Nissan Motor Co Ltd unveiled its "Battery Labo," a research facility for developing Li-ion secondary batteries intended for hybrid electric vehicles (HEV) and electric vehicles (EV), at the advanced technology briefing in August 2008.
The facility is used for formulating electrode materials, prototyping small cells and evaluating their properties.
Batteries to be prototyped in the battery labo will be smaller than the cells mounted on HEVs and EVs. The laminated cells for automobile batteries manufactured by Nissan measure several centimeters per side, but it is difficult to make cells of this size by hand. Therefore, small cells measuring 10cm in width are being prototyped in the labo, after confirming that the small cells are correlated with existing cells in practical use.
The labo is equipped with a mixer for formulating active materials of electrodes, a machine for applying active materials on aluminum sheets as well as a pressing machine for evening out the applied active materials.
Electrode materials, mixed with active materials, conducting aids and binders, are applied on aluminum sheets. Lithium manganate (hereinafter Mn series) is used as an active material for the positive electrode, while amorphous carbon is used for the negative electrode.
After the positive electrode and the negative electrode are created, a separator is placed between them and a terminal called tab is installed for transmitting the electrical current. The elements, stacked in layers and sealed by a resin film, are filled with electrolyte. Properties of the cells are evaluated by charge-discharge tests and analyses. The results are used for the development of different materials and structures.
The Mn series are used for the positive electrode, but the ratio of conducting aid (carbon series) is different between the electrodes for HEVs and those for EVs, according to Nissan.
Electrodes for HEVs, which contain higher ratio of conducting aid, are higher in output but have a disadvantage in terms of capacity, due to the decrease of active materials. On the other hand, electrodes for EVs, which contain less amount of conducting aid, are higher in capacity.
Nissan prepared two types of cells, one for HEVs and the other for EVs, which are intended for commercialization. It also exhibited a battery pack composed of EV cells and multiple other cells. Cells for EVs are larger than those for HEVs in terms of area, because they contain more amount of active materials so that they can store a large amount of energy.
Specifications of the batteries were partially disclosed. The output density, which indicates instantaneous output critical for HEV batteries, is 2,500W/kg, twice as much compared with the batteries used in the "Tino Hybrid," according to the company.
Meanwhile, energy-storing capacity is critical for EV batteries for longer cruising distance. The energy density, which indicates the capacity, has been improved to 140Wh/kg, according to Nissan.
Nissan is also conducting researches for adopting iron-series materials, which is believed to be safer than Mn series, as materials for positive electrodes.
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