Inspection method and manufacturing method of secondary battery
An inspection method of a secondary battery includes a charging step, an aging step, a pre-inspection discharge step, a voltage adjustment step, a self-discharge inspection step, and a deficiency determination step. A discharge condition in the pre-inspection discharge step is determined so that a voltage difference accumulation value Vs satisfies a predetermined range. The voltage difference accumulation value Vs is calculated by accumulating a value obtained by subtracting an output voltage from a predetermined voltage over a duration from start of the pre-inspection discharge step to end thereof.
1. An inspection method for a secondary battery, the inspection method comprising:
charging the secondary battery;
performing an aging process;
calculating a voltage difference accumulation value by integrating a difference between a predetermined voltage and a voltage of the secondary battery that changes over time, for a predetermined period from start of discharge to end of the discharge;
determining a discharge condition that allows the voltage difference accumulation value to be placed in a predetermined range;
performing pre-inspection discharge based on the discharge condition;
performing voltage adjustment;
performing self-discharge inspection; and
determining whether or not internal short-circuit occurs in the secondary battery based on a result of the self-discharge inspection.
2. The inspection method according to claim 1 , further comprising:
the predetermined range is determined based on the following formula:
Va =−0.589881 Ln ( Vs )+5.011706
where Va indicates a maximum fluctuation ratio of a voltage at a beginning of the self-discharge inspection, and Vs indicates the voltage difference accumulation value.
3. The inspection method according to claim 1 , wherein
the discharge condition satisfies that the voltage difference accumulation value is between 2,980 and 34,000 inclusive.
4. The inspection method according to claim 1 , further comprising:
determining a setting voltage based on the voltage difference accumulation value, the setting voltage being a voltage that is set at a time when the voltage adjustment is performed.
5. The inspection method according to claim 1 , further comprising:
determining a setting voltage that is set at a time when the voltage adjustment is performed, based on the following formula:
Vp=I×R+Vb
where Vp indicates the setting voltage, I indicates a cutoff current of constant-voltage discharge, a unit of I being ampere, R indicates an apparent resistance value calculated based on the voltage difference accumulation value, a unit of R being ohm, wherein:
the voltage adjustment includes charging the secondary battery to the setting voltage by constant-current charge, and then charging the secondary battery at the setting voltage by constant-voltage charge.
6. The inspection method according to claim 1 , wherein
the pre-inspection discharge includes performing constant-voltage discharge after constant-current discharge.
7. The inspection method according to claim 1 , wherein
a discharge final voltage in the pre-inspection discharge is between 1.8 V and 2.3 V inclusive.
8. A method for manufacturing a secondary battery, the method comprising:
preparing an electrode body including a positive electrode having a positive-electrode active material layer and a negative electrode having a negative-electrode active material layer, a surface area of the negative-electrode active material layer being larger than a surface area of the positive-electrode active material layer, and the negative-electrode active material layer including a part faced to the positive-electrode active material layer and a part not faced to the positive-electrode active material layer;
assembling a battery assembly by use of the electrode body and an electrolyte; and
inspecting whether or not internal short-circuit occurs in the secondary battery by an inspection method, so as to select a non-defective product,
the inspection method including:
charging the secondary battery;
performing an aging process;
calculating a voltage difference accumulation value by integrating a difference between a predetermined voltage and a voltage of the secondary battery that changes over time, for a predetermined period from start of discharge to end of the discharge;
determining the discharge condition that allows the voltage difference accumulation value to be placed in a predetermined range;
performing pre-inspection discharge based on the discharge condition;
performing voltage adjustment;
performing self-discharge inspection; and
determining whether or not internal short-circuit occurs in the secondary battery based on a result of the self-discharge inspection.