A method for detecting elemental iron in lithium iron phosphate powder

Abstract

The present invention relates to a method for detecting elemental iron in lithium iron phosphate powder, comprising: preparing a copper sulfate solution of a certain concentration; placing the lithium iron phosphate powder into a flask, and then adding the copper sulfate solution prepared in step 1 into the flask; placing the flask containing the lithium iron phosphate powder and the copper sulfate solution into an ultrasonic cleaning machine, ultrasonicating for 2 hours, with the ultrasonic temperature set to 55°C; after the ultrasonication is completed, filtering with a 0.45um mixed filter membrane to collect the filtrate; and subjecting the collected filtrate to an ICP test to obtain the content of the iron element, thereby deriving the elemental iron content. The present invention can accurately detect low levels of elemental iron content, thereby providing rapid feedback to the process or quality department, allowing problems to be identified or improvements to be made in a timely manner, thereby achieving the purpose of improving product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, and in particular to a method for detecting elemental iron in lithium iron phosphate powder. Background Art

[0002] During the current calcination process for lithium iron phosphate production, divalent or trivalent iron is easily reduced to elemental iron in a high-temperature reducing atmosphere. Lithium iron phosphate containing elemental iron can cause micro-short circuits in battery cells. Current detection methods include the magnetic foreign matter analysis method described in the national standard GB / T41704-2022. However, these methods fail to distinguish metallic foreign matter on a magnetic rod from metallic oxides, and the magnetic rod cannot absorb metallic foreign matter smaller than 5 μm. Chinese patent publication number CN106353269B discloses a method for detecting the elemental iron content in lithium iron phosphate. The main scheme involves: weighing lithium iron phosphate powder, a conductive agent, and a binder in a weight ratio of 8:1:1 to form a slurry, which is then coated and baked. A CR2016 buckle battery is fabricated using the baked positive electrode sheet as the positive electrode and copper foil as the negative electrode. The resulting CR2016 buckle battery is then subjected to constant voltage charging and disassembled, retaining the copper foil. The iron content on the copper foil surface is measured using atomic absorption spectroscopy. The defects of this detection method are: not all iron ions are accumulated at the negative electrode, and some will remain in the electrolyte and the positive electrode. Moreover, the iron ions are not necessarily generated from elemental iron. Iron oxide is dissolved in the electrolyte and will also accumulate at the negative electrode. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the present invention provides a method for detecting elemental iron in lithium iron phosphate powder, which solves the technical problem that the existing technology cannot accurately detect elemental iron in lithium iron phosphate powder.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for detecting elemental iron in lithium iron phosphate powder comprises the following steps:

[0006] Step 1: Prepare a copper sulfate solution of a certain concentration;

[0007] Step 2: Place lithium iron phosphate powder into a flask, and then add the copper sulfate solution prepared in step 1 into the flask;

[0008] Step 3: Place the flask containing lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaning machine and ultrasonicate for 1.8-2.5 hours at a temperature of 50-60°C. During the ultrasonication process, pick up the flask and shake it clockwise for 10-20 seconds every 8-25 minutes. After 1 hour, stir the bottom with a glass rod.

[0009] Step 4: After the ultrasound is completed, filter with a 0.4-0.5um mixed filter membrane and collect the filtrate;

[0010] Step 5: The collected filtrate is subjected to ICP testing to obtain the iron content and thus the elemental iron content.

[0011] Furthermore, the ultrasonic time in step 3 is 2 hours.

[0012] Furthermore, in step 3, the ultrasonic temperature is set to 55 degrees Celsius.

[0013] Furthermore, in step 3, the flask is shaken clockwise every 10 minutes or 20 minutes.

[0014] Furthermore, in step 4, a 0.45 um mixed filter membrane is used for filtration.

[0015] Furthermore, in step 5, the ICP test settings are: nebulizer flow rate 0.5 L / min, power 1150 W, and analysis pump speed 45 r / min.

[0016] Furthermore, it also includes:

[0017] Step 6: Perform spike recovery on the above experiment to verify the recovery rate. Compared with the existing technology, the technical solution of this application has the following beneficial effects:

[0018] The method for detecting elemental iron in lithium iron phosphate powder of the present invention can accurately detect low content of elemental iron. The production of elemental iron is inevitably caused by abnormal reaction of lithium iron phosphate in the kiln, which may be caused by imbalance in the ratio or abnormal atmosphere inside the kiln. The detection method of the present invention can effectively provide a fast response time for process or quality. DETAILED DESCRIPTION

[0019] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0020] Example 1: A method for detecting elemental iron in lithium iron phosphate powder, comprising the following steps:

[0021] Step 1: Prepare a copper sulfate solution of a certain concentration.

[0022] Step 2: Put lithium iron phosphate powder into a flask, and then add the copper sulfate solution prepared in step 1 into the flask.

[0023] Step 3: Place the flask containing lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaning machine and ultrasonicate for 1.8 hours at a temperature of 50°C. During the ultrasonication process, pick up the flask and shake it clockwise for 10 seconds every 8 minutes. After 1 hour, stir the bottom with a glass rod.

[0024] Step 4: After the ultrasound is completed, filter with a 0.4um mixed filter membrane and collect the filtrate.

[0025] The principle of this technology is: In the periodic table, the metal activity of iron is before copper, and it can undergo a replacement reaction with copper sulfate solution to replace copper. 2+ -Fe 2+ +Cu.

[0026] Step 5: The collected filtrate is subjected to ICP testing to obtain the iron content and thus the elemental iron content.

[0027] Example 2: A method for detecting elemental iron in lithium iron phosphate powder, comprising the following steps:

[0028] Step 1: Prepare a copper sulfate solution of a certain concentration.

[0029] Step 2: Pour lithium iron phosphate powder into a 500ml flask, and then add 200ml of the copper sulfate solution prepared in step 1 into the flask, slowly pouring it along the wall of the flask to prevent the powder from splashing.

[0030] Step 3: Place the flask containing lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaning machine and ultrasonicate for 2 hours at a temperature of 55°C. During the ultrasonication process, pick up the flask and shake it clockwise for 15 seconds every 10 minutes. After 1 hour, stir the bottom with a glass rod.

[0031] Step 4: After the ultrasound is completed, filter with a 0.45um mixed filter membrane and collect the filtrate.

[0032] Step 5: The collected filtrate is subjected to ICP testing to obtain the iron content and thus the elemental iron content.

[0033] Step 6: Perform spike recovery in the above experiment to verify the recovery rate.

[0034] Example 3: A method for detecting elemental iron in lithium iron phosphate powder, characterized in that it comprises the following steps:

[0035] Step 1: Prepare a copper sulfate solution of a certain concentration.

[0036] Step 2: Put lithium iron phosphate powder into a flask, and then add the copper sulfate solution prepared in step 1 into the flask.

[0037] Step 3: Place the flask containing lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaning machine and ultrasonicate for 2.2 hours at a temperature of 57°C. During the ultrasonication process, pick up the flask and shake it clockwise for 13 seconds every 15 minutes. After 1 hour, stir the bottom with a glass rod.

[0038] Step 4: After the ultrasound is completed, filter with a 0.47um mixed filter membrane and collect the filtrate.

[0039] Step 5: The collected filtrate is subjected to ICP testing to obtain the iron content and thus the elemental iron content.

[0040] Example 4: A method for detecting elemental iron in lithium iron phosphate powder, comprising the following steps:

[0041] Step 1: Preparation of copper sulfate solution: Prepare 1000 ml of 10% copper sulfate solution.

[0042] Step 2: Place lithium iron phosphate powder into a flask, then add the copper sulfate solution prepared in Step 1. Specifically, weigh 50 ± 0.0005 g of lithium iron phosphate powder into four 500 ml flasks, numbered 1, 2, 3, and 4, and add 0 g, 0.01 g, 0.5 g, and 0.1 g of high-purity elemental iron powder, respectively. Use a 0.1 ml doser to add 200 ml of 20% copper sulfate solution to flasks 1, 2, 3, and 4, respectively. Seal the flasks and place them in an ultrasonic cleaning chamber, ensuring the water level in the ultrasonic instrument is no lower than the liquid level in the flasks.

[0043] Step 3: Place the flask containing the lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaner. Set the ultrasonic cleaner to 180W of power, 52Hz of frequency, and 55°C for 2 hours. Shake the flask clockwise for 10-20 seconds every 20 minutes, and stir with a glass rod for 1 hour.

[0044] Step 4: After the ultrasound is completed, filter with a 0.45um mixed filter membrane and collect the filtrate;

[0045] Step 5: Subject the collected filtrate to ICP analysis to determine the iron content, and thus the elemental iron content. ICP settings: nebulizer flow rate 0.5 L / min, power 1150 W, analytical pump speed 45 r / min. Element wavelength and standard solution curve requirements are shown in Table 1.

[0046] Table 1 Element wavelength and standard solution curve

[0047]

[0048] Step 6: The above experiment was run through spike recovery to verify the recovery rate. The specific recovery rates are shown in Table 2. For a 1 mg / L concentration of the component being measured, the acceptable recovery limit is 80% to 120%; for concentrations between 1 and 100 mg / L, the acceptable recovery limit is 90% to 110%; and for concentrations greater than 100 mg / L, the acceptable recovery limit is 95% to 105%. Verification in Step 6 demonstrates that the above experiment is suitable and accurate for iron measurement.

[0049] Table 2 Recovery rates of spike recovery verification

[0050]

[0051] In summary, there are many reasons for the abnormal magnetic foreign matter in lithium iron phosphate, including internal factors and external environmental factors. The present invention can accurately detect low content of elemental iron, and the production of elemental iron must be caused by the abnormal reaction of lithium iron phosphate in the kiln, which may be caused by an imbalance in the ratio or an abnormal atmosphere inside the kiln. The technical solution of the above embodiment can effectively provide a fast response time for process or quality.

[0052] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0053] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for detecting elemental iron in lithium iron phosphate powder, characterized in that: The steps include: Step 1: Prepare copper sulfate solution; Step 2: Place lithium iron phosphate powder into a flask, and then add the copper sulfate solution prepared in step 1 into the flask; Step 3: Place the flask containing lithium iron phosphate powder and copper sulfate solution in an ultrasonic cleaning machine and ultrasonicate for 2 hours at a temperature of 55°C. During the ultrasonication process, pick up the flask and shake it clockwise for 10-20 seconds every 8-25 minutes. After 1 hour, stir the bottom with a glass rod. Step 4: After the ultrasound is completed, filter with a 0.45um mixed filter membrane and collect the filtrate; Step 5: The collected filtrate was subjected to an ICP test to determine the iron content and, in turn, the elemental iron content. The ICP test settings were: atomizer flow rate of 0.5 L / min, power of 1150 W, and analytical pump speed of 45 r / min. Step 6: Perform spike recovery to verify the recovery rate.

2. The method for detecting elemental iron in lithium iron phosphate powder according to claim 1, wherein: In step 3, the flask was shaken clockwise every 10 minutes or 20 minutes.

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