Page 580 - Polymer-based Nanocomposites for Energy and Environmental Applications

Hybrid materials based on polymer nanocomposites for environmental applications 533

it can be facilitated by a high-conductivity electrolyte. Besides, the ions intercalate the
electrodes during charge and discharge processes, that is, they are inserted between the
layers composed of the anode and the cathode. Therefore, the electrode materials
should have adequate shape and structure to optimize ion anchoring.
During the charge process, a generator supplies electrons to the cell. In the external
circuit, the electrons migrate from the cathode to the anode. The electric current flows
in the opposite direction, from the anode to the cathode. Consequently, the cathode
material will be oxidized, and the anode material will be reduced.
The global equation of the reversible charge-discharge reaction is

+
zLi +A x B y +ze >Li z A x B y (19.8)
The performance of a LIB depends on the materials used for electrodes and electro-
lyte. Fig. 19.15 shows the energy band diagram of a LIB. The potential difference
between the cathode and anode determines the open voltage of the battery according
to the expression

V OC ¼ μ μð C A ÞF (19.9)
+
where μ C and μ A are the chemical potentials of Li ions at the cathode and anode,
respectively, and F is the Faraday constant (¼96,485 C/mol).
Because of the loss due to the internal resistance R during discharge with a current
I O , the output voltage V O will be

(19.10)
V O ¼ V OC RI O

Energy

m A

m C
F.V OC

Cathode Anode

Electrolyte

Fig. 19.15 Schematic energy band diagram of a lithium-ion battery.