Battery system

A battery system comprising:

• a secondary battery including a power generation element configured to perform charging and discharging, an electrolyte, and a battery case, the power generation element comprising a negative electrode plate, a separator and a positive electrode plate being laminated in this order, the electrolyte being impregnated inside the power generation element, and the power generation element and the electrolyte being housed in the battery case;
• a temperature sensor configured to specify a temperature of the secondary battery;
• and a controller configured to:
• (a) calculate a deviation in salt concentration in the electrolyte in an x direction,
• wherein the x direction is perpendicular to a lamination direction of the negative electrode plate, the separator and the positive electrode plate,
• (b) calculate a first flow velocity and a second flow velocity at each position in the power generation element using a first equation defining a flow of the electrolyte,
• wherein the first flow velocity is a flow velocity of the electrolyte in the x direction when the electrolyte flows from an inside of the power generation element toward an outside of the power generation element,
• the second flow velocity is a flow velocity of the electrolyte in the x direction when the electrolyte flows from the outside of the power generation element toward the inside of the power generation element,
• the first equation includes a density of the electrolyte as an input parameter,
• the density is specified from the temperature, and
• the density changes according to the temperature of the secondary battery,
• (c) calculate a salt concentration distribution in the power generation element using a second equation,
• wherein the second equation includes the first flow velocity of the electrolyte in the x direction and the second flow velocity of the electrolyte in the x direction as input parameters, and
• (d) estimate a state of charge (SOC) of the secondary battery and control at least one of charging of the secondary battery based on the calculated salt concentration distribution.