Power storage system and method for controlling the same

1. A power storage system comprising:

a battery containing an electrolytic solution; and

a control device that controls, based on a temperature of said battery, permission and prohibition of charge/discharge of said battery,

said control device being configured to:

set a first determination temperature equal to or higher than a freezing point of said electrolytic solution and lower than a melting point of said electrolytic solution and a second determination temperature higher than said first determination temperature; and

prohibit charge/discharge of said battery when the temperature of said battery falls below said first determination temperature while said electrolytic solution is in a liquid state, and cancel the prohibition of charge/discharge of said battery when said electrolytic solution turns into the liquid state from a state in which said electrolytic solution is at least partially solidified, and when the temperature of said battery exceeds said second determination temperature.

2. The power storage system according to claim 1 , wherein

said second determination temperature is set to be higher than the melting point of said electrolytic solution by a prescribed temperature.

3. The power storage system according to claim 1 , further comprising:

an environmental temperature sensor configured to measure an environmental temperature of said battery, and

a surface temperature sensor configured to measure a surface temperature of said battery, wherein

said control device calculates an inside temperature of said battery from said environmental temperature and said surface temperature, and controls, based on said inside temperature, the permission and prohibition of charge/discharge of said battery.

4. The power storage system according to claim 1 , wherein

said power storage system is mounted in an electric-powered vehicle,

said electric-powered vehicle includes an operation unit for starting and shutting down a running system of said electric-powered vehicle, and

said control device being configured to:

prohibit charge/discharge of said battery when the temperature of said battery falls below said first determination temperature during an activated period that is a period from starting to shutting down of said running system by operation of said operation unit; and

refrain from canceling the prohibition of charge/discharge of said battery even though the temperature of said battery exceeds said second determination temperature during said activated period, and cancel the prohibition of charge/discharge of said battery when the temperature of said battery exceeds said second determination temperature during an activated period after said activated period.

5. The power storage system according to claim 1 , wherein

said first determination temperature being set based on a relation between the freezing point of said electrolytic solution and a degree of deterioration of said battery.

6. The power storage system according to claim 5 , wherein said degree of deterioration is calculated using a rate of increase in internal resistance of said battery or a capacity retention rate of said battery.

7. A method for controlling a power storage system comprising the steps of:

setting a first determination temperature equal to or higher than a freezing point of an electrolytic solution of a battery and lower than a melting point of said electrolytic solution;

setting a second determination temperature higher than said first determination temperature;

prohibiting charge/discharge of said battery when a temperature of said battery falls below said first determination temperature while said electrolytic solution is in a liquid state; and

canceling the prohibition of charge/discharge of said battery when said electrolytic solution turns into a liquid from a state in which said electrolytic solution is at least partially solidified, and when the temperature of said battery exceeds said second determination temperature.