Video Transcript
Which of the following statements
correctly describes the movement of lithium ions during discharge of a lithium-ion
battery? (A) From the positive graphite
electrode to the negative electrode, where they form a lithium compound. (B) From the negative graphite
electrode to the positive electrode, where they form a lithium compound. (C) From the negative electrode as
part of a lithium compound to the positive graphite electrode. (D) From the positive electrode as
part of a lithium compound to the negative graphite electrode.
A lithium-ion battery is an example
of a secondary galvanic cell. A secondary galvanic cell is a type
of electrochemical cell that can run as both a galvanic cell and an electrolytic
cell. When the galvanic cell is running,
it can power an external device. This process is known as
discharging.
In this problem, we need to
determine how lithium ions move when the lithium-ion battery is discharging. When the galvanic cell is running,
the anode is the negatively charged electrode and the cathode is the positively
charged electrode. The anode is made of lithium
graphite, or LiC6. The cathode is made of lithium
cobalt oxide, or LiCoO2. A plastic separator is located
between the two electrodes but does not prevent the movement of lithium ions. The electrolyte inside the cell is
liquid lithium hexafluorophosphate, or LiPF6.
During discharge at the anode,
lithium graphite separates into graphite, lithium ions, and electrons. The electrons move through the
circuit to the cathode. The lithium ions also move toward
the cathode by flowing through the electrolyte in the cell. At the cathode, the lithium ions
combine with electrons and cobalt oxide to form lithium cobalt oxide. In our drawing, we can see that
during discharge, lithium ions move from the negative graphite anode to the positive
cathode, where they become part of the lithium compound LiCoO2.
Therefore, the statement that
correctly describes the movement of lithium ions is statement (B), from the negative
graphite electrode to the positive electrode, where they form a lithium
compound.
