Electricity storage element charging method and electricity storage device

A charging method for charging N (N is equal to or larger than 3) electricity storage elements by connecting the electricity storage elements electrically using a connector,

• wherein a two-terminal circuit and a series degree of the two-terminal circuit are defined as follows:
• the two-terminal circuit has a circuit configuration in which a plurality of unit circuits are connected in series or a circuit configuration in which all the electricity storage elements are connected in parallel, each of the unit circuits being composed of a single electricity storage element or a plurality of the electricity storage elements connected in parallel, and
• the series degree is a number of unit circuits connected in series if the two-terminal circuit has the circuit configuration in which the plurality of unit circuits are connected in series;
• or
• the series degree is 1 if all the electricity storage elements are connected in parallel in the two-terminal circuit, and wherein
• the connector includes a single switch which is disposed between one terminal of an n-th electricity storage element (n=1, 2, . . . , N−1) and one terminal of an (n+1)-th electricity storage element, a single switch which is disposed between another terminal of the n-th electricity storage element and another terminal of the (n+1)-th electricity storage element, and a single switch which is disposed between the another terminal of the n-th electricity storage element (n=1, 2, . . . , N−1) and the one terminal of the (n+1)-th electricity storage element;
• and
• all the electricity storage elements are connected electrically to constitute the two-terminal circuit having the series degree S (S=1, 2, . . . , N),
• the charging method comprising:
• a first step in which the electricity storage elements are connected by the connector to configure the two-terminal circuit having a value of the series degree of 2 or larger and each of the electricity storage elements are charged by injecting a current into the two-terminal circuit configured by the connector;
• a second step in which a new two-terminal circuit is configured by changing a connection of the electricity storage elements to reduce the value of the series degree;
• and
• a third step in which a new two-terminal circuit is configured by changing the connection of the electricity storage elements to increase the value of the series degree and charging each of the electricity storage elements by injecting a current into the two-terminal circuit, wherein:
• the second step is started when a terminal voltage difference among the electricity storage elements becomes equal to or larger than a predetermined value;
• in the second step, at least one of the electricity storage element having a highest terminal voltage and the electricity storage element having a lowest terminal voltage out of the plurality of the storage elements are connected to another electricity storage element in parallel;
• in the third step, no electricity storage element having a terminal voltage below a specified voltage is connected in parallel to another electricity storage element;
• the third step is started when there is any electricity storage element whose terminal voltage is not reached the specified voltage after the second step, and
• the value of the series degree of the two-terminal circuit at the second step is larger than 1 and the value of the series degree of the two-terminal circuit at the third step is smaller than N.