex known as the zincate ion, Zn(OH)4 2-, from which zinc oxide (ZnO) precipitates as a solid. On charge, Zn(OH)4 2- is reduced to metallic Zn. Motivation to study the Zn electrode in rechargeable batteries is driven by a target overall battery energy density of 200 Wh/L that is sustainable for 500 or more charge-discharge cycles. This corresponds to a Zn electrode discharge density in the range of 650 mAh/mL. The cycle life of the porous Zn electrode in concentrated alkaline electrolyte is observed to decrease with increasing percentage of discharge capacity of Zn accessed. The percentage of discharge capacity of Zn accessed is known as the depth of discharge (DOD). Zn electrodes were cycled in the range of 1% to 15% Zn DOD in zinc-manganese dioxide (Zn-MnO2) batteries and in the range of 15% to 30% Zn DOD for zinc-nickel (Zn-Ni) batteries. Additives were incorporated into the zinc electrodes for the tests done on Zn-Ni batteries. Additives used were surfactant cetyltrimethylammonium bromide (CTAB), bismuth oxide (Bi2O3), synthetic layered silicate Laponite, and calcium hydroxide (Ca(OH)2). The potential values of the Zn electrodes vs. Hg/HgO reference electrodes were recorded. During healthy galvanostatic discharge, Zn electrodes displayed a nearly constant potential vs. Hg/HgO at approximately -1.35 V. Tests that failed due to Zn exhibited a shift from this equilibrium potential that corresponded to a loss of cell voltage. This shift may be attributed to concentration overpotential as ZnO is precipitated, thereby inhibiting the hydroxide ions from reaching the reacting metal interface. The shift may also be due to formation of a passivated layer on the electrode which effectively blocks the remaining active material. There are generally two regimes observed in the potential curves of the Zn electrode vs. Hg/HgO prior to cell failure. Beyond the healthy plateau at -1.35 V, the first regime consists of a sloping potential while the second regime is an additional plateau. The second plateau shifts with increasing cycle number and corresponds to cell death. See the attached figure for discharge curves of a Zn electrode cycled at 5% Zn DOD. The second plateau is believed to be due to passivation of the Zn electrode. The additives were observed to modify the discharge potential curve of the Zn electrode vs. Hg/HgO. Figure 1

Failure Analysis of the Rechargeable Porous Zinc Electrode in Alkaline Electrolyte

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, earth abundant metal. It has a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg/HgO) in concentrated alkaline electrolyte and a high gravimetric discharge capacity of 820 mAh/g. During discharge, Zn oxidizes and forms a dissolved complex known as the zincate ion, Zn(OH)4 2-, from which zinc oxide (ZnO) precipitates as a solid. On charge, Zn(OH)4 2- is reduced to metallic Zn. Motivation to study the Zn electrode in rechargeable batteries is driven by a target overall battery energy density of 200 Wh/L that is sustainable for 500 or more charge-discharge cycles. This corresponds to a Zn electrode discharge density in the range of 650 mAh/mL. The cycle life of the porous Zn electrode in concentrated alkaline electrolyte is observed to decrease with increasing percentage of discharge capacity of Zn accessed. The percentage of discharge capacity of Zn accessed is known as the depth of discharge (DOD). Zn electrodes were cycled in the range of 1% to 15% Zn DOD in zinc-manganese dioxide (Zn-MnO2) batteries and in the range of 15% to 30% Zn DOD for zinc-nickel (Zn-Ni) batteries. Additives were incorporated into the zinc electrodes for the tests done on Zn-Ni batteries. Additives used were surfactant cetyltrimethylammonium bromide (CTAB), bismuth oxide (Bi2O3), synthetic layered silicate Laponite, and calcium hydroxide (Ca(OH)2). The potential values of the Zn electrodes vs. Hg/HgO reference electrodes were recorded. During healthy galvanostatic discharge, Zn electrodes displayed a nearly constant potential vs. Hg/HgO at approximately -1.35 V. Tests that failed due to Zn exhibited a shift from this equilibrium potential that corresponded to a loss of cell voltage. This shift may be attributed to concentration overpotential as ZnO is precipitated, thereby inhibiting the hydroxide ions from reaching the reacting metal interface. The shift may also be due to formation of a passivated layer on the electrode which effectively blocks the remaining active material. There are generally two regimes observed in the potential curves of the Zn electrode vs. Hg/HgO prior to cell failure. Beyond the healthy plateau at -1.35 V, the first regime consists of a sloping potential while the second regime is an additional plateau. The second plateau shifts with increasing cycle number and corresponds to cell death. See the attached figure for discharge curves of a Zn electrode cycled at 5% Zn DOD. The second plateau is believed to be due to passivation of the Zn electrode. The additives were observed to modify the discharge potential curve of the Zn electrode vs. Hg/HgO. Figure 1

Cycle Life Study and Failure Analysis of the Rechargeable Porous Zinc Electrode in Alkaline Electrolyte

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, earth abundant metal. It has a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg/HgO) in concentrated alkaline electrolyte and a high theoretical gravimetric charge capacity of 820 mAh/g. During discharge, Zn oxidizes and forms a dissolved complex known as the zincate ion, Zn(OH)4 2-, from which zinc oxide (ZnO) precipitates as a solid. On charge, Zn(OH)4 2- is reduced to metallic Zn. Motivation to study the Zn electrode in rechargeable batteries is driven by a target overall battery energy density of 200 Wh/L that is sustainable for 1000 or more charge-discharge cycles. This corresponds to a Zn electrode charge density in the range of 650 mAh/mL. The percentage of charge capacity of Zn accessed is known as the depth of discharge (DOD). Battery energy density of 200 Wh/L motivates zinc electrode improvement to 20% Zn DOD. However, increased Zn DOD leads to a decrease in cycle life. A negative exponential relationship between cycle life and Zn DOD for the range of 1% to 15% Zn DOD for zinc-manganese dioxide (Zn-MnO2) batteries was observed experimentally. Over 2800 cycles were achieved in a Zn-MnO2 battery at 1% Zn DOD. The effect of additives on the Zn electrode at Zn DOD values in the range of 15% to 30% was studied in zinc-nickel (Zn-Ni) battery cycle tests. Additives used were surfactant cetyltrimethylammonium bromide (CTAB), bismuth oxide (Bi2O3), synthetic layered silicate Laponite, and calcium hydroxide (Ca(OH)2). A cycle life of 542 at 15% Zn DOD was observed for a Zn electrode containing CTAB, bismuth oxide, and Laponite. In both Zn-MnO2 and Zn-Ni batteries, absolute value of Zn potential vs. Hg/HgO on discharge decreased as cycle number increased, even before discharge capacity faded. The Zn electrode is associated with multiple failure mechanisms. Electrolyte depletion is due to a lack of hydroxide ions (OH-), either because of OH- consumption during battery discharge or an insufficient electrolyte reservoir. Pore plugging results from decreased electrode porosity associated with ZnO precipitation. Zn passivation occurs when precipitated ZnO films completely surround Zn. Shape change of the Zn electrode is a phenomenon in which Zn is not deposited uniformly during charge. The Zn electrode is also susceptible to gassing, in which the hydrogen (H2) evolution reaction occurs during charge. Water is reduced to gaseous H2, thus the flow of electrons into the electrode is not used to deposit metallic Zn, resulting in lower Zn plating efficiency. In order to further understand underlying physical, chemical, and electrochemical behavior of the Zn electrode as well as improve energy density and cycle life, future experimental and theoretical work is proposed. The effect of additives on the cycle life of Zn-MnO2 batteries will be studied. Additionally, electrode performance for Zn DOD values in the range of 15% to 30% Zn DOD will be investigated. A theoretical mathematical model of the Zn electrode will be formulated based on the governing equations of the system. Numerical solutions will be obtained for the spatial profiles of Zn(OH)4 2- concentration, OH- concentration, current density, potential, and porosity at extended cycle number. [1] Ingale, Nilesh D.; Gallaway, Joshua W.; Nyce, Michael; Couzis, Alexander; Banerjee, Sanjoy, “Rechargeability and economic aspects of alkaline zinc-manganese dioxide cells for electrical storage and load leveling,” Journal of Power Sources, 276 (2015), 7-18. [2] Wei, Xia; Desai, Divyaraj; Yadav, Gautam G.; Turney, Damn E.; Couzis, Alexander; Banerjee, Sanjoy. "Impact of anode substrates on electrodeposited zinc over cycling in zinc-anode rechargeable batteries," Electrochimica Acta, 212 (2016), 603-613. [3] Yadav, Gautam G.; Gallaway, Joshua W.; Turney, Damon E.; Nyce, Michael; Huang, Jinchao; Wei, Xia; Banerjee, Sanjoy. " Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries," Nature Communications, 8 (2017) 14424. [4] Turney, Damon; Gallaway, Joshua; Yadav, Gautam; Ramirez, Rodolfo; D'Ambrose, Michael; Kolhekar, Snehal; Nyce, Michael; Wei, Xia; Huang, Jinchao; Chen-Wiegart, Yu-chen; Wang, Jun; Banerjee, Sanjoy. "Rechargeable zinc alkaline anodes for long-cycle energy storage," Chemistry of Materials, under review.

A brief overview of secondary zinc anode development: The key of improving zinc-based energy storage systems

Electricity will increasingly be produced from sources that are geographically decentralized and/or intermittent in their nature. In consequents, there is an urgent need to increase the storage of energy to guarantee the continuity of energy supply. Rechargeable zinc-air battery is a promising technology due to the high theoretical energy density and the abundant and environmentally benign materials that are used. In the state of the art, the information about secondary zinc anode for rechargeable zinc-air batteries is scarce. The main development of the technology has been lately concentrated on the bifunctional air electrodes while the used zinc anode is mainly based on a planar zinc electrode providing low specific energy densities for the full system. This overview compiles the available information in the literature regarding the development and manufacturing of zinc anodes for electrical rechargeable batteries applications, where secondary porous zinc electrodes are generally desired. In this context, the zinc-based anode electrode composition (namely, active material, binder, conductive material, current collector, and additives), pretreatments, and processing techniques are described and their impact on the zinc anode performance analyzed.

Controlling the shape change and dendritic growth in Zn negative electrodes for application in Zn/Ni batteries

Abstract Porous zinc electrodes are elaborated, assembled in Zn/Ni 3–4 Ah prismatic batteries and monitored upon charge/discharge cycling (150 cycles at C/3 rate followed by 150 cycles at 1C rate). Migration of zinc within the thickness of the zinc electrodes is revealed by X-Ray radiography, scanning electron microscopy, and X-EDS elemental cartography. Electrodes using either zinc oxide plus calcium hydroxide or directly calcium zincate as active material show similar behavior: neither dendrite formation nor morphological shape changes are observed after 300 charge/discharge cycles. Upon cycling, zinc accumulates at the core of the porous electrode, in the vicinity of the primary current collector and not at the surface, therefore avoiding any risk of dendrite formation. This suggest that the electrode operation is controlled by a core-shell mechanism, with a core of active zinc in the vicinity of the primary current collector, trapped in an electrode shell which is created by the outer portion of the electrode (active material, conductive additives, binder …). However, changing from C/3 to 1C rate after 150 cycles significantly improves the capacity of batteries using calcium zincate; this is correlated to its initial atomic homogeneity associated with higher porosity and an optimal electronic percolation.

Evaluation of Porous Electrode Properties Using Metal-Air Electrochemical System

This work explores the use of metal-air electrochemical system to evaluate porous electrode properties i.e. specific surface area and pore volume density. Porous zinc electrodes are prepared from an acidic, chloride electrolytic bath of varying supporting electrolyte (NH4Cl) formulation to produce electrodeposits of distinctive properties. Nitrogen physisorption at 77 K is utilized to evaluate the specific surface area and pore volume density of the electrodes. The zinc electrodeposits prepared from all electrolytic bath formulations are then assembled into zinc-air cells as the anodic electrode and characterized according to their limiting current density and discharge capacity. It is found that the variation in limiting current density matches that of BET surface area and the trend for discharge capacity follows that of pore volume density.

The Anodic Behavior of Planar and Porous Zinc Electrodes in Alkaline Electrolyte

The electrochemical performance of planar and porous zinc electrodes in an actual Zn/ MnO 2 battery using lithium hydroxide (LiOH) electrolyte has been investigated. A large discharge capacity of 220 mAh/g is delivered by porous zinc electrodes while planar electrodes only deliver 130 mAh/g. The porous anode improves the rate capability of the rechargeable alkaline battery while enhancing the utilization of the active material. Using scanning electron microscopy and IR spectroscopy, the surface morphology and composition of the Zn anodes were studied at the end of the discharge process. While zincate ions and ZnO products were found after the discharge at the surface of the planar anode, no evidence for these products was found in the porous anode. The porosity of this surface prevents the detrimental buildup of zincate ions at the anodic surface that leads to passivation.

Effect of Polyaniline Coating on “Shape Change” Phenomenon of Porous Zinc Electrode

Performance of porous zinc electrode in alkaline secondary battery systems suffers mainly from shape change and dendrite growth. Polyaniline coating in direct contact with porous zinc electrode was found to restrict zincate movement away from the test electrode, which otherwise may lead to a decrease in electrode surface area (shape change of the electrode) on repeated cycling. Constant current charge/discharge cycles of the blank and polyaniline-coated zinc electrodes have been carried out to assess the performance of the polymer film. It was found that a fibrous network of polyaniline coating allows ions and restricts the diffusion of zincate ions.

On the impedance of porous electrodes – double-layer charging and charge transfer on an inhomogeneous inside electrode surface

A model of the impedance of porous electrodes was derived. The model generalized the de Levie model in so far that an inhomogeneous inside electrode surface is assumed. Then the charge transfer resistance and the double-layer capacity were assumed to be distributed. The width of the distribution is characterized by a distribution parameter. The inhomogeneities led to characteristic deviations of the Nyquist impedance plots compared to those for homogeneous inside electrode surfaces: the slope angle of the straight line for higher frequencies was less than π/4, the slope angle of π/2 of the straight line obtained for double-layer charging only and lower frequencies decreased and the semicircle behaviour obtained for double-layer charging and a Faradaic reaction in parallel were replaced by a depressed semicircle. The model allows the determination of the following parameters: the total effective double-layer capacity, the total effective charge transfer resistance, the distribution parameter and the total resistance of the electrolyte inside the pores. The impedance of porous zinc electrodes in weakly alkaline electrolyte can be theoretically well described with the new model. A scanning force microscopy 2-D-image of the morphology of the zinc electrode was performed and discussed.

Morphology and Spatial Distribution of ZnO Formed in Discharged Alkaline Zn / MnO2 AA Cells

A novel experimental technique was developed to extract the KOH solution from the porous zinc electrode in an inert environment. This technique permits the ZnO/electrolyte interface, the ZnO/Zn particle interface, and the spatial distribution of ZnO in the porous anode in commercial alkaline AA batteries to be characterized for the first time by optical and scanning electron microscopy. Both type I and type II ZnO, previously observed in oxidation of planar zinc electrodes, were found in each completely discharged zinc particle in the porous electrode. The morphology, size, and location of these two ZnO forms strongly suggested that they were produced by a solution-precipitation route. The drain rate had a significant impact on the spatial distribution of ZnO in the anode. The segregation of ZnO near the separator became dominant at drain rates higher than 500 mA. The mechanisms by which the morphology and segregation of ZnO within the porous electrode could result in the reduced battery runtime are discussed. © 2003 The Electrochemical Society. All rights reserved.

A zinc–air cell employing a porous zinc electrode fabricated from zinc–graphite-natural biodegradable polymer paste

Porous zinc anodes have been fabricated from a mixture of zinc and graphite powder using gelatinized agar solution as the binding agent. Agar is a biodegradable polysaccharide polymer extracted from marine algae. The graphite content and the agar solution concentration were varied to find the best electrode composition. Zinc–air cells were fabricated using the porous zinc anode, a commercially available air cathode sheet and KOH electrolyte in the form of elastic jelly granules. The electrode performance was evaluated from the zinc–air cell galvanostatic discharge capability. In the cell design, a thin agar layer was introduced between the electrode-gelled electrolyte interfaces, resulting in substantially improved cell discharge performance. The inclusion of particulate graphite into the electrode did not enhance the electrode performance due to the formation of a graphite-rich layer, which obscured the electrode porosity. A zinc–air cell employing the optimized porous zinc electrode demonstrated a capacity of 2066 mA h and specific energy density of 443 Wh kg−1.

Development of Ways To Diminish Corrosion of Zinc Electrode

The influence exerted by addition of α-hydroxynaphthoic acid and combined additive Hg + Pb + α-hydroxynaphthoic acid on the corrosion and self-discharge of a porous zinc electrode in alkali solution was studied.

Rechargeable batteries with aqueous electrolytes

In recent years, rechargeable batteries (RB’s) have found important new applications in rapidly expanding markets, such as portable computers (laptops), telecommunication equipment (handies), camcorders and tools. The interest in electric vehicles has continued to stimulate research on RB’s having improved specific energy. Attention has been focussed on nonaqueous battery systems, in particular on lithium batteries. Small rechargeable lithium batteries, available on the market today, show specific energies of 100–120 Wh kg −1. The upper limit surpasses those of aqueous electrolyte counterparts (nickel–cadmium or nickel–metal hydride) by a factor of 1.5–2. Is there still a future for aqueous electrolyte battery systems? This paper reviews the present status of the various RB’s with aqueous electrolytes and analyses their outlook for the future. Traditionally, lead, cadmium and iron were used as active materials in the negative electrode. In recent years, research on rechargeable zinc electrodes has been intensified. The development of metal hydride negative electrodes has resulted in RB’s with improved specific energy (60–70 Wh kg −1, under some conditions even 80 Wh kg −1). Similar values can be reached with nickel–zinc batteries, the latter having, however, a considerably lower cycle life. Rechargeable zinc–air batteries, with bifunctional air electrodes, are capable of specific energies matching those of lithium batteries. Their cycle life is, however, up to now still totally unsatisfactory. Systems with ‘mechanical recharge’ of the highly porous zinc electrodes have been tested in electric vehicles. Although the specific energy during discharge exceeded 200 Wh kg −1, this system has not gained any large scale practical acceptance. All metal–air batteries suffer, in principle, from a poor energy efficiency ( η<50%). At present, it appears unlikely that alternative negative electrode materials, such as anthraquinone, polypyrrole, or specially passivated lithium, can be adapted to permit long-term cycling in aqueous electrolytes. Regarding positive electrodes, no alternatives to lead dioxide and nickel-oxy hydroxide are in sight. Manganese dioxide electrodes tend to rapidly loose capacity during cycling. So far, active materials such as bromine, chlorine and insertion electrodes based on carbon, have not, and will probably not in the near future, see commercial use. The main advantages of aqueous electrolyte systems are low cost and ability to withstand overcharge (due to the establishment of the socalled oxygen cycle). This simplifies charging equipment. Due to high electrolyte conductivity, relatively thick electrodes can be used. Lead–acid batteries, in particular maintenance-free or sealed types, will remain ‘work horses’ in SLI and stationary (standby) applications. Large stationary redox cells may possibly find use for the storage of solar energy. Of all the aqueous systems, the metal hydride batteries might have the brightest future. Chances are good that their specific energy can be further improved. Negative and positive electrodes are both of the ‘insertion type’, thus avoiding a dissolution–redeposition step. This results in excellent cycle life. As to electric cars, aqueous–electrolyte fuel cell systems might some day become power sources being capable to beat lithium batteries with respect to specific energy and driving range.

99/01311 Studies with porous zinc electrodes with additives for secondary alkaline batteries : Shivkumar, R. et al. J. Power Sources, 1998, 75, (1), 90–100

A method of solving the classical problem of short cycle life with nickel/zinc secondary batteries is suggested by studying the effects of the negative electrode substrate on Zn deposition. The use of different coatings on the substrate, (the so-called current-collector) is studied by testing several working electrodes (Zn, Cd and Pb) in a zinc oxide saturated potassium hydroxide electrolyte. Cyclic voltammograms show that the nucleation potential of the Zn deposition on a Pb substrate is lower than that on Zn or Cd. Cathodic polarization curves at various temperatures are also obtained and reveal that slower electrode kinetics and more Cd or Pb coating can retard shape change and dendritic growth by leading to slow electrode kinetics and uniform current distribution. These coatings are applied to a Cu mesh and the effects of coating materials on the current-collector on Zn deposition in Ni/Zn secondary batteries are also studied. Application of Pb as a coating metal on the current-collector of negative electrode retards shape change and the dendritic Zn growth and, hence, increases cycle life.