Method of selecting used secondary battery and method of manufacturing battery pack

摘要

A method of selecting a used secondary battery includes an internal resistance measurement step of measuring a specific internal resistance (second internal resistance) at a specific battery temperature (second battery temperature) of each of used secondary batteries, and a selection step of selecting a used secondary battery or batteries having the specific internal resistance (second internal resistance) smaller than a preset threshold from the plurality of used secondary batteries whose specific internal resistances (second internal resistance) have been measured in order to exclude an electrode-deteriorated battery from the used secondary batteries.

主权项

1. A method of selecting a used secondary battery that is reusable from a plurality of collected used secondary batteries, comprising:
an internal resistance measurement step of measuring a specific internal resistance at a specific battery temperature of each of the used secondary batteries; and a selection step of selecting used secondary batteries having the specific internal resistance smaller than a preset threshold from the plurality of used secondary batteries whose specific internal resistances have been measured; the threshold being set by a process including a step of measuring the specific internal resistance of each of a plurality of sample secondary batteries that are used secondary batteries prepared for determining the threshold; continuously discharging each of the sample secondary batteries at a battery temperature equivalent to the specific battery temperature, and measuring a minimum voltage in the each sample secondary battery during a period of the discharge; plotting the specific internal resistances and the minimum voltages of each of the sample secondary batteries to create a correlation chart; determining a regression line of sample secondary batteries including at least all of the sample secondary batteries having a specific internal resistance not exceeding a reference value among the plurality of sample secondary batteries in the correlation chart; determining a lower limit line that is parallel to the regression line and shifted a predetermined value from the regression line to a side where the minimum voltage is lower in the correlation chart; calculating a value obtained by dividing a ranking number of batteries in region of the plurality of sample secondary batteries in ascending order of the specific internal resistance by a total number of sample secondary batteries, wherein the batteries in region are contained in a region of the correlation chart where the specific internal resistance is larger than the reference value and the minimum voltage does not exceed the lower limit line; specifying a battery having a smallest specific internal resistance out of the batteries contained in the region and having a calculated value exceeding a preset value; and setting the specific internal resistance of the specified battery contained in the region as the threshold.