Rapid Processing Techniques Applied to Sintered Nickel Battery Technologies for Utility Scale Applications
Sustainable Product Engineering Centre for Innovative, Functional, Industrial Coatings (SPECIFIC) is an academic and industrial consortium, led by Swansea University, with three global strategic partners - Tata Steel Europe, BASF and NSG Pilkington. The centre develops functional coatings for steel and glass products for a building envelope that can generate, store and release renewable energy. Electrical storage research is focused on the optimisation of materials and processes for large-scale printable batteries and rapid sintering techniques. SPECIFIC’s Pilot-line facilitates the up-scaling of laboratory-optimised products.
The Nickel-Iron (Ni-Fe) battery chemistry has been identified as a suitable solution to provide highly distributed micro-storage for micro generation at utility scale. Properties, such as tolerance of over-charge/discharge, sizable cycle life (up to 4,000 deep charge/discharge cycles), and extended useful life (20 years), all give credence to this proposal [1-3].
It is reported that sintered plaque electrodes improve the high-rate capabilities of NiFe technology . With conventional sintering techniques such as convection, this is typically very costly and labour intensive. The aim of the current study is to investigate whether ultra-fast sintering, in this case Near Infra-red (NIR) radiative sintering, can be utilised for production of sintered nickel plaques, resulting in vastly decreased production time. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) have been used for surface characterisation to determine if acceptable surface characteristics (structure, porosity) can be achieved upon NIR sintering proceedures.
In the current study, a precurser layer was deposited onto nickel plated steel100 mm x 100 mm coupons by printing Ni ink using an ATMA AT-45FA lab-scale screen printer. Sintering was then carried out using a (give make and model) high temperature tube furnace for 30 min at 800°C, 1L/min Nitrogen (ref). This was carried out in order to give a baseline for comparison with NIR sintering. The Scanning Electron Micrograph in Figure 1.a. shows a plaque obtained after traditional convection heat treatment. Further samples were sintered using an NIR (ADPHOS lab unit, 1m heated length) heat treatment where conditions were 70 % power at 5 m / min for 3 consecutive passes and 80 % power at 4 m/m for 2 consecutive passes, the microstructures of which are given in Figures 1.b) and 1.c) respectively. It can be observed from figure 1 that the porosity and sintered structure of samples produced using NIR is comparative to that of samples produced using the conventional convection method.
EDS analysis reveals an increased oxide presence of 32.6 % within the final sintered nickel plaque when compared to the 4.8 % of a sample prepared via the convection method in a nitrogen atmosphere, this is shown in Figure 2. It is thought that a reduction in this oxide may be achieved through inclusion of Carbon as a reducing agent (Figure 2).
A variety of electrochemical deposition methods, as well as chemical deposition methods, have been employed to deposit the Nickel (II) Hydroxide active material upon the sintered plaques and subsequent electrochemical cycling has been carried out at a variety of charge/discharge rates to provide information on rate capabilites, actual capacity and utilization.
NIR sintering has been shown to successfully create highly porous sintered structures for use as nickel plaques in nickel electrodes for Ni-Fe batteries. The use of NIR constitutes a ten-fold reduction in sintering time when compared with conventional convection sintering methods.
Further work will systematically investigate the incorporation of high temperature reducing agents (i.e. Carbon) into the original ink formulations in order to eliminate the need for controlled of atmosphere for NIR sintering.
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