CN111413190A - Carbon-coated lithium iron phosphate digestion device, digestion method and detection method - Google Patents
Carbon-coated lithium iron phosphate digestion device, digestion method and detection method Download PDFInfo
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- CN111413190A CN111413190A CN201910011392.4A CN201910011392A CN111413190A CN 111413190 A CN111413190 A CN 111413190A CN 201910011392 A CN201910011392 A CN 201910011392A CN 111413190 A CN111413190 A CN 111413190A
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- 230000029087 digestion Effects 0.000 title claims abstract description 189
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 50
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 50
- 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 50
- 238000000034 method Methods 0.000 title claims abstract description 43
- 238000001514 detection method Methods 0.000 title claims abstract description 18
- 239000011261 inert gas Substances 0.000 claims abstract description 34
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims abstract description 22
- 238000007789 sealing Methods 0.000 claims abstract description 16
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims abstract description 15
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 9
- 239000002253 acid Substances 0.000 claims description 8
- 239000003595 mist Substances 0.000 claims description 6
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 238000001914 filtration Methods 0.000 claims description 4
- 230000007246 mechanism Effects 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 238000007865 diluting Methods 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 238000004448 titration Methods 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 2
- 229910052734 helium Inorganic materials 0.000 claims description 2
- 239000001307 helium Substances 0.000 claims description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 2
- 238000002156 mixing Methods 0.000 claims description 2
- 230000033116 oxidation-reduction process Effects 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 abstract description 54
- 229910052742 iron Inorganic materials 0.000 abstract description 26
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 abstract description 22
- 239000000463 material Substances 0.000 abstract description 17
- 239000012298 atmosphere Substances 0.000 abstract description 11
- 230000008569 process Effects 0.000 abstract description 11
- 238000012360 testing method Methods 0.000 abstract description 7
- 150000001875 compounds Chemical class 0.000 abstract description 6
- 230000004308 accommodation Effects 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 43
- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 229910001447 ferric ion Inorganic materials 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 6
- 229910001448 ferrous ion Inorganic materials 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- YONPGGFAJWQGJC-UHFFFAOYSA-K titanium(iii) chloride Chemical compound Cl[Ti](Cl)Cl YONPGGFAJWQGJC-UHFFFAOYSA-K 0.000 description 3
- 238000005303 weighing Methods 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000003517 fume Substances 0.000 description 2
- 238000004445 quantitative analysis Methods 0.000 description 2
- DGXTZMPQSMIFEC-UHFFFAOYSA-M sodium;4-anilinobenzenesulfonate Chemical compound [Na+].C1=CC(S(=O)(=O)[O-])=CC=C1NC1=CC=CC=C1 DGXTZMPQSMIFEC-UHFFFAOYSA-M 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000003139 buffering effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000001506 fluorescence spectroscopy Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000120 microwave digestion Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- -1 polyethylene Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- XMVONEAAOPAGAO-UHFFFAOYSA-N sodium tungstate Chemical compound [Na+].[Na+].[O-][W]([O-])(=O)=O XMVONEAAOPAGAO-UHFFFAOYSA-N 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- BFKJFAAPBSQJPD-UHFFFAOYSA-N tetrafluoroethene Chemical group FC(F)=C(F)F BFKJFAAPBSQJPD-UHFFFAOYSA-N 0.000 description 1
- AXZWODMDQAVCJE-UHFFFAOYSA-L tin(II) chloride (anhydrous) Chemical compound [Cl-].[Cl-].[Sn+2] AXZWODMDQAVCJE-UHFFFAOYSA-L 0.000 description 1
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- 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
- G01N1/44—Sample treatment involving radiation, e.g. heat
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
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Abstract
The invention provides a carbon-coated lithium iron phosphate digestion device, a digestion method and a detection method, wherein the device comprises: clear up container and heater, wherein clear up the container including clear up the pipe, with clear up the pipe complex clear up the lid, set up in clear up two through-holes at lid top and with through-hole complex sealing plug, be equipped with at least one on the heater and clear up a pipe accommodation hole for place clear up the pipe. Inert gas is introduced into the device before digestion, so that the inert atmosphere in the digestion process is ensured, and the proportion of ferrous iron and ferric iron is protected from being damaged; the heater can complete digestion of a plurality of samples at one time, and digestion efficiency is high. The digestion method provided by the invention is simple to operate, and the components in the obtained digestion solution are equivalent to those in the original compound; the method for detecting the carbon-coated lithium iron phosphate provided by the invention takes the prepared digestion solution as a detection solution, and can accurately test the accurate contents of iron elements with different valence states in the carbon-coated lithium iron phosphate material.
Description
Technical Field
The invention relates to the technical field of analysis and detection, and particularly relates to a carbon-coated lithium iron phosphate digestion device, a carbon-coated lithium iron phosphate digestion method and a method for detecting the content of ferric iron in carbon-coated lithium iron phosphate.
Background
Almost all lithium iron phosphate on the market at present adopts a carbon-coated process design, due to the limitation of different process defects, a trace amount of ferric ions exist in a carbon-coated lithium iron phosphate material, the existence of ferric element is extremely unfavorable for the lithium iron phosphate material, and L iFePO can be caused by the ferric element4The self-discharge of the anode material is increased, the specific capacity is reduced, and the dissolution of iron and the precipitation on the carbon cathode can occur during the circulation process, so that the circulation performance is deteriorated, and the L iFePO is caused4One important reason for poor consistency in production, therefore L iFePO was produced4In time, L iFePO is controlled and accurately detected4The content of medium trivalent iron is particularly important. Due to the limited characterization means such as XPS, EDS and the like and large quantitative analysis error, the material must be digested for accurately measuring the content of ferric iron in the lithium iron phosphate. In the existing digestion analysis and test method of carbon-coated lithium iron phosphate, the conventional digestion method is simple and convenient to operate but cannot effectively seal the digestion process, and active ferrous ions are easily oxidized into ferric ions in the heating digestion process, so that the content of ferric ions is higher. Therefore, the digestion solution prepared by the conventional digestion means cannot accurately reflect the content of the ferric iron element in the material, and the subsequent test result cannot truly reflect the content of the ferric iron in the carbon-coated lithium iron phosphate material. In addition, (1) according to the principle of fluorescent spectrometry test, digestion of the carbon-coated lithium iron phosphate material is the first step which must be carried out, and digestion links adopt conventional capping, heating and digestion, and the conventional digestion has large damage to the proportion of ferric iron and ferrous iron in the raw materials. Secondly, the fluorescence spectroscopy is difficult to separate out a trace amount of ferric ions due to the limitation of the self-testing accuracy. (patent CN 201410223124-a method for detecting ferric ions by fluorescence); (2) the principle of the characterization methods of materials such as XPS, EDS, XNES, A-3 Mussbauer method and the like is feasible, the digestion sample is not required to be damaged, the direct scanning test can be carried out, but the error is larger during quantitative analysis, and the analysis is carried outThe method is complex, and the analysis cost is high for the factory, and the method is difficult to implement; (3) the microwave digestion method is complicated, inconvenient and high in detection cost, and the volatilization of a large amount of acid mist in the exhaust process after the digestion of the carbon element is carried out is bound to carry part of iron sources to reduce the content of the iron element.
In view of the above, the present invention provides a new digestion apparatus and method for carbon-coated lithium iron phosphate, which are the technical problems to be solved in the art.
Disclosure of Invention
The invention aims to provide a novel carbon-coated lithium iron phosphate digestion technical scheme aiming at the defects in the prior art so as to obtain digestion liquid equivalent to the components in the original compound, and further accurately test the accurate contents of iron elements with different valence states in the carbon-coated lithium iron phosphate material.
The object of the invention can be achieved by the following technical measures:
the invention provides a carbon-coated lithium iron phosphate digestion device in a first aspect, which comprises:
the digestion container comprises a digestion pipe, a digestion cover matched with the digestion pipe and two through holes formed in the top of the digestion cover;
a sealing plug matched with the through hole;
a heater having at least one digestion tube receiving well for receiving the digestion tube.
Preferably, the digestion cap is hemispherical.
Preferably, the sealing plug is a tap with a curved tip.
Preferably, the digestion tube and the digestion cap are sealingly engaged by threads.
Preferably, the apparatus further comprises:
an inert gas supply mechanism for charging an inert gas into the digestion vessel;
and the air inlet valve assembly is matched with the through hole.
The invention provides a carbon-coated lithium iron phosphate digestion method, which comprises the step of heating and digesting a first sample formed by mixing carbon-coated lithium iron phosphate and concentrated hydrochloric acid in a sealed environment in the presence of inert gas.
Preferably, the digestion method comprises the following steps:
placing a carbon-coated lithium iron phosphate sample in a digestion container, and adding concentrated hydrochloric acid into the digestion container to obtain a first sample;
sealing the digestion container, and introducing inert gas into the digestion container;
opening a heater, heating and digesting the first sample at 120-180 ℃, stopping supplying inert gas when condensed acid mist appears in a digestion container, continuing heating for 10-30 min until the sample is completely digested, and finishing the digestion process to obtain a digestion solution;
cooling the obtained digestion solution, and filtering the digestion solution in the presence of inert gas.
Preferably, the concentration of the concentrated hydrochloric acid is 36.5 wt%, and the ratio of the mass of the carbon-coated lithium iron phosphate sample to the volume of the concentrated hydrochloric acid is (1-3) g, (10-40) m L.
Preferably, the inert gas is nitrogen, argon or helium.
The third aspect of the invention provides a detection method of carbon-coated lithium iron phosphate, which comprises the following steps:
preparing digestion solution according to the digestion method;
diluting the digestion solution to a constant volume to obtain a solution to be detected;
and respectively measuring the total iron content and the ferrous iron content in the liquid to be detected by adopting an oxidation-reduction titration method, wherein the difference value of the total iron content and the ferrous iron content is the ferric iron content.
Compared with the prior art, the digestion device provided by the invention has the advantages that due to the unique design of the digestion cover, the inert gas is introduced before digestion, so that the inert atmosphere in the digestion process is ensured, ferrous iron is prevented from being oxidized into ferric iron, and the proportion of the ferrous iron and the ferric iron is further protected from being damaged; the heater of the digestion device is provided with a plurality of containing holes for placing the digestion tubes, so that the digestion of a plurality of samples can be completed at one time, and the digestion efficiency is high. The digestion method based on the digestion device is simple to operate, the judgment of the endpoint of the completely inert gas atmosphere is clear, and the components in the obtained digestion solution are equivalent to those in the original compound; according to the detection method of the carbon-coated lithium iron phosphate, the digestion solution prepared by the digestion method is used as a detection solution, so that the accurate content of iron elements with different valence states in the carbon-coated lithium iron phosphate material can be accurately tested.
Drawings
Fig. 1 is a schematic structural diagram of an digestion vessel provided by the embodiment of the invention.
Fig. 2 is a schematic structural diagram of a heater according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to make the description of the present disclosure more complete and complete, the following description is given for illustrative purposes with respect to the embodiments and examples of the present invention; it is not intended to be the only form in which the embodiments of the invention may be practiced or utilized. The embodiments are intended to cover the features of the various embodiments as well as the method steps and sequences for constructing and operating the embodiments. However, other embodiments may be utilized to achieve the same or equivalent functions and step sequences.
The invention provides a carbon-coated lithium iron phosphate digestion device, as shown in fig. 1 and 2, the device comprises: the digestion vessel 1, the heater 2 and the inert gas supply mechanism, wherein the digestion vessel 1 comprises a digestion tube 11, a digestion cover 12 hermetically matched with the digestion tube 11, and a first through hole 13 and a second through hole 13 which are arranged at the top of the digestion cover 12; the inert gas supply mechanism comprises an air inlet valve assembly 15 matched with the first through hole 13 or the second through hole 13, and the air inlet valve assembly 15 is used for introducing inert gas into the digestion container 1; be equipped with on the heater 2 and be used for placing the pipe of clearing up and hold hole 21, clear up the quantity that pipe held hole 21 can set up wantonly, for one or more for example, be equipped with a plurality of pipe of clearing up on the heater and hold the hole time, can realize clearing up a plurality of samples simultaneously, improve and clear up efficiency.
The digestion vessel 1 further comprises a sealing plug 14 cooperating with the first through hole 13 and the second through hole 13, the sealing plug 14 being a tap with a curved tip according to some embodiments of the invention. The end of the cock sharp mouth is provided with a fine gap which can play a role of buffering the air pressure increased in the digestion container. Before heating digestion, the sealing plugs 14 matched with the two through holes 13 are taken down, the gas inlet valve assembly 15 is installed on the first through hole 13 and used for introducing inert gas into the digestion container 1, other gases in the digestion container 1 can be discharged from the second through hole 13 due to the introduction of the inert gas, when the inert gas atmosphere is formed in the digestion container 1, the sealing plugs 14 of the second through holes 13 are plugged, and when the gas inlet valve assembly 15 arranged on the first through hole 13 continues to introduce the inert gas until the complete inert gas atmosphere is formed in the digestion container, the sealing plugs 14 of the first through holes 13 are plugged.
In the present invention, the digestion vessel may be made of any suitable material known in the art for resisting acid corrosion, such as PFA, the sealing engagement between the digestion tube 11 and the digestion cap 12 may be made in any suitable manner known in the art, such as screw sealing engagement, which is simple and convenient to operate, according to some embodiments of the present invention, the digestion cap 11 is semi-spherical and semi-transparent or transparent, when the digestion vessel is heated, the acid mist generated by the digestion reaction is observed when the digestion cap 11 is condensed, which indicates that the digestion reaction has started, the atmosphere has been completely removed, the supply of inert gas is stopped, the gas inlet valve assembly 15 disposed on the first through hole 13 is removed, the plug 14 is closed, and the digestion reaction is stopped after heating for a certain period of time.
Due to the unique design of the digestion cover, the digestion device provided by the invention introduces the inert gas before digestion, so that the inert atmosphere in the digestion process is ensured, ferrous iron is prevented from being oxidized into ferric iron, and the proportion of the ferrous iron and the ferric iron is further protected from being damaged; the heater of the digestion device is provided with a plurality of containing holes for placing the digestion tubes, so that the digestion of a plurality of samples can be completed at one time, and the digestion efficiency is high.
The invention provides a digestion method based on the digestion device, which comprises the steps of accurately weighing a carbon-coated lithium iron phosphate sample, placing the sample in a digestion container, and then adding concentrated hydrochloric acid into the digestion container in a fume hood to obtain a first sample; sealing the digestion container, placing the digestion container in a digestion tube accommodating hole of a heater, and introducing inert gas into the digestion container; when an inert gas atmosphere is formed in the digestion container, opening a heater, heating and digesting the first sample at 120-180 ℃, stopping the supply of inert gas when condensed acid mist appears on a digestion cover, and continuing to heat for a period of time until the sample is completely digested to obtain a digestion solution; cooling the obtained digestion solution, and filtering the obtained digestion solution in the presence of inert gas.
According to the method, the mass of a carbon-coated lithium iron phosphate sample is accurate to four digits (the accurate value is 0.0000g) after decimal point, the concentration of concentrated hydrochloric acid is 36.5 wt%, according to some embodiments of the invention, the ratio of the mass of the carbon-coated lithium iron phosphate sample to the volume of the concentrated hydrochloric acid is (1-3) g, (10-40) m L, the carbon-coated lithium iron phosphate sample is digested more completely under the proportion, and the obtained digestion solution components are closer to the components in the original compound.
According to some embodiments of the invention, after the supply of the inert gas is stopped, the sample is completely digested by continuously heating for 10-30 min, and the digestion reaction is finished. After the digestion reaction is finished, cooling the obtained digestion solution to room temperature, transferring the digestion container into a simple glove box filled with inert gas atmosphere, and filtering the digestion solution by using a syringe filter. The digestion method based on the digestion device provided by the invention is simple to operate, the judgment of the endpoint of the completely inert gas atmosphere is clear, and the components in the obtained digestion solution are equivalent to those in the original compound.
The invention also provides a method for detecting the carbon-coated lithium iron phosphate, which takes the digestion solution prepared by the digestion method as a detection solution, and respectively detects the total iron content and the ferrous iron content after diluting the digestion solution to a constant volume, wherein the difference value of the total iron content and the ferrous iron content is the ferric iron content in the detection solution. The method can accurately detect the accurate content of the iron elements with different valence states in the carbon-coated lithium iron phosphate material.
Example 1: the digestion device provided by the invention
(1) Accurately weighing 1-3 g (the accurate value after decimal point is 0.0000g) of a carbon-coated lithium iron phosphate material sample (apg032), and transferring the sample into a digestion tube;
(2) 30m L hydrochloric acid (36.5 wt% strength) was injected into the digestion tube in a fume hood, and the inner wall of the digestion tube was washed during the injection.
(3) Covering the digestion cover, connecting one end of a PE (polyethylene) material thin hose to the opening of the air inlet valve at the top of the digestion cover, connecting the other end of the thin hose to a nitrogen gas source, and slowly introducing nitrogen at the speed of 30m L/min.
(4) And opening the heater, adjusting the temperature of a heating plate of the heater to be 120-180 ℃, further stopping introducing nitrogen when condensed acid mist is seen at the top end of the digestion cover, and inserting a PFA (Perfluoro fluoro ethylene) elongated tip cock into the opening.
(5) After the digestion reaction is finished, the digestion solution is cooled to room temperature, the digestion container is transferred into a simple glove box filled with nitrogen atmosphere, the digestion solution is filtered into a PET bottle by a syringe filter, the dilution and the volume fixing are carried out, then the total iron content and the ferrous iron content in the digestion solution are respectively detected, and the detection result is shown in the following table 1.
Comparative example 1: the same carbon-coated lithium iron phosphate material sample (apg032) is prepared into a digestion solution according to a digestion device in patent CN 104678050A, then the digestion solution is filtered, diluted and subjected to constant volume, then the total iron content and the ferrous content in the digestion solution are respectively detected, and the detection results are shown in Table 1 below.
Comparative example 2: the same carbon-coated lithium iron phosphate material sample (apg032) is prepared into a digestion solution according to the national standard GBT33828-2017, then the digestion solution is filtered, diluted and subjected to constant volume, then the total iron content and the ferrous iron content in the digestion solution are respectively detected, and the detection results are shown in the following table 1.
The method for detecting the total iron content comprises the following steps: the detection is carried out according to the national standard GBT33828-2017
(1) Stannous dichloride is used as a primary oxidant to oxidize ferric ions in the digestion solution into ferrous ions;
(2) further dropwise adding sodium tungstate and titanium trichloride into the digestion solution in the step (1) to ensure that ferric ions in the digestion solution are completely oxidized to ferrous ions, and at the moment, the solution is blue due to excessive titanium trichloride;
(3) reducing excessive titanium trichloride by adopting potassium dichromate with thinner concentration until the solution is in a colorless transparent state;
(4) and (3) acidifying the digestion solution in the step (3) by using 3+3+4 sulfur and phosphorus mixed acid by using sodium diphenylamine sulfonate as an indicator. And (3) dripping standard solution of potassium dichromate of 0.1mol/l to obtain the total iron element content.
The ferrous content detection method comprises the following steps: according to potassium dichromate redox titration
Weighing a certain amount of digestion solution, and adding 3+3+4 mixed sulfuric acid and phosphoric acid; dropwise adding potassium dichromate to the digestion solution by using sodium diphenylamine sulfonate as an indicator; and (4) calculating to obtain the content of ferrous iron in the digestion solution.
TABLE 1 detection results of iron content in digestion solution prepared under different digestion devices
As can be seen from table 1: (1) the results of the total iron test for example 1 and comparative example 2 are close to theoretical values, and the total iron content is lower as tested for comparative example 1. Illustrating that the digestion apparatus in comparative example 1 had volatilized total iron content due to poor sealability; (2) example 1 tested the highest ferrous ion, comparative example 2 tested a relatively low ferrous ion. It can be shown that comparative example 2 has a high content of trivalent iron due to partial oxidation of divalent iron to trivalent iron during digestion and sample preparation.
From the above, in the link of digesting the carbon-coated lithium iron phosphate, if a digestion device which is strictly sealed is not provided, the total iron amount is easy to be lost; (2) the form of iron in the sample is slightly changed, namely the ratio of iron elements with different valence states in the digestion solution cannot be accurately equal to the ratio of iron elements with different valence states in the material.
Therefore, it can be seen from table 1 that the digestion apparatus provided by the present invention has good sealing performance, can ensure the inert atmosphere in the digestion process, prevent the ferrous iron from being oxidized into the ferric iron, further protect the ratio of the ferrous iron and the ferric iron from being damaged, make the components in the obtained digestion solution closer to those in the original compound, and make the measured result more accurate.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The utility model provides a carbon-coated lithium iron phosphate digestion device which characterized in that, the device includes:
the digestion container comprises a digestion pipe, a digestion cover matched with the digestion pipe and two through holes formed in the top of the digestion cover;
a sealing plug matched with the through hole;
a heater having at least one digestion tube receiving well for receiving the digestion tube.
2. The carbon-coated lithium iron phosphate digestion apparatus according to claim 1, wherein the digestion cover is hemispherical.
3. The carbon-coated lithium iron phosphate digestion apparatus according to claim 1, wherein the sealing plug is a cock with a curved tip.
4. The carbon-coated lithium iron phosphate digestion apparatus according to claim 1, wherein the digestion tube and the digestion cap are hermetically fitted by a screw thread.
5. The carbon-coated lithium iron phosphate digestion apparatus according to claim 1, further comprising:
an inert gas supply mechanism for charging an inert gas into the digestion vessel;
and the air inlet valve assembly is matched with the through hole.
6. A digestion method of carbon-coated lithium iron phosphate is characterized in that a first sample formed by mixing carbon-coated lithium iron phosphate and concentrated hydrochloric acid is heated and digested in a sealed environment in the presence of inert gas.
7. The method for digesting carbon-coated lithium iron phosphate according to claim 6, comprising the steps of:
placing a carbon-coated lithium iron phosphate sample in a digestion container, and adding concentrated hydrochloric acid into the digestion container to obtain a first sample;
sealing the digestion container, and introducing inert gas into the digestion container;
turning on a heater, heating and digesting the first sample at 120-180 ℃, and stopping the supply of inert gas and continuously heating for 10-30 min when condensed acid mist appears in a digestion container;
cooling the obtained digestion solution, and filtering the digestion solution in the presence of inert gas.
8. The method for digesting carbon-coated lithium iron phosphate according to claim 6, wherein the concentration of the concentrated hydrochloric acid is 36.5 wt%, and the ratio of the mass of the carbon-coated lithium iron phosphate sample to the volume of the concentrated hydrochloric acid is (1-3) g, (10-40) m L.
9. The method for digesting carbon-coated lithium iron phosphate according to claim 6, wherein the inert gas is nitrogen, argon or helium.
10. A detection method of carbon-coated lithium iron phosphate is characterized by comprising the following steps:
preparing a digestion solution according to the digestion method of any one of claims 6 to 9;
diluting the digestion solution to a constant volume to obtain a solution to be detected;
and detecting the content of the ferric iron in the liquid to be detected by adopting an oxidation-reduction titration method.
Priority Applications (1)
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