Where does the name Li-ion, or Lithium-ion, come from? The lithium lies in the positive electrodes, the negative electrodes and in the electrolyte of the battery. It is the lightest of all metals and possesses excellent electrochemical properties that offer a high energetic density relative to its weight; it is twice that of (Ni/Cd). Nevertheless, the lithium is not present in its metallic form but in its ionic form, hence the names Lithium-ion and Li-ion. The metallic form is not marketable for security reasons. The inherent instability of the structure pushed the industry to choose the ions of lithium, certainly of less energetic density but revealing itself to be much safer.

The cathode is mainly composed of Cobalt dioxide but some models using manganese can be found. On the other hand, the anode has been using graphite spheres since the research of Bell Lab in 1997, also called MCMB (Meso Carbon Micro Beads). The electrolyte is composed of a conducting salt. All of this is enveloped with a layer of insulating material. The positive section of the battery is coated in aluminium, unlike the negative part; which contains copper.

The exterior of a Li-ion accumulator

In theory, the cells can be placed in parallel or in series. In laptops, we see both at the same time. For example, the battery of our testing laptop, a Fujitsu Siemens M3438G-75005, contains 8 cells. Four accumulators ICR-18650 of 3.7 V are mounted in series to obtain a tension of 14.8 V (3.7 X 4) in two parallel “lines” in order to heighten the capacity, so that it reaches 4400 mAh.

The electric charge of each accumulator is 2200 mAh; this is then doubled because there are two parallel lines. Such a configuration is called 4S2P (4 accumulators in series, 2 parallel lines), but we can also find 9 cell batteries of type 3S3P or 12 cell of type 4S3P. Take into consideration that each battery uses different parts so the tension or intensity, just like the electric charge, can change with different models.