Basic unit of lithium-ion battery, battery pack comprising the same, and charge/discharge equalizing method thereof

A basic unit of lithium-ion battery pack, comprising:

• a) at least two serially-connected lithium-ion cells;
• b) at least one lithium-ion cell for balance;
• c) controllable switches with the same number as the at least two serially-connected lithium-ion cells;
• d) a drive module for the controllable switches;
• e) a voltage detection module for detecting a voltage at two ends of each of the at least two serially-connected lithium-ion cells;
• and
• f) a controller;
• wherein the at least one lithium-ion cell for balance is configured to be selectively connected in parallel to one of the at least two serially-connected lithium-ion cells that has a highest voltage among the at least two serially-connected lithium-ion cells during a charging operation of the basic unit of lithium-ion battery pack;
• wherein the at least one lithium-ion cell for balance is configured to be selectively connected in parallel to one of the at least two serially-connected lithium-ion cells that has a lowest voltage among the at least two serially-connected lithium-ion cells during a discharging operation of the basic unit of lithium-ion battery pack;
• the controllable switches respectively control the turn on/off of the parallel connection between the at least one lithium-ion cell for balance and one of the at least two serially-connected lithium-ion cells independently at each time to conduct charging or discharging;
• and
• the drive module for the controllable switches and the voltage detection module are connected to the controller.