GB/T 41704-2022Test methods of cathode materials for lithium ion battery—Determination of magnetic impurities content and residual alkali content (English PDF)

3.1 Magnetic Impurities

Magnetic impurities refer to impurities in the cathode materials for lithium ion battery that can be adsorbed by the magnetic bar with a magnetic induction intensity of not less than 0.5 T (5,000 Gauss).

3.2 Large Particle Magnetic Impurities

Large particle magnetic impurities refer to magnetic impurities with a diameter of not less than 10 µm under the scanning electron microscope.

3.3 Residual Alkali

Residual alkali refers to alkaline substances attached to the surface of the particles of the cathode materials for lithium ion battery.

4.1 Inductively Coupled Plasma Atomic Emission Spectrometry

4.1.1 Principle

In a clean environment free of magnetic impurities, use a magnetic bar to adsorb and enrich the magnetic impurities in the cathode material.

4.1.2 Reagents or materials

Unless it is otherwise specified, all reagents used in this Method are of guaranteed purity and Grade-1 water specified in GB/T 6682.

4.1.2.1 Nitric acid (rho = 1.42 g/mL).

4.1.2.6 Zinc standard stock solution (100 µg/mL), prepared from high-purity metals or compounds, or adopt a certified single-element standard stock solution.

4.1.2.7 Lithium standard stock solution (100 µg/mL), prepared from high-purity metals or compounds, or adopt a certified single-element standard stock solution.

4.1.2.11 Lithium standard solution B: transfer-take 20.00 mL of lithium standard solution A (4.1.2.10); place it in a 100 mL volumetric flask. Add 3 mL of nitric acid (4.1.2.1); use water to dilute to the scale; mix it well and immediately transfer it to a dry plastic jar. 1 mL of this solution contains 2 µg of lithium.

4.1.3 Instruments and equipment

4.1.3.1 Environmental iron removing rod: magnetic induction intensity >= 0.5 T (5,000 Gauss), wrapped with plastic wrap.

4.1.3.2 Plastic jar: 500 mL.

4.1.4 Sample

The particle of the sample shall be not greater than 0.154 mm.

4.1.5 Test procedures

4.1.5.4.1 Put the test portion in a 500 mL plastic jar (4.1.3.2), add 300.0 g of water, tighten the lid (to prevent leakage); place it on the ball mill (4.1.3.5), adjust the rotating speed to 60 r/min ~ 100 r/min; after rolling and mixing for 30 min, remove it.

4.1.5.4.3 Transfer the magnetic bar (4.1.3.3) to a clean 200 mL beaker; add water, until the magnetic bar (4.1.3.3) is immersed; prevent the water from directly rushing to the surface of the magnetic bar (4.1.3.3).

4.1.5.4.4 There are two optional modes for dissolution.

4.1.5.4.5 Remove the beaker or colorimetric tube. After cooling, transfer all the solution to a 50 mL volumetric flask. Use a small amount of water to rinse the magnetic bar (4.1.3.3); repeat for 3 times. Then, transfer all the washing solution to a volumetric flask and use water to reach a constant volume; record the volume as V.

4.1.5.1 Iron removal before test

Before the test, use aqua regia (4.1.2.2) to clean the magnetic bar (4.1.3.3); use the environmental iron removing rod (4.1.3.1) to carry out meticulous iron removal treatment on all instruments and supplies used in the test.

4.1.5.5 Preparation of standard series solutions

4.2.6 Processing of test data

Count the number of large particle magnetic impurities. Respectively count the number of iron and stainless steel (iron-chromium-nickel).

5.1 Principle

Use a certain volume of water to dissolve the residual alkali on the surface of the sample with a certain mass. After filtration, take the filtrate; use the standard titration solution of hydrochloric acid to perform titration.

5.2 Reagents or Materials

Unless it is otherwise specified, all reagents used in this Method are of guaranteed purity and Grade-1 water specified in GB/T 6682.

5.2.1 Standard titration solution of hydrochloric acid: 0.1 mol/L. Adopt a nationally recognized certified reference material within the validity period, or prepare it in accordance with the stipulations of GB/T 601.

5.2.2 Plastic wrap.

5.3 Instruments and Equipment

5.4 Sample

The particle of the sample shall be not greater than 0.154 mm.

5.5 Test Procedures

5.6 Processing of Test Data

5.6.1 The residual lithium carbonate content in the sample, in mass fraction wLi2CO3, shall be calculated in accordance with Formula (4).

5.6.2 The residual lithium hydroxide content in the sample, in mass fraction wLiOH, shall be calculated in accordance with Formula (5).

5.6.3 The residual alkali content in the sample, in mass fraction wra, shall be calculated in accordance with Formula (6).

5.6.4 The residual lithium content in the sample, in mass fraction wrl, shall be calculated in accordance with Formula (7).

5.6.5 The calculation results shall be expressed in three decimal places and rounded off in accordance with the stipulations of GB/T 8170.

5.7 Precision

5.7.1 Repeatability

In terms of the measured values of two independent test results obtained under repeatability conditions, within the range of average values provided in Table 2, the absolute difference between the two test results does not exceed the repeatability limit (r), and the circumstance of exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is obtained through linear interpolation or extrapolation in accordance with the data in Table 2.