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6 Nanomaterials for Batteries
6.4.1 Working Principle of Metal-Air Battery
The positive plate is pressed by a metal current collector, a waterproof layer, and
a catalytic layer in this order. The waterproof layer is a breathable hydrophobic
film made of carbon black and polytetrafluoroethylene emulsion (PTFE) that has the
function of preventing electrolyte leakage. The catalyst layer consists of polytetrafluoroethylene emulsion (PTFE), activated carbon black, and catalyst. For rechargeable
metal-air batteries, the catalyst not only has the ability to reduce oxygen but also to
have oxygen oxide ions. The positive electrode active material is oxygen in the air.
During the discharge process, oxygen is catalytically reduced to hydroxide ions at
the gas–liquid–solid three-phase interface by a catalyst.
The reaction equation is O 2 + 4e
−
+ 2H 2 O = 4OH
− E = 0.401 V.
The anode material of metal-air battery will be continuously consumed during
the discharge process, that is to say, how much the theoretical energy density is,
only depends upon how much the energy of the negative metal is released. This
is the only active material transferred in the battery. The discharge reaction on the
metal electrode depends on metals, electrolytes, and other factors, while oxygen is
introduced from the air. Discharge reaction is generally as follows:
M → M
n+
+ ne
battery discharge total reaction: 4M + nO 2 + 2mH 2 O → 4M(OH).
In the above formula: M represents the metal used in the battery, and the value of
n depends on the degree in the oxidation of the metal in the battery. Most metals are
unstable in the electrolyte solution and can erode or oxidize to H 2 . M + nH 2 O →
M(OH) + (n/2)H 2 . Figure 6.9 shows the structure diagram of metal-air battery.
The Coulombic efficiency on cathode fades away for self-discharge or half-etching
reaction, which must be controlled to reduce this capacity loss of the battery. The
metal battery also has a reactive negative electrode and an air electrode, and is formed
by electrochemical reaction. The cathode electrode reactant is inexhaustible. In some
cases, metal-air batteries have high mass-to-energy and volumetric energy, whose
ultimate energy depends on the negative current capacity of the negative electrode
and the storage and processing technology of the reaction product. Metal-air batteries
that have been researched and developed include primary batteries, storage batteries,
rechargeable batteries, and mechanical recharging batteries.
6.4.2 Electrolyte
Electrolyte solutions in metal-air batteries are mostly neutral salt solutions or strong
alkaline solutions. When a neutral electrolyte (such as sodium chloride and potassium
carbonate) is used, the corrosion of the anode is small, but the passivation of the metal
6 Nanomaterials for Batteries
6.4.1 Working Principle of Metal-Air Battery
The positive plate is pressed by a metal current collector, a waterproof layer, and
a catalytic layer in this order. The waterproof layer is a breathable hydrophobic
film made of carbon black and polytetrafluoroethylene emulsion (PTFE) that has the
function of preventing electrolyte leakage. The catalyst layer consists of polytetrafluoroethylene emulsion (PTFE), activated carbon black, and catalyst. For rechargeable
metal-air batteries, the catalyst not only has the ability to reduce oxygen but also to
have oxygen oxide ions. The positive electrode active material is oxygen in the air.
During the discharge process, oxygen is catalytically reduced to hydroxide ions at
the gas–liquid–solid three-phase interface by a catalyst.
The reaction equation is O 2 + 4e
−
+ 2H 2 O = 4OH
− E = 0.401 V.
The anode material of metal-air battery will be continuously consumed during
the discharge process, that is to say, how much the theoretical energy density is,
only depends upon how much the energy of the negative metal is released. This
is the only active material transferred in the battery. The discharge reaction on the
metal electrode depends on metals, electrolytes, and other factors, while oxygen is
introduced from the air. Discharge reaction is generally as follows:
M → M
n+
+ ne
battery discharge total reaction: 4M + nO 2 + 2mH 2 O → 4M(OH).
In the above formula: M represents the metal used in the battery, and the value of
n depends on the degree in the oxidation of the metal in the battery. Most metals are
unstable in the electrolyte solution and can erode or oxidize to H 2 . M + nH 2 O →
M(OH) + (n/2)H 2 . Figure 6.9 shows the structure diagram of metal-air battery.
The Coulombic efficiency on cathode fades away for self-discharge or half-etching
reaction, which must be controlled to reduce this capacity loss of the battery. The
metal battery also has a reactive negative electrode and an air electrode, and is formed
by electrochemical reaction. The cathode electrode reactant is inexhaustible. In some
cases, metal-air batteries have high mass-to-energy and volumetric energy, whose
ultimate energy depends on the negative current capacity of the negative electrode
and the storage and processing technology of the reaction product. Metal-air batteries
that have been researched and developed include primary batteries, storage batteries,
rechargeable batteries, and mechanical recharging batteries.
6.4.2 Electrolyte
Electrolyte solutions in metal-air batteries are mostly neutral salt solutions or strong
alkaline solutions. When a neutral electrolyte (such as sodium chloride and potassium
carbonate) is used, the corrosion of the anode is small, but the passivation of the metal