Metal Bulletin Research STRATEGIC OUTLOOK FOR THE PRIMARY BATTERY 2 | Page 3

Battery Metals

3 Battery Chemistry
The drawback of this design is the relatively low cycle life, of between 500-800 cycles, and low energy
density, of 30-50Wh/kg. There has also been some concern regarding the environmental impact of
improper disposal of batteries. The United States however has implemented one of the world’s most
successful recycling programmes, with 97% of all lead batteries recycled between 1997 and 2001.
Continuous improvement in battery recycling plants and furnace designs is however required in order to
keep pace with emission standards for lead smelters.

3.3 Nickel-Metal Hydride

The Ni-MH battery is the most well-known and most widely used of rechargeable battery technologies.
They use nickel oxyhydroxide as a cathode and some form of metallic alloy as an anode, with a potassium
hydroxide electrolyte. Ni-MH batteries will typically have an energy density of between 60 and 120Wh/kg.
The design’s capabilities are proven and they tend to have a long life cycle. However, it is heavier than the
lithium-ion battery and sensitive to the nickel price (3-6kg of Ni is required per kWh). It also requires cobalt,
which has recently become a very expensive input, and global production of cobalt is fairly limited. There
is definitely a deficiency of cobalt reserves necessary to produce a vehicle fleet in the order of what policy
makers are trying to achieve.
Even though some of today’s hybrid electric vehicles are powered by Ni-MH batteries, there have been
some severe drawbacks. These batteries tend to have less than ideal energy conversion efficiencies (i.e.
they tend to overheat) and they experience a high degradation if they are discharged completely, which
would be required for plug-in hybrid or fully electric vehicles. Currently, this problem of degradation is being
overcome by only charging and discharging 10% of the battery’s available capacity, so in effect most of
the available capacity is used as a buffer to ensure that the battery will meet a particular performance
standard after some degradation by the end of its 10-year lifespan.

3.4 Nickel-Cadmium

Nickel-cadmium (Ni-Cd) batteries are in some respects the technological predecessor to Ni-MH batteries.
They are rechargeable secondary batteries which consist of a nickel oxide cathode and a cadmium anode
with a potassium hydroxide electrolyte. They are used for a variety of purposes and are built in multiple
sizes, from the AA or AAA sizes of typically alkaline batteries to bulky box shapes of lead-acid batteries.
Ni-Cd batteries are indeed a competitor in both the personal electronics and automotive industries, though
they are more typically used as rechargeable batteries for personal electronics, where they compete with
non-rechargeable alkaline batteries. Originally built as unsealed, vented cells they are now often built as
sealed cells, depending on the end-use market.
The primary benefits of this battery type are their durability and long usage life. They can sustain multiple
discharges and recharges over a long period without any significant degradation to their energy capacity.
They can also be fully discharged and stored without damage and they have a lower rate of self-discharge
than Ni-MH batteries. They have a higher energy density than lead-acid batteries, at 45-80 Wh/kg, which
makes them superior to lead-acid batteries but inferior to Ni-MH.
However, they have some significant drawbacks. Primary amongst is the cost of cadmium and nickel. NiCd battery use is sensitive to fluctuations in both metal markets, with cadmium typically being the more
expensive. Because of this Ni-Cd batteries are uncompetitive against lead-acid batteries for large-scale
automotive applications. Cadmium is also highly toxic, creating a disposal problem. Ni-Cd battery chemistry
is also more sensitive to temperature changes than other batteries. As temperatures within a Ni-Cd battery
rise with charging, internal resistance falls and without control this could lead to battery failure.
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