CN114563537B - Method for rapidly judging cycle life of lithium iron phosphate battery - Google Patents
Method for rapidly judging cycle life of lithium iron phosphate battery Download PDFInfo
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- CN114563537B CN114563537B CN202210462529.XA CN202210462529A CN114563537B CN 114563537 B CN114563537 B CN 114563537B CN 202210462529 A CN202210462529 A CN 202210462529A CN 114563537 B CN114563537 B CN 114563537B
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- 238000000034 method Methods 0.000 title claims abstract description 29
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 131
- 229910010707 LiFePO 4 Inorganic materials 0.000 claims abstract description 34
- 229910052742 iron Inorganic materials 0.000 claims abstract description 34
- 239000000463 material Substances 0.000 claims abstract description 33
- 239000007774 positive electrode material Substances 0.000 claims abstract description 30
- 239000000654 additive Substances 0.000 claims abstract description 27
- 230000000996 additive effect Effects 0.000 claims abstract description 23
- 238000004090 dissolution Methods 0.000 claims abstract description 17
- 230000003749 cleanliness Effects 0.000 claims abstract description 12
- 239000010405 anode material Substances 0.000 claims abstract description 11
- 239000002131 composite material Substances 0.000 claims abstract description 9
- 238000012360 testing method Methods 0.000 claims abstract description 9
- 229910010710 LiFePO Inorganic materials 0.000 claims abstract description 8
- 239000000243 solution Substances 0.000 claims description 23
- 230000014759 maintenance of location Effects 0.000 claims description 21
- 238000002156 mixing Methods 0.000 claims description 19
- 239000012535 impurity Substances 0.000 claims description 14
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 13
- DGEZNRSVGBDHLK-UHFFFAOYSA-N [1,10]phenanthroline Chemical compound C1=CN=C2C3=NC=CC=C3C=CC2=C1 DGEZNRSVGBDHLK-UHFFFAOYSA-N 0.000 claims description 9
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims description 8
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 8
- 238000002835 absorbance Methods 0.000 claims description 6
- 229960005070 ascorbic acid Drugs 0.000 claims description 6
- 235000010323 ascorbic acid Nutrition 0.000 claims description 6
- 239000011668 ascorbic acid Substances 0.000 claims description 6
- 239000003792 electrolyte Substances 0.000 claims description 6
- 239000011259 mixed solution Substances 0.000 claims description 6
- 239000002253 acid Substances 0.000 claims description 5
- 239000000126 substance Substances 0.000 claims description 5
- 229910052782 aluminium Inorganic materials 0.000 claims description 4
- 239000010406 cathode material Substances 0.000 claims description 4
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 claims description 3
- SBLRHMKNNHXPHG-UHFFFAOYSA-N 4-fluoro-1,3-dioxolan-2-one Chemical compound FC1COC(=O)O1 SBLRHMKNNHXPHG-UHFFFAOYSA-N 0.000 claims description 3
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims description 3
- 239000003929 acidic solution Substances 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 230000000694 effects Effects 0.000 claims description 3
- VEWLDLAARDMXSB-UHFFFAOYSA-N ethenyl sulfate;hydron Chemical compound OS(=O)(=O)OC=C VEWLDLAARDMXSB-UHFFFAOYSA-N 0.000 claims description 3
- 238000010828 elution Methods 0.000 claims description 2
- -1 methylene methyl Chemical group 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims 1
- 238000001514 detection method Methods 0.000 abstract description 10
- 238000004519 manufacturing process Methods 0.000 abstract description 3
- 238000012545 processing Methods 0.000 abstract description 2
- 239000002994 raw material Substances 0.000 abstract description 2
- 238000011156 evaluation Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- 239000002033 PVDF binder Substances 0.000 description 3
- 239000011230 binding agent Substances 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000006256 anode slurry Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 2
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 238000002798 spectrophotometry method Methods 0.000 description 2
- 229920003048 styrene butadiene rubber Polymers 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- GWAOOGWHPITOEY-UHFFFAOYSA-N 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide Chemical compound O=S1(=O)CS(=O)(=O)OCO1 GWAOOGWHPITOEY-UHFFFAOYSA-N 0.000 description 1
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000002174 Styrene-butadiene Substances 0.000 description 1
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 239000006257 cathode slurry Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000011267 electrode slurry Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 1
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Images
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
- G01N21/73—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using plasma burners or torches
-
- 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
Abstract
The invention provides a method for rapidly judging the cycle life of a lithium iron phosphate battery, namely LiFePO tested by 4 methods 4 Rapid composite detection index of anode material for rapidly evaluating LiFePO 4 Cycle life of the positive electrode material. The composite detection indexes are respectively Fe 3+ And Fe 2+ Content index, iron dissolution rate index, cleanliness index and effective additive index, and weighting the four judgment indexes by a composite influence factor to judge LiFePO 4 Cycle life of the positive electrode material. The detection method is efficient, simple and convenient, can save a large amount of raw material cost, processing cost and long-period cost in battery manufacturing, and saves a large amount of manpower and material resources required in the circulating test.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a method for quickly judging the cycle life of a lithium iron phosphate battery.
Background
At present, the service life of the lithium ion battery is judged, and the battery generally needs to be subjected to long-time cycle test. In the period, the test condition, the environment change, the sudden failure and other condition changes are easily influenced, and huge manpower and material resources are consumed for carrying out long-term test. Therefore, the method for rapidly, simply and effectively judging the cycle life of the lithium iron phosphate battery is very important.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for quickly judging the cycle life of a lithium iron phosphate battery.
The purpose of the invention is realized by the following scheme:
the invention provides a method for quickly judging the cycle life of a lithium iron phosphate battery, which comprises the following steps:
determination of Fe 3+ And Fe 2+ The content index is as follows: spectrophotometric method for determining Fe in material 3+ Content and Fe 2+ And (4) content. LiFePO is added 4 Mixing the anode material with HCl solution, and detecting the concentration C of the iron element content in the solution Fe 3+ And C Fe 2+ To determine the content of ferric iron and ferrous iron in the positive electrode material;
and (3) determining the iron dissolution rate index: mixing LiFePO 4 Mixing the positive electrode material with a strong acid solution, reacting for 1-180min, and detecting the concentration M of the iron element content in the solution Fe So as to determine the dissolved iron amount of the mixed reaction at different time periods to judge the Fe dissolution rate in the positive electrode material;
and (3) determining cleanliness indexes: for LiFePO 4 Carrying out magnetic bar enrichment on the positive electrode material, then testing the enriched material on the magnetic bar by using a cleanliness meter, and judging LiFePO 4 The content percentage Q of the iron simple substance and other magnetic impurity materials contained in the anode material im /Q all ；
And (3) determining the effective additive index: calculating the effective additive content in the battery cell electrolyte to LiFePO 4 Ratio m of positive electrode material add /m Fe Effective additive pair LiFePO has been determined 4 Influence of the positive electrode material;
weighting the four judgment indexes to obtain a final judgment numerical value F:
wherein the constant influence factor a =0.1407 to 0.1431; b = -0.0511 to-0.0349; c =0.4632 to 0.4697; d = 0.0098 to 0.0092, e =0.0904 to 0.0982; f = -3.5811-2.0957; g =0.2466 to 0.2481; h =14.222 to 15.746; when only 1-3 indexes are selected from 4 indexes, the influence factor of the index constant without any index is 0. The cycle life impact factor F represents the predicted percent decay versus the normal cycle cell.
Preferably, fe is measured 2+ The content is specifically determined by LiFePO 4 Mixing the positive electrode material with HCl solution, adding 1,10-phenanthroline, and adding Fe when PH =2~9 2+ Generating orange red complex with 1,10-phenanthroline, and measuring absorbance of the filtered mixed solution at different concentrations at absorption wavelength (510 nm) of spectrophotometer to determine C Fe 2+ 。
Preferably, fe is measured 3+ The content is specifically LiFePO 4 Mixing the positive electrode material with HCl solution, adding ascorbic acid to obtain Fe in the solution 3+ All reduced to Fe 2+ Adding 1,10-phenanthroline, measuring absorbance of the filtered mixed solution at 510nm, and calculating to obtain total iron content, namely LiFePO 4 Fe in positive electrode material 3+ The content is equal to the total iron content minus Fe determined without ascorbic acid 2+ And (4) content.
Preferably, the specific method for determining the iron dissolution rate index is as follows: mixing LiFePO 4 Mixing the positive electrode material with a strong acid solution, measuring the iron dissolving amount by ICP method at different time, wherein the reaction time can be 1-180min, preferably 10-90min, more preferably 30-45min, and detecting the concentration M of the iron element content in the solution Fe (in the index of iron dissolution rate, the total of the concentrations of ferrous and ferric iron measured by ICP method) to determine the content of the positive electrode materialThe dissolution rate of Fe. The initial concentration of the strongly acidic solution is 0.001-1.5 mol L -1 In the range of (1), preferably 0.05 to 1 mol L is used -1 The concentration range of (c). The concentration of iron dissolved is characterized in ppm.
Preferably, the other magnetic impurity material includes Ni, mn, al.
Preferably, the effective additive comprises the total content of one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate and methylene methanedisulfonate.
Compared with the prior art, the invention has the following beneficial effects:
1. the detection method is efficient, simple and convenient, can save a large amount of raw material cost, processing cost and long-period cost in battery manufacturing, and saves a large amount of manpower and material resources required in the circulating test.
2. According to the detection method, indexes are closely related to battery attenuation, and the cycle life of the battery can be accurately predicted.
3. The detection method can be used in the actual production process, and can quickly and effectively predict the cycle life of batteries using different anode materials.
4. The detection method is particularly suitable for LiFePO 4 The selection of the anode material can effectively control the LiFePO 4 To help select long-lived LiFePO 4 A material.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 shows different Fe values in examples 1 to 3 3+ /Fe 2+ A 45 ℃ actual measurement cycle life diagram of the content proportion;
FIG. 3 shows the capacity retention ratio and Fe fitted in examples 1 to 3 3+ /Fe 2+ A plot of the decay linear dependence of the content;
FIG. 4 is a graph of the measured cycle life at 45 ℃ for LFP materials of different iron dissolution rates in examples 1, 4 and 5;
FIG. 5 is a plot of fitted capacity retention versus decay rate of iron dissolution for examples 1, 4, and 5;
FIG. 6 is a graph of the measured cycle life at 45 ℃ for LFP materials of different cleanliness in examples 1, 6 and 7;
FIG. 7 is a graph of fitted capacity retention versus cleanliness decay linearity for examples 1, 6, and 7;
FIG. 8 is a graph of the measured cycle life at 45 ℃ for LFP materials of different effective additive ratios in examples 1, 8 and 9;
FIG. 9 is a plot of the fitted capacity retention versus the decay linear of the effective additive ratio for examples 1, 8, and 9;
FIG. 10 is a graph of cycle performance at 45 ℃ for different indexes of univariate cycle performance and all indexes of composite cycle performance in examples 1, 2, 4, 6, 8 and 10.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
In the detection method of the invention, liFePO tested by 4 methods 4 Rapid composite detection index of anode material for rapidly evaluating LiFePO 4 Cycle life of the positive electrode material. The composite detection indexes are respectively Fe 3+ And Fe 2+ Content index, iron dissolution rate index, cleanliness index and effective additive index, and weighting the four judgment indexes by a composite influence factor to judge LiFePO 4 Cycle life of the positive electrode material.
A constant influence factor a =0.1407 to 0.1431; b = -0.0511 to-0.0349; c =0.4632 to 0.4697; d = 0.0098 to 0.0092, e =0.0904 to 0.0982; f = -3.5811-2.0957; g =0.2466 to 0.2481; h =14.222 to 15.746; when only 1-3 indexes are included in the 4 indexes, the influence factor of the index constant not included takes a value of 0. Wherein the content of the first and second substances,
、C Fe 2+ is Fe 3+ And Fe 2+ The content concentration is in ppm; m Fe The concentration of iron element is expressed in ppm; q im /Q all Is LiFePO 4 The content percentage of iron (Fe) and other magnetic impurity materials (possibly including Ni, mn and Al) contained in the cathode material. Q im Indicates the number of particles of impurity material (Q is an abbreviation for Quantity, im is an abbreviation for impurity); q all Indicates the number of all particles extracted by adsorption on the magnetic bar, including LiFePO 4 Particles of materials and particles of various impurities; m is add /m Fe Is the ratio of the effective additive content in the electrolyte of the cell to the lithium iron phosphate material, m add Represents the mass of effective additive contained in the electrolyte and has the unit of g (m is the abbreviation of mass, and add is the abbreviation of additives); m is Fe Indicating LiFePO in the cell 4 The mass of the material is given in g.
Example 1
As shown in fig. 1, a method for rapidly determining the cycle life of a lithium iron phosphate battery includes the following steps:
(1) Determination of Fe 3+ And Fe 2+ The content index is as follows: spectrophotometry method for determining Fe in material 3+ Content and Fe 2+ And (4) content.
2g of LiFePO 4 Mixing the positive electrode material with HCl solution, adding 1,10-phenanthroline, and adding Fe when PH =2~9 2+ Reacting with 1,10-phenanthroline to obtain orange red complex at 25 deg.C for 20min, and measuring the absorption wavelength (510 nm) of the filtered mixed solution in spectrophotometerDetermining the absorbance of the sample at different concentrations to determine C Fe 2+ 。
2g of LiFePO 4 Mixing the positive electrode material with HCl solution, adding ascorbic acid to obtain Fe in the solution 3+ All reduced to Fe 2+ Then 1,10-phenanthroline is added, the absorbance of the filtered mixed solution at 510nm is measured, and the total iron content, namely LiFePO, is obtained through calculation 4 C in the positive electrode material Fe 3+ The content is equal to the total iron content minus Fe determined without ascorbic acid 2+ Content of C is thereby obtained Fe 3+ /C Fe 2+ (ppm)=20。
Measuring the iron dissolution rate index: 2g of LiFePO 4 Cathode material and HCl/HNO 3 Solution (initial concentration at 0.5mol L) -1 ) Mixing, measuring dissolved iron amount by ICP method at 45 deg.C for 35min, and detecting iron content concentration M in the solution Fe 153ppm to determine the Fe elution rate in the positive electrode material.
And (3) determining cleanliness indexes: for 150g LiFePO 4 Performing magnetic bar enrichment on the positive electrode material, testing the enriched material on the magnetic bar by using a cleanliness meter, determining LiFePO, wherein the magnetic adsorption time is 30min, the reaction temperature is 25 ℃, the particle identification size interval is 15-1000 mu m 4 The content percentage Q of iron simple substance and other magnetic impurity materials (including Ni, mn and Al) contained in the anode material im /Q all Is 0.775%.
And (3) determining the effective additive index: selecting the same LiFePO 4 And preparing the positive electrode material into a battery.
The process for making the cell is as follows:
firstly, mixing slurry, wherein the anode slurry is prepared from small-particle lithium iron phosphate: conductive carbon black (SuperP), binder (polyvinylidene fluoride PVDF _ 5130), dispersant (polyvinylpyrrolidone PVP _ 30) =100: 2: 2.5: 0.5.
The negative electrode slurry comprises the following components in percentage by weight: conductive agent (Super P): binder (styrene butadiene rubber SBR): binder (sodium carboxymethylcellulose CMC — 500): h 2 O=100：2：2：0.8：99。
And then coating, namely coating the anode slurry on an aluminum foil, coating the cathode slurry on a copper foil, drying and rolling. Then, rolling is performed, and then slitting is performed. Then winding the pole core, and using the manufactured positive and negative pole pieces and the diaphragm, wherein the diaphragm adopts a PP diaphragm (12 mu m basal membrane +2 mu m Al) 2 O 3 Ceramic layer +1 μm PVDF glue layer). And (3) after the wound pole core is hot-pressed, welding the top cover, and then assembling the pole core into a shell to prepare the dry cell core.
And (4) injecting liquid after the dry battery cell is baked, and then carrying out formation and grading to obtain a finished product battery cell.
Calculating the effective additive content in the battery cell electrolyte to LiFePO 4 Ratio m of positive electrode material add /m Fe 0.4 to determine the effective additive to LiFePO 4 Influence of the positive electrode material; the effective additives include vinylene carbonate, fluoroethylene carbonate, vinyl sulfate and methylene methyl disulfonate.
Weighting the four judgment indexes to obtain a final judgment numerical value F:
wherein the constant impact factor a =0.1428; b = -0.0351; c =0.4667; d = -0.0095; e =0.0952; f = -2.1963; g =0.2476,h =15.664
The F value was calculated to be 89.7813. And performing fixed-point life prediction at a certain fixed turn number according to the F value, wherein the 500 th turn is used, and the predicted capacity retention rate is predicted to be the calculated F value at the 500 th turn.
Example 2 differs from example 1 only in that: constant impact factor a =0.1407; b = -0.0511; c =0.4632; d = -0.0098; e =0.0904; f = -3.5811; g =0.2466, h =14.222, and specific measurement values of the four indices and the calculated F value are shown in table 1.
Example 3 differs from example 1 only in that: constant impact factor a =0.1407; b = -0.0511; c =0.4632; d = -0.0098; e =0.0904; f = -3.5811; g =0.2466, h =14.222, and specific measurement values of the four indices and the calculated F value are shown in table 1.
The measurement methods of the four index parameters in examples 4 to 10 were the same as in example 1, and specific measurement values of the four indices and the calculated F value are shown in table 1.
Table 1, four index measurement values and F value of each example
| Battery with a battery cell | C Fe 3+ /C Fe 2+ (ppm) | M Fe (ppm) | Q im /Q all (%) | m add /m Fe | F value | |
| Example 1 | |
20 | 153 | 0.775 | 0.4 | 89.781 |
| Example 2 | |
74 | 138 | 0.823 | 0.4 | 88.067 |
| Example 3 | |
169 | 142 | 0.818 | 0.4 | 87.363 |
| Example 4 | |
18 | 586 | 0.792 | 0.4 | 87.868 |
| Example 5 | |
32 | 965 | 0.653 | 0.4 | 86.147 |
| Example 6 | |
12 | 102 | 1.245 | 0.4 | 89.949 |
| Example 7 | |
19 | 143 | 2.06 | 0.4 | 89.562 |
| Example 8 | |
22 | 117 | 0.583 | 0.22 | 89.273 |
| Example 9 | |
16 | 126 | 0.802 | 0.085 | 88.694 |
| Example 10 | LFP 10 | 277 | 1085 | 2.31 | 0.085 | 82.818 |
Wherein LFP 1 in the embodiment 1 is LiFePO with better 4 indexes 4 Cathode material, as void in this experimentWhite group baseline for comparing the effect of different index factors on the cyclic decay. LFP 1, LFP 2 and LFP 3 are selected, and the decay graphs of 1C/1C cycle performance of three LFP materials with different ferric iron contents at 45 ℃ are compared, as shown in FIG. 2, it can be seen from the graphs that the decay amplitude of the capacity retention rate of the battery is increased along with the rise of the ferric iron content. The linear relationship between the ferric iron content and the cycle decay life is shown in fig. 3, and the cycle capacity retention rate at the 500 th circle is taken as an evaluation point, so that the ferric iron content is increased, the capacity retention rate is reduced, and the decay amplitude of the cycle life conforms to the linear relationship.
The LFP 1, LFP 4 and LFP 5 in the embodiment 1, the embodiment 4 and the embodiment 5 are selected, and the decay graphs of the 1C/1C cycle performance at 45 ℃ of the LFP materials with three different iron dissolution rates are compared, as shown in FIG. 4, it can be seen that the decay amplitude of the capacity retention rate of the battery is increased along with the increase of the iron dissolution rate. The linear relationship between the iron dissolution amount and the cycle decay life is shown in fig. 5, and the cycle capacity retention rate at the 500 th circle is taken as an evaluation point, so that the larger the iron dissolution amount is, the lower the capacity retention rate is, and the decay amplitude of the cycle life conforms to the linear relationship.
The LFP 1, LFP 6 and LFP 7 in the embodiments 1, 6 and 7 are selected, and the decay graphs of 1C/1C cycle performance at 45 ℃ of three LFP materials with different cleanliness are compared, as shown in FIG. 6, the increase of impurity content and the increase of the decay amplitude of the capacity retention rate of the battery can be seen from the graphs. The linear relationship between the impurity content and the cycle decay life is shown in fig. 7, and the cycle capacity retention rate at the 500 th cycle is taken as an evaluation point. It can be seen that the larger the impurity amount, i.e., the worse the cleanliness of the material, the lower the capacity retention rate, and the linear relationship is satisfied with the magnitude of the decay of the cycle life.
The LFP 1, LFP 8 and LFP 9 in the embodiments 1, 8 and 9 are selected, and the decay graphs of the 1C/1C cycle performance at 45 ℃ of the LFP materials with the use ratios of the three effective additives are compared, as shown in FIG. 8, it can be seen from the graphs that the effective additive ratio is reduced, and the decay amplitude of the capacity retention rate of the battery is increased. The linear relationship between the usage proportion of the effective additive and the cycle decay life is shown in fig. 9, and the cycle capacity retention rate at the 500 th circle is taken as an evaluation point, so that the smaller the usage proportion of the effective additive is, the lower the capacity retention rate is, and the decay amplitude of the effective additive to the cycle life conforms to the linear relationship.
The LFP 1, LFP 2, LFP 4, LFP 6, LFP 8 and LFP 10 in example 1 (blank group), example 2, example 4, example 6, example 8 and example 10 were selected, and the measured cycle life diagrams at 45 ℃ of batteries with univariate and complex variable factors with poor four indexes of different factors were compared, respectively, as shown in fig. 10, the blank group in the diagrams was LFP materials with good 4 indexes, and other measured cycle life diagrams at 45 ℃ of batteries with complex variable factors with poor single variable and four indexes of different factors were compared, respectively. It can be seen from the figure that compared with the influence of single variables, the battery cycle attenuation with 4 index composite variable factors is obviously increased, and the battery has the weighting effect of different single variable influence attenuation.
The application of the prediction method of the invention has several advantages: firstly, the traditional lithium ion battery life test method needs to consume a large amount of manpower and material resources and long test time, for example, the traditional 1C/1C +30min shelf test method needs to consume 1.5-2 years of time when the battery is circulated to the EOL state, and the battery needs to be tested for more than 2 months when the battery is circulated for 500 circles. The prediction method of the invention is used for predicting and comparing the service life, and the prediction and comparison aiming at the cycle performance of the material can be completed only in 5-10 days, thereby greatly improving the evaluation efficiency. And secondly, some prediction methods only consider the influence of one variable and ignore the influence of other variables on the cycle life, and the method considers the influence factors of various coupling methods and improves the accuracy of the prediction of the cycle life of the material.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (7)
1. A method for rapidly judging the cycle life of a lithium iron phosphate battery is characterized by comprising the following steps:
determination of Fe 3+ And Fe 2+ The content index is as follows: mixing LiFePO 4 Mixing the anode material with an acidic solution, and detecting the iron content concentration C in the solution Fe 3+ And C Fe 2+ The content of ferric iron and ferrous iron in the anode material is judged, the content of ferric iron is increased, the capacity retention rate is reduced, and the attenuation amplitude of the cycle life conforms to a linear relation;
and (3) determining the iron dissolution rate index: mixing LiFePO 4 Mixing the positive electrode material with a strong acid solution, reacting for 1-180min, and detecting the concentration M of the iron element content in the solution Fe So as to measure the dissolved iron amount of the mixed reaction at different time periods to judge the Fe dissolution rate in the anode material, wherein the larger the dissolved iron amount is, the lower the capacity retention rate is, and the attenuation amplitude of the cycle life conforms to the linear relation;
and (3) determining cleanliness indexes: for LiFePO 4 Carrying out magnetic bar enrichment on the positive electrode material, then testing the enrichment material on the magnetic bar, and judging the LiFePO 4 The content percentage Q of the iron simple substance and other magnetic impurity materials contained in the anode material im /Q all (ii) a The other magnetic impurity materials comprise Ni, mn and Al, the larger the impurity amount is, namely the poorer the material cleanliness is, the lower the capacity retention rate is, and the attenuation amplitude of the cycle life conforms to the linear relation; wherein Q is im The number of the iron simple substance and other magnetic impurity material particles which are adsorbed on the magnetic bar and extracted is shown; q all Represents the number of all particles adsorbed on the magnetic bar and extracted;
and (3) determining an effective additive index: calculating the effective additive content in the battery cell electrolyte to LiFePO 4 Ratio m of positive electrode material add /m Fe To determine the effective additive to LiFePO 4 Influence of the cathode material, wherein m add Represents the mass of effective additive contained in the electrolyte, m Fe Indicating LiFePO in the cell 4 MaterialThe mass of (c); the smaller the use proportion of the effective additive is, the lower the capacity retention rate is, and the attenuation amplitude of the cycle life conforms to a linear relation; the effective additive is the total content of 4 effective additives of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate and methylene methyl disulfonate;
weighting the four judgment indexes to obtain a final judgment numerical value F:
wherein the constant influence factor a =0.1407 to 0.1431; b = -0.0511-0.0349; c =0.4632 to 0.4697; d = 0.0098 to 0.0092, e =0.0904 to 0.0982; f = -3.5811-2.0957; g =0.2466 to 0.2481; h =14.222 to 15.746; the cycle life impact factor F represents the predicted attenuation percentage of the compared normal cycle battery cell; the battery cycle attenuation with 4 index composite variable factors is obviously increased, and the weighting effect of different univariate influence attenuation is achieved.
2. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 1, wherein Fe is measured 2 + The content is specifically LiFePO 4 Mixing the positive electrode material with HCl solution, adding 1,10-phenanthroline, and adding Fe when PH =2~9 2+ Generating orange red complex with 1,10-phenanthroline, measuring absorbance of the filtered mixed solution at 510nm, and measuring C Fe 2 + 。
3. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 1, wherein Fe is measured 3 + The content is specifically LiFePO 4 Mixing the positive electrode material with HCl solution, adding ascorbic acid to obtain Fe in the solution 3+ All reduced to Fe 2+ Adding 1,10-phenanthroline, measuring absorbance of the filtered mixed solution at 510nm, and calculating to obtain total iron content, namely LiFePO 4 Fe in positive electrode material 3+ The content is equal to the total iron content minus no additionFe measured in ascorbic acid 2+ And (4) content.
4. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 1, wherein the specific method for determining the iron dissolution rate index is as follows: mixing LiFePO 4 Mixing the positive electrode material with a strong acid solution, measuring the iron dissolving amount of the mixture at different time by using an ICP method, reacting for 1-180min, and detecting the iron content concentration M in the solution Fe To determine the Fe elution rate in the positive electrode material.
5. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 4, wherein the reaction time is 10-90min.
6. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 4, wherein the initial concentration of the strong acidic solution is 0.001 to 1.5 mol L -1 。
7. The method for rapidly determining the cycle life of a lithium iron phosphate battery according to claim 6, wherein the initial concentration of the strong acid solution is 0.05 to 1 mol L -1 。
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