CN106353383A - Sensor for detecting hexafluorophosphate ions - Google Patents

Abstract

The invention provides a method for quantifying the content of lithium hexafluorophosphate by detecting hexafluorophosphate, that is, a glassy carbon electrode is used as a working electrode, a platinum wire is used as a counter electrode, and an Ag/AgCl electrode is used as a reference electrode. Electropolymerize in aqueous solution of 0.01-0.2mol/L pyrrole and 1.0x10 ^‑3-0.1mol /L lithium hexafluorophosphate for 10-60min, within the range of current density 1-15mA/ ^cm2 , electrodeposit doping on the surface of glassy carbon electrode There is a polypyrrole membrane (PF ₆ ^‑ ‑PPy/GC) with hexafluorophosphate ions, and the modified electrode is placed in a 0.1mol/L lithium hexafluorophosphate aqueous solution for 1h to obtain a highly sensitive hexafluorophosphate ion electrochemical sensor . Put the modified electrode (PF ₆ ^‑ _‑PPy /GC) as the working electrode and the Ag/ ^AgCl electrode as the reference electrode in the aqueous solution of lithium hexafluorophosphate ^. In an aqueous solution of 1.0x10 ^‑5 mol/L lithium hexafluorophosphate, there is a good linear relationship, with a slope of nearly 59.4mV/PF ₆ ^‑ .

Description

A sensor for detecting hexafluorophosphate ion

technical field

The present invention relates to a method for detecting the purity of lithium hexafluorophosphate, the raw material of electrolyte solution for lithium-ion batteries, in particular to an electrochemical method for detecting lithium hexafluorophosphate by using a polypyrrole-modified glassy carbon electrode doped with hexafluorophosphate ions as a working electrode and measuring the potential. Detection method.

Background technique

Lithium-ion battery is a hot research topic at present. Compared with traditional batteries, it has very obvious advantages. Due to its high voltage and relatively active negative electrode materials, non-aqueous electrolytes must be used. However, ordinary organic solvents have limited conductivity and cannot meet the needs of lithium-ion batteries. Lithium salts must be dissolved in them to achieve the required conductivity. Commonly used lithium salts mainly include LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiBF ₄ and LiCF ₃ SO ₃ . Among these lithium salts, LiPF ₆ has the highest electrical conductivity, and proper treatment can avoid electrolyte polymerization caused by its decomposition. So the current lithium-ion batteries basically use LiPF ₆ as the electrolyte. In common lithium-ion batteries, hexafluorophosphate is the main component in the electrolyte, and fluoride and phosphate ions are the main impurity ions. However, it is often difficult to separate and measure the mixed ions of the three by ordinary methods. Therefore, it is of great significance to further study the reaction mechanism of lithium-ion batteries and improve the performance of lithium-ion batteries to explore the method of simultaneously measuring their content under the condition of the coexistence of the three. The traditional methods for determining hexafluorophosphate are microtitration, ion chromatography, etc., but these methods cannot meet the requirements of high-purity hexafluorophosphate analysis.

Contents of the invention

The object of the present invention is to provide a sensor for detecting lithium hexafluorophosphate, which is used to detect An electrochemical detection method for the purity of lithium hexafluorophosphate or the content of lithium hexafluorophosphate in the electrolyte of lithium-ion batteries. This method has the advantages of high sensitivity, easy operation, fast analysis speed, and low cost, and can realize simple and rapid detection.

In order to solve the above problems, the technical solution adopted in the present invention is: an electrochemical method for detecting the content of lithium hexafluorophosphate, which is characterized in comprising the following steps:

(1) Preparation of deposition solution

An aqueous solution of pyrrole with a concentration of 0.01-0.2 mol/L and lithium hexafluorophosphate with a concentration of 1.0x10 ^-3 -0.1 mol/L is prepared with deionized water as the electrodeposition solution of the present invention.

(2) Preparation of sensor (PF ₆ ^- -PPy/GC)

The glassy carbon electrode is used as the working electrode, the platinum wire is used as the counter electrode, and the Ag/AgCl electrode is used as the reference electrode, and the cleaned glassy carbon electrode is respectively placed in the electrodeposition solution of pyrrole and lithium hexafluorophosphate aqueous solution described in step (1). , using constant current method for electrodeposition, the current density is 1-15mA/cm ² , the electropolymerization time is 10-60min, and the polypyrrole film (PF ₆ ^- -PPy/GC), soak the electrode modified by electrodeposition in 0.1mol/L lithium hexafluorophosphate aqueous solution for 1h, and obtain a highly sensitive hexafluorophosphate ion electrochemical sensor (PF ₆ ^- -PPy/GC).

(3) Drawing of standard curve

The sensor (PF ₆ ⁻ -PPy/GC) prepared in step (2) was used as a working electrode, and the Ag/AgCl electrode was placed in an aqueous solution of lithium hexafluorophosphate as a reference electrode for potential measurement. The negative logarithm is the abscissa, and the standard curve is drawn on the ordinate with the potential value corresponding to the concentration. The sensor (PF ₆ ^- -PPy/GC) has a good linear relationship with the corresponding potential value in a series of different concentrations of lithium hexafluorophosphate aqueous solution , the slope is nearly 59.4mV/PF ₆ ^- .

(4) Determination of samples

Take the processed sample solution to be tested, test according to the potential measurement method in step (3), and bring the obtained response potential value into the corresponding abscissa of the standard curve obtained in step (3), to obtain the concentration of lithium hexafluorophosphate .

As a limitation to the present invention, the treatment method of the glassy carbon electrode described in step (2) is: use a glassy carbon electrode with a diameter of 4mm as the base electrode, and grind it _{on Al2O3} polishing powder of 0.5 μm and 0.3 μm into After the mirror surface, ultrasonically wash with 1:1 nitric acid, ethanol and deionized water for 3 minutes.

The series of standard solutions with different concentrations described in step (3) refer to the lithium hexafluorophosphate aqueous solution with a concentration of 1.0x10 ^-1 ~ 1.0x10 ^-5 mol/L, respectively 1.0x10 ^-5 mol/L, 1.0x10 ^-4 mol /L, 1.0×10 ^-3 mol/L, 1.0× ^{10 -2 mol} /L and 1.0×10 ^-1 mol/L.

The described potentiometric method of step (3), test condition is as follows: reference electrode is Ag/AgCl, measures in TISAB solution, and the preparation method of TISAB solution is, gets the glacial acetic acid of 57ml, 58g NaCl and 4g sodium citrate Add 500ml of water, adjust the pH to 5-5.5 with 5mol/L NaOH, and obtain the TISAB solution.

The sample to be tested described in step (4) is processed according to the following method: take a certain amount of sample, set the volume to 50ml, filter with a 0.45μm filter membrane, and reserve the filtrate, and the measured value of the potential should be between 1.0x10 ^-1 ~ 1.0x10 ^{- 5} mol/L.

After adopting the technical scheme, the present invention has the following advantages:

(1) The present invention selects pyrrole, which is less affected by the pH value, as a monomer, and forms a polypyrrole film doped with hexafluorophosphate ions in the electrodeposition polymerization process, and the polypyrrole film is selective to the hexafluorophosphate ion recognition, thereby forming a potential response, and obtaining a polypyrrole membrane-modified glassy carbon electrode doped with hexafluorophosphate ions. The preparation process of the electrode is simple, and the modified glassy carbon electrode is used as a working electrode. Its performance is stable and has good reproducibility.

(2) The glassy carbon electrode modified with polypyrrole membrane doped with hexafluorophosphate ions can be used for direct electrochemical detection of hexafluorophosphate ions, which realizes the rapid detection of lithium hexafluorophosphate, making the detection process of each sample only need It can be done in minutes, and the detection cost is low.

(3) The highly sensitive hexafluorophosphate ion electrochemical sensor prepared by the present invention, the modified electrode (PF ₆ ^- -PPy/GC) exhibits good linearity in 1.0x10 ^-1 ~ 1.0x10 ^-5 mol/L lithium hexafluorophosphate aqueous solution relationship, the slope is nearly 59.4mV/PF ₆ ^- .

Description of drawings

Fig. 1 Potential response of the modified electrode (PF ₆ ^- -PPy/GC) at different concentrations of lithium hexafluorophosphate.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

In order to illustrate the content of the present invention more clearly, the present invention will be described in further detail in conjunction with the accompanying drawings and the following examples now, but it should be pointed out that these examples are for illustrative purposes only, and should not be construed as an explanation of the present invention. Implemented restrictions.

(1) The water used in the experiment was deionized water, the reagents used in the experiment were all analytically pure, and the experiments were all carried out at room temperature.

(2) Instruments and reagents used in this embodiment:

Electrochemical workstation CHI660D (Shanghai Chenhua Instrument Co., Ltd.) was used for constant current electrodeposition and potential measurement experiments. Three-electrode system: the working electrode is a polypyrrole-modified glassy carbon electrode doped with hexafluorophosphate ions, the reference electrode is an Ag/AgCl electrode, and the counter electrode is a platinum wire electrode.

Follow the steps below to determine the concentration of lithium hexafluorophosphate in the sample:

(1) Preparation of deposition solution

An aqueous solution of 0.1 mol/L pyrrole and 0.01 mol/L lithium hexafluorophosphate was prepared with deionized water as the electrodeposition solution of the present invention.

(2) Preparation of high-sensitivity lithium hexafluorophosphate sensor

A glassy carbon electrode with a diameter of 4 mm was used as the base electrode, which was polished to a mirror surface on 0.5 μm and 0.3 μm Al ₂ O ₃ polishing powder, respectively, and then ultrasonically washed with 1:1 nitric acid, ethanol and deionized water for 3 min.

Ultrasonicize the deposition solution prepared in step 1, place the above-mentioned treated glassy carbon electrodes in the deposition solution respectively, conduct electrodeposition by constant current method, the current density is 10mA/cm ² , and the electropolymerization time is 10min. Electrodeposition of polypyrrole film (PF ₆ ^- -PPy/GC) doped with hexafluorophosphate ions on the surface of the glassy carbon electrode, after electrodeposition, soaked in 0.1 mol/L lithium hexafluorophosphate aqueous solution for 1 hour, the modified electrode (PF 6 - -PPy/GC) was obtained. ₆ ^- -PPy/GC), so as to prepare the electrochemical sensor of lithium hexafluorophosphate.

(3) Detection experiment

The detection experiment is carried out on the CHI660D electrochemical workstation, the reference electrode is an Ag/AgCl electrode, the working electrode adopts the modified glassy carbon electrode prepared by the step (2) of the present invention, the supporting electrolyte is a TISAB solution, and different hexafluorophosphate ions are measured respectively. For the potential value under the concentration, the negative logarithm of the ion concentration of hexafluorophosphate is taken as the abscissa, and the potential value corresponding to the concentration is used as the ordinate to obtain the standard curve of lithium hexafluorophosphate, as shown in Figure 1, wherein the concentration of lithium hexafluorophosphate They are 1.0×10 ^-5 mol/L, 1.0×10 ^-4 mol/L, 1.0×10 ^-3 mol/L, 1.0×10 ^-2 mol/L and 1.0×10 ^-1 mol/L, respectively. The linear range of the lithium hexafluorophosphate electrochemical sensor is 1.0x10 ^-1 ~ 1.0x10 ^-5 mol/L mol/L, and the slope is nearly 59.4mV/PF ₆ ^- .

(4) Determination of samples to be tested

Take 10 μL of the sample containing lithium hexafluorophosphate, and perform an electrochemical test in the TISAB supporting electrolyte according to the detection test method and steps in step (3) to obtain the potential, and the obtained potential value is calculated according to the standard curve obtained in step (3). The concentration of lithium hexafluorophosphate in the sample. The samples were recovered by standard addition, and the recovery rate of standard addition was calculated, and the results are shown in Table 1.

Table 1 Determination results of spiked recovery of samples containing lithium hexafluorophosphate

^a is the average value of three determinations; RSD refers to: relative standard deviation

The relative standard deviations of the three parallel measurements of each sample are all lower than 5%, indicating that the method of the present invention has good precision in actual measurement; the recovery rate of standard addition is 96% to 102%, indicating that the method has good accuracy.

Based on the above test results, it can be seen that the method for electrochemical detection of lithium hexafluorophosphate of the present invention is simple to operate, convenient and fast, and has low detection cost, and at the same time realizes the electrochemical method for direct detection of lithium hexafluorophosphate. The above embodiments are only used to illustrate the content of the present invention, but not to limit the present invention.

Claims (5)

1. a kind of detection lithium hexafluoro phosphate electrochemical method it is characterised in that: described detection method comprises the following steps:

(1) preparation of deposition solution

Deionized water compound concentration is pyrroles and the 1.0x10 of 0.01～0.2mol/l^-3The lithium hexafluoro phosphate of～0.1mol/l Aqueous solution is as electric depositing solution；

(2) sensor (pf₆ ^-- ppy/gc) preparation

With glass-carbon electrode as working electrode, it is to electrode with platinum filament, ag/agcl electrode is reference electrode, clean glass will be processed Carbon electrode is respectively placed in pyrroles described in step (1) and the electric depositing solution of lithium hexafluoro phosphate aqueous solution, using galvanostatic method Carry out electro-deposition, electric current density is 1～15ma/cm², the electropolymerization time is 10～60min, mixes in glassy carbon electrode surface electro-deposition Miscellaneous polypyrrole film (the pf having hexafluorophosphoricacid acid ions₆ ^-- ppy/gc), the electrode modified through electro-deposition is placed in 0.1mol/l's Soak 1h in lithium hexafluoro phosphate aqueous solution, that is, obtain highly sensitive hexafluorophosphoricacid acid ions electrochemical sensor (pf₆ ^--ppy/ gc)；

(3) drafting of standard curve

Sensor (the pf being obtained in step (2)₆ ^-- ppy/gc) as working electrode, ag/agcl electrode is put as reference electrode In the aqueous solution of lithium hexafluoro phosphate, carry out potential measurement, with the negative logarithm of hexafluorophosphoricacid acid ions concentration as abscissa, with dense Spending corresponding potential value is vertical coordinate, draws standard curve, sensor (pf₆ ^-- ppy/gc) a series of variable concentrations hexafluoro It is in good linear relationship in lithium phosphate aqueous solution, slope is 59.4mv/pf₆ ^-；

(4) mensure of sample

Take the testing sample solution handled well, tested according to the potential measurement method in step (3), by the response obtaining electricity Place value is brought into the corresponding abscissa of standard curve that step (3) obtains, you can obtain the concentration of lithium hexafluoro phosphate.

2. as claimed in claim 1 detection lithium hexafluoro phosphate electrochemical method it is characterised in that: the described glass carbon of step (2) The processing method of electrode is: with the glass-carbon electrode of a diameter of 4mm as basal electrode, respectively in the al of 0.5 μm and 0.3 μm₂o₃Polishing After being polished into minute surface on powder, use 1:1 nitric acid, ethanol and deionized water supersound washing 3min successively.

3. as claimed in claim 1 detection lithium hexafluoro phosphate electrochemical method it is characterised in that: described in step (3) The concentration of the lithium hexafluoro phosphate aqueous solution of serial variable concentrations is respectively 1.0x10^-5mol/l、1.0×10^-4mol/l、1.0×10^-3mol/l、1.0×10^-2Mol/l and 1.0 × 10^-1mol/l.

4. as claimed in claim 1 detection lithium hexafluoro phosphate electrochemical method it is characterised in that: the electricity described in step (3) Position measurement method, test condition is as follows: reference electrode is ag/agcl, measures in tisab solution, wherein, tisab solution Compound method be to take glacial acetic acid, 58g nacl and the 4g sodium citrate of 57ml to add water 500ml, adjusted with the naoh of 5mol/l Ph is 5～5.5, obtains final product tisab solution.

5. as claimed in claim 1 detection lithium hexafluoro phosphate electrochemical method it is characterised in that: treating described in step (4) Test sample product are processed by the following method: take sample to be settled to 50ml, with 0.45 μm of membrane filtration, filtrate is standby, and potential measurement value 1.0x10 should be located at^-1～1.0x10^-5Between mol/l.