Battery pack having linear voltage profile, and SOC algorithm applying to the battery pack

1. A battery pack, comprising:

a rechargeable battery module; and

a battery management system for controlling charging and/or discharging of the battery module, wherein:

the battery module includes a substantially linear charging and discharging voltage-time profile within at least part of the charging and discharging cycle of the battery module, and the battery management system is configured to calculate a state of charge of the battery module by using linear charging and/or discharging characteristics of the battery module; and

wherein the battery management system is arranged to calculate a second state of charge of the battery module after a time period of charging or discharging by determining a first state of charge of the battery module and then using the linear charging and/or discharging characteristics of the battery module.

2. The battery pack according to claim 1 , wherein:

the first state of charge is a current state of charge of the battery module and the second state of charge is a predicted state of charge of the battery module, or the first state of charge is a previous state of charge of the battery module and the second state of charge is a current state of charge of the battery module.

3. The battery pack according to claim 1 , wherein the battery management system is configured to determine the first state of charge of the battery module by measuring an output voltage of the battery module.

4. The battery pack according to claim 1 , wherein the battery management system is configured to determine the substantially linear charging and discharging voltage-time profile.

5. The battery pack according to claim 4 , wherein the battery management system is arranged to determine a charging and discharging voltage-time profile over a sub-range of state of charges, and then use this to determine the substantially linear voltage-time profile for a wider range of state of charges.

6. The battery pack according to claim 4 , wherein the battery management system is arranged to use the determined substantially linear charging and discharging voltage-time profile to determine a substantially linear charging and discharging voltage-state of charge profile.

7. The battery pack according to claim 1 , wherein a charging and discharging voltage-state of charge profile of the battery module is linear within a range of states of charge from 70% to 90% state of charge.

8. The battery pack according to claim 1 , wherein the battery module consists of one or more lithium ion batteries.

9. The battery pack according to claim 8 , wherein the one or more lithium ion batteries each include a negative active material, the negative active material including carbon black and soft carbon.

10. The battery pack according to claim 9 , wherein the negative active material includes a total weight amount of the carbon black and the soft carbon that is made up of about 54.5 to 99.5% of the soft carbon and about 0.5 to 45.5% of the carbon black.

11. The battery pack according to claim 9 , wherein the negative active material includes about 54.5 to 99.5% of the soft carbon and about 0.5 to 45.5% of the carbon black.

12. A power apparatus for an idle stop and go system for starting an engine, comprising:

the battery pack according to claim 1 ;

a power generating module for charging the battery module; and

a starter motor arranged to be powered by discharge of the battery module.

13. The power apparatus according to claim 12 when dependent on claim 6 , wherein on starting the engine, the battery management system is arranged to determine an engine start voltage value of the battery module based on an elapsed time using the determined substantially linear charging and discharging voltage-time profile, and then using the engine start voltage value and the determined substantially linear charging and discharging voltage-state of charge profile to determine an engine start state of charge value.