6.1 Lead-Acid Batteries
109
6.1.1.2 Structure of Lead-Acid Batteries
Lead accumulator in charge state, is extremely spongy lead, is extremely lead dioxide;
both positive and negative are lead sulfate. At present, the accepted flow reaction
is the theory of disulfation, and the equation is shown in Eqs. (6.1) and (6.2). Its
correctness is verified from the following three aspects: ➀ Chemical analysis was
used to confirm the composition of positive active substances as PbO 2 , and the
composition of negative active substances was lead. ➁ When using 2F power, the
change of H 2 SO 4 concentration was measured, equivalent to 2 mol H 2 SO 4 , and
2 mol H 2 O, which was consistent with the battery reaction. ➂ The thermodynamic
data calculates the electromotive force of the battery, which is consistent with the
measured value.
Battery symbol and discharge reaction of lead-acid battery:
Pb, PbSO 4 |H 2 SO 4 |PbSO 4 , PbO 2 (or Pb|H 2 SO 4 |PbO 2 )
PbO 2 + 3H
+
+ HSO
−
4 + 2e = PbSO 4 + 2H 2 O
(6.1)
Pb + HSO
−
4 = PbSO 4 + H
+
+ 2e
(6.2)
Pb + PbO 2 + 2H
+
+ 2HSO
−
4 = 2PbSO 4 + 2H 2 O
Pb + PbO 2 + 4H
+
+ 2SO
2−
4 = 2PbSO 4 + 2H 2 O
(6.3)
The causes of self-discharge of lead-acid batteries can be analyzed from thermodynamics. From the potential of lead to pH, Pb + HSO
−
4 = PbSO 4 + H
+
+
2e, 2H
+
+ 2e = H 2 . This leads to a negative self-discharge in the conjugate reaction. 2H 2 O = 4H
+
+ O 2 + 4e, PbO 2 + 3H
+
+ HSO
−
4 + 2e = PbSO 4 + 2H 2 O. This
causes a positive self-discharge in the conjugate reaction (Liu et al. 2015).
6.1.2 The Performance of Lead-Acid Battery
Open-circuit voltage: the electromotive force of the battery is 2.045 V, so its rated
voltage is 2.0 V. The relationship between battery open-circuit voltage and electrolyte
density can be calculated in the next type.
Open-circuit voltage = 1.850 + 0.917(ρ l − ρ w ) or
Open-circuit voltage = ρ l + 0.84
(6.4)
ρ l in liquid is the density of the electrolyte, ρ w is the density of water.
Capacity: The capacity of lead-acid battery is a function of temperature and
discharge current. The hourly rate and temperature of the discharge are clearly defined
in the standard. The starting type lead-acid battery usually uses 20-h rate capacity, the
fixed type is commonly used in 10-h rate capacity, and the battery for power traction
109
6.1.1.2 Structure of Lead-Acid Batteries
Lead accumulator in charge state, is extremely spongy lead, is extremely lead dioxide;
both positive and negative are lead sulfate. At present, the accepted flow reaction
is the theory of disulfation, and the equation is shown in Eqs. (6.1) and (6.2). Its
correctness is verified from the following three aspects: ➀ Chemical analysis was
used to confirm the composition of positive active substances as PbO 2 , and the
composition of negative active substances was lead. ➁ When using 2F power, the
change of H 2 SO 4 concentration was measured, equivalent to 2 mol H 2 SO 4 , and
2 mol H 2 O, which was consistent with the battery reaction. ➂ The thermodynamic
data calculates the electromotive force of the battery, which is consistent with the
measured value.
Battery symbol and discharge reaction of lead-acid battery:
Pb, PbSO 4 |H 2 SO 4 |PbSO 4 , PbO 2 (or Pb|H 2 SO 4 |PbO 2 )
PbO 2 + 3H
+
+ HSO
−
4 + 2e = PbSO 4 + 2H 2 O
(6.1)
Pb + HSO
−
4 = PbSO 4 + H
+
+ 2e
(6.2)
Pb + PbO 2 + 2H
+
+ 2HSO
−
4 = 2PbSO 4 + 2H 2 O
Pb + PbO 2 + 4H
+
+ 2SO
2−
4 = 2PbSO 4 + 2H 2 O
(6.3)
The causes of self-discharge of lead-acid batteries can be analyzed from thermodynamics. From the potential of lead to pH, Pb + HSO
−
4 = PbSO 4 + H
+
+
2e, 2H
+
+ 2e = H 2 . This leads to a negative self-discharge in the conjugate reaction. 2H 2 O = 4H
+
+ O 2 + 4e, PbO 2 + 3H
+
+ HSO
−
4 + 2e = PbSO 4 + 2H 2 O. This
causes a positive self-discharge in the conjugate reaction (Liu et al. 2015).
6.1.2 The Performance of Lead-Acid Battery
Open-circuit voltage: the electromotive force of the battery is 2.045 V, so its rated
voltage is 2.0 V. The relationship between battery open-circuit voltage and electrolyte
density can be calculated in the next type.
Open-circuit voltage = 1.850 + 0.917(ρ l − ρ w ) or
Open-circuit voltage = ρ l + 0.84
(6.4)
ρ l in liquid is the density of the electrolyte, ρ w is the density of water.
Capacity: The capacity of lead-acid battery is a function of temperature and
discharge current. The hourly rate and temperature of the discharge are clearly defined
in the standard. The starting type lead-acid battery usually uses 20-h rate capacity, the
fixed type is commonly used in 10-h rate capacity, and the battery for power traction