Lithium secondary battery and method of controlling short resistance thereof
Provided is a lithium secondary battery including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a polymer electrolyte composition having a polymer electrolyte, a non-aqueous organic solvent, and a lithium salt. The content of the polymer electrolyte is 9 to 20 wt %, based on the total weight of the polymer electrolyte composition.
1. A method of controlling a short resistance of a secondary battery, comprising:
measuring an open circuit voltage (V OC ) of the secondary battery;
calculating a short circuit resistance (R SC ) using the measured open circuit voltage (V OC );
calculating a heating value W according to time using the calculated short circuit resistance (R SC );
calculating a time having the maximum instantaneous heating value, using the change in heating value (W) according to time,
determining the short circuit resistance (R SC ) value at the time having the maximum instantaneous heating value as a critical short resistance; and
adjusting an amount of a polymer electrolyte used in the secondary battery, according to the determined critical short resistance.
2. The method according to claim 1 , wherein the adjusting of the amount comprises adjusting the amount of the polymer electrolyte, such that the critical short resistance is not included in an R SC range having an ignition risk.
3. The method according to claim 2 , wherein the R SC range having an ignition risk occurs while the total heating value according to time is within 90% of the maximum level of the total heating value according to time.
4. The method according to claim 1 , wherein the heating value satisfies Equation 1:
W
=
(
V
oc
R
1
+
R
sc
+
R
)
2
*
R
sc
,
[
Equation
1
]
wherein V OC is an open circuit voltage, R 1 is a specific resistance of the secondary battery, R SC is a short circuit resistance, and R is a specific resistance of a shorting pin.
5. The method according to claim 4 , wherein calculating of the heating value (W) according to time is performed by applying changes in the short circuit resistance (R SC ) according to time to Equation 1.
6. The method according to claim 1 , wherein the short circuit resistance (R SC ) satisfies Equation 2:
R
sc
=
V
sc
(
R
1
+
R
)
V
oc
-
V
sc
,
[
Equation
2
]
wherein V OC is an open circuit voltage, V SC is a short circuit voltage, R 1 is a specific resistance of the secondary battery, and R is a specific resistance of a shorting pin.
7. The method according to claim 6 , wherein the calculating of the short circuit resistance (R SC ) is performed by applying changes in the measured open circuit voltage to Equation 2.
8. The method according to claim 1 , wherein a positive electrode collector and a negative electrode active material layer are short-circuited in the secondary battery.