CN1888893A - Ion chromatography method for measuring lithium salt density in lithiumion cell electrolyte - Google Patents

Abstract

An ion chromatogram method uses to test the lithium salt (LiPF6) concentration in lithium ion battery electrolyte. (1) Prepare F- and PO43- standard solution in different concentration and test in ion chromatogram method to protract C-A standard curve. (2) Add reverse chloroazotic acid into the need test electrolyte in equal volume and stay for 12-24 hours, then dilute the solution with secondary deionwater step by step and control its concentration inside the concentration range of standard curve. Test the concentration to F- and PO43- in ion chromatogram method at the same condition with step (1). (3) Calculate the lithium salt concentration C1 of the sample in formula (a) according the concentration to F-, calculate the lithium salt concentration C2 of the sample in formula (b) according the concentration to PO43-. It can test the lithium salt concentration according the concentration to F- and PO43- at the same time, and the data of the two groups complement and consult with each other with high veracity.

Description

A kind of ion chromatographic method of measuring lithium salt in the lithium-ion battery electrolytes

Technical field:

The present invention relates to a kind of method of measuring salt density in the battery electrolyte, especially a kind of method with lithium salt in the ion chromatography lithium-ion battery electrolytes

Background technology:

Lithium-ion battery electrolytes is very responsive to performances such as the energy density of electrode and battery, cycle life, securities.Therefore selecting suitable organic electrolyte is one of key issue that obtains high-energy-density, long circulation life and cell safety.The initial charge/discharge capacity of battery has sizable difference owing to the combination of material with carbon element and electrolytic solution is different, so lay special stress on electrolytic solution will adapt with carbon anode when the design battery.In the commodity lithium ion battery, the lithium salts that electrolytic solution is commonly used is LiPF ₆, solvent is that cyclic carbonate Arrcostab and chain alkyl carbonate mix the binary of composition, ternary or multicomponent system.The organic component of lithium-ion battery electrolytes mainly contains: dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate ester (EC), propylene glycol carbonate (PC), methyl ethyl carbonate (EMC).Organic electrolyte plays a part to carry lithium ion between the both positive and negative polarity of lithium ion battery, and lithium-ion battery electrolytes often adopts lithium hexafluoro phosphate (LiPF ₆) as electrolyte, the size of its concentration directly have influence on electrolyte conductivity can quality, and have influence on the quality of battery product, therefore, with regard to battery production producer, the detection of lithium salt in the electrolytic solution is necessary.

The patent of application number CN200410066174.4 " lithium salts assay method in the lithium-ion battery electrolytes " has been introduced a kind of method with the aas determination lithium salt, this method is by measuring elemental lithium content and then calculating the concentration of lithium salts, and its relative error is between 2%-2.7%.But up to the present, do not see relevant report as yet with chromatography of ions test lithium salt.

Summary of the invention:

The error that the objective of the invention is to overcome atomic absorption method is bigger, method inconvenience, the deficiency that equipment requirements is high, provide a kind of simple and easy to do, error is little, adopts the method for lithium salt in the ion chromatography lithium-ion battery electrolytes.

Lithium salts (LiPF in the mensuration lithium-ion battery electrolytes of the present invention ₆) ion chromatographic method of concentration, carry out according to following steps:

(1) F of preparation variable concentrations ^-And PO ₄ ^3-Solution with chromatography of ions test, obtains area response value separately; Make the C-A typical curve according to their concentration value C separately and corresponding peak area response A then;

(2) get the electrolytic solution sample, add contrary chloroazotic acid isopyknic with it, electrolytic solution is decomposed pre-service, processing time was at 12-24 hour, gained solution is carried out stepwise dilution with secondary deionized water, its concentration is in the concentration range of typical curve, with step (1) under the same condition, with chromatography of ions test F wherein ^-And PO ₄ ^3-Concentration;

(3) at last according to F ^-Concentration usefulness (a) formula calculates the lithium salt C in the testing sample ₁(mol/L); According to PO ₄ ^3-Concentration usefulness (b) formula calculates the lithium salt C in the testing sample ₂(mol/L);

$C_1=\frac{C_{F^{-}}\×P}{19\×6\×100}\left(a\right)$

$C_2=\frac{C_{{{\mathrm{PO}}_4}^{3-}}\×P}{94.97\×1000}\left(b\right)$

In the formula: C _F-And C _PO43-Represent the F of chromatography of ions test respectively ^-And PO ₄ ^3-Concentration (mg/L), P is the diluted sample multiple, and 19 is the atomic weight of F, and 19 * 6 represent 1mol LiPF ₆In contain 6mol F ^-, 94.97 is PO ₄ ^3-Atomic weight.

Lithium salts (LiPF in the mensuration lithium-ion battery electrolytes of the present invention ₆) ion chromatographic method of concentration, F in the described step (1) ^-And PO ₄ ^3-The variable concentrations of solution is 20-100mg/L.

Advantage of the present invention is that electrolytic solution can be simultaneously according to F after pre-treatment ^-And PO ₄ ^3-Carry out the mensuration of lithium salt, two groups of data of gained can complement each other and reference, experiment showed, according to PO ₄ ^3-The accuracy of the lithium salt that concentration calculates is higher, and the result is stable, and the relative error of test is within 0.8%-1.2%.

Embodiment:

The drafting of typical curve generally can select two points above (comprising two points) to carry out in the technical scheme of the present invention, and by the working curve accuracy height of four point-renderings, point selected in the time of also can further increasing curve plotting further improves degree of accuracy.Selected concentration range both can also can in order to improve accuracy of test, reduce test error in the present invention in high concentration range in low strength range, therefore be chosen in higher concentration (20-100mg/L) and test.In general, linear relationship then directly has influence on accuracy of test, and the interval between the therefore selected concentration is wide more, and its linear relationship is a little with regard to relative mistake, and degree of accuracy is not high.After the selected concentration range, can carry out stepwise dilution to specimen, its concentration is in the typical curve concentration range, thereby improve the precision of test according to its scope.

Below with between 20-100mg/L, choose four points be determined as the example the present invention is further illustrated:

Embodiment 1

(1) gets NaF (Aldrich product) 2.210g, KH respectively ₂PO ₄(Aldrich product) 1.433g, with secondary deionized water (18.2M Ω .cm) dilution constant volume 1L, and then with secondary deionized water it to be diluted to concentration respectively be 20mg/L, 30mg/L, 40mg/L, the standard solution of 100mg/L.

(2) with chromatography of ions above-mentioned standard solution is tested, made the C-A typical curve according to concentration C and peak area response A, its regression equation and linear coefficient are as shown in table 1.

The regression equation of table 1 typical curve and linear coefficient

Negative ion	Regression equation	Related coefficient	Standard deviation
				F - PO 4 3-	C 1＝0.0076A 1+0.86815 C 2＝0.0416A 2+7.7628	0.99918 0.99995	1.78330 0.44244

(3) get two kinds of known lithium salts and (be respectively A:1.12mol/L; B:1.15mol/L) each 10mL of lithium-ion battery electrolytes adds the contrary chloroazotic acid of 10mL then respectively, leaves standstill reaction 12h.

(4) above-mentioned reacted solution is carried out stepwise dilution (100 times * 10 times * 2 times) respectively, be sent from sub-chromatogram test F wherein ^-And PO ₄ ^3-Concentration C _F-And C _PO43-, and then calculating lithium salt according to formula (a) and formula (b), the result is as shown in table 2.

The table 2 sample test recovery and relative error

Negative ion	LiPF 6Addition (mol/L)	LiPF 6Measured value (mol/L)	LiPF 6The recovery (%)	Relative error (%)
					F - PO 4 3- F - PO 4 3-	1.12 1.12 1.00 1.00	1.187 1.134 1.047 1.008	106.0 101.2 104.7 100.8	6.0 1.2 4.7 0.8

This shows, adopt the chromatography of ions the negative ion F in the electrolytic solution ^-And PO ₄ ^3-Detect simultaneously, two groups of data references mutually, and according to PO ₄ ^3-The LiPF that calculates ₆The concentration accuracy is higher, and the relative error of test is within 0.8%-1.2%.

Claims (2)

1. an ion chromatographic method of measuring lithium salt in the lithium-ion battery electrolytes is characterized in that, carries out according to following steps:

(1) F of preparation variable concentrations ^-And PO ₄ ^3-Solution with chromatography of ions test, obtains area response value separately; Make the C-A typical curve according to their concentration value C separately and corresponding peak area response A then;

(2) get the electrolytic solution sample, add contrary chloroazotic acid isopyknic with it, electrolytic solution is decomposed pre-service, processing time was at 12-24 hour, gained solution is carried out stepwise dilution with secondary deionized water, its concentration is in the concentration range of typical curve, with step (1) under the same condition, with chromatography of ions test F wherein ^-And PO ₄ ^3-Concentration;

(3) at last according to F ^-Concentration usefulness (a) formula calculates the lithium salt C in the testing sample ₁(mol/L); According to PO ₄ ^3-Concentration usefulness (b) formula calculates the lithium salt C in the testing sample ₂(mol/L);

$C_1=\frac{C_{F^{-}}\×P}{19\×6\×1000}---\left(a\right)$

$C_2=\frac{C_{{{\mathrm{PO}}_4}^{3-}}\×P}{94.97\×1000}---\left(b\right)$

In the formula: C _F-And C _PO43-Represent the F of chromatography of ions test respectively ^-And PO ₄ ^3-Concentration (mg/L), P is the diluted sample multiple.

2. a kind of ion chromatographic method of measuring lithium salt in the lithium-ion battery electrolytes according to claim 1 is characterized in that, F in the described step (1) ^-And PO ₄ ^3-The variable concentrations of solution is 20-100mg/L.