Method for detecting content of phosphorus and iron in LiFePO4/C composite material

Abstract

The invention relates to a method for detecting content of phosphorus and iron in a LiFePO4 / C composite material. The method comprises the steps of mixing the LiFePO4 / C composite material with concentrated hydrochloric acid and concentrated nitric acid, heating to enable the LiFePO4 / C composite material to be dissolved, and filtering an insoluble black substance to obtain a LiFePO4 / C composite material to-be-detected solution; drawing a phosphorus standard curve; adding an ascorbic acid solution into the LiFePO4 / C material to-be-detected solution, enabling ferric iron in the solution to be reduced to ferrous iron, adding an ammonium molybdate solution, carrying the color development, measuring the absorbance of the obtained solution at a position of 720nm in a spectrophotometer by utilizing a cuvette, and finding the to-be-detected content of phosphorus (P) on the phosphorus standard curve according to the absorbance; drawing an iron standard curve; adding a hydroxylamine hydrochloride solution, a sodium acetate-acetic acid buffer solution as well as a phenanthroline solution into the LiFePO4 / C composite material to-be-detected solution, carrying out the color development, measuring the absorbance of the solution at the position of 510nm by utilizing the cuvette, and finding the to-be-detected content of iron (Fe) on the iron standard curve according to the absorbance; calculating the content of P and Fe in the LiFePO4 / C material. According to the method, the interactive effect of the P and Fe ions and the color influence caused by different C coating can be eliminated.

Description

technical field [0001] The present invention relates to a LiFePO 4 Test Method for Iron and Phosphorus in / C Composite Materials. Background technique [0002] Lithium-ion batteries have the advantages of high energy density, good cycle performance, and stable working voltage. The market demand for it is still increasing, especially in the field of power batteries. LiFePO 4 / C composite material (referred to as lithium iron phosphate) cathode material has excellent electrochemical properties such as unparalleled safety performance, high energy density, long life, excellent high temperature stability and chemical stability, and has been used in pure electric vehicles. Pilot projects for large-scale application of batteries and energy storage batteries. [0003] LiFePO 4 The chemical composition of the / C composite material determines the electrochemical performance of the cathode material, and the consistency and stability of its production are important factors restricti...

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Problems solved by technology

However, among these several methods, although the chemical titration method has high precision, it is complicated to operate and has high requirements for personnel. Different personnel have different judgments on the titration end point, which leads to test errors and test instability.

When using the gravimetric method to measure the P content, although this method is simple to operate and has good test stability, the test process not only requires sample preparation and reaction, but also requires a constant weight of the container before and after the whole process, which takes a long time, and the desired result cannot be obtained quickly.

Although the ICP test is fast from sample preparation to detection operation, and is accurate for most elements, but because it is suitable for trace element testing, the constant test requires more dilution times, which artificially increases the error, and the Fe and P The excitation is relatively close, and it is easy to interfere with each other in the test, and it is extremely difficult to test stability

[0005] While using UV spectrophotometry can test LiFePO 4 Fe and P in the / C composite material, and the operation is simple and the stability is good. The phenanthroline method is used to test the Fe content. Although the test method is simple, it has been verified that the Fe content is yellow due to the color reaction. 3+ The color of the solution is also yellow, therefore, there will be some interference to the color reaction, and the light transmittance will also bring great deviation to the accuracy of the test.

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