Battery system for secondary battery comprising blended cathode material, and apparatus and method for managing the same

1. A battery system, comprising:

(1) a battery management system (BMS); and

(2) a blended lithium secondary battery, comprising: (a) a cathode comprising a first cathode material and a second cathode material different from the first cathode material, wherein the first and second cathode materials have different operating voltage ranges; (b) an anode; and (c) a separator,

wherein the BMS is electrically connected to the blended lithium secondary battery and includes a sensor configured to measure a current and a voltage of the blended lithium secondary battery, and

wherein the BMS is configured to:

control the charge and discharge of the blended lithium secondary battery in a voltage range where the blended lithium secondary battery undergoes voltage relaxation;

monitor the current and voltage of the blended lithium secondary battery during operation of the blended lithium secondary battery according to time using the sensor;

detect a two-stage voltage relaxation from the change of voltage of the blended lithium secondary battery during operation of the battery system, wherein the voltage relaxation includes the transfer of operating ions between the first and second cathode active materials;

estimate a state of charge of the blended lithium secondary battery corresponding to the detected two-state voltage relaxation; and

update the state of charge of the blended lithium secondary battery based on the estimated state of charge.

2. The battery system according to claim 1 , wherein the BMS detects the two-stage voltage relaxation when the occurrence of an inflection point is identified in a changing pattern of the voltage, and

wherein the two-stage voltage relaxation includes two voltage rises before and after the inflection point.

3. The battery system according to claim 2 , wherein the BMS identifies the occurrence of the inflection point by using a first-order differential value or a second-order differential value of the voltage of the blended lithium secondary battery with respect to time.

4. The battery system according to claim 2 ,

wherein the BMS determines a reference parameter including a voltage corresponding to the inflection point, a time corresponding to the inflection point, a first-order differential value with respect to time calculated at the inflection point, a value obtained by integrating the voltage profile between predetermined two points before and after the inflection point, a first-order differential value or second-order differential value of the voltage profile calculated at a predetermined point before and/or after the inflection point with respect to time, or combinations thereof, and

wherein a state of the blended lithium secondary battery corresponding to the determined reference parameter is estimated by using a predetermined relationship between the reference parameter and the state of the blended lithium secondary battery.

5. The battery system according to claim 4 , wherein the predetermined relationship is a look-up table which is capable of mapping a state of the blended lithium secondary battery by means of at least one reference parameter.

6. The battery system according to claim 4 , wherein the predetermined relationship is a look-up function where at least one reference parameter and a state of the blended lithium secondary battery corresponding thereto are respectively defined as an input parameter and an output parameter.

7. The battery system according to claim 1 , wherein the BMS monitors the current and voltage of the blended lithium secondary battery when the blended lithium secondary battery comes to an idle state or a no-load state while being discharged.

8. The battery system according to claim 1 , wherein the first cathode material has a layered structure and the second cathode material has an olivine structure, and

wherein the first cathode material and the second cathode material are blended in a weight ratio of 7:3.

9. The battery system according to claim 8 , wherein the first cathode material comprises Li 1+x Ni a Co b , Mn c O 2 (NMC), where x>0; a=b=c=⅓, and

wherein the second cathode material comprises LiFePO 4 (LFP).