by Denis Gross
Primary Batteries
Primary batteries are non-rechargeable. In terms of volume, they account for somewhere in the region of 90% of all batteries in the world – mainly small, disposable batteries for consumer use. Non-rechargeable battery technologies include:
• Zinc-carbon primary batteries
• Non-rechargeable manganese zinc alkaline
• Non-rechargeable lithium
• Speciality non-rechargeable (including zinc-air, silver oxide and magnesium)
Secondary Batteries
The chemical reaction in a secondary battery can be reversed, which means that the battery can be recharged. Rechargeable battery types, although accounting for only some 10% of all batteries by volume, represent more than 60% of the global battery market in terms of value. The number of times a battery can be recharged depends upon the material used in its manufacture.
Statistics from the Laboratoire de Réactivité et de Chimie des Solides show that, in value terms, the rechargeable battery market accounts for 63% of the total market, around $19 billion of a total market valued at $30 billion. The non-rechargeable battery market (90% of the market in volume terms) is valued at $21 billion – or 37% of the total value. 
Within the rechargeable market, transportation is the most important application in value terms, accounting for almost half of the total (see chart). Applications include the automotive industry and other forms of transport such as ships and aircraft. Industrial applications include reserve power, UPS, telecoms and motive power (e.g. forklifts). In terms of units sold, lead-acid batteries – widely used in both the transportation and industrial markets – are by far the most important, accounting for just under 90% of the total. 
Rechargeable battery technologies include:
• Lead-acid
• Nickel-cadmium (NiCd, or ’nicad’)
• Nickel metal-hydride (NiMH)
• Lithium batteries (including lithium-ion and lithium-polymer)
• Speciality rechargeable batteries (rechargeable alkaline, nickel-zinc, silver-zinc, and silver-cadmium)
Lead-Acid Batteries
The very familiar lead-acid battery consists of a lead anode and a lead dioxide cathode in an electrolytic solution of dilute sulphuric acid. When the electrodes are connected via an external circuit, the lead anode dissociates into lead cations and electrons. At the cathode the arriving electrons combine with the lead dioxide cathode and hydrogen cations in the electrolyte to produce more lead cations and water. The lead cations generated associate with the dilute sulphate ions to produce lead sulphate.
Thus the electrodes dissolve as the battery discharges, with the sulphuric acid electrolyte becoming lead sulphate. The battery is charged by applying an external voltage to force electrons from the lead dioxide electrode to the lead electrode, thereby reversing the reactions that ran during the discharge phase and restoring the battery.
Nearly half the weight of a lead-acid battery consists of inert materials, such as grid metal, separators, connectors and terminals.
Lead-acids batteries fall into two categories - flooded and sealed.
Flooded lead-acid is the type of battery that has been in use for over 130 years, despite its relatively low specific energy and added weight through the large weight overhead of inert materials used in its construction The flooded lead-acid cell remains in wide useage thanks to its low cost, long lifetime and familiarity. However, it has two main disadvantages:
• The need for frequent maintenance, to top up the water lost to ‘gassing’: if the lead plates of the battery become overheated, often as a result of overcharging, hydrogen gas is generated and has to be vented. Water must then be added to the battery to replace the lost hydrogen.
• Acid stratification, where the concentration of the electrolyte becomes unevenly distributed within the cell. This can be rectified by overcharging, causing gassing that mixes the electrolyte, or by using a dedicated mixing system. The first is inefficient and the second requires an additional power source for the mixer.
These problems can be resolved by using valve-regulated lead-acid (VRLA) or sealed lead-acid (SLA) cells. They differ from the flooded type in that the electrolyte is immobilised (eliminating stratification) and they are fitted with a valve to regulate pressure, effectively sealing the cell (eliminating the need to add water). As well as removing a lot of the maintenance, the VRLA cells can be more compact. However, VRLAs are less robust, more costly and shorter-lived than flooded lead-acid batteries
Nickel-cadmium (NiCd)
A niche battery type, NiCd is used in industrial applications, mostly for back-up power and in some consumer and power tool applications. NiCd batteries have a longer cycle life than lead-acid batteries, but NiCd is problematic due to environmental issues (it is carcinogenic) and cadmium is in short supply.
Nickel metal-hydride (NiMH)
NiMH batteries have a higher energy density than lead-acid batteries, but a shorter cycle life than NiCd batteries. However, the technology can be combined with advanced battery monitoring systems and these batteries are appropriate for the automotive industry.
Lithium batteries
Lithium-ion (Li-ion) chemistry is currently one of the most popular battery chemistries used to power consumer electronics. This type of rechargeable battery is widely used in cameras, laptop computers, handheld computers and a host of portable electronic devices. There are also efforts under way to extend this technology to electric vehicles and even stationary applications.
The attractiveness of lithium-ion batteries stems from a very high energy-to-weight ratio, the slow loss of charge when idle, and no memory loss. Li-ion batteries most widely used to date employ graphite anodes and lithium cobalt oxide cathodes, and these have been prone to overheating and even exploding. This problem resides with the lithium cobalt oxide cathode, and manufacturers are looking at alternative cathode materials to provide more stable performance.
Alternatives include lithium manganese oxide and lithium phosphate – a technology around which Austin, Texas-based Valence Technology (NASDAQ:VLNC) has developed proprietary IP. Valence incorporates iron and manganese with the phosphate with encouraging results in terms of high specific energy and power, a long cycle life, low environmental impact and enhanced safety.
The advances in lithium-ion technology put this battery type in the frame for electric vehicles and transportation applications. Valence batteries, for example, have been deployed in Segway personal transporters and Smith electric vehicles.
A123 Systems, headquarted in Watertown, Massachusetts, with high power Li-ion phosphate batteries based on new nanoscale materials initially developed at MIT, claims significant performance advantages over alternative high power technologies. As well as electric vehicle, aircraft and transportation applications, A123 batteries are also deployed in grid stabilisation.
Other manufacturers in this market include Advanced Battery Technologies, whose Li-ion polymer batteries are used in electric automobiles, motorcycles, and portable and consumer electronics; Altair Nanotechnologies and Enerl, who manufacture Li-ion titanate batteries (with lithium titanate instead of graphite anodes).
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