1. Field of the Invention
The present invention relates to the rechargeable batteries and more particularly to electrolyte and electrode compositions for nickel-zinc rechargeable batteries.
2. Description of the Related Art
The advent of portable communication and computation devices that allow diverse mobile connectivity has fueled growth and innovation in the rechargeable battery field. Increased capacity and power has made possible the entry of rechargeable power sources in various fields including the power tool arena. Because power tools typically have large current demands, rechargeable power sources have necessarily evolved to accommodate rapid discharge characteristics. It can be appreciated that the present invention, as described later in this document, will also find use in power tool applications as well as various other applications including Uninterruptible Power Supplies (UPS), electric vehicles, and high demand consumer electronics—all of which require high carrying capacity and current discharging ability. Of course, the invention also applies to relatively lower discharge rate applications such as many mainstream consumer electronics applications.
Because of the hazardous nature of some of the commonly used materials for conventional rechargeable power sources, it would be desirable to replace these conventional power sources with a safer and more environmentally benign power source that reduces or eliminates the quantity of hazardous materials. In particular, it would be desirable to find a substitute for the widely used nickel cadmium (NiCd) battery cell.
Rechargeable nickel-zinc (NiZn) cells provide a power-to-weight ratio comparable to and even exceeding nickel cadmium cells at a reasonable cost. However, nickel-zinc battery technology has not been widely deployed in part because it has been found to have a relatively limited cycle life. In other words, a given nickel-zinc cell can fully charge and discharge for only a fraction of the cycles typically attained with a comparable nickel cadmium cell. As is known to researchers in the field, this is due, at least in part, to zinc redistribution and dendrite formation. The problem is most pronounced in nickel-zinc cells used in power tools and other devices requiring rapid discharge. Various advances in electrolyte composition have reduced these issues to an extent, but cycle life remains an important consideration. There is a need therefore for electrolytes that provide long cycle life in nickel-zinc cells. There is a further need for electrolytes that are capable of providing high discharge rate and good performance at low temperatures.