R&D on metal hydride materials and Ni–MH batteries in Japan
Section snippets
Background and market trend of Ni–MH batteries
Since the discovery of hydrogen storage alloys such as LaNi5 in about 1969, extensive research has been carried out [1], [2]. Initially, R&D on the alloys was focused on gas-phase applications such as hydrogen storage tanks, hydrogen purifiers and chemical heat pumps. In Japan, R&D on metal hydrides has been conducted mainly under “Sun-shine projects” sponsored by MITI, which were started just after the oil crisis in 1974. Osumi et al. [3], [4], [5], [6], [7], [8], [9], [10] developed low-cost
Mechanism and materials for Ni–MH batteries
The charge–discharge mechanism for the Ni–MH battery is very simple, merely the movement of hydrogen between a metal hydride (MH) electrode and a nickel hydroxide (Ni) electrode in an alkaline electrolyte, as shown in Fig. 4. This “rocking-chair” mechanism for the Ni–MH battery is the same as that for a lithium-ion battery, being clearly distinguished from the conventional Ni–Cd and Pb–acid batteries based on the dissolution–precipitation mechanism for Cd or Pb in which a dendrite can be formed
Performance and applications of Ni–MH batteries
The energy density per volume for Ni–MH batteries has doubled from 180 Wh/l in 1990 to 360 Wh/l in 1997, a value comparable to that for the lithium-ion battery, as shown in Fig. 7. The high energy density was achieved by improving the quality of the materials and by increasing the packing density in the cell. Compactness is very important for portable appliances such as cellular phones and lap-top computers, making the Ni–MH battery very competitive. The energy density per weight has also
Pure EVs
Scaling up of the battery has been carried out successfully by improving the high-temperature properties of the materials and also by a heat-management system. A 95 Ah,12 V module (EV-95) was stacked in series to make a battery pack (288 V, 95 Ah) for commercialized Toyota RAV4L EV, as shown in Fig. 8, which provides 50 kW power even in 90% depth of discharge (DOD), giving a top speed of 125 km/h [21], [22]. Driving range per charge is 215 km at 10–15 mode. The battery life is more than 1000
Concluding remarks
Extensive research for more than 20 years in the field of hydrogen storage alloys has combined with advanced battery technology to commercialize the Ni–MH battery. The high-performance battery has become one of the key components in the growing information and telecommunication industries, serving as a compact and light-weight power source that is also environmentally friendly. Sales of so-called eco-vehicles such as pure EV and hybrid EV that use large-sized Ni–MH batteries have begun. FCEV
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