A carbon-coated lithium manganese iron phosphate digestion agent and a method for detecting the content of main elements in carbon-coated lithium manganese iron phosphate

Abstract

The application provides a carbon-coated manganese iron lithium phosphate digestion agent and a method for detecting the content of main elements in the carbon-coated manganese iron lithium phosphate, and belongs to the technical field of lithium ion battery cathode materials. The digestion agent comprises a first digestion agent and a second digestion agent. The first digestion agent comprises a mixture of a nitric acid solution and a sulfuric acid solution. The mass concentration of the nitric acid solution is greater than or equal to 50 wt%. The mass concentration of the sulfuric acid solution is greater than or equal to 80 wt%. The volume ratio of the nitric acid solution to the sulfuric acid solution is not less than 0.3:1. The second digestion agent comprises a hydrochloric acid solution. The mass concentration of the hydrochloric acid solution is greater than or equal to 30 wt%. The volume ratio of the hydrochloric acid solution to the sulfuric acid solution is not less than 1:1. The digestion agent can completely digest the carbon-coated lithium iron phosphate, and improves the accuracy and consistency of the subsequent detection of the content of main elements in the carbon-coated lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a carbon-coated lithium manganese iron phosphate digester and a method for detecting the content of main elements in carbon-coated lithium manganese iron phosphate. Background Technology

[0002] The energy density of lithium iron phosphate (LFP) batteries has approached its theoretical limit, and lithium manganese iron phosphate (LFP) batteries are considered an important upgrade direction for LFP batteries, with promising application prospects and a broad market space. However, LFP batteries have poor conductivity, and the band gap for electron transitions in LFP batteries is 2 eV. Currently, the LFP battery industry commonly uses carbon coating of LFP batteries, which can improve the conductivity of LFP batteries to some extent.

[0003] In the production process of carbon-coated lithium manganese iron phosphate, it is necessary to determine the content of major elements (including at least one of Li, Mn, Fe, and P) in the powder to ascertain its qualification. Currently, the main methods for testing the content of major elements in carbon-coated lithium manganese iron phosphate are the titration method with ferrous ammonium sulfate standard solution and the inductively coupled plasma optical emission spectrometry (ICP-OES) analysis method.

[0004] For example, patent application CN 105372229 A discloses a method for detecting the content of main elements in carbon-coated lithium iron phosphate or lithium manganese iron phosphate, including the following steps: (1) Sample pretreatment: the sample to be tested is digested with acid, transferred to a fixed volume, allowed to stand, and after the solution separates into layers, the clear middle part is taken as the test solution; (2) Plotting a standard curve: a series of mixed standard solutions are prepared according to the types of main elements to be tested, and the standard curve is plotted using an inductively coupled plasma atomic emission spectrometer; (3) Determination of the content of main elements: the content of main elements in the test solution is determined using an inductively coupled plasma atomic emission spectrometer. However, this method uses hydrochloric acid as a digesting agent, which cannot completely dissolve the elements in carbon-coated lithium manganese iron phosphate, and filter paper is required for filtration, which increases the uncertainty of the test results.

[0005] For example, patent application CN 115267047 A discloses a method for detecting the manganese content in battery-grade carbon-coated lithium manganese iron phosphate, comprising: obtaining a dry-based sample containing battery-grade carbon-coated lithium manganese iron phosphate; sequentially adding a metal ion dissolving acid and phosphoric acid to the dry-based sample and heating it at a temperature of 150–250°C to obtain a mixed solution; adding nitric acid to the mixed solution and heating it at a temperature of 210–230°C, and adding ammonium nitrate for oxidation when no more flue gas is generated to obtain a titrant; titrating the titrant with a ferrous ammonium sulfate standard solution until light red, then adding an N-benzoic acid solution, and continuing titrating with the ferrous ammonium sulfate standard solution until bright yellow; and calculating the mass fraction of manganese in the dry-based sample. However, this method uses phosphoric acid and nitric acid, which cannot completely dissolve the elements in the carbon-coated lithium manganese iron phosphate, affecting the accuracy of the test results.

[0006] Patent application CN 115639313 A discloses a method for detecting manganese in carbon-coated manganese iron lithium phosphate. The specific detection method is as follows: S1, ferrous ammonium sulfate standardization; S2, weighing; S2-1, taking 0.3±0.0005g of sample; S2-2, adding a small amount of ultrapure water to the above sample; S2-3, adding digestion reagent and shaking to mix evenly; S3, digestion; S3-1, first placing a graphite furnace and heating the sample using the graphite furnace until the sample is completely dissolved; S3-2, after the sample is completely dissolved, removing the test tube to cool, and adding 20mL of concentrated phosphoric acid, shaking to mix evenly. And; S3-3, continue heating the mixed test tube until the internal solution turns deep purple and the small bubbles disappear; S3-4, remove the test tube and cool it to 70℃, then add 90mL of ultrapure water and shake thoroughly to completely dissolve the salts; S3-5, cool the test tube solution to room temperature; S4, titration; S4-1, titrate the sample with ferrous ammonium sulfate standard solution until it turns light red; S4-2, add 3 drops of N-benzoic acid indicator; S4-3, titrate until the solution changes from light purple to bright yellow, then stop; S4-4, record the titration result after 15s. However, this method requires pretreatment with perchloric acid in a graphite furnace at 320℃ to completely dissolve the carbon-coated lithium manganese iron phosphate. Perchloric acid can explode when it comes into contact with organic matter, endangering the personal safety of the test personnel. Summary of the Invention

[0007] This invention is based on the inventor's discovery and understanding of the following facts and problems: In related technologies, methods for detecting the content of main elements in carbon-coated lithium manganese iron phosphate all require the complete dissolution of the carbon-coated lithium manganese iron phosphate. This is crucial for testing the content of main elements in carbon-coated lithium manganese iron phosphate; otherwise, it will greatly affect the accuracy of the detection results. However, research on this aspect in related technologies is insufficient. Therefore, it is necessary to design a carbon-coated lithium manganese iron phosphate digesting agent and a method for detecting the content of main elements in carbon-coated lithium manganese iron phosphate.

[0008] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a carbon-coated lithium manganese iron phosphate digesting agent and a method for testing the content of major elements in carbon-coated lithium manganese iron phosphate. This digesting agent can completely dissolve carbon-coated lithium manganese iron phosphate, thereby greatly improving the accuracy and consistency of subsequent major element content detection.

[0009] The carbon-coated lithium manganese iron phosphate digester of this invention includes a first digester and a second digester. The first digester comprises a mixture of nitric acid solution and sulfuric acid solution, wherein the mass concentration of the nitric acid solution is 50 wt% or more, the mass concentration of the sulfuric acid solution is 80 wt% or more, and the volume ratio of the nitric acid solution to the sulfuric acid solution is not less than 0.3:1. The second digester comprises a hydrochloric acid solution, wherein the mass concentration of the hydrochloric acid solution is 30 wt% or more, and the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is not less than 1:1.

[0010] The advantages and technical effects of the carbon-coated lithium manganese iron phosphate digester of this invention are as follows:

[0011] (1) The digesting agent in this embodiment of the invention is divided into a first digesting agent and a second digesting agent. In the subsequent digestion process, the digestion is carried out in two separate steps. The first digesting agent first digests carbon-coated lithium manganese iron phosphate into a milky white lithium precipitate. The second digesting agent then completely dissolves the milky white lithium precipitate in the first digestion solution, thereby achieving the purpose of completely dissolving carbon-coated lithium manganese iron phosphate. The effect is significantly better than using the first digesting agent alone or using the second digesting agent alone.

[0012] (2) The digesting agent in this embodiment of the invention is divided into a first digesting agent and a second digesting agent. In the first digesting agent, sulfuric acid is the main component that plays a digesting role, while nitric acid plays a role in reducing the activation energy of the reaction and increasing the reaction rate. Therefore, by adjusting the volume ratio of nitric acid solution to sulfuric acid solution to not less than 0.3:1, carbon-coated lithium manganese iron phosphate can be quickly and thoroughly digested into a milky white lithium precipitate. At the same time, by adjusting the volume ratio of hydrochloric acid solution to sulfuric acid solution to not less than 1:1, the undissolved milky white lithium precipitate can be dissolved, thereby achieving the purpose of thoroughly dissolving carbon-coated lithium manganese iron phosphate.

[0013] (3) The digesting agent in this embodiment of the invention is divided into a first digesting agent and a second digesting agent. The digestion process is carried out in two separate steps instead of mixing the first digesting agent and the second digesting agent and then performing a single digestion. This ensures that the first digesting agent has a high concentration, thereby improving the oxidizing power of the first digesting agent and ultimately improving the dissolution effect on carbon-coated lithium manganese phosphate.

[0014] (4) In the digestion agent of the present invention, the mass concentrations of sulfuric acid solution, nitric acid solution and hydrochloric acid solution are within a limited range, which can ensure that the digestion agent has sufficient oxidizing power, thereby improving the digestion effect on carbon-coated lithium manganese phosphate.

[0015] In some embodiments, the sulfuric acid solution has a mass concentration of 95 wt% or more; and / or the nitric acid solution has a mass concentration of 60 wt% or more.

[0016] In some embodiments, the volume ratio of the nitric acid solution to the sulfuric acid solution is (0.3-4):1.

[0017] In some embodiments, the mass concentration of the hydrochloric acid solution is 35 wt% or higher.

[0018] In some embodiments, the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is (1-4):1.

[0019] This invention also provides a method for detecting the content of major elements in carbon-coated manganese iron phosphate, comprising the following steps:

[0020] (1) First, the first digesting agent in the digesting agent of the present invention and the carbon-coated lithium manganese iron phosphate are mixed, and a first digestion solution is obtained after the first digestion reaction; then the second digesting agent in the digesting agent of the present invention and the first digestion solution are mixed, and a second digestion solution is obtained after the second digestion reaction.

[0021] (2) Dilute the second digestion solution to a fixed volume to obtain a diluted solution;

[0022] (3) Prepare standard solutions containing the main element with gradient concentrations, test them using an inductively coupled plasma atomic emission spectrometer, and plot the standard curve;

[0023] (4) The content of the main elements in the diluted solution is determined by using an inductively coupled plasma atomic emission spectrometer, and the content of the main elements in the carbon-coated lithium manganese iron phosphate powder is calculated.

[0024] The advantages and technical effects of the method for detecting the main element content in carbon-coated manganese iron phosphate according to embodiments of the present invention are as follows:

[0025] (1) The detection method of this embodiment first uses the first digesting agent in the digesting agent of this embodiment to digest carbon-coated lithium iron phosphate for the first time to obtain a first digestion solution containing milky white lithium precipitate. Then, the second digesting agent in the digesting agent of this embodiment is used to digest the undissolved milky white lithium precipitate in the first digestion solution for the second time. This can achieve the purpose of completely dissolving carbon-coated lithium iron phosphate, thereby improving the accuracy and consistency of subsequent main element content detection.

[0026] (2) The detection method of the present invention is basically equivalent to the detection method of the related art that uses concentrated perchloric acid as a digesting agent. The standard relative deviation (RSD) of the test results of the two methods can be controlled within 1%. It can be seen that the detection method of the present invention has high accuracy and precision.

[0027] In some embodiments, in step (1), (2.5-4.5) mL of the sulfuric acid solution and not less than 1.2 mL of the nitric acid solution are added to every 0.2 g of the carbon-coated lithium manganese iron phosphate.

[0028] In some embodiments, in step (1), the digestion reaction is carried out by heating digestion at a temperature of 160-300°C.

[0029] In some embodiments, in step (1), after obtaining the first digestion solution, the solution is cooled to room temperature.

[0030] In some embodiments, in steps (3) and (4), the main element includes at least one of Li, Mn, Fe and P. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0032] This invention provides a carbon-coated lithium manganese iron phosphate digester, comprising a first digester and a second digester. The first digester comprises a mixture of nitric acid solution and sulfuric acid solution, wherein the mass concentration of the nitric acid solution is 50 wt% or higher, the mass concentration of the sulfuric acid solution is 80 wt% or higher, and the volume ratio of the nitric acid solution to the sulfuric acid solution is not less than 0.3:1. The second digester comprises a hydrochloric acid solution, wherein the mass concentration of the hydrochloric acid solution is 30 wt% or higher, and the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is not less than 1:1.

[0033] The digesting agent in this embodiment of the invention is divided into a first digesting agent and a second digesting agent. The digestion process is carried out in two separate steps. The first digesting agent first digests carbon-coated lithium manganese iron phosphate into a milky white lithium-containing precipitate. The second digesting agent then completely dissolves the milky white lithium-containing precipitate in the first digestion solution, thereby achieving the purpose of completely dissolving carbon-coated lithium manganese iron phosphate. The effect is significantly better than using the first digesting agent or the second digesting agent alone.

[0034] In the first digestion agent, sulfuric acid is the primary agent responsible for digestion, while nitric acid lowers the activation energy and increases the reaction rate. Therefore, by adjusting the volume ratio of nitric acid solution to sulfuric acid solution to no less than 0.3:1, carbon-coated lithium manganese iron phosphate can be quickly and thoroughly digested into a milky white lithium-containing precipitate. Simultaneously, by adjusting the volume ratio of hydrochloric acid solution to sulfuric acid solution to no less than 1:1, the undissolved milky white lithium-containing precipitate can be dissolved, achieving complete dissolution of the carbon-coated lithium manganese iron phosphate. If hydrochloric acid solution is used instead of nitric acid solution in the first digestion agent, the higher water content in the hydrochloric acid solution compared to the same volume of nitric acid solution will reduce the concentration and oxidizing power of sulfuric acid, leading to incomplete carbon removal. The second digestion agent can further digest the undissolved substance in the first digestion solution, i.e., the milky white lithium-containing precipitate, achieving complete digestion of the carbon-coated lithium manganese iron phosphate. If other types of acid are used instead, complete digestion of the carbon-coated lithium manganese iron phosphate cannot be achieved.

[0035] The digesting agent in this embodiment of the invention is divided into a first digesting agent and a second digesting agent. The digestion process is carried out in two separate steps, rather than mixing the first and second digesting agents and then performing a single digestion. This ensures that the first digesting agent has a high concentration, thereby improving its oxidizing properties and ultimately improving the dissolution effect on carbon-coated lithium manganese phosphate.

[0036] Furthermore, in the digestion agent of this invention, the mass concentrations of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution are within a limited range, ensuring that the digestion agent has sufficient oxidizing power, thereby improving the digestion effect on carbon-coated lithium manganese phosphate. In summary, the digestion agent of this invention can completely dissolve carbon-coated lithium manganese iron phosphate, thereby improving the accuracy and consistency of subsequent main element content detection.

[0037] In this embodiment of the invention, the sulfuric acid solution used to prepare the first digester has a mass concentration of 80 wt% or higher, and the nitric acid solution used to prepare the first digester has a mass concentration of 50 wt% or higher. If these conditions are not met, the mass concentration of acid in the first digester is insufficient, resulting in low oxidizing power and poor digestion effect. Consequently, some undissolved carbon remains in the final digestion product, affecting the accuracy and consistency of the detection of the main element content in carbon-coated lithium manganese iron phosphate. Preferably, in some embodiments, the sulfuric acid solution used to prepare the first digester has a mass concentration of 95 wt% or higher, and the nitric acid solution used to prepare the first digester has a mass concentration of 60 wt% or higher.

[0038] In some embodiments, the volume ratio of the nitric acid solution to the sulfuric acid solution is (0.3-4):1. When this volume ratio is less than 0.3:1, the viscosity of the first digesting agent is too high, causing the sample to bubble and splash during subsequent digestion reactions, affecting the stability of subsequent detection results. Simultaneously, the digestion reaction rate is too slow, failing to rapidly and effectively digest carbon-coated lithium manganese iron phosphate. Conversely, when the volume ratio is too high, it increases the unnecessary amount of nitric acid solution used, which is detrimental to cost reduction and efficiency improvement.

[0039] In this embodiment of the invention, the hydrochloric acid solution used to prepare the second digester has a mass concentration of 30 wt% or higher. When this mass concentration is lower than 30 wt%, the acid concentration in the second digester is insufficient, resulting in lower oxidizing power and poor dissolution of the milky white lithium precipitate. Consequently, some milky white undissolved matter remains in the final digestion product, affecting the accuracy and consistency of the detection of the main element content in carbon-coated lithium manganese iron phosphate. Preferably, in some embodiments, the hydrochloric acid solution used to prepare the second digester has a mass concentration of 35 wt% or higher.

[0040] In some embodiments, the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is (1-4):1. When this volume ratio is less than 1:1, the amount of hydrochloric acid solution used is too small, resulting in some milky white undissolved matter remaining in the final digestion product, affecting the accuracy and consistency of the detection of the main element content in carbon-coated lithium manganese iron phosphate. Conversely, when the volume ratio is too large, it increases the amount of hydrochloric acid solution used unnecessarily, which is not conducive to cost reduction and efficiency improvement.

[0041] This invention also provides a method for detecting the content of major elements in carbon-coated manganese iron phosphate, comprising the following steps:

[0042] (1) First, the first digesting agent in the digesting agent of the present invention and the carbon-coated lithium manganese iron phosphate are mixed, and a first digestion solution is obtained after the first digestion reaction; then the second digesting agent in the digesting agent of the present invention and the first digestion solution are mixed, and a second digestion solution is obtained after the second digestion reaction.

[0043] (2) Dilute the second digestion solution to a fixed volume to obtain a diluted solution;

[0044] (3) Prepare standard solutions containing the main element with gradient concentrations, test them using an inductively coupled plasma atomic emission spectrometer, and plot the standard curve;

[0045] (4) The content of the main elements in the diluted solution is determined by using an inductively coupled plasma atomic emission spectrometer, and the content of the main elements in the carbon-coated lithium manganese iron phosphate powder is calculated.

[0046] The detection method of this invention first uses the first digesting agent in the digesting agent of this invention to digest carbon-coated lithium iron phosphate for the first time, obtaining a first digestion solution containing a milky white lithium precipitate. Then, the second digesting agent in the digesting agent of this invention is used to digest the undissolved milky white lithium precipitate in the first digestion solution for the second time, which can achieve the purpose of completely dissolving carbon-coated lithium iron phosphate, thereby improving the accuracy and consistency of subsequent main element content detection. Compared with the detection method of related technologies that uses concentrated perchloric acid as a digesting agent, the detection methods of this invention detect the main element content to be basically equivalent, and the standard relative deviation (RSD) of the test results of both can be controlled within 1%. It can be seen that the detection method of this invention has high testing precision and accuracy.

[0047] In some embodiments, in step (1), 2.5-4.5 mL of the sulfuric acid solution and at least 1.2 mL of the nitric acid solution are added to every 0.2 g of carbon-coated lithium manganese iron phosphate. When the amount of sulfuric acid solution added to every 0.2 g of carbon-coated lithium manganese iron phosphate is less than 2.5 mL and the amount of nitric acid solution added is less than 1.2 mL, the first digesting agent is unlikely to completely digest the carbon-coated lithium iron phosphate into a milky white lithium precipitate. Some undissolved carbon remains in the first digestion solution, and subsequent treatment with the second digesting agent is also unlikely to completely digest it. Some undissolved carbon will still remain in the second digestion solution, thus affecting the accuracy and consistency of the detection of the main element content in carbon-coated lithium manganese iron phosphate. When the amount of sulfuric acid solution added to every 0.2 g of carbon-coated lithium manganese iron phosphate is greater than 4.5 mL, the first digestion reaction is very violent, and the solution splashes, which can easily lead to unstable subsequent detection results.

[0048] The detection method of this invention does not particularly limit the specific method of the two digestion reactions in step (1). For example, heating digestion, microwave digestion, precipitation method, etc. can be used. Preferably, in some embodiments, the digestion reaction in step (1) is heating digestion. For example, when the heating temperature is 160-300℃, the processing time of step (1) can be controlled within 10-20 minutes, indicating that heating digestion can greatly improve the testing efficiency, avoid the use of a large number of reagents and containers in precipitation method, and also avoid expensive instruments such as microwave digestion instruments, thus reducing the cost of detection auxiliary materials.

[0049] In some embodiments, in step (1), cooling to room temperature after obtaining the first digestion solution is to reduce the degree of reaction of the second digestion reaction and avoid the reaction being too violent and causing the solution to splash, thereby improving the stability of the subsequent detection of the main element content in carbon-coated lithium manganese iron phosphate.

[0050] In some embodiments, in steps (3) and (4), the main element includes at least one of Li, Mn, Fe, and P. It is understood that if the carbon-coated lithium manganese iron phosphate is also doped with elements such as Cu, Zn, Cr, Ti, V, Si, Na, K, Mg, and Ca, the content of these elements can also be obtained by the detection method of this embodiment.

[0051] The present invention will now be described in detail with reference to the embodiments.

[0052] Example 1

[0053] A carbon-coated lithium manganese iron phosphate digester includes a first digester and a second digester. The first digester is a mixture of 3 mL of 98 wt% sulfuric acid solution (GR grade) and 3 mL of 64 wt% nitric acid solution (GR grade), and the second digester is 3 mL of 37 wt% hydrochloric acid solution (GR grade).

[0054] A method for detecting the content of major elements in carbon-coated manganese iron phosphate includes the following steps:

[0055] (1) Select commercially available carbon-coated lithium manganese iron phosphate powder and dry it in a drying oven at 80°C for 2 hours.

[0056] (2) Weigh 0.2000g±0.0010g of carbon-coated manganese iron lithium phosphate powder from step (1) and add it to a 100mL quartz beaker.

[0057] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to a quartz beaker. Heat the mixture at 180°C using a graphite heating plate or an electric heating plate until it is completely milky white. Remove the acid to 2-4 mL and cool it to room temperature. Then add hydrochloric acid solution (GR grade) to the quartz beaker. Continue to heat the mixture at 180°C using a heating plate until it is clear and transparent. Remove the acid to 2-4 mL and cool it to room temperature. This is solution a after digestion of carbon-coated lithium manganese iron phosphate, hereinafter referred to as digestion solution a.

[0058] (4) The digestion solution a obtained in step (3) is diluted to 100 mL with ultrapure water in a volumetric flask to obtain the diluted solution b. 1 mL of diluted solution b and 2 mL of nitric acid solution (GR grade) are then diluted to 100 mL to obtain the diluted solution c.

[0059] (5) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 45 s, the number of tests to 2, and the nebulizer pressure to 300 kPa. Li was observed radially, and Mn, Fe, and P were observed axially. Take different volumes of multi-element (containing Li, Mn, Fe, and P) standard solutions of gradient concentrations and prepare standard solutions of 1.0 µg / mL, 2.0 µg / mL, 5.0 µg / mL, 10.0 µg / mL, and 15.0 µg / mL respectively to obtain the standard curves of multi-element (containing Li, Mn, Fe, and P), and fit the standard curve equations. The linearity is ≥0.999.

[0060] (6) Under the same test conditions as in step (5), the diluted solution c from step (4) was tested using an inductively coupled plasma atomic emission spectrometer. The spectral lines were selected as Li 670.784 nm, Mn 237.610 nm, Fe 259.939 nm, and P 214.914 nm, respectively, to obtain the content of the main elements (Li, Mn, Fe, P) in the diluted solution c.

[0061] (7) Calculation of results:

[0062] Step (1) Main element content (wt%) in carbon-coated manganese iron lithium phosphate powder = C × V × M / m × 10 -6 ×100%; where C is the molar concentration of a certain main element in the diluted solution c, in mol / L; V is the fixed volume of the fixed solution b, 100 × dilution factor 100, i.e., 10000, in mL; M is the molar mass of a certain main element, in g / mol; and m is the mass of carbon-coated manganese iron lithium phosphate powder, 0.2000 g ± 0.0010, in g.

[0063] Six parallel experiments were performed according to the detection method of Example 1, and they were recorded as groups 1-6. The contents of the main elements (Li, Mn, Fe, P) detected in groups 1-6 of Example 1 are shown in Table 1.

[0064] Table 1. Detection results obtained by the method for detecting the content of major elements in carbon-coated lithium manganese iron phosphate powder in Example 1.

[0065]

[0066] As can be seen from Table 1, the carbon-coated lithium manganese iron phosphate powder in Example 1 was completely dissolved, and the standard relative deviation (RSD) of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate powder was less than 1.0%, indicating that the method has good consistency in determining the main element (Li, Mn, Fe, P) content in carbon-coated lithium manganese iron phosphate.

[0067] Example 2

[0068] The carbon-coated lithium manganese iron phosphate digestant and detection method in this embodiment are the same as those in Example 1, except that the volume of the sulfuric acid solution is 4 mL and the volume of the nitric acid solution is 2 mL.

[0069] Example 3

[0070] The carbon-coated lithium manganese iron phosphate digestant and detection method in this embodiment are the same as those in Example 1, except that the volume of the sulfuric acid solution is 4.5 mL and the volume of the nitric acid solution is 1.5 mL.

[0071] Example 4

[0072] The carbon-coated lithium manganese iron phosphate digestant and detection method in this embodiment are the same as those in Example 1, except that the volume of the nitric acid solution is 6 mL.

[0073] Example 5

[0074] The carbon-coated lithium manganese iron phosphate digestant and detection method in this embodiment are the same as those in Example 1, except that the volume of the nitric acid solution is 9 mL.

[0075] Table 2. Detection results of the main element content in carbon-coated manganese iron lithium phosphate powders of Examples 1-5

[0076]

[0077] Example 6

[0078] The carbon-coated lithium manganese iron phosphate digestant and detection method in this embodiment are the same as those in Example 1, the only difference being that...

[0079] (2) Weigh 0.2000g±0.0010g of carbon-coated manganese iron lithium phosphate powder from step (1) and add it to the polytetrafluoroethylene digestion tube of the microwave digester.

[0080] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to the polytetrafluoroethylene digestion tube. Use a microwave digester to heat at 120°C for 10 min, 150°C for 10 min, and 180°C for 30 min according to the program. Then remove the tube and cool it to room temperature. Add hydrochloric acid solution (GR grade) to the polytetrafluoroethylene digestion tube. Use a microwave digester to heat at 120°C for 10 min, 150°C for 10 min, and 180°C for 30 min according to the program. Then remove the tube and cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0081] Table 3. Detection results obtained by the method for detecting the content of major elements in carbon-coated lithium manganese iron phosphate powder in Example 6.

[0082]

[0083] Comparative Example 1

[0084] The carbon-coated lithium manganese iron phosphate digester in this comparative example was 10 mL of 72 wt% perchloric acid solution (GR grade).

[0085] The method for detecting the main elements in carbon-coated lithium manganese iron phosphate in this comparative example is the same as that in Example 1, the only difference being that...

[0086] (3) Add concentrated perchloric acid (GR grade) to a quartz beaker, and heat the mixture at 300°C using a graphite heating plate or an electric heating plate until it is clear and transparent. Then remove the acid to 2-5 mL and cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0087] (4) Filter the digestion solution a obtained in step (3) with ultrapure water and medium-speed quantitative filter paper to a volumetric flask and make up to 100 mL. This is the volumetric solution b. Take 1 mL of volumetric solution b and 2 mL of nitric acid solution (GR grade) and make up to 100 mL. This is the dilution solution c.

[0088] Table 4. Detection results of the main element content in carbon-coated lithium manganese iron phosphate powder of Comparative Example 1.

[0089]

[0090] Table 4 shows that in comparative examples 1-6, the carbon-coated lithium manganese iron phosphate was completely dissolved, and the standard relative deviation (RSD) of the main element (Li, Mn, Fe, P) content in the detected carbon-coated lithium manganese iron phosphate powder was less than 1.0%, indicating that the method for determining the main element (Li, Mn, Fe, P) content in carbon-coated lithium manganese iron phosphate is consistent. The content of main elements (Li, Mn, Fe, P) detected in this comparative example is basically consistent with that in Example 1. Perchloric acid is easily evaporated, and the dense fumes from the evaporation will accumulate and condense in the ventilation ducts. When hot steam passes through, the condensed perchloric acid reacts with dust and organic matter, causing combustion and explosion. Extra caution is required during operation to avoid danger.

[0091] Comparative Example 2

[0092] The comparative example of carbon-coated lithium manganese iron phosphate digester was a mixture of 4.5 mL of 64 wt% nitric acid solution (GR grade) and 4.5 mL of 98 wt% sulfuric acid solution (GR grade).

[0093] The method for detecting the main element content in carbon-coated lithium manganese iron phosphate in this comparative example is the same as that in Example 1, except that:

[0094] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to a quartz beaker. Heat the mixture at 180°C using a graphite heating plate or an electric heating plate until it is completely milky white. Then remove the acid to 2-4 mL and cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0095] (4) Filter the digestion solution a obtained in step (3) with ultrapure water and medium-speed quantitative filter paper to a volumetric flask and make up to 100 mL. This is the volumetric solution b. Take 1 mL of volumetric solution b and 2 mL of nitric acid solution (GR grade) and make up to 100 mL. This is the dilution solution c.

[0096] Table 5. Detection results obtained by the detection method of main element content in carbon-coated manganese iron lithium phosphate powder of Comparative Example 2

[0097]

[0098] As shown in Table 5, the carbon-coated lithium manganese iron phosphate powder obtained in this comparative example was not completely dissolved. The standard relative deviation (RSD) of the main element (Li) content in the carbon-coated lithium manganese iron phosphate powder obtained in this comparative example was much higher than that in Example 1, indicating that the consistency of the main element (Li) content determination in the carbon-coated lithium manganese iron phosphate in this comparative example was relatively poor compared to Example 1. In addition, the average value of the main element (Li) content detected in this comparative example was lower than the average value in Example 1.

[0099] The reasons are analyzed as follows: This comparative example only uses the first digesting agent, which can digest the carbon coating layer to obtain a milky white mixture containing some milky white precipitate. However, since there is no second digesting agent, it is impossible to completely digest the milky white precipitate.

[0100] Comparative Example 3

[0101] The carbon-coated lithium manganese iron phosphate digester in this comparative example was 10 mL of 37 wt% hydrochloric acid solution (GR grade).

[0102] The detection method for this comparative example is the same as that in Example 1, except that:

[0103] (3) Add hydrochloric acid solution (GR grade) to a quartz beaker, and heat the mixture to 2-5 mL at 180°C using a graphite heating plate or an electric heating plate. Then remove the beaker and cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0104] (4) Filter the digestion solution a obtained in step (3) with ultrapure water and medium-speed quantitative filter paper to a volumetric flask and make up to 100 mL. This is the volumetric solution b. Take 1 mL of volumetric solution b and 2 mL of nitric acid solution (GR grade) and make up to 100 mL. This is the dilution solution c.

[0105] Table 6. Detection results of the main element content in carbon-coated manganese iron lithium phosphate powder of Comparative Example 3.

[0106]

[0107] As shown in Table 6, the carbon-coated lithium manganese iron phosphate powder in this comparative example was not completely dissolved, and the standard relative deviation (RSD) of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate powder detected in groups 1-6 was significantly higher than that in Example 1. This indicates that the consistency of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate powder determined in this comparative example was worse than that in Example 1. In addition, the average content of main elements (Li, Mn, Fe, P) in the carbon-coated lithium manganese iron phosphate powder detected in this comparative example was lower than that in Example 1.

[0108] The reasons are analyzed as follows: This comparative example only used the second digesting agent and not the first digesting agent. The oxidizing power of hydrochloric acid solution is not as strong as that of sulfuric acid solution, which makes it impossible to completely digest the carbon coating layer, and the resulting solution contains undissolved carbon.

[0109] Comparative Example 4

[0110] The carbon-coated lithium manganese iron phosphate digester in this comparative example was a mixture of 3 mL of 98 wt% sulfuric acid solution (GR grade), 3 mL of 64 wt% nitric acid solution (GR grade), and 3 mL of 37 wt% hydrochloric acid solution (GR grade).

[0111] The detection method for this comparative example is the same as that in Example 1, except that:

[0112] (3) Add the digesting agent of the comparative ratio into a quartz beaker, and heat the mixture to 2-5 mL at 180°C using a graphite heating plate or an electric heating plate. Then remove the beaker and cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0113] (4) The digestion solution a obtained in step (3) is filtered with ultrapure water and medium-speed quantitative filter paper and diluted to a volumetric flask to a volumetric volume of 100 mL. This is the diluted solution b after digestion of carbon-coated lithium manganese iron phosphate. Take 1 mL of diluted solution b and 2 mL of nitric acid solution (GR grade) and dilute to a volume of 100 mL to obtain the diluted solution c.

[0114] Table 7. Detection results of the main element content in carbon-coated lithium manganese iron phosphate powder of Comparative Example 4.

[0115]

[0116] As shown in Table 7, the carbon-coated lithium manganese iron phosphate powder obtained in this comparative example was not completely dissolved. The standard relative deviation (RSD) of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate powder obtained in groups 1-6 was significantly higher than that in Example 1, indicating that the consistency of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate determined in this comparative example was relatively poor compared to Example 1. In addition, the average values ​​of the main element (Li, Mn, Fe, P) content detected in this comparative example were all lower than the average values ​​in Example 1.

[0117] The reasons are analyzed as follows: In this comparative example, hydrochloric acid solution, nitric acid solution, and sulfuric acid solution were mixed together as digesting agents. Since the mass concentration of hydrochloric acid solution is lower than that of the other two acids, it contains too much water, which reduces the total mass concentration of the digesting agent. This weakens the oxidizing power of the digesting agent and makes it unable to completely digest the carbon coating layer.

[0118] Comparative Example 5

[0119] The carbon-coated lithium manganese iron phosphate digestant in this comparative example is the same as that in Example 1, except that the volume of the nitric acid solution is 3 mL and the volume of the sulfuric acid solution is 2 mL.

[0120] The detection method for this comparative example is the same as that in Example 1, except that:

[0121] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to a quartz beaker. Heat the mixture to 2-4 mL using a graphite heating plate or an electric heating plate at 180°C, then remove and cool to room temperature. Add hydrochloric acid solution (GR grade) to the quartz beaker and continue to heat the mixture to 2-4 mL using a heating plate at 180°C, then remove and cool to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0122] (4) The digestion solution a obtained in step (3) is filtered with ultrapure water and medium-speed quantitative filter paper and diluted to a volumetric flask to a volumetric volume of 100 mL. This is the diluted solution b after digestion of carbon-coated lithium manganese iron phosphate. Take 1 mL of diluted solution b and 2 mL of nitric acid solution (GR grade) and dilute to a volume of 100 mL to obtain the diluted solution c.

[0123] Comparative Example 6

[0124] The carbon-coated lithium manganese iron phosphate digester and detection method in this comparative example are the same as those in Example 1, except that the volume of the nitric acid solution is 3 mL and the volume of the sulfuric acid solution is 4.8 mL.

[0125] Comparative Example 7

[0126] The carbon-coated lithium manganese iron phosphate digestant in this comparative example is the same as that in Example 1, except that the volume of the nitric acid solution is 1 mL.

[0127] The detection method for this comparative example is the same as that in Example 1, except that:

[0128] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to a quartz beaker. Heat the mixture to 2-4 mL using a graphite heating plate or an electric heating plate at 180°C, then remove and cool to room temperature. Add hydrochloric acid solution (GR grade) to the quartz beaker and continue to heat the mixture to 2-4 mL using a heating plate at 180°C, then remove and cool to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0129] (4) The digestion solution a obtained in step (3) is filtered with ultrapure water and medium-speed quantitative filter paper and diluted to a volumetric flask to a volumetric volume of 100 mL. This is the diluted solution b after digestion of carbon-coated lithium manganese iron phosphate. Take 1 mL of diluted solution b and 2 mL of nitric acid solution (GR grade) and dilute to a volume of 100 mL to obtain the diluted solution c.

[0130] Comparative Example 8

[0131] The carbon-coated lithium manganese iron phosphate digestant in this comparative example is the same as that in Example 1, except that the volume of the hydrochloric acid solution is 2 mL.

[0132] The detection method for this comparative example is the same as that in Example 1, except that:

[0133] (3) Add nitric acid solution (GR grade) and sulfuric acid solution (GR grade) to a quartz beaker. Heat the mixture at 180°C using a graphite heating plate or an electric heating plate until it is completely milky white. Remove the acid to 2-4 mL and cool it to room temperature. Then add hydrochloric acid solution (GR grade) to the quartz beaker. Continue to heat the mixture at 180°C using a heating plate until it is 2-4 mL and then cool it to room temperature. This is carbon-coated lithium manganese iron phosphate digestion solution a.

[0134] (4) The digestion solution a obtained in step (3) is filtered with ultrapure water and medium-speed quantitative filter paper and diluted to a volumetric flask to a volumetric volume of 100 mL. This is the diluted solution b after digestion of carbon-coated lithium manganese iron phosphate. Take 1 mL of diluted solution b and 2 mL of nitric acid solution (GR grade) and dilute to a volume of 100 mL to obtain the diluted solution c.

[0135] Table 8. Detection results of the main element content in carbon-coated lithium manganese iron phosphate powder of Comparative Examples 5-8

[0136]

[0137] As shown in Tables 2 and 8, the carbon in the carbon-coated lithium manganese iron phosphate powder can be completely dissolved when 3 mL of sulfuric acid solution is used. However, if the amount of sulfuric acid solution used is less than 3 mL, such as 2 mL, the carbon coating layer cannot be completely dissolved, and black undissolved substances will remain. If the amount of sulfuric acid solution is increased to 4.5 mL, the effect on the detection results is not significant. However, if the amount of sulfuric acid solution used is greater than 4.5 mL, such as 4.8 mL, the reaction is violent and the stability of the detection results is easily reduced.

[0138] Nitric acid solution lowers the activation energy of the reaction and increases the reaction rate. Therefore, in Examples 3, 1, and 4-5, appropriately increasing the amount of nitric acid solution can adjust the reaction progress. However, when the amount of nitric acid solution is less than 1.5 mL, such as 1 mL, it will lead to an increase in the sulfuric acid concentration in the first digester, which will cause the first digester to react violently with the lithium manganese iron phosphate powder, causing the powder to splash. The splashed material cannot be completely dissolved, resulting in a lower test value of the main element.

[0139] The hydrochloric acid solution further digests the products of the first digestion agent. This invention found that 3 mL of hydrochloric acid solution is sufficient; increasing the amount above 3 mL has little effect on the detection results. However, if the amount of hydrochloric acid solution is reduced to below 3 mL, for example, to 2 mL, some milky white undissolved matter will appear in digestion solution a, leading to a lower and less consistent result for the main element (Li) content compared to Example 1.

[0140] Comparative Example 9

[0141] The carbon-coated lithium manganese iron phosphate digester in this comparative example is a mixture of 5 mL of 64 wt% nitric acid solution (GR grade) and 5 mL of 37 wt% hydrochloric acid solution (GR grade).

[0142] The comparative method for detecting the main elements in carbon-coated manganese iron phosphate includes the following steps:

[0143] (1) Select commercially available carbon-coated lithium manganese iron phosphate powder and dry it in a drying oven at 80°C for 2 hours.

[0144] (2) Weigh 0.2000g±0.0010g of carbon-coated manganese iron lithium phosphate powder from step (1) and add it to the polytetrafluoroethylene digestion tube of the microwave digester.

[0145] (3) Add hydrochloric acid solution (GR grade) and nitric acid solution (GR grade) to the polytetrafluoroethylene digestion tube. Use a microwave digester to heat at 120°C for 10 min, 150°C for 10 min, and 180°C for 30 min according to the program. After cooling to room temperature, it is carbon-coated lithium manganese iron phosphate digestion solution a. Digestion solution a is slightly blackish-yellow and contains black undissolved powder.

[0146] (4) Filter the digestion solution a obtained in step (3) with ultrapure water and medium-speed quantitative filter paper to a volumetric flask and make up to 100 mL. This is the volumetric solution b. Take 1 mL of volumetric solution b and 2 mL of nitric acid solution (GR grade) and make up to 100 mL. This is the dilution solution c.

[0147] Steps (5)-(7) are the same as in Example 1.

[0148] Table 9. Detection results of the main element content in carbon-coated lithium manganese iron phosphate powder of Comparative Example 9

[0149]

[0150] As shown in Table 9, the carbon-coated lithium manganese iron phosphate powder in this comparative example was not completely dissolved. The standard relative deviation (RSD) of the main element (Li, Mn, Fe, P) content in the carbon-coated lithium manganese iron phosphate powder detected in groups 1-6 was less than 2.0%, which basically met the testing requirements. Although the detected main element (Li, Mn, Fe, P) content in this comparative example was more accurate than that in comparative example 3, the carbon coating layer could not be completely dissolved, resulting in lower test values ​​for the main element (Li, Mn, Fe, P) content compared to example 6. In summary, using the digesting agent and detection method of this embodiment can completely dissolve the carbon-coated lithium manganese iron phosphate powder, thereby avoiding the problem of low main element content test results due to incomplete dissolution.

[0151] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A carbon-coated lithium manganese iron phosphate digester, characterized in that, The mixture includes a first digesting agent and a second digesting agent. The first digesting agent comprises a mixture of nitric acid solution and sulfuric acid solution, wherein the mass concentration of the nitric acid solution is 50 wt% or more, the mass concentration of the sulfuric acid solution is 80 wt% or more, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (0.3-4):

1. The second digesting agent comprises a hydrochloric acid solution, wherein the mass concentration of the hydrochloric acid solution is 30 wt% or more, and the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is 1:

1.

2. The carbon-coated lithium manganese iron phosphate digester according to claim 1, characterized in that, The sulfuric acid solution has a mass concentration of 95 wt% or higher; and / or the nitric acid solution has a mass concentration of 60 wt% or higher.

3. The carbon-coated lithium manganese iron phosphate digester according to claim 1, characterized in that, The hydrochloric acid solution has a mass concentration of 35 wt% or higher.

4. A method for detecting the content of major elements in carbon-coated manganese iron phosphate, characterized in that, Includes the following steps: (1) First, the first digesting agent in the digesting agent according to any one of claims 1-3 and the carbon-coated lithium manganese iron phosphate are mixed, and a first digestion solution is obtained after a first digestion reaction; then the second digesting agent in the digesting agent according to any one of claims 1-3 and the first digestion solution are mixed, and a second digestion solution is obtained after a second digestion reaction; (2) Dilute the second digestion solution to a fixed volume to obtain a diluted solution; (3) Prepare standard solutions containing the main element with gradient concentrations, test them using an inductively coupled plasma atomic emission spectrometer, and plot the standard curve; (4) The content of the main elements in the diluted solution is determined by using an inductively coupled plasma atomic emission spectrometer, and the content of the main elements in the carbon-coated lithium manganese iron phosphate powder is calculated.

5. The method for detecting the content of major elements in carbon-coated manganese iron phosphate according to claim 4, characterized in that, In step (1), (2.5-4.5) mL of the sulfuric acid solution and not less than 1.2 mL of the nitric acid solution are added to every 0.2 g of the carbon-coated lithium manganese iron phosphate.

6. The method for detecting the content of major elements in carbon-coated manganese iron phosphate according to claim 4, characterized in that, The digestion reaction is a heating digestion, with a heating temperature of 160-300℃.

7. The method for detecting the content of major elements in carbon-coated manganese iron phosphate according to claim 4, characterized in that, In step (1), the first digestion solution is obtained and then cooled to room temperature.

8. The method for detecting the content of major elements in carbon-coated manganese iron phosphate according to claim 4, characterized in that, In steps (3) and (4), the main element includes at least one of Li, Mn, Fe and P.

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