Notebooks:Batteries RJ Brodd, Broddarp of Nevada, Inc., Henderson, NV, USA & 2009 Elsevier B.V. All rights reserved. Introduction Notebook computers are complex devices. Figure 1 depicts the basic elements that comprise a notebook computer and shows how they fit together. It includes the operating environment and user, as well as the computer, battery pack, and the fundamental electrochemical cell that drives its operation. Since notebooks are portable, it is essential to have a lightweight, sealed battery to pre- vent leakage of electrolyte into the computer case. Two types of batteries are found in a notebook computer. One is a rechar geable battery pack that pro- vides the energy for its operation. The pack is usually composed of several lithium-ion cells in series and par- allel arrangements along with an electronic battery management unit to control the operation and to provide communication between the battery pack and the computer. The second battery, typically a small lithium primary cell, maintains the memory for the bas ic input/output system (BIOS). The operating system of a notebook computer is located in its hard drive and is unavailable when the computer is first turned on. The computer microprocessor gets its first instructions for loading its operating system from the BIOS and assumes control of the personal computer (PC). The primary function of BIOS is to prepare the notebook computer during start- up by providing instructions to load the operat ing system programs that are stored in its hard drive. The BIOS is stored in a flash memory chip that is usually protected by a small lithium primary battery. Both primary and re- chargeable cells can be used for memory protection. Rechargeable Energy Batteries Early in the development of the portable computer, the sealed nickel–cadmium (Ni–Cd) battery was the only rechargeable battery available. In the late 1980s, the higher-ener gy nickel–metal hydride (Ni–MH) batteries were introduced and in 1991 the lithium-ion batteries were introduced by Sony. By the year 2000, essentially all computer batteries were lithium-ion because of their light weight and high energy storage capability. There were over 15 large-scale producers of lithium-ion bat- teries worldwide. Table 1 provides a comparison of the characteristics of the three systems. The three battery systems that have been used to power note book computers are Ni–Cd, Ni–MH, and lithium-ion; each uses the spiral wrap cell construction. This construction provides a high surface area electrode str ucture and is amenable to high-speed automated production. Notebook computer s do not use individual cells; they use only packs. The battery packs are com- posed of 3–12 cells connected in series and parallel Cell Charger Pack Notebook computer User Environment Figure 1 Depiction of the components of a notebook computer. Table 1 Characteristics of principal battery systems Characteristic Ni–Cd Ni–MH Li-ion a Construction Sealed Sealed Sealed Nominal voltage (V) 1.2 1.2 4.2 Temperature range (1C) À 40 to þ 50 1C 0to þ 501C 0to þ 50 1C Discharge characteristic Flat Flat Sloping Memory effect Yes Yes No Overcharge Tolerant Tolerant Damages cathode Overdischarge Tolerant Tolerant Plates Li metal Electrolyte Aqueous KOH Aqueous KOH Organic LiPF 6 Charger characteristic Constant current Constant current Constant current– voltage limited Cycle life 1000 1000 500 Self-discharge (%/Mo) 10 25 3–5 Nominal Wh L À1 100 150 500 Nominal Wh kg À1 50 100 200 a Typical Li-ion cell with a LiCoO 2 cathode. 22 . nickel–metal hydride (Ni–MH) batteries were introduced and in 1991 the lithium-ion batteries were introduced by Sony. By the year 2000, essentially all computer batteries were lithium-ion because. Notebooks: Batteries RJ Brodd, Broddarp of Nevada, Inc., Henderson, NV, USA & 2009 Elsevier B.V battery. Both primary and re- chargeable cells can be used for memory protection. Rechargeable Energy Batteries Early in the development of the portable computer, the sealed nickel–cadmium (Ni–Cd) battery