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

Abstract

The electrochemical performance of planar and porous zinc electrodes in an actual Zn/MnO 2 battery using lithium hydroxide ͑LiOH͒ 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.The requirements for high specific energy, high specific power, and low cost materials for aqueous alkaline batteries, for example, for hybrid electric vehicle applications, make zinc an attractive negative electrode candidate. The low equilibrium potential and high overpotential for the hydrogen reaction of zinc mean that this metal has the lowest standard potential among all the elements that can be efficiently reduced from aqueous electrolytes. 1 This makes zinc uniquely suitable for high energy density batteries, and as a result, interest in the electrochemical behavior of zinc in aqueous systems has increased.Commercial, alkaline batteries using MnO 2 as cathode and Zn as the anode employing potassium hydroxide ͑KOH͒ as the electrolyte are currently in demand because they are mercury-free and have a high rate capability. This primary Zn-MnO 2 battery remains widely in use for a variety of electronic applications. 2 Recently, we showed that a primary battery can be transformed into a high performance secondary battery using aqueous lithium hydroxide ͑LiOH͒ as an electrolyte. 3 In an extension, to improve the rechargeability of our Zn͉LiOH͉MnO 2 cell suitable for high rate applications, we investigated the effects of doping the MnO 2 electrodes with a range of additives 4,5 by physically mixing them into a MnO 2 cathode. These additives were reported to suppress the formation of manganese oxyhydroxides in the MnO 2 while enhancing the lithium insertion reversibly. 4,5 The discharge performance of the LiOH alkaline battery still however needs to be significantly improved to be suitable for high power applications. Hence, in our present study we focus specifically on the anodic behavior of Zn in LiOH media.The electrochemical reaction of the zinc metal in a battery normally occurs via a dissolution-precipitation mechanism. 6,7 The utilization efficiency of Zn is lowered due to the formation of a passive film on the Zn particles preventing the metal beneath from undergoing further electron transfer. Zn anodes in commercial battery systems are generally in the form of a gelled mass or are produced by electroplating metallic Zn from a solution of Z...

Olivine-type cathode for rechargeable batteries: Role of chelating agents

“…This is reflected in increasing capacity during multiple cycling. The role of anodic zinc dissolution in aqueous LiOH solution during electrochemical discharge /charge cycles is reported by us earlier [27] which could inhibit the cycleability. To be suitable for practical applications, further work is needed to improve the specific capacity together with the cycle life of the olivine cathode mixed with all the three chelating agents (CA+ TEA+ PVP).…”

Metal–Air Batteries with High Energy Density: Li–Air versus Zn–Air

“…Although it is not precisely an example of a zinc-air cell, Minakshi et al also showed that in the alkaline electrolyte LiOH, a porous anode electrode composed of zinc powder improves the rate capability and has a higher capacity in alkaline Zn-MnO 2 cells than that of a zinc planar electrode. [ 120 ] Recently, a study of porous electrodes with various shaped zinc particles, not just planar zinc electrodes, has also received attention. [ 121 ] Generally, when preparing a zinc anode with powder, mercury has been added to the zinc anode to give better electrical conductivity between the zinc particles and the current collectors.…”

Zinc Electrode Morphology Evolution in High Energy Density Nickel-Zinc Batteries

“…In a NiZn battery, higher zinc electrode surface area should lead to enhanced materials utilization and higher power density and reduce passivation at high discharge rates [20]. Porous electrode structure provides higher energy density due to short ion transport length and easy charge transfer reaction on electrode-electrolyte interface [39][40][41][42]. Therefore, high surface area for a zinc electrode is desirable as it should improve battery performance by providing enhanced path lengths for both electron and Zn ion transport, electrode/electrolyte contact area, and accommodation of the strain of the Zn ion insertion/extraction [43,44] [34,35].…”