Capacity estimation method, degradation estimation method and degradation estimation apparatus for lithium-ion cells, and lithium-ion batteries

A method for providing a degradation estimation for a Li-ion cell, comprising the steps of:

• obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is a time difference from a first time when a charge voltage reaches a predetermined voltage Vs in a constant current charge mode to a second time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode;
• calculating an estimated capacity Ce of said Li-ion cell by using a function of said elapsed time t;
• and
• determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity Cmin.

A degradation estimation apparatus for a Li-ion cell, comprising:

• means for obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is a time difference from a first time when a charge voltage reaches a predetermined voltage Vs in a constant current charge mode to a second time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode;
• and
• a circuit to calculate an estimated capacity Ce of said Li-ion cell by using a function of said elapsed time t;
• and
• means for outputting a signal indicating that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity Cmin.

A Li-ion battery having a charge and discharge control arrangement, comprising:

• a memory to store numerical data used to calculate an estimated capacity Ce of Li-ion cells in said Li-ion battery;
• means for obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is a time difference from a first time when a charge voltage reaches a predetermined voltage Vs in a constant current charge mode to a second time when charge condition is changed from a constant current charge mode to a constant voltage charge mode;
• and
• a circuit for calculating said estimated capacity Ce of said Li-ion cells by using said elapsed time t and said numerical data.

A capacity estimation apparatus for a Li-ion cell, comprising:

• means for obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is a time difference from a first time when a charge voltage reaches a predetermined voltage Vs in a constant current charge mode to a second time when the charge voltage reaches a charge limit voltage Vc;
• and
• a first circuit to calculate an estimated specific capacity Ce/Co of said Li-ion cell by using an equation Ce/Co=At+B, wherein Ce is an estimated capacity of said Li-ion cell, Co is a nominal capacity of said Li-ion cell, and A and B are positive constants;
• a second circuit to estimate a degradation state of said Li-ion cell based on said estimated specific capacity Ce/Co, and providing an estimated degredation state;
• and
• means for at least one of displaying the estimated degradation state and generating an alarm to warn of the estimated degradation state.

A Li-ion battery having a charge and discharge control arrangement, comprising:

• a memory to store numerical data used for calculating an estimated specific capacity Ce/Co of Li-ion cells in said Li-ion battery, wherein Ce is an estimated capacity of said Li-ion cells and Co is a nominal capacity of said Li-ion cells;
• means for obtaining an elapsed time t, which is a time difference from a first time when a charge voltage from a constant current charge reaches a predetermined voltage Vs in a constant current charge mode to a second time when the charge voltage reaches a charge limit voltage Vc, said Li-ion cell being charged by a constant current and a constant voltage process;
• and
• a circuit to calculate said estimated specific capacity Ce/Co of said Li-ion cell by using an equation Ce/Co=At+B and said numerical data, wherein A and B are positive constants;
• means for outputting said estimated specific capacity Ce/Co.

A method for providing a capacity estimation of a Li-ion cell, comprising the steps of:

• repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• obtaining, when said Li-ion cell is charged by the constant current and the constant voltage process, an elapsed time tα, which is a time difference from a first time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode to a second time when a charge current is a product of a factor α and another charge current Ic0 in said constant current charge mode, wherein the factor α is between 0 and 1;
• obtaining an estimated specific capacity Ce/Co by using a first equation Ce/Co=−Atα+B when said elapsed time tα increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is an estimated capacity, Co is a nominal capacity and A and B are positive constants;
• obtaining said estimated specific capacity Ce/Co by using a second equation Ce/Co=+Atα+B′ when said elapsed time tα decreases as the number of repetitions of said charge and discharge cycle increases, wherein B′ is a positive constant;
• and
• obtaining said estimated capacity Ce by using said estimated specific capacity Ce/Co and said nominal capacity Co.

A method for providing a capacity estimation for a Li-ion cell, comprising the steps of:

• repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• obtaining a charge current Itm after a lapse of a predetermined time tm from a time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode, wherein a first condition 0<tm≦0.8Co/Ic0 is satisfied, Co is a nominal capacity of said Li-ion cell and Ic0 is a charge current in said constant current charge mode;
• obtaining a first estimated specific capacity Ce/Co by using a first equation Ce/Co=−MItm+N′, when said charge current Itm increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is a specific capacity of said Li-ion cell and M and N′ are positive constants;
• obtaining a second estimated specific capacity Ce/Co by using a second equation Ce/Co=+MItm+N′, when said charge current Itm decreases as the number of repetitions of said charge and discharge cycle increases, wherein N′ is a positive constant;
• and
• obtaining said estimated capacity Ce by using said first and second estimated specific capacity Ce/Co and said nominal capacity Co.

A method for providing a degradation estimation of a Li-ion cell, comprising the steps of:

• repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• obtaining, when said Li-ion cell is charged by a constant current and a constant voltage method, an elapsed time tα, which is a time difference from a first time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode to a second time when a charge current is a product of α and a charge current Ic0 in said constant current charge mode, wherein α is between 0 and 1;
• obtaining a first estimated specific capacity Ce/Co by using a first equation Ce/Co=−Atα+B, when said elapsed time tα increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is an estimated capacity, Co is a nominal capacity and A and B are positive constants;
• obtaining a second estimated specific capacity Ce/Co by using a second equation Ce/Co=+Atα+B′, when said elapsed time tα decreases as a number of repetitions of said charge and discharge cycle increases, wherein A and B′ are positive constants;
• and
• obtaining said estimated capacity Ce by using said first and second estimated specific capacity Ce/Co and said nominal capacity Co;
• and
• determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity.

A method for providing a degradation estimation of a Li-ion cell, comprising the steps of:

• repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• obtaining a charge current Itm after a lapse of a predetermined time tm from a time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode, wherein 0<tm≦0.8Co/Ic0 is satisfied, Co is a nominal capacity of said Li-ion cell and Ic0 is a charge current in said constant current charge mode;
• obtaining a first estimated specific capacity Ce/Co by using a first equation Ce/Co=−MItm+N′, when said charge current Itm increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is an estimated capacity of said Li-ion cell and M and N′ are positive constants;
• obtaining a second estimated specific capacity Ce/Co by using a second equation Ce/Co=+MItm+N′, when said charge current Itm decreases as the number of repetitions of said charge and discharge cycle increases, wherein N′ is a positive constant;
• and
• obtaining said estimated capacity Ce by using said first and second estimated specific capacity Ce/Co and said nominal capacity Co;
• determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity.

A degradation estimation apparatus for a Li-ion cell, comprising:

• a cell control arrangement comprising:
• means for repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• means for obtaining, when said Li-ion cell is charged by the constant current and constant voltage process, an elapsed time tα from a first time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode to a second time when a charge current is a product of α and a charge current Ic0 in said constant current charge mode, wherein α is between 0 and 1;
• a memory to store said elapsed time tα as a function tα(n) of n in an nth cycle for each charge and discharge cycle;
• a logic circuit including:
• means for obtaining a first estimated specific capacity Ce/Co by using a first equation Ce/Co=−Atα+B, when said elapsed time tα increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is an estimated capacity, Co is a nominal capacity and A and B are positive constants;
• means for obtaining a second estimated specific capacity Ce/Co by using a second equation Ce/Co=+Atα+B′, when said elapsed time tα decreases as the number of repetitions of said charge and discharge cycle increases, wherein B′ is a positive constant;
• and
• means for obtaining said estimated capacity Ce by using said first and second estimated specific capacity Ce/Co and said nominal capacity Co;
• and
• means for determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity.

A degradation estimation apparatus for a Li-ion cell, comprising:

• a cell control arrangement comprising:
• means for repeating a charge and discharge cycle a plurality of times, wherein said charge and discharge cycle includes a charge period, in which said Li-ion cell is charged by a constant current and a constant voltage process to provide a charged Li-ion cell, and a discharge period, in which said charged Li-ion cell is discharged;
• means for obtaining a charge current Itm after a lapse of a predetermined time tm from a time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode, wherein a condition of 0<tm≦0.8Co/Ic0 is satisfied, Co is a nominal capacity of said Li-ion cell and Ic0 is a charge current in said constant current charge mode;
• a memory to store said charge current Itm as a function Itm(n) of n in an nth cycle for each charge and discharge cycle;
• a logic circuit including:
• means for obtaining a first estimated specific capacity Ce/Co by using a first equation Ce/Co=−MItm+N′, when said charge current Itm increases or remains unchanged as a number of repetitions of said charge and discharge cycle increases, wherein Ce is an estimated capacity of said Li-ion cell and M and N′ are positive constants;
• means for obtaining a second estimated specific capacity Ce/Co by using a second equation Ce/Co=+MItm+N′, when said charge current Itm decreases as the number of repetitions of said charge and discharge cycle increases, wherein N′ is a positive constant;
• and
• means for obtaining said estimated capacity Ce by using said first and second estimated specific capacity Ce/Co and said nominal capacity Co;
• means for determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity.

A Li-ion battery comprising:

• a measuring part, when a charge and discharge cycle is repeated a plurality of times, obtaining an elapsed time tα from a first time when charge condition is changed from a constant current charge mode to a constant voltage charge mode to a second time when a charge current is a product of α and a charge current Ic0 in said constant current charge mode, wherein said charge and discharge cycle includes a charge period in which said Li-ion cell is charged by a constant current and constant voltage process and a discharge period in which said charged Li-ion cell is discharged;
• a memory storing said elapsed time tα as a function tα(n) of n in the nth cycle for each cycle;
• a logic circuit comprising:
• means for obtaining an estimated specific capacity Ce/Co by using a first equation Ce/Co=−Atα+B when said elapsed time tα increases or remains unchanged as the number of repetition of said cycle increases, wherein Ce is a specific capacity, Co is a nominal capacity and A and B are positive constants;
• means for obtaining said estimated specific capacity Ce/Co by using a second equation Ce/Co=+Atα+B′ when said elapsed time tα decreases as the number of repetition of said cycle increases, wherein B′ is a positive constant;
• and
• means for obtaining said estimated capacity Ce by using said estimated specific capacity Ce/Co and said nominal capacity Co;
• and
• means for judging that said Li-ion cell is degraded when said estimated capacity Ce becomes smaller than a predetermined limit capacity.

A Li-ion battery comprising:

• a measuring arrangement, when a charge and discharge cycle is repeated a plurality of times, obtaining a charge current Itm after a lapse of a predetermined time tm from the time when charge condition is changed from a constant current charge mode to a constant voltage charge mode, wherein 0<tm≦0.8Co/Ic0 is satisfied, Co is a nominal capacity of said Li-ion cell and Ic is charge current in said constant current charge mode, wherein said charge and discharge cycle includes a charge period in which said Li-ion cell is charged by a constant current and constant voltage method and a discharge period in which said charged Li-ion cell is discharged;
• a memory to store said charge current Itm as a function Itm(n) of n in the nth cycle for each cycle;
• a logic circuit comprising:
• means for obtaining an estimated specific capacity Ce/Co by using a first equation Ce/Co=−MItm+N′ when said charge current Itm increases or remains unchanged as the number of repetition of said cycle increases, wherein Ce is a specific capacity of said Li-ion cell and M and N′ are positive constants;
• means for obtaining said estimated specific capacity Ce/Co by using a second equation Ce/Co=+MItm+N′ when said charge current Itm decreases as the number of repetition of said cycle increases, wherein N′ is a positive constant;
• and
• means for obtaining said estimated capacity Ce by using said estimated specific capacity Ce/Co and said nominal capacity Co;
• means for judging that said Li-ion cell is degraded when said estimated capacity Ce becomes smaller than a predetermined limit capacity.

A method for providing a degradation estimation for a Li-ion cell, comprising the steps of:

• obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is the time from when a charge condition is changed from a constant current charge mode to a constant voltage charge mode to another time when a charge current is a product of α and another charge current in said constant current charge mode, where α is between 0 and 1;
• obtaining an estimated capacity Ce of said Li-ion cell by using an equation Ce/Co=At+B and said elapsed time t, wherein Co is a nominal capacity of said Li-ion cell and A and B are positive constants;
• and
• determining that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity Cmin.

A degradation estimation apparatus for a Li-ion cell, comprising:

• means for obtaining, when said Li-ion cell is charged by a constant current and a constant voltage process, an elapsed time t, which is a time from a first time when a charge condition is changed from a constant current charge mode to a constant voltage charge mode to a second time when a charge current is a product of α and another charge current in said constant current charge mode, where α is between 0 and 1;
• a circuit to obtain an estimated capacity Ce of said Li-ion cell by using said elapsed time t;
• and
• means for outputting a signal indicating that said Li-ion cell is degraded when said estimated capacity Ce is smaller than a predetermined limit capacity Cmin.