Patent ID: 8538711

Claim:
A nonaqueous electrolyte type lithium ion secondary battery system comprising: a voltage obtaining part for obtaining charging voltage when a charging current is applied to a nonaqueous electrolyte type lithium ion secondary battery and obtaining discharging voltage when a discharging current is generated by the nonaqueous electrolyte type lithium ion secondary battery; a coefficient calculating part for calculating a coefficient of a quadratic term of an approximated curve of a quadratic function with respect to changes in value within a previously set sampling period for each of the charging voltage and the discharging voltage obtained by the voltage obtaining part, and repeating the calculation over a plurality of the sampling periods; and a deposition determining part for determining whether or not there is a possibility of lithium deposition in the nonaqueous electrolyte type lithium ion secondary battery based on a tendency of changing with time of the coefficients of charging voltage and discharging voltage calculated by the coefficient calculating part.