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J. Zhu et al.
6.2.2.1 Lithium-air Battery
Lithium-air battery has the highest theoretical energy density except H 2 –O 2 fuel
cell. Its theoretical energy density can reach 11,140 Wh/kg, which is close to the
theoretical energy density of gasoline engine and is more than 10 times of the theoretical energy density of high-performance lithium-ion battery at present. Therefore,
researchers have paid much attention to it. Compared with the existing lithium-ion
battery, since the anode of the lithium-air battery does not use heavy metal oxides,
the actual power storage capacity is four to five times that of the lithium-ion battery.
Lithium-air batteries can be divided into four categories according to the electrolyte used: nonaqueous solvent, aqueous solvent, nonaqueous/aqueous hybrid and
all-solid-state electrolyte [40–42]. Among them, nonaqueous solvent type lithium-air
battery is the research hotspot of lithium-air secondary battery.
(1) Charging and discharging mechanism of lithium-air battery
In nonaqueous organic electrolysis, the discharge reaction of lithium-air battery is
[40, 41]:
4Li + O 2 → 2Li 2 O (E 8 = 2.9 V).
2Li + O 2 → Li 2 O 2 (E 8 = 3.1 V).
Theoretically, when the lithium-air battery discharges, the negative metal Li loses
electrons to form Li
+ which enters the electrolyte and is transported to the positive
electrode through the electrolyte. Positive oxygen is reduced under the catalysis of
an air electrode catalyst to generate O
2− and O 2
2− . O
2− and O 2
2− combine with Li
+
transported from the electrolyte to generate lithium oxide (Li 2 O) or lithium peroxide
(Li 2 O 3 ). Due to the poor solubility of lithium oxide in organic electrolyte, it deposits
on the positive electrode and gradually blocks the air channel to cover the catalyst.
The final discharge is terminated. The discharge process is shown in Fig. 6.8.
During charging, Li
+ in the electrolyte obtains electron-generating metal Li deposition on the negative electrode and returns to the nondischarged metal state; O
2−
and O 2
2− in Li 2 O or Li 2 O 3 at one end of the positive electrode lose electrons to
become O 2 and volatilize into the air, and the released Li
+ enters the electrolyte and
is transmitted to one end of the negative electrode to supplement the reduction of Li
+
concentration caused by Li deposition in the electrolyte near the negative electrode
until Li 2 O or Li 2 O 3 in the positive electrode is completely electrolyzed, and charging
is completed at this time.
The actual charging and discharging situation is far from simple. When
discharging, O 2 at one end of the positive electrode first obtains an electron under
the action of an air electrode catalyst to form superoxide anion O
2− , and combines
with Li
+ to form lithium superoxide LiO 2 . LiO 2 either decomposes to release O 2
to generate Li 2 O 3 , or another electron is obtained and combined with Li
+ to form
lithium peroxide Li 2 O 3 , and Li 2 O 3 obtains another two electrons and combines with
2 Li
+ to form lithium oxide Li 2 O.
J. Zhu et al.
6.2.2.1 Lithium-air Battery
Lithium-air battery has the highest theoretical energy density except H 2 –O 2 fuel
cell. Its theoretical energy density can reach 11,140 Wh/kg, which is close to the
theoretical energy density of gasoline engine and is more than 10 times of the theoretical energy density of high-performance lithium-ion battery at present. Therefore,
researchers have paid much attention to it. Compared with the existing lithium-ion
battery, since the anode of the lithium-air battery does not use heavy metal oxides,
the actual power storage capacity is four to five times that of the lithium-ion battery.
Lithium-air batteries can be divided into four categories according to the electrolyte used: nonaqueous solvent, aqueous solvent, nonaqueous/aqueous hybrid and
all-solid-state electrolyte [40–42]. Among them, nonaqueous solvent type lithium-air
battery is the research hotspot of lithium-air secondary battery.
(1) Charging and discharging mechanism of lithium-air battery
In nonaqueous organic electrolysis, the discharge reaction of lithium-air battery is
[40, 41]:
4Li + O 2 → 2Li 2 O (E 8 = 2.9 V).
2Li + O 2 → Li 2 O 2 (E 8 = 3.1 V).
Theoretically, when the lithium-air battery discharges, the negative metal Li loses
electrons to form Li
+ which enters the electrolyte and is transported to the positive
electrode through the electrolyte. Positive oxygen is reduced under the catalysis of
an air electrode catalyst to generate O
2− and O 2
2− . O
2− and O 2
2− combine with Li
+
transported from the electrolyte to generate lithium oxide (Li 2 O) or lithium peroxide
(Li 2 O 3 ). Due to the poor solubility of lithium oxide in organic electrolyte, it deposits
on the positive electrode and gradually blocks the air channel to cover the catalyst.
The final discharge is terminated. The discharge process is shown in Fig. 6.8.
During charging, Li
+ in the electrolyte obtains electron-generating metal Li deposition on the negative electrode and returns to the nondischarged metal state; O
2−
and O 2
2− in Li 2 O or Li 2 O 3 at one end of the positive electrode lose electrons to
become O 2 and volatilize into the air, and the released Li
+ enters the electrolyte and
is transmitted to one end of the negative electrode to supplement the reduction of Li
+
concentration caused by Li deposition in the electrolyte near the negative electrode
until Li 2 O or Li 2 O 3 in the positive electrode is completely electrolyzed, and charging
is completed at this time.
The actual charging and discharging situation is far from simple. When
discharging, O 2 at one end of the positive electrode first obtains an electron under
the action of an air electrode catalyst to form superoxide anion O
2− , and combines
with Li
+ to form lithium superoxide LiO 2 . LiO 2 either decomposes to release O 2
to generate Li 2 O 3 , or another electron is obtained and combined with Li
+ to form
lithium peroxide Li 2 O 3 , and Li 2 O 3 obtains another two electrons and combines with
2 Li
+ to form lithium oxide Li 2 O.