LITHIUM ION BATTERY SYSTEM

PROBLEM TO BE SOLVED: To provide a technique that enhances the detection precision of deposition of lithium.SOLUTION: In a lithium ion battery system, the absolute humidity in a battery case in which a battery cell is mounted is calculated from the temperature and humidity in the battery case by temperature and humidity measuring processing S2 and absolute humidity calculation processing S4 in battery deterioration monitoring processing executed by a battery monitoring ECU, and the integration amount of a water amount infiltrated into the battery case is calculated on the basis of predetermined relationship between the water amount infiltrated into the battery case per unit time and the absolute humidity in the battery case by water infiltration amount calculation processing S6 and water infiltration amount integration processing S8. Determination processing S10 based on the infiltration amount integration value compares the integration amount of the infiltrated water amount with a permissible limit amount over which lithium will deposit, and estimates that lithium deposits when the integration amount exceeds the permissible limit amount. 【課題】リチウムの析出の検出精度を向上する技術を提供する。【解決手段】本明細書で開示するリチウムイオン電池システムは、バッテリ監視ＥＣＵが実行するバッテリ劣化監視処理において、温湿度計測処理Ｓ２及び絶対湿度算出処理Ｓ４により、電池セルを収容するバッテリケース内の温度及び湿度からバッテリケース内の絶対湿度を算出し、水分浸入量算出処理Ｓ６及び水分浸入量積算処理Ｓ８により、単位時間当たりにバッテリケース内に浸入する水分量とバッテリケース内の絶対湿度との予め求められた関係に基づいてバッテリケース内に浸入した水分量の積算量を算出し、浸入量積算値に基づく判定処理Ｓ１０により、浸入した水分量の積算量を、それを超えるとリチウム析出に至る許容限界量と比較して積算量が許容限界量を超えた場合にリチウムが析出したと推定する。【選択図】図３