Phone Battery 101: What Are Li-Ion Batteries?

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Phone Battery 101: What Are Li-Ion Batteries?

When searching for a mobile phone battery, Lithium ion batteries (or Li-Ion batteries) are the most appropriate batteries on the market for this type of appliance. These extremely versatile batteries can be constructed in almost any size and shape imaginable, and provide superior energy storage capacity and durability when compared to their lead-acid, nickel-cadmium or alkaline battery counterparts. The essential product features, as well as the advantages and disadvantages of Li-Ion batteries will be discussed in the sections below.

Battery Comparison

Li-Ion batteries are far superior to older battery styles in many respects, such as an increased storage capacity, and reduced dependence on dangerous chemicals for the storage of charge. A comparison of several popular battery designs is shown in the table below:

Battery Type

Charge Density (Watt hours per kg)

Efficiency (per cent)

Average number of cycles before failure

Average lifetime (years)

Alkaline

85

/

100-1000

<5 >

Lead-acid

30-40

70-92

500-800

20

Lithium-ion

150-250

99

1200-10000

2-6

Nickel-cadmium

40-60

70-90

1500

/

Based on the information shown above, Li-Ion batteries have the greatest charge density, highest efficiency, and the greatest average number of cycles before failure when compared to the other most common battery types available, but they do not have as long an average lifetime as static lead-acid batteries (although it should be noted that lead-acid batteries used in cars and other vehicles have a dramatically shorter lifetime due to the vibration and operating conditions present within these vehicles).

Lithium Ion Properties

The large differences in energy density arise from the properties of the element lithium used in the cells of the Li-Ion battery. Since lithium is a particularly reactive element, much more energy can be stored within its chemical bonds than within those of lead or nickel, for example. Li-Ion batteries are also surprisingly light, owing to the lightweight lithium and carbon electrodes in place within the battery's structure. Batteries of this type also have a very low rate of charge loss; a Li-Ion battery loses approximately 5 per cent of its charge per month when not in use (a significant proportion of which is due to the on board computer used to record the battery's vital statistics), while an otherwise comparable battery can lose up to 20 per cent of its charge per month.

How Li-Ion Batteries Work

Li-ion batteries consist of multiple smaller cells consisting of the chemicals which are responsible for storing the battery's charge. Each individual cell is composed of a metal case used to maintain the internal pressure required for correct operation for the cell, and to hold the electrolyte solution, which is usually an organic solvent such as ether. The metal casing also contains a small valve required to prevent explosive rupture of the cell during exposure to temperatures outside the normal operating range of the battery. Each of these metal casings houses a tightly wound laminated spiral consisting of a positive electrode, made of lithium cobalt oxide, and negative electrode, made of carbon, as well as a thin layer separating the two. This separator layer contains microscopic holes which allow the passage of ions between the two electrodes, thus facilitating the passage of charge between them. While the battery is charging, lithium ions move from the positive electrode to the negative electrode, thus storing potential energy. During discharge, the lithium ions move from the negative electrode back to the positive electrode, thereby resolving the potential energy and promoting the flow of current. The particular chemistry of these batteries gives each Li-Ion cell a much greater storage capacity than other classes of battery.

Other Features

Many of the more modern Li-Ion batteries have an in-built computer system designed to measure critical statistics regarding the battery, such as the battery's temperature and the individual charge state of each of the cells. The battery also contains a voltage convertor and regulator circuit designed to prevent excess energy being discharged into the appliance, as well as a circuit designed to monitor and regulate the charging process, and protect the battery while it is connected to the mains.

The Memory Effect

The memory effect is an effect common among nickel-cadmium batteries whereby the battery's maximum charge capacity diminishes if the battery is only partially discharged before recharging commences. The battery is said to remember the lesser capacity. It should be noted that the memory effect only applies for the nickel-cadmium style of battery, and becomes an issue only when the batteries are repeatedly discharged to a specific point and then fully recharged without overcharge. Overcharging the battery, or varying the degree to which the battery is discharged each cycle, can help to eliminate the memory effect. While this true memory effect only affects these nickel cadmium batteries, there are a variety of effects collectively referred to as memory effects, although not actually true memory effects.

Difference Between Memory Effect and Voltage Depression

Voltage depression is commonly mistaken for the memory effect. Voltage depression occurs when the battery's peak voltage drops much more quickly than normal (although the total energy output of the battery remains almost unaltered), and, therefore, electronic devices will read that the battery is draining much more quickly than it should. This problem is caused by overcharging, which causes the electrolyte to crystallise on the plates of some cells, therefore resulting in increased resistance within these cells. Because of this, some cells discharge much more rapidly than others, thereby lowering the overall voltage output of the battery. This effect can be found among many types of battery, and can be reversed by deep cycling each cell of the battery individually.

Potential Problems with Li-Ion Batteries

An important problem to be considered when investigating Li-Ion batteries is their susceptibility to decay. As soon as these batteries are assembled, their constituents begin to decay. This decay gives Li-Ion batteries a comparatively short lifetime of just 2-6 years, regardless of the duration and extremity of use. Li-Ion battery decay is also exacerbated by high temperature, so simply keeping a phone in a pocket will result in heat sufficient to speed the decay of the battery, as do warm ambient temperatures and placement in direct sunlight. Although there are many other effects which can damage a battery, the main advantage of a Li-Ion battery is its resistance to the memory effect, and common memory effect-like phenomena. While Li-Ion batteries can stand up to much harsher conditions than many other batteries on the market, they will not tolerate deep discharge. Deep discharge results in a battery's charge being reduced to effectively zero during use. This scenario creates a problem because each cell of any battery is subtly different, with some cells fractionally smaller than others. As the battery's overall charge approaches zero, the smallest cells will become fully discharged, and thus susceptible to reverse charging: a process by which the stronger cells attempt to force their remaining current through the weaker cells, causing damage. It is, therefore, not advisable to attempt to reduce the occurrence of a memory effect by fully discharging a battery.

Finding Li-Ion Batteries on eBay

eBay is a treasure-trove of item, including Li-Ion batteries to suit the vast majority of mobile phones. To find the appropriate battery on eBay, a simple search for 'Li-Ion battery' will provide a set of results much too broad for useful analysis. To compensate for this problem, eBay's categories system may be used. On the eBay homepage, hover over Electronics & Technology and select Mobile Phones & Communication. From here, choose Mobile Phone Accessories, then Batteries. Within this section, it is now possible to search for Li-Ion and receive only results specific to mobile phone batteries. The check boxes on the left of the screen also provide an intuitive way to filter the results further by phone brand (such as Samsung or HTC), and by price.

Conclusion

Picking the correct Li-Ion battery to suit the type of phone required is of the utmost importance, as each type of phone has its own individual power requirements and size restraints. Thorough research into the type of battery each phone requires is, therefore, critical. Armed with the information provided in the guide above, the avid reader should be able to gain enough information to make an informed and carefully considered decision about the type of Li-Ion battery required.

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