Method for analyzing lithium ion concentration by voltammetry, electrode for lithium ion voltammetric analysis and preparation method thereof, and device for lithium ion voltammetric analysis

Abstract

The present invention provides a method for voltammetric analysis of lithium using a polyanionic compound material, a polyanionic compound electrode for lithium ion voltammetric analysis and a preparation method thereof, and a device for lithium ion voltammetric analysis, belonging to the technical field of lithium ion analysis. This method conducts voltammetric analysis of lithium ions using a polyanionic compound through an electrochemical reduction or oxidation reaction, and determines the lithium ion concentration by utilizing the linear relationship presented between the obtained current and the lithium ion concentration; wherein, during voltammetric analysis, lithium ions can be embedded in the polyanionic compound or lithium ions can be removed from the lithium-containing polyanionic compound. The present invention uses a polyanionic compound material to voltammetrically analyze the lithium ion concentration. The material has good conductivity, is simple to synthesize, and has good selectivity for lithium ions.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion analysis. Specifically, it relates to a method for voltammetric analysis of lithium ion concentration using a polyanion compound material, a polyanion compound electrode for lithium ion voltammetric analysis and its preparation method, and a device for lithium ion voltammetric analysis. Background Art

[0002] In the processes of field exploration and industrial production, rapid detection of lithium ion concentration in aqueous solutions is very important. At present, the commonly used detection methods for lithium ion concentration are atomic absorption spectrometry and inductively coupled plasma emission spectrometry. However, once the above two detection method devices are installed, they are difficult to move, and acetylene or argon gas is required during the detection process, resulting in high detection costs.

[0003] Lithium ion selective electrodes are made of materials selective to lithium ions and are divided into two categories: voltage lithium ion selective electrodes and current lithium ion selective electrodes. When a voltage lithium ion selective electrode works, it is immersed in a lithium-containing solution together with a reference electrode to form a primary battery. The potential of the primary battery is linearly related to the logarithm of the solution lithium concentration. Based on this, the solution lithium concentration can be detected. Materials such as crystal membranes, ion-association complexes, and neutral carriers have been successively used to make voltage lithium ion selective electrodes. However, the above materials are either expensive, difficult to use for a long time, or have poor anti-interference ability against homologous impurity elements, and all of them are difficult to meet the requirements. When a current lithium ion selective electrode works, voltammetric testing is carried out on it, and the resulting current is linearly related to the solution lithium concentration. Based on this, the solution lithium concentration can be detected, but the materials used are organic materials with poor conductivity. At the same time, the material structure is complex, the synthesis difficulty is large, and the selectivity for lithium ions is poor, such as 6,6-dibenzyl-14-crown-4. Summary of the Invention

[0004] Aiming at the problems existing in the field of the present invention, the purpose of the present invention is to provide a method for voltammetric analysis of lithium ion concentration using a polyanion compound material, a polyanion compound electrode for lithium ion voltammetric analysis and its preparation method, and a device for lithium ion voltammetric analysis.

[0005] In a first aspect, the present invention provides a method for voltammetric analysis of lithium ion concentration using a polyanion compound material. Through electrochemical reduction or oxidation reactions, voltammetric analysis of lithium ions is carried out using a polyanion compound, and the lithium ion concentration is determined by using the linear relationship presented between the resulting current and the lithium ion concentration; wherein, when voltammetric analysis is carried out, lithium ions can be embedded in the polyanion compound or lithium ions can be removed from the lithium-containing polyanion compound.

[0006] Preferably, the polyanion compound is one of FePO 4 and its doped derivatives; wherein, the FePO 4The doping derivative of is Me x Fe y PO 4 One of those in, Me is one or a mixture of several of Mg, Al, Ti, Ni, Co, Mn, Mo, Nb; 0 < x < 1, 0 < y < 1.

[0007] Preferably, FePO 4 is obtained by electrochemical de-lithiation or chemical de-lithiation of LiFePO 4 , and the doping derivative of FePO 4 is obtained by electrochemical de-lithiation or chemical de-lithiation of the lithium-containing doping derivative. Further preferably, the polyanionic compound is iron phosphate, obtained by electrochemical de-lithiation of lithium iron phosphate.

[0008] Preferably, the voltammetric analysis is insertion voltammetric analysis and insertion-extraction voltammetric analysis. The insertion voltammetric analysis is to perform a lithium-ion insertion scan on the polyanionic compound material, and the insertion-extraction voltammetric analysis is to first insert lithium ions into the polyanionic compound under a constant potential and then perform a lithium-ion extraction scan on it.

[0009] Preferably, the current obtained from the insertion voltammetric analysis is the peak current of the lithium-ion insertion sweep voltammetry curve, and the current obtained from the insertion-extraction voltammetric analysis is the plateau current of the lithium-ion insertion current-time curve under a constant potential and the peak current of the lithium-ion extraction sweep voltammetry curve.

[0010] Preferably, the scan is one of linear sweep, differential pulse sweep, and square wave sweep.

[0011] In a second aspect, the present invention provides a polyanionic compound electrode for lithium-ion voltammetric analysis, comprising: a conductive substrate and a polyanionic compound material layer provided on the conductive substrate.

[0012] Preferably, the polyanionic compound is one of FePO 4 and its doping derivatives; wherein, the doping derivative of FePO 4 is one of Me x Fe y PO 4 One of those in, Me is one or a mixture of several of Mg, Al, Ti, Ni, Co, Mn, Mo, Nb; 0 < x < 1, 0 < y < 1.

[0013] Preferably, FePO 4 is obtained by electrochemical de-lithiation or chemical de-lithiation of LiFePO 4 , and FePO 4The doped derivative is obtained by electrochemically or chemically de-lithiating a lithium-containing doped derivative. Further preferably, the polyanion-type compound is iron phosphate, which is obtained by electrochemically de-lithiating lithium iron phosphate.

[0014] Preferably, the conductive matrix is one of metallic titanium, metallic zirconium, metallic hafnium, metallic tantalum, metallic niobium, metallic gold, metallic platinum, and their alloys.

[0015] Preferably, the conductive matrix is one of graphite, carbon paper, and carbon fiber cloth.

[0016] In a third aspect, the present invention provides a device for lithium-ion voltammetric analysis, including a working electrode, which is the polyanion-type compound electrode for lithium-ion voltammetric analysis provided in the second aspect above.

[0017] In a fourth aspect, the present invention provides a method for preparing the polyanion-type compound electrode for lithium-ion voltammetric analysis provided in the second aspect above, including: forming a layer of the polyanion-type compound material on the conductive matrix.

[0018] Preferably, a slurry containing the polyanion-type compound material is coated on the conductive matrix and then dried.

[0019] Preferably, the slurry includes a polyanion-type compound, a binder, and a solvent.

[0020] Preferably, the slurry includes a conductive agent.

[0021] Preferably, the conductive agent is carbon black, acetylene black, carbon nanotubes, or Ketjen black.

[0022] Preferably, the binder is PVDF and SBR, and the solvent is NMP and water.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The ion diffusion channels of the polyanion-type compound material are one-dimensional, allowing only lithium ions to pass through, and having good selectivity for lithium ions;

[0025] 2. The polyanion-type compound material has good conductivity and is simple to synthesize. Description of the Drawings

[0026] Figure 1 For Example 1 of the present invention, the linear relationship between the peak current of the lithium-ion insertion cyclic voltammetry curve measured within the range of 100 - 1000 ppm and the solution lithium concentration for the insertion voltammetric analysis of lithium ions using Al 0.1 Fe 0.9 PO 4 ;

[0027] Figure 2 For the lithium ion insertion - extraction voltammetric analysis provided in Example 2 of the present invention using Mn 0.5 Fe 0.5 PO 4 The linear relationship between the plateau current of the lithium ion insertion current - time curve and the solution lithium concentration measured in the range of 0.1 - 100 ppm;

[0028] Figure 3 For the cyclic voltammograms of the polyanionic compound FePO obtained by electrochemical de - lithiumization provided in Example 3 of the present invention 4 in 1 mol / L lithium chloride, sodium chloride, potassium chloride, and magnesium chloride solutions;

[0029] Figure 4 For the lithium ion insertion - extraction voltammetric analysis provided in Example 3 of the present invention using FePO 4 The linear relationship between the peak current of the lithium ion extraction sweep voltammogram and the solution lithium concentration measured in the range of 1 - 100 ppm;

[0030] Figure 5 For the lithium ion insertion - extraction voltammetric analysis provided in Example 4 of the present invention using Mg 0.02 Nb 0.06 Fe 0.92 PO 4 The linear relationship between the peak current of the lithium ion extraction sweep voltammogram and the solution lithium concentration measured in the range of 0.1 - 100 ppm;

[0031] Figure 6 For the lithium ion insertion - extraction voltammetric analysis provided in Example 5 of the present invention using Co 0.01 Ni 0.01 Ti 0.01 Fe 0.97 PO 4 The linear relationship between the peak current of the lithium ion extraction sweep voltammogram and the solution lithium concentration measured in the range of 20 - 100 ppm;

[0032] Figure 7 For the lithium ion insertion - extraction voltammetric analysis provided in Example 6 of the present invention using Mn 0.2 Fe 0.8 PO 4 The linear relationship between the plateau current of the lithium ion insertion current - time curve and the solution lithium concentration measured in the range of 1 - 20 ppm. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be specifically described below in conjunction with embodiments and the accompanying drawings. It is necessary to point out that the following embodiments are only used to explain and illustrate the present invention and are not used to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content still fall within the protection scope of the present invention.

[0034] Example 1

[0035] Mix LiAl 0.1 Fe 0.9 PO 4 , acetylene black, and PVDF evenly according to a mass ratio of 6:2:2, add NMP, stir evenly, coat on zirconium and dry. Under the condition of 25°C, control the current at 0.1 mA, and electrolyze to remove 80% of lithium. Then, perform an insertion voltammetry test in a lithium nitrate solution with a lithium concentration of 100 - 1000 ppm. Use linear sweep, scan from the open circuit voltage to -0.8 V (vs SCE) at a sweep rate of 30 mV / s. The linear relationship between the peak current of the obtained lithium ion insertion cyclic voltammetry curve and the solution lithium concentration is as Figure 1 shown.

[0036] Prepare lithium nitrate solutions with different concentrations and perform tests according to the above method. Compare the obtained current with the Figure 1 linear relationship line to measure the solution lithium concentration. The detection results and recovery rates are shown in Table 1.

[0037] Table 1

[0038] Number True Concentration / ppm Detected Concentration / ppm Recovery Rate / % 1 350.0 348.8 99.66 2 620.0 621.4 100.22 3 880.0 877.9 99.76

[0039] Example 2

[0040] Mix LiMn 0.5 Fe 0.5 PO 4 , and PVDF evenly according to a mass ratio of 9:1, add NMP, stir evenly, coat on platinum and dry. Under the condition of 25°C, control the current at 0.2 mA, and electrolyze to remove 40% of lithium. Then, perform an insertion - extraction voltammetry test in a lithium sulfate solution with a lithium concentration of 0.1 - 100 ppm. Control the potential at 0.3 V (vs SCE) and insert lithium for 50 s. The linear relationship between the plateau current of the obtained lithium ion insertion current - time curve and the solution lithium concentration is as Figure 2 shown.

[0041] Prepare lithium sulfate solutions with different concentrations and perform tests according to the above method. Compare the obtained current with the Figure 2 linear relationship line to measure the solution lithium concentration. The detection results and recovery rates are shown in Table 2.

[0042] Table 2

[0043] Number True Concentration / ppm Detected Concentration / ppm Recovery Rate / % 1 0.1500 0.1527 101.80 2 0.6200 0.6183 99.72 3 1.500 1.492 99.47 4 6.200 6.224 100.39 5 15.00 15.04 100.27 6 62.00 62.52 100.84

[0044] Example 3

[0045] Mix LiFePO 4 , Ketjen black, and PVDF evenly in a mass ratio of 7:2:1, add NMP, stir evenly, coat on titanium, and dry. At 15 °C, control the potential at 0.5 V (vs SCE), and apply electricity to remove 100% of the lithium. Figure 3 Figure Figure 3 shows the cyclic voltammogram of the iron phosphate obtained by electrochemical de-lithiation in 1 mol / L lithium chloride, sodium chloride, potassium chloride, and magnesium chloride solutions. It can be seen from

[0046] that the iron phosphate obtained by electrochemical de-lithiation preferentially intercalates lithium and has good selectivity for lithium ions.

[0046] Perform intercalation - deintercalation voltammetry tests on the electrode obtained by the above method in a chloride solution with a lithium concentration of 1 - 100 ppm, a sodium ion concentration of 1 g / L, a magnesium ion concentration of 2 g / L, and a potassium ion concentration of 1.5 g / L. Control the potential at -0.15 V (vs SCE), intercalate lithium for 40 s, and then perform a de-lithiation scan test. Use linear scanning, scan from -0.15 V (vs SCE) to 0.5 V (vs SCE) at a scan rate of 2 mV / s. The linear relationship between the peak current of the obtained lithium ion deintercalation scan voltammogram and the solution lithium concentration is as shown in Figure 4 .

[0047] Prepare chloride solutions with different lithium concentrations, a sodium ion concentration of 1 g / L, a magnesium ion concentration of 2 g / L, and a potassium ion concentration of 1.5 g / L, and perform tests according to the above method. Compare the obtained current with the Figure 4 linear relationship line to measure the solution lithium concentration. The detection results and recovery rates are shown in Table 3.

[0048] Table 3

[0049] Number True Concentration / ppm Detected Concentration / ppm Recovery Rate / % 1 1.500 1.533 102.20 2 6.200 6.131 98.89 3 35.00 34.86 99.60 4 88.00 88.35 100.40

[0050] Example 4

[0051] Mix LiMg 0.02 Nb 0.06 Fe 0.92 PO 4, carbon nanotubes, SBR are mixed evenly according to the mass ratio of 8:1:1, water is added, stirred evenly, coated on hafnium and dried. Under the condition of 35°C, the current is controlled at 0.2 mA, and 100% of lithium is removed by electrification. Then, an insertion-extraction voltammetry test is carried out in a lithium chloride solution with a lithium concentration of 0.1 - 100 ppm. The potential is controlled at -0.3 V (vs SCE), lithium insertion is carried out for 20 s, and then a lithium extraction scanning test is carried out. Square wave scanning is used, scanning from -0.3 V (vs SCE) to 0.7 V (vs SCE), the scanning rate is 5 mv / s, and the amplitude is 50 mv. The linear relationship between the peak current of the obtained lithium ion extraction scanning voltammetry curve and the solution lithium concentration is as Figure 5 shown.

[0052] Lithium chloride solutions with different concentrations are prepared and tested according to the above method. The obtained current is compared with the Figure 5 linear relationship straight line, and the solution lithium concentration can be measured. The detection results and recovery rates are shown in Table 4.

[0053] Table 4

[0054]

[0055]

[0056] Example 5

[0057] LiCo 0.01 Ni 0.01 Ti 0.01 Fe 0.97 PO 4 , acetylene black, PVDF are mixed evenly according to the mass ratio of 7:2:1, NMP is added, stirred evenly, coated on graphite and dried. Under the condition of 25°C, 100% of lithium is removed with a sodium persulfate solution with a concentration of 0.1 mol / L. Then, an insertion-extraction voltammetry test is carried out in a lithium chloride solution with a lithium concentration of 20 - 100 ppm. The potential is controlled at -0.1 V (vs SCE), lithium insertion is carried out for 30 s, and then a lithium extraction scanning test is carried out. Differential pulse scanning is used, scanning from -0.1 V (vs SCE) to 0.6 V (vs SCE), the scanning rate is 5 mv / s, and the amplitude is 50 mv. The linear relationship between the peak current of the obtained lithium ion extraction scanning voltammetry curve and the solution lithium concentration is as Figure 6 shown.

[0058] Lithium chloride solutions with different concentrations are prepared and tested according to the above method. The obtained current is compared with the Figure 6 linear relationship straight line, and the solution lithium concentration can be measured. The detection results and recovery rates are shown in Table 5.

[0059] Table 5

[0060] Number True Concentration / ppm Detected Concentration / ppm Recovery Rate / % 1 25.00 24.87 99.48 2 60.00 60.26 100.43 3 88.00 87.64 99.59

[0061] Example 6

[0062] Mix LiMn 0.2 Fe 0.8 PO 4 acetylene black, and PVDF evenly at a mass ratio of 8:1:1, add NMP thereto, stir evenly, coat on titanium and dry. Under the condition of 10 °C, control the current at 0.1 mA, and electrolyze to remove 60% of lithium. Then, perform insertion-extraction voltammetry test in a lithium chloride solution with a lithium concentration of 1 - 20 ppm. Control the potential at -0.3 V (vs SCE), and insert lithium for 90 s. The linear relationship between the plateau current of the obtained lithium-ion insertion current-time curve and the solution lithium concentration is as Figure 7 shown.

[0063] Prepare lithium sulfate solutions with different concentrations and perform tests according to the above method. Compare the obtained currents with the Figure 7 linear relationship line, and the solution lithium concentration can be measured. The detection results and recovery rates are shown in Table 6.

[0064] Table 6

[0065] Number True Concentration / ppm Detected Concentration / ppm Recovery Rate / % 1 3.500 3.472 99.20 2 8.800 8.839 100.44 3 15.00 14.91 99.40

[0066] From the above Examples 1 - 6 and the content in Tables 1 - 6, it can be seen that the method for voltammetric analysis of lithium-ion concentration using polyanion-type compound materials provided by the present invention has better selectivity for lithium ions, the test results have a small difference from the true values, and the test results of lithium-ion concentration are accurate.

[0067] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for voltammetric analysis of lithium ion concentration using a polyanionic compound material, characterized in that, through an electrochemical reduction or oxidation reaction, voltammetric analysis of lithium ions is carried out using a polyanionic compound, and the lithium ion concentration is determined by using the linear relationship presented between the obtained current and the lithium ion concentration; wherein, during voltammetric analysis, lithium ions can be embedded in the polyanionic compound or lithium ions can be removed from the lithium-containing polyanionic compound. The polyanionic compound is one of FePO 4 and its doped derivatives; wherein, the doped derivative of FePO 4 is one of Me x Fe y PO 4 , where Me is one or a mixture of several of Mg, Al, Ti, Ni, Co, Mn, Mo, Nb; 0 < x < 1, 0 < y < 1.

2. The method according to claim 1, characterized in that, FePO 4 obtained by electrochemically de-lithiating or chemically de-lithiating LiFePO 4 , and the doped derivative of FePO 4 is obtained by electrochemically de-lithiating or chemically de-lithiating a lithium-containing doped derivative.

3. The method according to claim 1, characterized in that, the voltammetric analysis is embedding voltammetric analysis and embedding-dedoping voltammetric analysis. The embedding voltammetric analysis is to perform a lithium ion embedding scan on the polyanionic compound material, and the embedding-dedoping voltammetric analysis is to first embed lithium ions in the polyanionic compound under a constant potential and then perform a lithium ion removal scan on it.

4. The method according to claim 3, characterized in that, the current obtained from the embedding voltammetric analysis is the peak current of the lithium ion embedding scan voltammogram curve, and the current obtained from the embedding-dedoping voltammetric analysis is the plateau current of the lithium ion embedding current-time curve under a constant potential and the peak current of the lithium ion removal scan voltammogram curve.

5. The method according to claim 3, characterized in that, the scan is one of linear scan, differential pulse scan, and square wave scan.

6. A polyanionic compound electrode for lithium ion voltammetric analysis, characterized in that, comprising: a conductive substrate and a polyanionic compound material layer provided on the conductive substrate; The polyanionic compound is one of FePO 4 and its doped derivatives; wherein, the doped derivative of the FePO 4 is one of Me x Fe y PO 4 , Me is one or a mixture of several of Mg, Al, Ti, Ni, Co, Mn, Mo, Nb; 0 < x < 1, 0 < y < 1.

7. The electrode according to claim 6, characterized in that, FePO 4 obtained by electrochemically de-lithiating or chemically de-lithiating LiFePO 4 , and the doped derivative of FePO 4 is obtained by electrochemically de-lithiating or chemically de-lithiating the lithium-containing doped derivative.

8. The electrode according to claim 6, characterized in that, the conductive substrate is one of metal titanium, metal zirconium, metal hafnium, metal tantalum, metal niobium, metal gold, metal platinum and their alloys; or, the conductive substrate is one of graphite, carbon paper, and carbon fiber cloth.

9. A device for lithium ion voltammetric analysis, characterized in that, comprising a working electrode, and the working electrode is the electrode according to any one of claims 6-8.

10. A method for preparing a polyanionic compound electrode for lithium ion voltammetric analysis according to any one of claims 6-8, characterized in that, comprising: forming the polyanionic compound material layer on the conductive substrate.

11. According to the preparation method of claim 10, a slurry containing the polyanionic compound material is coated on the conductive substrate and then dried.

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