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6 Nanomaterials for Batteries
plays a vital role in the performance of the lithium-air battery. A good air electrode must have the following aspects: (1) fast oxygen diffusion; (2) good electrical
conductivity; (3) high specific surface; (4) stable electrode composition; (5) fast ion
conductivity.
It is not the specific surface area of the carbon porous material but the average
pore size and pore volume that is correlated with the battery capacity. In pace with the
increase of them, the discharge time and specific capacity raise accordingly. When
the electrode reaction occurs, the precipitates do not block the active charge transfer
center, but block the electrode surface pores. Besides, the impedance test results
of the electrode material further confirm this conclusion. It was found that after
mixing the porous carbon material with the binder in a certain proportion, too much
binder will block the pores of the air electrode, leading to a sharp drop in battery
capacity. Sandhu et al. proposed that the current density is lower, the utilization rate
of the electrode is higher through mathematical simulation; at a current density, the
thickness of the electrode is reduced and the specific capacitance of the battery is
greatly increased. In short, the air electrode material of the lithium-air battery is not
only required to ensure the normal transmission of oxygen and lithium ions, but
also does not block the electrode surface pores, and then accommodate more lithium
oxide. Mesoporous carbon materials and macroporous carbon materials can meet the
above requirements. Study about the air electrode material mainly concentrated in
the porous carbon material, carbon nanotubes, graphene.
6.4.5.4 Magnesium-Air Battery
The theoretical voltage of the magnesium-air battery remains 3.1 V, and the theoretical specific energy gets 6.8 k Wh/Kg. Magnesium or magnesium alloy are used
as the anode electrode active material for Magnesium/air battery, oxygen is used as
the active material of positive electrode (Rahman et al. 2013). Under the different
electrolytes used, reaction mechanisms differ as well. In an aqueous solution system
(Fig. 6.13),
Anode reaction: Mg → Mg
2+
+ 2e
Cathode reaction: O 2 + H 2 O + 4e → 4OH
−
Battery reaction: Mg + 1
2O 2 + H 2 O → Mg(OH) 2
The battery reaction is in the non-aqueous system: Mg + 1
2O 2 → MgO
The advantage of this battery system is the low price and no pollution. The theoretical energy density of magnesium is second only to light metal lithium and aluminum,
and therefore it is an ideal electrode material for the battery (Zhang et al. 2014).
However, there are still many problems to overcome in the actual research process.
The main problems currently faced by magnesium-air batteries for water systems
are still the problem of hydrogen evolution from corrosion and the activation and
passivation of magnesium alloys, because these problems determine the stability,
6 Nanomaterials for Batteries
plays a vital role in the performance of the lithium-air battery. A good air electrode must have the following aspects: (1) fast oxygen diffusion; (2) good electrical
conductivity; (3) high specific surface; (4) stable electrode composition; (5) fast ion
conductivity.
It is not the specific surface area of the carbon porous material but the average
pore size and pore volume that is correlated with the battery capacity. In pace with the
increase of them, the discharge time and specific capacity raise accordingly. When
the electrode reaction occurs, the precipitates do not block the active charge transfer
center, but block the electrode surface pores. Besides, the impedance test results
of the electrode material further confirm this conclusion. It was found that after
mixing the porous carbon material with the binder in a certain proportion, too much
binder will block the pores of the air electrode, leading to a sharp drop in battery
capacity. Sandhu et al. proposed that the current density is lower, the utilization rate
of the electrode is higher through mathematical simulation; at a current density, the
thickness of the electrode is reduced and the specific capacitance of the battery is
greatly increased. In short, the air electrode material of the lithium-air battery is not
only required to ensure the normal transmission of oxygen and lithium ions, but
also does not block the electrode surface pores, and then accommodate more lithium
oxide. Mesoporous carbon materials and macroporous carbon materials can meet the
above requirements. Study about the air electrode material mainly concentrated in
the porous carbon material, carbon nanotubes, graphene.
6.4.5.4 Magnesium-Air Battery
The theoretical voltage of the magnesium-air battery remains 3.1 V, and the theoretical specific energy gets 6.8 k Wh/Kg. Magnesium or magnesium alloy are used
as the anode electrode active material for Magnesium/air battery, oxygen is used as
the active material of positive electrode (Rahman et al. 2013). Under the different
electrolytes used, reaction mechanisms differ as well. In an aqueous solution system
(Fig. 6.13),
Anode reaction: Mg → Mg
2+
+ 2e
Cathode reaction: O 2 + H 2 O + 4e → 4OH
−
Battery reaction: Mg + 1
2O 2 + H 2 O → Mg(OH) 2
The battery reaction is in the non-aqueous system: Mg + 1
2O 2 → MgO
The advantage of this battery system is the low price and no pollution. The theoretical energy density of magnesium is second only to light metal lithium and aluminum,
and therefore it is an ideal electrode material for the battery (Zhang et al. 2014).
However, there are still many problems to overcome in the actual research process.
The main problems currently faced by magnesium-air batteries for water systems
are still the problem of hydrogen evolution from corrosion and the activation and
passivation of magnesium alloys, because these problems determine the stability,