CN117800307A - Standard substance for detecting carbon content in lithium iron phosphate positive electrode material, preparation and application thereof - Google Patents
Standard substance for detecting carbon content in lithium iron phosphate positive electrode material, preparation and application thereof Download PDFInfo
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- CN117800307A CN117800307A CN202311809697.2A CN202311809697A CN117800307A CN 117800307 A CN117800307 A CN 117800307A CN 202311809697 A CN202311809697 A CN 202311809697A CN 117800307 A CN117800307 A CN 117800307A
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- iron phosphate
- lithium iron
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 107
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 107
- 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 66
- 239000000126 substance Substances 0.000 title claims abstract description 59
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 20
- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- 239000011159 matrix material Substances 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 25
- 238000001514 detection method Methods 0.000 claims abstract description 14
- 239000000725 suspension Substances 0.000 claims description 20
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 18
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 claims description 18
- 238000001035 drying Methods 0.000 claims description 16
- 239000012086 standard solution Substances 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 14
- 238000007873 sieving Methods 0.000 claims description 13
- 239000000243 solution Substances 0.000 claims description 13
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims description 12
- 239000013558 reference substance Substances 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 11
- 239000005955 Ferric phosphate Substances 0.000 claims description 10
- 229940032958 ferric phosphate Drugs 0.000 claims description 10
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims description 10
- 239000002904 solvent Substances 0.000 claims description 10
- 239000002253 acid Substances 0.000 claims description 9
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 9
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 9
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 8
- 229910021642 ultra pure water Inorganic materials 0.000 claims description 8
- 239000012498 ultrapure water Substances 0.000 claims description 8
- 238000002372 labelling Methods 0.000 claims description 7
- 239000012925 reference material Substances 0.000 claims description 7
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 6
- 238000000227 grinding Methods 0.000 claims description 6
- 239000007787 solid Substances 0.000 claims description 6
- 238000003746 solid phase reaction Methods 0.000 claims description 6
- 238000004140 cleaning Methods 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- 239000011261 inert gas Substances 0.000 claims description 4
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 4
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 3
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 3
- 239000004744 fabric Substances 0.000 claims description 3
- 238000004108 freeze drying Methods 0.000 claims description 3
- 238000000265 homogenisation Methods 0.000 claims description 3
- 229910017604 nitric acid Inorganic materials 0.000 claims description 3
- 230000035484 reaction time Effects 0.000 claims description 3
- 229910000398 iron phosphate Inorganic materials 0.000 claims description 2
- 238000011084 recovery Methods 0.000 abstract description 16
- 238000012360 testing method Methods 0.000 abstract description 10
- 238000004458 analytical method Methods 0.000 abstract description 7
- 239000006185 dispersion Substances 0.000 abstract description 5
- 238000005259 measurement Methods 0.000 abstract description 5
- 238000003908 quality control method Methods 0.000 abstract description 5
- 238000012795 verification Methods 0.000 abstract description 4
- 238000004164 analytical calibration Methods 0.000 abstract description 3
- 238000011156 evaluation Methods 0.000 abstract description 3
- 238000002485 combustion reaction Methods 0.000 description 10
- 229910000831 Steel Inorganic materials 0.000 description 8
- 239000010959 steel Substances 0.000 description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 4
- 229910052721 tungsten Inorganic materials 0.000 description 4
- 239000010937 tungsten Substances 0.000 description 4
- 239000010405 anode material Substances 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- ZTOZIUYGNMLJES-UHFFFAOYSA-K [Li+].[C+4].[Fe+2].[O-]P([O-])([O-])=O Chemical compound [Li+].[C+4].[Fe+2].[O-]P([O-])([O-])=O ZTOZIUYGNMLJES-UHFFFAOYSA-K 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000012937 correction Methods 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 229910000805 Pig iron Inorganic materials 0.000 description 1
- 229910001315 Tool steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000000498 ball milling Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000009841 combustion method Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000006184 cosolvent Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 230000005674 electromagnetic induction Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 229910052754 neon Inorganic materials 0.000 description 1
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 description 1
- 235000011837 pasties Nutrition 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 239000011265 semifinished product Substances 0.000 description 1
- -1 separators Substances 0.000 description 1
- 238000001132 ultrasonic dispersion Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N2001/2893—Preparing calibration standards
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- General Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Inorganic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
The invention belongs to the technical field of chemical standard sample preparation, and particularly relates to a standard substance for detecting carbon content in a lithium iron phosphate positive electrode material, and preparation and application thereof. The standard substance takes lithium iron phosphate as a matrix, and the prepared standard substance can realize customization of the carbon element content by introducing target carbon element, and can be directly applied to instrument calibration in the process of detecting the carbon content in a lithium iron phosphate sample, quality control and detection capability verification in the evaluation and measurement processes of an analysis method. Compared with the standard substance for detecting the carbon content, which does not contain the lithium iron phosphate matrix material in the prior art, the standard substance provided by the invention is used for detecting the carbon content, has obviously smaller standard deviation and relative standard deviation, has obviously smaller dispersion of carbon content test data, and has better repeatability of the addition recovery rate when a sample is tested.
Description
Technical Field
The invention belongs to the technical field of chemical standard sample preparation, and particularly relates to a standard substance for detecting carbon content in a lithium iron phosphate positive electrode material, and preparation and application thereof.
Background
Clean energy such as solar energy, nuclear power, wind energy and the like which do not depend on petroleum energy stands at the peak of the age again, and occupies more market share; the research and development and sales of low-emission and even zero-emission hybrid electric vehicles and pure electric vehicles are again hot; while research on battery materials with better performance, including positive electrode materials, negative electrode materials, separators, electrolytes, and the like, has kept continuous enthusiasm.
In order to improve the performance of the positive electrode material, particularly, for the positive electrode material with poor conductivity like lithium iron phosphate, a form of coating or doping carbon is generally adopted to improve the conductivity of the positive electrode material, so as to further improve the discharge capacity, the cycle performance and the like of the battery.
For the detection of carbon doping amount, there are two methods at present: one is to burn the sample and the cosolvent in a high temperature tube furnace with oxygen introduced, oxidize the carbon completely to carbon dioxide, and calculate the carbon content based on the volume of carbon dioxide produced. Reference is made to: GB/T223.69 method for measuring the carbon content of steel and alloy in a tubular furnace after combustion. The method has the advantages that the operation process is complicated, high-pressure and high-purity oxygen is used, the tube furnace is burned to 1200-1350 ℃, the upper limit of the temperature of the tube furnace is approached, and certain potential safety hazards exist. The other is detection using a carbon-sulfur analyzer, wherein the standard substance of carbon used in the high-frequency combustion infrared absorption method for measuring iron ore carbon and sulfur content of reference document GB/T6730.61 is barium carbonate powder, but barium carbonate is not a national standard substance with evidence. The reference document GB/T20123 is a high-frequency induction furnace combustion infrared absorption method (conventional method) for determining the total carbon and sulfur content of steel, and the standard substance of carbon used in the reference document GB/T20123 is a carbon-containing steel evidence reference substance. The principle of carbon measurement by the high-frequency combustion method is as follows: the sample and its carbon-containing components are heated up rapidly by electromagnetic induction in an alternating electric field, and burned rapidly in a high purity oxygen atmosphere to produce carbon dioxide, which is detected by an infrared detector. The matrix effect brought by the anode material is ignored in the preparation and use processes of the two carbon standard substances.
The existing carbon-coated lithium iron phosphate material is characterized in that a barium carbonate or steel standard substance which does not contain a matrix material is used for detecting the carbon content of the existing carbon-coated lithium iron phosphate material, the matrix effect of the lithium iron phosphate cannot be eliminated, and the analysis detection and quality control of the carbon content of the existing carbon-coated lithium iron phosphate material are not facilitated.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a standard substance for detecting the carbon content in a lithium iron phosphate positive electrode material, and preparation and application thereof, so as to solve the technical problems of poor accuracy and repeatability of a test result and the like caused by the fact that the standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material in the prior art does not contain a lithium iron phosphate matrix material.
In order to achieve the above object, the present invention provides a method for preparing a standard substance for detecting carbon content in a lithium iron phosphate positive electrode material, comprising the steps of:
(1) Mixing high-purity ferric phosphate and high-purity lithium carbonate in proportion, and carrying out high-temperature solid-phase reaction under the protection of inert gas to obtain a lithium iron phosphate material;
(2) Removing impurities in the lithium iron phosphate material in the step (1) by adopting acid liquor, and drying, grinding and sieving the obtained solid after cleaning to obtain a high-purity lithium iron phosphate matrix material;
(3) Dissolving or dispersing a carbon-containing reference substance in a solvent to obtain a standard solution/uniformly dispersed suspension of carbon;
(4) Uniformly mixing the high-purity lithium iron phosphate matrix material in the step (2) and the standard solution/uniformly dispersed suspension of the carbon in the step (3) to obtain a labeling mixture;
(5) And (3) drying the labeled mixture in the step (4), and then regrinding and sieving to obtain the standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material.
Preferably, the purity of the high-purity ferric phosphate in the step (1) is greater than or equal to 99.9%, the purity of the high-purity lithium carbonate is greater than or equal to 99.5%, and the temperature of the high-temperature solid-phase reaction is 500-800 ℃; the reaction time is 8-12 h.
Preferably, the acid solution of step (2) is selected from the group consisting of aqueous hydrochloric acid, aqueous sulfuric acid and aqueous nitric acid; the mesh number of the screen cloth is 120-800 meshes during sieving.
Preferably, the carbonaceous reference material of step (3) is one or more of sodium carbonate, calcium carbonate or barium carbonate.
Preferably, the solvent of step (3) is one or more of ultrapure water, ethanol and azamethylpyrrolidone.
Preferably, the concentration of carbon element in the standard solution/uniformly dispersed suspension of carbon in the step (3) is less than or equal to 1000ppm.
Preferably, the mass ratio of the high-purity lithium iron phosphate matrix material to the standard solution/uniformly dispersed suspension of carbon in the step (4) is 1:10-1:500; the mixing is specifically carried out by adopting a homogenizer for homogenization.
Preferably, the drying in the step (5) is freeze drying, and the drying time is 6-24 hours; the mesh number of the screen mesh in the step (5) is 120-800 meshes.
According to another aspect of the invention, a standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material prepared by the preparation method is provided.
According to another aspect of the invention, there is provided the use of the standard substance as a standard substance for carbon content detection in lithium iron phosphate positive electrode materials.
In general, the above technical solutions conceived by the present invention have the following compared with the prior art
The beneficial effects are that:
(1) The method takes the high-purity ferric phosphate and the high-purity lithium carbonate as raw materials, the high-purity ferric phosphate is obtained through high-temperature solid reaction under the protection of nitrogen, then the high-purity ferric phosphate is taken as a matrix, and target carbon elements are introduced through the steps of adding standard, homogenizing, drying, sieving and the like, so that the prepared standard substance has good uniformity and stable property, and can be directly applied to instrument calibration in the carbon content detection process in the ferric phosphate sample, quality control and detection capability verification in the evaluation and measurement process of an analysis method.
(2) The invention provides a standard substance for detecting carbon content in lithium iron phosphate, which takes lithium iron phosphate as a matrix, introduces a target amount of carbon element to prepare the carbon content detection standard substance, can realize customization of the carbon element content, and is directly applied to instrument calibration in the process of detecting the carbon content in a lithium iron phosphate sample, analysis method evaluation and quality control and detection capability verification in the measuring process. Compared with the standard substance for detecting the carbon content, which does not contain the lithium iron phosphate matrix material in the prior art, the standard substance provided by the invention is used for detecting the carbon content, has obviously smaller standard deviation and relative standard deviation, has obviously smaller dispersion of carbon content data, and has obviously better repeatability of the addition of the standard substance during the test of the sample.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the prior art, a carbon-containing steel evidence reference substance or barium carbonate is used as a standard substance for carbon content detection, when the carbon content in the lithium iron phosphate anode material is detected, the influence caused by the lithium iron phosphate serving as a matrix cannot be reflected, and the element analysis signal to be detected can generate loss and signal drift with different degrees, so that the analysis detection and quality control of the carbon content in the lithium iron phosphate material are not facilitated. Therefore, the invention provides a preparation method of a standard substance for detecting the carbon content in a lithium iron phosphate positive electrode material, which comprises the following steps:
(1) Mixing high-purity ferric phosphate and high-purity lithium carbonate in proportion, and carrying out high-temperature solid-phase reaction under the protection of inert gas to obtain a lithium iron phosphate material;
(2) Removing impurities in the lithium iron phosphate material in the step (1) by adopting acid liquor, and drying, grinding and sieving the obtained solid after cleaning to obtain a high-purity lithium iron phosphate matrix material;
(3) Dissolving or dispersing a carbon-containing reference substance in a solvent to obtain a standard solution/uniformly dispersed suspension of carbon;
(4) Uniformly mixing the high-purity lithium iron phosphate matrix material in the step (2) and the standard solution/uniformly dispersed suspension of the carbon in the step (3) to obtain a labeling mixture;
(5) And (3) drying the standard adding mixture in the step (4), and then regrinding and sieving to obtain the standard substance for detecting the carbon content in the lithium iron phosphate anode material.
In some embodiments, the purity of the high purity ferric phosphate of step (1) is greater than or equal to 99.9%, the purity of the high purity lithium carbonate is greater than or equal to 99.5%, and the temperature of the high temperature solid phase reaction is 500 ℃ to 800 ℃; the reaction time is 8-12 h. The inert gas is one or more of nitrogen, helium, neon and argon.
In some embodiments, step (1) combines high purity iron phosphate and high purity lithium carbonate in a molar ratio of 1 (1.01-1.05).
In some embodiments, the acid solution in step (2) is selected from an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, an aqueous solution of nitric acid, etc., and the concentration of the acid solution is adjusted according to the need, and is generally 5% -15% by volume; the acid purity is generally electronic grade. The mesh number of the screen cloth is 120-800 meshes during sieving.
In some embodiments, a 10% hydrochloric acid solution is formulated with electronic grade hydrochloric acid and ultrapure water, and the resulting lithium iron phosphate material is dispersed into this hydrochloric acid solution, sonicated for 30min, and centrifuged. Repeating the operation for 3 times, drying the obtained solid at 120 ℃ for 2 hours, grinding and sieving to obtain the high-purity lithium iron phosphate matrix material. Other acid solutions can be treated according to the same cleaning and impurity removing method.
Step (3) dissolving or dispersing a carbon-containing reference substance in a solvent to obtain a standard solution/uniformly dispersed suspension of carbon; here "/" is the meaning of or. The carbonaceous reference material may be a water-soluble carbonaceous reference material or a water-insoluble carbonaceous reference material. In some embodiments, the carbonaceous reference material of step (3) is one or more of sodium carbonate, calcium carbonate, or barium carbonate. The purity of the carbon-containing reference substance is greater than or equal to 99.9%.
And (3) dissolving or dispersing the carbon-containing reference substance in a solvent, wherein the solvent is selected from solvent types which can be volatilized and removed by heating in the drying process. In some embodiments, the solvent of step (3) is one or more of ultrapure water, ethanol, and azamethylpyrrolidone. And (3) the concentration of carbon element in the standard solution/uniformly dispersed suspension of the carbon in the step (3) is less than or equal to 1000ppm.
In some embodiments, the mass ratio of the high purity lithium iron phosphate matrix material to the standard solution/uniformly dispersed suspension of carbon of step (4) is 1:10 to 1:500; optionally adding appropriate amount of ultrapure water, and mixing. The mixing is specifically carried out by adopting a homogenizer for homogenization.
In some embodiments, the drying in step (5) is freeze-drying, and the drying time is 6-24 hours; the mesh number of the screen mesh in the step (5) is 120-800 meshes. And (3) screening in the step (2) and the step (5) to obtain undersize.
The invention combines the carbon-containing reference substance solution/suspension with the high-purity lithium iron phosphate matrix material, and then homogenously mixes, freezes and dries the semi-finished product, thereby finally ensuring that the uniform and stable carbon content reference substance is obtained. The standard substance prepared by the method can be used as a standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material. Compared with the standard substance for detecting the carbon content without the lithium iron phosphate matrix material in the prior art, the standard substance provided by the invention has the advantages that the standard substance for detecting the carbon content has obviously smaller standard deviation and relative standard deviation, the carbon content data has obviously smaller dispersion, and the repeatability of the standard adding recovery rate in the process of detecting the sample is obviously better than that of the standard substance without the lithium iron phosphate matrix in the prior art.
The following are examples:
example 1
Fully and uniformly mixing high-purity ferric phosphate (more than or equal to 99.9%) and high-purity lithium carbonate (more than or equal to 99.5%) according to the molar ratio of 1:1.02, reacting for 10 hours at 750 ℃ under the protection of nitrogen, cooling and ball-milling to obtain a lithium iron phosphate material;
preparing 10% hydrochloric acid solution with electronic grade hydrochloric acid and ultrapure water, dispersing the lithium iron phosphate material into the hydrochloric acid solution, performing ultrasonic dispersion for 30min, and centrifuging. Repeating the operation for 3 times, drying the obtained solid for 2 hours at 120 ℃, grinding and sieving with a 200-mesh sieve to obtain the high-purity lithium iron phosphate matrix material.
Preparing a 1000mg/L carbon standard solution A by taking sodium carbonate (more than or equal to 99.9%) as a reference substance;
0.5g of the sieved high-purity lithium iron phosphate is taken, 5.0mL of 1000mg/L of carbon standard solution A and 25mL of ultrapure water are added, and the mixture is uniformly mixed on a refiner.
The well-mixed pasty labeling mixture is taken out and placed in a 500mL glass beaker, spread on the bottom of the beaker and dried for 10h on a freeze dryer. Grinding and sieving with 200 mesh sieve to obtain carbon content standard substance.
And (3) selecting the self-made carbon standard substance as a standard substance in a standard adding experiment, and taking commercially available carbon-coated lithium iron phosphate as a sample for testing.
And verifying the prepared carbon content standard substance:
and (3) verifying a carbon content standard substance by using a steel Nake CS2800 carbon-sulfur analyzer. The crucible is treated in a muffle furnace at 1000 ℃ for 1h, and is cooled slightly and then transferred into a dryer for cooling.
Baseline: an empty crucible is placed on the crucible holder and an arbitrary mass (typically 1 g) is input at "sample mass" and then "start" is clicked on, waiting for the analysis to end. The operation is performed for 3 times, and the air in the air path is discharged, so that the baseline is stabilized.
And (3) standard sample correction: the carbon in the certified reference material-pig iron was corrected, and the reference materials having carbon contents of 0.0006%, 0.472%, 1.18% and 2.19% were selected for blank and 3-point correction. The specific operation is as follows: placing an empty crucible on a balance linked with a carbon-sulfur analyzer to weigh 0.2 g+/-0.05 g (accurate to 0.0001 g) of a proven reference substance, and adding about 1.6g of tungsten particle combustion improver; the standard sample quality and tungsten particle combustion improver quality software can be automatically read and filled. Placing the crucible with the weighed standard sample and the weighed combustion improver on a crucible support, and clicking to start the test.
Verification of the prepared carbon content standard substance: placing an empty crucible on a balance linked with a carbon-sulfur analyzer to weigh about 0.3g of pure iron combustion improver; after the balance is zeroed, about 0.2 g+/-0.05 g (accurate to 0.0001 g) of the prepared carbon content standard substance is weighed, and finally about 1.6g of tungsten particle combustion improver is weighed, and the sample mass and tungsten particle combustion improver mass software are automatically read and filled. The crucible, from which the sample and the combustion improver have been weighed, is placed on the crucible holder and the test is started by clicking "start".
The homemade carbon standard of example 1 was subjected to 10 replicates and the results are shown in table 1. The relative standard deviation RSD is 1.373% according to calculation, and meets the fixed value requirement. The commercial carbon-coated lithium iron phosphate is detected, the standard adding recovery rate is in the range of 98.94-103.16%, and the standard adding recovery rate is between 90-110%, so that the standard adding recovery rate meets the constant value requirement.
Table 1 continuous measurement of 10 prepared carbon content standards and commercial sample labeling test results
Example 2
The difference from example 1 was that the carbon standard substance was a barium carbonate suspension, and 0.0084g of barium carbonate (. Gtoreq.99.9%) and 30mL of ultrapure water were mixed to prepare a suspension. The suspension was mixed with 0.5g of the sieved high purity lithium iron phosphate on a refiner. The subsequent operations are the same.
10 replicates were tested and the results are shown in Table 2.
Table 2 results of carbon standard substance synthesized with suspension and labeling test of commercially available samples were measured 10 times in succession
As can be seen from Table 2, the relative standard deviation RSD was calculated to be 1.93%, which meets the fixed value requirements. The commercial carbon-coated lithium iron phosphate is detected, the standard adding recovery rate is in the range of 98.09-103.47 percent, and the standard adding recovery rate is between 90-110 percent, thereby meeting the constant value requirement.
Comparative example 1
The standard substance adopts a standard sample of steel standard substance NCS 01414 carbon tool steel industry, which is numbered YSBC11421a-2021, and the specified carbon content value is 1.18%. The labeled recovery data for 10 replicates and commercial carbon-coated lithium iron phosphate is shown in Table 3. The standard deviation was calculated to be 0.0245 and the relative standard deviation RSD was 2.06% greater than the homemade carbon standard of examples 1 and 2. The normalized recovery rate is in the range of 98.03% -104.76%, and although the normalized recovery rate is also in the range of 90% -110%, the normalized recovery rate is significantly wider than that of example 1 and example 2, especially example 1.
TABLE 3 results of 10 consecutive measurements of the standard substance for carbon in iron and steel and the commercial sample for the labeling test
From the above examples and comparative examples, it can be seen that the lithium iron phosphate carbon content standard substance prepared in the form of a solution or a suspension satisfies the requirement of the constant value test, although the dispersion of the carbon standard substance prepared in the form of a suspension is slightly large. Compared with the comparative example, the self-made carbon content detection standard substance containing the lithium iron phosphate matrix has smaller standard deviation and relative standard deviation, and the carbon content data has smaller dispersion.
In addition, although the standard recovery rates were all within the prescribed ranges, the standard recovery rate ranges of example 1 and example 2 were significantly smaller than the standard recovery rate ranges of comparative example 1 without lithium iron phosphate matrix standard substances when applied to the commercial lithium iron phosphate carbon content detection. The range of the standard recovery rate of the example 1 is the smallest and 98.94-103.16%, and the range of the standard recovery rate of the comparative example 1 is the largest and 98.03-104.76%. This demonstrates that examples 1 and 2 effectively eliminate the matrix effect caused by lithium iron phosphate using a standard substance containing a matrix of lithium iron phosphate.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. The preparation method of the standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material is characterized by comprising the following steps of:
(1) Mixing high-purity ferric phosphate and high-purity lithium carbonate in proportion, and carrying out high-temperature solid-phase reaction under the protection of inert gas to obtain a lithium iron phosphate material;
(2) Removing impurities in the lithium iron phosphate material in the step (1) by adopting acid liquor, and drying, grinding and sieving the obtained solid after cleaning to obtain a high-purity lithium iron phosphate matrix material;
(3) Dissolving or dispersing a carbon-containing reference substance in a solvent to obtain a standard solution/uniformly dispersed suspension of carbon;
(4) Uniformly mixing the high-purity lithium iron phosphate matrix material in the step (2) and the standard solution/uniformly dispersed suspension of the carbon in the step (3) to obtain a labeling mixture;
(5) And (3) drying the labeled mixture in the step (4), and then regrinding and sieving to obtain the standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material.
2. The method of claim 1, wherein the purity of the high purity iron phosphate in step (1) is greater than or equal to 99.9%, the purity of the high purity lithium carbonate is greater than or equal to 99.5%, and the temperature of the high temperature solid phase reaction is 500 ℃ to 800 ℃; the reaction time is 8-12 h.
3. The method of claim 1, wherein the acid solution in step (2) is selected from the group consisting of aqueous hydrochloric acid, aqueous sulfuric acid, and aqueous nitric acid; the mesh number of the screen cloth is 120-800 meshes during sieving.
4. The method of claim 1, wherein the carbonaceous reference material of step (3) is one or more of sodium carbonate, calcium carbonate or barium carbonate.
5. The method of claim 1, wherein the solvent of step (3) is one or more of ultrapure water, ethanol, and azamethylpyrrolidone.
6. The method according to claim 1, wherein the concentration of carbon element in the standard solution/uniformly dispersed suspension of carbon in the step (3) is 1000ppm or less.
7. The method according to claim 1, wherein the mass ratio of the high-purity lithium iron phosphate matrix material to the standard solution/uniformly dispersed suspension of carbon in the step (4) is 1:10 to 1:500; the mixing is specifically carried out by adopting a homogenizer for homogenization.
8. The method according to claim 1, wherein the drying in the step (5) is freeze-drying, and the drying time is 6-24 hours; the mesh number of the screen mesh in the step (5) is 120-800 meshes.
9. The standard substance for detecting the carbon content in the lithium iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 8.
10. Use of the standard substance according to claim 9 as a standard substance for carbon content detection in lithium iron phosphate positive electrode materials.
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