76 Chapter 7 you could create a battery with the same energy as NiMh but it would be about half the size and half the weight. For portable power applications such as laptops and cell phones, this meant longer run times and longer life batteries. How does lithium-ion work? Well, in fact, it works much like any other battery type, as a current is applied ions are forced from the anode to the cathode. In the lithium-ion battery, energy flow is created as the lithium-ions within the cathode are transferred through an electrolyte medium into the anode, this represents a charging event.
A discharging event is represented by the lithium-ions being transferring through an electrolyte medium from anode into the cathode ( Figure 3 below). This does seem counterintuitive for most of us but when the battery is discharging the ions are passing from anode to cathode. In the diagram below a charging event is being shown, with the lithium-ions passing from the cathode material through the electrolyte to the separator and then again through the electrolyte and to the anode material. This action creates a voltage flow up the copper current collector and, in a closed circuit loop, to the positive current collector.
One of the other benefits of lithium-ion chemistries over nickel- and lead-based batteries is the higher voltage. Typical NiMh and NiCd rechargeable cells operate at about 1.2–1.5 V nominal, whereas lithium-ion cells typically operate between 3.2 and 3.8 V nominal. Having a higher voltage is important in that it means that you need to connect fewer cells together in series in order to achieve your desired pack voltage. For instance, a NiMh battery pack with 350 V may require 292 cells to achieve that voltage (350 V/1.2 V = 292 cells). Whereas a lithium-ion-based battery pack would only require about 98 cells to achieve the same system voltage (350 V/3.6 V = 98 cells).
In addition to having higher voltage and energy density, lithium-ion also has a lower rate of self-discharge. This means that its natural capacity loss over time when the batteries are in ƵƌƌĞŶƚ&ůŽǁ;ŚĂƌŐĞͿ Figure 3 Lithium-ion cell ion flow. Ͳ ŽƉƉĞƌƵƌƌĞŶƚŽůůĞĐƚŽƌ ůĞĐƚƌŽůLJƚĞ н ůƵŵŝŶƵŵƵƌƌĞŶƚŽůůĞĐƚŽƌ >ŝƚŚŝƵŵͲŝŽŶƐ ŶŽĚĞ ĂƚŚŽĚĞ ^ĞƉĂƌĂƚŽƌ