Battery-state estimation device

A battery-state estimation device comprising:

• an obtaining unit which obtains, at a first timing, a first resistance value corresponding to a first open circuit voltage of a lithium-ion secondary battery and a second resistance value corresponding to a second open circuit voltage, which is higher than the first open circuit voltage, of the lithium-ion secondary battery and which obtains, at a second timing which is different from the first timing, a third resistance value corresponding to the first open circuit voltage and a fourth resistance value corresponding to the second open circuit voltage;
• and
• a determination unit which determines presence or absence of lithium deposition in the lithium-ion secondary battery, based on a magnitude relation between a first variation amount of the third resistance value with respect to the first resistance value and a second variation amount of the fourth resistance value with respect to the second resistance value,
• wherein the lithium-ion secondary battery has, in a correspondence relation between an internal resistance and an open circuit voltage, a peak internal resistance at which the internal resistance stops increasing and starts decreasing with increase in the open circuit voltage,
• the lithium-ion secondary battery has a third open circuit voltage which is lower than an open circuit voltage corresponding to the peak internal resistance and at which an internal resistance is equal to the peak internal resistance,
• the obtaining unit divides a range of the open circuit voltage into a first range in which the open circuit voltage is lower than the third open circuit voltage and a second range in which the open circuit voltage is higher than the third open circuit voltage,
• the first open circuit voltage is in the first range, and
• the second open circuit voltage is in the second range.