Battery system for secondary battery comprising blended cathode material, and apparatus and method for managing the same
Disclosed is a battery system for a secondary battery including a blended cathode material, and an apparatus and method for managing a secondary battery having a blended cathode material. The blended cathode material includes at least a first cathode material and a second cathode material. The first and second cathode materials have different operating voltage ranges. When the secondary battery comes to an idle state or a no-load state, the battery system detects a voltage relaxation occurring by the transfer of operating ions between the first and second cathode materials.
1. A secondary battery managing apparatus, comprising:
a battery management system (BMS) configured to electrically connect to a secondary battery comprising: (a) a cathode comprising a first cathode material and a second cathode material, wherein the first and second cathode materials have different operating voltage ranges; (b) an anode; and (c) a separator,
said BMS comprising:
a sensor configured to measure a current and a voltage of the secondary battery during operation of the secondary battery; and
a control unit configured to:
prepare a voltage profile and optionally a current profile from the measured current and voltage of the secondary battery, and
detect an occurrence of a two-stage voltage relaxation caused by a transfer of operating ions between the first and second cathode materials when the secondary battery comes to an idle state or a no-load state in an intrinsic voltage range.
2. The secondary battery managing apparatus according to claim 1 , wherein a constant current or substantially constant current is drawn from the secondary battery when the secondary battery comes to an idle state or a no-load state.
3. The secondary battery managing apparatus according to claim 1 , wherein a current less than 1 c-rate is drawn from the secondary battery when the secondary battery comes to an idle state or a no-load state.
4. The secondary battery managing apparatus according to claim 1 , wherein a current less than 0.5 c-rate is drawn from the secondary battery when the secondary battery comes to an idle state or a no-load state.
5. The secondary battery managing apparatus according to claim 1 , wherein a current less than 0.1 c-rate is drawn from the secondary battery when the secondary battery comes to an idle state or a no-load state.
6. The secondary battery managing apparatus according to claim 1 ,
wherein the BMS comprises a circuit model, and
wherein the circuit model includes:
an anode material circuit unit comprising an open-circuit voltage component and optionally an impedance voltage component of the anode material; and
a cathode material circuit unit comprising a first cathode material circuit unit comprising an open-circuit voltage component and an impedance voltage component of the first cathode material and a second cathode material circuit unit comprising an open-circuit voltage component and an impedance voltage component of the second cathode material.
7. The secondary battery managing apparatus according to claim 6 , wherein the anode material circuit unit and the cathode material circuit unit are connected to each other in series and the first and second cathode material circuit units are connected to each other in parallel.
8. The secondary battery managing apparatus according to claim 6 , wherein each impedance voltage component comprises a circuit element selected from the group consisting of one or more resistance component, one or more capacity component, one or more inductor component and combinations thereof.
9. The secondary battery managing apparatus according to claim 6 ,
wherein each impedance voltage component includes a plurality of circuit elements, and
wherein the plurality of circuit elements are connected in series and/or in parallel.
10. The secondary battery managing apparatus according to claim 6 , wherein the anode material includes at least one impedance voltage component.
11. The secondary battery managing apparatus according to claim 6 , wherein each impedance voltage component comprises one or more circuit component selected from the group consisting of at least one RC circuit and at least one resistor.
12. The secondary battery managing apparatus according to claim 11 , wherein each impedance voltage component comprises a RC circuit and a resistor connected thereto in series.
13. The secondary battery managing apparatus according to claim 11 , wherein the voltage component formed by the RC circuit is calculated from the following equation expressed as a discrete time equation:
V
[
k
+
1
]
=
V
[
k
]
ⅇ
-
Δ
t
RC
+
R
(
1
-
ⅇ
-
Δ
t
RC
)
i
[
k
]
wherein k is a time index, R and C are a resistance and a capacitance of a resistor and a capacitor included in the RC circuit, respectively, and V and i are a voltage and a current of the RC circuit, respectively.
14. The secondary battery managing apparatus according to claim 1 , wherein at least one of the first and second cathode materials has a voltage profile with a plateau portion, wherein said plateau portion has a substantially constant voltage.
15. The secondary battery managing apparatus according to claim 1 ,
wherein the first cathode material comprises an alkali metal compound expressed by a general chemical formula A[A x M y ]O 2+z wherein A is at least one of Li, Na and K; M is at least one element selected from the group consisting of Ni, Co, Mn, Ca, Mg, Al, Ti, Si, Fe, Mo, V, Zr, Zn, Cu, Al, Mo, Sc, Zr, Ru and Cr; x≧0, 1≦x+y≦2, −0.1≦z≦2; and x, y, z and stoichiometric coefficients of components included in M are selected so that the alkali metal compound maintains electrical neutrality or xLiM 1 O 2 -(1-x)Li 2 M 2 O 3 wherein M 1 includes at least one element with an average oxidation state of +3; M 2 includes at least one element with an average oxidation state of +4; and 0≦x≦1, and selectively coated with a carbon layer, an oxide layer or a fluoride layer.
16. The secondary battery managing apparatus according to claim 15 ,
wherein the first cathode material comprises an alkali metal compound expressed by Li[Li a Ni b Co c Mn d ]O 2+z (a≧0; a+b+c+d=1; at least one of b, c and d is not zero; −0.1≦z≦2) and selectively coated with a carbon layer, an oxide layer or a fluoride layer.
17. The secondary battery managing apparatus according to claim 1 ,
wherein the second cathode material comprises lithium metal phosphate expressed by a general chemical formula Li a M 1 x Fe 1-x M 2 y P 1-y M 3 z O 4-z wherein M 1 is at least one element selected from the group consisting of Ti, Si, Mn, Co, V, Cr, Mo, Fe, Ni, Nd, Al, Mg and Al; M 2 is at least one element selected from the group consisting of Ti, Si, Mn, Co, V, Cr, Mo, Fe, Ni, Nd, Al, Mg, Al, As, Sb, Si, Ge, V and S; M 3 is at least one element selected from a halogen group containing F; 0<a≦2, 0≦x≦1, 0≦y<1, 0≦z<1; and a, x, y, z, and stoichiometric coefficients of components included in M 1 , M 2 , and M 3 are selected so that the lithium metal phosphate maintains electrical neutrality or Li 3 M 2 (PO 4 ) 3 wherein M is at least one element selected from the group consisting of Ti, Si, Mn, Fe, Co, V, Cr, Mo, Ni, Al, Mg and Al, and selectively coated with a carbon layer, an oxide layer or a fluoride layer.
18. The secondary battery managing apparatus according to claim 17 ,
wherein the second cathode material comprises at least one selected from the group consisting of LiFePO 4 , LiMn x Fe y PO 4 (0<x+y≦1), Li 3 Fe 2 (PO 4 ) 3 , LiFePO 4 coated with a carbon layer, an oxide layer or a fluoride layer, LiMn x Fe y PO 4 (0<x+y≦1) coated with a carbon layer, an oxide layer or a fluoride layer, and Li 3 Fe 2 (PO 4 ) 3 coated with a carbon layer, an oxide layer or a fluoride layer.