CN105527581A - Identification method for hybrid cathode material lithium ion battery key parameter and capacity attenuation mechanism - Google Patents
Identification method for hybrid cathode material lithium ion battery key parameter and capacity attenuation mechanism Download PDFInfo
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Abstract
The invention discloses an identification method for a hybrid cathode material lithium ion battery key parameter, comprising steps of performing discharging on a battery to be detected in a fully-charged state with constant current, obtaining an anode balance electric potential curve of the battery, a cathode balance electric potential curve, balance electric potential curves of active materials of all components in the hybrid anode material and a dQ/d V curve of the active materials of all components, calculating an estimation value of terminal voltage of the battery according to the cathode electric potential, the balance electric potential of the active materials of all components in the hybrid cathode material, the dQ/dV curve of the active materials of all the components in the hybrid anode, constant discharging current and an initial set value of the key parameter of the battery, performing correlation on an initial set value of the key parameters until the root-mean-square error RMSE between estimation value of the terminal voltage of the battery and the real value achieves a minimal value to obtain a final correction result of the key parameter. The invention also discloses an identification method for identifying the attenuation mechanism of the capacity of the hybrid anode material lithium ion battery.
Description
Technical field
The invention belongs to technical field of battery management, be specifically related to the discrimination method of mixed type anode material lithium ion battery key parameter and the discrimination method of capacity attenuation mechanism.
Background technology
Lithium ion battery has high power/feature such as energy density, long-life, the large-scale application that electric automobile obtains.Lithium ion battery is generally made up of positive electrode, negative material, barrier film and electrolytic solution etc., and wherein the performance of positive electrode to battery has a great impact.The positive electrode active materials of conventional lithium ion battery has LiFePO4 (LFP), cobalt acid lithium (LCO), LiMn2O4 (LMO) and the ternary material such as nickel cobalt manganese (NCM) or nickel cobalt aluminium (NCA).But, single positive electrode active materials cannot make the performance of battery reach optimum, in actual production, two kinds of different positive electrode active materials are mixed, composition mixed type anode material, realize the mutual supplement with each other's advantages of different positive electrode active materials, become a kind of method promoting lithium ion battery chemical property.Through test and the screening of long period, the practical application that the mixed type anode materials such as LMO-NCM (NCA) mixed type anode material, LFP-NCM (NCA) mixed type anode material, LCO-NCM (NCA) mixed type anode material all obtain.
The health status SOH of battery has various definitions method, as passed through capacity definition, i.e. SOH=C/C
0, wherein C is battery current capacities, C
0for the initial capacity of battery.The health status of battery can also be defined according to parameters such as the internal resistance of battery, energy/power density simultaneously.But the method for estimation of the cell health state SOH of present stage is only that to estimate that battery capacity decays how many, instead of the mechanism analyzing battery capacity decay determines the Trueattenuation situation of inside battery.
The capacity attenuation mechanism of battery may be lost due to positive electrode active materials, the reason such as loss of negative active core-shell material loss or available lithium ion causes.For the lithium ion battery of mixed type anode material, because mixed type anode material comprises different active material component, the loss more complicated of its active material.For the loss of LMO-NCM mixed type anode material.The loss of LMO active material and the loss of NCM active material all can cause the loss of LMO-NCM mixed type anode material.In battery use procedure, LMO, NCM two kinds of positive electrode active materials also may can present different rate of decay.
For the research of battery capacity kill mechanism, battery is often needed to disassemble, utilize XRD (X-RayDiffraction, X-ray diffraction), SEM (ScanningElectronMicorscope, scanning electron microscope) etc. method analyze, but this is completely infeasible on actual electrical motor-car.Chinese patent application CN103576097A proposes a kind of harmless health state of lithium ion battery SOH method of estimation, but the method is only applicable to the battery of single positive electrode active materials.
Summary of the invention
In view of this, necessaryly a kind of discrimination method of mixed type anode material lithium ion battery key parameter and the discrimination method of capacity attenuation mechanism is provided.
First the present invention provides a kind of discrimination method of mixed type anode material lithium ion battery key parameter, comprises the steps:
S1: discharge with the mesuring battary of steady current to full power state, and record the constant-current discharge voltage curve in discharge process, obtain not the actual value of battery terminal voltage in the same time, be designated as V (t);
S2: the equalize potential curve obtaining each composition activity material in the positive pole equalize potential curve of this mesuring battary, negative pole equalize potential curve, mixed type anode material, and electricity increment (dQ/dV) curve of each composition activity material;
S3: the estimated value calculating the terminal voltage of mesuring battary according to the initial set value of the key parameter of the dQ/dV curve of each composition activity material in composition activity material equalize potential each in negative pole equalize potential, mixed type anode material, mixed type anode, constant discharge current and mesuring battary, is designated as V
sim(t);
S4: revise the initial set value of this key parameter, until the estimated value V of this mesuring battary terminal voltage
simt the root-mean-square error RMSE between () and actual value V (t) reaches minimum value, obtain the final correction result of key parameter.
The present invention also provides a kind of mixed type anode material lithium ion battery capacity attenuation mechanism discrimination method, comprises the steps:
S1: discharge with the mesuring battary of steady current to full power state, and record the constant-current discharge voltage curve in discharge process, obtain not the actual value of battery terminal voltage in the same time, be designated as V (t); And
S2: the equalize potential curve obtaining each composition activity material in the positive pole equalize potential curve of this mesuring battary, negative pole equalize potential curve, mixed type anode material, and the dQ/dV curve of each composition activity material;
S3: the estimated value calculating the terminal voltage of mesuring battary according to the initial set value of the key parameter of the dQ/dV curve of each composition activity material in composition activity material equalize potential each in negative pole equalize potential, mixed type anode material, mixed type anode, constant discharge current and mesuring battary, is designated as V
sim(t);
S4: revise the initial set value of this key parameter, until the estimated value V of this mesuring battary terminal voltage
simt the root-mean-square error RMSE between () and actual value V (t) reaches minimum value, obtain the final correction result of key parameter; And
S5: the capacity attenuation mechanism obtaining battery according to the final correction result of key parameter.
Compared with prior art, the present invention is directed to the lithium ion battery of mixed type anode material, consider that the attenuation law due to composition activity material each in mixed type anode material is different, and the factor that the mass ratio of each composition activity material can change along with decay, propose discrimination method and the capacity attenuation mechanism discrimination method of the lithium ion battery key parameter being applicable to mixed type anode material.The outstanding advantage of the method is nondestructively identification to obtain the attenuation of each composition activity material of inside lithium ion cell of mixed type anode material.
Accompanying drawing explanation
Fig. 1 be one embodiment of the invention with LMO-NCM mixed type material be positive electrode active materials, constant-current discharge voltage curve after the graphite lithium ion battery differential declines circulation that is negative active core-shell material.
Fig. 2 is the equalize potential curve of the graphite cathode of one embodiment of the invention.
Fig. 3 is the equalize potential curve of the LMO-NCM mixed type anode material of one embodiment of the invention and component LMO thereof, NCM.
Fig. 4 is the dQ/dV curve of the LMO-NCM mixed type anode material of one embodiment of the invention and component LMO thereof, NCM.
Fig. 5 be one embodiment of the invention with LMO-NCM mixed type anode material be positive electrode active materials, the graphite inside lithium ion cell Mechanism of electrochemical behaviors of anhydrous schematic diagram that is negative active core-shell material.
Fig. 6 is that LMO-NCM mixed type anode material internal lithium ion (electric current) of one embodiment of the invention distributes mechanism schematic diagram.
Fig. 7 be one embodiment of the invention with LMO-NCM mixed type anode material be positive electrode active materials, the change curve of both positive and negative polarity equalize potential in the graphite lithium ion battery discharge process that is negative active core-shell material.
Fig. 8 be one embodiment of the invention with LMO-NCM mixed type anode material be positive electrode active materials, the estimated value of battery terminal voltage of the graphite lithium ion battery that is negative active core-shell material after differential declines circulation and the comparison diagram of actual value.
Fig. 9 be one embodiment of the invention with LMO-NCM mixed type anode material be positive electrode active materials, the identification result figure of the inside key parameter of the graphite lithium ion battery that is negative active core-shell material.
Embodiment
Below with reference to accompanying drawing, the discrimination method of mixed type anode material lithium ion battery key parameter of the present invention and the discrimination method of capacity attenuation mechanism are described in further detail.
First-selection, makes an explanation to some nouns related in instructions of the present invention.
" electricity " (electriccharge) mentioned in instructions of the present invention refers to the actual electricity that battery at a time has.
" capacity " (capacity) mentioned in instructions of the present invention refers to the actual electricity that battery has in fully charged state, namely the battery maximum electricity that can store.
" active material " mentioned in instructions of the present invention refers in lithium ion battery plus-negative plate the material participating in Lithium-ion embeding in charge and discharge process/deviate from reaction, conventional positive electrode active materials comprises LiFePO4 (LFP), cobalt acid lithium (LCO), LiMn2O4 (LMO) and nickel-cobalt-manganese ternary material (NCM) or nickel cobalt aluminium ternary material (NCA) etc., and conventional negative active core-shell material comprises graphite and lithium titanate etc.
" the mixed type anode material " mentioned in instructions of the present invention refers to the positive electrode active materials that positive electrode comprises two or more, is different from the positive electrode only comprising single positive electrode active materials.Particularly, this mixed type anode material can comprise two or more positive electrode active materials any in prior art.Common mixed type anode material includes but not limited to LMO-NCM mixed type anode material, LMO-NCA mixed type anode material, LFP-NCM mixed type anode material, LFP-NCA mixed type anode material, LCO-NCM mixed type anode material and LCO-NCA mixed type anode material in the market.
In " the mixed type anode material lithium ion battery " mentioned in instructions of the present invention, positive electrode is this mixed type anode material, and namely positive pole comprises two or more positive electrode active materials, and negative pole preferably only comprises a kind of negative active core-shell material.
" equalize potential " mentioned in instructions of the present invention refers to electrode potential when Lithium-ion embeding slowly/deviate from reaction (namely very little current charge-discharge electricity) occur battery plus-negative plate material, now can think that electrode material is in quasi-balanced state always.The equalize potential of lithium ion battery plus-negative plate material and the lithium ion mark one_to_one corresponding of material, generally represent with to lithium electromotive force.
" the electricity increment " mentioned in instructions of the present invention refers under different voltage V, the electricity dQ of battery releasing and the ratio of corresponding cell voltage decreasing value dV.Such as, when cell voltage is V, release electricity dQ, cause cell voltage to reduce dV, then corresponding electricity increment is dQ/dV.
" the lithium ion mark " mentioned in instructions of the present invention refers to the normalization content of lithium ion in both positive and negative polarity active material, and interval is [0,1].For negative pole, the chemical formula of negative active core-shell material is Li
xc
6, x is wherein the lithium ion mark of negative active core-shell material, and during the complete embedding full lithium of negative active core-shell material, x equals 1, and completely during de-lithium, x equals 0.
The invention provides a kind of discrimination method of mixed type anode material lithium ion battery key parameter, comprise the following steps:
S1: discharge with the mesuring battary of steady current to full power state, and record the constant-current discharge voltage curve in discharge process, obtain the actual value of any time battery terminal voltage, be designated as V (t);
S2: obtain each composition activity material equalize potential curve in the positive pole equalize potential curve of this mesuring battary, negative pole equalize potential curve, mixed type anode material, and electricity increment (dQ/dV) curve of each composition activity material;
S3: the estimated value calculating the terminal voltage of battery according to the initial set value of the key parameter of the dQ/dV curve of each composition activity material in composition activity material equalize potential each in negative pole equalize potential, mixed type anode material, mixed type anode, constant discharge current and battery, is designated as V
sim(t);
S4: revise the initial set value of key parameter, until the estimated value V of battery terminal voltage
simt the standard error RMSE between () and actual value V (t) reaches minimum value, obtain the final correction result of key parameter.
In step S1, this discharge process from full power state to the whole discharge time of emptying state be t
1to t
n, total n sampled point, n is positive integer, and any instant is t
k.This voltage curve can be voltage-time curve or voltage-capacity curve.
In step S2, the equalize potential curve of each component material of battery plus-negative plate equalize potential curve and mixed type anode material can obtain by carrying out the methods such as small area analysis (being less than 0.04C) discharge and recharge to half cell, is not repeated herein.
This mesuring battary positive pole can comprise the first positive electrode active materials, is designated as A, and the second positive electrode active materials, is designated as B.This step S2 can obtain this first positive electrode active materials equalize potential curve and dQ/dV curve respectively, and the equalize potential curve of the second positive electrode active materials and dQ/dV curve.
This key parameter can comprise capacity and the lithium ion mark of a certain composition activity material in mixed type anode material, the capacity of negative active core-shell material, the lithium ion mark of negative active core-shell material and the internal resistance of this mesuring battary.
This dQ/dV curve can reflect the chemical reaction process of inside battery, can obtain (as Chinese publication application CN103698714A), also repeat no more at this by methods such as several somes methods.At same voltage place, the dQ/dV value of mixed type anode material is the dQ/dV value of the first positive electrode active materials and the dQ/dV value sum of the second positive electrode active materials.This is because in the charge and discharge process of battery, this first positive electrode active materials and these two kinds of active materials of the second positive electrode active materials are in the state of being connected in parallel.In lithium ion battery discharge process, lithium ion is deviate from from negative pole, by electrolytic solution and barrier film, is embedded in positive electrode.In mixed type anode material, this first positive electrode active materials and two kinds of component moment of the second positive electrode active materials are in equal equalize potential, be equivalent to the two be connected in parallel, lithium ion embeds in this first positive electrode active materials and the second positive electrode active materials according to the proportion of the two dQ/dV value under this equalize potential respectively, to ensure that the equalize potential of this first positive electrode active materials and the second positive electrode active materials keeps equal.
In an embodiment of the present invention, the estimated value V of the terminal voltage of this mesuring battary
sim(t
k)=V
p(t
k)-V
n(x (t
k))-I × R, wherein V
p(t
k) be t
kthe positive pole equalize potential in moment, V
n(x (t
k)) be t
kmoment lithium ion mark is x (t
k) negative pole equalize potential, R is the initial set value of the internal resistance of cell, and I is this steady current, and namely per time instance embeds the lithium ion total amount in positive electrode.
In an embodiment of the present invention, this V
p(t
k) meet V
p(t
k)=V
p,A(y
a(t
k))=V
p,B(y
b(t
k)), y
a(t
k) be t
kthe lithium ion mark of moment first positive electrode active materials, V
p,A(y
a(t
k)) be t
kmoment lithium ion mark is y
a(t
k) the equalize potential of the first positive electrode active materials, y
b(t
k) be t
kthe lithium ion mark of moment second positive electrode active materials, V
p,B(y
b(t
k)) be t
kmoment lithium ion mark is y
b(t
k) the equalize potential of the second positive electrode active materials.
This y
a(t
k) and x (t
k) can meet respectively:
x(t
k)＝x
0-I×t
k/C
N；
Wherein, x (t
k) be t
kthe lithium ion mark of moment negative active core-shell material, x
0for the initial set value of the lithium ion mark of negative active core-shell material, C
nfor the initial set value of the capacity of negative active core-shell material, P (t
k) be t
kthe moment lithium ion quantity embedded in this first positive electrode active materials accounts for the proportion of whole lithium ion quantity, y
0, Abe the initial set value of the lithium ion mark of the first positive electrode active materials, C
abe the initial set value of the capacity of the first positive electrode active materials, Δ t is sampling time interval.
This P (t
k) can meet:
Wherein dQ
a/ dV is the electricity increment of the first positive electrode active materials, dQ
b/ dV is the electricity increment of the second positive electrode active materials, and c is the mass ratio (m of the second positive electrode active materials and the first positive electrode active materials
b/ m
a).
The terminal voltage estimated value V of this mesuring battary
simt the root-mean-square error RMSE between () and actual value V (t) is:
The present invention further provides a kind of discrimination method of mixed type anode material lithium ion battery capacity attenuation mechanism, comprise above-mentioned steps S1 ~ S4, and comprise step S5 further: the capacity attenuation mechanism obtaining battery according to the final correction result of key parameter.
This step S5 can be included in the final correction result obtaining this key parameter after this mesuring battary experiences not homogeneous charge and discharge cycles respectively, thus obtains the attenuation rate that this key parameter changes with this mesuring battary charge and discharge cycles number of times.This attenuation rate is the initial set value X of a certain key parameter
0and the ratio (=(X of the difference between final correction result X ' and initial set value
0-X ')/X
0× 100%), according to this key parameter with the increase of charge and discharge cycles number of times ever-reduced attenuation rate, the attenuation degree of this key parameter can be analyzed, thus judge whether the capacity attenuation of this battery is caused by the decay of this key parameter.
This step S5 can comprise the amount Σ (Li/Li of the available lithium ion obtaining this mesuring battary inside according to the final correction result of this key parameter further
+),
Σ(Li/Li
+)＝x’
0C’
N+y’
0,AC’
A+y’
0,BC’
B，
Wherein x '
0for t
0the modified value of the lithium ion mark of moment negative active core-shell material, C '
nfor the modified value of the capacity of negative active core-shell material, y '
0, Afor t
0the modified value of the lithium ion mark of moment first positive electrode active materials, C '
abe the modified value of the capacity of the first positive electrode active materials, y '
0, Bfor t
0the modified value of the lithium ion mark of moment second positive electrode active materials, C '
bbe the modified value of the capacity of the second positive electrode active materials, y '
0, Baccording to V
p,A(y '
0, A)=V
p,B(y '
0, B) y '
0, Acalculate, C '
b=c × k
0× C '
a.K
0be the initial capacity ratio of the first positive electrode active materials and the second positive electrode active materials, i.e. C
a/ C
b
This step S5 can comprise the amount Σ (Li/Li according to obtaining available lithium ion further
+) attenuation rate, obtain the attenuation rate of the key parameter of mesuring battary and the amount of available lithium ion in combining step S5, the attenuated inside mechanism of this mesuring battary can be obtained.
Be LMO-NCM mixed type anode material below with positive electrode, negative active core-shell material be the lithium ion battery of graphite as mesuring battary, the discrimination method of lithium ion battery key parameter of the present invention and the discrimination method of capacity attenuation mechanism are further described in detail.
In step S1, Fig. 1 is positive electrode is LMO-NCM mixed type anode material, and negative active core-shell material is the constant-current discharge voltage curve in the lithium ion battery differential declines situation of graphite.The constant-current discharge voltage curve of the new battery of 0 cyclic representation in Fig. 1,120 circulations, 240 circulations, 360 cyclic representation batteries are respectively through the constant-current discharge voltage curve after 120 times, 240 times and 360 permanance circulations.As can be seen from Figure 1, in differential declines situation, the constant-current discharge voltage curve of battery is very different, and is not the relation of simple Pan and Zoom.The present invention is intended to capacity attenuation mechanism and the SOH that the constant-current discharge voltage curve after according to certain circulation of mesuring battary analyzes this mesuring battary.
In step S2, Fig. 2 is the equalize potential curve of the graphite cathode of lithium ion battery in the present embodiment.The equalize potential of graphite cathode changes along with the change of inner lithium ion mark, and lithium ion mark is more close to 1, and the electromotive force of graphite is lower.It should be noted that lithium ion mark here refers to equivalent lithium ion mark, when definition graphite equalize potential is 0.05V, lithium ion mark is 1, and when equalize potential is 1.5V, lithium ion mark is 0.In battery charge and discharge process, lithium ion embeds/deviates from reaction in negative material inside, and the change in 0 to 1 is interval of lithium ion mark, correspondingly, negative pole equalize potential also changes in 0 to 1.5V interval.
Fig. 3 is the LMO-NCM mixed type anode material of lithium ion battery in the present embodiment and the equalize potential curve of component LMO and NCM thereof.Same, it is also equivalent lithium ion mark that lithium ion mark here refers to, and when definition equalize potential is 3V, lithium ion mark is 1, and when equalize potential is 4.3V, lithium ion mark is 0.In battery charge and discharge process, lithium ion embeds/deviates from reaction at positive electrode, and the change in 0 to 1 is interval of lithium ion mark, correspondingly, positive pole equalize potential also changes in 3 to 4.3V intervals.As can be seen from Figure 3, the equalize potential slope of a curve of NCM material is relatively steep, and the equalize potential curve of LMO material is relatively flat, and the equalize potential curve of LMO-NCM mixed type anode material is between therebetween.
Fig. 4 is electricity increment (dQ/dV) curve of LMO-NCM mixed type anode material and component LMO and NCM thereof in the present embodiment.As can be seen from Figure 4, at same voltage place, the dQ/dV value of LMO-NCM mixed type anode material is the dQ/dV value of LMO and the dQ/dV value sum of NCM.This is because in the charge and discharge process of battery, LMO and NCM two kinds of active materials are in the state of being connected in parallel, as shown in Figure 5.For electric discharge, in lithium ion battery discharge process, lithium ion is deviate from from negative pole, by electrolytic solution and barrier film, is embedded in positive electrode.In mixed type anode material, two kinds of component moment of LMO and NCM are in equal equalize potential, be equivalent to the two be connected in parallel, lithium ion embeds wherein according to the ratio code reassignment of the two dQ/dV value under this equalize potential, to ensure that the equalize potential of LMO and NCM keeps equal.The process of Lithium-ion embeding mixed type anode material is analyzed for the potential change of NCM, at t in Fig. 6
kin the moment, the lithium ion mark in NCM is y
nCM(t
k), corresponding equalize potential is V
p, NCM(y
nCM(t
k)), now according to the dQ/dV value of LMO and NCM, the proportion (the number ratio of lithium ion) that the lithium ion that can calculate in embedding NCM material accounts in whole lithium ion is P (t
k):
Wherein, c is in mixed type anode material, and the mass ratio of LMO and NCM, initial value is set to 1.T
k+1in the moment, in NCM material, the recruitment of lithium ion mark is Δ y
nCM(t
k), and
Δy
NCM(t
k)＝P(t
k)·I·Δt/C
NCM，
Wherein I is discharge current, and namely per time instance embeds the lithium ion total amount in positive electrode, and Δ t is sampling time interval, C
nCMfor the capacity of NCM active material.T can be obtained accordingly
k+1the lithium ion mark y of moment NCM
nCM(t
k+1)=y
nCM(t
k)+Δ y
nCM(t
k).The rest may be inferred, can calculate the lithium ion mark in each moment NCM.
In step S3, calculate the estimated value of the terminal voltage of battery according to the initial set value of the key parameter of the dQ/dV curve of each composition activity material in composition activity material equalize potential each in negative pole equalize potential, mixed type anode material, mixed type anode, constant discharge current and battery, be designated as V
sim(t).Key parameter comprises, the capacity of NCM, the lithium ion mark of NCM, the capacity of graphite cathode, the lithium ion mark of graphite cathode and the internal resistance of cell.Here, the initial set value of the capacity of NCM is C
nCM, the initial value of the lithium ion mark of NCM is set to y
0, NCM, the initial set value of the capacity of graphite cathode is C
n, the initial value of the lithium ion mark of graphite cathode is set to x
0, the initial value of the internal resistance of cell is set to R, and steady current is I.Discharge process, t
kmoment, the lithium ion mark y of NCM
nCM, the computing formula of the lithium ion mark x of graphite cathode is:
x(t
k)＝x
0-I×t
k/C
N(3)
As shown in Figure 6, the terminal voltage V of battery
sim(t
k) equal the difference of both positive and negative polarity equalize potential, deduct the loss of voltage that internal resistance causes, computing formula is as follows simultaneously:
V
sim(t
k)＝V
p(t
k)-V
n(x(t
k))-I×R(4)
Wherein the equalize potential of mixed type anode material equals the equalize potential of NCM, as follows:
V
p(t
k)＝V
p,NCM(y
NCM(t
k))＝V
p,LMO(y
LMO(t
k))
In step S4, if whole discharge time t
1to t
n, total n sampled point, the terminal voltage estimated value V of battery
simt the root-mean-square error RMSE between () and actual value V (t) is obtained by following formulae discovery:
Given different [x
0, C
n, y
0, NCM, C
nCM, c, R], different battery terminal voltage estimated value V can be obtained
simt (), corresponding root-mean-square error RMSE can be calculated by formula (6).Utilize the optimal estimation algorithms such as genetic algorithm to key parameter [x
0, C
n, y
0, NCM, C
nCM, c, R] revise, optimum key parameter can be found, make the estimated value V of battery terminal voltage
simt the root-mean-square error RMSE between () and actual value V (t) is minimum, as shown in Figure 7.
Estimated value and the actual value curve of the battery terminal voltage of battery after the circulation of different number of times is compared in Fig. 8.Compare for convenience, in figure, also depict corresponding both positive and negative polarity equalize potential curve.In Fig. 8,1. be the comparative result of new battery, 2., 3. and be 4. respectively battery have passed through the circulation of 120,240,360 permanance after the comparing of terminal voltage estimated value and actual value, can see, after the permanance circulation of different number of times, it is very good that the estimated value of battery terminal voltage and actual value coincide, and the root-mean-square error of the two remains within 6mV always.
The present invention further provides a kind of discrimination method of mixed type anode material lithium ion battery capacity attenuation mechanism, comprise above-mentioned steps S1 ~ S4, and comprise step S5 further: the capacity attenuation mechanism obtaining battery according to the final correction result of key parameter.
In step S5, according to the optimum correction result of key parameter, the capacity attenuation mechanism of lithium ion battery can be obtained.Key parameter [the x obtained
0, C
n, y
0, NCM, C
nCM, c, R] in, C
nCMand C
ndirectly can reflect the change of the capacity of NCM and graphite cathode, R can reflect the change of the internal resistance of cell.In addition, the capacity C of LMO
lMOcan obtain with formulae discovery below, wherein k
0for the initial capacity ratio of NCM and LMO, can calculate according to dQ/dV curve.
C
LMO＝c×k
0×C
NCM(7)
The decay of lithium ion battery is also likely caused by the loss of available lithium ion, and according to the key parameter obtained, the amount of the available lithium ion of inside battery can calculate with following formula:
Σ(Li/Li
+)＝x
0C
N+y
0，NCMC
NCM+y
0，LMOC
LMO(8)
Fig. 9 is the identification result of the internal mechanism key parameter obtaining battery according to one embodiment of present invention, comprises the capacity of LMO, NCM, graphite cathode capacity, the amount of available lithium ion and the internal resistance of cell.
Pass through embodiment, can find out, the mixed type anode material lithium ion battery kill mechanism discrimination method that the present invention proposes can obtain the kill mechanism of inside battery, and especially the attenuation of each component material in mixed type anode material, contributes to the health status fullying understand battery.
In addition, those skilled in the art can also do other changes in spirit of the present invention, and these changes done according to the present invention's spirit all should be included in the present invention's scope required for protection.
Claims (10)
1. a discrimination method for mixed type anode material lithium ion battery key parameter, comprises the steps:
S1: discharge with the mesuring battary of steady current to full power state, and record the constant-current discharge voltage curve in discharge process, obtain not the actual value of battery terminal voltage in the same time, be designated as V (t);
S2: the equalize potential curve obtaining each composition activity material in the positive pole equalize potential curve of this mesuring battary, negative pole equalize potential curve, mixed type anode material, and the electricity incremental rate curve of each composition activity material;
S3: the estimated value calculating the terminal voltage of mesuring battary according to the initial set value of the key parameter of the electricity incremental rate curve of each composition activity material in composition activity material equalize potential each in negative pole equalize potential, mixed type anode material, mixed type anode, constant discharge current and mesuring battary, is designated as V
sim(t);
S4: revise the initial set value of this key parameter, until the estimated value V of this mesuring battary terminal voltage
simt the root-mean-square error RMSE between () and actual value V (t) reaches minimum value, obtain the final correction result of key parameter.
2. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 1, it is characterized in that, this key parameter comprises capacity and the lithium ion mark of a certain composition activity material in mixed type anode material, the capacity of negative active core-shell material, the lithium ion mark of negative active core-shell material and the internal resistance of this mesuring battary.
3. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 1, it is characterized in that, the whole discharge time of this discharge process is t
1to t
n, total n sampled point, n is positive integer, and any instant is t
k, the estimated value V of the terminal voltage of this mesuring battary
sim(t
k)=V
p(t
k)-V
n(x (t
k))-I × R, wherein V
p(t
k) be t
kthe positive pole equalize potential in moment, V
n(x (t
k)) be t
kmoment lithium ion mark is x (t
k) negative pole equalize potential, R is the initial set value of the internal resistance of cell, and I is this steady current.
4. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 3, it is characterized in that, this mesuring battary positive pole comprises the first positive electrode active materials, is designated as A, and the second positive electrode active materials, is designated as B, this V
p(t
k) meet:
V
p(t
k)＝V
p,A(y
A(t
k))＝V
p,B(y
B(t
k))，
Wherein y
a(t
k) be t
kthe lithium ion mark of moment first positive electrode active materials,
V
p,A(y
a(t
k)) be t
kmoment lithium ion mark is y
a(t
k) the equalize potential of the first positive electrode active materials,
Y
b(t
k) be t
kthe lithium ion mark of moment second positive electrode active materials,
V
p,B(y
b(t
k)) be t
kmoment lithium ion mark is y
b(t
k) the equalize potential of the second positive electrode active materials.
5. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 4, is characterized in that, this y
a(t
k) and x (t
k) meet respectively:
x(t
k)＝x
0-I×t
k/C
N；
Wherein, x (t
k) be t
kthe lithium ion mark of moment negative active core-shell material,
X
0for the initial set value of the lithium ion mark of negative active core-shell material,
C
nfor the initial set value of the capacity of negative active core-shell material,
P (t
k) be t
kthe moment lithium ion quantity embedded in this first positive electrode active materials accounts for the proportion of whole lithium ion quantity,
Y
0, Abe the initial set value of the lithium ion mark of the first positive electrode active materials,
C
abe the initial set value of the capacity of the first positive electrode active materials,
Δ t is sampling time interval.
6. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 5, is characterized in that, this P (t
k) meet:
Wherein dQ
a/ dV is the electricity increment of the first positive electrode active materials, dQ
b/ dV is the electricity increment of the second positive electrode active materials, and c is the mass ratio of the second positive electrode active materials and the first positive electrode active materials.
7. the discrimination method of mixed type anode material lithium ion battery key parameter as claimed in claim 1, is characterized in that, the terminal voltage estimated value V of this mesuring battary
simt the root-mean-square error RMSE between () and actual value V (t) is:
8. a mixed type anode material lithium ion battery capacity attenuation mechanism discrimination method, comprise the step S1 ~ S4 in claim 1 ~ 7 in any one, and comprise step S5 further: the capacity attenuation mechanism obtaining battery according to the final correction result of key parameter.
9. mixed type anode material lithium ion battery capacity attenuation mechanism discrimination method as claimed in claim 8, it is characterized in that, this step S5 is included in the final correction result obtaining this key parameter after this mesuring battary experiences not homogeneous charge and discharge cycles respectively, thus obtains the attenuation rate that this key parameter changes with this mesuring battary charge and discharge cycles number of times.
10. mixed type anode material lithium ion battery capacity attenuation mechanism discrimination method as claimed in claim 8, it is characterized in that, this step S5 comprises the amount Σ (Li/Li of the available lithium ion obtaining this mesuring battary inside according to the final correction result of this key parameter further
+):
Σ(Li/Li
+)＝x’
0C’
N+y’
0,AC’
A+y’
0,BC’
B，
Wherein x '
0for the modified value of the lithium ion mark of negative active core-shell material,
C '
nfor the modified value of the capacity of negative active core-shell material,
Y '
0, Abe the modified value of the lithium ion mark of the first positive electrode active materials,
C '
abe the modified value of the capacity of the first positive electrode active materials,
Y '
0, Bbe the modified value of the lithium ion mark of the second positive electrode active materials,
C '
bit is the modified value of the capacity of the second positive electrode active materials.
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