CN117368747A - Battery capacity decay analysis method - Google Patents
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- 238000004458 analytical method Methods 0.000 title claims abstract description 26
- 239000007774 positive electrode material Substances 0.000 claims abstract description 92
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 30
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 30
- 238000012360 testing method Methods 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims abstract description 19
- 238000007599 discharging Methods 0.000 claims description 25
- 239000011149 active material Substances 0.000 claims description 21
- 230000002238 attenuated effect Effects 0.000 claims description 5
- 230000006872 improvement Effects 0.000 abstract description 4
- 238000013461 design Methods 0.000 abstract description 3
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 35
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 35
- 239000000463 material Substances 0.000 description 10
- 239000010406 cathode material Substances 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- -1 Nickel Cobalt Aluminum Chemical compound 0.000 description 3
- 230000006399 behavior Effects 0.000 description 3
- 238000009831 deintercalation Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- DTQVDTLACAAQTR-UHFFFAOYSA-N Trifluoroacetic acid Chemical compound OC(=O)C(F)(F)F DTQVDTLACAAQTR-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000009830 intercalation Methods 0.000 description 2
- 230000002687 intercalation Effects 0.000 description 2
- 230000014759 maintenance of location Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- FFBHFFJDDLITSX-UHFFFAOYSA-N benzyl N-[2-hydroxy-4-(3-oxomorpholin-4-yl)phenyl]carbamate Chemical compound OC1=C(NC(=O)OCC2=CC=CC=C2)C=CC(=C1)N1CCOCC1=O FFBHFFJDDLITSX-UHFFFAOYSA-N 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000005562 fading Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 229910001428 transition metal ion Inorganic materials 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/374—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] with means for correcting the measurement for temperature or ageing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/10—Measuring sum, difference or ratio
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/3865—Arrangements for measuring battery or accumulator variables related to manufacture, e.g. testing after manufacture
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention belongs to the field of battery testing, and particularly relates to a battery capacity attenuation analysis method, which comprises the following steps: n batteries C are prepared by N different positive electrode active materials in the mixed positive electrode material 1 、C 2 、…C n The method comprises the steps of carrying out a first treatment on the surface of the (II) Battery C 1 、C 2 、…C n Performing parallel charge and discharge and independent charge and discharge tests; by comparing the difference between the full charge voltage of the same battery during parallel charge and discharge and the full charge voltage of the same battery during individual charge and discharge, and comparing the difference between the empty charge voltage of the same battery during parallel charge and discharge and the empty charge voltage of the same battery during individual charge and dischargeThe influence primary and secondary relation of different positive electrode active materials on the capacity attenuation of the battery is broken. The method can simply, nondestructively and rapidly analyze the attenuation primary and secondary conditions of different positive electrode active materials in the lithium ion battery with the mixed positive electrode material, and provides a targeted improvement measure for the design of a battery system with the mixed positive electrode material.
Description
Technical Field
The invention belongs to the field of battery testing, and particularly relates to a battery capacity attenuation analysis method.
Background
The lithium ion battery has the characteristics of high specific energy, high voltage, long cycle and the like, and is widely applied in the fields of consumption, power, energy storage and the like. In view of the stringent standards of batteries in terms of high safety and the urgent demands for improving energy density, the effect of positive electrode materials on battery performance is increasingly receiving attention. Currently, commonly used positive electrode active materials of lithium ion batteries include ternary materials such as Lithium Cobalt Oxide (LCO), lithium Manganate (LMO), lithium iron phosphate (LFP), nickel Cobalt Manganese (NCM) or Nickel Cobalt Aluminum (NCA), and the like. However, a single positive electrode active material cannot bring the battery performance into play optimally, and in actual production, a plurality of positive electrode active materials of different types are mixed to form a mixed positive electrode material, so that the advantages of different positive electrode active materials are complemented, and the electrochemical performance which is more balanced than that of a single positive electrode active material is obtained, so that the method for improving the electrochemical performance of the lithium ion battery is realized. Through long-time experiments and screening, LCO-NCM (NCA) mixed positive electrode materials, LMO-NCM (NCA) mixed positive electrode materials, LFP-NCM (NCA) mixed positive electrode materials and other mixed positive electrode materials are practically applied.
For the lithium ion battery with the mixed positive electrode material, the loss of the active materials is complex because the mixed positive electrode material contains different active material components, the intercalation/deintercalation behavior of lithium ions in one active material can be influenced by the other active material, and even the lithium ion diffusion coefficient and other material physical properties, all of the factors influence the charge and discharge performance and the voltage of the mixed positive electrode material. Taking lithium ion battery capacity fading of LCO-NCM mixed cathode material as an example, both the loss of LCO active material and the loss of NCM active material can cause the loss of LCO-NCM mixed cathode material. In the use process of the battery, the two positive electrode active materials LCO and NCM can show different decay rates due to the differences of lithium ion intercalation/deintercalation behaviors or uneven stress and the like, so that simpler and feasible technical means are needed for rapidly analyzing the positive electrode active materials mainly lost in a mixed positive electrode material battery system.
In the prior art, the capacity attenuation analysis of lithium ion batteries of mixed positive electrode materials lacks effective technical means, most of the lithium ion battery capacity attenuation analysis focused on single positive electrode active materials is performed by using a main analysis means which is damage detection, namely, the function of the active materials in the capacity attenuation of the batteries is determined through battery disassembly, pole piece observation and material test analysis. It has two disadvantages: on the one hand, it is important that the battery be reasonably and effectively disassembled before the sample is collected and screened. At present, manual disassembly or semi-automatic disassembly is mostly carried out, and hidden dangers such as short circuit, damage to key materials and the like exist in the disassembly process, so that the final active material failure analysis result can be influenced; on the other hand, such a destructive inspection requires expensive testing equipment and complicated operations, such as XRD (X-Ray Diffraction), SEM (Scanning Electron Micorscope, scanning electron microscope), etc., which are not only demanding on testing conditions and samples, but also costly, and from the standpoint of efficiency and efficiency, it is more desirable to develop an analysis method with high efficiency, accuracy and universality based on the existing conventional testing techniques, which puts higher demands on designing test analysis procedures.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a battery capacity attenuation analysis method.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a battery capacity fade analysis method comprising the steps of:
n batteries C are prepared by N different positive electrode active materials in the mixed positive electrode material 1 、C 2 、…C n ；
(II) Battery C 1 、C 2 、…C n Performing parallel charge and discharge and independent charge and discharge tests; and judging the influence primary-secondary relation of different positive electrode active materials on the capacity attenuation of the battery by comparing the difference value of the full-charge voltage of the same battery during parallel charging and discharging with the full-charge voltage of the same battery during independent charging and discharging and comparing the difference value of the empty-charge voltage of the same battery during parallel charging and discharging with the empty-charge voltage of the same battery during independent charging and discharging.
The specific steps of the step (II) are as follows:
s1, battery C 1 、C 2 、…C n Parallel connection is carried out, the batteries are separated after the batteries are charged to a full-charge state by constant current, the batteries are stood still and the parallel full-charge voltage of each battery is recorded and is recorded as V A1 、V A2 、…V An ；
S2: full battery C in step S1 1 、C 2 、…C n Discharging to the idle state with constant current, standing, and recording the idle voltage of each battery, denoted as V B1 、V B2 、…V Bn ；
S3, the hollow electric battery C in the step S2 1 、C 2 、…C n Charging to full state with constant current, standing, and recording full voltage of each battery, denoted as V C1 、V C2 、…V Cn ；
S4: full battery C in step S3 1 、C 2 、…C n Then the batteries are connected in parallel, the batteries are separated immediately after the constant current is discharged to the empty state, the batteries are stood still and the parallel empty voltage of each battery is recorded, and the V is recorded D1 、V D2 、…V Dn ；
S5: full-charge voltage V when the same battery is charged and discharged in parallel A1 、V A2 、…V An Voltage V of air-electricity D1 、V D2 、…V Dn Full-charge voltage V when charging and discharging independently C1 、V C2 、…V Cn Voltage V of air-electricity B1 、V B2 、…V Bn And performing differential comparison analysis to judge the influence primary and secondary relation of each component active material in the mixed positive electrode material on the capacity attenuation of the battery.
The judging method in the step S5 is as follows:
ΔV full (1) ＝V A1 -V C1 ，ΔV Air (1) ＝V D1 -V B1 ；
ΔV Full (2) ＝V A2 -V C2 ，ΔV Air (2) ＝V D2 -V B2 ；
…
ΔV Full (n) ＝V An -V Cn ，ΔV Air (n) ＝V Dn -V Bn ；
Comparison of DeltaV Full (1) 、ΔV Full (2) …ΔV Full (n) The larger the numerical value is, the corresponding battery prepared by the positive electrode active material is overcharged, the corresponding positive electrode active material is excessive in lithium ion removal, the structure of the positive electrode material in the battery is changed, the reversibility is damaged, and the capacity of the battery is attenuated;
comparison of DeltaV Air (1) 、ΔV Air (2) …ΔV Air (n) The smaller the numerical value is, the corresponding battery prepared by the positive electrode active material is overdischarged, the corresponding positive electrode active material is excessively embedded with lithium ions, the volume of the positive electrode material is excessively expanded, and the capacity loss of the battery is caused.
In the step (one), n=2 to 4. Preferably n=2.
Step S1 is the same as the charging system in step S3; step S2 is identical to the discharge system in step S4.
The charging system in the step S1 is I A Constant current is charged to 4.4V of full voltage; wherein I is A < 1C; preferably, I A ＝0.5C。
The discharge system in the step S2 is I B Discharging constant current to 3V; wherein I is B < 1C; preferably, I B ＝0.5C。
The rest time in steps S1, S2, S3, S4 is 10-60 minutes, preferably 30 minutes.
And (II) placing the battery in a constant temperature box for testing, and keeping the temperature constant at 20-60 ℃.
The battery in the step (II) is a fresh battery or a circulating battery after circulating for a certain number of times.
Compared with the prior art, the invention has the beneficial effects that:
according to the technical scheme, the complex physical and chemical reaction process of the mixed positive electrode material in the battery is simulated through the battery parallel test analysis method, the influence weight and the primary and secondary relation of the mixture of various positive electrode active materials in a certain stage are reversely analyzed, the capacity attenuation of the mixed positive electrode material can be accurately estimated, hidden dangers such as damage to the active materials due to disassembly of the battery are avoided, dynamic analysis can be carried out on the battery capacity attenuation in different temperature working conditions (normal temperature or high temperature) and different cycle periods on the basis of a conventional test technology, and the method can simply, nondestructively and rapidly analyze the attenuation primary and secondary situations of different positive electrode active materials in the lithium ion battery of the mixed positive electrode material, so that a targeted improvement measure is provided for the design of a battery system of the mixed positive electrode material.
Drawings
FIG. 1 is a graph showing the cycle performance of LCO and NCM lithium-ion pouch cells of the present application cycled 100 times at 45 ℃;
fig. 2 is a graph showing the cycle performance at 45 ℃ of an improved battery prepared from the LCO-NCM hybrid positive electrode material according to the present embodiment.
Detailed Description
The present invention will be described in further detail below with reference to the drawings and preferred embodiments, so that those skilled in the art can better understand the technical solutions of the present invention.
Example 1
In this application, n=2 (N may be 3 or 4), specifically, LCO-NCM mixed cathode material; LCO (lithium cobalt oxide) material has high platform voltage, high compaction density and high price; NCM (Nickel cobalt manganese) materials have high capacity, high energy density and relatively low price. The synergistic effect can be exerted by mixing the LCO and NCM positive electrode active materials, so that the energy density of the battery is improved, and the manufacturing cost of the battery is reduced. However, when the two materials are mixed for charging and discharging, the deintercalation behavior of lithium ions in LCO or NCM may be affected by another active material, so that differences such as lithium ion diffusion coefficient or material stress may present different attenuation rates of LCO and NCM, and the loss of LCO active material and the loss of NCM active material may cause the loss of LCO-NCM mixed positive electrode material, which will affect the charging and discharging curve and voltage of the mixed positive electrode material lithium ion battery, resulting in rapid attenuation of battery capacity. The attenuation of the LCO-NCM mixed cathode material can be accelerated along with the increase of the service temperature of the battery or the extension of the cycle period, so that the main and secondary attenuation conditions of LCO and NCM can be rapidly identified and analyzed, and the improvement of the cycle performance of the lithium ion battery of the LCO-NCM mixed cathode material is necessary;
the battery capacity fade analysis method comprises the following steps:
LCO and NCM in the mixed positive electrode active material are respectively used as single positive electrode active material, and are matched with the same negative electrode, diaphragm and electrolyte to prepare the 4Ah lithium ion soft package battery C according to the same formula and process 1 (the positive electrode active material is LCO, hereinafter referred to as LCO soft-pack battery), C 2 (the positive electrode active material is NCM, hereinafter referred to as NCM pouch cell);
(II) in a constant temperature box at 25 ℃, adopting a battery charging and discharging device to charge the fresh battery C 1 、C 2 Performing parallel charge and discharge and independent charge and discharge tests; and judging the influence primary-secondary relation of different positive electrode active materials on the capacity attenuation of the battery by comparing the difference value of the full-charge voltage of the same battery during parallel charging and discharging with the full-charge voltage of the same battery during independent charging and discharging and comparing the difference value of the empty-charge voltage of the same battery during parallel charging and discharging with the empty-charge voltage of the same battery during independent charging and discharging.
The method specifically comprises the following steps:
s1: firstly, connecting an LCO soft package battery and an NCM soft package battery in parallel, immediately separating the batteries after the LCO soft package battery and the NCM soft package battery are charged to 4.4V full voltage with constant current of 0.5 ℃, standing for 30min, and recording the parallel full voltage V of the batteries A V respectively A1 、V A2 The method comprises the steps of carrying out a first treatment on the surface of the The results are shown in Table1 shows; v (V) A1 ＝4366mV、V A2 ＝4385mV；
S2: discharging the full-charge battery of the previous step to 3V at constant current of 0.5C, standing for 30min, and recording the independent empty-charge voltage V of the battery B V respectively B1 、V B2 The method comprises the steps of carrying out a first treatment on the surface of the The results are shown in table 1;
s3: the empty battery in the last step is respectively charged to 4.4V of full charge voltage at 0.5C constant current, the rest is carried out for 30min, and the independent full charge voltage V of the battery is recorded c V respectively C1 、V C2 ；
S4: the full-power batteries in the last step are connected in parallel, the batteries are immediately separated after being discharged to 3V by 0.5C constant current, the batteries are placed for 30min, and the parallel empty-power voltages V of the batteries are respectively recorded D V respectively D1 、V D2 ；
S5, parallel full-charge voltage V of the same battery A1 、V A2 And a single full power voltage V C1 、V C2 Parallel air-to-electric voltage V D1 、V D2 With a separate space-electricity voltage V B1 、V B2 And performing difference processing to obtain a voltage difference value between the LCO battery and the NCM battery when the LCO battery and the NCM battery are charged and discharged in parallel and are charged and discharged independently.
ΔV Full of ＝V A -V C ，ΔV Empty space ＝V D -V B ；
The method comprises the following steps: deltaV Full (1) ＝V A1 -V C1 ，ΔV Air (1) ＝V D1 -V B1 ；
ΔV Full (2) ＝V A2 -V C2 ，ΔV Air (2) ＝V D2 -V B2 ；
Wherein 1 represents a first positive electrode active material; 2 represents a second positive electrode active material; deltaV Full (1) The full-charge voltage difference value between the parallel connection and the independent charge and discharge of the LCO battery as the first positive electrode active material is obtained; deltaV Air (1) The first positive electrode active material battery LCO is connected in parallel with an empty electric voltage difference value when being charged and discharged independently; deltaV Full (2) The full-charge voltage difference value between the parallel connection and the independent charge and discharge of the second positive electrode active material battery NCM is obtained; deltaV Air (2) The second positive electrode active material battery NCM is connected in parallel with an empty electric voltage difference value when being charged and discharged independently; the values are shown in Table 1.
TABLE 1
| Testing battery | V A /mV | V B /mV | V C /mV | V D /mV | ΔV Full of /mV | ΔV Empty space /mV |
| LCO-1# | 4366 | 3330 | 4383 | 3169 | -17 | -161 |
| LCO-2# | 4369 | 3333 | 4383 | 3166 | -14 | -167 |
| NCM-1# | 4385 | 3442 | 4365 | 3457 | 20 | 15 |
| NCM-2# | 4383 | 3441 | 4365 | 3457 | 18 | 16 |
Wherein LCO-1# and NCM-1# are subjected to parallel connection test, LCO-2# and NCM-2# are subjected to parallel connection test. As can be seen from the comparison of the data in table 1, the NCM parallel full voltage is about 19mV higher than the full voltage alone, which is an overcharged state; LCO parallel full voltage is about 16mV lower than single full voltage, and is in shallow charge state; the NCM parallel null voltage is about 16mV higher than the independent null voltage and is in a shallow discharge state; LCO parallel connection air-electric voltage is about 163mV lower than single air-electric voltage, and is in over-discharge state; considering that the mixed positive electrode material actually discharges and intercalates lithium in the battery to reach an equilibrium potential, deltaV Full (NCM) Greater than DeltaV Full (LCO) The NCM in the LCO-NCM mixed type positive electrode material is excessively extracted from lithium ions, so that the structure of the NCM positive electrode material is collapsed, and the irreversible loss of the battery capacity is caused, therefore, the LCO-NCM mixed type positive electrode material takes the loss of the NCM active material as a main influence, and the capacity of the lithium ion battery based on the mixed type positive electrode material is sharply attenuated.
Further, LCO and NCM lithium ion soft package batteries are placed in a 45 ℃ incubator, and the batteries are subjected to 100-cycle test by adopting battery charging and discharging equipment. The cycle test system is that 1C is charged for 30min, then 0.7C is charged to 4.4V, the current of 0.05C is cut off, and then 0.5C is discharged to 3V, which is a cycle period.
Then parallel charge and discharge and independent charge and discharge tests are carried out, and the specific process is as follows:
s1: firstly, connecting LCO and NCM lithium ion soft package batteries after 100 times of circulation in parallel, charging the batteries to 4.4V full charge voltage with 0.5C constant current, immediately separating the batteries, standing for 30min, and respectively recording the parallel full charge voltage V of the batteries A V respectively A1 、V A2 ；
S2: discharging the full-charge battery of the previous step to 3V at constant current of 0.5C, standing for 30min, and recording the independent empty-charge voltage V of the battery B V respectively B1 、V B2 ；
S3: the empty batteries in the last step are respectively charged to 4.4V of full charge voltage at 0.5C constant current, the rest is carried out for 30min, and the independent full charge voltage V of the batteries is respectively recorded c V respectively C1 、V C2 ；
S4: the full-power batteries in the last step are connected in parallel, the batteries are immediately separated after being discharged to 3V by 0.5C constant current, the batteries are placed for 30min, and the parallel empty-power voltages V of the batteries are respectively recorded D V respectively D1 、V D2 ；
Further, the parallel full voltage V of the same battery is performed on the recorded detailed voltage data A1 、V A2 And a single full power voltage V C1 、V C2 Parallel air-to-electric voltage V D1 、V D2 With a separate space-electricity voltage V A1 、V A2 And performing difference treatment to obtain the voltage difference value between the LCO battery and the NCM battery after 100 times of circulation when the LCO battery and the NCM battery are charged and discharged in parallel and are charged and discharged independently.
ΔV Full (1) ＝V A1 -V C1 ，ΔV Air (1) ＝V D1 -V B1 ；
ΔV Full (2) ＝V A2 -V C2 ，ΔV Air (2) ＝V D2 -V B2 ；
Wherein 1 represents a first positive electrodeAn active material; 2 represents a second positive electrode active material; deltaV Full (1) The full-charge voltage difference value between the parallel connection and the independent charge and discharge of the LCO battery as the first positive electrode active material is obtained; deltaV Air (1) The first positive electrode active material battery LCO is connected in parallel with an empty electric voltage difference value when being charged and discharged independently; deltaV Full (2) The full-charge voltage difference value between the parallel connection and the independent charge and discharge of the second positive electrode active material battery NCM is obtained; deltaV Air (2) The second positive electrode active material battery NCM is connected in parallel with an empty electric voltage difference value when being charged and discharged independently;
and the magnitude relation of full-power voltage difference or empty-power voltage difference is also compared, and the main attenuation active material of the LCO-NCM mixed cathode material after the high-temperature cycle of 45 ℃ for 100 times is obtained through analysis. Table 2 is the voltage values of the lithium ion soft pack battery after 100 cycles at 45 ℃ for parallel charge and discharge and independent charge and discharge;
TABLE 2
| Testing battery | V A /mV | V B /mV | V C /mV | V D /mV | ΔV Full of /mV | ΔV Empty space /mV |
| LCO-1# | 4374 | 3276 | 4387 | 3388 | -13 | 112 |
| LCO-2# | 4375 | 3277 | 4388 | 3378 | -13 | 101 |
| NCM-1# | 4369 | 3423 | 4355 | 3489 | 14 | 66 |
| NCM-2# | 4369 | 3427 | 4354 | 3495 | 15 | 68 |
Also, as can be seen from the comparison of the data in table 2, the NCM parallel full voltage is about 15mV (average, the same applies below) higher than the full voltage alone, which is an overcharged state; LCO parallel full voltage is about 13mV lower than single full voltage, and is in shallow charge state; the NCM parallel void voltage is about 67mV higher than the individual void voltage, and is in a shallow discharge state; LCO parallel connection air-electric voltage is about 105mV higher than single air-electric voltage and is in shallow discharge shapeA state; therefore DeltaV Full (NCM) Greater than DeltaV Full (LCO) The NCM in the LCO-NCM mixed positive electrode material is excessive in lithium ion removal, so that the structure of the NCM positive electrode material collapses, and the battery capacity is irreversibly lost, therefore, the LCO-NCM mixed positive electrode material is mainly lost of the NCM active material after 100 cycles at a high temperature of 45 ℃, and the lithium ion battery capacity based on the mixed positive electrode material is rapidly attenuated.
As shown in fig. 1, when the lithium ion soft-pack battery with LCO and NCM as single positive electrode active materials in the mixed positive electrode material is circulated for 100 times at a high temperature of 45 ℃, the capacity retention rate of the LCO battery is obviously higher than that of the NCM battery, which also proves that the LCO-NCM mixed positive electrode material battery system is really based on the loss of the active materials with the NCM as the main active materials, and the attenuation of the whole capacity of the battery is caused.
As shown in fig. 2, the capacity of the LCO-NCM hybrid positive electrode material battery is rapidly attenuated due to the main activity loss of the NCM material in the hybrid positive electrode material, so that the improvement and optimization of the hybrid positive electrode material battery system are performed with respect to the performance of the NCM material, mainly considering the suitability problem of the electrolyte and the hybrid positive electrode material, and on the basis of the original electrolyte (including 15% lithium hexafluorophosphate, 25% ethylene carbonate, 60% methyl ethyl carbonate) design, a fluorinated solvent or an additive (including 15% lithium hexafluorophosphate, 17% ethylene carbonate, 51% ethylene carbonate, and 17% trifluoroacetic acid) is used, so that a stable electrode-electrolyte interface can be constructed on the NCM surface, the cracking of secondary particles is reduced, the contact area between the positive electrode and the electrolyte is reduced, the poor electrical contact, the side reaction and the dissolution of transition metal ions are greatly inhibited, and the obstacles such as serious NCM capacity attenuation are overcome. The capacity retention rate of the improved LCO-NCM mixed positive electrode material battery is improved under the high-temperature cycle of 45 ℃, and the improved LCO-NCM mixed positive electrode material battery has targeted guiding significance for improving the battery performance and designing a battery system.
In summary, the technical scheme of the application simulates the complex physicochemical reaction process of the mixed positive electrode material in the battery through the battery parallel test analysis method, reversely analyzes the influence weight and primary and secondary relation of the mixture of various positive electrode active materials at a certain stage, can accurately evaluate the capacity attenuation of the mixed positive electrode material, not only avoids hidden danger of breaking the active materials due to disassembly of the battery, but also can dynamically analyze the capacity attenuation of the battery under different temperature working conditions (normal temperature or high temperature) and different cycle periods on the basis of the conventional test technology.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. A battery capacity fade analysis method, comprising the steps of:
n batteries C are prepared by N different positive electrode active materials in the mixed positive electrode material 1 、C 2 、…C n ；
(II) Battery C 1 、C 2 、…C n Performing parallel charge and discharge and independent charge and discharge tests; and judging the influence primary-secondary relation of different positive electrode active materials on the capacity attenuation of the battery by comparing the difference value of the full-charge voltage of the same battery during parallel charging and discharging with the full-charge voltage of the same battery during independent charging and discharging and comparing the difference value of the empty-charge voltage of the same battery during parallel charging and discharging with the empty-charge voltage of the same battery during independent charging and discharging.
2. The battery capacity fade analysis method according to claim 1, wherein the specific steps of step (two) are:
s1, battery C 1 、C 2 、…C n Parallel connection is carried out, the batteries are separated after the constant current is charged to a full state, and the batteries are stood still and recordedFull charge voltage, denoted as V A1 、V A2 、…V An ；
S2: full battery C in step S1 1 、C 2 、…C n Discharging to the idle state with constant current, standing, and recording the idle voltage of each battery, denoted as V B1 、V B2 、…V Bn ；
S3, the hollow electric battery C in the step S2 1 、C 2 、…C n Charging to full state with constant current, standing, and recording full voltage of each battery, denoted as V C1 、V C2 、…V Cn ；
S4: full battery C in step S3 1 、C 2 、…C n Then the batteries are connected in parallel, the batteries are separated immediately after the constant current is discharged to the empty state, the batteries are stood still and the parallel empty voltage of each battery is recorded, and the V is recorded D1 、V D2 、…V Dn ；
S5: full-charge voltage V when the same battery is charged and discharged in parallel A1 、V A2 、…V An Voltage V of air-electricity D1 、V D2 、…V Dn Full-charge voltage V when charging and discharging independently C1 、V C2 、…V Cn Voltage V of air-electricity B1 、V B2 、…V Bn And performing differential comparison analysis to judge the influence primary and secondary relation of each component active material in the mixed positive electrode material on the capacity attenuation of the battery.
3. The battery capacity fade analysis method according to claim 2, characterized in that the method judged in step S5 is:
ΔV full (1) ＝V A1 -V C1 ，ΔV Air (1) ＝V D1 -V B1 ；
ΔV Full (2) ＝V A2 -V C2 ，ΔV Air (2) ＝V D2 -V B2 ；
…
ΔV Full (n) ＝V An -V Cn ，ΔV Air (n) ＝V Dn -V Bn ；
Comparison of DeltaV Full (1) 、ΔV Full (2) …ΔV Full (n) The larger the numerical value is, the corresponding battery prepared by the positive electrode active material is overcharged, the corresponding positive electrode active material is excessive in lithium ion removal, the structure of the positive electrode material in the battery is changed, the reversibility is damaged, and the capacity of the battery is attenuated;
comparison of DeltaV Air (1) 、ΔV Air (2) …ΔV Air (n) The smaller the numerical value is, the corresponding battery prepared by the positive electrode active material is overdischarged, the corresponding positive electrode active material is excessively embedded with lithium ions, the volume of the positive electrode material is excessively expanded, and the capacity loss of the battery is caused.
4. The battery capacity fade analysis method according to claim 1, characterized in that n=2 to 4 in step (1); preferably n=2.
5. The battery capacity fade analysis method according to claim 2, characterized in that step S1 is the same as the charging system in step S3; step S2 is identical to the discharge system in step S4.
6. The method of claim 5, wherein the charging system of step S1 is defined as I A Constant current is charged to 4.4V of full voltage; wherein I is A < 1C; preferably, I A ＝0.5C。
7. The method of claim 5, wherein the discharging system in step S2 is defined as I B Discharging constant current to 3V; wherein I is B < 1C; preferably, I B ＝0.5C。
8. The battery capacity fade analysis method according to claim 1, characterized in that the rest time in steps S1, S2, S3, S4 is 10 to 60 minutes, preferably 30 minutes.
9. The method of analyzing the capacity fade of a battery according to claim 6, wherein in the step (two), the battery is placed in an incubator for testing at a constant temperature of 20 to 60 ℃.
10. The method of claim 1, wherein the battery in the second step is a fresh battery or a recycled battery after a certain number of cycles.
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