Antimony-free batteries

Completely antimony-free batteries represent the state-of-the-art in the original equipment (OEM) starter-battery business at the beginning of the 21st century. Accordingly, there is no longer any need for topping-up with water over the life of... 

During cycling operation between Iio and I20 at 20°C gel batteries with flat plates achieve a cycle life of about 250-300 cycles up to a residual capacity of 80% of the initial capacity. In order to achieve this life with antimony-free valve-regulated batteries an especially highly controlled production technology of the positive plates, which normally limit the cycle life of antimony-free batteries, is required. 

However, at constant cell voltage, the amount of antimony released from the posidve grid is too small to affect the potential of the negative electrode markedly. Therefore the very low initial gassing rate, which is of the same order as experienced with antimony-free batteries, remains almost constant. 

Of the elements commonly found in lead alloys, zinc and bismuth aggravate corrosion in most circumstances, while additions of copper, tellurium, antimony, nickel, silver, tin, arsenic and calcium may reduce corrosion resistance only slightly, or even improve it depending on the service conditions. Alloying elements that are of increasing importance are calcium especially in maintenance-free battery alloys and selenium, or sulphur combined with copper as nucleants in low antimony battery alloys. Other elements of interest are indium in anodesaluminium in batteries and selenium in chemical lead as a grain refiner ". 

The basis for the performance of the alloy in VRLA batteries is corrosion of the lead-cadmium-antimony alloy to produce antimony in the corrosion layer of the positive grid, which thus eliminates the antimony-free eifect of pure lead or lead-calcium alloys. During corrosion, small amounts of antimony and cadmium present in the lead matrix are introduced into the corrosion product and thereby dope it with antimony and cadmium oxides. The antimony and cadmium give excellent conductivity through the corrosion product. The major component of the alloy, the CdSb intermetallic alloy, is not significantly oxidized upon float service, but may become oxidized in cycling service. 

K. Fuchida, K. Okada, S. Hattori, M. Kono, M. Yamane, T. Takayama, J. Yamashita, Y. Nakayama, Yuasa Battery Co., lEZRO Project EE-276 Antimony-free grids for deep discharge, Final Report 1 January 1978 to 31 December 1981, International Lead Zinc Research Organization, Inc., Research Triangle Park, NC, USA, 1982. 

At the end of the twentieth century, maintenance-free VRLA batteries were invented. The first VRLA batteries employed lead—calcium grids. The antimony-free effect exhibited fully, which forced metallurgists to switch back to Pb—Sb alloys for the positive grids, minimising... 

Antimonial-lead alloys are the main additional by-product, but returns depend on local demand and the particular alloys required, and are difficult to quantify in a general way. With the popularity of calcium-lead alloys for sealed, maintenance free batteries, the price of aniimonial alloys declined, but has resurged due to increased demand for specialised batteries. Clearly this market is quite volatile. 

Figure 7.20 shows that normal lead-acid batteries with antimony-free alloys (e.g. Gro E cells have a cycle life of less than 200 cycles (DIN/IEC cycles)). 

Important for the maintenance-free properties of these batteries was the possibility to use antimony-free grid alloys instead of the conventional lead-antimony alloys, which were used only at this time. Because antimony in the grid alloys provides a high cycle life for the battery, it was necessary to develop more sophisticated methods in battery manufacturing in order to achieve the required product properties. 

Besides the usage of clean materials and antimony-free lead alloys for the construction of batteries, the so-called oxygen recombination is the basis for the function of valve-regulated maintenance-free lead-acid batteries. Because of the thermodynamic locations of hydrogen and lead, a complete prevention of decomposition of small amounts of water generally is not possible. But the oxygen... 

The performance of wet batteries degrades with long periods of inactivity, especially when stored at warm temperatures. A loss of 1 to 3% of capacity each day is possible with SLI batteries that contain antimonial lead grids. The loss on stand can be much lower for maintenance-free batteries (0.1 to 3%/day). When lead-acid batteries must be stored for a long time, especially in high ambient temperatures, or when batteries are shipped for export, their performance can be stabilized by removal of the electrolyte by one of several methods. 

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